Study Of Solvent Effects Research Articles

Theoretical Studies of Solvent Effects on Binding of Sn (CH3)2(N-acetyl-L-cysteinate) with Single-walled Carbon Nanotube

The potential of nanotechnology to revolutionise medicine in particular seems endless, and one significant application of this technology is the use of carbon nanotubes for the targeted delivery of drug molecules. Sn(CH3)2(N-acetyl-L-cysteinate) is a drug that has been proposed as a therapeutic against the human hepatocarcinoma HCC Hep G2 cells. In our model, (N-acetyl-Lcysteinato-O,S) dimethyl tin(IV) (Sn(CH3)2(N-acetyl-L-cysteinate)) was binded to carbon nanotube. Quantum chemical ab initio calculations at HF/ (LanL2DZ+STO-3G), and HF/ (LanL2DZ+6-31G) levels in gas phase and solution have been carried out to calculate the optimized geometry, energies, dipole moments and thermochemical analysis of Sn(CH3)2(N-acetyl-L-cysteinate)-CNT complex. Results from frequency calculation (large negative values of the ΔG and high positive values of ΔS) confirmed the structural stability of the Sn(CH3)2(NAC) – CNT in both gas phase and in solution. NMR parameters such as isotropic magnetic shielding constants (σiso), anisotropic magnetic shielding tensors (σaniso), Chemical shifts (δ) and total atomic charges were also calculated using the GIAO and CSGT approaches in both gas phase and in solution to determine the structural characterization of the complex. The results in solution show that the δ, σiso, and σaniso are sensitive to hydrogen-bonding interactions. A different influence of various hydrogen bond types, N5-H·····O, C-O1·····H, and C=O24·····H was observed on the calculated NMR parameters. Finally the NMR parameters obtained from GIAO method are in good agreement with the CSGT results.

DFT/TD-DFT study of solvent effect as well the substituents influence on the different features of TPP derivatives for PDT application

Spectral characteristics study of meso-tetraphenylporphyrin derivatives (TPP1 and TPP2) used as photosensitizers for utilization in photodynamic therapy (PDT) has been performed by density functional theory (DFT) and time dependent DFT (TD-DFT) calculations at B3LYP/6-31G(d) level of theory using PCM solvation model. The geometrical parameters of porphyrins have been studied for ground and excited-state geometry to deduce the influence of various substituents as well as solvent effect on the deformation of porphyrin ring. Two theoretical approaches – linear response (LR) and external iteration (EI) – have been performed to replicate absorption and fluorescence emission spectra. Experimental and theoretical investigations have shown that EI method reproduces the absorption energies very well for both singlet–singlet and triplet–triplet transitions, whereas the LR approach is more coherent with experimental fluorescence emission spectra. Spectral features and HOMO–LUMO band gap analysis have shown that TPP1 can be more useful in PDT. Calculations have revealed that two the highest occupied and two the lowest unoccupied molecular orbitals are responsible for the Q-band absorption and are located mainly on the porphyrin ring. In order to verify the substituent effect on the activity of tested compounds in their ground and excited states, the molecular electrostatic potential surfaces have been analyzed.

Water Structure, Dynamics, and Spectral Signatures: Changes Upon Model Cavity–Ligand Recognition

It is becoming increasingly evident that water plays an active role in noncovalent receptor-ligand association. In this study, hydrophobic cavity-ligand association in a model system is characterized through the analysis of the structure, dynamics, and corresponding spectral signatures of water at different stages of the binding process. Molecular dynamics simulations reveal that the reorientation of the water molecules around the ligand becomes faster as the receptor-ligand distance reduces, which is correlated with the decrease in number of water-water hydrogen bonds within the ligand hydration shells. Prompted by the need for calculating physical quantities that can be amenable to experimental validation, the changes in the spectroscopic features upon cavity-ligand binding are investigated. The analysis of both linear and nonlinear infrared spectra allows direct insight into the evolution of water structure and dynamics around the ligand. In particular, characteristic spectroscopic features emerge at key stages of the binding process, which are related to changes in the hydrogen-bond topology of water around the ligand. This study demonstrates that computer simulations and vibrational spectroscopy could be integrated to facilitate the direct study of solvent effects in biomolecular association.

Ruthenium‐Catalyzed Asymmetric Hydrogenation of 3‐Oxoglutaric Acid Derivatives: A Study of Unconventional Solvent and Substituent Effects

A series of 3-oxoglutaric acid derivatives have been hydrogenated in different solvents in the presence of [RuCl(benzene)(S)-SunPhos]Cl (SunPhos = (2,2,2',2'-tetramethyl-[4,4'-bibenzo[d][1,3]dioxole]-5,5'-diyl)bis(diphenylphosphine)). Unlike simple β-keto acid derivatives, these advanced analogues can be readily hydrogenated in uncommon solvents such as THF, CH(2)Cl(2), acetone, and dioxane with high enantioselectivities. Two possible catalytic cycles have been proposed to explain the different reactivities of these 1,3,5-tricarbonyl substrates in the tested solvents. The C-2 and C-4 substituents had notable but irregular influence on the reactivity and enantioselectivity of the reactions. More pronounced solvent effects were observed: the ee values increased from around 20% in EtOH or THF to 90% in acetone. Inversion of the product configuration was observed when the solvent was changed from EtOH to THF or acetone, and a mixed solvent system can lead to better enantioselectivity than a single solvent.

Thermodynamics and kinetics of Na+/K+-formate ion pairs association in polarizable water: A molecular dynamics study

To enhance our understanding of ion specific activity in biological systems, the potential of mean force approach was utilized to study solvent effects on the interactions between two alkali cations (Na+ and K+) with a formate anion in water. A very complex free energy landscape was observed, much more so than alkali–halide ion pairs. Furthermore, a stronger binding between the Na+-formate pair was found in comparison to the K+-formate pair in water, which is in agreement with experimental and theoretical studies [1–4]. The kinetics of ion-pair inter-conversions was studied using the transition rate theory, along with a number of theoretical approaches such as the Kramers and Grote–Hynes theories. These kinetic results were used to predict solvent effects on dynamical features of ion-pair association, in which we have found that the dynamics of K+-formate pairs is faster than Na+-formate pairs.

Two-photon solvatochromism. I. Solvent effects on two-photon absorption cross section of 4-dimethylamino-4′-nitrostilbene (DANS)

This Letter reports a systematic study of solvent effect on two-photon absorption (2PA) spectra of a model chromophore, 4-dimethylamino-4′-nitrostilbene (DANS). The two-photon solvatochromic behavior of DANS was investigated in selected solvents using the Z-scan measurement technique. The obtained results demonstrate that the examined molecule possesses slightly different 2PA response in solvents of different polarity. A decrease in the two-photon absorption strength is observed when the solvent is changed from chloroform and dichloromethane to the more polar dimethyl sulfoxide.

1-(Hydroxyacetyl)pyrene a new fluorescent phototrigger for cell imaging and caging of alcohols, phenol and adenosine

1-(Hydroxyacetyl)pyrene has been introduced as a new fluorescent phototrigger for alcohols and phenols. Alcohols and phenols were protected as their corresponding carbonate esters by coupling with fluorescent phototrigger, 1-(hydroxyacetyl)pyrene. Photophysical studies of caged carbonates showed that they all exhibited strong fluorescence properties. Irradiation of the caged carbonates by visible light (≥410 nm) in aqueous acetonitrile released the corresponding alcohols or phenols in high chemical (95-97%) and quantum (0.17-0.21) yields. The mechanism for the photorelease was proposed based on Stern-Volmer quenching experiments and solvent effect studies. Importantly, 1-(hydroxyacetyl)pyrene showed as a phototrigger for rapid photorelease of the biologically active molecule adenosine. In vitro biological studies revealed that 1-(hydroxyacetyl)pyrene has good biocompatibility, cellular uptake property and cell imaging ability.

Isotope Effects Suggest a Stepwise Mechanism for Berberine Bridge Enzyme

The flavoprotein Berberine Bridge Enzyme (BBE) catalyzes the regioselective oxidative cyclization of (S)-reticuline to (S)-scoulerine in an alkaloid biosynthetic pathway. A series of solvent and substrate deuterium kinetic isotope effect studies were conducted to discriminate between a concerted mechanism, in which deprotonation of the substrate phenol occurs before or during the transfer of a hydride from the substrate to the flavin cofactor and substrate cyclization, and a stepwise mechanism, in which hydride transfer results in the formation of a methylene iminium ion intermediate that is subsequently cyclized. The substrate deuterium isotope effect of 3.5 on k(red), the rate constant for flavin reduction, is pH-independent, indicating that C-H bond cleavage is rate-limiting during flavin reduction. Solvent isotope effects on k(red) are equal to 1 for both wild-type BBE and the E417Q mutant, indicating that solvent exchangeable protons are not in flight during or before flavin reduction, thus eliminating a fully concerted mechanism as a possibility for catalysis by BBE. An intermediate was not detected by rapid chemical quench or continuous-flow mass spectrometry experiments, indicating that it must be short-lived.

A DFT study on the mechanisms for the cycloaddition reactions between 1−aza-2-azoniaallene cations and acetylenes

The mechanisms of cycloaddition reactions between 1-aza-2-azoniaallene cations 1 and acetylenes 2 have been investigated using the global electrophilicity and nucleophilicity of the corresponding reactants as global reactivity indexes defined within the conceptual density functional theory. The reactivity and regioselectivity of these reactions were predicted by analysis of the energies, geometries, and electronic nature of the transition state structures. The theoretical results revealed that the reaction features a tandem process: an ionic 1,3-dipolar cycloaddition to produce the cycloadducts 3 H-pyrazolium salts 3 followed by a [1,2]-shift affording the thermodynamically more stable adducts 4 or 5. The mechanism of the cycloaddition reactions can be described as an asynchronous concerted pathway with reverse electron demand. The model reaction has also been investigated at the QCISD/6-31++G(d,p) and CCSD(T)/6-31++G(d,p)//B3LYP/6-31++G(d,p) levels as well as by the DFT. The polarizable continuum model, at the B3LYP/6-31++G(d,p) level of theory, was used to study solvent effects on all the studied reactions. In solvent dichloromethane, all the initial cycloadducts 3 were obtained via direct ionic process as the result of the solvent effect. The consecutive [1,2]-shift reaction, in which intermediates 3 are rearranged to the five-membered heterocycles 4/5, is proved to be a kinetically controlled reaction, and the regioselectivity can be modulated by varying the migrant. The LOL function and RDG function based on localized electron analysis were used to analysis the covalent bond and noncovalent interactions in order to unravel the mechanism of the title reactions.

Kinetic study of solvent effects on the aminolysis of O‐ethyl S‐aryl dithiocarbonates

The nucleophilic substitution reactions of a series of O‐ethyl S‐aryl dithiocarbonates with a series of secondary alicyclic amines have been investigated, all in water–ethanol mixtures and some of them in protic and dipolar aprotic solvents. The solvent effects on rate and mechanism are studied using a multiparametric approach with solvent parameters such as acidity, basicity and polarity/polarizability. These results show that in a concerted mechanism, rate constants are increased by the increase of the solvent dipolarity/polarizability. Copyright © 2012 John Wiley & Sons, Ltd.

NMR Shielding and thermodynamic density functional theory (DFT) studies of solvent effect on B10N11H7(Ala)2 Nano Cone

B3LYP/3-21G density functional theory (DFT) are carried out on the structure and stability of B10N11H7(Ala)2 in bulk and different solvent medium, using Gaussian 98 package of program. NMR parameters and thermodynamic properties were calculated to obtain stability and solvent effect. It was found that computationally efficient solvent modeling is possible to find better results and also molecular structure of B10N11H7(Ala)2. The results show that, because of high stability of B10N11 nanocone, it can be the best candidate and much favorable in biological systems and drug delivery. Key words: Solvent effect, density functional theory (DFT), NMR parameters, B10N11H7(Ala)2, nanocone, thermodynamic properties.

Ring opening/closure reactions of novel diheteroarylethenes derivatives. Solvent effects

Three novel diarylethenes derived from benzothiophene were synthesized and their photochemical optical properties studied in four solvents (n‐hexane, toluene, acetonitrile and methanol). It was determined that these compounds dramatically increase the light absorption in the visible region upon exposure to UV light, showing two absorption maxima at 420 nm and 520 nm, respectively. The observed change is completely reverted upon exposure to visible light. The three compounds demonstrate negligible fatigue, excellent stability in the four solvents, and absence of photodegradation and thermal back reactions. This paper also describes a complete study of solvent effects on the kinetics of the ring opening and cycloreversion. While, the UV spectra are little sensitive both to the substitution pattern and to the solvent influence, the kinetics of ring opening/cycloreversion reactions exhibit a more interesting behavior that differs from other diarylethenes reported in the literature. The cyclization kinetics shows a complex order, well fitted by an exponential equation, while the cycloreversion presents first‐order kinetics. The whole complex reaction scheme can be explained by the unusual presence of two conformers of the open form, a parallel and an antiparallel conformation. Though other alternative mechanism could explain the kinetics, additional evidence is consistent with the conformational equilibrium proposed: i.e. the solvent influence on the kinetics of the nitro‐substituted substrate, and the double signals for the methyl protons and for the methoxy protons (when present) observed in the nuclear magnetic resonance spectra. These observations are relevant in relation to the application of these novel diarylethenes as potential optical materials. Copyright © 2012 John Wiley & Sons, Ltd.

Mass spectrometry and ion mobility spectrometry of G-quadruplexes. A study of solvent effects on dimer formation and structural transitions in the telomeric DNA sequence d(TAGGGTTAGGGT)

We survey here state of the art mass spectrometry methodologies for investigating G-quadruplexes, and will illustrate them with a new study on a simple model system: the dimeric G-quadruplex of the 12-mer telomeric DNA sequence d(TAGGGTTAGGGT), which can adopt either a parallel or an antiparallel structure. We will discuss the solution conditions compatible with electrospray ionisation, the quantification of complexes using ESI-MS, the interpretation of ammonium ion preservation in the complexes in the gas phase, and the use of ion mobility spectrometry to resolve ambiguities regarding the strand stoichiometry, or separate and characterise different structural isomers. We also describe that adding electrospray-compatible organic co-solvents (methanol, ethanol, isopropanol or acetonitrile) to aqueous ammonium acetate increases the stability and rate of formation of dimeric G-quadruplexes, and causes structural transitions to parallel structures. Structural changes were probed by circular dichroism and ion mobility spectrometry, and the excellent correlation between the two techniques validates the use of ion mobility to investigate G-quadruplex folding. We also demonstrate that parallel G-quadruplex structures are easier to preserve in the gas phase than antiparallel structures.

Molecular dynamics simulation study of solvent effects on conformation and dynamics of polyethylene oxide and polypropylene oxide chains in water and in common organic solvents

In this paper, the conformation and dynamics properties of polyethylene oxide (PEO) and polypropylene oxide (PPO) polymer chains at 298 K have been studied in the melt and at infinite dilution condition in water, methanol, chloroform, carbon tetrachloride, and n-heptane using molecular dynamics simulations. The calculated density of PEO melt with chain lengths of n = 2, 3, 4, 5 and, for PPO, n = 7 are in good agreement with the available experimental data. The conformational properties of PEO and PPO show an increasing gauche preference for the O-C-C-O dihedral in the following order water>methanol>chloroform>carbon tetrachloride = n-heptane. On the contrary, the preference for trans conformation has a maximum in carbon tetrachloride and n-heptane followed in the order by chloroform, methanol, and water. The PEO conformational preferences are in qualitative agreement with results of NMR studies. PEO chains formed different types of hydrogen bonds with polar solvent molecules. In particular, the occurrence of bifurcated hydrogen bonding in chloroform was also observed. Radii of gyration of PEO chains of length larger than n = 9 monomers showed a good agreement with light scattering data in water and in methanol. For the shorter chains the observed deviations are probably due to the enhanced hydrophobic effects caused by the terminal methyl groups. For PEO the fitting of end-to-end distance distributions with the semi-flexible chain model at 298 K provided persistence lengths of 0.375 and 0.387 nm in water and methanol, respectively. Finally, the radius of gyration of Pluronic P85 turned out to be 2.25 ± 0.4 nm at 293 K in water in agreement with experimental data.

Thermodynamic study of solvent effects on nanostructures: phosphatidylserine and phosphatidylinositol membranes

At present, quantum chemistry is almost universally applicable to the interpretation of physical and chemical properties of various compounds. Phospholipids are an important part of biological lipids and are commonly used in biophysical studies. A quantum calculation for two phospholipids PS and PI was performed using the ab initio software. Geometry optimisation and thermodynamic data over the 304–340 K temperature range are included in the supporting information. The effect of the polarity of the environment on the conformation of the membrane lipid PS and PI head groups has been investigated with calculation at the Hartree-Fock level using the STO-3G, 3-21G, 6-31G and 6-31G* basis sets together with the Onsager continuum solvation model with the program GAUSSIAN 98. The different basis sets were used in order to understand the effects of environmental polarity on the conformation and geometry optimisation of PS and PI in various solvents by SCRF theory. Further, the solvent effect on the stability of PS and PI molecules were discussed using Onsager model.

L‐Proline‐Derived Dendritic Tetrakis(diperoxotungsto)phosphate: Synthesis and Enantioselective Oxidation Catalysis

AbstractAs a part of our ongoing research towards the synthesis of chiral dendritic polyoxometalate (DENDRI‐POM) hybrids that are able to catalyze oxidation of organic substrates with high selectivity and enantioselectivity, we have prepared an enantiopure DENDRI‐POM salt by coupling a well‐defined L‐proline‐derived tetrapropylammonium dendron with the tetrakis(diperoxotungsto)phosphate [PO4{WO(O2)2}4]3–. This DENDRI‐POM hybrid was characterized by infrared, NMR spectroscopy, polarimetry, and elemental analysis. The data obtained are consistent with the structure in which the trianionic POM is surrounded by three L‐proline‐based dendrons. This DENDRI‐POM oxidized sulfides with moderate activity and very low enantioselectivities (up to 4 %), whereas alkenes were efficiently oxidized with up to 37 % enantiomeric excess (ee), and good yields. Although these ee values are still not satisfactory for practical asymmetric synthesis, 37 % ee represents the best enantioselectivity reported to date in the oxidation of organic substrate with chiral POM hybrids. Studies of temperature, solvent, and catalyst loading effects on the outcome of the reaction indicate that the ee is sensitive to the nature of the solvent. Moreover, the catalyst was recovered at low temperature and reused while retaining its activity and enantioselectivity. These results contrast and complement our reported results in which DENDRI‐POMs based on phenylethylamine‐derived ligands efficiently oxidize sulfides with up to 14 % ee, whereas alkenes were not oxidized with this family of chiral POM compounds. Thus, the influence of the nature of the chiral countercation on the POM properties is again observed.

Solvent and polymer matrix effects on TIPS-pentacene/polymer blend organic field-effect transistors

We report on a systematic study of solvent and polymer matrix effects on the phase segregation behavior of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) blends incorporated into two different amorphous polymer matrices, poly (α-methyl styrene) and poly (triarylamine), and using two solvents, chlorobenzene and tetralin. Optical microscopy, X-ray diffraction analyses, and optical absorption measurements are used to evaluate the film morphology, crystallinity, and optical density, respectively. These analyses are correlated with the extent of vertical segregation of TIPS-pentacene, as observed for the blended films by depth-profile XPS analyses. The microstructure and vertical phase segregation of TIPS-pentacene in blend films are found to be strongly influenced by the choice of solvent. Tetralin, a solvent with a high boiling temperature, was found to be more desirable for achieving distinct phase segregation/crystallization of TIPS-pentacene in blend films and best performance in OFETs with a dual-gate geometry. The electrical properties of top and bottom channels were consistent with the morphological characterization and OFETs processed from tetralin showed higher mobility values than those from chlorobenzene. Further modification of the annealing conditions in the TIPS-pentacene/PTAA/tetralin ternary system led to top-gate OFETs with mobility values up to 2.82 cm2/Vs.

Solvent-induced supramolecular isomers, structural diversity, and unprecedented in situ formation of both inorganic and organic ions in inorganic–organic mercury(ii) complexes

Reported here is, for the first time, an important study of solvent effect on structural diversity in inorganic-organic mercury(II) complexes. As a result, the first supramolecular isomer in mercury(II) complexes is obtained. Importantly, a previously unobserved in situ generation of both inorganic (Cl(-)) and organic ([CH(3)-L1-CH(3)](2+)) ions was also observed.

High Pressure ESR Studies of Electron Self-Exchange Reactions of Organic Radicals in Solution

Simple electron self-exchange reactions are often used to study the role of the reaction medium on a chemical process, commonly implying the use of various solvents with different physical properties. In principle, similar studies may be conducted using a single solvent, changing its physical properties by application of elevated pressures, but so far only little information is available on pressure dependent exchange reactions. In this work, we have used a recently constructed high pressure apparatus for use with electron spin resonance (ESR) spectroscopy to investigate simple electron self-exchange reactions involving 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and tetracyanoethylene (TCNE) and their respective radical anions as well as TMPPD and its radical cation in three different solvents. The self-exchange was observed by ESR line broadening experiments, yielding rate constants and volumes of activation. The experimental results were compared to theoretical calculations based on Marcus theory and taking into account solvent dynamic effects. The use of elevated pressures has enabled the study of solvent effects without commonly encountered problems like solubility issues or chemical reactions between solvent and solute which sometimes limit the range of useable solvents.

Spectroscopic study of solvent effects on the electronic absorption spectra of flavone and 7-hydroxyflavone in neat and binary solvent mixtures.

The solvatochromic characteristics of flavone and 7-hydroxyflavone were investigated in neat and binary solvent mixtures. The spectral shifts of these solutes were correlated with the Kamlet and Taft parameters (α, β and π*) using linear solvation energy relationships. The multiparametric analysis indicates that both specific hydrogen bond donor ability and non-specific dipolar interactions of the solvents play an important role in absorption maxima of flavone in pure solvents. The hydrogen bond acceptor ability of the solvent was the main parameter affecting the absorption maxima of 7-hydroxyflavone. The simulated absorption spectra using a TD-DFT method were in good agreement with the experimental ones for both flavones. Index of preferential solvation was calculated as a function of solvent composition. Preferential solvation by ethanol was detected in cyclohexane-ethanol and acetonitrile-ethanol mixtures for flavone and in acetonitrile-ethanol mixtures for 7-hydroxyflavone. These results indicate that intermolecular hydrogen bonds between solute and solvent are responsible for the non-linear variation of the solvatochromic shifts on the mole fraction of ethanol in the analyzed binary mixtures.