Chemistry

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The anisotropy of the electronic interactions between fullerenes in crystalline solids was examined using a confocal fluorescence microscope by probing the polarization of the fluorescence emission arising from fullerene excimer-like emitting states. Crystals of C60 obtained by vacuum-sublimation or from chloroform solution exhibited no or little polarization (p = 0 or 0.11, respectively), as expected from the high symmetry of the C60 fcc lattice or the low degree of anisotropy induced by included solvent molecules. The use of hydrogen-bonding to supramolecularly control interfullerene electronic interactions was explored using a fullerene derivative (1) combining a solubilizing 3,4-di-tert-butylbenzene group and a barbituric acid hydrogen-bonding (H-B) moiety. The crystal structure of 1 establishes the existence of fullerene H-B tapes along which interfullerene electronic interactions are expected to be large. In agreement with this, we observe very strong polarization of the fullerene excimer-like emission (p = 0.78), indicative of a high degree of anisotropy in the fullerene interactions. The charge-carrier mobility of 1 as determined from OFET devices was found to be lower than that of C60 (1.2 × 10-4 vs 1.2 × 10-2 cm2/s V), which is rationalized on the basis of the reduced dimensionality of 1 as a wire-like semiconductor and variations in the morphology of the device active layer revealed by AFM measurments. © 2010 American Chemical Society.

World University root node

(SoNS) School of Natural Sciences

Journal of the American Chemical Society

Self-assembly of supramolecular fullerene ribbons via hydrogen-bonding interactions and their impact on fullerene electronic interactions and charge carrier mobility

Two coumarin derived dyes (compounds La and L) have been synthesized in high yields by Schiff base condensation. On probing with a femtosecond laser, none of these compounds show any two-photon activity in the wavelength range, 760-860 nm. However, La in presence of Zn(II) and L in presence of Mg(II), exhibit large two-photon absorption as well as emission in the same wavelength range. Theoretical calculations at the B3LYP functional with 6-31G and LanL2DZ mixed basis set under DFT formalism support experimental results. © 2010 Elsevier B.V. All rights reserved.

Inorganica Chimica Acta

Coumarin derived chromophores in the donor-acceptor-donor format that gives fluorescence enhancement and large two-photon activity in presence of specific metal ions

Refractive indices for molecular crystals are obtained from Hartree-Fock wavefunctions constrained to reproduce a set of experimental X-ray structure factors. Coupled-perturbed Hartree-Fock theory is used to calculate the in-crystal effective polarizabilities from which the refractive indices are obtained, thus eliminating the need for the calibration procedure used in earlier work by Whitten et al. [J. Chem. Phys. 2006, 125, 174505]. The results clearly demonstrate that these X-ray constrained Hartree-Fock (XCHF) wavefunctions reflect genuine effects of intermolecular interactions in crystals. Molecular dipole moments are consistently in excellent agreement with ab initio MP2 estimates that incorporate the effects of the crystal field. Consistent agreement of the XCHF refractive indices with experimental measurements at optical frequencies confirms that this approach can provide both meaningful results and considerable insight into the relative importance of molecular properties and crystal field effects in determining the detailed nature of the refractivity tensor. © 2009 the Owner Societies.

Fulltext

Physical Chemistry Chemical Physics

Refractive indices for molecular crystals from the response of X-ray constrained Hartree-Fock wavefunctions

Two components self-assembly of a Pd4 neutral molecular rectangle driven by Pd–O bond coordination has been achieved and this $\Pi$-electron rich rectangle shows fluorescence quenching in presence of nitroaromatics, which are the chemical signatures of many explosives. {\textcopyright} 2009 The Royal Society of Chemistry.

Journal of the Chemical Society. Dalton Transactions

Self-assembly of a PdII neutral molecular rectangle via a new organometallic PdII2 molecular clip and oxygen donor linker

The concept of molecular structure is fundamental to the practice and understanding of chemistry, but the meaning of this term has evolved and is still evolving. The Born - Oppenheimer separation of electronic and nuclear motions lies at the heart of most modern quantum chemical models of molecular structure. While this separation introduces a great computational and practical simplification, it is neither essential to the conceptual formulation of molecular structure nor universally valid. Going beyond the Born - Oppenheimer approximation introduces new paradigms, bringing fresh insight into the chemistry of fluxional molecules, proteins, superconductors and macroscopic dielectrics, thus opening up new avenues for exploration. But it requires that our ideas of molecular structure need to evolve beyond simple ball-and-stick-type models. © Springer Science+Business Media B.V. 2008.

Foundations of Chemistry

The chemist's concept of molecular structure

Titanium(II) solutions, prepared by dissolving titanium metal in triflic acid+HF, react readily with chelated complexes of Ag(III), nickel(IV) and copper(III). Reactions with excess Ti(II) yield Ti(III) and are strongly catalyzed by added Ti(IV), but stoichiometry is unaffected. Rapid reactions of Ti(II) with nonchelated oxidants, VO2+, UO22 + and MnO4- do not exhibit catalysis by Ti(IV). Reductions by Ti(III) are unaffected by Ti(IV). The Ag(III)-Ti(II) reaction, as catalyzed by Ti(IV), is subject to kinetic saturation with an association quotient 4 × 102 M-1 for the Ti(IV)-activated species. It is proposed that the catalyzed reductions of the Ag(III) and Ni(IV) oxidants are initiated by 1e- steps, but that the initially formed cation pairs undergo geminate follow-up reactions to give the observed stable products. © 2008 Elsevier B.V. All rights reserved.

Electron transfer. Part 166 [1]. Reactions of Ti(II)(aq) with oxidants having strongly positive potentials

(Chemical Equation Presented) A powerful intramolecular Schmidt reaction starting from primary azidoalcohols is reported. This approach involves a nonacidic activation of the alcohol via triflation. The synthetic potential offered by the mild reaction conditions is demonstrated by a highly selective synthesis of (-)-indolizidine 167B. {\textcopyright} 2009 American Chemical Society.

Intramolecular schmidt reaction involving primary azidoalcohols under nonacidic conditions: Synthesis of indolizidine (-)-167B

Titanium(ii) solutions, prepared by dissolving titanium metal in triflic acid and HF, react readily with derivatives of Cr(vi), Cr(v) and Cr(iv). Reductions of Cr(vi) and Cr(iv), carried out with [Co(NH3) 5Br]2+ as a scavenger for Cr(ii), yield no detectable Co2+, indicating that 2e- steps, bypassing Cr(v) and Cr(iii), are not operative. Catalysis by Ti(iv) is observed only for reduction of Cr(vi). Rates for reduction by Ti(iii) are remarkably similar to those for the corresponding reductions by Ti(ii). The addition of Ti(iii) to triflic acid and HF results in rapid and quantitative disproportionation to Ti(ii) and Ti(iv). © 2009 The Royal Society of Chemistry.

Dalton Transactions

Reactions of aquatitanium(II) with hypervalent chromium species

Enzyme linked immunosorbent assay (ELISA) was used for the analysis of tetracycline, chlortetracycline, oxytetracycline, and their transformed compounds in environmental water samples. The antibodies employed in ELISA showed high relative affinity for tetracycline, epitetracycline, chlortetracycline, and epichlortetracycline as compared to anhydrotetracycline, epianhydrotetracycline, and anhydrochlortetracycline. The specificity and crossreactivity of these antibodies are discussed in relation to the electrostatic potentials and average local ionization energies computed on the molecular surfaces of tetracycline antibiotics and their transformed compounds with an objective of identifying common features as well as differences that may be related to the experimentally observed variation in cross-reactivity values. The computations were performed at both the HF/STO-3G and HF/6-31+G * levels using the Gaussian 98 program. The results in this study are based upon molecular electrostatic potentials and local ionization energies computed on isodensity molecular surfaces. The surface electrostatic potentials are characterized in terms of a group of statistically defined quantities, which include the average deviation, the positive, negative, and total variances, positive and negative surface extrema, and a parameter indicating the degree of electrostatic balance. © 2009 American Chemical Society.

Journal of Physical Chemistry A

Computational prediction of antibody binding sites on tetracycline antibiotics: Electrostatic potentials and average local ionization energies on molecular surfaces

Erratum: Computational Prediction of Antibody Binding Sites on Tetracycline Antibiotics: Electrostatic Potentials and Average Local Ionization Energies on Molecular Surfaces