bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coupling of ionic liquid‐based headspace single‐drop microextraction with GC for sensitive detection of phenols
Authors: Zhao Fa‐Qiong , Li Jing , Zeng Bai‐Zhao 
Published: August 2008

AbstractA headspace single‐drop microextraction (SDME) based on ionic liquid (IL) has been developed for the gas chromatographic determination of phenols. The volume of IL microdrop used was 1 μL. After extraction, the analytes were desorbed from the drop in the injection port and the involatile IL was withdrawn into the microsyringe. To facilitate the withdrawal of IL the upper diameter of the split inlet liner was enlarged to some extent. Some parameters were optimized for the determination of phenols. Under the selected conditions, i.e., desorption for 100 s at 210°C after extraction for 25 min at 50°C in solutions (pH 3) containing 0.36 g/mL sodium chloride, the LODs, RSDs, and the average enrichment factors of phenols were 0.1–0.4 ng/mL, 3.6–9.5% (n = 5), and 35–794, respectively. The proposed procedure was applied to the determination of phenols in lake water and wastewater samples, and the spiked recoveries were in the range of 81–111% at a spiked level of 0.4 μg/mL. This method is a promising alternative for the sensitive determination of phenolic compounds.
Enantioselective determination of chloroquine and its n‐dealkylated metabolites in plasma using liquid‐phase microextraction and LC‐MS
Authors: dos Santos Magalhães Igor Rafael , Sueli Bonato Pierina 
Published: August 2008

AbstractA selective method using three‐phase liquid‐phase microextraction (LPME) in conjunction with LC‐MS‐MS was devised for the enantioselective determination of chloroquine and its n‐dealkylated metabolites in plasma samples. After alkalinization of the samples, the analytes were extracted into n‐octanol immobilized in the pores of a polypropylene hollow fiber membrane and back extracted into the acidic acceptor phase (0.1 M TFA) filled into the lumen of the hollow fiber. Following LPME, the analytes were resolved on a Chirobiotic V column using methanol/ACN/glacial acetic acid/diethylamine (90:10:0.5:0.5 by volume) as the mobile phase. The MS detection was carried out using multiple reaction monitoring with ESI in the positive ion mode. The optimized LPME method yielded extraction recoveries ranging from 28 to 66%. The method was linear over 5–500 ng/mL and precision (RSD) and accuracy (relative error) values were below 15% for all analytes. The developed method was applied to the determination of the analytes in rat plasma samples after oral administration of the racemic drug.
In situ localisation and quantification of surfactins in a Bacillus subtilis swarming community by imaging mass spectrometry
Authors: Debois Delphine , Hamze Kassem , Guérineau Vincent , Le Caër Jean‐Pierre , Holland I. Barry , Lopes Philippe , Ouazzani Jamal , Séror Simone J. , Brunelle Alain , Laprévote Olivier 
Published: August 2008

AbstractSurfactins are a family of heptacyclopeptides in which the C‐terminal carbonyl is linked with the β‐hydroxy group of a fatty acid acylating the N‐terminal function of a glutamic acid residue. The fatty acyl chain is 12–16 carbon atoms long. These compounds, which are secreted by the Gram‐positive bacterium Bacillus subtilis in stationary phase in liquid cultures, play an important role in swarming communities on the surface of agar media in the formation of dendritic patterns. TOF secondary ion MS (TOF‐SIMS) imaging was used to map surfactins within 16–17 h swarming patterns, with a 2 μm spatial resolution. Surfactins were mainly located in the central mother colony (the site of initial inoculation), in a ‘ring’ surrounding the pattern and along the edges of the dendrites. In the mother colony and the interior of the dendrites, surfactins with shorter chain lengths are present, whereas in the ring surrounding the swarm community and between dendrites, surfactins with longer fatty acyl chain lengths were found. A quantitative analysis by MALDI‐TOF MS showed a concentration gradient of surfactin from the mother colony to the periphery. The concentration of surfactin was ∼400 pmol/mL in the mother colony and ∼10 pmol/mL at the base of the dendrites, decreasing to 2 pmol/mL at their tips.
Synthesis, characterization, and properties of copolymer of acrylamide and complex pseudorotaxane monomer consisting of cucurbit[6]uril with butyl ammonium methacrylate
Authors: Huang Xiaoling , Tan Yebang , Wang Yuexia , Yang Hui , Cao Jie , Che Yuju 
Published: August 2008

AbstractThe novel copolymers of acrylamide (AM) with complex pseudorotaxane monomer (BAMACB) of butyl ammonium methacrylate (BAMA) and cucurbit[6]uril (CB[6]) were prepared via free‐radical polymerization in aqueous solution. The copolymers containing pseudorotaxane (PAM/BAMACB) were characterized by 1H‐NMR, FTIR, elemental analysis, TGA, and DSC. The glass transition temperature (Tg) of the copolymer PAM/BAMACB are higher than that of the copolymer of acrylamide and butyl ammonium methacrylate (PAM/BAMA) because of the enhanced rigidity and the bulky steric hindrance of BAMACB side chain in PAM/BAMACB. The molecular weights of copolymer PAM/BAMACB were obtained via static light scattering. The hydrodynamic radii of coils or aggregates were investigated by dynamic light scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5999–6008, 2008
Manganese(III) acetate‐catalyzed synthesis of polyguaiacol
Authors: Hwang Sangpill , Lee Yong‐Woo , Lee Chang‐Ha , Ahn Ik‐Sung 
Published: August 2008

AbstractPolyguaiacol was synthesized in the mixtures of water and various organic solvents using manganese(III) acetate as a new catalyst for radical polymerization and a biomimetic model for manganese peroxidase. Aqueous solutions of 30–70% (v/v) acetonitrile, 1,4‐dioxane, and methanol were used as model solvent mixtures. The polymer yield in the methanol (<30%) solution was lower than that in the acetonitrile or 1,4‐dioxane solution (60–90%). The average molecular weight of the polymer was also lowest in the methanol solution. Difference UV absorption spectroscopy analysis revealed that nonhydrated guaiacol clusters were found to be dominant in acetonitrile and 1,4‐dioxane solutions, especially when the content of 1,4‐dioxane was 50% (v/v) or higher. In the methanol solution, only the hydrated guaiacol clusters were observed. From the comparison of 1H NMR data for polyguaiacol and products of guaiacol oxidation by manganese(III) acetate, 3‐(4‐hydroxy‐3‐methoxy‐phenyl)‐5,3′‐dimethoxy‐4,4′‐biphenol and a mixture of 5‐(4‐hydroxy‐3‐methoxyphenyl)‐3,3′‐dimethoxy‐4,4′‐biphenoquinone and 3‐(4‐hydroxy‐3‐methoxyphenyl)‐5,3′‐dimethoxy‐4,4′‐biphenoquinone were found to be the major structural units of polyguaiacol. Water molecule is not involved in the formation of these compounds. Therefore, the polymerization should take place readily not in methanol but in acetonitrile and 1,4‐dioxane solutions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6009–6015, 2008
Branched polystyrene with abundant pendant vinyl functional groups from asymmetric divinyl monomer
Authors: Dong Zhong‐Min , Liu Xiao‐Hui , Lin Ying , Li Yue‐Sheng 
Published: August 2008

AbstractBranched polystyrenes with abundant pendant vinyl functional groups were prepared via radical polymerization of an asymmetric divinyl monomer, which possesses a higher reactive styryl and a lower reactive butenyl. Employing a fast reversible addition fragmentation chain transfer (RAFT) equilibrium, the concentration of active propagation chains remained at a low value and thus crosslinking did not occur until a high level of monomer conversion. The combination of a higher reaction temperature (120 °C) and RAFT agent cumyl dithiobenzoate was demonstrated to be optimal for providing both a more highly branched architecture and a higher polymer yield. The molecular weights (Mws) increased with monomer conversions because of the controlled radical polymerization characteristic, whereas the Mw distributions broadened showing a result of the gradual increase of the degree of branching. The evolution of branched structure has been confirmed by a triple detection size exclusion chromatography (TRI‐SEC) and NMR technique. Furthermore, the double bonds in the side chains were successfully used for chemical modification reactions. 1H NMR and FTIR measurements reveal that the great mass of pendant vinyl groups were converted to the corresponding objective end‐groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6023–6034, 2008
Nylon 610/functionalized multiwalled carbon nanotube composite prepared from in‐situ interfacial polymerization
Authors: Jeong Jae‐Yong , Lee Hwa‐Jeong , Kang Sang‐Wook , Tan Loon‐Seng , Baek Jong‐Beom 
Published: August 2008

AbstractPristine multiwalled carbon nanotubes (P‐MWNTs) were functionalized with 4‐chlorobenzoic acid via “direct” Friedel‐Crafts acylation in polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5) medium. The resultant 4‐chlorobenzoyl‐functionalized MWNTs (F‐MWNTs) were soluble in chlorinated solvents such as dichloromethane, chloroform, and carbon tetrachloride. A large scale of nylon 610/F‐MWNT composite could be conveniently prepared by in situ interfacial polymerization of 1, 6‐hexamethylenediamine (HMDA) in an aqueous phase, and sebacoyl chloride with F‐MWNTs in an organic phase. Similarly, nylon 610/P‐MWNT composite was also prepared for comparison. The state of F‐MWNTs dispersion in nylon 610 matrix was distinctively better than that of P‐MWNTs, which could be clearly discerned by both naked eye and scanning electron microcopy (SEM). As a result, the tensile strength of nylon 610/F‐MWNT composite was 4.9‐fold higher than that of nylon 610/P‐MWNT composite. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6041–6050, 2008
Copolymerization behavior of titanium imidazolin‐2‐iminato complexes
Authors: Stelzig Simon H. , Tamm Matthias , Waymouth Robert M. 
Published: August 2008

AbstractMonocyclopentadienyl titanium imidazolin‐2‐iminato complexes [Cp′Ti(L)X2] 1a (Cp′ = cyclopentadienyl, L = 1,3‐di‐tert‐butylimidazolin‐2‐imide, X = Cl), 1b (X = CH3); 2 (Cp′ = cyclopentadienyl, L = 1,3‐diisopropylimidazolin‐2‐imide, X = Cl); 3 (Cp′ = tert‐butylcyclopentadienyl, L = 1,3‐di‐tert‐butylimidazolin‐2‐imide, X = Cl), upon activation with methylaluminoxane (MAO) were active for the polymerization of ethylene and propylene and the copolymerization of ethylene and 1‐hexene. Catalysts derived from imidazolin‐2‐iminato tropidinyl titanium complex 4 = [(Trop)Ti(L)Cl2] (Trop = tropidinyl, L = 1,3‐di‐tert‐butylimidazolin‐2‐imide) were much less active. Narrow polydispersities were observed for ethylene and propylene polymerization, but the copolymerization of ethylene/hexene led to bimodal molecular weight distributions. The productivity of catalysts derived from the dialkyl complex 1b activated with [Ph3C][B(C6F5)4] or B(C6F5)3 were less active for ethylene/hexene copolymerization but yielded ethylene/hexene copolymers of narrower molecular weight distributions than those derived from 1a/MAO. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6064–6070, 2008
Molecularly defined (L)‐lactic acid oligomers and polymers: Synthesis and characterization
Authors: Takizawa Kenichi , Nulwala Hunaid , Hu Jerry , Yoshinaga Kohji , Hawker Craig J. 
Published: August 2008

AbstractThe synthesis of (L)‐lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t‐butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3‐dicyclohexylcarbodiimide or 1‐[3‐(dimethylamino)propyl]‐3‐ethylcarbodiimide hydrochloride were high (70–100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X‐ray scattering demonstrated a close correlation between the molecular structure of the well‐defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977–5990, 2008
New approach to fabricate an extremely super‐amphiphobic surface based on fluorinated silica nanoparticles
Authors: Sheen Yuung‐Ching , Huang Yuan‐Chang , Liao Chun‐Syong , Chou Hisn‐Yi , Chang Feng‐Chih 
Published: August 2008

AbstractSuperoleophobic surfaces possessing static contact angles greater than 140° with organic liquids are extremely rare. A simple approach has been developed to fabricate an extremely superamphiphobic coating material based on fluorinated silica nanoparticles resulting contact angles of water and diiodomethane at 167.5° and 158.6°, respectively. The contact angle of diiodomethane at 158.6° is substantially higher than the highest literature reported value we know of at 110°. In addition, this developed film also possesses extremely high contact angles with other organic liquids such as soybean oil (146.6°), decahysronaphthalene (142.5°), diesel fuel (140.4°), and xylene (140.5°). This developed superamphiphobic organic–inorganic hybrid film possesses unique liquid repellency for both water and organic liquids that can be used as functional coatings on numerous substrates by a simple coating process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1984–1990, 2008
Ionoluminescence characterization of microwave and hot‐filament CVD diamonds
Authors: Calvo del Castillo H. , Ruvalcaba J. L. , Belmont E. , Calderón T. , Meléndrez R. , Barboza‐Flores M. 
Published: August 2008

AbstractThe ionoluminescence (IL) spectrum resulting through the interaction of proton beams with bulk samples has become an adequate technique for material characterization. In the present work, we have investigated the IL response of microwave (MW) and hot‐filament (HF) CVD diamonds, by examining the radiative recombination induced by a 1.9 MeV proton beam (0.25–3.0 μA) on the diamond films. The IL spectral characteristics were different for dissimilar diamond films. The HFCVD diamond showed two broad IL bands around 300–450 nm and/or 500–750 nm. The bands may be associated to intrinsic defects and to [N–V] and [N–V–N] centers. In some cases the H3‐center band around 503 nm (2.46 eV) was also clearly depicted. The HFCVD diamond displayed mainly a well‐defined dislocation‐related A band centered at 440 nm (2.82 eV). The results indicated that the IL technique is a practical tool to obtain spectral information about defects and centers in CVD diamonds. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrogen in nano‐diamond films: experimental and computational studies
Authors: Michaelson Sh. , Akhvlediani R. , Hoffman A. , Silverman A. , Adler J. 
Published: August 2008

AbstractWe present studies related to the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament (HF), micro wave (MW) and direct current glow discharge (dc GD) chemical vapor deposition. The size of the diamond grains which constitute the films varies in the following way: hundreds of nm in the case of HF CVD (“sub‐micron size”, ∼300 nm), tens of nm in the case of MW CVD (3–30 nm) and a few nm in the case of dc GD CVD (“ultra nano‐crystalline diamond”, ∼5 nm). Secondary ion mass spectroscopy (SIMS) and high resolution electron energy loss spectroscopy (HR‐EELS) were applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating that most likely hydrogen is bonded and trapped in grain boundaries as well as on the internal grain surfaces. HR‐EELS analysis shows that at least part of this hydrogen is bonded to sp2‐ and sp3‐hybridized carbon, thus giving rise to typical C–H vibration modes. The vibrational spectroscopies show the increase of sp2 C–H modes in transition from sub‐micron to ultra nano‐crystalline grain size. These conclusions are supported by preliminary results of computer simulations which show that hydrogen atoms at the boundary between a nano‐diamond particle and an amorphous shell have lower energy than hydrogen atoms within either the nano‐diamond or the amorphous region. These results suggest that hydrogen is expected to be localized at the nano‐diamond/amorphous carbon interface as experimentally found. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The isoflavones mixture from Trifolium pratense L. protects HCN 1‐A neurons from oxidative stress
Authors: Occhiuto Francesco , Palumbo Dora Rita , Samperi Stefania , Zangla Giuseppe , Pino Annalisa , Pasquale Rita De , Circosta Clara 
Published: August 2008

AbstractOxidative stress‐induced neuronal cell death has been implicated in different neurological disorders and neurodegenerative diseases such as Alzheimer's disease and Parkinson's. Using the Alzheimer's disease‐associated hydrogen peroxide (H2O2), we investigated the neuroprotective efficacy of a natural mixture of phytoestrogenic isoflavones (genistein, daidzein, biochanin A and formononetin) from Trifolium pratense L. (Red clover) against oxidative stress‐induced cell death in human cortical cell line HCN 1‐A maintained in culture. Neuronal viability was determined by MTT or trypan blue test and neuronal integrity by morphological analysis.The results obtained indicate that exposure of HCN 1‐A cell cultures to hydrogen peroxide resulted in a concentration‐dependent decrease in neuron viability. Concentration of H2O2 ranging from 50 to 200 µg/ml were toxic to these cultures. A 24‐hour pretreatment with 0.5, 1 and 2 µg/ml isoflavones extract significantly increased cell survival as evidenced by MTT or trypan blue test and significantly prevented the morphological disruption caused by H2O2 as shown by microscopical inspection, indicating that neurons treated with isoflavones were protected from the cell death induced by H2O2 exposure. These findings imply that the neuroprotective effect of isoflavones extract is partly associated with its antioxidant activity. Further, results of these investigations indicate that although isoflavones extract exert a neuroprotective effect, it do not promoted cortical neuron process outgrowth. Copyright © 2008 John Wiley & Sons, Ltd.
Theoretical study on the reactive sites and intramolecular interactions in taxol and its four analogues
Authors: Zhou Hongwei , Zhang Zhiqiang , Cheung Hon‐Yeung 
Published: August 2008

AbstractA density‐functional study of the paclitaxel (Taxol) molecule and its four analogues has been performed. The theory of Bader's atoms in molecules (AIM) was applied to examine the electronic structure of these molecules at their ground state. Topological analysis reveals that the esterification of hydroxyl group attached to the oxetane ring results in great change of conformation of the taxane ring, and thus is responsible for bioactivity of the oxetane oxygen atom. It was found that there exists some intramolecular interactions in the molecule, including normal hydrogen bonds (HBs) and double HBs. Visualization of the molecule shows that the central bodies (the four fused rings) of the molecules are wrapped by the intramolecular interactions. It is supposed that these intramolecular interactions lower the aqueous solubility and protect the flexible oxetane ring, which is regarded as the dominating bioactivity site of the drug, from being opened. Our results provide an extended and consistent set of data to gauge classical force fields in view of the atomistic investigations of the interaction of the bioactive molecules. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Use of noninteger n‐Slater type orbitals in combined Hartree–Fock–Roothaan theory for calculation of isoelectronic series of atoms Be to Ne
Authors: Guseinov I. I. , Ertürk M. 
Published: August 2008

AbstractThe ground state calculations in the combined Hartree–Fock–Roothaan approach are performed for the neutral and the first 20 cationic members of the isoelectronic series of atoms from Be to Ne using noninteger n‐Slater type orbitals. For the total energies obtained, only a small deviation has been found. At the same time, the size of the present noninteger n‐Slater type orbitals is smaller than that of the usual extended integer n‐Slater functions in literature. All of the nonlinear parameters are fully optimized. The relationship between optimized parameters and atomic number Z is also investigated. For each atom, the total energies are given in tables. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Does Møller–Plesset perturbation theory converge? A look at two‐electron systems
Authors: Herman Mark S. , Hagedorn George A. 
Published: August 2008

AbstractWe study the convergence or divergence of the Møller–Plesset Perturbation series for systems with two electrons and a single nucleus of charge Z > 0. This question is essentially to determine if the radius of convergence of a power series in the complex perturbation parameter λ is greater than 1. The power series is centered at λ = 0, so we try to find whether or not the singularity closest to λ = 0 is inside the closed unit disk in the complex plane. We give a description of possible causes for divergence in the general problem and then examine two Helium‐like models. The first model is a simple one‐dimensional model with delta functions in place of Coulomb potentials. The second is the realistic three‐dimensional model. For each model, we show rigorously that if the nuclear charge Z is sufficiently large, there are no singularities for real values of λ between −1 and 1. Using a finite difference scheme, we present numerical results for the delta function model. The numerics are consistent with proven results and also suggest that the closest singularity occurs where λ is real and negative. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Theoretical electronic structure of the molecule ScI
Authors: Korek M. , Kontar S. , Taher‐Mansour F. , Allouche A. R. 
Published: August 2008

AbstractTheoretical investigation of the 18 lowest electronic states of the molecule ScI in the representation 2S+1Λ(±) has been performed via CASSCF and MRCI (single and double excitation with Davidson correction) calculations. To the best of our knowledge these calculated electronic states are the first ones from ab initio methods. Thirteen electronic states between 4,500 cm−1 and 21,000 cm−1 have been studied for the first time and have not yet been observed experimentally. The harmonic frequency ωe, the internuclear distance Re, the electronic transition energy with respect to the ground state Te, and the rotational constant Be have been calculated for the considered electronic states. By using the canonical functions approach the eigenvalues Eυ and the rotational constants Bυ have also been calculated for the six lowest‐lying electronic states. The comparison of these results with the theoretical and the experimental data available in the literature shows a good agreement. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Transfer of electron density as a result of hydrogen bond formation
Authors: Sadlej‐Sosnowska Nina 
Published: August 2008

AbstractIt has been found that the amount of charge transfer between donor and acceptor molecules in four sets of hydrogen‐bonded complexes may be adequately described as an exponential function of the equilibrium distance between the hydrogen atom and the nearest atom of the acceptor molecule. The exponential factors of the transfer are of the same order but somewhat larger than the factors found otherwise in the investigations of dynamic electron transfer. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009