Dielectric increments

For glycine, it is known that the dielectric constants of water increases rapidly and linearly with the concentration of the amino acid, reaching a value of about 135 at a concentration of 2.5 mol liter" at 25 C. D is given by D = 78.54 + 22.58C, where 78.54 is the measured value of D for pure water, 22.58 is the numerical value of the dielectric increment, and C is the concentration in mol/liter. This great increase of D reflects the extremely large moment of glycine as a dipolar ion, and the linearity of the relationship represents the proportionality between D and polarizability that is characteristic of strongly polar media. 

When an alternating electric field of small amplitude is applied, we can measure the chemically induced complex dielectric increment (e )ch = ( )ch — i(e")ch [i = (— 1)1/2] as a function of frequency to. It can be shown (124) that t is then given by... 

From another point of view, the dielectric increment, Aer> of the p relaxation process is 0.52, which is much smaller than the one calculated for... 

Fig. 29. Dielectric increment (Ae) and intensity of o-Positronium (IQ ps) versus surfactant concentration (top AOT/C6H6, bottom DAP/C6H6) at 25 °C. Helv. Chim. Acta 61, 2258 (1978)]...

This technique represents a novelty among the many methods used to investigate nonpolar detergent solutions. It appears that, similarly to the dielectric increment determinations, the system is not disturbed by the measurements and is, therefore, particularly suited to detect characteristic parameters of the system. This technique1, already well-known in other areas of physical chemistry, has recently been introduced by Ache and coworkers100, 101 to the study of aqueous and nonpolar micellar systems. 

Very recent studies52 compared dielectric increment, Ae with I2 changes in the system DAP and AOT in benzene, see Fig. 29. The coincidence of the breaks in the corresponding curves is remarkable. It appears, however, that the drop in the Ae-curve is more distinct in the AOT/benzene system as compared with DAP/benzene. 

The case of DNA in the double helix form is of especial interest because dipoles along the oppositely directed helical strands cancel to leave little or no resultant dipole moment. The observed dielectric increments, i.e., excess of permittivity over that of solvent water,are very large, however, and reach a static value only at audio or subaudio frequencies, showing the necessity of some mechanism of considerable charge displacements which develop slowly. 

The effect of divalent ions such as SO4 " has been studied either by electric permittivity techniques, or by viscosimetry. It was experimentally observed that the dielectric increment is larger than in the presence of monovalent ions. In the presence of the bivalent counterions there are two opposite effects. From one hand, the bivalent ions tend to increase the dielectric increment through a charge effect, while from the other hand the observed reduction of the viscosity proves that in the presence of SO4 - the polyions contract76). 

Hydration Numbers from Dielectric Increment Measurements... 

In the further elaboration two different types of conductivity and dielectric increment can be introduced, viz., with respect to od and with respect to the volume fraction (p of the colloid. (In static experiments only the latter is relevant). Regarding the former, we can write... 

Table 7 Comparison of dielectric increments (T calculated from equation (37)...

The quantity Asj, = — stands for the (total) dielectric increment of the dispersion effect. The relaxation spectrum is characterized by the parameter h whidi satisfies the condition 1 > > 0 and by a special... 

The same mechanism must in prindple apply to globular proteins. However, because of the small dimensions of these biopolymers the dielectric increments are of comparatively small magnitude. Furthermore, their dispersion falls in the same frequency range as that of the rotational polarization mechanism of permanent dipole moments. Since the latter is apparently predominant, it would be difficult to distinguish the coimterion effect. 

V = the Laplacian operator). For small values of/x ykr these differential equations can be solved without serious difficulties. After evaluation of the distribution of the polar molecules, the corre onding complex dielectric increment follows as ... 

A detailed theoretical discussion of the problem can be found elsewhere. The complex dielectric increment due to the orientation of permanent dipoles (exc t those eventually present in HA and A ) turns out to be... 

By means of equation (1) the total dielectric increment due to the chemical effect may be expressed as... 

This result has been confirmed by a correlation-function treatment/ For sufficiently fast rotational relaxation (i.e. Tch tj) we apparently obtmn Ta K T so that dielectric dispersion is controlled by Tr only. Equation (71) then becomes the dassical expression of (31) and (32). A measurable dielectric increment controlled by chemical relaxation may, however, be detected if Tch S tt- Its absolute magnitude wUl be proportional to... 

In the same frequency range, the dispersion of the dielectric increment Ae of solution can be observed. The curves of dielectric dispersion almost coincide with the dispersion curves for EB (Fig. 59) so that both mechanisms of molecular motion are identical and are represented by dispersion Eq. (81) for kinetically rigid mol ules. 

Dielectric Increment 8D (M)for Glycine in Aqueous-Organic Mixtures as a Function of Temperature"... 

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