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61.
Juan Jos Berzas Nevado Rosa Carmen Rodríguez Martín-Doimeadis Francisco Javier Guzmn Bernardo Nuria Rodríguez Farias 《Microchemical Journal》2007,86(2):183-188
An analytical methodology was proposed and validated to be applied to the determination of p,p′-DDT and its metabolites p,p′-DDE and p,p′-DDD in fish oil. The analytical procedure presented in this paper involves a single-step clean up process prior to the analysis. A solution of 1,2,3,4-tetrachloronaphtalene was used as internal standard.The analytical technique used was gas chromatography coupled to an electron capture detector. Details on the validation process are provided.The limits of detection ranged from 2.6 to 4.7 pg μL− 1. The BCR 598 standard reference material (cod liver oil) was used to evaluate the performance of the methodology with satisfactory recoveries for all the compounds.The analytes were determined in three different fish oil pills sold in Spain as a supplementary vitamin support. The sum of p,p′-DDT and metabolites was from 13.2 to 51.3 ng g− 1, the dominant compound being p,p′-DDE. 相似文献
62.
Philippe Gerbier Daniel Ruiz-Molina Neus Domingo David B. Amabilino José Vidal-Gancedo Javier Tejada David N. Hendrickson Jaume Veciana 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):265-276
Summary. A new modified approach for the synthesis of Mn12 clusters, based on the use of complex [Mn12O12(O2C
t
Bu)16(H2O)4] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us
to obtain complex [Mn12O12(O2CC6H4N(O•)
t
Bu)16(H2O)4] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn12Ac (1). Complex 3 bearing open-shell radical units, was prepared to increase the total spin number of its ground state, and consequently, to
increase T
B
, with the expectation that the radical ligands may couple ferromagnetically with the Mn12 core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn12 core to yield a S = 2 magnetic ground state.
Corresponding author. E-mail: vecianaj@icmab.es
Received March 27, 2002; accepted May 2, 2002 相似文献
63.
Yang Shen Ioanna Kalograiaki Alessio Prunotto Matthew Dunne Samy Boulos Nicholas M. I. Taylor Eric T. Sumrall Marcel R. Eugster Rebecca Martin Alicia Julian-Rodero Benjamin Gerber Petr G. Leiman Margarita Menndez Matteo Dal Peraro Francisco Javier Caada Martin J. Loessner 《Chemical science》2021,12(2):576
Endolysins are bacteriophage-encoded peptidoglycan hydrolases targeting the cell wall of host bacteria via their cell wall-binding domains (CBDs). The molecular basis for selective recognition of surface carbohydrate ligands by CBDs remains elusive. Here, we describe, in atomic detail, the interaction between the Listeria phage endolysin domain CBD500 and its cell wall teichoic acid (WTA) ligands. We show that 3′O-acetylated GlcNAc residues integrated into the WTA polymer chain are the key epitope recognized by a CBD binding cavity located at the interface of tandem copies of beta-barrel, pseudo-symmetric SH3b-like repeats. This cavity consists of multiple aromatic residues making extensive interactions with two GlcNAc acetyl groups via hydrogen bonds and van der Waals contacts, while permitting the docking of the diastereomorphic ligands. Our multidisciplinary approach tackled an extremely challenging protein–glycopolymer complex and delineated a previously unknown recognition mechanism by which a phage endolysin specifically recognizes and targets WTA, suggesting an adaptable model for regulation of endolysin specificity.Combining genetic, biochemical and computational approaches, we elucidated the molecular mechanisms underlying the recognition of Listeria wall teichoic acid by bacteriophage-encoded SH3b repeats. 相似文献
64.
Laura Marcu Javier A. Jo Pramod V. Butte William H. Yong Brian K. Pikul Keith L. Black Reid C. Thompson 《Photochemistry and photobiology》2004,80(1):98-103
Fluorescence spectroscopy of the endogenous emission of brain tumors has been researched as a potentially important method for the intraoperative localization of brain tumor margins. We investigated the use of time‐resolved, laser‐induced fluorescence spectroscopy for demarcation of primary brain tumors by studying the time‐resolved spectra of gliomas. The fluorescence of human brain samples (glioblastoma multiforme, cortex and white matter: six patients, 23 sites) was induced ex vivo with a pulsed nitrogen laser (337 nm, 3 ns). The time‐resolved spectra were detected in a 360–550 nm wavelength range using a fast digitizer and gated detection. Parameters derived from both the spectral‐ (intensities from narrow spectral bands) and the time domain (average lifetime) measured at 390 and 460 nm were used for tissue characterization. We determined that high‐grade gliomas are characterized by fluorescence lifetimes that varied with the emission wavelength (>3 ns at 390 nm, <1 ns at 460 nm) and their emission is overall longer than that of normal brain tissue. Our study demonstrates that the use of fluorescence lifetime not only improves the specificity of fluorescence measurements but also allows a more robust evaluation of data collected from brain tissue. Combined information from both the spectraland the time domain can enhance the ability of fluorescencebased techniques to diagnose and detect brain tumor margins intraoperatively. 相似文献
65.
The reaction of several α-amino acids and peptides (containing Gly, L-Ala, L-Leu, L- or DL-Phe, and/or L- or D-Val) with air-diluted nitrogen oxides has been studied to roughly mimic the N-nitrosation of peptide bonds that the contaminated urban air might produce in pulmonary tissues. Most N-protected α-amino acids give practically quantitative yields of N-nitroso derivatives. N-Protected dipeptides afford either dinitrosated peptides, mixtures of di- and mononitrosated compounds, selectively mononitrosated products, or no reaction at all, depending mainly on steric effects. The same trends are observed for some higher peptides. The (po1y)nitrosated Peptides, which retain the chirality of the starting materials, have been characterized by 1H and 13C NMR spectroscopy and are cleaved by pyrrolidine and amino esters under mild conditions to give (new) amides or peptides plus diazo derivatives. 相似文献
66.
Grotjahn DB Van S Combs D Lev DA Schneider C Incarvito CD Lam KC Rossi G Rheingold AL Rideout M Meyer C Hernandez G Mejorado L 《Inorganic chemistry》2003,42(10):3347-3355
Inter- and intramolecular hydrogen bonding of an N-H group in pyrazole complexes was studied using ligands with two different groups at pyrazole C-3 and C-5. At C-5, groups such as methyl, i-propyl, phenyl, or tert-butyl were present. At C-3, side chains L-CH(2)- and L-CH(2)CH(2)- (L = thioether or phosphine) ensured formation of chelates to a cis-dichloropalladium(II) fragment through side-chain atom L and the pyrazole nitrogen closest to the side chain. The significance of the ligands is that by placing a ligating side chain on a ring carbon (C-3), rather than on a ring nitrogen, the ring nitrogen not bound to the metal and its attached proton are available for hydrogen bonding. As desired, seven chelate complexes examined by X-ray diffraction all showed intramolecular hydrogen bonding between the pyrazole N-H and a chloride ligand in the cis position. In addition, however, intermolecular hydrogen bonding could be controlled by the substituent at C-5: complexes with either a methyl at C-5 or no substituent there showed significant intermolecular hydrogen bonding interactions, which were completely avoided by placing a tert-butyl group at C-5. The acidity of two complexes in acetonitrile solutions was estimated to be closer to that of pyridinium ion than those of imidazolium or triethylammonium ions. 相似文献
67.
LetEçS 1 be a set with Minkowski dimensiond(E)1. We consider the Hardy-Littlewood maximal function, the Hilbert transform and the maximal Hilbert transform along the directions ofE. The main result of this paper shows that these operators are bounded onL rad p (R2) forp>1+d(E) and unbounded whenp<1+d(E). We also give some end-point results. 相似文献
68.
J. Miguel Vadillo M. Esther Gonzalez Isabel Carretero J. Javier Laserna 《Mikrochimica acta》1995,118(3-4):273-282
Micellar liquid chromatography (MLC) and capillary zone electrophoresis (CZE) have been evaluated for the analysis of twelve banned drugs in sport including diuretics and -blockers. In MLC, a sodium dodecylsulphate aqueous solution has been used as mobile phase using an octadecylsilica column. In CZE, a pH 8 buffer solution and a silica capillary have been employed. Parameters of retention and efficiency have been compared. Limits of detection with UV detection at 254 nm and relative standard deviations for atenolol, furosemide, nadolol, spironolactone and triamterene were established and compared in both techniques. Examples of direct urine injection into the separation systems are presented. Drugs overlapping in MLC are well resolved in CZE, while the opposite is true for a limited number of drugs. Some interferences from urine may arise in CZE. The selectivity of analysis would be greatly enhanced by using both techniques, which require only filtration as pre-treatment. 相似文献
69.
J. Ignacio Extremiana Aldana L. Javier Herná ndez Paricio M. Teresa Rivas Rodrí guez 《Proceedings of the American Mathematical Society》1996,124(11):3545-3553
For each integer , we give a distinct closed model category structure to the category of pointed spaces such that the corresponding localized category is equivalent to the standard homotopy category of -connected CW-complexes. The structure of closed model category given by Quillen to is based on maps which induce isomorphisms on all homotopy group functors and for any choice of base point. For each , the closed model category structure given here takes as weak equivalences those maps that for the given base point induce isomorphisms on for .
70.
Chiral 1,3-perhydrobenzoxazines 1, 2, and 9-14, prepared by condensation of 8-(benzylamino)menthol with different aldehydes, react with alkylmagnesium bromides and trimethylaluminum leading to the open amino alcohols 3a-d, 4a-d, and 15-20 in excellent chemical yields and good to excellent diastereomeric excess. The sequential elimination of the menthol appendage by heating with P(2)O(5) and the benzyl group by hydrogenolysis lead to primary amines 7a-d, 8a-d, and 27-30 in excellent chemical yields and ee. The addition of the alkyl group from the Grignard derivatives and the methyl group from the trimethylaluminum occurs from opposite sides of the heterocycle, yielding the final primary amines with the same stereochemistry. 相似文献