Carbon dioxide interaction with isolated imidazole or attached on gold clusters and surface: Competition between σ H-bond and π stacking interaction

Using first principle methodologies, we investigate the subtle competition between σ H-bond and π stacking interaction between CO 2 and imidazole either isolated, adsorbed on a gold cluster or adsorbed on a gold surface. These computations are performed using MP2 as well as dispersion corrected density functional theory (DFT) techniques. Our results show that the CO 2 interaction goes from π-type stacking into σ-type when CO 2 interacts with isolated imidazole and Au clusters or surface. The balance between both types of interactions is found when an imidazole is attached to a Au 20 gold cluster. Thus, the present study has great significance in understanding and controlling the structures of weakly-bound molecular systems and materials, where hydrogen bonding and van der Waals interactions are competing. The applications are in the fields of the control of CO 2 capture and scattering, catalysis and bio- and nanotechnologies. © 2014 the Partner Organisations

Anisotropic diffusion of water molecules in hydroxyapatite nanopores

Funded by EPSRC Grant EP/K000128/1

The first microsolvation step for furans : new experiments and benchmarking strategies

The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight

Counteractive Effects of Choline Geranate (CAGE) ILs and Ethanol on Insulin’s Stability—A Leap Forward towards Oral Insulin Formulation

Choline geranate (CAGE) ionic liquids (ILs) stabilize insulin, thereby aiding its oral delivery, whereas ethanol (EtOH) affects its stability by disrupting the hydrophobic interactions. In this study, cognizance of the stabilization mechanism of insulin dimer in the presence of both CAGE ILs and EtOH mixtures is achieved through biased and unbiased molecular dynamics (MD) simulations. Here, two order parameters are employed to study the insulin dimer dissociation using well-tempered metadynamics (WT-MetaD). The stability of insulin is found to be strongly maintained until a 0.20 mole fraction of EtOH. Besides, higher concentrations of EtOH marginally affect the insulin stability. Moreover, geranate anions form a higher number of H-bonding interactions with water molecules, which aids insulin stabilization. Conversely, the addition of EtOH minimizes the water-mediated H-bonding interactions of geranate. Additionally, geranate traps the EtOH molecules, thereby preventing the interactions between insulin and EtOH. Furthermore, the free energy landscape (FEL) reveals the absence of dimer dissociation along with noticeable deviations in the distances R and the number of contacts Q. The dimerization free energy of insulin was calculated to be −16.1 kcal/mol at a 0.20 mole fraction of EtOH. Moreover, increments in mole fractions of EtOH effectuate a decrease in the insulin stability. Thus, the present study represents CAGE ILs as efficient insulin dimer stabilizes at low concentrations of EtOH

Structure, stability and spectral signatures of monoprotic carborane acid–water clusters (CBW<SUB>n</SUB>, where n = 1–6)

The gas phase structure, stability, spectra, and proton transfer properties of monoprotic carborane acid–water clusters[CB11FmH11−m(OH2)1]–(H2O)n (where m = 0, 5, and 10; n = 1–6) have been calculated using density functional theory (DFT) with the Becke's three-parameter hybrid exchange functional and Lee–Yang–Parr correlation functional (B3LYP) using 6-31+G* basis set. Results reveal that Eigen cation defects are found in CBWn (where n = 2–6) clusters and these clusters are significantly more stable than the non-Eigen geometry. In addition to the conventional hydrogen bond (H-bond) the role of dihydrogen bond (DHB) and halogen bond (XB) in the stabilization of these clusters can be observed from the molecular graphs derived from the atoms in molecules (AIM) analysis. Spectral information shows the features of Eigen cation and proton oscillation involved in the proton transfer process. The dissociation of proton from the perfluoro derivatives with two water molecules is more favorable when compared to the other derivatives

Microscopic investigations of site and functional selectivity of triazole for CO 2 capture and catalytic applications

International audienc

Toughness Governs the Rupture of the Interfacial H‑Bond Assemblies at a Critical Length Scale in Hybrid Materials

The geometry and material property mismatch across the interface of hybrid materials with dissimilar building blocks make it extremely difficult to fully understand the lateral chemical bonding processes and design nanocomposites with optimal performance. Here, we report a combined first-principles study, molecular dynamics modeling, and theoretical derivations to unravel the detailed mechanisms of H-bonding, deformation, load transfer, and failure at the interface of polyvinyl alcohol (PVA) and silicates, as an example of hybrid materials with geometry and property mismatch across the interface. We identify contributing H-bonds that are key to adhesion and demonstrate a specific periodic pattern of interfacial H-bond network dictated by the interface mismatch and intramolecular H-bonding. We find that the maximum toughness, incorporating both intra- and interlayer strain energy contributions, govern the existence of optimum overlap length and thus the rupture of interfacial (interlayer) H-bond assemblies in natural and synthetic hybrid materials. This universally valid result is in contrast to the previous reports that correlate shear strength with rupture of H-bonds assemblies at a finite overlap length. Overall, this work establishes a unified understanding to explain the interplay between geometric constraints, interfacial H-bonding, materials characteristics, and optimal mechanical properties in hybrid organic–inorganic materials

Recognition of aromatic amino acids and proteins with p-sulfonatocalix[4]arene - a luminescence and theoretical approach

The host–guest interaction of p-sulfonatocalix[4]arene (p-SC4) with aromatic amino acids (AAs) and two proteins has been studied using UV–Vis absorption, fluorescence, and theoretical methods. Spectral studies supported by binding constant and calculated binding energy (BE) values show that p-SC4 binds more strongly with tyrosine compared with other AAs. The application of Bader's theory of atoms in molecule shows the involvement of various types of noncovalent interactions in the formation of the host–guest complexes. Both tyrosine and histidine have strong electrostatic interaction with the sulfonato group and other two AAs have dominant π−π interaction with the aromatic rings of calixarene. In addition, the role of C−H···O, C−H···π and lone pair···π (lp···π) interactions in the stabilization of p-SC4-AA complexes has also been realized from the atoms in molecule analysis. The electron density at the bond critical points varies with the calculated BEs and trend in BEs is in good agreement with the experimental binding constant values. The work has been extended to the binding of p-SC4 with proteins, bovine serum albumin and ovalbumin. Ovalbumin exhibits stronger binding with p-SC4 than bovine serum albumin

Toughness Governs the Rupture of the Interfacial H‑Bond Assemblies at a Critical Length Scale in Hybrid Materials

The geometry and material property mismatch across the interface of hybrid materials with dissimilar building blocks make it extremely difficult to fully understand the lateral chemical bonding processes and design nanocomposites with optimal performance. Here, we report a combined first-principles study, molecular dynamics modeling, and theoretical derivations to unravel the detailed mechanisms of H-bonding, deformation, load transfer, and failure at the interface of polyvinyl alcohol (PVA) and silicates, as an example of hybrid materials with geometry and property mismatch across the interface. We identify contributing H-bonds that are key to adhesion and demonstrate a specific periodic pattern of interfacial H-bond network dictated by the interface mismatch and intramolecular H-bonding. We find that the maximum toughness, incorporating both intra- and interlayer strain energy contributions, govern the existence of optimum overlap length and thus the rupture of interfacial (interlayer) H-bond assemblies in natural and synthetic hybrid materials. This universally valid result is in contrast to the previous reports that correlate shear strength with rupture of H-bonds assemblies at a finite overlap length. Overall, this work establishes a unified understanding to explain the interplay between geometric constraints, interfacial H-bonding, materials characteristics, and optimal mechanical properties in hybrid organic–inorganic materials

H₂, N₂, and CH₄ Gas Adsorption in Zeolitic Imidazolate Framework-95 and -100: Ab Initio Based Grand Canonical Monte Carlo Simulations

A multiscale approach based on ab initio and grand canonical Monte Carlo (GCMC) simulations is used to report the H₂, N₂, and CH₄ uptake behaviors of two zeolitic imidazolate frameworks (ZIFs), ZIF-95 and -100, with exceptionally large and complex colossal cages. The force fields describing the weak interactions between the gas molecules and ZIFs in GCMC simulations are based on ab initio MP2 level of theory aimed at accurately describing the London dispersions. We report the total and excess gas uptakes up to 100 bar at 77 and 300 K. Our results unravel the interplay between the uptake amount, pore volume, guest molecule size, temperature, chlorine functional group, and isosteric heat of adsorption in ZIFs. We found that while the uptake capacity of ZIF-100 outperforms ZIF-95 for small molecules (H₂), ZIF-95 offers a superior adsorption capacity for large molecules (CH₄). Moderately sized molecules (N₂) exhibit a more complex uptake behavior depending on the temperature. Furthermore, we show that the induced dipole interactions, such as those caused by −Cl functional groups, play a vital role on gas adsorption behaviors. This work provides the first report on the N₂ and CH₄ uptake of ZIF-95 and -100 using ab initio based GCMC simulations