Monte Carlo evaluation of hydrocarbon chain molecules' shape

The study of the physical and chemical properties of hydrocarbon chain molecules is very important for the development of many technological areas and for a better understanding of the structural features and functioning of various biological systems. In describing various phenomena (the viscous flow of molecules, adsorption on surfaces, absorption and diffusion in porous systems, etc.), it is important to take into account the shape of the molecules. In the present work, the conformational behavior of 65 chain hydrocarbon molecules of the following structure was studied by the Monte Carlo method at temperatures T = 293, 303, and 313 K: CH3- (CH2) a- (CH2-CH2-CH2) d- (CH2) b-CH 3 (where a, b, d are integers); the number of carbon atoms in the backbone of the chains N = 16, 18, 20, 22, the number of cis-double bonds d = 0, 1, 6. Prototypes of molecules are the residues of fatty acids of phospholipid molecules. The simulation of all molecules was carried out in a uniform manner, in the unperturbed state, a "classical flexible model" of the chain was used. When generating the values ​​of torsional angles, the significant sample method was used in the range 0-360 °, taking into account the interdependence of each three angles along the chain. Approximation of the conformations of each molecule by rectangular parallelepipeds was carried out and the average characteristics of the form ("spins") were calculated. The dependences of the calculated characteristics on the number of carbon atoms in the chain, the number of double bonds and their positions in molecules (the relationship between structure and properties) are studied. They are based on the characteristic features of internal rotations in the chains of the chemical structure under consideration.