Other Studies on Proteins and Related Substances

One of the features of ATR spectroscopy is that the depth of penetration d of the radiation incident on the sample is a function of the wavelength according to the following equation (Harrick, 1963)  

It should be noted that all the frequencies reported by Baddiel are corrected frequencies, that is, corrected to correspond with transmission data, since differences were constant and empirical adjustments could be made (ATR frequencies were always lower by 3-4cm in the 3333cm region and 2-3cm in the 1667 to 1250cm region). 

Absorbance at the 1710 cm absorption maximum was calculated by the peak-height method. In this case, the peak-height method had a distinct advantage over the peak-area method because near the carboxyl peak there would have been a negative difference spectrum, due to carboxylate ions, at 1550cm , and the area of the peak could have been complicated by this factor. 

The determination of AT-terminal amino acids of polypeptides or proteins by means of reaction with 2,4-dinitrofluorobenzene is used as a chemical method for the estimation of molecular weight. This operation is rather complex because of the need for hydrolysis, separation of DNP-amino acids, and colorimetric comparison with a standard curve. Schiedt and Restle (1954) have estimated the degree of polymerization of oligopeptides using dinitrophenylation and infrared spectroscopic 

The determination of molecular weight by measurement of the integrated absorbance of functional groups introduced by forming chemical derivatives has been described by O Brien and Swindlehurst (1967). 

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