bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zn2+ Complexes of Di‐ and Tri‐nucleating Azacrown Ligands as Base‐Moiety‐Selective Cleaving Agents of RNA 3′,5′‐Phosphodiester Bonds: Binding to Guanine Base
Authors: Wang Qi , Leino Ewelina , Jancsó Attila , Szilágyi István , Gajda Tamás , Hietamäki Emilia , Lönnberg Harri 
Published: June 2008

AbstractThe ability of the dinuclear Zn2+ complex of 1,4‐bis[(1,5,9‐triazacyclododecan‐3‐yloxy)methyl]benzene (L1) to promote the cleavage of the phosphodiester bond of dinucleoside‐3′,5′‐monophosphates that contain a guanine base has been studied over a narrow pH range from pH 5.8 to 7.2 at 90 °C. Comparative measurements have been carried out by using the trinuclear Zn2+ complex of 1,3,5‐tris[(1,5,9‐triazacyclododecan‐3‐yloxy)methyl]benzene (L2) as a cleaving agent and guanylyl‐3′,5′‐guanosine (5′‐GpG‐3′) as a substrate. The strength of the interaction between the cleaving agent and the starting material has been elucidated by UV spectrophotometric titrations. The speciation and binding mode have been clarified by potentiometric titrations with hydrolytically stable 2′‐O‐methylguanylyl‐3′,5′‐guanosine and 1H NMR spectroscopic measurements with guanylyl‐3′,5′‐guanosine. The results show that the guanine base is able to serve as a site for anchoring for the Zn2+–azacrown moieties of the cleaving agents L1 and L2, analogously to uracil base. The interaction is, however, weaker than with the uracil base and, hence, only the 5′‐GpG‐3′ site (in addition to 5′‐GpU‐3′ and 5′‐UpG‐3′ sites) is able to markedly modulate the phosphodiester cleavage by the Zn2+ complexes of di‐ and trinucleating azacrown ligands containing an ether oxygen as a potential H‐bond‐acceptor site.
Benzene Polyphosphates as Tools for Cell Signalling: Inhibition of Inositol 1,4,5‐Trisphosphate 5‐Phosphatase and Interaction with the PH Domain of Protein Kinase Bα
Authors: Mills Stephen J. , Vandeput Fabrice , Trusselle Melanie N. , Safrany Stephen T. , Erneux Christophe , Potter Barry V. L. 
Published: June 2008

AbstractNovel benzene polyphosphates were synthesised as inositol polyphosphate mimics and evaluated against type‐I inositol 1,4,5‐trisphosphate 5‐phosphatase, which only binds soluble inositol polyphosphates, and against the PH domain of protein kinase Bα (PKBα), which can bind both soluble inositol polyphosphates and inositol phospholipids. The most potent trisphosphate 5‐phosphatase inhibitor is benzene 1,2,4‐trisphosphate (2, IC50 of 14 μM), a potential mimic of D‐myo‐inositol 1,4,5‐trisphosphate, whereas the most potent tetrakisphosphate Ins(1,4,5)P3 5‐phosphatase inhibitor is benzene 1,2,4,5‐tetrakisphosphate, with an IC50 of 4 μM. Biphenyl 2,3′,4,5′,6‐pentakisphosphate (4) was the most potent inhibitor evaluated against type I Ins(1,4,5)P3 5‐phosphatase (IC50 of 1 μM). All new benzene polyphosphates are resistant to dephosphorylation by type I Ins(1,4,5)P3 5‐phosphatase. Unexpectedly, all benzene polyphosphates studied bind to the PH domain of PKBα with apparent higher affinity than to type I Ins(1,4,5)P3 5‐phosphatase. The most potent ligand for the PKBα PH domain, measured by inhibition of biotinylated diC8‐PtdIns(3,4)P2 binding, is biphenyl 2,3′,4,5′,6‐pentakisphosphate (4, Ki=27 nm). The approximately 80‐fold enhancement of binding relative to parent benzene trisphosphate is explained by the involvement of a cation–π interaction. These new molecular tools will be of potential use in structural and cell signalling studies.
Rhizobium rubiT: A Gram‐Negative Phytopathogenic Bacterium Expressing the Lewis B Epitope on the Outer Core of its Lipooligosaccharide Fraction
Authors: Gargiulo Valentina , Garozzo Domenico , Lanzetta Rosa , Molinaro Antonio , Sturiale Luisa , De Castro Cristina , Parrilli Michelangelo 
Published: June 2008

AbstractThe structure of the core oligosaccharide from the phytopathogenic bacterium Rhizobium rubi was deduced by combining information from complementary chemical approaches (alkaline and acid hydrolysis), similar to the “overlap peptide” strategy. This structure is new and it contains two main oligosaccharide backbones that differ in the substitution degree of the external Kdo unit. The relevant feature shared by both oligosaccharides is the presence of a tetrasaccharide motif that is similar to the blood group Lewis B antigen (LeB). This epitope differs from LeB in the glycosidic configuration of the glucosamine unit (α and not β) and in the occurrence of acetyls substituents at O3 and/or O4 of the galactose moiety. Other notable structural features are the location of the Dha residue, the presence of a α‐glucose unit that is linked to the inner Kdo unit, the high number of acid sugars and the highly branched core structure.
Ultrasonic measurement of the reaction kinetics of the setting of calcium sulfate cements using implicit calibration
Authors: Carlson Johan E. , Taavitsainen Veli‐Matti 
Published: June 2008

AbstractInjectable bone cements based on calcium sulfate and calcium phosphates are being developed for use as bone defect filling and reinforcement of osteoporotic bones. For developers and end‐users, kinetic properties of the setting reaction of such cements are of great interest. Existing standards for setting time measurement are based on visual examination of the cement surface and thus suffer from poor repeatability and subjectivity. Implicit calibration provides the means of determining parameters of a physical model at the same time as a calibration based on regression. This enables the use of indirect observations for the determination of implicit model parameters. In this paper, we study the hydration of calcium sulfate hemihydrate into calcium sulfate dihydrate, by combining multivariate calibration with a physical model of the reaction kinetics. The physical model contains three parameters, the reaction rate, the reaction order and a time delay. These parameters are estimated from ultrasound amplitude spectra. The resulting model fit has an R2 value of 99.9%. Copyright © 2008 John Wiley & Sons, Ltd.
“Click Chemistry” in Zeolites: Copper(I) Zeolites as New Heterogeneous and Ligand‐Free Catalysts for the Huisgen [3+2] Cycloaddition
Authors: Chassaing Stefan , Sani Souna Sido Abdelkarim , Alix Aurélien , Kumarraja Mayilvasagam , Pale Patrick , Sommer Jean 
Published: June 2008

AbstractFor the first time, copper(I)‐exchanged zeolites were developed as catalysts in organic synthesis. These solid materials proved to be versatile and efficient heterogeneous, ligand‐free catalytic systems for the Huisgen [3+2] cycloaddition. These cheap and easy‐to‐prepare catalysts exhibited a wide scope and compatibility with functional groups. They are very simple to use, easy to remove (by filtration), and are recyclable (up to three times without loss of activity). Investigations with deuterated alkynes and deuterated zeolites proved that this CuI‐zeolite‐catalyzed “click” reaction exhibited a mechanism different from that reported for the Meldal–Sharpless version.
Visible‐Light Photochromism of Triarylamine‐ or Ferrocene‐Bound Diethynylethenes that Switches Electronic Communication between Redox Sites and Luminescence
Authors: Sakamoto Ryota , Kume Shoko , Nishihara Hiroshi 
Published: June 2008

AbstractRedox‐active ferrocene‐ and triarylamine‐terminated diethynylethene derivatives have been synthesized and their photochromic properties and switching behavior based on through‐bond electronic communication between the two redox sites, as well as their emissions, have been examined. Both bis(ferrocenylethynyl)ethene 1 and bis(triarylaminoethynyl)ethene 2 show visible‐light photochromism induced by donor–acceptor charge‐transfer (CT) transitions from the ferrocene or triarylamine to the diethynylethene moieties. The reversibility and quantum yields of the photochromism of 2 (ΦE→Z=6.1×10−2, ΦZ→E=1.4×10−2) are far higher than those of 1 (ΦE→Z=8.6×10−6, ΦZ→E=2.5×10−6). The higher efficiency in 2 may be attributed to the absence of the heavy atom effect and of a low‐lying 3LF state, which are characteristic of ferrocenyl compounds. This proposition is further supported by the fact that bis(ferrocenylbuta‐1,3‐diynyl)ethene 3, which, unlike 1, is free from steric interference between the two ferrocenyl groups in the Z form, does not show a significant improvement in its photoisomerization quantum yields (ΦE→Z=6.2×10−5, ΦZ→E=3.4×10−5). The visible‐light photochromism of 1 and 2 is accompanied by a switch in the strength of the electronic communication between the two redox sites in their mixed‐valence states (ΔE0′ values are 70 and 48 mV for (E)‐1 and (Z)‐1, and 74 and 63 mV for (E)‐2 and (Z)‐2). In the case of 2, further evaluations were carried out through intervalence charge‐transfer (IVCT) band analyses and DFT calculations. We have also demonstrated that steric repulsion between the methyl ester moieties in the Z form is implicated in the reduction in the through‐bond electronic communication. Compound 2 exhibits photoluminescence, which is more efficient in the E form than in the Z form, whereas 1 and 3 show no photoluminescence.
Fragmentation of Carbohydrate Anomeric Alkoxyl Radicals: New Synthesis of Chiral 1‐Fluoro‐1‐halo‐1‐iodoalditols
Authors: Francisco Cosme G. , González Concepción C. , Kennedy Alan R. , Paz Nieves R. , Suárez Ernesto 
Published: June 2008

AbstractA new general methodology for the synthesis of 1,1,1‐trihaloalditols by starting from 1,5‐anhydro‐2‐deoxy‐hex‐1‐enitol derivatives (glycals) is described. The halogens are introduced sequentially in each of the three different steps of the process. The fluorine is introduced in the first step by electrophilic fluorination of the starting glycal; next, hydroxyhalogenation of the resulting vinyl fluoride allows the addition of any halogen (F, Cl, Br or I) at will, and finally, an iodine atom is inserted through an alkoxyl radical fragmentation reaction. This methodology allows the preparation of diverse types of 1,1,1‐trihalogenated compounds (RCF2I, RCFI2, RCFClI and RCFBrI) under mild conditions compatible with sensitive substituents. In some cases, the diastereomeric mixtures generated from RCFClI and RCFBrI can be chromatographically separated, and their configuration determined by X‐ray crystallographic analysis. The synthetic usefulness of these compounds has been preliminarily assessed by examining the reactivity of the fluorinated radical generated by rupture of the CI bond.
Intramolecular Charge Transfer of Carotene‐porphyrin‐fullerene Triad: Sequential or Superexchange Cechanism
Authors: SUN Yu , CHEN Yue‐Hui , LI Yuan‐Zuo , LI Yong‐Qing , MA Feng‐Cai 
Published: June 2008

AbstractAs an excellent artificial photosynthetic reaction center, the carotene (C)‐porphyrin (P)‐fullerene (F) triad was extensively investigated experimentally. To reveal the mechanism of the intramolecular charge transfer (ICT) on the mimic of photosynthetic solar energy conversion (such as singlet energy transfer between pigments, and photoinduced electron transfer from excited singlet states to give long‐lived charge‐separated states), the ICT mechanisms of C‐P‐F triad on the exciton were theoretically studied with quantum chemical methods as well as the 2D and 3D real space analysis approaches. The results of quantum chemical methods reveal that the excited states are the ICT states, since the densities of HOMO are localized in the carotene or porphyrin unit, and the densities of LUMO are localized in the fullerene unit. Furthermore, the excited states should be the intramolecular superexchange charge transfer (ISCT) states for the orbital transition from the HOMO whose densities are localized in the carotene to the LUMO whose densities are localized in the fullerene unit. The 3D charge difference densities can clearly show that some excited states are ISCT excited states, since the electron and hole are resident in the fullerene and carotene units, respectively. From the results of the electron‐hole coherence of the 2D transition density matrix, not only 3D results are supported, but also the delocalization size on the exciton can be observed. These phenomena were further interpreted with non‐linear optical effect. The large changes of the linear and non‐linear polarizabilities on the exciton result in the charge separate states, and if their changes are large enough, the ICT mechanism can become the ISCT on the exciton.
Interaction of N′‐(1‐Carboxyethylidene)salicylhydrazide with Bovine Serum Albumin
Authors: ZHANG Ye‐Zhong , DAI Jie , LIU Cheng , ZHANG Xiao‐Ping , DING Xin‐Liang , LIU Yi 
Published: June 2008

Abstract Under the simulated physiological condition of an animal body, the interaction between N′‐(1‐carboxyethylidene)salicylhydrazide (CESH) and bovine serum albumin (BSA) was investigated by fluorescence spectra, UV‐Vis absorption spectra and circular dichroism (CD) spectra. The experiment results showed that the fluorescence of BSA was strongly quenched by CESH because of the formation of a CESH‐BSA complex, indicating a static quenching mechanism in the binding process. The modified Stern‐Volmer quenching constants (Ka) were 11.23×104, 7.103×104, 4.934×104 and 2.495×104 L·mol−1 at 292, 298, 304 and 310 K, respectively. The thermodynamic parameters ΔG, ΔH and ΔS at the four temperatures were calculated according to van't Hoff equation and the results indicated that hydrogen bonds and van der Waals force played major roles in stabilizing the CESH‐BSA complex. The distance r=4.26 nm between the donor BSA and acceptor CESH was obtained according to F?rster's non‐radiative energy transfer theory. The synchronous fluorescence spectral results indicated that the hydrophobicity of tyrosine residue increased while the microenvironment around tryptophan residue had no change. The CD and three‐dimensional fluorescence spectral results showed that in the presence of CESH, the α‐helix content of BSA decreased and the microenvironment and conformation of BSA changed.
Reduction of NO2 in Flue Gas by CO and Propylene over CuO‐CeO2/SiO2 in the Presence of O2
Authors: LU Mo‐Hong , LI Ming‐Shi , SHAN Yu‐Hua , SESHAN K. , LEFFERTS Leon 
Published: June 2008

AbstractCatalytic reduction of NO2 with CO and/or propylene in the presence of NO and excess oxygen, a model mixture for flue gas, was studied over a series of CuO‐CeO2/SiO2 catalysts between 120–260 °C. The effect of HCl, an impurity in flue gas, on the activity of the catalysts was evaluated. It was found that a binary oxide catalyst, 2% CuO‐8% CeO2/SiO2, was active for the reduction of NO2 by CO and/or propylene. CO was effective for selective reduction of NO2 in the presence of NO and O2 in a temperature window between 160–200 °C while propylene was effective at temperature higher than 200 °C. In the presence of HCl, the activity of the catalyst for reduction of NO2 with CO was irreversibly deactivated. However, the activity for reduction of NO2 with propylene was not influenced by HCl.
Novel Flower‐Like Ag‐SiO2‐MgO‐Al2O3 Material: Preparation, Characterization and Catalytic Application in Methanol Dehydrogenation
Authors: LI Jing‐Xia , REN Li‐Ping , DAI Wei‐Lin , CAO Yong , FAN Kang‐Nian 
Published: June 2008

AbstractCatalytic direct dehydrogenation of methanol to formaldehyde was carried out over Ag‐SiO2‐MgO‐Al2O3 catalysts prepared by sol‐gel method. The optimal preparation mass fractions were determined as 8.3% MgO, 16.5% Al2O3 and 20% silver loading. Using this optimum catalyst, excellent activity and selectivity were obtained. The conversion of methanol and the selectivity to formaldehyde both reached 100%, which were much higher than other previously reported silver supported catalysts. Based on combined characterizations, such as X‐ray diffraction (XRD), scanning electronic microscopy (SEM), diffuse reflectance ultraviolet‐visible spectroscopy (UV‐Vis, DRS), nitrogen adsorption at low temperature, temperature programmed desorption of ammonia (NH3‐TPD), desorption of CO2 (CO2‐TPD), etc., the correlation of the catalytic performance to the structural properties of the Ag‐SiO2‐ MgO‐Al2O3 catalyst was discussed in detail. This perfect catalytic performance in the direct dehydrogenation of methanol to formaldehyde without any side‐products is attributed to its unique flower‐like structure with a surface area less than 1 m2/g, and the strong interactions between neutralized support and the nano‐sized Ag particles as active centers.
Kinetics of the Oxidation of D‐Glucose and Cellobiose by Acidic Solution of N‐Bromoacetamide Using Transition Metal Complex Species, [RuCl3(H2O)2OH] −, as Catalyst
Authors: SINGH Ashok Kumar , SRIVASTAVA Jaya , SRIVATAVA Shalini , RAHMANI Shahla 
Published: June 2008

AbstractThe kinetics of Ru(III)‐catalyzed and Hg(II)‐co‐catalyzed oxidation of D‐glucose (Glc) and cellobiose (Cel) by N‐bromoacetamide (NBA) in the presence of perchloric acid at 40 °C have been investigated. The reactions exhibit the first order kinetics with respect to NBA, but tend towards the zeroth order to higher NBA. The reactions are the first order with respect to Ru(III) and are fractional positive order with respect to [reducing sugar]. Positive effect of Cl− and Hg(OAc)2 on the rate of reaction is also evident in the oxidation of both reducing sugars. A negative effect of variation of H+ and acetamide was observed whereas the ionic strength (µ) of the medium had no influence on the oxidation rate. The rate of reaction decreased with the increase in dielectric constant and this enabled the computation of dAB, the size of the activated complex. Various activation parameters have been evaluated and suitable explanation for the formation of the most reactive activated complex has been given. The main products of the oxidation are the corresponding arabinonic acid and formic acid. HOBr and [RuCl3(H2O)2OH]− were postulated as the reactive species of oxidant and catalyst respectively. A common mechanism, consistent with the kinetic data and supported by the observed effect of ionic strength, dielectric constant and multiple regression analysis, has been proposed. Formation of complex species such as [RuCl3·S·(H2O)OH]− and RuCl3·S·OHgBr·OH during the course of reaction was fully supported by kinetic and spectral evidences.
Interaction of Antitumor Drug Aclacinomycin‐A with DNA and Its Specific Sequence Site
Authors: CHENG Gui‐Fang , ZHANG Fan , TAN Xue‐Lian , HE Pin‐Gang , FANG Yu‐Zhi 
Published: June 2008

Abstract Through UV and fluorescence spectrophotometries, the interaction of aclacinomycin‐A (ACM‐A) with DNA and its specific sequence have been investigated with the aid of circular dichroism spectrophotometry and differential pulse voltammetry method. The results demonstrated that ACM‐A was capable of intercalating DNA double helix, the π‐π electronic overlapping between π‐electrons of ACM‐A and base pair of DNA stabilized the ACM‐A‐DNA adduct, and through electrostatic interaction, the trisaccharide interacted with the minor groove of DNA owing to an amino group at C(3′). Electrochemical and spectroelectrochemical studies revealed that the original form of ACM‐A had higher affinity for DNA than the reduction form in which the trisaccharide group at C(7) was lost. According to the results obtained in this paper, ACM‐A showed preference for AT base pairs of the deoxyribonucleic acid duplex, and it was apt to interact with cytosine and thymine rather than the adenine of oligonucleotide.
Synthesis and Optical Properties of 2,13‐Dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6
Authors: HUANG Zhi‐Bin , KIM Sung‐Hong , SHI Da‐Qing , KANG Tai‐Jong , CHANG Seung‐Hyun 
Published: June 2008

AbstractA new crown ether of 2,13‐dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6 was synthesized from 2,13‐diformyl‐ dibenzo[b,k]‐18‐crown‐6 with 2‐aminothiophenol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na+, K+, Rb+ and Cs+ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied.
Synthesis of 14‐{[(Un)substituted phenyl] or alkyl}‐14H‐dibenzo[a,j]xanthenes Using Yb(OTf)3 as an Efficient Catalyst under Solvent‐free Conditions
Authors: WANG Li‐Min , SUI Yuan‐Yuan , ZHANG Liang 
Published: June 2008

AbstractA series of 14‐{[(Un)substituted phenyl] or alkyl}‐14H‐dibenzo[a,j]xanthenes were prepared under solvent‐free conditions by Yb(OTf)3 catalyzed condensation reactions of β‐naphthol with various aldehydes. The process presented here is operationally simple, environmentally benign and has good to excellent yields. Furthermore, the catalyst can be recovered conveniently and reused efficiently.
Substituent Effect on the C–NO2 and N–NO2 Bond Dissociation Energies of Nitroaromatic Molecules
Authors: FANG, Ming Ming , LI Zhe , FU Yao 
Published: June 2008

AbstractSix density function theory methods (B3LYP, B3P86, MPWB1K1, MPWPW91, PBEPBE, TPSS1KCIS3) were used to calculate bond dissociation enthalpies of nitro compounds, where the B3P86 method was found to give the most accurate predictions. Using the B3P86 method meta‐ and para‐substituted nitroaromatics were systematically studied for the first time. The remote substituent effects, Hammett relationships, and the origin of the substituent effects were discussed on the basis of the calculated results. Both meta‐ and para‐substituted nitromethyl‐benzenes showed significant substituent effects and a fair correlation against substituent constants σp+ The ground state effects were found to play the major role in determining the overall substituent effects. Meanwhile, nitroamino‐ benzenes showed irregular substituent effects and a poorer Hammett correlation, where both ground and radical state effects contributed to the overall substituent effects.
Design, Synthesis and Antitumor Activity of Asymmetric Bis(s‐triazole Schiff‐base)s Bearing Functionalized Side‐Chain
Authors: HU Guo‐Qiang , HOU Li‐Li , XIE Song‐Qiang , HUANG Wen‐Long 
Published: June 2008

Abstract1‐Amino‐2‐pyrid‐3‐yl‐5‐(2‐benzoylethylthio)‐s‐triazole (1) was condensed with 1‐amino‐3‐mercapto‐5‐ [(un)substituted phenyl]‐s‐triazoles and subsequently substituted with chloroacetic acid to afford bis‐s‐triazole sulfanylacetic acid mono‐Schiff bases (3a–3e), which were condensed with 9‐formylanthracene to produce asymmetric bis(s‐triazole Schiff base) sulfanylacetic acids (4a–4e). The structures of new synthesized compounds were characterized by elemental analysis and spectral data, and their in vitro antitumor activity against L1210, CHO and HL60 cell lines was evaluted via the respective IC50 values by methylthiazole trazolium (MTT) assay.
Evaluation of Solvent Accessibility Epitopes for Different Dehydrogenase Inhibitors
Authors: Ludwig Christian , Michiels Paulus J. A. , Lodi Alessia , Ride John , Bunce Chris , Günther Ulrich L. 
Published: June 2008

AbstractKnowledge about the orientation of ligands or inhibitors bound to a protein is vital for the development of new drugs. It was recently shown that solvent accessibility epitopes for protein ligands can be mapped by transferring magnetization from water molecules to the ligand to derive the ligand orientation. This is based on the fact that NMR signals of ligands arising from magnetization transferred from solvent molecules via the protein have a different sign from those arising from direct magnetization transfer from bulk water. Herein we critically evaluate the applicability of solvent accessibility mapping to derive binding orientations for ligands of two dehydrogenases (AKR1C3 and HSD17β1) with very different binding pockets, including complexes in which the ligand is buried more deeply inside the protein. We also evaluate the possibility of using co‐solvents, such as DMSO, for magnetization transfer.