Quantum Chemical Analysis of Thermodynamics of 2D Cluster Formation of n-Thioalcohols at the Air/Water Interface

Abstract

The semiempirical PM3 method is used to calculate the thermodynamic parameters of the formation of monomers, dimers, trimers, tetramers, and one of the possible hexamers of saturated thioalcohols with normal structure and alkyl chain lengths of 6-16 carbon atoms. The dependencies of the potential energy surfaces on the torsion angles for monomers and dimers of normal thioalcohols are calculated. The most stable conformations of monomers and dimers are determined and used to construct the structures of trimers, tetramers, and larger clusters. For various conformations of dimers, trimers, tetramers, and for the hexamer, the thermodynamic parameters of clusterization (enthalpy, entropy, and Gibbs energy) are calculated. It is found that these parameters are stepwise-dependent on the alkyl chain length. It is shown that a two-dimensional square-symmetric infinite cluster and clusters constructed on the basis of cyclic trimers are formed for alkyl chain lengths of 14-15 carbon atoms and above.

Simplified method of the quantum chemical analysis for determination of thermodynamic parameters of 2D cluster formation of amphiphilic compounds at the air/water interface

“…In our previous studies, the thermodynamic parameters of the clusterization process were calculated for saturated alcohols [6,7], carboxylic acids [8], thioalcohols [9], and amines [10]. In the present work, we introduce a simplified approach for the estimation of thermodynamic parameters of clusterization of amphiphilic compounds at the air/water interface, being in general agreement with the thermodynamical parameters of clusterization calculated earlier for certain classes of amphiphiles.…”

“…Using the additive schemes on the basis of the calculated thermodynamic parameters of clusterization for these classes of compounds (see Refs. [6][7][8][9][10]) enabled us to calculate the clusterization parameters for the clusters of the studied structures and any size, including the infinite clusters. For all classes of compounds mentioned above, the thermodynamic parameters of the formation and clusterization of dimers, trimers and tetramers were calculated (for the total of 317 compounds, including the corresponding monomers).…”

“…In particular, the contributions from one intermolecular H-H interaction to the variation of standard enthalpy and entropy of cluster formation are: −9.20 ± 0.08 kJ/mol and −18.40 ± 0.60 J/(mol K) for alcohols [6], −10.20 ± 0.15 kJ/mol and −23.16 ± 0.75 J/(mol K) for carboxylic acids (for the alkyl residue the parameters used in Ref. [8] were those relevant for the alcohol residue), −10.31 ± 0.11 kJ/mol and −21.29 ± 1.17 J/(mol K) for thioalcohols [9], and −10.35 ± 0.04 kJ/mol and −27.34 ± 1.09 J/(mol K) for amines [10].…”

“…frequencies are disregarded. Therefore, similar to our previous papers, these contributions were manually calculated [6][7][8][9][10].…”

Theoretical description of 2D-cluster formation of nonionic surfactants at the air/water interface

“…Assuming that adjacent atoms contribute to the maximal increment in the energy of the intermolecular interaction, we demonstrated in refs. [32,104,149,196,[198][199][200][201] that the interaction between two next-neighbor surfactant molecules can be expanded into the sum of increments contributed by the pairwise interactions between the nextneighbor methylene units and between the next-neighbor functional groups. The structure of the hydrocarbon substituents is like as the terminal interacting atoms of the methylene units are hydrogen atoms.…”