The O1/H3-preferred 1:1 H-bonding and the electron-cloud migration induced by H-bonding or non-specific interactions: A systematic study on the interactions between dimethyl phthalate and 1-, 2- or 3-alkanol (C2-C6)

Add time:07/29/2019    Source:sciencedirect.com

H-bonding and non-specific interactions between dimethyl phthalate (DMP) and different human body substances were considered to be mainly responsible for various health dysfunctions. However, the manner of H-bonding and the adaptability of the structure of DMP that may underpin the H-bonding/non-specific interactions have been difficult to assess and remain elusive. In this study, we set out to gain an insight into the subjects above through a systematic investigation on the interactions between DMP and 1-, 2- or 3-alkanol (C2 - C6). We calculated the H-bond distances, the CO and CO bond lengths and other selected structural essentials at B3LYP 6-311G(d) level. We recorded the infrared spectra Band I and Band II of CO of DMP when dissolving DMP into 11 different alkanol/n-Hexane binary solvent systems. We created and fit the equations to delineate the dependence of the absorption intensity ratio of Band II to Band I (AII/AI) on the volume-ratio of the alkanol component (x). Based on the equations, we obtained the percent of the major alkanol associates (−p), the binding constant of the 1:1 and 1:2 DMP-alkanol complexes (K1 and K2) and the ratio of the molar absorptivity of H-bonded CO to the molar absorptivity of non-bonded CO (εhb/εns). The −p, K1, K2 and εhb/εns values confirmed the calculated results. It can be concluded that H-bonds mainly form the 1:1 complexes at O1 and H3, leading to species O5-H1⋯O1 = C1 for 3-alkanols and species O5-H1⋯O1 = C1 and Ph-H3⋯O5 for 2-alkanols. The differences of the affinity of H-bonding were mainly attributed to the steric hindrance and to a lesser extent to the hydrophobic interactions and the multi-H-bond cooperativity. The electron-cloud of the DMP molecule was supposed to migrate mainly in the E1 or E4 mode to adapt to the H-bonding or non-specific interactions, respectively.

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