Peptidomimetics with tunable tertiary amide bond containing substituted β-proline and β-homoproline

Tunable cis/trans prolyl amide bond configuration in substituted β-proline (β-Pro) and β-homoproline (β-Hpro) homodimers was explored, based on position and nature of the substituent. Tertiary amide bond in β-proline (β^2,3-substituted) dimers show distinct trans configuration and β-homoproline (β³-substituted) dimers preferably exhibited cis configuration.     

Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons and its application for the synthesis of diaryl ethers

Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons support for the synthesis of diaryl ethers via Ullmann type coupling is reported. The catalyst showed excellent performance for C–O cross coupling reactions under ligand free condition. The catalyst was characterized by various techniques such as SEM, TEM, XRD, EDX, BET, TGA, and UV spectrophotometry. It was recycled several times without significant loss in its catalytic activity.     

Synthesis of tetrahedral diarylheptanoid ent-diospongin A and epimer-diospongin B by employing Julia–Kocienski olefination

Total synthesis of ent-diospongin A and epimer-diospongin B has been accomplished in good yield with high optical purity. The key steps of diospongin synthesis involve Julia–Kocienski olefination, Weinreb amide formation, Grignard reaction, reduction, acetonide deprotection, Lewis acid catalyzed cyclization, and Wacker oxidation.     

Synthesis and characterization of microstructured sheets of semiconducting Ca[TCNQ]2 via redox-driven solid-solid phase transformation of TCNQ microcrystals

Microstructured sheets of semiconducting Ca[TCNQ]₂ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) have been synthesized via electrochemically driven (TCNQ)/Ca[TCNQ]₂ solid-solid phase transformation that occurs upon one-electron reduction of solid TCNQ, mechanically attached to an electrode surface, in the presence of an aqueous Ca²⁺ _(aq) electrolyte solution. Voltammetric probing of the electrochemically irreversible TCNQ/Ca[TCNQ]₂ interconversion revealed that it is highly dependent on scan rate and Ca²⁺ _(aq) electrolyte concentration. This voltammetric behavior, supported by double potential-step chronoamperometric evidence, clearly attests that formation of Ca[TCNQ]₂ takes place via a rate-determining nucleation/growth process, which involves ingress of Ca²⁺ _(aq) cations into the TCNQ^·? crystal lattice at the triple phase TCNQ/TCNQ^·? _(s)│GC_(s)│Ca²⁺ _(aq) electrolyte junction. The overall redox process associated with this chemically reversible solid-solid transformation can be described by the equation: TCNQ⁰ _(S)?+?2e^??+?Ca²⁺ _(aq) ? {Ca[TCNQ]₂}_(S). SEM characterization of the morphology of the generated Ca[TCNQ]₂ material showed the formation of microstructured sheets, which are substantially different from those of parent TCNQ crystals and the needle-shaped crystals of group I cations (M⁺?=?Li, Na, K, Rb, and Cs). The kinetic and thermodynamic implications of the ΔE _p and E _m values as a function of scan rate are discussed in terms of nucleation–growth and their relevance to those reported for the conceptually related group I cations and binary M[TCNQ]₂ (M²⁺?=?Mn, Fe, Co, and Ni)-based coordination polymers.     

Calorimetry and thermal analysis studies on the binding of 13-phenylalkyl and 13-diphenylalkyl berberine analogs to tRNAphe

The interaction of 13- monophenylalkyl and diphenylalkyl berberine analogs with tRNA^phe has been investigated using various thermochemical techniques like thermal melting, isothermal titration calorimetry, and differential scanning calorimetry experiments. Thermal melting studies revealed that all the analogs stabilized the tRNA^phe better than berberine. The binding affinity for the analogs was of the order of 10⁵ M^?1. Calorimetry results suggested that the binding of these analogs was predominantly entropy driven with small negative enthalpy contribution to the standard molar Gibbs energy. The temperature dependence of the standard molar enthalpy changes yielded negative values of standard molar heat capacity changes for the complexation revealing substantial hydrophobic contribution in the RNA binding of these analogs. An enthalpy–entropy compensation behavior was also seen in all the systems. The diphenylalkyl analogs were found to be more effective tRNA^phe binders compared to the monophenylalkyl analogs. The utility of the present work lies in understanding the structural and energetic aspects of the interaction of these berberine analogs with tRNA, which may be useful in the development of RNA-targeted drugs.     

Synthesis and Antimicrobial Studies of Selenadiazolo Benzimidazoles

An efficient and eco‐friendly method has been developed for the synthesis of selenadiazolo benzimidazoles by the condensation of N‐benzylbenzo[c][1,2,5]selenadiazole‐4,5‐diamine with various aromatic aldehydes catalyzed by xanthan sulfuric acid. All the synthesized compounds 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j were evaluated for in vitro antibacterial activity against Gram‐positive bacterial strains (Bacillus subtilis, Staphylococcus aureus, and Streptococcus pyogenes), and Gram‐negative bacterial strains (Escherichia coli, Klebsiella pneumonia, and Salmonella typhimurium) and antifungal against Aspergillus niger, Candida albicans, and Aspergillus flavus (Fungi). Compound 5i emerged as the most interesting compound in this series exhibiting excellent antimicrobial activity.     

Surface-assisted laser desorption-ionization mass spectrometry of oligosaccharides using magnesium oxide nanoparticles as a matrix

We describe the use of magnesium oxide nanoparticles (MgO-NPs) as a new matrix for the analysis of oligosaccharides (maltoheptaose, palatinose, D-panose, N-acetyllactosamine and β-gentiobiose) by surface-assisted laser desorption-ionization time-of-flight mass spectrometry (SALDI-MS). The use of MgO-NPs results in mass spectra without background noise and no fragmented ions in the low-mass region. The MgO-NPs were characterized by FT-IR, scanning electron microcopy, transmission electron microscopy which reveal that the particles are well dispersed in solution. The system allows the detection of the analytes at <20 nM concentrations, with limits of detection of 4.0, 5.5, 6.0, 10.0 and 7.0 nM, respectively. The calibration plots are linear (R ² values between 0.9896 and 0.9985), and relative standard deviations are <10 %. We conclude that MgO-NPs-based SALDI-MS enables the efficient and sensitive analysis of oligosaccharides in the low-mass region.