bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chiral compounds of essential oils XIX. 4‐methyl‐5‐decanolide: Chirospecific analysis, structure and properties of the stereoisomers
Authors: Bartschat Dietmar , Lehmann Detmar , Dietrich Armin , Mosandl Armin , Kaiser Roman 
Published: March 2007

AbstractRacemic mixtures of synthetic cis‐ or trans‐4‐methyl‐5‐decanolide were separated by enantioselective high performance liquid chromatography with Chiraspher‐RT to yield all four stereoisomers as enantiopure compounds of distinct odour activities. In order to elucidate stereochemical features the isolated stereoisomers were reduced to their corresponding 4‐methyl‐1,5‐decandiols by reductive ester cleavage with lithium aluminium hydride. Absolute configurations were derived from proton nuclear magnetic resonance studies of diastereomeric di‐(R)‐2′‐methoxy‐2′‐trifluoromethylphenylacetic acid esters of these 1,5‐diols. Using enantioselective multidimensional capillary gas chromatography (column combination SE 52/heptakis‐(2,3‐di‐O‐methyl‐6‐O‐tert butyldimethylsilyl)‐β‐cyclodextrin), the direct enantioselective analysis of all four lactone stereoisomers was achieved. The application of this method to the scent of living, white flowering orchids (Aerangis confusa) proves cis‐(4S)‐methyl‐(5S)‐decanolide as the unique and genuine stereoisomer of Aerangis lactone.
Fast ion bombardment mass spectrometry of sanguinarine and coptisine from Chelidonium majus L. callus cells
Authors: Rasetti Maria Francesca , Colombo Maria Laura , Bosisio Enrica , De Angelis Leonardo , Galli Giovanni , Tomè Franca 
Published: March 2007

AbstractThis paper reports the identification of sanguinarine and coptisine isolated from the crude extract of callus culture of Chelidonium majus by positive fast ion bombardment (FIB+) mass spectrometry (MS) and FIB+ tandem mass spectrometry (MS‐MS). Callus was cultivated on Gamborg B5 medium for three weeks at 25°C and extracted with 70% ethanol. The alkaloids were extracted into chloroform, following ion pair formation, and then separated on a silica gel column. The presence of sanguinarine and coptisine was initially determined from chromatographic analysis, and the structures of the compounds were confirmed by MS. MS‐MS analysis was not suitable for coptisine since this compound did not produce daughter ions.
Evaporative light scattering and thermospray mass spectrometry: Two alternative methods for detection and quantitative liquid chromatographic determination of ginkgolides and bilobalide in Ginkgo biloba leaf extracts and phytopharmaceuticals
Authors: Camponovo Fabrizio F. , Wolfender Jean‐Luc , Maillard Marc P. , Potterat Olivier , Hostettmann Kurt 
Published: March 2007

AbstractEvaporative light scattering and thermospray mass spectrometry have been investigated as two alternative methods for the liquid chromatographic detection of ginkgolides and bilobalide. Both techniques were used to quantify these metabolites in leaf extracts and in some phytopharmaceuticals. Only a minimum of sample pre‐purification was required. Results were compared with those obtained by gas chromatography (flame ionization detection), which is one of the most suitable methods for routine determinations of such compounds. The isolation of ginkgolides A, B, C, and J and bilobalide from leaves of Ginkgo biloba is also described.
Concentrations of taxol and related taxanes in the needles of different Taxus cultivars
Authors: Elsohly Hala N. , Croom Edward M. , Kopycki Wlodzimierz J. , Joshi Alpana S. , Elsohly Mahmoud A. , McChesney James D. 
Published: March 2007

AbstractThe taxane content of the needles of 57 cultivars obtained from five major nurseries in the United States is presented. The analysis of taxol (1), and five other related taxanes, 10‐desacetyl‐7‐epi‐taxol (2), cephalomannine (3), 10‐desacetyl taxol (4), baccatin III (5) and 10‐desacetyl baccatin III (6) was carried out using a high performance liquid chromatographic method developed in our laboratory. The results of these analyses showed that the total “useful” taxanes varied between 0.0232%‐0.113%, with 1 and 6 being the most abundant taxanes. The survey identified 11 cultivars with a content of 1 ranging from 0.028% to 0.062%, and ten cultivars with a content of 6 ranging from 0.028% to 0.066%; 3 and 4 each represented approximately 30%‐50% of the concentration of taxol in most cultivars. Therefore, the needles of ornamental Taxus represent a significant, rich and renewable source for taxol and other related taxanes.
Gas liquid chromatographic determination of canthinone alkaloids in Hannoa chlorantha root bark and tissue cultures
Authors: Diakanamwa Carlos , Diallo Billo , Vanhaelen‐Fastré Renée , Vanhaelen Maurice , Jaziri Mondher , Homès Jacques 
Published: March 2007

AbstractA capillary gas chromatographic method has been developed for the determination of canthinone alkaloids. The method was applied to the semi‐quantitative determination of canthin‐6‐one, 1‐methoxycanthin‐6‐one, 1‐hydroxycanthin‐6‐one, 8‐hydroxycanthin‐6‐one, 10‐hydroxycanthin‐6‐one, and canthin‐6‐one‐3‐N‐oxide in callus and shoot cultures, and in root barks of Hannoa chlorantha. The results showed that their concentrations were highly dependent on the sample origin and on the culture conditions.
Direct isolation of olefinic and acetylenic 3‐alkyl‐4‐hydroxy‐butenolides occurring within the apiaceae
Authors: Werner Andreas , Hadaček Franz 
Published: March 2007

AbstractUnderivatized alkylbutenolides from several Peucedanum species including P. alsaticum L., P. austriacum (Jacq.) Koch, P. arenarium Waldst. & Kit., P. venetum (Sprengel) Koch and P. rablense (Wulfen) Koch (Apiaceae‐Apioideae) were separated by high performance liquid chromatography and preparative chromatography on a reversed phase system at a pH of 2.5. The chromatographic separation on RP‐18 with methanol: water as eluent is strongly affected by the enol‐enolate equilibrium of these compounds. In protic solutions these compounds exist as enolate anions. The dissociation constant of alkylbutenolides in methanol‐:water mixtures was determined. The alkylbutenolides show rather good solubility in polar solvents and high acidity compared to the corresponding fatty acids.
Solubilization and extraction of allantoinase and allantoicase from the green alga Chlamydomonas reinhardtii
Authors: Piedras Pedro , Cárdenas Jacobo , Pineda Manuel 
Published: March 2007

AbstractSeveral physical and chemical methods for the solubilization and extraction of allantoinase and allantoicase from the unicellular green alga Chlamydomonas reinhardtii have been tested and compared. Of all the methods employed (i.e. freezing‐thawing, extraction at high ionic strength, disruption with the French press, sonication, and detergent solubilization) sonication gave the best results for extraction of both substances, while sodium deoxycholate extracted allantoinase optimally but not allantoicase. Allantoinase and allantoicase were characterized as two separate enzyme proteins differently associated with membranes or located in different cellular compartments. It is also demonstrated that allantoate is enzymatically degraded in vitro by a cell‐free algal extract and that allantoicase is the enzyme responsible for this catabolism.
Agmatine determination in plant material: Aspects of the benzoylation and high performance liquid chromatographic analysis
Authors: Wehr J. Bernhard 
Published: March 2007

AbstractVarious steps in the existing procedure (Slocum, R. D., Flores, H. E., Galston, A. W. and Weinstein, L. H., Plant Physiol. (1989) 89, 512) for the analysis of agmatine as its benzoyl derivative were found to impair the quantification of agmatine, leading to irreproducible results. Degradation of benzoylated agmatine is a major factor contributing to erratic results, and two mechanisms of degradation have been observed. Firstly, benzoylagmatine undergoes a temperature‐dependent hydrolysis in alkaline solution and this reaction has a half‐life of 168 min at 22°C. Therefore, the benzoylation reaction time and temperature have to be controlled in order to ensure reliable results; a maximum yield of benzoylagmatine may be obtained after incubation for 30 min. Secondly, benzoylagmatine can undergo rapid alkali‐catalysed methanolysis with a half‐life of 12 min at 22°C. Methanolysis produces a degradation product that was originally considered to be agmatine or benzoylurea, but is probably N‐benzoylmethoxybenzamidomethylene imine. The formation of benzoylagmatine depends on the amount of benzoylchloride added since small volumes of the reagent do not exhaustively derivatize agmatine, hence leading to unreliable results. Mass spectrometry of benzoylagmatine showed that tribenzoylagmatine is the main derivative formed. The suggested modifications to the existing procedure enable the rapid and reliable determination of agmatine in various plant materials.
Indirect spectrophotometric determination of phytic acid with zinc chloranilate
Authors: Kamaya Minori , Furuki Tomohiro , Nagashima Kunio , Ishii Eizen , Saito Hirotsuga 
Published: March 2007

AbstractThe indirect spectrophotometric determination of phytic acid with zinc chloranilate has been studied. The method, based on the measurement of chloranilate released by the replacement reaction of phytic acid and zinc chloranilate, could be used to determine phytic acid in the range of 0.3 to 3.0 × 10−5 M. The method showed high reproducibility for measuring phytate in foods, and was more rapid than conventional methods.
Sample preparation for gas chromatography‐isotope ratio mass spectrometry: An investigation with volatile components from strawberries
Authors: Schumacher Katja , Turgeon Heidi , Mosandl Armin 
Published: March 2007

AbstractThe influence of sample preparation on the accuracy of 13C/12C‐ratios is investigated. Dynamic headspace, simultaneous distillation‐extraction and solvent extraction are used as methods of sample preparation in order to gain access to the volatiles of strawberries.
Survey of solvents for the extraction of grape seed phenolics
Authors: Kallithraka Stamatina , Garcia‐Viguera Cristina , Bridle Peter , Bakker Johanna 
Published: March 2007

AbstractThe effect of different solvents on the extraction of some phenolic compounds from grape seeds was investigated. The main compounds identified by high performance liquid chromatography were gallic acid, (+)‐catechin, (‐)‐epicatechin, the dimeric procyanidins B1 and B2, the trimeric procyanidin C1 and epicatechin gallate. The solvents tested were water, absolute ethanol, 75% ethanol, acetone, 70% acetone, methanol, n‐butanol, diethyl ether, ethyl acetate and a combination of diethyl ether followed by ethyl acetate. Results showed that methanol was the best solvent for the extraction of (+)‐catechin, (‐)‐epicatechin and epigallocatechin, whereas 70% acetone yielded the largest amounts of procyanidins and 75% ethanol yielded the largest amount of gallic acid. The greatest amount of total phenols was extracted by 70% acetone.
Phycobiliproteins: Determination of chromophore composition and content
Authors: Stadnichuk I. N. 
Published: March 2007

AbstractPhycobiliproteins are homologous, intensively coloured protein pigments functioning as photosynthetic light‐harvesting complexes. Their ability to absorb light in the visible spectrum is due to various chromophore prosthetic groups, which are linear tetrapyrroles covalently attached to apoprotein. The chromophore composition influences spectral properties and serves as one of the main characteristics of these pigments. The procedures for determining phycobiliprotein chromophore composition and content are described.
Application of off‐line supercritical fluid extraction—gas chromatography for the investigation of chemical constituents in Curcuma zedoaria
Authors: Ma Xizhong , Yu Xiaobing , Han Jun 
Published: March 2007

AbstractAnalytical supercritical fluid extraction (SFE) was used to investigate the chemical constituents of Curcuma zedoaria, a very useful Chinese herbal medicine. The qualitative and quantitative analysis of extracts was performed by gas chromatography with mass spectrometry. The effects of pressure, temperature and flow rate of the extracting fluid on the extraction efficiency of SFE were investigated quantitatively. It was found that at a fixed density, changing temperature in a given experimental range had no great influence on the distribution of SFE products, but that an appropriate increase of flow rate and fluid volume improves the extraction efficiency. SFE using supercritical carbon dioxide was a more efficient extraction technique than steam distillation.
Palladium‐mediated copolymerization of diazocarbonyl compounds with phenyldiazomethane
Authors: Ihara Eiji , Kida Masami , Fujioka Masayasu , Haida Nobuyuki , Itoh Tomomichi , Inoue Kenzo 
Published: March 2007

AbstractPhenyldiazomethane was found to be polymerized by the reaction with palladium‐based initiating systems. Homopolymerization of phenyldiazomethane afforded a polymer, whose main chain consists of phenylmethylene framework (–CHPh–) and azo groups (–NN–). The incorporation of the azo group was suggested from the results of elemental analyses, and confirmed by Raman spectroscopy. Palladium‐mediated copolymerization of phenyldiazomethane with (E)‐1‐diazo‐3‐nonen‐2‐one or ethyl diazoacetate proceeded to give copolymers having phenylmethylene framework, azo group, and acylmethylene or ethoxycarbonylmethylene framework in the main chain, with a variety of their compositions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1536–1545, 2007
Amine‐blocked polyisocyanates. I. Synthesis of novel N‐methylaniline‐blocked polyisocyanates and deblocking studies using hot‐stage fourier transform infrared spectroscopy
Authors: Sankar Govindarajan , Nasar A. Sultan 
Published: March 2007

AbstractA series of substituted N‐methylaniline‐blocked polyisocyanates based on 4,4′‐methylenebis(phenyl isocyanate) and poly(tetrahydrofuran) were prepared and characterized thoroughly with FTIR, 1H NMR, and 13C NMR spectroscopy methods. Compared with unsubstituted N‐methylaniline, a blocking agent with an electron‐releasing substituent at the para position took a shorter time, whereas those with an electron‐releasing substituent at the ortho position or an electron‐withdrawing substituent at the ortho and para positions took longer times for the blocking reaction. The thermal dissociation reactions of blocked polyisocyanates were carried out with an FTIR spectrophotometer attached to hot‐stage accessories under dynamic and isothermal conditions. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate the deblocking kinetics and activation parameters. The cure times of blocked polyisocyanates with hydroxyl‐terminated polybutadiene were also determined. The deblocking temperatures, the results of cure‐time studies, and the kinetic parameters revealed that the thermal dissociation of the N‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron‐withdrawing substituents. The action of N‐methylanilines as blocking agents for isocyanate was explained by the formation of a four‐center, intramolecularly hydrogen‐bonded ring structure during the thermal dissociation of the blocked polyisocyanates. The formation of such a hydrogen‐bonded ring structure was confirmed and supported by variable‐temperature 1H NMR studies and entropy parameters, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1557–1570, 2007
Evolution of prokaryotic subtilases: Genome‐wide analysis reveals novel subfamilies with different catalytic residues
Authors: Siezen Roland J. , Renckens Bernadet , Boekhorst Jos 
Published: March 2007

AbstractSubtilisin‐like serine proteases (subtilases) are a very diverse family of serine proteases with low sequence homology, often limited to regions surrounding the three catalytic residues. Starting with different Hidden Markov Models (HMM), based on sequence alignments around the catalytic residues of the S8 family (subtilisins) and S53 family (sedolisins), we iteratively searched all ORFs in the complete genomes of 313 eubacteria and archaea. In 164 genomes we identified a total of 567 ORFs with one or more of the conserved regions with a catalytic residue. The large majority of these contained all three regions around the “classical” catalytic residues of the S8 family (Asp‐His‐Ser), while 63 proteins were identified as S53 (sedolisin) family members (Glu‐Asp‐Ser). More than 30 proteins were found to belong to two novel subsets with other evolutionary variations in catalytic residues, and new HMMs were generated to search for them. In one subset the catalytic Asp is replaced by an equivalent Glu (i.e. Glu‐His‐Ser family). The other subset resembles sedolisins, but the conserved catalytic Asp is not located on the same helix as the nucleophile Glu, but rather on a β‐sheet strand in a topologically similar position, as suggested by homology modeling. The Prokaryotic Subtilase Database (www.cmbi.ru.nl/subtilases) provides access to all information on the identified subtilases, the conserved sequence regions, the proposed family subdivision, and the appropriate HMMs to search for them. Over 100 proteins were predicted to be subtilases for the first time by our improved searching methods, thereby improving genome annotation. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Detection of structural changes in a cofactor binding protein by using a wheat germ cell‐free protein synthesis system coupled with unnatural amino acid probing
Authors: Abe Masato , Ohno Satoshi , Yokogawa Takashi , Nakanishi Takeshi , Arisaka Fumio , Hosoya Takamitsu , Hiramatsu Toshiyuki , Suzuki Masaaki , Ogasawara Tomio , Sawasaki Tatsuya , Nishikawa Kazuya , Kitamura Masaya , Hori Hiroyuki , Endo Yaeta 
Published: March 2007

AbstractA cell‐free protein synthesis system is a powerful tool with which unnatural amino acids can be introduced into polypeptide chains. Here, the authors describe unnatural amino acid probing in a wheat germ cell‐free translation system as a method for detecting the structural changes that occur in a cofactor binding protein on a conversion of the protein from an apo‐form to a holo‐form. The authors selected the FMN‐binding protein from Desulfovibrio vulgaris as a model protein. The apo‐form of the protein was synthesized efficiently in the absence of FMN. The purified apo‐form could be correctly converted to the holo‐form. Thus, the system could synthesize the active apo‐form. Gel filtration chromatography, analytical ultracentrifugation, and circular dichroism‐spectra studies suggested that the FMN‐binding site of the apo‐form is open as compared with the holo‐form. To confirm this idea, the unnatural amino acid probing was performed by incorporating 3‐azido‐L‐tyrosine at the Tyr35 residue in the FMN‐binding site. The authors optimized three steps in their system. The introduced 3‐azido‐L‐tyrosine residue was subjected to specific chemical modification by a fluorescein‐triarylphosphine derivative. The initial velocity of the apo‐form reaction was 20 fold faster than that of the holo‐form, demonstrating that the Tyr35 residue in the apo‐form is open to solvent. Proteins 2007. © 2007 Wiley‐Liss, Inc.
New possibilities for determination of solids surface parameters by X‐ray reflectivity
Authors: Fodchuk I. , Balovsyak S. 
Published: March 2007

AbstractNew possibilities for research on solids surface morphology by X‐ray reflectivity (XRR) methods are presented. The method for reconstruction of surface geometry fragments is suggested. A series of GaAs crystals with a periodic surface relief and SiO2 plates with a random surface relief are investigated as test samples. Correlation of parameters of the XRR curves and surface relief with the results of atomic‐force microscopy is refined. The algorithms of the XRR curves calculation and surface‐profile reconstruction are complemented. The fractal approach to describing the shape of the XRR curves and surface profiles is used. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence properties of GaSb epitaxial layers passivated in hydrogen plasma
Authors: Gladkov P. 
Published: March 2007

AbstractUndoped and Si‐doped GaSb layers grown by low pressure MOVPE have been treated in hydrogen plasma and the effect of this treatment on photoluminescent (PL) and electrical properties is presented. Hall‐effect and PL measurements reveal that hydrogenation leads to reduction in the concentration of electrically active native acceptors, while the concentration of shallow acceptor SiSb remain practically unaffected. The hydrogenation of layers grown at Sb rich conditions results in nearly complete quenching of the PL line peaking at 896.5 meV, denoted in the literature as BE4. The origin of the BE4 line is ascribed to radiative recombination of excitons bound to a “bare” gallium vacancy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal and non‐thermal saturation effects in the output characteristic of UV‐to‐violet emitting (AlGaIn)N LEDs
Authors: Baeumler M. , Kunzer M. , Schmidt R. , Liu S. , Pletschen W. , Schlotter P. , Köhler K. , Kaufmann U. , Wagner J. 
Published: March 2007

AbstractUV‐to‐violet emitting (AlGaIn)N LEDs have been investigated with respect to the temperature‐dependence of the output power characteristics and non‐thermal rollover of the quantum efficiency at higher current densities. Analyzing MOVPE grown LED chips emitting in the 377 to 428 nm wavelength interval, the temperature sensitivity was found to increase and the output power to decrease with decreasing wavelength λ for λ < 400 nm. A sub‐linear increase of the output power with increasing injection current even in the absence of any thermal effects, i.e. a non‐thermal rollover of the quantum efficiency, was observed to be most pronounced for longer wavelength LEDs (λ > 400 nm). Furthermore, the transient temperature rise after turn‐on has been studied for differently packaged 377 nm LEDs, for which the temperature coefficient of the output power has been found to be particularly large. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local control of SiC polytypes
Authors: Pezoldt J. , Morales F. M. , Kalnin A. A. 
Published: March 2007

AbstractIn the case of SiC different methods for the formation of laterally and vertically stacked desired polytype inclusions are presented. The methods are based on a combination of ion implantation and annealing combined with epitaxial growth by sublimation technique. Nanoheteropolytype structures were formed using CVD. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of non‐linear theory to analysis of Benedicks effect in semiconductors
Authors: Piotrowski T. , Jung W. , Sikorski S. 
Published: March 2007

AbstractBenedicks thermovoltage resulting from non‐symmetric distribution of temperature gradients for different surface recombinations on sample surfaces has been determined in this paper using non‐linear system of transport equations. Density distributions of generalised Price internal current Jp, taking into account the excess carrier generation and Γ potential being the measure of charge carrier injection have also been determined. Minority carrier distributions and quasi‐fermi levels variations for electron and holes resulting from Fermi level splitting due to thermoinjection have been calculated. Quasi‐fermi level variations were used for determination thermo emf values. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)