Raman Spectral Optical Activity Induced in Azo Dyes by Formation of Complex Compounds with Bovine Serum Albumin

Abstract

The vibrational optical activity due to the chirality induced in biphenyl-type azo dyes by the interaction with bovine serum albumin (BSA) or human serum albumin (HSA) was measured with the Raman optical activity (ROA) method. The induced chirality was examined by use of the circular dichroism (CD) method. The induced chirality is found to vary remarkably among the dye-albumin combinations this is at variance with the reported experimental observation that the binding of azo dyes with albumins is in general nonspecific. The induced chirality is most intense for the BSA-trypan red (TR) system. The intensity of the induced CD for this system reaches a maximum for a BSA/TR molar ratio of 1. Raman and ROA measurements were then carried out for BSA-TR system (1/1), making use of the intensity enhancement due to the resonance Raman effect. The SO₃^- stretching Raman band clearly changed upon complexation, suggesting that the SO₃^- group plays an important role in the formation of the complex compound of BSA and TR. Reproducible ROA signals were obtained in the wavenumber region of Ph-N =stretching and SO₃^- stretching vibrations, but no ROA signal was observed for azo group vibrations. These results indicate that the vibrational optical activity in this case originates from twisting in the biphenyl moiety of the dye molecule by the BSA-TR complex formation.