Non covalent interaction of small ligands with large biomolecules is at the basis of most fundamental processes in cell biology and many pharmacological and biotechnological applications.  Understanding the interplay between the two molecular partners and the possible chemical consequences requires the characterization of the complexes as individual species and, in particular, the determination of their structure. In the presence of ligands with photoactive chromophores this information  is a prerequisite, for example, for the control of drug phototoxicity  and development of new photoactivated therapies. 

We have recently developed  an approach aimed at a  structurally based understanding  of the mechanism of light induced processes in biomolecular complexes, based on the combined application of a variety of experimental techniques (spectroscopic, photochemical, analytical, microcalorimetric) and methods of computational modelling.  The interaction  of selected derivatives of important drug families (arylpropionic acids, quinolones, anthracyclines, chalcones, porphyrin-like derivatives) with albumin and telomeric DNA will be described. Reliable structures for the protein complexes in solution have been obtained by the combination of  circular dichroism and  quantum mechanical estimation of rotational strengths.  Control of photofragmentation, photobinding, photoinduced electron transfer and energy transfer processes by the biomolecular matrix will be illustrated