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  • Articles  (36)
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  • Articles  (36)
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  • Springer  (36)
  • American Chemical Society
  • American Institute of Physics
  • American Meteorological Society
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  • 1995-1999  (36)
  • 1990-1994
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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
    Chemiluminescence in evaluating thermal oxidative stability of acrylonitrile-butadiene-styrene (ABS) copolymers. III. Emulsion-grade products (1995)
    Springer
    Journal of polymers and the environment 3 (1995), S. 199-203 
    Details
    ISSN: 1572-8900
    Keywords: Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermal oxidative stability of various formulations based on emulsion-grade ABS was studied by the chemiluminescence technique. Emulsion products were found to be essentially less stable than ionic mass polymerization resins. Among the antioxidants studied, Santonox R is clearly more efficient than Irganox 1076 and Irganox 3114, and its superiority is reflected primarily in improved induction period values. The introduction of Tinuvin 770 and Tinuvin 328 UV stabilizers into emulsion resins does not change the durability of the products. In mixtures where both Irganox 1076 and UV stabilizers are present, a certain antagonistic effect was noted at high UV stabilizer concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02068674
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    The stability of 12-molybdosilicic, 12-tungstosilicic, 12-molybdophosphoric and 12-tungstophosphoric acids in aqueous solution at various pH (1995)
    Springer
    Catalysis letters 34 (1995), S. 237-244 
    Details
    ISSN: 1572-879X
    Keywords: metal-oxygen cluster compounds ; heteropoly acids ; stability ; pH ; aqueous solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The stabilities of the solid superacids H3Mo12O40, H3PW12O40, H4SiMo12O40 and H4SiW12O40 in aqueous solution have been measured at various values of pH by use of ion chromatographic analyses. The aforementioned acids are completely decomposed at values of pH, 4.0, 5.2, 7.0 and 11.0, respectively. The stabilities in aqueous solution with respect to pH follow the order H4SiW12O40 〉 H3PW12O40 〉 H4SiMo12O40 〉 H3PMo12O40.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808338
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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    A survey on stability of chemical species in solution during storage: the BCR experience (1995)
    Springer
    Microchimica acta 118 (1995), S. 131-141 
    Details
    ISSN: 1436-5073
    Keywords: stability ; chemical species ; solutions ; calibration ; interlaboratory studies ; measurement and testing programme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The stability of chemical species in solution during storage is one of the critical aspect that has to be carefully studied e.g. for calibration purposes or prior to the organization of interlaboratory studies using synthetic solutions. The Measurements and Testing Programme (formerly BCR) is currently undertaking projects to improve the quality of speciation analysis for a variety of species (e.g. As, Hg, Sn, Pb, Cr). In all the cases the stability of these species was carefully studied in the solutions provided to the participants. This paper gives an overview of some of the results obtained in different BCR-projects on speciation analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01242236
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    The relationship between physical property and function of highly activated mutants of thermolysin (1995)
    Springer
    Molecular engineering 5 (1995), S. 245-253 
    Details
    ISSN: 1572-8951
    Keywords: Protein engineering ; thermolysin ; activity ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermolysin mutants having a variety of amino acid at the 119th position are designed by considering electrostatic field effect upon the active area. The most activated mutant has five times higher hydrolytic activity than the wild type. Negative correlation between the activity and the thermal stability is observed. A combined effect of the flexibility of the substrate binding site and the negative electrostatic field around the site is suggested as a key to enhance the activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00999593
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  • 11
    Electronic Resource
    Electronic Resource
    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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  • 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
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00491681
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  • 14
    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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  • 15
    Electronic Resource
    Electronic Resource
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165053
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  • 16
    Electronic Resource
    Electronic Resource
    A New Strategy for Enhancing the Stability of Lyophilized Protein: The Effect of the Reconstitution Medium on Keratinocyte Growth Factor (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1447-1452 
    Details
    ISSN: 1573-904X
    Keywords: proteins ; aggregation ; reconstitution ; lyophilization ; additives ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Protein stabilization during lyophilization has previously focused on optimization of the formulation as well as the freezing and dehydration process parameters. However, the effect of the reconstitution medium has been largely neglected. We have investigated its effect on aggregate formation using recombinant keratinocyte growth factor (KGF). Methods. The protein was lyophilized under suboptimal conditions to induce aggregation and precipitation upon reconstitution with water. A series of additives were examined by UV spectrophotometry and size exclusion chromatography (SEC-HPLC) for their effects on decreasing the degree of KGF aggregation and precipitation by the increase in recovery of soluble monomer. Results. Several additives resulted in a significant reduction of aggregation, including sulfated polysaccharides, surfactants, polyphosphates, and amino acids. A similar effect was achieved by adjusting the ionic strength of the reconstitution medium. SEC-HPLC indicated that the amount of soluble monomer was also increased by these additives suggesting that the recovery of the soluble protein correlates with the native, monomeric protein. Conclusions. These results suggest that optimization of reconstitution conditions will be a useful methodology for increasing the recovery of soluble, active proteins and that for KGF, the recovery of the soluble protein correlates with the native, monomeric form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016219000963
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  • 17
    Electronic Resource
    Electronic Resource
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016222501079
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  • 18
    Electronic Resource
    Electronic Resource
    Hydroxypropyl-β-Cyclodextrin Increases the Aqueous Solubility and Stability of Pilocarpine Prodrugs (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1371-1375 
    Details
    ISSN: 1573-904X
    Keywords: prodrug ; bispilocarpic acid diester ; hydroxypropyl-β-cyclodextrin ; inclusion complex ; solubility ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The effects of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) on the aqueous solubility and stability of two lipophilic bispilocarpine prodrugs were investigated at pH 7.4. Methods. The solubility of prodrugs was studied by phase-solubility method (0–72.5 mM HP-β-CD). The stability of one of the prodrugs was investigated as a function of temperature (40°C–70°C) and HP-β-CD concentration (0–72.5 mM). The apparent rate constants (k 1, k 2) for degradation of prodrug in 1:1 and 1:2 inclusion complexes and apparent stability constants (K 1:1, K l:2) were calculated by the curve-fitting method. Results. The phase-solubility diagrams were classified as Ap-type and the apparent stability constants (K l:l, K l:2) for 1:1- and 1:2-inclusion complexes were calculated to be 143–815 M−l and 29–825 M−1, respectively. The stability of prodrug increased as a function of HP-β-CD concentration over the studied temperature range. The shelf-life (t 90%, calculated by the Arrhenius equation) of the prodrug in 72.5 mM HP-β-CD solution increased 5.1-fold and 6.1-fold at 25°C and 4°C, respectively. Conclusions. The solubility of the prodrugs was shown to increase markedly in phase-solubility studies. The degradation rate of prodrug in stability studies was shown to be slower in the l:2-complex than in the l:l-complex and the relative amounts of complex species were found to be dependent on CD concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016290127371
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  • 19
    Electronic Resource
    Electronic Resource
    The Distribution of Oleic Acid Between Salbutamol Base Drug and Different Propellant Blends (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 715-719 
    Details
    ISSN: 1573-904X
    Keywords: salbutamol base drug ; oleic acid ; propellant ; metered-dose inhaler ; stability ; adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The distribution of oleic acid between Salbutamol base drug and the solvent in metered-dose inhalers (MDI's) has been investigated. The equilibrium surfactant concentration in the drug dispersions has been determined using a colorimetric method. The samples examined contained Salbutamol base drug particles and oleic acid dispersed in different propellant blends of freon 11 and 12. The maximum equilibrium concentration observed depended on the propellant blend used. The propellant blend and the distribution of the surfactant affected the dispersion stability. The effect of the surfactant is illustrated by the adsorption isotherm for oleic acid onto the Salbutamol particles. The results are correlated with zeta-potentials and particle size measurements made on similar systems in order to characterize the properties of surfactant stabilized MDI's.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016263610165
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  • 20
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016238110533
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    Some Factors Associated with the Ultrasonic Nebulization of Proteins (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 53-59 
    Details
    ISSN: 1573-904X
    Keywords: aerosol ; lactate dehydrogenase ; nebulizers ; proteins ; ultrasonic nebulization ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ultrasonic nebulization of lactate dehydrogenase (LDH) was investigated using a DeVilbiss “Aerosonic” nebulizer. The enzyme (8ml, 0.025mg/ml Na2HPO4, pH 7.0) was completely inactivated after 20 minutes of operation. However, the inactivation profile observed during ultrasonic nebulization was different from that previously observed using air-jet nebulization. At least two mechanisms are involved, one associated with heating and the other with aerosol production. By preventing heating of the nebulizer fluid during operation, the denaturation profile was dramatically altered. By additionally including 0.01% w/v Tween 80 or l%w/v PEG 8000, almost all activity was retained. Similar results were obtained by preventing aerosol production and heating. However, 100% of activity was lost when heating was allowed to occur without aerosol formation. The results demonstrate that cooling in conjunction with a surfactant is one approach that could be used to stabilize proteins to ultrasonic nebulization. However, cooling also significantly reduced solute output from the nebulizer. When operated at 10°C output was negligible. At 50°C the output was 5× greater than that found at room temperature. The median droplet size (µm) was not significantly influenced by the operating temperature of the nebulizer fluid (3.6 ± 0.4, 21°C; 3.9 ± 0.2, 50°C, p = NS (n = 6)) although the size distribution was noted to increase at the higher temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016282502954
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    The Importance of Structural Factors on the Rate and the Extent of N,O-acyl Migration in Cyclic and Linear Peptides (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 323-328 
    Details
    ISSN: 1573-904X
    Keywords: acyl migration ; peptides ; cyclosporin ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The chemistry associated with the process of N,O-acyl migration was explored in both cyclic and linear peptides under aqueous acid conditions. The importance of backbone cyclization and N-methylation of the peptide bond on the kinetics of N,O-acyl migration in a series of linear and cyclic peptides related in structure to cyclosporin A (CsA) were examined. The similarity in the chemical reactivity of the cyclic peptide [MeLeu (3-OH)]1-CsA and the corresponding linear peptide [Val-MeLeu (3-OH)-Abu], suggested that for this series, cyclization of the peptide backbone may not play an important role in controlling the kinetics of N,O-acyl migration. In contrast, the disparity in the chemical reactivity of tripeptides [Val-MeLeu (3-OH)-Abu] and [Val-Leu (3-OH)-Abu], indicated that N-methylation of amide bond significantly impacted the kinetics. Various hypothesis are proposed to account for this observation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016231913858
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    Stabilization of Chimeric BR96-Doxorubicin Immunoconjugate (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 215-222 
    Details
    ISSN: 1573-904X
    Keywords: chimeric antibody ; protein ; immunoconjugate ; lyophilization ; freeze-drying ; stability ; aggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Chimeric BR96-doxorubicin conjugate (BR96-DOX) is an immunoconjugate designed to specifically target and kill certain tumor cells. The linker between the chimeric BR96 antibody and DOX is an acid-labile hydrazone group which was designed to undergo lysosomal hydrolysis to release DOX in vivo. Stability studies indicated that acid-catalyzed hydrazone hydrolysis was the major degradation route in vitro. Even under optimal conditions of pH and temperature, the stability of BR96-DOX in solution was not acceptable for long-term storage. Lyophilization of BR96-DOX in the presence of added sugars, such as lactose or sucrose, and subsequent storage of the lyophile under refrigeration significantly improved the stability. Therefore lyophilization appears to be a viable approach for achieving long-term stabilization of BR96-DOX.
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    URL: http://dx.doi.org/10.1023/A:1016274825322
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    Chemical Pathways of Degradation of the Bradykinin Analog, RMP-7 (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 305-308 
    Details
    ISSN: 1573-904X
    Keywords: RMP-7 ; bradykinin ; stability ; diketopiperazine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016203731682
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    A microstructural investigation of the nonlinear response of electrorheological suspensions (1995)
    Springer
    Rheologica acta 34 (1995), S. 417-429 
    Details
    ISSN: 1435-1528
    Keywords: Electrorheology ; nonlinear ; simulations ; stability ; steady shear
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Particle-level simulations are employed to investigate the transition from linear to nonlinear rheological behavior for electrorheological suspensions under start-up of steady shear flow. This transition is found to first arise from the very slight rearrangement of structures, as opposed to the gross rupture of particulate columns. Linear stability analysis shows that these rearrangements occur when the structures are sheared into electrostatically unstable configurations. The rearrangements also produce a second type of relaxation phenomenon that appears at low frequencies and finite strain amplitudes. Incorporating more realistic force descriptions into the idealized simulation model shifts the transition to nonlinear deformation to smaller strain amplitudes, approaching experimentally observed values. The role of the rearrangement of unstable structures on the oscillatory shear flow response is investigated in the following paper, Part II.
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    URL: http://dx.doi.org/10.1007/BF00396555
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    A microstructural investigation of the nonlinear response of electrorheological suspensions (1995)
    Springer
    Rheologica acta 34 (1995), S. 430-439 
    Details
    ISSN: 1435-1528
    Keywords: Electrorheology ; nonlinear ; simulations ; stability ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In the preceding paper, Part 1, the transition from linear to nonlinear behavior for electrorheological (ER) suspensions under start-up of steady shear flow was found to first arise from the slight rearrangement of unstable structures. In this paper, we investigate the transition to nonlinear behavior for ER suspensions under oscillatory shear flow, focusing on the role of the rearrangement of unstable structures, and employing experimental and simulation results. Again, we find that nonlinear deformation first arises from these rearrangements, as opposed to the gross rearrangement or rupture of particulate chains. The Fourier transform of the simulated time-dependent shear stress is employed to quantify the dependence of the critical strain on the deformation frequency and electric field strength. The predicted behavior is consistent with experimental trends. Methods for verifying the predictions are discussed, as well as possible avenues for exploiting this information in improved operating strategies and improved ER fluids.
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    URL: http://dx.doi.org/10.1007/BF00396556
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  • 27
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    Efficacy Evaluation of a Novel Submicron Miconazole Emulsion in a Murine Cryptococcosis Model (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 223-230 
    Details
    ISSN: 1573-904X
    Keywords: submicron ; emulsion ; miconazole ; stability ; toxicity ; cryptococcosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Submicron emulsions of miconazole were stabilized by using a combination of three emulsifiers comprising phospholipids, poloxamer, and deoxycholic acid (DCA). The presence of DCA was vital for prolonged emulsion stability owing to its contribution to the elevated zeta potential of the emulsion. Further, the results by the phospholipid surface labelling colorimetric technique clearly suggested that poloxamer molecules interacted with phospholipid polar-head groups of the mixed DCA-phospholipid interfacial film, resulting in the stabilization of the emulsion by a steric enthalpic entropic mechanism. The plain emulsion vehicle was well tolerated up to a dose of 0.6 ml injected i.v. to BALB/c mice. The maximum tolerated dose of miconazole was 80 and 250 mg/kg in Daktarin® i.v. (a marketed product) and emulsion, respectively, showing an improved safety ratio of 1 to 3 in favor of the emulsion. These results tended to confirm that the adverse effects associated with Daktarin® i.v. injection should be associated with the vehicle rather than with the miconazole itself. In a murine cryptococcosis model, only one mouse out of ten remained alive by day 15 in the infected group treated with Daktarin® i.v., while in the miconazole emulsion treated group, mice began to die from day 16 up to day 25 post inoculation. Thus, the multiple-dose treatment with the miconazole emulsions improved the protection offered to the infected mice. However, the therapeutic levels of miconazole that were reached in the target organ (brain) were lower than those required for complete eradication of Cryptococcus neoformans, which is known to multiply preferentially in the brain.
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    URL: http://dx.doi.org/10.1023/A:1016226909392
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    Optimization of Lyophilization Conditions for Recombinant Human Interleukin-2 by Dried-State Conformational Analysis Using Fourier-Transform Infrared Spectroscopy (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1250-1259 
    Details
    ISSN: 1573-904X
    Keywords: lyophilization ; interleukin-2 ; protein conformation ; infrared spectroscopy ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Examination of the dried-state conformation of interleukin-2 (IL-2) was used to determine the pH conditions and stabilizers that provide optimal storage stability for the lyophilized product. Methods. Fourier-transform infrared spectroscopy and accelerated stability studies which examined solubility, aggregate formation, and covalent cross-linking were used. Results. Varying the pH in the absence of excipients resulted in dramatic differences in the dried state conformation of IL-2. At pH 7, IL-2 unfolds extensively upon lyophilization while at pH below 5 it remains essentially native. Additional unfolding was observed upon incubation at elevated temperatures. A strong direct correlation between the retention of the native (aqueous) structure during freeze-drying and enhanced stability is demonstrated. IL-2 prepared at pH 5 is approximately an order of magnitude more stable than at pH 7 with regard to formation of soluble and insoluble aggregates. A similar pH profile was observed in the presence of excipients, although the excipients alter the overall stability profile. Additional accelerated stability studies examined the stabilizers necessary for optimal stability. Conclusions. Excipients with the capacity to substitute for water upon dehydration better preserve the native structure resulting in enhanced stability. Those that have high glass transition temperatures provide the highest level of stability during storage, although they do not prevent dehydration induced unfolding.
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    URL: http://dx.doi.org/10.1023/A:1016296801447
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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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    URL: http://dx.doi.org/10.1007/BF02228320
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    Spectrophotometric study of the complexation of iodine with 1,7-diaza-15-crown-5 in chloroform solution (1995)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 22 (1995), S. 99-105 
    Details
    ISSN: 1573-1111
    Keywords: DA15C5-iodine complex ; stoichiometry ; stability ; rate constant ; spectrophotometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The complex formation reaction between iodine and 1,7-diaza-15-crown-5 (DA15C5) has been studied spectrophotometrically in chloroform at 25°C. The resulting 1:2 (DA15C5:I2) molecular complex was formulated as (DA15C5...;I+)I 3 − . The spectrophotometric results, as well as the conductivity measurements, revealed that the gradual release of triiodide ion from its contact ion paired form in the molecular complex into the solution is the rate determining step of the reaction. The rate constant was calculated ask=(8.8±0.2)×10−3 min−1. The formation constant of the molecular complex was evaluated from the computer fitting of the absorbance-mole ratio data as logK f=6.89±0.09.
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    URL: http://dx.doi.org/10.1007/BF00707685
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    New backbone cyclic substance P analogs (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 121-124 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00119137
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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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    URL: http://dx.doi.org/10.1007/BF00122922
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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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    URL: http://dx.doi.org/10.1007/BF00128499
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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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    URL: http://dx.doi.org/10.1007/BF00119162
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    Oligodienyl compounds of d- and f-transition metals: synthesis and stability (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 9-17 
    Details
    ISSN: 1573-9171
    Keywords: oligodienyl chain ; transition metals ; synthesis ; stability ; π-coordination ; IR spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The results of investigations performed in the Laboratory of Organometallic Catalysis of the A. V. Topchiev Institute of Petrochemical Synthesis of the RAS are reviewed. The oligodienyl compounds of a series of transition metals, R n olM and R n olMXm (Rol= R′(diene)3–10, where R′ is an alkyl, allyl, alkenyl, or H; (diene)3–10 is an oligodienyl group with 3–10 monomeric diene units; M = Ti3+, Cr2+, Mn2+, Co2+, Ni2+, Nd3+, Pr3+, Sm3+, and Gd3+; X is a halogen or an electronegative group), have been synthesized for the first time and some of their properties have been studied. The stability of oligodienyl compounds is much higher than that of the corresponding π-alkenyl derivatives. The IR spectra of the compounds synthesized allowed us to conclude that their stability and some peculiarities of the reactions of these compounds can be explained by π-coordination of the isolated double bond of the oligodienyl chain to the transition metal.
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    URL: http://dx.doi.org/10.1007/BF00696949
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