Belträge zur Chemie der Silicium-Schwefel-Verbindungen. XIV. Reaktion der Silanthiole und cyclo-Disilthiane mit o-Hydroxymercuribenzoesäure

Contributions to the Chemistry of Silicon-Sulphur-Compounds. XIV. Reaction of Silanethiols and cyclo-Disilthianes with o-Hydroxymercuribenzoic Acid. The reaction of trialkoxysilanethiols, di-t-butoxysilanedithiol and tetra-t-butoxy-cyclo-disilthiane with o-hydroxymercuribenzoic acid by means of titration was investigated. By this method some informations about the hydrolytic stability of the Si—S-bound were received.     

Studies on silver(I) solvation in binary solvent mixtures containing dimethylsulfoxide. IV determination of solvent transference numbers for AgSCN and ionic coordination numbers of Ag+ in methanol-dimethylsulfoxide mixtures at 25°C

Solvent transport by AgSCN in the methanol (M)+dimethylsulfoxide (DMSO) system has been studied at 25°C by e.m.f. measurements. The solvent transference number of DMSO is positive as its concentration increases in the cathode compartment during electrolysis. The solubility of AgSCN has been determined in methanol, in DMSO and in methanol-DMSO mixtures. Using the known Gibbs free energy of solvation for the Ag⁺ ion, the corresponding energy for SCN, was found to be independent of the mole fraction. The experimental solvent transference numbers therefore only represent the contribution of Ag⁺, this is because it is preferentially solvated by DMSO. A coordination model has been applied to the Gibbs free energy of transfer of Ag⁺ in order to obtain coordination numbers thereby allowing calculation of solvent transference numbers. The experimental and the calculated solvent transference numbers are in good agreement at mole fractions of DMSO greater than 0.5. In highly methanolic solutions the assumption that the solvation of Ag⁺ in the solvent system studied is adequately represented by a total coordination number of four, proves to be too simple.     

Improvements on the protein–dipole Langevin–dipole model

The protein–dipole Langevin–dipole (PDLD) model developed by Warshel and co-workers is an approach to evaluate electrostatic interactions in protein systems from microscopic sights. This model grasped the main physical factors and required little computations. But it might need the tests from every aspect. In the present work, we have chosen the solvation energies of Asp3, Glu7, Glu49, and Asp50 in bovine pancreatic trypsin inhibitor (BPTI) as a calibration to discuss the influences of parameters and conditions on the simulation results in the PDLD model. Some improvements have been proposed. The calculated solvation energies associated with ionizing the four acidic groups in BPTI and aspartic acid in solution are found in good agreement with the corresponding observed results if the improved PDLD approach and computational methods are used. © 1992 by John Wiley & Sons, Inc.     

Solvatochromism and preferential solvation of Brooker's merocyanine in water–methanol mixtures

The excitation energy of Brooker's merocyanine in water–methanol mixtures shows nonlinear behavior with respect to the mole fraction of methanol, and it was suggested that this behavior is related to preferential solvation by methanol. We investigated the origin of this behavior and its relation to preferential solvation using the three‐dimensional reference interaction site model self‐consistent field method and time‐dependent density functional theory. The calculated excitation energies were in good agreement with the experimental behavior. Analysis of the coordination numbers revealed preferential solvation by methanol. The free energy component analysis implied that solvent reorganization and solvation entropy drive the preferential solvation by methanol, while the direct solute–solvent interaction promotes solvation by water. The difference in the preferential solvation effect on the ground and excited states causes the nonlinear excitation energy shift. © 2017 Wiley Periodicals, Inc.     

Hydratisierung von und auf Oberflächen

Scanning tunneling microscopy offers the opportunity to image water ice formation on surfaces on the molecular scale, from single water molecules up to closed water layers. The variation of the growth conditions leads to a large variety of ice structure, both amorphous and crystalline ones. Our studies open up the possibility to investigate solvation of surfaces as well as of single adsorbed molecules and the influence of this solvation on photo reactions on the molecular scale. The results will contribute to understanding the influence of solvents onto reactions within the hot topic of solvation science.     

The enthalpies of solution of water, <Emphasis Type="Italic">o</Emphasis>-xylene,and triton X-100 in isopropanol

The enthalpies of solution of water, o-xylene, and Triton X-100 in 2-propanol were measured calorimetrically at 288.15, 298.15, and 313.15 K. The results obtained and literature data were used to calculate the heats of condensation, solution, and solvation of these nonelectrolytes. The influence of the nature of nonelectrolytes and temperature on the enthalpies of nonspecific and specific solvation is discussed.     

Dampfdruck- und Leitfähigkeitsuntersuchungen der Ionensolvatation in Amiden

The solvating properties of formamide, N-methylformamide, dimethylformamide, N-ethylformamide and diethylformamide have been investigated by means of vapour pressure and conductivity measurements. For the salts and ions, resp. average solvation numbers have been calculated from vapour pressure data and limiting ionic conductances. The solvation numbers are used for a discussion of the influence of N-substituents on the solvating properties of the amides.

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The impact of surface area,volume, curvature,and Lennard–Jones potential to solvation modeling

This article explores the impact of surface area, volume, curvature, and Lennard–Jones (LJ) potential on solvation free energy predictions. Rigidity surfaces are utilized to generate robust analytical expressions for maximum, minimum, mean, and Gaussian curvatures of solvent–solute interfaces, and define a generalized Poisson–Boltzmann (GPB) equation with a smooth dielectric profile. Extensive correlation analysis is performed to examine the linear dependence of surface area, surface enclosed volume, maximum curvature, minimum curvature, mean curvature, and Gaussian curvature for solvation modeling. It is found that surface area and surfaces enclosed volumes are highly correlated to each other's, and poorly correlated to various curvatures for six test sets of molecules. Different curvatures are weakly correlated to each other for six test sets of molecules, but are strongly correlated to each other within each test set of molecules. Based on correlation analysis, we construct twenty six nontrivial nonpolar solvation models. Our numerical results reveal that the LJ potential plays a vital role in nonpolar solvation modeling, especially for molecules involving strong van der Waals interactions. It is found that curvatures are at least as important as surface area or surface enclosed volume in nonpolar solvation modeling. In conjugation with the GPB model, various curvature‐based nonpolar solvation models are shown to offer some of the best solvation free energy predictions for a wide range of test sets. For example, root mean square errors from a model constituting surface area, volume, mean curvature, and LJ potential are less than 0.42 kcal/mol for all test sets. © 2016 Wiley Periodicals, Inc.     

Pathway dependence of the efficiency of calculating free energy and entropy of solute–solute association in water

In this study we investigate two alternative pathways to compute the free energy and the entropy of small molecule association (ΔF_assoc and ΔS_assoc) in water. The first route (direct pathway) uses thermodynamic integration as function of the distance R between the solutes. The mean force and the mean covariance of the force with the energy in solution are calculated from molecular dynamics simulation followed by integration of these quantities with respect to the reaction coordinate R. The alternative approach examined (solvation pathway) would first remove the solutes from the solution using thermodynamic integration as function of a solvation coupling parameter λ, change the solute–solute distance in vacuo and then solvate back the solute pair at the new separation distance. The system studied was a pair of CH₄ molecules in water. We investigate the influence of the CH₄–water interaction strength on the obtained ΔF_assoc and ΔS_assoc values by changing van der Waals and Coulomb interaction and evaluated the accuracy and efficiency for the two pathways. We find that the direct route seems more suitable for the calculation of free energies of hydrophobic solutes while the solvation pathway performs better when calculating entropy changes for solutes that have a stronger interaction with the solvent.     

Etude de copolymères ABS (acrylonitrile–butadiène–styrène): Solvatation préférentielle du polybutadiène par les promoteurs

ABS resins formed by copolymerization of styrene and acrylonitrile (AN) in presence of polybutadiene, consist of a mixture of SAN graft copolymer on polybutadiene (PBut) and of ungrafted SAN copolymer (styrene-co-acrylonitrile). The kinetic study was completed by showing a preferential solvation of polybutadiene by the initiator. This solvation effect was studied as a function of the concentration ratio SAN/PBut and in relation with the type of initiator. The adsorption of initiator appeared to be maximum when its solubility parameter (σ) is close to that of polybutadiene. As a function of the polybutadiene characteristics, this selective adsorption can be given by where I₁ is the quantity of initiator in the polybutadiene medium, I is the total amount of peroxide, [PBut] is the concentration of polybutadiene, and M?_n its molecular weight. It has been shown furthermore that the preferential solvation of polybutadiene by the benzoyl peroxide can be increased by addition of SAN or acrylonitrile. The consequences of this solvation effect on the characteristics of the grafting reaction, more precisely on the molecular weight of grafted and ungrafted SAN and on the rate of polymerization, were examined.     

Solvatochromism and preferential solvation of <Emphasis Type="Italic">para</Emphasis>-derivatives of guaiacol in water-N,N-dimethylformamide mixtures

The influence of the composition of the water-N,N-dimethylformamide mixed solvent on the position of the B absorption band in UV spectra of 2-methoxyphenol, its para-substituted derivatives, and corresponding phenolate anions simulating base units of natural lignin is investigated. The data obtained are interpreted in terms of the model of preferential solvation. The preferential solvation parameters and compositions of the solvation shells are calculated.     

Das Innere der Zelle: Ein komplexes Lösungsmittel

The interior of a living cell is very distinct from dilute aqueous solutions that are often used to study the function of proteins and enzymes experimentally. Here, we discuss novel experimental techniques and modeling approaches that provide a deeper understanding of the effects of crowding, intermolecular interactions, and the influence of osmolytes in realistic biological environments, including cells. Further, we discuss adaptation mechanisms involving in‐cell solvation environments to extreme conditions, such as high pressure in the deep sea, and their relevance to biotechnology.     

Quantitative Analyse von Schichtsystemen mit der Methode der Rutherford-Weitwinkelstreuung

The use of Rutherford backscattering for the investigation of monocrystals overlaid with thin amorphous layers is briefly described. Using silicon crystals covered with silicon nitride and aluminium layers, methods are exhibited, which provide special informations about surface layers (mass and area concentration of the layer atoms, composition of the layers and density and thickness, respectively).      

Ultrafast electron transfer, localization and solvation at ice–metal interfaces: Correlation of structure and dynamics

The interaction of an excess electron with a polar molecular environment is well known as electron solvation. This process is characterized by an energetic stabilization and by changes of the electronic spatial extent due to screening of the localized charge through molecular rearrangement. At metal–ice interfaces we photo-inject delocalized electrons from the metal substrate into adsorbed ice layers and analyze the ultrafast dynamics of electron transfer, localization and solvation by femtosecond time- and angle-resolved two-photon photoemission spectroscopy. To acquire further understanding of the individual steps of the complex process we vary the interfacial structure. The substrate is changed between Cu(1 1 1) and Ru(0 0 1) and the electron dynamics in ice islands are compared to closed D₂O layers. Contrasting crystalline and amorphous ice we found that electron solvation is mediated through electron localization at favorable structural sites, which occurs very efficiently in amorphous ice, but is less likely in a crystalline layer. Next, we find that in an open ice structure like ice islands the energetic stabilization due to electron solvation proceeds at a rate of 1 eV/ps which is three times faster than in a closed ice layer. We attribute this behavior to differences in the molecular coordination, which determines the molecular mobility and, thus, the transfer rate of electronic energy to solvent modes. The substrate’s electronic structure, on the other hand, is important to understand the transfer rates from electrons in ice back to the metal. First experiments on trapped electrons in crystalline ice underline the potential to study electron solvation not only during the equilibration process, but also in quasi-static conditions, where we find that the stabilization continues, although at much weaker rates.     

Study of Microheterogeneity in Acetonitrile–Water Binary Mixtures by using Polarity‐Resolved Solvation Dynamics

The solvation dynamics of three coumarin dyes with widely varying polarities were studied in acetonitrile–water (ACN–H₂O) mixtures across the entire composition range. At low ACN concentrations [ACN mole fractions (X_ACN)≤0.1], the solvation dynamics are fast (<40 ps), indicating a nearly homogeneous environment. This fast region is followed by a sudden retardation of the average solvation time (230–1120 ps) at higher ACN concentrations (X_ACN≈0.2), thus indicating the onset of nonideality within the mixture that continues until X_ACN≈0.8. This nonideality regime (X_ACN≈0.2–0.8) comprises of multiple dye‐dependent anomalous regions. At very high ACN concentrations (X_ACN≈0.8–1), the ACN–H₂O mixtures regain homogeneity, with faster solvation times. The source of the inherent nonideality of the ACN–H₂O mixtures is a subject of debate. However, a careful examination of the widths of time‐resolved emission spectra shows that the origin of the slow dynamics may be due to the diffusion of polar solvent molecules into the first solvation shell of the excited coumarin dipole.     

Lithium solvation in bis(trifluoromethanesulfonyl)imide-based ionic liquids

The lithium solvation in (1 -x)(EMI-TFSI), xLiTFSI ionic liquids where EMI(+) is the 1-ethyl-3-methylimidazolium cation and TFSI(-) the bis(trifluoromethanesulfonyl)imide anion, is shown by Raman spectroscopy to involve essentially [Li(TFSI)(2)](-) anionic clusters for 0 < x < 0.4, but addition of stoichiometric amounts of solvents S such as oligoethers changes the lithium solvation into [Li(S)(m)](+) cationic clusters; the lithium transference number in TFSI-based ionic liquid electrolytes for lithium batteries should thus be strongly improved.     

Theoretical thermodynamic study of the adenine–thymine tautomeric equilibrium: Electronic structure calculations and steered molecular dynamic simulations

Free energy of the tautomeric equilibrium A‐T ? A*‐T* between the canonical and noncanonical DNA base equilibrium in aqueous solution was theoretically determined by applying electronic structure methods (at the M06‐2X‐PCM/6‐311++G(d,p) level) and steered molecular dynamic simulations. Concerted and stepwise mechanisms were considered for the double proton transfer in an effort to explain the anomalous behavior of this system where an unfavorable process without a transition state can be observed depending on the level of calculation used. Of the different mechanisms used in the simulations, the stepwise mechanism, in which the first step implies the transference of a proton from thymine to adenine, and a second step with the transference of a different proton from adenine to thymine, was the only one that showed two transition states and a reaction intermediate. However, a concerted and stepwise mechanism has similar kinetic and thermodynamic behavior, with similar reaction and activation energies. Simple proton transfer was more favorable for the transference of the hydrogen from the adenine to the thymine. The inclusion of an aqueous medium in this study only slightly modified these energies, but the barrier energy was higher when the solvent was described as a discrete medium. Transition states and intermediate structures were analyzed at molecular dynamic level.     

Ab initio study of the structure of isocytosine–cytosine standard Watson–Crick base pairs in the gas phase and in water

Ab initio quantum chemical studies at the HF and MP2 levels with the 6-31G* basis set were performed for H-bonded isocytosine–cytosine standard Watson–Crick base pairs (denoted as iCC1) in the gas phase and in a water solution. Full geometry optimizations at the HF level without any constraints on the planarity of these complexes were carried out. The water solution was modeled by the explicit inclusion of one, two, four, and six water molecules. Six waters create the first full coordination sphere around the iCC1 base pair. All potentially possible hydration positions of the iCC1 base pair with one and two water molecules were considered. The interaction and solvation energies were corrected for the basis-set superposition error by using the full Boys–Bernardi counterpoise correction scheme. It was shown that inclusion of six instead of one, two, or four water molecules has a crucial effect on the geometry of the iCC1 base pair. In the case of six water molecules, the iCC1 moiety becomes strongly nonplanar, while in the case of a smaller number of water molecules, it deviates only slightly from the planar conformation as is adopted in the gas phase. Based on the results of these calculations, the nature of the specific H-bonding interactions, solvation effects, and the interaction energies are discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 37–47, 1998     

A new set of atomic radii for accurate estimation of solvation free energy by Poisson–Boltzmann solvent model

The Poisson–Boltzmann implicit solvent (PB) is widely used to estimate the solvation free energies of biomolecules in molecular simulations. An optimized set of atomic radii (PB radii) is an important parameter for PB calculations, which determines the distribution of dielectric constants around the solute. We here present new PB radii for the AMBER protein force field to accurately reproduce the solvation free energies obtained from explicit solvent simulations. The presented PB radii were optimized using results from explicit solvent simulations of the large systems. In addition, we discriminated PB radii for N‐ and C‐terminal residues from those for nonterminal residues. The performances using our PB radii showed high accuracy for the estimation of solvation free energies at the level of the molecular fragment. The obtained PB radii are effective for the detailed analysis of the solvation effects of biomolecules. © 2014 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

Influence of Van der Waals Interactions on the Solvation Energies of Adsorbates at Pt-Based Electrocatalysts

Solvation can significantly modify the adsorption energy of species at surfaces, thereby influencing the performance of electrocatalysts and liquid-phase catalysts. Thus, it is important to understand adsorbate solvation at the nanoscale. Here we evaluate the effect of van der Waals (vdW) interactions described by different approaches on the solvation energy of *OH adsorbed on near-surface alloys (NSAs) of Pt. Our results show that the studied functionals can be divided into two groups, each with rather similar average *OH solvation energies: (1) PBE and PW91; and (2) vdW functionals, RPBE, PBE-D3 and RPBE-D3. On average, *OH solvation energies are less negative by ∼0.14 eV in group (2) compared to (1), and the values for a given alloy can be extrapolated from one functional to another within the same group. Depending on the desired level of accuracy, these concrete observations and our tabulated values can be used to rapidly incorporate solvation into models for electrocatalysis and liquid-phase catalysis.