An iron Schiff base complex loaded mesoporous silica nanoreactor as a catalyst for the synthesis of pyrazine-based heterocycles

An iron Schiff base complex was encapsulated in SBA-15 mesoporous silica to afford a Fe(III)-Schiff base/SBA-15 heterogeneous nanocatalyst for the synthesis of pyridopyrazine and quinoxaline heterocycles. These reactions proceeded in water with excellent yields. The catalyst was characterized by physico-chemical and spectroscopic methods and found to retain the characteristic channel structures of the SBA-15, allowing good accessibility of the encapsulated metal complex.     

Synthesis and characterization of derivatives including thiazolidine-2,4-dione/1-H- imidazole and evaluation of antimicrobial,antioxidant, and cytotoxic properties of new synthetic heterocyclic compounds

Several new derivatives of thiazolidine-2,4-dione and 1-H-imidazole were prepared using imidazole aldehydes 6a–6f in ethanol as a solvent. Products 7a–7f were obtained in reasonable yields and great purity. The antioxidant activity for finish products was evaluated by DPPH radical scavenging activity and showed relatively good activity against ascorbic acid. Compounds 7d, 7e, and 7f had the highest antioxidant activity. Compound 7c showed the lowest amount of IC50 versus ascorbic acid. The antimicrobial activity of these compounds against gram-positive bacteria including Bacillus anthracis (B. anthracis) and Staphylococcus aureus (S. aureus) and gram-negative bacteria including Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) bacteria was evaluated by the inhibition zone diameter assay method, and the compounds showed moderate to low antibacterial activity. The toxicity properties of all synthesized compounds against cisplatin were investigated. Most of the compounds showed good activity against the positive control group, and the toxicity of compound 7b was higher than that of other compounds.

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Highly efficient and chemoselective acetalization of carbonyl compounds catalyzed by new and reusable zirconyl triflate,ZrO(OTf)2

Various types of aromatic aldehydes were efficiently converted to their corresponding 1,3‐dioxanes and 1,3‐dioxolane with 1,3‐propanediol and ethylene glycol, respectively, in the presence of catalytic amount of ZrO(OTf)₂ in acetonitrile at room temperature. The catalyst can be reused several times without loss of its catalytic activity. Very short reaction times, selective acetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones, very mild reaction conditions, reusability of the catalyst, and easy workup are noteworthy advantages of this method. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:131–135, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20523     

Atomic-scale studies of impurities in superconductors with a scanning tunneling microscope

Imaging and spectroscopy with a cryogenic scanning tunneling microscope (STM) have been used to study the local variation of electronic states on the atomic scale in both low-T_c and high-T_c superconductors. These experiments provide an atomic-scale perspective of impurity scattering by directly probing the localized excitations that are induced by individual impurities.     

Dirac Nodal Arc Semimetal PtSn4: An Ideal Platform for Understanding Surface Properties and Catalysis for Hydrogen Evolution

Conductivity, carrier mobility, and a suitable Gibbs free energy are important criteria that determine the performance of catalysts for a hydrogen evolution reaction (HER). However, it is a challenge to combine these factors into a single compound. Herein, we discover a superior electrocatalyst for a HER in the recently identified Dirac nodal arc semimetal PtSn₄. The determined turnover frequency (TOF) for each active site of PtSn₄ is 1.54 H₂ s^?1 at 100 mV. This sets a benchmark for HER catalysis on Pt‐based noble metals and earth‐abundant metal catalysts. We make use of the robust surface states of PtSn₄ as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently. In addition, PtSn₄ displays excellent chemical and electrochemical stabilities after long‐term exposure in air and long‐time HER stability tests.