原位低场核磁共振弛豫法定量监测光催化Cr(Ⅵ)还原反应

本文利用原位低场核磁共振（LF-NMR）技术在真实固液反应环境中对光催化还原Cr（Ⅵ）反应进行了定量研究,并对Ag纳米颗粒负载量不同的Ag担载石墨相氮化碳复合光催化剂（Ag/g-C₃N₄）在可见光照射下催化Cr（Ⅵ）还原为Cr（Ⅲ）的性能进行了研究.研究发现,Ag纳米颗粒负载（负载量分别为1 wt.%、2 wt.%、5 wt.%和10 wt.%）可以有效提高g-C₃N₄的光催化性能;且负载量为5 wt.%时光催化性能最优,为无Ag负载的g-C₃N₄的4倍.此外,本文还通过横向弛豫时间（T₂）定量分析了反应体系中顺磁性Cr（Ⅲ）离子的浓度,证实了采用LF-NMR弛豫法评价光催化Cr（Ⅵ）还原反应性能的可行性.     

Anomerization reaction of bare and microhydrated d‐erythrose via explicitly correlated coupled cluster approach. Two water molecules are optimal

We present a comprehensive benchmark computational study which has explored a complete path of the anomerization reaction of bare d ‐erythrose involving a pair of the low‐energy α‐ and β‐furanose anomers, the former of which was observed spectroscopically (Cabezas et al., Chem. Commun. 2013, 49, 10826). We find that the ring opening of the α‐anomer yields the most stable open‐chain tautomer which step is followed by the rotational interconversion of the open‐chain rotamers and final ring closing to form the β‐anomer. Our results indicate the flatness of the reaction's potential energy surface (PES) corresponding to the rotational interconversion path and its sensitivity to the computational level. By using the explicitly correlated coupled cluster CCSD(T)‐F12/cc‐pVTZ‐F12 energies, we determine the free energy barrier for the α‐furanose ring‐opening (rate‐determining) step as 170.3 kJ/mol. The question of the number of water molecules (n ) needed for optimal stabilization of the erythrose anomerization reaction rate‐determining transition state is addressed by a systematic exploration of the PES of the ring opening in the α‐anomer‐(H₂O)_n and various β‐anomer‐(H₂O)_n (n = 1–3) clusters using density functional and CCSD(T)‐F12 computations. These computations suggest the lowest free energy barrier of the ring opening for doubly hydrated α‐anomer, achieved by a mechanism that involves water‐mediated multiple proton transfer coupled with the furanose C O bond breakage. Among the methods used, the G4 performed best against the CCSD(T)‐F12 reference at estimating the ring‐opening barrier heights for both the hydrated and bare erythrose conformers. Our results for the hydrated species are most relevant to an experimental study of the anomerization reaction of d ‐erythrose to be carried out in microsolvation environment. © 2016 Wiley Periodicals, Inc.     

DLPNO‐CCSD(T) scaled methods for the accurate treatment of large supramolecular complexes

In this work, we present scaled variants of the DLPNO‐CCSD(T) method, dubbed as (LS)DLPNO‐CCSD(T) and (NS)DLPNO‐CCSD(T), to obtain accurate interaction energies in supramolecular complexes governed by noncovalent interactions. The novel scaled schemes are based on the linear combination of the DLPNO‐CCSD(T) correlation energies calculated with the standard (LoosePNO and NormalPNO) and modified (Loose2PNO and Normal2PNO) DLPNO‐CCSD(T) accuracy levels. The scaled DLPNO‐CCSD(T) variants provide nearly TightPNO accuracy, which is essential for the quantification of weak noncovalent interactions, with a noticeable saving in computational cost. Importantly, the accuracy of the proposed schemes is preserved irrespective of the nature and strength of the supramolecular interaction. The (LS)DLPNO‐CCSD(T) and (NS)DLPNO‐CCSD(T) protocols have been used to study in depth the role of the CH–π versus π–π interactions in the supramolecular complex formed by the electron‐donor truxene‐tetrathiafulvalene (truxTTF) and the electron‐acceptor hemifullerene (C₃₀H₁₂). (NS)DLPNO‐CCSD(T)/CBS calculations clearly reveal the higher stability of staggered (dominated by CH–π interactions) versus bowl‐in‐bowl (dominated by π–π interactions) arrangements in the truxTTF•C₃₀H₁₂ heterodimer. Hemifullerene and similar carbon‐based buckybowls are therefore expected to self‐assemble with donor compounds in a richer way other than the typical concave–convex π–π arrangement found in fullerene‐based aggregates. © 2017 Wiley Periodicals, Inc.     

Simple and rapid surface-enhanced Raman Spectroscopy assay for safranine T and its application in highly sensitive determination of mercury (Ⅱ)

A simple and sensitive surface-enhanced Raman spectroscopy (SERS) method for the detection of safranine T (ST) and Hg²⁺ using silver nanoparticles (AgNPs) as substrate was developed. ST can absorb on the surface of AgNPs through electrostatic interaction, the electromagnetic effect combined with chemical adsorption effect give a notable Raman enhancement for ST. The presence of Hg²⁺ well decreased the absorbed ST molecules on AgNPs, leading to a significant decrease of SERS signals thus enabling to detect Hg²⁺. The determination conditions for SERS, including the amount of AgNPs, the concentration of NaCl, the concentration of HCl, the concentration of ST and the reaction time, were optimised. Under the optimised experimental conditions, good linear responses were obtained for ST and Hg²⁺ in the concentration ranges of 0.01–4.0 μmol L^?1 (3.5–1403.4 ng mL^?1) and 0.01–2.0 μmol L^?1 (2.0–401.2 ng mL^?1), the limit of detection were 3.0 nmol L^?1 (1.1 ng mL^?1) and 2.0 nmol L^?1 (0.4 ng mL^?1), respectively. The present method was subsequently applied to the determination of ST in tomato sauces and Hg²⁺ in environmental waters, the recoveries of ST and Hg²⁺ in spiked samples are 95.5–107.8% and 91.4–110.8 %, respectively.     

Magnetic bead based immunoassay for enumeration of CD4 T lymphocytes on a microfluidic device

Human immunodeficiency virus (HIV) diagnostics are urgently needed in resource-scarce settings. Monitoring of HIV-infected patients requires accurate counting of CD4⁺ T lymphocytes. However, the current methods for enumeration of CD4⁺ T lymphocytes are of high cost, technically complex and time-consuming. In this paper, we developed a simple, rapid and inexpensive one-step immunomagnetic method for separating and counting CD4⁺ T lymphocytes on microfluidic devices with enlarged reaction chambers. CD4⁺ T lymphocytes were successfully separated and captured from the cell suspension obtained from mouse thymus. CD4 counts were determined under an optical microscope in a rapid and simple format. In order to acquire the maximum efficiency of cell capture, relative parameters were investigated, including section area of the reaction chamber and injection flow rate of the cell suspension. The enlarged reaction chamber with two symmetrical cone-shaped ends was helpful for cell capture, and the maximum capability of captured CD4⁺ T lymphocytes was about 700 cells μL⁻¹. Our investigations avoided the complex sample pre-treatment, and the entire analysis time was significantly reduced to 15 min. This CD4 counting microdevice had the potential to reduce the cost for HIV diagnosis in resource-limited settings.     

Sheet AA2024‐T3: a new investigation of microstructure and composition

Sheet AA2024‐T3 is probably one of the most studied aluminium alloys in the corrosion field, because, with copper as an alloying addition, it is one of the most corrosion‐prone aluminium alloys. This paper reports new findings on the composition and distribution of intermetallic (IM) particles in AA2024‐T3 through the examination of over 80 000 compositional domains in nearly 18 000 IM particles. This work was achieved by using an electron microprobe to map out 2 × 2 mm² at a step size of 400 nm. This study revealed that the composition of individual particles can vary considerably from ‘accepted’ compositions. Domains within particles were extensive across the surface. Because such a large area was mapped, it was possible to subdivide this area and to look at the variation of particle statistics from region to region, providing some information on the statistical variation for small electrodes. Copyright © 2010 John Wiley & Sons, Ltd.     

New approach for measurement of non-SHBG-bound testosterone in human plasma

Testosterone (T) circulates in the blood tightly bound to sex hormone-binding globulin (SHBG) and weakly to albumin. Measuring protein unbound T (free) or non-SHBG-bound T rather than total T has been recommended for the evaluation of androgen disorders in humans. Ammonium sulfate precipitation has been widely used to separate [SHBG-T] complex from free and albumin-bound T. To achieve more specificity in this separation, we used monoclonal anti-SHBG antibody and developed a suitable and convenient immunoassay for measuring non-SHBG-bound T. Magnetic beads were covalently coupled to a monoclonal anti-SHBG antibody to capture [SHBG-T] complex from plasma samples. Magnetic separation was then performed to allow measurement of non-SHBG-bound T in the supernatant by direct radioimmunoassay. When 300 μL of plasma samples were incubated at room temperature with 10 μL of anti-SHBG beads, residual SHBG concentration was undetectable in the supernatant. The specificity of proteins retained on anti-SHBG beads was further demonstrated by peptide mass fingerprint on a MALDI-TOF analyzer. The non-specific adsorption of T on beads was low (5%), and dissociation of T from SHBG-T complex was less than 5% after 180 min of incubation. The plasma concentrations of non-SHBG-bound T using anti-SHBG beads were highly correlated to those obtained using ammonium sulfate precipitation. We conclude that SHBG immunocapture is a highly specific and useful tool for an experimental direct measurement of plasma non-SHBG-bound T. This methodology is also convenient and appropriate for routine and automated assay.     

LC/ESI‐MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain

Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti‐adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI‐MS) and ESI‐MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI‐MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI‐MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI‐MS/MS analysis of fraction I showed the presence of C₁₃, C₁₄ and C₁₅ surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na]⁺ at m/z 1030, 1044 and 1058. LC/ESI‐MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H]⁺ at m/z 1478 and 1506 corresponding to C₁₇ fengycin A and C₁₇ fengycin B, respectively. Other homologues (C₁₄ to C₁₆) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Enrichment,incorporation and oxidation of copper during anodising of aluminium–copper alloys

Porous anodic oxides generated on copper‐containing aluminium alloys are less regular than anodic oxides generated on pure aluminium. Specifically, a porous oxide morphology comprising layers of embryo pores, generated by a cyclic process of oxide film growth and oxygen evolution, is generally observed. In this work, the relation between the oxidation behaviour of copper during anodising and the specific porous oxide film morphology was investigated by electrochemical techniques, transmission electron microscopy and Rutherford backscattering spectroscopy (RBS). It was found that the anodising potential determines the oxidation behaviour of copper, and the latter determines the porous oxide morphology. At low voltage, relatively straight pores with continuous cell walls were obtained on Al? Cu alloys, but selective oxidation of aluminium atoms resulted in the occlusion of copper‐containing metallic nanoparticles in the anodic film. At higher potentials, copper oxidation promoted oxygen evolution within the barrier layer, and generation of a less regular film morphology. RBS, performed on Al? Cu alloy specimens, revealed a high volume fraction of copper atoms in the anodic films generated at low potentials and a reduced amount of copper atoms in the anodic oxide films generated at high potentials. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of Monomeric and Dimeric Repeating Units of the Zwitterionic Type 1 Capsular Polysaccharide from Streptococcus pneumoniae

Zwitterionic polysaccharides (ZPSs) from Bacteroides fragilis and Streptococcus pneumoniae display unique T‐cell activities. The first synthesis of a hexasaccharide representing two repeating units of the zwitterionic capsular polysaccharide from S. pneumoniae type 1 (Sp1) is reported. Key elements of the approach are stereoselective construction of 1,4‐cis‐α‐galactose linkages based on a reactive trichloroacetimidate donor that incorporates a 6‐O‐acetyl group, which may contribute to the high α selectivity in glycosylation. After assembly of the fully protected hexasaccharide from five monosaccharide synthons 2 – 4 , 24 and 25 , selective deprotection of the primary hydroxyl groups of the four galactose residues followed by oxidation to the corresponding uronic acids provides hexasaccharide 19 . The trisaccharide counterpart 1 was synthesized in similar fashion from three synthons, 2 – 4 . This approach employed both conventional and dehydrative glycosylation methodologies and avoids the use of poorly reactive uronic acid derived glycosyl donors and acceptors.