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13 pages, 459 KiB

Open AccessArticle

Application of Surface Complexation Modeling to Investigate the Mechanism of Cu²⁺ Adsorption on TiO₂, Al₂O₃, and SiO₂ Under High Surface Coverage

by Wojciech Piasecki and Karolina Lament

Molecules 2024, 29(23), 5595; https://doi.org/10.3390/molecules29235595 (registering DOI) - 26 Nov 2024

Abstract

We have shown that the adsorption of Cu²⁺ ions on various metal oxides, depending on the pH of the solution, can be described assuming the formation of only two surface complexes with surface hydroxyl groups SOH: SOCu(OH) and SOCu⁺. Using [...] Read more.

We have shown that the adsorption of Cu²⁺ ions on various metal oxides, depending on the pH of the solution, can be described assuming the formation of only two surface complexes with surface hydroxyl groups SOH: SOCu(OH) and SOCu⁺. Using an ion-selective electrode for Cu²⁺, we determined the adsorption edges, i.e., the dependence of the amount of adsorbed metal expressed as a percentage depending on the solution pH for three oxides: TiO₂, Al₂O₃, and SiO₂. The measurements were carried out with high surface coverage where the ratio of the adsorption sites/copper ions in the system were from 2 to 3, depending on the oxide. Simultaneously, with the adsorption edge, the hydrogen surface charge density and the electrokinetic potential of the oxide particles were measured as a function of pH. These three types of experimental data were fitted all together using the surface complexation model (2-pK TLM). In modeling, it was not necessary to consider the precipitation of Cu(OH)₂ on the oxide surface to obtain good agreement with the data. Additionally, it was shown that the presence of charged surface species SOCu⁺ (about 10% of total adsorbed copper) was crucial to fit the data for zeta potential. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

13 pages, 1948 KiB

Open AccessArticle

Mechanical Behavior of Plasma-Treated Metal–Rubber Assemblies

by Lazhar Benyahia, Marisol Ji and Fabienne Poncin-Epaillard

Molecules 2024, 29(23), 5590; https://doi.org/10.3390/molecules29235590 - 26 Nov 2024

Abstract

Metal–elastomer assemblies, such as aluminum–NBR and stainless steel–FKM, widely used for sealing or damping functions in various fields, are currently prepared with highly toxic bonding agents. To substitute the use of these liquids, plasma technologies were applied. The chemical nature of the plasma [...] Read more.

Metal–elastomer assemblies, such as aluminum–NBR and stainless steel–FKM, widely used for sealing or damping functions in various fields, are currently prepared with highly toxic bonding agents. To substitute the use of these liquids, plasma technologies were applied. The chemical nature of the plasma polymerized adhesives is found to have no influence on the viscoelastic properties of the elastomer. Furthermore, cohesive assemblies were prepared with acetylene, acrylic acid or maleic anhydride as plasma polymerized layers. Their adhesive performances were evaluated thanks to a tack-like test. Their adhesion mechanisms, even if complex, are namely identified as the interdiffusion of elastomer chains within the plasma-based polymer film and the thermodynamic adhesion. Specifically, we propose that the adhesiveness of metal–rubber assemblies, correlated to the maximum stress at failure in the tack-like test, is proportional to an energy per unit volume. This new variable is determined as the ratio of the surface tension to the thinness of the plasma adhesive. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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7 pages, 266 KiB

Open AccessArticle

Stokes–Einstein Relation in Different Models of Water

by Sergey Khrapak and Alexey Khrapak

Molecules 2024, 29(23), 5587; https://doi.org/10.3390/molecules29235587 - 26 Nov 2024

Abstract

The purpose of this paper is to discuss to which extent a microscopic version of the Stokes–Einstein (SE) relation without the hydrodynamic radius applies to liquid water. We demonstrate that the self-diffusion and shear viscosity data for five popular water models, recently reported [...] Read more.

The purpose of this paper is to discuss to which extent a microscopic version of the Stokes–Einstein (SE) relation without the hydrodynamic radius applies to liquid water. We demonstrate that the self-diffusion and shear viscosity data for five popular water models, recently reported by Ando [J. Chem. Phys. 159, 101102 (2023)], are in excellent agreement with the SE relation. The agreement with experimental results is also quite impressive. The limitations on the applicability of the SE relation are briefly discussed. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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14 pages, 3429 KiB

Open AccessArticle

Heat Capacities of α-, β-, and γ- Polymorphs of Glycine

by Václav Pokorný, Vojtěch Štejfa, Jakub Havlín, Michal Fulem and Květoslav Růžička

Molecules 2024, 29(22), 5366; https://doi.org/10.3390/molecules29225366 - 14 Nov 2024

Viewed by 297

Abstract

As a part of our effort to establish reliable thermodynamic data for amino acids, the heat capacity and phase behavior are reported for two stable polymorphs (α and γ) of glycine (aminoacetic acid, CAS RN: 56-40-6). Prior to heat capacity measurement, thermogravimetric analysis [...] Read more.

As a part of our effort to establish reliable thermodynamic data for amino acids, the heat capacity and phase behavior are reported for two stable polymorphs (α and γ) of glycine (aminoacetic acid, CAS RN: 56-40-6). Prior to heat capacity measurement, thermogravimetric analysis and X-ray powder diffraction were performed to determine decomposition temperatures and initial crystal structures, respectively. The literature heat capacities obtained by adiabatic calorimetry are available in the temperature interval (7–304). The literature data were used for validating performance of our relaxation (heat-pulse) calorimeter, which was used for measurement of the heat capacity of α-glycine in the temperature interval (2–267) K. The crystal heat capacities of the α- and γ-glycine were extended towards higher temperatures using Tian–Calvet calorimetry in the temperature interval (262–358) and power compensation DSC in the temperature interval (310–449) K. As a result, reference heat capacities and thermodynamic functions for the crystalline phase from 0 K up to 450/435 K for α/γ-glycine were developed. The literature heat capacities for β-glycine over the range 0 K to 295 K were treated in the same manner in order to provide thermodynamic data for all three polymorphs existing at the atmospheric pressure. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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18 pages, 6787 KiB

Open AccessArticle

Multifunctional Dy³⁺ Complexes with Triphenylmethanolates: Structural Diversity, Luminescence, and Magnetic Relaxation

by Gautier Félix, Aleksei O. Tolpygin, Aurore Larquey, Ilia A. Gogolev, Yulia V. Nelyubina, Yannick Guari, Joulia Larionova and Alexander A. Trifonov

Molecules 2024, 29(22), 5343; https://doi.org/10.3390/molecules29225343 - 13 Nov 2024

Viewed by 381

Abstract

The coordination environment of magneto-luminescent Dy³⁺-based Single-Molecule Magnets (SMM) is a crucial factor influencing both magnetic and luminescent properties. In this work, we explore how triphenylmethanolate (Ph₃CO⁻), in combination with other ligands, can modulate the structure and, [...] Read more.

The coordination environment of magneto-luminescent Dy³⁺-based Single-Molecule Magnets (SMM) is a crucial factor influencing both magnetic and luminescent properties. In this work, we explore how triphenylmethanolate (Ph₃CO⁻), in combination with other ligands, can modulate the structure and, therefore, the magnetic properties of Dy³⁺-based SMM. Using triphenylmethanolate in combination with THF and pyridine (Py) as co-ligands, we synthesized a series of mononuclear cis-[Dy(OCPh₃)₂(THF)₄][BPh₄]·(2,6-Me₂C₅H₃N) (1), trans-Dy(OCPh₃)₃(THF)₂ (2), fac-Dy(OCPh₃)₃(py)₃ (3) and dinuclear [(Ph₃CO)Dy(THF){(μ²–Cl)₂Li(THF)₂}μ²–Cl]₂ (4) complexes where the Dy³⁺ ion presents five- or six-coordinate geometries. Dinuclear compound 4 exhibits a genuine SMM behavior with a relatively high energy barrier of 421 cm⁻¹, while mononuclear complexes 1–3 are field-induced SMM. These complexes also present Dy³⁺-characteristic luminescence, highlighting their multifunctional character. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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15 pages, 3940 KiB

Open AccessArticle

Supersaturated Liquid Formulation of Pazopanib Hydrochloride Loaded with Synergistic Precipitation Inhibitors

by Jin Woo Park, Sa-Won Lee, Jun Hak Lee, Jun-Pil Jee, Han-Joo Maeng, Dong-Jin Jang and Kwan Hyung Cho

Molecules 2024, 29(22), 5267; https://doi.org/10.3390/molecules29225267 - 7 Nov 2024

Viewed by 449

Abstract

This study aimed to develop a supersaturated liquid formulation (SSLF) to enhance the solubility and dissolution of pazopanib hydrochloride (PZH). SSLFs were prepared by a simple stirring method in a heated silicon oil bath (70 °C). PZH showed highly pH-dependent solubility (pH 1.2 [...] Read more.

This study aimed to develop a supersaturated liquid formulation (SSLF) to enhance the solubility and dissolution of pazopanib hydrochloride (PZH). SSLFs were prepared by a simple stirring method in a heated silicon oil bath (70 °C). PZH showed highly pH-dependent solubility (pH 1.2 > water >> pH 4.0 and pH 6.8) at 37 °C. The SSLF containing glycerol and polyvinylpyrrolidone K30 (PVP K30) increased PZH dispersion solubility (273.66 ± 48.91 μg/mL) at pH 6.8 by more than 50-fold compared with that of glycerol alone (<5 μg/mL), and the PZH precipitate particle size was considerably small (<100 nm). Moreover, the dispersion solubility of PZH from SSLF containing additional propylene glycol (PG) increased to 364.41 ± 2.47 μg/mL. The optimized SSLF10 (PZH/glycerol/PG/PVP K30 = 10/50/20/20, w/w) exhibited a high dissolution rate at pH 4.0 (>90%) and 6.8 (>55%) until 360 min, whereas PZH powder and PZH glycerol solution showed pH-dependent, low dissolution rates (<10%) under similar conditions. The supersaturation ratio of SSLF10 was very high at 29.88 and 18.36 at pH 6.8 and 4.0, respectively, indicating a stable PZH supersaturation solution. In the transmission electron microscopy analysis, PVP K30 and PG in SSLF10 synergistically suppressed PZH precipitation and recrystallization with small amorphous particles (<200 nm). Therefore, SSLF10 would be a promising formulation with enhanced solubility and dissolution rates regardless of medium pH. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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22 pages, 1315 KiB

Open AccessArticle

The Ordered Structures Formed by Janus-like Particles on a Triangular Lattice

by Andrzej Patrykiejew

Molecules 2024, 29(21), 5215; https://doi.org/10.3390/molecules29215215 - 4 Nov 2024

Viewed by 678

Abstract

The formation of ordered structures by Janus-like particles, composed of two parts (A and B), with orientation-dependent interactions on a triangular lattice was studied using Monte Carlo methods. The assumed lattice model allows each particle to take on one of the six orientations. [...] Read more.

The formation of ordered structures by Janus-like particles, composed of two parts (A and B), with orientation-dependent interactions on a triangular lattice was studied using Monte Carlo methods. The assumed lattice model allows each particle to take on one of the six orientations. The interaction between the A parts of neighboring particles was assumed to be attractive, while the AB and BB interactions were assumed to be repulsive. Moreover, it was assumed that the interaction between a pair of neighboring particles depended on the degrees to which their AA, AB, and BB parts face each other. It was shown that several ordered phases of different densities and structures may appear, depending on the magnitudes of AB and BB interactions. In particular, we found several structures composed of small clusters consisting of three (

O T

), four (

O R

), and seven (S) particles, surrounded by empty sites, the lamellar phases (

O L

,

O L_{1}

, and

O L_{3}

), the structures with hexagonal symmetry (

R_{3 \times 3}

and K), as well as the structures with more complex symmetry (

R_{5 \times 5}

and

L A D)

. Several phase diagrams were evaluated, which demonstrated that the stability regions of different ordered phases are primarily determined by the strengths of repulsive AB and BB interactions. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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20 pages, 903 KiB

Open AccessArticle

Adsorption and Permeation Events in Molecular Diffusion

by Denis S. Grebenkov

Molecules 2024, 29(21), 5012; https://doi.org/10.3390/molecules29215012 - 23 Oct 2024

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Abstract

How many times can a diffusing molecule permeate across a membrane or be adsorbed on a substrate? We employ an encounter-based approach to find the statistics of adsorption or permeation events for molecular diffusion in a general confining medium. Various features of these [...] Read more.

How many times can a diffusing molecule permeate across a membrane or be adsorbed on a substrate? We employ an encounter-based approach to find the statistics of adsorption or permeation events for molecular diffusion in a general confining medium. Various features of these statistics are illustrated for two practically relevant cases: a flat boundary and a spherical confinement. Some applications of these fundamental results are discussed. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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12 pages, 3730 KiB

Open AccessArticle

Microfluidics-Assisted Polymer Vesicle Budding in Emulsion Systems: A Promising Approach for the Preparation and Application of Polymer Vesicles

by Donghua Dong, Jilai Zhan, Guoxing Liao, Tong Zhu, Qianqian Yu, Wei Zhang and Linge Wang

Molecules 2024, 29(20), 4802; https://doi.org/10.3390/molecules29204802 - 11 Oct 2024

Viewed by 676

Abstract

The challenge of producing polymer vesicles remains difficult, despite numerous attempts to modulate the kinetics of polymer vesicle budding and achieve precise control over the membrane characteristics. An innovative approach that incorporates the use of copolymer-loaded single-emulsion droplets is proposed to address this [...] Read more.

The challenge of producing polymer vesicles remains difficult, despite numerous attempts to modulate the kinetics of polymer vesicle budding and achieve precise control over the membrane characteristics. An innovative approach that incorporates the use of copolymer-loaded single-emulsion droplets is proposed to address this challenge. This method enables the precise manipulation of micelles and polymer vesicles’ composition, structures and dimensions. The emulsion contracts and forms microspheres when the copolymer concentrations exceed > 0.5 wt%, resulting in the formation of nano polymer vesicles. Conversely, the copolymer spontaneously forms micro polymer vesicles and micelles through vesicle budding at lower concentrations. The spontaneous production of vesicles and micelles can be induced by modifying the copolymer concentration in the emulsion. Our discoveries have a significant impact relative to the development of copolymer membranes and contribute to an enhanced comprehension of the mass manufacturing of polymer vesicles from single emulsions. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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27 pages, 9632 KiB

Open AccessArticle

In Situ Raman Spectroscopy as a Valuable Tool for Monitoring Crystallization Kinetics in Molecular Glasses

by Roman Svoboda, Nicola Koutná, Magdalena Hynková and Marek Pakosta

Molecules 2024, 29(19), 4769; https://doi.org/10.3390/molecules29194769 - 9 Oct 2024

Viewed by 790

Abstract

The performance of in situ Raman microscopy (IRM) in monitoring the crystallization kinetics of amorphous drugs (griseofulvin and indomethacin) was evaluated using a comparison with the data obtained via differential scanning calorimetry (DSC). IRM was found to accurately and sensitively detect the initial [...] Read more.

The performance of in situ Raman microscopy (IRM) in monitoring the crystallization kinetics of amorphous drugs (griseofulvin and indomethacin) was evaluated using a comparison with the data obtained via differential scanning calorimetry (DSC). IRM was found to accurately and sensitively detect the initial stages of the crystal growth processes, including the rapid glass–crystal surface growth or recrystallization between polymorphic phases, with the reliable localized identification of the particular polymorphs being the main advantage of IRM over DSC. However, from the quantitative point of view, the reproducibility of the IRM measurements was found to be potentially significantly hindered due to inaccurate temperature recording and calibration, variability in the Raman spectra corresponding to the fully amorphous and crystalline phases, and an overly limited number of spectra possible to collect during acceptable experimental timescales because of the applied heating rates. Since theoretical simulations showed that, from the kinetics point of view, the constant density of collected data points per kinetic effect results in the smallest distortions, only the employment of the fast Raman mapping functions could advance the performance of IRM above that of calorimetric measurements. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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14 pages, 3954 KiB

Open AccessArticle

Exploring the Impact of Subtle Differences in the Chemical Structure of 1-Alkylsulfates and 1-Alkylsulfonates on Their Interactions with Human Serum Albumin

by Ola Grabowska, Ankur Singh, Krzysztof Żamojć, Sergey A. Samsonov and Dariusz Wyrzykowski

Molecules 2024, 29(19), 4598; https://doi.org/10.3390/molecules29194598 - 27 Sep 2024

Viewed by 457

Abstract

The objective of this study was to examine the interactions between anionic surfactants, specifically 1-alkylsulfonates (KXS) and 1-alkylsulfates (SXS) ions, with human serum albumin (HSA). A combination of experimental techniques, including isothermal titration calorimetry (ITC), steady-state fluorescence spectroscopy (SF), and molecular dynamics-based approaches [...] Read more.

The objective of this study was to examine the interactions between anionic surfactants, specifically 1-alkylsulfonates (KXS) and 1-alkylsulfates (SXS) ions, with human serum albumin (HSA). A combination of experimental techniques, including isothermal titration calorimetry (ITC), steady-state fluorescence spectroscopy (SF), and molecular dynamics-based approaches was employed to gain a comprehensive understanding of these processes. It has been demonstrated that the subtle variations in the charge distribution on the anionic surfactant headgroups have a significant impact on the number of binding sites, the stoichiometry of the resulting complexes, and the strength of the interactions between the surfactants and the protein. Additionally, we established that the affinity of the investigated ligands to specific regions on the protein surface is governed by both the charge of the surfactant headgroup and the length of the aliphatic hydrocarbon chain. In summary, the findings highlight the crucial role of charge distribution on surfactant functional groups in the binding mode and the thermodynamic stability of surfactant–protein complexes. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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12 pages, 18301 KiB

Open AccessArticle

Effects of Antisolvent Treatment on Copper(I) Thiocyanate Hole Transport Layer in n-i-p Perovskite Solar Cells

by Sehyun Jung, Seungsun Choi, Woojin Shin, Hyesung Oh, Nahyun Kim, Sunghun Kim, Namkook Kim, Kyuhyun Kim and Hyunbok Lee

Molecules 2024, 29(18), 4440; https://doi.org/10.3390/molecules29184440 - 19 Sep 2024

Viewed by 738

Abstract

Copper(I) thiocyanate (CuSCN) is considered an efficient HTL of low cost and with high stability in perovskite solar cells (PSCs). However, the diethyl sulfide solvent used for CuSCN preparation is known to cause damage to the underlying perovskite layer in n-i-p PSCs. Antisolvent [...] Read more.

Copper(I) thiocyanate (CuSCN) is considered an efficient HTL of low cost and with high stability in perovskite solar cells (PSCs). However, the diethyl sulfide solvent used for CuSCN preparation is known to cause damage to the underlying perovskite layer in n-i-p PSCs. Antisolvent treatment of CuSCN during spin-coating can effectively minimize interfacial interactions. However, the effects of antisolvent treatment are not sufficiently understood. In this study, the effects of five different antisolvents were investigated. Scanning electron microscopy and X-ray diffraction analyses showed that the antisolvent treatment improved the crystallinity of the CuSCN layer on the perovskite layer and reduced damage to the perovskite layer. However, X-ray and ultraviolet photoelectron spectroscopy analyses showed that antisolvent treatment did not affect the chemical bonds or electronic structures of CuSCN. As a result, the power conversion efficiency of the PSCs was increased from 14.72% for untreated CuSCN to 15.86% for ethyl-acetate-treated CuSCN. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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19 pages, 7747 KiB

Open AccessArticle

Modeling UV/Vis Absorption Spectra of Food Colorants in Solution: Anthocyanins and Curcumin as Case Studies

by Sara Gómez, Piero Lafiosca and Tommaso Giovannini

Molecules 2024, 29(18), 4378; https://doi.org/10.3390/molecules29184378 - 14 Sep 2024

Viewed by 778

Abstract

We present a comprehensive computational study of UV/Vis absorption spectra of significant food colorants, specifically anthocyanins and curcumin tautomers, dissolved in polar protic solvents, namely water and ethanol. The absorption spectra are simulated using two fully polarizable quantum mechanical (QM)/molecular mechanics (MM) models [...] Read more.

We present a comprehensive computational study of UV/Vis absorption spectra of significant food colorants, specifically anthocyanins and curcumin tautomers, dissolved in polar protic solvents, namely water and ethanol. The absorption spectra are simulated using two fully polarizable quantum mechanical (QM)/molecular mechanics (MM) models based on the fluctuating charge (FQ) and fluctuating charge and dipoles (FQF

μ

) force fields. To accurately capture the dynamical aspects of the solvation phenomenon, atomistic approaches are combined with configurational sampling obtained through classical molecular dynamics (MD) simulations. The calculated QM/FQ and QM/FQF

μ

spectra are then compared with experiments. Our findings demonstrate that a precise reproduction of the UV/Vis spectra of the studied pigments can be achieved by adequately accounting for configurational sampling, polarization effects, and hydrogen bonding interactions. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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18 pages, 5017 KiB

Open AccessArticle

Thermodynamic Study on Biomimetic Legionella gormanii Bacterial Membranes

by Katarzyna Pastuszak, Marta Palusińska-Szysz, Agnieszka Ewa Wiącek and Małgorzata Jurak

Molecules 2024, 29(18), 4367; https://doi.org/10.3390/molecules29184367 - 14 Sep 2024

Viewed by 613

Abstract

The presented studies were aimed at determining the interactions in model membranes (Langmuir monolayers) created of phospholipids (PL) isolated from Legionella gormanii bacteria cultured with (PL + choline) or without (PL − choline) choline and to describe the impact of an antimicrobial peptide, [...] Read more.

The presented studies were aimed at determining the interactions in model membranes (Langmuir monolayers) created of phospholipids (PL) isolated from Legionella gormanii bacteria cultured with (PL + choline) or without (PL − choline) choline and to describe the impact of an antimicrobial peptide, human cathelicidin LL-37, on PL’s monolayer behavior. The addition of choline to the growth medium influenced the mutual proportions of phospholipids extracted from L. gormanii. Four classes of phospholipids—phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL), and their mixtures—were used to register compression isotherms with or without the LL-37 peptide in the subphase. Based on them the excess area (

A_{e}

), excess (

Δ G_{e}

), and total (

Δ G_{m}

) Gibbs energy of mixing were determined. The thermodynamic analyses revealed that the PL − choline monolayer showed greater repulsive forces between molecules in comparison to the ideal system, while the PL + choline monolayer was characterized by greater attraction. The LL-37 peptide affected the strength of interactions between phospholipids’ molecules and reduced the monolayers stability. Accordingly, the changes in interactions in the model membranes allowed us to determine the difference in their susceptibility to the LL-37 peptide depending on the choline supplementation of bacterial culture. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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14 pages, 2053 KiB

Open AccessArticle

SF₆ Negative Ion Formation in Charge Transfer Experiments

by Sarvesh Kumar, Masamitsu Hoshino, Boutheïna Kerkeni, Gustavo García, Ghofrane Ouerfelli, Muneerah Mogren Al-Mogren and Paulo Limão-Vieira

Molecules 2024, 29(17), 4118; https://doi.org/10.3390/molecules29174118 - 30 Aug 2024

Viewed by 620

Abstract

In the present work, we report an update and extension of the previous ion-pair formation study of Hubers, M.M.; Los, J. Chem. Phys. 1975, 10, 235–259, noting new fragment anions from time-of-flight mass spectrometry. The branching ratios obtained from the [...] Read more.

In the present work, we report an update and extension of the previous ion-pair formation study of Hubers, M.M.; Los, J. Chem. Phys. 1975, 10, 235–259, noting new fragment anions from time-of-flight mass spectrometry. The branching ratios obtained from the negative ions formed in K + SF₆ collisions, in a wide energy range from 10.7 up to 213.1 eV in the centre-of-mass frame, show that the main anion is assigned to SF₅⁻ and contributing to more than 70% of the total ion yield, followed by the non-dissociated parent anion SF₆⁻ and F⁻. Other less intense anions amounting to <20% are assigned to SF₃⁻ and F₂⁻, while a trace contribution at 32u is tentatively assigned to S⁻ formation, although the rather complex intramolecular energy redistribution within the temporary negative ion is formed during the collision. An energy loss spectrum of potassium cation post-collision is recorded showing features that have been assigned with the help of theoretical calculations. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom are performed to support the experimental findings. Apart from the role of the different resonances participating in the formation of different anions, the role of higher-lying electronic-excited states of Rydberg character are noted. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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27 pages, 6045 KiB

Open AccessArticle

Nanostructured Molecular–Network Arsenoselenides from the Border of a Glass-Forming Region: A Disproportionality Analysis Using Complementary Characterization Probes

by Oleh Shpotyuk, Malgorzata Hyla, Adam Ingram, Yaroslav Shpotyuk, Vitaliy Boyko, Pavlo Demchenko, Renata Wojnarowska-Nowak, Zdenka Lukáčová Bujňáková and Peter Baláž

Molecules 2024, 29(16), 3948; https://doi.org/10.3390/molecules29163948 - 21 Aug 2024

Viewed by 762

Abstract

Binary As_xSe_100−x alloys from the border of a glass-forming region (65 < x < 70) subjected to nanomilling in dry and dry–wet modes are characterized by the XRPD, micro-Raman scattering (micro-RS) and revised positron annihilation lifetime (PAL) methods complemented by [...] Read more.

Binary As_xSe_100−x alloys from the border of a glass-forming region (65 < x < 70) subjected to nanomilling in dry and dry–wet modes are characterized by the XRPD, micro-Raman scattering (micro-RS) and revised positron annihilation lifetime (PAL) methods complemented by a disproportionality analysis using the quantum–chemical cluster modeling approach. These alloys are examined with respect to tetra-arsenic biselenide As₄Se₂ stoichiometry, realized in glassy g-As₆₅Se₃₅, glassy–crystalline g/c-As₆₇Se₃₃ and glassy–crystalline g/c-As₇₀Se₃₀. From the XRPD results, the number of rhombohedral As and cubic arsenolite As₂O₃ phases in As-Se alloys increases after nanomilling, especially in the wet mode realized in a PVP water solution. Nanomilling-driven amorphization and reamorphization transformations in these alloys are identified by an analysis of diffuse peak halos in their XRPD patterning, showing the interplay between the levels of a medium-range structure (disruption of the intermediate-range ordering at the cost of an extended-range one). From the micro-RS spectroscopy results, these alloys are stabilized by molecular thioarsenides As₄Se_n (n = 3, 4), regardless of their phase composition, remnants of thioarsenide molecules destructed under nanomilling being reincorporated into a glass network undergoing a polyamorphic transition. From the PAL spectroscopy results, volumetric changes in the wet-milled alloys with respect to the dry-milled ones are identified as resulting from a direct conversion of the bound positron–electron (Ps, positronium) states in the positron traps. Ps-hosting holes in the PVP medium appear instead of positron traps, with ~0.36–0.38 ns lifetimes ascribed to multivacancies in the As-Se matrix. The superposition of PAL spectrum peaks and tails for pelletized PVP, unmilled, dry-milled, and dry–wet-milled As-Se samples shows a spectacular smoothly decaying trend. The microstructure scenarios of the spontaneous (under quenching) and activated (under nanomilling) decomposition of principal network clusters in As₄Se₂-bearing arsenoselenides are recognized. Over-constrained As_6·(2/3) ring-like network clusters acting as pre-cursors of the rhombohedral As phase are the main products of this decomposition. Two spontaneous processes for creating thioarsenides with crystalline counterparts explain the location of the glass-forming border in an As-Se system near the As₄Se₂ composition, while an activated decomposition process for creating layered As₂Se₃ structures is responsible for the nanomilling-driven molecular-to-network transition. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Physical Chemistry, 2nd Edition)

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16 pages, 2296 KiB

Open AccessArticle

Why Do Ionic Surfactants Significantly Alter the Chemiluminogenic Properties of Acridinium Salt?

by Magdalena Mańkowska, Karol Krzymiński, Dariusz Wyrzykowski, Beata Zadykowicz and Sergey A. Samsonov

Molecules 2024, 29(16), 3736; https://doi.org/10.3390/molecules29163736 - 7 Aug 2024

Viewed by 732

Abstract

Acridinium esters, due to their capability for chemiluminescence (CL), are employed as indicators and labels in biomedical diagnostics and other fields. In this work, the influence of ionic surfactants, hexadecyltrimethylammonium chloride and bromide (CTAC and CTAB, cationic) and sodium dodecyl sulphate (SDS, anionic) [...] Read more.

Acridinium esters, due to their capability for chemiluminescence (CL), are employed as indicators and labels in biomedical diagnostics and other fields. In this work, the influence of ionic surfactants, hexadecyltrimethylammonium chloride and bromide (CTAC and CTAB, cationic) and sodium dodecyl sulphate (SDS, anionic) on the CL parameters and mechanism of representative emitter, 10-methyl-9-[(2-methylphenoxy)carbonyl]acridinium trifluoromethanesulphonate (2MeX) in a H₂O₂/NaOH environment, is studied. Our investigations revealed that the type of surfactant and its form in solution have an impact on the CL kinetic constants and integral efficiencies, while changes in those emission properties resulting from the type of ion (Cl⁻ vs. Br⁻) are negligible. The major changes were recorded for systems containing surfactants at concentrations higher than the critical micelle concentration. The cationic surfactants (CTAC, CTAB) cause a substantial increase in CL emission kinetics and a moderate increase in its integral efficiency. At the same time, the opposite effect is observed in the case of SDS. Molecular dynamics simulations suggest that changes in emission parameters are likely due to differences in the binding strength of 2MeX substrate with surfactant molecules, which is higher for SDS than for CTAC. The results can help in rational designing of optimal acridinium CL systems and demonstrate their usefulness in distinguishing the pre- and post-micellar environment and the charge of surfactants. Full article

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35 pages, 1479 KiB

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Novel Criteria to Provide a Locality/Normality Degree in Molecules and Their Relevance in Physical Chemistry

by Eduardo Suárez, Oscar Guzmán-Juárez and Renato Lemus

Molecules 2024, 29(15), 3490; https://doi.org/10.3390/molecules29153490 - 25 Jul 2024

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Abstract

In contrast to the traditional analysis of molecules using local mode behavior, where the degree of locality is given through a function in terms of Morse potential parameters, new criteria for locality/normality (LN) suitable for application to any molecular system are proposed. The [...] Read more.

In contrast to the traditional analysis of molecules using local mode behavior, where the degree of locality is given through a function in terms of Morse potential parameters, new criteria for locality/normality (LN) suitable for application to any molecular system are proposed. The approach is based on analysis of the connection between the algebraic normal and local mode representations. It is shown that both descriptions are equivalent as long as the polyad (total number of quanta) in the local representation is not conserved. The constraint of a local polyad conservation naturally provides a criterion for assigning an LN degree in quantitative form, without an analogue in configuration space. The correlation between the different parameters reveals the physical properties of molecules. A clear connection between the LN degree (based on the fundamentals) and spectroscopic properties is also presented, suggesting a promising approach for identifying mixtures of isotopologues. Full article

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20 pages, 3446 KiB

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Molecular-Network Transformations in Tetra-Arsenic Triselenide Glassy Alloys Tuned within Nanomilling Platform

by Oleh Shpotyuk, Malgorzata Hyla, Yaroslav Shpotyuk, Zdenka Lukáčová Bujňáková, Peter Baláž, Pavlo Demchenko, Andrzej Kozdraś, Vitaliy Boyko and Andriy Kovalskiy

Molecules 2024, 29(14), 3245; https://doi.org/10.3390/molecules29143245 - 9 Jul 2024

Cited by 1 | Viewed by 837

Abstract

Polyamorphic transformations driven by high-energy mechanical ball milling (nanomilling) are recognized in a melt-quenched glassy alloy of tetra-arsenic triselenide (As₄Se₃). We employed XRPD analysis complemented by thermophysical heat-transfer and micro-Raman spectroscopy studies. A straightforward interpretation of the medium-range structural [...] Read more.

Polyamorphic transformations driven by high-energy mechanical ball milling (nanomilling) are recognized in a melt-quenched glassy alloy of tetra-arsenic triselenide (As₄Se₃). We employed XRPD analysis complemented by thermophysical heat-transfer and micro-Raman spectroscopy studies. A straightforward interpretation of the medium-range structural response to milling-driven reamorphization is developed within a modified microcrystalline model by treating diffuse peak-halos in the XRPD patterns of this alloy as a superposition of the Bragg-diffraction contribution from inter-planar correlations, which are supplemented by the Ehrenfest-diffraction contribution from inter-atomic and/or inter-molecular correlations related to derivatives of thioarsenide As₄Se_n molecules, mainly dimorphite-type As₄Se₃ ones. These cage molecules are merely destroyed under milling, facilitating the formation of a polymerized network with enhanced calorimetric heat-transfer responses. Disruption of intermediate-range ordering, due to weakening of the FSDP (the first sharp diffraction peak), accompanied by an enhancement of extended-range ordering, due to fragmentation of structural entities responsible for the SSDP (the second sharp diffraction peak), occurs as an interplay between medium-range structural levels in the reamorphized As₄Se₃ glass alloy. Nanomilling-driven destruction of thioarsenide As₄Se_n molecules followed by incorporation of their remnants into a glassy network is proved by micro-Raman spectroscopy. Microstructure scenarios of the molecular-to-network polyamorphic transformations caused by the decomposition of the As₄Se₃ molecules and their direct destruction under grinding are recognized by an ab initio quantum-chemical cluster-modeling algorithm. Full article

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11 pages, 2389 KiB

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Hydroxyl Group as the ‘Bridge’ to Enhance the Single-Molecule Conductance by Hyperconjugation

by Xin Lv, Chang Li, Meng-Meng Guo, Wenjing Hong, Li-Chuan Chen, Qian-Chong Zhang and Zhong-Ning Chen

Molecules 2024, 29(11), 2440; https://doi.org/10.3390/molecules29112440 - 22 May 2024

Viewed by 1078

Abstract

For designing single-molecule devices that have both conjugation systems and structural flexibility, a hyperconjugated molecule with a σ–π bond interaction is considered an ideal candidate. In the investigation of conductance at the single-molecule level, since few hyperconjugation systems have been involved, the strategy [...] Read more.

For designing single-molecule devices that have both conjugation systems and structural flexibility, a hyperconjugated molecule with a σ–π bond interaction is considered an ideal candidate. In the investigation of conductance at the single-molecule level, since few hyperconjugation systems have been involved, the strategy of building hyperconjugation systems and the mechanism of electron transport within this system remain unexplored. Based on the skipped-conjugated structure, we present a rational approach to construct a hyperconjugation molecule using a hydroxyl group, which serves as a bridge to interact with the conjugated fragments. The measurement of single-molecule conductance reveals a two-fold conductance enhancement of the hyperconjugation system having the ‘bridging’ hydroxyl group compared to hydroxyl-free derivatives. Theoretical studies demonstrate that the hydroxyl group in the hyperconjugation system connects the LUMO of the two conjugated fragments and opens a through-space channel for electron transport to enhance the conductance. Full article

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18 pages, 4004 KiB

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Physicochemical Characterization of Hydroxyapatite Hybrids with Meloxicam for Dissolution Rate Improvement

by Lauretta Maggi, Valeria Friuli, Beatrice Cerea, Giovanna Bruni, Vittorio Berbenni and Marcella Bini

Molecules 2024, 29(11), 2419; https://doi.org/10.3390/molecules29112419 - 21 May 2024

Viewed by 827

Abstract

Organic–inorganic hybrids represent a good solution to improve the solubility and dissolution rates of poorly soluble drugs whose number has been increasing in the last few years. One of the most diffused inorganic matrices is hydroxyapatite (HAP), which is a biocompatible and osteoconductive [...] Read more.

Organic–inorganic hybrids represent a good solution to improve the solubility and dissolution rates of poorly soluble drugs whose number has been increasing in the last few years. One of the most diffused inorganic matrices is hydroxyapatite (HAP), which is a biocompatible and osteoconductive material. However, the understanding of the hybrids’ functioning mechanisms is in many cases limited; thus, thorough physicochemical characterizations are needed. In the present paper, we prepared hybrids of pure and Mg-doped hydroxyapatite with meloxicam, a drug pertaining to the Biopharmaceutical Classification System (BCS) class II, i.e., drugs with low solubility and high permeability. The hybrids’ formation was demonstrated by FT-IR, which suggested electrostatic interactions between HAP and drug. The substitution of Mg in the HAP structure mainly produced a structural disorder and a reduction in crystallite sizes. The surface area of HAP increased after Mg doping from 82 to 103 m²g⁻¹ as well as the pore volume, justifying the slightly high drug amount adsorbed by the Mg hybrid. Notwithstanding the low drug loading on the hybrids, the solubility, dissolution profiles and wettability markedly improved with respect to the drug alone, particularly for the Mg doped one, which was probably due to the main distribution of the drug on the HAP surface. Full article

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13 pages, 3325 KiB

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A Combined Molecular Dynamics and Hydropathic INTeraction (HINT) Approach to Investigate Protein Flexibility: The PPARγ Case Study

by Federica Agosta and Pietro Cozzini

Molecules 2024, 29(10), 2234; https://doi.org/10.3390/molecules29102234 - 10 May 2024

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Abstract

Molecular Dynamics (MD) is a computational technique widely used to evaluate a molecular system’s thermodynamic properties and conformational behavior over time. In particular, the energy analysis of a protein conformation ensemble produced though MD simulations plays a crucial role in explaining the relationship [...] Read more.

Molecular Dynamics (MD) is a computational technique widely used to evaluate a molecular system’s thermodynamic properties and conformational behavior over time. In particular, the energy analysis of a protein conformation ensemble produced though MD simulations plays a crucial role in explaining the relationship between protein dynamics and its mechanism of action. In this research work, the HINT (Hydropathic INTeractions) LogP-based scoring function was first used to handle MD trajectories and investigate the molecular basis behind the intricate PPARγ mechanism of activation. The Peroxisome Proliferator-Activated Receptor γ (PPARγ) is an emblematic example of a highly flexible protein due to the extended ω-loop delimiting the active site, and it is responsible for the receptor’s ability to bind chemically different compounds. In this work, we focused on the PPARγ complex with Rosiglitazone, a common anti-diabetic compound and analyzed the molecular basis of the flexible ω-loop stabilization effect produced by the Oleic Acid co-binding. The HINT-based analysis of the produced MD trajectories allowed us to account for all of the energetic contributions involved in interconverting between conformational states and describe the intramolecular interactions between the flexible ω-loop and the helix H3 triggered by the allosteric binding mechanism. Full article

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12 pages, 2021 KiB

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Insights on Stability Constants and Structures of Complexes between Coumarin Derivatives and Pb(II) in Aqueous Media

by Emilia Furia, Vincenzo Lettera, Anna Napoli and Donatella Aiello

Molecules 2024, 29(9), 1911; https://doi.org/10.3390/molecules29091911 - 23 Apr 2024

Viewed by 878

Abstract

In the frame of a systematic study on the sequestering ability of natural antioxidants towards metal cations, here the complexation of coumarin-3-carboxilic acid (HCCA) with Pb(II) and the overall stability constants of the resulting complexes, at 37 °C and in 0.16 M NaClO [...] Read more.

In the frame of a systematic study on the sequestering ability of natural antioxidants towards metal cations, here the complexation of coumarin-3-carboxilic acid (HCCA) with Pb(II) and the overall stability constants of the resulting complexes, at 37 °C and in 0.16 M NaClO₄, are discussed. Reaction of Pb(ClO₄)₂ with HCCA in an aqueous medium at a pH range from 2 to 6 and various ratios (1:1–1:10) yielded the Pb–CCA complexes, which were characterized spectrometrically by laser desorption ionization mass spectrometry (LD-MS). LD-MS has provided the composition and structure of Pb–CCA species according to the speciation model proposed on the basis of the potentiometric data. The graphic representation of the complex’s concentration curves is given by the distribution diagram, which provides a whole depiction of the species present in the solution at the selected pH ranges. Full article

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21 pages, 3544 KiB

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A Study of the Micellar Formation of N-Alkyl Betaine Ethyl Ester Chlorides Based on the Physicochemical Properties of Their Aqueous Solutions

by Monika Geppert-Rybczyńska, Anna Mrozek-Wilczkiewicz, Patrycja Rawicka and Piotr Bartczak

Molecules 2024, 29(8), 1844; https://doi.org/10.3390/molecules29081844 - 18 Apr 2024

Viewed by 1265

Abstract

In this study, a series of four surface-active compounds—N-alkyl betaine ethyl ester chlorides, C_nBetC₂Cl—were synthesized and characterized in aqueous solutions. As with other alkyl betaines, these amphiphiles can be practically used, for example, as co-surfactants and/or solubility [...] Read more.

In this study, a series of four surface-active compounds—N-alkyl betaine ethyl ester chlorides, C_nBetC₂Cl—were synthesized and characterized in aqueous solutions. As with other alkyl betaines, these amphiphiles can be practically used, for example, as co-surfactants and/or solubility enhancers acting according to hydrotropic or micellar mechanisms, depending on the alkyl chain length in the amine. We focused on the representatives of the medium alkyl chain length (C₆–C₁₂) to find the dependence between the alkyl chain length in N-alkyl betaine ethyl ester chlorides and the surface, volumetric, acoustic, and viscometric properties of their solutions. Ethyl esters, the derivatives of amino acids, were chosen to increase functionality and take advantage of possible hydrolysis in solutions at higher pH, which is also a key parameter in biodegradability. The micellization parameters were calculated based on the physicochemical characteristics. We focused our interest on the ester with a dodecyl substituent since we can compare and discuss its properties with some other C₁₂ representatives that are available in literature. Surprisingly, its micellization characteristic is almost temperature-independent in the investigated temperature range, t = (15–45) °C. Particularly interesting are the results of dynamic light scattering (DLS), which show that the changes in physicochemical parameters of the C₁₂ homolog around the CMC are caused by the two types of micelles of different sizes present in solutions. Full article

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15 pages, 2548 KiB

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Adsorption of O₂ on the Preferred -O-Au Sites of Small Gold Oxide Clusters: Charge-dependent Interaction and Activation

by Lulu Huang, Wen Liu and Xiaopeng Xing

Molecules 2024, 29(7), 1645; https://doi.org/10.3390/molecules29071645 - 6 Apr 2024

Viewed by 843

Abstract

Decades of research have illuminated the significant roles of gold/gold oxide clusters in small molecule catalytic oxidation. However, many fundamental questions, such as the actual sites to adsorb and activate O₂ and the impact of charge, remain unanswered. Here, we have utilized [...] Read more.

Decades of research have illuminated the significant roles of gold/gold oxide clusters in small molecule catalytic oxidation. However, many fundamental questions, such as the actual sites to adsorb and activate O₂ and the impact of charge, remain unanswered. Here, we have utilized an improved genetic algorithm program coupled with the DFT method to systematically search for the structures of Au_1–5O_x^−/+/0 (x = 1–4) and calculated binding interactions between Au_1–5O_x^−/+/0 (x = 1–2) and O₂, aiming to determine the active sites and to elucidate the impact of different charge states in gold oxide systems. The results revealed that the reactivity of all three kinds of small gold oxide clusters toward O₂ is strongly site-dependent, with clusters featuring an -O-Au site exhibiting a preference for adsorption. The charges on small gold oxide clusters significantly impact the interaction strength and the activation degree of adsorbed O₂: in the case of anionic cluster, the interaction between O₂ and the -O-Au sites leads to a chemical reaction involving electron transfer, thereby significantly activating O₂; in neutral and cationic clusters, the adsorption of O₂ on their -O-Au sites can be viewed as an electrostatic interaction. Pointedly, for cationic clusters, the highly concentrated positive charge on the Au atom of the -O-Au sites can strongly adsorb but hardly activate the adsorbed O₂. These results have certain reference points for understanding the gold oxide interfaces and the improved catalytic oxidation performance of gold-based systems in the presence of atomic oxygen species. Full article

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23 pages, 7478 KiB

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Predicting Organometallic Intermediates in the Surface-Assisted Ullmann Coupling of Chrysene Isomers

by Jakub Lisiecki and Paweł Szabelski

Molecules 2024, 29(7), 1553; https://doi.org/10.3390/molecules29071553 - 30 Mar 2024

Cited by 1 | Viewed by 932

Abstract

On-surface polymerization of functional organic molecules has been recently recognized as a promising route to persistent low-dimensional structures with tailorable properties. In this contribution, using the coarse-grained Monte Carlo simulation method, we study the initial stage of the Ullmann coupling of doubly halogenated [...] Read more.

On-surface polymerization of functional organic molecules has been recently recognized as a promising route to persistent low-dimensional structures with tailorable properties. In this contribution, using the coarse-grained Monte Carlo simulation method, we study the initial stage of the Ullmann coupling of doubly halogenated chrysene isomers adsorbed on a catalytically active (111) crystalline surface. To that end, we focus on the formation of labile metal-organic precursor structures preceding the covalent bonding of chrysene monomers. Four monomeric chrysene units with differently distributed halogen substituents were probed in the simulations, and the resulting precursor structures were compared and quantified. Moreover, the effect of (pro)chirality of chrysene tectons on the structure formation was elucidated by running separate simulations in enantiopure and racemic systems. The calculations showed that suitable manipulation of the halogen substitution pattern allows for the creation of diverse precursor architectures, ranging from straight and winded chains to cyclic oligomers with enantiopure, racemic, and nonracemic composition. The obtained findings can be helpful in developing synthetic strategies for covalent polymers with predefined architecture and functionality. Full article

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16 pages, 6822 KiB

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Exploring the Influence of Morphology on Bipolaron–Polaron Ratios and Conductivity in Polypyrrole in the Presence of Surfactants

by Thaneeya Samwang, Nozomi Morishita Watanabe, Yukihiro Okamoto and Hiroshi Umakoshi

Molecules 2024, 29(6), 1197; https://doi.org/10.3390/molecules29061197 - 7 Mar 2024

Cited by 3 | Viewed by 1202

Abstract

This research aims to deepen the understanding of the relationship between conductivity and morphology in polypyrrole (PPy) via a comparison of the bipolaron to polaron ratios with a focus on the C-H deformation area. PPy samples were synthesized with different surfactants: sodium dodecyl [...] Read more.

This research aims to deepen the understanding of the relationship between conductivity and morphology in polypyrrole (PPy) via a comparison of the bipolaron to polaron ratios with a focus on the C-H deformation area. PPy samples were synthesized with different surfactants: sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and tween 80 (TW). This study revealed that SDS significantly altered the bipolaron and polaron in the C-H deformation region and showed higher conductivity than other surfactants. Notably, the morphological shifts to a sheet-like structure when using ammonium sulfate (APS) contrasted with the particle-like form observed with ferric chloride (FeCl₃). These results showed that if the oxidant changed, the bipolaron and polaron ratios in C-H deformation were unrelated to PPy morphology. However, this work showed a consistent relationship between SDS use, the bipolaron and polaron ratios in the C-H deformation, and the conductivity properties. Moreover, the natural positive charge of PPy and negatively charged SDS molecules may lead to an electrostatic interaction between PPy and SDS. This work assumes that this interaction might cause the transformation of polaron to bipolaron in the C–H deformation region, resulting in improved conductivity of PPy. This work offers more support for the future investigation of PPy characteristics. Full article

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15 pages, 6279 KiB

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First-Principles Study of Bimetallic Pairs Embedded on Graphene Co-Doped with N and O for N₂ Electroreduction

by Haozhe Dong, Hao Sun, Guanru Xing, Shize Liu, Xuemei Duan and Jingyao Liu

Molecules 2024, 29(4), 779; https://doi.org/10.3390/molecules29040779 - 8 Feb 2024

Cited by 1 | Viewed by 1227

Abstract

The electrocatalytic nitrogen reduction reaction (NRR) is considered a viable alternative to the Haber–Bosch process for ammonia synthesis, and the design of highly active and selective catalysts is crucial for the industrialization of the NRR. Dual-atom catalysts (DACs) with dual active sites offer [...] Read more.

The electrocatalytic nitrogen reduction reaction (NRR) is considered a viable alternative to the Haber–Bosch process for ammonia synthesis, and the design of highly active and selective catalysts is crucial for the industrialization of the NRR. Dual-atom catalysts (DACs) with dual active sites offer flexible active sites and synergistic effects between atoms, providing more possibilities for the tuning of catalytic performance. In this study, we designed 48 graphene-based DACs with N₄O₂ coordination (MM′@N₄O₂-G) using density functional theory. Through a series of screening strategies, we explored the reaction mechanisms of the NRR for eight catalysts in depth and revealed the “acceptance–donation” mechanism between the active sites and the N₂ molecules through electronic structure analysis. The study found that the limiting potential of the catalysts exhibited a volcano-shaped relationship with the d-band center of the active sites, indicating that the synergistic effect between the bimetallic components can regulate the d-band center position of the active metal M, thereby controlling the reaction activity. Furthermore, we investigated the selectivity of the eight DACs and identified five potential NRR catalysts. Among them, MoCo@N₄O₂-G showed the best NRR performance, with a limiting potential of −0.20 V. This study provides theoretical insights for the design and development of efficient NRR electrocatalysts. Full article

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14 pages, 5613 KiB

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Beryllium Dimer Reactions with Acetonitrile: Formation of Strong Be−Be Bonds

by Fei Cong, Liyan Cai, Juanjuan Cheng, Zhen Pu and Xuefeng Wang

Molecules 2024, 29(1), 177; https://doi.org/10.3390/molecules29010177 - 28 Dec 2023

Cited by 1 | Viewed by 1423

Abstract

Laser ablated Be atoms have been reacted with acetonitrile molecules in 4 K solid neon matrix. The diberyllium products BeBeNCCH₃ and CNBeBeCH₃ have been identified by D and ¹³C isotopic substitutions and quantum chemical calculations. The stabilization of the diberyllium [...] Read more.

Laser ablated Be atoms have been reacted with acetonitrile molecules in 4 K solid neon matrix. The diberyllium products BeBeNCCH₃ and CNBeBeCH₃ have been identified by D and ¹³C isotopic substitutions and quantum chemical calculations. The stabilization of the diberyllium species is rationalized from the formation of the real Be−Be single bonds with bond distances as 2.077 and 2.058 Å and binding energies as −27.1 and −77.2 kcal/mol calculated at CCSD (T)/aug-cc-pVTZ level of theory for BeBeNCCH₃ and CNBeBeCH₃, respectively. EDA-NOCV analysis described the interaction between Be₂ and NC···CH₃ fragments as Lewis “acid−base” interactions. In the complexes, the Be₂ moiety carries positive charges which transfer from antibonding orbital of Be₂ to the bonding fragments significantly strengthen the Be−Be bonds that are corroborated by AIM, LOL and NBO analyses. In addition, mono beryllium products BeNCCH₃, CNBeCH₃, HBeCH₂CN and HBeNCCH₂ have also been observed in our experiments. Full article

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24 pages, 8708 KiB

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Compact Combustion Mechanisms of Typical n-Alkanes Developed by the Minimized Reaction Network Method

by Jiangtao Shentu, Yanrong Lu, Yiwei Li, Juanqin Li, Yebing Mao and Xiangyuan Li

Molecules 2023, 28(23), 7695; https://doi.org/10.3390/molecules28237695 - 21 Nov 2023

Viewed by 1342

Abstract

The existing combustion kinetic modeling method which aims at developing phenomenological combustion mechanisms characterized by multiple reactions confronts several challenges, including the conflicts between computing resources and mechanism scales during numerical simulation, etc. In order to address these issues, the minimized reaction network [...] Read more.

The existing combustion kinetic modeling method which aims at developing phenomenological combustion mechanisms characterized by multiple reactions confronts several challenges, including the conflicts between computing resources and mechanism scales during numerical simulation, etc. In order to address these issues, the minimized reaction network method for complex combustion system modeling based on the principle of simultaneous chemical equilibrium is proposed, which is aimed to develop combustion mechanisms with minimal reaction steps under a limited number of species. The concept of mechanism resolution is proposed in this method, and the reaction network with minimal reaction steps under a given mechanism resolution is constructed so that the scale of mechanisms is compressed greatly. Meanwhile, distinguishing from other mechanisms, the reversible form of elementary reactions is adopted and the classical two-parameter (A, E_a) Arrhenius equation fits the rate constants. Typical n-alkanes including n-butane, n-heptane, n-octane, n-decane, n-dodecane and n-hexadecane were taken as examples to indicate the development process of mechanisms and systematic kinetic validations were carried out. Results show that this method leads to very compact mechanisms with satisfactory accuracy, and it eliminates the process of mechanism reduction and is beneficial for mechanism optimization. This method and the derived kinetic mechanisms are hoped to contribute to combustion engineering applications. Full article

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Silicon-28-Tetrafluoride as an Educt of Isotope-Engineered Silicon Compounds and Bulk Materials for Quantum Systems

by Owen C. Ernst, David Uebel, Roman Brendler, Konstantin Kraushaar, Max Steudel, Jörg Acker and Edwin Kroke

Molecules 2024, 29(17), 4222; https://doi.org/10.3390/molecules29174222 - 5 Sep 2024

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Abstract

This review provides a summary of the existing literature on a crucial raw material for the production of isotopically pure semiconductors, which are essential for the development of second-generation quantum systems. Silicon-28-tetrafluoride (²⁸SiF₄) is used as an educt for [...] Read more.

This review provides a summary of the existing literature on a crucial raw material for the production of isotopically pure semiconductors, which are essential for the development of second-generation quantum systems. Silicon-28-tetrafluoride (²⁸SiF₄) is used as an educt for several isotope-engineered chemicals, such as silane-28 (²⁸SiH₄) and silicon-28-trichloride (²⁸SiHCl₃), which are needed in the pursuit of various quantum technologies. We are exploring the entire chain from the synthesis of ²⁸SiF₄ to quantum applications. This includes the chemical properties of SiF₄, isotopic enrichment, conversion to silanes, conversion to bulk ²⁸Si and thin films, the physical properties of ²⁸Si (spin neutrality, thermal conductivity, optical properties), and the applications in quantum computing, photonics, and quantum sensing techniques. Full article

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28 pages, 10526 KiB

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Application of Strain Engineering in Solar Cells

by Houzhi Fei, Caiyi Shang, Dandan Sang, Changxing Li, Shunhao Ge, Liangrui Zou and Qinglin Wang

Molecules 2024, 29(14), 3260; https://doi.org/10.3390/molecules29143260 - 10 Jul 2024

Cited by 1 | Viewed by 815

Abstract

Solar cells represent a promising innovation in energy storage, offering not only exceptional cleanliness and low cost but also a high degree of flexibility, rendering them widely applicable. In recent years, scientists have dedicated substantial efforts to enhancing the performance of solar cells, [...] Read more.

Solar cells represent a promising innovation in energy storage, offering not only exceptional cleanliness and low cost but also a high degree of flexibility, rendering them widely applicable. In recent years, scientists have dedicated substantial efforts to enhancing the performance of solar cells, aiming to drive sustainable development and promote clean energy applications. One approach that has garnered significant attention is strain engineering, which involves the adjustment of material microstructure and organization through mechanical tensile or compressive strain, ultimately serving to enhance the mechanical properties and performance stability of materials. This paper aims to provide a comprehensive review of the latest advancements in the application of strain engineering in solar cells, focused on the current hot research area—perovskite solar cells. Specifically, it delves into the origins and characterization of strain in solar cells, the impact of strain on solar cell performance, and the methods for regulating stable strain. Furthermore, it outlines strategies for enhancing the power conversion efficiency (PCE) and stability of solar cells through strain engineering. Finally, the paper conducts an analysis of the challenges encountered in the development process and presents a forward-looking perspective on further enhancing the performance of solar cells through strain engineering. Full article

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