13C and 15N spectral editing inside histidine imidazole ring through solid-state NMR spectroscopy

Improved Photocatalytic H2 Evolution by Cobaloxime-Tethered Imidazole-Functionalized Periodic Mesoporous Organosilica

Molecular cobaloxime-based heterogeneous systems have attracted great interest during the last decades in light-driven hydrogen production. Here, we present a novel cobaloxime-tethered periodic mesoporous organosilica (PMO) hybrid (Im-EtPMO-Co) prepared through the immobilization of a molecular cobaloxime complex on the imidazole groups present in ethylene-bridged PMO. The successful assembly of a molecular cobaloxime catalyst via cobalt-imidazole axial ligation has been evidenced by several techniques, such as 13C NMR, Raman spectroscopy, ICP-MS, and XPS. The catalytic performance of Im-EtPMO-Co catalyst was essayed on the hydrogen evolution reaction (HER) under visible light in presence of a photosensitizer (Eosin Y) and an electron donor (TEOA). It showed an excellent hydrogen production of 95 mmol hydrogen at 2.5 h, which corresponded to a TON of 138. These results reflect an improved photocatalytic activity with respect to its homogenous counterpart [Co(dmgH)2(Im)Cl] as well as a previous cobaloxime-PMO system with pyridine axial ligation to the cobaloxime complex.

Chitosan-cellulose hydrogel conjugated with L-histidine and zinc oxide nanoparticles for sustained drug delivery: Kinetics and in-vitro biological studies

Functionalised nanohybrid hydrogel using L-Histidine (HIS) conjugated chitosan, phyto-synthesised zinc oxide nanoparticles (ZNPs) and dialdehyde cellulose (DAC) was formulated as a sustained drug delivery carrier for the polyphenol drugs - Naringenin (NRG), Quercetin (QE) and Curcumin (CUR). A maximum loading efficiency of 90.55 %, 92.84 % and 89.89 %, respectively were optimised for NRG, QE and CUR in the hybrid hydrogel. The maximum drug release was favoured for the optimum drug loading and at pH-5. HIS-chitosan conjugation stabilised the hydrogel and enabled a sustained drug delivery. Drug release kinetics predicted a non-Fickian diffusion-based mechanism along with polymer erosion. Prominent antimicrobial activity against Staphylococcus aureus and Trichophyton rubrum strains were predicted to evolve based on the synergic formulation. Significant biocompatibility towards L929 cells revealed their support for normal cell survival. Anticancer studies towards A431 cells exhibited excellent cytotoxicity with a 15 to 30-fold increase using the hybrid carrier, compared to the free polyphenol drugs.

Quantitative analysis of 14N quadrupolar coupling using 1H detected 14N solid-state NMR

Magic-angle spinning solid-state NMR is increasingly utilized to study the naturally abundant, spin-1 nucleus 14N, providing insights into the structure and dynamics of biological and organic molecules. In particular, the characterisation of 14N sites using indirect detection has proven useful for complex molecules, where the 'spy' nucleus provides enhanced sensitivity and resolution. Here we exploit the sensitivity of proton detection, to indirectly characterise 14N sites using a moderate rf field to generate coherence between the 1H and 14N at moderate and fast-magic-angle spinning frequencies. Efficient numerical simulations have been developed that have allowed us to quantitatively analyse the resulting 14N lineshapes to determine both the size and asymmetry of the quadrupolar interaction. Exploiting only naturally occurring abundant isotopes will aid the analysis of materials with the need to resort to isotope labelling, whilst providing additional insights into the structure and dynamics that the characterisation of the quadrupolar interaction affords.

Geometric and energetic consequences of prototropy for adenine and its structural models – a review

Prototropy for adenine and its convenient models causes parallel changes of geometric (HOMED) and energetic (ΔE) parameters for neutral tautomers.

Differentiation of histidine tautomeric states using (15)N selectively filtered (13)C solid-state NMR spectroscopy

The histidine imidazole ring in proteins usually contains a mixture of three possible tautomeric states (two neutral - τ and π states and a charged state) at physiological pHs. Differentiating the tautomeric states is critical for understanding how the histidine residue participates in many structurally and functionally important proteins. In this work, one dimensional (15)N selectively filtered (13)C solid-state NMR spectroscopy is proposed to differentiate histidine tautomeric states and to identify all (13)C resonances of the individual imidazole rings in a mixture of tautomeric states. When (15)N selective 180° pulses are applied to the protonated or non-protonated nitrogen region, the (13)C sites that are bonded to the non-protonated or protonated nitrogen sites can be identified, respectively. A sample of (13)C, (15)N labeled histidine powder lyophilized from a solution at pH 6.3 has been used to illustrate the usefulness of this scheme by uniquely assigning resonances of the neutral τ and charged states from the mixture.