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25th Anniversary of Molecules—Recent Advances in Physical Chemistry

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Physical Chemistry".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 48219

Special Issue Editors

Prof. Dr. Anan Yaghmur

E-Mail Website
Guest Editor
Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
Interests: biophysical characterization of nano-self-assemblies; cubosomes; hexosomes; nanodispersions of inverse non-lamellar liquid crystalline phases; drug and functional food soft self-assembled nanocarriers; lyotropic liquid crystalline phases; microemulsions
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Federico Totti

E-Mail Website
Co-Guest Editor
Dipartimento di Chimica "U.Schiff" and UdR INSTM, Università degli Studi di Firenze, Sesto Fiorentino, Italy
Interests: ab initio; DFT; modeling; magnetic clusters
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As the oldest journal of the MDPI family, /Molecules/ is going to reach a remarkable milestone by publishing its 25th volume. In celebration of this important occasion, we are pleased to launch the Special Issue "25th Anniversary of Molecules—Recent Advances in Physical Chemistry".

Over the years, Molecules has been increasing its visibility and scientific standards, with more than 20,000 papers published to date. The journal’s website currently attracts more than 115,000 monthly visits and 395,000 monthly page views. We express our deepest gratitude and greatly appreciate readers, authors, reviewers, editors, and Molecules staff members. We thank you all for your contributions to the journal and are looking forward to further achievements.

This Special Issue will collect original research and review articles in all physical chemistry research areas including theoretical, fundamental, and applied research topics; computation; and papers covering the interface of physical chemistry, medicine, and biology.

Prof. Dr. Anan Yaghmur
Prof. Dr. Federico Totti
Guest Editors

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Published Papers (17 papers)

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Research

17 pages, 11425 KiB  
Article
Quantification of Porous Properties of Shear Crystallized Lipids
by Brandon D. Howard and Farnaz Maleky
Molecules 2022, 27(3), 631; https://doi.org/10.3390/molecules27030631 - 19 Jan 2022
Viewed by 1763
Abstract
The aim of this study was to investigate the impact that shear and composition have on the structural properties associated with the porous phases of lipids. To accomplish this aim, we developed eight main crystallized samples using cocoa butter (CB) or trilaurin (TL) [...] Read more.
The aim of this study was to investigate the impact that shear and composition have on the structural properties associated with the porous phases of lipids. To accomplish this aim, we developed eight main crystallized samples using cocoa butter (CB) or trilaurin (TL) in the presence or absence of monostearate (M) (5% w/w). The samples were sheared at 500 s−1 using random (RS) or laminar (LS) shear at a cooling rate of 2 °C/min. Using the maximal ball (MB) algorithm, several empirical void measurements such as connectivity (z), pore and throat volume weighted radii (R43), and void fraction (v) were quantified using 3D X-ray microcomputed tomography images. Most void features were identified as micropores (R ≥ 10 μm) possibly originating from the crystallization process and post-process crystal growth. Likewise, depending on the applied treatments, mechanisms impacting void formation were found to produce noticeable variation in v (0.019 to 0.139) and to determine whether void morphology was spherical, irregular, and/or highly connected. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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13 pages, 980 KiB  
Article
Incorporation of Molecular Reorientation into Modeling Surface Pressure-Area Isotherms of Langmuir Monolayers
by José Agudelo, Guilherme Volpe Bossa and Sylvio May
Molecules 2021, 26(14), 4372; https://doi.org/10.3390/molecules26144372 - 20 Jul 2021
Cited by 2 | Viewed by 1999
Abstract
Langmuir monolayers can be assembled from molecules that change from a low-energy orientation occupying a large cross-sectional area to a high-energy orientation of small cross-sectional area as the lateral pressure grows. Examples include cyclosporin A, amphotericin B, nystatin, certain alpha-helical peptides, cholesterol oxydation [...] Read more.
Langmuir monolayers can be assembled from molecules that change from a low-energy orientation occupying a large cross-sectional area to a high-energy orientation of small cross-sectional area as the lateral pressure grows. Examples include cyclosporin A, amphotericin B, nystatin, certain alpha-helical peptides, cholesterol oxydation products, dumbbell-shaped amphiphiles, organic–inorganic nanoparticles and hybrid molecular films. The transition between the two orientations leads to a shoulder in the surface pressure-area isotherm. We propose a theoretical model that describes the shoulder and can be used to extract the energy cost per molecule for the reorientation. Our two-state model is based on a lattice–sublattice approximation that hosts the two orientations and a corresponding free energy expression which we minimize with respect to the orientational distribution. Inter-molecular interactions other than steric repulsion are ignored. We provide an analysis of the model, including an analytic solution for one specific lateral pressure near a point of inflection in the surface pressure-area isotherm, and an approximate solution for the entire range of the lateral pressures. We also use our model to estimate energy costs associated with orientational transitions from previously reported experimental surface pressure-area isotherms. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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21 pages, 3623 KiB  
Article
Four Isotope-Labeled Recombination Pathways of Ozone Formation
by Dmitri Babikov, Elizaveta Grushnikova, Igor Gayday and Alexander Teplukhin
Molecules 2021, 26(5), 1289; https://doi.org/10.3390/molecules26051289 - 27 Feb 2021
Cited by 2 | Viewed by 2504
Abstract
A theoretical approach is developed for the description of all possible recombination pathways in the ozone forming reaction, without neglecting any process a priori, and without decoupling the individual pathways one from another. These pathways become physically distinct when a rare isotope [...] Read more.
A theoretical approach is developed for the description of all possible recombination pathways in the ozone forming reaction, without neglecting any process a priori, and without decoupling the individual pathways one from another. These pathways become physically distinct when a rare isotope of oxygen is introduced, such as 18O, which represents a sensitive probe of the ozone forming reaction. Each isotopologue of O3 contains two types of physically distinct entrance channels and two types of physically distinct product wells, creating four recombination pathways. Calculations are done for singly and doubly substituted isotopologues of ozone, eight rate coefficients total. Two pathways for the formation of asymmetric ozone isotopomer exhibit rather different rate coefficients, indicating large isotope effect driven by ΔZPE-difference. Rate coefficient for the formation of symmetric isotopomer of ozone (third pathway) is found to be in between of those two, while the rate of insertion pathway is smaller by two orders of magnitude. These trends are in good agreement with experiments, for both singly and doubly substituted ozone. The total formation rates for asymmetric isotopomers are found to be somewhat larger than those for symmetric isotopomers, but not as much as in the experiment. Overall, the distribution of lifetimes is found to be very similar for the metastable states in symmetric and asymmetric ozone isotopomers. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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12 pages, 4181 KiB  
Article
Thermodynamics of Mg–Al Order-Disorder Reaction in MgAl2O4-Spinel: Constrained by Prolonged Annealing Experiments at 773–1123 K
by Yunlu Ma, Xinjian Bao and Xi Liu
Molecules 2021, 26(4), 872; https://doi.org/10.3390/molecules26040872 - 7 Feb 2021
Cited by 5 | Viewed by 2145
Abstract
MgAl2O4-spinel has wide industrial and geological applications due to its special structural and physical–chemical features. It is presumably the most important endmember of complex natural spinel solid solutions, and therefore provides a structural model for a large group of [...] Read more.
MgAl2O4-spinel has wide industrial and geological applications due to its special structural and physical–chemical features. It is presumably the most important endmember of complex natural spinel solid solutions, and therefore provides a structural model for a large group of minerals with the spinel structure. There exists a well known but still inadequately understood phenomenon in the structure of MgAl2O4-spinel, the Mg–Al cations readily exchanging their positions in response to variations of temperature, pressure, and composition. A large number of experiments were performed to investigate the Mg–Al cation order-disorder process usually quantified by the inversion parameter x (representing either the molar fraction of Al on the tetrahedral T-sites or the molar fraction of Mg on the octahedral M-sites in the spinel structure), and some thermodynamic models were thereby constructed to describe the x-T relation. However, experimental data at some key T were absent, so that the different performance of these thermodynamic models could not be carefully evaluated. This limited the interpolation and extrapolation of the thermodynamic models. By performing some prolonged annealing experiments with some almost pure natural MgAl2O4-spinel plates and quantifying the x values with single-crystal X-ray diffraction technique, we obtained some critical equilibrium x values at T down to 773 K. These new x-T data, along with those relatively reliable x values at relatively high T from early studies, clearly indicate that the CS94 Model (a model constructed by Carpenter and Salje in 1994) better describes the Mg–Al cation order-disorder reaction in MgAl2O4-spinel for a wide range of T. On the basis of the CS94 Model, a geothermometer was established, and its form is T-closure = 21362 × x3 − 12143 × x2 + 6401 × x − 10 (T-closure standing for the closure temperature of the Mg–Al cation exchange reaction). This geothermometer can be used to constrain the thermal history of the geological bodies containing MgAl2O4-spinel. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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8 pages, 273 KiB  
Article
Non-Equilibrium Thermodynamics View on Kinetics of Autocatalytic Reactions—Two Illustrative Examples
by Miloslav Pekař
Molecules 2021, 26(3), 585; https://doi.org/10.3390/molecules26030585 - 22 Jan 2021
Cited by 3 | Viewed by 2189
Abstract
Autocatalytic reactions are in certain contrast with the linear algebra of reaction stoichiometry, on which rate equations respecting the permanence of atoms are constructed. These mathematical models of chemical reactions are called conservative. Using a non-equilibrium thermodynamics-based theory of chemical kinetics, it is [...] Read more.
Autocatalytic reactions are in certain contrast with the linear algebra of reaction stoichiometry, on which rate equations respecting the permanence of atoms are constructed. These mathematical models of chemical reactions are called conservative. Using a non-equilibrium thermodynamics-based theory of chemical kinetics, it is shown how to introduce autocatalytic step into such (conservative) rate equation properly. Further, rate equations based on chemical potentials or affinities are derived, and conditions for the consistency of rate equations with the entropic inequality (the second law of thermodynamics) are illustrated. The theory illustrated here can be viewed as a tool for verifying and generalizing traditional mass-action kinetics by means of modern non-equilibrium thermodynamics, which is able to deal also with such rather problematic cases. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
15 pages, 1798 KiB  
Article
Substituent Effects on the Solubility and Electronic Properties of the Cyanine Dye Cy5: Density Functional and Time-Dependent Density Functional Theory Calculations
by Austin Biaggne, William B. Knowlton, Bernard Yurke, Jeunghoon Lee and Lan Li
Molecules 2021, 26(3), 524; https://doi.org/10.3390/molecules26030524 - 20 Jan 2021
Cited by 21 | Viewed by 3886
Abstract
The aggregation ability and exciton dynamics of dyes are largely affected by properties of the dye monomers. To facilitate aggregation and improve excitonic function, dyes can be engineered with substituents to exhibit optimal key properties, such as hydrophobicity, static dipole moment differences, and [...] Read more.
The aggregation ability and exciton dynamics of dyes are largely affected by properties of the dye monomers. To facilitate aggregation and improve excitonic function, dyes can be engineered with substituents to exhibit optimal key properties, such as hydrophobicity, static dipole moment differences, and transition dipole moments. To determine how electron donating (D) and electron withdrawing (W) substituents impact the solvation, static dipole moments, and transition dipole moments of the pentamethine indocyanine dye Cy5, density functional theory (DFT) and time-dependent (TD-) DFT calculations were performed. The inclusion of substituents had large effects on the solvation energy of Cy5, with pairs of withdrawing substituents (W-W pairs) exhibiting the most negative solvation energies, suggesting dyes with W-W pairs are more soluble than others. With respect to pristine Cy5, the transition dipole moment was relatively unaffected upon substitution while numerous W-W pairs and pairs of donating and withdrawing substituents (D-W pairs) enhanced the static dipole difference. The increase in static dipole difference was correlated with an increase in the magnitude of the sum of the Hammett constants of the substituents on the dye. The results of this study provide insight into how specific substituents affect Cy5 monomers and which pairs can be used to engineer dyes with desired properties. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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9 pages, 1697 KiB  
Article
Hydrogenation of CO2 Promoted by Silicon-Activated H2S: Origin and Implications
by Xing Liu
Molecules 2021, 26(1), 50; https://doi.org/10.3390/molecules26010050 - 24 Dec 2020
Cited by 2 | Viewed by 3193
Abstract
Unlike the usual method of COx (x = 1, 2) hydrogenation using H2 directly, H2S and HSiSH (silicon-activated H2S) were selected as alternative hydrogen sources in this study for the COx hydrogenation reactions. Our results [...] Read more.
Unlike the usual method of COx (x = 1, 2) hydrogenation using H2 directly, H2S and HSiSH (silicon-activated H2S) were selected as alternative hydrogen sources in this study for the COx hydrogenation reactions. Our results suggest that it is kinetically infeasible for hydrogen in the form of H2S to transfer to COx at low temperatures. However, when HSiSH is employed instead, the title reaction can be achieved. For this approach, the activation of CO2 is initiated by its interaction with the HSiSH molecule, a reactive species with both a hydridic Hδ− and protonic Hδ+. These active hydrogens are responsible for the successive C-end and O-end activations of CO2 and hence the final product (HCOOH). This finding represents a good example of an indirect hydrogen source used in CO2 hydrogenation through reactivity tuned by silicon incorporation, and thus the underlying mechanism will be valuable for the design of similar reactions. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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13 pages, 3330 KiB  
Article
Computational Insights into Allosteric Conformational Modulation of P-Glycoprotein by Substrate and Inhibitor Binding
by Juan Xing, Shuheng Huang, Yu Heng, Hu Mei and Xianchao Pan
Molecules 2020, 25(24), 6006; https://doi.org/10.3390/molecules25246006 - 18 Dec 2020
Cited by 12 | Viewed by 2370
Abstract
The ATP-binding cassette (ABC) transporter P-glycoprotein (P-gp) is a physiologically essential membrane protein that protects many tissues against xenobiotic molecules, but limits the access of chemotherapeutics into tumor cells, thus contributing to multidrug resistance. The atomic-level mechanism of how substrates and inhibitors differentially [...] Read more.
The ATP-binding cassette (ABC) transporter P-glycoprotein (P-gp) is a physiologically essential membrane protein that protects many tissues against xenobiotic molecules, but limits the access of chemotherapeutics into tumor cells, thus contributing to multidrug resistance. The atomic-level mechanism of how substrates and inhibitors differentially affect the ATP hydrolysis by P-gp remains to be elucidated. In this work, atomistic molecular dynamics simulations in an explicit membrane/water environment were performed to explore the effects of substrate and inhibitor binding on the conformational dynamics of P-gp. Distinct differences in conformational changes that mainly occurred in the nucleotide-binding domains (NBDs) were observed from the substrate- and inhibitor-bound simulations. The binding of rhodamine-123 can increase the probability of the formation of an intermediate conformation, in which the NBDs were closer and better aligned, suggesting that substrate binding may prime the transporter for ATP hydrolysis. By contrast, the inhibitor QZ-Leu stabilized NBDs in a much more separated and misaligned conformation, which may result in the deficiency of ATP hydrolysis. The significant differences in conformational modulation of P-gp by substrate and inhibitor binding provided a molecular explanation of how these small molecules exert opposite effects on the ATPase activity. A further structural analysis suggested that the allosteric communication between transmembrane domains (TMDs) and NBDs was primarily mediated by two intracellular coupling helices. Our computational simulations provide not only valuable insights into the transport mechanism of P-gp substrates, but also for the molecular design of P-gp inhibitors. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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23 pages, 6232 KiB  
Article
Thermodynamic Analysis of Trisiloxane Surfactant Adsorption and Aggregation Processes
by Joanna Karasiewicz and Joanna Krawczyk
Molecules 2020, 25(23), 5669; https://doi.org/10.3390/molecules25235669 - 1 Dec 2020
Cited by 11 | Viewed by 2984
Abstract
The trisiloxane polyether surfactant (3-[3-(hydroxy)(polyethoxy)propyl]-1,1,1,3,5,5,5 -heptamethyltrisiloxane) (TS-EO12) was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt catalyst. The structural analysis of the surfactant was done by 1H-NMR, 13C-NMR, 29Si-NMR and FT-IR analysis. In addition the thermal stability [...] Read more.
The trisiloxane polyether surfactant (3-[3-(hydroxy)(polyethoxy)propyl]-1,1,1,3,5,5,5 -heptamethyltrisiloxane) (TS-EO12) was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt catalyst. The structural analysis of the surfactant was done by 1H-NMR, 13C-NMR, 29Si-NMR and FT-IR analysis. In addition the thermal stability of TS-EO12 was studied by the thermogravimetric measurements. On the one hand the surface properties of TS-EO12 at the water-air interface were investigated by surfactant aqueous solutions surface tension measurements carried out at 293 K, 303 K and 313 K, and on the other the aggregation properties were analyzed based on the solubilization properties of TS-EO12 aggregates at different temperatures. On the basis of the obtained thermodynamic parameters of adsorption and micellization of studied surfactant the temperature impact on its surface and volume properties were deduced. It was proved that the tendency of the studied surfactant molecules to adsorb at the water-air interface and to form micelles weakens with decreasing temperature. It was also concluded that the structure of the adsorption layer changes with temperature. Optical microscopy measurements were used for the TS-EO12 micelle morphology determination. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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18 pages, 3273 KiB  
Article
The Equilibria in Lipid–Lipoic Acid Systems: Monolayers, Microelectrophoretic and Interfacial Tension Studies
by Paulina Laszuk, Wiesław Urbaniak and Aneta D. Petelska
Molecules 2020, 25(16), 3678; https://doi.org/10.3390/molecules25163678 - 12 Aug 2020
Cited by 10 | Viewed by 2760
Abstract
In this examination, we investigated the effect of lipoic acid (LA) on the properties of biological membrane models (monolayers, bilayers, and liposomes) formed from phosphatidylcholine (PC) or phosphatidylserine (PS) using the Langmuir, microelectrophoresis, and interfacial tension methods. The Langmuir technique allowed us to [...] Read more.
In this examination, we investigated the effect of lipoic acid (LA) on the properties of biological membrane models (monolayers, bilayers, and liposomes) formed from phosphatidylcholine (PC) or phosphatidylserine (PS) using the Langmuir, microelectrophoresis, and interfacial tension methods. The Langmuir technique allowed us to calculate the π–A isotherms and determine the molecular surface areas of pure and mixed monolayers. Using mathematical equations, we established that LA and the lipids formed complexes at a 1:1 ratio. The interfacial tension method was based on Young and Laplace’s equation. We assumed the formation of a 1:1 complex in the PC–LA system. Using the mathematical relationships, we derived the parameters characterizing the resulting complex, i.e., the surface occupied by the complex and the interfacial tension and stability constant of the formed complex. The microelectrophoretic method was used to determine the dependence of the zeta potential of the lipid membranes as a function of the pH (pH 2 to 10) of the electrolyte solution. The results indicate that modification of PC or PS membranes with LA affects changes in the zeta potential and the isoelectric point values. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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15 pages, 1508 KiB  
Article
Long-Time Non-Debye Kinetics of Molecular Desorption from Substrates with Frozen Disorder
by Victor N. Bondarev, Volodymyr V. Kutarov, Eva Schieferstein and Vladimir V. Zavalniuk
Molecules 2020, 25(16), 3662; https://doi.org/10.3390/molecules25163662 - 11 Aug 2020
Viewed by 2148
Abstract
The experiments on the kinetics of molecular desorption from structurally disordered adsorbents clearly demonstrate its non-Debye behavior at “long” times. In due time, when analyzing the desorption of hydrogen molecules from crystalline adsorbents, attempts were made to associate this behavior with the manifestation [...] Read more.
The experiments on the kinetics of molecular desorption from structurally disordered adsorbents clearly demonstrate its non-Debye behavior at “long” times. In due time, when analyzing the desorption of hydrogen molecules from crystalline adsorbents, attempts were made to associate this behavior with the manifestation of second-order effects, when the rate of desorption is limited by the rate of surface diffusion of hydrogen atoms with their subsequent association into molecules. However, the estimates made in the present work show that the dominance of second-order effects should be expected in the region of times significantly exceeding those where the kinetics of H2 desorption have long acquired a non-Debye character. To explain the observed regularities, an approach has been developed according to which frozen fluctuations in the activation energy of desorption play a crucial role in the non-Debye kinetics of the process. The obtained closed expression for the desorption rate has a transparent physical meaning and allows us to give a quantitative interpretation of a number of experiments on the desorption kinetics of molecules not only from crystalline (containing frozen defects) but also from amorphous adsorbents. The ways of further development of the proposed theory and its experimental verification are outlined. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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16 pages, 16360 KiB  
Article
Thermo-Electrical Conduction of the 2,7-Di([1,1′-Biphenyl]-4-yl)-9H-Fluorene Molecular System: Coupling between Benzene Rings and Stereoelectronic Effects
by Judith Helena Ojeda Silva, Juan Sebastián Paez Barbosa and Carlos Alberto Duque Echeverri
Molecules 2020, 25(14), 3215; https://doi.org/10.3390/molecules25143215 - 14 Jul 2020
Cited by 5 | Viewed by 2459
Abstract
Theoretical and analytical thermal and electrical properties are studied through the 2,7-Di([1,1′-biphenyl]-4-yl)-9H-fluorene aromatic system as a prototype of a molecular switch. Variations of the dihedral angles between the two Benzene rings at each end of the molecule have been considered, thus determining the [...] Read more.
Theoretical and analytical thermal and electrical properties are studied through the 2,7-Di([1,1′-biphenyl]-4-yl)-9H-fluorene aromatic system as a prototype of a molecular switch. Variations of the dihedral angles between the two Benzene rings at each end of the molecule have been considered, thus determining the dependence on the structural variation of the molecule when the aromatic system is connected between metal contacts. The molecule is modeled through a Tight-Binding Hamiltonian where—from the analytical process of decimation and using Green’s functions—the probability of transmission (T) is calculated by using the Fisher–Lee relationship. Consequently, the thermal and electrical transport properties such as I − V curves, quantum noise (S), Fano factor (F), electrical conductance (G), thermal conductance ( κ ), Seebeck coefficient (Q), and merit number ( Z T ) are calculated. The available results offer the possibility of designing molecular devices, where the change in conductance or current induced by a stereoelectronic effect on the molecular junctions (within the aromatic system) can produce changes on the insulating–conductive states. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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14 pages, 2147 KiB  
Article
Unusual Complexes of P(CH)3 with FH, ClH, and ClF
by Janet E. Del Bene, Ibon Alkorta and José Elguero
Molecules 2020, 25(12), 2846; https://doi.org/10.3390/molecules25122846 - 19 Jun 2020
Cited by 2 | Viewed by 2503
Abstract
Ab initio MP2/aug’-cc-pVTZ calculations have been performed to determine the structures and binding energies of complexes formed by phosphatetrahedrane, P(CH)3, and HF, HCl, and ClF. Four types of complexes exist on the potential energy surfaces. Isomers A form at the P [...] Read more.
Ab initio MP2/aug’-cc-pVTZ calculations have been performed to determine the structures and binding energies of complexes formed by phosphatetrahedrane, P(CH)3, and HF, HCl, and ClF. Four types of complexes exist on the potential energy surfaces. Isomers A form at the P atom near the end of a P-C bond, B at a C-C bond, C at the centroid of the C-C-C ring along the C3 symmetry axis, and D at the P atom along the C3 symmetry axis. Complexes A and B are stabilized by hydrogen bonds when FH and ClH are the acids, and by halogen bonds when ClF is the acid. In isomers C, the dipole moments of the two monomers are favorably aligned but in D the alignment is unfavorable. For each of the monomers, the binding energies of the complexes decrease in the order A > B > C > D. The most stabilizing Symmetry Adapted Perturbation Theory (SAPT) binding energy component for the A and B isomers is the electrostatic interaction, while the dispersion interaction is the most stabilizing term for C and D. The barriers to converting one isomer to another are significantly higher for the A isomers compared to B. Equation of motion coupled cluster singles and doubles (EOM-CCSD) intermolecular coupling constants J(X-C) are small for both B and C isomers. J(X-P) values are larger and positive in the A isomers, negative in the B isomers, and have their largest positive values in the D isomers. Intramolecular coupling constants 1J(P-C) experience little change upon complex formation, except in the halogen-bonded complex FCl:P(CH3) A. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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18 pages, 4020 KiB  
Article
Tocopheryl Succinate-Induced Structural Changes in DPPC Liposomes: DSC and ANS Fluorescence Studies
by Grażyna Neunert, Jolanta Tomaszewska-Gras, Stanislaw Witkowski and Krzysztof Polewski
Molecules 2020, 25(12), 2780; https://doi.org/10.3390/molecules25122780 - 16 Jun 2020
Cited by 13 | Viewed by 2939
Abstract
Recent studies show that alpha-tocopheryl succinate (TS) exhibits selective toxicity against cancer cells. In this study, we investigated the effect of TS’s presence on the physico-chemical and structural properties of DPPC liposomes using fluorescence parameters (intensity, lifetime, and position of emission maximum) of [...] Read more.
Recent studies show that alpha-tocopheryl succinate (TS) exhibits selective toxicity against cancer cells. In this study, we investigated the effect of TS’s presence on the physico-chemical and structural properties of DPPC liposomes using fluorescence parameters (intensity, lifetime, and position of emission maximum) of 1-anilino-8-naphtalene sulphonate (ANS), differential scanning calorimetry (DSC) and zeta potential methods. Increasing the TS presence in the DPPC gel phase produced ANS fluorescence enhancement with a hypsochromic shift of the maximum. The zeta potential measurements show an increase in the negative surface charge and confirmed that this process is connected with the hydrophobic properties of dye, which becomes located deeper into the interphase region with a progressing membrane disorder. Temperature dependence studies showed that an increase in temperature increases the ANS fluorescence and shifts the ANS maximum emission from 464 to 475 nm indicating a shift from hydrophobic to a more aqueous environment. In the liquid crystalline phase, the quenching of ANS fluorescence occurs due to the increased accessibility of water to the ANS located in the glycerol region. The DSC results revealed that increasing the presence of TS led to the formation of multicomponent DSC traces, indicating the formation of intermediate structures during melting. The present results confirmed that TS embedded into the DPPC membrane led to its disruption due to destabilisation of its structure, which confirmed the measured biophysical parameters of the membrane. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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14 pages, 1289 KiB  
Article
Solubility Data of the Bioactive Compound Piperine in (Transcutol + Water) Mixtures: Computational Modeling, Hansen Solubility Parameters and Mixing Thermodynamic Parameters
by Faiyaz Shakeel, Nazrul Haq and Sultan Alshehri
Molecules 2020, 25(12), 2743; https://doi.org/10.3390/molecules25122743 - 13 Jun 2020
Cited by 7 | Viewed by 3081
Abstract
The solubility values and thermodynamic parameters of a natural phytomedicine/nutrient piperine (PPN) in Transcutol-HP (THP) + water combinations were determined. The mole fraction solubilities (xe) of PPN in THP + water combinations were recorded at T = 298.2–318.2 K and [...] Read more.
The solubility values and thermodynamic parameters of a natural phytomedicine/nutrient piperine (PPN) in Transcutol-HP (THP) + water combinations were determined. The mole fraction solubilities (xe) of PPN in THP + water combinations were recorded at T = 298.2–318.2 K and p = 0.1 MPa by the shake flask method. Hansen solubility parameters (HSPs) of PPN, pure THP, pure water and THP + water mixtures free of PPN were also computed. The xe values of PPN were correlated well with “Apelblat, Van’t Hoff, Yalkowsky–Roseman, Jouyban–Acree and Jouyban–Acree–Van’t Hoff” models with root mean square deviations of < 2.0%. The maximum and minimum xe value of PPN was found in pure THP (9.10 × 10−2 at T = 318.2 K) and pure water (1.03 × 10−5 at T = 298.2 K), respectively. In addition, HSP of PPN was observed more closed with that of pure THP. The thermodynamic parameters of PPN were obtained using the activity coefficient model. The results showed an endothermic dissolution of PPN at m = 0.6–1.0 in comparison to other THP + water combinations studied. In addition, PPN dissolution was recorded as entropy-driven at m = 0.8–1.0 compared with other THP + water mixtures evaluated. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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12 pages, 3446 KiB  
Article
Activation of Peracetic Acid with Lanthanum Cobaltite Perovskite for Sulfamethoxazole Degradation under a Neutral pH: The Contribution of Organic Radicals
by Xuefei Zhou, Haowei Wu, Longlong Zhang, Bowen Liang, Xiaoqi Sun and Jiabin Chen
Molecules 2020, 25(12), 2725; https://doi.org/10.3390/molecules25122725 - 12 Jun 2020
Cited by 45 | Viewed by 4564
Abstract
Advanced oxidation processes (AOPs) are effective ways to degrade refractory organic contaminants, relying on the generation of inorganic radicals (e.g., •OH and SO4•−). Herein, a novel AOP with organic radicals (R-O•) was reported to degrade contaminants. Lanthanum [...] Read more.
Advanced oxidation processes (AOPs) are effective ways to degrade refractory organic contaminants, relying on the generation of inorganic radicals (e.g., •OH and SO4•−). Herein, a novel AOP with organic radicals (R-O•) was reported to degrade contaminants. Lanthanum cobaltite perovskite (LaCoO3) was used to activate peracetic acid (PAA) for organic radical generation to degrade sulfamethoxazole (SMX). The results show that LaCoO3 exhibited an excellent performance on PAA activation and SMX degradation at neutral pH, with low cobalt leaching. Meanwhile, LaCoO3 also showed an excellent reusability during PAA activation. In-depth investigation confirmed CH3C(O)O• and CH3C(O)OO• as the key reactive species for SMX degradation in LaCoO3/PAA system. The presence of Cl− (1–100 mM) slightly inhibited the degradation of SMX in the LaCoO3/PAA system, whereas the addition of HCO3− (0.1–1 mM) and humic aid (1–10 mg/L) could significantly inhibit SMX degradation. This work highlights the generation of organic radicals via the heterogeneous activation of PAA and thus provides a promising way to destruct contaminants in wastewater treatment. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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15 pages, 1147 KiB  
Article
Solubility Data and Computational Modeling of Baricitinib in Various (DMSO + Water) Mixtures
by Saad M. Alshahrani and Faiyaz Shakeel
Molecules 2020, 25(9), 2124; https://doi.org/10.3390/molecules25092124 - 1 May 2020
Cited by 19 | Viewed by 3641
Abstract
The solubility and thermodynamic analysis of baricitinib (BNB) in various dimethyl sulfoxide (DMSO) + water mixtures were performed. The “mole fraction solubilities (xe)” of BNB in DMSO and water mixtures were determined at “T = 298.2–323.2 K” and “ [...] Read more.
The solubility and thermodynamic analysis of baricitinib (BNB) in various dimethyl sulfoxide (DMSO) + water mixtures were performed. The “mole fraction solubilities (xe)” of BNB in DMSO and water mixtures were determined at “T = 298.2–323.2 K” and “p = 0.1 MPa” using an isothermal saturation technique. “Hansen solubility parameters (HSPs)” of BNB, pure DMSO, pure water and “DMSO + water” mixtures free of BNB were also estimated. The xe data of BNB was regressed well by five different thermodynamics-based co-solvency models, which included “Apelblat, Van’t Hoff, Yalkowsky-Roseman, Jouyban-Acree and Jouyban-Acree-Van’t Hoff models” with overall deviations of <5.0%. The highest and lowest xe value of BNB was computed in pure DMSO (1.69 × 10−1 at T = 323.2 K) and pure water (2.23 × 10−5 at T = 298.2 K), respectively. The HSP of BNB was found to be closer to that of pure DMSO. Based on activity coefficient data, maximum solute–solvent molecular interactions were observed in BNB-DMSO compared to BNB-water. The results of “apparent thermodynamic analysis” indicated endothermic and entropy-drive dissolution of BNB in all “DMSO + water” combinations including mono-solvents (water and DMSO). “Enthalpy-entropy compensation analysis” showed enthalpy-driven to be the main mechanism of solvation of BNB. Full article
(This article belongs to the Special Issue 25th Anniversary of Molecules—Recent Advances in Physical Chemistry)
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