Influence of Ag+ on the Magnetic Response of [2.2.2]Paracyclophane: NMR Properties of a Prototypical Organic Host for Cation Binding Based on DFT Calculations

The complexation of metal cations into a host–guest situation is particularly well exemplified by [2.2.2]paracyclophane and Ag^I, which leads to a strong cation–π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretical reasons for the observed experimental results with an aim to determine the role of the cation–π interaction in a host–guest scenario. From an analysis of certain components of the induced magnetic field and the ¹³C NMR shielding tensor under its own principal axis system (PAS), the local and overall magnetic behavior can be clearly described. Interestingly, the magnetic response of such a complex exhibits a large axis-dependent behavior, which leads to an overall shielding effect for the coordinating carbon atoms and a deshielding effect for the respective uncoordinated counterparts, evidence that complements previous experimental results. This proposed approach can be useful to gain further insight into the local and overall variation of NMR shifts for host–guest pairs involving both inorganic and organic hosts.     

离子色谱法测定蓝藻培养液中有机酸和无机阴离子

建立了一种利用阴离子交换色谱柱分离,电导检测器同时测定17种有机酸和7种阴离子的方法。采用Ionpac AS11-HC阴离子交换柱,KOH溶液作为淋洗液,梯度洗脱,流量为1.0mL/min,柱温为30℃,进样体积为25μL。24种分析物测定结果的相对标准偏差在0.31%~2.67%之间,线性相关系数均大于0.996,平均加标回收率在80.3%~108.5%之间。该方法可用于微生物培养液中有机酸和阴离子的同时测定。     

Characterization of Glycan Structures of Chondroitin Sulfate-Glycopeptides Facilitated by Sodium Ion-Pairing and Positive Mode LC-MS/MS

Purification and liquid chromatography-tandem mass spectrometry (LC-MS/MS) characterization of glycopeptides, originating from protease digests of glycoproteins, enables site-specific analysis of protein N- and O-glycosylations. We have described a protocol to enrich, hydrolyze by chondroitinase ABC, and characterize chondroitin sulfate-containing glycopeptides (CS-glycopeptides) using positive mode LC-MS/MS. The CS-glycopeptides, originating from the Bikunin proteoglycan of human urine samples, had ΔHexAGalNAcGlcAGalGalXyl-O-Ser hexasaccharide structure and were further substituted with 0-3 sulfate and 0-1 phosphate groups. However, it was not possible to exactly pinpoint sulfate attachment residues, for protonated precursors, due to extensive fragmentation of sulfate groups using high-energy collision induced dissociation (HCD). To circumvent the well-recognized sulfate instability, we now introduced Na⁺ ions to form sodiated precursors, which protected sulfate groups from decomposition and facilitated the assignment of sulfate modifications. Sulfate groups were pinpointed to both Gal residues and to the GalNAc of the hexasaccharide structure. The intensities of protonated and sodiated saccharide oxonium ions were very prominent in the HCD-MS2 spectra, which provided complementary structural analysis of sulfate substituents of CS-glycopeptides. We have demonstrated a considerable heterogeneity of the bikunin CS linkage region. The realization of these structural variants should be beneficial in studies aimed at investigating the importance of the CS linkage region with regards to the biosynthesis of CS and potential interactions to CS binding proteins. Also, the combined use of protonated and sodiated precursors for positive mode HCD fragmentation analysis will likely become useful for additional classes of sulfated glycopeptides.

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Split injection: A simple introduction of subnanoliter sample volumes for chip electrophoresis

The ability to accurately inject small volumes of sample into microfluidic channels is of great importance in electrophoretic separations. While electrokinetic injection of nanoliter scale volumes is commonly utilized in microchip capillary electrophoresis (MCE), mobility and matrix bias makes quantitation difficult. Herein, we describe a new injection method based on the simple patterning of the crossing of channels that does not require sophisticated instrumentation. The sample volume injected into the separation channel is dependent on the ratio of the widths of the crossing channels. This injection method is capable of introducing, into a separation channel, multiple plugs of sample on a large scale. This injection technique is tested for zone electrophoresis in native and surface modified poly(dimethylsiloxane) (PDMS) chips.     

Physical properties of small water clusters in low and moderate electric fields

Likely candidates for the lowest minima of water clusters (H(2)O)(N) for N ≤ 20 interacting with a uniform electric field strength in the range E ≤ 0.6 V/? have been identified using basin-hopping global optimization. Two water-water model potentials were considered, namely TIP4P and the polarizable Dang-Chang potential. The two models produce some consistent results but also exhibit significant differences. The cluster internal energy and dipole moment indicate two varieties of topological transition in the structure of the global minimum as the field strength is increased. The first takes place at low field strengths (0.1 V/? 10) usually forming helical structures.     

Correlating the scattered intensities of P3HT and PCBM to the current densities of polymer solar cells

Grazing-incidence X-ray diffraction and rocking scans have quantified the structure of poly(3-hexylthiophene) and [6,6]-phenyl-C(61)-butyric acid methyl ester in the active layers of organic solar cells. Our study reveals that the device J(SC) correlates with the local structural development of pure PCBM and, to second order, the extent of out-of-plane P3HT π-stacking.     

A facile method to tune zeolite L crystals with low aspect ratio

We demonstrate an alternative route to tune the morphology of zeolite L crystals using C(2)H(5)OH as the co-solvent in the synthesis gel. A low aspect ratio (0.2 to 0.4) of zeolite L crystals was obtained at lower synthesis temperature (150 °C) and shorter synthesis duration (3 days).     

From microscopic insights of H2 adsorption to uptake estimations in MOFs

The adsorption of hydrogen in MOFs takes place mainly close to the inorganic secondary building unit (IBU). The adsorption capacities on MIL-88, UiO-66, MIL-47 and MFU-1 were investigated. Quantum chemical calculations at the ab initio HF/MP2 theoretical level were employed to estimate the maximum uptake of H(2) molecules per metallic centre. Extrapolating the results on small clusters to the unit cell of each particular MOF, the H(2) uptakes (gravimetric and volumetric) were estimated. The loading of hydrogen per metal atom (H(2) molecules/M-atom) and the density of metal atoms (M-atoms ?(-3)) were defined as useful parameters to assess hydrogen storage properties and to estimate the optimum density that the material should have to be a good H(2) adsorbent. It was found that values above 3 H(2) molecules/M-atom and around 0.004 M-atoms ?(-3) for MOFs with densities around 0.7-1.0 g cm(-3) are required to reach the 2015 storage targets.     

Determination of the enantiomeric excess of α-hydroxy acids

This work describes a convenient and accurate method for optical purity determination of α-hydroxy acids. Their derivatization with commercially available valine methyl ester affords diastereoisomers easily separable by HPLC using achiral C₁₈ columns.     

Flow-injection spectrofluorimetric determination of paracetamol

A flow-injection spectrofluorimetric determination of paracetamol is reported, based on the oxidation of the analyte with potassium hexacyanoferrate(III) immobilized on an anion-exchange resin, the fluorescence being enhanced with N,N′-dimethylformamide. Concentrations of paracetamol in the range 0.04–17.60 mg l^?1 are determined with a relative standard deviation of 1.5%. The injection rate is 25 samples h^?1. The influence of foreign species and the determination of paracetamol in several pharamaceutical formulations are also reported.