Abstract
Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H2O2) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H2O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H2O2 as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H2O. In the case of H2O2 as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different.
Highlights
In the last decade, the development of drug-like cocrystals became one of the topical issues in pharmaceutical chemistry [1,2,3], owing to a possible synergetic effect of their components [4]
In accordance with the literature data [32], the enthalpy of hydrogen bonds (H-bonds) formed by H2O as a proton acceptor is systematically higher than the analogous values of H-bonds formed by H2O2. As it follows from the data (Table 1), the value of the enthalpy of the bifurcate H-bond formed by the OH group is significantly higher than the enthalpy of the ordinary H-bond formed by another OH group of H2O or H2O2
After excluding crystals with structurally disordered H2O2 molecules, crystals in which H2O2 molecules directly interact with the Li+, Na+, K+, NH4+ ions or with other H2O2 molecules, the number of analyzed peroxosolvates decreased to 38
Summary
The development of drug-like cocrystals became one of the topical issues in pharmaceutical chemistry [1,2,3], owing to a possible synergetic effect of their components [4]. The energy/enthalpy of H-bonds in peroxosolvates composed by H2O2 as a proton donor is usually greater than the corresponding EHB/∆HHB of H-bonds formed by the H2O molecule [15,32]. An accurate comparison of the energy of the H-bond formed by H2O and H2O2 as acceptors of protons in the solid state involves the study of multicomponent organic crystals that form isomorphic (isostructural) hydrates and peroxosolvates. [15,32] in isomorphic crystalline hydrates and peroxosolvates of several amino acids These studies show that the hydrogen peroxide molecule usually forms shorter (strong) donor H-bonds than the water molecule. As it follows from the data (Table 1), the value of the enthalpy of the bifurcate H-bond formed by the OH group is significantly higher than the enthalpy of the ordinary H-bond formed by another OH group of H2O or H2O2
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