Physchem, Volume 1, Issue 2 (September 2021) – 8 articles

The Three-Dimensional Reference Interaction Site Model (3D-RISM) with Kovalenko−Hirata (KH) closure is applied to calculate the 1,9-Decadiene/Water partition coefficients for a diverse class of compounds. The liquid state of 1,9-Decadiene is represented with the united atom TraPPE force field parameters. The 3D-RISM-KH computed partition functions are in good agreement with the experimental results. Our computational scheme can be used for a quantitative structure partitioning prediction for decadiene-water system, which has been used in membrane-mimicking of the egg-lecithin/water permeability experiments. Full article

NMR spectroscopic literature data are used, in a wide temperature-pressure range (180–350 K and 0.1–400 MPa), to study the water polymorphism and the validity of the liquid–liquid transition (LLT) hypothesis. We have considered the self-diffusion coefficient $D_S$ and the reorientational correlation time ${\tau }_{\theta }$ (obtained from spin-lattice $T_1$ relaxation times), measured, respectively, in bulk and emulsion liquid water from the stable to well inside the metastable supercooled region. As an effect of the hydrogen bond (HB) networking, the isobars of both these transport functions evolve with T by changing by several orders of magnitude, whereas their pressure dependence become more and more pronounced at lower temperatures. Both these transport functions were then studied according to the Adam–Gibbs model, typical of glass forming liquids, obtaining the water configurational entropy and the corresponding specific heat contribution. The comparison of the evaluated $C_{P,conf}$ isobars with the experimentally measured water specific heat reveals the full consistency of this analysis. In particular, the observed $C_{P,conf}$ maxima and its diverging behaviors clearly reveals the presence of the LLT and with a reasonable approximation the liquid–liquid critical point (LLCP) locus in the phase diagram. Full article

Тhe adequacy of chemical property predictions strongly depends on the structure representation, including the proper treatment of the tautomeric and isomeric forms. A combination of an in-house developed open-source tool for automatic generation of tautomers, Ambit-Tautomer, based on H-atom shift rules and standard quantum chemical (DFT) calculations is used for a detailed investigation of the possible geometric isomers, conformers and tautomers of unsubstituted and para-substituted phenylhydrazones, systems with experimentally observed unusual para-substituent effects on the intramolecular hydrogen bond (IMHB) for E-isomers of the compounds. The computational results show that the energetically preferred E-isomers are characterized by stronger IMHBs than the corresponding Z-isomers. The HN–N=C–C=N molecular fragment in the E-configurations is less sensitive to the substitution effect than the HN–N=C–C=O fragment in the isomers with Z-configuration. A probable reason for this decreased sensitivity of E-isomers to phenyl ring substitution is the more efficient conjugation and charge distribution in the HN–N=C–C=N fragment. Full article

Efficient and environmentally responsible use of resources requires the development and optimization of gas separation processes. A promising approach is the use of liquids that are designed for specific tasks, e.g., the capture of carbon dioxide or other greenhouse gases. This requires an accurate determination of gas solubilities for a broad range of temperatures and pressures. However, state of the art measurement techniques are often very time consuming or exhibit other pitfalls that prevent their use as efficient screening tools. Here, we show that the application of Raman spectroscopy through a compact measuring system can simplify data acquisition for the determination of gas solubilities in liquids. To demonstrate that this approach is expedient, we determined gas solubilities of carbon dioxide in water for three isotherms T = (288.15, 293.15, 298.15) K over a pressure range from p = (0.5–5) MPa and in three imidazolium-based ionic liquids for one isotherm T = 298.15 K at pressures from p = (0.1–5) MPa. When compared to data in the literature, all results are within the reported uncertainties of the measurement techniques involved. The developed analysis method eliminates the need for a lengthy volume or mass calibration of the sample prior to the measurements and, therefore, allows for fast screening of samples, which can help to advance gas separation processes in scientific and industrial applications. Full article

More sustainable solutions are needed to produce chemicals and fuels, mainly to face rising demands and mitigate climate change. Light, as a reagent, has emerged as a route to activate small molecules, e.g., H₂O, CO₂, N₂, and make complex chemicals in a process called photocatalysis. Several photosystems have been proposed, with plasmonic technology emerging as one the most promising technologies due to its high optical absorption and hot-carrier formation. However, the lifetime of hot carriers is unsuitable for direct use; therefore, they are normally coupled with suitable charge-accepting materials, such as semiconductors. Herein, a system is reported consisting of Au supported in p-Cu₂O. The combination of p-Cu₂O intrinsic photoactivity with the plasmonic properties of Au extended the system’s optical absorption range, increasing photocatalytic efficiency. More importantly, the system enabled us to study the underlying processes responsible for hot-hole transfer to p-Cu₂O. Based on photocatalytic studies, it was concluded that most of the holes involved in aniline photo-oxidation come from hot-carrier injections, not from the PIRET process. Full article

A large number of peripheral membrane proteins transiently interact with lipids through a combination of weak interactions. Among them, electrostatic interactions of clusters of positively charged amino acid residues with negatively charged lipids play an important role. Clusters of charged residues are often found in intrinsically disordered protein regions, which are highly abundant in the vicinity of the membrane forming what has been called the disordered boundary of the cell. Beyond contributing to the stability of the lipid-bound state, the pattern of charged residues may encode specific interactions or properties that form the basis of cell signaling. The element of this code may include, among others, the recognition, clustering, and selective release of phosphatidyl inositides, lipid-mediated protein-protein interactions changing the residence time of the peripheral membrane proteins or driving their approximation to integral membrane proteins. Boundary effects include reduction of dimensionality, protein reorientation, biassing of the conformational ensemble of disordered regions or enhanced 2D diffusion in the peri-membrane region enabled by the fuzzy character of the electrostatic interactions with an extended lipid membrane. Full article

PEGylated lipid nanoparticles have a continuously expanding range of applications, particularly within pharmaceutical areas. Hereby, it is shown with the help of the Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and other surface sensitive techniques that, at room temperature, PEGylated liposomes and lipodisks adhere strongly to silica surfaces resulting in the displacement of the hydration layer of silica and the formation of immobilized nanoparticle films. Furthermore, it is shown that drastic changes in the structure of the immobilized films occur if the temperature is increased to >35 °C. Thus, intact immobilized PEGylated liposomes rupture and spread, even in the gel phase state; immobilized lipodisks undergo complete separation of their components (bilayer forming lipids and PEGylated lipids) resulting in a monolayer of adsorbed PEGylated lipids; and PEGylated supported lipid bilayers release part of the water trapped between the lipid membrane and the surface. It is hypothesized that these changes occur mainly due to the changes in the configuration of PEG chains and a drastic decrease of the affinity of the polymer for water. The observed phenomena can be applied, e.g., for the production of defect-free supported lipid bilayers in the gel or liquid ordered phase states. Full article

Molecular terms of dioxygen and nitic oxide are presented. Electron spin resonance spectra of diatomic molecules corresponding to these terms are discussed. Gas-phase ESR can be a convenient method of monitoring paramagnetic pollutants in the atmosphere. We ran additional calculations in molecular physics for terms of these molecules and Zeeman transitions. Full article