INTERNAL-ROTATION IN AURAMINE-O

The fluorescence quantum yield and excited singlet state lifetime measured for Auramine O in different alcohols increase with increasing microviscosity of the solvent. The results can be explained quantitatively in terms of current theoretical models in which internal rotation of the N,N-dimethyaniline groups is an activationless process controlled entirely by viscous flow. Auramine O binds to deoxyribonucleic acid (DNA) and horse liver alcohol dehydrogenase (HLADH) in neutral aqueous solution, Binding to DNA is accompanied by modest increases in fluorescence yield and lifetime of the dye whereas binding to HLADH facilitates a dramatic increase in fluorescence. There appear to be two binding sites for Auramine O on the protein, and in one particular site the conformation of the dye is essentially frozen in a form unfavourable for rotational diffusion.