On the Recursive Sequence

The boundedness, global attractivity, oscillatory and asymptotic periodicity of the nonnegative solutions of the difference equation?in the title is investigated, where all the coefficients are nonnegative real numbers. The paper is motivated by an open problem proposed by Ladas [Open problems and conjectures, J. Differ. Equations?Appl., 5 (1999), 211–215].     

Electrochemical, spectroelectrochemical, and molecular quadratic and cubic nonlinear optical properties of alkynylruthenium dendrimers

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.     

cis-[PtBr2{PPh2(4-catechol)}2]: synthesis, crystal structure, and computational modelling of its binding to nanocrystalline TiO2

The complex cis-[PtBr(2){PPh(2)(4-catechol)}(2)]1 has been synthesized by cleavage of the four methyl groups from cis-[PtCl(2){PPh(2)(4-veratrole)}(2)] using BBr(3), followed by work-up in the presence of excess bromide. An X-ray crystal structure of 1.(ethanol)(2) confirms that the two catechol rings are adjacent to each other and approximately parallel, and therefore well structured to act as double bidentate ligands for adjacent metal atoms on the surface of a nanocrystal. The crystal packing of 1.(ethanol)(2) involves intermolecular hydrogen-bonding interactions and a parallel fourfold phenyl embrace between PPh(2) moieties. Density functional calculations have demonstrated that conformational variability of the aryl rings in cis-[PtBr(2){PPh(2)(4-catechol)}(2)] is energetically feasible, and two conformations of cis-[PtBr(2){PPh(2)(4-catechol)}(2)] as a complex ligand for Ti atoms on the various surfaces of the anatase and rutile structures of TiO(2) have been assessed for geometrical commensurability. Three structural models for adsorbates of cis-[PtBr(2){PPh(2)(4-catechol)}(2)] on TiO(2) are developed for anatase (110), anatase (101), and rutile (001).     

Synthesis of tin oxides SnO2–x in the entire composition range (x = 0 to 1) by ion‐beam sputter‐deposition

Ion‐beam sputter‐deposition (IBSD) was used to reactively deposit tin oxide crystalline films at oxygen fluxes of 3–15 sccm and at substrate temperatures of 100–600 °C. Analysing the samples by X‐ray diffraction and Raman spectro‐ scopy yields a map of the crystalline structures in dependence on the growth parameters. In addition to SnO₂, pure SnO films of high quality and an intermediate phase such as Sn₂O₃ or Sn₃O₄ can be reproducibly obtained. Thus, IBSD is, to our knowledge, the only thin‐film deposition technique verified yet to reliably produce samples in the entire composition range of tin oxides. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Polyazapodands Derived from Biphenyl. Study of their Behaviour as Conformationally Regulated Fluorescent Sensors

Eight new polyazapodands containing a 4,4′-substituted biphenyl moiety have been synthesised. Four (7, 8, 9 and 11) are functionalised on positions 4 and 4′ with a nitro group and four (1, 2, 3 and 10) with a dimethylamino substituent. Comparison of the emission behaviour of 1, 2, 3 with that of the reference compounds 10 and tetramthylbenzidine, clearly suggests that a modification in the dihedral angle between the biphenyl rings is an important factor in determining the fluorescent response of the molecule. The fluorescence is pH dependent, due to the formation of intramolecular hydrogen bonds between protonated aliphatic nitrogens and a carbonyl oxygen, which influences the aforementioned dihedral angle. A crystal structure resolved by X-ray diffraction of 7·2HCl has been determined, and confirms the dependence of the angle and the rigidity on the hydrogen bonding. The complexation properties of these ligands have been studied with Zn²⁺, Cd²⁺, Ni²⁺, Cu²⁺ and Pb²⁺, which show that the number of amino groups within the pendants has a strong influence on the nature of the complexation and the fluorescent response of each ligand.     

A substructure-based SAR model for odor perception in humans relevant to health risk assessments

The ability of humans to perceive odors is a very complex phenomenon involving the selective binding of molecules to approximately 1000 olfactory receptors. Accordingly, the derivation of a substructure-based SAR model can be expected to be problematic. Yet, based upon published data on odor thresholds of volatile organic chemicals, we were able to derive such an SAR model. An examination of the structural determinants and related modulators indicates that lipophilicity is a major contributor to olfactory perception. The availability of a substructure-based SAR model permits an examination of the relationship between the presence in the environment of odorous chemicals and public health risks.