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Recently, a new formulation has been proposed about a strictly short-range anisotropic potential acting on biaxial apolar particles dissolved in a uniaxial medium [Chem. Phys. Lett. 342, 375 (2001)], where the solute-solvent interactions are treated at a molecular level and the solute order parameters are calculated by making use of the Monte Carlo–Metropolis sampling scheme. In the present paper the cited model has been used for the study of 1,4-difluorobenzene, 1,4-dichlorobenzene, and 1,4-dibromobenzene molecules and the simulated order parameters have been compared with the [sup 1]H-NMR experimental data for the solutes in the nematic solvents ZLI1132 (a Merck commercial eutectic mixture of alkylcyclohexylcyanobenzenes and alkylcyclohexylcyanobiphenyl), EBBA [the N-(4-ethoxybenzylidene)-4[sup ′]-n-butylaniline], and in the zero average electric field gradient nematic mixture 55 wt% ZLI1132+EBBA (the so-called “magic” mixture). The orientations predicted by the model match almost perfectly the experimental Saupe matrices of the molecules dissolved in the “magic” mixture: implications of this result are discussed in terms of nature of the interactions in the different nematic phases and reliability and effectiveness of the suggested intermolecular potential. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Very accurate bond distances can be derived from dipolar couplings, Dij, obtained by analysis of the NMR spectra of samples dissolved in anisotropic solvents (LXNMR). To do this, however, the couplings must be corrected for the averaging produced by vibrational motion. The vibrational corrections require a knowledge of the force field, which may be obtained by fitting experimental vibrational frequencies or, much more easily, from quantum-mechanical computations. In the present study, the reliability of the methods used to calculate the force field and the effects on the accuracy of the vibrational corrections to the Dij is tested on benzene for which a very accurate structural study is available. [ABSTRACT FROM AUTHOR]

The induction of a cholesteric phase by doping an achiral nematic liquid crystal with an enantiopure solute is a phenomenon that, as in all general supramolecular phenomena of chiral amplification, depends in a subtle way on intermolecular interactions. The micrometric helical deformation of the phase director in the cholesteric phase is generated by the interplay of anisotropy and chirality of probe-medium interactions. In the case of a flexible chiral dopant, the solvent can influence the twisting power in two ways, difficult to disentangle: it is responsible for the solute orientational order, an essential ingredient for the emergence of phase chirality; but also it can affect the dopant conformational distribution and then the chirality of the structures present in the solution. In this work we have investigated methyl phenyl sulfoxide, a flexible, chiral molecule that, when dissolved in different nematics, can produce cholesteric phases of opposite handedness. This peculiar, intriguing sensitivity to the environment makes MPS a suitable probe for a thorough investigation of the effects of solute-solvent interactions on chiral induction in liquid crystals. NMR experiments in various nematic solvents have been performed in addition to twisting power measurements. From the analysis of partially averaged ¹H-¹H and 13C-¹H dipolar couplings, the effects of solvent on solute conformation and orientational order are disentangled, and this information is combined with the modeling of the chirality of intermolecular interactions, within a molecular field theory. The integration of different techniques allows an unprecedented insight into the role of solvent in mediating the chirality transfer from molecule to phase. [ABSTRACT FROM AUTHOR]

In this Letter, a general expression is derived for the conformational distribution function of a molecule dissolved in an anisotropic condensed fluid medium by combining an a priori model with the maximum entropy principle applied to treatment of liquid crystalline-NMR data. The recently proposed additive potential maximum entropy (APME) method is recovered as a special case, when the AP is chosen as the a priori model and the orientational order is low. [ABSTRACT FROM AUTHOR]

In this paper, a chirality-sensitive effective orientational potential is, for the first time, proposed. It describes, within the Molecular Field approximation, different solute-solvent ordering interactions, according to the P (clockwise) or M (counterclockwise) nature of helical particles dissolved in uniaxial anisotropic solvents composed, in their turn, of helical P or M particles. By making use of Monte Carlo-simulated order parameters, it is shown that the model is, in principle, able to lead to the absolute enantiorecognition of the unknown chirality of the helical solute particles. This makes it a possible interesting tool for exploiting NMR anisotropic observables in order to achieve the absolute enantiomer assignment of chiral helical solutes. Unlabelled Image • Helical solutes orientationally ordered in organized helical solvents are studied. • A mean torque potential sensitive to P (clockwise) and M (counterclockwise) chirality is formulated. • The effectiveness and reliability of the proposed model is tested on Monte Carlo simulated order parameters. • The model proved to be, in principle, a useful tool for absolute enantiorecognition of the solutes. [ABSTRACT FROM AUTHOR]