Quantum Chemical Modeling the Structure of Complexes of Copolymer of N-Vinylpyrrolidone and Triethylene Glycol Dimethacrylate with Metformin

The structure of metformin (dimethylbiguanide) complexes with the copolymer of N-vinylpyrrolidone and triethylene glycol dimethacrylate in aqueous solutions is studied by means of DFT (Gaussian 09 software; TPSSh functional; 6-31G*//6-311++G** basis set) and the QTAIM model (AIMALL software). It is shown that both metformin and water molecules coordinate via the oxygen atom of the С=O bond of lactam rings, and that this process is exothermic. One oxygen atom can coordinate one or two water molecules, and water can form bridges connecting two adjacent C=O groups in addition to common terminal coordination. The formation of the second hydration shell after the formation of the first is possible due to the chain addition of water molecules; its structure depends on the mutual orientation of the С=О groups. It was shown that metformin is oriented with respect to electron donor groups in a strictly determined way; it can displace water upon coordination with the copolymer.