Speech:

The Potential Energy Landscapes of Biologically Relevant Molecules Revealed by Matrix-Isolation Infrared Spectroscopy and Quantum Chemical Calculations

Abstract
The importance of molecular conformations in biochemistry (as in chemistry and physics) is well accepted. The conformations assumed by the molecules and their associated potential energy landscapes determine, for instance, catalytic mechanisms in enzymes, antifreeze cryoprotectants efficiency or membrane properties, and are the basis of the general phenomenon of molecular recognition. Conformational changes are key events in the vision process, in the control of membrane permeability and different mechanism of molecular transport in cells. Protein folding is controlled by conformations of the constituting amino acids, and the preferred spatial arrangements of the nucleic acid bases are also essential in determining the functioning of these later.

Conformational studies on small molecules which are the fundamental constituents of biomolecules (like the above mentioned amino acids and nucleic acid bases) or that exhibit pharmacological activity, have been providing the basis for our understanding of the structures and mechanisms of functioning of the complex biochemical systems and drugs.

Since its invention by George Pimentel in 1954 [1], matrix isolation has been given an enormous contribution to the study of molecular structure and reactivity. Investigation of thermal and light-induced reactions of biologically relevant molecules in cryogenic matrices is nowadays a hot topic of research [2], in particular because these studies can shed light on important details of their mechanisms of action. The success of this approach may also be partially ascribed to the concomitant development of computational chemistry, which provides sound theoretical foundations for the interpretation of the experimental data (and also to the availability at relatively low cost of tunable lasers, which can be used as adequate irradiation sources to investigate specific processes in an elegant and powerful way).

In this lecture, besides a general introduction to matrix isolation, a series of case studies will be presented which illustrate the use of the method in the investigation of the potential energy landscapes of a series of judiciously chosen representative biologically relevant molecules. The relevance of such potential energy landscapes in determining the thermal reactivity or the light-induced processes (either triggered by UV-visible or IR light) will be emphasized.