Introduction of the aminooxy group on to nitroaromatic and heterocyclic rings : Synthesis and properties of O-(nitroaryl)hydroxylamines

The reaction of halonitrobenzenes with t-butyl N-hydroxycarbamate (2), gave t-butyl N(nitroaryloxy)carbamates (3), which yielded on acidolysis with trifluoroacetic acid, O-(nitroaryl)hydroxylamines (4). Compounds 4 were utilized for the amination of anionic nitrogens and of carbanions. Attempts to apply the method to the synthesis of hydroxylamines substituted on the oxygen by heterocyclic rings (pyridine, pyrimidine, pyrazine, triazine, purine and benzothiazole) yielded only the corresponding hydroxy compounds. However, the formation of a N,O-dipyridylhydroxylamine derivative (22b) indicates that O(5-nitro-2-pyridyl)hydroxylamine (17) existed as a highly reactive intermediate.     

Determination of paraquat in marijuana by reversed-phase paired-ion high performance liquid chromatography.

A sensitive and selective method is described for the quantitative determination of paraquat in marijuana. Paraquat is extracted from finely ground plant material with hydrochloric acid with sonification, and the resulting acidic solution is extracted with chloroform:isopropanol (9:1) and evaporated to dryness. The residue is reconstituted with aqueous phosphate buffer pH 7.0; the solution is passed through a C-18 SEP-PAK TM and is analyzed with high performance liquid chromatography, using a reversed-phase column and an "ion pairing" reagent in the mobile phase. The recovery of paraquat in laboratory-spiked material varied from 90-97%. Results obtained with confiscated, field-sprayed marijuana by the procedure described were in excellent agreement with those obtained with a well-established ultraviolet procedure. The calculated limit of detection with this method is 2 ng of paraquat.     

Richtigkeit bei der Bestimmung von Spurenelementen in Lebensmitteln mit der Graphitrohrtechnik AAS

Ohne Zusammenfassung

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Accuracy of the graphite furnace AAS for trace determinations in foodstuffs

     

Identification and determination of phase II nabumetone metabolites by high-performance liquid chromatography with photodiode array and mass spectrometric detection

Chromatographic analyses play an important role in the identification and determination of phase I and phase II drug metabolites. While the chemical standards of phase I metabolites are usually available from commercial sources or by various synthetic, degradation or isolation methods, the phase II drug metabolites have usually more complicated structures, their standards are in general inaccessible and their identification and determination require a comprehensive analytical approach involving the use of xenobiochemical methods and the employment of hyphenated analytical techniques. In this work, various high-performance liquid chromatography (HPLC) methods were employed in the evaluation of xenobiochemical experiments leading to the identification and determination of phase II nabumetone metabolites. Optimal conditions for the quantitative enzymatic deconjugation of phase II metabolites were found for the samples of minipig bile, small intestine contents and urine. Comparative HPLC analyses of the samples of above-mentioned biomatrices and of the same biomatrices after their enzymatic treatment using beta-glucuronidase and arylsulfatase afforded the qualitative and quantitative information about phase II nabumetone metabolites. Hereby, three principal phase II nabumetone metabolites (ether glucuronides) were discovered in minipig's body fluids and their structures were confirmed using liquid chromatography (LC)-electrospray ionization mass spectrometric (MS) analyses.     

Competition between transferrin and the serum ligands citrate and phosphate for the binding of aluminum

A key issue regarding the speciation of Al(3+) in serum is how well the ligands citric acid and phosphate can compete with the iron transport protein serum transferrin for the aluminum. Previous studies have attempted to measure binding constants for each ligand separately, but experimental problems make it very difficult to obtain stability constants with the accuracy required to make a meaningful comparison between these ligands. In this study, effective binding constants for Al-citrate and Al-phosphate at pH 7.4 have been determined using difference UV spectroscopy to monitor the direct competition between these ligands and transferrin. The analysis of this competition equilibrium also includes the binding of citrate and phosphate as anions to apotransferrin. The effective binding constants are 10(11.59) for the 1:1 Al-citrate complexes and 10(14.90) for the 1:2 Al-citrate complexes. The effective binding constant for the 1:2 Al-phosphate complex is 10(12.02). No 1:1 Al-phosphate complex was detected. Speciation calculations based on these effective binding constants indicate that, at serum concentrations of citrate and phosphate, citrate will be the primary low-molecular-mass ligand for aluminum. Formal stability constants for the Al-citrate system have also been determined by potentiometric methods. This equilibrium system is quite complex, and information from both electrospray mass spectrometry and difference UV experiments has been used to select the best model for fitting the potentiometric data. The mass spectra contain peaks that have been assigned to complexes having aluminum:citrate stoichiometries of 1:1, 1:2, 2:2, 2:3, and 3:3. The difference UV results were used to determine the stability constant for Al(H(-1)cta)-, which was then used in the least-squares fitting of the potentiometric data to determine stability constants for Al(Hcta)+, Al(cta), Al(cta)2(3-), Al(H(-1)cta)(cta)(4-), Al2(H(-1)cta)2(2-), and Al3(H(-1)cta)3(OH)(4-).     

Multiple steady states in a CSTR with total condenser: Comparison of equilibrium and nonequilibrium models

Comparison of equilibrium and nonequilibrium models of a CSTR with total condenser focused on the multiple steady states and dynamic behaviour was carried out. The steady-state behaviour of the model system, MTBE synthesis from methanol and isobutene in a reactive distillation column, was studied in terms of the input parameters, i. e. feed flow rate of methanol or butenes, reflux ratio, and mass of catalyst. The dynamic behaviour of the system during the start-up was investigated and perturbations of manipulated variables were found to cause transitions between the parallel steady states. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Preparation and steric structure of 2-Alkoxy-2,5-dioxo-4,4-bis(trifluoromethyl)-7(8)-chloro-1,3,2λ5-benzodioxaphosphepins

The reaction of hexafluoroacetone with 2-alkoxy-6(7)-chloro-1,3,2-benzodioxaphosphorin-4-ones yielded 7-and 8-chloro-substituted 2-alkoxy-2,5-dioxo-4,4-bis(trifluoromethyl)-1,3,2λ⁵-benzodioxaphosphepines. Their steric structure was studied by single-crystal X-ray diffraction. The effect of fluorinated substituents on the crystal packing of the benzophosphepines was demonstrated. Hydrolysis of these compounds gave the corresponding 4-and 5-chloro-substituted 2-(2-hydroxyphenyl)-2-oxo-1,1-bis(trifluoromethyl)-ethanols; the structure of 2-(2-hydroxy-5-chlorophenyl)-2-oxo-1,1-bis(trifluoromethyl)ethanol was also proved by single-crystal X-ray diffraction.     

Phlomoside D — an iridoid glycoside fromPhlomis regelii

A new iridoid – phlomoside D- has been isolated from the epigeal organs ofPhlomis regelii (M. Pop). Its structure has been established on the basis of chemical transformations and spectral characteristics.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 551–553, July–August, 1996. Original article submitted February 5, 1996.     

Synthesis and ozonization of (+)-4α-(1-trimethylsilyloxyethen-1-yl)-2-carene

(+)-4-(1-Trimethylsilyloxyethen-1-yl)-2-carene was synthesized, and the products of its ozonization were identified.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1984–1987, October, 1995.     

The synthesis and membrane transport characteristics of macrocyclic polyether ligands composed of 1,10-phenanthroline as carriers for primary amine species

Four macrocyclic polyether derivatives of o-phenanthroline were synthesized and used as neutral carriers for preparing poly(vinyl chloride) (PVC) membrane electrodes to sense primary amine species. The potentiometric response characteristics of the electrodes prepared were investigated. The electrode sensitive to benzyl amine as model analyte showed a linear response range of 8.0 x 10(-6)-0.1 mol/l with a detection limit of 8.9 x 10(-7) mol/l and a slope of 56.5 mV/decade. The linear potentiometric response of the mexiletine-sensitive electrode was 4.7 x 10(-6)-0.1 mol/l, and the detection limit was 5.0 x 10(-7)1 mol/l with a slope of 59.0 mV/decade. The transfer behavior of amines and ammonium ions through an organic phase was investigated by means of the bulk liquid membrane transport experiment. The effects of pH, counter anions and other factors on the transfer of the amine and ammonium species were studied. The mass transfer rates of the test species facilitated by macrocyclic polyether derivatives of o-phenanthroline were determined and the following sequence was found: benzyl amine > ethyl amine > tetramethyl ammonium > triethyl amine > diethyl amine > K(+) > ammonium > Na(+) > Ca(2+) > Mg(2+). This was exactly the potentiometric selectivity sequence of the membrane electrodes prepared by using these carriers. The mechanism of transfer of benzyl amine through a membrane phase induced by the carriers has been elucidated on the basis of experimental observations.