Near Infrared Spectroscopy in Structural Problems of Biochemistry
Near infrared spectra have found biochemical applications in equilibrium and in kinetic problems. The region of the spectrum between 1.4 and 1,6 μ is especially useful for following transformations of —NH or —OH groups. The particular chemical state of these groups can be readily identified by the positions of the absorption maxima due to the first overtone of their stretching vibrations. Relative proportions of species can be evaluated from extinction coefficients which can be accurately determined. The equilibrium state of the peptide unit in a number of synthetic polyamino acids (poly-L-alanine, poly-l-leucine, poly-l-methionine, and polybenzyl- L-glutamate) has been followed as a function of solvent composition under conditions where the transitions in other physical properties of these polymers have been interpreted as simple peptide hydrogen-bonded helix to coil transitions. Spectral data demonstrate that these conversions involve protonated peptide species and are far more complicated than has hitherto been assumed.
KeywordsNear Infrared Spectroscopy Peptide Residue Inert Solvent Polyglutamic Acid Methyl Morpholine
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