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  • 1
    ISSN: 0935-6304
    Keywords: Resolution of atropisomers ; Alkylated biphenyls ; Polychlorinated biphenyls (PCBs) ; Dynamic gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selectively alkylated cyclodextrins have been used to resolve the enantiomers of 2,2′ alkylated biphenyls. The configurational stability of 2,2′-dimethyl and 2,2′-diethyl biphenyls is insufficient for gas chromatographic separation even at ambient temperature. 2-Isopropyl-2′-t-butyl- and 2,2′-di-t-butylbiphenyl are configurationally stable under the conditions applied, whereas 2,2′-diisopropyl- and 2,2′-bis(trifluoromethyl)biphenyl show temperature-dependent interconversion of the enantiomers during chromatography. The gas chromatographic separation of the enantiomers of some ortho trichlorinated biphenyls carrying 4, 5, and 6 chlorine substituents has been demonstrated for the first time.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 0947-3440
    Keywords: Atropisomers ; Biphenyls, axially chiral ; Enantiomerization ; Dynamic gas chromatography ; Polarimetry ; Energy barriers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have synthesized a series of 2,2′-substituted biphenyls and particularly derivatives of 2,2′-bis(trifluoromethyl)biphenyl (4) with either one or two fluoro, chloro, bromo, amino, nitro or methoxy substituents in the para positions for investigating the influence of these substituents on the rotational energy barrier of the biphenyls by polarimetry and dynamic gas chromatography (DGC). Axially chiral biphenyls with at least two bulky substituents in the ortho positions were separated by gas chromatography on selectively modified cyclodextrins. Due to competition between resolution and enantiomerization in the gas chromatographic column 2-tert-butyl-2′-isopropyl- (2), 2-isopropyl-2′-(trifluoromethyl)biphenyl (5), and some para-substituted derivatives of 4 show temperature-dependent interconversion profiles and coalescence phenomena in analogy to dynamic NMR studies. The accelerating effect on the rate of enantiomerization of electron-donating groups in the para positions and the decelerating effect of electron-accepting groups has been determined. Dynamic gas chromatography is shown to be a useful supplement to studies of thermal enantiomerization kinetics of optically enriched or separated compounds by polarimetry for the investigation of energy barriers of atropisomeric biphenyls.
    Additional Material: 3 Ill.
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  • 3
    ISSN: 0899-0042
    Keywords: chiral capillary gas chromatography ; chiral high-performance liquid chromatography ; stationary cyclodextrin phases ; chiral pollutants ; enantioselective processes ; microbial degradation processes ; photochemical degradation processes ; enzymatic degradation processes ; blood-brain barrier ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric ratios of 11 chiral environmental pollutants determined in different compartments of the marine ecosystem by chiral capillary gas chromatography and chiral high-performance liquid chromatography allow discrimination between the following processes: enantioselective decomposition of both enantiomers with different velocities by marine microorganisms (α-HCH, β-PCCH, γ-PCCH); enantioselective decomposition of one enantiomer only by marine microorganisms (DCPP); enantioselective decomposition by enzymatic processes in marine biota (α-HCH, β-PCCH, trans-chlordane, cis-chlordane, octachlordane MC4, octachlordane MC5, octachlordane MC7, oxychlordane, heptachlor epoxide); enantioselective active transport through the “blood-brain barrier” (α-HCH); nonenantioselective photochemical degradation (α-HCH, β-PCCH). © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0899-0042
    Keywords: Horeau's method ; configuration of secondary alcohols ; enantioselective gas chromatography ; 2-phenylbutyric acid ; cyclodextrin derivative ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of optically active secondary alcohols with excess of racemic 2-phenylbutyric acid anhydride in pyridine proceeds at different rates to the diastereoisomeric esters (kinetic partial resolution). According to Horeau the (unknown) absolute configuration of the alcohol can be derived from the optical rotation of the remaining excess of 2-phenylbutyric acid in the reaction mixture. Measuring the optical rotation may be very difficult in cases of small absolute rotation values and may be inaccurate due to the necessity to completely remove all chiral impurities. The application of Horeau's method is greatly facilitated by gas chromatographic determination of the enantiomeric ratio of the remaining 2-phenylbutyric acid after methylation using a short capillary column with heptakis(2,6-di-O-methyl-3-O-pentyl)-β-cyclodextrin as a chiral stationary phase. Baseline resolution of the enantiomers is achieved after approximately 10 min of retention time. Due to the high selectivity of capillary gas chromatography the probability of impurities in the mixture to interfere with the measurement of the enantiomeric ratio is extremely low. © 1994 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 5
    ISSN: 0899-0042
    Keywords: capillary zone electrophoresis ; axially chiral biphenyls ; energy barrier ; cyclodextrin derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new technique is presented for the investigation of the rotational energy barrier of axially chiral biphenyls, based on capillary zone electrophoresis using cyclodextrin derivatives as chiral selectors. Only minute amounts are required for the investigation of dynamic processes with energy barriers of 100-130 kJ/mol. The influence of the chiral selector on the conformational stability of atropisomers can be determined separately for each enantiomer. Additionally, segmentation of the capillary into different buffer zones allows us to exclude any influence of the chiral selector on the rotational energy barrier. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1976 (1976), S. 2011-2020 
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Structure of the Peptide Antibiotic StenothricinThe structure of the peptide antibiotic Stenothricin was investigated by combined application of chromatography, degradation, derivatization, and mass spectrometry. Most probably Stenothricin is β-ketoacyl-D-Cys(O3H)-L-Val-D-Ser-L-Lys-Sar-D-αThr-L-Ser-L-diaminopropionic acid. The β-ketoacyl residues consist of several isomers having chain lengths of 14 to 17 carbon atoms.
    Notes: Die Struktur des Peptidantibiotikums Stenothricin wurde durch Chromatographie, Abbau und Derivatbildungsmethoden sowie Massenspektrometrie untersucht. Danach ist Stenothricin mit großer Wahrscheinlichkeit β-Ketoacyl-D-Cys(03H)-L-Val-D-ser-L-Lys-sar-D-αThr-L-Ser-L-Diaminopropionsäure, wobei die β-Ketoacyl-Reste aus mehreren Isomeren mit Kettenlängen zwischen 14 und 17 C-Atomen bestehen.
    Additional Material: 4 Ill.
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  • 7
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactions of Amino Acids and Peptides, II. - Preparation of 2-Aminooxazole Derivatives from Peptide Amides with Hexafluoroacetic AnhydrideC-Terminal amino acid amide residues of peptide amides react with hexafluoroacetic anhydride to form stable 5-(trifluoroacetylamino)oxazole derivatives. Several representatives of this class of compounds have been synthesized and their structures determined by 1H-NMR and mass spectrometry and by their chemical reactions. The heterocyclization reaction can be used for the formation of volatile derivatives in the analysis of peptide amides on a microgram scale and for the identification of the C-terminal amino acid residue in peptide amides.
    Notes: C-Terminale Aminosäureamidreste von Peptidamiden reagieren mit Hexafluoracetanhydrid in guten Ausbeuten zu stabilen 5-(Trifluoracetylamino)oxazolderivaten. Verschiedene Vertreter dieser Verbindungen wurden dargestellt und ihre Struktur durch 1H-NMR-, Massenspektrometrie und chemische Reaktionen charakterisiert. Die Heterocyclisierungsreaktion kann im Mikrogramm-Maßstab zur Herstellung flüchtiger Derivate bei der Analytik von Peptidamiden und zur Identifizierung der C-terminalen Aminosäure von Peptidamiden benutzt werden.
    Additional Material: 2 Ill.
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  • 8
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactions of Amino Acids and Peptides, III1).  -  Preparation of 1,3-Oxazolidin-5-one Derivatives from N-Methyl Amino Acids with Hexafluoroacetic AnhydrideN-Methyl amino acids react with hexafluoroacetic anhydride to give 1,3-oxazolidin-5-one derivatives in good yields. The structure of these products has been derived by 1H-NMR, mass and IR spectroscopy. Alkaline hydrolysis results in the formation of α-keto carboxylic acids. The reaction of 4-trifluoroacetylmethylene-1,3-oxazolidin-5-one derivatives with ammonia yields Δ3-pyrrolin-2-one derivatives, while methanol results in ring opening and formation of methyl esters of α,β-unsaturated N-methyl amino acids.
    Notes: N-Methylaminosäuren reagieren mit Hexafluoracetanhydrid in guten Ausbeuten zu den 1,3-Oxazolidin-5-on-Derivaten 1a - c und 3a - c, deren Struktur durch 1H-NMR-, Massen- und IR-Spektroskopie bestimmt wurde. 4-Benzyliden-3-methyl-2-trifluormethyl-1,3-oxazolidin-5-on (1b) wurde alkalisch zu Phenylbrenztraubensäure hydrolysiert. Bei der Reaktion der 4-Trifluoracetyl-methylen-1,3-oxazolidin-5-on-Derivate mit NH3 entstehen Δ3-Pyrrolin-2-on-Derivate. Mit Methanol bilden sich unter Ringöffnung die Methylester α,β-ungesättigter N-Methylaminosäuren.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1981 (1981), S. 1606-1609 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactions of Amino Acids and Peptides, IV. - Synthesis of Furan Derivatives from N-Methyl Amino AcidsIn the reaction of N-methyl homophenylalanine and N-methyl norleucine with hexafluoroacetic anhydride the expected 1,3-oxazolidin-5-one derivatives are formed only as by-products. As main products 3-[methyl(trifluoroacetyl)amino]-2,5-bis(trifluoromethyl)furan derivatives could be isolated, the structures of which were identified by spectroscopic methods.
    Notes: Bei der Reaktion von N-Methylhomophenylalanin und N-Methylnorleucin mit Hexafluoracetanhydrid entstehen die erwarteten 1,3-Oxazolidin-5-on-Derivate nur als Nebenprodukte. Als Hauptprodukte konnten 3-[Methyl(trifluoracetyl)amino]-2,5-bis(trifluormethyl)furan-Derivate isoliert werden, deren Konstitutionen mit spektroskopischen Methoden ermittelt wurden.
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  • 10
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sequenz und Konformation von Suzukacillin ADie Sequenz des spannungsabhängige Membranporen bildenden Polypeptidantibiotikums Suzukacillin A wurde bestimmt durch eine Kombination von trifluoracetolytischer Spaltung, präparativer Isolierung von Fragmenten und Analyse durch Gaschromatographie - Massenspektrometrie sowie Felddesorptions- und Fast-Atom-Bombardment-Massenspektrometrie. Suzukacillin A ist ein mikroheterogenes Eikosapeptidantibiotikum (Ac-Aib-L-Ala-Aib-Ala-Aib-Ala(Aib)-Gln-Aib-Aib(Leu)-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib(D-Iva)-Gln-Gln-Phl) mit einer Sequenz, einer α-helicalen Konformation (nach13C-NMR- und Circulardichroismus-Messungen) und membranmodifizierenden Eigenschaften, die dem Alamethicin ähnlich sind.
    Notes: The sequence of the potential-dependent membrane pore-forming polypeptide antibiotic suzukacillin A was determined by a combination of trifluoroacetolytic cleavage, preparative isolation of fragments, and analysis by gas chromatography - mass spectrometry, field-desorption and fast-atom bombardment mass spectrometry. Suzukacillin A is a microheterogeneous eicosapeptide antibiotic (Ac-Aib-L-Ala-Aib-Ala-Aib-Ala(Aib)-Gln-Aib-Aib(Leu)-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib(D-Iva)-Gln-Gln-Phl) with a sequence, an α-helical conformation (according to 13C NMR and circular dichroism), and membrane-modifying properties related to alamethicin.
    Additional Material: 13 Ill.
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