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13 pages, 3118 KiB

Open AccessArticle

Azo-Linkage Redox Metal–Organic Framework Incorporating Carbon Nanotubes for High-Performance Aqueous Energy Storage

by Hualei Zhang, Xinlei Wang, Jie Zhou and Weihua Tang

Molecules 2023, 28(22), 7479; https://doi.org/10.3390/molecules28227479 - 8 Nov 2023

Viewed by 1208

Abstract

The design of well-defined hierarchical free-standing electrodes for robust high-performance energy storage is challenging. We report herein that azo-linkage redox metal–organic frameworks (MOFs) incorporate single-walled carbon nanotubes (CNTs) as flexible electrodes. The in situ-guided growth, crystallinity and morphology of UiO-66-NO₂ MOFs were [...] Read more.

The design of well-defined hierarchical free-standing electrodes for robust high-performance energy storage is challenging. We report herein that azo-linkage redox metal–organic frameworks (MOFs) incorporate single-walled carbon nanotubes (CNTs) as flexible electrodes. The in situ-guided growth, crystallinity and morphology of UiO-66-NO₂ MOFs were finely controlled in the presence of CNTs. The MOFs’ covalent anchoring to CNTs and solvothermal grafting anthraquinone (AQ) pendants endow the hybrid (denoted as CNT@UiO-66-AQ) with greatly improved conductivity, charge storage pathways and electrochemical dynamics. The flexible CNT@UiO-66-AQ displays a highest areal specific capacitance of 302.3 mF cm⁻² (at 1 mA cm⁻²) in −0.4~0.9 V potential window, together with 100% capacitance retention over 5000 cycles at 5 mA cm⁻². Its assembled symmetrical supercapacitor (SSC) achieves a maximum energy density of 0.037 mWh cm⁻² and a maximum power density of 10.4 mW cm⁻², outperforming many MOFs-hybrids-based SSCs in the literature. Our work may open a new avenue for preparing azo-coupled redox MOFs hybrids with carbaneous substrates for high-performance robust aqueous energy storage. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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20 pages, 5897 KiB

Open AccessArticle

Influence of Co₃O₄ Nanostructure Morphology on the Catalytic Degradation of p-Nitrophenol

by Huihui Chen, Mei Yang, Yuan Liu, Jun Yue and Guangwen Chen

Molecules 2023, 28(21), 7396; https://doi.org/10.3390/molecules28217396 - 2 Nov 2023

Cited by 1 | Viewed by 1143

Abstract

The design and fabrication of nanomaterials with controllable morphology and size is of critical importance to achieve excellent catalytic performance in heterogeneous catalysis. In this work, cobalt oxide (Co₃O₄) nanostructures with different morphologies (nanoplates, microflowers, nanorods and nanocubes) were [...] Read more.

The design and fabrication of nanomaterials with controllable morphology and size is of critical importance to achieve excellent catalytic performance in heterogeneous catalysis. In this work, cobalt oxide (Co₃O₄) nanostructures with different morphologies (nanoplates, microflowers, nanorods and nanocubes) were successfully constructed in order to establish the morphology–property–performance relationship of the catalysts. The morphology and structure of the nanostructured Co₃O₄ were characterized by various techniques, and the catalytic performance of the as-prepared nanostructures was studied by monitoring the reduction of p-nitrophenol to p-aminophenol in the presence of excess NaBH₄. The catalytic performance was found to be strongly dependent on their morphologies. The experimental results show that the pseudo-first-order reaction rate constants for Co₃O₄ nanostructures with various shapes are, respectively, 1.49 min⁻¹ (nanoplates), 1.40 min⁻¹ (microflowers), 0.78 min⁻¹ (nanorods) and 0.23 min⁻¹ (nanocubes). The Co₃O₄ nanoplates exhibited the highest catalytic activity among the four nanostructures, due to their largest specific surface area, relatively high total pore volume, best redox properties and abundance of defect sites. The established correlation between morphology, property and catalytic performance in this work will offer valuable insight into the design and application of nanostructured Co₃O₄ as a potential non-noble metal catalyst for p-nitrophenol reduction. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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13 pages, 2740 KiB

Open AccessArticle

Effects of Methyl Substitution and Leaving Group on E2/S_N2 Competition for Reactions of F⁻ with RY (R = CH₃, C₂H₅, ⁱC₃H₇, ^tC₄H₉; Y = Cl, I)

by Wenqing Zhen, Siwei Zhao, Gang Fu, Hongyi Wang, Jianmin Sun, Li Yang and Jiaxu Zhang

Molecules 2023, 28(17), 6269; https://doi.org/10.3390/molecules28176269 - 27 Aug 2023

Viewed by 1614

Abstract

The competition between base-induced elimination (E2) and bimolecular nucleophilic substitution (S_N2) is of significant importance in organic chemistry and is influenced by many factors. The electronic structure calculations for the gas-phase reactions of F⁻ + RY (R = CH₃ [...] Read more.

The competition between base-induced elimination (E2) and bimolecular nucleophilic substitution (S_N2) is of significant importance in organic chemistry and is influenced by many factors. The electronic structure calculations for the gas-phase reactions of F⁻ + RY (R = CH₃, C₂H₅, ⁱC₃H₇, ^tC₄H₉, and Y = Cl, I) are executed at the MP2 level with aug-cc-pVDZ or ECP/d basis set to investigate the α-methyl substitution effect. The variation in barrier height, reaction enthalpy, and competition of S_N2/E2 as a function of methyl-substitution and leaving group ability has been emphasized. And the nature of these rules has been explored. As the degree of methyl substitution on α-carbon increases, the E2 channel becomes more competitive and dominant with R varying from C₂H₅, ⁱC₃H₇, to ^tC₄H₉. Energy decomposition analysis offers new insights into the competition between E2 and S_N2 processes, which suggests that the drop in interaction energy with an increasing degree of substitution cannot compensate for the rapid growth of preparation energy, leading to a rapid increase in the S_N2 energy barrier. By altering the leaving group from Cl to I, the barriers of both S_N2 and E2 monotonically decrease, and, with the increased number of substituents, they reduce more dramatically, which is attributed to the looser transition state structures with the stronger leaving group ability. Interestingly, ∆E₀^‡ exhibits a positive linear correlation with reaction enthalpy (∆H) and halogen electronegativity. With the added number of substituents, the differences in ∆E₀^‡ and ∆H between Y = Cl and I likewise exhibit good linearity. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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14 pages, 4511 KiB

Open AccessFeature PaperArticle

Mass Spectra Fitting as Diagnostic Tool for Magnetron Plasmas Generated in Ar and Ar/H₂ Gases with Tungsten Targets

by Cristina Craciun, Silviu Daniel Stoica, Bogdana Maria Mitu, Tomy Acsente and Gheorghe Dinescu

Molecules 2023, 28(15), 5664; https://doi.org/10.3390/molecules28155664 - 26 Jul 2023

Cited by 3 | Viewed by 1052

Abstract

In this work, we describe an ion mass spectra processing method from plasmas generated in Ar and Ar/H₂ gases in contact with tungsten surfaces. For this purpose, advanced model functions, i.e., those suitable for fitting the experimental mass peak profiles, are used. [...] Read more.

In this work, we describe an ion mass spectra processing method from plasmas generated in Ar and Ar/H₂ gases in contact with tungsten surfaces. For this purpose, advanced model functions, i.e., those suitable for fitting the experimental mass peak profiles, are used. In addition, the peak positions, peak shapes, abundances, and ion ratios are the parameters considered for building these functions. In the case of a multielement magnetron target, the calibration of the mass spectra with respect to the peak shape and position on the m/z scale is helpful in reducing the number of free variables during fitting. The mass spectra fitting procedure is validated by the obtained isotopic abundances of W ions in W/Ar magnetron plasmas, which, in turn, are comparable with their natural abundance. Moreover, its usefulness is exemplified by calculating the ratio of WH⁺/W⁺ ions in W/Ar/H₂ plasma. This work paves the way for obtaining relevant results regarding ion species in plasma even in the case of using general-purpose mass spectrometers with limited resolution and accuracy. Although this method is illustrated for the W/Ar/H₂ plasma system, it can be easily extendable to any plasma type. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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12 pages, 1352 KiB

Open AccessArticle

Bragg–Williams Theory for Particles with a Size-Modulating Internal Degree of Freedom

by Guilherme Volpe Bossa and Sylvio May

Molecules 2023, 28(13), 5060; https://doi.org/10.3390/molecules28135060 - 28 Jun 2023

Cited by 1 | Viewed by 1382

Abstract

The field of soft matter teems with molecules and aggregates of molecules that have internal size-modulating degrees of freedom. Proteins, peptides, microgels, polymers, micelles, and even some colloids can exist in multiple—often just two dominating—states with different effective sizes, where size can refer [...] Read more.

The field of soft matter teems with molecules and aggregates of molecules that have internal size-modulating degrees of freedom. Proteins, peptides, microgels, polymers, micelles, and even some colloids can exist in multiple—often just two dominating—states with different effective sizes, where size can refer to the volume or to the cross-sectional area for particles residing on surfaces. The size-dependence of their accessible states renders the behavior of these particles pressure-sensitive. The Bragg–Williams model is among the most simple mean-field methods to translate the presence of inter-particle interactions into an approximate phase diagram. Here, we extend the Bragg–Williams model to account for the presence of particles that are immersed in a solvent and exist in two distinct states, one occupying a smaller and the other one a larger size. The basis of the extension is a lattice–sublattice approximation that we use to host the two size-differing states. Our model includes particle–solvent interactions that act as an effective surface tension between particles and solvent and are ignorant of the state in which the particles reside. We analyze how the energetic preference of the particles for one or the other state affects the phase diagrams. The possibility of a single phase-two phases-single phase sequence of phase transitions as a function of increasing temperature is demonstrated. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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12 pages, 45938 KiB

Open AccessArticle

High-Throughput UV Photoionization and Fragmentation of Neutral Biomolecules as a Structural Fingerprint

by Siwen Wang, Yerbolat Dauletyarov and Daniel A. Horke

Molecules 2023, 28(13), 5058; https://doi.org/10.3390/molecules28135058 - 28 Jun 2023

Cited by 1 | Viewed by 1456

Abstract

We present UV photofragmentation studies of the structural isomers paracetamol, 3-Pyridinepropionic acid (3-PPIA) and (R)-(-)-2-Phenylglycine. In particular, we utilized a new laser-based thermal desorption source in combination with femtosecond multiphoton ionization at 343 nm and 257 nm. The continuous nature of our molecule [...] Read more.

We present UV photofragmentation studies of the structural isomers paracetamol, 3-Pyridinepropionic acid (3-PPIA) and (R)-(-)-2-Phenylglycine. In particular, we utilized a new laser-based thermal desorption source in combination with femtosecond multiphoton ionization at 343 nm and 257 nm. The continuous nature of our molecule source, combined with the 50 kHz repetition rate of the laser, allowed us to perform these experiments at high throughput. In particular, we present detailed laser intensity dependence studies at both wavelengths, producing 2D mass spectra with highly differential information about the underlying fragmentation processes. We show that UV photofragmentation produces highly isomer-specific mass spectra, and assign all major fragmentation pathways observed. The intensity-dependence measurements, furthermore, allowed us to evaluate the appearance intensities for each fragmentation channel, which helped to distinguish competing from consecutive fragmentation pathways. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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15 pages, 5187 KiB

Open AccessArticle

Effect of Reaction Temperature on the Microstructure and Properties of Magnesium Phosphate Chemical Conversion Coatings on Titanium

by Yi-Bo Li, Yu-Peng Lu, Chun-Miao Du, Kang-Qing Zuo, Yu-Ying Wang, Kang-Le Tang and Gui-Yong Xiao

Molecules 2023, 28(11), 4495; https://doi.org/10.3390/molecules28114495 - 1 Jun 2023

Cited by 3 | Viewed by 1700

Abstract

Magnesium phosphate (MgP) has garnered growing interest in hard tissue replacement processes due to having similar biological characteristics to calcium phosphate (CaP). In this study, an MgP coating with the newberyite (MgHPO₄·3H₂O) was prepared on the surface of pure [...] Read more.

Magnesium phosphate (MgP) has garnered growing interest in hard tissue replacement processes due to having similar biological characteristics to calcium phosphate (CaP). In this study, an MgP coating with the newberyite (MgHPO₄·3H₂O) was prepared on the surface of pure titanium (Ti) using the phosphate chemical conversion (PCC) method. The influence of reaction temperature on the phase composition, microstructure, and properties of coatings was systematically researched with the use of an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a laser scanning confocal microscope (LSCM), a contact angle goniometer, and a tensile testing machine. The formation mechanism of MgP coating on Ti was also explored. In addition, the corrosion resistance of the coatings on Ti was researched by assessing the electrochemical behavior in 0.9% NaCl solution using an electrochemical workstation. The results showed that temperature did not obviously affect the phase composition of the MgP coatings, but affected the growth and nucleation of newberyite crystals. In addition, an increase in reaction temperature had a great impact on properties including surface roughness, thickness, bonding strength, and corrosion resistance. Higher reaction temperatures resulted in more continuous MgP, larger grain size, higher density, and better corrosion resistance. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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11 pages, 2745 KiB

Open AccessArticle

On the Gas-Phase Interactions of Alkyl and Phenyl Formates with Water: Ion–Molecule Reactions with Proton-Bound Water Clusters

by Malick Diedhiou and Paul M. Mayer

Molecules 2023, 28(11), 4431; https://doi.org/10.3390/molecules28114431 - 30 May 2023

Cited by 1 | Viewed by 1207

Abstract

Ion–molecule reactions between the neutral ethyl- (EF), isopropyl- (IF), t-butyl- (TF) and phenyl formate (PF) and proton-bound water clusters W₂H⁺ and W₃H⁺ (W = H₂O) showed that the major reaction product is water loss from [...] Read more.

Ion–molecule reactions between the neutral ethyl- (EF), isopropyl- (IF), t-butyl- (TF) and phenyl formate (PF) and proton-bound water clusters W₂H⁺ and W₃H⁺ (W = H₂O) showed that the major reaction product is water loss from the initial encounter complex, followed ultimately by the formation of the protonated formate. Collision-induced dissociation breakdown curves of the formate–water complexes were obtained as a function of collision energy and modeled to extract relative activation energies for the observed channels. Density functional theory calculations (B3LYP/6-311+G(d,p)) of the water loss reactions were consistent with reactions having no reverse energy barrier in each case. Overall, the results indicate that the interaction of formates with atmospheric water can form stable encounter complexes that will dissociate by sequential water loss to form protonated formates. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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18 pages, 5032 KiB

Open AccessArticle

Structural Quantification of the Surface-Confined Metal-Organic Precursors Simulated with the Lattice Monte Carlo Method

by Jakub Lisiecki and Paweł Szabelski

Molecules 2023, 28(10), 4253; https://doi.org/10.3390/molecules28104253 - 22 May 2023

Cited by 1 | Viewed by 1480

Abstract

The diversity of surface-confined metal-organic precursor structures, which recently have been observed experimentally, poses a question of how the individual properties of a molecular building block determine those of the resulting superstructure. To answer this question, we use the Monte Carlo simulation technique [...] Read more.

The diversity of surface-confined metal-organic precursor structures, which recently have been observed experimentally, poses a question of how the individual properties of a molecular building block determine those of the resulting superstructure. To answer this question, we use the Monte Carlo simulation technique to model the self-assembly of metal-organic precursors that precede the covalent polymerization of halogenated PAH isomers. For this purpose, a few representative examples of low-dimensional constructs were studied, and their basic structural features were quantified using such descriptors as the orientational order parameter, radial distribution function, and one- and two-dimensional structure factors. The obtained results demonstrated that the morphology of the precursor (and thus the subsequent polymer) could be effectively tuned by a suitable choice of molecular parameters, including size, shape, and intramolecular distribution of halogen substituents. Moreover, our theoretical investigations showed the effect of the main structural features of the precursors on the related indirect characteristics of these constructs. The results reported herein can be helpful in the custom designing and characterization of low-dimensional polymers with adjustable properties. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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27 pages, 5696 KiB

Open AccessArticle

Exploring the Role of Anionic Lipid Nanodomains in the Membrane Disruption and Protein Folding of Human Islet Amyloid Polypeptide Oligomers on Lipid Membrane Surfaces Using Multiscale Molecular Dynamics Simulations

by Ngoc Nguyen, Amber Lewis, Thuong Pham, Donald Sikazwe and Kwan H. Cheng

Molecules 2023, 28(10), 4191; https://doi.org/10.3390/molecules28104191 - 19 May 2023

Cited by 3 | Viewed by 2350

Abstract

The aggregation of human Islet Amyloid Polypeptide (hIAPP) on cell membranes is linked to amyloid diseases. However, the physio-chemical mechanisms of how these hIAPP aggregates trigger membrane damage are unclear. Using coarse-grained and all-atom molecular dynamics simulations, we investigated the role of lipid [...] Read more.

The aggregation of human Islet Amyloid Polypeptide (hIAPP) on cell membranes is linked to amyloid diseases. However, the physio-chemical mechanisms of how these hIAPP aggregates trigger membrane damage are unclear. Using coarse-grained and all-atom molecular dynamics simulations, we investigated the role of lipid nanodomains in the presence or absence of anionic lipids, phosphatidylserine (PS), and a ganglioside (GM1), in the membrane disruption and protein folding behaviors of hIAPP aggregates on phase-separated raft membranes. Our raft membranes contain liquid-ordered (Lo), liquid-disordered (Ld), mixed Lo/Ld (Lod), PS-cluster, and GM1-cluster nanosized domains. We observed that hIAPP aggregates bound to the Lod domain in the absence of anionic lipids, but also to the GM1-cluster- and PS-cluster-containing domains, with stronger affinity in the presence of anionic lipids. We discovered that L16 and I26 are the lipid anchoring residues of hIAPP binding to the Lod and PS-cluster domains. Finally, significant lipid acyl chain order disruption in the annular lipid shells surrounding the membrane-bound hIAPP aggregates and protein folding, particularly beta-sheet formation, in larger protein aggregates were evident. We propose that the interactions of hIAPP and both non-anionic and anionic lipid nanodomains represent key molecular events of membrane damage associated with the pathogenesis of amyloid diseases. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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21 pages, 7193 KiB

Open AccessArticle

Adsorption of Brilliant Green Dye onto a Mercerized Biosorbent: Kinetic, Thermodynamic, and Molecular Docking Studies

by Andra-Cristina Enache, Corneliu Cojocaru, Petrisor Samoila, Victor Ciornea, Roxana Apolzan, Georgeta Predeanu and Valeria Harabagiu

Molecules 2023, 28(10), 4129; https://doi.org/10.3390/molecules28104129 - 16 May 2023

Cited by 17 | Viewed by 2846

Abstract

This study reports the valorization of pistachio shell agricultural waste, aiming to develop an eco-friendly and cost-effective biosorbent for cationic brilliant green (BG) dye adsorption from aqueous media. Pistachio shells were mercerized in an alkaline environment, resulting in the treated adsorbent (PS_NaOH [...] Read more.

This study reports the valorization of pistachio shell agricultural waste, aiming to develop an eco-friendly and cost-effective biosorbent for cationic brilliant green (BG) dye adsorption from aqueous media. Pistachio shells were mercerized in an alkaline environment, resulting in the treated adsorbent (PS_NaOH). The morphological and structural features of the adsorbent were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy, and polarized light microscopy. The pseudo-first-order (PFO) kinetic model best described the adsorption kinetics of the BG cationic dye onto PS_NaOH biosorbents. In turn, the equilibrium data were best fitted to the Sips isotherm model. The maximum adsorption capacity decreased with temperature (from 52.42 mg/g at 300 K to 46.42 mg/g at 330 K). The isotherm parameters indicated improved affinity between the biosorbent surface and BG molecules at lower temperatures (300 K). The thermodynamic parameters estimated on the basis of the two approaches indicated a spontaneous (ΔG < 0) and exothermic (ΔH < 0) adsorption process. The design of experiments (DoE) and the response surface methodology (RSM) were employed to establish optimal conditions (sorbent dose (SD) = 4.0 g/L and initial concentration (C₀) = 10.1 mg/L), yielding removal efficiency of 98.78%. Molecular docking simulations were performed to disclose the intermolecular interactions between the BG dye and lignocellulose-based adsorbent. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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14 pages, 8638 KiB

Open AccessArticle

Hybrid Nanocomposites of Tenoxicam: Layered Double Hydroxides (LDHs) vs. Hydroxyapatite (HAP) Inorganic Carriers

by Lauretta Maggi, Valeria Friuli, Giovanna Bruni, Alessia Rinaldi and Marcella Bini

Molecules 2023, 28(10), 4035; https://doi.org/10.3390/molecules28104035 - 11 May 2023

Cited by 4 | Viewed by 1657

Abstract

The search for effective systems to facilitate the release of poorly bioavailable drugs is a forefront topic for the pharmaceutical market. Materials constituted by inorganic matrices and drugs represent one of the latest research strategies in the development of new drug alternatives. Our [...] Read more.

The search for effective systems to facilitate the release of poorly bioavailable drugs is a forefront topic for the pharmaceutical market. Materials constituted by inorganic matrices and drugs represent one of the latest research strategies in the development of new drug alternatives. Our aim was to obtain hybrid nanocomposites of Tenoxicam, an insoluble nonsteroidal anti-inflammatory drug, with both layered double hydroxides (LDHs) and hydroxyapatite (HAP). The physicochemical characterization on the base of X-ray powder diffraction, SEM/EDS, DSC and FT-IR measurements was useful to verify the possible hybrids formation. In both cases, the hybrids formed, but it seemed that the drug intercalation in LDH was low and, in fact, the hybrid was not effective in improving the pharmacokinetic properties of the drug alone. On the contrary, the HAP–Tenoxicam hybrid, compared to the drug alone and to a simple physical mixture, showed an excellent improvement in wettability and solubility and a very significant increase in the release rate in all the tested biorelevant fluids. It delivers the entire daily dose of 20 mg in about 10 min. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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13 pages, 3123 KiB

Open AccessArticle

Effects of HAT-CN Layer Thickness on Molecular Orientation and Energy-Level Alignment with ZnPc

by Eunah Joo, Jin Woo Hur, Joon Young Ko, Tae Gyun Kim, Jung Yeon Hwang, Kevin E. Smith, Hyunbok Lee and Sang Wan Cho

Molecules 2023, 28(9), 3821; https://doi.org/10.3390/molecules28093821 - 29 Apr 2023

Cited by 3 | Viewed by 2493

Abstract

Efficient energy-level alignment is crucial for achieving high performance in organic electronic devices. Because the electronic structure of an organic semiconductor is significantly influenced by its molecular orientation, comprehensively understanding the molecular orientation and electronic structure of the organic layer is essential. In [...] Read more.

Efficient energy-level alignment is crucial for achieving high performance in organic electronic devices. Because the electronic structure of an organic semiconductor is significantly influenced by its molecular orientation, comprehensively understanding the molecular orientation and electronic structure of the organic layer is essential. In this study, we investigated the interface between a 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) hole injection layer and a zinc-phthalocyanine (ZnPc) p-type organic semiconductor. To determine the energy-level alignment and molecular orientation, we conducted in situ ultraviolet and X-ray photoelectron spectroscopies, as well as angle-resolved X-ray absorption spectroscopy. We found that the HAT-CN molecules were oriented relatively face-on (40°) in the thin (5 nm) layer, whereas they were oriented relatively edge-on (62°) in the thick (100 nm) layer. By contrast, ZnPc orientation was not significantly altered by the underlying HAT-CN orientation. The highest occupied molecular orbital (HOMO) level of ZnPc was closer to the Fermi level on the 100 nm thick HAT-CN layer than on the 5 nm thick HAT-CN layer because of the higher work function. Consequently, a considerably low energy gap between the lowest unoccupied molecular orbital level of HAT-CN and the HOMO level of ZnPc was formed in the 100 nm thick HAT-CN case. This may improve the hole injection ability of the anode system, which can be utilized in various electronic devices. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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15 pages, 4936 KiB

Open AccessArticle

Design and Synthesis of a Novel ICT Bichromophoric pH Sensing System Based on 1,8-Naphthalimide Fluorophores as a Two-Input Logic Gate and Its Antibacterial Evaluation

by Alaa R. Sakr, Nikolai I. Georgiev and Vladimir B. Bojinov

Molecules 2023, 28(8), 3631; https://doi.org/10.3390/molecules28083631 - 21 Apr 2023

Cited by 5 | Viewed by 1920

Abstract

The synthesis, sensor activity, and logic behavior of a novel 4-iminoamido-1,8-naphthalimide bichromophoric system based on a “fluorophore-receptor” architecture with ICT chemosensing properties is reported. The synthesized compound showed good colorimetric and fluorescence signaling properties as a function of pH and proved [...] Read more.

The synthesis, sensor activity, and logic behavior of a novel 4-iminoamido-1,8-naphthalimide bichromophoric system based on a “fluorophore-receptor” architecture with ICT chemosensing properties is reported. The synthesized compound showed good colorimetric and fluorescence signaling properties as a function of pH and proved itself as a promising probe for the rapid detection of pH in an aqueous solution and base vapors in a solid state. The novel dyad is able to work as a two-input logic gate with chemical inputs H⁺ (Input 1) and HO⁻ (Input 2) executing INHIBIT logic gate. The synthesized bichromophoric system and the corresponding intermediates demonstrated good antibacterial activity toward Gram (+) and Gram (−) bacteria when compared with the Gentamycin standard. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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20 pages, 4552 KiB

Open AccessArticle

An Expedited Route to Optical and Electronic Properties at Finite Temperature via Unsupervised Learning

by Fulvio Perrella, Federico Coppola, Nadia Rega and Alessio Petrone

Molecules 2023, 28(8), 3411; https://doi.org/10.3390/molecules28083411 - 12 Apr 2023

Cited by 8 | Viewed by 1671

Abstract

Electronic properties and absorption spectra are the grounds to investigate molecular electronic states and their interactions with the environment. Modeling and computations are required for the molecular understanding and design strategies of photo-active materials and sensors. However, the interpretation of such properties demands [...] Read more.

Electronic properties and absorption spectra are the grounds to investigate molecular electronic states and their interactions with the environment. Modeling and computations are required for the molecular understanding and design strategies of photo-active materials and sensors. However, the interpretation of such properties demands expensive computations and dealing with the interplay of electronic excited states with the conformational freedom of the chromophores in complex matrices (i.e., solvents, biomolecules, crystals) at finite temperature. Computational protocols combining time dependent density functional theory and ab initio molecular dynamics (MD) have become very powerful in this field, although they require still a large number of computations for a detailed reproduction of electronic properties, such as band shapes. Besides the ongoing research in more traditional computational chemistry fields, data analysis and machine learning methods have been increasingly employed as complementary approaches for efficient data exploration, prediction and model development, starting from the data resulting from MD simulations and electronic structure calculations. In this work, dataset reduction capabilities by unsupervised clustering techniques applied to MD trajectories are proposed and tested for the ab initio modeling of electronic absorption spectra of two challenging case studies: a non-covalent charge-transfer dimer and a ruthenium complex in solution at room temperature. The K-medoids clustering technique is applied and is proven to be able to reduce by ∼100 times the total cost of excited state calculations on an MD sampling with no loss in the accuracy and it also provides an easier understanding of the representative structures (medoids) to be analyzed on the molecular scale. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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11 pages, 4174 KiB

Open AccessArticle

Electrodeposition of High-Quality Ni/SiC Composite Coatings by Using Binary Non-Ionic Surfactants

by Han Rao, Weiping Li, Fuzhen Zhao, Yongfa Song, Huicong Liu, Liqun Zhu and Haining Chen

Molecules 2023, 28(8), 3344; https://doi.org/10.3390/molecules28083344 - 10 Apr 2023

Cited by 2 | Viewed by 2095

Abstract

In order to increase the hardness, wear resistance and corrosion resistance of nickel-based coatings, pure nickel is often co-electrodeposited with silicon carbide (SiC) particles. However, SiC particles tend to agglomerate and precipitate in the bath, which reduces the amounts of nanoparticles and causes [...] Read more.

In order to increase the hardness, wear resistance and corrosion resistance of nickel-based coatings, pure nickel is often co-electrodeposited with silicon carbide (SiC) particles. However, SiC particles tend to agglomerate and precipitate in the bath, which reduces the amounts of nanoparticles and causes nonuniformity. Herein, we solve these problems by using binary non-ionic surfactants (Span 80 and Tween 60) to effectively disperse SiC particles (binary-SiC) in the bath, which suppresses nanoparticles agglomeration and leads to uniformly distributed SiC particles in the composite coatings. In comparison to the Ni/SiC coatings electrodeposited from the commonly used SDS-modified SiC, the coatings prepared with binary-SiC (Ni/binary-SiC) show finer crystallization and a smoother surface. In addition, the Ni/binary-SiC coatings exhibit higher hardness (556 Hv) and wear resistance (2.95 mg cm⁻²). Furthermore, higher corrosion resistance is also achieved by the Ni/binary-SiC coatings. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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13 pages, 3156 KiB

Open AccessArticle

Systematic Theoretical Study on the pH-Dependent Absorption and Fluorescence Spectra of Flavins

by Jinyu Wang and Yajun Liu

Molecules 2023, 28(8), 3315; https://doi.org/10.3390/molecules28083315 - 8 Apr 2023

Cited by 2 | Viewed by 1997

Abstract

Flavins are a class of organic compounds with the basic structure of 7,8-dimethy-10-alkyl isoalloxazine. They are ubiquitous in nature and participate in many biochemical reactions. Due to various existing forms, there is a lack of systematic research on the absorption and fluorescence spectra [...] Read more.

Flavins are a class of organic compounds with the basic structure of 7,8-dimethy-10-alkyl isoalloxazine. They are ubiquitous in nature and participate in many biochemical reactions. Due to various existing forms, there is a lack of systematic research on the absorption and fluorescence spectra of flavins. In this study, employing the density functional theory (DFT) and time-dependent (TD) DFT, we calculated the pH-dependent absorption and fluorescence spectra of flavin of three redox states (quinone, semiquinone, and hydroquinone) in solvents. The chemical equilibrium of three redox states of flavins and the pH effect on the absorption spectra and fluorescence spectra of flavins were carefully discussed. The conclusion helps with identifying the existing forms of flavins in solvent with different pH values. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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13 pages, 3113 KiB

Open AccessArticle

Intramolecular and Intermolecular Interaction Switching in the Aggregates of Perylene Diimide Trimer: Effect of Hydrophobicity

by Peiyuan Su, Guangliu Ran, Hang Wang, Jianing Yue, Qingyu Kong, Zhishan Bo and Wenkai Zhang

Molecules 2023, 28(7), 3003; https://doi.org/10.3390/molecules28073003 - 28 Mar 2023

Cited by 2 | Viewed by 2501

Abstract

The research on perylene diimide (PDI) aggregates effectively promotes their applications in organic photovoltaic solar cells and fluorescent sensors. In this paper, a PDI fabricated with three peripheral PDI units (N, N’-bis(6-undecyl) perylene-3,4,9,10-bis(dicarboximide)) is investigated. The trimer shows different absorption and fluorescence properties [...] Read more.

The research on perylene diimide (PDI) aggregates effectively promotes their applications in organic photovoltaic solar cells and fluorescent sensors. In this paper, a PDI fabricated with three peripheral PDI units (N, N’-bis(6-undecyl) perylene-3,4,9,10-bis(dicarboximide)) is investigated. The trimer shows different absorption and fluorescence properties due to hydrophobicity when dissolved in the mixed solvent of tetrahydrofuran (THF) and water. Through comprehensive analysis of the fluorescence lifetime and transient absorption spectroscopic results, we concluded that the trimer underwent different excited state kinetic pathways with different concentrations of water in THF. When dissolved in pure THF solvent, both the intramolecular charge-transfer and excimer states are formed. When the water concentration increases from 0 to 50% (v/v), the formation time of the excimer state and its structural relaxation time are prolonged, illustrating the arising of the intermolecular excimer state. It is interesting to determine that the probability of the intramolecular charge-transfer pathway will first decrease and then increase as the speed of intermolecular excimer formation slows down. The two inflection points appear when the water concentration is above 10% and 40%. The results not only highlight the importance of hydrophobicity on the aggregate properties of PDI multimers but also guide the further design of PDI-based organic photovoltaic solar cells. Full article

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12 pages, 2637 KiB

Open AccessArticle

Partial Oxidation to Extend the Lifetime of Nanoporous Carbon in an Ultracapacitor with Li₂SO₄ Electrolyte

by Maike Käärik, Mati Arulepp and Jaan Leis

Molecules 2023, 28(7), 2944; https://doi.org/10.3390/molecules28072944 - 25 Mar 2023

Cited by 2 | Viewed by 1387

Abstract

A TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC), oxidized by a modified Hummers method, were studied as promising electrode materials for electrochemical energy storage. To evaluate the electrochemical properties of the carbon materials, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy [...] Read more.

A TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC), oxidized by a modified Hummers method, were studied as promising electrode materials for electrochemical energy storage. To evaluate the electrochemical properties of the carbon materials, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy measurements were performed in 1 M Li₂SO₄ using 2- and 3-electrode cells. A partially oxidized surface was shown to improve the capacitance and electrochemical stability of a nanoporous CDC at positive potential values. The respective anodic capacitance of 80 F cm⁻³ reveals a 15% improvement over the non-oxidized CDC. At negative potential values, the capacitance of two carbon materials is almost equal, 97 vs. 93 F cm⁻³, for the non-oxidized and partially oxidized CDC materials, respectively. An asymmetric 2-electrode ultracapacitor containing ox-red-CDC as the anode and pristine CDC as the cathode demonstrated an excellent cycle life. The temporary repolarization of the 2-electrode cell after thousands of charge–discharge cycles increased the capacitance and improved the cycling characteristics, likely due to regeneration and cleaning of the electrode surface. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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17 pages, 2996 KiB

Open AccessArticle

Combined Description of the Equation of State and Diffusion Coefficient of Liquid Water Using a Two-State Sanchez–Lacombe Approach

by Valeriy V. Ginzburg, Enza Fazio and Carmelo Corsaro

Molecules 2023, 28(6), 2560; https://doi.org/10.3390/molecules28062560 - 11 Mar 2023

Cited by 1 | Viewed by 1747

Abstract

Water is one of the most important compounds on Earth, yet its material properties are still poorly understood. Here, we use a recently developed two-state, two-(time)scale (TS2) dynamic mean-field model combined with the two-state Sanchez–Lacombe (SL) thermodynamic theory in order to describe the [...] Read more.

Water is one of the most important compounds on Earth, yet its material properties are still poorly understood. Here, we use a recently developed two-state, two-(time)scale (TS2) dynamic mean-field model combined with the two-state Sanchez–Lacombe (SL) thermodynamic theory in order to describe the equation of state (density as a function of temperature and pressure) and diffusivity of liquid water. In particular, it is shown that in a relatively wide temperature and pressure range (160 K < T < 360 K; 0 < P < 100 MPa), density and self-diffusion obey a special type of dynamic scaling, similar to the “τTV” scaling of Casalini and Roland, but with the negative exponent γ. The model predictions are consistent with experimental data. The new equation of state can be used for various process models and generalized to include multicomponent mixtures. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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14 pages, 2594 KiB

Open AccessArticle

Solid–Liquid Equilibrium in Co-Amorphous Systems: Experiment and Prediction

by Alžběta Zemánková, Fatima Hassouna, Martin Klajmon and Michal Fulem

Molecules 2023, 28(6), 2492; https://doi.org/10.3390/molecules28062492 - 8 Mar 2023

Cited by 3 | Viewed by 2167

Abstract

In this work, the solid–liquid equilibrium (SLE) of four binary systems combining two active pharmaceutical ingredients (APIs) capable of forming co-amorphous systems (CAMs) was investigated. The binary systems studied were naproxen-indomethacin, naproxen-ibuprofen, naproxen-probucol, and indomethacin-paracetamol. The SLE was experimentally determined by differential scanning [...] Read more.

In this work, the solid–liquid equilibrium (SLE) of four binary systems combining two active pharmaceutical ingredients (APIs) capable of forming co-amorphous systems (CAMs) was investigated. The binary systems studied were naproxen-indomethacin, naproxen-ibuprofen, naproxen-probucol, and indomethacin-paracetamol. The SLE was experimentally determined by differential scanning calorimetry. The thermograms obtained revealed that all binary mixtures investigated form eutectic systems. Melting of the initial binary crystalline mixtures and subsequent quenching lead to the formation of CAM for all binary systems and most of the compositions studied. The experimentally obtained liquidus and eutectic temperatures were compared to theoretical predictions using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state and conductor-like screening model for real solvents (COSMO-RS), as implemented in the Amsterdam Modeling Suite (COSMO-RS-AMS). On the basis of the obtained results, the ability of these models to predict the phase diagrams for the investigated API–API binary systems was evaluated. Furthermore, the glass transition temperature (T_g) of naproxen (NAP), a compound with a high tendency to recrystallize, whose literature values are considerably scattered, was newly determined by measuring and modeling the T_g values of binary mixtures in which amorphous NAP was stabilized. Based on this analysis, erroneous literature values were identified. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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15 pages, 4683 KiB

Open AccessArticle

Density Functional Study on Adsorption of NH₃ and NO_x on the γ-Fe₂O₃ (111) Surface

by Wei Huang, Liang Wang, Lu Dong, Hongyun Hu and Dongdong Ren

Molecules 2023, 28(5), 2371; https://doi.org/10.3390/molecules28052371 - 4 Mar 2023

Cited by 5 | Viewed by 1971

Abstract

γ-Fe₂O₃ is considered to be a promising catalyst for the selective catalytic reduction (SCR) of nitrogen oxide (NO_x). In this study, first-principle calculations based on the density function theory (DFT) were utilized to explore the adsorption mechanism of [...] Read more.

γ-Fe₂O₃ is considered to be a promising catalyst for the selective catalytic reduction (SCR) of nitrogen oxide (NO_x). In this study, first-principle calculations based on the density function theory (DFT) were utilized to explore the adsorption mechanism of NH₃, NO, and other molecules on γ-Fe₂O₃, which is identified as a crucial step in the SCR process to eliminate NO_x from coal-fired flue gas. The adsorption characteristics of reactants (NH₃ and NO_x) and products (N₂ and H₂O) at different active sites of the γ-Fe₂O₃ (111) surface were investigated. The results show that the NH₃ was preferably adsorbed on the octahedral Fe site, with the N atom bonding to the octahedral Fe site. Both octahedral and tetrahedral Fe atoms were likely involved in bonding with the N and O atoms during the NO adsorption. The NO tended to be adsorbed on the tetrahedral Fe site though the combination of the N atom and the Fe site. Meanwhile, the simultaneous bonding of N and O atoms with surface sites made the adsorption more stable than that of single atom bonding. The γ-Fe₂O₃ (111) surface exhibited a low adsorption energy for N₂ and H₂O, suggesting that they could be adsorbed onto the surface but were readily desorbed, thus facilitating the SCR reaction. This work is conducive to reveal the reaction mechanism of SCR on γ-Fe₂O₃ and contributes to the development of low-temperature iron-based SCR catalysts. Full article

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20 pages, 3242 KiB

Open AccessArticle

Simultaneous Predictions of Chemical and Phase Equilibria in Systems with an Esterification Reaction Using PC-SAFT

by Moreno Ascani, Gabriele Sadowski and Christoph Held

Molecules 2023, 28(4), 1768; https://doi.org/10.3390/molecules28041768 - 13 Feb 2023

Cited by 4 | Viewed by 3050

Abstract

The study of chemical reactions in multiple liquid phase systems is becoming more and more relevant in industry and academia. The ability to predict combined chemical and phase equilibria is interesting from a scientific point of view but is also crucial to design [...] Read more.

The study of chemical reactions in multiple liquid phase systems is becoming more and more relevant in industry and academia. The ability to predict combined chemical and phase equilibria is interesting from a scientific point of view but is also crucial to design innovative separation processes. In this work, an algorithm to perform the combined chemical and liquid–liquid phase equilibrium calculation was implemented in the PC-SAFT framework in order to predict the thermodynamic equilibrium behavior of two multicomponent esterification systems. Esterification reactions involve hydrophobic reacting agents and water, which might cause liquid–liquid phase separation along the reaction coordinate, especially if long-chain alcoholic reactants are used. As test systems, the two quaternary esterification systems starting from the reactants acetic acid + 1-pentanol and from the reactants acetic acid + 1-hexanol were chosen. It is known that both quaternary systems exhibit composition regions of overlapped chemical and liquid–liquid equilibrium. To the best of our knowledge, this is the first time that PC-SAFT was used to calculate simultaneous chemical and liquid–liquid equilibria. All the binary subsystems were studied prior to evaluating the predictive capability of PC-SAFT toward the simultaneous chemical equilibria and phase equilibria. Overall, PC-SAFT proved its excellent capabilities toward predicting chemical equilibrium composition in the homogeneous composition range of the investigated systems as well as liquid–liquid phase behavior. This study highlights the potential of a physical sound model to perform thermodynamic-based modeling of chemical reacting systems undergoing liquid–liquid phase separation. Full article

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18 pages, 3357 KiB

Open AccessArticle

Electric Dipole Moments from Stark Effect in Supersonic Expansion: n-Propanol, n-Butanol, and n-Butyl Cyanide

by Zbigniew Kisiel and Krzysztof Habdas

Molecules 2023, 28(4), 1692; https://doi.org/10.3390/molecules28041692 - 10 Feb 2023

Viewed by 2190

Abstract

The orientation and magnitude of the molecular electric dipole moment are key properties relevant to topics ranging from the nature of intermolecular interactions to the quantitative analysis of complex gas-phase mixtures, such as chemistry in astrophysical environments. Stark effect measurements on rotational spectra [...] Read more.

The orientation and magnitude of the molecular electric dipole moment are key properties relevant to topics ranging from the nature of intermolecular interactions to the quantitative analysis of complex gas-phase mixtures, such as chemistry in astrophysical environments. Stark effect measurements on rotational spectra have been the method of choice for isolated molecules but have become less common with the practical disappearance of Stark modulation spectrometers. Their role has been taken over by supersonic expansion measurements within a Fabry-Perot resonator cavity, which introduces specific technical problems that need to be overcome. Several of the adopted solutions are described and compared. Presently, we report precise electric dipole moment determinations for the two most stable conformers of the selected molecules of confirmed or potential astrophysical relevance: n-propanol, n-butanol, and n-butyl cyanide. All dipole moment components have been precisely determined at supersonic expansion conditions by employing specially designed Stark electrodes and a computer program for fitting the measured Stark shifts, inclusive of cases with resolved nuclear quadrupole hyperfine structure. The experimental values are compared with suitable quantum chemistry computations. It is found that, among the tested levels of computation, vibrationally averaged dipole moments are the closest to the observation and the molecular values are, as in the lighter molecules in the series, largely determined by the hydroxyl or nitrile groups. Full article

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17 pages, 5046 KiB

Open AccessArticle

How to Regulate the Migration Ability of Emulsions in Micro-Scale Pores: Droplet Size or Membrane Strength?

by Qi Sun, Zhao-Hui Zhou, Lu Han, Xin-Yuan Zou, Guo-Qiao Li, Qun Zhang, Fan Zhang, Lei Zhang and Lu Zhang

Molecules 2023, 28(4), 1672; https://doi.org/10.3390/molecules28041672 - 9 Feb 2023

Cited by 4 | Viewed by 1751

Abstract

Micro visualization has become an important means of solving colloid and interface scientific problems in enhanced oil recovery. It can establish a relationship between a series of performance evaluations of an oil-water interface under macroscopic dimensions and the actual application effect in confined [...] Read more.

Micro visualization has become an important means of solving colloid and interface scientific problems in enhanced oil recovery. It can establish a relationship between a series of performance evaluations of an oil-water interface under macroscopic dimensions and the actual application effect in confined space, and more truly and reliably reflect the starting and migration behavior of crude oil or emulsion in rock pores. In this article, zwitterionic surfactant alkyl sulfobetaine (ASB) and anionic extended surfactant alkyl polyoxypropylene sulfate (A145) were employed as flooding surfactants. The macroscopic properties of the surfactant solutions, such as the oil-water interfacial tension (IFT), the interfacial dilational rheology and the viscosity of crude oil emulsions, have been measured. At the same time, we link these parameters with the oil displacement effect in several visual glass models and confirm the main factors affecting the migration ability of emulsions in micro-scale pores. The experimental results show that ASB reduces the IFT through mixed adsorption with crude oil fractions. The flat arrangement of the large hydrophilic group of ASB molecules enhances the interactions between the surfactant molecules on the oil-water interface. Compared with sulfate, betaine has higher interfacial membrane strength and emulsion viscosity. A145 has a strong ability to reduce the IFT against crude oil because of the larger size effect of the PO chains at the oil side of the interface. However, the membrane strength of A145 is moderate and the emulsion does not show a viscosity-increasing effect. During the displacement process, the deformation ability of the front emulsions or oil banks is the main controlling factor of the displacement efficiency, which is determined by the membrane strength and emulsion viscosity. The strong interfacial membrane strength and the high emulsion viscosity are not conducive to the migration of droplets in pore throats and may result in low displacement efficiency. Full article

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18 pages, 5244 KiB

Open AccessArticle

Tautomeric Equilibrium in 1-Benzamidoisoquinoline Derivatives

by Patryk Rybczyński, Anna Kaczmarek-Kędziera, Alex Iglesias-Reguant, Damian Plażuk and Borys Ośmiałowski

Molecules 2023, 28(3), 1101; https://doi.org/10.3390/molecules28031101 - 22 Jan 2023

Viewed by 1893

Abstract

In this study, the tautomeric equilibrium of a sequence of 1-benzamidoisoquinoline derivatives was investigated with the tools of NMR spectroscopy and computational chemistry. The equilibrium between different tautomers in these systems could be controlled via the substitution effect, and the relative content of [...] Read more.

In this study, the tautomeric equilibrium of a sequence of 1-benzamidoisoquinoline derivatives was investigated with the tools of NMR spectroscopy and computational chemistry. The equilibrium between different tautomers in these systems could be controlled via the substitution effect, and the relative content of the amide form varied from 74% for the strong electron-donating NMe

_{2}

substituent to 38% for the strong electron-accepting NO

_{2}

group in the phenyl ring. In contrast to the previously investigated 2-phenacylquinoline derivatives, the most stable and thus most abundant tautomer in the 1-benzamidoisoquinoline series except the two most electron-accepting substituents was an amide. The intramolecular hydrogen bond present in the enol tautomer competed with the intermolecular hydrogen bonds created with the solvent molecules and thus was not a sufficient factor to favor this tautomer in the mixture. Although routinely computational studies of tautomeric equilibrium are performed within the continuum solvent models, it is proven here that the inclusion of the explicit solvent is mandatory in order to reproduce the experimental tendencies observed for this type of system, facilitating strong intermolecular hydrogen bonds. Full article

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18 pages, 11324 KiB

Open AccessArticle

Evolution of the Composition and Melting Behavior of Spinnable Pitch during Incubation

by Qian Li, Pingping Zuo, Shijie Qu and Wenzhong Shen

Molecules 2023, 28(3), 1097; https://doi.org/10.3390/molecules28031097 - 21 Jan 2023

Cited by 2 | Viewed by 1710

Abstract

The physical and chemical properties of spinnable pitch showed a huge impact on the performance of resultant pitch carbon fiber even if its physical and chemical properties were slightly changed. Various polycyclic aromatic compounds and abundant free radicals existed in spinnable pitch, and [...] Read more.

The physical and chemical properties of spinnable pitch showed a huge impact on the performance of resultant pitch carbon fiber even if its physical and chemical properties were slightly changed. Various polycyclic aromatic compounds and abundant free radicals existed in spinnable pitch, and there are many interactions among molecules and free radicals. The molecular structure and composition of spinnable pitch were investigated during incubation, and the effect of molecular evaluation on rheological properties of spinnable pitch was illustrated using various characterization methods in this work. It indicated that n-hexane soluble fraction mainly occurred condensation or cleavage, and a small number of heavy components were generated after a long period. The fraction of n-hexane insoluble/toluene soluble underwent molecular condensation and cross-linking in the presence of oxygen-containing radicals and aromatic hydrocarbon radicals, while toluene insoluble/tetrahydrofuran soluble fraction tended to change in large molecules of polycyclic aromatic hydrocarbons. Lastly, tetrahydrofuran insoluble fraction was condensed due to its high aromaticity during the incubation process, and the content of aromatic carbon increased. These changes of composition and structure of spinnable pitch led to its softening point, increase in viscosity and flow activation energy, and deterioration of the rheological property. Full article

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22 pages, 4770 KiB

Open AccessArticle

Conformations of Steroid Hormones: Infrared and Vibrational Circular Dichroism Spectroscopy

by Yanqing Yang, Anna Krin, Xiaoli Cai, Mohammad Reza Poopari, Yuefei Zhang, James R. Cheeseman and Yunjie Xu

Molecules 2023, 28(2), 771; https://doi.org/10.3390/molecules28020771 - 12 Jan 2023

Cited by 8 | Viewed by 3144

Abstract

Steroid hormone molecules may exhibit very different functionalities based on the associated functional groups and their 3D arrangements in space, i.e., absolute configurations and conformations. Infrared (IR) and vibrational circular dichroism (VCD) spectra of four different steroid hormones, namely dehydroepiandrosterone (DHEA), 17α [...] Read more.

Steroid hormone molecules may exhibit very different functionalities based on the associated functional groups and their 3D arrangements in space, i.e., absolute configurations and conformations. Infrared (IR) and vibrational circular dichroism (VCD) spectra of four different steroid hormones, namely dehydroepiandrosterone (DHEA), 17α-methyltestosterone (MTTT), (16α,17)-epoxyprogesterone (Epoxy-P4), and dehydroepiandrosterone acetate (AcO-DHEA), were measured in deuterated dimethyl sulfoxide and some also in carbon tetrachloride. Extensive conformational searches were carried out using the recent developed conformer-rotamer ensemble sampling tool (CREST) which also accounts for solvent effects using an implicit solvation model. All the CREST conformational candidates were then reoptimized at the B3LYP-D3BJ/def2-TZVPD with the PCM of solvent. The good agreements between the experimental IR and VCD spectra and the theoretical simulations provide a conclusive information about their conformational distribution and absolute configurations. The experimental and theoretical IR and VCD spectra of AcO-DHEA in the carbonyl and alkene stretching region showed some discrepancies, and the possible causes related to solvent effects, large amplitude motions and levels of theory used in the modelling were explored in detail. As part of the investigation, additional calculations at the B3LYP-D3BJ/6-31++G (2d,p) and B3LYP-D3BJ/cc-pVTZ levels, as well as some ‘mixed’ calculations with the double-hybrid functional B2PLYP-D3 were also carried out. The results indicate that the double-hybrid functional is important for predicting the correct IR band pattern in the carbonyl and alkene stretching region. Full article

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12 pages, 5054 KiB

Open AccessArticle

Molecular Dynamics Insight into the CO₂ Flooding Mechanism in Wedge-Shaped Pores

by Lu Wang, Weifeng Lyu, Zemin Ji, Lu Wang, Sen Liu, Hongxu Fang, Xiaokun Yue, Shuxian Wei, Siyuan Liu, Zhaojie Wang and Xiaoqing Lu

Molecules 2023, 28(1), 188; https://doi.org/10.3390/molecules28010188 - 26 Dec 2022

Cited by 8 | Viewed by 2037

Abstract

Because of the growing demand for energy, oil extraction under complicated geological conditions is increasing. Herein, oil displacement by CO₂ in wedge-shaped pores was investigated by molecular dynamics simulation. The results showed that, for both single and double wedge-shaped models, pore Ⅱ [...] Read more.

Because of the growing demand for energy, oil extraction under complicated geological conditions is increasing. Herein, oil displacement by CO₂ in wedge-shaped pores was investigated by molecular dynamics simulation. The results showed that, for both single and double wedge-shaped models, pore Ⅱ (pore size from 3 to 8 nm) exhibited a better CO₂ flooding ability than pore Ⅰ (pore size from 8 to 3 nm). Compared with slit-shaped pores (3 and 8 nm), the overall oil displacement efficiency followed the sequence of 8 nm > double pore Ⅱ > single pore Ⅱ > 3 nm > double pore Ⅰ > single pore Ⅰ, which confirmed that the exits of the wedge-shaped pores had determinant effects on CO₂ enhanced oil recovery over their entrances. “Oil/CO₂ inter-pore migration” and “siphoning” phenomena occurred in wedge-shaped double pores by comparing the volumes of oil/CO₂ and the center of mass. The results of the interaction and radial distribution function analyses indicate that the wide inlet and outlet had a larger CO₂–oil contact surface, better phase miscibility, higher interaction, and faster displacement. These findings clarify the CO₂ flooding mechanisms in wedge-shaped pores and provide a scientific basis for the practical applications of CO₂ flooding. Full article

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15 pages, 4623 KiB

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Luminescent Properties of Phosphonate Ester-Supported Neodymium(III) Nitrate and Chloride Complexes

by Miriam Gerstel, Ingo Koehne, Johann Peter Reithmaier, Rudolf Pietschnig and Mohamed Benyoucef

Molecules 2023, 28(1), 48; https://doi.org/10.3390/molecules28010048 - 21 Dec 2022

Cited by 3 | Viewed by 1990

Abstract

This study examines the synthesis of two geminal bisphosphonate ester-supported Ln³⁺ complexes [Ln(L3)₂(NO₃)₃] (Ln = Nd³⁺ (5), La³⁺ (6)) and optical properties of the neodymium(III) complex. These results [...] Read more.

This study examines the synthesis of two geminal bisphosphonate ester-supported Ln³⁺ complexes [Ln(L3)₂(NO₃)₃] (Ln = Nd³⁺ (5), La³⁺ (6)) and optical properties of the neodymium(III) complex. These results are compared to known mono-phosphonate ester-based Nd³⁺ complexes [Nd(L1/L2)₃X₃]_n (X = NO₃⁻, n = 1; Cl⁻, n = 2) (1–4). The optical properties of Nd³⁺ compounds are determined by micro-photoluminescence (µ-PL) spectroscopy which reveals three characteristic metal-centered emission bands in the NIR region related to transitions from ⁴F_3/2 excited state. Additionally, two emission bands from ⁴F_5/2, ²H_9/2 → ⁴I_J (J = 11/2, 13/2) transitions were observed. PL spectroscopy of equimolar complex solutions in dry dichloromethane (DCM) revealed remarkably higher emission intensity of the mono-phosphonate ester-based complexes in comparison to their bisphosphonate ester congener. The temperature-dependent PL measurements enable assignment of the emission lines of the ⁴F_3/2 → ⁴I_9/2 transition. Furthermore, low-temperature polarization-dependent measurements of the transitions from R₁ and R₂ Stark sublevel of ⁴F_3/2 state to the ⁴I_9/2 state for crystals of [Nd(L3)₂(NO₃)₃] (5) are discussed. Full article

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19 pages, 2935 KiB

Open AccessFeature PaperArticle

Behavior of Auramine O in the Aqueous Solution of Two Kolliphors and Their Mixture

by Katarzyna Szymczyk, Andrzej Lewandowski, Anna Zdziennicka, Magdalena Szaniawska and Bronisław Jańczuk

Molecules 2022, 27(23), 8493; https://doi.org/10.3390/molecules27238493 - 2 Dec 2022

Cited by 1 | Viewed by 2234

Abstract

The studies on the behavior of Auramine O (AuO) at the water–air interface and in the bulk phase of the aqueous solution of Kolliphor^® ELP (ELP) and Kolliphor^® RH 40 (RH40) and their mixture were based on the results obtained from [...] Read more.

The studies on the behavior of Auramine O (AuO) at the water–air interface and in the bulk phase of the aqueous solution of Kolliphor^® ELP (ELP) and Kolliphor^® RH 40 (RH40) and their mixture were based on the results obtained from the measurements of the contact angle of water, formamide and diiodomethane on the polytetrafluoroethylene covered by the AuO layer, the surface tension of the aqueous solution of AuO, AuO + ELP, AuO + RH40, AuO + ELP + RH40, density and fluorescence intensity. Based on the obtained results, it was possible to determine components and parameters of the AuO surface tension, concentration and composition of the mixed monolayer, including AuO, ELP and RH40, as well as that of the mixed micelles, and to determine the Gibbs standard free energy of adsorption, micellization and AuO solubilization. The obtained results also showed that surface tension isotherms of the studied solutions can be described by the Szyszkowski equation and the exponential function of the second order and predicted by the Fainerman and Miller equation. In addition, the mixed surface layer composition can be predicted based on the contribution of the components of this layer to the water surface tension reduction. Full article

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15 pages, 660 KiB

Open AccessArticle

Heat Capacity Estimation Using a Complete Set of Homodesmotic Reactions for Organic Compounds

by Sergey L. Khursan

Molecules 2022, 27(22), 7814; https://doi.org/10.3390/molecules27227814 - 13 Nov 2022

Cited by 3 | Viewed by 1885

Abstract

Reliable information about isobaric heat capacities C_P is necessary to determine the energies of organic compounds and chemical processes at an arbitrary temperature. In this work, the possibility of theoretical estimation of C_P by the homodesmotic method is analyzed. Three cases [...] Read more.

Reliable information about isobaric heat capacities C_P is necessary to determine the energies of organic compounds and chemical processes at an arbitrary temperature. In this work, the possibility of theoretical estimation of C_P by the homodesmotic method is analyzed. Three cases of C_P calculation applying the methodology of the complete set of homodesmotic reactions (CS HDRs) are considered: the gas- and liquid-phase C_P of organic compounds of various classes at 298 K (the mean absolute value of reaction heat capacity, MA ΔC_P = 1.44 and 2.83 J/mol·K for the gas and liquid phase, correspondingly); and the gas-phase C_P of n-alkanes C₂–C₁₀ in the temperature range of 200–1500 K with an average error in calculating the heat capacity of 0.93 J/mol·K. In the latter case, the coefficients of the Shomate equation are determined for all n-alkanes that satisfy the homodesmoticity condition. New values of gas- and liquid-phase heat capacities are obtained for 41 compounds. The CS HDRs-based approach for estimating the C_P of organic compounds is characterized by high accuracy, which is not inferior to that of the best C_P-additive schemes and allows us to analyze the reproducibility of the calculation results and eliminate unreliable reference data. Full article

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25 pages, 4413 KiB

Open AccessArticle

Luminescent Carbon Dots from Wet Olive Pomace: Structural Insights, Photophysical Properties and Cytotoxicity

by Diogo A. Sousa, Luís F. V. Ferreira, Alexander A. Fedorov, Ana M. B. do Rego, Ana M. Ferraria, Adriana B. Cruz, Mário N. Berberan-Santos and José V. Prata

Molecules 2022, 27(19), 6768; https://doi.org/10.3390/molecules27196768 - 10 Oct 2022

Cited by 9 | Viewed by 2910

Abstract

Carbon nanomaterials endowed with significant luminescence have been synthesized for the first time from an abundant, highly localized waste, the wet pomace (WP), a semi-solid by-product of industrial olive oil production. Synthetic efforts were undertaken to outshine the photoluminescence (PL) of carbon nanoparticles [...] Read more.

Carbon nanomaterials endowed with significant luminescence have been synthesized for the first time from an abundant, highly localized waste, the wet pomace (WP), a semi-solid by-product of industrial olive oil production. Synthetic efforts were undertaken to outshine the photoluminescence (PL) of carbon nanoparticles through a systematic search of the best reaction conditions to convert the waste biomass, mainly consisting in holocellulose, lignin and proteins, into carbon dots (CDs) by hydrothermal carbonization processes. Blue-emitting CDs with high fluorescence quantum yields were obtained. Using a comprehensive set of spectroscopic tools (FTIR, Raman, XPS, and ¹H/¹³C NMR) in combination with steady-state and time-resolved fluorescence spectroscopy, a rational depiction of WP-CDs structures and their PL properties was reached. WP-CDs show the up-conversion of PL capabilities and negligible cytotoxicity against two mammalian cell lines (L929 and HeLa). Both properties are excellent indicators for their prospective application in biological imaging, biosensing, and dynamic therapies driven by light. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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17 pages, 2216 KiB

Open AccessArticle

Mechanism of the Micellar Solubilization of Curcumin by Mixed Surfactants of SDS and Brij35 via NMR Spectroscopy

by Xiao Zhan, Zhaoxia Wu, Zhong Chen and Xiaohong Cui

Molecules 2022, 27(15), 5032; https://doi.org/10.3390/molecules27155032 - 8 Aug 2022

Cited by 11 | Viewed by 2721

Abstract

The micellar solubilization mechanism of curcumin by mixed surfactants of SDS and Brij35 was investigated at the molecular scale by NMR spectroscopy. Through the investigation of the micelle formation process, types and structures of mixed micelles and solubilization sites, the intrinsic factors influencing [...] Read more.

The micellar solubilization mechanism of curcumin by mixed surfactants of SDS and Brij35 was investigated at the molecular scale by NMR spectroscopy. Through the investigation of the micelle formation process, types and structures of mixed micelles and solubilization sites, the intrinsic factors influencing the solubilization capacity were revealed. For systems with α_SDS = 0.5 and 0.2, the obtained molar solubilization ratios (MSRs) are consistent with the MSR_ideal values. However, for α_SDS = 0.8, the solubilization capacity of curcumin is weakened compared to the MSR_ideal. Furthermore, only one single mixed SDS/Brij35 micelles are formed for α_SDS = 0.5 and 0.2. However, for α_SDS = 0.8, there are separate SDS-rich and Brij35-rich mixed micelles formed. In addition, NOESY spectra show that the interaction patterns of SDS and Brij35 in mixed micelles are similar for three systems, as are the solubilization sites of curcumin. Therefore, for α_SDS = 0.5 and 0.2 with single mixed micelles formed, the solubility of curcumin depends only on the mixed micelle composition, which is almost equal to the surfactant molar ratio. Although curcumin is solubilized in both separate micelles at α_SDS = 0.8, a less stable micelle structure may be responsible for the low solubility. This study provides new insights into the investigation and application of mixed micelle solubilization. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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23 pages, 1491 KiB

Open AccessArticle

All-Atom Molecular Dynamics of Pure Water–Methane Gas Hydrate Systems under Pre-Nucleation Conditions: A Direct Comparison between Experiments and Simulations of Transport Properties for the Tip4p/Ice Water Model

by André Guerra, Samuel Mathews, Milan Marić, Phillip Servio and Alejandro D. Rey

Molecules 2022, 27(15), 5019; https://doi.org/10.3390/molecules27155019 - 7 Aug 2022

Cited by 8 | Viewed by 2848

Abstract

(1) Background: New technologies involving gas hydrates under pre-nucleation conditions such as gas separations and storage have become more prominent. This has necessitated the characterization and modeling of the transport properties of such systems. (2) Methodology: This work explored methane hydrate systems under [...] Read more.

(1) Background: New technologies involving gas hydrates under pre-nucleation conditions such as gas separations and storage have become more prominent. This has necessitated the characterization and modeling of the transport properties of such systems. (2) Methodology: This work explored methane hydrate systems under pre-nucleation conditions. All-atom molecular dynamics simulations were used to quantify the performance of the TIP4P/2005 and TIP4P/Ice water models to predict the viscosity, diffusivity, and thermal conductivity using various formulations. (3) Results: Molecular simulation equilibrium was robustly demonstrated using various measures. The Green–Kubo estimation of viscosity outperformed other formulations when combined with TIP4P/Ice, and the same combination outperformed all TIP4P/2005 formulations. The Green–Kubo TIP4P/Ice estimation of viscosity overestimates (by 84% on average) the viscosity of methane hydrate systems under pre-nucleation conditions across all pressures considered (0–5 MPag). The presence of methane was found to increase the average number of hydrogen bonds over time (6.7–7.8%). TIP4P/Ice methane systems were also found to have 16–19% longer hydrogen bond lifetimes over pure water systems. (4) Conclusion: An inherent limitation in the current water force field for its application in the context of transport properties estimations for methane gas hydrate systems. A re-parametrization of the current force field is suggested as a starting point. Until then, this work may serve as a characterization of the deviance in viscosity prediction. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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10 pages, 1648 KiB

Open AccessArticle

Never Cared for What They Do: High Structural Stability of Guanine-Quadruplexes in the Presence of Strand-Break Damage

by Tom Miclot, Cécilia Hognon, Emmanuelle Bignon, Alessio Terenzi, Stéphanie Grandemange, Giampaolo Barone and Antonio Monari

Molecules 2022, 27(10), 3256; https://doi.org/10.3390/molecules27103256 - 19 May 2022

Cited by 2 | Viewed by 1895

Abstract

DNA integrity is an important factor that assures genome stability and, more generally, the viability of cells and organisms. In the presence of DNA damage, the normal cell cycle is perturbed when cells activate their repair processes. Although efficient, the repair system is [...] Read more.

DNA integrity is an important factor that assures genome stability and, more generally, the viability of cells and organisms. In the presence of DNA damage, the normal cell cycle is perturbed when cells activate their repair processes. Although efficient, the repair system is not always able to ensure complete restoration of gene integrity. In these cases, mutations not only may occur, but the accumulation of lesions can either lead to carcinogenesis or reach a threshold that induces apoptosis and programmed cell death. Among the different types of DNA lesions, strand breaks produced by ionizing radiation are the most toxic due to the inherent difficultly of repair, which may lead to genomic instability. In this article we show, by using classical molecular simulation techniques, that compared to canonical double-helical B-DNA, guanine-quadruplex (G4) arrangements show remarkable structural stability, even in the presence of two strand breaks. Since G4-DNA is recognized for its regulatory roles in cell senescence and gene expression, including oncogenes, this stability may be related to an evolutionary cellular response aimed at minimizing the effects of ionizing radiation. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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19 pages, 2508 KiB

Open AccessReview

Effects and Influence of External Electric Fields on the Equilibrium Properties of Tautomeric Molecules

by Ivan Angelov, Lidia Zaharieva and Liudmil Antonov

Molecules 2023, 28(2), 695; https://doi.org/10.3390/molecules28020695 - 10 Jan 2023

Cited by 9 | Viewed by 2696

Abstract

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an [...] Read more.

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an oriented external electric field (OEEF) on excited-state intramolecular proton transfer (ESIPT) from the studies available to date. The possibilities provided by OEEF for regulating several processes and studying physicochemical processes in tautomers have turned this direction into an attractive area of research due to its numerous applications. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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26 pages, 6933 KiB

Open AccessReview

Organic Small-Molecule Electrodes: Emerging Organic Composite Materials in Supercapacitors for Efficient Energy Storage

by Yuanyuan He, Qiaoqiao Wei, Ning An, Congcong Meng and Zhongai Hu

Molecules 2022, 27(22), 7692; https://doi.org/10.3390/molecules27227692 - 9 Nov 2022

Cited by 13 | Viewed by 3125

Abstract

Organic small molecules with electrochemically active and reversible redox groups are excellent candidates for energy storage systems due to their abundant natural origin and design flexibility. However, their practical application is generally limited by inherent electrical insulating properties and high solubility. To achieve [...] Read more.

Organic small molecules with electrochemically active and reversible redox groups are excellent candidates for energy storage systems due to their abundant natural origin and design flexibility. However, their practical application is generally limited by inherent electrical insulating properties and high solubility. To achieve both high energy density and power density, organic small molecules are usually immobilized on the surface of a carbon substrate with a high specific surface area and excellent electrical conductivity through non-covalent interactions or chemical bonds. The resulting composite materials are called organic small-molecule electrodes (OMEs). The redox reaction of OMEs occurs near the surface with fast kinetic and higher utilization compared to storing charge through diffusion-limited Faraday reactions. In the past decade, our research group has developed a large number of novel OMEs with different connections or molecular skeletons. This paper introduces the latest development of OMEs for efficient energy storage. Furthermore, we focus on the design motivation, structural advantages, charge storage mechanism, and various electrode parameters of OMEs. With small organic molecules as the active center, OMEs can significantly improve the energy density at low molecular weight through proton-coupled electron transfer, which is not limited by lattice size. Finally, we outline possible trends in the rational design of OMEs toward high-performance supercapacitors. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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21 pages, 28902 KiB

Open AccessReview

A Ten-Year Perspective on Twist-Bend Nematic Materials

by Richard J. Mandle

Molecules 2022, 27(9), 2689; https://doi.org/10.3390/molecules27092689 - 21 Apr 2022

Cited by 41 | Viewed by 3102

Abstract

The discovery of the twist-bend nematic phase (N_TB) is a milestone within the field of liquid crystals. The N_TB phase has a helical structure, with a repeat length of a few nanometres, and is therefore chiral, even when formed by [...] Read more.

The discovery of the twist-bend nematic phase (N_TB) is a milestone within the field of liquid crystals. The N_TB phase has a helical structure, with a repeat length of a few nanometres, and is therefore chiral, even when formed by achiral molecules. The discovery and rush to understand the rich physics of the N_TB phase has provided a fresh impetus to the design and characterisation of dimeric and oligomeric liquid crystalline materials. Now, ten years after the discovery of the N_TB phase, we review developments in this area, focusing on how molecular features relate to the incidence of this phase, noting the progression from simple symmetrical dimeric materials towards complex oligomers, non-covalently bonded supramolecular systems. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry)

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