Microchemical investigation of medicinal plants. XV

Summary A method is described for the determination of alkaloids in morning glory leaves by means of spectrophotofluorimetry. The total alkaloidal contents found in different batches of leaves ranged from 0.027 to 0.04%.

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Zusammenfassung Ein Verfahren zur Bestimmung der Gesamtalkaloide in den Blättern vonIpomoea violacea wurde angegeben. Spektralfluoreszenzmessungen ergaben für verschiedene Chargen solcher Blätter Gehalte von 0,027 bis 0,04%.

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For part XIV see Mikrochim. Acta [Wien]1976 I, 227.     

The cyclic fixation and reduction of molecular nitrogen with [WH4(Ph2PCH2CH2PPh2)2] in γ-irradiated solutions

Yields of NH₃ and N₂H₄ in radiation-catalytic reduction of N₂ by means of a hydride complex of W^IV with dppe in thf solution and in mixtures of thf with other solvents have been estimated. A mechanism proposed earlier of reduction of coordinated N₂ has been confirmed and the role of solvent in reduction of N₂ to NH₃ and amines has been explained.     

The kinetics of radical polymerization—XXVII. Investigation of the radical reactivity of 3,3′- and 4,4′-disubstituted azobenzenes in the polymerization of vinylacetate

A study was made on the inhibition by some 3,3′- and 4,4′-disubstituted azobenzenes of the polymerization of vinylacetate initiated by azoisobutyronitrile at 50°. The inhibitory effects of these substances can be attributed to their ability to engage in radical addition giving a less reactive hydrazyl type radical. The mechanism of the inhibition has been established by ESR and kinetic (stoichiometric) measurements. The value of k₅/k₂ (characteristic of the reactivity of an inhibitor) was determined for 9 substituents. The radical reactivity of the aromatic azo group was decreased by electron donor substituents and increased by electron acceptors. The substituent effect can be well interpreted by the Hammett equation; the value of the reaction constant was ? = +0.53.     

Solid-phase reagent for molecular spectroscopic determination of heavy metal speciation in natural water

A solid-phase reagent based on 1-(4-adamantyl-2-thiasolylazo)-2-naphthol adsorbed onto silica gel was prepared for Co(II) recovery and preconcentration prior to its sorption-spectroscopic detection. The immobilized reagent was applied to the determination of free cobalt ions in natural water. The solid-phase reagent and chemiluminescent method coupled with membrane filtration, gel-permeation and ion-exchange chromatography were applied to the study of the speciation of iron and cobalt in water from the Dnieper reservoirs and lakes of Kyiv City; their predominant forms were complexes of Fe(III) and Co(II) with dissolved organic matter and fulvic acids play a main role in their complexation.     

Determination of gentamycin by synchronous derivative fluorimetry

Use of synchronous first-derivative fluorimetry for determination of gentamycin is described. Gentamycin reacts with acetylacetone and formaldehyde in pH 5.6 HOAc/NaOAc buffer solution to form N-gentamyl-2,6-dimethyl-3,5-diacethyl-1,4-dihydropyridine[I] which is a fluorescent substance. Spectra of [I] and the reagent blank can be separated with synchronous derivative fluorimetry, and gentamycin can be determined directly. The synchronous spectral peaks of [I] and the reagent blank are at 434 and 411 nm, respectively. The first-derivative peak of [I] is at 425 nm. Effects of pH, foreign ions, buffer system, and heating time on the determination of gentamycin have been examined. The linear regression equation of the calibration graph is C=0.0513H-0.0416, with a correlation coefficient of linear regression of 0.9978. C means total potency of gentamycin: U ml(-1); H means peak height in the linear regression equation calibration graph. The linear range for the determination of gentamycin is from 0.00 to 3.00 U ml(-1). Recovery is from 95.06 to 112.0%, R.S.D. of 3.8%. The results determined by the fluorimetric method agreed roughly with those by the microbiological method. The method is simple and has low detection limit.     

Simple <Emphasis Type="Italic">b</Emphasis> ions have cyclic oxazolone structures. A neutralization-reionization mass spectrometric and computational study of oxazolone radicals

The 2-methyloxazol-5-on-2-yl radical (3) and its deuterium labeled analogs were generated in the gas-phase by femtosecond electron-transfer and studied by neutralization-reionization mass spectrometry and quantum chemical calculations. Radical 3 undergoes fast dissociation by ring opening and elimination of CO and CH(3)CO. Loss of hydrogen is less abundant and involves hydrogen atoms from both the ring and side-chain positions. The experimental results are corroborated by the analysis of the potential energy surface of the ground electronic state in 3 using density functional, perturbational, and coupled-cluster theories up to CCSD(T) and extrapolated to the 6-311 ++ G(3df,2p) basis set. RRKM calculations of radical dissociations gave branching ratios for loss of CO and H that were k(CO)/k(H) > 10 over an 80-300 kJ mol(-1) range of internal energies. The driving force for the dissociations of 3 is provided by large Franck-Condon effects on vertical neutralization and possibly from involvement of excited electronic states. Calculations also provided the adiabatic ionization energy of 3, IE(adiab) = 5.48 eV and vertical recombination energy of cation 3(+), RE(vert) = 4.70 eV. The present results strongly indicate that oxazolone structures can explain fragmentations of b-type peptide ions upon electron capture, contrary to previous speculations.     

Synthesis of stable azomethine ylides by the rearrangement of 1,3-dipolar cycloadducts of 3,4-dihydroisoquinoline-2-oxides with DMAD

1-Aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines were prepared according to a one-pot procedure involving the reaction of 2-(3,4-dimethoxyphenyl)-ethylamine with aromatic aldehydes in TFA at reflux. The tetrahydroisoquinolines were treated with H₂O₂-WO₄²⁻ in methanol at room temperature to give the corresponding 3,4-dihydroisoquinoline-2-oxides. Treatment of these cyclic nitrones with DMAD in toluene at room temperature gave the corresponding isoxazolo[3,2-a]isoquinolines. These compounds were heated in toluene at reflux to give the corresponding ylides in high yields (Method A). The effect of the substituents on the rate of the rearrangement of such compounds prompted us to discuss a new mechanism involving consecutive C-C bond heterolysis and 1,3-sigmatropic shift. A one-pot reaction involving the treatment of the nitrones with equimolar amounts of DMAD in refluxing toluene also gave the ylides (Method B). The structures of the prepared compounds were elucidated by spectral means and elemental analyses.     

Manual and automated enrichment procedures for biological samples using lipophilic gels

Aspects of the use of lipophilic gels in manual sample preparation procedures are reviewed. Neutral gels with a controlled hydrophobicity are used for sorbent extraction of non-polar and medium polarity compounds from biological fluids. Acidic amphiphilic compounds can be extracted as ion-pairs with decyltrimethylammonium ions. Solvent or detergent extracts of tissues or faeces can be mixed with hydrophobic gels for transfer of analytes from a solvent to a gel phase, permitting subsequent sample preparation in gel bed systems. Hydrophobic gels, alkyl-bonded silica and polystyrene matrices can be used in series for extraction of compounds with a wide range of polarities. Group fractionations are performed on neutral and ion-exchanging lipophilic gels to yield fractions of neutral, basic and acidic metabolites within selected polarity ranges. Selective isolation of phenolic acids on a strong anion exchanger, of ethynylic steroids on a strong cation exchanger in silver form and of oximes of ketonic steroids on a strong cation exchanger in hydrogen form is possible. A computerized system for automatic sample preparation is also described. It consists of an extraction bed, a cation-exchange column and an anion-exchange column. The pumps and switching valves are arranged so that the columns can operate in series or parallel for isolation of neutral, basic and acidic metabolites of amphiphilic compounds and for regeneration of the column beds. Fractions can be collected, or the effluent from the column beds can be diluted with water to permit sorption on a solid phase. The applicability of the automated method to the analysis of bile acids and metabolites of mono(2-ethylhexyl) phthalate is demonstrated.     

Application of high-performance liquid chromatography of some antibiotics in clinical microbiology

During recent years high-performance liquid chromatography has become an excellent tool for the determination of antibiotics in biological fluids. Compared with biological assays, the major benefits of this method are specificity and rapidity. In particular, the determination of biologically inactive metabolites emphasizes that this technique plays an outstanding role for the analysis of antibiotics. This paper describes how the method can be used in the analysis of several antibiotics and demonstrates the efficacy of this method for clinical microbiology. Methods for the determination in biological fluids of acylaminopenicillins (azlocillin, mezlocillin, piperacillin and aspoxicillin), quinolones (ciprofloxacine, norfloxacine and ofloxacine), a penem (imipenem) and a cephalosporin (cefixime) are summarized. Furthermore, their application to in vitro studies and their trial in clinical studies are described.