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Hydroxylamine
Terms modified by Hydroxylamine Selected AbstractsPreparation of Hydroxylamine and O -Methylhydroxylamine Complexes of Manganese and RheniumEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Gabriele Albertin Abstract Hydroxylamine and O -methylhydroxylamine complexes [M(NH2OH)(CO)nP5,n]BPh4 and [M(NH2OCH3)(CO)nP5,n]BPh4 [M = Mn, Re; n = 1, 2, 3; P = P(OEt)3, PPh(OEt)2, PPh2OEt] were prepared by allowing hydrides MH(CO)nP5,n to react first with triflic acid and then with an excess of hydroxylamine. Bidentate phosphane and phosphite can also be used to prepare both NH2OH and NH2OCH3 complexes of manganese and rhenium of the [M(NH2OR)(CO)2(P,P)-{P(OEt)3}]BPh4 and [M(NH2OR)(CO)3(P,P)]BPh4 [R = H, CH3; P,P = Ph2POCH2CH2OPPh2, Ph2PO(CH2)3OPPh2, Ph2PN(CH3)CH2CH2N(CH3)PPh2] types with the use of MH(CO)2(P,P){P(OEt)3} and MH(CO)3(P,P) as precursors. The complexes were characterized spectroscopically and by theX-ray crystal-structure determination of [Re(NH2OCH3)(CO)2{PPh(OEt)2}3]BPh4 and [Re(NH2OCH3)(CO)3{Ph2PO(CH2)3OPPh2}]BPh4. Oxidation of the hydroxylamine complexes with Pb(OAc)4 was studied at ,40 °C and led to an unstable compound tentatively characterized as a nitroxyl [M],N(H)=O derivative.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Quantitation of the Effect of Hydroxylamine on Rhodopsin Palmitylation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Wesley Jackson Rhodopsin (the photosensitive rod visual pigment) has been a model for photobiologic studies of the opsins as well as a structural model for G-protein-coupled receptors. The two palmitate groups attached to cysteines 322 and 323 are thought to serve as membrane anchors for the rhodopsin C-terminus, but the absence of the palmitates does not alter membrane localization. However, removal of the palmitates affects rhodopsin function. Therefore, it is important to quantitate the stability of rhodopsin palmitates to hydroxylamine, which is a widely utilized reagent in biochemical preparations of the apoprotein. We have developed a mass spectrometric method to quantitate the resulting opsin palmitylation. Our data show that both of the bovine rhodopsin palmitates are labile to hydroxylamine, with significant depalmitylation occurring at concentrations of ,100 mm, with an EC50 of 220 mm L,1. The palmitate at position 322 is the more stable to hydroxylamine. Samples prepared in the presence of >50 mm should therefore be considered to be at least partially depalmitylated and the results interpreted accordingly. [source] Direct Synthesis of Aromatic Nitriles from Aldehydes Using Hydroxylamine and Oxalyl Chloride.CHEMINFORM, Issue 31 2007Barahman Movassagh Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A Nonparametrized ab initio Determination of the Heat of Formation of Hydroxylamine, NH2OHCHEMINFORM, Issue 5 2004David Feller Abstract For Abstract see ChemInform Abstract in Full Text. [source] Amperometric L -Lactate Biosensor Based on Gold NanoparticlesELECTROANALYSIS, Issue 7-8 2007Bikash, Kumar Jena Abstract A novel amperometric biosensor for the sensing of L -lactate is developed using L -lactate dehydrogenase (LDH) and hydroxylamine enlarged gold nanoparticles (GNPs). LDH and GNPs have been integrated with the sol,gel 3-D silicate network derived from 3-(mercaptopropyl)trimethoxysilane (MPTS). The biosensing of L -lactate is based on the electrocatalytic determination of enzymatically generated NADH by GNPs of the integrated assembly. The GNPs on the network efficiently catalyze the oxidation of NADH at ,0.065,V, which is ca. 915,mV less positive than on the bulk Au electrode. The biosensor was characterized in terms of the effects of enzyme loading, solution pH, and cofactor concentration. The integrated biosensor was successfully utilized for the amperometric sensing of L -lactate and it shows excellent sensitivity with a detection limit of 100,nM. The common interfering electroactive compounds in the biological system do not interfere the amperometric measurement of L -lactate. This biosensor linearly responds to L -lactate in the range of 0,0.8,mM and the sensitivity of the electrode was 0.446,nA/nM. Excellent reproducibility, long time storage and operational stability have been achieved. [source] Mutagenicity of nitroaromatic degradation compoundsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2003Ranjit S. Padda Abstract The mutagenicity of 2,4-dinitrotoluene (24DNT), and 2,6-dinitrotoluene (26DNT), and their related transformation products such as hydroxylamine and amine derivatives, which are formed by Clostridium acetobutylicum, were tested in crude cell extracts using Salmonella typhimurium TA100. A previous publication already reported the mutagenic activities of 2,4,6-trinitrotoluene (TNT) and its related hydroxylamine derivatives in this test system. A time course of the mutagenicity during the anaerobic transformation of TNT, 24DNT, and 26DNT was also investigated under the same conditions to compare with the results from the pure compounds. The monohydroxylamino intermediates 2-hydroxylamino-4-nitrotoluene (2HA4NT), 4-hydroxylamino-2-nitrotoluene (4HA2NT) and 2-hydroxylamino-6-nitrotoluene (2HA6NT) formed during anaerobic transformation of dinitrotoluenes were proven to be mutagenic in the Ames test using Salmonella typhimurium TA100. This study reports that 4HA2NT is the most stable derivative, whereas 2HA4NT and 2HA6NT are less stable and these intermediates are mutagenic in the Ames test. Both 24DNT and 26DNT and their final metabolites 2,4-diaminotoluene (24DAT) and 2,6-aminotoluene (26DAT) appeared nonmutagenic. In a time-course study of TNT degradation, the temporal sample containing 85% of 2,4-dihydroxylamino-6-nitrotoluene (24HA6NT) is most mutagenic. These observations suggest that the bioremediation approach for treatment of 24DNT and 26DNT should be carried past the hydroxylamino intermediate. [source] Preparation of Hydroxylamine and O -Methylhydroxylamine Complexes of Manganese and RheniumEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Gabriele Albertin Abstract Hydroxylamine and O -methylhydroxylamine complexes [M(NH2OH)(CO)nP5,n]BPh4 and [M(NH2OCH3)(CO)nP5,n]BPh4 [M = Mn, Re; n = 1, 2, 3; P = P(OEt)3, PPh(OEt)2, PPh2OEt] were prepared by allowing hydrides MH(CO)nP5,n to react first with triflic acid and then with an excess of hydroxylamine. Bidentate phosphane and phosphite can also be used to prepare both NH2OH and NH2OCH3 complexes of manganese and rhenium of the [M(NH2OR)(CO)2(P,P)-{P(OEt)3}]BPh4 and [M(NH2OR)(CO)3(P,P)]BPh4 [R = H, CH3; P,P = Ph2POCH2CH2OPPh2, Ph2PO(CH2)3OPPh2, Ph2PN(CH3)CH2CH2N(CH3)PPh2] types with the use of MH(CO)2(P,P){P(OEt)3} and MH(CO)3(P,P) as precursors. The complexes were characterized spectroscopically and by theX-ray crystal-structure determination of [Re(NH2OCH3)(CO)2{PPh(OEt)2}3]BPh4 and [Re(NH2OCH3)(CO)3{Ph2PO(CH2)3OPPh2}]BPh4. Oxidation of the hydroxylamine complexes with Pb(OAc)4 was studied at ,40 °C and led to an unstable compound tentatively characterized as a nitroxyl [M],N(H)=O derivative.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Uranium and thorium isotopes in the rivers of the Amazonian basin: hydrology and weathering processesHYDROLOGICAL PROCESSES, Issue 1 2003Aguinaldo N. Marques Jr. Abstract Two expeditions (October 1989 and May 1992) were carried out to two points of the main Amazon River channel and four tributaries. The Solimões and Madeira rivers, taking their origin in the Andes, are whitewater rivers. The Negro River is a typical acid, blackwater river. The Trombetas River flows through bauxite-rich areas, and is characterized by low concentrations of dissolved humic substances. The 238U, 234U, 232Th and 230Th activities were recorded from dissolved, suspended particulate phases and river bank sediments. The latter were analysed for their 226Ra, 228Ra and 210Pb contents, and also subjected to leaching with 0·2 M hydroxylamine,hydrochloride solution to determine the concentrations of radionuclides bound to amorphous Fe hydroxides and Mn oxides and hydroxides. The dissolved U average concentration in the Amazon system is ten times lower than the mean world river concentration. The uranium concentration observed at Óbidos in the lower Amazon (0·095 µg L,1), where the U content in the river bank sediments and suspended matter is lowest, suggests U release from the solid phase during river transport. About 485 t of U are transported annually to the Amazon delta area in dissolved form, and 1943 t bound to suspended particulate matter. Total U and Th concentrations in the river bank sediments ranged from 1·59 to 7·14 µg g,1 and from 6·74 to 32 µg g,1, respectively. The highest concentrations were observed in the Trombetas River. The proportion extracted by means of the hydroxylamine solution (HL) was relatively high for U in the Trombetas river bank sediment (31%) and for Th in the Solimões sediment (30%). According to the alpha recoil effects, the 234U/238U activity ratios of the Andean river waters and downstream Amazon water (Óbidos) were >1, but were <1 in the Negro River (at Manaus). The activity ratios of dissolved U correlate with pH and also with the U activity ratios in the river bank sediment hydroxylamine extracts. As expected, the 234U/238U activity ratios in river bank sediments were <1 in the Andean rivers and in the downstream Amazon, but they were >1 in the Trombetas and Negro rivers. Such ratios probably result from the binding of dissolved uranium to solid sediment. The 228Th/232Th ratios of river bank sediments were close to unity (except for the Negro River, where it is lower), suggesting no significant Th exchanges between the river water and the sediment. The 226Ra/232Th activity ratios were <1, and the 226Ra/228Ra activity ratios generally were significantly higher than the activity ratios of their respective parents. This perhaps is the result of easier leaching of the 226Ra parent, 230Th, from solid material (owing to the alpha recoil effect) than of the 228Ra parent. Uranium and thorium isotopes were used as tools to evaluate the chemical weathering rate of rocks in the Amazon system, which was estimated to be 2·7 cm 1000 year,1 s,1. Copyright © 2002 John Wiley & Sons, Ltd. [source] ,-Ionone reactions with the nitrate radical: Rate constant and gas-phase productsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2009Joel C. Harrison The bimolecular rate constant of k (9.4 ± 2.4 × 10,12 cm3 molecule,1 s,1 was measured using the relative rate technique for the reaction of the nitrate radical (NO3,) with 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-buten-2-one (,-ionone) at (297 ± 3) K and 1 atmosphere total pressure. In addition, the products of ,-ionone + NO3, reaction were also investigated. The identified reaction products were glyoxal (HC(O)C(O)H), and methylglyoxal (CH3C(O)C(O)H). Derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and N,O-bis(trimethylsilyl)trifluoroacetamide were used to propose the other major reaction products: 3-oxobutane-1,2-diyl nitrate, 2,6,6-trimethylcyclohex-1-ene-carbaldehyde, 2-oxo-1-(2,6,6-trimethylcyclohex-1-en-1-yl)ethyl nitrate, pentane-2,4-dione, 3-oxo-1-(2,6,6-trimethylcyclohex-1-en-1-yl)butane-1,2-diyl dinitrate, 3,3-dimethylcyclohexane-1,2-dione, and 4-oxopent-2-enal. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible ,-ionone + NO3, reaction mechanisms based on previously published volatile organic compound + NO3, gas-phase mechanisms. The additional gas-phase products 5-acetyl-2-ethylidene-3-methylcyclopentyl nitrate, 1-(1-hydroxy-7,7-dimethyl-2,3,4,5,6,7-hexahydro-1 H-inden-2-yl)ethanone, 1-(1-hydroxy-3a,7-dimethyl-2,3,3a,4,5,6,-hexahydro-1 H-inden-2-yl)ethanone, and 5-acetyl-2-ethylidene-3-methylcyclopentanone are proposed to be the result of cyclization through a reaction intermediate. © 2009 Wiley Periodicals, Inc., Int J Chem Kinet 41: 629,641, 2009 [source] The hydroxyl radical reaction rate constant and products of 3,5-dimethyl-1-hexyn-3-ol,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2004J. R. Wells A bimolecular rate constant,kDHO, of (29 ± 9) × 10,12 cm3 molecule,1 s,1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5-dimethyl-1-hexyn-3-ol (DHO, HCCC(OH)(CH3)CH2CH(CH3)2) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH3)2CO), 3-butyne-2-one (3B2O, HCCC(O)(CH3)), 2-methyl-propanal (2MP, H(O)CCH(CH3)2), 4-methyl-2-pentanone (MIBK, CH3C(O)CH2CH(CH3)2), ethanedial (GLY, HC(O)C(O)H), 2-oxopropanal (MGLY, CH3C(O)C(O)H), and 2,3-butanedione (23BD, CH3C(O)C(O)CH3). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O -(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O -bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534,544, 2004 [source] A Dual Gold-Iron Catalysis for a One-Pot Synthesis of 2,3-Dihydroisoxazoles from Propargylic Alcohols and N-Protected HydroxylaminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Olivier Debleds Abstract A concise one-pot route for the synthesis of 2,3-dihydroisoxazoles via a dual gold-iron catalysis has been devised. The method, based on the addition of binucleophilic protected hydroxylamine to propargylic alcohols, enables a one-pot, highly selective synthesis of these heterocycles (10 examples, up to 86% yield). [source] Developmental differences in the immortalization of lung fibroblasts by telomeraseAGING CELL, Issue 5 2003Nicholas R. Forsyth Summary The role of ambient (21%) and physiological oxygen (2,5%) in the immortalization of fetal vs. adult human lung fibroblasts was examined. Growth in low oxygen and antioxidants extended the lifespan of both fetal and adult strains. As the ectopic expression of telomerase could immortalize adult lung fibroblasts cultured in ambient oxygen, the lifespan-shortening effects of 21% oxygen must have been largely limited to telomeres. By contrast, fetal lung fibroblasts could not be immortalized in ambient oxygen in spite of telomere elongation by telomerase, suggesting more widespread oxidative damage. The long-term culture requirements for the immortalization of WI-38 fetal lung fibroblasts included supplementation with N-(tert) butyl hydroxylamine, dexamethasone, zinc and vitamin B12, in addition to growth in physiological oxygen. The mechanisms regulating telomere shortening remain controversial. The present results suggest that both end-replication and oxidative damage events contribute to telomere shortening in lung fibroblasts in vitro. These observations emphasize the need for better analytical techniques to distinguish whether the correlation of short telomeres with disease and mortality in humans reflects the consequences of increased proliferation, telomere shortening as a result of oxidative damage or some combination of these processes. [source] Transglutaminase Catalysis of Modified Whey Protein DispersionsJOURNAL OF FOOD SCIENCE, Issue 4 2010Debra A. Clare ABSTRACT:, Transglutaminase (TGase) cross-linking reactions were accomplished using a heat-modified whey protein concentrate (mWPC) substrate after pH adjustment to 8. Based on earlier reports, the degree of lactosylation with respect to ,-lactoglobulin was lower in mWPC dispersions than measured in commercial whey concentrate (cWPC) protein solutions. In this study, a higher concentration of free sulfhydryl groups was detected in soluble supernatant fractions. Both factors potentially impact the availability of reactive lysine/glutaminyl residues required for TGase reactivity. The addition of 10 mM dithiothreitol (DTT) to the substrate mix, CBZ-glutaminyl glycine and hydroxylamine, revealed a 3.6-fold increase in TGase activity, likely due in part to maintenance of the catalytic cysteine residue in a reduced state. Furthermore, inclusion of DTT to mWPC dispersions significantly raised the apparent viscosity, independently of enzyme modification, while the rate of polymerization increased 2-fold based on OPA assay measurements. Limited cross-linking slightly increased the apparent viscosity, whereas extensive coupling lowered these values compared to equivalent nonenzyme-treated mWPC samples. Carbohydrate-staining revealed formation of glyco-polymers due to covalent linkages between glucosamine and mWPC proteins after TGase processing. Again, the apparent viscosity decreased after extensive enzymatic modification. Larger particles, sized 11.28 ,m, were observed in the structural matrix of TGase-mWPC-fixed samples compared to 8 ,m particles in control mWPC samples as viewed in scanning electron micrographs. Ultimately, the functional characteristics of TGase-mWPC ingredients may be custom-designed to deliver alternative functional attributes by adjusting the experimental reaction conditions under which catalysis is achieved. Practical Application: Taken together, these results suggest that unique TGase-mWPC and/or TGase-mWPC-glucosamine ingredients may be designed to provide novel, value-added, polymeric/glyco-polymeric protein products that afford added benefit for the milk industry. [source] Singlet Oxygen Detection in Skim Milk by Electron Spin Resonance SpectroscopyJOURNAL OF FOOD SCIENCE, Issue 2 2003D.G. Bradley ABSTRACT: 2,2,6,6-Tetramethyl-4-piperidone (TMPD) can react with singlet oxygen to produce the corresponding nitroxide, 2,2,6,6-tetramethyl-4-piperidone-1-oxyl (TAN), which can be detected by electron spin resonance (ESR) spectroscopy. ESR detected the formation of TAN in 5 ,M riboflavin phosphate buffer, or skim milk containing 20 mM TMPD during illumination. The effects of illumination, riboflavin, and oxygen on the formation of TAN indicated that the presence of each was required for singlet oxygen formation. The photo reduced riboflavin might reduce TAN to the hydroxylamine of TAN, thus decreasing the paramagnetic TAN signal. Maximum concentration of TAN was obtained at an added 10 mM riboflavin in buffer solution or in skim milk after 15 min of illumination in the presence of oxygen. [source] A facile synthesis of substituted 3-amino-1H -quinazoline-2,4-dionesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2005Tuan P. Tran A new synthesis of a series of 3-amino-1H -quinazoline-2,4-diones is described. The 1H -quinazoline-2,4-dione 10 was made starting with fluorobenzoic acid in three high yielding steps. The key step of this synthesis involved the generation of the dianion of urea 7 and the subsequent intramolecular nucleophilic displacement of the 2-fluoro to form the quinazolinedione ring. The 3-amino moiety was incorporated using (2,4-dinitro-phenyl)-hydroxylamine as the aminating reagent. [source] Studies with 1-functionally substituted alkyl azoles: Novel synthesis of functionally substituted azolylbenzimidazoles and functionally substituted azolyl-1,2,4-triazolesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2002Mohamed Abdel-Megid ,-Azolylacetophenones 1 and 2 react with dimethylformamide dimethylacetal to yield enaminones 7,8 that were converted into azolylazoles via reaction with hydrazine and with hydroxylamine. Compounds 1,2 also coupled with aromatic diazonium salts to yield arylhydrazones and reacted with nitrous acid to yield corresponding oximes. [source] Studies with enaminones: synthesis of new coumarin-3-yl azoles, coumarin-3-yl azines, coumarin-3-yl azoloazines, coumarin-3-yl pyrone and coumarin-2-yl benzo[b]FuransJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2001Fathy Mohamed Abel Aziz El-Taweel 3-Acetylcoumarine was condensed with dimethylformamide dimethylacetal (DMFDMA) to yield the enaminone, which reacts readily with hydroxylamine and with hydrazines to yield coumarin-3-ylisoxazoles and coumarin-3-ylpyrazoles respectively. Reaction of the enaminone with benzamidine hydrochloride and 3-amino-1,2,4-1H -triazole affords the pyrimidine and triazolo[3,4- b]pyrimidine. The enaminone reacts with hippuric acid and with the dithiocarboxylic acid to yield pyranones. The reaction of the enaminone with 3-amino-1H -1,2,4-triazole gives the triazolo[3,4- b]pyrimidine. The enaminone underwent self dimerization on reflux in acetic acid ammonium acetate to yield the coumarinyl pyridines and reacted with ketone under the same conditions to yield the pyridine. The reaction of the enaminone with 1,4-benzoquinone and 1,4-naphthoquinone gives benzofuryl coumarine derivatives. [source] Nucleophilic addition to 3-methyl-1-(4-nitrophenyl)-2-phenyl-4,5-dihydroimidazolium iodideJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2000Chizhong Xia Reactions of the 1,2-diaryl 4,5-dihydroimidazolium, represented by 3-methyl-1-(4-nitrophenyl)-2-phenyl-4,5-dihydroimidazolium iodide 1, with ethylenediamine afforded a benzylidyne unit transferred product, 2-phenyl-2-imidazoline 2; a ring-opened adduct 4 was produced when excess ethylenediamine was used. Reactions of 1 with hydroxylamine, malononitrile, and nitromethane anions produced ring-opened products, 5, 7, and 8 respectively. [source] A new synthetic entry to 3-carboxamido-4-carboxylic acid derivatives of isoxazole and pyrazoleJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2000Chiara B. Vicentini Ethyl 2-amino-3-methoxycarbonyl-4-oxo-2-pentenoate (3) reacts with hydroxylamine or hydrazines to give isoxazole and pyrazole ortho-dicarboxylic acid esters 4 and 5, respectively. Partial hydrolysis of diesters 4 and 5 afforded the corresponding dicarboxylic acid monoesters 6 and 7. Amidation of the intermediate acid chlorides 8,9 followed by hydrolysis of 4-methylesters 10, 11 gave the title compounds 1 and 2, respectively. [source] GC-MS analysis of multiply derivatized opioids in urineJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2007Bud-Gen Chen Abstract Opiates such as hydrocodone, hydromorphone, oxycodone, noroxycodone, and oxymorphone reportedly may interfere with the analysis of morphine and codeine. The analysis of these compounds themselves also is an important issue. Thus, double derivatization approaches utilizing methoxyamine and hydroxylamine to first form oxime products with keto-opiates, followed by the derivatization with trimethylsilyl (TMS) or propionyl groups, have been developed for the simultaneous analysis of these compounds. However, these studies have not included all compounds of interest and resulted in inadequate chromatographic resolution or significant intensity cross-contribution between the ions designating the analyte and its deuterated internal standard for certain compounds. By exploring three-step derivatization approaches with the combination of various derivatization groups and orders, this study concluded that application of methoxyimino/propionyl/TMS groups, in the order listed, facilitated the simultaneous analysis of eight opiates (morphine, 6-acetylmorphine, hydromorphone, oxymorphone, codeine, hydrocodone, oxycodone and noroxycodone) in urine samples, achieving satisfactory limits of quantitation and detection. In addition, the adapted approach resulted in two usable products for morphine and codeine providing alternatives, should interferences render any of these products non-usable. Copyright © 2007 John Wiley & Sons, Ltd. [source] Preparation of cyclic peptide libraries using intramolecular oxime formationJOURNAL OF PEPTIDE SCIENCE, Issue 11 2004Dr Kade D. Roberts Abstract A new method for the synthesis of cyclic head-to-side chain peptide libraries has been developed in which the key cyclization step involves reaction between a C -terminal ketone and an N -terminal hydroxylamine to form a macrocyclic oxime. This methodology efficiently delivers cyclic products that consist of mixtures of syn and anti isomers. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] Intramolecular general base catalysis exerted by the carboxilate group in the spontaneous dehydration of the carbinolamine formed from benzoylformic anion and hydroxylamine at early values of pHJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2007M. Calzadilla Abstract Data obtained from the reaction of oxime formation from benzoylformic anion lead to the suggestion that the spontaneous dehydration observed after pH,,,5.0, proceeds through a transition state in which an intramolecular general base catalysis is exerted by the carboxylate group. Copyright © 2007 John Wiley & Sons, Ltd. [source] On the mechanism of the N,N -dimethyl amination of Grignard reagents: a kinetic studyJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2007Ender Erdik Abstract A direct kinetic study is reported for the electrophilic amination of substituted phenylmagnesium bromides with N,N -dimethyl O -(mesitylenesulfonyl)hydroxylamine in THF. Rate data, Hammett relationship, and activation entropy are consistent with a SN2 displacement involving the attack of carbanions to sp3N in the amination reagent (AR). Copyright © 2007 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman scattering study of the red dye laccaic acidJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2007M. V. Cańamares Abstract FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied to the study of lac dye, a highly fluorescent anthraquinone red dye. The SERS spectra were obtained at different pH values, on Ag nanoparticles prepared by chemical reduction with citrate and hydroxylamine, and at several excitation wavelengths, in order to find the best experimental conditions for the detection of the lac dye. The lower detection limit was achieved using nanoparticles prepared by reduction with hydroxylamine, excitation at 514.5 nm, and slightly acidic pH conditions, thus exploiting a combination of factors including lower electrostatic repulsion between dye and nanoparticles and resonance Raman enhancement. A comparison between the adsorption of laccaic acid (LA) and carminic acid (CA), another anthraquinone red dye, was also done, based on the SERS spectra of both dyes. Copyright © 2007 John Wiley & Sons, Ltd. [source] Analysis of aldehydes via headspace SPME with on-fiber derivatization to their O -(2,3,4,5,6-pentafluorobenzyl)oxime derivatives and comprehensive 2D-GC-MSJOURNAL OF SEPARATION SCIENCE, JSS, Issue 19 2008Hans-Georg Schmarr Abstract A method for the analysis of the homologous series of alkanals, (E)-2-alkenals, and (E,E)-2,4-alkadienals is described utilizing a headspace solid-phase microextraction (HS-SPME) step and on-fiber derivatization with O -(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) hydrochloride. Oxime derivatives formed on the fiber are desorbed in the gas chromatographic injector and analyzed by comprehensive 2-D GC coupled to quadrupole MS (GC×GC-qMS). Selecting specific fragment ions within the electron impact mass spectra of the oxime derivatives provides a suitable method for the target analysis of these aldehyde classes, which furthermore benefits from the increased separation efficiency by GC×GC. The analysis of higher molecular weight aldehydes is described in wine and grape seed oil as examples. Quantification of the aldehydes utilizes a stable isotope dilution analysis (SIDA) assay with octan-d16 -al as isotopomeric internal standard. Besides the selectivity and sensitivity of aldehyde analysis using PFBHA derivatives, critical aspects on background level contamination and repeatability of the sample preparation method are discussed. Optimization of GC×GC-qMS parameters allowed a considerable saving of the cryogenic medium, involving additional (unmodulated) conditioning runs, rendering the method more amenable to routine analysis. [source] Structure of the products of condensation of hydroxylamine with trifluoromethyl-,-diketones: assignments of the diastereotopic protons of the 4-methylene group in 5-hydroxy-5-trifluoromethyl-,2 -isoxazolinesMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2005Dionisia Sanz Abstract The combined use of 1H NMR spectroscopy with theoretical calculations of chemical shifts (GIAO) and coupling constants (B3LYP/6-311 ++G**) of a 5-hydroxy-5-trifluoromethyl-,2 -isoxazoline has enabled solving the problem of the assignments of the diastereotopic protons in this compound. This result has been extended to 5-hydroxy-5-trifluoromethyl-,2 -pyrazolines and the corresponding 5-trichloromethyl derivatives. Copyright © 2005 John Wiley & Sons, Ltd. [source] Quantitation of the Effect of Hydroxylamine on Rhodopsin Palmitylation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Wesley Jackson Rhodopsin (the photosensitive rod visual pigment) has been a model for photobiologic studies of the opsins as well as a structural model for G-protein-coupled receptors. The two palmitate groups attached to cysteines 322 and 323 are thought to serve as membrane anchors for the rhodopsin C-terminus, but the absence of the palmitates does not alter membrane localization. However, removal of the palmitates affects rhodopsin function. Therefore, it is important to quantitate the stability of rhodopsin palmitates to hydroxylamine, which is a widely utilized reagent in biochemical preparations of the apoprotein. We have developed a mass spectrometric method to quantitate the resulting opsin palmitylation. Our data show that both of the bovine rhodopsin palmitates are labile to hydroxylamine, with significant depalmitylation occurring at concentrations of ,100 mm, with an EC50 of 220 mm L,1. The palmitate at position 322 is the more stable to hydroxylamine. Samples prepared in the presence of >50 mm should therefore be considered to be at least partially depalmitylated and the results interpreted accordingly. [source] Chromophore Interaction in Xanthorhodopsin,Retinal Dependence of Salinixanthin Binding,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Eleonora S. Imasheva Xanthorhodopsin is a light-driven proton pump in the extremely halophilic bacterium Salinibacter ruber. Its unique feature is that besides retinal it has a carotenoid, salinixanthin, with a light harvesting function. Tight and specific binding of the carotenoid antenna is controlled by binding of the retinal. Addition of all- trans retinal to xanthorhodopsin bleached with hydroxylamine restores not only the retinal chromophore absorption band, but causes sharpening of the salinixanthin bands reflecting its rigid binding by the protein. In this report we examine the correlation of the changes in the two chromophores during bleaching and reconstitution with native all- trans retinal, artificial retinal analogs and retinol. Bleaching and reconstitution both appear to be multistage processes. The carotenoid absorption changes during bleaching occurred not only upon hydrolysis of the Schiff base but continued while the retinal was leaving its binding site. In the case of reconstitution, the 13-desmethyl analog formed the protonated Schiff base slower than retinal, and provided the opportunity to observe changes in carotenoid binding at various stages. The characteristic sharpening of the carotenoid bands, indicative of its reduced conformational heterogeneity in the binding site, occurs when the retinal occupies the binding site but the covalent bond to Lys-240 via a Schiff base is not yet formed. This is confirmed by the results for retinol reconstitution, where the Schiff base does not form but the carotenoid exhibits its characteristic spectral change from the binding. [source] Dual Chromophore-Nitroxides: Novel Molecular Probes, Photochemical and Photophysical Models and Magnetic MaterialsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Gertz I. Likhtenstein Over the last decades scientists have faced growing requirements in novel methods of fast and sensitive analysis of antioxidant status of biological systems, spin redox probing and spin trapping, investigation of molecular dynamics, and of convenient models for studies of photophysical and photochemical processes. In approaching this problem, methods based upon the use of dual chromophore-nitroxide (CN) compounds have been suggested and developed. A CN consists of two molecular sub-functionality (a chromophore and a stable nitroxide radical) tethered together by spacers. In the dual compound the nitroxide is a strong intramolecular quencher of the fluorescence from the chromophore fragment. Reduction to hydroxylamine, oxidation of the nitroxide fragment or addition of an active radical yield the fluorescence increase and the parallel decay of the fragment electron spin resonance (ESR) signal. At certain conditions the dual molecules undergo photomagnetic switching and form excited state multi-spin systems. These unique properties of CN were intensively exploited as the basis for several methodologies, which include molecular probing, modeling intramolecular photochemical and photophysical processes, and construction of new magnetic materials. [source] Method for estimating decomposition characteristics of energetic chemicalsPROCESS SAFETY PROGRESS, Issue 4 2003Sima Chervin Experimental data on the decomposition characteristics of approximately400 chemicals, representing various classes of energetic materials, were summarized by chemical class and statistically analyzed. Average decomposition characteristics, such as energy of decomposition and decomposition onset temperature, were determined for chemical classes containing the following energetic groups: nitro, nitroso, N-oxide, oxime, hydroxylamine, tetrazole, azide, triazene, triazole, diazo, azo, hydrazine, and perchlorate. Additional statistical information is presented for each chemical class, such as number of chemicals analyzed, ranges, and standard deviations for the decomposition parameters analyzed. For chemical classes containing an energetic group attached to an aromatic ring, the presence and position of another substituting group in the ring can significantly influence the decomposition onset temperature. The study summarizes the list of activating and deactivating functional groups, and the positions in the ring where the strongest activation or deactivation occurs. The authors also recommend a method for estimating decomposition parameters of new chemicals. [source] | ||||||||||||||||||||||||||||||||||