Elena F. Quantum-chemical analysis of cluster formation of a-amino acids at water/air interface

The results of quantum-chemical calculations within the frameworks of semiempirical method РМ3 of the enthalpy, entropy and Gibbs' energy of formation and clusterization of a-amino acids at the water/air interface are presented in this thesis. Spontaneous cluster formation threshold either for enantiomerical pure or racemic a-amino acids is 11-12 carbon atoms in the molecular chain at 278 K. These values agree well with existing experimental data.The results of quantum-chemical calculations shows that the geometric parameters of the unit cell of the substituted alkanes (including a-amino acids) are determined by the 'a' type of intermolecular CH-HC-interactions, and the tilt of moleculas with respect to the interface is defined by the volume and structure of the functional groups. Calculated parameters of the unit cells of the homo- and heterochiral monolayers of a-amino acids agree well with existing experimental values. The usage of the superimposed-additive approach shows that values of enthalpy, entropy and Gibbs' energy of formation and cluster formation of a-amino acids can be calculated as sum of corresponding values of amines and carboxylic acids deducting corresponding values of alkanes.