Electronic structure of hydrogen-bonded imidazole chains. Influence of the proton position

Acetylphenyl-substituted imidazolium salts: synthesis, characterization, in silico studies and inhibitory properties against some metabolic enzymes

Herein, we present how to synthesize thirteen new 1-(4-acetylphenyl)-3-alkylimidazolium salts by reacting 4-(1-H-imidazol-1-yl)acetophenone with a variety of benzyl halides that contain either electron-donating or electron-withdrawing groups. The structures of the new imidazolium salts were conformed using different spectroscopic methods (1H NMR, 13C NMR, 19F NMR, and FTIR) and elemental analysis techniques. Furthermore, these compounds' the carbonic anhydrase (hCAs) and acetylcholinesterase (AChE) enzyme inhibition activities were investigated. They showed a highly potent inhibition effect toward AChE and hCAs with Ki values in the range of 8.30 ± 1.71 to 120.77 ± 8.61 nM for AChE, 16.97 ± 2.04 to 84.45 ± 13.78 nM for hCA I, and 14.09 ± 2.99 to 69.33 ± 17.35 nM for hCA II, respectively. Most of the synthesized imidazolium salts appeared to be more potent than the standard inhibitor of tacrine (TAC) against AChE and Acetazolamide (AZA) against CA. In the meantime, to prospect for potential synthesized imidazolium salt inhibitor(s) against AChE and hCAs, molecular docking and an ADMET-based approach were exerted.

Steroid-Functionalized Imidazolium Salts with an Extended Spectrum of Antifungal and Antibacterial Activity

It is established that high rates of morbidity and mortality caused by fungal infections are related to the current limited number of antifungal drugs and the toxicity of these agents. Imidazolium salts as azole derivatives can be successfully used in the treatment of fungal infections in humans. Steroid-functionalized imidazolium salts were synthesized using a new, more efficient method. As a result, 20 salts were obtained with high yields, 12 of which were synthesized and characterized for the first time. They were derivatives of lithocholic acid and 3-oxo-23,24-dinorchol-4-ene-22-al and were fully characterized by ¹H and ¹³C nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and high resolution mass spectrometry (HRMS). Due to the excellent activity against bacteria and Candida albicans, new research was extended to include tests on five species of pathogenic fungi and molds: Aspergillus niger ATCC 16888, Aspergillus fumigatus ATCC 204305, Trichophyton mentagrophytes ATCC 9533, Cryptococcus neoformans ATCC 14116, and Microsporum canis ATCC 11621. The results showed that the new salts are almost universal antifungal agents and have a broad spectrum of activity against other human pathogens. To initially assess the safety of the synthesized salts, hemocompatibility with host cells and cytotoxicity were also examined. No toxicity was observed at the concentration at which the compounds were active against pathogens.

NMR Crystallography: Evaluation of Hydrogen Positions in Hydromagnesite by 13 C{1 H} REDOR Solid-State NMR and Density Functional Theory Calculation of Chemical Shielding Tensors

Solid-state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational-echo double-resonance (REDOR) NMR to interrogate ¹³ C-¹ H distances is exploited along with DFT determinations of the ¹³ C tensor of carbonates (CO₃ ^2- ). Nearby ¹ H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO₃ ⋅Mg(OH)₂ ⋅4 H₂ O]. A match between the calculated structure and solid-state NMR was found by testing multiple semi-local and dispersion-corrected DFT functionals and applying them to optimize atom positions, starting from X-ray diffraction (XRD)-determined atomic coordinates. This was validated by comparing calculated to experimental ¹³ C{¹ H} REDOR and ¹³ C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid-state NMR, XRD, and DFT can improve structure refinement for hydrated materials.

Importance of dynamic hydrogen bonds and reorientation barriers in proton transport

The dynamic nature of hydrogen bonds in phenolic polymers, where the hydrogen bond donor/acceptor reorientation can occur in a single site, presents lower barriers for proton transport.

Proton transfer in imidazole-based molecular crystals

Heterocycles' aggregates show rather good proton conductivity. In particular, condensed structures formed by imidazole rings that are held together by polymeric chains have attracted some interest as possible candidate materials for fuel cell membranes. However, the details of the proton diffusion process could not be resolved by means of experimental measurements because of the fast rearrangement of the structure after each proton exchange. In this work, we report in detail the results of ab initio molecular dynamics calculations, which were briefly presented in a previous Letter [M. Iannuzzi and M. Parrinello, Phys. Rev. Lett. 93, 025901 (2004)]. The conformational changes associated with the diffusion of protons in model crystalline structures containing chains of imidazole rings are described in the framework of an atomistic approach. In particular, the bonding pattern characterizing the structure of imidazole-2-ethylene-oxide doped by an excess proton is also studied through the calculation of the 1H NMR chemical shifts. The unresolved resonances appearing in the experimental spectra could be associated with specific structural features, in connection with the fluctuating hydrogen bonding. The analysis of the distortions that induce or are induced by the mobility of the protons offers some new hints for the engineering of new proton conducting materials.

Theoretical models of directional proton molecular transport

The important topic of proton transport through molecular wires is usually associated with the Grotthuss mechanism. In this paper we propose an alternative conductor based on chains of lone pairs. B3LYP/6-31+G** and PW91 DFT calculations on model compounds (1,2,3,4-tetrasubstituted benzenes) show that these compounds could play the role of proton conductors.