Study Of Solvent Effects Research Articles

Four-dimensional structural dynamics of sheared collagen networks

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Density functional theory (DFT) based study of solvent effect on B10N11 and B10N11H7 (Gly)2 nano structures

In this present work, all calculations were carried out with the Gaussian 98 program based on density functional theory (DFT) at B3LYP/3-21G level of theory. Then stability and grand state of B10N11 and B10N11H7 (Gly)2 nanocones in bulk and different solvents were investigated. It is clear that solvent effects were reviewed with concentration on quantitative values of Gibbs free energy, enthalpy, internal energy and dipole moment in the spread of solvents around these two nano structures and temperature effect was studied on the stability of these novel structures in the same solvents. Furthermore we compared the results of gas phase and different solvents when surrounding these two nano structures. In this work, NMR shielding parameters were calculated based on each atom to recognize active sites in these two systems. The results showed that because of high stability of B10N11 and B10N11H7 (Gly)2, these novel structures could be the best candidates and most favorable in biological systems and drug delivery.

Theoretical study of solvent effect on NMR shielding tensors of luciferin derivatives

Luciferins as the substrates of protein enzyme luciferase are oxidised in the presence of the enzyme luciferase to produce oxyluciferin and energy in the form of light. The solvent effect in biological media and interactions between solvents and luciferin are major points to explain bioluminescence reaction. In this study, we have focussed on the Hartree–Fock calculations of solvent-induced effects on the structural changes of keto and enolate and twisted intra-molecular charge transfer forms of oxyluciferin in different solvent media including water, dimethyl sulphoxide, acetonitryl, ethanol, aniline and cyclohexane using 6-311++G** basis set considering Onsager continuum solvation model, frequency analysis and nuclear magnetic resonance shielding calculation with gauge-included atomic orbital method. The polarity of the environment imposed a significant effect on the relative atomic charge distribution on the selected atoms of luciferin and its derivatives. So, this fact motivated us to report the changes of the relative CHELP – charges from electrostatic potentials – atomic charges of each luciferin derivatives. Among different employed solvents, water as a protic solvent could be suggested as the most suitable solvent. All solvents had no effect on the geometry conformation of luciferin; however, the results have shown that the case of keto luciferin was obviously different and ethanol could affect more the keto luciferin form. This investigation has given useful information about the improved potential activity of luciferin derivatives and its dependence on the environment that are known as the remarkable factors in colour shift.

Methyltrioxorhenium-catalyzed oxidation of pseudocumene for vitamin E synthesis: A study of solvent and ligand effects

Vitamin E is an essential food component of major economical relevance with important antioxidant properties and biological activity. The oxidation of pseudocumene to trimethyl-1,4-benzoquinone would be a key transformation in an alternative industrial production of α-tocopherol that is important for the antioxidant activity of vitamin E. The methyltrioxorhenium (MTO)-catalyzed oxidation of pseudocumene has been revisited to offer a more environmentally friendly, economically beneficial and milder approach to this important industrial product. It has been observed that by choosing the solvent and Lewis base additives (as ligands of MTO), both yield and chemoselectivity are considerably improved, allowing milder reaction conditions compared to previously reported protocols.

Solvatochromism and Preferential Solvation of 4-Pentacyanoferrate 4′-Aryl Substituted Bipyridinium Complexes in Binary Mixtures of Hydroxylic and Non-hydroxylic Solvents

The intense solvatochromic behavior of several pentacyanoferrate complexes with aryl substituted 4,4′-bipyridines acting as ligands, was investigated in six hydroxylic and non hydroxylic solvents using UV-Visible spectroscopy. The metal-to-ligand-charge-transfer bands of the visible spectra of these compounds proved to be markedly affected by solvent polarity. In order to quantify the extent of the observed solvatochromism and reveal the dominant interactions which take place in the cybotactic region, resulting in solvatochromism, the Kamlet-Taft equation was used. This is a multiparametric linear-solvation-energy-relationship (LSER) widely used for the study of solvent effects on various physicochemical properties. Through this analysis it was proved that both specific and non specific interactions contribute to the observed solvatochromism. Furthermore, the preferential solvation of the complex salts was studied in binary solvent mixtures. Solvatochromism was used as the key approach to rationalize solvent-solute and solvent-solvent interactions in the binary solvent mixtures studied.

Would the solvent effect be the main cause of band shift in the theoretical absorption spectrum of large lanthanide complexes?

As most reactions take place in solution, the study of solvent effects on relevant molecular properties – either by experimental or theoretical methods – is crucial for the design of new processes and prediction of technological properties. In spite of this, only few works focusing the influence of the solvent nature specifically on the spectroscopic properties of lanthanide complexes can be found in the literature. The present work describes a theoretical study of the solvent effect on the prediction of the absorption spectra for lanthanide complexes, but other possible relevant factors have been also considered such as the molecular geometry and the excitation window used for interaction configuration (CI) calculations. The [Eu(ETA) 2· nH 2O] +1 complex has been chosen as an ideal candidate for this type of study due to its small number of atoms (only 49) and also because the absorption spectrum exhibits a single band. Two Monte Carlo simulations were performed, the first one considering the [Eu(ETA) 2] +1 complex in 400 water molecules, evidencing that the complex presents four coordinated water molecules. The second simulation considered the [Eu(ETA) 2·4H 2O] +1 complex in 400 ethanol molecules, in order to evaluate the solvent effect on the shift of the maximum absorption in calculated spectra, compared to the experimental one. Quantum chemical studies were also performed in order to evaluate the effect of the accuracy of calculated ground state geometry on the prediction of absorption spectra. The influence of the excitation window used for CI calculations on the spectral shift was also evaluated. No significant solvent effect was found on the prediction of the absorption spectrum for [Eu(ETA) 2·4H 2O] +1 complex. A small but significant effect of the ground state geometry on the transition energy and oscillator strength was also observed. Finally it must be emphasized that the absorption spectra of lanthanide complexes can be predicted with great accuracy by the combined use of semiempirical Sparkle/AM1 and INDO/S-CIS as long as the largest possible excitation window is used in the configuration interaction calculation.

N‐2‐Aryl‐1,2,3‐triazoles: A Novel Class of UV/Blue‐Light‐Emitting Fluorophores with Tunable Optical Properties

The N-2-aryl-1,2,3-triazole derivatives (NATs) were developed as a new class of UV/blue-light-emitting fluorophores. Though both N-1-aryl-1,2,3-triazoles and N-2-aryl-1,2,3-triazoles gave strong photo absorption under excitation at 330 nm, only the N-2-analogous showed strong fluorescence emission in the UV/blue range with high efficiency in various solvents (quantum yield Φ around 0.3-0.5). Significant substituted group effects were observed, allowing tunable optical properties with emission (λ(max)) from 350-400 nm and Stokes shift from 38-93 nm. The computational studies along with X-ray crystal structures indicated the significance of the effective conjugation between triazole ring and aryl groups on the N-2 position. The planar intramolecular charge transfer (PICT) mechanism was proposed, which was supported by solvent effect studies. Simple derivatizations gave NAT-modified lysine and strong UV/blue emitting bis-NAT (Φ=0.76, λ(max)=390), which suggested the great potential of this new class of fluorophores in biological and material science research.

Dudley Williams

Dudley Williams

Theoretical Study of Specific Solvent Effects on the Optical and Magnetic Properties of Copper(II) Acetylacetonate

Specific and basicity solvent effects on the visible near-infrared electronic transitions and the electron paramagnetic resonance (EPR) parameters of the copper(II) acetylacetonate complex, Cu(acac)2, have been investigated at the density functional theory level. The computed absorption transitions as well as the EPR parameters show a strong dependence on the direct coordination environment around the Cu(II) complex. High solvatocromic shifts are observed for 3d-3d transitions, with the highest effect observed for the dz(2)→dxy transition, which is red-shifted by 6000 cm(-1) and 9000 cm(-1) in water and pyridine solvent models, respectively. Compared to the electronic g-tensors, the hyperfine coupling constants of the Cu(acac)2 complex show a more pronounced dependence on the effect of base strength of solvent. Overall, the present methodology satisfactorily models the solvent effect on the optical and magnetic properties of the Cu(acac)2 complex, and theory and experiment agree sufficiently well to warrant the use of the computed optical and EPR parameters to elucidate the coordination environment of the Cu(II) systems in basic solutions.

Theoretical study of substituent and solvent effects on the thermodynamics for cis/trans isomerization and intramolecular rearrangements of 2,2′-diphenoquinones

Enthalpies (ΔisomH(g)o), Gibbs free energies (ΔisomG(g)o), and equilibrium constants (log Kisom) for the trans → cis isomerization of various 3,3′-, 4,4′-, and 5,5′- disubstituted 2,2′-diphenoquinones with a range of electron withdrawing and releasing moieties (methyl, fluoro, chloro, bromo, trifluoromethyl, and amino) were calculated in the gas phase and in the solvent phase (n-hexane, benzene, n-octanol, acetonitrile, and water). In the gas phase, the trans isomer of the parent and all substituted 2,2′-diphenoquinones is predicted to be more thermodynamically stable than the cis configuration, with log Kisom ranging from −2.8 to −7.0. For all compounds, increasing solvent polarity/proticity progressively favors shifting the cis/trans equilibrium towards greater contributions of the cis configuration and substantially increases the log Kisom by up to 5.1 units relative to the gas phase. In polar protic and polar aprotic solvents, the estimated log Kisom ranges as low as −0.4, indicating significant populations of the cis isomers should be present. The findings support the polar solvent phase mechanistic predictions for a cis configuration of 2,2′-diphenoquinones participating in the thermal transformation of trans-2,2′-diphenoquinones to oxepino[2,3-b]benzofurans. With limited exceptions for some amino derivatives, the cis-2,2′-diphenoquinone to oxepino[2,3-b]benzofuran isomerization is expected to be thermodynamically favorable for all substituents/phases under consideration. The cis-2,2′-diphenoquinone to oxepino[2,3-b]benzofuran rearrangement is predicted to become less thermodynamically favored with increasing solvent polarity/proticity.

Enantioselective fluorescent recognition of mandelic acid by unsymmetrical salalen and salan sensors

As sensors with multiple chiral centers, salalen 1 and salan 2 composed of trans-cyclohexane-1,2-diamine (trans-DACH) and 1,1'-bi-2-naphthol (BINOL) units were designed and synthesized. Fluorescent recognition studies of resulting sensors towards mandelic acid (MA) reveal that salan 2a containing (R)-BINOL and (R,R)-DACH exhibits highly sensitive and enantioselective response towards MA. The relationship between the chirality combination and the enantioselectivity is discussed. Based on the studies of concentration and solvent effect on the recognition process of 2a, it was found that the sensitivity and enantioselectivity could be enhanced via changing the concentration of sensors or altering the polarity of solvents. To explain why higher enantioselectivity can be achieved in moderate polar solvent other than in nonpolar or polar solvent, a solvent-guest competition mechanism, which may shed a light on the enhancement of the enantioselectivity of chiral recognition and noncovalent asymmetric catalysis, has been proposed and validated.

Applications of molecular dynamics simulation in nonlinear optics

Organic nonlinear optical molecular materials have a number of important applications in frequency transformation, electrooptic modulation, two-photon absorption and so on. In this paper, we introduce the main applications of molecular dynamics simulation in theoretical study on nonlinear optical properties of organic molecules, including the electric field poling effects, the local field factors, the nonlinear susceptibilities, and the two-photon absorption. In addition, the important roles played by molecular dynamics simulation in the study of solvent and aggregation effects are also illustrated in combination with the recent research.

Study of solvent effect on the stability of water bridge-linked carboxyl groups in humic acid models

Molecular dynamics simulations have been performed by means of density functional theory with tight binding (DFTB) in order to describe the structure and the energetic stability of water bridges in humic substances (HS) model. This model is constructed from two parallel aliphatic chains geometrically restrained on one end and terminated with a carboxyl group on the other to supply the structural pattern for supramolecular contact of two HS chains through hydrogen bonds. Molecular dynamics simulations were used to analyze the interactions of the carboxylic groups with a variable number of water molecules up to 14 representing domains of micro hydration states of polar centers in humic acids. For the present geometrical arrangements of the model five water molecules form a stable bridge between the two carboxylic groups located at each aliphatic chain. The effect of environment through three solvents of different polarities (n-hexane, acetonitrile and water) was investigated. Distribution profiles of oxygen atoms of carboxyl and chain water molecules show that the environmental effect of the solvent with moderate polarity (acetonitrile) is most pronounced in exerting an ordering effect on the water bridge. Energy profiles for incremental addition of water molecules and hydrogen bond analysis demonstrate the remarkable stability of the five water complex as compared to all other models investigated in both gas phase and in acetonitrile. These findings correlate nicely with experimentally observed antiplasticizing effects of water bridges in organic matrices.

Kinetic and thermodynamic study of inter- and intramolecular proton transfer in N ′-acetyl formohydrazide tautomers

Nine tautomers and eleven possible tautomeric interconversions of N′-acetyl formohydrazide have been studied at B3LYP/6-311++G** level of theory. From these calculations, optimized geometries, molecular parameters, IR frequencies, NMR chemical shifts, and energetic results are obtained. In all tautomers except tautomers 4, E isomer is more stable than Z isomer. Energetic data were used to calculate the energy barriers of tautomeric interconversions and very high energy barriers were obtained for all tautomeric interconversions. Moreover, study of solvent effects on relative stabilities of tautomers and transition states showed that they are similar to those in the gas phase. In addition, intermolecular proton transfer with the assistance of one to three water molecules has been studied and the results showed that activation barriers in water-assisted tautomerism are in general lower than those in the gas phase. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Influence of pressure effect on Fermi resonance in binary solution

The Fermi resonance behaviours of the two groups of binary solutions — pyridine and methanol, benzene and carbon tetrachloride, under different pressures are investigated according to their Raman spectra. The effect of pressure on Fermi resonance in binary solution differs significantly from that in pure liquid. In a binary solution, with the intermolecular distance shortening, the intermolecular interaction potential increases, the shift rates of the Raman spectral lines increase, the spectral line splitting occurs ahead of that in pure liquid, and the wavenumber separation Δ0 between the unperturbed harmonic levels shifts more quickly, too. The Fermi resonance parameters, the coupling coefficient W and the intensity ratio R of the two Raman bands, decrease rapidly with pressure increasing, and the pressure at which Fermi resonance phenomenon disappears is much lower than that in pure liquid, especially in the solution whose molecules are of the same polarity. This article is valuable in the identification and the assignment of spectral lines under high pressure, as well as the study of high pressure effect, intermolecular interaction, and solvent effects in different cases, etc.

Hydrogen bonded foldamer-bridged biscoumarins: A UV-Vis absorption and fluorescent study of the solvent effect

Three arylamide-bridged biscoumarin derivatives 1–3 have been designed and prepared. Compounds 1 and 2 are induced by the intramolecular N-H…O and N-H…F hydrogen bonding to possess a helical conformation, and 3 is induced to have an extended conformation. A comparison of their absorption and fluorescent spectra in a variety of solvents of a wide range of polarity with those of control compound 4 reveals that, for foldamers 1 and 2, the intramolecular hydrogen bonding and the helical conformations exist in most solvents, but do not exist or are very weak in DMF and DMSO.

Theoretical study of solvent effect on the structure, first electronic excited state, and nonlinear optical properties of substituted stilbazolium cations

AbstractMolecular structure, first excited state properties and charge distribution of a series of substituted stilbazolium cations in different media are theoretically investigated. First static hyperpolarizability (β0) of considered compounds is studied by both finite‐field and two‐state model methods. In contrast to the recent theoretical studies, in present contribution the mutually consistent description of solvent polarity dependence of β0 calculated by both employed approaches is achieved. It is shown that the ground‐to‐excited state intramolecular charge‐transfer is significantly affected by the solvent that provides the hyperpolarizability variation. Taking into account both solvent polarity and substituent effect the peculiarities of β0 behavior of stilbazolium derivatives are re‐examined. The effect of molecular geometry on the calculated electronic excitation properties is investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Tautomerization and solvent effects on the absorption and emission properties of the Schiff base N,N′-bis(salicylidene)-p-phenylenediamine – A TDDFT study

Time-dependent density functional theory combined with a polarized continuum model has been applied to study solvent effects on the geometrical and energetic properties, as well as the absorption and emission properties, of three tautomeric forms of N,N′-bis(salicylidene)-p-phenylenediamine (BSP). The calculated properties are in agreement with the available experimental data. It was observed that the solvent environment does not affect the vertical excitation energies significantly, whereas tautomerization strongly affects both the absorption and emission spectra of BSP.

DNA/RNA: Building Blocks of Life Under UV Irradiation

During the last 10 years, intense experimental and theoretical work has proven the existence of ultrafast nonradiative decay routes for UV-excited monomeric nucleic acid bases, accounting for their high photostability. This mechanism has been explained by the occurrence of easily accessible conical intersections connecting the first excited ππ* state with the ground state. However, recent studies of substituent and solvent effects indicate that the situation is more complicated than what was initially thought, notably by the presence of dark excited states. Moreover, the actual shape of the excited-state potential energy surface may induce nonexponential dynamics. Further efforts are needed in order to clarify how various environmental factors affect the structural and dynamical aspects of the nucleic acid base excited states.

Substituent and solvent effects on the structural bioactivity and anticancer characteristic of catechin as a bioactive constituent of green tea

In this study, quantum chemical calculations using density functional theory and 6-311G (d) basis set have been applied to analyze the substituent effect on the electronic structural properties including thermochemical parameters as well as anticancer characteristics of catechin as a bioactive constituent of green tea. It has been found out that different substituents with two kinds of electron donating and electron withdrawing groups including NO2, NH2, Cl, OCH3, and CH3 leaded to different structural stabilities. The catechin with chloro substituents has been referred to the most stable catechin derivatives based on the minimum energy of investigated compounds. In this study, the calculated values have been compared in gas phase and different solvent media with a wide range of solvent dielectrics using the self-consistent reaction field method with polarizable continuum model. Relative interaction energies between solute and solvent as well as dipole moment values have been analyzed. The results of solvent effect study revealed that the formation of hydrogen bonds accounts for the stabilization of catechin. These calculated data were found to be a logical way in predicting the relative stability of catechin derivatives and can be useful for drug design of anticancer drugs and would open a new door for the researchers who are interested in natural products. The results presented in this article will be helpful to improve existing model and will open up a whole new arena of study to understand the anticancer characteristic of these antioxidant drugs derived from natural products against the photosensitizing DNA damage induce by catechin extracts and enable a much clearer understanding of how anticancer drugs mediate their effects on the specific spot. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011