bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automated tissue segmentation and blind recovery of1H MRS imaging spectral patterns of normal and diseased human brain
Authors: Du Shuyan , Mao Xiangling , Sajda Paul , Shungu Dikoma C. 
Published: March 2007

AbstractConstrained non‐negative matrix factorization (cNMF) with iterative data selection is described and demonstrated as a data analysis method for fast and automatic recovery of biochemically meaningful and diagnostically specific spectral patterns of the human brain from1H MRS imaging (1H MRSI) data. To achieve this goal, cNMF decomposesin vivomultidimensional1H MRSI data into two non‐negative matrices representing (a) the underlying tissue‐specific spectral patterns and (b) the spatial distribution of the corresponding metabolite concentrations. Central to the proposed approach is automatic iterative data selection which uses prior knowledge about the spatial distribution of the spectra to remove voxels that are due to artifacts and undesired metabolites/tissues such as the strong lipid and water components. The automatic recovery of diagnostic spectral patterns is demonstrated for long‐TE1H MRSI data on normal human brain, multiple sclerosis, and serial brain tumor. The results show the ability of cNMF with iterative data selection to automatically and simultaneously recover tissue‐specific spectral patterns and achieve segmentation of normal and diseased human brain tissue, concomitant with simplification of information content. These features of cNMF, which permit rapid recovery, reduction and interpretation of the complex diagnostic information content of large multi‐dimensional spectroscopic imaging data sets, have the potential to enhance the clinical utility ofin vivo1H MRSI. Copyright © 2007 John Wiley & Sons, Ltd.
Compositional analysis of intact alkyl esters in leaf epicuticular wax of swede by capillary gas chromatography and electron‐impact mass spectrometry
Authors: Shepherd T. , Robertson G. W. , Griffiths D. W. 
Published: March 2007

AbstractA method for the separation and identification of complex mixtures of more than 50 different intact esters in epicuticular wax of swede, Brassica napus var. rapifera cv. Doon Major, using combined gas chromatography‐mass spectrometry (GC‐MS) has been developed. The esters were separated at temperatures of up to 350°C by automatic pressure programming (for capillary GC) or by manually increasing helium carrier gas pressure (for GC‐MS) in order to maintain flow at high temperatures. Esters in the range C41‐C50 were detected, with regular repeating acid/alcohol combinations. Individual acid and alcohol moieties were identified from [RCO2H2]+ ions in the mass spectra of intact esters and, following trans‐esterification and silylation, from the mass spectral and chromatographic characteristics of the methyl esters of the acid components (C14‐C23) and trimethylsilyl derivatives of the alcohol components (C23‐C31). The major compounds were doubly branched C44 and C46 esters, composed of anteiso‐C17/anteiso‐C27 (32.7%), anteiso‐C17/anteiso‐C29 (11.9%) and anteiso‐C19/anteiso‐C27 (13.1%) acid/alcohol combinations, respectively, singly branched C43 and C45 esters, composed of n‐C16/anteiso‐C27 (8.5%), anteiso‐C17/n‐C26 (3.9%), n‐C18/anteiso‐C27 (6.8%), anteiso‐C17/n‐C28 (2.3%) and anteiso‐C19/n‐C26 (1.6%), were minor components.
Use of a porous graphitic carbon column to separate isomers of piperidino‐type chromone alkaloids
Authors: Houghton Peter J. , Woldemariam Tibebe Z. 
Published: March 2007

AbstractA liquid chromatography procedure which rapidly separates the two isomers of schumannificine and N‐methylschumannificine, chromone alkaloids isoilated from Schumanniophyton magnificum (Rubiaceae), is described. The procedure uses a porous graphitic carbon high performance liquid chromatographic column and is compared with other chromatographic and chemical methods which were tried unsuccessfully. The method was adapted in an attempt to prepare the individual isomers of schumannificine and N‐methylschumannificine in mg amounts but interconversion of the isomers in aqueous medium was shown to occur too rapidly for this to be feasible.
Synthesis and enantiodifferentiation of riesling acetals
Authors: Dollmann B. , Full G. , Schreier P. , Winterhalter P. , Güntert M. , Sommer H. 
Published: March 2007

AbstractThe cyclic acetals 1b/c were prepared in a biomimetic‐type reaction via the Mosher‐esters 5a/b of their natural precursor 2,6,10,10‐tetramethyl‐1‐oxaspiro[4.5]dec‐6‐ene‐2,8‐diol (6) which were available from 3,4‐didehydro‐β‐ionone (2) by photosensitized oxidation and subsequent reduction with thiourea. The racemic cis‐diols 3 so‐obtained were esterified with (–)‐α‐methoxy‐α‐trifluoromethyl‐phenylacetyl chloride and the resulting diastereo‐meric esters (4a/b) isolated in pure form (diastereomeric excess >95%) by preparative high performance liquid chromatography. Configuration at C‐6 was determined after bio‐oxidative cleavage of 4a/b to dehydrovomifo‐liols 8a/b. The hemiacetals 5a/b obtained from esters 4a/b by hydrogenation (Pd/BaSO4) were subjected to thermal treatment at pH 3 yielding two optically enriched isomers of Riesling acetal which were subsequently obtained in optically pure form by preparative gas chromatography using a modified cyclodextrin column. Their relative configuration was established by NOE‐experiments. In addition, the structures and the heats of formation of the different diastereomers were calculated using a force field program and the semi‐empirical MNDO, AMI and PM3 methods. The absolute configurations were found from the results of the NOESY experiment, the calculations and the stereoselective synthesis. Riesling acetal enantiomers differed distinctly in their odour properties. (+)‐Riesling acetal 1b showed a weak “woody, fruity, ionone, flowery” note, whereas the (‐)‐isomer 1c exhibited a slight “camphoraceous, flowery” note. Enantiodifferentiation of 1b/c in a number of natural sources with the help of multidimensional gas chromatography (DB‐Wax/C‐Dex B) revealed a nearly racemic composition of 1b/c.
Prosapogenins from Dodonaea attenuata
Authors: Han Andrew Y. T. , Van Gorkom Leon , McFarlane Ian J. , Barrow Kevin D. 
Published: March 2007

AbstractSaponins have been extracted from the seed of Dodonaea attenuata and converted to prosapogenins by mild acid hydrolysis. Partially acetylated derivatives of the sapogenin, R1‐barrigenol, were characterized by extensive two dimensional nuclear magnetic resonance spectroscopy. The complete assignments of 1H and 13C resonances and nuclear Overhauser effects of these partly acetylated sapogenins has allowed a straightforward assignment of the structures of the prosapogenins, including the location of the individual ester groups and the presence of artefacts from the acidic hydrolysis conditions.
Capillary electrophoresis: A new technique in the analysis of plant secondary metabolites
Authors: Tomás‐Barberán F. A. 
Published: March 2007

AbstractThe possibilities and applications of capillary electrophoresis (CE) as an analytical technique for plant secondary metabolites are reviewed. Applications of both capillary zone electrophoresis and micellar electrokinetic capillary chromatography for this purpose are described. CE is compared with high pressure liquid chromato‐graphy (HPLC) as an analytical technique, and the advantages and criticisms of CE are described. The effects of the applied voltage, capillary temperature, electrolyte concentration and nature (complexing or non‐complexing buffers), buffer pH, micelle concentration and nature (sodium dodecyl sulphate or cetyltrimethylammonium bromide and the addition of organic modifiers to the running buffer (organic solvents, cyclodextrins, urea, cholate) on the parameters of separation and resolution of different secondary metabolites are discussed. The applications of CE to the analysis of flavonoid aglycones and glycosides, phenolic acids, quinones, coumarins, alkaloids, capsacinoids, glucosinolates, polyamines, monoterpenes, diterpenes, phytoecdysteroids, cardiac glycosides and saponins are shown. It is concluded that CE is a very promising analytical technique in the analysis of plant secondary metabolites, and it will become an indispensable tool, together with HPLC and gas liquid chromatography, in phytochemical laboratories since these techniques are in many ways complementary, and problems that are difficult to solve by HPLC can often be solved using CE.
Capillary electrophoresis of isoquinoline alkaloids from Chelidonium Majus L.
Authors: Pietta P. G. , Mauri P. L. , Gardana C. , Colombo M. L. , Tomè F. 
Published: March 2007

AbstractThe determination of six different isoquinoline alkaloids from Chelidonium majus (leaves and roots) using capillary electrophoresis is described. Analyses were performed on fused silica capillaries with 66 mM phosphate buffer at pH 2.4 containing 40% methanol. The analytes were monitored by on‐line ultraviolet (UV) detection to identify sanguinarine, chelerythrine, berberine and chelidonine. Both coptisine and DL‐stylopine were isolated by semi‐preparative high performance liquid chromatography (HPLC), and their structure assessed by UV and mass spectrometry. Capillary electrophoresis is confirmed as a useful complementary technique to HPLC.
Aspects of the extraction and purification of solasodine from Solanum aculeastrum tissues
Authors: Drewes F. E. , Van Staden J. 
Published: March 2007

AbstractA protocol has been developed for the extraction and purification of solasodine from plant material to complement the use of benzoylation for derivatization of the compound prior to high performance liquid chromatographic (HPLC) determination. Solasodine glycosides were extracted in 80% ethanol, the samples defatted with chloroform and then hydrolysed with 0.5 M hydrochloric acid. The extracts were washed with ethyl acetate, prior to increasing the pH to between 8 and 9, whereafter solasodine was extracted with chloroform. Flash chromatography using a 15 cm silica gel column was necessary for purification of the extracts, which were then benzoylated and subjected to HPLC. In green Solanum aculeastrum Dun. berries, 0.016% solasodine was detected, whereas in callus cultures of the same species no solasodine was detectable.
Identification of lipophilic flavonols by a combination of chromatographic and spectral techniques
Authors: Greenham Jenny , Williams Christine , Harborne Jeffrey B. 
Published: March 2007

AbstractIsocratic and gradient elution high performance liquid chromatographic techniques are compared for separating different methylated and isoprenylated flavonols. The identification of individual flavonols from their isomers, based on retention times, thin layer chromatographic data and ultraviolet spectroscopy is discussed. These data are provided for 23 kaempferol, quercetin and myricetin O‐methyl ethers, for seven C‐methyl ethers and 15 isoprenylated derivatives.
Permeation chromatography on extracted Wolffia
Authors: Ehwald Rudolf , Klein Petra , Jungnickel Fritz , Dongowski Gerhard 
Published: March 2007

AbstractVesicular packing materials (VP) formed by the cell wall frame of denaturated and extracted Wolffia arrhiza and W. columbiana were investigated for possible applications in permeation chromatography. Two types of VP were studied: W0, being fronds extracted with ethanol and water, and W1, obtained from W0 by treatment with pancreatic enzymes in order to remove the insoluble protoplast residues. The cell wall material of W. arrhiza is characterized by a high content of pectin which is rich in homogalacturonan with low contents of L‐rhamnose, D‐galactose and L‐arabinose, and a low degree of esterification. In permeation chromatography on both W0 and W1, excluded components formed a sharp peak at an elution volume which was 26‐30% of the total bed volume. The critical size, in terms of Stokes' diameter, for the exclusion of macromolecules by W0 is about 5 nm, and this allows for complete exclusion of most proteins. At linear flow rates below 0.1 mL/cm2/min the column length necessary for complete separation of sugars or salts from excluded macromolecules may be less than 10 cm. Because of their smaller particle size the materials prepared from W. columbiana showed a smaller peak variance for permeable compounds. The potentially low price of the W0 material suggests its use as an alternative to gel filtration media for the fast removal of low molecular weight solutes from proteins and other hydrophilic colloidal materials on a technical scale.
Stereoisomeric flavour compounds. LXX: 1‐p‐menthene‐8‐thiol: Separation and sensory evaluation of the enantiomers by enantioselective gas chromatography‐olfactometry
Authors: Lehmann Detmar , Dietrich Armin , Hener Uwe , Mosandl Armin 
Published: March 2007

AbstractThe gas chromatographic separation of the 1‐p‐menthene‐8‐thiol enantiomers has been achieved using heptakis(2,3‐di‐O‐methyl‐6‐O‐TBDMS)‐β‐cyclodextrin as the chiral stationary phase in enantioselective gas chromatography. The sensory evaluation of the pure enantiomers has been realized by enantioselective gas chromatography‐olfactometry. (R)‐1‐p‐menthene‐8‐thiol was found to be of formative influence on the natural odour of grapefuit whilst the odour of the (S)‐enantiomer was weak and non‐specific.
13C‐nuclear magnetic resonance spectra of some andrographolide derivatives
Authors: Fan Dajing , Wu Xiaoyun , Qin Guowei 
Published: March 2007

AbstractThe 13C‐nuclear magnetic resonance spectra of some andrographolide derivatives have been assigned based on two‐dimensional correlation spectroscopy (COSY) and correlation via long‐range coupling (COLOC) spectra and comparison with known compounds. The assignment of triacetate of andrographolide, reported in literature, has been revised.
Cyanide content of the leaves and stems of edible aroids
Authors: Bradbury J. Howard , Egan Sylvia V. , Matthews Peter J. 
Published: March 2007

AbstractThe edible aroids taro (Colocasia esculenta), tannia (Xanthosoma violaceum), giant taro (Alocasia macrorrhizos), giant swamp taro (Cyrtosperma chamissonis) and elephant foot yam (Amorphophallus paeonifolius) have been shown to contain varying amounts of cyanide in their leaves and stems using a screening assay and a more accurate acid hydrolysis method. The cyanogenic glucoside triglochinin (previously identified in giant taro) was found to be less stable to acid hydrolysis (requiring only 15 min) compared with 50 min hydrolysis for linamarin and lotaustralian (from cassava) under the same experimental conditions. The amounts of cyanide present in the leaves (0‐3 mg HCN/100 g fresh weight) and in the stems (0—0.3 mg HCN/100 g fresh weight) of Colocasia and Xanthosoma are only about 1‐5% of that found in cassava leaves and tubers and are not a cause for concern for human nutrition. Cyrtosperma stems and Amorphophallus leaves contain only small amounts of cyanide. In contrast, all Alocasia varieties contained much more cyanide in leaves (2‐30 mg HCN/100 g fresh weight) and in stems (0.5‐4 mg HCN/100 g fresh weight).
Identification of bioactive metabolites from the bark of Pericopsis (Afrormosia) laxiflora
Authors: Tringali Corrado 
Published: March 2007

AbstractThe α‐methyldeoxybenzoins angolensin, 2‐O‐methyl‐angolensin and the pterocarpan maackiain (demethylpterocarpin) have been isolated by bioactivity‐guided fractionation (brine shrimp test) from the bark of the medicinal African plant, Pericopsis (Afrormosia) laxiflora.
Layer effects of photovoltaic heterojunction of fully conjugated heterocyclic aromatic rigid‐rod polymer poly‐p‐phenylenebenzobisoxazole
Authors: Huang Jen‐Wei , Bai Shih Jung 
Published: March 2007

AbstractPoly‐p‐phenylenebenzobisoxazole (PBO) contains a fully conjugated rod‐like backbone entailing excellent optoelectronic properties and superior stabilities. Poly(2,3‐dihydrothieno‐1,4‐dioxin):polystyrenesulfonate (PEDOT:PSS) is a hole transferring medium, which was spun into a thin‐film between PBO and indium‐tin‐oxide to facilitate photovoltaic (PV) effect by forming a donor‐acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and Isc were achieved with a LiF thickness of 1–2 nm because of possible electric dipole effect leading to an increase of Voc from 0.7 to 0.92 V and of Isc from about 0.1 to 0.2 μA. No PV response was observed for all PBO homojunctions because of insufficient exciton separation into electrons and holes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 988–993, 2007
Conformational states and folding pathways of peptides revealed by principal‐independent component analyses
Authors: Nguyen Phuong H. 
Published: March 2007

AbstractPrincipal component analysis is a powerful method for projecting multidimensional conformational space of peptides or proteins onto lower dimensional subspaces in which the main conformations are present, making it easier to reveal the structures of molecules from e.g. molecular dynamics simulation trajectories. However, the identification of all conformational states is still difficult if the subspaces consist of more than two dimensions. This is mainly due to the fact that the principal components are not independent with each other, and states in the subspaces cannot be visualized. In this work, we propose a simple and fast scheme that allows one to obtain all conformational states in the subspaces. The basic idea is that instead of directly identifying the states in the subspace spanned by principal components, we first transform this subspace into another subspace formed by components that are independent of one other. These independent components are obtained from the principal components by employing the independent component analysis method. Because of independence between components, all states in this new subspace are defined as all possible combinations of the states obtained from each single independent component. This makes the conformational analysis much simpler. We test the performance of the method by analyzing the conformations of the glycine tripeptide and the alanine hexapeptide. The analyses show that our method is simple and quickly reveal all conformational states in the subspaces. The folding pathways between the identified states of the alanine hexapeptide are analyzed and discussed in some detail. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Free energy landscape of a biomolecule in dihedral principal component space: Sampling convergence and correspondence between structures and minima
Authors: Maisuradze Gia G. , Leitner David M. 
Published: March 2007

AbstractDihedral principal component analysis (dPCA) has recently been developed and shown to display complex features of the free energy landscape of a biomolecule that may be absent in the free energy landscape plotted in principal component space due to mixing of internal and overall rotational motion that can occur in principal component analysis (PCA) [Mu et al., Proteins: Struct Funct Bioinfo 2005;58:45–52]. Another difficulty in the implementation of PCA is sampling convergence, which we address here for both dPCA and PCA using a tetrapeptide as an example. We find that for both methods the sampling convergence can be reached over a similar time. Minima in the free energy landscape in the space of the two largest dihedral principal components often correspond to unique structures, though we also find some distinct minima to correspond to the same structure. Proteins 2007. © 2007 Wiley‐Liss, Inc.
An unsuspected ecdysteroid/steroid phosphatase activity in the key T‐cell regulator, Sts‐1: Surprising relationship to insect ecdysteroid phosphate phosphatase
Authors: Davies Lyndsay , Anderson Ian P. , Turner Philip C. , Shirras Alan D. , Rees Huw H. , Rigden Daniel J. 
Published: March 2007

AbstractThe insect enzyme ecdysteroid phosphate phosphatase (EPP) mobilizes active ecdysteroids from an inactive phosphorylated pool. Previously assigned to a novel class, it is shown here that it resides in the large histidine phosphatase superfamily related to cofactor‐dependent phosphoglycerate mutase, a superfamily housing notably diverse catalytic activities. Molecular modeling reveals a plausible substrate‐binding mode for EPP. Analysis of genomic and transcript data for a number of insect species shows that EPP may exist in both the single domain form previously characterized and in a longer, multidomain form. This latter form bears a quite unexpected relationship in sequence and domain architecture to vertebrate proteins, including Sts‐1, characterized as a key regulator of T‐cell activity. Long form Drosophila melanogaster EPP, human Sts‐1, and a related protein from Caenorhabditis elegans have all been cloned, assayed, and shown to catalyse the hydrolysis of ecdysteroid and steroid phosphates. The surprising relationship described and explored here between EPP and Sts‐1 has implications for our understanding of the function(s) of both. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Luminescence characteristics of LiCaAlF6:Eu phosphor
Authors: Aghalte G. A. , Omanwar S. K. , Moharil S. V. 
Published: March 2007

AbstractA simple method for preparing LiCaAlF6:Eu2+ phosphor is reported. Photoluminescence (PL) and thermoluminescence (TL) studies were carried out. The TL sensitivity of the phosphor is nearly twice that of CaSO4:Dy TLD phosphor. Several other properties required for TL dosimetry are superior as well. It is suggested that the phosphor can be a suitable replacement for CaSO4:Dy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low temperature photoluminescence of pure and doped paratellurite (TeO2) crystals
Authors: Dafinei Ioan , Dujardin Christophe , Longo Egidio , Vignati Marco 
Published: March 2007

AbstractPhotoluminescence measurements aimed at defining the precise nature of scintillation reported in paratellurite (TeO2) crystals [Coron et al., Nucl. Instrum. Methods Phys. Res. A 520, 159 (2004)] are presented. Measurement results are discussed for TeO2 crystal samples (pure and Mg, Mn, Nb, Zr doped) studied for their photoluminescence properties in the 30–300 K temperature range and the nature of scintillation peaks reported on these samples is explained. Conclusions are drawn concerning the possibility to improve the scintillation yield of TeO2 crystals to be used as cryogenic bolometers operated at 10 mK in experiments studying the ββ decays of 130Te. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thin‐film field‐emission cathode with Pt or Au interlayer between insulator and Zn0.75Mg0.25O
Authors: Wang Zengmei , Li Dejie 
Published: March 2007

AbstractA thin‐film field‐emission cathode with Al/Ta2O5/(Pt or Au)/Zn0.75Mg0.25O/Pt–Au–Ag structure is proposed. Here, a Pt or Au interlayer is introduced between the insulator (Ta2O5) and semiconductor (Zn0.75Mg0.25O) layers in the metal‐insulator‐semiconductor‐metal (MISM) structure, in order to effectively control the interfacial electron‐energy‐state distribution. Consequently, the transmission current waveform of the proposed cathode becomes completely symmetric, while stable and uniform electron emission is reproducibly obtained. Maximum electron emission efficiency of 0.055% is obtained with a cathode using a Au interlayer and a Pt–Au–Ag top electrode. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)