bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic reconnection via tearing instability in a rotating viscous fluid
Authors: Bian N.H.
Published: September 2007

The resistive tearing instability of a sheet pinch, first investigated by Kuang & Roberts (1990) for the case of a rapidly rotating inviscid fluid, is studied for arbitrary rotation rate in a visco‐resistive fluid. Altogether there are three regimes of the resistive tearing instability which correspond to the particular parameter domain in the (Ω, Pm) plane. Here Ω is the angular velocity of the medium which is normalized to the Alfvén time and Pm is the magnetic Prandtl number. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Searching extra dimensions in compact stars
Authors: Barnaföldi G.G. , Lévai P. , Lukács B.
Published: September 2007

The electro‐magnetic and particle radiation detected from the direction of Cygnus X3 raise the question of the existence of special long‐lived, neutral particles. We investigate the origin of these particles in a special approach: the source object may contain compactified extra dimension and these particles are messengers of this state. We describe hyperon stars in 3 + 1 dimension and introduce the description of a compact stars in 3 + 1c + 1 dimensional space‐time. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Updated catalogue of the light curve solutions of contact binary stars
Authors: Csizmadia Sz. , Marton G. , Klagyivik P. , Spindler Sz.
Published: September 2007

The catalogue of the light curve solutions of contact binary stars was updated. Based on the catalogue data we call the attention to a remarkable gap in the temperature distribution of contact binaries which remained unexplained. The absolute dimensions of the components were calculated in a reliable way. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular cloud abundances and anomalous diffusion
Authors: Marschalkó G. , Forgács‐Dajka E. , Petrovay K.
Published: September 2007

The chemistry of molecular clouds has been studied for decades, with an increasingly general and sophisticated treatment of the reactions involved. Yet the treatment of turbulent diffusion has remained extremely sketchy, assuming simple Fickian diffusion with a scalar diffusivity D. However, turbulent flows similar to those in the interstellar medium are known to give rise to anomalous diffusion phenomena, more specifically superdiffusion (increase of the diffusivity with the spatial scales involved). This paper considers to what extent and in what sense superdiffusion modifies molecular abundances in interstellar clouds. For this first exploration of the subject we employ a very rough treatment of the chemistry and the effect of non‐uniform cloud density on the diffusion equation is also treated in a simplified way. The results nevertheless clearly demonstrate that the effect of superdiffusion is quite significant, abundance values at a given radius being modified by order of unity factors. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Studying Blazhko RR Lyrae stars with the 24‐inch telescope of the Konkoly Observatory
Authors: Sódor Á.
Published: September 2007

About a dozen field RR Lyrae stars have been observed with the 24‐inch Heyde‐Zeiss telescope of the Konkoly Observatory at Svábhegy, Budapest, since its refurbishment in 2003. Most of the observing time is allocated for the investigation of the Blazhko modulation, a phenomenon that still does not have a satisfactory explanation. The obtained multicolour CCD observations are unique in extent. The accuracy of the measurements makes it possible to detect low amplitude modulation of the light curve as well. The discovery of Blazhko stars with low modulation amplitudes warns that the incidence rate of the Blazhko modulation is, in fact, much larger than it was previously expected. This makes the efforts exploring the cause of the modulation even more important. A summary of our measurements and results achieved during the last 3 years is presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The double‐mode RR Lyrae variable BS Com
Authors: Dékány I.
Published: September 2007

We present the frequency analysis of the multicolour time series photometry of the field RRd variable BS Comae. The large number of data points in each of the BV (RI)C bands and the ∼0.01 magnitude accuracy of the individual measurements allow us a high precision analysis of the properties of the combination frequencies due to nonlinear coupling. Through the combination of the frequency spectra in different colors we show that except for the components corresponding to the linear combinations of the two pulsation modes, there are no other components present above the millimagnitude amplitude level. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Blazhko behavior of RV UMa
Authors: Hurta Zs.
Published: September 2007

RV UMa is one of the most extensively studied RR Lyrae stars showing Blazhko modulation. Its photometric observations cover more than 90 years. The published photoelectric observations of RV UMa obtained at the Konkoly Observatory (Kanyó 1976) were re‐considered and completed with previously unpublished data. During the time interval of the observations the periods of both the pulsation and the modulation varied within the ranges of 0.000007 and 0.9 days, respectively. We have found a definite but not strict inverse relation between the pulsation and modulation periods of RV UMa. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radial velocities of five globular clusters obtained with AAOmega
Authors: Székely P. , Kiss L.L. , Szatmáry K. , Csák B. , Bakos G.Á. , Bedding T.R.
Published: September 2007

Using the recently commissioned multi‐object spectrograph AAOmega on the 3.9m AAT we have obtained mediumresolution near‐infrared spectra for 10 500 stars in and around five southern globular clusters. The targets were 47 Tuc, M12, M30, M55 and NGC 288. We have measured radial velocities to ± 1 kms‐ 1 with the cross correlation method and estimated metallicity, effective temperature, surface gravity and rotational velocity for each star by fitting synthetic model spectra. An analysis of the velocity maps and velocity dispersion of member stars revealed systemic rotation in four of the target clusters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A mixed‐α,β miniprotein stereochemically reprogrammed to high‐binding affinity for acetylcholine
Authors: Rana Soumendra , Kundu Bijoy , Durani Susheel
Published: September 2007

The protein‐structure space is limited to L configuration in the asymmetric α‐amino acid structures; the function space, on other hand, seems limitless because of the chemical diversity in the amino acid side chain structures. The chemical diversity in side chain structure may be multiplied beneficially with the stereochemical diversity in main chain structure; thus, de novo protein design may be explored for customizing molecular structures stereochemically and molecular functions chemically. Illustrating de novo design in the structure space of L and D alphabet, canonical all‐β folds of poly‐L structure were reprogrammed as bracelet, boat, and canoe‐shaped molecules—the “boat” as a receptor‐like pocket and the “canoe” as a metal‐ion receptor—simply by mutating specific L‐amino acid residues to the corresponding D stereochemical structure. Demonstrating customization of molecular shape stereochemically and function chemically, a 15‐residue mixed‐α, β miniprotein of canonical poly‐L structure is now reprogrammed stereochemically as a cup‐shaped receptor for acetylcholine via cation‐π interaction with a triad of aromatic side chains placed in mimicry of the acetylcholine‐receptor sites both natural and artificial. Evidence from CD, fluorescence, NMR, DSC, ITC, MD, and molecular‐docking studies is presented to show that a rationally designed 15‐residue mixed‐L, D peptide is a cooperatively ordered molecular fold in the stereochemically specified molecular morphology, submicromolar in affinity of acetylcholine and thus an acetylcholine receptor exceptionally small and simple. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 231–243, 2007.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
The investigation of protein A and Salmonella antibody adsorption onto biosensor surfaces by atomic force microscopy
Authors: Lee Kyoung G. , Pillai Shreekumar R. , Singh Shree R. , Willing Gerold A.
Published: September 2007

The investigation of Protein A and antibody adsorption on surfaces in a biological environment is an important and fundamental step for increasing biosensor sensitivity and specificity. The atomic force microscope (AFM) is a powerful tool that is frequently used to characterize surfaces coated with a variety of molecules. We used AFM in conjunction with scanning electron microscopy to characterize the attachment of protein A and its subsequent binding to the antibody and Salmonella bacteria using a gold quartz crystal. The rms roughness of the base gold surface was determined to be approximately 1.30 nm. The average step height change between the solid gold and protein A layer was approximately 3.0 ± 1.0 nm, while the average step height of the protein A with attached antibody was approximately 6.0 ± 1.0 nm. We found that the antibodies did not completely cover the protein A layer, instead the attachment follows an island model. Salt crystals and water trapped under the protein A layer were also observed. The uneven adsorption of antibodies onto the biosensor surface might have led to a decrease in the sensitivity of the biosensor. The presence of salt crystals and water under the protein A layer may deteriorate the sensor specificity. In this report, we have discussed the application and characterization of protein A bound to antibodies which can be used to detect bacterial and viral pathogens. Biotechnol. Bioeng. 2008;99: 949–959. © 2007 Wiley Periodicals, Inc.
Metabolite profiling analysis of Methylobacterium extorquens AM1 by comprehensive two‐dimensional gas chromatography coupled with time‐of‐flight mass spectrometry
Authors: Guo Xiaofeng , Lidstrom Mary E.
Published: September 2007

Methylobacterium extorquens AM1 is a facultative methylotroph, which is a potential candidate to be used in commercial processes to convert simple one‐carbon compounds to a variety of multicarbon chemicals and products. To better understand C1 metabolism in M. extorquens AM1 at the systems level, metabolite profiling tools were developed and applied in this bacterium. Comprehensive two‐dimensional gas chromatography coupled with time‐of‐flight mass spectrometry (GC × GC‐TOFMS) was used to obtain metabolite profiles of M. extorquens AM1 (primarily organic acids) and to identify the metabolite differences between cells grown on methanol (C1 substrate) and succinate (multicarbon substrate). In this study, a list of compounds that included amino acids and major intermediates of central C1 and multicarbon metabolism were studied as target metabolites. For these, calibration curves were obtained for absolute quantification by spiking different amounts of standard mixtures to cell cultures. Parallel factor analysis (PARAFAC) was used for accurate peak quantification. Unknown chemical differences between cells grown on methanol and succinate were identified by applying Fisher ratio analysis at a selective mass channel (m/z 147). Thirty‐six compounds were discovered to be statistically differentially expressed between C1 and multicarbon metabolism. Among these, 13 were identified by matching to library mass spectra, and the rest were novel compounds that were not included in libraries. These differentially expressed compounds have provided clues to new pathways that are specifically linked to C1 metabolism. Biotechnol. Bioeng. 2008;99: 929–940. © 2007 Wiley Periodicals, Inc.
Bis(ZnII–cyclen) Complex as a Novel Receptor of Barbiturates in Aqueous Solution
Authors: Koike Tohru , Takashige Megumi , Kimura Eiichi , Fujioka Haruto , Shiro Motoo
Published: September 2007

A new bis‐zinc(II) receptor (Zn2L), which has two macrocyclic 12‐membered tetraamine (cyclen) ZnII complexes connected through a p‐xylene bridge, has been synthesized as a novel host molecule to recognize barbiturates (such as barbital (bar)) in aqueous solution. Each of the zinc(II) ions in the biszinc(II) receptor was originally intended to match the dianionic barbital anion (bar2−) with supplementary hydrogen bonds between the cyclen NH's and the three carbonyl oxygens in complementary positions to yield a 1:1 complex, Zn2L–bar2−. From an aqueous solution of equimolar Zn2L and barbital at pH 8, however, a cyclic 2:2 complex, (Zn2L‐bar2−)2, was isolated and characterized by X‐ray crystal analysis. The NMR study in 10% (v/v) D2O/H2O has revealed dissociation of (Zn2L–bar2−)2 solely into the original target 1:1 complex Zn2L–bar2− and established the dimerization constant for 2Zn2L–bar2− → (Zn2L–bar2−)2, Kd ( = [(Zn2L–bar2−)2]/[Zn2L–bar2−]2) to be 103.4 M−1. The thermodynamic parameters were evaluated from the NMR measurements at 25, 35, 45, and 55°C: ΔG = –1.9 × 104 J mol−1, ΔH = – 3.3 × 104 J mol−1, ΔS = – 49 J mol−1 K−1 at 25°C. Potentiometric pH titration of Zn2L (1 mM) and barbital (1 mM) disclosed extremely facile deprotonation of the two imido groups of barbital at pH less than 7 to form the dianionic barbital‐bound ZnII complexes Zn2L–bar2− and (Zn2L–bar2−)2, where‐by the barbital binding affinity for Zn2L was estimated to be Kbar ( = [Zn2L–bar2−]/[uncomplexed Zn2L][uncomplexed barbital]) = 105.8 M−1 at pH 8 and 25°C with I = 0.10 (NaNO3). The significance of the bis‐zinc(II) receptor in stabilizing the dianionic barbital is evident by comparison with the interaction of ZnII–cyclen complex (ZnL) with barbital, which yields only a 1:1 monoanionic barbital complex, ZnL–bar− (Kbar = [ZnL–bar−]/[uncomplexed ZnL][uncomplexed barbital] = 104.2M−1 at pH 8 and 25°C with I = 0.10 (NaNO3)).
Self‐assembling Tetrathiafulvalene‐based Rotaxanes and Catenanes
Authors: Li Zhan‐Ting , Stein Paul C. , Becher Jan , Jensen Dorthe , Mørk Pernille , Svenstrup Niels
Published: September 2007

A general stepwise approach is described for the preparation of tetrathiafulvalene (TTF)‐based linear and monoand dimacrocyclic compounds incorporating one or two 1,4‐dioxyphenylene, 9,10‐dioxyanthrylene, or 1,5‐ or 2,6‐dioxynaphthylene units from readily available starting materials. By utilizing the π–π stacking interactions of the TTF unit with the dipyridinium dication of 1,1′‐[1,4‐phenylenebis (methylene)] bis‐4,4′‐bipyridinium bis(hexafluorophosphate), a rotaxane and two [2]catenanes were synthesized starting from the linear and monomacrocyclic compounds, respectively. From the dioxyphenylene‐based dimacrocycle, three [3]pseudocatenanes (trans, cis, and a mixture of cis/trans isomers) were obtained with the trans compound as the major product. From the dioxyanthrylene dimacrocycle, only the trans‐[3]pseudocatenane was obtained. Catenane products were formed quantitatively from the 1,5‐dioxynaphthylene dimacrocycle in a template‐directed reaction, affording a trans‐[3]pseudo‐catenane together with a [4]pseudocatenane (mixture of cis/trans isomers). From the 2,6‐dioxynaphthylene dimacrocycle, a cis‐[3]pseudocatenane was obtained as the major product and a trans‐[3]pseudocatenane as the minor one. For the [3]pseudocatenanes (i.e., both the cis and trans catenanes), in which the TTF units were clamped by the tetracationic macrocycle, isomerizations were completely prevented even in the presence of trifluoroacetic acid. All new rotaxanes and catenanes were characterized by electrospray mass spectrometry, and the cis‐ and trans‐ [3]pseudocatenanes were additionally investigated by 1H NMR spectroscopy. The electrochemical and spectral properties of the rotaxane and the catenanes are reported. Catenane formation increases the redox potentials of the TTF unit. The results demonstrate the versatility of TTF as a building block in the construction of supramolecular structures.
Conformational Studies of Chiral Vinylogous Sulfonamidopeptides
Authors: Gennari Cesare , Salom Barbara , Potenza Donatella , Longari Chiara , Fioravanzo Elena , Carugo Oliviero , Sardone Nicola
Published: September 2007

The conformational preferences of chiral vinylogous aminosulfonic acids (vs‐amino acids) and of the corresponding oligomers (vs‐peptides) were investigated by a combination of X‐ray crystallography, variable‐temperature (VT) 1H NMR spectroscopy, FT‐IR spectroscopy, and NOE experiments. The major source of conformational freedom in the monomers is the rotation around the CC bond connecting the double bond with the allylic stereocenter (NC*CC). The allylic conformational preferences can be altered in the oligomers by the formation of secondary structures enforced by hydrogen bonding. Twelve‐membered‐ring hydrogen bonding is detected in the crystal structure of vs‐dipeptide 9, while fourteen‐membered‐ring hydrogen bonding is the most common folding pattern for the oligomers in chloroform solution. The experimental results are complemented by computer modeling: suitable force‐field (FF) parameters for the unsaturated sulfonamide group were developed from ab initio calculations. A Goodman–Still systematic pseudo‐Monte‐Carlo search was used for the conformational search. The conformers were minimized in chloroform with the GB/SA model. The calculations correctly predicted both the size of the hydrogen‐bonded ring and its relative importance, in agreement with the experimental data in solution.
Dimensional reduction in II‐VI materials: A2Cd3Q4 (A = K, Q = S, Se, Te; A = Rb, Q = S, Se), novel ternary low‐dimensional cadmium chalcogenides produced by incorporation of A2Q in CdQ
Authors: Axtell Enos A. , Liao Ju‐Hsiou , Pikramenou Zoe , Kanatzidis Mercouri G.
Published: September 2007

The synthesis of the isomorphous, layered chalcogenides K2Cd3S4 (I), Rb2Cd3S4 (II), K2Cd3Se4 (III), Rb2Cd3Se4 (IV), and K2Cd3Te4 (V) in molten A2Qx fluxes in reported (A = K, Rb; Q = S, Se, Te; x = 2 to 3). The compounds form as (Cd3Q4) layers interspersed with A + cations; the layers are composed of Cd3Q2−4 units shaped as truncated cubes. The compounds have room‐temperature band gaps of 2.75, 2.92, 2.36, 2.37, and 2.26 eV for I, II, III, IV, and V, respectively, and also display strong photoluminescence. The thermal analysis data for all compounds are reported. The properties of these compounds are compared with those of the three‐dimensional compounds CdS, CdSe, and CdTe, as well as those of the nanometer‐sized CdQ clusters. A conceptual context is presented to connect all these different types of compounds.
A bis(diimidazole)Copper Complex Possessing a Reversible CuII/CuI Couple with a High Redox Potential
Authors: McMaster Jonathan , Beddoes Roy L. , Collison David , Eardley David R. , Helliwell Madeleine , Garner C. David
Published: September 2007

The new diimidazole ligand, bis (1‐methyl‐4,5‐diphenylimidazol‐2‐yl)ketone (BIMDPK), has been synthesised, characterised and shown to form four‐coordinate bis(diimidazole) CuII and CuI complexes in the salts [Cu(bimdpk)2]‐[BF4]2 and [Cu(bimdpk)2][PF6], the structures of which have been determined by X‐ray crystallography. The cations of these salts have a very similar geometry with CuII–Nav = 1.949 and CuI–Nav = 1.999 Å; the N‐Cu‐N interbond angles are constrained by 1) the bite angle of the BIMDPK ligand to 94 ± 2° and 2) the interligand steric interactions, which lead to the dihedral angle of the intraligand CuN2 planes of 68.2° for CuII and 74.9° for CuI–that is, a CuN4 geometry intermediate between tetrahedral and square planar. The X‐band EPR spectrum for the powdered CuII compound is typical of an approximately D2 CuN4 centre possessing a dxy ground state (gx = 2.080, gy = 2.075, gz = 2.291; Az = 112.3 × 10−4 cm−1). The UV/vis spectra are dominated by charge‐transfer bands, and both the CuII and CuI systems are intensely coloured. The EPR and electronic spectra indicate that these cations have a very similar structure in the solid state and in solution; the potential of the [Cu(bimdpk)2]2+/[Cu(bimdpk)2]+ couple is 0.59 V vs. SCE in MeCN and 0.80 V vs. SCE in CH2Cl2, and the electron self‐exchange constant in MeCN is 1.9 × 104M−1S−1. Comparisons are made between the properties of the [Cu(bimdpk)2]2+/+ centres and related Cu centres in chemical and biological systems; the results of this study reinforce the view that a [Cu(His)4] centre should not be precluded from consideration in biological electron transport.
Pseudorotaxanes Formed Between Secondary Dialkylammonium Salts and Crown Ethers
Authors: Ashton Peter R. , Chrystal Ewan J. T. , Glink Peter T. , Menzer Stephan , Schiavo Cesare , Spencer Neil , Stoddart J. Fraser , Tasker Peter A. , White Andrew J. P. , Williams David J.
Published: September 2007

A very simple self‐assembling system, which produces inclusion complexes with pseudorotaxane geometries, is described. The self‐assembly of eight pseudorotaxanes with a range of stoichiometries–1:1, 1:2, 2:1, and 2:2 (host:guest)–has been achieved. These pseudorotaxanes self‐assemble from readily available components–well‐known crown ethers, such as dibenzo[24]crown‐8 and bis‐p‐phenylene[34]crown‐10, and secondary dialkylammonium hexafluorophosphate salts, such as (PhCH2)2NH+2PF−6 and (nBu)2NH+2PF−6–and have been characterized not only in the solid state, but also in solution and in the “gas phase”. The pseudorotaxanes are stabilized largely by hydrogen‐bonding interactions and, in some instances, by aryl‐aryl interactions.
Self‐assembling [2]‐ and [3]Rotaxanes from Secondary Dialkylammonium Salts and Crown Ethers
Authors: Aston Peter R. , Glink Peter T. , Stoddart J. Fraser , Tasker Peter A. , White Andrew J. P. , Williams David J.
Published: September 2007

The self‐assembly of three new rotaxanes—two [2]rotaxanes and a [3]rotaxane—formed by a “threading followed by stoppering” approach is described. These template‐directed syntheses rely on the formation of pseudorotaxane intermediates, which self‐assemble in solution from functionalized secondary dialkylammonium hexafluorophosphate threads and macrocyclic polyether rings (either dibenzo‐[24]crown‐8 or its asymmetric constitutional isomer). The stoppers—substituted 1,2,3‐triazoles–were created by thermally allowed 1,3‐dipolar cycloadditions between azido groups, which terminate the threads, and di‐tert‐butyl acetylenedicarboxylate.
On the Definition of Chirality
Authors: Barron Laurence D.
Published: September 2007

Should Lord Kelvin's definition of chirality be modified to accommodate concepts associated with the chirality of large random supramolecular structures? Stimulated by a recent article by D. Avnir et al. (Chem. Eur. J. 1996, 2, 174), L. D. Barron discusses this question. In their reply D. Avnir et al. further clarify and discuss their original thesis.
Novel Sulfur‐Containing Inorganic Aprotic Superacids as Effective Initiators of Low‐Temperature Cracking and Isomerization of Alkanes
Authors: Akhrem Irena , Gudima Svetlana , Vol'pin Mark
Published: September 2007

A novel family of inorganic aprotic superacids has been found. Oxochlorides and chloride of sulfur combined with aluminium halides (SOCl2·n AlX3, SO2Cl2·n AlX3, MeSO2Cl·n AlX3, CF3SO2Cl·n AlX3, S2Cl2·n AlX3; n = 2 or 3, X = Br or Cl) are found to be effective promoters for the cracking and isomerization of alkanes at room temperature.
Dynamic Behavior in Solution of the Trans‐Hydridodihydrogen Complex [OsHCl(n2‐H2)(CO)(PiPr3)2]: Ab Initio and NMR Studies
Authors: Bakhmutov Vladimir I. , Bertrán Juan , Esteruelas Miguel A. , Lledós Agustí , Maseras Feliu , Modrego Javier , Oro Luis A. , Sola Eduardo
Published: September 2007

Reaction of complex [OsHCl‐(CO)(PiPr3)2] (1) with hydrogen gives the trans‐hydridodihydrogen complex [OsH‐Cl(n2‐H2)(CO)(PiPr3)2] (2). The H‐H distance in the dihydrogen ligand, determined by variable‐temperature 1H T1 measurements, is 0.8 Å. The fast‐spinning nature of the dihydrogen ligand of 2 has been deduced by evaluating the deuterium quadrupole coupling constant for the n2‐D2 ligand of [OsDCl(n2‐D2)(CO)(PiPr3)2] ([D3]2). Measurements of the equilibrium constants for formation of 2 (K) give ΔH0 = – 14.1 ± 0.5 kcal mol−1 and ΔS0 = – 30 ±1 e.u. An equilibrium isotope effect Kd/K of 2.8 is found for this reaction. The activation parameters for the H2 loss from 2 are ΔH‡ = 14.6 ± 0.2 kcal mol−1 and ΔS‡ = 9.9 ± 0.5 e.u. Hydrogen exchange between the hydrido and n2‐H2 ligands of 2 takes place at a slow rate (kobs2) at high temperatures. Activation parameters ΔH‡ = 17.4 ± 0.5 kcal mol−1 and ΔS‡ = 1.3 ± 1 e.u., and a kinetic isotope effect (kobs2/kobs2d) of 4.6 at 333 K have been determined for this exchange. Ab initio calculations on the model system [OsH‐Cl(H2)(CO)(PH3)2] confirm that the trans‐hydridodihydrogen complex [OsH‐Cl(n2‐H2)(CO)(PH3)2] (4) is the most stable species (rHH = 0.84 Å). In addition, a cis‐hydridodihydrogen complex 5, with a relative energy of 13.8 kcal mol−1, occupies a local minimum in the potential hypersurface. The energy of other possible trihydrido isomers have also been evaluated. On the basis of the thermodynamic and kinetic data, and the results of the ab initio calculations, the possible mechanism for the H/n2‐H2 exchange is discussed.
The β‐Lactone Route to a Totally Stereoselective Synthesis of Carnitine Derivatives
Authors: Bernabei Ida , Castagnani Roberto , Angelis Francesco De , Fusco Enrico De , Giannessi Fabio , Misiti Domenico , Muck Sandra , Scafetta Nazareno , Tinti Maria Ornella
Published: September 2007

The syntheses of the enantiomerically pure, carnitine‐related β‐lactones 10 and 12 starting from various carnitine precursors of opposite configuration (or carnitine itself) are described. (R)‐3‐Chlorocarnitine (20) has also been directly prepared from (S)‐carnitine (14) and has been cyclized to 12 by a second inversion of configuration of the stereogenic centre. By nucleophilic attack at the carbonyl carbon, the β‐lactone carnitine derivatives have been converted into esters, amides and guanidino congeners. Following this route, it is possible to obtain the biologically active isomer (R)‐carnitine (1) starting from the otherwise useless industrial by‐product (S)‐carnitine (14). Nucleophilic attack by selected ambidient nucleophiles at the β‐carbon of the same β‐lactone derivatives results in a second inversion of configuration of the stereogenic centre. Besides aminocarnitine (3), chiral acetylcarnitine (2) and acetylthiocarnitine (5) have been synthesized in homochiral forms following this latter procedure.
Nanometre‐Scale Molecular Ribbons
Authors: Breidenbach Stefan , Ohren Stefan , Vögtle Fritz
Published: September 2007

The longest molecular ribbons known to date (3–10), composed of a series of [3.3]metacyclophane units, have been synthesised by means of a repetitive synthetic strategy. These multiple ring systems with up to nine bridged benzene rings in a row are the longest structurally perfect cyclophane sequences known to date. The synthetic strategy comprises three steps: ester reduction to a tetrakis(hydroxymethyl) compound, derivatisation to the corresponding tetrakis(bromomethyl) derivative, and double cyclisation with the new key building block 14, which was especially developed for this sequence. Single‐crystal X‐ray analyses (3 a–7 a) and 1H NMR spectroscopy (3–10) show that, regardless of their length, these molecules adopt zigzag folded all‐syn conformations. π‐Stacks of nanometre dimensions are thus formed.
Conformation and Self‐Association of a Hybrid Peptide of Cecropin A and Melittin with Improved Antibiotic Activity
Authors: Fernández Imma , Ubach Josep , Fuxreiter Monika , Andreu José Manuel , Andreu David , Pons Miquel
Published: September 2007

A 15‐residue hybrid peptide containing residues 1–7 from cecropin A and residues 2–9 from melittin, CA‐(1–7)M(2–9), is a potent antibiotic with broader activity than cecropin A, but without the cytotoxic character of melittin. The conformational behaviour of CA(1–7)M(2–9) including the formation of multimeric species in solution has been investigated by circular dichroism, ultracentrifugation, electrospray mass spectrometry, NMR and energy calculations. Addition of hexafluoroisopropanol or liposomes causes the appearance of a CD spectrum characteristic of a helical structure that changes with pH, buffer and peptide concentration. The concentration dependence is atypical, as the ellipticity at 222 nm decreases with peptide concentration and is not correlated with a corresponding decrease in helix content as measured from the NMR spectra. The presence of aggregated structures is demonstrated by ultracentrifugation and ES‐MS experiments, which also provide an indication of the stoichiometry. Longrange NOEs suggest a model of aggregation with neighbouring molecules packed antiparallel. Aggregation causes very slow proton‐deuterium exchange in some amide protons in the C‐terminal region and provides a method for estimating a very large association constant (ca. 106M−1) as well as the stoichiometry of the aggregates. The tendency to aggregate seems to be an inherited feature from melittin and may enhance the antibiotic activity either by facilitating the incorporation of the peptide into the membrane in large quantities or by promoting the disruption of the membrane.
Synthesis of 4‐Silylcyclobut‐2‐enethiones and their Use in Cyclobutadiene Generation
Authors: Müller Martin , Förster Wolf‐Rüdiger , Holst Andreas , Kingma Arend J. , Schaumann Ernst , Adiwidjaja Gunadi
Published: September 2007

Alkynyl silyl sulfides 2 reacted with ynamines 3 to give 1:1 adducts. The structure of 4‐silylcyclobut‐2‐enethiones 4 was confirmed by X‐ray analysis of 4a. A cyclobutadiene intermediate is probably not involved in this reaction; we think that it is initiated by a silyl transfer from 2 to 3, and that this is followed by a combination of the resulting ions to give the unsaturated thioketene 7, which undergoes an electrocyclization to give products 4. In the reaction of thiones 4 with trimethyloxonium tetrafluoroborate (Meerwein salt) selective methylation at sulfur was observed to give cyclobutenethionium ions 16. Ions 16 underwent fluoride‐induced desilylation with various fluoride sources to give cyclobutadienes 17, which could not be isolated, but trapping of 17 a‐c was possible with dimethyl acetylenedicarboxylate yielding regioisomeric benzene derivatives 20–23. Similarly, 17 a and bis(methylthio)methylene malononitrile (24) led to hexatriene derivative 27 by a sequence of cycloaddition and two ring‐opening reactions. In contrast, silyl‐substituted cyclobutadienes 17d,e dimerized even in the presence of trapping agents to anti‐tricyclo‐[4.2.0.02,5]octadienes 29; this suggests that a two‐step cycloaddition is taking place, rather than a concerted Diels‐Alder reaction. Attempts to intercept 17d, e, generated from 16d,e with cyclopentadiene (30), gave deprotonation of 30 leading to substitution of the methylthio group in 16 and finally to formation of cyclobutenes 33 through a hydrogen shift.
Effects of Nitrogen Substitution in Poly(Pyrazolyl)Borato Ligands: From Orbital Energy Levels to C–H ⃛ O Hydrogen Bonding
Authors: Janiak Christoph , Scharmann Tobias G. , Green Jennifer C. , Parkin Richard P. G. , Kolm Mario J. , Riedel Erwin , Mickler Wulfhard , Elguero José , Charamunt Rosa M. , Sanz Dionisia
Published: September 2007

The electronic effect of substituting CH with N in poly(pyrazolyl)‐borato ligands and their transition‐metal complexes is shown to be a decrease in energy of the filled metal and ligand orbitals. This conclusion is based on the cyclovoltammograms and photoelectron spectra of bis(hydrotris(azolyl)borato)‐iron(II) and ‐cobalt(II) complexes (azolyl = pyrazolyl and 1,2,4‐triazolyl) and on MO calculations. 57Fe Mössbauer spectra of bis(hydrotris(1,2,4‐triazolyl)‐borato)iron(II) show that there is a fine‐tuning of the HOMO–LUMO gap by a shift in transition temperature for the spin equilibrium. 15N NMR spectroscopy supports the assignment of a higher negative charge to the exodentate N‐4 nitrogen than to the endodentate N‐2 or N‐3 positions in the poly(azolyl)borato anions, where azolyl is 1,2,4‐triazolyl or tetrazolyl. The electron withdrawing effect of the additional nitrogen atoms and the in‐corporation of water of crystallization by O–H ⃛ N bonding both assist in the formation of (azolyl)C–H ⃛ O bonds.
Photoreactions of Phenyl‐Substituted N‐(pent‐4‐enyl‐1‐oxy)Pyridine‐2(1 H)‐Thiones
Authors: Hartung Jens , Hiller Margit , Schmidt Philipp
Published: September 2007

A series of hitherto unknown N‐(pent‐4‐enyl‐1‐oxy)pyridine‐2(1 H)‐thiones (6) were prepared from substituted pent‐4‐enyl tosylates or benzylic chlorides. On irradiation with incandescent light heterocycles 6 liberated alkoxy radicals 2, which were studied for rearrangement reactions. Surprisingly, all transformations involving the 1‐phenylpent‐4‐enyl‐1‐oxy radical (2a), for example, to give the substituted thioether 8, 2‐bro‐momethyl‐5‐phenyltetrahydrofuran (11), or the tetrahydrofuran 14a, were not stereoselective. On the other hand 2‐, 3‐ mono‐, and 1,5‐disubstituted pent‐4‐enyl‐1‐oxy radicals 2d‐e and 2g cyclized in good yields and with good to excellent stereoselectivities to give the corresponding 2,4‐cis‐ and 2,3‐trans‐phenyltetra‐hydrofurfuryl radicals 3d‐e, and the trans‐2‐benzyl‐5‐methyl substituted intermediate 3g. The major reaction mode of the 4‐phenylpent‐4‐enyl‐1‐oxy radical (2f) was the 6‐endo cyclization, which afforded 3‐phenyltetrahydropyran (13f) as the major product (endo:exo = 93:7) after trapping with hydrogen donors. According to the experimental data of the present study, the unusual reactivity of the 1‐phenylpent‐4‐enyl‐1‐oxy radical (2a) in 5‐exo–trig ring closures could be caused by a coplanar arrangement of the benzyloxy moiety in the transition state of the cyclization. This interaction would lock the radical center in 2a in a preferred conformation, which would result in similar steric effects for both cis‐ and trans‐ cyclizations.
Reactions of the Double‐Stranded Oligonucleotide d(TTGGCCAA)2withcis‐[Pt(NH3)2(H2O)2]2+and [Pt(NH3)3(H2O)]2+
Authors: Reeder Franziska , Gonnet Florence , Kozelka Jiří , Chottard Jean‐Claude
Published: September 2007

The kinetics of the reactions between the GG‐containing double‐stranded oligonucleotide d(TTGGCCAA)2(II) and the platinum complexescis‐[Pt‐(NH3)2(H2O)2]2+(1) and [Pt(NH3)3‐(H2O)]2+(2) were studied and compared with those already determined for the reactions of the single‐stranded octanucleotide d(CTGGCTCA) (I).[1]The results were as follows: i) Complex1reacted faster than2with bothIandII. ii) Both complexes1and2reacted faster withIIthan withI. This acceleration was greater for1(x 13) than for2(x4) and only due to the increase of the platination rate of the 5′‐G of the GG sequence. iii) For bothIandII, the first platination by1and2was faster on the 5′‐G than on the 3′‐G. This difference was more significant for the platination ofII(k5′/k3′= 12 for1and 5 for2) than ofI(k5′/k3′≤ 2). iv) The cyclization reaction of the monoadducts (G*) of1to yield the GGcis‐Pt(NH3)2+2chelate (G*G*) was considerably slowed down in the duplex. This rate decrease was significantly larger for the chelation of the 5′‐G*(factor of 16) than of the 3′‐G*(factor of 4) monoadducts. v) The intrastrand chelation of the 3′‐G*monoadducts (k3′c) was faster than that of the 5′‐G*monoadducts (k5′c), both forIandII(k3′c/k5′c= 3 and 13, respectively). vi) In addition to the intrastrand G*G*crosslink, we also observed the interstrand crosslink d(GG*CC)–d(GG*CC) between the two 3′‐Gs of the central tetranucleotide. The rate constant for the interstrand crosslinking (k3′i) was half that of the intrastrand chelation (k3′c). vii) The 5′ monoadduct, which was formed faster (k5′k3′i<k3′c), exhibited a half‐life of 3.2 h under our experimental conditions.
TiIV‐BINOLate‐Catalyzed Highly Enantioselective Additions of β‐Substituted Allylstannanes to Aldehydes
Authors: Weigand Stefan , Brückner Reinhard
Published: September 2007

Enantiomerically pure homoallyl alcohols were prepared from aldehydes R1‐CHO (R1 = Ph, pentyl, Ph‐CHCH‐, iPr) and β‐substituted allyl‐stannanes H2CCR2‐CH2‐SnBu3 (R2 = pentyl, tBuPh2SiO‐CH2‐, tBuPh2SiO‐CH2‐CH2‐, PhS‐CH2‐CH2‐). These reactions were catalyzed by the same additives—Ti(OR)4 (10 mol%) and (R)‐BINOL (20 mol%)—that Keck et al. used in analogous reactions with methallyl‐and allyltributylstannane. To attain optimum ee values (96.4–99.2% in the reaction with hexanal) these additives had to be premixed for 2 h at room temperature. Ti(OEt)4 and Ti(OiPr)4 gave equally good results, while Ti(OMe)4, Ti(OCHEt2)4, and Ti(OtBu)4 were inferior. Our procedure works in the absence of molecular sieves [which were previously found to give rather unreliable results in reactions catalyzed by Ti(OiPr)4/(R)‐BINOL] and can be extended to enantioselective addition reactions with allyl‐ and methallyltributylstannane, too (+ hexanal: 97.4 and 97.0% ee, respectively).
Dendritic Models of Redox Proteins: X‐ray Photoelectron Spectroscopy and Cyclic Voltammetry Studies of Dendritic bis(Terpyridine) iron(II) Complexes
Authors: Chow Hak‐Fun , Chan Ida Y.‐K. , Chan Dominic T. W. , Kwok Raymund W. M.
Published: September 2007

A series of iron‐containing metallodendrimers from the zeroth to the third generation was synthesized and characterized. The iron(II) ion of these metal complexes is encapsulated within a hydrophobic polyether dendritic envelope. X‐ray photoelectron spectroscopy analysis revealed that the bonding environment of the iron atom was essentially ronment of the iron atom was essentially the same in dendrimers of different generations. However, cyclic voltammetry studies indicated that the reversibility of the metal redox process decreased in the higher‐generation dendrimers. These observations were similar to those of a related electrochemical study conducted on the redox protein cytochrome C, in which the decrease in electron transfer reversibility was explained as a result of the increasing remoteness of the metal ion of the higher‐generation dendrimers from the electrode surface.
Catalytic Properties of Layered Gold–Palladium Colloids
Authors: Schmid Günter , West Heike , Malm Jan‐Olle , Bovin Jan‐Olv , Grenthe Carl
Published: September 2007

Layered bimetallic gold‐palladium colloids in the size range of 20–56 nm have been synthesized by the seed=growth method: gold seeds were covered by palladium layers of various thickness and vice versa. The outer metal was coordinated by trisulfonated triphenylphosphine and sodium sulfanilate ligands to stabilize the bimetallic particles to such an extent that they could be isolated in the solid state. Owing to the hydrophilic ligand shell, redispersion in water was possible in any concentration. High‐resolution transmission electron microscopy and energy‐dispersive X‐ray analysis was used to characterized the colloids. Stabilized and nonstabilized gold‐palladium and palladium‐gold systems on a TiO2 support were used as heterogeneous catalysts for the hydrogenation of hex‐2‐yne to cis‐hex‐2‐ene. Both the palladium‐plated gold seeds and the gold‐plated palladium particles showed considerably increased activities compared with the pure metals. The ligand shell seems not to influence the catalytic behavior because protected and unprotected colloids behave very similarly.
Peptide Helices as Rigid Molecular Rulers: A Conformational Study of Isotactic Homopeptides from α‐Methyl‐α‐isopropylglycine, [L‐(αMe)Val]n
Authors: Polese Alessandra , Formaggio Fernando , Crisma Marco , Valle Giovanni , Toniolo Claudio , Bonora Gian Maria , Broxterman Quirinus B. , Kamphuis Johan
Published: September 2007

Terminally blocked, isotactic homopeptides from the sterically demanding α‐methylvaline of general formula Y‐[L‐(αMe)Val]n‐OtBu (Y = Z, pBrBz, Ac; n = 2–8) have been prepared step‐by‐step in solution and fully characterized. The conformations preferred in solution (β‐turn and right‐handed 310‐helix) have been assessed by FT‐IR, 1H NMR and CD spectroscopy. The molecular and crystal structures of the Z‐protected trimer, hexamer, heptamer and octamer have been determined by X‐ray diffraction. In the crystal state, while the trimer is folded in a type III β‐turn conformation, the longest homopeptides form well‐developed, regular, right‐handed 310‐helices. The screw sense in the helix of the pBrBz‐blocked octamer has been confirmed to be right‐handed by solid‐state and solution CD spectroscopy. The possible exploitation of these peptide helices as rigid and precise molecular rulers is discussed.
A Convergent Synthesis of Carbohydrate‐Containing Dendrimers
Authors: Ashton Peter R. , Boyd Sue E. , Brown Christopher L. , Jayaraman Narayanaswamy , Nepogodiev Sergey A. , Stoddart J. Fraser
Published: September 2007

The synthesis of carbohydratecontaining dendrimers has been achieved by a convergent growth approach. The synthetic strategy involves: 1) the synthesis of the triglucosylated derivative of tris(hydroxymethyl)methylamine (TRIS), 2) the introduction of a glycine‐derived spacer and 3,3′‐iminodipropionic acid derived branching units on to the TRIS derivative by amide bond formation, 3) condensation of the above saccharidecontaining dendrons with a trifunctional 1,3,5‐benzenetricarbonyl derivative, used as the core, by formation of amide bonds, and 4) deprotection of the saccharide units. A 9‐mer and an 18‐mer, carrying nine and eighteen saccharide units at the periphery, respectively, have been synthesized, in high yields at each step, by this synthetic strategy. By a variety of chromatographic and spectroscopic techniques, the dendrimers were shown to be structurally homogeneous, monodisperse, and error‐free at all steps in their growth. These investigations were complemented by molecular modeling studies on the dendrimers. The presence of slightly distorted C3 symmetry was noted in both the 9‐mer and the 18‐mer.
Thermal and Light‐Induced Spin Transition in [Fe(bpen)X2] (bpen = 1,6‐Bis(2‐pyridyl)‐2,5‐diazahexane, X = NCS‐, NCSe‐)
Authors: Buchen T. , Gütlich P. , Toftlund H.
Published: September 2007

The thermal and light‐induced spin transitions in [Fe(bpen)(NCS)2] and [Fe(bpen)(NCSe)2] have been investigated by means of magnetic susceptibility and Mössbauer measurements. The HS → LS transition in [Fe(bpen)(NCS)2] is detected at temperatures below 120 K (T1/2 [when the fraction of high‐spin species γHS = 0.5] = 68 K) with a residual HS fraction of 8% at 20 K. The transition is fairly abrupt and no hysteresis is observed, in contrast to earlier studies (ref. [8]). The generation of metastable HS states in [Fe(bpen)(NCS)2] is achieved by rapid cooling of the sample and by irradiating the compound at low temperatures with light of appropriate wavelengths (LIESST). The HS → LS relaxation of the metastable spin states after rapid cooling is observed at temperatures between 35 and 42.5 K and shows strong deviations from single exponential behavior. The spin‐transition behavior changes drastically on substitution of the thiocyanate ions by NCSe‐. In [Fe(bpen)(NCSe)2] a gradual and complete spin transition between 140 and 250 K is observed (T1/2 = 181 K). Irradiation of the compound with green light at low temperatures does not result in formation of long‐lived metastable HS states. The spintransition curves derived from magnetic susceptibility and Mössbauer studies show good agreement for each compound, and no hints of significantly different Lamb–Mössbauer factors for the HS and LS states are observed.
High‐Spin → Low‐Spin Relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and Thermal Spin‐State Trapping—Dynamics of Spin Transition Versus Dynamics of Phase Transition
Authors: Buchen T. , Gütlich P. , Sugiyarto K. H. , Goodwin H. A.
Published: September 2007

The iron(II) complex [Fe(bpp)2]‐(CF3SO3)2 H2O (bpp = 2,6‐bis(pyrazolyl‐3‐yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≈︁285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse‐LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin‐state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin‐state trapping is triggered by an additional structural phase transition of the system.
9,10‐Dimetallatriptycenes of Group 14: A Novel Synthetic Approach from ortho‐Phenylenemagnesium
Authors: Dam Matheus A. , Akkerman Otto S. , De Kanter Franciscus J. J. , Bickelhaupt Friedrich , Veldman Nora , Spek Anthony L.
Published: September 2007

9,10‐Dimetallatriptycenes of Group 14 are readily accessable by a novel synthetic approach: reaction of ortho‐phenylenemagnesium (1) with RMCl3 afforded 9,10‐dimethyl‐9,10‐dimetallatriptycenes (3; M = Si, Ge, Sn) or 9, 10‐dimethyl‐9‐germa‐10‐stannatriptycene (11). The reaction can even be tuned to afford unsymmetrically substituted triptycenes such as 9‐methyl‐10‐phenyl‐9,10‐digermatriptycene (8); in some of these reactions, strong indications were obtained for the intermediacy of tri‐Grignard reagents RM(2‐C6H4MgCl)3 (5, 10). The new triptycenes were characterised by their spectral data and in the case of 3c (M = Sn) by an X‐ray crystal structure determination.
The Unimolecular Chemistry of Protonated Glycinamide and the Proton Affinity of Glycinamide—Mass Spectrometric Experiments and Theoretical Model
Authors: Uggerud Einar , Hvistendahl Georg , Rasmussen Bård , Kinser Robin D. , Ridge Douglas P.
Published: September 2007

The potential energy hypersurface of protonated glycinamide (GAH+) has been investigated experimentally and theoretically. The calculated G2(MP2) value for the proton affinity of glycinamide, PAcalcd = 919 kJ mol‐1, is in good agreement with the measured value of 908PAexp<914kJ mol‐1. The fact that the amide group is a better hydrogenbond acceptor explains why glycinamide has a higher PA than glycine. Proton transfer experiments with glycinamide performed in a Fourier transform mass spectrometer and analysis of metastable GAH+ ions in a four‐sector mass spectrometer show that the lowest‐energy unimolecular reactions are two distinct processes: 1) loss of CO, which has a substantial barrier for the reverse reaction, and 2) loss of CO plus NH3, which has no barrier for the reverse reaction. Ab initio quantum chemical calculations give a reaction model that is consistent with the observed fragmentation pattern.