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1.
Marilena Vasilescu Titus Constantinescu Mariana Voicescu Helge Lemmetyinen Elina Vuorimaa 《Journal of fluorescence》2003,13(4):315-322
The spectrophotometric study of luminol (LH2) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH2 absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L2–) formation at 3 × 10–4 – 2.4 × 10–3
M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH2-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH2-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH+
3 cation formation. In LH2-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH2-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed. 相似文献
2.
The Böckelheide reaction was accomplished with a number of imidazo[4,5-b]pyrazine N-oxides, and the N-oxidation of the resulting acetoxy(hydroxy)methyl derivatives of imidazo[4,5-b]pyrazine and 6-bromo-1-methylimidazo[4,5-b]pyrazine was studied. The hydrolytic cleavage of 6-bromo-1-methylimidazo[4,5-b]pyrazine and its 4-N-oxide was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–693, May, 1975. 相似文献
3.
The interaction of aryldiazonium ions with some Schiff-base complexes of cobalt and ruthenium have been studied. With cobalt, one-electron oxidation of [Co(II)Salen] occurred; with [Co(I)Salen] the corresponding Co(III)-aryl complexes were isolated. In the case of ruthenium oxidation also occurs, [Ru(Salen)(CO)py] gave the corresponding monocation. The results, especially for ruthenium, are in contrast to the stabilisation of both nitrosyl and aryldiazonium adducts in analogous porphyrin complexes. 相似文献
4.
Vilar RB da Silva R Schossler P Cataluña Veses R Piatnicki C Samios D Caramão EB 《Journal of chromatography. A》2003,985(1-2):367-373
This work reports preliminary studies on the characterisation of anhydrous ethanol (AEA) used as an automotive fuel mixed with gasoline in Porto Alegre (South Brazil). Pre-concentration of the impurities contained in 1000 ml of AEA was carried on through solid-phase extraction using XAD4 resin. The main compounds in the extract were identified by means of spectral data from the library of the equipment. The concentrate was then fractionated using a preparative liquid chromatographic column filled with activated silica gel and the elution procedure was carried out with, n-hexane, n-hexane-benzene (1:1, v/v) and dichloromethane. Prior to analysis by GC-MS, each fraction was reduced to 1 ml with a gentle stream of nitrogen. Saturated linear hydrocarbons and aromatic hydrocarbons eluted in the first fraction and oxygenated compounds such as aldehydes. ketones and alcohols, eluted in the second one. were the main compounds detected in the sample. 相似文献
5.
Two isomeric mono-N-oxides of 2-aminopyrazine and the 1,4-di-N-oxide have been synthesized. A marked fall in the capacity of these compounds for nucleophilic exchange reactions and for rearrangements in acid and alkaline media has been found, which distinguishes them from the corresponding N-oxides of 2-aminoquinoxaline.For part I, see [5]. 相似文献
6.
do Nascimento Filho I Schossler P Santos Freitas L Melecchi MI Rodrigues Vale MG Bastos Caramão E 《Journal of chromatography. A》2004,1027(1-2):167-170
In this work a simple method was described for selective extraction of benzoic acid from landfill leachate samples. The samples were submitted to solid-phase extraction (SPE) with XAD-4 resin as the stationary phase and ion-exchange chromatography (IEC) using the ion-exchange resin Amberlyst A-27. The instrumental analysis was performed by gas chromatography with mass spectrometric detection (GC-MSD). Benzoic acid was isolated, identified and quantified. The extraction process is rapid, simple and of low cost. It was also environmental friendly, that is, it was used a minimum amounts of hazardous organic solvents and produced also minimum quantities of residues. 相似文献
7.
G. P. Syrova Yu. N. Sheinker I. S. Musatova A. S. Elina 《Chemistry of Heterocyclic Compounds》1972,8(2):240-246
The PMR spectra of pyrazine, its 2-substituted derivatives, and the corresponding N-oxides and N,N-dioxides were investigated. The character of the change in the chemical shifts in the N-oxides and N,N-dioxides of unsubstituted pyrazine indicates the electron-donor effect of the NO group. An additive effect of the NO groups on the chemical shifts of the ring protons is observed in pyrazine N,N-dioxide. An appreciable interaction of the substituent with the N(1)O group and a weak interaction with the N(4)O group occur in N-oxides and N,N-dioxides of 2-substituted pyrazines. A significant increase in the ortho and meta spin-spin coupling constants of the ring protons is noted when the nitrogen atoms are oxidized. The sign of the spin-spin coupling constant (J35) through the NO group was determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 266–273, February, 1972. 相似文献
8.
Sulfonated polystyrene latex particles were prepared by a two-stage shot-growth emulsion polymerization process in the absence of emulsifier. Sodium styrene sulfonate (NaSS) was used as an ionic co-monomer to produce a series of latex particles with the same particle size but with different surface charge densities. The electrophoretic mobility of this functionalized model colloid was studied in the presence of various types of inorganic electrolytes. The e curves of these latexes exhibit a pronounced maximum at high electrolyte concentrations: 5·10–2 M for 11 electrolytes and 10–2 M for 21 and 12 electrolytes. When a 31 electrolyte (LaCl3) was used, the electrophoretic mobility changed to positive values at high concentration due to the specific adsorption of lanthanum species. The experimental results for the electrokinetic characterization of these sulfonated polystyrene model colloids suggest that the surface of the particles is covered by a layer of oligomers or polymer chains which shift the shear plane toward the bulk solution, increasing the anomalous surface conductance of the polystyrene microsphere-electrolyte solution interface. 相似文献
9.
Abrunhosa F Faria S Gomes P Tomaz I Pessoa JC Andreu D Bastos M 《The journal of physical chemistry. B》2005,109(36):17311-17319
The interaction of two hybrid peptides of cecropin A and melittin [CA(1-8)M(1-18) and CA(1-7)M(2-9)] with liposomes was studied by differential scanning calorimetry (DSC), circular dichroism (CD), and quasi-elastic light scattering (QELS). The study was carried out with large unilamellar vesicles (LUVs) of three different lipid compositions: 1,2-dimyristoil-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DMPG) and a binary mixture of DMPC/DMPG, in a wide range of peptide-to-lipid (P:L) molar ratios (0 to 1:7). DSC results indicate that, for both peptides, the interaction depends on membrane composition, with very different behavior for zwitterionic and anionic membranes. CD data show that, although the two peptides have different secondary structures in buffer (random coil for CA(1-7)M(2-9) and predominantly beta-sheet for CA(1-8)M(1-18)), they both adopt an alpha-helical structure in the presence of the membranes. Overall, results are compatible with a model involving a strong electrostatic surface interaction between the peptides and the negatively charged liposomes, which gives place to aggregation in the gel phase and precipitation after a threshold peptide concentration. In the case of zwitterionic membranes, a progressive surface coverage with peptide molecules destabilizes the membrane, eventually leading to membrane disruption. Moreover, delicate modulations in behavior were observed depending on the peptide. 相似文献
10.