Hydrogen bond docking site competition in methyl esters

Study of the Interactions between MeOH and Daidzein at the Molecular Level

In this study, the interactions between daidzein and methanol were studied to investigate isoflavone extraction. The complexes of MeOH-daidzein = 1:1, 2:1, 4:1, and 7:1 were studied using DFT/B3LYP-D3. According to the findings of this study, daidzein can act as a hydrogen bond donor as well as an acceptor. Binding energies demonstrate that more MeOH molecules interacting with daidzein could give more stability to the system. The strengths of the hydrogen bonds reveal that daidzein prefers to act as a hydrogen bond donor than an acceptor. The atoms in molecules (AIM) topological analysis was performed to analyze the nature of the hydrogen bonds. Moreover, daidzein, genistein, and glycitein are the most common soybean isoflavones, and their properties during extraction were also studied. The binding energies show that the soy isoflavone genistein is more reactive with the solvent than daidzein, followed by glycitein. The extraction conditions of the three common soy isoflavones in MeOH solution were obtained at 321, 328, and 348 K for genistein, daidzein, and glycitein, respectively. The generalized Kohn-Sham energy decomposition analysis (GKS-EDA) results indicate that the solute-solvent molecular interactions are typical hydrogen bonds with predominantly electrostatic and exchange energies in nature.

Supramolecular salts assembled by melamine and two organic hydroxyl acids: synthesis, structure, hydrogen bonds, and luminescent property

Two novel supramolecular salts are synthesized by melamine and organic hydroxyl carboxylic acids. The structure prediction, purity, luminescent property, and thermal stability are investigated by theoretical and experimental analysis.

N–H⋯O hydrogen bonding to the alkoxy oxygen of a carboxylic ester group: crystal structures of methyl 2,6-diaminobenzoate and its derivatives

Molecules with hydrogen bonds from amino groups to both oxygens of a carboxylic ester are described, and other examples of hydrogen bonding to an ester's alkoxy oxygen atom are highlighted.

FTIR study of hydrogen bonding interaction between fluorinated alcohol and unsaturated esters

The 1:1 complexes of two unsaturated esters with 2,2,2-trifluoroethanol (TFE) were investigated experimentally and computationally. The experimental observations of the spectral shifts of the OH-stretching vibrational transitions were obtained at 113cm^-1 for TFE-methyl acrylate (MA) and 92cm^-1 for TFE-vinyl acetate (VA). There are three docking sites in the two unsaturated esters for the incoming TFE. The predicted red shifts of the OH-stretching vibrational transitions were found to be larger for the OH⋯OC hydrogen bonded conformer than those for the OH⋯π and OH⋯O ones. The binding energies further prove that the OH⋯OC hydrogen bonded conformers are the most stable ones. On the basis of the DFT calculations as well as previous works, the carbonyl group is the best docking site for TFE. Furthermore, the thermodynamic equilibrium constants of TFE-MA and TFE-VA were obtained at 0.28 and 0.15 by combining the experimental spectra data and the DFT calculations. Consequently, the Gibbs free energies of formation were determined to be 3.2 and 4.8kJmol^-1 for TFE-MA and TFE-VA, respectively. The quantum theory of atoms in molecules (AIM) and generalized Kohn-Sham energy decomposition analysis (GKS-EDA) were carried out for further characterization of the hydrogen bonding interactions. GKS-EDA shows an "electrostatic" dominated hydrogen bonding character for the OH⋯OC hydrogen bonds.

Conformational Preference Determined by C-H···π Interaction of an O-H···O Hydrogen-Bonded Binary Complex of p-Fluorophenol with 2,5-Dihydrofuran: A Laser-Induced Fluorescence Spectroscopy Study

Conformational preferences of a binary hydrogen-bonded complex between p-fluorophenol (pFP) and 2,5-dihydrofuran (DHF) have been studied by means of laser induced fluorescence (LIF) spectroscopy in a supersonic jet expansion. Calculation predicts two major conformers for this complex, one having a nearly linear geometry in which the two molecular moieties are bound only by an O-H···O H-bond, but in the other an additional C-H···π type interaction between an ortho C-H group of pFP and ethylene group of DHF contributes to the binding stabilization and results in a folded geometry for the complex with respect to a global view, although the H-bond angle of the latter is relatively larger. This prediction is realized experimentally by identifying transitions corresponding to the two discrete conformers in a vibrationally resolved LIF excitation spectrum of the complex, and the red shifts of S₁-S₀ origin band of pFP moiety of the two conformers are 542 and 659 cm^-1, respectively. The assignments are corroborated by means of dispersed fluorescence (DF) spectroscopy. In comparison, the LIF spectral bands for the pFP-tetrahydrofuran complex can be corresponded to only one conformer, whose S₁-S₀ origin transition shows a red shift (563 cm^-1) somewhat similar to the linear conformer of pFP-DHF complex. Such similarities in spectral shifting behavior is consistent with the predictions of electronic structure calculations. The DF spectra also reveal that the energy threshold and pathways of vibrational dynamics in S₁ of the two conformers show different behavior. Excitation to 6a¹ level of pFP moiety of the folded conformer displays signatures of restricted intramolecular vibrational energy redistribution (IVR), whereas the linear form displays the emission feature for dissipative IVR.

Rotational spectroscopy of the methyl glycidate–water complex: conformation and water and methyl rotor tunnelling motions

Rotational transitions of methyl glycidate–water exhibit relatively large water tunnelling splittings, a surprise considering that water is quite tightly bound.