bluuebunny/crossref_metadata_2025_split huggingface dataset:
Understanding the Plasticity of the α/β Hydrolase Fold: Lid Swapping on the Candida antarctica Lipase B Results in Chimeras with Interesting Biocatalytic Properties
Authors: Skjøt Michael , De Maria Leonardo , Chatterjee Robin , Svendsen Allan , Patkar Shamkant A. , Østergaard Peter R. , Brask Jesper 
Published: January 2009

AbstractThe best of both worlds. Long molecular dynamics (MD) simulations of Candida antarctica lipase B (CALB) confirmed the function of helix α5 as a lid structure. Replacement of the helix with corresponding lid regions from CALB homologues from Neurospora crassa and Gibberella zeae resulted in new CALB chimeras with novel biocatalytic properties. The figure shows a snapshot from the MD simulation.magnified imageThe Candida antarctica lipase B (CALB) has found very extensive use in biocatalysis reactions. Long molecular dynamics simulations of CALB in explicit aqueous solvent confirmed the high mobility of the regions lining the channel that leads into the active site, in particular, of helices α5 and α10. The simulation also confirmed the function of helix α5 as a lid of the lipase. Replacing it with corresponding lid regions from the CALB homologues from Neurospora crassa and Gibberella zeae resulted in two new CALB mutants. Characterization of these revealed several interesting properties, including increased hydrolytic activity on simple esters, specifically substrates with Cα branching on the carboxylic side, and much increased enantioselectivity in hydrolysis of racemic ethyl 2‐phenylpropanoate (E>50), which is a common structure of the profen drug family.
Synthesis, Characterization, Cytotoxicity, and Hydrolytic Behavior of C2‐ and C1‐Symmetrical TiIV Complexes of Tetradentate Diamine Bis(Phenolato) Ligands: A New Class of Antitumor Agents
Authors: Peri Dani , Meker Sigalit , Shavit Michal , Tshuva Edit Y. 
Published: January 2009

AbstractCarefully design your ligand! A new family of highly cytotoxic TiIV complexes demonstrates strong dependence of activity on the particular ligand employed, in which small structural modifications dramatically affect both hydrolytic behavior and biological activity (see picture). Different structure‐dependence patterns are observed for hydrolysis and cytotoxicity, which are, nonetheless, strongly related.magnified imageWe recently introduced a new class of bis(isopropoxo)–TiIV complexes with diamine bis(phenolato) ligands that possess antitumor activity against colon HT‐29 and ovarian OVCAR‐1 cells that is higher than that of the known TiIV compounds titanocene dichloride and budotitane as well as that of cisplatin. Herein, we elaborate on this family of compounds; we discuss the effect of structural parameters on the cytotoxic activity and hydrolytic behavior of these complexes, seeking a relationship between the two. Whereas complexes with small steric groups around the metal center possess high activity and lead mostly to formation of O‐bridged polynuclear complexes with bound bis(phenolato) ligand upon water addition, bulky complexes hydrolyze to release all free ligands and are inactive. Slightly increasing the size of the N‐donor substituents probably weakens the ligand binding in solution, and, thus, rapid hydrolysis is observed, leading to a lack of cytotoxicity, supporting the requirement for ligand inertness. Replacing the two isopropoxo ligands with a single catecholato unit gives a complex with a different geometry that exhibits slower hydrolysis and reduced cytotoxicity, suggesting some participation of labile ligand hydrolysis in the cytotoxicity mechanism. A crystallographically characterized O‐bridged polynuclear species obtained from a biologically active bis(isopropoxo) complex upon water addition is inactive, which rules out its participation as the active species, yet suggests some role of the particular steric and electronic requirements allowing its formation in the activity mechanism. Additional measurements support rapid formation of the active species in the presence of cells prior to O‐bridged TiIV cluster formation.
Enzymatic Esterification in Aqueous Miniemulsions
Authors: Aschenbrenner Eugen M. , Weiss Clemens K. , Landfester Katharina 
Published: January 2009

AbstractJust a drop of water: Esterification in water is possible by confining the reactants in small miniemulsion droplets protected by nonionic surfactants. A lipase located at the interface between the droplet and aqueous surroundings catalyzes the esterification and expels generated water from the reaction site (see picture). High yields of the ester can be obtained after short reaction times under ambient conditions.magnified imageMonoesters of various linear carboxylic acids (C7–C12) with ω‐phenyl‐labeled primary alcohols (C1–C5) were synthesized in aqueous miniemulsions with various lipases as biocatalysts. The reactants were dispersed in an aqueous solution of a nonionic surfactant to form long‐term stable miniemulsions. The esterification of all of the systems could be catalyzed by the applied enzyme and yielded significant conversions of about 90 %. The hydrophilicity of the reactants and the specificity of the enzyme toward the substrates determine the reaction velocity and the final conversion. As a model system the reaction of nonanoic acid and 3‐phenylpropanol was extensively studied. Among various lipases, Lipase PS was determined to be the most effective, and for this reaction the parameters were optimized. A maximum conversion of 80 % could be obtained in less than one hour of reaction time. In comparison with an acid‐catalyzed esterification performed in miniemulsion with the same reaction parameters, the enzyme‐catalyzed reaction showed a significantly faster conversion. The reactions proved that the application of the miniemulsion technique enables efficient direct enzyme‐catalyzed esterification reactions from carboxylic acids and alcohols in the presence of large amounts of water.
Single‐Crystalline Molybdenum Trioxide Nanoribbons: Photocatalytic, Photoconductive, and Electrochemical Properties
Authors: Cheng Liang , Shao Mingwang , Wang Xiuhua , Hu Haibo 
Published: January 2009

AbstractMolecular highways: A facile one‐step, surfactant‐free route was applied to produce high‐purity and uniform α‐MoO3 nanoribbons (see figure), and their photocatalytic, photoconductive, and electrochemical properties were investigated. The results showed that the as‐prepared products had superior photo and electro properties.magnified imageLarge‐scale, high‐purity and uniform α‐MoO3 nanoribbons have been synthesized by a facile hydrothermal route without employing surfactants or templates. The as‐prepared α‐MoO3 nanoribbons were up to several micrometers in length, 100 nm in width, 15–20 nm in thickness, and grew along the [001] direction. The obtained nanoribbons exhibited a quantum size effect in optical properties, showing a blue shift of the band gap and direct transitions compared with the values of bulk MoO3. The nanoribbons also showed superior photocatalytic ability in the photodegradation reaction of an aqueous solution of Rhodamine B under visible light. Furthermore, the as‐prepared α‐MoO3 materials exhibited linear current–voltage (I–V) characteristics and excellent photoresponse. As the light source was switched on and off, the currents could be reversibly switched between high and low value at the voltage of 0.1 V. Electrochemical measurements predicted that the α‐MoO3/carbon fiber modified microelectrode would display excellent electrochemical characters and high sensitivity toward neurotransmitter dopamine. The modified electrode was also quite stable and had good reproducibility, which might have application in the electrochemical analysis.
Nucleation and Growth of CeF3 and NaCeF4 Nanocrystals
Authors: Li Shuai , Xie Ting , Peng Qing , Li Yadong 
Published: January 2009

AbstractStudying growth: The diffusion‐controlled kinetic (DCK) model and the surface chemical thermodynamics (SCT) model have been successfully applied to interpret the nucleation and growth mechanism of CeF3 (see TEM images) and NaCeF4 nanocrystals, and may generally give light to the size‐control and morphology prediction of rare‐earth fluorides at the nanoscale level.magnified imageMonodisperse CeF3 and NaCeF4 nanocrystals have been synthesized by using the liquid–solid–solution (LSS) approach. The nucleation and growth of nanocrystalline CeF3 and NaCeF4 were controlled by both kinetics and thermodynamics, which can be investigated by the diffusion‐controlled kinetic (DCK) model and surface chemical thermodynamics (SCT) theory. The DCK and SCT models were introduced to explain how the ripening time, reaction temperature, and initial concentrations affected the size transition of CeF3 and NaCeF4 nanocrystals in detail. Also, these models are believed to be universal and can be applied to explore the morphology evolution of almost all rare‐earth fluoride nanocrystals.
Chiral Poly(4‐ethynylbenzoyl‐L‐valine)‐Induced Helical Self‐Assembly of Alkynylplatinum(II) Terpyridyl Complexes with Tunable Electronic Absorption, Emission, and Circular Dichroism Changes
Authors: Chan Kenneth Hoi‐Yiu , Lam Jacky Wing‐Yip , Wong Keith Man‐Chung , Tang Ben‐Zhong , Yam Vivian Wing‐Wah 
Published: January 2009

AbstractThe aggregation and self‐assembly of square‐planar alkynylplatinum(II) complexes is induced by the use of a chiral polyacetylene with a helical conformation (see scheme). The chain helicity of the chiral polyacetylene under basic conditions has also been demonstrated to be enhanced by the presence of the positively charged platinum(II) complexes.magnified imageA chiral amino acid‐containing polyacetylene, poly(4‐ethynylbenzoyl‐L‐valine), was found to induce the aggregation and self‐assembly of square‐planar alkynylplatinum(II) terpyridyl complexes by electrostatic binding of the positively charged metal complexes to the anionic sites of the polyacetylene, as revealed by the appearance of new UV/Vis absorption and emission bands upon mixing under basic conditions. The induced complex self‐assembly was found to be influenced by the polyacetylene and/or base concentration, and the effect of pH on the reversibility of the aggregate/monomer interconversion was also studied. The conformational changes of the polyacetylene were probed by circular dichroism (CD) spectroscopy, in which the chirality signal of the corresponding chain helicity in the presence of the base was enhanced and stabilized upon addition of the platinum(II) complexes. The induced complex aggregation was dependent on the structural properties of the polyacetylene, while the chirality of the polyacetylene was strongly influenced by the introduction of the complex.
Supramolecular Templates for Nanoflake–Metal Surfaces
Authors: Shen Yanfei , Wang Jiaobing , Kuhlmann Uwe , Hildebrandt Peter , Ariga Katsuhiko , Möhwald Helmuth , Kurth Dirk G. , Nakanishi Takashi 
Published: January 2009

AbstractA sustainable method for the fabrication of metallic surfaces with flower‐like fractal morphology was developed by using a three‐dimensional supramolecular assembly as a template. Modifying Au nanoflakes with self‐assembled monolayers or polymers allows the surface wettability to be adjusted from superhydrophobic to superhydrophilic (see figure). Furthermore, Au nanoflakes present excellent substrates for surface‐enhanced Raman spectroscopy (SERS).magnified image
ESI‐FTICRMS Characterization of the Intermediates in Cycloisomerization of Trifluoromethyl‐substituted Enynols through Changing the Protecting Group of Substrate
Authors: QIAN Rong , GUO Yinlong , LÜ Long 
Published: January 2009

AbstractA chemical method of changing the protecting group was coupled to MS, deuterium‐labeled and NMR methods to characterize the intermediates in the palladium(II)‐catalyzed cycloisomerization of trifluoromethyl‐substituted enynols. It was demonstrated that the method of changing the protecting group of substrates not only caused a decrease in reaction speed, but also provided long‐lived reaction intermediates detectable by conventional spectroscopic techniques. In this sense, two assumed reaction intermediates were intercepted and detected by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS). For further characterization of these intermediates, the gas‐phase behavior of these intermediates was studied by sustained off‐resonance irradiation collision‐activated dissociation (SORI‐CAD) experiments. On the basis of the detailed, spectral interpretation of the palladium‐containing species, the fragmentation pathways of the intermediates have been proposed. The deuterium‐labeled experiment helped confirm the nature of the intermediates.
Synthesis and Complexation Studies of Calix[4]crown Telomers Intermolecularly Bridged with Calixarene Segments
Authors: LI Haibing , TIAN Demei , CHEN Yuanyin , GAO Zhinong 
Published: January 2009

AbstractThree derivatived calix[4]crowns were condensed with calixarene segments: 2,6‐bis(bromomethyl)‐4‐methyl‐anisole (BBA) to afford their telomers TCA[4] in rational yields. The binding sites may complex metal ions or amino acids selectively. The telomers shows different metal ions selectivity in comparison with their monomers, which suggests that calixarene segment bridges play an important role in ion‐binding. The liquid‐liquid extraction experiment showed that telomer TCA[4]‐III was excellent receptor for zwitterionic α‐amino acids and soft cations Ag+ and Pb2+. The extraction percentage of tryptophan and histidine was as high as 87.9% and 91.5%, respectively.
Reaction of Perfluoroalkanesulfinyl Chlorides with Enamines: A Facile Synthesis of α‐Perfluoroalkanesulfinyl Ketones and Aldehydes
Authors: LI Xiaobo , CHEN Lingjun , WANG Xiaojin , LIU Jintao 
Published: January 2009

AbstractThe reaction of perfluoroalkanesulfinyl chlorides with enamines was achieved in the presence of triethylamine, and α‐perfluoroalkanesulfinyl carbonyl compounds were obtained in moderate to good yields after hydrolysis of the reaction intermediates with dilute hydrochloric acid.
Facile Synthesis of Monofluoro γ ‐Lactones and Pyrrolidine Derivatives via Electrophilic Fluorination of Allenoic Acids and Amides
Authors: CUI Haifeng , CHAI Zhuo , ZHAO Gang , ZHU Shizheng 
Published: January 2009

AbstractA convenient method to synthesize a series of monofluoro γ‐lactones and pyrrolidine derivatives in moderate to good yields via the electrophilic fluorination of γ‐allenoic acids and tosylamides using Selectfluor was developed.
An Efficient Method for the Preparation of Pentafluoroiodoethane from Chloropentafluoroethane
Authors: ZHANG Chengpan , LIN Jinhong , QIANG Zhenwei , XIAO Jichang 
Published: January 2009

AbstractAn efficient method was developed for the synthesis of pentafluoroiodoethane from chloropentafluoroethane. Sulfinatodechlorination of CF3CF2Cl was carefully investigated. Subsequent iodination can be conducted in one pot without further purification, giving the corresponding CF3CF2I in practically acceptable yield.
Versatile Chiral Building Blocks from D‐Xylose
Authors: ZHEN Zhibin , GAO Jian , WU Yikang 
Published: January 2009

AbstractSeveral new chiral building blocks containing a hidden 1,3‐syn diol motif were developed from inexpensive and readily available D‐xylose through an efficient route without involving any expensive/highly toxic reagents or tedious operations.
Chiral Separation of Calcium (−)‐2(S)‐2‐Benzyl‐4‐oxo‐4‐(cis‐hexahydro‐2‐isoindolinyl)butyrate Enantiomers by High‐performance Liquid Chromatography
Authors: ZHANG Zhefeng , YANG Gengliang , GAO Wenhui , CHEN Yi 
Published: January 2009

AbstractA chiral high‐performance liquid chromatographic method was developed for the enantioseparation of a new insulinotropic drug of the glinide class with rapid onset. The chiral separation was performed on a Sumichiral OA‐3300 column (250 mm×4.6 mm, 5 µm) with methanol containing 0.05 mol/L ammonium acetate as the optimized mobile phase at detection wavelengh 210 nm. Baseline separation of the two enantiomers was obtained in 22 min with a resolution of 3.01. Calibration graphs were constructed in a range of 0.028–5.6 µg·mL−1forS‐ and 0.03–6.0 µg·mL−1forR‐(−)‐enantiomer, respectively. The linear correlation equations are:y=1.32×103x−2.54 (r=0.9997) forS‐enantiomer andy=1.15×103x−1.78 (r=0.9998) forR‐enantiomer, respectively. The limits of detection obtained byS/N=3 were 0.15 ng forS‐ and 0.10 ng forR‐enantiomer, respectively. RSD of the method was below 1.0% (n=5).
Theoretical Studies on the Reaction Mechanisms of C3H2 (cyclopropenylidene) and O(3P) Radicals
Authors: XIE Xiaohua , SHEN Wei , HE Rongxing , ZHANG Jinsheng , LI Ming 
Published: January 2009

AbstractThe complex potential energy surface for the reaction of C3H2 (cyclopropenylidene) with O(3P) was explored computationally using a density functional and ab initio QCISD(T) methods. The geometries of all the stationary points (transition states, intermediates and products) were fully optimized at the B3LYP/6‐311++G∗︁∗︁ computational level, and the single point calculation including full population analysis was performed by employing QCISD(T). Our results show that the product P1 (C2H+HCO) is the major product, while the products P2 (C2H2+CO) and P3 (HC3O+H) are minor products, as confirmed by experiment. Product P1 could be gained through the path: R→IM1→IM2→P1, and the C3H2+O(3P) reaction was expected to be rapid. So, the C3H2+O(3P) reaction may be an efficient strategy for producing C2H using cyclopropenylidene in atmosphere. The present results can lead us to understand deeply the mechanism of the title reaction.
Pt and Pt‐Ru Nanoparticles Dispersed on Ethylenediamine Grafted Carbon Nanotubes as New Electrocatalysts: Preparation and Electrocatalytic Properties for Ethanol Electrooxidation
Authors: ZHONG Xinxian , ZHANG Xiaohua , SUN Xinping , LIU Bo , KUANG Yafei , CHEN Jinhua 
Published: January 2009

AbstractAs the support of Pt and Pt‐Ru catalysts for ethanol electrooxidation, the ethylenediamine (ED)‐grafted multiwalled carbon nanotubes (MWNT) were prepared by a chemical synthesis method and characterized by Fourier transform infrared spectroscopy. The morphology and elemental composition of the Pt‐Ru/ED/MWNT and Pt/ED/MWNT catalysts were characterized by transmission electron microscopy (TEM) and energy dispersive X‐ray spectroscopy. TEM results demonstrate that the ED‐grafted MWNT is beneficial to loading Pt‐Ru and Pt electrocatalysts with well dispersion and small particle sizes. On the other hand, the electrocatalytic properties of the Pt‐Ru/ED/MWNT and Pt/ED/MWNT catalysts were characterized by cyclic voltammetry and chronoamperometry. Under the same loading mass of catalyst, the electrocatalytic activities of both Pt‐Ru/MWNT/graphite and Pt/MWNT/graphite electrodes are enhanced obviously by the introduction of ED. The electrocatalytic activity of the Pt/ED/MWNT/graphite electrode is even higher than that of the Pt‐Ru/MWNT/graphite electrode. These results indicate that the ED/MWNT is a promising catalyst support for ethanol electrooxidation.
DNA Probe and Cleavage Studies Based on the Interaction between DNA and Yb, Er Complexes of 2‐[(Trifluoroaceto)aceto]thinophene‐piperidine Ligands
Authors: YIN Caixia , HUO Fangjun , WU Yanbo , LIU Yanlin , YANG Pin 
Published: January 2009

AbstractTwo kinds of Ln complexes of [Ln(TTA)4]·HP (Ln=Yb or Er, TTA=2‐[(Trifluoroaceto)aceto]thinophene, HP=piperidine) have been synthesized and characterized, and their DNA‐binding properties investigated using UV spectra, fluorescent spectra, viscometry and molecular modeling. The results show that they can intercalate into the double helices of DNA. More important thing is that their fluorescence intensity can be enhanced by DNA, thererfore, a sensitive fluorescence method for the determination of DNA may be developed. The cleavage reaction on plasmid DNA has been monitored by agarose gel electrophoresis. Interestingly, the complexes can cleave circular plasmid pBR322 DNA at pH=7.2 and 37 °C. In addition, BDNPP [bis(2,4‐dinitrophenyl)‐phosphate] was chosen as a model compound to further study their cleavage mechanism of pBR322 DNA. From the first‐order kinetics equation, it was proved indirectly that the mechanism may be a hydrolytic cleavage.
Synthesis, Crystal Structure and Photoluminescent Properties of Two Novel Two‐dimensional Coordination Networks Assembled by Lanthanide Salts and Carboxylate Ligand
Authors: LI Yajuan , SONG Huihua , LIANG Qing , HE Rong , WEI Zhen 
Published: January 2009

AbstractTwo novel two‐dimensional (2D) lanthanide(III) coordination polymers [Ln(PDC)(OH)(H2O)2]n (Ln=Eu (1) and Tb (2), H2PDC=pyridine‐3,4‐dicarboxylic acid) have been synthesized under hydrothermal conditions, and characterized by elemental analysis, IR, TGA and single‐crystal X‐ray diffraction. Both compounds show the same 2D layer containing 1D Ln–O–Ln chains, and the layers are further connected through hydrogen‐bonding as well as π‐π stacking interactions into a three‐dimensional supramolecular network. Furthermore, both compounds exhibit intense fluorescent emission bands in the solid state at room temperature.
Brønsted Acid Mediated (sp3)Carbon‐Fluorine Bond Activation: Inter‐ and Intramolecular Arylation of Trifluoromethylated Arenes
Authors: WANG Fei , HU Jinbo 
Published: January 2009

Abstract Trifluoromethanesulfonic acid (triflic acid) was found to be able to efficiently activate the benzylic sp3 C–F bond. Thus, under the catalysis of triflic acid at room temperature, trifluoromethylated arenes readily reacted with benzene to give benzophenones in moderate to good yields. Under similar B?nsted acid catalysis, intramolecular arylation also happened in the cases of some CF3‐arene substrates bearing an additional nucleophilic aryl group. Strong CF···H+ interaction or hydrogen bonding, is believed to play an important role in the current Br?nsted acid‐mediated C–F bond activation chemistry.
Increased ovarian cancer risk associated with menopausal estrogen therapy is reduced by adding a progestin
Authors: Pearce Celeste Leigh , Chung Karine , Pike Malcolm C. , Wu Anna H. 
Published: January 2009

AbstractBACKGROUND.It has become increasingly clear that use of menopausal hormone therapy (HT) is associated with an increased risk of ovarian cancer; however, the effects by type of formulation and duration of use are less clear. A systematic review of the HT and ovarian cancer literature was conducted to identify population‐based case‐control studies, cohort studies, and randomized trials that examined effects by formulation of HT (estrogen‐alone [ET] and estrogen plus progestin [EPT]) and duration of use.METHODS.Pub‐Med (www.pubmed.gov) was used to identify relevant publications through December 2007; 14 studies were identified. The authors abstracted relative risks (RRs) and 95% confidence intervals (CIs) in relation to duration of HT use (ET and EPT separately). The authors used the risk estimates per year of HT use if these were provided; otherwise, they calculated a duration‐response for a log‐linear model of the duration of HT use against risk.RESULTS.Ovarian cancer risk was increased among ET users (RR per 5 years of use, RR5 = 1.22; 95% CI, 1.18‐1.27; P < .0001), and a lower but still statistically significant increased risk was seen with EPT use (RR5 = 1.10; 95% CI, 1.04‐1.16; P = .001). The increased risk in ET users was statistically significantly higher than the increased risk in EPT users (P = .004).CONCLUSIONS.ET use increases risk of ovarian cancer in a duration‐dependent manner, and it appears that the addition of progestins blocks this effect, at least to some extent. Whether the effect of estrogens would be completely blocked if progestins were given every day is unclear. Cancer 2009. © 2009 American Cancer Society.