DFT Modelling of Molecular Structure, Vibrational and UV-Vis Absorption Spectra of T-2 Toxin and 3-Deacetylcalonectrin

This paper discusses the applicability of optical and vibrational spectroscopies for the identification and characterization of the T-2 mycotoxin. Vibrational states and electronic structure of the T-2 toxin molecules are simulated using a density-functional quantum-mechanical approach. A numerical experiment aimed at comparing the predicted structural, vibrational and electronic properties of the T-2 toxin with analogous characteristics of the structurally similar 3-deacetylcalonectrin is performed, and the characteristic spectral features that can be used as fingerprints of the T-2 toxin are determined. It is shown that theoretical studies of the structure and spectroscopic features of trichothecene molecules facilitate the development of methods for the detection and characterization of the metabolites.

A DFT examination of the role of proximal boron functionalities in the S-alkylation of sulfenic acid anions

DFT modelling predicts proximal boron groups can accelerate sulfenate alkylation reactions, depending on boron substituents and boron distance from the reaction site.

Direct SN2 or SN2X Manifold – Mechanistic Study of Ion-Pair Catalyzed Carbon(sp3)-Carbon(sp3) Bond Formation

Density functional theory (DFT) is used in this work to predict the mechanism for constructing congested quaternary-quaternary carbon(sp3)–carbon(sp3) bonds in a pentanidium catalyzed substitution reaction. Computational mechanistic studies were carried out to investigate the proposed SN2X manifold, which consists of two primary elementary steps: halogen atom transfer (XAT) and subsequent SN2. For the first calculated model on original experimental substrates, XAT reaction barriers were more kinetically competitive than an SN2 pathway and connects to thermodynamically stable intermediates. Extensive computational screening-modelling were then done on various substrate combinations designed to study steric influence and to understand the mechanistic rationale, and calculations reveal that sterically congested substrates prefer the SN2X manifold over SN2. Different halides as leaving groups were also screened and it was found that the reactivity increases in order of Br > Cl > F in agreement of the strength of C–X bonds. However, DFT modelling suggests that chlorides can be a viable substrate for the SN2X process which should be further explored experimentally. Finally, ONIOM calculations on the full catalyst model were carried out to rationalize the stereoselectivity which corroborates with experimental results.

Synergy of Single Atoms Pd and Oxygen Vacancies on In2O3 for Highly Selective C1 Oxygenates Production from Methane under Visible Light

Methane (CH4) oxidation to high value chemicals under mild conditions through photocatalysis is a sustainable and appealing pathway, nevertheless confronting the critical issues on both conversion and selectivity. Herein, under visible irradiation (420 nm), the synergy of palladium (Pd) atom cocatalyst and oxygen vacancies (OVs) on In2O3 nanorods enabled superior photocatalytic CH4 activation by O2. The optimised catalyst reached ca. 100 µmol·h− 1 of C1 oxygenates, with a selectivity of primary products (CH3OH and CH3OOH) up to 82.5 %. Mechanism investigation elucidated that such superior photocatalysis was induced by the dedicated function of Pd single atoms and oxygen vacancies on boosting hole and electron transfer pathway, respectively. O2 was proven to be the only oxygen source for CH3OH production, while H2O acted as the promoter for efficient CH4 activation through ·OH production and facilitated product desorption as indicated by DFT modelling. This work thus provides new understandings on simultaneous regulation of activity and selectivity by the significant synergy of single atom cocatalysts and oxygen vacancies.

17O-EPR determination of the structure and dynamics of copper single-metal sites in zeolites

The bonding of copper ions to lattice oxygens dictates the activity and selectivity of copper exchanged zeolites. By 17O isotopic labelling of the zeolite framework, in conjunction with advanced EPR methodologies and DFT modelling, we determine the local structure of single site CuII species, we quantify the covalency of the metal-framework bond and we assess how this scenario is modified by the presence of solvating H216O or H217O molecules. This enables to follow the migration of CuII species as a function of hydration conditions, providing evidence for a reversible transfer pathway within the zeolite cage as a function of the water pressure. The results presented in this paper establish 17O EPR as a versatile tool for characterizing metal-oxide interactions in open-shell systems.

Ligand-Tuning of the Stability of Pd(II) Conjugates with Cyanocobalamin

Besides the well-known functions performed by vitamin B12 (CblCN) in biochemical processes of the human body, an increasing interest has been raised by the possibility of its use as a transmembrane drug carrier, capable, among others, of enhancing the accumulation of inorganic cytostatics in cancer cells. The present study was aimed at determining the possibility of the formation of CblCN conjugates with Pd(II) complexes. A key aspect was their stability, which we attempted to tune by appropriate choice of ligands. Syntheses, spectroscopic analysis of postreaction systems and kinetic investigations of conjugate formation reactions, have been complemented by DFT modelling. The obtained results showed that ligand charge, geometry and electron affinity may have a significant impact on carrier binding and release leading to the activation of the Pd(II) complex. This provides a rationale to expect that with appropriate composition of the coordination sphere, it will be possible to extend the spectrum of less toxic inorganic chemotherapeutics.

Hydrogen-Bonded Cyclic Dimers at Large Compression: The Case of 1H-pyrrolo[3,2-h]quinoline and 2-(2′-pyridyl)pyrrole

1H-pyrrolo[3,2-h]qinoline (PQ) and 2-(2′-pyridyl)pyrrole (PP) are important systems in the study of proton-transfer reactions. These molecules possess hydrogen bond donor (pyrrole) and acceptor (pyridine) groups, which leads to the formation of cyclic dimers in their crystals. Herein, we present a joint experimental (Raman scattering) and computational (DFT modelling) study on the high-pressure behaviour of PQ and PP molecular crystals. Our results indicate that compression up to 10 GPa (100 kbar) leads to considerable strengthening of the intermolecular hydrogen bond within the cyclic dimers. However, the intramolecular N–H∙∙∙N interaction is either weakly affected by pressure, as witnessed in PQ, or weakened due to compression-induced distortions of the molecule, as was found for PP. Therefore, we propose that the compression of these systems should facilitate double proton transfer within the cyclic dimers of PQ and PP, while intramolecular transfer should either remain unaffected (for PQ) or weakened (for PP).