Importance Of Solvation Research Articles

State-of-the-art for the development of Cu-based heterogeneous catalysts for efficient utilization of furfural to value chemicals via liquid-phase and gas-phase reactions

ABSTRACT In the present review, we aim to provide important insights into copper-based heterogeneous catalytic systems and discuss the conversion of furfural (FF) through hydrogenation. Each discussed catalyst and the support used for the catalytic reactions play a vital role in the reaction mechanism along with different factors enhancing the catalytic activity. Also, the importance of Cu-based materials along with support, the importance of solvent in the liquid-phase reaction, and the importance of pre-reduction of catalysts are explained in detail. In addition, the superior activity of the catalyst and a few reports from the last decade for Cu-based catalytic systems have been summarized along with the tabulation of different synthesis procedures, mechanistic study, and detailed descriptions with tables and figures. Finally, the conclusions with future aspects for the development of the catalytic hydrogenation process via Cu-based catalytic systems are overviewed.

Conformational Features and Hydration Dynamics of Proteins in Cosolvents: A Perspective from Computational Approaches.

The importance of solvent in stabilizing protein structures has long been recognized. Water is the common solvent for proteins, and hydration is elemental in governing protein stability, flexibility, and function through various interactions. The addition of small organic molecules known as cosolvents may deploy stabilization (folding) or destabilization (unfolding) effects on native protein conformations. Despite exhaustive literature, the molecular mechanism by which cosolvents regulate protein conformations and dynamics is controversial. Specifically, the cosolvent behavior has been unpredictable with the nature and concentrations that lead to protein stabilizing/destabilizing effects as it changes in water content near the vicinity of proteins. With the massive development of computational resources, advancement of computational methods, and the availability of numerous experimental techniques, various theoretical and computational studies of proteins in a mixture of solvents have been instigated. The growing interest in such studies has been to unravel the underlying mechanism of protein folding and cosolvent/solvent-protein interactions that have significant implications in biomedical and biotechnological applications. In this mini-review, apart from the brief overview of important theories and force-field model-based cosolvent effects on proteins, we present the current state of knowledge and recent advances in the field to describe cosolvent-guided conformational features of proteins and hydration dynamics from computational approaches. The mini-review further explains the mechanistic details of protein stability in various popularly used cosolvents, including limitations of present studies and future outlooks. The counteracting effects of cosolvent on the proteins in the mixture of stabilizing and destabilizing cosolvents are also presented and discussed.

Importance of Solvent in Guiding the Conformational Properties of an Intrinsically Disordered Peptide.

Aggregated form of α-synuclein in the brain has been found to be the major component of Lewy bodies that are hallmarks of Parkinson's disease (PD), the second most devastating neurodegenerative disorder. We have carried out room-temperature all-atom molecular dynamics (MD) simulations of an ensemble of widely different α-synuclein1-95 peptide monomer conformations in aqueous solution. Attempts have been made to obtain a generic understanding of the local conformational motions of different repeat unit segments, namely R1-R7, of the peptide and the correlated properties of the solvent at the interface. The analyses revealed relatively greater rigidity of the hydrophobic R6 unit as compared to the other repeat units of the peptide. Besides, water molecules around R6 have been found to be less structured and weakly interacting with the peptide. These are important observations as the R6 unit with reduced conformational motions can act as the nucleation site for the aggregation process, while less structured weakly interacting water around it can become displaced easily, thereby facilitating the hydrophobic collapse of the peptide monomers and their association during the nucleation phase at higher concentrations. In addition, we demonstrated presence of doubly coordinated highly ordered as well as triply coordinated relatively disordered water molecules at the interface. We believe that while the ordered water molecules can favor water-mediated interactions between different peptide monomers, the randomly ordered ones on the other hand are likely to be expelled easily from the interface, thereby facilitating direct peptide-peptide interactions during the aggregation process.

Theoretical studies of capsular complexes of C2V-symmetrical resorcin[4]arene tetraesters with tetramethylammonium cation

Dimeric capsular complexes of two C2V-symmetrical resorcin[4]arene tetraesters with tetramethylammonium cation have been analyzed by a number of theoretical tools to rationalize the experimentally observed preferential formation of heterodimeric complexes over homodimeric ones. These tools range from purely empirical (force fields) to quantum chemical (density-functional theory) approaches. The importance of solvent and thermal effects on the final stabilities of capsular complexes has also been addressed. It has been clearly demonstrated that the quality of results obtained with the empirical force fields improves through the respective molecular dynamics simulations employing Mulliken atomic charges in both gas phase and in a solvent. On the quantum chemical side, density-functional theory calculations including the solvent model based on density (SMD) and thermal corrections resulted in a correct energetic preference of a heterodimeric structure over homodimeric ones.

The N, N-Dimethylformamide Annealing for Enhanced Performance of Perovskite Solar Cells Fabricated in Ambient Air

By adopting N, N-Dimethylformamide (DMF) atmosphere annealing at room temperature, planar perovskite solar cells with a p-i-n structure of ITO/PEDOT:PSS/Perovskite/PCBM/C[Formula: see text]/Al are fabricated by a simple one-step solution process in ambient air with humidity around 50%, and the influence of DMF atmosphere on perovskite solar cells (PSCs) is systematically investigated. Compared to the reference device without DMF reaction, the perovskite films treated by modest DMF annealing show a better distribution and a higher densification, and thus the power conversion efficiency (PCE), short circuit current density ([Formula: see text] and fill factor (FF) are increased by about 17%, 8% and 6%, respectively. This work displays the importance of solvent annealing for perovskite film prepared by the one-step spin-coating method, and possibly provides a simple and cost-effective way to efficiently fabricate PSCs in ambient air.

Effect of solvent composition of electrospun PLGA fibers on paclitaxel release

ABSTRACTSite-directed delivery of antimicrobial agents for inflammatory diseases showed significant medical advances, which can be realized through drug-loaded electrospun fibers. In this study, paclitaxel was applied as model hydrophobic drug, and the effect of solvent ratio on drug distribution and release kinetics would be discussed. It was found that different co-solvent ratios (9:1, 7:3, and 5:5, v:v) of chloroform and dimethylformamide could alter the resultant fiber diameter and morphology as well as paclitaxel release kinetics. Slower release was observed with higher ratio of chloroform. XPS results showed that this is primarily due to a better dispersion of paclitaxel in the fibers prepared from solvent ratio of 9:1 whereas the drug was found to accumulate on the surface for samples 5:5 and 7:3. Our results provided insight into the importance of solvent and solvent ratio not just in fabrication of required fibrous structure but also on release of active compounds.

Theoretical and Computational Study of a Complex System Consisting of Transition Metal Element(s): How to Understand and Predict Its Geometry, Bonding Nature, Molecular Property, and Reaction Behavior

Abstract Complex chemical systems consisting of transition metal element(s) are important and attractive research targets in both experimental chemistry and theoretical chemistry. Transition-metal complexes with carbon dioxide are discussed as one example, in which the coordination geometry, bonding nature, and reactivity are understood well and predicted with the HOMO and the number of d electrons. The spin-multiplicity of inverse sandwich-type dinuclear transition-metal complexes, which have been synthesized recently as a new type of compound, is discussed as another example based on CASPT2 calculations, in which the clear relationship between the spin multiplicity of its ground state and the number of d electrons is presented. Theoretical understanding of various organometallic reactions has been an important endeavor over the last two decades. Insertion reactions of olefin and carbon dioxide into M–H and M–alkyl bonds and σ-bond activation reactions are discussed with orbital interaction diagrams based on perturbation theory. In particular, detailed discussion of the characteristic features of a new type of oxidative addition to an M–L moiety (L = neutral ligand such as alkene and alkyne) and heterolytic σ-bond activation by an M–X moiety (X = anionic ligand). It is still a central challenge to elucidate the reaction mechanisms of catalytic reactions by transition metal complexes. The reaction mechanisms and electronic processes of Ru-catalyzed hydrogenation of carbon dioxide, Pt-, Rh-, and Zr-catalyzed hydrosilylations of alkene, Ir-catalyzed borylation of benzene, and the Hiyama cross-coupling reaction are analyzed based on computational results. We wish to present how to understand the mechanism based on the number of d electrons and the energy of d orbitals in discussion. Also, the importance of solvation and crystalline effects in the theoretical study of transition-metal complexes is discussed based on our recent theoretical studies of mixed-valence complex and a single crystal of a Pt(II) complex.

RELATED PROPERTIES TO ACIDITY AND BASICITY FROM COMPUTATIONAL CHEMISTRY APPROACH

Analytical Chemistry books lack a clear link between thermodynamic and equilibrium approaches involving acids and bases. In this work, theoretical calculations were performed to search for these relations. An excellent relationship was found between difference in Gibbs free energy, ∆G of acid dissociation reaction and ∆G of hydrolysis reaction of the corresponding conjugate base. A relationship between ∆G of hydrolysis reaction of conjugate acids and their corresponding atomic radius was also identified, showing that stability plays an important role in hydrolysis reactions. Finally, the importance of solvation in acid/base behavior was demonstrated when comparing the corresponding theoretical and experimental ∆G´s.

Probing the role of solvation in predicting the π-facial selectivity of 5-Fluoro-2-methyleneadamantane with per-acid: A case study

Many qualitative, semi-quantitative and transition state models have been developed to rationalize and predict the π-face selectivity of various nucleophilic, electrophilic and radical organic reactions. However, there are cases where such models and theories are unable to explain the face selectivity. 5-Fluoro-2-methyleneadamantane (I) represents one such case to understand the stereoinduction with per-acid, where much discussed orbital and electrostatic models fail to explain the observed stereoselectivity. This work is focused with the rationalization and prediction of stereoselective electrophilic addition of per-acid to I using quantum chemical and molecular dynamics studies. The importance of solvent in controlling the π-face selectivity of I is reported employing ab initio and DFT studies. We have also presented here the effect of distortional asymmetry in the π-face of 5-Fluoro-2-methyleneadamantane (I) in solvent, which leads to predict the correct observed stereoselectivity. The ab initio molecular dynamics (AIMD) calculations attribute the asymmetric distortions in the ground state of I, which can be a constituent of the bulk transitional state differential for this reaction. The sterically unbiased olefins 4-substituted 9-methylenenorsnoutanes (II) and 5,6-cis,exo-disubstituted bicyclic[2.2.2]oct-2-enes (III) have also been studied as reference in the present study.

Constant Enthalpy Change Value during Pyrophosphate Hydrolysis within the Physiological Limits of NaCl

A decrease in water activity was thought to result in smaller enthalpy change values during PPi hydrolysis, indicating the importance of solvation for the reaction. However, the physiological significance of this phenomenon is unknown. Here, we combined biochemistry and calorimetry to solve this problem using NaCl, a physiologically occurring water activity-reducing reagent. The pyrophosphatase activities of extremely halophilic Haloarcula japonica, which can grow at ∼4 M NaCl, and non-halophilic Escherichia coli and Saccharomyces cerevisiae were maximal at 2.0 and 0.1 M NaCl, respectively. Thus, halophilic and non-halophilic pyrophosphatases exhibit distinct maximal activities at different NaCl concentration ranges. Upon calorimetry, the same exothermic enthalpy change of -35 kJ/mol was obtained for the halophile and non-halophiles at 1.5-4.0 and 0.1-2.0 M NaCl, respectively. These results show that solvation changes caused by up to 4.0 M NaCl (water activity of ∼0.84) do not affect the enthalpy change in PPi hydrolysis. It has been postulated that PPi is an ATP analog, having a so-called high energy phosphate bond, and that the hydrolysis of both compounds is enthalpically driven. Therefore, our results indicate that the hydrolysis of high energy phosphate compounds, which are responsible for biological energy conversion, is enthalpically driven within the physiological limits of NaCl.

Pressure effects on the dynamics of ions and solvent molecules in liquid methanol under ambient and cold conditions: Importance of solvent's H-bonding network

The effects of pressure on the dynamics of ions in liquid methanol at 258 and 298K are investigated by classical molecular dynamics simulations. It is found that the self-diffusion coefficient of ions in methanol decreases with pressure at both temperatures. The similar fashion of the translational and rotational dynamics of solvent molecules is also observed with application of pressure. Unlike aqueous solution, no such pressure dependence anomaly is observed when an ion (Na+/Cl−) is dissolved in methanol. To explore the observed behavior, we have calculated the hydrogen bond properties of liquid methanol, and it is found that methanol is more like chain-structure with a maximum number of two hydrogen bonds. The hydrogen-bond lifetime and structural–relaxation time of methanol are increasing monotonically with application of pressure and the results are more prominent at low temperatures, whereas in case of water, an opposite trend of the hydrogen bond dynamics is observed under similar conditions.

Equilibrium constants and protonation site for N-methylbenzenesulfonamides

The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO2 (3d), in aqueous sulfuric acid were studied at 25 °C by UV–vis spectroscopy. As expected, the values for the acidity constants are highly dependent on the electron-donor character of the substituent (the pKBH+ values are −3.5 ± 0.2, −4.2 ± 0.2, −5.2 ± 0.3 and −6.0 ± 0.3 for 3a, 3b, 3c and 3d, respectively). The solvation parameter m* is always higher than 0.5 and points to a decrease in the importance of solvation on the cation stabilization as the electron-donor character of the substituent increases. Hammett plots of the equilibrium constants showed a better correlation with the σ+ substituent parameter than with σ, which indicates that the initial protonation site is the oxygen atom of the sulfonyl group.

The importance of solvation in the design of ligands targeting membrane proteins

A crucial contribution to the ligand-receptor binding affinity is, in addition to their electrostatic and van der Waals interactions, the desolvation of the ligand. This is of special relevance in membrane proteins because the ligand has to be transferred from the aqueous environment to the transmembrane binding site crevice. Herein we report the synthesis of new serotonin 5-HT4receptor antagonists that replace a key carbonyl group by the thiocarbonyl bioisoster. This modification enhances experimental 5-HT4 receptor binding affinities by as much as 91 times. Free energy perturbation calculations have shown that the significant decrease of the penalty of desolvation, facilitating the entrance of the ligands into the binding site crevice, compensates for the weaker ligand-receptor interaction.

Importance of solvation in understanding the chiroptical spectra of natural products in solution phase: garcinia acid dimethyl ester.

The optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectra of (+)-garcinia acid dimethyl ester have been measured and analyzed by comparison with the corresponding spectra predicted by quantum chemical methods for (2S,3S)-garcinia acid dimethyl ester. For solution-phase calculations the recently developed continuous surface charge polarizable continuum model (PCM) has been used. It is found that gas-phase predictions and PCM predictions at the B3LYP/aug-cc-pVDZ level yield nearly mirror-image ECD spectra in the 190-250 nm region for the same absolute configuration and that gas-phase ECD predictions lead to incorrect absolute configuration. At the CAM-B3LYP/aug-cc-pVDZ level, however, gas-phase predictions and PCM predictions of ECD in the 190-250 nm region are not so different, but PCM predictions provide better agreement with the experimental observations. For carbonyl stretching vibrations, the vibrational band positions predicted at the B3LYP/aug-cc-pVDZ level in gas-phase calculations differ significantly from the corresponding experimentally observed band positions, and this discrepancy has also been corrected by the use of PCM. In addition, the solution-phase VCD predictions provided better agreement (with experimental VCD observations) than gas-phase VCD predictions. These observations underscore the importance of including solvent effects in quantum chemical calculations of chiroptical spectroscopic properties.

The Structure of Aβ42 C-Terminal Fragments Probed by a Combined Experimental and Theoretical Study

The C-terminus of amyloid β-protein (Aβ) 42 plays an important role in this protein's oligomerization and may therefore be a good therapeutic target for the treatment of Alzheimer's disease. Certain C-terminal fragments (CTFs) of Aβ42 have been shown to disrupt oligomerization and to strongly inhibit Aβ42-induced neurotoxicity. Here we study the structures of selected CTFs [Aβ( x–42); x = 29–31, 39] using replica exchange molecular dynamics simulations and ion mobility mass spectrometry. Our simulations in explicit solvent reveal that the CTFs adopt a metastable β-structure: β-hairpin for Aβ( x–42) ( x = 29–31) and extended β-strand for Aβ(39–42). The β-hairpin of Aβ(30–42) is converted into a turn-coil conformation when the last two hydrophobic residues are removed, suggesting that I41 and A42 are critical in stabilizing the β-hairpin in Aβ42-derived CTFs. The importance of solvent in determining the structure of the CTFs is further highlighted in ion mobility mass spectrometry experiments and solvent-free replica exchange molecular dynamics simulations. A comparison between structures with solvent and structures without solvent reveals that hydrophobic interactions are critical for the formation of β-hairpin. The possible role played by the CTFs in disrupting oligomerization is discussed.

ChemInform Abstract: Synthesis of Merocyanine Dye Nanorods: The Importance of Solvent, Kinetic and Thermodynamic Control, and Steric Effects on Self‐Assembly.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of Merocyanine Dye Nanorods: The Importance of Solvent, Kinetic and Thermodynamic Control, and Steric Effects on Self-Assembly

Aggregation of dipolar merocyanine dyes into antiparallel dimers with high binding constant is an interesting binding motif for the construction of functional supramolecular architectures. This dipolar aggregation has been utilized for the formation of well-defined cylindrical nanorods. The self-assembly of these nanorods is profoundly influenced by solvent polarity which determines nanorod growth under kinetic or thermodynamic control. A newly synthesized series of bis(merocyanine) dyes bearing alkyl substituents of different chain lengths and branching further reveals that small structural changes of the monomeric building blocks have a considerable impact on the stability and structure of the aggregates. The knowledge acquired by the present study should be helpful for the development of self-assembled nanomaterials.

Lanthanide cation binding to a phosphoryl-calix[4]arene: the importance of solvent and counterions investigated by molecular dynamics and quantum mechanical simulations

Molecular dynamics simulations on the 1:1 M3+ lanthanide (La3+, Eu3+ and Yb3+) “inclusion” complex of a t-butyl-calix[4]arene L substituted at the narrow rim by four CH2–P(O)Ph2 arms demonstrate the role of hydration and counterions on the cation binding mode and shielding. In dry chloroform and in the absence of counterions, the cation is “endo”, fully encapsulated within the pseudo-cavity delineated by the four phosphoryl arms and the four phenolic oxygens. This “endo” bidentate binding mode is supported by full ab initio quantum mechanical optimization of the calixarene M3+ complexes. In biphasic solution, the complexes are shown to be surface active and to adsorb at an “oil”/water interface with the cationic site pointing towards water and the hydrophobic t-butyl groups in “oil”. The cation is not encapsulated, but adopts an “exo ” position, coordinated to the four PO oxygens of L, to water molecules, and to counterions. This complex is too hydrophilic to be extracted from the interface to an organic phase. The unexpected binding mode has important implications concerning the mechanism of liquid–liquid ion extraction and the microscopic state of the extracted complex in the organic phase.

Efficient Synthesis of the Anticancer Drug Etoposide 4‘-Phosphate: Use of Benzylic Ether-Protecting Groups on the Carbohydrate Segment1

The prodrug etoposide phosphate 2 is synthesized efficiently in three steps in 54.6% overall yield from 4‘-demethylepipodophyllotoxin 3. The strategy pursued in the synthesis of 2 places the phosphate on 3 prior to coupling with the sugar and employs benzyl ether-protecting groups on both the phosphate and the sugar, allowing easy removal in one step. The importance of solvent, steric effects, and electronic effects in the coupling reaction is demonstrated. Two features of the synthesis are an unusual thermal anomerization of the carbohydrate component 5a and completely diastereoselective, one-pot crystallization of the coupled product 6a-β. The process has been demonstrated on multi-kilogram scale.

Vinylidenecarbenoid. The importance of solvation and electron correlation effects on its structure

According to ab initio calculations of valence double-zeta quality at RHF and MP2 (CISD) levels of optimization the structure of vinylidenecarbenoid is extremely sensitive to solvation as well as electron correlation effects. Solvation, as mimicked by coordination of three water molecules to lithium, causes a lengthening of the carbon-lithium bond. On the other hand optimization at electron correlation level (MP2) induces a considerable shortening of the carbon-chlorine bond. The importance of this effect in determining the geometry of the carbenoid structure is rationalized in terms of qualitative considerations.