: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

In isotropic solution, internuclear dipolar couplings average to zero as a result of rotational diffusion. By dissolving macromolecules in a dilute aqueous nematic discotic liquid-crystalline medium containing widely spaced magnetically oriented particles, a tunable degree of solute alignment with the magnetic field can be created while retaining the high resolution and sensitivity of the regular isotropic nuclear magnetic resonance (NMR) spectrum. Dipolar couplings between1H-1H, 1H-13C,1H-15N, and 13C-13C pairs in such an oriented macromolecule no longer average to zero, and are readily measured. Distances and angles derived from dipolar couplings in human ubiquitin are in excellent agreement with its crystal structure. The approach promises to improve the accuracy of structures determined by NMR, and extend the size limit.

/pdf/direct-measurement-of-distances-and-angles-in-biomolecules-27rjfsnkz5.pdf

Direct Measurement of Distances and Angles in Biomolecules by NMR in a Dilute Liquid Crystalline Medium

Applied Numerical Analysis. By C.F. Gerald. Pp. xii, 340. £3·60. 1970. (Addison-Wesley.)

An overview on the recent developments in the field of liquid crystalline bent-core molecules (so-called banana liquid crystals) is given. After some basic issues, dealing with general aspects of the systematisation of the mesophases, development of polar order and chirality in this class of LC systems and explaining some general structure–property relationships, we focus on fascinating new developments in this field, such as modulated, undulated and columnar phases, so-called B7 phases, phase biaxiality, ferroelectric and antiferroelectric polar order in smectic and columnar phases, amplification and switching of chirality and the spontaneous formation of superstructural and supramolecular chirality.

/pdf/bent-core-liquid-crystals-polar-order-superstructural-17m3bst2sc.pdf

Bent-core liquid crystals: polar order, superstructural chirality and spontaneous desymmetrisation in soft matter systems

International Tables for X-Ray Crystallography (Published for the International Union of Crystallography.) Vol. 1: Symmetry Groups. Edited by Norman F. M. Henry and Kathleen Lonsdale. Pp. xi + 558. (Birmingham: Kynoch Press, 1952.) 105s.

/pdf/international-tables-for-x-ray-crystallography-1t8sk98xrd.pdf

International Tables for X-Ray Crystallography

Liquid crystals have become ubiquitous in the displays for electronic devices, ranging from wrist watches to laptop computers. Nuclear magnetic resonance is one of the important mechanisms for determining their structures tures and properties. This book covers NMR techniques used in studying liquid crystals and present up to date results from such studies. Ronald Dong has worked on NMR in liquid crystals for much of his professional career. Topics covered include: Nuclear spin dynamics, orientational order, molecular field theories of liquid-crystal molecules, nuclear spin relaxation, spin relaxation, rotational and translational dynamics, internal dynamics of liquid-crystal molecules, NMR in liquid crystals; an appendix covers rotations, Euler angles and Wigner rotation matrices.

Nuclear Magnetic Resonance of Liquid Crystals

We have extended the scheme for computing deuterium quadrupolar splittings of a flexible solute in a nematic solvent [Ferroelectrics 30, 83 (1980)] to study chain ordering in the 4‐n‐alkyl‐4′‐cyanobiphenyl liquid crystals (nCB). All possible configurations {φ} of the nCB molecule are generated by the rotational isomeric state model of Flory. Each {φ} has a separate ordering matrix whose diagonal elements are assumed to scale with the shape anisotropy of the molecule as prescribed by the principal moments of inertia of the configuration I{φ}. Two models for identifying the molecular‐fixed‐frame are considered: (1) The frame diagonalizes I{φ}; (2) the frame is stationary on the nCB core. The variation of deuterium quadrupolar splittings along the alkyl chain can be satisfactorily explained by the calculations, however, the detailed behavior of the computed splittings are sensitive to the assumptions about the placement of the molecular‐fixed‐frame.

Chain ordering and molecular orientational order in liquid crystals

Solving Complex NMR Spectra of Solutes in Liquid Crystals (E E Burnell et al.) Analytical Potentials of NAD-NMR in Oriented Solvents (P Lesot & C Aroulande) Noble Gas Probes in NMR Studies of Liquid Crystals (J Jokisaari) Bicelles - Magic Wand to Study Membrane Proteins by NMR (R Soong et al.) Advances in Proton NMR Relaxometry in Thermotropics (P J Sebastiao et al.) Magnetic Field Distortions of Ferroelectric Mesogens by DNMR (R Y Dong) DNMR of Random Quenched Disorder in 12CB (D Finotello & V Pandya) Dynamics of Liquid Crystals by DNMR Relaxation (C A Veracini & V Domenici) Translational Self-diffusion in Liquid Crystals by NMR Diffusometry (M Cifelli) DNMR Studies of Static and Dynamic Director Alignment in Nematics (A Sugimura & G R Luckhurst) Viscoelastic Properties of Liquid Crystals (A V Zakharov) Carbon-13 NMR Studies of Calamitic Liquid Crystals (R Y Dong) DFT and Carbon-13 NMR in a Biaxial Bent-core Mesogen (A Marini et al.).

Nuclear magnetic resonance spectroscopy of liquid crystals

Materials that undergo stimulus-induced optical changes are important for many new technologies. In this paper, we describe a new free-standing silica-based composite film that exhibits reversible thermochromic reflection, induced by a liquid crystalline guest in the pores of iridescent mesoporous films. We demonstrate that selective reflection from the novel mesoporous organosilica material with chiral nematic organization can be reversibly switched by thermal cycling of the 8CB guest between its isotropic and liquid crystalline states, which was proven by solid-state NMR experiments. The switching of the optical properties of the chiral solid-state host by stimulus-induced transitions of the guest opens the possibility of applications for these novel materials in sensors and displays.

Thermal switching of the reflection in chiral nematic mesoporous organosilica films infiltrated with liquid crystals.

We report on a deuteron NMR study of quadrupolar splittings and spin-lattice relaxation times T1Q and T1Z as a function of temperature and at two different Larmor frequencies in the columnar phase of hexakis(n-hexyloxy)triphenylene (HAT6). The additive potential method is used to model the quadrupolar splittings, from which the potential of mean torque is parameterized, and the order parameter tensor for an “average” conformer is determined. The small-step rotational diffusion model is used to find the rotational diffusion constants D∥ and D⊥ for the spinning and tumbling motions of the molecular core. It is found that D⊥ is slightly larger than D∥ in contrast with the findings in calamitic liquid crystals. The decoupled model of Dong for correlated internal rotations in the end chains is used for the first time in a discotic liquid crystal. Both jump constants for one- and three-bond motions are nearly independent of temperature, while the jump constant for two-bond motion is thermally activated. The rot...

Ronald Y. Dong

Papers

Nuclear Magnetic Resonance of Liquid Crystals

Chain ordering and molecular orientational order in liquid crystals

Nuclear magnetic resonance spectroscopy of liquid crystals

Thermal switching of the reflection in chiral nematic mesoporous organosilica films infiltrated with liquid crystals.

Orientational ordering and dynamics in the columnar phase of a discotic liquid crystal studied by deuteron nmr spectroscopy