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.

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

Some constitutive equations for liquid crystals

Photoalignment of Liquid-Crystal Systems.

Proton and carbon-13 nmr spectra of unsonicated lipid bilayers and biological membranes are generally dominated by strong proton–proton and proton–carbon dipolar interactions. As a result the spectra contain a large number of overlapping resonances and are rather difficult to analyse. Nevertheless, important information on the structure and dynamic behaviour of lipid systems has been provided by these techniques (Wennerstrom & Lindblom, 1977).

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Deuterium magnetic resonance: theory and application to lipid membranes.

This review discusses the physical properties of nematic, cholesteric, and smectic liquid crystals. Molecular theories of the liquid crystal phases are discussed and the molecular field theories of the phase transitions between the various liquid crystal phases are presented. The elastic theory and hydrodynamics of liquid crystals is developed. A wide variety of phenomena in liquid crystals, including elastic distortions, disclinations, flow properties, fluctuations, light scattering, wave propagation, nuclear magnetic resonance, effects of magnetic and electric fields, electrohydrodynamics, and optical properties, is discussed.

Physics of liquid crystals

Mit Beschränkung auf den Dipol-Dipol-Anteil der reinen Dispersionswechselwirkungen als dem für die Existenz einer kristallinflüssigen Phase vermutlich maßgebenden Teil der zwischenmolekularen Kräfte wird durch geeignete Mittelungen ein Ausdruck für das auf das Einzelmolekül wirkende mittlere Innere Feld einer nematischen Molekülanordnung abgeleitet. Es wird gezeigt, daß dieses Innere Feld in einem gewissen Temperaturbereich einen nematischen Ordnungszustand bewirken muß und daß dieser Ordnungszustand bei einer bestimmten Temperatur diskontinuierlich und unter Energieaufnahme in die isotrope Molekülanordnung übergehen muß. Die Theorie liefert also einen Umwandlungspunkt 1. Ordnung, wie er experimentell auch beobachtet wird. Die Umwandlungstemperatur wird im wesentlichen durch die Anisotropie der optischen Übergangsmomente der Moleküle bestimmt.

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Eine einfache molekular-statistische Theorie der nematischen kristallinflüssigen Phase. Teil II

Eine einfache molekulare Theorie des nematischen kristallinflüssigen Zustandes

High-Resolution Nuclear Magnetic Resonance Spectra of Orientated Molecules

A theoretical study of nuclear magnetic resonances in liquid crystals and in liquid crystalline solutions is given. The average ordering of the molecules in liquid crystals, as far as it is of importance for nuclear resonance researches, can be described by a symmetrical matrix. With the help of this matrix the coupling constants of the effective average spin HAMiLTONIAN can be expressed by the constants belonging to a fixed molecular orientation. For experimental work solutions in nematic liquid crystals are most useful. In such solutions high resolution spectra of the orientated solute molecules can be gained without any disturbance by intermolecular nuclear dipole-dipole interaction. Precise informations can be obtained on the intra-molecular dipole-dipole interaction, the anisotropy of chemical shift, and the quadrupole interaction. The matrix of order can be determined if the molecular structure is sufficiently known. In favorable cases the absolute sign of the indirect spin-spin coupling constants can also be determined.

Kernresonanzen in kristallinen Flüssigkeiten und in kristallinflüssigen Lösungen. Teil I

A theory of orientation polarization in nematic liquid crystals is developed for a molecular dipole moment parallel to the long axis of the molecule. The theory is essentially an extension of the Debye model for normal polar liquids to take into account the strong intermolecular potential which is responsible for the nematic state. It is shown in detail that the relaxation time depends strongly on the nematic potential and also on whether the polarization takes place parallel or perpendicular to the symmetry axis of the crystal. In the first case, the relaxation time increases from its value in the isotropic liquid phase by a “retardation factor” which may amount to several orders of magnitude, depending on the strength of the nematic potential. In the second case, the relaxation time decreases slightly. The calculated retardation factor is smaller than the experimental one. It is suggested that this discrepancy is due to the neglect of molecular short-range order.

Alfred Saupe

Papers

Eine einfache molekular-statistische Theorie der nematischen kristallinflüssigen Phase. Teil II

Eine einfache molekulare Theorie des nematischen kristallinflüssigen Zustandes

High-Resolution Nuclear Magnetic Resonance Spectra of Orientated Molecules

Kernresonanzen in kristallinen Flüssigkeiten und in kristallinflüssigen Lösungen. Teil I

Extended Debye theory for dielectric relaxations in nematic liquid crystals