In the present work we show that structural and kinetic information can be obtained from the paramagnetic resonance spectrum of a rather simple stable radical chemically bonded to biomolecules. Paramagnetic nitroxide radicals colntaining the group R R Me> jMe Me N-Me are remarkably stable and inert,1 and show sharp, well-resolved, and simple paramagnetic resonance spectra2 that are sensitive to molecular motion,3 and, to a lesser extent, sensitive to polarity of the molecular environment.4 As shown below, such nitroxide radicals containing an isocyanate group can be bound to proteins and synthetic polypeptides in a manner similar to that used previously to attach fluorescent dyes.5 Here we report a preliminary study of the paramagnetic resoiiance of a nitroxide radical bonded to bovine serum albumin and to poly-L-lysine. It is evident from the present study that there are many other potential applicatioiis of this method to biological systems.

Most molecular theories of nematic liquid crystals assume that the constituent molecules are cylindrically symmetric. However, although this may be a useful approximation the molecules of real nematogens are of lower symmetry ; here we develop a theory for an ensemble of such particles based on a general expansion of the pairwise intermolecular potential together with the molecular field approximation. The dependence of the orientational properties of the uniaxial mesophase on the deviation from molecular cylindrical symmetry is calculated from the series expansio n of the pseudopotential. In these calculations the number of arbitrary parameters in the orientational pseudo-potential is reduced by assuming that the anisotropic intermolecular potential originates solely from dispersion forces. The theoretical predictions for the values of the ordering matrix and the entropy change at the nematic-isotropic transition are found to be in good agreement with those observed for 4,4'-dimethoxyazoxybenzene. In addition, the theory provides a reasonable account of the temperature dependence of the order parameter at constant volume for this nematogen. The allowance for deviations from molecular cylindrical symmetry appears to remove many of the discrepancies between the Maier-Saupe theory and experiment.

An explicit form for the orientating potential acting in uniaxial liquid crystal phases is derived, by analogy with the surface anchoring potential which determines the orientation of macroscopic anisometric particles. The surface of a molecule is determined by describing the molecule as an assembly of van der Waals spheres. The model is successfully applied to predict the ordering tensors for a variety of systems, namely, solutions in nematic solvents of small and rigid probes, or relatively long n-alkanes with many degrees of internal freedom, and pure nematogens formed by aromatic cores attached to flexible chains

A phenomenological theory for the cholesteric phase induced by a chiral solute in a nematic solvent is derived from (i) the continuum representation of twist deformation of the nematic solvent, and (ii) the surface anchoring energy approximation for the interactions between the solvent and a solute of given shape. This allows a simple explanation of the stabilization of the solvent twist deformation by the interactions with chiral solute. A straightforward statistical elaboration leads to the well known inverse proportionality between the pitch of the cholesteric phase and the solute concentration. The corresponding proportionality coefficient, i.e., the twisting power of the solute, is then related to the asymmetry of the solute shape through a chirality order parameter

The relaxation theory for paramagnetic molecules dissolved in liquid crystals, having the same elongated shape of the solvent molecules so as to act as probes of their dynamical behavior, has been revised. The diffusion equation is solved as a series expansion of Wigner rotation matrix elements, employing a simplified orientating potential, and the solution is used to evaluate the effects of the molecular fluctuations on the electron spin resonance line shapes. The irreducible components of the dipole and g interaction tensors relax with a spectrum of characteristic times, which are functions of an alignment parameter and cause any contribution to the linewidth to vanish in the limit of complete ordering.