bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the Selective Trifluoroacetolytic Scission of Native Peptaibols and Model Peptides Using HPLC and ESI‐CID‐MS
Authors: Theis Christoph , Degenkolb Thomas , Brückner Hans 
Published: November 2008

AbstractRepresentative members of a group of linear, N‐acylated polypeptide antibiotics (peptaibols) containing α‐aminoisobutyric acid (Aib) and, in part, isovaline (Iva), as well as proteinogenic amino acids and a C‐terminal‐bonded 2‐amino alcohol, were treated with anhydrous trifluoroacetic acid (TFA) at 37° for 0.5–26 h. The resulting fragments were separated by HPLC and characterized by electrospray ionization collision‐induced dissociation mass spectrometry (ESI‐CID‐MS). The following 16–20‐residue peptaibols were investigated: natural, microheterogeneous mixtures of antiamoebins and alamethicin F50, uniform paracelsin A, and synthetic trichotoxin A50/E. In the natural peptides, bonds formed between Aib (Iva) and Pro (Hyp) were rapidly and selectively cleaved within 0.5 h. Furthermore, TFA esters of the C‐terminal amino alcohols were formed. Depending on time, release of C‐terminal tri‐ and tetrapeptides as well as amino acids from the major fragments was observed. Synthetic homooligopeptides, namely Z‐ and Ac‐(Aib)10‐OtBu and Z‐(Aib)7‐OtBu, were analyzed for comparison. On treatment with TFA, a regular series of Z‐(Aib)10–5‐OH from Z‐(Aib)10‐OtBu were detected within 0.5 h, and, after 3 h, release of a regular series of Z‐(Aib)7–3‐OH from Z‐(Aib)7‐OtBu were observed. Moreover, concomitant release of the series of H‐(Aib)10–3‐OH from the decapeptide occurred. From these data, a repetitive cleavage mechanism via intermediate formation of C‐terminal oxazolones on trifluoroacetolysis is proposed. Furthermore, their formation and stability in native peptaibols are correlated with subtle structural differences in protein amino acids linked to Aib. From the conspicuous concordance of the formation and abundance of regular series of trifluoroacetolytic fragments and of positive ions of the b‐series in CID‐MS, the generation of intermediate oxazolonium ions in both gas and liquid phase is concluded.
Properties of Recombinant Staphylococcus haemolyticus Cystathionine β‐Lyase (metC) and Its Potential Role in the Generation of Volatile Thiols in Axillary Malodor
Authors: Troccaz Myriam , Benattia Faiza , Borchard Gerrit , Clark Anthony J. 
Published: November 2008

AbstractEnzymes implicated in cysteine and methionine metabolism such as cystathionine β‐lyase (CBL; EC 4.4.1.8), a pyridoxal‐5′‐phosphate (PLP)‐dependent carbon–sulfur lyase, have been shown to play a central role in the generation of sulfur compounds. This work describes the unprecedented cloning and characterization of the metC‐cystathionine β‐lyase from the axillary‐isolated strain Staphylococcus haemolyticus AX3, in order to determine its activity and its involvement in amino acid biosynthesis, and in the generation of sulfur compounds in human sweat. The gene contains a cysteine/methionine metabolism enzyme pattern, and also a sequence capable to effect β‐elimination. The recombinant enzyme was shown to cleave cystathionine into homocysteine and to convert methionine into methanethiol at low levels. No odor was generated after incubation of the recombinant enzyme with sterile human axillary secretions; sweat components were found to have an inhibitory effect. These results suggest that the generation of sulfur compounds by Staphylococci and the β‐lyase activity in human sweat are mediated by enzymes other than the metC gene or by the concerted activities of more than one enzyme.
Antiviral Activity of Benzimidazole Derivatives. I. Antiviral Activity of 1‐Substituted‐2‐[(Benzotriazol‐1/2‐yl)methyl]benzimidazoles
Authors: Tonelli Michele , Paglietti Giuseppe , Boido Vito , Sparatore Fabio , Marongiu Fabio , Marongiu Esther , La Colla Paolo , Loddo Roberta 
Published: November 2008

AbstractForty‐three 2‐[(benzotriazol‐1/2‐yl)methyl]benzimidazoles, bearing either linear (dialkylamino)alkyl‐ or bulkier (quinolizidin‐1‐yl)alkyl moieties at position 1, were evaluated in cell‐based assays for cytotoxicity and antiviral activity against viruses representative of two of the three genera of the Flaviviridae family, i.e. Flaviviruses (Yellow Fever Virus (YFV)) and Pestiviruses (Bovine Viral Diarrhoea Virus (BVDV)), as Hepaciviruses can hardly be used in routine cell‐based assays. Compounds were also tested against representatives of other virus families. Among ssRNA+ viruses were a retrovirus (Human Immunodeficiency Virus type 1 (HIV‐1)), two picornaviruses (Coxsackie Virus type B2 (CVB2), and Poliovirus type‐1, Sabin strain (Sb‐1)); among ssRNA− viruses were a Paramyxoviridae (Respiratory Syncytial Virus (RSV)) and a Rhabdoviridae (Vesicular Stomatitis Virus (VSV)) representative. Among double‐stranded RNA (dsRNA) viruses was a Reoviridae representative (Reo‐1). Two representatives of DNA virus families were also included: Herpes Simplex type 1, (HSV‐1; Herpesviridae) and Vaccinia Virus (VV; Poxviridae). Most compounds exhibited potent activity against RSV, with EC50 values as low as 20 nM. Moreover, some compounds, in particular when bearing a (quinolizidin‐1‐yl)alkyl residue, were also moderately active against BVDV, YFV, and CVB2.
New Phytotoxic Metabolites from Pestalotiopsis sp. HC02, a Fungus Residing in Chondracris rosee Gut
Authors: Zhang Ying Lao , Ge Hui Ming , Li Fang , Song Yong Chun , Tan Ren Xiang 
Published: November 2008

AbstractTwo new phytotoxic γ‐lactones, pestalotines A and B (1 and 2, resp.), along with 4‐oxo‐4H‐pyran‐3‐acetic acid (3) and 6‐hydroxyramulosin (=3,4,4a,5,6,7‐hexahydro‐6,8‐dihydroxy‐3‐methyl‐1H‐2‐benzopyran‐1‐one; 4), were isolateded from the culture of Pestalotiopsis sp. HC02, a fungus residing in the Chondracris rosee gut. Structures of the new metabolites were elucidated on the basis of their IR, NMR, and MS data. Pestalotines A and B (1 and 2, resp.) significantly inhibited the radical growth of Echinochloa crusgalli with IC50 values of 1.85×10−4 and 2.50×10−4 M, respectively, comparable to that of 2‐(2,4‐dichlorophenoxy)acetic acid (0.94×10−4 M) used as a positive control.
Synthesis, Characterization, and Antifungal Activity of Boron‐Containing Thiosemicarbazones
Authors: Hicks Justin W. , Kyle Christian B. , Vogels Christopher M. , Wheaton Susan L. , Baerlocher Felix J. , Decken Andreas , Westcott Stephen A. 
Published: November 2008

AbstractAddition of thiosemicarbazide, 4‐allylthiosemicarbazide, and 4‐phenylthiosemicarbazide to (formylphenyl)boronic acids affords a series of thiosemicarbazones containing boronic acids. Addition of 2‐formylphenylboronic acid to the thiosemicarbazides gave the corresponding cyclic 2,3,1‐benzodiazaborines. All new compounds have been investigated for potential antifungal activity.
Study of Antimalarial Activity of Chemical Constituents from Diospyros quaesita
Authors: Ma Cui‐Ying , Musoke Sebisubi Fred , Tan Ghee Teng , Sydara Kongmany , Bouamanivong Somsanith , Southavong Bounhoong , Soejarto D. Doel , Fong Harry H. S. , Zhang Hong‐Jie 
Published: November 2008

AbstractBioassay‐directed fractionation led to the isolation of seven compounds from a sample of the dried leaves, twigs, and branches of Diospyros quaesita Thw. (Ebenaceae). One of the isolates, betulinic acid 3‐caffeate (1), showed in vitro antimalarial activity against Plasmodium falciparum clones D6 (chloroquine‐sensitive) and W2 (chloroquine‐resistant) with IC50 values of 1.40 and 0.98 μM, respectively. Evaluation of compound 1 in the human oral epidermoid (KB) cancer cell line revealed cytotoxicity at ED50 of 4.0 μM. In an attempt to reduce the cytotoxicity of 1, the acetylated derivative 1a and betulinic acid (1b) were prepared. Of the seven isolates, diospyrosin (2) was determined to be a new neolignan. In addition to 1, other known compounds isolated in this study were pinoresinol, lariciresinol, N‐benzoyl‐L‐phenylalaninol, scopoletin, and poriferast‐5‐en‐3β,7α‐diol. The structure of 2 was elucidated based on spectroscopic data analysis including 1D‐ and 2D‐NMR, and HR‐ESI‐MS.
Identification of the Chemotypes of Ocimum forskolei and Ocimum basilicum by NMR Spectroscopy
Authors: Fatope Majekodunmi O. , Marwah Ruchi G. , Al Hadhrami Nabil M. , Onifade Anthony K. , Williams John R. 
Published: November 2008

AbstractThe chemotypes of Ocimum forskolei Benth and Ocimum basilicum L. growing wild in Oman have been established by 13C‐NMR analyses of the vegetative and floral oils of the plants. The chemotypes, estragole for O. forskolei and linalool for O. basilicum, suggested by 13C‐NMR fingerprinting were also confirmed by GC‐FID and GC/MS analyses. The oil of O. forskolei demonstrated better activities against bacteria and dermatophytes. The significance of the presence of estragole and linalool in the volatile oils of plants whose fragrances are traditionally inhaled, added to food, or rubbed on the skin are discussed.
Investigation of Biosynthetic Pathways to Hydroxycoumarins During Post‐Harvest Physiological Deterioration in Cassava Roots by Using Stable Isotope Labelling
Authors: Bayoumi Soad A. L. , Rowan Michael G. , Beeching John R. , Blagbrough Ian S. 
Published: November 2008

AbstractCassava (Manihot esculenta Crantz) is an important starch‐rich crop, but the storage roots only have a short shelf‐life due to post‐harvest physiological deterioration (PPD), which includes the over‐production and polymerisation of hydroxycoumarins. Key aspects of coumarin secondary‐metabolite biosynthesis remain unresolved. Here we exploit the accumulation of hydroxycoumarins to test alternative pathways for their biosynthesis. Using isotopically labelled intermediates (p‐coumarate‐2‐13C, caffeate‐2‐13C, ferulate‐2‐13C, umbelliferone‐2‐18O and esculetin‐2‐18O), we show that the major biosynthetic pathway to scopoletin and its glucoside, scopolin, in cassava roots during PPD is through p‐coumaric, caffeic and then ferulic acids. An alternate pathway through 2′,4′‐dihydroxycinnamate and umbelliferone leads to esculetin and esculin. We have used C18O2‐carboxylate‐labelled cinnamic and ferulic acids, and feeding experiments under an atmosphere of 18O2, to investigate the o‐hydroxylation and cyclisation steps. We demonstrate that the major pathway is through o‐hydroxylation and not via a proposed spirolactone‐dienone intermediate.
Evidence for Dual Pathway in Through‐Space Singlet Energy Transfers in Flexible Cofacial Bisporphyrin Dyads
Authors: Pognon Grégory , Wytko Jennifer A. , Harvey Pierre D. , Weiss Jean 
Published: November 2008

AbstractFlexible “pacman” scaffolds built upon a calix[4]arene platform bearing a [18]crown‐6 ether and either two OH functions or two OPr groups at the lower rim have been used to generate donor–acceptor (D–A) dyads incorporating a zinc–porphyrin donor and a free‐base porphyrin acceptor. Through‐space singlet energy transfer (SET) in the D–A dyads was studied by time‐resolved fluorescence spectroscopy. Although the effects of conformational changes are well documented when the chromophores switch from a non‐cofacial to a cofacial arrangement, little is known about flexible pacman scaffolds in which the changes are limited to the distance between the chromophores. The known SET rates for reported, geometrically well‐defined, rigid pacman D–A dyads were used as calibration to estimate the D–A distances in the flexible pacman dyads. Due to the flexibility of the calix[4]arene spacer, the D–A dyads adopt a “closed” or “open” geometry that is tuned by intramolecular hydrogen bonds (OH⋅⋅⋅[18]crown‐6 ether) and by solvent interactions. Changes in the SET rates between the open and closed geometries were surprisingly less dramatic than expected, and are explained by a dual SET pathway that is specific to the calix[4]arene platform. Time‐resolved fluorescence studies support the hypothesis that, for the “open” conformer, the preferred through space SET pathway (i.e., at the shortest distance) is located within the calix[4]arene cavity through the cofacial phenyl groups. For the “closed” conformer, the preferred through space SET route is located between the zinc and free‐base porphyrins.
Fluorescence Emission from 2,6‐Naphthylene‐Bridged Mesoporous Organosilicas with an Amorphous or Crystal‐Like Framework
Authors: Mizoshita Norihiro , Goto Yasutomo , Kapoor Mahendra P. , Shimada Toyoshi , Tani Takao , Inagaki Shinji 
Published: November 2008

AbstractWe report that 2,6‐naphthylene‐bridged periodic mesoporous organosilicas exhibit unique fluorescence behavior that reflects molecular‐scale periodicities in the framework. Periodic mesoporous organosilicas consisting of naphthalene–silica hybrid frameworks were synthesized by hydrolysis and condensation of a naphthalene‐derived organosilane precursor in the presence of a template surfactant. The morphologies and meso‐ and molecular‐scale periodicities of the organosilica materials strongly depend on the synthetic conditions. The naphthalene moieties embedded within the molecularly ordered framework exhibited a monomer‐band emission, whereas those embedded within the amorphous framework showed a broad emission attributed to an excimer band. These results suggest that the naphthalene moieties fixed within the crystal‐like framework are isolated in spite of their densely packed structure, different from conventional organosilica frameworks in which only excimer emission was observed for both the crystal‐like and amorphous frameworks at room temperature. This key finding suggests a potential to control interactions between organic groups and thus the optical properties of inorganic/organic hybrids.
Prathap's best‐fit paradigm and optimal strain recovery points in indeterminate tapered bar analysis using linear element
Authors: Mukherjee Somenath , Jafarali P. 
Published: November 2008

AbstractIn stress analysis procedures using the finite element method, where the results are generated through approximations using interpolation functions, there is a need to establish optimal points in a typical element that correspond to the exact values of stresses and strains. Conventionally, Gauss' points and Barlow's points are used as optimal points for stress recovery. In this paper it is shown that the justification for the existence of optimal strain/stress recovery points, referred to as Prathap points in an element, is a consequence of the best‐fit paradigm, originally proposed by Prathap through the stress correspondence principle.Through the analysis of a statically indeterminate structure like a simple bar of linearly varying elastic rigidity with fixed ends, the existence of Prathap's points has been demonstrated through the best‐fit paradigm that remains valid even for statically indeterminate problems in a subtle manner. The present paper reconciles the prima facie, yet misleading, violation of the best‐fit rule with the fundamental theory of the finite element method, and effectively restores the validity of the best‐fit paradigm even for statically indeterminate problems in a deeper sense. Furthermore, consistent modified definitions of the global and local errors from the strain point of view are prescribed here. Copyright © 2008 John Wiley & Sons, Ltd.
Thermodynamic and Structural Characterization of the Transformation from a Metastable Low‐Density to a Very High‐Density Form of Supercooled TIP4P‐Ew Model Water
Authors: Paschek Dietmar , Rüppert Andreas , Geiger Alfons 
Published: November 2008

AbstractWe explore the phase diagram of the metastable TIP4P‐Ew liquid model water from 360 K down to 150 K at densities ranging from 0.950 to 1.355 g cm−3. In addition to the low‐density/high‐density (LDL/HDL) liquid–liquid transition, we observe a structural high‐density/very high‐density (HDL/VHDL) transformation for the lowest temperatures at 1.30 g cm−3. The characteristics of the isobars and isotherms suggest the presence of a stepwise HDL/VHDL transition with first‐order‐like appearance. In addition, we also identify an apparent pretransition at 1.24 g cm−3, which suggests that the experimentally detected LDA/VHDA transformation might evolve into a multiple‐step process with different local structures representing local minima in the free‐energy landscape. Such a scenario is supported by a pronounced correlation between the isothermal density dependence of the pressure, with a stepwise increase of the oxygen coordination number, due to the appearance of interstitial water molecules.
The Solvent‐Dependent Shift of the Amide I Band of a Fully Solvated Peptide as a Local Probe for the Solvent Composition in the Peptide/Solvent Interface
Authors: Paschek Dietmar , Pühse Matthias , Perez‐Goicochea Arnold , Gnanakaran S. , García Angel E. , Winter Roland , Geiger Alfons 
Published: November 2008

AbstractWe determine the shift and line shape of the amide I band of a model AK peptide from molecular dynamics (MD) simulations of the peptide dissolved in methanol/water mixtures with varying composition. The IR spectra are determined from a transition dipole coupling exciton model. A simplified empirical model Hamiltonian is employed, which takes into account both the effect of hydrogen bonding and the intramolecular vibrational coupling. We consider a single isolated AK peptide in a mostly helical conformation, while the solvent is represented by 2600 methanol or water molecules, simulated for a pressure of 1 bar and a temperature of 300 K. Over the course of the simulations, minor reversible conformational changes at the termini are observed, which are found to only slightly affect the calculated spectral properties. Over the entire composition range, which varies from pure water to the pure methanol solvent, a monotonous shift towards higher frequency of the IR amide I band of about 8 wavenumbers is observed. This shift towards higher frequency is comparable to the shift found in preliminary experimental data also presented here on the amide I′ band. The shift is found to be caused by two counter‐compensating effects. An intramolecular red shift of about 1.2 wavenumbers occurs, due to stronger intramolecular hydrogen bonding in a methanol‐rich environment. Dominating, however, is the intermolecular solvent‐dependent shift towards higher frequency of about 10 wavenumbers, which is attributed to the less effective hydrogen‐bond‐donor capabilities of methanol compared to water. The importance of the solvent contribution to the IR shift, as well as the significantly different hydrogen formation capabilities of water and methanol, makes the amide I band sensitive to composition changes in the local environment close to the peptide/solvent interface. This allows, in principle, an experimental determination of the composition of the solvent in close proximity to the peptide surface. For the AK peptide case, we observe at low methanol concentrations a significantly enhanced methanol concentration at the peptide/solvent interface, supposedly promoted by the partially hydrophobic character of the AK peptide’s solvent‐accessible surface.
Protective effect of CPUX1, a progesterone, on hydrogen peroxide‐induced oxidative damage in PC12 cells
Authors: Ji Bian‐sheng , He Ling 
Published: November 2008

AbstractThe protective effect of CPUX1, a novel progesterone analog, on hydrogen peroxide (H2O2)‐induced oxidative damage was investigated in rat pheochromocytoma (PC12) cells. Following the exposure of PC12 cells to H2O2, there was a reduction in cell survival and activities of superoxide dismutase (SOD) and mitochondrial membrane potential (MMP) accompanied by increased levels of lactate dehydrogenase (LDH) release, malondialdehyde (MDA) production, and intracellular reactive oxygen species (ROS) and intracellular [Ca2+]i levels. Preincubation of cells with CPUX1 prior to H2O2 exposure attenuated all these changes mentioned and had a protective effect against H2O2‐induced toxicity in PC12 cells, indicating that the compound may have potential therapeutic benefit for CNS disorders influenced by oxidative damage. Drug Dev Res 69: 2008 ©2008 Wiley‐Liss, Inc.
Sensitivity and reproducibility of indirect calorimetry in measurement of resting metabolic rate
Authors: Karlsson Cecilia , Lystig Theodore , Hartford Marianne , Carlsson Björn 
Published: November 2008

AbstractThe aim of this study was to assess indirect calorimetry measurement of resting metabolic rate (RMR) with respect to sensitivity and reproducibility in a human study population suitable for early clinical studies to evaluate new anti‐obesity candidate drugs. Twenty‐four overweight, but otherwise healthy males were included in this randomized, single‐blind, placebo‐controlled, crossover study. Three different doses of epinephrine (0.005, 0.01, 0.03 µg · kg fat‐free mass (FFM)−1 · min−1) were used as active treatment. There were two identical study periods, separated by a 4‐week washout. Increases in RMR were seen with all tested concentrations of epinephrine when compared with placebo. Changes in RMR of ≥1.8% could be detected with 90% power in this crossover study design. The RMR values measured at the two study periods revealed a highly significant correlation (Spearman correlation 0.803, P=0.0007). To conclude, indirect calorimetry is a sensitive and robust means of measuring RMR. The method can be used to assess RMR in diverse clinical settings, even when considering modest differences. Drug Dev Res 69: 2008. © 2008 Wiley‐Liss, Inc.
Spatial gradients in ecohydrologic properties within a pinyon‐juniper ecosystem
Authors: Madsen M. D. , Chandler D. G. , Belnap J. 
Published: November 2008

AbstractThe influence of woody vegetation and biological soil crusts on infiltration capacity is one of the several uncertainties associated with the ecohydrologic effects of woody plant encroachment into arid and semi‐arid land systems. The objective of this study was to quantify the effects of Utah juniper (Juniperus osteosperma) and pinyon pine (Pinus edulis) on subcanopy and intercanopy ecohydrologic properties. We measured soil sorptivity, unsaturated hydraulic conductivity [K(h)], soil water content (SWC), and water repellency along radial line transects from under Juniperus and Pinus trees into the centre of the intercanopy space between trees. In the subcanopy, litter mounds, hydrophobic soils, and roots all appear to contribute to preferential flow to below‐surface soils via wetted patches. For both Juniperus and Pinus, K(h) was significantly lower in the subcanopy than the intercanopy average; however, line transect measurements did not show distinct boundaries in K(h) between the two regions. K(h) increased by eight‐fold across a gradient extending outward from near the edge of the canopy to approximately 2 times the canopy radius (CR). This suggests that the influence of these species on hydrologic properties extends significantly into the intercanopy region. Analysis of biological soil crust cover within the intercanopy showed that beyond the gradient zone, increasing structural development of biological soil crust was associated with increased K(h). Furthermore, these results indicate that the distance from the canopy and direction should be considered in the assessment and modelling of woody plant and biological soil crust influence on infiltration capacity. Copyright © 2008 John Wiley & Sons, Ltd.