Moffitt equation coils

The origin of nonzero bo values in these cases is not entirely clear, but it can be formally traced to the difference between Xo and values for the simple dispersion of random coils and hence to a failure of the assumption that Xo equals Xo. If K equals Xo, then the first term of the Moffitt equation will of course be the same as the simple Drude expression known to describe the data and, there being no necessity for a second term, bo will vanish. However, if Xo differs from Xo, the Moffitt plot may still be linear but with a nonvanishing slope. Thus dispersion data that are simple when referred to one dispersion constant may appear complex when plotted against another by a form that sees matters as complex, thereby generating what may be properly suspected as pseudocomplexity. The Moffitt equation was initially intended to describe the complex dispersion of polypeptides for which the simple Drude equation is inadequate, but, as will be seen, its form is also applied to protein dispersions which can be expressed equally well by either formula. It is therefore important to examine more fully the relation of the two equations for cases in which both fit the data. 

G. The Moffitt Equation for Mixtures of Helices and Random Coils... 

This equation for the mixture is thus of Moffitt form and is characterized by coefficients each of which is a linear function of / and the constants appropriate for a complete coil and a perfect helix. That [m ]x is also a linear function of / and constants pertaining to the two forms is shown by recasting Eq. (30) in terms of alone. 

On the other hand, the dispersions obtained by Yang and Doty (1957) for poly-y-benzyl-L-glutamate in a mixture of /3-forms and coil forms did not obey the simple Drude equation, and Imahori s analysis of these data yielded positive Moffitt slopes and intercepts after corrections had been made for the intrinsic residue contribution (Imahori, 1960). Imahori has moreover found that denatured bovine serum albumin and ovalbumin in solution display positive ba and corrected ao values in sharp contrast to the negative slopes characteristic of the native proteins and has in addition been able to correlate the positive slopes with the /3-form in the protein precipitates by infrared spectra. Wada et al. (1961) have recently carried forward this suggestion that the (8-conformation displays complex disper-... 

The dependence of the molar optical activity of coils on the wavelength of polarized light can be described by a one-term Drude equation. In the case of helices, the Moffitt-Yang equation is better. The constants Xo are completely unaffected by the solvent, while aa and ba assume different values (Table 4-9). For a given polymer in different helicogenic solvents, bo is found to be more or less constant, while m still depends on the solvent. For various poly(a-aminocarboxylic acids), bo has approximately the same value so long as these are in the helix conformation, bo is therefore a typical constant for the helix conformation of poly(a-aminocarboxylic acids), while gq contains contributions from the helix and the asymmetric carbon atoms. 

The dependence of the molar optical activity of coils on the wavelength of polarized light can be described by a one-term Drude equation. In the case of helices, the Moffitt-Yang equation is better. The constants Aq are completely unaffected by the solvent, while Oq and Bq assume different values (Table 4-10). For a given polymer in different helicogenic solvents. 

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