Cooperativity in alkane-1,2- and 1,3-polyols: NMR, QTAIM, and IQA study of O─H… OH and C─H… OH bonding interactions

Proton nuclear magnetic resonance chemical shifts and atom-atom interaction energies for alkanepolyols with 1,2-diol and 1,3-diol repeat units, and for their 1:1 pyridine complexes, are computed by density functional theory calculations. In the 1,3-polyols, based on a tG'Gg' repeat unit, the only important intramolecular hydrogen bonding interactions are O─H^… OH. By quantum theory of atoms in molecules analysis of the electron density, unstable bond and ring critical points are found for such interactions in 1,2-polyols with tG'g repeat units, from butane-1,2,3,4-tetrol onwards and in their pyridine complexes from propane-1,2,3-triol onwards. Several features (OH proton shifts and charges, and interaction energies computed by the interacting quantum atoms approach) are used to monitor the dependence of cooperativity on chain length: This is much less regular in 1,2-polyols than in 1,3-polyols and by most criteria has a higher damping factor. Well defined C─H^… OH interactions are found in butane-1,2,3,4-tetrol and higher members of the 1,2-polyol series, as well as in their pyridine complexes: There is no evidence for cooperativity with O─H^… OH bonding. For the 1,2-polyols, there is a tenuous empirical relationship between the existence of a bond critical point for O─H^… OH hydrogen bonding and the interaction energies of competing exchange channels, but the primary/secondary ratio is always less than unity.

Competitive Interactions Within Cm(III) Solvation in Binary Water/Methanol Solutions

Competitive forces exist in multicomponent solutions, and within electrolytes they consist of both ion-solvent and solvent-solvent interactions. These can influence a myriad of processes, including ligand complexation. In the case of water/alcohol solutions, recent work revealed an interesting dilemma regarding the overall solution dynamics and organization as compared to solute-solvent interactions. This is particularly true for highly charged ions in solution, whose ion-solvent interactions were demonstrated to be highly sensitive to the composition of the immediate solvation environment. Faster solvent exchange should be observed about the ion, considering that second-order Møller-Plesset perturbation theory predicts an average decrease in ion-solvent dissociation energy when methanol enters the first solvation shell of Cm³⁺_(aq). Yet the addition of methanol to water causes the dynamic features of the hydrogen-bond network of the entire solution to slow. The apparent competition between these contrary forces was examined using a combination of electronic structure calculations with both ab initio and classical molecular dynamics simulations, using binary water/methanol solutions and Cm³⁺ as a representative solute. This combination of theoretical methods predicts that, among the competitive effects of the solvent-solvent and ion-solvent interactions, the solution-phase dynamics imparted by the addition of methanol to water kinetically restricts the solvation exchange rates about Cm³⁺ in these binary solutions.

New insights into the solubility of graphene oxide in water and alcohols

One of the main advantages of graphene oxide (GO) over its non-oxidized counterpart is its ability to form stable solutions in water and some organic solvents. At the same time, the nature of GO solutions is not completely understood; the existing data are scarce and controversial. Here, we demonstrate that the solubility of GO, and the stability of the as-formed solutions depend not just on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface. By the DFT and QTAIM calculations, we demonstrate that the solubility of GO is afforded by strong hydrogen bonding established between GO functional groups and solvent molecules. The main functional groups taking part in hydrogen bonding are tertiary alcohols; epoxides play only a minor role. The magnitude of the bond energy values is significantly higher than that for typical hydrogen bonding. The hydrogen bond energy between GO functional groups and solvent molecules decreases in the sequence: water > methanol > ethanol. We support our theoretical results by several experimental observations including solution calorimetry. The enthalpy of GO dissolution in water, methanol and ethanol is -0.1815 ± 0.0010, -0.1550 ± 0.0012 and -0.1040 ± 0.0010 kJ g^-1, respectively, in full accordance with the calculated trend. Our findings provide an explanation for the well-known, but poorly understood solvent exchange phenomenon.

Using the C-O stretch to unravel the nature of hydrogen bonding in low-temperature solid methanol-water condensates

Transmission infrared spectroscopy has been used in a systematic laboratory study to investigate hydrogen bonding in binary mixtures of CH3OH and H2O, vapour deposited at 30 K, as a function of CH3OH/H2O mixing ratio, R. Strong intermolecular interactions are evident between CH3OH and H2O with infrared band profiles of the binary ices differing from that of the pure components and changing significantly with R. Consistent evidence from the O-H and C-H band profiles and detailed analysis of the C-O stretch band reveal two different hydrogen bonding structural regimes below and above R = 0.6-0.7. The vapour deposited solid mixtures were found to exhibit behaviour similar to that of liquids with evidence of inhomogeneity and higher coordination number of hydrogen bonds that are concentration dependent. The C-O stretch band is found to consist of three components around 1039 cm(-1) ('blue'), 1027 cm(-1) ('middle') and 1011 cm(-1) ('red'). The 'blue' and 'middle' components corresponding to environments with CH3OH dominating as a proton donor (PD) and proton acceptor (PA) respectively reveal preferential bonding of CH3OH as a PA and H2O as a PD in the mixtures. The 'red' component is only present in the presence of H2O and has been assigned to the involvement of both lone pairs of electrons on the oxygen atom of CH3OH as a PA to two PD H2O atoms. Cooperative effects are evident with concurrent blue-shifts in the C-H stretching modes of CH3OH below R = 0.6 indicating CH3 group participation in hydrogen bonding.

CH3OH⋯(H2O)n [n = 1-4] clusters in external electric fields

For hydrogen-bonded neutral molecular clusters, response to an externally applied electric field can critically affect molecular cooperativity. In this light, response of dilute methanol-water admixtures to an external, perturbative electric field is studied at the simplest molecular level in the cluster configurations CH3OH⋯(H2O)n with "n" chosen to range from 1 to 4, employing the M06-2X hybrid functional in conjunction with the 6-311++G(2d,2p) basis set, well-suited for hydrogen bonding. Methanol is seen to favorably bond with the water molecules at its hydroxyl end up to certain characteristic maximum threshold field strengths beyond which the HOMO-LUMO energy-gap abruptly drops to zero culminating into a complete breakdown of the cluster. In the interim regime prior to breakdown, the electric field significantly alters the hydrogen bonding pattern primarily by elongating the cluster, resulting in a marked enhancement in its electric dipole moment leading to alterations in the molecular electrostatic potential. With the application of electric field, certain "exotic" O-H vibration bands appear that at the threshold field fall in the frequency range of 2510 cm(-1)-1880 cm(-1) in the IR spectra, in contrast with their normal (zero-field) counterparts that occur in the range of ∼3300-3900 cm(-1).

Bonding topology, hydrogen bond strength, and vibrational chemical shifts on hetero-ring hydrogen-bonded complexes — Theoretical insights revisited

This work presents a theoretical study about the interaction strength of the hydrogen-bonded complexes C2H4O···HF, C3H6O···HF, C2H4O···HCF3, and C3H6O···HCF3 at the B3LYP/6–311++G(d,p) level. The structures, hydrogen bond energies, charge transfers, and dipole moments of these complexes were analyzed in accordance with routine spectroscopy events, such as the red- and blue-shifts on the stretch frequencies of the proton donors (HF and HCF3). The ChelpG atomic charges were used to quantify the charge-transfer fluxes from electron donor (O) towards to acceptors (HF or HCF3). Moreover, the topological calculations on the basis of the quantum theory of atoms in molecules (QTAIM) approach were also used to unveil the hydrogen bond strength (O···H), mainly in the determination of their electronic densities and Laplacian shapes.