bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photomechanical Control of the Electronic Properties of Linear π‐Conjugated Systems
Authors: Jousselme Bruno , Blanchard Philippe , Gallego‐Planas Nuria , Levillain Eric , Delaunay Jacques , Allain Magali , Richomme Pascal , Roncali Jean 
Published: November 2003

AbstractPhotodynamic molecular architectures have been synthesized by covalent fixation of a photoisomerizable dimethylazobenzene group at two fixed points of conformationally flexible π‐conjugated quater‐ and sexithiophene chains. Theoretical geometry optimization shows, in excellent agreement with crystallographic structures, that the mode of fixation of the azo group plays a determining role in the geometry of the final molecular architecture and on its ability to perform the expected photoinduced molecular motion. Thus, covalent fixation ofmeta‐dimethylazobenzene on a quaterthiophene chain results in a conformationally locked system in which photoisomerization of the azo group is hindered. However, the experimental results of optical,1H NMR spectroscopic, and electrochemical investigations show that when an azobenzene group is connected at theparapositions of the phenyl rings,trans‐to‐cisphotoisomerization of the azo group induces a conformational transition and dimensional changes in the underlying π‐conjugated oligothiophene chain. These experimental results unequivocally show that the photochemically induced geometrical changes produce in turn an increase in the HOMO level and a narrowing of the HOMO–LUMO gap. This therefore provides the first evidence of photomechanical control of the electronic properties of linear π‐conjugated systems.
Resorcinarenes as Templates
Authors: Gibb Bruce C. 
Published: November 2003

AbstractMetal ions are superb at templating the synthesis of small macrocycles that are decorated with Lewis basic sites. However, for the synthesis of larger macrocycles, or the synthesis of macrocycles devoid of an array of Lewis basic sites, metal ions are less useful. Here we demonstrate that resorcinarenes can be used as templates to engender the efficient formation of large crown ethers. A three step process of 1) tethering moieties to the template, 2) linking those moieties, and 3) then cleaving off the template leads to the efficient formation of a family of aromatic crown ethers. If adaptable, this approach will prove useful for the construction of macrocycles that are hard to obtain from a step‐wise synthesis.
Activation and Functionalization of White Phosphorus at Rhodium: Experimental and Computational Analysis of the [(triphos)Rh (η1:η2‐P4RR′)]Y Complexes (triphos=MeC(CH2PPh2)3; R=H, Alkyl, Aryl; R′=2 Electrons, H, Me)
Authors: Barbaro Pierluigi , Ienco Andrea , Mealli Carlo , Peruzzini Maurizio , Scherer Otto J. , Schmitt Guido , Vizza Francesco , Wolmershäuser Gotthelf 
Published: November 2003

AbstractThermal reaction of white phosphorus with [(triphos)RhH3] (1) in THF affords [(triphos)Rh(η1:η2‐P4H)] (2), triphos=MeC(CH2PPh2)3. Similar complexes [(triphos)Rh(η1:η2‐P4R)] (R=Me (7), Et (8), Ph (9)) also form at lower temperature by the reaction of P4 and [(triphos)Rh(R)(η2‐C2H4)] with elimination of ethene. In contrast, a double‐insertion process follows the reaction of [(triphos)Rh(H)(η2‐C2H4)] and P4 to generate tetraphosphido ethyl complex 8. Compounds 2, 7, 8 and 9 are thermally unstable and eventually decompose into the cyclotriphosphorus complex [(triphos)Rh(η3‐P3)] (3) plus other unidentified phosphorus‐containing species. Otherwise, PH3 or PH2R is generated in the presence of H2. The formation of PH3 and 3 is quantitative starting from the precursor 2. The electrophilic attack of MeOTf or HBF4 on the P4R ligand in the complexes 2, 7–9 is regioselective, and yields a cationic product of formula [(triphos)Rh(η1:η2‐P4RR′)]+. The direct attack on the substituted p‐R phosphorus atom is demonstrated by crossing experiments. Complexes of the latter type have been isolated in the solid state for the combinations R=H and R′=Me (11) or R=Ph and R′=Me (12). The latter species, [(triphos)Rh(η1:η2‐P4PhMe′)]OTf⋅2 CH2Cl2 (OTf=triflate), has been characterised by X‐ray methods. The geometry at the metal is better described as a trigonal bipyramidal than pseudo‐octahedral. In fact, the P4RR′ unit acts as a bidentate ligand with its exocyclic PR2 donor group and the endocyclic, dihapto‐coordinated PP linkage. The latter group lies in the equatorial plane, in a similar way to a classic olefin ligand that is coordinated to a butterfly‐shaped L4M fragment (M=d8). DFT calculations on a model of 2 and all possible protonated isomers confirm that double substitution at the exocyclic P‐donor positions of the open P4 unit is energetically favoured. A multinuclear and multidimensional NMR analysis confirms that this structure is maintained in solution for both the parent and the protonated compounds.
Coordination Solids via Assembly of Adaptable Components: Systematic Structural Variation in Alkaline Earth Organosulfonate Networks
Authors: Côté Adrien P. , Shimizu George K. H. 
Published: November 2003

AbstractA family of alkaline earth organosulfonate coordination solids is reported. In contrast to more typical crystal engineering approaches, these solids are sustained by the assembly of building blocks that are coordinatively adaptable rather than rigid in their bonding preferences. The ligand, 4,5‐dihydroxybenzene‐1,3‐disulfonate, L, progressively evolves from a 0D, 1D, 2D, to a 3D microporous network with the Group II cations Mg2+, Ca2+, Sr2+, and Ba2+, (compounds 1–4), respectively. This trend in dimensionality can be explained by considering factors such as hard–soft acid–base principles and cation radii, a rationalization which follows salient crystal engineering principles. The selective gas sorption properties of the microporous 3D network [Ba(L)(H2O)]⋅H2O, 4, with different gaseous guests are also presented.
Trimeric Perfluoro‐ortho‐phenylenemercury: A Versatile Lewis Acidic Host
Authors: Haneline Mason R. , Taylor Robert E. , Gabbaï François P. 
Published: November 2003

AbstractTrimeric perfluoro‐ortho‐phenylenemercury (1) constitutes one of the simplest trifunctional Lewis acidic hosts. In addition to cooperative effects arising from the proximity of the mercury(II) centers, the electron‐withdrawing properties of the backbone and the accessibility of the electrophilic sites lead to the facile complexation of neutral and electron rich substrates. The planarity of the structure as well as its overall polarizability compounded with relativistic effects at mercury also permits the occurrence of non‐covalent interactions and accounts for the tendency of this compound to form cofacial dimers. Collectively, the Lewis acidic properties of 1 as well as its ability to engage in non‐covalent interactions can be held responsible for its ability to form extended binary supramolecular stacks with arenes. The photoluminescence observed in some of these supramolecular complexes corresponds to the phosphorescence of the aromatic substrate and indicate the occurrence of a mercury heavy atom effect.
Sensitized Near‐Infrared Emission from Complexes of YbIII, NdIII and ErIII by Energy‐Transfer from Covalently Attached PtII‐Based Antenna Units
Authors: Shavaleev Nail M. , Moorcraft Lucy P. , Pope Simon J. A. , Bell Zöe R. , Faulkner Stephen , Ward Michael D. 
Published: November 2003

AbstractA series of dinuclear platinum(II)–lanthanide(iii) complexes has been prepared in which a square‐planar PtII unit, either [(PPh3)2Pt(pdo)] (H2pdo=5,6‐dihydroxyphenanthroline) or [Cl2Pt(dppz)] [dppz=2,3‐bis(2‐pyridyl)pyrazine], is connected to a {Ln(dik)3} unit (“dik”=a 1,3‐diketonate ligand). The mononuclear complexes [(PPh3)2Pt(pdo)] and [Cl2Pt(dppz)] both have external, vacant N,N‐donor diimine‐type binding sites that react with various [Ln(dik)3(H2O)2] units to give complexes [(PPh3)2Pt(μ‐pdo)Ln(tta)3] (series A; Htta=thenoyltrifluoroacetone), [Cl2Pt(μ‐dppz)Ln(tta)3] (series B); and [Cl2Pt(μ‐dppz)Ln(btfa)3] (series C; Hbtfa=benzoyltrifluoroacetone); in all of these the lanthanide centres are eight‐coordinate. The lanthanides used exhibit near‐infrared luminescence (Nd, Yb, Er). Crystal structures of members of each series are described. In all complexes, excitation into the Pt‐centred absorption band (at 520 nm for series A complexes; 440 nm for series B and C complexes) results in characteristic near‐IR luminescence from the Nd, Yb or Er centres in both the solid state and in CH2Cl2, following energy‐transfer from the Pt antenna chromophore. This work demonstrates how d‐block‐derived chromophores, with their intense and tunable electronic transitions, can be used as sensitisers to achieve near‐infrared luminescence from lanthanides in suitably designed heterodinuclear complexes based on simple bridging ligands.
Phosphodiester Cleavage of Ribonucleoside Monophosphates and Polyribonucleotides by Homo‐ and Heterodinuclear Metal Complexes of a Cyclohexane‐Based Polyamino–Polyol Ligand
Authors: Jancsó Attila , Mikkola Satu , Lönnberg Harri , Hegetschweiler Kaspar , Gajda Tamás 
Published: November 2003

AbstractThe ability of the dinuclear complexes of tdci [1,3,5‐trideoxy‐1,3,5‐tris(dimethylamino)‐cis‐inositol] to promote the cleavage of the phosphodiester bonds of nucleoside 2′,3′‐cyclic monophosphates, dinucleoside monophosphates and polyribonucleotides has been studied. The homodinuclear copper(II) and zinc(II) complexes efficiently promote the hydrolysis of cyclic nucleotides. The second‐order rate constant (k2≈0.44 M−1 s−1) estimated for the cleavage of 2′,3′‐cAMP induced by dinuclear copper(II) complexes is about 107 times greater than that for the hydroxide‐ion‐catalysed reaction. The complex selectively cleaves the 2′OP bond of 2′,3′‐cUMP and forms the 3′‐product in 91 % yield. An equimolar mixture of copper(II), zinc(II) and tdci proved to be more efficient than either of the binary systems: a 7–20‐fold rate enhancement was observed for the cleavage of 2′,3′‐cNMP substrates. The half‐life for the hydrolysis of 2′,3′‐cAMP decreased from 300 days to five minutes at 25 °C when the concentration of each of the three components was 2.5 mM. In contrast to the copper(II) or zinc(II) complexes of tdci, the heterodinuclear species promoted the hydrolysis of several dinucleoside monophosphates. For two ApA isomers, cleavage of the 3′,5′‐bond was about 6.5 times faster than cleavage of the 2′,5′‐bond. On the basis of the kinetic data, a trifunctional mechanism is suggested for the heterodinuclear‐complex‐promoted cleavage of the phosphodiester bond. Double Lewis acid activation occurs when the metal ions bind to the phosphate oxygen atoms. In particular, a metal‐bound hydroxide ion serves as a general base or a nucleophilic catalyst, and, presumably, a zinc(II)‐bound aqua ligand behaves as a general acid and facilitates the departure of the leaving alkoxide group. The effect of the complexes on the hydrolysis of poly(U), poly(A) and type III native RNA was also investigated, and, for the first time, kinetic data on the cleavage of the phosphodiester bonds of polyribonucleotides by a dinuclear complex was obtained.
Cover Picture: Trimeric Perfluoro‐ortho‐phenylenemercury: A Versatile Lewis Acidic Host (Chem. Eur. J. 21/2003)
Authors: Haneline Mason R. , Taylor Robert E. , Gabbaï François P. 
Published: November 2003

AbstractThe cover picture shows how trimeric perfluoro‐ortho‐phenylene mercury (center), one of the simplest trifunctional Lewis acidic hosts, interacts with organic molecules to afford various adducts. The planarity of this trinuclear complex as well as its overall polarizability compounded with relativistic effects at mercury permits the occurrence of noncovalent interactions and accounts for the tendency of this compound to form cofacial dimers as observed in the structure of the acetone adduct (top left). With a triply coordinated acetone molecule, the structure of this adduct also substantiates the cooperative effects that arise from the proximity and accessibility of the mercury centers. The complexation of arenes, such as benzene (bottom left) and naphthalene (bottom right), also occurs and leads to the formation of binary stacks in which the arene establishes multiple linkages with the mercury centers of the trifunctional Lewis acids. In addition to displaying unusual coordination environment, the arene units present in those stacks exhibit remarkable phosphorescent properties. For more details, see the paper by F. P. Gabbaï, R. E. Taylor, and M. R. Haneline on p. 5188 ff.
Chancen und Grenzen der Mikroverkapselung in der modernen Lebensmittelverarbeitung
Authors: Kunz B. , Krückeberg S. , Weißbrodt J. 
Published: November 2003

AbstractDie Mikroverkapselung ist in der Lebensmittelindustrie immer bedeutender geworden, besonders im Bereich der funktionellen Lebensmittel und der Nahrungsergänzungsmittel. Die Verkapselung dient dem Schutz des eingeschlossenen Materials vor schädlichen Einflüssen. Das Verfahren birgt ein großes Potenzial für die Entwicklung neuer Produkte. Der Einschluss von ernährungsphysiologisch positiv zu bewertenden Substanzen führt zu Produkten mit einem zusätzlichen gesundheitlichen Nutzen (Added Value). Obwohl die Mikroverkapselung sich erst am Anfang ihrer Entwicklung befindet, ist es sinnvoll, die Chancen und Risiken dieser vielversprechenden Technologie abzuschätzen. Der Beitrag gibt einen Überblick über die Möglichkeiten der Mikroverkapselung in der Lebensmittelindustrie und zeigt zugleich die Grenzen der neuen Technologie auf.
QM/MM Car‐Parrinello Molecular Dynamics Study of the Solvent Effects on the Ground State and on the First Excited Singlet State of Acetone in Water
Authors: Röhrig Ute F. , Frank Irmgard , Hutter Jürg , Laio Alessandro , VandeVondele Joost , Rothlisberger Ursula 
Published: November 2003

AbstractWe present a hybrid Car–Parrinello quantum mechanical/molecular mechanical (QM/MM) approach that is capable of treating the dynamics of molecular systems in electronically excited states in complex environments. The potential energy surface in the excited state is described either within the restricted open‐shell Kohn–Sham (ROKS) formalism or within time‐dependent density functional theory (TDDFT). As a test case, we apply this technique to the study of the solvent effects on the ground state and on the first excited singlet state of acetone in water. Our results demonstrate that for this system a purely classical description of the solvent is sufficient, since inclusion of the first solvent shell of 12 water molecules into the quantum system does not show a significant effect on this transition. The excited‐state energies calculated with ROKS are red shifted by a constant value compared to the TDDFT results, while the relative variations of the excitation energy for different configurations are in very good agreement. The experimentally observed blue shift of the excitation energy in going from gas phase to condensed phase is well reproduced. Excited‐state dynamics carried out with ROKS yield the relaxation of the solute and the rearrangement of the solvent structure on a picosecond timescale. The calculated Stokes shift is in reasonable agreement with experimental data.
Nanotubes à la Carte: Wetting of Porous Templates
Authors: Steinhart Martin , Wendorff Joachim H. , Wehrspohn Ralf B. 
Published: November 2003

AbstractNanotubes have an outstanding potential both for applications in nanotechnology and as the subject of basic research. Wetting of porous templates is a simple technique that overcomes many limitations of established preparation methods. It extends the range of processable materials, for example, by a broad range of multicomponent mixtures or by high‐performance polymers such as poly(oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK) and polytetrafluoroethylene (PTFE). Inducing controlled phase transitions generates a large specific surface, a specific nanoporosity, or oriented crystalline domains within the nanotube walls. Template wetting provides customized nanotubes and allows us to investigate how the wall curvature affects the structure formation.
Aligned Nanotubes
Authors: Dai Liming , Patil Ajeeta , Gong Xiaoyi , Guo Zhixin , Liu Luqi , Liu Yong , Zhu Daoben 
Published: November 2003

AbstractSince the discovery of carbon nanotubes by Iijima in 1991, various carbon nanotubes with either a single‐ or multilayered graphene cylinder(s) have been produced, along with their noncarbon counterparts (for example, inorganic and polymer nanotubes). These nanostructured materials often possess size‐dependent properties and show new phenomena related to the nanosize confinement of the charge carriers inside, which leads to the possibility of developing new materials with useful properties and advanced devices with desirable features for a wide range of applications. In particular, carbon nanotubes have been shown to exhibit superior properties attractive for various potential applications, ranging from their use as novel electron emitters in flat‐panel displays to electrodes in electrochemical sensors. For many of the applications, it is highly desirable to have aligned/patterned forms of carbon nanotubes so that their structure/property can be easily assessed and so that they can be effectively incorporated into devices. In this Review, we present an overview on the development of aligned and micropatterned nanotubes, with an emphasis on carbon nanotubes.
Topological and Electron‐Transfer Properties of Yeast Cytochrome c Adsorbed on Bare Gold Electrodes
Authors: Bonanni Beatrice , Alliata Dario , Bizzarri Anna Rita , Cannistraro Salvatore 
Published: November 2003

AbstractThe redox metalloprotein yeast cytochrome c was directly self‐chemisorbed on “bare” gold electrodes through the free sulfur‐containing group Cys102. Topological, spectroscopic, and electron transfer properties of the immobilised molecules were investigated by in situ scanning probe microscopy and cyclic voltammetry. Atomic force and scanning tunnelling microscopy revealed individual protein molecules adsorbed on the gold substrate, with no evidence of aggregates. The adsorbed proteins appear to be firmly bound to gold and display dimensions in good agreement with crystallographic data. Cyclic voltammetric analysis showed that up to 84 % of the electrode surface is functionalised with electroactive proteins whose measured redox midpoint potential is in good agreement with the formal potential. Our results clearly indicate that this variant of cytochrome c is adsorbed on bare gold electrodes with preservation of morphological properties and redox functionality.
A Combined Atomic Force Microscopy and Molecular Dynamics Simulation Study on a Plastocyanin Mutant Chemisorbed on a Gold Surface
Authors: Bizzarri Anna Rita , Bonanni Beatrice , Costantini Giulio , Cannistraro Salvatore 
Published: November 2003

AbstractA mutant of copper plastocyanin, covalently bound to an Au (111) surface through an engineered disulfide bridge, was investigated in aqueous medium by atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Tapping‐mode AFM images revealed adsorption of single molecules which are homogeneously distributed over the substrate and strongly bound to gold and display uniform lateral size. A statistical analysis of the height of the macromolecules on the gold substrate evidenced a distribution around a mean value consistent with that expected from the crystallographic data and with a relatively large standard deviation. A 10‐ns classical MD simulation of mutated plastocyanin, hydrated by a layer of water, covalently bound to a gold surface by one or two sulfur atoms, was performed. The simulations indicate that the bound protein retains, in both cases, its overall tertiary structure during the dynamic evolution. Moreover, the macromolecule can assume different orientations with respect to the gold substrate, which give rise to a distribution of heights on the gold substrate. Experimental and MD simulation results are compared and discussed in connection with the topological and dynamical properties of the protein system.
A High‐speed Atomic Force Microscope for Studying Biological Macromolecules in Action
Authors: Ando Toshio , Kodera Noriyuki , Naito Yasuyuki , Kinoshita Tatsuya , Furuta Ken'ya , Toyoshima Yoko Y. 
Published: November 2003

AbstractThe atomic force microscope (AFM), which was invented by Binnig et al. in 1986, can image at nanometer resolution individual biological macromolecules on a substrate in solution. This unique capability awoke an expectation of imaging processes occurring in biological macromolecules at work. However, this expectation was not met, because the imaging rate with available AFMs was too low to capture biological processes. This expectation has at last been realized by the high‐speed AFM developed by our research group at Kanazawa University. In this article, after a brief review of the development of our apparatus, its recent advancement and imaging data obtained with motor proteins are presented.
Cover Picture: QM/MM Car‐Parrinello Molecular Dynamics Study of the Solvent Effects on the Ground State and on the First Excited Singlet State of Acetone in Water (ChemPhysChem 11/2003)
Authors: Röhrig Ute F. , Frank Irmgard , Hutter Jürg , Laio Alessandro , VandeVondele Joost , Rothlisberger Ursula 
Published: November 2003

AbstractThe cover picture shows…︁‥the solvent effect of water upon the lowest‐lying singlet excitation in acetone. The transition, which involves the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), is blue‐shifted in water (sol) with respect to the gas phase (vac), since the HOMO is stronger stabilized in water than the LUMO. The authors calculate the absorption and fluorescence spectra of acetone in water with a hybrid Car–Parrinello quantum chemical/classical molecular dynamics approach and investigate the influence of the solvent. The lower part of the picture shows the excitation energy during a simulation. One configuration with a very high excitation energy (three hydrogen bonds, short CO bond) and one configuration with a very low excitation energy (two hydrogen bonds, long CO bond) are shown in detail. Find out more in the article by Rothlisberger and co‐workers on pages pp. 1177–1182.
Czochralski growth and constitutional studies on single crystals of potassium lithium niobate (KLN)
Authors: Podlojenov S. , Burianek M. , Mühlberg M. 
Published: November 2003

AbstractThe ferroelectric phase of potassium lithium niobate K3Li2−xNb5+xO15 (KLN) is a very promising material for the conversion of infrared light to light in the visible region. However, growing of single crystals is known to be complicated due to the considerable anisotropy of the growth rate and the thermal expansion behaviour. The single crystals of KLN, Mg2+‐doped KLN, as well as the mixed crystals of potassium lithium tantalate niobate K3Li2(Nb1−xTax)5O15 (KLTN) were grown by the Czochralski technique. The chemical analyses of the samples were performed by atomic absorption spectroscopy (AAS) and X‐ray fluorescence analysis (XRF). The element concentrations along the single crystals were measured by the electron microprobe analysis (EMPA) to clarify the segregation phenomena in the grown crystals. The elements distribution coefficients were also calculated. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)