bluuebunny/crossref_metadata_2025 huggingface dataset:
A Distinctive Example of the Cooperative Interplay of Structure and Environment in Tuning of Intramolecular Charge Transfer in Second‐Order Nonlinear Optical Chromophores
Authors: Abbotto Alessandro , Beverina Luca , Bradamante Silvia , Facchetti Antonio , Klein Christopher , Pagani Giorgio A. , Redi‐Abshiro Mesfin , Wortmann Rüdiger
Published: May 2003

The strongly enhanced cooperative influence of medium polarity and organic structural design on the first hyperpolarizability β of a novel family of highly polarizable azinium‐(CHCH‐thienyl)‐dicyanomethanido chromophores 1–3 is described. The dyes can be efficiently synthesized by regioselective protonation/alkylation of the corresponding bidentate anion precursors. Consecutive annelation of the pyridyl ring of 1 (pyridine→quinoline→acridine) and medium polarity effects are responsible for an extraordinarily variable range of intramolecular charge transfer (ICT), leading to a large set of π‐electron distribution patterns. Accordingly, systems with remarkably different zwitterionic/quinoid character in the ground and excited states present β values in a broad range, eventually switching from negative to positive. Our investigation is based on a combination of experimental (UV/Vis spectroscopy, multinuclear NMR spectroscopy, and electrooptical absorption measurements) and computational (ab initio) approaches. It is shown that: 1) β and μβ are dramatically influenced, even by orders of magnitude, by a complex, non‐monotonic interplay of structure and medium action, which in turn affects molecular ICT and bond length alternation (BLA), 2) the computations, validated by different experimental data, are to be recommended as an extremely useful tool in the search for a greatly improved set of molecular nonlinear optical (NLO) responses (in the case of 1–3 they show that such conditions may be attained only in a narrow and limited range of dielectric constants in which the annelation effect operates most efficiently), and 3) the search for the most favorable molecular NLO response of a highly polarizable chromophore both in solution and in solid matrices should simultaneously take into account not only the molecular design supplemented by annelation effects but also the polarity of the medium.
Mechanisms of Electrochemically‐Induced Retro‐Cyclopropanation Reactions of Fullerene Derivatives Using Digital Simulations
Authors: Carano Maurizio , Echegoyen Luis
Published: May 2003

Three C60 derivatives, 1, 2 and 3, have been studied by cyclic voltammetry (CV) under high vacuum in anhydrous tetrahydrofuran (THF). The CV behavior was essentially similar to that already observed for other cyclopropanated fullerene derivatives. After the second reduction processes all compounds undergo a chemical reaction that generates another electroactive species. This “new” chemical species is likely to be the compound with the cyclopropane ring open. Differences in CV behavior were observed for the different addends. Electrochemical data obtained at different scan rates for a given potential window, were fit with the BAS digital simulation program, DigiSim. The purpose of this study was to probe the proposed mechanisms and to obtain reliable estimations of the kinetic constants for the homogeneous chemical reactions taking place during the CV experiments. Calculations at the PM3 level lend additional support to the conclusions derived from digital simulations. The proposed mechanism is similar for all the compounds and involves two main chemical reactions in a reversible square scheme.
Nε Functionalization of Metal and Organic Protected L‐Histidine for a Highly Efficient, Direct Labeling of Biomolecules with [Tc(OH2)3(CO)3]+
Authors: Pak Jae Kyoung , Benny Paul , Spingler Bernhard , Ortner Kirstin , Alberto Roger
Published: May 2003

Two different pathways for the introduction of an acetyl group at Nε in a Nα, Nδ, and ‐COO protected histidine to afford Nε‐(CH2COOH)‐histidine derivative 7 b are presented. The purpose of this study is the coupling of 7 b to amino groups in bioactive molecules such as peptides. After full deprotection of such a bioconjugate, histidine provides three coordination sites which efficiently coordinate to [99mTc(OH2)3(CO)3]+ or [Re(OH2)3(CO)3]+ in a facial geometry. This allows the development of novel radiopharmaceuticals. Selective derivatization at the Nε position has conveniently been achieved by concomitant protection of Nα and Nδ with a carbonyl group forming a six‐membered urea. Cyclic urea ring opening with Fm‐OH, coupling of phenylalanine as a model to 7 b through its primary amine and removing of all protecting groups in one step gave a histidine derivative of phenylalanine which could be labeled at 10−5 M with 99mTc in very high yield and even in about 50 % yield at 10−6 M. The Xray structure of a complex with [Re(CO)3]+ in which anilin is coupled to 7 b confirms the facial arrangement of histidine. A second pathway applies directly the [Re(CO)3]+ moiety as a protecting group. This is one of the rare examples in which a metal fragment is used as a protecting group for organic functionalities. The coordination to histidine protects the Nα, Nδ and COO group in one single step, subsequent alkylation with BrCH2COOH(R) at Nε, coupling to phenylalanine and oxidative deprotection of [Re(CO)3]+ to [ReO4]− gave the corresponding bioconjugate in which histidine is coupled to phenylalanine through an acetylamide at Nε. Both methods offer convenient pathways to introduce histidine in a biomolecule under retention of its three coordination sites. The procedures are adaptable to any biomolecule with pendant amines and allow the development of novel radiopharmaceuticals or inversed peptides.
Bonding Energetics in Alkaline Metal Alkoxides and Phenoxides
Authors: Nunes Paulo , Leal Joāo P. , Cachata Vera , Raminhos Henrique , Minas da Piedade Manuel E.
Published: May 2003

The bonding energetics in a variety of alkaline metal, alkoxides and phenoxides, MOR, was investigated based on the corresponding enthalpies of formation in the crystalline state determined by reaction‐solution calorimetry. The results obtained at 298.15 K were as follows: ΔfH$\rm{_{m}^{\,o}}$ (MOR, cr)/kJ mol−1 = 382.7±1.4 (LiOC6H5), 513.6±2.5 (NaO‐nC6H13), 326.4±1.4 (NaOC6H5), 375.2±3.4 (KOCH3), 434.5±2.7 (KOC2H5), 467.1±5.2 (KO‐nC3H7), 459.3±2.1 (KO‐nC4H9), 464.6±5.7 (KO‐tC4H9), 464.3±2.5 (KO‐nC6H13), 333.3±3.1 (KOC6H5), 380.6±2.9 (RbOCH3), 434.1±2.9 (RbOC2H5), 345.3±2.9 (LiOC6H5), 379.1±3.0 (CsOCH3), 432.3±3.1 (CsOC2H5), 466.9±5.0 (CsO‐nC3H7), 461.3±3.5 (CsO‐nC4H9), 461.9±2.5 (CsO‐tC4H9), 349.2±1.4 (CsOC6H5). These results together with revised ΔfH$\rm{_{m}^{\,o}}$ (MOR, cr) values from the literature, were used to derive a consistent set of lattice energies for the MOR compounds and discuss general trends in the structure–energetics relationship based on the Kapustinskii equation.
Diastereoselective Solution and Multipin‐Based Combinatorial Array Synthesis of a Novel Class of Potent Phosphinic Metalloprotease Inhibitors
Authors: Makaritis Anastasios , Georgiadis Dimitris , Dive Vincent , Yiotakis Athanasios
Published: May 2003

The solution‐phase synthesis and resolution of new phosphinopeptidic building blocks containing a triple bond was realized in high yields and optical purities (units 3 a–d). The absolute configuration of the target compounds was unambiguously established by NMR studies. A post‐assembly diversification strategy of these blocks was developed through 1,3‐dipolar cycloaddition of a variety of in situ prepared nitrile oxides. This strategy led to the rapid and efficient diastereoselective preparation of a novel class of isoxazole‐containing phosphinic peptides (peptides 5 a–i). Solid‐phase version of this strategy was efficiently achieved on multipin solid technology, by developing a new protocol for the coupling of Punprotected dipeptidic blocks with solid supported amino acids in a quantitative and diastereoselective manner. Optimization of dipolar cycloadditions onto pin‐embodied phosphinic peptides allowed the convenient preparation of this new class of pseudopeptides. The crude phosphinic peptides (9 a–k) were obtained in high yields and purity as determined by RP‐HPLC. Inhibition assays of some of these peptides revealed that they behave as very potent inhibitors of MMPs, outmatching previously reported phosphinic peptides, in terms of potency (Ki in the range of few nM).
Pyrene‐Derived Novel One‐ and Two‐Component Organogelators
Authors: Babu P. , Sangeetha N. M. , Vijaykumar P. , Maitra Uday , Rissanen Kari , Raju A. R.
Published: May 2003

A new class of alkyl‐chain‐appended pyrene derivatives 4–14 were synthesized and evaluated for their gelation abilities. Depending on the nature of the linking group, these compounds gelated a number of organic solvents, either in the presence or in the absence of the acceptor molecule 2,4,7‐trinitrofluorenone (TNF). Compounds with ester, ether, or alkyl linkages gelated a number of hydroxylic and hydrocarbon solvents by means of a charge‐transfer interaction with TNF, while compounds with amide, urethane and urea linkers formed gels on their own in a variety of solvents by means of π–π stacking and hydrogen‐bonding interactions. The Xray crystal structure of urethane (S)‐12 showed hydrogen‐bonding and stacking features, as suggested by the model. The gels obtained were investigated by spectroscopic and electron microscopic techniques which provided structural insights.
Ternary Complexes between Cationic GdIII Chelates and Anionic Metabolites in Aqueous Solution: An NMR Relaxometric Study
Authors: Botta Mauro , Aime Silvio , Barge Alessandro , Bobba Gabriella , Dickins Rachel S. , Parker David , Terreno Enzo
Published: May 2003

The 1H and 17O NMR relaxometric properties of two cationic complexes formed by GdIII with a macrocyclic heptadentate triamide ligand, L1, and its Nmethylated analogue, L2, have been investigated in aqueous media as a function of pH, temperature and magnetic field strength. The complexes possess two water molecules in their inner coordination sphere for which the rate of exchange has been found to be sensibly faster for the Nmethylated derivative and explained in terms of electronic effects (decrease of the charge density at the metal center) and perturbation of the network of hydrogen‐bonded water molecules in the outer hydration sphere. The proton relaxivity shows a marked dependence from pH and decreases of about six units in the pH range 6.5 to 9.0. This has been accounted for by the displacement of the two water molecules by dissolved carbonate which acts as a chelating anion. The formation of ternary complexes with lactate, malonate, citrate, acetate, fluoride and hydrogenphosphate has been monitored by 1H NMR relaxometric titrations at 20 MHz and pH 6.3 and the value of the affinity constant, K, and of the relaxivity of the adducts could be obtained. Lactate, malonate and citrate interact strongly with the complexes (log K ≥3.7) and coordinate in a bidendate mode by displacing both water molecules. Larger affinity constants have been measured for GdL2. Acetate, fluoride and hydrogenphosphate form monoaqua ternary complexes which were investigated in detail with regard to their relaxometric properties. The NMR dispersion (NMRD) profiles indicate a large contribution to the relaxivity of the adducts from water molecules belonging to the second hydration shell of the complexes and hydrogen‐bonded to the anion. A VT 17O NMR study has shown a marked increase of the rate of water exchange upon binding which is explained by coordination of the anion in an equatorial site, thus leaving the water molecule in an apical position, more accessible for interactions with the solvent molecules of the second hydration shell which facilitate the exchange process.
Theoretical Evidence of Persistent Chirality in D3 Homoleptic Hexacoordinate Complexes with Monodentate Ligands
Authors: Alemany Pere , Alvarez Santiago , Avnir David
Published: May 2003

A theoretical study of the enantiomer interconversion pathway relevant to racemization reactions of hexacoordinate transition‐metal complexes is presented based on density functional calculations. The potential‐energy surface for the trigonal twist pathway of the [Zr(SH)6]2− model compound has been explored. The optimum structure reproduces, to a very good approximation, the experimental geometry of the analogous compound in which the thiolato groups have C6H4‐4‐OMe substituents instead of H atoms. A barrier of about 19 kcal mol−1 is estimated for the racemization of [Zr(SH)6]2− and exploratory calculations for [Zr(SC6H4‐4‐OMe)6]2− indicate that a larger barrier should be expected. For the chiral homoleptic organometallic complexes [ZrMe6]2− and [RhMe6]3− no significant racemization barrier is expected.
Novel and Anti‐Inflammatory Constituents of Garcinia subelliptica
Authors: Weng Jing‐Ru , Lin Chun‐Nan , Tsao Lo‐Ti , Wang Jih‐Pyang
Published: May 2003

Four novel phloroglucinol derivatives, garcinielliptones A (1), B (2), C (3), D (4), a novel triterpenoid, garcinielliptone E (5), and three known compounds were isolated from the seeds of Garcinia subelliptica. The structures, including relative configurations, were elucidated by means of spectroscopic data. Known compounds garsubellin A (6) and garcinielliptin oxide (7) showed potent inhibitory effects on the release of β‐glucuronidase, and β‐glucuronidase and histamine, respectively, from peritoneal mast cells stimulated with compound 48/80 in a concentration‐dependent manner with IC50 values of 15.6±2.5, and 18.2±3.6 and 20.0±2.7 μM, respectively. Compound 7 showed potent inhibitory effects on the release of β‐glucuronidase and lysozyme from neutrophils stimulated with formyl‐Met‐Leu‐Phe(fMLP)/cytochalasin B (CB) in a concentration‐dependent manner with IC50 values of 15.7±3.0 and 23.9±3.2 μM, respectively. Compound 7 also showed potent inhibitory effect on superoxide formation from neutrophils stimulated with fMLP/CB also in a concentration‐dependent manner with an IC50 value of 17.9±1.5 μM.
Gold Glyconanoparticles: Synthetic Polyvalent Ligands Mimicking Glycocalyx‐Like Surfaces as Tools for Glycobiological Studies
Authors: Barrientos África G , de la Fuente Jesús M. , Rojas Teresa C. , Fernández Asunción , Penadés Soledad
Published: May 2003

A simple and versatile methodology is described for tailoring sugar‐functionalised gold nanoclusters (glyconanoparticles) that have 3D polyvalent carbohydrate display and globular shapes. This methodology allows the preparation of glyconanoparticles with biologically significant oligosaccharides as well as with differing carbohydrate density. Fluorescent glyconanoparticles have been also prepared for labelling cells in biological tests. The materials are water soluble, stable under physiological conditions and present an exceptional small core size. All of them have been characterised by 1H NMR, UV and IR spectroscopy, TEM and elemental analysis. Their highly polyvalent network can mimic glycosphingolipid clustering and interactions at the plasma membrane, providing an controlled system for glycobiological studies. Furthermore, they are useful building blocks for the design of nanomaterials.
Coordination Chemistry of the Soluble Metal Oxide Analogue [Mo5O13(OCH3)4(NO)]3− with Manganese Carbonyl Species
Authors: Villanneau Richard , Proust Anna , Robert Francis , Gouzerh Pierre
Published: May 2003

The reactions of neutral or cationic manganese carbonyl species towards the oxo‐nitrosyl complex [Na(MeOH){Mo5O13(OCH3)4(NO)}]2− have been investigated in various conditions. This system provides an unique opportunity for probing the basic reactions involved in the preparation of solid oxide‐supported heterogeneous catalysts, that is, mobility of transition‐metal species at the surface and dissolution–precipitation of the support. Under nitrogen and in the dark, the reaction of in situ generated fac‐{Mn(CO)3}+ species with (nBu4N)2[Na(MeOH)‐{Mo5O13(OMe)4(NO)}] in MeOH yields (nBu4N)2[Mn(CO)3(H2O){Mo5O13(OMe)4(NO)}] at room temperature, while (nBu4N)3[Na{Mo5O13(OMe)4(NO)}2{Mn(CO)3}2] is obtained under reflux. The former transforms into the latter under reflux in methanol in the presence of sodium bromide; this involves the migration of the fac‐{Mn(CO)3}+ moiety from a basal κ2O coordination site to a lateral κ3O site. Oxidation and decarbonylation of manganese carbonyl species as well as degradation of the oxonitrosyl starting material and reaggregation of oxo(methoxo)molybdenum fragments occur in non‐deareated MeOH, and both (nBu4N)4[Mn(H2O)2{Mo5O16(OMe)2}2{Mn(CO)3}2] and (nBu4N)4[Mn(H2O)2{Mo5O13(OMe)4(NO)}2] as well as (nBu4N)2[MnBr{Mo5O13(OMe)4(NO)}] have been obtained in this way. The rhenium analogue (nBu4N)2[Re(CO)3(H2O){Mo5O13(OMe)4(NO)}] has also been synthesized. The crystal structures of (nBu4N)2[Re(CO)3(H2O){Mo5O13(OMe)4(NO)}], (nBu4N)3[Na{Mo5O13(OMe)4(NO)}2{Mn(CO)3}2], (nBu4N)4[Mn(H2O)2{Mo5O16(OMe)2}2{Mn(CO)3}2], (nBu4N)4[Mn(H2O)2{Mo5O13(OMe)4(NO)}2] and (nBu4N)2[MnBr{Mo5O13(OMe)4(NO)}] have been determined.
Formation of Novel Sulfur‐Containing C60F16 Cycloadducts between Tetrathiafulvalene and C60F18; A Unique Six‐Electron Cycloaddition of a Fullerene Involving F2 Loss
Authors: Darwish Adam D. , Avent Anthony G. , Boltalina Olga V. , Gol′dt Ilya , Kuvytchko Igor , Da Ros Tatiana , Street Joan M. , Taylor Roger
Published: May 2003

Co‐evaporation of solutions of C60F18 and tetrathiafulvalene in toluene produces an unsymmetrical C60F16:tetrathiafulvalene adduct through a unique six‐electron cycloaddition involving displacement of two fluorine atoms by a terminal CC double bond of the fulvalene. The adduct rearranges into two further adducts, one of which is characterised as a new type of fullerene derivative, a thiiranofullerene, formed by elimination of a thioketene moiety from the tetrathiafulvalene adduct. The initial addition also produces a bisadduct in which the addends comprise one tetrathiafulvalene molecule and one in which carbon disulfide has been eliminated. The latter adduct involves cycloaddition of an unsaturated aromatic dithiolactone moiety.
Mutations in Distant Residues Moderately Increase the Enantioselectivity of Pseudomonas fluorescens Esterase towards Methyl 3Bromo‐2‐methylpropanoate and Ethyl 3Phenylbutyrate
Authors: Horsman Geoff P. , Liu Andrew M. F. , Henke Erik , Bornscheuer Uwe T. , Kazlauskas Romas J.
Published: May 2003

Directed evolution combined with saturation mutagenesis identified six different point mutations that each moderately increases the enantioselectivity of an esterase from Pseudomonas fluorescens (PFE) towards either of two chiral synthons. Directed evolution identified a Thr230Ile mutation that increased the enantioselectivity from 12 to 19 towards methyl (S)‐3‐bromo‐2‐methylpropanoate. Saturation mutagenesis at Thr230 identified another mutant, Thr230Pro, with higher‐than‐wild‐type enantioselectivity (E=17). Previous directed evolution identified mutants Asp158Asn and Leu181Gln that increased the enantioselectivity from 3.5 to 5.8 and 6.6, respectively, towards ethyl (R)‐3‐phenylbutyrate. In this work, saturation mutagenesis identified other mutations that further increase the enantioselectivity to 12 (Asp158Leu) and 10 (Leu181Ser). A homology model of PFE indicates that all mutations lie outside the active site, 12–14 Å from the substrate and suggests how the distant mutations might indirectly change the substrate‐binding site. Since proteins contain many more residues far from the active site than close to the active site, random mutagenesis is strongly biased in favor of distant mutations. Directed evolution rarely screens all mutations, so it usually finds the distant mutations because they are more common, but probably not the most effective.
Theoretical Study on the Mechanism of Iron Carbonyls Mediated Isomerization of Allylic Alcohols to Saturated Carbonyls
Authors: Branchadell Vicenç , Crévisy Christophe , Grée René
Published: May 2003

The conversion of allylic alcohols to enols mediated by Fe(CO)3 has been studied through density functional theoretical calculations. From the results obtained a complete catalytic cycle has been proposed in which the first intermediate is the [(allyl alcohol)Fe(CO)3] complex. This intermediate evolves to the [(enol)Fe(CO)3] complex through two consecutive 1,3‐hydrogen shifts involving a π‐allyl hydride intermediate. The highest Gibbs energy transition state corresponds to the partial decoordination ot the enol ligand prior to the coordination of a new allyl alcohol molecule that regenerates the first intermediate. Alternative processes for the [(enol)Fe(CO)3] complex such as [Fe(CO)3]‐mediated enol–aldehyde transformation and enol isomerization have also been considered. The results obtained show that the former process is unfavourable, whereas the enol isomerization may compete with the enol decoordination step of the catalytic cycle.
Improved One‐Pot Synthesis of Styryl Tetrahydrofurans and Cyclohexanes by Radical Addition to β‐Nitrostyrenes in the Presence of Benzoyl Peroxide
Authors: Jang Yeong‐Jiunn , Shih Yuh‐Kuo , Liu Jing‐Yuan , Kuo Wen‐Yu , Yao Ching‐Fa
Published: May 2003

Stereoselective styryl derivatives have been prepared based on radical substitution (addition–elimination) of heterocycles or cyclohydrocarbons units to (E)‐β‐nitrostyrenes 1 using a common radical initiator benzoyl peroxide. High reactivity and selectivity with wide substrate scope were attained by using this easy methodology. The reactions using easily obtained and one‐pot potential starting materials gave excellent trans‐selectivity with medium to high yields in all cases. Synthetic utility of this approach has been demonstrated by the preparation of various trans‐styryl derivatives.
Rational Chemical Strategies for Carbon Nanotube Functionalization
Authors: Banerjee Sarbajit , Kahn Michael G. C. , Wong Stanislaus S.
Published: May 2003

Whereas the chemistry of fullerenes is well‐established, the chemistry of single‐walled carbon nanotubes (SWNTs) is a relatively unexplored field of research. Investigations into the bonding of moieties onto SWNTs are important because they provide fundamental structural insight into how nanoscale interactions occur. Hence, understanding SWNT chemistry becomes critical to rational, predictive manipulation of their properties. Among the strategies discussed include molecular metal complexation with SWNTs to control site‐selective chemistry in these systems. In particular, work has been performed with Vaska's and Wilkinson's complexes to create functionalized adducts. Functionalization should offer a relatively simple means of tube solubilization and bundle exfoliation, and also allows for tubes to be utilized as recoverable catalyst supports. Solubilization of oxidized SWNTs has also been achieved through derivatization by using a functionalized organic crown ether. The resultant adduct yielded concentrations of dissolved nanotubes on the order of 1 g L−1 in water and at elevated concentrations in a range of organic solvents, traditionally poor for SWNT manipulation. To further demonstrate chemical processability of SWNTs, we have subjected them to ozonolysis, followed by treatment with various independent reagents, to rationally generate a higher proportion of oxygenated functional groups on the nanotube surface. This protocol has been found to purify nanotubes. More importantly, the reaction sequence has been found to ozonize the sidewalls of these nanotubes. Finally, SWNTs have also been chemically modified with quantum dots and oxide nanocrystals. A composite heterostructure consisting of nanotubes joined to nanocrystals offers a unique opportunity to obtain desired physical, electronic, and chemical properties by adjusting synthetic conditions to tailor the size and structure of the individual sub‐components, with implications for self‐assembly.
Cycloadditions of Isobenzofuran to a Constrained Template Bearing Neighboring Dienophiles
Authors: Stoermer Martin J. , Butler Douglas N. , Warrener Ronald N. , Weerasuria K. D. V. , Fairlie David P.
Published: May 2003

A high yielding synthesis of the pentacyclic diene–dione 1 has enabled investigation of its reactivity as a double dienophile in Diels–Alder [4+2] cycloadditions with isobenzofuran, leading to novel and highly symmetrical three‐sided cavitands 3 and 4.
Hydrogen–Hydrogen Bonding: A Stabilizing Interaction in Molecules and Crystals
Authors: Matta Chérif F. , Hernández‐Trujillo Jesús , Tang Ting‐Hua , Bader Richard F. W.
Published: May 2003

Bond paths linking two bonded hydrogen atoms that bear identical or similar charges are found between theortho‐hydrogen atoms in planar biphenyl, between the hydrogen atoms bonded to the C1–C4 carbon atoms in phenanthrene and other angular polybenzenoids, and between the methyl hydrogen atoms in the cyclobutadiene, tetrahedrane and indacene molecules corseted with tertiary‐tetra‐butyl groups. It is shown that each such H–H interaction, rather than denoting the presence of “nonbonded steric repulsions”, makes a stabilizing contribution of up to 10 kcal mol−1to the energy of the molecule in which it occurs. The quantum theory of atoms in molecules—the physics of an open system—demonstrates that while the approach of two bonded hydrogen atoms to a separation less than the sum of their van der Waals radii does result in an increase in the repulsive contributions to their energies, these changes are dominated by an increase in the magnitude of the attractive interaction of the protons with the electron density distribution, and the net result is a stabilizing change in the energy. The surface virial that determines the contribution to the total energy decrease resulting from the formation of the H–H interatomic surface is shown to account for the resulting stability. It is pointed out that H–H interactions must be ubiquitous, their stabilization energies contributing to the sublimation energies of hydrocarbon molecular crystals, as well as solid hydrogen. H–H bonding is shown to be distinct from “dihydrogen bonding”, a form of hydrogen bonding with a hydridic hydrogen in the role of the base atom.
1H and 13C NMR Characterization of Hemiamidal Isoniazid‐NAD(H) Adducts as Possible Inhibitors Of InhA Reductase of Mycobacterium tuberculosis
Authors: Broussy Sylvain , Coppel Yannick , Nguyen Michel , Bernadou Jean , Meunier Bernard
Published: May 2003

Isoniazid (INH) is easily oxidized with manganese(III) pyrophosphate, a chemical model of the KatG protein involved in activation of INH inside the bacteria Mycobacterium tuberculosis. Performed in the presence of NAD+, this oxidation generates a family of isomeric INH–NAD(H) adducts, which have been shown to be effective inhibitors of InhA, an enzyme essential in mycolic acid biosynthesis. In this work, we fully characterized by 1H and 13C NMR spectroscopy four main species of INH–NAD(H) adducts that coexist in solution. Two of them are open diastereoisomers consisting of the covalent attachment of the isonicotinoyl radical at position four of the nicotinamide coenzyme. The other two result from a cyclization involving the amide group from the nicotinamide and the carbonyl group from the isonicotinoyl radical to give diastereoisomeric hemiamidals. Although an INH–NAD(H) adduct with a 4S configuration has been characterized within the active site of InhA from Xray crystallography and this bound adduct interpreted as an open form (Rozwarski et al., Science 1998, 279, 98–102), it is legitimate to raise the question about the effective active form(s), open or cyclic, of INH–NAD(H) adduct(s). Is there a single active form or are several forms able to inhibit the InhA activity with different levels of inhibitory potency?
Alternative Heterocycles for DNA Recognition: The Benzimidazole/Imidazole Pair
Authors: Briehn Christoph A. , Weyermann Philipp , Dervan Peter B.
Published: May 2003

Boc‐protected benzimidazole‐pyrrole, benzimidazole‐imidazole, and benzimidazole‐methoxypyrrole amino acids were synthesized and incorporated into DNA binding polyamides, comprised of N‐methyl pyrrole and N‐methyl imidazole amino acids, by means of solid‐phase synthesis on an oxime resin. These hairpin polyamides were designed to determine the DNA recognition profile of a side‐by‐side benzimidazole/imidazole pair for the designated six base pair recognition sequence. Equilibrium association constants of the polyamide‐DNA complexes were determined at two of the six base pair positions of the recognition sequence by quantitative DNase I footprinting titrations on DNA fragments each containing matched and single base pair mismatched binding sites. The results indicate that the benzimidazole‐heterocycle building blocks can replace pyrrole‐pyrrole, pyrrole‐imidazole, and pyrrole‐hydroxypyrrole constructs while retaining relative site specifities and subnanomolar match site affinities. The benzimidazole‐containing hairpin polyamides represent a novel class of DNA binding ligands featuring tunable target recognition sequences combined with the favorable properties of the benzimidazole type DNA minor groove binders.
Cover Picture: Hydrogen–Hydrogen Bonding: A Stabilizing Interaction in Molecules and Crystals (Chem. Eur. J. 9/2003)
Authors: Matta Chérif F. , Hernández‐Trujillo Jesús , Tang Ting‐Hua , Bader Richard F. W.
Published: May 2003

The cover picture shows a schematic representation of the change in structure accompanying the planarization of biphenyl through the formation of bond paths between the pairs of ortho‐hydrogen atoms. The top figure for the twisted equilibrium structure portrays four of the rings of hydrogen atoms, each shown as a spatial region defined by the intersection of its C|H interatomic surface with the van der Waals surface defined by the 0.001 au electron density envelope, the surfaces for the pairs of ortho‐hydrogen atoms touching at the geometry of the equilibrium structure. Planarization results in a lengthening of the CC separation between the rings by ∼0.01 Å, and the ortho‐hydrogen atoms are brought to separations ∼0.04 Å less than twice their van der Waals radii. The resulting increase in the energy of the carbon atoms is, however, largely negated by HH bonding, that is, the formation of an interatomic surface and an associated bond path linking each pair of ortho‐hydrogen atoms. Thus the ortho‐hydrogen atoms in planar biphenyl do not experience “steric nonbonded repulsions”, but rather, like all interactions denoted by a bond path, make a stabilizing contribution to the energy of ∼10 kcal mol−1 per HH interaction. HH bonding is present between the corresponding hydrogen atoms in polybenzenoids, such as phenanthrene and chrysene, and it is the presence of such interactions between the hydrogens of methyl groups in neighboring tetra‐tert‐butyl groups that encapsulate and stabilize the otherwise unstable tetrahedrane and cyclobutadiene molecules. For further details see the article by R. F. W. Bader et al. on p. 1940 ff.
Deletion of mdmB impairs mitochondrial distribution and morphology in Aspergillus nidulans
Authors: Koch Katrin V. , Suelmann Rüdiger , Fischer Reinhard
Published: May 2003

Mitochondria form a dynamic network of interconnected tubes in the cells of Saccharomyces cerevisiae or filamentous fungi such as Aspergillus nidulans, Neurospora crassa, or Podospora anserina. The dynamics depends on the separation of mitochondrial fragments, their movement throughout the cell, and their subsequent fusion with the other parts of the organelle. Interestingly, the microtubule network is required for the distribution in N. crassa and S. pombe, while S. cerevisiae and A. nidulans appear to use the actin cytoskeleton. We studied a homologue of S. cerevisiae Mdm10 in A. nidulans, and named it MdmB. The open reading frame is disrupted by two introns, one of which is conserved in mdm10 of P. anserina. The MdmB protein consists of 428 amino acids with a predicted molecular mass of 46.5 kDa. MdmB shares 26% identical amino acids to Mdm10 from S. cerevisiae, 35% to N. crassa, and 32% to the P. anserina homologue. A MdmB‐GFP fusion protein co‐localized evenly distributed along mitochondria. Extraction of the protein was only possible after treatment with a non‐ionic and an ionic detergent (1% Triton X‐100; 0.5% SDS) suggesting that MdmB was tightly bound to the mitochondrial membrane fraction. Deletion of the gene in A. nidulans affected mitochondrial morphology and distribution at 20°C but not at 37°C. mdmB deletion cells contained two populations of mitochondria at lower temperature, the normal tubular network plus some giant, non‐motile mitochondria. Cell Motil. Cytoskeleton 55:114–124, 2003. © 2003 Wiley‐Liss, Inc.
Dynamic association of a tumor amplified kinase, Aurora‐A, with the centrosome and mitotic spindle
Authors: Stenoien D. L. , Sen S. , Mancini M.A. , Brinkley B. R.
Published: May 2003

Aurora‐A kinase, also known as STK15/BTAK kinase, is a member of a serine/threonine kinase superfamily that includes the prototypic yeast Ipl1 and Drosophila aurora kinases as well as other mammalian and non‐mammalian aurora kinases involved in the regulation of centrosomes and chromosome segregation. The Aurora‐A gene is amplified and overexpressed in a wide variety of human tumors. Aurora‐A is centrosome‐associated during interphase, and binds the poles and half‐spindle during mitosis; its over‐expression has been associated with centrosome amplification and multipolar spindles. GFP‐Aurora‐A was used to mark centrosomes and spindles, and monitor their movements in living cells. Centrosome pairs labeled with GFP‐Aurora‐A are motile throughout interphase undergoing oscillations and tumbling motions requiring intact microtubules and ATP. Fluorescence recovery after photobleaching (FRAP) was used to examine the relative molecular mobility of GFP‐Aurora‐A, and GFP‐labeled α‐tubulin, γ‐tubulin, and NuMA. GFP‐Aurora‐A rapidly exchanges in and out of the centrosome and mitotic spindle (t1/2∼3 sec); in contrast, both tubulins are relatively immobile indicative of a structural role. GFP‐NuMA mobility was intermediate in both interphase nuclei and at the mitotic spindle (t1/2∼23–30 sec). Deletion mapping identifies a central domain of Aurora‐A as essential for its centrosomal localization that is augmented by both the amino and the carboxyl terminal ends of the protein. Interestingly, amino or carboxy terminal deletion mutants that maintained centrosomal targeting exhibited significantly slower molecular exchange. Collectively, these studies contrast the relative cellular dynamics of Aurora‐A with other cytoskeletal proteins that share its micro‐domains, and identify essential regions required for targeting and dynamics. Cell Motil. Cytoskeleton 55:134–146, 2003. © 2003 Wiley‐Liss, Inc.
Universal instability of dust ion‐sound waves and dust‐acoustic waves
Authors: Tsytovich V. N. , Watanabe K.
Published: May 2003

It is shown that the dust ion‐sound waves (DISW) and the dust‐acoustic waves (DAW) are universally unstable for wave numbers less than some critical wave number. The basic dusty plasma state is assumed to be quasineutral with balance of the plasma particle absorption on the dust particles and the ionization with the rate proportional to the electron density. An analytical expression for the critical wave numbers, for the frequencies and for the growth rates of DISW and DAW are found using the hydrodynamic description of dusty plasma components with self‐consistent treatment of the dust charge variations and by taking into account the change of the ion and electron distributions in the dust charging process. Most of the previous treatment do not take into account the latter process and do not treat the basic state self‐consistently. The critical lengths corresponding to these critical wave numbers can be easily achieved in the existing experiments. It is shown that at the wave numbers larger than the critical ones DISW and DAW have a large damping which was not treated previously and which can be also measured. The instabilities found in the present work on their non linear stage can lead to formation of different types of dust self‐organized structures.
Axial structure of plasma column sustained by non‐symmetric electromagnetic surface wave
Authors: Olefir V.P. , Azarenkov N.A. , Sporov A.E.
Published: May 2003

This article presents the results of theoretical study of the axial structure of gas discharge that is sustained by a non‐symmetric electromagnetic surface wave (SW) with azimuth wavenumberm= –2. The phase and attenuation characteristics of the wave, and the spatial wave field structure were studied as well. The wave considered propagates along the magnetized slightly nonuniform in axial direction plasma column and sustains it. The influence of external magnetic field value and finite plasma column radius on the discharge stability, on the plasma density axial profile and on the SW properties has been studied in the case of the diffusion regime of gas discharge sustaining.
Study of uniformity of plasmas produced in a wall‐stabilized arc
Authors: Książek I. , Pawelec E.
Published: May 2003

In this contribution the plasma of an arc discharge in a mixture of helium and argon is studied. The gas mixture is introduced uniformly along the arc column between each of the stabilizing plates. From the measured lateral distribution of radiation (HeI, HI, ArI, ArII, NI, FI line intensity and width measurements), after Abel inversion, the radial temperature distributions were obtained at various positions of the arc column. Beside the expected radial temperature gradients, a distinct temperature gradient along the arc column was found.
Investigation of the electrical breakdown mechanism in neon at 13.3 mbar pressure using the time delay method
Authors: Radović M.K. , Jovanović T.V. , Maluckov Č.A. , Stepanović O.M.
Published: May 2003

The results of the investigation of electrical breakdown in neon filled diode at 13.3 mbar pressure in function of distances between electrodes (0.1 < d < 20 mm), using electrical breakdown time delay method, are presented in this paper. The Paschen curve, as well as the electrical breakdown time delay mean values, and discharge formative time dependence of distance between electrodes are analyzed. The electrical breakdown time delay distributions and Laue diagrams, both as the functions of the distances between electrodes, were used in consideration. The shapes of the established distributions indicate the complex nature of the discharge formation mechanism. The results also indicate that on the right hand side of the Paschen curve (pd > 15 mbar · cm) the transition regime between Townsend and streamer mechanism of electrical breakdown is dominant.
Role of the wall ablation in the operation of a 46.9 nmAr capillary discharge soft x‐ray laser
Authors: Ritucci A. , Tomassetti G. , Reale A. , Palladino L. , Reale L. , Limongi T. , Flora F. , Mezi L. , Khuklevsky S.V. , Faenov A. , Pikuz T. , Kaiser J.
Published: May 2003

A capillary discharge pumped soft x‐ray laser operating at 46.9 nm on the 3p–3s transition of the Ne‐like Ar has been realized by pumping the active medium with a relatively slow current pulse (dI/dt ≈ 6 · 1011 A/s). In order to study the role of the ablation in the production of the laser effect, the intensity of the amplified 46.9 nm line has been investigated using the same pumping current pulses in the plastic (polyacetal) and ceramic (Al2O3). We showed that the ablation of the capillary walls is unfavorable both for the compression and stability of the plasma and consequently for the soft x‐ray laser production. The amplification and lasing effects are observed only in the ceramic channel. The measurements of the line intensity at 46.9 nm showed the lasing with a gain‐length product of ≈ 9, a laser pulse energy of ≈ 5 μJ, a pulse duration of 1.3 ns and a beam divergence of ≈ 3.5 mrad. In addition, effect of the scaling of the time of lasing with the initial plasma diameter was demonstrated experimentally and compared with a one‐dimensional MHD model.
Similarity rules for collisionless hot‐filament discharges
Authors: Jelić N. , Kuhn S. , Schrittwieser R.
Published: May 2003

The plasma parameters of a collisionless hot‐filament discharge are investigated theoretically and experimentally as functions of a dimensionless variable called the discharge efficiency, which is a product of several relevant external parameters. It is found that the main plasma parameters, as measured in plasma chambers that are either geometrically different or filled with different working gases, depend on this variable in approximately the same way. Consequently, the number of experimental data necessary for discharge characterization may be drastically reduced.
Effects of electron‐absorbing boundaries on the plasma parameters of a hot‐filament discharge
Authors: Jelić N. , Schrittwieser R. , Kuhn S.
Published: May 2003

In this paper we investigate theoretically and experimentally the plasma parameters in a double‐plasma device in the presence of an additional electron‐absorbing boundary. The latter is formed by an electrode of variable size immersed in the plasma. It is found that, depending on its size and bias potential, such an anode can considerably influence the plasma parameters. Good qualitative and fair quantitative agreement between theoretical predictions and laboratory measurements of the plasma parameters is found for various discharge conditions. In addition we discuss the consequences of our results with respect to the existence conditions of anode‐type double layers in double‐plasma devices.
A high‐speed‐execution method for a program written in factory‐automation‐cell control language
Authors: Koyama Masahiro , Miyake Norihisa , Fujii Kenjiro , Komoda Norihisa
Published: May 2003

A new programming method called Cell Control Language (CCL) for factory‐automation systems has been developed. In CCL programming, an action sequence of each functional unit in each operation mode is first described as a net module. This net module is a subclass of Petri nets, and this subclass is equivalent to a state‐transition diagram (a conventional design method). Several net modules are merged and translated into an internal code program, which is executed in a cell controller. To improve the ability of the controller to respond to state changes, we developed two new methods based on CCL. One is that for efficiently describing a CCL program, which needs a quick response to state changes, and the other is that for executing the program in a short cycle. The execution method was applied to an actual cell controller, which confirmed that it can improve the ability to respond to state changes without reducing the total control performance. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 34–42, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10167
Changes of vitamin E content in rice bran with different heat treatment
Authors: Ko Soon‐Nam , Kim Chul‐Jin , Kim Chong‐Tai , Kim Hakryul , Chung Soo‐Hyun , Lee Sun‐Mi , Yoon Hye‐Hyun , Kim In‐Hwan
Published: May 2003

Oil yield from unheated rice bran was 17.6% whereas that of microwave‐heated rice bran increased to up to 18.4%. Content and composition of vitamin E in rice bran oil were affected by microwave heating. Especially, contents of α‐tocopherol, α‐tocotrienol, and γ‐tocotrienol as well as total vitamin E were significantly (P <0.05) increased when the rice bran was subjected to microwave heating for up to 30 s. When rice bran was heated in an electric roaster up to 20 min at 170 °C, 5 min at 180 °C, and 3 min at 190 °C, the total vitamin E content in rice bran oil increased significantly (P <0.05) followed by a considerable decline beyond those time points. Microwave heating was more effective for an increase in the vitamin E content than electric roaster heating. However, longer heating with both microwave and electric roaster caused a significant degradation of vitamin E resulting in a decreased content of total vitamin E.
A Convenient Synthesis of 1‐Deoxy‐8a‐epi‐Castanospermine Diastereoisomers (6R,7R,8S,8aS)‐6,7,8‐Trihydroxyindolizidine and (6R,7R,8R,8aS)‐6,7,8‐Trihydroxyindolizidine
Authors: Zhang Honglu , Ni Yi‐Ke , Zhao Gang , Ding Yu
Published: May 2003

An efficient synthesis of (6R,7R,8S,8aS)‐6,7,8‐trihydroxyindolizidine and (6R,7R,8R,8aS)‐6,7,8‐trihydroxyindolizidine is described from readily available N‐BOC‐L‐proline, (BOC = tert‐butoxycarbonyl) which involves the addition of ethyl lithiopropiolate to the aldehyde derived from N‐BOC‐L‐proline as a key step, then cyclization to construct indolizidine skeletons and asymmetric dihydroxylation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
To What Extent Can Nine‐Membered Monocycles Be Aromatic?
Authors: von Ragué Schleyer Paul , Nyulászi László , Kárpáti Tamás
Published: May 2003

Ab initio and density functional computations have been used to characterize the heteronins. New targets for synthesis are suggested on the basis of the results. The aromaticity of the heteronins was evaluated via numerous criteria such as magnetic properties (NICS and δH), geometric indices (Bird, BDSHRT and HOMA), aromatic stabilization energies (ASE), and the barriers to planarity. Along with the experimentally characterized cyclononatetraenyl (1CH−) and azonide (1N−) anions, the phosphonide ion (1P−, which has not been reported before), favors planar (C2v) symmetry. All the other heteronins are nonplanar in order to alleviate ring strain. Comparisons of the neutral planar heteronins (constrained to C2v symmetry) show the extent to which heteroatoms like P and S, as well as N and O (in oxonin, 1O), can participate in the cyclic electron delocalization. Due to hyperconjugation, the C2v‐symmetric 9,9‐distannylcyclononatetraene 1C(SnH3)2 is moderately aromatic, in contrast to 1CH2, which is a nonaromatic, conjugated system. The planar C2v‐symmetric 1BH and 1AlH and 1CF2 are antiaromatic, like the planar form of 1CH+. Annelation with three‐membered rings resulted in planar heteronins. The sole exception was phosphonin (8PH), but the barrier to planarity decreased to 1.8 kcal/mol in 8PR, due to the bulky R: 2,6‐di‐tert‐butylphenyl substituent at the phosphorus atom. Among the 8π heteronins, only the previously reported 1CH+ is Möbius‐aromatic; 1BH, 1AlH and 1CF2 also have C2 structures but are nonaromatic due to large torsional angles which preclude cyclic delocalization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)