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21.
Cooper SM Laosripaiboon W Rahman AS Hothersall J El-Sayed AK Winfield C Crosby J Cox RJ Simpson TJ Thomas CM 《Chemistry & biology》2005,12(7):825-833
Mupirocin, a polyketide-derived antibiotic from Pseudomonas fluorescens NCIMB10586, is a mixture of pseudomonic acids (PA) that target isoleucyl-tRNA synthase. The mup gene cluster encodes both type I polyketide synthases and monofunctional enzymes that should play a role during the conversion of the product of the polyketide synthase into the active antibiotic (tailoring). By in-frame deletion analysis of selected tailoring open-reading frames we show that mupQ, mupS, mupT, and mupW are essential for mupirocin production, whereas mupO, mupU, mupV, and macpE are essential for production of PA-A but not PA-B. Therefore, PA-B is not simply produced by hydroxylation of PA-A but is either a precursor of PA-A or a shunt product. In the mupW mutant, a new metabolite lacking the tetrahydropyran ring is produced, implicating mupW in oxidation of the 16-methyl group. 相似文献
22.
Abstract Experiments were performed to ascertain whether superoxide anion (O2 − ) was produced by the photodynamic activation of hematoporphyrin derivative (HPD). Three different systems were utilized to detect formation of O2 − , oxidation of epinephrine to adrenochrome, reduction of cytochrome c and reduction of nitro blue tetrazolium (NBT). The effects on these detectors under identical conditions for HPD + h ν were compared to those obtained with two O2 − generating systems, riboflavin + by and xanthine-xanthine oxidase, and to a singlet oxygen generating system, photoradiation of methylene blue. The results indicated that HPD + hv differed from the two O2 − generating systems in failing to reduce cytochrome c or NET, and that HPD + h ν was similar to the behavior of methylene blue + h ν . In addition, HPD + h ν but not the O2 − generating systems could inhibit mitochondrial cytochrome c oxidase activity. We conclude that the photodynamic activation of HPD does not produce O2 − as a major oxygen radical and that the effects of HPD + h ν on mitochondrial cytochrome c oxidase are not caused by O2 − . 相似文献
23.
J. B. Wong Shing W. E. Baker K. E. Russell 《Journal of polymer science. Part A, Polymer chemistry》1995,33(4):633-642
The kinetics of grafting a basic monomer, 2-(dimethylamino)-ethyl methacrylate (DMAEMA) to hydrocarbon substrates have been investigated. These systems were chosen as models for the grafting of a homopolymerizable monomer to polyolefins such as polyethylene. The reactions with squalane and n-eicosane were initiated by an organic peroxide, 2,5-dimethyl 2,5 dit-butylperoxy)-3-hexyne; grafting yields become significant at high reaction temperatures and low monomer concentrations. In squalane, the order of reaction with respect to monomer increased from about 1.1 for 0.22?0.44M DMAEMA to almost 2 at 0.69M DMAEMA; the order with respect to initiator was 0.56. The overall activation energy in the 130?160°C temperature range was, however, surprisingly low, 42±5 kJ mol?1. When analytical data were used to separate the overall rate into those for grafting and homopolymerization, different kinetic paths were observed for the competing reactions. These results are interpreted in terms of two different mechanisms; intramolecular chain transfer plays an important role in grafting, while depropagation becomes a major factor in homopolymerization at temperatures above 150°C. © 1995 John Wiley & Sons, Inc. 相似文献
24.
Paul C. Unangst David T. Connor S. Russell Stabler Robert J. Weikert 《Journal of heterocyclic chemistry》1987,24(3):811-815
Methods for the synthesis of novel 3-hydroxy, 3-alkoxy, and 3-alkyl indole-2-carboxylic acids and esters are described. Dieckmann cyclization of various 2-[(carboxymethyl)amino]benzoic acid diesters yielded 1-unsubstituted-, 1-methyl-, and 1-phenyl-3-hydroxy-1H-indole-2-carboxylic acid esters. An Ullmann reaction with bromobenzene converted 1H-indoles to 1-phenylindoles. 相似文献
25.
Russell G. Ross 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(1-2):227-233
The thermal conductivity and the heat capacity per unit volumec
p
have been measured for the urea-hexadecane inclusion compound using the transient hot-wire method. Measurements were made under isobaric conditions at a pressure of 0.1 GPa and in the temperature range of 100–300 K. There was evidence for a phase transition at a temperature of about 160 K, in reasonable agreement with previous work. For the high-temperature phase was independent of temperature within ±1%. The low-temperature phase showed a weak temperature dependence, with (d In/d InT)
p
= –0.13. It was inferred that interaction between acoustic phonons and low-frequency vibrational excitations of the guest molecules made a major contribution to the thermal resistivity. For the quantityc
p
a weak maximum was observed in the region of the phase transition temperature.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena. 相似文献
26.
Several enones are converted into their alpha-iodo derivatives in excellent yields and carbonylated with palladium catalysis in the presence of alcohol or amines to the alpha-carbonyl enones in satisfactory yields. 相似文献
27.
Gilar M Fountain KJ Budman Y Neue UD Yardley KR Rainville PD Russell RJ Gebler JC 《Journal of chromatography. A》2002,958(1-2):167-182
An ion-pair reversed-phase HPLC method was evaluated for the separation of synthetic oligonucleotides. Mass transfer in the stationary phase was found to be a major factor contributing to peak broadening on porous C18 stationary phases. A small sorbent particle size (2.5 microm), elevated temperature and a relatively slow flow-rate were utilized to enhance mass transfer. A short 50 mm column allows for an efficient separation up to 30mer oligonucleotides. The separation strategy consists of a shallow linear gradient of organic modifier, optimal initial gradient strength, and the use of an ion-pairing buffer. The triethylammonium acetate ion-pairing mobile phases have been traditionally used for oligonucleotide separations with good result. However, the oligonucleotide retention is affected by its nucleotide composition. We developed a mathematical model for the prediction of oligonucleotide retention from sequence and length. We used the model successfully to select the optimal initial gradient strength for fast HPLC purification of synthetic oligonucleotides. We also utilized ion-pairing mobile phases comprised of triethylamine (TEA) buffered by hexafluoroisopropanol (HFIP). The TEA-HFIP aqueous buffers are useful for a highly efficient and less sequence-dependent separation of heterooligonucleotides. 相似文献
28.
Lead concentrations of 59 different types of vinegars (15-307 μg l−1 in balsamic vinegars and 36-50 μg l−1 in wine vinegars) were determined using both inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS). Although the precision of direct analyses, following simple aqueous dilutions, with either instrumental method was poor; that precision, following nitric acid and/or hydrogen peroxide digestions, markedly improved with either instrument and the values obtained with the two instruments were in good agreement. The efficacy of different digestions, including (1) nitric acid using a heating block, with or without addition of hydrogen peroxide and (2) mixtures of nitric acid and hydrogen peroxide using ultraviolet (UV) photolysis, were then assessed. The latter procedure was found to be much faster and more efficient, but it was limited by the relatively high levels of contaminant lead in hydrogen peroxide. Consequently, it is recommended that lead concentrations in vinegar be measured following a nitric acid digestion and UV photolysis to oxidize all organic matter before ICP-MS or GFAAS analysis; and it is further recommend that the thermal settings for the latter analyses be adjusted to account for the apparent presence of relatively volatile organolead compounds in vinegar digests. 相似文献
29.
The dansylated derivatives of ammonia, 1.3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, spermidine, histamine, and spermine were separated by one ascending development in chloroform—triethylamine (5:1) on a 250-μm silica gel 60 plate. Putrescine, cadaverine, spermidine, and spermine in human urine were quantitated by a direct scan of the fluorescent intensity of the spots corresponding to these compounds. Higher amounts of spermidine and spermine were found in the urines of cancer patients compared to the values of these substances in normal urine. 相似文献
30.
Scott L. Gibson My Lien Nguyen Thomas H. Foster Geoffrey White Russell Hilf 《Photochemistry and photobiology》1995,61(2):196-199
Abstract— Photodynamic therapy has demonstrated efficacy toward primary, metastatic and recurrent human tumors. Here, we investigated the ability of photodynamic therapy, using Photofrin, to inhibit growth of R3230AC mammary adenocarcinomas when tumors were treated as original implants and again as lesions recurring at the initial treatment site. The results demonstrate that both initial implants and lesions recurring after the first photodynamic treatment respond similarly to the same photodynamic therapy protocol, with mean tumor volume doubling times of ˜ 11 days in both cases. Cells cultured from original tumor implants or tumors that recurred after photodynamic treatment accumulate equivalent amounts of [14 C]polyhematoporphyrin. Single cell suspensions prepared from either original or recurrent tumors from animals administered 5 mg/kg Photofrin and exposed to light in vitro displayed comparable phototoxicity. Additionally, examination of tumors by light microscopy revealed no morphological differences between the original tumor implants and the recurrent lesions. Taken together, these data indicate that lesions which recurred at the site of the initial photodynamic treatment were not resistant to a second identical course of photodynamic therapy. 相似文献