Isolation,structure elucidation and enzyme inhibition studies of a new hydroxy ester and other compounds from Berberis jaeschkeana Schneid stem

Bioassay-guided isolation and fractionation of Berberis jaeschkeana Schneid var. jaeschkeana stem resulted in the isolation and characterisation of a new long chain hydroxy ester named as berberinol (1) along with six known compounds (2–7). All the structures were established from 1D and 2D spectroscopic data. Crude extract, sub-fractions and all the isolated compounds were evaluated for their anti-fungal and urease enzyme inhibition properties. All of the sub-fractions and compounds showed good anti-fungal and urease enzyme inhibition properties. Minimum inhibitory concentrations (MICs) were calculated for all active samples in case of urease enzyme inhibition. MICs values were found to be in the range of 39.03–49.78 μg/mL for urease enzyme inhibition.     

Effect of alkaline pretreatment on delignification of wheat straw

This study was conducted to analyse structural changes through scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) after alkaline pretreatment of wheat straw for optimum steaming period. During the study, 2 mm size of substrate was soaked in 2.5% NaOH for 1 h at room temperature and then autoclaved at 121°C for various steaming time (30, 60, 90 and 120 min). Results revealed that residence time of 90 min at 121°C has strong effect on substrate, achieving a maximum cellulose content of 83%, delignification of 81% and hemicellulose content of 10.5%. Further SEM and FTIR spectroscopy confirmed structural modification caused by alkaline pretreatment in substrate. Maximum saccharification yield of 52.93% was achieved with 0.5% enzyme concentration using 2.5% substrate concentration for 8 h of incubation at 50°C. This result indicates that the above-mentioned pretreatment conditions create accessible areas for enzymatic hydrolysis.     

Chemical characterisation of bioactive compounds in Medicago sativa growing in the desert of Oman

Medicago sativa Linn growing in Omani desert were chemically characterised using flame photometry, inductively coupled plasma, gas chromatography–mass spectrometry and high performance liquid chromatographic (HPLC) analysis. HPLC analyses were performed to determine the phenolics and flavonoids present in M. sativa. The major compounds detected in M. sativa leaves were protchaechenic acid (3.22%), hydroxyl benzoic acid (1.05%), β-Phenyl caffate (0.97%) and kaempherol (0.89%). Pterostilbene, a cholesterol-lowering compound, was detected in M. sativa.     

In vitro anti-oxidant potential of new metabolites from Hypericum oblongifolium (Guttiferae)

Phytochemical investigations on Hypericum oblongifolium led to the isolation of a flavone named folicitin (1) and a bicyclic conjugated lactone, folenolide (2) from the ethyl acetate fraction of methanolic extract. Both metabolites were characterised as new compounds based on detailed spectroscopic analyses. In vitro anti-oxidant potential of both the compounds was evaluated by the DPPH radical scavenging assay. Compound 1 exhibited significant antioxidant activity while compound 2 was found inactive.     

Stereoselective interactions of chiral dipeptides on amylose based chiral stationary phases

Dipeptides are stereo-specifically involved in several biological functions that are challenging to separate enantiomerically. Elution order of enantiomers is an important issue in chiral chromatography. Amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase(CSP) is the best and most-widely-used CSP in chiral separations, but experimental data of enantiomeric separation of dipeptides on this CSP is lacking. Simulation studies were conducted to determine the order of elution and the chiral recognition mechanism of didpetides on this CSP. Results indicated that the docking energy of SR-enantiomers were higher than SS-antipodes. The range of docking energies for SR-enantiomers was -7.44 to -5.92 kcal/mol with CSP, but -7.15 to -5.87 kcal/mol for SS-stereoisomers. Therefore it is predicted that SS-enantiomer will elute first, followed by SR-antipode. Furthermore, hydrogen bondings, van der Waal’s interactions and electrostatic interactions were observed among SR- and SSenantiomers and chiral grooves of CSP. The number of hydrogen bonds was one in each enantiomer binding except S-Ala-R-Tyr, which contained two hydrogen bonds. No hydrogen bond was found in S-Ala-R-Trp, S-Leu-S-Trp, and S-Leu-S-Tyr dipeptides bindings. The chiral recognition mechanisms dictate different strengths of stereoselective bindings of the enantiomers on CSP.     

Metal–Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction

Inspired by the metal–sulfur (M-S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N₂ availability on a catalytic surface, which suppresses the hydrogen evolution reaction (HER) and improves the rate of NH₃ production. Ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M-S linkages. A high faradaic efficiency (11 %) with an improved NH₃ yield (50 μg h⁻¹ mg⁻¹) is achieved at −0.1 V vs. RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N₂ adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst shows excellent stability and recyclability for NH₃ production, as confirmed by rigorous control experiments including ¹⁵N isotope labeling experiments.     

Trisaminomethane–cobalt complex supported on Fe3O4 magnetic nanoparticles as an efficient recoverable nanocatalyst for oxidation of sulfides and C–S coupling reactions

In this work, trisaminomethane–cobalt complex immobilized onto the surface of Fe₃O₄ magnetic nanoparticles was successfully prepared via a simple and inexpensive procedure. The prepared nanocatalyst was considered a robust and clean nanoreactor catalyst for the oxidation and synthesis of sulfides under green conditions. This ecofriendly heterogeneous catalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, inductively coupled plasma-atomic emission spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, X-ray mapping, scanning electron microscopy, and transmission electron microscopy techniques. Use of green medium, easy separation and workup, excellent reusability of the nanocatalyst, and short reaction time are some outstanding advantages of this method.     

A switchable ionic liquid with polarity swing-assisted regeneration properties used for the preconcentration of cadmium in biological samples

In the present study the cadmium (Cd) was determined in serum samples of psoriatic patients. The severity of psoriasis was evaluated according to criteria based on standard clinical diagnosis using Psoriasis Area Severity Index (PASI) score. In present study, an innovative tunable green solvent system based microextraction (TSS-ME) was applied for the enrichment of Cd in acid digested serum samples prior to determination with flame atomic absorption spectrometry. The hydrophobic complex of Cd-ammonium pyrrolidine thiocarbamate was extracted in a tunable solvent system which was prepared from a polybasic amine (N, N, N′, N′-tetramethyl-1, 4-diaminobutane), decanol and water system. The tunable green solvent system (TSS) which has zero ionic strength was converted to homogeneous monophasic polar hydrophilic phase via exposure to CO₂ at different pressure and time duration. Then hydrophobic enriched Cd- ammonium pyrrolidine thiocarbamate was back extracted, using HNO₃ (0.1 to 0.5 mol L⁻¹) then the second round of TSS-ME was applied. The acidic aqueous phase enrich with analyte was separated from tunable solvent. The separated TSS was easily reused for up to 10 time for preconcentration purposes without loss of its enrichment character. The smoker and nonsmoker psoriatic patients at PASI >10, have two to three folds higher Cd levels in serum samples than healthy persons.     

Synthesis,characterization, and biological screening of metal complexes of novel sulfonamide derivatives: Experimental and theoretical analysis of sulfonamide crystal

This study reports the synthesis of sulfonamide-derived Schiff bases as ligands L ¹ and L ² as well as their transition metal complexes [VO(IV), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II)]. The Schiff bases (4-{E-[(2-hydroxy-3-methoxyphenyl)methylidene]amino}benzene-1-sulfonamide ( L ¹ ) and 4-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}-N-(5-methyl-1,2-oxazol-3-yl)benzene-1-sulfonamide ( L ² ) were synthesized by the condensation reaction of 4-aminobenzene-1-sulfonamide and 4-amino-N-(3-methyl-2,3-dihydro-1,2-oxazol-5-yl)benzene-1-sulfonamide with 2-hydroxy-3-methoxybenzaldehyde in an equimolar ratio. Sulfonamide core ligands behaved as bidentate ligands and coordinated with transition metals via nitrogen of azomethine and the oxygen of the hydroxyl group. Ligand L ¹ was recovered in its crystalline form and was analyzed by single-crystal X-ray diffraction technique which held monoclinic crystal system with space group (P2₁/c). The structures of the ligands L ¹ and L ² and their transition metal complexes were established by their physical (melting point, color, yields, solubility, magnetic susceptibility, and conductance measurements), spectral (UV–visible [UV–Vis], Fourier transform infrared spectroscopy, ¹H NMR, ¹³C NMR, and mass analysis), and analytical (CHN analysis) techniques. Furthermore, computational analysis (vibrational bands, frontier molecular orbitals (FMOs), and natural bonding orbitals [NBOs]) were performed for ligands through density functional theory utilizing B3LYP/6-311+G(d,p) level and UV–Vis analysis was carried out by time-dependent density functional theory. Theoretical spectroscopic data were in line with the experimental spectroscopic data. NBO analysis confirmed the extraordinary stability of the ligands in their conjugative interactions. Global reactivity parameters computed from the FMO energies indicated the ligands were bioactive by nature. These procedures ensured the charge transfer phenomenon for the ligands and reasonable relevance was established with experimental results. The synthesized compounds were screened for antimicrobial activities against bacterial (Streptococcus aureus, Bacillus subtilis, Eshcheria coli, and Klebsiella pneomoniae) species and fungal (Aspergillus niger and Aspergillus flavous) strains. A further assay was designed for screening of their antioxidant activities (2,2-diphenyl-1-picrylhydrazine radical scavenging activity, total phenolic contents, and total iron reducing power) and enzyme inhibition properties (amylase, protease, acetylcholinesterase, and butyrylcholinesterase). The substantial results of these activities proved the ligands and their transition metal complexes to be bioactive in their nature.