Band assignments peptide groups

The amide V mode, which seems to be very sensitive to chain conformation, is found as a strong IR band at 708 cm" and is fairly well predicted by the calculation. Its assignment to the Bu(l) species is likely on the basis of the structure, but it could also have an Au( ) component because of the orientation of the peptide group this can be decided only from polarized IR spectra on an oriented sample. 

Band assignments have been made by using the criteria given previously. In addition, Type-D frequency (1680-1610 cm" ) was introduced to denote the peptide carbonyl group. The exact frequency of this group depends on the nature of the neighboring groups. 

Band Assignments for Peptide Groups as Delineated by K.T. Hecht and D.L. Wood... 

The three aromatic amino acids (Phe, Tyr, Trp) have side-chain groups corresponding to the benzene, phenol, and indole chromophores, respectively. The spectroscopic properties of the rat transitions in these chromophores have been reviewed.136-381 Coupling of aromatic transitions among themselves and with peptide transitions can give rise to CD bands in the near and far (k < 250 nm) UV. Near-UV CD bands are useful indicators of the environment of the aromatic chromophores and can frequently be assigned to specific types of side chain, based upon band position, presence of vibrational fine structure, etc. Far-UV CD bands due to aromatic side chains, except for the La band of Tyr (-230 nm) and the Bb band of Trp (-225 nm), are generally difficult to resolve from peptide CD bands and can complicate the conformational analysis of peptides. 

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