Chirality transfer through hydrogen-bonding: experimental and ab initio analyses of vibrational circular dichroism spectra of methyl lactate in water

The infrared vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of methyl lactate were measured in the 1000-1800 cm(-1) region in the CCl(4) and H(2)O solvents, respectively. In particular, the chirality transfer effect, i.e. the H-O-H bending bands of the achiral water subunits that are hydrogen-bonded to the methyl lactate molecule exhibit substantial VCD strength, was detected experimentally. A series of density functional theory calculations using B3PW91 and B3LYP functionals with 6-311++G(d,p) and aug-cc-pVTZ basis sets were carried out to simulate the VA and VCD spectra of the methyl lactate monomer and the methyl lactate-(H(2)O)(n) complexes with n = 1, 2, 3. The population weighted VA and VCD spectra of the methyl lactate monomer are in good agreement with the experimental spectra in CCl(4). Implicit polarizable continuum model was found to be inadequate to account for the hydrogen-bonding effect in the observed VA and VCD spectra in H(2)O. The methyl lactate-(H(2)O)(n) complexes with n = 1, 2, 3 were used to model the explicit hydrogen-bonding. The population weighted VA and VCD spectra of the methyl lactate-H(2)O binary complex are shown to capture the main spectral features in the observed spectra in aqueous solution. The theoretical modeling shows that the extent of chirality transfer depends sensitively on the specific binding sites taken by the achiral water molecules. The observation of chirality transfer effect opens a new spectral window to detect and to model the hydrogen-bonding solvent effect on VCD spectra of chiral molecules.     

Syndiotactic‐specific radical polymerization of N,N‐dimethylacrylamide in the presence of tartrates: A proposed mechanism for the polymerization

Radical polymerization of N,N‐dimethylacrylamide (DMAAm) was investigated in the presence of tartrates, such as diethyl L ‐tartrate, diisopropyl L ‐tartrate, and di‐n‐butyl L ‐tartrate, in toluene at low temperatures. Syndiotactic polymers were obtained in the presence of tartrates, whereas isotactic polymers were obtained in the absence of tartrates. The syndiotactic‐specificity increased with increasing amount of tartrates and with decreasing polymerization temperature. NMR analysis suggested that DMAAm and tartrates formed a 1:1 complex through double hydrogen bonding. A mechanism for the syndiotactic‐specific radical polymerization of DMAAm is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1192–1203, 2009     

Dimeric molecular association of dimethyl sulfoxide in solutions of nonpolar liquids

Although many vibrational spectroscopic studies using infrared (IR) absorption and Raman scattering (RS) techniques revealed that dimethyl sulfoxide (DMSO) forms intermolecular dimeric associations in the pure liquid state and in solutions, the results of a number of dielectric relaxation studies did not clearly show the presence of such dimers. Recently, we found the presence of dimeric DMSO associations in not only the pure liquid but also in solutions of nonpolar solvents, such as tetrachloromethane (CCl(4)) and benzene (Bz), using dielectric relaxation (DR) techniques, which ranged from 50 MHz to 50 GHz at 25 °C. The dimeric DMSO associations cause a slow dielectric relaxation process with a relaxation time of ca. 23 ps for solutions in CCl(4) (ca. 17 ps in Bz) due to the dissociation into monomeric DMSO molecules, while the other fast relaxation is caused by monomeric DMSO molecules with a relaxation time of ca. 5.0 ps (ca. 5.5 ps in Bz) at 25 °C. A comparison of DR and vibrational spectroscopic data for DMSO solutions demonstrated that the concentration dependence of the relative magnitude of the slow and fast DR strength corresponds well to the two IR and RS bands assigned to the vibrational stretching modes of the sulfoxide groups (S═O) of the dimeric associations and the monomeric DMSO molecules, respectively. Moreover, the concentrations of the dimeric associations ([DIM]) and monomeric DMSO molecules ([MON]) were governed by a chemical equilibrium and an equilibrium constant (K(d) = [DIM](2)[MON](-1)) that was markedly dependent on the concentration of DMSO and the solvent species (K(d) = 2.5 ± 0.5 M(-1) and 0.7 ± 0.1 M(-1) in dilute CCl(4) and Bz solutions, respectively, and dramatically increased to 20-40 M(-1) in pure DMSO at 25 °C).     

Solvation of propylene oxide in water: vibrational circular dichroism, optical rotation, and computer simulation studies

The solvation of propylene oxide (PO) in water has been studied using vibrational circular dichroism (VCD) spectroscopy, optical rotation dispersion (ORD) spectroscopy, molecular dynamics simulations, and ab initio calculations. VCD and ORD measurements were carried out for PO as neat liquid, in CCl4, and in water solutions. The classical molecular dynamics simulations were carried out for the PO + water binary mixtures at different concentrations, and the solvation information was derived from the radial distribution functions obtained in the simulations. The total number of water molecules within the closest vicinity of PO was predicted to be about 3. The geometry optimizations, vibrational frequencies, and VCD intensities were evaluated for the PO monomer and the PO-(H2O)n clusters with n = 1-3 , using density functional theory calculations at the B3LYP/aug-cc-pVTZ level of theory. The chirality transfer VCD feature, which is a direct result of the explicit H-bonding between water and the chiral PO solute, was detected experimentally at the water bending band region. This feature exhibits high sensitivity to the solvation structure around PO. Comparison of the calculated and experimental chirality transfer features leads to the conclusion that the PO-water binary complex is the dominating species in aqueous solution at room temperature and the anti conformation, where water is on the opposite side of the oxirane ring of the PO methyl group, is preferred over the syn one. This conclusion is also supported by the complementary ORD studies. Possible contributions from the ternary and quaternary PO-water complexes are also discussed.     

A single chiroptical spectroscopic method may not be able to establish the absolute configurations of diastereomers: dimethylesters of hibiscus and garcinia acids

Electronic circular dichroism (ECD), optical rotatory dispersion (ORD), and vibrational circular dichroism (VCD) spectra of hibiscus acid dimethyl ester have been measured and analyzed in combination with quantum chemical calculations of corresponding spectra. These results, along with those reported previously for garcinia acid dimethyl ester, reveal that none of these three (ECD, ORD, or VCD) spectroscopic methods, in isolation, can unequivocally establish the absolute configurations of diastereomers. This deficiency is eliminated when a combined spectral analysis of either ECD and VCD or ORD and VCD methods is used. It is also found that the ambiguities in the assignment of absolute configurations of diastereomers may also be overcome when unpolarized vibrational absorption is included in the spectral analysis.     

Thermodynamics of Mixtures Containing Organic Carbonates. Part XV. Application of the Kirkwood-Buff Theory to the Study of Interactions in Liquid Mixtures Containing Dialkyl Carbonates and Alkanes,Benzene, CCl4 or 1-Alkanols

Binary liquid mixtures containing a dialkyl carbonate (dimethyl or diethyl carbonate) and organic solvents such as alkanes, benzene, CCl₄, or 1-alkanols were studied within the framework of the Kirkwood-Buff formalism. The Kirkwood-Buff integrals, linear coefficients of preferential solvation and local mole fractions were calculated. Results were interpreted assuming that the mixtures with alkanes or 1-alkanols are not random mixtures, which can be ascribed to the existence of strong dipolar interactions between like molecules. Systems containing benzene or CCl₄ are both random and more ordered because of the charge transfer or dipole/induced dipole interactions between the polar group of the solute (O–CO–O) and the polarizable solvent molecules. The effect of increasing temperature was also examined.     

Chiroptical spectroscopic determination of molecular structures of chiral sulfinamides: t-butanesulfinamide

The absolute configuration of t-butanesulfinamide has been determined as (-)-(S) using three different chiroptical spectroscopic methods, namely, vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD). Furthermore, the predominant conformation of this molecule is determined to have S=O and NH2 groups staggered with respect to the three methyl groups and to have amine hydrogens in gauche orientation with respect to S=O. The quality of predictions obtained for vibrational properties, namely, vibrational absorption and VCD, is found to be satisfactory with the B3LYP functional and 6-31G* basis set. However, this basis set is found to be inadequate for obtaining reliable predictions of electronic properties, namely, electronic absorption and ECD, but a larger aug-cc-pVDZ basis set is found to provide satisfactory prediction of electronic properties. t-Butanesulfinamide serves as an example which invalidates the recommendation of using the 6-31G* basis set for molecules that exhibit the same sign for the long-wavelength ECD band and ORD. This molecule also emphasizes the importance of simultaneous investigation of ECD and ORD, and the use of multiple chiroptical spectroscopic methods, for reliable determination of molecular stereochemistry.     

手性酒石酸酯对不对称环氧化反应动力学拆分DL-1-十四烯-3-醇的催化选择性

利用Sharpless不对称环氧化反应动力学拆分二级烯丙醇DL-1-十四烯-3-醇,研究了不同手性酒石酸酯催化剂[酒石酸乙酯(DET)、酒石酸异丙酯(DIPT)、酒石酸环己酯(DCHT)以及酒石酸环十二酯(DCDT)]对该反应的催化选择性,拆分所得的烯丙醇的光学纯度有一定差异,从90%到99?.     

Structure and dynamics of water confined in dimethyl sulfoxide.

We study the structure and dynamics of hydrogen-bonded complexes of H2O/D2O and dimethyl sulfoxide (DMSO) by infrared spectroscopy, NMR spectroscopy and ab initio calculations. We find that single water molecules occur in two configurations. For one half of the water monomers both OH/OD groups form strong hydrogen bonds to DMSO molecules, whereas for the other half only one of the two OH/OD groups is hydrogen-bonded to a solvent molecule. The H-bond strength between water and DMSO is in the order of that in bulk water. NMR deuteron relaxation rates and calculated deuteron quadrupole coupling constants yield rotational correlation times of water. The molecular reorientation of water monomers in DMSO is two-and-a-half times slower than in bulk water. This result can be explained by local structure behavior.     

Nonideality in diffusion of ionic and neutral solutes and hydrogen bond dynamics in dimethyl sulfoxide-chloroform mixtures of varying composition

Molecular dynamics simulations of charged and neutral solutes in dimethyl sulfoxide (DMSO)-chloroform mixtures reveal pronounced nonideality in the solute diffusion with changes of composition of the mixtures. The diffusion coefficient of the anionic solute first decreases, passes through a minimum at DMSO mole fraction of about 0.50, and then increases to reach its value for pure DMSO. The diffusion coefficients of the cationic and neutral solutes are found to decrease with increase in DMSO content of the solvent mixture. The extent of nonideality in the diffusion and orientational relaxation of solvent molecules is found to be somewhat stronger than that in diffusion of the anionic solute in these mixtures. We have also calculated the relaxation of hydrogen bonds formed between DMSO and chloroform molecules. The lifetimes of DMSO-chloroform hydrogen bonds are found to increase monotonically with increase in DMSO concentration. The average number of hydrogen bonds and their average energies are also computed. It is found that an increase in DMSO concentration causes a decrease in the number of DMSO-chloroform hydrogen bonds per DMSO or chloroform molecules but increases the strength of these hydrogen bonds.     

Effects of strong and weak hydrogen bond formation on VCD spectra: a case study of 2-chloropropionic acid

The vibrational circular dichroism (VCD) spectrum of S-(-) and R-(+)-2-chloropropionic acid is thoroughly analyzed. Besides the VCD spectrum of the monomer, the dimers (stabilized by strong hydrogen bonds) and the 2-chloropropionic acid-CHCl(3) complexes (stabilized by a weak hydrogen bond) are studied both experimentally (in solution and in low-temperature Ar matrix) and by quantum chemical computations. It is shown that dimer formation drastically changes, and even weak complex formation can also substantially affect the overall shape of the VCD spectrum. The present and previous results can be generalized for the practice of absolute configuration determination of carboxylic acids by VCD spectroscopy. For these measurements, if bulky groups do not block dimer formation, comparison of the computed spectra of the dimers with the experimental spectra recorded in relatively concentrated (～0.1 mol dm(-3)) solutions is suggested. Our study also shows that due to the stabilization of monomers and/or the formation of weak complexes, the VCD spectrum recorded in CHCl(3) is more complex and, like in the present case, can have a lower intensity than that of the spectrum recorded in CCl(4). Therefore, if solubility allows, CCl(4) is a much preferred solvent over CHCl(3).     

Understanding Solvent Effects in Vibrational Circular Dichroism Spectra: [1,1'-Binaphthalene]-2,2'-diol in Dichloromethane, Acetonitrile, and Dimethyl Sulfoxide Solvents

We present a combined experimental and computational investigation of the vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of [1,1'-binaphthalene]-2,2'-diol. First, the sensitive dependence of the experimental VA and VCD spectra on the solvent is demonstrated by comparing the experimental spectra measured in CH(2)Cl(2), CD(3)CN, and DMSO-d(6) solvents. Then, by comparing calculations performed for the isolated solute molecule to calculations performed for molecular complexes formed between solute and solvent molecules, we identify three main types of perturbations that affect the shape of the VA and VCD spectra when going from one solvent to another. These sources of perturbations are (1) perturbation of the Boltzmann populations, (2) perturbation of the electronic structure, and (3) perturbation of the normal modes.     

Catalytic conversions of dialkyl disulfides

The results of the studies of catalytic conversions of lower dialkyl disulfides performed at the Boreskov Institute of Catalysis (Siberian Branch, Russian Academy of Sciences) are summarized. The selective hydrogenolysis of dimethyl and diethyl disulfides with the formation of alkanethiols occurs in a hydrogen medium on transition metal sulfides. Dimethyl disulfide turns into dimethyl sulfide in an inert gas medium on oxide catalysts with acid and basic sites on their surface. Lower dialkyl disulfides are dehydrocyclized to thiophene under the action of sulfide catalysts. In an oxygen medium on the metal oxides and salts, diethyl disulfide and a lower disulfide concentrate are selectively oxidized to form alkanethiolsulfinates, alkanethiolsulfonates, and alkanesulfonic acids.     

Enantiospecific electrodeposition of chiral CuO films on single-crystal Cu(111)

Epitaxial films of monoclinic CuO have been electrodeposited on single-crystal Cu(111) from solutions containing either (S,S)- or (R,R)-tartrate. X-ray pole figure analysis reveals that the CuO film grown from (S,S)-tartrate exhibits a (1) out-of-plane orientation while the film grown from (R,R)-tartrate has a (11) orientation. Even though CuO does not crystallize within a chiral space group, the orientations obtained exhibit a surface chirality similar to that obtained from high index fcc metal surfaces. The films were shown to be enantioselective toward the catalytic oxidation of tartrate molecules by cyclic voltammetry. The technique should prove to be applicable to the electrodeposition of chiral surfaces of other low-symmetry materials on achiral substrates and should prove to be of use to those interested in the synthesis, separation, and detection of chiral molecules.     

Lactic acid in solution: investigations of lactic acid self-aggregation and hydrogen bonding interactions with water and methanol using vibrational absorption and vibrational circular dichroism spectroscopies

The infrared vibrational absorption (VA) and vibrational circular dichroism (VCD) spectral features of L-(+)-lactic acid (LA) in CDCl3 solution are concentration dependent, showing evidence of oligomerization with increasing concentrations. To understand the observed spectra, geometry optimizations, vibrational frequencies, and VA and VCD intensities were evaluated for (LA)n with n=1-4 using density functional theory calculations at the B3LYP6-311++G(d,p), B3LYP/cc-pVTZ, and in some cases, B3LYP/aug-cc-pVTZ levels of theory. Comparisons with the experimental spectra indicate that the lowest energy LA dimer (AA), formed by two C Double Bond O...HO hydrogen bonds, is one of the dominating species in solution at room temperature. Possible contributions from the LA trimer and tetramer are also discussed. To model the VA and VCD spectra of LA in water and in methanol, both implicit polarizable continuum model and explicit hydrogen bonding considerations were used. For explicit hydrogen bonding, geometry optimizations of the AA-(water)n and AA-(methanol)n complexes, with n=2,4,6, were performed, and the corresponding VA and VCD spectra were simulated. Comparisons of the calculated and experimental VA and VCD spectra in the range of 1000-1800 cm(-1) show that AA-(water)n with n=6 best reproduces the experimental spectra in water. On the other hand, AA-(methanol)n with n=2 reproduces well the experimental results taken in methanol solution. In addition, we found evidence of chirality transfer, i.e., some vibrational bands of the achiral water subunits gain VCD strength upon complexation with the chiral LA solute. The study is the first to use VCD spectroscopy to probe the structures of LA aggregates and hydrogen bonding solvation clusters in the solution phase.     

Conformations of Serine in Aqueous Solutions as Revealed by Vibrational Circular Dichroism

Vibrational circular dichroism (VCD) spectroscopy is utilized to reveal the detailed conformational distributions of the dominant serine species in aqueous solutions under three representative pH conditions of 1.0, 5.7, and 13.0, together with vibrational absorption (VA) spectroscopy, density functional theory (DFT), and molecular dynamics simulation. The experimental VA and VCD spectra of serine in H₂O and D₂O in the fingerprint region under three pH values are obtained. DFT calculations at the B3LYP/6‐311++G(d,p) level are carried out for the protonated, zwitterionic, and deprotonated serine species. The lowest‐energy conformers of all three species are identified and their corresponding VA and VCD spectra simulated. A comparison between the gas‐phase simulations and the experimental VA and VCD spectra suggests that one or two of the most stable conformers of each species contribute predominantly to the observed data, although some discrepancies are noted. To account for the solvent effects, both the polarizable continuum model and the explicit solvation model are considered. Hydrogen‐bonded protonated, zwitterionic, and deprotonated serine–(water)₆ clusters are constructed based on radial distribution function analyses and molecular dynamics snapshots. Geometry optimization and VA and VCD simulations are performed for these clusters at the B3LYP/6‐311++G(d,p) level. Inclusion of the explicit water molecules is found to improve the agreement between theory and experiment noticeably in all three cases, thus enabling conclusive conformational distribution analyses of serine in aqueous solutions directly.     

Intermolecular interactions and disorder in six isostructural celecoxib solvates

Six isostructural crystalline solvates of the active pharmaceutical ingredient celecoxib {4‐[5‐(4‐methylphenyl)‐3‐(trifluoromethyl)pyrazol‐1‐yl]benzenesulfonamide; C₁₇H₁₄F₃N₃O₂S} are described, containing dimethylformamide (DMF, C₃H₇NO, 1 ), dimethylacetamide (DMA, C₄H₉NO, 2 ), N‐methylpyrrolidin‐2‐one (NMP, C₅H₉NO, 3 ), tetramethylurea (TMU, C₅H₁₂N₂O, 4 ), 1,3‐dimethyl‐3,4,5,6‐tetrahydropyrimidin‐2(1H)‐one (DMPU, C₆H₁₂N₂O, 5 ) or dimethyl sulfoxide (DMSO, C₂H₆OS, 6 ). The host celecoxib structure contains one‐dimensional channel voids accommodating the solvent molecules, which accept hydrogen bonds from the NH₂ groups of two celecoxib molecules. The solvent binding sites have local twofold rotation symmetry, which is consistent with the point symmetry of the solvent molecule in 4 and 5 , but introduces orientational disorder for the solvent molecules in 1 , 2 , 3 and 6 . Despite the isostructurality of 1 – 6 , the unit‐cell volume and solvent‐accessible void space show significant variation. In particular, 4 and 5 show an enlarged and skewed unit cell, which can be attributed to a specific interaction between an N—CH₃ group in the solvent molecule and the toluene group of celecoxib. Intermolecular interaction energies calculated using the PIXEL method show that the total interaction energy between the celecoxib and solvent molecules is broadly correlated with the molecular volume of the solvent, except in 6 , where the increased polarity of the S=O bond leads to greater overall stabilization compared to the similarly‐sized DMF molecule in 1 . In the structures showing disorder, the most stable orientations of the solvent molecules make C—H…O contacts to the S=O groups of celecoxib.     

Conformational Distributions of N‐Acetyl‐L‐cysteine in Aqueous Solutions: A Combined Implicit and Explicit Solvation Treatment of VA and VCD Spectra

The conformational distributions of N‐acetyl‐L ‐cysteine (NALC) in aqueous solutions at several representative pH values are investigated using vibrational absorption (VA), UV/Vis, and vibrational circular dichroism (VCD) spectroscopy, together with DFT and molecular dynamics (MD) simulations. The experimental VA and UV/Vis spectra of NALC in water are obtained under strongly acid, neutral, and strongly basic conditions, as well as the VCD spectrum at pH 7 in D₂O. Extensive searches are carried out to locate the most stable conformers of the protonated, neutral, deprotonated, and doubly deprotonated NALC species at the B3LYP/6‐311++G(d,p) level. The inclusion of the polarizable continuum model (PCM) modifies the geometries and the relative stabilities of the conformers noticeably. The simulated PCM VA spectra show significantly better agreement with the experimental data than the gas‐phase ones, thus allowing assignment of the conformational distributions and dominant species under each experimental condition. To further properly account for the discrepancies noted between the experimental and simulated VCD spectra, PCM and the explicit solvent model are utilized. MD simulations are used to aid the modelling of the NALC–(water)_N clusters. The geometry optimization, harmonic frequency calculations, and VA and VCD intensities are computed for the NALC–(water)_3,4 clusters at the B3LYP/6‐311++G(d,p) level without and with the PCM. The inclusion of both explicit and implicit solvation models at the same time provides a decisively better agreement between theory and experiment and therefore conclusive information about the conformational distributions of NALC in water and hydrogen‐bonding interactions between NALC and water molecules.     

Microscopic study of binary mixtures between pyrrolidinium bis(triflorosulfonyl)imide and dimethyl sulfoxide/acetonitrile

Molecular interactions of a representative pyrrolidinium-based ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(triflorosulfonyl)-imide([BMPyrr][TFSI]) with dimethyl sulfoxide(DMSO) and acetonitrile(AN) have been analyzed in this work. Attenuated total reflection Fourier transform infrared spectroscopy(ATR-FTIR) and density functional theory(DFT) calculations are used in the investigation, while excess infrared spectra and two-dimensional correlation spectroscopy are used to explore the data in detail. It has been found that the molecular solvents can interact with TFSI-(mainly with S=O and weakly with S–N–S group). AN interacts feebly with BMPyrr~+ as compared with the strong interaction of DMSO. The strength of the interactions depends on the electron donating ability of the solvent. Upon mixing, hydrogen bonds regarding C-Hs in cation and S–N–S in anion are weakened, while that regarding S=O in anion is strengthened. Among the C-Hs which are connected directly with the N of the cation, C1-H is the main interaction site for both DMSO and AN. This means that C1-H is the most acidic hydrogen in pyrrolidinium cation.     

Concentration-dependent frequency shifts and Raman spectroscopic noncoincidence effect of the C=O stretching mode in dipolar mixtures of acetone/dimethyl sulfoxide. Experimental, theoretical, and simulation results

The nu(C=O) Raman band frequencies of acetone have been analyzed to separate the contributions of the environmental effect and the vibrational coupling to the gas-to-liquid frequency shifts of this band and to elucidate the changes in these two contributions upon dilution in DMSO. We have measured the frequencies of the nu((12)C=O) band in acetone/DMSO binary mixtures, the nu((13)C=O) band of the acetone-(13)C=O present as a natural abundance isotopic impurity in these mixtures, and both the nu((12)C=O) and nu((13)C=O) bands in the acetone-(12)C=O/acetone-(13)C=O isotopic mixtures at infinite dilution. These frequencies are compared with those of the nu((12)C=O) band in the acetone/CCl(4) binary mixtures measured previously. We have found the following three points: (i) The negative environmental contribution for the nu((12)C=O) oscillator of acetone completely surrounded by DMSO is reduced in magnitude by +5.5 cm(-1) and +7.8 cm(-1) upon the complete substitution of DMSO with acetone and CCl(4) molecules, respectively, indicating the progressive reduction of the attractive forces exerted by the environment on the nu((12)C=O) mode of acetone. (ii) In DMSO and other solvents, the contribution of the vibrational coupling to the frequency of the isotropic Raman nu((12)C=O) band of acetone becomes progressively more negative with increasing acetone concentration up to a value of -5.5 cm(-1), while the contribution to the frequency of the anisotropic Raman band remains approximately unchanged. The only difference resides in the curvatures of the concentration dependencies of these contributions which depend on the relative solute/solvent polarity. (iii) The noncoincidence effect (separation between the anisotropic and isotropic Raman band frequencies) of the nu(C=O) mode in the acetone/DMSO mixtures exhibits a downward (concave) curvature, in contrast to that in the acetone/CCl(4) mixtures, which shows an upward (convex) curvature. This result is supported by MD simulations and by theoretical predictions and is interpreted as arising from the reduction and enhancement of the short-range orientational order of acetone in the acetone/DMSO and acetone/CCl(4) mixtures, respectively.