A three‐dimensional mixed‐valence CuII/CuI coordination polymer constructed from biphenyl‐3,4′,5‐tricarboxylate and 1,4‐bis(1H‐imidazol‐1‐yl)benzene ligands

Coordination polymers (CPs) built by coordination bonds between metal ions/clusters and multidentate organic ligands exhibit fascinating structural topologies and potential applications as functional solid materials. The title coordination polymer, poly[diaquabis(μ₄‐biphenyl‐3,4′,5‐tricarboxylato‐κ⁴O³:O^3′:O^4′:O⁵)tris[μ₂‐1,4‐bis(1H‐imidazol‐1‐yl)benzene‐κ²N³:N^3′]dicopper(II)dicopper(I)], [Cu^II₂Cu^I₂(C₁₅H₇O₆)₂(C₁₂H₁₀N₄)₃(H₂O)₂]_n, was crystallized from a mixture of biphenyl‐3,4′,5‐tricarboxylic acid (H₃bpt), 1,4‐bis(1H‐imidazol‐1‐yl)benzene (1,4‐bib) and copper(II) chloride in a water–CH₃CN mixture under solvothermal reaction conditions. The asymmetric unit consists of two crystallographically independent Cu atoms, one of which is Cu^II, while the other has been reduced to the Cu^I ion. The Cu^II centre is pentacoordinated by three O atoms from three bpt³⁻ ligands, one N atom from a 1,4‐bib ligand and one O atom from a coordinated water molecule, and the coordination geometry can be described as distorted trigonal bipyramidal. The Cu^I atom exhibits a T‐shaped geometry (CuN₂O) coordinated by one O atom from a bpt³⁻ ligand and two N atoms from two 1,4‐bib ligands. The Cu^II atoms are extended by bpt³⁻ and 1,4‐bib linkers to generate a two‐dimensional network, while the Cu^I atoms are linked by 1,4‐bib ligands, forming one‐dimensional chains along the [20] direction. In addition, the completely deprotonated μ₄‐η¹:η¹:η¹:η¹ bpt³⁻ ligands bridge one Cu^I and three Cu^II cations along the a (or [100]) direction to form a three‐dimensional framework with a (10³)₂(10)₂(4².6.10².12)₂(4².6.8².10)₂(8) topology via a 2,2,3,4,4‐connected net. An investigation of the magnetic properties indicated a very weak ferromagnetic behaviour.     

Purine 3′:5′‐cyclic nucleotides with the nucleobase in a syn orientation: cAMP,cGMP and cIMP

Purine 3′:5′‐cyclic nucleotides are very well known for their role as the secondary messengers in hormone action and cellular signal transduction. Nonetheless, their solid‐state conformational details still require investigation. Five crystals containing purine 3′:5′‐cyclic nucleotides have been obtained and structurally characterized, namely adenosine 3′:5′‐cyclic phosphate dihydrate, C₁₀H₁₂N₅O₆P·2H₂O or cAMP·2H₂O, (I), adenosine 3′:5′‐cyclic phosphate 0.3‐hydrate, C₁₀H₁₂N₅O₆P·0.3H₂O or cAMP·0.3H₂O, (II), guanosine 3′:5′‐cyclic phosphate pentahydrate, C₁₀H₁₂N₅O₇P·5H₂O or cGMP·5H₂O, (III), sodium guanosine 3′:5′‐cyclic phosphate tetrahydrate, Na⁺·C₁₀H₁₁N₅O₇P⁻·4H₂O or Na(cGMP)·4H₂O, (IV), and sodium inosine 3′:5′‐cyclic phosphate tetrahydrate, Na⁺·C₁₀H₁₀N₄O₇P⁻·4H₂O or Na(cIMP)·4H₂O, (V). Most of the cyclic nucleotide zwitterions/anions [two from four cAMP present in total in (I) and (II), cGMP in (III), cGMP⁻ in (IV) and cIMP⁻ in (V)] are syn conformers about the N‐glycosidic bond, and this nucleobase arrangement is accompanied by C_rib—H…N_pur hydrogen bonds (rib = ribose and pur = purine). The base orientation is tuned by the ribose pucker. An analysis of data obtained from the Cambridge Structural Database made in the context of syn–anti conformational preferences has revealed that among the syn conformers of various purine nucleotides, cyclic nucleotides and dinucleotides predominate significantly. The interactions stabilizing the syn conformation have been indicated. The inter‐nucleotide contacts in (I)–(V) have been systematized in terms of the chemical groups involved. All five structures display three‐dimensional hydrogen‐bonded networks.     

Electrospun‐Technology‐Derived High‐Performance Electrochemical Energy Storage Devices

Electrospinning, as a novel nontextile filament technology, is an important method to prepare continuous nanofibers and has shown its remarkable advantages, such as a broadly applicable material system, controllable fiber size and structure, and simple process. Electrospun nanofiber membranes prepared by electrospinning have shown promising applications in many fields, such as supercapacitors, lithium‐ion batteries, and sodium‐ion batteries, owing to their large specific surface area and adjustable network pore structure. The principle of electrospinning and key points relevant to its usage in the preparation of high‐performance electrochemical energy storage materials are reviewed herein based on recent publications, particularly focusing on research progress of relative materials. Also, this review describes a distinctive conclusion and perspective on the future challenges and opportunities in electrospun nanomaterials.     

Influence of sodium alginate pretreated by ultrasound on papain properties: Activity,structure, conformation and molecular weight and distribution

The aim of the study was to investigate the impact of sodium alginate (ALG) pretreated by ultrasound on the enzyme activity, structure, conformation and molecular weight and distribution of papain. ALG solutions were pretreated with ultrasound at varying power (0.05, 0.15, 0.25, 0.35, 0.45 W/cm²), 135 kHz, 50 °C for 20 min. The maximum relative activity of papain increased by 10.53% when mixed with ALG pretreated by ultrasound at 0.25 W/cm², compared with the untreated ALG. The influence of ultrasound pretreated ALG on the conformation and secondary structure of papain were assessed by fluorescence spectroscopy and circular dichroism spectroscopy. The fluorescence spectra revealed that ultrasound pretreated ALG increased the number of tryptophan on papain surface, especially at 0.25 W/cm². It indicated that ultrasound pretreatment induced molecular unfolding, causing the exposure of more hydrophobic groups and regions from inside to the outside of the papain molecules. Furthermore, ultrasound pretreated ALG resulted in minor changes in the secondary structure of the papain. The content of α-helix was slightly increased after ultrasound pretreatment and no significant change was observed at different ultrasound powers. ALG pretreated by ultrasound enhanced the stability of the secondary structure of papain, especially at 0.25 W/cm². The free sulfhydryl (SH) content of papain was slightly increased and then decreased with the increase of ultrasonic power. The maximum content of free SH was observed at 0.25 W/cm², under which the content of the free SH increased by 6.36% compared with the untreated ALG. Dynamic light scattering showed that the effect of ultrasound treatment was mainly the homogenization of the ALG particles in the mixed dispersion. The gel permeation chromatography coupled with the multi-angle laser light scattering photometer analysis showed that the molecular weight (M_w) of papain/ALG was decreased and then increased with the ultrasonic pretreatment. Results demonstrated that the activity of immobilized papain improved by ultrasonic pretreatment was mainly caused by the variation of the conformation of papain and the effect of interactions between papain and ALG. This study is important to explain the intermolecular interactions of biopolymers and the mechanism of enzyme immobilization treated by ultrasound in improving the enzymatic activity. As expected, ALG pretreated by appropriate ultrasound is promising as a bioactive compound carrier in the field of immobilized enzyme.     

Theoretical study of solvent effect on π-EDA complexation II. Complex between TCNE and two benzene molecules

Formation of tetracyanoethylene—benzene 1: 1 and 1: 2 complexes was modeled using the Møller—Plesset second-order theory (MP2) and polarized continuum model (PCM). The MP2 calculated geometry of 1: 1 complex presents a plane-parallel C _2υ sandwich structure with interplanar distance 3.05 × 10^?10 m, while the 1: 2 complex has D _2h geometry where the planparallel distance is equal to 3.09 × 10^?10 m. The MP2 calculations indicate that the main part of formation enthalpy in both complexes is dispersion energy due to intermolecular electron correlation. The calculations also show that the formation entropy destabilizes both complexes since from the two constituent molecules one complex molecule arises. The MP2/6-31G* procedure showed to be a suitable tool for the estimation of the relative importance of 1: 2 complexation compared to the 1: 1 complexation. In the gas phase the ratio of the equilibrium constants of both complexes K _1:2/K _1:1 = 0.09 was calculated. The presence of solvent, treated by the PCM, further destabilized the 1: 2 complex with respect to the 1: 1 complex. The ratio K _1:2/K _1:1 in CH₂Cl₂ calculated by the PCM method was 0.022, i.e. the 1: 2 complex was almost 50 times less stable than the 1: 1 complex, which is in agreement with available experimental data. According to the calculations, solvent always destabilizes complex with respect to the isolated (solvated) components.It was also found that charge polarization in the 1: 2 complex with respect to that in the 1: 1 complex was not strictly additive due to the presence of the second benzene molecule in the 1: 2 complex. Non-additive were also formation enthalpy, entropy, polarizability, charge transfer from donors to acceptor molecule and other properties. This fact is caused by a slightly changed interaction between constituent molecules in the 1: 2 complex in comparison with the 1: 1 complex as well as by the interaction between benzene molecules in the 1: 2 complex which is missing in the 1: 1 complex.Preliminary CIS/6-31G* theoretical study regarding a few first-electron (electron charge transfer) transitions in both complexes indicates the presence of Frenkel excitn and Davydov transition energy splitting in the 1: 2 “supercomplex” with the first allowed π → π* absorption transition at λ = 355 nm, while the first allowed transition in the case of 1: 1 complex was characterized by λ = 392 nm with the oscillator strength only half of that of the 1: 2 complex, which is in agreement with experiment. These unexpected large hypso-and hypochromic effects predicted by the theory could allow to overcome difficulties of the experimental determination of the 1: 2 complexation.     

Solubilizing sodium fluoride in acetonitrile: synthesis, molecular structure, and complexation behavior of bis(organostannyl)methyl-substituted crown ethers

The synthesis of the crown-ether-substituted bis(organostannyl)methanes Ph(3)SnCH(2)Sn(Ph(2))-CH(2)-[16]crown-5 (1) and Ph(2)ISnCH(2)Sn(I)(Ph)-CH(2)-[16]crown-5 (2) is reported. Both compounds have been characterized by elemental analyses, (1)H, (13)C, (19)F, and (119)Sn NMR spectroscopy, and in the case of compound 2 also by electrospray ionization mass spectrometry. Single-crystal X-ray diffraction analysis revealed for the aqua complex 2.H(2)O trigonal-bipyramidal-configured tin atoms with intramolecular Sn(1)-O(1) and Sn(2)-O(1W) distances of 2.555(2) and 2.440(3) A, respectively. The water molecule is trapped in a sandwich-like fashion between the crown ether oxygen atoms O(2) and O(4) and the Sn(2) atom. NMR spectroscopy unambiguously proved the ability of compound 2 in acetonitrile to overcome the high lattice energy of sodium fluoride and to complex the latter under charge separation.     

Spectroscopic calculation of the bond-dissociation energy of CH bonds in fluoro derivatives of methane,ethane, ethene,propene, and benzene

The bond-dissociation energy of CH bonds in fluoro derivatives of methane, ethane, ethene, propene, and benzene is determined by spectroscopic and quantum chemical methods. The spectroscopic values of the bond-dissociation energy of CH bonds are calculated in terms of fundamental absorption bands in the anharmonic approximation by the variational method using the Morse anharmonic basis. The quantum chemical calculations are performed using the 6-311G(3df, 3pd)/B3LYP basis set. The obtained regularities in variations of the CH bond dissociation energy values upon changes in the molecule structure are discussed.     

Selective Oxidation of Clopidogrel by Peroxymonosulfate (PMS) and Sodium Halide (NaX) System: An NMR Study

A selective transformation of clopidogrel hydrogen sulfate (CLP) by reactive halogen species (HOX) generated from peroxymonosulfate (PMS) and sodium halide (NaX) is described. Other sustainable oxidants as well as different solvents have also been investigated. As result of this study, for each sodium salt the reaction conditions were optimized, and four different degradation products were formed. Three products were halogenated at C-2 on the thiophene ring and have concomitant functional transformation, such as N-oxide in the piperidine group. A halogenated endo-iminium product was also observed. With this condition, a fast preparation of known endo-iminium clopidogrel impurity (new counterion) was reported as well. The progress of the reaction was monitored using nuclear magnetic resonance spectroscopy as an analytical tool and all the products were characterized by 1D-, 2D-NMR and HRMS.     

十水硫酸钠体系潜热蓄热材料的研究

本文研究了 十水硫酸钠 体系潜热蓄热及其熔冻行为,并对熔化热的测定技术及计 算 公式进行 了研 究.该 蓄热材料经 15。。次熔冻循环后,蓄热客量仍在 30 C al·g一`以上.     

一种新的甲硝唑荧光光纤传感器的研制

将1,4-二(苯并(噁)唑-1',3'-基-2')苯(BBOB)包埋在增塑的聚氯乙烯膜中,研制了一种新的荧光猝灭型甲硝唑光纤传感器.猝灭机制包括甲硝唑的初级内滤效应和甲硝唑与BBOB形成电荷转移复合物两种作用.传感器可逆性好,响应时间小于30s,响应线性范围是4.00×10^-6～1.00×10^-4mol/L,检测限为1.00×10^-6mol/L,对1.00×10^-4mol/L甲硝唑的相对偏差为0.82%(n=10).常见的无机离子、药物不影响甲硝唑的测定,对商品制剂中甲硝唑的测定结果与药典法一致.