Electronic structure effects on stability and quantum conductance in 2D gold nanowires

In this study, we have investigated the stability and conductivity of unsupported, two-dimensional infinite gold nanowires using ab initio density functional theory (DFT). Two-dimensional ribbon-like nanowires with 1–5 rows of gold atoms in the non-periodic direction and with different possible structures have been considered. The nanowires with >2 rows of atoms exhibit dimerization, similar to finite wires, along the non-periodic direction. Our results show that in these zero thickness nanowires, the parallelogram motif is the most stable. A comparison between parallelogram- and rectangular-shaped nanowires of increasing width indicates that zero thickness (111) oriented wires have a higher stability over (100). A detailed analysis of the electronic structure, reveals that the (111) oriented structures show increased delocalization of s and p electrons in addition to a stronger delocalization of the d electrons and hence are the most stable. The density of states show that the nanowires are metallic and conducting except for the double zigzag structure, which is semiconducting. Conductance calculations show transmission for a wide range of energies in all the stable nanowires with more than two rows of atoms. The conductance channels are not purely s and have strong contributions from the d levels, and weak contributions from the p levels.     

Self-assembled metalla-bowls for selective sensing of multi-carboxylate anions

Two new tetranuclear cationic metalla-bowls 4 and 5 were self-assembled from a bis-pyridine amide ligand (H(2)L) (1) and arene-ruthenium acceptors, [(Ru(2)(μ-η(4)-C(2)O(4))(η(6)-p-cymene)(2)](O(3)SCF(3))(2) (2) and [Ru(2)(dhnd)(η(6)-p-cymene)(2)](O(3)SCF(3))(2) (dhnd = 6,11-dihydroxy-5,12-naphthacenedionato) (3), respectively. The metalla-bowls were characterized by multinuclear NMR, ESI-MS, UV-Vis spectroscopy, and single crystal X-ray diffraction study of 4. The crystal structure of 4 reveals unambiguous proof for the molecular shape of the metalla-bowl and the encapsulation of one triflate anion in the cavity through hydrogen bonding. The metalla-bowl 5 has been evaluated for anion binding studies by use of amide ligand as a hydrogen bond donor and arene-Ru acceptor as a signalling unit. UV-Vis titration studies showed that 5 selectively binds with multi-carboxylate anions such as oxalate, tartrate and citrate in a 1?:?1 fashion with high binding constants of 4.0-5.5 × 10(4) M(-1). Furthermore, the addition of multi-carboxylate anions into a solution of 5 gave rise to a large enhancement of fluorescence intensity attributable to the blocking of a photo-induced electron transfer process from the arene-ruthenium moiety to the amidic donor in 5. However, the fluorescence intensity almost remains unchanged upon addition of other anions including F(-), Cl(-), PF(6)(-), MeCOO(-), NO(3)(-) and PhCOO(-), as identically seen in the UV-Vis titration experiments, pointing to the high selectivity of 5 for the sensing of multi-carboxylate anions.     

Coordination-driven self-assembly of ruthenium-based molecular-rectangles: synthesis, characterization, photo-physical and anticancer potency studies

A suite of eight cationic, tetra-metallic molecular rectangles (1-8) was generated via coordination-driven self-assembly using four dicarboxylate-bridged arene-Ru precursors (A1-A4) with one of two dipyridyl ligands (D1, D2). The high-yielding (84-92%) rectangles were characterized by (1)H NMR and HR-ESI-MS to support their structural assignments. The molecular structure of 5 was determined by single crystal X-ray analysis, which indicated that two D2 ligands bridge two A1 acceptors to form a rectangular construct. The photophysical properties of these metalla-rectangles and their molecular precursors were also investigated, as well as an MTT assay to evaluate the in vitro cytotoxicities relative to two chemotherapeutic agents, cisplatin and doxorubicin. MTT assays were conducted using SK-hep-1 (liver cancer) and HCT-15 (colon cancer) human cancer cell lines. Compounds 3, 4, 7 and 8 showed significant activity, with IC(50) values comparable to those of cisplatin and doxorubicin.     

Patterned assembly of Yarrowia lipolytica yeast cells onto thermally evaporated octadecylamine films

Thermally evaporated patterned films of the lipid, octadecylamine (ODA), have been used in the immobilization of the hydrocarbon-degrading cells, Yarrowia lipolytica. The immobilization of the yeast cells occurs on hydrophobic surfaces presented by the lipid film elements in the patterned structure, the attachment of the cells to the lipid film occurring possibly through hydrophobic interactions between the hydrocarbon chains of the fatty amine film and the cell wall of the yeasts. It is observed that the cell immobilization is extremely faithful to the underlying lipid template indicating potential use in tissue engineering as well as materials applications involving specific enzyme-based biotransformations.     

In situ FTIR study of the adsorption geometry of bisulfate accepted ions on a platinum electrode

It is shown that a better understanding of the geometry of adsorbed bisulfate species on the surface is gained by monitoring simultaneously more than one vibrational mode of the molecule. We propose that in the double layer region the bisulfate ions are adsorbed via an oxygen atom of its SO₃ unit with the Pt-O-S linkage along the surface normal. In the oxide region the bisulfate ions are adsorbed on the oxygen covered surface of the platinum electrode via the hydrogen atom by hydrogen bonding with the hydrogen bond showing a significant tilt (approximately 60° ).     

Mechanism of chloramine-T oxidation of methyl vinyl ketone and isopropyl methyl ketone in aqueous alkaline media

The oxidation kinetics of methyl vinyl ketone and isopropyl ketone by chloramine-T in aqueous alkaline solutions show first-order dependence on chloramine-T, both substrates and alkali. No effect of p-toluenesulphonamide was evident. Observed stoichiometry, negligible effect of ionic strength and a positive dielectric effect point to a mechanism involving interaction of enolate anions with chloramine-T in the rate determining step. Activation parameters and the isolation of the product formaldehyde are in agreement with the proposed mechanism.     

Regioselective ortho-C-cyclohexylation of phenols with cyclohexanol in the presence of transition metal modified zeolite-Hβ

The cyclohexylation of various phenols with cyclohexanol as an alkylating agent in the presence of Ti⁴⁺, Sb³⁺, Fe³⁺, Sn⁴⁺, Al³⁺, and Zr⁴⁺ metal modified zeolite-Hβ catalysts was carried out. The best catalyst was Sn⁴⁺ exchanged Hβ, activated at 120 °C (Hβ-SnA120), which displayed a selectivity of more than 95% towards 2-cyclohexylphenol. The reaction was found to proceed through the formation of cyclohexyl phenyl ether. Cyclohexylation of different phenols has also been studied.     

Cation effects on the vibrational frequencies of adsorbed thiocyanate on platinum

Infrared spectra of thiocyanate adsorbed on a platinum electrode surface were obtained in the presence of perchlorate electrolytes of various alkali metal cations. It was discovered that the vibrational frequency of the C-N stretching mode is dependent upon the nature of the supporting electrolyte cation. Two bands were observed in the 2050 to 2150 cm⁻¹ range; one band was attributed to nitrogen-bound thiocyanate, and the other to species adsorbed via the sulfur atom. Each of these bands demonstrated independent frequency dependencies on cation nature and on the applied electric field within the interfacial region. Differences were also observed in the intensity dependence of the bands on the applied potential. The results were explained in terms of changes in the distance between the outer Helmholtz plane (OHP) and the surface of the electrode, and also in terms of the possible influence of coadsorbed alkali metal cations on the vibrational frequency of thiocyanate species adsorbed through the nitrogen atom. The effects that variations in the OHP-electrode distance impart on the magnitude of the potential drop across the interface, and the influence of small changes in this potential field on the C-N stretching frequency of N- and S-adsorbed thiocyanate species, are discussed.