Probing the beta-1,3:1,4 glucanase, CtLic26A, with a thio-oligosaccharide and enzyme variants

The substrate binding regions of a beta-1,3:1,4 glucanase are revealed through structural analysis with a thio-oligosaccharide and kinetics of enzyme variants.     

Hydroxyapatite micro- and nanoparticles: nucleation and growth mechanisms in the presence of citrate species

Hydroxyapatite (HAP) particles with different morphologies were precipitated from homogeneous calcium/citrate/phosphate solutions at physiological temperature. Small variations of the starting solution pH in the range 7.4相似文献   

Comparison of models for estimation of measurement uncertainties. Determination of BOD<Subscript>5</Subscript> in wastewaters using a manometric method

Biochemical oxygen demand after 5 days (BOD₅) is a bioassay frequently used to determine the polluting strength of wastewaters. It quantifies the mass concentration of dissolved O₂ consumed during an incubation period of 5 days at 20 °C, in the dark, by biological oxidation of organic and/or inorganic matter in wastewater. In this work, the BOD₅ measurand is reported as γ(O₂). Reporting analytical results with estimation of uncertainty is an ISO/IEC 17025:2005 requirement and allows results to be compared and their fitness for purpose to be demonstrated. The γ(O₂) uncertainty was estimated using two models: the individual components’ model (model 1) and the quality-control-criteria model in which the trueness component is calculated using the equation for recovery from CRMs (model 2.A) and the standard deviation of all recoveries (model 2.B). Model 1 provides a realistic strategy for estimation of γ(O₂) uncertainty and for assessment of performance. Models 2.A and 2.B are expeditious and simple procedures for the 100–800 mg L⁻¹ range. When γ(O₂) < 100 mg L⁻¹ model 1 must be used because with both Models 2 uncertainty was underestimated, more drastically close to the limit of quantification. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Evaluation of two chelators for labelling a PNA monomer with the fac-[Tc(CO)3] moiety

A PNA monomer containing thymine as nucleobase (1) was synthesized, characterized and coupled to the pyrazolyl containing ligand 3,5-Me₂pz(CH₂)₂N((CH₂)₃COOH)(CH₂)₂NHBoc (2) and to a modified cysteine S-(carboxymethyl-pentafluorphenyl)-N-[(trifluor)carbonyl]-l-cysteine methyl ester (3) yielding the bifunctional chelators 6 and 7, respectively. Reactions of 6 and 7 with the Re(I) tricarbonyl starting material [Re(CO)₃(H₂O)₃]Br afforded the complexes fac-[Re(CO)₃(κ³-6)]⁺ (8) and fac-[Re(CO)₃(κ³-7)] (9), respectively. The identity of 8 and 9 has been established based on IR spectroscopy, elemental analysis, ESI-MS spectrometry and HPLC. The multinuclear NMR spectroscopy (¹H, ¹³C, g-COSY, g-HSQC) has also been very informative in the case of complex 8, showing the presence of rotamers in solution. For 9 the NMR spectrum was too complex due to the presence of rotamers and diastereoisomers. The radioactive congeners of complexes 8 and 9, fac-[^99mTc(CO)₃(κ³-6)]⁺ (8a) and fac-[^99mTc(CO)³(κ³-7)] (9a), have been prepared by reacting the precursor fac-[^99mTc(CO)₃(H₂O)₃]⁺ with the corresponding ligands being their identity established by comparing their HPLC chromatograms with the HPLC of the rhenium surrogates.     

Synthesis of Azobenzene Dyes Mediated by CotA Laccase

An eco‐friendly protocol for the synthesis of azobenzene dyes by oxidative coupling of primary aromatic amines is reported. As efficient biocatalytic systems, CotA laccase and CotA laccase/ABTS (2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid)) enable the oxidation of various substituted anilines, in aqueous medium, ambient atmosphere and under mild reaction conditions of pH and temperature. A series of azobenzene dyes were prepared in good to excellent yields in an one‐pot reaction. A mechanistic proposal for the formation of the azo derivatives is presented. Our strategy offers an alternative approach for the direct synthesis of azobenzene dyes, avoiding the harsh conditions generally required for most of the traditional synthetic methods.     

Injectivity relative to closed submodules

Let R be a ring. An R-module X is called c-injective if, for every closed submodule L of every R-module M, every homomorphism from L to X lifts to M. It is proved that if R is a Dedekind domain then an R-module X is c-injective if and only if X is isomorphic to a direct product of homogeneous semisimple R-modules and injective R-modules. It is also proved that a commutative Noetherian domain R is Dedekind if and only if every simple R-module is c-injective.     

The antigenic determinants on HIV p24 for CD4+ T cell inhibiting antibodies as determined by limited proteolysis, chemical modification, and mass spectrometry

In the last decade, mass spectrometry has been employed by more and more researchers for identifying the proteins in a macromolecular complex as well as for defining the surfaces of their binding interfaces. This characterization of protein-protein interfaces usually involves at least one of several different methodologies in addition to the actual mass spectrometry. For example, limited proteolysis is often used as a first step in defining regions of a protein that are protected from proteolysis when the protein of interest is part of a macromolecular complex. Other techniques used in conjunction with mass spectrometry for determining regions of a protein involved in protein-protein interactions include chemical modification, such as covalent cross-linking, acetylation of lysines, hydrogen-deuterium exchange, or other forms of modification. In this report, both limited proteolysis and chemical modification were combined with several mass spectrometric techniques in efforts to define the protein surface on the HIV core protein, p24, recognized by two different monoclonal human antibodies that were isolated from HIV+ patients. One of these antibodies, 1571, strongly inhibits the CD4+ T cell proliferative response to a known epitope (PEVIPMFSALSEGATP), while the other antibody, 241-D, does not inhibit as strongly. The epitopes for both of these antibodies were determined to be discontinuous and localized to the N-terminus of p24. Interestingly, the epitope recognized by the strongly inhibiting antibody, 1571, completely overlaps the T cell epitope PEVIPMFSALSEGATP, while the antibody 241-D binds to a region adjacent to the region of p24 recognized by the antibody 1571. These results suggest that, possibly due to epitope competition, antibodies produced during HIV infection can negatively affect CD4+ T cell-mediated immunity against the virus.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

Differentiation of aminomethyl corrole isomers by mass spectrometry

Two new isomeric aminomethyl corrole derivatives of [5,10,15-tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas-phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M-py?+?H](+) precursors, by (CH(3) )(2) NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi-empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M-py?+?CH(3) O](-) through (CH(3) )(2) N(.) and HF losses.     

Differentiation of aminomethyl corrole isomers by mass spectrometry

Two new isomeric aminomethyl corrole derivatives of [5,10,15‐tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas‐phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M‐py + H]⁺ precursors, by (CH₃)₂NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi‐empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M‐py + CH₃O]^‐ through (CH₃)₂ N^. and HF losses. Copyright © 2012 John Wiley & Sons, Ltd.