bluuebunny/crossref_metadata_2025_split huggingface dataset:
Protective effects of melatonin and N‐acetylserotonin on aflatoxin B1‐induced lipid peroxidation in rats
Authors: Gesing Adam , Karbownik‐Lewinska Malgorzata 
Published: September 2007

AbstractAflatoxin B1 (AFB1) is a potent hepatotoxic and hepatocarcinogenic mycotoxin. Reactive oxygen species are considered to participate in the main mechanism of aflatoxin toxicity. Melatonin (Mel) is a hormone which has antioxidative activities. N‐acetylserotonin (NAc‐5HT) is an immediate precursor of Mel. Melatonin is documented to be completely safe in humans and animals. The aim of our study was to examine the potential protective effects of Mel or NAc‐5HT against lipid peroxidation (LPO), caused by AFB1 in male Wistar rats. Mel and NAc‐5HT were intraperitoneally (i.p.) injected for 3 weeks in late afternoon (16:00–18:00) injections (20 mg kg−1 BW/daily). AFB1 (50 µg kg−1 BW/daily) was administered i.p. 6 h prior to indoleamine injections. Concentrations of malondialdehyde + 4‐hydroxyalkenals (MDA + 4‐HDA), as an index of LPO, were measured in liver, brain, lung, testis and kidney homogenates. The level of LPO in tissue homogenates was expressed as the amount of MDA + 4‐HDA (nmol) per milligram of protein. AFB1 increased LPO in the liver, lung, brain and testis, but not the kidney. The increase of LPO caused by AFB1 injections was completely prevented by either Mel or NAc‐5HT in all the tissues examined. Melatonin can be considered as a protective pharmacological agent in intoxication with AFB1 and the protective effect of NAc‐5HT against aflatoxin‐induced LPO broadens the knowledge about its antioxidative properties. Copyright © 2007 John Wiley & Sons, Ltd.
The Role Played by the α‐Helix in the Unfolding Pathway and Stability of Azurin: Switching Between Hierarchic and Nonhierarchic Folding
Authors: Manetto Gaetano D. , Grasso Domenico M. , Milardi Danilo , Pappalardo Matteo , Guzzi Rita , Sportelli Luigi , Verbeet Martin P. , Canters Gerard W. , La Rosa Carmelo 
Published: September 2007

AbstractThe role played by the α‐helix in determining the structure, the stability and the unfolding mechanism of azurin was addressed by studying a helix‐depleted azurin variant produced by sitedirected mutagenesis. The protein structure was investigated by CD, 1D 1H NMR, fluorescence spectroscopy measurements and MD simulations, whilst EPR, UV‐visible and cyclic voltammetry experiments were carried out to investigate the geometry and the properties of the CuII site. The effects of the α‐helix depletion on the thermal stability and the unfolding pathway of the protein were determined by DSC, UV/visible and fluorescence measurements at increasing temperature. The results show that, in the absence of the α‐helix segment, the overall protein structure is maintained, and that only the Cu site is slightly modified. In contrast, the protein stability is diminished by about 60 % with respect to the wild‐type azurin. Moreover, the unfolding pathway of the mutant azurin involves the presence of detectable intermediates. In comparison with previous studies concerning other small β‐sheet cupredoxins, the results as a whole support the hypothesis that the presence of the α‐helix can switch the folding of azurin from a hierarchic to a nonhierarchic mechanism in which the highly conserved β‐sheet core provides a scaffold for cooperative folding of the wild‐type protein.
Biochemical Studies of the Thermal Effects on DNA Modifications by the Antitumor Cisplatin and Their Repair
Authors: Halamikova Anna , Vrana Oldrich , Kasparkova Jana , Brabec Viktor 
Published: September 2007

AbstractUsing biochemical methods, we have examined the effect of two factors that might play a role in the mechanism of the biological activity of cisplatin at elevated temperatures (>37°C). We show that increased temperatures result in distinct alterations in the modification of the target DNA by cisplatin, and in the repair of these modifications. Our in vitro results support the view that the enhanced DNA‐cross‐linking efficiency of cisplatin and the lower efficiency of native DNA repair mechanisms at higher temperature play at least a partial role in the potentiation of the antitumor effects of cisplatin under conditions of mild hyperthermia.
Synthesis and Characterization of the First Fluorescent Nonpeptide NPY Y1 Receptor Antagonist
Authors: Schneider Erich , Keller Max , Brennauer Albert , Hoefelschweiger Bianca K. , Gross Dietmar , Wolfbeis Otto S. , Bernhardt Günther , Buschauer Armin 
Published: September 2007

AbstractCyanine‐5‐labelled neuropeptide Y (NPY) was demonstrated to be an ideal universal fluorescent ligand for the combined investigation of NPY Y1, Y2 and Y5 receptors. With respect to improved stability, detection of receptor subtypes in cells and tissues, and prevention of receptor internalization, small nonpeptidic fluorescent antagonists should be superior. Here we present a set of four fluorescent nonpeptide NPY Y1 receptor (Y1R) antagonists. The highest affinity was obtained by labelling an NG‐(6‐aminohexanoyl)argininamide derived from the Y1R antagonist BIBP 3226, with Py‐1, a small pyrylium dye. The fluorescent pyridinium‐type Y1R antagonist, compound 4 had Ki values of 29 nM and 2.7 nM, which were determined by radioligand binding and flow cytometry under equilibrium conditions, respectively; 4 had a Kb value of 0.6 nM (Ca2+ assay). The large Stoke's shift (541 vs. 615 nm) in buffer (PBS, pH 7.4) in the presence of 1 % BSA and the red emission (quantum yield 56 %) are advantageous with respect to the signal‐to‐noise ratio. The new probe was successfully used in fluorescence‐based binding experiments evaluated by flow cytometry and confocal microscopy; this demonstrates the potential of pyrylium dyes for the preparation of fluorescent ligands that are applicable for the study of G protein‐coupled receptors on living cells.
On the Characterization of Dynamic Supramolecular Systems: A General Mathematical Association Model for Linear Supramolecular Copolymers and Application on a Complex Two‐Component Hydrogen‐Bonding System
Authors: Odille Fabrice G. J. , Jónsson Stefán , Stjernqvist Susann , Rydén Tobias , Wärnmark Kenneth 
Published: September 2007

AbstractA general mathematical model for the characterization of the dynamic (kinetically labile) association of supramolecular assemblies in solution is presented. It is an extension of the equal K (EK) model by the stringent use of linear algebra to allow for the simultaneous presence of an unlimited number of different units in the resulting assemblies. It allows for the analysis of highly complex dynamic equilibrium systems in solution, including both supramolecular homo‐ and copolymers without the recourse to extensive approximations, in a field in which other analytical methods are difficult. The derived mathematical methodology makes it possible to analyze dynamic systems such as supramolecular copolymers regarding for instance the degree of polymerization, the distribution of a given monomer in different copolymers as well as its position in an aggregate. It is to date the only general means to characterize weak supramolecular systems. The model was fitted to NMR dilution titration data by using the program Matlab®, and a detailed algorithm for the optimization of the different parameters has been developed. The methodology is applied to a case study, a hydrogen‐bonded supramolecular system, salen 4+porphyrin 5. The system is formally a two‐component system but in reality a three‐component system. This results in a complex dynamic system in which all monomers are associated to each other by hydrogen bonding with different association constants, resulting in homo‐ and copolymers 4n5m as well as cyclic structures 6 and 7, in addition to free 4 and 5. The system was analyzed by extensive NMR dilution titrations at variable temperatures. All chemical shifts observed at different temperatures were used in the fitting to obtain the ΔH° and ΔS° values producing the best global fit. From the derived general mathematical expressions, system 4+5 could be characterized with respect to above‐mentioned parameters.
Synthesis of Highly Modified DNA by a Combination of PCR with Alkyne‐Bearing Triphosphates and Click Chemistry
Authors: Gierlich Johannes , Gutsmiedl Katrin , Gramlich Philipp M. E. , Schmidt Alexandra , Burley Glenn A. , Carell Thomas 
Published: September 2007

AbstractWe report the combination of “click chemistry” with PCR by using alkyne‐modified triphosphates for efficient and homogeneous labeling of DNA. A series of modified PCR products of different lengths (300, 900, and 2000 base pairs) were prepared by using a variety of alkyne‐ and azide‐containing triphosphates and different polymerases. After intensive screening of real‐time PCR methods, protocols were developed that allow the amplification of genes by using these modified triphosphates with similar efficiency to that of standard PCR. The click reaction on the highly modified PCR fragments provided conversion rates above 90 % and resulted in the functionalization of hundreds of alkynes on large DNA fragments with superb selectivity and efficiency.
Configurational Stability of Oxymethyllithiums as Intermediates in Intramolecular Rearrangements
Authors: Kapeller Dagmar C. , Brecker Lothar , Hammerschmidt Friedrich 
Published: September 2007

AbstractSeveral homochiral oxymethyllithiums, chiral by virtue of the hydrogen isotopes protium and deuterium, were prepared. They were tested for their microscopic configurational stability in intramolecular isomerizations, such as the silyl‐ and germyl‐[1,2]‐retro‐Brook and the sigmatropic[2,3]‐Wittig rearrangement. The influence of temperature, solvent, and migrating group on the stability of the intermediate carbanions was studied. Furthermore, the stereochemical course of these rearrangements was elucidated, resulting in highly enantioenriched alcohols (90–97 % ee; ee=enantiomeric excess) up to temperatures of 0 °C.
Investigation of the Adsorption and Self Assembly of Isocyanide Derivatives on Au(111) Surface
Authors: Zhou Jun‐Hong , Shi Liang‐Wei , Zhang Tao , Chen Min‐Bo 
Published: September 2007

AbstractThe adsorption and self‐assembly of isocyanide derivatives on Au(111) surface were investigated by density functional theory (DFT) and molecular dynamics simulation. The calculation for phenyl isocyanide by DFT was based on cluster and slab models. The self‐assembled monolayers of 2‐isocyanoazulene and 1,3‐diethoxycarbonyl‐ 2‐isocyanoazulene on Au(111) were simulated using Au‐C force field parameters developed by us. It was found that the top site was the most preferred position, and the isocyanoazulene and its derivatives could form the ordered face to edge self‐assembled monolayer on gold surface indeed, and the molecules stood on the gold surface vertically.
Adsorption Behavior of Potassium Ion on Planting Materials
Authors: Paunpassanan Dechprasitthichokea , Sunanta Wangkarna , Sakdiphon Thiansemb , Ponlayuth Sooksamitic , Orn‐anong Arquero 
Published: September 2007

AbstractCharacterization of planting materials used as adsorbent has been studied in order to compare potassium ion adsorption on two types of planting materials, which are a fired planting material (FPM) made from a mixture of 4 kinds of wastes (bottom ash, flue gas desulfurization (FGD) gypsum, paddy soil and sawdust) formed and fired at 850 °C and the commercial planting material called "hydroball" (HDB) bought from Jatujak market, Bangkok. The physical characteristics of both types of planting materials indicate that the FPM has a larger specific surface area than the HDB. The factors affecting potassium adsorption on both the planting materials such as an equilibration time and some solid/solution ratios were investigated. The suitable equilibration time for the adsorption to reach an equilibrium on the FPM and HDB is one and two hours, respectively. The highest amounts of potassium ion adsorbed on both the planting materials were obtained when the solid/solution ratio was 1:15. The adsorption behavior on both the planting materials tends to correspond with the Freundlich isotherm.
Study on the Interaction of Colloidal Gold with Taq DNA Polymerase
Authors: Zhu Hong‐Ping , Mi Li‐Juan , Chen Shi‐Mou , Wang Wen‐Feng , Yao Si‐Dea 
Published: September 2007

Abstract The interaction of colloidal gold with Taq DNA polymerase (Taq) was investigated in this study. Taq‐gold conjugate was formed by adding the enzyme to the colloidal gold solution, as evidenced by UV‐Vis spectroscopy, X‐ray photoelectron spectroscopy, and photon cross correlation spectroscopy measurements. The conjugate was further characterized by transmission electron microscopy. It was found that the Taq‐gold conjugate particles were still spherical and well‐dispersed. The influence of gold nanoparticles on the bioactivity of Taq was studied by analyzing the yield of the polymerase chain reaction amplification. Results indicated that the enzymatic activity of Taq decreased after interaction with the colloidal gold.
Photovoltaic Characteristics of a Naphthylamine Derivative
Authors: Fu Hui‐Ying , Song Qun‐Liang , Sun Xiao‐Yu , Hou Xiao‐Yuan , Xiao Fei , Shao Bing‐Xian 
Published: September 2007

AbstractOrganic photovoltaic (OPV) cells were fabricated via vacuum vapor deposition with {4‐[2‐(3‐dicyanomethylidene‐5,5‐dimethylcyclohexenyl)vinyl]phenyl}di(1‐naphthyl)amine (DNP‐2CN) as the electron donor, and fullerene (C60) as the electron acceptor. A thin film (10 nm) of tris(8‐quinolinolato)aluminum (Alq3) was adopted as the buffer layer. A device based on this DNP‐2CN exhibited an open circuit voltage (Voc) of 370 mV, a short‐circuit current density (Jsc) of 0.61 mA·cm−2, and a white‐light power conversion efficiency (() of 0.09% (AM1.5, 75 mW·cm−2).
Comparative Study of Hypophosphite H2PO−2Adsorption on Ni(111) and Ag(111) Surfaces by DFT
Authors: Zeng Yue , Ou Li‐Hui , Li Ze‐Lin , Xiao Xiao‐Ming , Xia Shao‐Xi 
Published: September 2007

AbstractSurface structures and electronic properties of hypophosphiteon Ni(111) and Ag(111) surfaces were investigated by means of density functional theory at B3LYP/6‐31++G(d,p) level. The most stable structure was that in which theadsorbs with its two P–O bonds faced to the substrate surface. The results of the Mulliken population analysis showed that because of the subtle difference of electron configuration, the adsorption energy was larger on the Ni surface than on the Ag surface, and the amounts of both donation and back donation were larger on the Ni(111) surface than on the Ag(111) surface. There were more negative Mulliken charge transfer from H2PO−2to substrate clusters on Ni surface than on Ag surface and more positive Mulliken charges on P atom in Ni4H2PO−2than in Ag4H2PO−2, which means that P atom in Ni4H2PO−2is easily attacked by a nucleophile such as OH−. Thus, H2PO−2is more easily oxidated on Ni(111) surface than on Ag(111) suface. These results indicated that the silver surface is inactive for the oxidation reaction of the hypophosphite anion.
Spectrofluorimetric Study on the Weak Interaction between ATP and Nα‐4‐Tosyl‐L‐arginine Methyl Ester Hydrochloride
Authors: Ma Yan‐Qing , LÜ Gong‐Xuan , Li Ying , Liu Shu‐Hua , Xian Liang 
Published: September 2007

AbstractIn this paper, some new results on the selective weak interaction between Nα‐4‐tosyl‐L‐arginine methyl ester hydrochloride (TAME) and adenosine‐5′‐triphosphate (ATP) have been reported. Fluorescence spectrophotometry and Fourier transform infrared (FT‐IR) spectroscopy were used to investigate this kind of weak interaction. In fluorescence experiments, obvious fluorescence quenching phenomena were observed when TAME was added, which indicated the weak interactions between TAME and ATP. It has been identified by fluorescence titration experiments that TAME exhibited high selectivity to ATP over ADP and AMP. FT‐IR spectral results showed that an ATP‐TAME adduct was formed. The experimental results indicated that the interaction sites were the guanidinium group of TAME main‐chain and the γ‐phosphate group of ATP, and the interaction took place through hydrogen bonding and electrostatic force. In addition, the effects of metal ions on the weak interaction between ATP and TAME, or between ATP and analogues of L‐arginine were studied.
Ionic Conduction in Ba0.95Ce0.8Ho0.2O3−α
Authors: Wang Mao‐Yuan , Qiu Li‐Gan , Ma Gui‐Lin 
Published: September 2007

AbstractBa0.95Ce0.8Ho0.2O3−α was prepared by high temperature solid‐state reaction. X‐ray diffraction (XRD) pattern showed that the material was of a single perovskite‐type orthorhombic phase. Using the material as solid electrolyte and porous platinum as electrodes, the measurements of ionic transport number and conductivity of Ba0.95Ce0.8Ho0.2O3−α were performed by gas concentration cell and ac impedance spectroscopy methods in the temperature range of 600–1000 °C in wet hydrogen, dry and wet air respectively. Ionic conduction of the material was investigated and compared with that of BaCe0.8Ho0.2O3−α. The results indicated that Ba0.95Ce0.8Ho0.2O3−α was a pure protonic conductor with the protonic transport number of 1 during 600–700 °C in wet hydrogen, a mixed conductor of protons and electrons with the protonic transport number of 0.97–0.93 in 800–1000 °C. But BaCe0.8Ho0.2O3−α was almost a pure protonic conductor with the protonic transport number of 1 in 600–900 °C and 0.99 at 1000 °C in wet hydrogen. In dry air and in the temperature range of 600–1000 °C, they were both mixed conductors of oxide ions and electronic holes, and the oxide‐ionic transport numbers were 0.24–0.33 and 0.17–0.30 respectively. In wet air and in the temperature range of 600–1000 °C, they were both mixed conductors of protons, oxide ions and electronic holes, the protonic transport numbers were 0.11–0.00 and 0.09–0.01 respectively, and the oxide‐ionic transport numbers were 0.41–0.33 and 0.27–0.30 respectively. Protonic conductivity of Ba0.95Ce0.8Ho0.2O3−α in both wet hydrogen and wet air was higher than that of BaCe0.8Ho0.2O3−α in 600–800 °C, but lower in 900–1000 °C. Oxide‐ionic conductivity of the material was higher than that of BaCe0.8Ho0.2O3−α in both dry air and wet air in 600–1000 °C.
Determination of Tetracyclines in Honey Using Liquid Chromatography with Ultraviolet Absorbance Detection and Residue Confirmation by Mass Spectrometry
Authors: Liu Yan , Xu Jin‐Zhong , Ding Tao , Li Gong‐Hai 
Published: September 2007

AbstractA determination method has been optimized and validated for the simultaneous analysis of tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC) in honey. Tetracyclines (TCs) were removed from honey samples by chelation with metal ions bound to small Chelating Sepharose Fast Flow columns and eluted with Na2EDTA‐Mcllvaine pH 4.0 buffers. Extracts were further cleaned up by Oasis HLB solid‐phase extraction (SPE), while other solid‐phase extraction cartridges were compared. Chromatographic separation was achieved using a polar end‐capped C18 column with an isocratic mobile phase consisting of oxalic acid, acetonitrile, and methanol. LC with ultraviolet absorbance at 355 nm resulted in the quantitation of all four tetracycline residues from honey samples fortified at 15, 50, and 100 ng/g, with liner ranges for tetracyclines of 0.05 to 2 µg/mL. Mean recoveries for tetracyclines were greater than 50% with R.S.D. values less than 10% (n=18). Detection limits of 5, 5, 10, 10 ng/g for oxytetracycline, tetracycline, chlortetracycline and doxycycline, respectively and quantitation limits of 15 ng/g for all the four tetracyclines were determined. Direct confirmation of the four residues in honey(2–50 ng/g) was realized by liquid chromatography‐tandem mass spectrometry (LC/MS/MS). The linear ranges of tetracyclines determined by LC/MS/MS were between 5 to 300 ng/mL, with the linear correlation coefficient r>0.995. The limits of detection of 1 to 2 ng/g were obtained for the analysis of the TCs in honey.
Synthesis of a 1,2,7,8‐Tetraoxa‐spiro[5.5]undecane
Authors: Zhang Qi , Li Yun , Wu Yi‐Kang 
Published: September 2007

AbstractSynthesis of a new spiro organic peroxide is described. The peroxy bonds were incorporated into the substrate framework via an acid‐catalyzed ketal exchange reaction using hydrogen peroxide as the source of peroxy linkage. The hydroperoxyl groups were then bonded at the OH ends via Hg(II)‐induced electrophilic additions to the C‐C double bonds, giving a novel sprio structure with one peroxy bond in each of the two six‐membered rings. The ester functionalities in the side chains also make it possible to conduct further structural modifications.
Three‐Component Barbier Allylation‐Friedel‐Crafts Alkylation Promoted by BuPyCl/SnCl2·2H2O: Application to the Synthesis of 4‐(Substituted phenyl)chromans
Authors: Zhao Xian‐Liang , Liu Li , Chen Yong‐Jun , Wang Dong 
Published: September 2007

AbstractBarbier allylation and Friedel‐Crafts alkylation of (un)substituted benzaldehydes, allylbromide and phenols can be combined in a one‐pot process in ionic liquid (BuPyCl/SnCl2·2H2O) to directly synthesize 4‐(2‐hydroxyphenyl)‐ 4‐[(un)substituted phenyl]but‐1‐ene compounds, which were applied to the synthesis of 4‐(substituted phenyl)chromans through intramolecular cyclization reactions.
Inhibition of Homo‐coupling of Arylboronic Acids in Ligand Free Pd(II)‐Catalyzed Suzuki Reaction
Authors: Tao Xiao‐Chun , Zhang Yue‐Ping , He Tian‐Xiong , Shen Dong 
Published: September 2007

AbstractA series of solvents were examined for the ligand free Pd(II)‐catalyzed Suzuki reaction of 4‐bromotoluene with phenylboronic acid. It was found that the PdCl2/i‐PrOH system could efficiently inhibit the homo‐coupling of phenylboronic acid and give a cross‐coupling product in high yields. The substrates with a wide variety of functional groups were tolerated in the system. A possible mechanism for this system was proposed.
Synthesis and Luminescence Property of 4,4′‐Bis(2,2‐di(4‐fluorophenyl)vinyl)biphenyl for Organic Blue‐Light‐Emitting Diodes
Authors: Chai Sheng‐Yong , Bie Guo‐Jun , Li Tian‐Le , Li Wen‐Lian , Chen Zhi‐Qun , Liu Bo 
Published: September 2007

AbstractThe novel fluorinated distyrylarylene, 4,4′‐bis(2,2‐di(4‐fluorophenyl)vinyl)biphenyl (DFPVBi), was synthesized and fully characterized. The structure was confirmed with IR, 1H NMR, 13C NMR, 19F NMR and MS analyses. Its electronic and photoluminescence properties were investigated by UV‐Vis absorption, cyclic voltammetry and fluorescence spectroscopy. The energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are −5.77 and −2.75 eV, respectively. The electroluminescence properties of the organic light‐emitting diode fabricated by DFPVBi were also studied. The device exhibits a pure blue emission peaked at 454 nm, which indicates a maximum luminance of 5872 cd/m2 at 14.2 V and a maximum current efficiency of 2.82 cd/A at 10V, respectively.
Measurement and Correlation of the Ionic Conductivity of Ionic Liquid‐Molecular Solvent Solutions
Authors: Li Wen‐Jing , Han Bu‐Xing , Tao Ran‐Ting , Zhang Zhao‐Fu , Zhang Jian‐Ling 
Published: September 2007

AbstractThe ionic conductivity of the solutions formed from 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF4]) or 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim][PF6]) and different molecular solvents (MSs) were measured at 298.15 K. The molar conductivity of the ionic liquids (ILs) increased dramatically with increasing concentration of the MSs. It was found that the molar conductivity of the IL in the solutions studied in this work could be well correlated by the molar conductivity of the neat ILs and the dielectric constant and molar volume of the MSs.