Adsorption of Acetone Vapor by Cu-BTC: An Experimental and Computational Study

We report an experimental and theoretical study of acetone adsorption in the metal–organic framework (MOF) compound Cu-BTC. The isosteric heat of adsorption could be derived experimentally and was found to be −60 kJ mol^–1. This value matches the theoretical data obtained by DFT-based methods at zero coverage. In situ DRIFT measurements allowed us to precisely describe the adsorption steps from zero coverage to saturation. Two main adsorption sites were determined for the adsorption of acetone. The small cavities were found to interact through van der Waals interaction with acetone, while the Cu­(II) site was found to interact with the carbonyl function of acetone. On the basis of the in situ infrared experiments, it was demonstrated that the small cavities were first in interaction with acetone. DFT proved consistent with these findings by giving the energy of interaction in the different sites explored but also by providing calculated infrared spectra of adsorbed acetone in Cu-BTC. Using acetone as a probe allowed showing that dispersive interactions with the pore sites of the Cu-BTC can be dominant among all other interactions. Additionally, the adsorption of acetone in Cu-BTC proved not fully reversible unless exposed to atmospheric moisture

Prediction of p<i>K</i>_a Using DFT: the Nicotianamine Polyacid Example

The determination of p<i>K</i>_a values for molecules containing multiple acidic groups in solution is challenging both experimentally and theoretically. We propose a general method to obtain these values by combining a graphical analysis based on a predominance diagram, for amino acids and nicotianamine polyacid, with first principle DFT calculations. Implicit and semiexplicit water solvent models were included to account for solvation. This strategy enables the investigation of the protonation states of compounds containing acidic moieties in solution depending on the pH domain. The method was first validated on a set of amino acids with p<i>K</i>_a values calculated with an accuracy within 0.5–1.0 p<i>K</i>_a unit and then on the chalenging nicotianamine polyacid with six p<i>K</i>_a values. This approach is particularly well suited for such a complex system including both zwitterionic structures and unknown experimental p<i>K</i>_a values

Hydrophobic α,α-Disubstituted Disilylated TESDpg Induces Incipient 3₁₀-Helix in Short Tripeptide Sequence

To evaluate the contribution of triethylsilyl α,α-di-<i>n</i>-propylglycine, namely TESDpg, to induce a defined secondary structure, we have prepared model tripeptides in which TESDpg was inserted in three different positions. Studies in solid state and in solution with adapted techniques showed that TESDpg was able to induce a nascent 3₁₀ helix in both crystal and solution states

Correction to “First Direct Insight into the Local Environment and Dynamics of Water Molecules in the Whewellite Mineral Phase: Mechanochemical Isotopic Enrichment and High-Resolution ¹⁷O and ²H NMR Analyses”

Correction to “First Direct Insight into the Local Environment and Dynamics of Water Molecules in the Whewellite Mineral Phase: Mechanochemical Isotopic Enrichment and High-Resolution 17O and 2H NMR Analyses

Calibration of 1,2,4-Triazole-3-Thione, an Original Zn-Binding Group of Metallo-β-Lactamase Inhibitors. Validation of a Polarizable MM/MD Potential by Quantum Chemistry

In the context of the SIBFA polarizable molecular mechanics/dynamics (PMM/PMD) procedure, we report the calibration and a series of validation tests for the 1,2,4-triazole-3-thione (TZT) heterocycle. TZT acts as the chelating group of inhibitors of dizinc metallo-β-lactamases (MBL), an emerging class of Zn-dependent bacterial enzymes, which by cleaving the β-lactam bond of most β-lactam antibiotics are responsible for the acquired resistance of bacteria to these drugs. Such a study is indispensable prior to performing PMD simulations of complexes of TZT-based inhibitors with MBL’s, on account of the anchoring role of TZT in the dizinc MBL recognition site. Calibration was done by comparisons to energy decomposition analyses (EDA) of high-level <i>ab initio</i> QC computations of the TZT complexes with two probes: Zn­(II), representative of “soft” dications, and water, representative of dipolar molecules. We performed distance variations of the approach of each probe to each of the two TZT atoms involved in Zn ligation, the S atom and the N atom <i>ortho</i> to it, so that each SIBFA contribution matches its QC counterpart. Validations were obtained by performing in- and out-of-plane angular variations of Zn­(II) binding in monoligated Zn­(II)–TZT complexes. The most demanding part of this study was then addressed. How well does Δ<i>E</i>(SIBFA) and its individual contributions compare to their QC counterparts in the dizinc binding site of one MBL, L1, whose structure is known from high-resolution X-ray crystallography? Six distinct complexes were considered, namely each separate monozinc site, and the dizinc site, whether ligated or unligated by TZT. Despite the large magnitude of the interaction energies, in all six complexes Δ<i>E</i>(SIBFA) can match Δ<i>E</i>(QC) with relative errors <2% and the proper balance of individual energy contributions. The computations were extended to the dizinc site of another MBL, VIM-2, and its complexes with two other TZT analogues. Δ<i>E</i>(SIBFA) faithfully reproduced Δ<i>E</i>(QC) in terms of magnitude, ranking of the three ligands, and trends of the separate energy contributions. A preliminary extension to correlated calculations is finally presented. All these validations should enable a secure design of a diversity of TZT-containing MBL inhibitors: a structurally and energetically correct anchoring of TZT should enable all other inhibitor groups to in turn optimize their interactions with the other target MBL residues