The applicability of two frequently used interaction potentials for water, the five-site ST2 model and the four-site TIP4P model, is investigated in computer simulations of water droplets of varying cluster size from N=64 to N=512. The orientation of the water molecules in the surface region is investigated for the both models. Surface properties, such as work of cluster formation, local density profiles, kinetic and total energy profiles, and pressure profiles as a function of the droplet size, obtained using the two models are compared. Moreover, the surface potential and the electric potential profiles are calculated. Surface tension is calculated and its dependence on the cluster size is investigated. It is found that surface properties are very sensitive to the used potential models. For example, the water molecules are found to lie differently in the inner region of the surface layer, the ST2 molecules being predominantly perpendicular to the surface, while the TIP4P molecules lie mainly parallel to the surface. In the outer surface region, the molecular planes are perpendicular to the surface for the both models. The TIP4P model allows a calculation of the surface tension, giving a value 54 mN/m which is somewhat lower than the experimental value for the plane surface, while for the ST2 model, larger clusters are needed than those treated in the present study.

Clusters containing 64 molecules of water or bromine were investigated by the molecular dynamics method. Several water models and a bromine model were taken into consideration in order to test the modern theory of the surface potential of polar liquid and to find out the dipole and quadrupole contribution to this potential. The results of the simulations confirm strongly the theoretical conclusion that equally with the dipole contribution there is a purely quadrupolar contribution to the surface potential.

Methanol clusters have been studied based on Molecular Dynamics simulations. The methanols are described using the three-site OPLS potential model by Jorgensen. Five separate clusters with sizes up to 512 molecules are treated at two different temperatures, 200 K and 300 K, respectively. Several properties, for example, the local density, electric potential and the normal pressure, are calculated. Also, the surface potential of methanol is computed, based on the radial profiles of the electric potential. It is shown, once again, that the quadrupolar contribution to the surface potential is important to the total value of the surface potential. Using the size dependence of the work of cluster formation, it is found that the surface tension of methanol decreases monotonously upon decreasing the radius of the dividing surface approaching a limiting value. The calculated limiting value for surface tension agrees well with that, observed experimentally for the plane surface of methanol.

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The reactions of hydroxymethylcubanes with nitric acid result in the respective nitroxy methylcubanes.The search for the drugs to treat cardiovascular and oncological diseases is currently highly topical. The prepa ration of new polyfunctional compounds, study of their structures and properties will allow expansion of the spec trum of exogenous NO donors as potential drugs.Nitrates (or nitroesters) are a well known class of or ganic substances the pharmacological activity of which is determined by their metabolism with NO liberation (see Ref. 2). They include such compounds as Nitroglycerin, Nitrosorbide, Erinite, and others, which are commonly * For Part 9, see Ref. 1. † Deceased. Scheme 1used to treat ischemic cardiovascular diseases, for ex ample, stenocardia. It is known that cubane derivatives also show rather high anti ischemic activity. 3,4With the aim of search for new anti ischemic drugs, we performed the synthesis of nitroesters of the cubane series.Previously, 5,6 it has been shown that the reduction of dimethyl cubane 1,4 dicarboxylate (1a) and methyl 4 bromocubane 1 carboxylate (2) afforded 1,4 bis (hydroxymethyl)cubane (3) and 4 bromo 1 hydroxy methylcubane (4). In the present work, 1,4 bis(nitroxy methyl)cubane (5) and 4 bromo 1 nitroxymethylcubane