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  • Articles  (41)
  • kinetics  (23)
  • NMR  (18)
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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of alternating silane copolymers: (Me2Si−R2Si−Me2Si) n (1995)
    Springer
    Journal of inorganic and organometallic polymers and materials 5 (1995), S. 217-236 
    Details
    ISSN: 1572-8870
    Keywords: Polysilane ; NMR ; pyrolysis ; randomization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bimodal molecular weight distributions of alternating copolymers of the type (Me2Si−R2Si−SiMe2) n , where R=hexyl and butyl, were obtained by polymerization of BrSiMe2−R2Si−Me2SiBr, using the Wurtz coupling method. Analysis of the samples by pyrolysis GC MS and solution29Si NMR indicated that some randomization occurred, due to cleavage of the original Si−Si bonds in the monomer. The extent of randomization was significantly greater in the high molecular weight fractions. Based on the nature of the rings from the py MGC/MS traces and the number on nonads found in the29Si spectra, two types of randomization processes have been proposed, involving backbiting followed by (1) ring expulsion or (2) redistribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01057894
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  • 2
    Electronic Resource
    Electronic Resource
    Direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexing (1995)
    Springer
    Journal of solution chemistry 24 (1995), S. 1249-1263 
    Details
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; carbon-13 ; nitrogen-15 ; NMR ; magnesiumisothiocyanate complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexation in aqueous mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate1H,13C, and15N NMR signals are observed for coordinated and bulk water molecules and anions. The1H NMR spectra reveal signals for the hexahydrate and the mono-through triisothiocyanato complexes, as well as two small signals attributed to [Mg(H2O)5(OH)]1+ and [Mg(H2O)4(OH)(NCS)]. Accurate hydration numbers were obtained from signal area integrations at each NCS− concentration. In the15N NMR spectra, signals also were observed for the mono-through triisothiocyanato complexes, and a small signal believed to be due to [Mg(H2O)4(OH)(NCS)]. Coordination number contributions for NCS− were measured from these spectra and when combined with the hydration numbers they totalled essentially six at each anion concentration. Signals for [Mg(H2O)5(NCS)]1+ through [Mg(H2O)3(NCS)3]1− also were observed in the13C NMR spectra and the area evaluations were comparable to the15N NMR results. An analysis of the magnitude and sign of the coordinated NCS− chemical shifts identified the nitrogen atom as the anion binding site. All spectra indicated [Mg(H2O)5(NCS)]1+ and [Mg(H2O)4(NCS)2] were the dominat isothiocyanato complexes over the entire range of anion concentrations. The inability to detect evidence for complexes higher than the triisothiocyanato reflects the competitive binding ability of water molecules and perhaps the decreased electrostatic interaction between NCS− and negatively charged higher complexes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00972831
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  • 3
    Electronic Resource
    Electronic Resource
    Sensitivity of PSA process performance to input variables (1995)
    Springer
    Adsorption 1 (1995), S. 133-151 
    Details
    ISSN: 1572-8757
    Keywords: PSA process ; sensitivity ; equilibria ; kinetics ; heats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Mathematical models for pressure swing adsorption (PSA) processes essentially require the simultaneous solutions of mass, heat and momentum balance equations for each step of the process using appropriate boundary conditions for the steps. The key model input variables needed for estimating the separation performance of the process are the multicomponent adsorption equilibria, kinetics and heats of adsorption for the system of interest. A very detailed model of an adiabatic Skarstrom PSA cycle for production of high purity methane from a ethylene-methane bulk mixture is developed to study the sensitivity of the process performance to the input variables. The adsorption equilibria are described by the heterogeneous Toth model which accounts for variations of isosteric heats of adsorption of the components with adsorbate loading. A linear driving force model is used to describe the kinetics. The study shows that small errors in the heats of adsorption of the components can severely alter the overall performance of the process (methane recovery and productivity). The adsorptive mass transfer coefficients of the components also must be known fairly accurately in order to obtain precise separation performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705001
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  • 4
    Electronic Resource
    Electronic Resource
    The steric structure of multiflorine methylation products (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 233-239 
    Details
    ISSN: 1434-4475
    Keywords: Enaminoketones ; Lupin alkaloid ; Multiflorine ; NMR ; Nucleophilic methylation ; Stereospecificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Multiflorin (1), ein Lupin-Nebenalkaloid, ergibt bei Umsetzung mit Methyllithium oder Methylmagnesiumiodid 4S-4-Hydroxy-4-methyl-2,3-didehydrospartein (2) und 2S-2-Methyl-4-oxospartein (3) als Hauptprodukte. Ihre NMR-spektroskopisch (1H und13C) aufgeklärte räumliche Struktur weist auf eine Stereoselektivität der erwähnten Reaktionen hin. Die beobachteten nucleophilen 1,2- und 1,4-Additionen zeigen, daß sich die Regiospezifität der Einwirkung von MeLi oder MeMgl auf Multiflorin von jener bis jetzt bekannter Alkylierungen von Enaminoketonen unterscheidet.
    Notes: Summary Multiflorine (1) — a minor lupine alkaloid — treated by methyl lithium or methyl magnesium iodide affords 4S-4-hydroxy-4-methyl-2,3-didehydrosparteine (2) and 2S-2-methyl-4-oxosparteine (3), respectively, as the dominating products. Their steric structure, determined by1H and13C NMR techniques, points to stereospecific preferences of these reactions. The observed nucleophilic 1,2- and 1,4-additions indicate that regiospecificity of the action of MeLi or MeMgI on multiflorine is different from that of the so far known similar alkylation of other enamino ketones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00812252
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis and stereochemistry of 8-methyl-5-nitro-1-octalones (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 1011-1019 
    Details
    ISSN: 1434-4475
    Keywords: Precursors of strigol analogues ; Michael reaction ; NMR ; Molecular modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung BasenkatalysierteMichael-Addition von 5-Nitropentan-2-on-ethylenketal (1) und Cyclohex-2-enon (2), anschließende Entfernung der Schutzgruppe und darauffolgende Aldolkondensation liefert isomer 8-Methyl-5-nitro-1-octalone (5a,b). Struktur, relative Konfiguration und Konformation von5a und5b wurden mittels1H- und13C-NMR-Spektroskopie aufgeklärt.
    Notes: Summary Base catalyzedMichael addition of 5-nitropentan-2-one ethylene ketal (1) and cyclohex-2-enone (2), subsequent deprotection, and intramolecular aldol condensation yields the 8-methyl-5-nitro-1-octalone isomers (5a,b). The structure, relative configuration, and conformation of5a and5b were elucidated utilizing the results of1H and13C NMR investigations
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811021
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis of aluminum rich MCM-41 (1995)
    Springer
    Catalysis letters 31 (1995), S. 267-272 
    Details
    ISSN: 1572-879X
    Keywords: MCM-41 synthesis ; NMR ; FTIR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The synthesis of MCM-41 mesoporous compounds with Si/Al ratios as low as 2 without observing the presence of octahedral Al in27AlMAS NMR is reported. FTIR spectra of chemisorbed pyridine indicated that MCM-41 materials in their protonated form exhibit both Brønsted and Lewis acid sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808839
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  • 7
    Electronic Resource
    Electronic Resource
    Partial hydrogenation of benzene to cyclohexene in a continuously operated slurry reactor (1995)
    Springer
    Catalysis letters 31 (1995), S. 431-438 
    Details
    ISSN: 1572-879X
    Keywords: partial hydrogenation of benzene ; production of cyclohexene ; kinetics ; reaction mechanism ; ruthenium catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A method has been developed for direct measurement of reaction rates in a continuously operated slurry (CST-) reactor. In contrast to the usual procedure in a two-liquid-phase system the reactor contains only one liquid phase, an aqueous zinc chloride solution in which a ruthenium lanthanoxide catalyst is suspended. The selectivity of benzene hydrogenation with respect to cyclohexene is higher when the new one-liquid-phase procedure is applied. With decreasing degree of benzene conversion the selectivity with respect to cyclohexene approaches 100%. The conclusion is that cyclohexane is formed only by consecutive hydrogenation of cyclohexene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808607
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  • 8
    Electronic Resource
    Electronic Resource
    MBOHO calculations of phosphorus-carbon nuclear spin-spin coupling constants (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 61-65 
    Details
    ISSN: 1432-2234
    Keywords: NMR ; Nuclear spin coupling constant ; Maximum bond order hybrid orbital ; Phosphorus-carbon coupling ; Net atomic charge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The novel generalized correlation of the nuclear spin-spin coupling constants with the atomic hybrids and net charges is employed to give a new relationship for calculating the directly bonded phosphorus-carbon coupling constants by use of the maximum bond order hybrid orbital procedure together with the extended Hückel molecular orbital calculation. The calculated coupling constants of phosphorus-carbon are all in good agreement with the experimental data, which shows that the new relationship obtained in the present paper is quite satisfactory for calculation of the phosphorus-carbon coupling constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134204
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  • 9
    Electronic Resource
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    Determination of the structure of fusaproliferin by1H-NMR and distance geometry (1995)
    Springer
    Structural chemistry 6 (1995), S. 183-189 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; distance geometry ; cluster analysis ; absolute configuration ; fusaproliferin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The absolute configuration of fusaproliferin, a toxic metabolite produced byFusarium proliferation, was determined by the combined use of1H NMR and distance geometry. The configuration of double bonds has been determined in agreement with NOESY buildup data. An R configuration for C10 was determined using Mosher's method. Processing the constraints obtained from NOESY experiments with a distance geometry program, a limited number (80) of possible structures was derived. An agglomerative nonhierarchical method of clustering was used in order to place these structures into classes suggested by the data, and not previously defined in any way. This statistical method showed that indeed the structures could be grouped in four classes. One of these classes is represented by a single structure, with the highest sum of violations and was discarded. All other structures have the same chirality; respectively S for C14 and R for C15. In solution the overall conformation is quite well defined in the region of the five-member ring and the planes of double bonds C2–C3 and C11–C12, while near to C8 and C9 internal flexibility appears evident.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02286446
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  • 10
    Electronic Resource
    Electronic Resource
    A continuous and mechanistic representation of calcite reaction-controlled kinetics in dilute solutions at 25°C and 1 atm total pressure (1995)
    Springer
    Aquatic geochemistry 1 (1995), S. 105-130 
    Details
    ISSN: 1573-1421
    Keywords: calcite ; precipitation ; dissolution ; kinetics ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Calcite dissolution rates were measured using a free-drift technique at 25°C, 1 atm total pressure, and various $$P_{CO_2 } $$ in deionized water. The data were corrected for gas phase disequilibrium and fitted to a kinetic expression derived by coupling the mechanistic models of Plummeret al. (1987a) and Chouet al. (1989) to the surface complexation model of Van Cappellenet al. (1993). Corrected dissolution and precipitation rate measurements from previous investigations were combined to our data set and fitted to the same expression. The following reactions provide an adequate description of the calcite dissolution and precipitation mechanism in dilute solutions: for which the overall reaction rate is given by where 〉i are the densities of surface complexes (mol/m2),a i are the activities of dissolved species and,k i are the rate constants corresponding to the above reactions. This rate equation satisfies the principle of microscopic reversibility and applies to both dissolution and precipitation reactions over a wide range of $$P_{CO_2 } $$ , pH and saturation states. The rate constants obtained from fitting the data set to Equation (3) are compatible with values reported by Plummeret al. and Chouet al., as well as yielding a very good estimate of the thermodynamic solubility constant of calcite, K 0 sp .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01025233
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  • 11
    Electronic Resource
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    Acetylcholinesterase from desert Cobra (Walterinnesia aegyptia) venom: Optimization and kinetics study (1995)
    Springer
    Molecular and cellular biochemistry 151 (1995), S. 21-26 
    Details
    ISSN: 1573-4919
    Keywords: acetylcholinesterase ; optimization ; kinetics ; venom ; turnover number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Acetylcholinesterase (AChE) was investigated inWalterinnesia aegyptia venom and characterized with respect to its kinetic properties. It was found that 4.0 ug of crude venom protein and an incubation time of 4.0 min were suitable conditions for linearity of AChE activity at 25°C. The optimum strength of the sodium phosphate buffer was 0.05 M, and the optimum pH was 7.75. The optimum temperature was 30°C. The activation energy and the heat of activation were observed to be 6510 and 5922 cal/mole. The AChE was specific for acetylthiocholine but it did not hydrolyse butyrylthiocholine. The optimum substrate concentration was 3.0 mM but at higher substrate concentrations, the AChE activity declined. The ASCh concentration ranges for different orders of the reactions were determined and kinetic parameters (Km, Vmax, kcat, and ksp) were established at each order of the reaction.
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    URL: http://dx.doi.org/10.1007/BF01076891
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  • 12
    Electronic Resource
    Electronic Resource
    NMR study of the selective inhibition of water permeability of rat erythrocyte membrane (1995)
    Springer
    Bioscience reports 15 (1995), S. 55-63 
    Details
    ISSN: 1573-4935
    Keywords: water transport mechanisms ; NMR ; rat erythrocytes ; tritium effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The inhibition of water diffusion across the rat erythrocyte membrane was studied by NMR using two basically different types of inhibitory agents: PCMB andin vivo irradiation. The contribution of lipid and protein to water permeability revealed the inhibitory effect of each pathway. Internal contamination with tritium (25–115 mGy) reduces water permeability due to protein modifications; for doses higher than 100 mGy the lipid mediated mechanism seems also to be impaired. The same procedure enables one to assess the extent to which the higher water permeability of rat, compared to human, erythrocyte is due to one of the two pathways.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01200215
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  • 13
    Electronic Resource
    Electronic Resource
    Structure-property relationships in thin films and membranes (1995)
    Springer
    Journal of sol gel science and technology 4 (1995), S. 117-133 
    Details
    ISSN: 1573-4846
    Keywords: kinetics ; precursor chemistry ; silica ; permeability ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The molecular-scale species distributions and intermediate-scale structure of silicate sols influence the microstructures of the corresponding thin films prepared by dip-coating. Using multi-step hydrolysis procedures, we find that, depending on the sequence and timing of the successive steps, the species distributions (determined by 29Si NMR) and intermediate scale structure (determined by SAXS) can change remarkably for sols prepared with the same nominal composition. During film formation, these kinetic effects cause differences in the efficiency of packing of the silicate species, leading to thin film structures with different porosities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00491678
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  • 14
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    Chemical and rheological investigations of the sol-gel transition in organically-modified siloxanes (1995)
    Springer
    Journal of sol gel science and technology 4 (1995), S. 151-162 
    Details
    ISSN: 1573-4846
    Keywords: sol-gel transition ; rheology ; siloxane ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ormosils are well-known organic-inorganic sol-gel derived materials also called heteropolysiloxanes. This paper presents two basic heteropolysiloxane structures where the organic part is either a short organic chain bridging two silicon atoms for the first material or an organic polymer backbone for the second. Their synthesis is detailed and a variety of experimental techniques (IR, 13C and 29Si NMR and CP-MAS NMR, GPC) have been employed to investigate the chemical structure of these new materials. Their mechanical properties, more precisely their viscoelastic behaviour, have been evaluated using dynamic rheological techniques. The storage and loss moduli have been followed during the sol-gel transition at fixed and variable oscillation frequencies. The results have been correlated to the 29Si CP-MAS NMR informations concerning the network polycondensation and compared to a pure inorganic sol-gel material prepared from tetraethoxysilane.
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    URL: http://dx.doi.org/10.1007/BF00491681
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  • 15
    Electronic Resource
    Electronic Resource
    Probing a functional role of Glu87 and Trp89 in the lid ofHumicola lanuginosa lipase through transesterification reactions in organic solvent (1995)
    Springer
    The protein journal 14 (1995), S. 217-224 
    Details
    ISSN: 1573-4943
    Keywords: Hydrolase ; site-directed mutagenesis ; kinetics ; cyclohexane ; butanoic acid esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract To reveal the functional role of Glu87 and Trp89 in the lid ofHumicola lanuginosa lipase, site-directed mutagenesis at Glu87 and Trp89 was carried out. The catalytic performance of wild-type and mutated lipases was studied in transesterification reactions in cyclohexane at a controlled water activity. Two different acyl donors were used in the investigation: tributyrin, a natural substrate for a lipase, and vinyl butyrate, an activated ester suitable for fast and efficient lipase-catalyzed transformations in preparative organic synthesis. As acyl acceptor 1-heptanol was used. The Glu87Ala mutation decreased theV max,app value with tributyrin and vinyl butyrate by a factor of 1.5 and 2, respectively. TheK m,app for tributyrin was not affected by the Glu87Ala mutation, but theK m,app for vinyl butyrate increased twofold compared to the wild-type lipase. Changing Trp89 into a Phe residue afforded an enzyme with a 2.7- and 2-fold decreasedV max,app with the substrates tributyrin and vinyl butyrate, respectively, compared to the wild-type lipase. No significant effects on theK m,app values for tributyrin or vinyl butyrate were seen as a result of the Trp89Phe mutation. However, the introduction of a Glu residue at position 89 in the lid increased theK m,app for tributyrin and vinyl butyrate by a factor of 〉5 and 2, respectively. The Trp89Glu mutated lipase could not be saturated with tributyrin within the experimental conditions (0–680 mM) studied here. With vinyl butyrate as a substrate theV max,app was only 6% of that obtained with wild-type enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01886762
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  • 16
    Electronic Resource
    Electronic Resource
    15N resonance assignments of oxidized and reducedChromatium vinosum high-potential iron protein (1995)
    Springer
    The protein journal 14 (1995), S. 115-126 
    Details
    ISSN: 1573-4943
    Keywords: NMR ; high-potential iron protein ; 15N assignment ; heteronuclear correlation ; paramagnetic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The15N resonances in reduced and oxidizedChromatium vinosum high-potential iron protein have been assigned by use of1H-1H COSY spectra and1H-15N HMQC, HMQC-COSY, and HMQC-NOESY spectra. Unambiguous assignment of 70 of 85 backbone15N resonances in the reduced protein and 62 of 85 resonances in the oxidized protein are made, as are 12 of 21 side-chain15N resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01980323
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  • 17
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    Kinetics of the course of reactivation of aminoacylase reconstituted using Mn2+ ions (1995)
    Springer
    The protein journal 14 (1995), S. 695-701 
    Details
    ISSN: 1573-4943
    Keywords: Aminoacylase ; metal ion ; reactivation ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetic theory of the substrate reaction during irreversible change of enzyme activity previously described by Tsou (Tsou (1988),Adv. Enzymol. Relat. Areas Mol. Biol.61, 381–436] has been applied to a study of the kinetics of the course of reactivation during reconstitution of apo-aminoacylase using Mn2+ or Zn2+. The kinetic parameters for Mn2+-and Zn2+-reconstituted enzymes and the microscopic rate constants for reactivation during reconstitution were determined. The kinetic analysis suggests the presence of a second Mn2+ binding site in Mn2+-reconstituted aminoacylase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01886908
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  • 18
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    Complexes of rhodium carbonylchloride and phosphorus(iii) cyanides in mediated electrochemical reduction of 2-carbomethoxy-2-methyl-1,1-dichlorocyclopropane (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 1890-1891 
    Details
    ISSN: 1573-9171
    Keywords: electrochemistry ; metal complexes ; dichlorocyclopropane ; kinetics ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Electrochemical reduction of the complexes Rh(CO)ClL2 [L = (EtO)2PCN (1), Ph2PCN (2)] and Rh2(CO)4L [L = P(CN)3 (3), $$Ph\begin{array}{*{20}c} P \\ | \\ {CN} \\ \end{array} ---\begin{array}{*{20}c} P \\ | \\ {CN} \\ \end{array} Ph$$ (4)] and their catalytic properties in electrochemical reduction of 2-carbomethoxy-2-methyl-1,1-dichloro-cyclopropane were studied. The catalytic electroreduction of a substrate at the reduction potentials of the central ion was developed for complexes2–4. This process is accelerated substantially for complexes2 and3 in the presence of anthracene.
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    URL: http://dx.doi.org/10.1007/BF00707219
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  • 19
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    Photochemical transformations of 1-arylcyanomethyl-9,10-anthraquinones (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 1907-1913 
    Details
    ISSN: 1573-9171
    Keywords: photochemical transformations ; 1-arylcyanomethyl-9 ; 10-anthraquinones ; nucleophilic addition ; oxidation ; kinetics ; quantum-chemical calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Photochemical transformations of 1-arylcyanomethyl-9,10-anthraquinones were studied. It was established that under irradiation, the hydrogen atom of the substituted methyl group is transferred to aperi-quinoid oxygen atom to form the corresponding 9-hydroxy1, 10-anthraquinone-1-arylcyanomethides. Dark transformations of photoinduced quinonemethides result from three competing parallel processes: intramolecular transfer of the hydrogen atom, a reaction with a solvent (alcohol), and oxidation by dissolved oxygen. The kinetics of these reactions were studied.
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    URL: http://dx.doi.org/10.1007/BF00707225
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  • 20
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    Kinetics of the thermal decomposition of bis(2,2-dinitropropyl)-N-fluoroamine (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 847-850 
    Details
    ISSN: 1573-9171
    Keywords: fluoroamines, thermal decomposition ; nitrocompounds ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the thermal decomposition of bis(2,2-dinitropropyl)-N-fluoroamine are studied in the liquid phase. The reaction is autocatalytic in a melt. In dilute solution, the reaction rate is described by the first-order law. It is tens of times faster in polar sulfolan than in weakly polar dimethyl phthalate. A mechanism of the decomposition involving the formation of a cyclic transition state at the first, limiting stage of the process is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696915
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  • 21
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    Salt effects and the mechanism of electrophilic mercuration of unsaturated compounds (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 336-344 
    Details
    ISSN: 1573-9171
    Keywords: solvomercuration ; mechanism of reaction ; mercury acetate ; salt effect ; alkenes ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the addition of Hg(OAc)2 to strained and unstrained alkenes was studied in MeOH solution in the presence of NaOAc. Based on salt effects, the HgOAc ion was shown to be the actual reagent in the reaction of the unstrained alkenes, whereas Hg(OAc)2 was the reagent in the case of the strained alkenes. The mechanisms of the solvomercuration of alkenes of various structures were proposed.
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    URL: http://dx.doi.org/10.1007/BF00702148
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    Kinetic peculiarities of redox reactions sensitized by colloidal CdS under steady-state irradiation. The effect of adsorption-desorption processes on the reaction (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 236-246 
    Details
    ISSN: 1573-9171
    Keywords: photocatalyst ; adsorption ; surfactant ; kinetics ; colloid ; cadmium sulfide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Photoreduction of Methyl Orange dye (MOr) by sodium sulfide was studied under steady-state photolysis (λ = 365 nm). The reaction was sensitized by the CdS colloid with the characteristic ∼5-nm particle size. The quantum yield of the reaction is independent of the light intensity when the latter is less than 5 mW cm−2. The form of the dependence of the initial quantum yield of the reaction on [MOr] coincides qualitatively with the adsorption isotherm of the dye on the CdS surface. The reaction kinetics under steady-state irradiation were analyzed. The kinetics in solution as a whole are shown to be adequate to those on a single colloidal particle. On the basis of the experimental data, two types of surfaces of the colloidal particles are suggested (“open” and “covered” with macromolecules of a colloid stabilizer), which significantly differ in the rate at which they establish an adsorption-desorption equilibrium with the solution.
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    URL: http://dx.doi.org/10.1007/BF00702128
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    Kinetic scheme of homogeneous acid-catalyzed transformation of isopentenols (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 840-843 
    Details
    ISSN: 1573-9171
    Keywords: isopentenols, reaction scheme ; Prins reaction ; acid catalysis ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reactions occurring in an equilibrium mixture of 3-methyl-1-buten-3-ol and 3-methyl-2-buten-1-ol in 24–49 % aqueous solutions of H2SO4 yield isoprene, 3-methyl-3-buten-1-ol, isobutylene, formaldehyde, 3-methylbutane-1,3-diol. Isobutylene is rapidly hydrated to give 2-methylpropan-2-ol. The presence of formaldehyde in the reaction mixture indicates that the transformations involve the reverse Prins reaction. On the basis of experimental and literature data, two most probable reaction schemes were suggested.
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    URL: http://dx.doi.org/10.1007/BF00696913
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    Sorption of rubidium chloride by crown-containing polymer (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 989-991 
    Details
    ISSN: 1573-9171
    Keywords: sorption ; kinetics ; mechanism ; polymer ; dibenzo-18-crown-6 ; RbCl ; equilibrium constant ; diffusion coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics and mechanism of the sorption of rubidium chloride from ethanol by granulated polymer containing immobilized dibenzo-18-crown-6 are studied. The sorption of RbCl is controlled by internal diffusion accompanied by complex formation in the polymer. The equilibrium constants of the sorption and diffusion coefficients of the electrolyte in the sorbent are calculated.
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    URL: http://dx.doi.org/10.1007/BF00707040
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    Invertomers at nitrogen in aziridine carboxylates by mltltinuclear (1H,13C,17O, and15N) NMR study (1995)
    Springer
    Chemistry of heterocyclic compounds 31 (1995), S. 1071-1078 
    Details
    ISSN: 1573-8353
    Keywords: NMR ; 1H NMR ; 13C NMR ; 17O NMR ; 15N NMR ; aziridine-carboxylates ; configurational analysis ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by1H ,13C,17O, and15N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.
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    URL: http://dx.doi.org/10.1007/BF01165053
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    Isothermal and Nonisothermal Decomposition of Famotidine in Aqueous Solution (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 599-604 
    Details
    ISSN: 1573-904X
    Keywords: famotidine ; degradation ; isothermal ; nonisothermal ; kinetics ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of hydrolysis of famotidine in aqueous solution was studied by isothermal and nonisothermal method over the pH range of 1.71 to 10.0. Nonisothermal kinetics was studied with the purpose of determining its use in the establishment of the expiration date of pharmaceutical preparations, particularly drugs in solutions and for assessment of stability characteristics of pharmaceutical formulations during the development stage. A comparison of isothermal (55, 70 and 85°C) and nonisothermal kinetics was performed. Aqueous solutions of famotidine were buffered at pH 1.71, 2.24, 2.66, 4.0, 8.5, 9.0 and 10.0 were used. In the nonisothermal studies, the temperature rate of the reaction was continuously varied throughout the experiment. The energies of activation were found to be in close agreement for isothermal and nonisothermal studies, indicating that nonisothermal studies may save considerable amount of time in the early stages of drug development and stability testing. Logk-pH profiles were constructed for 55, 70 and 85°C from the first-order rate constants obtained from isothermal studies at pH values ranging from 1.71 to 10.00. The pH-rate profile indicated that famotidine undergoes specific acid catalysis in the acidic region and general base catalysis in the alkaline region. Hydrolysis in the acidic and alkaline media resulted in the formation of four and five degradation products, respectively. A possible degradation pathway for the acidic and alkaline hydrolysis was discussed.
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    URL: http://dx.doi.org/10.1023/A:1016222501079
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    A Novel Oligodeoxynucleotide Inhibitor of Thrombin. I. In VitroMetabolic Stability in Plasma and Serum (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1937-1942 
    Details
    ISSN: 1573-904X
    Keywords: oligodeoxynucleotides ; nuclease degradation ; plasma stability ; kinetics ; in vitrometabolism ; thrombin inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To determine the degradation rates and pathways of GS-522, a potent oligodeoxynucleotide (GGTTGGTGTGGTTGG) inhibitor of thrombin, in serum and plasma. Methods. A stability-indicating, anion-exchange HPLC method was developed and used to determine concentrations of GS-522 and metabolites. Results. In monkey plasma at 2 µM or below, the degradation of GS-522 can be fit to a first-order exponential with a kp obs ~ 0.01 min−1. At 3 µM and above the degradation process deviates from a monoexponential decay profile. An initial fast degradation process is followed by a slower phase with an observed rate constant equal to that observed at 2 µM and below. In monkey serum, the KMand Vmaxare 8.4 µM and 0.87 µM min−1, respectively. Conclusions. The kinetics are consistent with an equilibrium binding of GS-522 to prothrombin in plasma (Kd = 50 nM) which saturates at GS-522 concentrations 〉2 µM. Compared to a scrambled sequence (GGTGGTGGTTGTGGT), with no defined tertiary structure, GS-522 is 4-fold more stable in serum. The metabolic profile in plasma is consistent with a 3′-exonuclease catalyzed hydrolysis of GS-522.
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    URL: http://dx.doi.org/10.1023/A:1016243923195
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    Hydrolysis of the Prodrug, 2′, 3′, 5′ -Triacetyl-6-azauridine (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1361-1370 
    Details
    ISSN: 1573-904X
    Keywords: 2′,3′,5′-triacetyl-6-azauridine ; prodrug ; hydrolysis ; pH-profile ; arrhenius plots ; CI-MS ; NMR ; liquid chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The purposes were to study the kinetics of hydrolysis of 2′,3′,5′-triacetyl-6-azauridine ( 1 ) in aqueous solution (µ = 0.5) and to identify the main intermediates and products of the reaction. Methods. A stability indicating isocratic LC assay was used to study the rate of degradation of 1 A gradient LC assay was used to study the time courses of the degradants. The products of hydrolysis were isolated by preparative liquid chromatography and identified by 1H-NMR and CI-MS. The pKa value was obtained by potentiometric titration. Results. At 36.8°C, the pH-rate profile of 1 in water was adequately described by a four-term rate equation. The intermediates were identified as the primary and secondary di-acetates, and the primary and secondary mono-acetates. The final product was 6-azauridine. Conclusions. A simplified kinetic scheme could be used to describe the concentration-time profiles of 1, the intermediates and the final product.
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    URL: http://dx.doi.org/10.1023/A:1016238110533
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    Dielectric method for detection of phase separation and its kinetics in TMPC/PS blends (1995)
    Springer
    Colloid & polymer science 273 (1995), S. 524-532 
    Details
    ISSN: 1435-1536
    Keywords: Blends ; tetramethyl polycarbonate ; polystyrene ; LCST ; phase separation ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new method for the detection of phase separation and its kinetics through real-time measurements is presented using the dielectric technique. The kinetics of phase separation were determined for a blend of tetramethyl bisphenol-A polycarbonate TMPC and polystyrene PS at different temperatures. The temperature dependence of the rate constant of phase separation was determined. The activation energy of phase separation process is found to be equal to 46 kcal/mole. In addition, it was possible to determine the variation in the composition of the TMPC-rich phase with time. The results obtained were compared with the literature data and were found to be in good agreement.
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    URL: http://dx.doi.org/10.1007/BF00658681
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    Electron transfer from cytochromeb 5 to cytochromec (1995)
    Springer
    Journal of bioenergetics and biomembranes 27 (1995), S. 331-340 
    Details
    ISSN: 1573-6881
    Keywords: Cytochromeb 5 ; cytochromec ; electron transfer ; kinetics ; ruthenium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The reaction of cytochromeb 5 with cytochromec has become a very prominent system for investigating fundamental questions regarding interprotein electron transfer. One of the first computer modeling studies of electron transfer and protein/protein interaction was reported using this system. Subsequently, numerous studies focused on the experimental determination of the features which control protein/protein interactions. Kinetic measurements of the intracomplex electron transfer reaction have only appeared in the last 10 years. The current review will provide a summary of the kinetic measurements and a critical assessment of the interpretation of these experiments.
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    URL: http://dx.doi.org/10.1007/BF02110102
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    Control of mitochondrial and cellular respiration by oxygen (1995)
    Springer
    Journal of bioenergetics and biomembranes 27 (1995), S. 583-596 
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    ISSN: 1573-6881
    Keywords: Oxygen limitation ; p 50 ; critical oxygen pressure ; respirometry ; polarographic oxygen sensor ; human endothelial cells ; rat liver mitochondria ; intracellular $$p_{O_2 } $$ ; oxygen gradients ; kinetics ; nonequilibrium thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Control and regulation of mitochondrial and cellular respiration by oxygen is discussed with three aims: (1) A review of intracellular oxygen levels and gradients, particularly in heart, emphasizes the dominance of extracellular oxygen gradients. Intracellular oxygen pressure, $$p_{O_2 } $$ , is low, typically one to two orders of magnitude below incubation conditions used routinely for the study of respiratory control in isolated mitochondria. The $$p_{O_2 } $$ range of respiratory control by oxygen overlaps with cellular oxygen profiles, indicating the significance of $$p_{O_2 } $$ in actual metabolic regulation. (2) A methodologically detailed discussion of high-resolution respirometry is necessary for the controversial topic of respiratory control by oxygen, since the risk of methodological artefact is closely connected with far-reaching theoretical implications. Instrumental and analytical errors may mask effects of energetic state and partially explain the divergent views on the regulatory role of intracellular $$p_{O_2 } $$ . Oxygen pressure for half-maximum respiration,p 50, in isolated mitochondria at state 4 was 0.025 kPa (0.2 Torr; 0.3 ΜM O2), whereasp 50 in endothelial cells was 0.06–0.08 kPa (0.5 Torr). (3) A model derived from the thermodynamics of irreversible processes was developed which quantitatively accounts for near-hyperbolic flux/ $$p_{O_2 } $$ relations in isolated mitochondria. The apparentp 50 is a function of redox potential and protonmotive force. The protonmotive force collapses after uncoupling and consequently causes a decrease inp 50. Whereas it is becoming accepted that flux control is shared by several enzymes, insufficient attention is paid to the notion of complementary kinetic and thermodynamic flux control mechanisms.
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    Kinetic and regulatory aspects of the function of the alternative oxidase in plant respiration (1995)
    Springer
    Journal of bioenergetics and biomembranes 27 (1995), S. 387-396 
    Details
    ISSN: 1573-6881
    Keywords: Plant mitochondria ; alternative oxidase ; kinetics ; regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The kinetic modelling of the respiratory network in plant mitochondria is discussed, with emphasis on the importance of the choice of boundary conditions, and of modelling of both quinol-oxidising and quinone-reducing pathways. This allows quantitative understanding of the interplay between the different pathways, and of the functioning of the plant respiratory network in terms of the kinetic properties of its component parts. The effects of activation of especially succinate dehydrogenase and the cyanide-insensitive alternative oxidase are discussed. Phenomena, such as respiratory control ratios depending on the substrate, shortcomings of the Bahr and Bonner model for electron distribution between the oxidases and reversed respiratory control, are explained. The relation to metabolic control analysis of the respiratory network is discussed in terms of top-down analysis.
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    Dynamic measurements of adsorption of hydrolyzed polyacrylamide (HPAM) onto hematite (1995)
    Springer
    Colloid & polymer science 273 (1995), S. 1028-1032 
    Details
    ISSN: 1435-1536
    Keywords: Hydrolyzed polyacrylamide ; hematite ; adsorption ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The adsorption measurements of hydrolyzed polyacrylamide (HPAM) onto hematite suspension are carried out to study the dynamics of the polymer adsorption onto the suspension particles and to investigate the mode of the polymer adsorption. The polymer is found to show much affinity for the adsorption because of the opposite charges possessed by the polymeric flocculant and the suspension particles. Various adsorption parameters such as adsorption coefficient, the rate constants for the adsorption and desorption, are evaluated with the help of a recently proposed kinetic scheme. It is found that the extent of adsorption and the adsorption rate are adequately affected by increasing the pH of the suspension while, unexpectedly, the adsorption is found to show only a marginal increase on addition of Na2SO4. Both the amount of the adsorbed polymer and the adsorption rate are also found to increase with the degree of hydrolysis of the polyelectrolyte.
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    Mammalian exocrine secretions: IX. Constituents of preorbital secretion of oribi,Ourebia, ourebi (1995)
    Springer
    Journal of chemical ecology 21 (1995), S. 1191-1215 
    Details
    ISSN: 1573-1561
    Keywords: Ourebia ourebi ; Bovidae ; mammalian semiochemicals ; mammalian pheromones ; exocrine secretion ; preorbital secretion ; dimethyl disulfide derivatization ; skipped dienes ; chemical-ionization mass spectrometry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Using gas chromatography-mass spectrometry in conjunction with ancillary techniques such as chemical ionization with different reactant gases, determination of the position of double bonds by means of dimethyl disulfide derivatization, and finally gas chromatographic and mass spectrometric comparison with authentic synthetic material, 75 constituents were identified in the preorbital secretion of the male oribi,Ourebia ourebi. The secretion contains compounds with long-chain, unbranched structures similar to those found in many other preorbital secretions but with a finite volatility range, in contrast to the seemingly endlessly increasing chain lengths typical of other preorbital secretions.
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    Manganese cycling in a eutrophic lake — Rates and pathways (1995)
    Springer
    Aquatic geochemistry 1 (1995), S. 399-426 
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    ISSN: 1573-1421
    Keywords: manganese reduction ; manganese oxidation ; organic matter oxidation ; kinetics ; bacteria ; alkalinity ; lake chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The redox processes regulating transport of Mn in the water column of a eutrophic, dimictic lake (Lake Norrviken, Sweden) are interpreted based on a one-dimensional diffusion-reaction model for Mn(II). It is found that rates and rate constants for oxidation and reduction vary greatly with depth and also with time during the season of stratification. Calculated rates show that Mn(II) oxidation and reduction generally occur in narrow depth intervals (25–50 cm). This is in good agreement with measured profiles of particulate Mn (MnO x ). Maximum oxidation rate constants (assuming first order kinetics) at each date are in the first half of the season 〈1 d−1, but then increases to a rather constant value of about 25 d−1. These high rate constants are indicative of microbiological involvement in the Mn(II) oxidation. This is further evidenced by SEM-EDS analysis showing Mn enriched particles morphologically similar toMetallogenium. Reductive dissolution of Mn oxides occurs mainly in the zone just below the zone of maximum oxidation rate. The release of Mn(II) is accompanied by production of alkalinity and ΣCO2. The relation between production rates of Mn(II) and alkalinity indicates that Mn oxides act as terminal electron acceptors in the bacterially mediated oxidation of organic matter. However, the ΔMn2+/ΔΣCO2 ratio is significantly lower than what is expected from this process. It is suggested that the Mn reduction is coupled to fermentation. Close coexistence of Mn reduction and oxidation at high rates, such as found in the water column of this lake, facilitates rapid and continuous regeneration of reducible Mn oxides. This gives rise to a quantitatively important mechanism of organic matter oxidation in the water column.
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    New backbone cyclic substance P analogs (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 121-124 
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    ISSN: 1573-3904
    Keywords: Backbone cyclization ; Substance P ; NMR ; Molecular dynamics ; Conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Structure-activity relationships of cyclic substance P (SP) analogs were extensively studied in our laboratories utilizing the new concept of backbone cyclization. Employing the C-terminal hexapeptide SP6–11, we examined the influence of chemical changes in peptides containing backbone-to-amino-end cyclization. These changes in the ring have significant influence on activity, and should be carefully designed in order to optimize pharmacological feature.
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    Production, isolation and characterization of [Leu4]- and [Ile4]surfactins from Bacillus subtilis (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 41-47 
    Details
    ISSN: 1573-3904
    Keywords: Biosurfactant ; Lipopeptide ; NMR ; Hydrophobic substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Bacillus subtilis coproduces several surfactin variants that are powerful biosurfactants and have potential applications in biology and industry. A single amino acid substitution in the heptapeptide moiety of surfactins strongly modifies their properties. To better establish structure-activity relationships and to search new variants with enhanced properties, Bacillus subtilis was grown into two modified culture media. Two new variants were isolated by chromatographic methods and studied by NMR spectroscopy. As planned, modifications consisted in the substitution of the l-valine residue at the fourth position by a more hydrophobic residue, i.e., leucine or isoleucine. These [Leu4]- and [Ile4]surfactins have a higher affinity for hydrophobic solvents and a twice improved surfactant power. Structure-property correlations were confirmed by analysis of the hydrophobic residue distribution in the three-dimensional model of the structure of surfactin in solution.
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    Structure of Leu5-enkephalin bound to a model membrane as determined by high-resolution NMR (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 59-70 
    Details
    ISSN: 1573-3904
    Keywords: Opioid peptide ; NMR ; Enkephalins ; Micelles ; Dodecylphosphocholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Opioid peptides are thought to interact with the cell membrane in their biological journey to the membrane-bound receptor. Both organic solvents and model membranes have been used previously to determine the stable solution conformations of peptide hormones. Leucine enkephalin has been studied in a number of different environments, but with limited resolution. Here it is shown that leucine enkephalin forms a stable type IV β-turn structure in dodecylphosphocholine micelles. We have observed a highly solvent-shielded amide proton with no evidence for a complementary hydrogen bond acceptor. The structural details of the peptide as determined by NMR spectroscopy in solution are described.
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    New conformationally constrained Xxx-Pro bicyclic mimetics (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 161-164 
    Details
    ISSN: 1573-3904
    Keywords: Cyclised peptide ; Dioxopiperazine ; Thiazolidine ; NMR ; Computer modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Conformationally constrained peptidomimetics of the Lys-Pro sequence have been obtained using a new polycyclic structure. Bicyclic compounds containing a dioxopiperazine-thiazolidine fused ring have been synthesised starting from N-lysyl-4-ethoxycarbonylthiazolidine-2-carboxylic acid. The carboxyl group in either position 2 or 4 of the thiazolidine ring was reacted with the N-terminal amino group, giving different regioisomers. NMR and computer modelling were used to study the configuration of isomers and the lysine side-chain orientation with respect to the pseudoproline ring.
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    URL: http://dx.doi.org/10.1007/BF00119143
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    Synthesis and conformational analysis of AzAsx-containing oligopeptides (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 239-242 
    Details
    ISSN: 1573-3904
    Keywords: Pseudopeptide ; Triphosgene ; Beta-turn ; NMR ; FT-IR ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the sake of improving synthetic methods and evaluating the conformational perturbation induced by the substitution of AzAsx for the Asx residue in the cognate dipeptide R-CO-Asx-Pro-NHR′, we prepared the AzAsx-dipeptide sequence by making use of the crystalline triphosgene. This reagent allows, in situ and under very mild experimental conditions, both the carbonylation and the activation of the properly substituted and N-protected hydrazine before coupling with the proline partner. With regard to conformational behaviour, the azadipeptide sequence displays a β-fold, unlike the cognate dipeptide which adopts an Asx-turn.
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    Kinetics and mechanism of azidomercuration of alkenes, cycloalkenes, and their derivatives with a mercuric acetate-sodium azide system (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 2375-2381 
    Details
    ISSN: 1573-9171
    Keywords: azidomercuration ; alkenes ; cycloalkenes ; strained double bond ; kinetics ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of azidomercuration of alkenes, cycioalkenes, and their derivatives with a Hg(OAc)2-NaN3 system (1 ∶ 1, 1 ∶ 2, and 1 ∶ 3) was studied. Based on the data on the product structure and kinetic results, it was concluded that HgOAcN3 and Hg(N3)2 play the role of azidomercuration reagents. The reactions with alkenes having a strained double bond occur by a concerted scheme. With nonstrained alkenes, a multistep mechanism is realized, its first reversible step involving the formation of a mercurinium intermediate with an ion pair structure.
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