Moffitt—Yang equation

At first, estimations were carried out by using optical rotatory dispersion (ORD) this was necessary because of instrumental limitations. Conventionally, the Moffitt-Yang equation [Eq. (23)] can be modified to ... 

Another important factor for the polymer conformation is the solvent effect. As the usual solvents for the copolymers in question are DMSO and DMF, which have absorption in the UV region, CD spectral measurements are impossible. However, the optical rotation measurements and analyses using the Moffitt-Yang equation give the Moffitt parameter bo for the copolymers (Table 21). Hie parameter is known to be related to the helix content of poly-(a-amino acids). The b0 value of polycarboben-... 

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. 

Parameters of the Moffitt-Yang Equation for Several Proteins in Alcohol or Dioxan Solution ... 

Experiments with poly-a-amino acids or proteins have been in perfect agreement with the above when A0 = 212 nm and b0 = —630. Equation (23) is also called Moffitt s equation or Moffitt-Yang s equation. 

Figure 12.3 shows a typical rotatory dispersion curve, where there is no maximum or minimum. Figure 12.4 shows a plot of m versus X, in which a protein in denatured form is compared with the same protein in native form. The plot of the Moffit-Yang equation s shown in Rgure 12.5. If a synthetic polypeptide is in a random conformation, the rotatory dispersion, which is simple, may be adequately expressed by a one-term Drude equation. If a synthetic polypeptide is in an ot-helical conformation, the Moffitt-Yang plot may be employed to describe the rotatory dispersion. 

The equation of Moffitt and Yang (1956), although without adequate theoretical basis (Moffitt et al, 1957), does describe the optical rotatory... 

In order to apply this general relationship to the empirical data of helical polymers, Moffitt and Yang (1956) then developed a phenomenological equation in which the above sums are replaced by single terms and thus derived an expression that is analogous to the simple Drude equation. 

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-... 

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