Probing the Acid−Base Equilibrium in Acid−Benzimidazole Complexes by 1H NMR Spectra and Density Functional Theory Calculations

Enhanced dielectric properties with a significantly reduced loss tangent in (Mg2+, Al3+) co-doped CaCu3Ti4O12 ceramics: DFT and experimental investigations

CaCu3Ti4O12 and CaCu2.95Mg0.05Ti3.95Al0.05O12 ceramics were fabricated via a solid-state reaction method. A single-phase of CaCu3Ti4O12 was found in these two ceramics. Very great grain size expansion was produced by co-doping with Mg2+ and Al3+. DFT results indicate that both Mg and Al atoms preferentially occupy Cu sites, creating liquid-phase sintering decomposition at grain boundary layers. Very high dielectric permittivity of ∼58 397 and low loss tangent of about 0.047 were achieved in a CaCu2.95Mg0.05Ti3.95Al0.05O12 ceramic. Additionally, the temperature stability of the dielectric response was improved. Better dielectric properties in the co-doped ceramic have possible origins from enhanced grain boundary responses, especially from the influences of metastable phases and oxygen enrichment at the grain boundaries. Experimental and computational results indicate that the colossal dielectric properties in CaCu3Ti4O12 ceramics might be correlated with an internal barrier layer capacitor structure.

Synthesis and evaluation of the oil removal potential of 3-bromo-benzimidazolone polymer grafted silica gel

This work reports the synthesis of 3-bromo-benzimidazolone using melt condensation, its polymerization and functionalization on silica which was extracted from diatomaceous earth in our previous work. The synthesized compounds were characterized using FTIR, NMR, SEM-EDS and TEM. The FTIR and NMR spectra of the synthesized benzimidazolones showed the compounds to have several functional groups: A band due to Si-O-C at 1085.41 cm-1, a broad band at 3380 cm-1 and chemical shifts: positive distortionless enhancement by polarization transfer (DEPT) 13C peaks (indicating lack of CH2 and CH3 groups), 1H NMR - 11.053 ppm (N-H), 7.086 ppm (Ar-H); 13C NMR - 155.34 ppm (C[double bond, length as m-dash]O), 101.04 ppm (C-Br) characteristic of benzimidazolones. SEM-EDS of the functionalized silica showed a rough irregular morphology with Si and O as the major elements. Carbon was also present indicating that silica was successfully functionalized with 3-bromo-benzimidazolone and TEM showed interconnected smear-like particles arranged irregularly. The functionalized silica was then applied in the treatment of oily wastewater and factors like initial oil concentration, adsorption dosage and time were optimized using the central composite design of response surface methodology in the design expert software. The amount of oil adsorbed was obtained by quantifying the total organic carbon using TOC test kits. Results showed that the optimum conditions for oil removal were 6650 mg L-1 oil concentration, with adsorbent dosage of 0.004 g and a contact time of 16 h. Under these conditions, the percentage adsorption was 97.9% with a desirability of 0.99. The materials were therefore seen to be applicable to field wastewaters.

A series of Mn(i) photo-activated carbon monoxide-releasing molecules with benzimidazole coligands: synthesis, structural characterization, CO releasing properties and biological activity evaluation

Five Mn(i) photo-activated carbon monoxide-releasing molecules were synthesized by reactions of MnBr(CO)₅ with L1–L4, and characterized via single crystal X-ray diffraction, ¹H-NMR, ¹³C-NMR, IR, UV-vis and fluorescence spectroscopy.

Ab initio study of hydrogen bonding in the H3PO2 dimer and H3PO2-DMF complex

The molecular structures and H-bonding interactions in the phosphinic acid dimer and the complex of phosphinic acid with N,N-dimethylformamide (DMF) were investigated by density functional theory calculations at the B3LYP level of theory. In order to better understand these phenomena, the individual molecules were also studied. The results were compared with previously obtained data for similar H-bonded complexes of phosphoric and phosphorous acids with DMF. Various correlations were found between geometric characteristics and parameters derived from Bader's theory and natural bond orbital analysis. Graphical abstract Irina V. Fedorova and Lyubov P. Safonova. Ab initio study of hydrogen bonding in the H₃PO₂ dimer and H₃PO₂-DMF complex. The acids of phosphorus are considered suitable candidates for ionomers due to their efficient proton transport properties. In order to better understand their molecular structures and their H-bond characteristics in real liquids, the most stable configurations of the H₃PO₂ dimer and the H₃PO₂-DMF complex were examined using computational methods in quantum chemistry. It was found that the strength of the H-bonding interactions in these systems depends strongly on the environment.

Maleimide: a potential building block for the design of proton exchange membranes studied by ab initio molecular dynamics simulations

Ab initio molecular dynamics (AIMD) simulations are applied to the study of proton transport in solid state maleimide.

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

This paper reports the ¹H, ¹³C and ¹⁵N NMR experimental study of five benzimidazoles in solution and in the solid state (¹³C and ¹⁵N CPMAS NMR) as well as the theoretically calculated (GIAO/DFT) chemical shifts. We have assigned unambiguously the "tautomeric positions" (C3a/C7a, C4/C7 and C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (blocked tautomerism). In the case of 1H-benzimidazole itself we have measured the prototropic rate in HMPA-d₁₈.

Hydrogen bonding analysis of phosphoric acid-N,N-dimethylformamide mixtures

An analysis of H-bonding in phosphoric acid (H3PO4)-N,N-dimethylformamide (DMF) mixtures was performed across the full range of mixture compositions using the results from molecular dynamics simulations. The distribution of molecules according to the number of H-bonds they formed with OH groups or О(=Р) atoms of acid molecules and О(=С) atoms of DMF molecules was calculated. The dependence of the average number of H-bonds per acid molecule on the concentration when the acid molecule acted as a proton acceptor was discerned, as were the corresponding dependences when the acid molecule acted as a proton donor towards H3PO4 and/or DMF. The dependence of the average number of H-bonds per DMF molecule (which always acted as a proton acceptor) on the concentration was also determined.

Synergetic proton conducting effect in acid–base composite of phosphonic acid functionalized polystyrene and triazolyl functionalized polystyrene

Three orders of magnitude improvement in proton conductivity was observed in the PS-PA/PS-Tri composite membrane.

Hydrogen bond and proton transport in acid-base complexes and amphoteric molecules by density functional theory calculations and 1H and 31P nuclear magnetic resonance spectroscopy

Intermolecular and intramolecular hydrogen bond (H-bond) and proton transport in acid-base complexes and amphoteric molecules consisting of phosphonic acid groups and nitrogenous heterocyclic rings are investigated by density functional theory calculations and (1)H NMR and (31)P NMR spectroscopy. It is concluded that a phosphonic acid group can act both as H-bond donor and H-bond acceptor, while an imine nitrogen atom can only act as H-bond acceptor and an amine group as H-bond donor. And the intramolecular H-bond is weaker than the intermolecular H-bond attributing to configurational restriction. In addition, the strongest H-bond interaction is observed between a phosphonic acid and a 1H-indazole because of the formation of double H-bonds. The (1)H NMR and (31)P NMR chemical shifts for the acid-base complexes are consistent with the density functional theory calculations. From the (1)H NMR chemical shifts, fast proton exchange is observed between a phosphonic acid and 1H-benzimidazole or 1H-indazole. Finally, it is proposed that polymeric material tethered with 1H-benzimidazole or 1H-indazole rings is a favorable component for high-temperature proton exchange membranes based on acid-base complexes or acid-base amphoteric molecules.