A spectroscopic technique for measuring slow rotational diffusion of macromolecules. 1: Preparation and properties of a triplet probe.

Slow rotational diffusion may be investigated by measuring the decay of dichroism of flash-induced transient absorption changes of suitable probes. The preparation of the covalent "triplets" probe eosin isothiocyanate is described together with investigations of spectroscopic properties of eosin-protein conjugates. Triplet state lifetimes of air-equilibrated solutions of eosin-protein conjugates are in the order of 10 mus, demonstrating that the probe is protected from oxygen quenching by the protein. Experiments with the sucrase-isomaltase complex from small intestine show that its enzymatic activity is little affected by binding up to 2 mol of eosin/mol of protein.