Structure and State of Water in Branched N-Vinylpyrrolidone Copolymers as Carriers of a Hydrophilic Biologically Active Compound

Hydrated copolymers of N-vinylpyrrolidone (VP) with triethylene glycol dimethacrylate as a promising platform for biologically active compounds (BAC) were investigated by different physical chemical methods (dynamic light scattering, infrared spectroscopy, thermal gravimetric analysis, and differential scanning calorimetry) and the quantum chemical modeling of water coordination by the copolymers in a solution. According to the quantum chemical simulation, one to two water molecules can coordinate on one O-atom of the lactam ring of VP units in the copolymer. Besides the usual terminal coordination, the water molecule can form bridges to bind two adjacent C=O groups of the lactam rings of VP units. In addition to the first hydration shell, the formation of a second one is also possible due to the chain addition of water molecules, and its structure depends on a mutual orientation of C=O groups. We showed that N,N-dimethylbiguanidine hydrochloride (metformin) as a frontline drug for the treatment of type 2 diabetes mellitus can be associated in aqueous solutions with free and hydrated C=O groups of the lactam rings of VP units in studied copolymers. Based on the characteristics of the H-bonds, we believe that the level of the copolymer hydration does not affect the behavior and biological activity of this drug, but the binding of metformin with the amphiphilic copolymer will delight in the penetration of a hydrophilic drug across a cell membrane to increase its bioavailability.