To understand of the mechanism of self-assembly of DNA base molecules on the Au(111) surface, molecular dynamics simulations of different surface coverage of guanine, adenine, cytosine, and thymine molecules at 300 and 400 K are performed. At low coverage, guanine, adenine, and thymine form hydrogen bonded chains on the surface, while cytosine molecules cluster into islands. At larger coverage, simulations indicate that adenine molecules form ordered two-dimensional hexagonal structures, while guanine, cytosine, and thymine molecules aggregate into small random clusters. These observations agree with scanning tunneling microscopy (STM) experiments of the DNA bases on gold surfaces. The simulations show that arrangement of the molecules on the gold surface is controlled by baseÀbase interactions. The hydrogen bond interactions and stability of baseÀbase homopairs, which are the smallest components of the self-assembled structures on the Au(111) surface, are calculated and compared with calculations of the homopairs in the gas phase and with values available in the literature. The binding energies per base on the surface initially decrease in magnitude with increasing surface coverage and then reach a constant plateau at large coverages. The mechanisms of molecular mobility for the bases with one and two molecule coverage on the surface are analyzed at two temperatures.

To study the type, nature, and amount of interactions in binary systems including 1-hexyl-3-methylimidazolium nitrate ([Hmim]­[NO3]) ionic liquid and a homologous series of 1-alkanols (1-hexanol up to 1-decanol), some thermophysical properties via density and viscosity measurements were calculated at temperatures of 293.15–323.15 K. Also, to study the behavior of systems with temperature, values of the thermal expansion coefficient, α, excess thermal expansion coefficient, αE, isothermal coefficient of excess molar enthalpy, (∂H m E/∂P) T,x , and partial molar volume, V̅ i , for five binary mixtures at various temperatures were calculated. Findings demonstrate that strong interactions between the mixture components occur and intermolecular forces become weaker with the increase in the length of the alcoholic chain and temperature. For a theoretical study of mentioned mixtures, perturbed-chain statistical associating fluid theory was implemented. The density and partial molar volume of mixtures were correlated and predicted by this theory, and the results show that outcomes are fairly consistent with the experimental data.

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