In this work, pendant drop techniques and molecular dynamics (MD) simulations were employed to investigate the effect of asphaltene concentrations on the interfacial tension (IFT) of the oil/water interface. Here, oil and asphaltene were represented by, respectively, common organic solvents and Violanthrone-79, and two types of concentration, i.e., bulk concentration and surface concentration, were examined. Correlations between the IFTs from experiments and MD simulations revealed that surface concentration, rather than the commonly used bulk concentration, determines the reduction of oil/water IFTs. Through analyzing the hydrogen bonding, the underlying mechanism for the IFT reduction was proposed. Our discussions here not only enable the direct comparison between experiments and MD simulations on the IFTs but also help with future interfacial studies using combined experimental and simulation approaches. The methodologies used in this work can be extended to many other oil/water interfaces in the presence of interfacially active compounds.

Vibrational optical activity spectroscopies, namely vibrational circular dichroism (VCD) and Raman optical activity (ROA), have been emerged in the past decade as powerful spectroscopic tools for stereochemical information of a wide range of chiral compounds in solution directly. More recently, their applications in unveiling solvent effects, especially those associated with water solvent, have been explored. In this review article, we first select a few examples to demonstrate the unique sensitivity of VCD spectral signatures to both bulk solvent effects and explicit hydrogen-bonding interactions in solution. Second, we discuss the induced solvent chirality, or chiral transfer, VCD spectral features observed in the water bending band region in detail. From these chirality transfer spectral data, the related conformer specific gas phase spectroscopic studies of small chiral hydration clusters, and the associated matrix isolation VCD experiments of hydrogen-bonded complexes in cold rare gas matrices, a general picture of solvation in aqueous solution emerges. In such an aqueous solution, some small chiral hydration clusters, rather than the chiral solutes themselves, are the dominant species and are the ones that contribute mainly to the experimentally observed VCD features. We then review a series of VCD studies of amino acids and their derivatives in aqueous solution under different pHs to emphasize the importance of the inclusion of the bulk solvent effects. These experimental data and the associated theoretical analyses are the foundation for the proposed “clusters-in-a-liquid” approach to account for solvent effects effectively. We present several approaches to identify and build such representative chiral hydration clusters. Recent studies which applied molecular dynamics simulations and the subsequent snapshot averaging approach to generate the ROA, VCD, electronic CD, and optical rotatory dispersion spectra are also reviewed. Challenges associated with the molecular dynamics snapshot approach are discussed and the successes of the seemingly random “ad hoc explicit solvation” reported before are also explained. To further test and improve the “clusters-in-a-liquid” model in practice, future work in terms of conformer specific gas phase spectroscopy of sequential solvation of a chiral solute, matrix isolation VCD measurements of small chiral hydration clusters, and more sophisticated models for the bulk solvent effects would be highly valuable.

In this work, a series of pendant drop measurements and molecular dynamics (MD) simulations were performed to investigate the effects of temperature and salinity on the interfacial tension (IFT) of water/toluene binary systems. Both experimental measurements and theoretical simulations demonstrated that elevating temperature decreased the IFT, while adding salts resulted in an increment of IFT. Furthermore, it was found that the presence of model asphaltene compound could alleviate the effects of temperature and salinity on the IFTs. That is, in the presence of the model asphaltene compound, the decrement effect of elevating temperature as well as the increment effect of adding salts was reduced. Through detailed analysis of the simulated systems, the underlying mechanisms for the effects of temperature and salinity on the IFTs were clarified for cases with and without the presence of the model asphaltene. The results reported here can help to modulate the IFT values of oil/water interfaces in petroleum processing.

Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of methyl mandelate, a prototype chiral molecule, in a series of organic solvents, namely methanol (MeOH-d(4)), dimethyl sulfoxide (DMSO-d(6)), and chloroform (CDCl(3)), have been measured in the finger print region from 1800 to 1150 cm(-1). Implicit solvation models in the form of polarizable continuum model and explicit solvation models have been employed independently and simultaneously. The goal is to evaluate their efficiencies in dealing with solvent effects in each solution and to establish a general strategy to adequately account for effects of solvents. Molecular dynamics (MD) simulation and radial distribution function analysis have been performed to aid the construction of the explicit solvation models. Initial geometry searches have been carried out at the B3LYP/6-31G(d) level for the methyl mandelate monomer and its explicit 1 : 1 and 1 : 2 solute-solvent hydrogen-bonded complexes. B3LYP/cc-pVTZ has been used for all the final geometry optimizations, the vibrational frequency, VA and VCD intensity, and optical rotation dispersion (ORD) calculations. The results show that inclusion of solvent explicitly and implicitly at the same time has significant impacts on the appearance of the VA and VCD spectra, and is crucial for reliable spectral assignments when solvents are capable of hydrogen-bonding interactions with solutes. When no strong solvent-solute hydrogen-bonding interactions in the case of chloroform are expected, the gas phase monomer model is adequate for spectral interpretation, while inclusion of implicit solvation improves the frequency agreement with experiment. ORD spectra of methyl mandelate in the aforementioned solvents at different concentrations under 5 excitation wavelengths have also been measured. The comparison between the calculated and the experimental ORD spectra supports the conclusions drawn from the VA and VCD investigations.

We report extremely strong chirality transfer from achiral nickel complex to solvent molecules detected as Raman optical activity (ROA). Electronic energies of the complex were in resonance with the excitation-laser light. The phenomenon was observed for aw ide range of achiral and chiral solvents. Forchiral 2-butanol, the induced ROAwas even stronger than the natural one.T he observations were related to so-called quantum (molecular) plasmons that enable as trong chiral Rayleigh scattering of the resonating complex. According to am odel presented here,t he maximal induced ROAi ntensity occurs at ac ertain distance from the solute,i nathreedimensional "ring of fire", even after rotational averaging. Most experimental ROAsigns and relative intensities could be reproduced. The effect might significantly increase the potential of ROAspectroscopyinbioimaging and sensitive detection of chiral molecules.Most important molecules in living organisms are chiral and thus sensitive to circularly polarized light. This sensitivity was first explored by Pasteur, [1] and since then an amazing variety of chiroptical methods has been developed for fundamental studies and practical applications. [2] One of the youngest and most dynamically evolving tools is Raman optical activity (ROA). [3] It can provide rich stereochemical information because of the large number of vibrational bands usually exhibited by chiral molecules,a nd is directly applicable to solutions.However,the ROAeffect is weak, and alarge amount of the sample is usually needed for the analysis.T his has prompted vigorous searches for enhancement techniques, utilizing,f or example,m olecular resonance, [4] nanoplasmons (resonating metallic nanoparticles), [5] and molecular aggregation. [6] Interesting phenomena such as ROAi nduction in achiral reporter molecules in the presence of nanoplasmons or asolvent-signal enhancement under hyper-Raman scattering have been observed. [5c,7,8] Even though many properties of the nanoplasmons can be explained by established electro-magnetic and chemical theories, [9] the ROAenhancement and many chirality-transfer effects have so far resisted detailed interpretation.In this context, we believe that the strong chirality transfer under resonance conditions described in this work significantly contributes to the understanding of molecular interactions with chiral light. We report strong ROAofarange of solvents induced by achiral nickel complex under resonance conditions.C ontrary to common belief,t he chirality transfer appears quite general, and the induced ROAs ignals were even stronger than those of the Ni complex itself.F or 2butanol, ac hiral solvent, the induced ROAi ntensity was stronger than the natural one.Ther esonance-ROA phenomenon itself,a na rea of intense experimental and theoretical interest, can be rationalized only in simple cases. [4a, 10] None of them, however,i s applicable to the observations presented here.B ased on extensive experimental data and model calculations,weshow that the effect is not caused by spe...