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81.
A multilaboratory trial for determining ceftiofur-related residues in bovine and swine kidney and muscle, and bovine milk was conducted following regulatory guidelines of the U.S. Food and Drug Administration, Center for Veterinary Medicine. The methods convert all desfuroylceftiofur-related residues containing the intact beta-lactam ring to desfuroylceftiofur acetamide to establish ceftiofur residues in tissues. Four laboratories analyzed 5 sets of samples for each tissue. Each sample set consisted of a control/blank sample and 3 control samples fortified with ceftiofur at 0.5 Rm, Rm, and 2 Rm, respectively, where Rm is the U.S. tolerance assigned for ceftiofur residue in each tissue/matrix: 0.100 microg/mL for milk, 8.0 microg/g for kidney (both species), 1.0 microg/g for bovine muscle, and 2.0 microg/g for swine muscle. Each sample set also contained 2 samples of incurred-residue tissues (one > Rm and one < Rm) from animals treated with ceftiofur hydrochloride. All laboratories completed the method trial after a familiarization phase and test of system suitability in which they demonstrated > 80% recovery in pretrial fortified test samples. Results showed that the methods met all acceptable performance criteria for recovery, accuracy, and precision. Although sample preparation was easy, solid-phase extraction cartridge performance must be carefully evaluated before samples are processed. The liquid chromatography detection system was easily set up; however, the elution profile may require slight modifications. The procedures could clearly differentiate between violative (> Rm) and nonviolative (< Rm) ceftiofur residues. Participating laboratories found the procedures suitable for ceftiofur residue determination. 相似文献
82.
Fast-atom-bombardment mass spectrometry (FABMS) is used for the semiquantitative determination of the fatty acids of complex lipids directly from intact algal cells, crude algal lipid extracts, and vegetable oils. Carboxylate ions, RCOO?, corresponding to the fatty acid moieties of the complex lipids are detected. The relative abundances of the carboxylate fatty acid ions in the FAB mass spectra agreed with the relative percentages found by gas chromatography of the fatty acid methyl esters derived from the extracted lipids. Chemical ionization/fast-atom-bombardment mass spectrometry (CI/FABMS) is discussed with respect to enhancing the molecular ions of the fatty acids and triacylglycerols from these materials. The use of FABMS requires little sample preparation, and FABMS enables rapid fatty acid screening, directly from crude biological materials. 相似文献
83.
SYNERGISTIC LETHAL ACTION OF ULTRAVIOLET-VIOLET RADIATIONS AND MILD HEAT IN ESCHERICHIA COLI 总被引:1,自引:0,他引:1
Abstract— The lethal interaction of far ultraviolet (254nm), near ultraviolet (334 and 365nm) and violet visible (405nm) radiation treatment with mild heat treatment was studied. Except at 254nm, a strong positive radiation dose-dependent interaction (synergism) was always observed. The efficiency of sensitisation to heat, as a function of dose at each wavelength, was found to be directly correlated with the dose necessary to eliminate the shoulder from the survival curve of a repair proficient strain but was apparently unrelated to the relative near-ultraviolet sensitivities of a repair deficient strain. The interaction was independent of the order of treatments. A radiation dose of 106 Jm-2 at 365nm slightly sensitised a cell population to 45°C incubation (normally non-lethal) and strongly sensitised the cells to 48°C treatment (normally 80 percent survival after 2 hours). It is proposed that in addition to DNA damage, both heat treatment and near ultraviolet treatment interfere with DNA recovery mechanisms so that the combination of the two agents inevitably leads to a strong positive interaction. 相似文献
84.
The oxidation of [RuIII(hedta)(H2O)]=(1) to its RuIV monomeric complex at a glassy carbon electrode is abserved to promote oxidation of alcohols bearing an a-hydrogen (i-PrOH benzyl alcohol,sec-phenethyl alcohol). Tertiary substitution blocks the oxidation (t-BuOH). The oxidation of the alcohols is detected by an enhancement in the current of the RuIV/III waves at potentials above 0.96V, caused by scavenging (reduction) of RuIV by the alcohols. Binuclear complexes which possess RuIV bridged by oxo to either a second RuIV or to RuIII in species of composition [LRuORuL]n−, L=hedta3−, fail to oxidize the alcohols. The terminal oxo moiety attached to RuIV is postulated to facilitate the oxidation of primary and secondary alcohols in a manner analogous to Meyer's [RuO(trpy)(bpy)]2+ catalyst. The dissociation of the (III,IV) binuclear complex into its monomers provides a pathway which increases catalytic
activity at the expense of the inactive (III, IV) binuclear complex's concentration.
TMC 2531 相似文献
85.
Slocik Joseph M. Ward Matthew S. Somayajula Kasi V. Shepherd Rex E. 《Transition Metal Chemistry》2001,26(3):351-364
The 'caged NO' reagent, RuCl3NO(H2O)2, has been studied by n.m.r. and i.r. methods with imidazole, histidine, histamine, and N-methyliminodiacetate as complexing ligands. These ligands are representative of cellular donors that would be encountered as RuCl3NO(H2O)2 migrates through biological cells. [RuCl3NO(imH)(H2O)], [RuCl3(NO)(imH)2] and [RuCl2(NO)(imH)3]+ complexes (imH = imidazole) have been detected by 1H-n.m.r. and i.r. and electrospray mass spectrometry (e.s.i.–m.s.) methods. Based upon the effect of cis ligand addition on the (NO) frequency causing a decrease in frequency, the 1:1 and 1:2 complexes have the imidazole donors in the plane cis to the NO+ moiety, whereas the 1:3 species has the third imidazole trans to the NO+. The trans imidazole donor causes 'trans-strengthening' of the N–O bond of the {RuNO}6 chromophore. 1H-n.m.r. shows that the monodentate imidazole donor(s) is (are) in rapid exchange with free imidazole in solution for each of the n = 1–3 species. Histidine and histamine make kinetically more stable 1:1 complexes with the major isomer having an axially-coordinated histidine imidazole donor, but in-plane donation for histamine. The carboxylate of coordinated histidine remains pendant according to i.r. and 13C-n.m.r. data. From syntheses carried out at pH ca. 5, the amino donor is H-bonded to an in-plane H2O in the major species (ca. 75%) and coordinated with displacement of the in-plane H2O in the lesser isomer (25%). By contrast, the histamine ligand binds with an in-plane bound imidazole and a pendant protonated amino group (94%). The remaining 6% has an in-plane chelated histamine, analogous to the bis imidazole species and the known fac, cis-[RuCl3NO(en)] complex. N-Methyliminodiacetate is observed to form one main [RuCl(NO)(mida)(H2O)] complex (85%) with two chelated glycinato donor groups with RuCl3NO(H2O)2, one glycinato group chelated 'in-plane' with the central amine donor and one axial coordinated glycinato donor. A second [RuCl(NO)(mida)(H2O)] complex (the remaining 15%) has the amine donor trans to NO+ and chelated glycinato groups which coordinate in the RuClO2(OH2) plane, either cis or trans to each other, in a 60:40 split (ca. 9% and 6%). The presence of one Cl– and one H2O in the [RuCl(NO)(mida)(H2O)] complexes was established by e.s.i.–m.s. These results show that RuCl3NO(H2O)2 is likely to be freely mobile within a cellular environment, forming stable complexes via bidentate chelation with 'two-point' nitrogen donors (en, his, etc). 相似文献
86.
Abstract— The modification of the lethal interaction between near-UV (365 nm) radiation and a second DNA-damaging agent by incubation between treatments in either a minimal salts medium or complete growth medium has been studied in the wild-type bacterial strain Escherichia coli K12 AB 1157. The results indicate that the lethal interaction may be separated into at least two distinct processes whose evaluation may help in classifying DNA-damaging agents in terms of the repairability of the DNA lesions induced. An observation of changes when methyl methane sulphonate is given prior to the irradiation treatment indicates that this chemical irreversibly damages repair enzymes. 相似文献
87.
Ru2II(ttha)(H2O)2]2– (ttha6–= triethylene tetramine hexa-acetate), prepared by the reduction of the ruthenium(III) precursor, reacts with 2,2-bipyridine (2,2-bpy) in a multi-step fashion. The first 2,2-bpy equivalent (1:1) adds with bidentate chelation at one ruthenium(II) site as revealed by separate ruthenium(II)/(III) waves at 0.03 and 0.54V vs. n.h.e. A second equivalent of 2,2-bpy (1:2) is initially stored and retained as the [Zn(2,2-bpy)]2+ complex. Further addition of 2,2-bpy initiates coordination at the second ruthenium(II) site. [Ru2(ttha)-(2,2-bpy)(H2O)]2– forms a strong ion-pair with zinc(II) that is in rapid equilibrium with the Zn(H2O)62+/Zn(2,2-bpy)]2+ pool. The solubility of the ion-pair is low. The ion-pair exhibits a shifted ruthenium(II)/(III) wave at 0.60V. Higher amounts of 2,2-bpy recomplex the zinc(II), solubilizing the complex and returning the E1/2 value to 0.54V. Other ligands which either have a higher affinity for ruthenium(II) centres than for zinc(II) as bidentate donors (1,10-phenanthroline), or ligands that cannot form bidentate zinc(II) complexes [(2-methylpyrazine, 4,4-bipyridine (4,4-bpy), and 2,3-bipyridine (2,3-bpy)] do not exhibit the unusual competition by zinc(II). These ligands all add statistically to the ruthenium(II) centres forming 1:2 complexes with 1:2 stoichiometries. 1H-n.m.r. studies of the Ru(II)polyaminopolycarboxylate complexes [RuII(hedta)(H2O)]– complex, and [Ru2(ttha)(H2O)2]2– itself, reveal that substitution of 2,3-bpy at ruthenium(II) sites occurs with an initial kinetic split between the pyridyl rings of the 3- less-hindered and 2-more-hindered ring. A slower rearrangement occurs, producing the isomer of the more-hindered 2-substituted ring. A process is driven by forming a more -accepting system when ruthenium(II) binds to the 2-ring of 2,3-bpy. Understanding the unusual influence of zinc(II) on the substitution of 2,2-bpy with [Ru2(ttha)(H2O)2]2– clarifies the nature of the 1:1 complex – namely that the 2,2-bpy becomes bidentate at one ruthenium(II) centre rather than serving as a trans-bridging ligand between both ruthenium(II) centres within one [Ru2(ttha)]2– unit. 相似文献
88.
The cis-(R,S)-[Pd(egta)]2– complex, egta4–=glycine, N,N-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]), has been examined by 1H- and 13C-n.m.r. methods over the 18.0 to 95.0°C range in D2O. A dynamic process occurs above 65°C which makes the protons on the NCH2 functionalities of the egta tether become 1H-n.m.r. equivalent. The two states that interconvert coalesce at 81°C. Evidence from 13C-n.m.r. spectra obtained at 81°C show that the in-plane coordinated carboxylates are not lost, but rather a pendant carboxylate becomes attached with loss of the central imino donor. The resultant palladium(II)NO3 intermediate is able to reform cis-(R,S)-[Pd(egta)]2– or, presumably, give trans-(R,R)-[Pd(egta)]2–. The rate limiting step occurs with a rate constant of 178s–1 at 81°C and an activation energy of 20.5kJ/mol. However, competitive aquation of glycinato donors above 85°C prevents isolation of a stable trans-(R,R)-[Pd(egta)]2– isomer. 相似文献
89.
OXYGEN-DEPENDENCE OF NEAR UV (365 NM) LETHALITY AND THE INTERACTION OF NEAR UV AND X-RAYS IN TWO MAMMALIAN CELL LINES 总被引:2,自引:0,他引:2
Abstract— The colony-forming ability of Chinese hamster cells (V-79) and HeLa cells has been measured after near-ultraviolet (UV) irradiation, predominantly at 365 nm. To avoid the production of toxic photoproducts, cells were irradiated in an inorganic buffer rather than in tissue culture medium. Under these circumstances near-UV lethality was strongly oxygen-dependent. Both cell lines were approximately 104 times more sensitive to 254 nm irradiation than to 365 nm radiation when irradiated aerobically. Pretreatment with 6 times 105 Jm-2 365 nm radiation sensitised the HeLa, but not the V-79 cell line to subsequent X-irradiation. Pretreatment of cells with 17 Jm-2 254 nm radiation, a dose calculated to produce twenty times more pyrimidine dimers than the 365 nm dose, produced only slight sensitisa-tion to X-rays. It is suggested that the sensitisation to X-rays seen in the HeLa cells after 365 nm treatment is not the result of lesions induced in DNA by the near-UV radiation, but may reflect the disruption of DNA-repair systems. 相似文献
90.
David R. Lisgarten Joanna S. Fell Brian S. Potter Rex A. Palmer 《Journal of chemical crystallography》2003,33(2):131-137
The crystal and molecular structure of 17-hydroxy-17 methylandrostano[3,2-c]pyrazole ethanoate (stanazolol ethanol solvate), C2H30N2OC2H5OH, has been determined by direct methods and refined by full-matrix least squares to a final R of 0.0577 for 4021 observed reflections and 245 parameters using Cu K radiation, = 1.54178 Å. The compound crystallizes in space group P212121 with Z = 4 molecules per unit cell. In the steroid skeleton the ring A adopts a half-chair conformation, being considerably strained, as a consequence of the fused planar pyrazole ring E. Rings B and C however are chairs and ring D has a 13,14 half-chair conformation. All rings of the steroid skeleton are trans-connected. The OH group of the solvated ethanol molecule is hydrogen bonded to the -oriented carbonyl substituent O(20) of ring D. The molecules are further held together in the crystal structure by head–tail hydrogen bonding between N(1)H in the pyrazole ring and O(20), which consequently is an acceptor for the two H-bonds. Overall the molecule lacks any significant curvature with no interplanar dihedral angle greater than 7°. Possible binding modes of stanazolol with the human androgen receptor are discussed. 相似文献