From Quantum Chemistry to Quantum Biochemistry

Three periods may be discerned in the development of quantum biochemistry. In the first, simple Hückel theory was applied to conjugated units of biochemical interest. Despite the simplicity of the method, careful analysis has allowed the interpretation of a considerable number of experimental facts, and also a number of predictions. The second stage is linked to the development of all‐valence‐electron and all‐electron theories and techniques. Now the electronic structure of saturated and partially saturated – biomolecules could be investigated, as well as the large field of conformational problems. The third, and present, period is concerned with the study of environmental effects, in particular solvent effects, on molecular structure and properties. Efforts in this field are developing along two lines: one is the “traditional” continuum model which attempts to account for the bulk effect of the medium; the second employs a model that combines the interacting entities as a “supermolecule”. The “dipeptide” protein model, the backbone of nucleic acids, the polar heads of phospholipids, have been subjected to an analysis of the second type. As for proteins, a conclusion of conceptual significance could be arrived at, namely, that the “protein effect” does not create “extraordinary” conformations. In other words sites of attack on biomolecules can be determined through evaluation of molecular electrostatic potentials.