bluuebunny/crossref_metadata_2025 huggingface dataset:
Adamantanes, Nortricyclenes, and Dendrimers with Extended Silicon Backbones
Authors: Fischer Roland , Baumgartner Judith , Kickelbick Guido , Hassler Karl , Marschner Christoph
Published: February 2004

By reaction of the hexabromoheptasilane MeSi(SiMe2SiMeBr2)3 (1 a) with H2O, H2S, NH3, and H2NMe the heptasilaadamantanes MeSi(SiMe2SiMeO)3 (4), MeSi(SiMe2SiMeS)3 (5), MeSi(SiMe2SiMeNH)3 (6 a), and MeSi(SiMe2SiMeNMe)3 (6 b), respectively, were prepared in good to moderate yields. Molecular structures of 4, 5, 6 a, and 6 b were determined by X‐ray crystallography. The symmetry of the cages is approximately C3v, and the geometry around the nitrogen atoms is essentially planar. Ab initio SCF/HF calculations with the 6‐31G* basis set confirm these results. Reduction of MeSi(SiMe2SitBuBr2)3 (1 b) with lithium naphthalenide afforded the heptasilanortricyclene MeSi(SiMe2SitBu)3 (7). The 29Si NMR spectrum of 7 consists of three signals with chemical shifts that agree closely with values predicted by ab initio calculations. 29Si INADEQUATE spectra also strongly support the nortricyclene structure. Ab initio SCF/HF calculations were performed for the parent molecule Si7H10, and the ring strain of the cage was estimated as 168.8 kJ mol−1 by using the homodesmic reaction Si7H10 + 3 Si2H6→Si13H28. Compound 1 a also served as the starting material for the preparation of first‐generation dendrimer 2 a by reaction with six equivalents of Ph2MeSiLi. Subsequent protodearylation with HBr and reaction with (Me2PhSi)2SiMeK afforded second‐generation dendrimer 3. All dendrimers were characterized by multinuclear NMR spectroscopy.
Nonswelling Macroporous Synbeads for Improved Efficiency of Solid‐Phase Biotransformations
Authors: Basso Alessandra , Braiuca Paolo , De Martin Luigi , Ebert Cynthia , Gardossi Lucia , Linda Paolo , Verdelli Silvia , Tam Andrea
Published: February 2004

An application of novel, highly porous nonswelling resins (Synbeads) for enzymatic catalysis on solid supports is reported. These new resins combine easy handling of the beads, chemical stability, improved accessibility of proteins and higher productivity relative to swelling polymers. The present study demonstrates that the resin porosity greatly affects the efficiency in solid‐phase biotransformations and that Synbead resins are valuable alternatives to swelling polymers for solid‐phase chemistry and biocatalysis. The present study investigates the influence of key parameters, such as porosity and reactive functional‐group density, on the reaction efficiency.
Dendrimers as Ligands: An Investigation into the Stability and Kinetics of Zn2+ Complexation by Dendrimers with 1,4,8,11‐Tetraazacyclotetradecane (Cyclam) Cores
Authors: Saudan Christophe , Balzani Vincenzo , Gorka Marius , Lee Sang‐Kyu , van Heyst Jeroen , Maestri Mauro , Ceroni Paola , Vicinelli Veronica , Vögtle Fritz
Published: February 2004

We have investigated the complexation of Zn2+ with 1,4,8,11‐tetrakis(naphthylmethyl) cyclam (1; cyclam=1,4,8,11‐tetraazacyclotetradecane) and with two dendrimers consisting of a cyclam core with four dimethoxybenzene and eight naphthyl appendages (2), and twelve dimethoxybenzene and sixteen naphthyl appendages (3). An important, common feature of model compound 1 and dendrimers 2 and 3 is that their potentially fluorescent naphthyl units are quenched by exciplex formation with the cyclam nitrogen atoms. Complexation with Zn2+, however, prevents exciplex formation and results in the appearance of an intense naphthyl fluorescence signal that can be used for monitoring the complexation process. Luminescence titration, together with competition experiments and 1H NMR titration, have shown that 1:1 and 1:2 (metal/ligand) complexes are formed in the cases of 2 and 3, whereas model compound 1 gives only a 1:1 complex. We have also investigated the 1:1 complexation kinetics by the stopped‐flow technique. In the case of 1, a second‐order process (k1=44×105 M−1 s−1) is followed by two consecutive first‐order steps (k2=0.53 s−1 and k3=0.10 s−1). For 2, a slower second‐order process (k1=4.9×105 M−1 s−1) is followed by a slow first‐order step (k2=0.40 s−1). In the case of 3, only a very slow second‐order process was observed (k1=1.2×105 M−1 s−1). The different metal–ion incorporation rates for model compound 1 and dendrimers 2 and 3 have been discussed in terms of conformational changes of the dendron subunits affecting the chelating properties of the cyclam core. This work reports the first kinetic study on metal–ion coordination by dendrimers with a well‐defined coordination site.
Mechanism of Dioxygen Activation in 2‐Oxoglutarate‐Dependent Enzymes: A Hybrid DFT Study
Authors: Borowski Tomasz , Bassan Arianna , Siegbahn Per E. M.
Published: February 2004

The reaction mechanism for dioxygen activation in 2‐oxoglutarate‐dependent enzymes has been studied by means of hybrid density functional theory. The results reported here support a mechanism in which all chemical transformations take place on a quintet potential‐energy surface. More specifically, the activated dioxygen species attacks the carbonyl group of the co‐substrate producing the FeII–persuccinate–CO2 complex, which readily releases the carbon dioxide molecule. The step in which the FeII–peracid–CO2 complex is formed is found to be rate‐limiting and irreversible. Subsequent heterolysis of the OO bond in the FeII–persuccinate complex proceeds in two one‐electron steps and produces the high‐valent iron–oxo species FeIVO, which is most likely to be responsible for oxidative reactions catalyzed by 2‐oxoglutarate‐dependent enzymes. The concerted pathway for simultaneous OO and CC bond cleavage on the septet potential‐energy surface is found to be less favorable. The relative stability of different forms of the active iron–oxo species is assessed, and the quintet five‐coordinate complex is found to be most stable.
A Critical Evaluation of the Factors Determining the Effect of Intramolecular Hydrogen Bonding on the OH Bond Dissociation Enthalpy of Catechol and of Flavonoid Antioxidants
Authors: Lucarini Marco , Pedulli Gian Franco , Guerra Maurizio
Published: February 2004

New experimental results on the determination of the bond dissociation enthalpy (BDE) value of 3,5‐di‐tert‐butylcatechol, a model compound for flavonoid antioxidants, by the EPR radical equilibration technique are reported. By measurement of the equilibrium constant for the reaction between 3,5‐di‐tert‐butylcatechol and the 2,6‐di‐tert‐butyl‐4‐methylphenoxyl radical, in UV irradiated isooctane solutions at different temperatures, it has been shown that the thermodynamic parameters for this reaction are ΔH° = −2.8±0.1 kcal mol−1 and ΔS° = +1.3±0.2 cal mol−1 K−1. This demonstrates that the entropic variations in the hydrogen exchange reaction between phenols and the corresponding phenoxyl radicals are also negligible when one of the reacting species is a polyphenol and that the EPR radical equilibration technique also allows the determination of the OH BDEs in intramolecularly hydrogen‐bonded polyphenols.

The BDE of 3,5‐di‐tert‐butylcatechol (78.2 kcal mol−1) was determined to be identical to that of α‐tocopherol. Through use of the group additivity rule, this piece of data was also used to calculate the strength of the intramolecular hydrogen bond between the hydroxyl proton and the oxygen radical centre in the corresponding semiquinone radical (5.6 kcal mol−1), which is responsible both for the excellent antioxidant properties of catechols and for the BDE of catechol (81.8 kcal mol−1). These values are in poor agreement with those predicted by DFT calculations reported in the literature (9.5 kcal mol−1 and 77.6 kcal mol−1, respectively). Extensive theoretical calculations indicate that the BDE of catechol is reproduced well (81.6 kcal mol−1) by use of diffuse functions on oxygen and the CCSD method.
The Diphosphate Monoanion in the Gas Phase: A Joint Mass Spectrometric and Theoretical Study
Authors: Ricci Andreina , Pepi Federico , Stefano Marco Di , Rosi Marzio
Published: February 2004

H3P2O7− ions were obtained in an electrospray ion source of a Fourier transform ion cyclotron resonance (ESI/FTICR) mass spectrometer from a CH3CN/H2O (1:1) pyrophosphoric acid solution and in the ionic source of a triple quadrupole (TQ) mass spectrometer from the chemical ionisation (CI) of pyrophosphoric acid introduced by a thermostatically controlled direct insertion probe. The ions were structurally characterised by mass spectrometric techniques and theoretical calculations. Consistent with collisionally activated dissociation (CAD) mass spectrometric results, theoretical calculations identified the linear diphosphate anion (I) as the most stable isomer on the H3P2O7− potential energy surface. The joint application of mass spectrometric techniques and theoretical methods provided information on the dissociative processes of diphosphate anions in the gas phase. Finally, this study provides an insight into the structures and stabilities of the [H3PO4⋅⋅⋅PO3]−, [HP2O6⋅⋅⋅H2O]− and [H2PO4⋅⋅⋅HPO3]− clusters and allows the stability and structure of the dimetaphosphate anion, HP2O6−, to be investigated at the B3LYP6‐31+G* and CCSD(T) levels of theory.
Aided Self‐Assembly of Porphyrin Nanoaggregates into Ring‐Shaped Architectures
Authors: Lensen Marga C. , Takazawa Ken , Elemans Johannes A. A. W. , Jeukens Cecile R. L. P. N. , Christianen Peter C. M. , Maan Jan C. , Rowan Alan E. , Nolte Roeland J. M.
Published: February 2004

The formation of micrometer‐sized, highly ordered porphyrin rings on surfaces has been investigated. The porphyrin‐based nanoarchitectures are formed by deposition from evaporating solutions through a surface dewetting process which can be tuned by variations in the substitution pattern of the molecules used, the coating of the surface and the conditions under which the evaporation takes place. Control over the combined self‐assembly and surface dewetting results in nanorings possessing a defined internal architecture. The ordering of the molecules within the rings has been studied by a variety of microscopy techniques (TEM, AFM, fluorescence microscopy) and the exact ordering of the porphyrins within the rings has been quantified.
Straightforward Synthesis of (R)‐(−)‐Kjellmanianone
Authors: Christoffers Jens , Werner Thomas , Frey Wolfgang , Baro Angelika
Published: February 2004

A direct route to enantiomerically pure (−)‐kjellmanianone is reported. The synthesis involves a cerium‐catalyzed α‐hydroxylation and an enzyme‐catalyzed procedure to resolve tertiary alcohols at key stages. The intermediate β‐oxo ester was α‐hydroxylated to give good yields of racemic kjellmanianone. The resolution of the racemic material was achieved by enzymatic saponification, followed by a chemical decarboxylation sequence to give enantiopure (−)‐kjellmanianone with 99 % ee. Bromination then afforded the (−)‐bromo derivative, whose X‐ray structure provided evidence for the R configuration of (−)‐kjellmanianone.
The Control of the Nitrogen Inversion in Alkyl‐Substituted Diaziridines
Authors: Trapp O. , Schurig V. , Kostyanovsky R. G.
Published: February 2004

For the first time the nitrogen inversion barriers in 3,3‐unsubstituted trans‐diaziridines, such as 1,2‐di‐tert‐butyldiaziridine (1) and 1,2‐di‐n‐butyldiaziridine (2) were determined. Enantioselective stopped‐flow multidimensional gas chromatography was used to investigate the enantiomerization barrier of 1 between 126.2 and 171.0 °C (ΔG${{{\ne}\hfill \atop {\rm gas}\hfill}}$(150.7 °C) = 135.8±0.2 kJ mol−1, ΔH${{{\ne}\hfill \atop {\rm gas}\hfill}}$ = 116.1±2.5 kJ mol−1, ΔS${{{\ne}\hfill \atop {\rm gas}\hfill}}$ = −46±2 J K−1 mol−1). The separation of the enantiomers has been achieved in presence of the chiral stationary phase (CSP) Chirasil‐β‐Dex with a high separation factor (α = 1.44 at 80 °C). In a complementary approach, the enantiomerization barriers of 1,2‐di‐tert‐butyldiaziridine (1), 1,2‐di‐n‐butyldiaziridine (2), 1‐n‐butyl‐3,3‐dimethyldiaziridine (3), and 1,2,3,3‐tetramethyldiaziridine (4) were determined for comparison by enantioselective dynamic chromatography (DGC) and computer simulation of the dynamic elution profiles.

The enantiomerization barrier of 2 was shown to be the highest among the nonsterically hindered diaziridines studied so far, whereas 1 exhibited the highest value found for strained nitrogen‐containing rings, that is, aziridines, diaziridines and oxaziridines.
Binding N2, N2H2, N2H4, and NH3 to Transition‐Metal Sulfur Sites: Modeling Potential Intermediates of Biological N2 Fixation
Authors: Sellmann Dieter , Hille A. , Rösler A. , Heinemann F. W. , Moll M. , Brehm G. , Schneider S. , Reiher M. , Hess B. A. , Bauer W.
Published: February 2004

In the quest for low‐molecular‐weight metal sulfur complexes that bind nitrogenase‐relevant small molecules and can serve as model complexes for nitrogenase, compounds with the [Ru(PiPr3)(‘N2Me2S2’)] fragment were found (‘N2Me2S2’2−=1,2‐ethanediamine‐N,N′‐dimethyl‐N,N′‐bis(2‐benzenethiolate)2−). This fragment enabled the synthesis of a first series of chiral metal sulfur complexes, [Ru(L)(PiPr3)(‘N2Me2S2’)] with L=N2, N2H2, N2H4, and NH3, that meet the biological constraint of forming under mild conditions. The reaction of [Ru(NCCH3)(PiPr3)(‘N2Me2S2’)] (1) with NH3 gave the ammonia complex [Ru(NH3)(PiPr3)(‘N2Me2S2’)] (4), which readily exchanged NH3 for N2 to yield the mononuclear dinitrogen complex [Ru(N2)(PiPr3)(‘N2Me2S2’)] (2) in almost quantitative yield. Complex 2, obtained by this new efficient synthesis, was the starting material for the synthesis of dinuclear (R,R)‐ and (S,S)‐[μ‐N2{Ru(PiPr3)(‘N2Me2S2’)}2] ((R,R)‐/(S,S)‐3). (Both 2 and 3 have been reported previously.) The as‐yet inexplicable behavior of complex 3 to form also the R,S isomer in solution has been revealed by DFT calculations and 2D NMR spectroscopy studies. The reaction of 1 or 2 with anhydrous hydrazine yielded the hydrazine complex [Ru(N2H4)(PiPr3)(‘N2Me2S2’)] (6), which is a highly reactive intermediate. Disproportionation of 6 resulted in the formation of mononuclear diazene complexes, the ammonia complex 4, and finally the dinuclear diazene complex [μ‐N2H2{Ru(PiPr3)(‘N2Me2S2’)}2] (5). Dinuclear complex 5 could also be obtained directly in an independent synthesis from 1 and N2H2, which was generated in situ by acidolysis of K2N2(CO2)2. Treatment of 6 with CH2Cl2, however, formed a chloromethylated diazene species [{Ru(PiPr3)(‘N2Me2S2’)}‐μ‐N2H2{Ru(Cl)(‘N2Me2S2CH2Cl’)}] (9) (‘N2Me2S2CH2Cl’2− =1,2‐ethanediamine‐N,N′‐dimethyl‐N‐(2‐benzenethiolate)1−‐N′‐(2‐benzenechloromethylthioether)1−]. The molecular structures of 4, 5, and 9 were determined by X‐ray crystal structure analysis, and the labile N2H4 complex 6 was characterized by NMR spectroscopy.
Molecular Structure, Spectroscopy and Matrix Photochemistry of Fluorocarbonyl Iodide, FC(O)I
Authors: Chiappero M. S. , Argüello G. A. , Garcia P. , Pernice H. , Willner H. , Oberhammer H. , Peterson K. A. , Francisco J. S.
Published: February 2004

The molecular structure of FC(O)I has been determined by gas electron diffraction. High‐level ab initio methods, including coupled‐cluster and the new correlation‐consistent basis sets for fourth row elements, have been used to calculate the structure of FC(O)I. A comprehensive vibrational spectroscopic study (both IR and Raman) complemented by high‐level calculations has also been performed. Furthermore, UV, mass, and NMR spectra have been recorded for FC(O)I. The matrix photochemistry of FC(O)I has been studied with a low‐pressure mercury lamp and with a high‐pressure xenon lamp in combination with interference and cut‐off filters. UV photolysis revealed the formation of the OC⋅⋅⋅IF and OC⋅⋅⋅FI complexes and further photolysis of these complexes at λ>320 nm resulted in a re‐formation of FC(O)I. The structural conformation of the complexes has been characterized by comparing shifts in their CO and IF vibrational modes with respect to those of the free species. The structures, vibrational properties, and stability of the complexes were analyzed with the aid of coupled‐cluster ab initio calculations.
Iodine(III)‐Mediated Preparations of Nitrogen‐Containing Sulfur Derivatives: Dramatic Influence of the Sulfur Oxidation State
Authors: Leca Dominique , Song Kai , Amatore Muriel , Fensterbank Louis , Lacôte Emmanuel , Malacria Max
Published: February 2004

Reaction of sulfonamides with iodosobenzene leads to phenyliodinanes. A new catalysis reaction of the decomposition of these products in the presence of sulfoxides that allows the smooth synthesis of sulfoximines has been evidenced and studied: copper(II) salts were used to prepare compounds 4 a–j and 5 b, d, f, j, k from the corresponding, easily prepared, sulfoxides. The reactions proceed with retention of configuration at the sulfur center, and copper(II) triflate is the best candidate for the catalyst for the imination. Switching from sulfonamides to sulfinamides in the preparation of the starting iodinanes completely alters the reaction pathway: iodinanes are no longer accessible, and sulfonimidates 7 a–j are obtained instead. This behavior can be rationalized by the increase in pKa brought about by the removal of one oxygen atom from the sulfur center. Sulfonimidates are interesting molecules with varied applications. Optimization of their one‐pot synthesis has been achieved by carrying out the reaction in acetonitrile. The stereochemical study has shown that the transformation proceeds with global retention of the configuration at the sulfur center, albeit with erosion of the enantiomeric purity. A model accounting for this outcome is proposed. In addition, the presence of oxidized sulfonamide by‐products has been explained, and this latter pathway becomes the sole one when alcohol is replaced by water. Good yields of the oxidized products are obtained.
Overcoming the Insolubility of Carbon Nanotubes Through High Degrees of Sidewall Functionalization
Authors: Dyke Christopher A. , Tour James M.
Published: February 2004

The use of carbon nanotubes in materials applications has been slowed due to nanotube insolubility and their incompatibility with polymers. We recently developed two protocols to overcome the insoluble nature of carbon nanotubes by affixing large amounts of addends to the nanotube sidewalls. Both processes involve reactions with aryl diazonium species. First, solvent‐free functionalization techniques remove the need for any solvent during the functionalization step. This delivers functionalized carbon nanotubes with increased solubility in organic solvents and processibility in polymeric blends. Additionally, the solvent‐free functionalization process can be done on large scales, thereby paving the way for use in bulk applications such as in structural materials development. The second methodology involves the functionalization of carbon nanotubes that are first dispersed as individual tubes in surfactants within aqueous media. The functionalization then ensues to afford heavily functionalized nanotubes that do not re‐rope. They remain as individuals in organic solvents giving enormous increases in solubility. This protocol yields the highest degree of functionalization we have obtained thus far—up to one in nine carbon atoms on the nanotube has an organic addend. The proper characterization and solubility determinations on nanotubes are critical; therefore, this topic is discussed in detail.
Theoretical Studies on the Smallest Fullerene: from Monomer to Oligomers and Solid States
Authors: Chen Zhongfang , Heine Thomas , Jiao Haijun , Hirsch Andreas , Thiel Walter , Schleyer Paul von Ragué
Published: February 2004

Hybrid B3LYP and density‐functional‐based tight‐binding (DFTB) computations on the solid‐state structures and electronic properties of the C20 fullerene monomer and oligomers are reported. C20 cages with C2, C2h, Ci, D3d, and D2h symmetries have similar energies and geometries. Release of the very high C20 strain is, in theory, responsible for the ready oligomerization and the formation of different solid phases. Open [2+2] bonding is preferred both in the oligomers and in the infinite one‐dimensional solids; the latter may exhibit metallic character. Two types of three‐dimensional solids, the open [2+2] simple cubic and the body‐centered cubic (bcc) forms, are proposed. The energy of the latter is lower due to the better oligomer bonding. The open [2+2] simple cubic solid should be a conductor, whereas the bcc solids are insulators. The most stable three‐dimensional solid‐state structure, an anisotropically compressed form of the bcc solid, has a HOMO–LUMO gap of approximately 2 eV and a larger binding energy than that of the proposed C36 solid.
Three‐Coordinate Organoboron Compounds BAr2R (Ar = Mesityl, R = 7‐Azaindolyl‐ or 2,2′‐Dipyridylamino‐Functionalized Aryl or Thienyl) for Electroluminescent Devices and Supramolecular Assembly
Authors: Jia Wen‐Li , Bai Dong‐Ren , McCormick Theresa , Liu Qin‐De , Motala Michael , Wang Rui‐Yao , Seward Corey , Tao Ye , Wang Suning
Published: February 2004

Eight novel three‐coordinate boron compounds with the general formula BAr2L, in which Ar is mesityl and L is a 7‐azaindolyl‐ or a 2,2′‐dipyridylamino‐functionalized aryl or thienyl ligand, have been synthesized by Suzuki coupling, Ullmann condensation methods, or simple substitution reactions (L = p‐(2,2′‐dipyridylamino)phenyl, 1; p‐(2,2′‐dipyridylamino)biphenyl, 2; p‐(7‐azaindolyl)phenyl, 3; p‐(7‐azaindolyl)biphenyl, 4; 3,5‐bis(2,2′‐dipyridylamino)phenyl, 5; 3,5‐bis(7‐azaindolyl)phenyl, 6; p‐[3,5‐bis(2,2′‐dipyridylamino)phenyl]phenyl, 7; 5‐[p‐(2,2′‐dipyridylamino)phenyl]‐2‐thienyl, 8). The structures of 1, 3, and 5–7 have been determined by X‐ray diffraction analyses. These new boron compounds are bright blue emitters. Electroluminescent devices using compound 2 or 8 as the emitter and the electron‐transport layer have been successfully fabricated. Molecular orbital calculations (Gaussian 98) have established that the blue emission of compounds 1–8 originates from charge transfer between the π orbital of the ligand L and the pπ orbital of the boron center. The ability of these boron compounds to bind to metal centers to form supramolecular assemblies was demonstrated by treatment of compound 2 with Zn(O2CCF3)2, which generated a 1:1 chelate complex {2⋅Zn(O2CCF3)2} (10), and also by treatment of compound 4 with AgNO3, yielding a 2:1 coordination compound {(4)2⋅Ag(NO3)} (11). In the solid state, compounds 10 and 11 form interesting head‐to‐head and tail‐to‐tail extended structures that host solvent molecules such as benzene.
Cover Picture: Iodine(III)‐Mediated Preparations of Nitrogen‐Containing Sulfur Derivatives: Dramatic Influence of the Sulfur Oxidation State (Chem. Eur. J. 4/2004)
Authors: Leca Dominique , Song Kai , Amatore Muriel , Fensterbank Louis , Lacôte Emmanuel , Malacria Max
Published: February 2004

The cover picture shows the iodine‐mediated one‐pot stereoselective synthesis of a chiral sulfonimidate starting from a sulfinamide in the presence of methanol. The X‐ray diffraction structure determination of the major diastereoisomer indicated that the reaction mainly occurred with retention of configuration, presumably through an early intermediate, which was transformed following two different pathways. Rearrangement via a four‐atom transition state afforded sulfonimidates with retention of configuration. A competitive three‐atom rearrangement would cause the partial racemization. A discussion of these proposals, as well as the synthesis of free sulfonimidates and a convenient preparation of sulfoximines and sulfonamides are described by Malacria et al. on p. 906 ff.
Molecular Basis of the Dynamic Strength of the Sialyl Lewis X—Selectin Interaction
Authors: Zhang Xiaohui , Bogorin Daniela F. , Moy Vincent T.
Published: February 2004

The selectins are Ca2+‐dependent cell adhesion molecules that facilitate the initial attachment of leukocytes to the vascular endothelium by binding to a carbohydrate moiety as exemplified by the tetrasaccharide, sialyl Lewis X (sLeX). An important property of the selectin‐sLeX interaction is its ability to withstand the hydrodynamic force of the blood flow. Herein, we used single‐molecule dynamic force spectroscopy (DFS) to identify the molecular determinants within sLeX that give rise to the dynamic properties of the selectin/sLeX interaction. Our atomic force microscopy (AFM) measurements revealed that the unbinding of the selectin/sLeX complexes involves overcoming at least two activation barriers. The inner barrier, which determines the dynamic response of the complex at high forces, is governed by the interaction between the Fuc residue of sLeX and a Ca2+ ion chelated to the lectin domain of the selectin molecule, whereas the outer activation barrier can be attributed to interactions involving the sialic acid residue of sLeX. Due to their steep inner activation barriers, the selectin‐sLeX complexes are less sensitive to high pulling forces. Hence, besides its contribution to the bond energy, the Ca2+ ion also grants the selectin–sLeX complexes a tensile strength that is crucial for the selectin‐mediated rolling of leukocytes.
The Gas‐Phase Hydrogen Bond Complexes between Formic Acid with Hydroxyl Radical: A Theoretical Study
Authors: Torrent‐Sucarrat Miquel , Anglada Josep M.
Published: February 2004

We report a theoretical study on seven radical hydrogen bond complexes between syn‐HCOOH and OH and eight radical hydrogen bond complexes between anti‐HCOOH and OH, that have been carried out by using the B3 LYP, MP2, QCISD, and CCSD(T) theoretical approaches with the 6‐311+G(2df,2p) basis set. In all cases, the bonding features were analysed using the atoms in molecules (AIM) theory by Bader and the natural bond orbital (NBO) partition scheme by Weinhold et al. We have found twelve complexes having a single hydrogen bond and three complexes presenting a cyclic structure with multiple bonds, pointing out the existence of a cooperative effect. One of them presents a bound O⋅⋅⋅O interaction producing a stabilisation effect. The stability of these complexes has been calculated to be in the −0.81 and −5.96 kcal mol−1range and their possible implication in the HCOOH plus OH reaction is also discussed. Finally, we also report the computed harmonic vibrational frequencies of the two OH stretching modes and the HOC out‐of‐plane wagging mode, along with the frequency red‐shifts originated by the complex formation and the corresponding computed intensity ratio relative to the monomers.
Visualization of Atomic Processes on Ruthenium Dioxide using Scanning Tunneling Microscopy
Authors: Over H. , Knapp M. , Lundgren E. , Seitsonen A. P. , Schmid M. , Varga P.
Published: February 2004

The visualization of surface reactions on the atomic scale provides direct insight into the microscopic reaction steps taking place in a catalytic reaction at a (model) catalyst's surface. Employing the technique of scanning tunneling microscopy (STM), we investigated the CO oxidation reaction over the RuO2(110) and RuO2(100) surfaces. For both surfaces the protruding bridging O atoms are imaged in STM as bright features. The reaction mechanism is identical on both orientations of RuO2. CO molecules adsorb on the undercoordinated surface Ru atoms from where they recombine with undercoordinated O atoms to form CO2 at the oxide surface. In contrast to the RuO2(110) surface, the RuO2(100) surface stabilizes also a catalytically inactive c(2×2) surface phase onto which CO is not able to adsorb above 100 K. We argue that this inactive RuO2(100)‐c(2×2) phase may play an important role in the deactivation of RuO2 catalysts in the electrochemical Cl2 evolution and other heterogeneous reactions.
Manganese, Iron, Cobalt, and Nickel Oxo‐, Peroxo‐, and Superoxoclusters: A Density Functional Theory Study
Authors: Uzunova Ellie L. , Nikolov Georgi St. , Mikosch Hans
Published: February 2004

The 3d‐transition‐metal dioxo‐, peroxo‐, and superoxoclusters with the general composition MO2, M(O2), and MOO (M=Mn, Fe, Co, and Ni) were studied by DFT by the B1LYP functional. The dioxides in their ground states represent the global minima for the M+O2 system. Both ground‐state dioxides and the lowest‐energy peroxides are in their (d‐only) highest spin states. The 6A1 state of Co(O2) exceeds the d‐only spin‐multiplicity value (quartet), being nearly isoenergetic with the 4A1 state of Co(O2). The energy gain on transforming the peroxides to the corresponding dioxides decreases in the order Mn(O2)>Fe(O2)>Co(O2)>Ni(O2) and varies in the range 0.27–1.8 eV. The dissociation energy to M+O2 for all studied peroxides is less than 1 eV being the lowest (0.47 eV) for Mn(O2). The Mn and Fe peroxides need less than 0.3 eV to rupture one of the MO bonds to form the corresponding superoxide. Mn and Fe superoxides are less stable than the corresponding peroxides; the superoxide of Co is more stable than its peroxide, while Ni superoxide is unstable—its energy is above the limit of dissociation to Ni+O2. According to the electrostatic potential maps, the oxygen atoms in the peroxides are more nucleophilic than those in the dioxides and superoxides, in which the terminal oxygen atom is more nucleophilic than the M‐bonded oxygen atom. This result differs from the expectations based on charge‐distribution analysis.
Improper Hydrogen CH⋅⋅⋅O Bonds Cause Self‐Association of α,β‐Enaminoketones Containing Fluorosubstituted Alkyl Groups
Authors: Wójcik Jacek , Kamienska‐Trela Krystyna , Pecul Magdalena , Bartoszak‐Adamska Elzbieta , Vdovienko Siergiej I. , Gerus Igor I.
Published: February 2004

Concentration‐ and temperature‐dependent IR, NMR and dipole‐moment studies on 4‐N,N‐dimethylamino‐1,1,1‐trifluoro‐3‐buten‐2‐one and two of its higher homologues showed that these compounds undergo reversible dimerization in nonpolar solvents. Antiparallel “closed” dimers are formed with a network of improper intermolecular CH⋅⋅⋅O hydrogen bonds. Quantitative analysis of the 1H NMR data yielded ΔH0=−17.6 kJ mol−1 and ΔS0=‐46.9 J deg−1 mol−1. The interactions observed are the strongest among those involving a CH group reported so far. The complex described here is the first example of a cyclic complex stabilized by two improper CH⋅⋅⋅O hydrogen bonds. The conclusions drawn from the solution and solid‐state data were confirmed by ab initio calculations.
Stability condition and steady‐state solution of various α–β filters for linear FM pulse compression radars
Authors: Amishima Takeshi , Ito Masayoshi , Kosuge Yoshio
Published: February 2004

Pulse compression is often used in radar to increase the detection range while suppressing the peak transmission power and to prevent a drop in the range resolution. However, a drawback of this technique is the target range is observed offset by an amount proportional to the range rate of the target. On the other hand, various α–β filters have been derived based on the differences in motion models. These filters define the process noise in a discrete system in terms of the velocity, the acceleration, or the n‐th derivative of the acceleration, or discretized after defining the process noise in a continuous system in terms of the acceleration. For the process noise in a discrete system defined in terms of the acceleration, we propose an α–β filter that tracks while internally correcting the bias observation error described above. In this paper, we show a necessary and sufficient stability condition of various stable α–β filters that track while internally correcting the bias observation error. We show that the stable gain region does not depend on the Doppler shift time constant and is invariant. Then we formulate the relationship between α and β and the error covariance matrix. In addition, for α–β filters where the process noise in a discrete system is defined in terms of the velocity or the acceleration, or where the process noise in a continuous system is defined in terms of the acceleration and then discretized, we showed that, in practice, the α–β filter with the process noise defined in terms of the velocity in discrete time, has superior performance, when the performance is measured in terms of error covariance matrix given a fixed maneuver index. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 87(6): 13–22, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10134
Detecting changes of buildings using stereo matching from aerial images taken at different positions and times
Authors: Watanabe Shintaro , Miyajima Koji , Inoue Ushio , Nakamura Taichi
Published: February 2004

GIS base maps are updated by using parallax to compare two aerial images taken at different times to interpret structural changes. Since an aerial image generally photographs a wide range, this interpretation work requires a great deal of time. Therefore, in this paper, the authors propose a method of automatically extracting structural changes with high precision to reduce the load of this interpretation work. Not only do the times differ at which the aerial images used for comparison were taken, but the shooting positions also frequently differ. This causes differences in shadow shapes and differences in structure viewing methods, and when aerial images are compared during automatic interpretation, it will cause the detection precision of structural changes to decrease. To deal with this problem, the authors eliminated the effects of differences in structure viewing methods by applying stereo matching and letting noncorresponding regions be structural change candidates. In addition, to correctly detect structural changes from those candidates, the authors used the outdoor light source model, which had been proposed by previous authors, to eliminate the effects of differences in shadow shapes. The results that were obtained by the proposed method showed that the detection precision of structural changes was approximately four times that of the conventional method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 87(6): 55–65, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20084
Surface receptors identify mouse NK1.1+ T cell subsets distinguished by function and T cell receptor type
Authors: Stenström Martin , Sköld Markus , Ericsson Anna , Beaudoin Lucie , Sidobre Stephane , Kronenberg Mitchell , Lehuen Agnès , Cardell Susanna
Published: February 2004

Natural killer T (NKT) lymphocytes rapidly produce several cytokines, including IL‐4 and IFN‐γ, upon activation, and act as regulatory cells at an early interphase of innate and adaptive immune responses. They have been implicated as important elements in diverse immune responses including the regulation of autoimmune disease, the immune response to infections, and the prevention of tumor metastasis. The broad spectrum of their activities suggested that functionally different subsets of NKT cells may exist. We demonstrate two functionally distinct splenic NKT populations identified by the expression of CD49b and CD69, respectively. Each NKT subset was represented by the amplified transgenic NKT cell population in a distinct transgenic mouse line expressing a CD1d‐restricted TCR. CD49bhigh CD69– NKT cells, termed NKT1 cells by us, were high producers of IFN‐γ after stimulation, but essentially devoid of IL‐4‐synthesizing cells. Most NKT1 cells used diverse (non‐Vα14‐canonical) TCR. The CD69+ CD49–/low NKT cell population, which we term NKT2, produced large quantities of IL‐4 and substantial amounts of IFN‐γ upon activation and were dominated by cells using the canonical Vα14‐Jα18 T cell receptor. Knowledge of the unique roles of the different NKT cell subsets in specific situations will be essential for our understanding of NKT cell biology.
Characterization of three CpG oligodeoxynucleotide classes with distinct immunostimulatory activities
Authors: Vollmer Jörg , Weeratna Risini , Payette Paul , Jurk Marion , Schetter Christian , Laucht Meike , Wader Tanja , Tluk Sibylle , Liu Ming , Davis Heather L. , Krieg Arthur M.
Published: February 2004

Oligodeoxynucleotides (ODN) with unmethylated deoxycytidyl‐deoxyguanosine (CpG) dinucleotides (CpG ODN) mimic the immunostimulatory activity of bacterial DNA and are recognized by the Toll‐like receptor 9 (TLR9). CpG ODN of the B‐Class stimulate strong B cell and NK cell activation and cytokine production. The highest degrees of NK stimulation as well as IFN‐α secretion by plasmacytoid DC were found to occur only with A‐Class ODN. A third class of CpG ODN combines the immune effects of A‐ and B‐Class CpG ODN. C‐Class ODN strongly stimulate B cell or NK cell activation and IFN‐α production. In contrast to the A‐Class, the C‐Class is wholly phosphorothioate, has no poly‐G stretches, but has palindromic sequences combined with stimulatory CpG motifs. All classes stimulate TLR9‐dependent signaling, but with strikingly different dose‐response relationships that are quite in contrast to those observed for IFN‐α. Effects similar to those on human cells were observed on mouse splenocytes. In contrast, splenocytes from TLR9‐deficient mice did not show any response to the three CpG ODN classes. In vivo studies demonstrate that C‐Class ODN are very potent Th1adjuvants. C‐Class ODN may represent new therapeutic drugs that combine the effects of A‐ and B‐Class ODN for broad applications in infectious disease or cancer therapy.
Cyclopentenone prostaglandins induce endothelial cell apoptosis independent of the peroxisome proliferator‐activated receptor‐γ
Authors: Erl Wolfgang , Weber Christian , Zernecke Alma , Neuzil Jiri , Vosseler Claudia A. , Kim Hyo Jung , Weber Peter C.
Published: February 2004

Cyclopentenone prostaglandins (CP‐PG), such as prostaglandin A1 (PGA1) or 15‐deoxy‐Δ12,14‐prostaglandin J2 (PGJ2), induce apoptosis in different cell types. PGJ2 is also a potent activator of the peroxisome proliferator‐activated receptor‐γ (PPARγ). We investigated whether PPARγ regulates CP‐PG‐induced apoptosis in endothelial cells (EC). We show that CP‐PG induce apoptosis in human umbilical vein EC (HUVEC). Incubation with PGA1 or PGJ2 for 24 h reduced HUVEC number and viability, while the synthetic activators Wy14643 or rosiglitazone had no effect. Flow cytometry and cell cycle analysis revealed externalized phosphatidylserine, caspase‐3 activation, and an increased percentage of cellswith a reduced DNA content by CP‐PG treatment. EMSA demonstrated an activation of PPARγ by PGJ2 and rosiglitazone. Immunohistochemistry of HUVEC and immunoblot analyses of protein extracts showed that PPARγ was localized in the nuclei of HUVEC, and that CP‐PG treatment decreased the amount of PPARγ protein. This degradation was prevented by a pan‐caspase inhibitor. Treatment of differentiated, endothelial‐like PPARγ‐deficient stem cells, or of HUVEC transfected with dominant‐negative PPARγ with CP‐PG, induced cell death and apoptosis. Our findings show that PGA1 and PGJ2 induce apoptosis in endothelial cells independent of PPARγ. As the synthesis of PGJ2 is increased at sites of inflammation, our results may suggest a possiblemechanism for endothelial damage.
FcγRII expression on follicular dendritic cells and immunoreceptor tyrosine‐based inhibition motif signaling in B cells
Authors: Aydar Yüksel , Wu Jiuhua , Song Jingmei , Szakal Andras K. , Tew John G.
Published: February 2004

Immune complexes (IC) initiate immunoreceptor tyrosine‐based inhibition motif (ITIM) signaling and inhibit B cell activation by coligating B cell receptor for antigen (BCR) and FcγRII. Nevertheless, IC on follicular dendritic cells (FDC) stimulate rapid germinal center (GC) B cell proliferation suggesting that interactions between IC and FDC render IC capable of B cell activation. Tounderstand this, we studied the kinetics of FDC FcγRII and complement receptors 1 and 2 (CR1&2) expressions during the GC reaction and determined whether FDC FcγRII could bind Fc in IC and block ITIM signaling. Mice were immunized with sheep red blood cells (SRBC), and CR1&2 and FcγRII levels in FDC reticula were monitored. The role of FDC FcγRII was studied using anti‐BCR‐stimulated A20 cells. Levels of FDC FcγRII in spleens of SRBC‐injected mice increased within 24 h and were dramatically increased (∼50‐fold) on days 3 and 5. In contrast, CR1&2 levels increased less than twofold. Addition of normal FDC, but not FDC lacking FcγRII, reduced and reversed anti‐BCR‐induced SH2 domain‐containing inositol phosphatase (SHIP)‐1 phosphorylation in A20 cells. FDC wereable to induce normal recall responses even after overnight incubation of the lymphocytes with IC to stimulate ITIM signaling. Engagement of Ig Fc with numerous FcγRII on FDC appears to minimize IC‐induced ITIM signaling. Thus, rapid up‐regulation of FDC FcγRII may explain why poorly immunogenic IC are rendered highly immunogenic when presented by FDC in GC.
Identification of a novel thioredoxin‐related protein, PC‐TRP, which is preferentially expressed in plasma cells
Authors: Wrammert Jens , Källberg Eva , Leanderson Tomas
Published: February 2004

Using cDNA subtraction we have identified a previously unknown cDNA, termed plasma cell thioredoxin‐related protein (PC‐TRP), which was overexpressed in plasma cells in vitro. The full‐length 2636‐bp PC‐TRP cDNA contained an open reading frame coding for 417 amino acids. The cDNA sequence was mapped to a region on mouse chromosome 13 and the PC‐TRP gene consists of ten exons distributed over a 28‐kb region. The PC‐TRP was found to contain three atypical thioredoxin domains and showed functional thioredoxin activity in vitro. A more detailed analysis revealed that PC‐TRP was expressed at a high level in plasma cells, both at the mRNA and protein level, while present at very low levels in all other cells and tissues examined. Immunohistological analysis revealed that PC‐TRP was expressed at high levels in all plasma cells isolated from bone marrow or lamina propria, irrespective of their Ig isotype. In the spleen, however, 60% of the IgG‐expressing plasma cells showed only a dull staining at day 14 after immunization, while >90% of the IgG‐secreting cells in the spleen expressed PC‐TRP at day 21 after immunization. In addition, an IgG‐secreting, PC‐TRPdull plasma cell population could also be observed after B cell activation in vitro.
The human C‐type lectin CLECSF8 is a novel monocyte/macrophage endocytic receptor
Authors: Arce Ignacio , Martínez‐Muñoz Laura , Roda‐Navarro Pedro , Fernández‐Ruiz Elena
Published: February 2004

Cell surface lectin receptors play important roles in the function of macrophages. Herein, we have identified and characterized the human orthologue of the mouse Mcl/Clecsf8.Human CLECSF8 codes for a type II membrane glycoprotein of 215 amino acids that belongs to the human calcium‐dependent lectin family (C‐type lectin). The cytoplasmic tail of CLECSF8 lacks consensus signaling motifs and its extracellular region shows a single carbohydrate recognition domain (CRD). The CLECSF8 gene has been localized on the telomeric region of the NK gene complex on chromosome 12p13 close to MINCLE. CLECSF8 mRNA shows a monocyte/macrophage expression pattern. Biochemical analysis of CLECSF8 on transiently transfected cells showed a glycoprotein of 30 kDa. Cross‐linking of the receptor leads to a rapid internalization suggesting that CLECSF8 constitutes and endocytic receptor.

See accompanying commentary http://dx.doi.org/10.1002/eji.200324641
CD4 T cells guarantee optimal competitive fitness of CD8 memory T cells
Authors: Johansen Pål , Stamou Panagiota , Tascon Ricardo E. , Lowrie Douglas B. , Stockinger Brigitta
Published: February 2004

We studied the contribution of CD4 T cell help to survival and competitive fitness of CD8 memory T cells specific for influenza virus nucleoprotein. In agreement with recent studies, the optimal generation of functional memory CD8 T cells required CD4 help, although long‐term maintenance of resting CD8 memory T cells did not absolutely depend on the presence of CD4 T cells. Nonetheless, CD4 T cells were essential during differentiation of CD8 memory T cells to imprint on them the capacity to compete effectively with other memory T cells. CD8 memory cells generated with help survived better in secondary polyclonal hosts, and co‐transfer into lymphopenic hosts together with "un‐helped" CD8 memory cells showed improved homeostatic expansion of CD8 memory cells that had been generated with CD4 help. Therefore, the requirement for CD4 help in CD8 T cell memory extends to homeostatic parameters that ensure the maintenance and competitive fitness of memory clones.
Antibody‐mediated bacterial clearance from the lower respiratory tract of mice requires complement component C3
Authors: Pishko Elizabeth J. , Kirimanjeswara Girish S. , Pilione Mylisa R. , Gopinathan Lakshmi , Kennett Mary J. , Harvill Eric T.
Published: February 2004

To assess the contribution of complement to respiratory immunity in the context of a natural bacterial infection, we used mice genetically deficient in complement components and the murine pathogen Bordetella bronchiseptica. Complement component C3 was not required for the control of bacterial infection or for the generation of infection‐induced protective immunity. However, C3‐deficient (C3–/–) mice were severely defective, compared to wild type, in vaccine‐induced protective immunity. Adoptively transferred immune serum from convalescent wild‐type or C3–/– animals rapidly cleared B. bronchiseptica from the lungs of wild‐type mice but did not affect its growth in C3–/– mice, indicating that the defect is not in the generation of protective immunity, but in its function. Immune serum was effective in C5‐deficient mice but had little effect in the lungs of mice lacking either Fcγ receptors (FcγR) or CR3, suggesting bacterial clearance is not via direct complement‐mediated lysis. Together, these data indicate that complement is required for antibody‐mediated clearance of Bordetella and suggest the mechanism involves C3 opsonization of bacteria for phagocytosis that is both CR3‐ and FcγR‐dependent.
Pulmonary tuberculosis in BALB/c mice with non‐functional IL‐4 genes: changes in the inflammatory effects of TNF‐α and in the regulation of fibrosis
Authors: Hernandez‐Pando Rogelio , Aguilar Diana , Hernandez Maria Luz Garcia , Orozco Hector , Rook Graham
Published: February 2004

In BALB/c mice, as in man, progressive pulmonary tuberculosis is accompanied by increasing expression of IL‐4. Therefore we have used BALB/c mice with disrupted IL‐4 genes (IL‐4–/–) to investigate the role of IL‐4 in pulmonary tuberculosis, with particular emphasis on the toxicity of TNF‐α and on fibrosis, both of which are neglected aspects of human tuberculosis. Delayed‐type hypersensitivity (DTH) sites in IL‐4+/+ mice were sensitive to the toxicity of locally injected TNF‐α, whereas DTH sites in IL‐4–/– mice were not. However, intravenous administration of IL‐4 to IL–4–/– mice restored the sensitivity of the DTH sites to pro‐inflammatory effects of TNF‐α. In late disease, the lungs of IL‐4+/+ mice expressed low IFN‐γ, but high TGF‐β and IL‐4, correlating with fibrosis, detected as a high hydroxyproline content. In contrast, TGF–β peaked 7 days after infection in the lungs of the IL‐4–/– mice, and then fell to very low levels in the late disease, while IFN‐γ remained high. Accordingly, hydroxyproline content was reduced in infected IL‐4–/– mice compared to IL‐4+/+ controls. In conclusion, the findings suggest that IL‐4 has modestly detrimental effects on the antibacterial efficacy of the Th1 response, and larger effects on the toxicity of TNF‐α, and on fibrosis.