Lithium adsorption on armchair graphene nanoribbons

Lithium adsorption on two dimensional graphene and armchair graphene nanoribbons is studied using advanced density functional theory calculations. The relative stability of different adsorption sites is investigated taking into account different ribbon widths, adsorbate densities, and spin states. We find the singlet spin state to be the true ground state of the systems considered. For this spin state, the binding energy increases with decreasing adatom density due to lower Coulomb repulsion between the partially charged Li atoms. At low adsorbate densities the favorable adsorption sites on the nanoribbons are found to be the hollow sites near the edges of the ribbon, whereas at higher densities, Li atoms tend to couple on next-nearest neighboring hexagons close to the ribbon's edge. Adsorption of the metal atoms is found to significantly decrease the bandgaps of all systems studied, turning them metallic for sufficiently large adatom densities. This suggests lithium doping as a possible route for bandgap engineering of graphitic systems.     

Cartan Subalgebras in C*-Algebras of Haus dorff étale Groupoids

The reduced C*-algebra of the interior of the isotropy in any Hausdorff étale groupoid G embeds as a C*-subalgebra M of the reduced C*-algebra of G. We prove that the set of pure states of M with unique extension is dense, and deduce that any representation of the reduced C*-algebra of G that is injective on M is faithful. We prove that there is a conditional expectation from the reduced C*-algebra of G onto M if and only if the interior of the isotropy in G is closed. Using this, we prove that when the interior of the isotropy is abelian and closed, M is a Cartan subalgebra. We prove that for a large class of groupoids G with abelian isotropy—including all Deaconu–Renault groupoids associated to discrete abelian groups—M is a maximal abelian subalgebra. In the specific case of k-graph groupoids, we deduce that M is always maximal abelian, but show by example that it is not always Cartan.     

New thermally stable and organosoluble heterocyclic poly(naphthaleneimide)s

As majority of polyheteroarylenes based on bis(naphthalic anhydrides), are difficult to process due to their infusiblity and insolubility in common organic solvents and solubility only in strong acids, this study is concerned with the synthesis and properties of new, easily processable polyimides and copolyimides containing naphthalene and oxadiazole rings. These polymers have been synthesized and their properties have been compared with regard to the influence of oxadiazole and naphthalene units on their physical properties. The polyimides were prepared by polycondensation reaction in solution of the aromatic diamines containing preformed oxadiazole ring with two dianhydrides having naphthalene units, at high temperature. Also, copolyimides were prepared by using a mixture of each naphthalene‐containing dianhydride, with hexafluoroisopropylidene‐dianhydride in the polycondensation reaction with the same diamino‐oxadiazoles. Most of the resulting polyimides and copolyimides were soluble in polar amidic solvents and in less polar solvents, and their solutions gave flexible films when spread onto glass plates. The thermal stability and glass transition temperature of these polyimides and copolyimides were measured and compared. The quality and the roughness of the spin‐coated films of these polymers were investigated by atomic force microscopy. The photoluminescence properties of the polymers in solution were studied to determine the color of emission. The UV absorption was also studied to determine the Stokes shift, and hence the possible reabsorption effects. The properties of the present polyimides make them attractive for applications in advanced optoelectronics and other related fields. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymeric conjugates of drugs and antibodies for site-specific drug delivery

The synthesis of targetable conjugates of doxorubicin bound to N-(2-hydroxypropyl)methacrylamide copolymers was investigated. Anti-CD3 antibody against TCR/CD3 complex was used to target the conjugates to T-cells. The effect of structure of the oligopeptide spacer between the drug and polymer as well as of the polymer modification with the antibody on the rate of drug release from the polymeric carrier system incubated in vitro with cathepsin B or with a mixture of intracellular enzymes (tritosomes) is discussed. The results of in vitro drug-release experiments are correlated with the evaluation of T-cell cytotoxicity of targeted and nontargeted polymer-bound doxorubicin conjugates measured in vitro as the inhibition of Con-A stimulated growth of human peripheral blood lymphocytes (³H-thymidine incorporation method).     

ChemInform Abstract: Coordination of Cu+ and Cu2+ Ions in ZSM‐5 in the Vicinity of Two Framework Al Atoms.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Role of hydration in the phase transition of polypeptides investigated by NMR and Raman spectroscopy

NMR, Raman spectroscopy and ab initio quantum-chemical calculations have been employed to investigate the role of the hydration water in the inverse temperature transition of elastin-derived biopolymers represented by poly(Gly-Val-Gly-Val-Pro) and poly(Ala-Val-Gly-Val-Pro). Temperature and concentration dependences of the Raman spectra measured for water solutions of polymers and of a low-molecular-weight model have been correlated with the vibrational frequencies calculated at the DFT (B3LYP) and MP2 levels for the peptide segment surrounded by a growing number of water molecules. The results indicate strong hydration before the transition that, in addition to water hydrogen-bonded to amide groups, includes hydrophobic hydration of non-polar groups by a dynamic cluster of several water molecules. According to ¹H longitudinal and transverse relaxation of HOD signals in D₂O solutions, the number of water molecules motionally correlated with the polymer is about 4 per one amino acid residue.     

The distributions of enhancement factors in close‐packed and nonclose‐packed surface‐enhanced Raman substrates

A method employing photochemical hole burning, previously developed to measure the distribution of Raman enhancement factors on a nanostructured substrate for surface‐enhanced Raman scattering, is used to compare the enhancement distributions of benzenethiol adsorbed on substrates optimized for 532 nm laser excitation consisting of close‐packed (CP) or nonclose‐packed (NCP) nanospheres. The ensemble‐averaged Raman enhancement factor was 2.8 times smaller for the NCP substrate. The measured distributions revealed additional information. For instance, 92% of the molecules on the CP substrate and 93.6% of the molecules on the NCP substrate had Raman enhancements below average. The minimum enhancements on both substrates were ~10⁴, but on the NCP substrate the maximum enhancement was 1.2 × 10⁸, whereas on the CP substrate the maximum was 2 × 10¹⁰. The Ag‐coated nanospheres form hemisphere‐on‐cylinder mushroom‐like structures on both lattices, but on the NCP lattice, one third of the molecules are on the flat regions between the mushrooms. The flats on the NCP lattice have enhancements of ~10⁴, showing they are part of a resonant plasmonic structure. The highest NCP enhancements of ~10⁸ are tentatively associated with regions at the bases of the mushrooms, whereas the highest CP enhancements of 2 × 10¹⁰ are tentatively associated with gaps between nanospheres where 0.0025% of the molecules reside. Copyright © 2011 John Wiley & Sons, Ltd.