bluuebunny/crossref_metadata_2025_split huggingface dataset:
Overlap concentration of an aqueous poly(N‐vinylcaprolactam) solution in the dynamic and static states
Authors: Foroutan Masoumeh , Khoee Sepideh , Zarrabi Mona 
Published: April 2008

AbstractThe overlap concentration of poly(N‐vinylcaprolactam)s (PVCLs) of low molecular weights was studied with dynamic and static methods (with viscosity and refractive‐index measurements) at three temperatures (25, 30, and 35°C). This concentration, determined by viscometry, was lower than the overlap concentration determined by refractometry. Also, the influence of the temperature and molecular weight on the viscosity and refractive index was investigated, and the opposite effect of the temperature on the viscosity and refractive index of PVCL solutions was observed. The experimental overlap concentration values were compared with those calculated with the Rao, Huggins, and Fuoss equations. The results showed that the Huggins equation is the best equation to describe the dilute solution properties of this polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Photodissociation of CH2I2 and Subsequent Electron Transfer in Solution
Authors: Saitow Ken‐ichi , Naitoh Yukito , Tominaga Keisuke , Yoshihara Keitaro 
Published: April 2008

AbstractWe studied photoinduced reactions of diiodomethane (CH2I2) upon excitation at 268 nm in acetonitrile and hexane by subpicosecond–nanosecond transient absorption spectroscopy. The transient spectra involve two absorption bands centered at around 400 (intense) and 540 nm (weak). The transients probed over the range 340–740 nm show common time profiles consisting of a fast rise (<200 fs), a fast decay (≈500 fs), and a slow rise. The two fast components were independent of solute concentration, whereas the slow rise became faster (7–50 ps) when the concentration in both solutions was increased. We assigned the fast components to the generation of a CH2I radical by direct dissociation of the photoexcited CH2I2 and its disappearance by subsequent primary geminate recombination. The concentration‐dependent slow rise produced the absorption bands centered at 400 and 540 nm. The former consists of different time‐dependent bands at 385 and 430 nm. The band near 430 nm grew first and was assigned to a charge‐transfer (CT) complex, CH2I2δ+⋅⋅⋅Iδ−, formed by a photofragment I atom and the solute CH2I2 molecule. The CT complex is followed by full electron transfer, which then develops the band of the ion pair CH2I2+⋅⋅⋅I− at 385 nm on the picosecond timescale. On the nanosecond scale, I3− was generated after decay of the ion pair. The reaction scheme and kinetics were elucidated by the time‐resolved absorption spectra and the reaction rate equations. We ascribed concentration‐dependent dynamics to the CT‐complex formation in pre‐existing aggregates of CH2I2 and analyzed how solutes are aggregated at a given bulk concentration by evaluating a relative local concentration. Whereas the local concentration in hexane monotonically increased as a function of the bulk concentration, that in acetonitrile gradually became saturated. The number of CH2I2 molecules that can participate in CT‐complex formation has an upper limit that depends on the size of aggregation or spatial restriction in the neighboring region of the initially photoexcited CH2I2. Such conditions were achieved at lower concentrations in acetonitrile than in hexane.
Brief functional anlaysis and treatment of elopement in preschoolers with autism
Authors: Perrin Christopher J. , Perrin Stefanie H. , Hill Elizabeth A. , DiNovi Kristin 
Published: April 2008

AbstractAs a result of the impact of functional analysis methodologies in identifying maintaining variables of problem behavior, considerable research has been devoted to tailoring the methodologies to be practical for an outpatient setting. The purpose of this study was (a) to use brief functional analysis (BFA) methodologies to empirically demonstrate the function of elopement exhibited by two preschoolers diagnosed with autism and (b) to develop function‐based interventions derived from the results of the BFA. In phase one, a BFA consisting of 5‐min sessions with multiple repetitions of each condition was conducted with each participant. In phase two, the efficacy of function‐based interventions was assessed using a pairwise design. Both participants' rates of elopement were differentially lower during the implementation of the function‐based intervention relative to baseline. Collectively, these results demonstrated that brief functional methodologies could be applied successfully to the assessment and treatment of elopement. Moreover, the application of BFA and the ensuing treatment in an outpatient setting extend the existing research on functional analysis. Copyright © 2008 John Wiley & Sons, Ltd.
Effects of a supervisory intervention on assessment of interobserver agreement by educational service providers
Authors: Garrity Meredith L. , Luiselli James K. , McCollum Sara A. 
Published: April 2008

AbstractEffective data collection requires routine assessment of interobserver agreement (IOA). This study evaluated a supervisory intervention to increase the frequency of IOA assessments performed by educational staff at a school for children with developmental disabilities. Intervention components included action directives, strategic posting of IOA recording forms, and performance feedback (positive reinforcement and correction). Implemented in a multiple baseline design, intervention increased IOA assessments targeting skill acquisition and behavior support plans. The study illustrates a systems‐level approach towards performance enhancement of human services personnel. Copyright © 2008 John Wiley & Sons, Ltd.
Synthesis of dendritic stationary phases with surface‐bonded L‐phenylalanine derivate as chiral selector and their evaluation in HPLC resolution of racemic compounds
Authors: Yin Chuan‐Qi , He Bao‐Jiang , Huang Shao‐Hua , Zhang Jun‐Yi , Bai Zheng‐Wu , Li Zao‐Ying 
Published: April 2008

AbstractFour dendrimers were synthesized on aminopropyl‐modified silica gel using methyl acrylate and ethylene diamine as building blocks by divergent method. Four generations of chiral stationary phases (CSPs) were prepared by coupling of L‐2‐(p‐toluenesulfonamido)‐3‐phenylpropionyl chloride to corresponding dendrimers. The derivatives prepared on silica gel were characterized by FT‐IR, 1H NMR, and elemental analysis. The selector loadings of these four generations of CSPs generally showed a decrease tendency with the increase of generation numbers of dendrimers. The enantioseparation properties of these CSPs were preliminarily investigated by high‐performance liquid chromatography. The CSP derived from the three‐generation dendrimer exhibited the best enantioseparation capability. Effects of the mobile phase composition and molecular structures of racemic mixtures on enantioseparation were further studied. Chirality, 2008. © 2008 Wiley‐Liss, Inc.
Discrimination of chiral guests by chiral channels: Variable temperature studies by SXRD and solid state 13C NMR of the deoxycholic acid complexes of camphorquinone and endo‐3‐bromocamphor
Authors: Tahir Mohamed I. M. , Rees Nicholas H. , Heyes Stephen J. , Cowley Andrew R. , Prout Keith 
Published: April 2008

Abstract3α,12α‐Dihydroxy‐5β‐cholan‐24‐oic acid (deoxycholic acid DCA) is able to discriminate between the R‐ and S‐enantiomers of camphorquinone and endo‐(+)‐3‐bromocamphor and select only the S‐enantiomers from a racemic mixture. DCA forms novel well ordered 1:1 adducts with (1S)‐(+)‐camphorquinone and (1S)‐endo‐(‐)‐3‐bromocamphor, both of which have been characterized by single crystal X‐ray diffraction (SXRD). When DCA is cocrystallized with (RS)‐camphorquinone and (RS)‐endo‐3‐bromocamphor, 1:1 adducts of the S‐enantiomers are produced together with crystals of the free racemic guest. In contrast, in the absence of (1S)‐(+)‐camphorquinone, DCA forms a 2:1 adduct with (1R)‐(−)‐camphorquinone. In this 2:1 adduct the guest is disordered at ambient temperature and undergoes a phase change in the region 160–130 K similar to that observed for the ferrocene adduct, but with only partial ordering of the guest. The SXRD structure of the low temperature form and the variable temperature 13C CP/MAS NMR are reported. Cocrystallizing DCA with (1R)‐endo‐(+)‐3‐bromocamphor gives the free guest and a glassy solid. Chirality, 2008. © 2008 Wiley‐Liss, Inc.
Analysis of the mechanism of asymmetric amplification by chiral auxiliary trans‐1,2‐diaminocyclohexane bistriflamide
Authors: Asakura Kouichi , Isoda Yuuki , Kondepudi Dilip K. , Yamaguchi Tomohiko 
Published: April 2008

AbstractAsymmetric amplification is a phenomenon in which the enantiomeric excess (ee) of a product is higher than that of a chiral auxiliary for a catalyst. We analyzed the mechanism of asymmetric amplification observed in the addition of diethylzinc (Et2Zn) to benzaldehyde (PhCHO) to synthesize 1‐phenyl‐1‐propanol in the presence of trans‐1,2‐diaminocyclohexane bistriflamide (DCBF) and titanium tetraisopropoxide (TIOP). In a manner similar to the reaction in which 1‐piperidino‐3,3‐dimethyl‐2‐butanol is a chiral auxiliary for the catalyst, when asymmetric amplification was observed, the ee of the product varied as the reaction progressed. The mechanisms of variation in ee in the two reactions, however, were different. No asymmetric amplification was observed when TIOP and PhCHO were added to a mixture of DCBF and Et2Zn, while the ee of the product was always higher than that of DCBF when PhCHO and Et2Zn were added to a mixture of DCBF and TIOP. In the latter case, the product ee decreased as the reaction progressed. The results indicate that DCBF forms inactive heterochiral complex causing an increase in the ee of DCBF in the solution, which is the chiral auxiliary for the catalyst. But the complex is not very stable and gradually dissociates due to the reaction with Et2Zn. As a result, the asymmetric amplification decreases as the reaction progresses. Chirality, 2008. © 2008 Wiley‐Liss, Inc.
Rock around the Ring: An Experimental and Theoretical Study of the Molecular Dynamics of Stannyltriphospholes with Chiral Tin Substituents
Authors: Hofmann Martin , Clark Tim , Heinemann Frank W. , Zenneck Ulrich 
Published: April 2008

AbstractThe reaction of diphenyltin dichloride with enantiopure Grignard reagents prepared in situ leads to diphenyltin chlorides 7a–e, which contain chiral organyl substituents. The 2‐bornyl derivative 7a forms a mixture of exo and endo isomers and the (–)‐menthyl derivative 7b yields a mixture of epimers, whereas the cis‐ and trans‐myrtanyl complexes 7c and 7d and the m‐(2‐bornyl‐2‐ene)phenyl species 7e form only one enantiomer as the tin atom is separated from the next stereogenic centre by a methylene or m‐phenylene group. The target chirally modified 1‐(triorganylstannyl)‐1,2,4‐triphospholes 2a–e are accessible from 7a–e by treatment of the latter with the salt (3,5‐di‐tert‐butyl‐1,2,4‐triphospholyl)sodium (Na5) in good yield. As for 7c–e, complexes 2c–e exhibit enantiopure organyl tin substituents that combine with the planar chiral 1,2,4‐triphosphole moiety to form diastereomers. X‐ray diffraction studies on crystalline phases of 2a,b,d and 7b,c confirm the stereochemical interpretations of their spectroscopic data with the help of absolute structure parameter determinations. Dynamic NMR spectroscopy experiments with these compounds demonstrate for the first time a facile stannyl group shift between the two adjacent P atoms (P1 and P2) of the heterocycles that includes ring inversion through a planar transition state (Ti). In line with the NMR spectroscopic results for 2a–e, density functional calculations with the simplified model compound (trimethylstannyl)‐1,2,4‐triphosphole (9) point to 1‐(trimethylstannyl)‐1,2,4‐triphosphole (9a) as the global energetic minimum for 9 and an almost isoenergetic 1,2‐shift and ring inversion as the main epimerisation processes of the two enantiomers of 9a.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Monomeric Boron and Tin(II) Heterocyclic Derivatives of 1,8‐Diaminonaphthalenes: Synthesis, Characterization and X‐ray Structures
Authors: Jiménez‐Pérez Víctor M. , Muñoz‐Flores Blanca M. , Roesky Herbert W. , Schulz Thomas , Pal Aritra , Beck Tobias , Yang Zhi , Stalke Dietmar , Santillan Rosa , Witt Michael 
Published: April 2008

AbstractThe reaction of the diaminonaphthalene dilithium salt(THF)2Li2[(NSiMe3)2C10H6] with BX3 (X = Cl, Br) in hexane provides the monomeric compounds BX[(NSiMe3)2C10H6] [3 (X = Cl), 4 (X = Br)] with a tricoordinate boron atom. Attempts to reduce 3 and 4 with lithium, sodium, potassium or sodium/potassium alloy with the intention to isolate a boranide resembling a carbene were unsuccessful. However, the diaminonaphthalene dilithium salt (THF)2Li2[(NSi‐iPr3)2C10H6] (2) reacts with SnCl2 in THF to provide the carbene analog 5. Compounds 2, 3 and 5 were characterized by single‐crystal X‐ray structure analysis. The structures of 3 and 5 show the naphthalene backbone to be nearly planar, while the heterocycles in 3 and 5 containing boron and tin atoms, respectively, have torsion angles (3: 30.06°; 5: 37.27°) with respect to the naphthalene plane. The boron atom has a trigonal‐planar environment, and the stannylene tin–nitrogen bonds form a very acute N–Sn–N angle of 92.2°.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Stereoselective Synthesis of a cis‐1,2‐Dialkylcyclopentane Building Block and Its Application in Isoprostane Synthesis (5‐ent‐F2c‐IsoP)
Authors: Elsner Petteri , Jetter Peter , Brödner Kerstin , Helmchen Günter 
Published: April 2008

AbstractThe all‐cis substituted cyclopentane 3a, an analogue of the Corey lactone, has been prepared from a readily available nortricyclanone derivative by a five‐step sequence in an overall yield of 34 %. This chiral building block has been applied in total syntheses of two diastereomeric isoprostanes belonging to the 5‐F2 family: ent‐5‐F2c‐IsoP (ent‐1) and 5‐epi‐ent‐5‐F2c‐IsoP (ent‐2). Key features of the syntheses are the introduction of the two unsaturated alkyl side chains through an E‐selective Horner–Wadsworth–Emmons reaction with the base‐sensitive syn‐aldehyde 10, along with a Z‐selective Wittig olefination.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Determination of Trace Manganese by Square‐Wave Stripping Voltammetry
Authors: Wang Shujie , Ye Baoxian 
Published: April 2008

AbstractA novel method of determining trace manganese by square‐wave stripping voltammetry with simultaneous plating mercury electrode is described in this paper. Well‐defined stripping peaks of manganese are obtained in H3BO4‐NaOH buffer (pH 8.0) and peak currents are in good linear relationship with manganese concentrations in two ranges: from 0.36 nM to 36 nM and from 73 nM to 909 nM. The obtained detection limit is 0.18 nM and relative standard deviation is 2.3% (n=7) under a predeposition time of 90 s. This proposed method has been used for the determination of trace manganese in real plasma samples with satisfiable results and good matching with the results of graphite furnace atomic absorption spectrometry.
Biomolecule‐Doped Organic/Inorganic Hybrid Nanocomposite Film for Label‐Free Electrochemical Immunoassay of α‐1‐Fetoprotein
Authors: Hong Chenglin , Yuan Ruo , Chai Yaqin , Zhuo Ying 
Published: April 2008

AbstractA new electrochemical immunosensor for the detection of α‐1‐fetoprotien (AFP) was developed based on AFP antibody (anti‐AFP)‐functionalized organic/inorganic hybrid nanocomposite membrane. To fabricate such a hybrid composite membrane, 3,4,9,10‐perylenetetracarboxylic acid‐bound thionine molecules (PTCTH) were initially doped into titania colloids (TiO2), and then gold nanoparticles and anti‐AFP were immobilized onto the composite film in turn. Comparison with the electrode fabricated only with thionine not 3,4,9,10‐perylenetetracarboxylic acid, the immunosensor with PTCTH exhibited high sensitivity and fast electron transfer. The presence of gold nanoparticles provided a good microenvironment for the immobilization of biomolecules, enhanced the surface coverage of protein, and improved the sensitivity of the immunosensor. The modified process was characterized by scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The surface topography of the membrane was investigated by scanning electron microscopy (SEM). Under optimal conditions, the proposed immunosensor exhibited a wide linear range from 2.5 to 200.0 ng/mL towards AFP with a detection limit of 0.5 ng/mL (S/N=3). The stability, reproducibility and precision of the immunosensor were acceptable. Comparison with the conventional enzyme‐linked immunosorbent assay (ELISA), the present method did not require more labeled procedures and washing steps. Significantly, the detection methodology provides a promising approach for other proteins or biosecurities.
Electrochemically Induced Modulation of the Catalytic Activity of a Reversible Redoxsensitive Riboswitch
Authors: Strohbach Denise , Turcu Florin , Schuhmann Wolfgang , Müller Sabine 
Published: April 2008

AbstractOver the past decade, RNA conformation has been shown to respond to external stimuli. Thus, dependent on the presence of a high affinity ligand, specifically designed ribozymes can be regulated in a classical allosteric way. In this scenario, a binding event in one part of the RNA structure induces conformational changes in a separated part, which constitutes the catalytic centre. As a result activity is switched on (positive regulation) or off (negative regulation). We have developed a hairpin aptazyme responding to flavine mononucleotide (FMN). Ribozyme activity is dependent on binding of FMN and thus is switched on in the presence of FMN in its oxidized form. Under reducing conditions, however, FMN changes its molecular geometry, which is associated with loss of binding and consequently down‐regulation of ribozyme activity. While in previous experiments sodium dithionite was used for reduction of FMN, we now present an assay for electrochemically induced activity switching. We have developed an electrochemical microcell that allows for iterative cycles of reduction/oxidation of FMN in an oxygen free atmosphere and thus for reversible switching of ribozyme activity. The reaction proceeds in droplets of 3 to 10 μL at micro‐ to nanomolar concentrations of the reaction components.
Potentiometric DNA Sensor Based on Electropolymerized Phenothiazines for Protein Detection
Authors: Evtugyn Gennady A. , Porfireva Anna V. , Hianik Tibor , Cheburova Maria S. , Budnikov Herman C. 
Published: April 2008

AbstractNovel method of potentiometric detection of DNA‐protein interactions has been proposed. For this purpose, polymeric phenothiazine dyes, methylene blue (MB) and methylene green (MG), were electrochemically deposited onto the glassy carbon electrode and covered with double stranded DNA (dsDNA) as a target for antibodies (DNA‐sensor) or DNA aptamer specific to human α‐thrombin (aptasensor). The biosensors were consecutively incubated at pH 7.5 and 3.0 and the difference in potentials, ΔE, was used as a measure of protein concentration. The potentiometric DNA‐sensors were tested in standard serum of autoimmune disease patients (systemic lupus erythemathosus (SLE) and autoimmune thyroidites). It was shown, that the ΔE value of DNA‐sensor depends on the dilution of serum in the range from 1 : 1 to 1 : 100. Nonthermostated serum exhibited bell‐shape dependence of ΔE on serum dilution due to interfering effect of serine proteins at maximum dilution between 1 : 20 and 1 : 50. For SLE serum thermostated at 56 °C the ΔE linearly decreased as a function of serum dilution and reached saturation at dilution 1 : 20. Similarly the changes in the potential of aptasensor allowed us to determine the α‐thrombin in the range from 1 nM to 1 μM. The Faradic impedance spectra measured at presence of redox probe [Fe(CN)6]4−/3− revealed changes in the resistance and capacitance attributed to the shielding effect of anti‐DNA antibodies and an increase in the electron transfer. The developed potentiometric biosensors can be used for preliminary diagnostics of autoimmune diseases and thrombin detection with sensitivity comparable to traditional methods. The developed assay is, however simpler and cheaper in comparison with commonly used methods.
Effect of blockage on free vibration of a circular cylinder at low Re
Authors: Prasanth T. K. , Mittal S. 
Published: April 2008

AbstractThe effect of the blockage on vortex‐induced vibrations of a circular cylinder of low non‐dimensional mass (m*=10) in the laminar flow regime is investigated in detail. A stabilized space–time finite element formulation is utilized to solve the incompressible flow equations in primitive variables form in two dimensions. The transverse response of the cylinder is found to be hysteretic at both ends of synchronization/lock‐in region for 5% blockage. However, for the 1% blockage hysteresis occurs only at the higher Re end of synchronization/lock‐in region. Computations are carried out at other blockages to understand its effect on the hysteretic behavior. The hysteresis loop at the lower Re end of the synchronization decreases with decrease in blockage and is completely eliminated for blockage of 2.5% and less. On the other hand, hysteresis persists for all values of blockage at the higher Re end of synchronization/lock‐in. Although the peak transverse oscillation amplitude is found to be same for all blockage (∼0.6D), the peak value of the aerodynamic coefficients vary significantly with blockage. The r.m.s. values show lesser variation with blockage. The effect of streamwise extent of computational domain on hysteretic behavior is also studied. The phase between the lift force and transverse displacement shows a jump of almost 180° at, approximately, the middle of the synchronization region. This jump is not hysteretic and is independent of blockage. Copyright © 2008 John Wiley & Sons, Ltd.
Differential involvement of TNFα in hypoxic suppression of astrocyte glutamate transporters
Authors: Boycott Hannah E. , Wilkinson Jenny A. , Boyle John P. , Pearson Hugh A. , Peers Chris 
Published: April 2008

AbstractTransporter‐mediated glutamate uptake is a principal function of astrocytes. Our previous studies have shown that this process is compromised under hypoxic conditions through the NF‐κB mediated inhibition of expression of the glutamate transporters EAAT‐1 and EAAT‐2. Here, we demonstrate that identical conditions of hypoxia (1% O2, 24 h) lead to a dramatic increase in TNFα production from astrocytes without altering their viability. This hypoxia‐evoked production of TNFα was prevented in the presence of any of three mechanistically distinct NF‐κB inhibitors. Exogenous application of TNFα was without effect on EAAT‐1 expression as determined by Western blotting, but mimicked the effects of hypoxia to suppress expression of EAAT‐2. Furthermore thalidomide, which prevents TNFα production, was without effect on hypoxic suppression of EAAT‐1 but prevented hypoxic suppression of EAAT‐2. These data indicate that regulation of glutamate transporter expression in astrocytes by hypoxia is subtype specific. Regulation of both EAAT‐1 and EAAT‐2 is mediated by NF‐κB, and this transcriptional regulator is also required for increased production of TNFα. However, while TNFα is essential for hypoxic suppression of EAAT‐2, hypoxic modulation of EAAT‐1 expression is unaffected by this cytokine. © 2008 Wiley‐Liss, Inc.