bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR Structure of the (+)‐CPI‐indole/d(GACTAATTGAC)‐d(GTCAATTAGTC) Covalent Complex
Authors: Bassarello Carla , Cimino Paola , Bifulco Giuseppe , Boger Dale L. , Smith Jarrod A. , Chazin Walter J. , Gomez‐Paloma Luigi 
Published: November 2003

AbstractWe report the NMR solution structure of (+)‐CPI‐indole (CPI, 1,2,8,8a‐tetrahydrocyclopropa[c]pyrrolo[3,2‐e]indol‐4(5H)‐one), an agent belonging to the CC‐1065/duocarmycin family of antitumor compounds. This (+)‐CPI‐indole structure is covalently bound to d(G1ACTAATTGTC11)‐d(G12TCAATTAGTC22), a synthetic DNA duplex containing a high‐affinity binding site. The three‐dimensional structure has been determined by several cycles of restrained molecular dynamics calculations with a total of 563 NMR‐derived constraints, both in vacuo and by using the generalized Born solvent continuum model. In‐depth analysis of the structure of this ligand–DNA complex led to a detailed knowledge of the bound state conformation of the CPI‐indole, the most simplified agent related to CC‐1065 and duocarmycins, the parent members of a family of extremely potent antitumor compounds. Comparison of the CPI‐indole bound conformation with those previously found for (+)‐duocarmycin SA (DSA), its unnatural enantiomer (−)‐DSA, and the demethoxylated analogue (+)‐DSI in their DNA complexes provided additional evidence of the tight correlation between the catalytic effect exerted by DNA on the alkylation reaction and the extent of angular twist between the two planar heteroaromatic subunits of these agents. Additionally, comparison of the structural features of the DNA‐bound state of a “naked” ligand, such as CPI‐indole, with those of various other duocarmycin agents provided useful information for the interpretation of the observed effects on chemical reactivity of the different substitution patterns at the hemispheres of these types of complex.
Induction of Cell Death of Gastric Cancer Cells by a Modified Compound of the Annonaceous Acetogenin Family
Authors: Huang Guo‐Rui , Jiang Sheng , Wu Yu‐Lin , Jin Yan , Yao Zhu‐Jun , Wu Jia‐Rui 
Published: November 2003

AbstractAnnonaceous acetogenins are a family of natural products with antitumor activities. The polyether mimic AA005 has been synthesized. The cytotoxic mechanism of AA005 was investigated. It was found that AA005 can induce the cell death of gastric tumor cells. Most AA005‐induced cell death is due to necrosis but partial and p53‐independent apoptosis is also detected. An expanded study with gastric tumor cells and a cell‐free system indicates that AA005 affects NADH:ubiquinone oxidoreductase (complex I; NADH=nicotinamide adenine dinucleotide, reduced form) in the mitochondrial electron transport system. These results show for the first time that the polyether mimic AA005 acts on the same biological target as the natural annonaceous acetogenins.
Cover Picture: A Cyclic CCK8 Analogue Selective for the Cholecystokinin Type A Receptor: Design, Synthesis, NMR Structure and Binding Measurements (ChemBioChem 11/2003)
Authors: De Luca Stefania , Ragone Raffaele , Bracco Chiara , Digilio Giuseppe , Aloj Luigi , Tesauro Diego , Saviano Michele , Pedone Carlo , Morelli Giancarlo 
Published: November 2003

AbstractThe cover picture shows a molecular model of the interaction between the new CCK8 analogue, Cycle29,34[Dpr29,Lys34]‐CCK8 (shown as a CPK model) and the receptor fragment CCKA‐R(1–47) (represented by a pink ribbon). The introduction of the cyclic constraint between the Dpr29 sidechain and the CCK8 C terminus (Lys34) decreases the flexibility of the molecule to stabilize the bioactive conformation of Cycle29,34[Dpr29,Lys34]‐CCK8. The Trp30 and Met31 side chains are in favorable orientations for interaction with the CCKA receptor. Expansions of the aromatic/amide regions of the 1H NMR spectra of Cycle29,34[Dpr29,Lys34]‐CCK8 in aqueous solution (top) and in presence of dodecylphosphocholine‐d38 micelles (bottom) are shown in the inset. Further details can be found in the article by Morelli and co‐workers on p. 1176 ff.
Mechanism of Hydroxyl Radical‐Induced Breakdown of the Herbicide 2,4‐Dichlorophenoxyacetic Acid (2,4‐D)
Authors: Peller Julie , Wiest Olaf , Kamat Prashant V. 
Published: November 2003

AbstractOxidative transformations by the hydroxyl radical are significant in advanced oxidation processes for the breakdown of organic pollutants, yet mechanistic details of the reactions are lacking. A combination of experimental and computational methods has been employed in this study to elucidate the reactivity of the hydroxyl radical with the widely used herbicide 2,4‐D (2,4‐dichlorophenoxyacetic acid). The experimental data on the reactivity of the hydroxyl radical in the degradation of the herbicide 2,4‐D were obtained from γ‐radiolysis experiments with both 18O‐labeled and unlabeled water. These were complemented by computational studies of the .OH attack on 2,4‐D and 2,4‐DCP (2,4‐dichlorophenol) in the gas phase and in solution. These studies firmly established the kinetically controlled attack ipso to the ether functionality as the main reaction pathway of .OH and 2,4‐D, followed by homolytic elimination of the ether side chain. In addition, the majority of the early intermediates in the reaction between the hydroxyl radical and 2,4‐DCP, the major intermediate, were identified experimentally. While the hydroxyl radical attacks 2,4‐D by .OH‐addition/elimination on the aromatic ring, the oxidative breakdown of 2,4‐DCP occurs through .OH addition followed by either elimination of chlorine or formation of the ensuing dichlorophenoxyl radical.
Investigation of the Origin of Selectivity in Cavitand‐Based Supramolecular Sensors
Authors: Paolesse Roberto , Di Natale Corrado , Nardis Sara , Macagnano Antonella , D'Amico Arnaldo , Pinalli Roberta , Dalcanale Enrico 
Published: November 2003

AbstractThe sensing properties of functionalized cavitands have been studied by thin‐film coating TMSR chemical sensors and by measuring their responses towards model analytes. We studied the relationship between the sensor performance, in terms of sensitivity and selectivity, and the molecular recognition properties of the cavitands. The Langmuir‐like shape of the adsorption isotherm, obtained in the case of short‐chain alcohols, demonstrated that selective binding can be achieved by the synergistic interactions of the cavity and the bridging POin groups. In the absence of these substituents, the peripheral alkyl chains necessary for the formation of highly permeable thin films attenuate the cavity effect because of nonspecific dispersion interactions. This completely overrides the response originating from molecular recognition. The same effect is observed when the PO groups are oriented outward from the cavity. The use of multivariate chemometrics and the study of the correlations between sensors sensitivity and analyte properties provided further evidence of molecular recognition phenomena, whose intensity is enhanced by the permanent free volume created by the rigid cavity surrounding the POin group.
Intrinsically Stable Secondary Structure Elements of Proteins: A Comprehensive Study of Folding Units of Proteins by Computation and by Analysis of Data Determined by X‐ray Crystallography
Authors: Perczel András , Jákli Imre , Csizmadia Imre G. 
Published: November 2003

AbstractDifferent protein architectures show strong similarities regardless of their amino acid composition: the backbone folds of the different secondary structural elements exhibit nearly identical geometries. To investigate the principles of folding and stability properties, oligopeptide models (that is, HCO‐(NH‐L‐CHR‐CO)n‐NH2) have been studied. Previously, ab initio structure determinations have provided a small amount of information on the conformational building units of di‐ and tripeptides. A maximum of nine differently folded backbone types is available for any natural α‐amino acid residue, with the exception of proline. All of these conformers have different relative energies. The present study compiles an ab inito database of optimized HCO‐(L‐Xxx)n‐NH2 structures, where 1≤n≤8 and Xxx=Ala or Gly. All homoconformers (α helix, β sheet, collagen helix, etc.) of the different backbone folds were optimized, along with additional β‐turn‐type heteroconformers. The comprehensive analysis of more than 150 fully optimized polyalanine and polyglycine structures reveals the same energy‐preference profile of major secondary structures as is found in globular proteins. The analysis of relative energies at three different levels of theory (RHF/3‐21G, RHF/6‐311++G(d,p)//RHF/3‐21G, and RHF/6‐311++G(d,p)) for the above‐mentioned achiral (Xxx=Gly) and chiral (Xxx=Ala) molecular structures shows how these common secondary structure elements gradually become more and more stable folds in the oligopeptides as the length of the peptide chain increases. This indicates that stability (local energy preference) of conformational building units seems to be a major driving force in peptide and protein folding. Furthermore, the preferred conformers of the gas phase are rather similar to those observed in proteins crystallized from aqueous media. Indeed, the relative energies for the different computed conformers show remarkable agreement with the frequency of occurrence of the same structural motifs retrieved from a nonhomologous X‐ray crystallography database.
Synthesis and Characterization of Carboxylate Complexes of SnIV Porphyrin Monomers and Oligomers
Authors: Hawley Joanne C. , Bampos Nick , Sanders Jeremy K. M. 
Published: November 2003

AbstractMost of the porphyrin‐recognition chemistry we have investigated previously has centred on kinetically labile metal–ligand interactions, such as ZnN and RuN. Our interest in the broader scope of molecular recognition required a metal with the ability to specifically recognise non‐nitrogen‐based ligands, with a significantly different binding interaction to distinguish it from nitrogen‐based analogues. In this report we describe interactions of SnIV porphyrins that bind oxygen‐based ligands and for which the SnIVO bond is in slow exchange on the NMR timescale. A series of carboxylate complexes is employed to highlight the structural/geometric features of porphyrin monomers and cyclic oligomers. Where more than one porphyrin unit is present in a molecular scaffold, we report the effect of carboxylate binding on the complex when the two porphyrins contain different metals (typically SnIV and ZnII). The unexpected spectroscopic and structural properties of the Sn2(9‐anthroic acid)porphyrin dimer are also reported.
Addition Reaction of Vinylic Reagents, Derived from α‐Chloroenones, to Carbonyl Compounds Promoted by Samarium Diiodide
Authors: Concellón José M. , Bernad Pablo L. , Huerta Mónica , García‐Granda Santiago , Díaz M. Rosario 
Published: November 2003

AbstractA new samarium diiodide‐promoted addition reaction of vinylsamarium reagents, derived from (Z)‐α‐chloro‐α,β‐unsaturated phenones 1, to both ketones (in THF) and aldehydes (in acetonitrile) led to (Z)‐2‐(1‐hydroxyalkyl)‐2,3‐unsaturated ketones in good yield. These transformations took place with total or very high inversion of the stereochemistry of the CC double bond of the starting chloroenone, producing the Z diastereoisomer. A new methodology to prepare SmI2 in acetonitrile by sonic treatment of 1,2‐diiodoethane with Sm powder is also described. A mechanism to explain this transformation is proposed.
Effect of Chirality on the Structural Behaviour of Hydrogen‐Bonded n‐Alkylammonium Pyroglutamates in the Crystalline and Smectic State
Authors: Tsiourvas Dimitris , Paleos Constantinos M. , Skoulios Antoine 
Published: November 2003

AbstractA set of optically active and racemic n‐alkylammonium pyroglutamates from dodecyl to octadecyl were synthesized and characterised. Their thermotropic polymorphism was investigated by polarizing optical microscopy, differential scanning calorimetry and dilatometry. Their structure in the crystalline and smectic state was analysed by X‐ray diffraction. The hydrogen bonding of the molecules in the crystalline and smectic layers was examined by infrared spectroscopy. The chirality control over the supramolecular self‐assembly of the molecules along with the homochiral and heterochiral architecture of the self‐assembled dimers are briefly discussed.
Creation of Double Silica Nanotubes by Using Crown‐Appended Cholesterol Nanotubes
Authors: Jung Jong Hwa , Lee Seok‐Hoon , Yoo Jong Shin , Yoshida Kaname , Shimizu Toshimi , Shinkai Seiji 
Published: November 2003

AbstractNew crown‐appended cholesterol‐based organogelators 1–3, which have one or two cholesterol skeletons as a chiral aggregate‐forming site, two amino groups as an acidic proton binding site, and one crown moiety as a cation binding site, were synthesized, and the gelation ability was evaluated in organic solvents. These gelators could gelatinize several organic solvents under 1.0 wt %, indicating that 1–3 act as a versatile gelator of various organic solvents. We observed CD spectra of the acetic acid or propionic acid gels of 1–3 to characterize the aggregation mode in the organogel system. In the CD spectrum of the acetic acid gel 1, the positive sign for the first Cotton effect indicates that the dipole moments of azobenzene chromophores tend to orient into the clockwise direction. On the other hand, propionic acid gels 2 and 3, bearing only one cholesterol, moiety exhibit a negative sign for the first Cotton effect, strongly suggesting that the dipole moments of the azobenzene chromophores orient into the anticlockwise direction. The TEM images of the 1+acetic acid gel resulted in the helical ribbon and tubular structures. Sol‐gel polycondensation of tetraethoxysilane (TEOS) was carried out with 1–3 as templates in the gel phase. The silica obtained from the 1+acetic acid gel showed the helical ribbon with 200–1700 nm width and the tubular structure of the silica with constant about 560 nm outer diameter. As far as can be recognized, all the helicity possesses a right‐handed helical motif. Since the exciton coupling band of the organogel also shows P (right‐handed) helicity, we consider that a microscopic helicity is reflected by a macroscopic helicity. On the other hand, the tubular structure of the silica obtained from the organogels 2 and 3 is somewhat different from that prepared from the organogel 1. The careful examination of SEM and TEM pictures revealed that the tube wall of the silica features a roll‐paper‐like multilayer structure. Thus, this paper demonstrates successful and rare examples for precise transcription of gel superstructures into inorganic silica materials.
Synthesis, Biochemical Properties and Molecular Modelling Studies of Organometallic Specific Estrogen Receptor Modulators (SERMs), the Ferrocifens and Hydroxyferrocifens: Evidence for an Antiproliferative Effect of Hydroxyferrocifens on both Hormone‐Dependent and Hormone‐Independent Breast Cancer Cell Lines
Authors: Top Siden , Vessières Anne , Leclercq Guy , Quivy Jacques , Tang J. , Vaissermann J. , Huché Michel , Jaouen Gérard 
Published: November 2003

AbstractA series of ferrocene derivatives based upon the structure of the antiestrogenic drug tamoxifen or of its active metabolite hydroxytamoxifen has been prepared and named by analogy ferrocifens and hydroxyferrocifens. This series includes 1‐[4‐(O(CH2)nNMe2)phenyl]‐1‐phenyl‐2‐ferrocenyl‐but‐1‐ene and 1‐[4‐(O(CH2)nNMe2)phenyl]‐1‐(4‐hydroxyphenyl)‐2‐ferrocenyl‐but‐1‐ene, with n=2, 3, 5 and 8, and 1‐[4‐(O(CH2)2NMe2)phenyl]‐1‐(4‐hydroxyphenyl)‐2‐ferrocenylethene. Most of these molecules have been synthesised by McMurry cross‐coupling of the appropriate ketones, except for the ethene complexes, which were prepared by a four‐step reaction sequence starting from the ferrocenylacetic acid. All these compounds were obtained as mixtures of Z and E isomers. The isomers were separated in the cases of the ferrocenyl derivatives of tamoxifen and hydroxytamoxifen (n=2). No isomerisation of the Z and E isomers occurred in DMSO after one day, while a 50:50 mixture of the isomers was obtained within one hour in chloroform. The X‐ray structure of (E)‐1‐[4‐(O(CH2)2NMe2)phenyl]‐1‐(4‐hydroxyphenyl)‐2‐ferrocenyl‐but‐1‐ene has been determined. The relative binding affinity (RBA) values of the hydroxyferrocifens for the estrogen receptor alpha (ERα) was good to moderate, with values decreasing progressively with the length of the basic chain. The RBA values found for the estrogen receptor beta (ERβ) are equal to or slightly less than those found for the alpha form. The lipophilicity of the hydroxyferrocifens are superior to the values found for estradiol and increase with lengthening of the chain. The antiproliferative effects of the four hydroxyferrocifens with n=2, 3, 5 and 8 were studied on four breast cancer cell lines (MCF7, MDA‐MB231, RTx6 and TD5) possessing different levels of ERα. On MCF7 cells containing high levels of ERα, hydroxyferrocifens behave as antiestrogens. At a molarity of 1 μM the effect is close to that of hydroxytamoxifen (used for reference) when n=2 or 5, more marked when n=3, and weaker when n=8. Ferrocene alone has no effect. For the MDA‐MB231 cells, classed as a hormone‐independent breast cancer cell line, on the other hand, the hydroxyferrocifens show remarkable antiproliferative behaviour while the hydroxytamoxifen is completely inactive. Hydroxyferrocifens therefore show the unique property of being active both on hormone‐dependent and on hormone‐independent breast cancer cell lines. The molecular modelling study provides some clues for understanding of the antagonist effect of these molecules, while an additional cytotoxic effect due to the vectorised ferrocenyl unit is revealed in some occasions.
Mild Synthesis of Polyfunctional Benzimidazoles and Indoles by the Reduction of Functionalized Nitroarenes with Phenylmagnesium Chloride
Authors: Dohle Wolfgang , Staubitz Anne , Knochel Paul 
Published: November 2003

AbstractPhenylmagnesium chloride has been used for the conversion of selected nitroarenes into nitrenes. Their insertion into a neighboring sp2 CH bond yielded functionalized heterocycles. A novel and mild synthesis of polyfunctional benzimidazoles and indoles is described.
Dimethylsulfoxide as a Ligand for RhI and IrI Complexes—Isolation, Structure, and Reactivity Towards XH Bonds (X=H, OH, OCH3)
Authors: Dorta Reto , Rozenberg Haim , Shimon Linda J. W. , Milstein David 
Published: November 2003

AbstractNovel neutral and cationic RhI and IrI complexes that contain only DMSO molecules as dative ligands with S‐, O‐, and bridging S,O‐binding modes were isolated and characterized. The neutral derivatives [RhCl(DMSO)3] (1) and [IrCl(DMSO)3] (2) were synthesized from the dimeric precursors [M2Cl2(coe)4] (M=Rh, Ir; COE=cyclooctene). The dimeric IrI compound [Ir2Cl2(DMSO)4] (3) was obtained from 2. The first example of a square‐planar complex with a bidentate S,O‐bridging DMSO ligand, [(coe)(DMSO)Rh(μ‐Cl)(μ‐DMSO)RhCl(DMSO)] (4), was obtained by treating [Rh2Cl2(coe)4] with three equivalents of DMSO. The mixed DMSO–olefin complex [IrCl(cod)(DMSO)] (5, COD=cyclooctadiene) was generated from [Ir2Cl2(cod)2]. Substitution reactions of these neutral systems afforded the complexes [RhCl(py)(DMSO)2] (6), [IrCl(py)(DMSO)2] (7), [IrCl(iPr3P)(DMSO)2] (8), [RhCl(dmbpy)(DMSO)] (9, dmbpy=4,4′‐dimethyl‐2,2′‐bipyridine), and [IrCl(dmbpy)(DMSO)] (10). The cationic O‐bound complex [Rh(cod)(DMSO)2]BF4 (11) was synthesized from [Rh(cod)2]BF4. Treatment of the cationic complexes [M(coe)2(OCMe2)2]PF6 (M=Rh, Ir) with DMSO gave the mixed S‐ and O‐bound DMSO complexes [M(DMSO)2(DMSO)2]PF6 (Rh=12; Ir=in situ characterization). Substitution of the O‐bound DMSO ligands with dmbpy or pyridine resulted in the isolation of [Rh(dmbpy)(DMSO)2]PF6 (13) and [Ir(py)2(DMSO)2]PF6 (14). Oxidative addition of hydrogen to [IrCl(DMSO)3] (2) gave the kinetic product fac‐[Ir(H)2Cl(DMSO)3] (15) which was then easily converted to the more thermodynamically stable product mer‐[Ir(H)2Cl(DMSO)3] (16). Oxidative addition of water to both neutral and cationic IrI DMSO complexes gave the corresponding hydrido–hydroxo addition products syn‐[(DMSO)2HIr(μ‐OH)2(μ‐Cl)IrH(DMSO)2][IrCl2(DMSO)2] (17) and anti‐[(DMSO)2(DMSO)HIr(μ‐OH)2IrH(DMSO)2(DMSO)][PF6]2 (18). The cationic [Ir(DMSO)2(DMSO)2]PF6 complex (formed in situ from [Ir(coe)2(OCMe2)2]PF6) also reacts with methanol to give the hydrido–alkoxo complex syn‐[(DMSO)2HIr(μ‐OCH3)3IrH(DMSO)2]PF6 (19). Complexes 1, 2, 4, 5, 11, 12, 14, 17, 18, and 19 were characterized by crystallography.
Membranen für Polymerelektrolyt‐Brennstoffzellen
Authors: Glüsen A. , Stolten D. 
Published: November 2003

AbstractDie Polymerelektrolyt‐Membran ist das Herzstück von wasserstoffbetriebenen Polymerelektrolyt‐Brennstoffzellen (PEFC) und methanolbetriebenen Direktmethanol‐Brennstoffzellen (DMFC). Membranen aus sulfonierten Fluoropolymeren sind derzeit kommerziell erhältlich. Wichtige Forschungs‐ und Entwicklungsziele sind derzeit für die PEFC die Erhöhung der Betriebstemperatur, ohne die Membran zusätzlich befeuchten zu müssen, und für die DMFC die Verringerung des Methanoltransportes durch die Membran. Zusätzlich sollen durch die Verwendung fluorfreier Polymere die Kosten der Membran und die Umweltbelastung reduziert werden. Dabei spielen bereits in der industriellen Entwicklung befindliche Membranen ebenso eine Rolle wie neue Membrankonzepte aus der Grundlagenforschung.
Application of Gas Permeation in Fuel Cell Powered Vehicles
Authors: Klinkhammer B. , Matthias C. , Melin T. 
Published: November 2003

AbstractMain motivation for the use of a polymer electrolyte membrane fuel cell (PEMFC) in traffic applications is its significant higher vehicle efficiency compared to internal combustion engines (ICE) especially under low‐load operation. Hydrogen is the ideal fuel for PEMFCs as it yields the highest level of fuel cell performance. Three different applications for gas permeation inside a fuel cell system have been investigated: water recovery, hydrogen purification, and oxygen enrichment. The focus was on the analysis of the technical feasibility and the availability of capable membranes on the pilot‐scale size for each application.
Polymeric Membranes for Medical Applications
Authors: Krause B. , Storr M. , Ertl T. , Buck R. , Hildwein H. , Deppisch R. , Göhl H. 
Published: November 2003

AbstractThe commercial application of membranes in dialysis treatment has started already 40 years ago. Today, dialysis is the application in medicine using the largest number of membrane surface area per year. Integration of the membrane production process into dialyzer manufacturing was the key element in the successful transition from small scale production to large scale dialyzer manufacturing. Automatization techniques are heavily integrated into this process to fulfill the high quality and safety demands in medical technology. This paper gives an overview on the different membrane applications in medical industry. The material selection for manufacturing dialysis membranes and the different membrane morphologies are discussed. In the second part the different manufacturing steps in dialyzer production are presented.
Magneto‐Optical Studies of HgTe/HgxCd1−xTe(S) Core–Shell Nanocrystals
Authors: Fradkin Leonid , Langof Lidia , Lifshitz Efrat , Rogach Andrey , Gaponik Nikolai , Weller Horst , Eychmüller Alex 
Published: November 2003

AbstractThe synthesis and magneto‐optical properties of HgTe nanocrystals capped with HgxCd1−xTe(S) alloyed shells have been investigated. The magneto‐optical measurements included the use of optically detected magnetic resonance (ODMR) and circular polarized photoluminescence (CP‐PL) spectroscopy. The PL spectra suggest the existence of luminescence events from both the core HgTe and the HgxCd1−xTe(S) shells. The continuous‐wave (cw) and time‐resolved ODMR measurements revealed that the luminescence at the shell regime is associated with a trap‐to‐band recombination emission. The electron trap is comprised of a Cd–Hg mixed site, confirming the existence of an alloyed HgxCd1−xTe(S) composition. The ODMR data and the CP‐PL measurements together revealed the g‐values of the trapped electron and the valence band hole.