Red Dichroism in Protein Studies

The NH deformation modes behave similarly, and in this case the a-form has perpendicular dichroism and the /3-form parallel dichroism. Similar data can also be obtained from the 4810 cm  

This interpretation of the results in which only a single form of hydrogen bond is proposed for a-keratin and similar structures was criticised by Darmon and Sutherland [6] as an over-simplification, and they point out that the attachment of numerical values to dichroic ratios is hazardous in view of the discrepancy between the small dichroic ratios found for NH in a-keratin and nylon and the large ratio to be expected [6]. 

The need for caution in the interpretation of polarisation studies is indicated by the recent work of Fraser and Price [59]. They point out that the transition moment of the carbonyl stretching mode responsible for the amide I absorption will be displaced from the CO direction due to interaction with the C—N vibration, and to an orbital following effect. They have calculated the dichroism of an oriented polypeptide in which the chains have the configuration of Pauling and Corey [60] with a 3.7 residue helix, and have shown that if allowance is made for a displacement of the CO transition moment by 20° towards the NO, the dichroic value obtained is very close to that observed experimentally [54]. The objection to the 3.7 helix based on polarisation studies [61] cannot therefore be maintained. 

Randall, Fowler, Fuson and Dangl, Infra-red Determination of Organic 

Bamford, Brown, Elliott, Hanby and Trotter, Proc. Roy. Soc., 1953,141B, 

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