Electric birefringence molecules

The rotational diffusion constant in water at 25° and neutral pH as measured by electric birefringence (258) is 230 X 105 sec-1 or 0.73 X HT8 sec as a relaxation time. For a hydrodynamic ellipsoid of dimensions 66 X 22 A and a molecular weight of 14,000, the calculated relaxation tilde is 0.72 X 10-8 sec. However, the apparent asymmetry of the molecule from the X-ray structure corresponds to an axial ratio of no more than 2 1 rather than 3 1. 

The investigation of the electric birefringence is an excellent tool for the study of the PPP polyelectrolytes because this method is highly sensitive and therefore particularly suited for very dilute solutions [40-42]. At low field strength, the birefringence observed in solutions or suspensions of non-interacting molecules or particles rises with the square of field strength (Kerr s law) and in proportion with concentration [43] ... 

A combination of molecular mechanics calculations and electric birefringence (electrooptical Kerr effect) measurements of group IVB aryl compounds has been used to study conformational effects in these molecules [504l... 

Electric birefringence (EB) or the Kerr effect is widely used in molecular optics as a method for the investigation of the molecular structure of low molecular weight substances. The study of the Kerr effect in the gas phase or in solutions in combination with other methods, such as refraction, light scattering, dielectric measurements etc. permits to ascertain the spatial arrai ement of atoms in the molecule and thus to calculate the main values of the polarizability tensor of the molecule and to obtain information about the value and direction of its dipole moment ... 

The present contribution reviews recent advances in the highly accurate calculation of frequency-dependent properties of atoms and small molecules, electronic struc-mre methods, basis set convergence and extrapolation techniques. Reported applications include first and second hyperpolarizabilities, Faraday, Buckingham and Cotton-Mouton effects as well as Jones and magneto-electric birefringence... 

Besides being enormously expanded and spheroidal, the mucins also appear very flexible evidence for this derives from the ease with which these molecules are deformed with shear, as shown in streaming-birefringence experiments, from the concentration dependence of viscosity, and the temperature-dependence of sedimentation coeflScients. Mikkelsen and co-workers confirmed these observations by using the dependence on field strength of electric birefringence relaxation-phenomena. Evidence for local flexibility in the carbohydrate side-chains has come from, for example, n.m.r.-spectral studies. ... 

In solutions and suspensions of anisotropic molecules directing external forces such as a hydrodynamic flow or electric field forces may cause signal changes 55 originating from molecule rotations. In particular optically and electrically anisotropic (dipolar or polarizable) macromolecules exhibit major electric dichroism and electric birefringence. 

In this paper, the optical anisotropy and dipole motnent experimentally determined from flow birefringence and electrical birefringence (the Kerr effect) were used for the quantitative evaluation of the degree of intramolecular order of the molecule. 

Fig. 3 shows the experimental dependences of the ratio of electric birefringence An at the field frequency V to the value of An<. Physically, this phenomenon means that the orientation of molecules of mesogenic polymers is of the dipole type the molecule is oriented in the electric field as a whole. 

Sauer and Calvin (1962) demonstrated the orientation of some pigment molecules in spinach quantasomes. These particles exhibit electric birefringence and electric dichroism. Thus the orientation of pigment molecules is not solely related to the whole lamellar system, but is a property of the basic macromolecular particle involved in quantum conversion. 

Another technique to study the dimensions of macromolecules on the basis of their charge properties is electric birefringence. In flow birefringence macromolecules were aligned with the help of hydrodynamic shear. In electric birefringence an electric field is used to align the macromolecules and the alignment is determined by the electrical properties of the molecules. 

In addition to the substantial literature on solvent and small-molecule translational diffusion, there is also a significant literature on small-molecule rotational diffusion. Experimental methods that report rotational diffusion behavior include VH tight scattering, as examined in different time domains with Fabry-Perot interferometry and photon correlation methods, nuclear magnetic resonance, oscillatory electrical birefringence, and time-resolved optical spectroscopy. 

Quadratic Kerr effect has been mainly studied in polydiacetylene solutions and gels (Kapitulnik et al.(1984), Lim and Heeger (1985) Lim et al. (1985) Kapitulnik et al. (1986)). Strong electric birefringence was observed with large rotational diffusion constants (t 0.1 -r 0.2 s), characteristic for very long molecules. 

---