Accurate redetermination of the X-ray structure and electronic bonding in adenosylcobalamin

The electronic structure of adenosylcobalamin (B12 coenzyme, AdoCbl) has been calculated by a density functional method, using the orthogonalized linear combination of the atomic orbital method (OLCAO). Since a fixed accurately determined geometry was needed in such calculations, the crystal structure of adenosylcobalamin has been redone and refined to R = 0.065, using synchrotron diffraction data. Comparison with the recently reported electronic structures of cyano- (CNCbl) and methylcobalamin (MeCbl) shows that the net charges and bond orders vary only on the axial donors. The values in the three cobalamins suggest that the Co-C bond in MeCbl has a strength similar to that in AdoCbl, but it is significantly weaker that that in CNCbl. Present results are compared with those previously reported for the analogous corrin derivatives; i.e., simplified cobalamins with the side chains a-f replaced by H atoms. Despite a qualitative agreement, a discrepancy in the calculated HOMO-LUMO gap is found.     

双功能型嵌入镍纳米颗粒的碳棱柱状微米棒电极用于电化学甲醇氧化助力的节能产氢

With the rapid development of human society, clean energy forms are imperative to sustain the normal operations of various mechanical and electrical facilities under a cozy environment. Hydrogen is considered among the most promising clean energy sources for the future. Recently, electrochemical water splitting has been considered as one of the most efficient approaches to harvest hydrogen energy, which generates only non-pollutant water on combustion. However, the sluggish anodic oxygen evolution reaction significantly restricts the efficiency of water splitting and requires a relatively high cell voltage to drive the electrolysis. Therefore, seeking a thermodynamically favorable anodic reaction to replace the sluggish oxygen evolution reaction by utilizing highly active bifunctional electrocatalysts for the anodic reaction and hydrogen evolution are crucial for achieving energy-efficient hydrogen production for industrial applications. Nevertheless, it is known that the oxygen evolution reaction can be replaced with other useful and thermodynamically favorable reactions to reduce the electrolysis voltage for realizing energy-efficient hydrogen production. Therefore, in this study, we present a bifunctional nickel nanoparticle-embedded carbon (Ni@C) prism-like microrod electrocatalyst synthesized via a two-step method involving the synthesis of a precursor metal-organic framework-74 and subsequent carbonization treatment for methanol oxidation and hydrogen evolution. The interfacial structure consisting of a nickel and carbon skeleton was realized via in situ carbonization. However, the dispersed nickel nanoparticles do not easily aggregate owing to the partition by the surrounding carbon as it would sufficiently expose the active Ni sites to the electrolytes, ensuring fast charge transfer between the catalyst and electrolytes by accelerating the electrochemical kinetics. In the anodic methanol oxidation, the products were detected as carbon dioxide and formate with faradaic efficiencies of 36.2% and 62.5%, respectively, at an applied potential of 1.55 V. Meanwhile, the Ni@C microrod catalyst demonstrated high activity and durability (2.7% current decay after 12 h of continuous operation) toward methanol oxidation, which demonstrates that methanol oxidation precedes oxidation under voltage forces. Notably, the bifunctional catalyst not only exhibits excellent performance toward methanol oxidation but also yields a low overpotential of 155 mV to drive 10 mA∙cm⁻² toward hydrogen evolution in 1.0 mol∙L⁻¹ KOH aqueous solution with 0.5 mol∙L⁻¹ methanol at room temperature, which guarantees the hydrogen production efficiency. More importantly, the constructed two-electrode electrolyzer produced a current density of 10 mA∙cm⁻² at a low cell voltage of 1.6 V, which decreased by 240 mV after replacing the oxygen evolution reaction with methanol oxidation.     

不同种类羧酸钠对草酸钙结晶过程中晶相的影响

采用X射线衍射法研究了水溶液中不同种类羧酸钠对尿结石主要成份草酸钙结晶的影响，这些羧酸钠分别为含有一、二、三和四个羧基的羟基乙酸钠（NaGly）、酒石酸钠（Na2Tart）、柠檬酸钠（Na3Cit）和EDTA二钠盐（Na2EDTA）.结果表明，随着羧酸钠浓度的增加，草酸钙的晶相均发生规律性的变化：从最稳定的一水草酸钙（COM），到不稳定的二水草酸钙（COD），最后转化为次稳定的三水草酸钙（COT）.不同结构羧酸钠抑制COM生长、促进COD生成的顺序为:Na3Cit >Na2Tart >Na2EDTA >NaGly.该结果将为临床上选择防结石药物提供新的思路.     

Effects of temperature and sodium carboxylate additives on mineralization of calcium oxalate in silica gel systems

Urolithiasis remains a major medical problem in China, especially in Guangdong Province in the southest of China[1]. A survey in Shenzhen city, the most southern city in China, showed the incidence of renal calculus was 4.87%, being 6.12% in the males and 4.07% in the females[2]. The prevalence of renal calculus has been more as the age advances and in the male population and so was in the less-educated population. The recurrence rate is more than 80%, with a moderate improvement by conventi…     

Z‐bpy,a New C2‐Symmetric Bipyridine Ligand and Its Application in Enantioselective Copper(I)‐Catalyzed Cyclopropanation of Olefins

A rigid C₂‐symmetric chiral bipyridine ligand Z‐bpy with a triptycene‐like backbone was designed and synthesized from simple chemicals in a scalable route. Using this new ligand, copper(I) catalyzed cyclopropanation of styrenes with commercial ethyl diazoacetate produced various corresponding cyclopropanes in high yields, diastereoselectivity and enantioselectivity up to 97% ee.     

Immobilization of carboxyl-modified multiwalled carbon nanotubes in chitosan-based composite membranes for U(VI) sorption

Journal of Radioanalytical and Nuclear Chemistry - The carboxyl-modified multiwalled carbon nanotubes were immobilized in chitosan-based composite membranes (CS-CNTs) which were used as efficient...     

The MAP/PH/N retrial queue in a random environment

We consider the MAP/PH/N retrial queue with a finite number of sources operating in a finite state Markovian random environment. Two different types of multi-dimensional Markov chains are investigated describing the behavior of the system based on state space arrangements. The special features of the two formulations are discussed. The algorithms for calculating the stationary state probabilities are elaborated, based on which the main performance measures are obtained, and numerical examples are presented as well.     

Filling the Charge–Discharge Voltage Gap in Flexible Hybrid Zinc-Based Batteries by Utilizing a Pseudocapacitive Material

The high charge–discharge voltage gap is one of the main bottlenecks of zinc–air batteries (ZABs) because of the kinetically sluggish oxygen reduction/evolution reactions (ORR/OER) on the oxygen electrode side. Thus, an efficient bifunctional catalyst for ORR and OER is highly desired. Herein, honeycomb-like MnCo₂O_4.5 spheres were used as an efficient bifunctional electrocatalyst. It was demonstrated that both ORR and OER catalytic activity are promoted by Mn^IV-induced oxygen vacancy defects and multiple active sites. Importantly, the multivalent ions present in the material and its defect structure endow stable pseudocapacitance within the inactive region of ORR and OER; as a result, a low charge–discharge voltage gap (0.43 V at 10 mA cm⁻²) was achieved when it was employed in a flexible hybrid Zn-based battery. This mechanism provides unprecedented and valuable insights for the development of next-generation metal–air batteries.     

In Situ Nitrogen Retention of Carbon Anode for Enhancing the Electrochemical Performance for Sodium-Ion Battery

Retaining nitrogen for polyacrylonitrile (PAN) based carbon anode is a cost-effective way to make full use of the advantages of PAN for sodium-ion batteries (SIBs). Here, a simple strategy has been successfully adopted to retain N atoms in situ and increase production yield of a novel composite PAZ by mixing 3 wt % of zinc borate (ZB) with poly (acrylonitrile-co-itaconic acid) (PANIA). Among the prepared carbonised fibre (CF) samples, PAZ-CF-700 maintains the highest N content, retaining 90 % of the original N from PANIA. It represents the highest capacity storage contribution (80.55 %) and the lowest impedance R_ct (117 Ω). Consequently, the specific capacity increases from 60 mAh g⁻¹ of PANIA-CF-700 to 190 mAh g⁻¹ of PAZ-CF-700 at a current density of 100 mA g⁻¹. At the same time, PAZ-CF-700 exhibits a good rate performance and excellent long-term cycling stability with a specific capacity of 94 mAh g⁻¹ after 4000 cycles at 1.6 A g⁻¹.