Mercuric chloride and iodide mediated cyclization of tethered alkynedithioacetals as a general route to five- and six-membered rings: tuning of regioselectivity by alkyne substitution

[reaction: see text] Mercuric chloride mediated cyclization of tethered alkynedithioacetals has been established as a general route to five- and six-membered carbocycles and heterocycles. Substitution at the alkyne terminus leads to preferential formation of five-membered rings, whereas unsubstituted alkynedithioacetals give six-membered rings as the major products. Mercuric iodide interrupts the reaction at the intermediate dithioacetal stage.     

Spectroscopy, crystal structure, valance molecular orbital energy level diagram and DFT study of cis-[Cr(2,2'-bipy)2Cl2](Cl)0.38(PF6)0.62

A new octahedral chromium(III) complex having 2,2'-bipyridine as ligand system was synthesized in methanol. Single crystal X-ray diffraction analysis shows that it possesses non-stoichiometry in its anionic primary covalency. It has also been studied by elemental analyses, optical spectroscopy (UV-vis, IR) and magnetic susceptibility data. DFT calculations (with B3LYP functional and double-xi quality LANLDZ(D95V) basis set) were carried out to interpret the electronic and infrared spectra of the complex. The DFT optimized geometric structure for the complex is compared with the X-ray crystallographic data; the theory-experiment agreement is satisfactory.     

New route to the synthesis of bis[N-(2-aminoethyl) salicylaldiminato] chromium(III) chloride monohydrate Spectroscopic characterization, crystal structure and interaction with DNA

The reaction of [Cr(urea)(6)]Cl(3).3H(2)O with H(2)salen (H(2)salen=N,N(')-ethylenebis(salicylaldimine) in water-methanol mixture (40:60v/v) under reflux yielded the complex bis[N-(2-aminoethyl)salicylaldiminato]chromium(III) chloride monohydrate, [Cr(aesaldmn)(2)]Cl.H(2)O. The complex was characterized by elemental analysis, molar conductance, magnetic susceptibility, spectroscopic (UV-vis and IR) data and X-ray diffraction studies. The new ligand, N-(2-aminoethyl)salicylaldimine, Haesaldmn, possibly resulted from the hydrolytic cleavage of one end of the H(2)salen ligand during reflux. Binding of this chromium(III) complex to CT DNA has been studied using UV-vis spectroscopy with an apparent binding constant of 2.68 x 10(3)M(-1). It shows that the binding mode is electrostatic while the emission of ethidium bromide to CT DNA in the absence and in the presence of the complex show that it binds DNA with partial intercalation.     

Use of fluorous chemistry in the solubilization and phase transfer of nanocrystals, nanorods, and nanotubes

Fluorous chemistry, involving the use of a fluorous label for the functionalization of a substrate and a fluorous solvent for extraction of the functionalized substrate, is shown to be effective in solubilizing gold and CdSe nanoparticles in a fluorous medium, through phase transfer from an aqueous or a hydrocarbon medium. While these nanoparticles were functionalized with a fluorous thiol, single-walled carbon nanotubes and ZnO nanorods could be solubilized in a fluorous medium by reacting them with a fluorous amine. Fluorous chemistry enables the solubilization of the nanostructures in the most nonpolar liquid medium possible.     

VECTOR BUNDLES ON CURVES ADMITTING A CONNECTION

Let k be any infinite perfect field. Let E be a vector bundleover a smooth projective curve defined over k. We prove thatE admits a connection if the degree of every indecomposablecomponent of E is zero. This has been proved (when k = ) inM. F. Atiyah [2] and A. Weil [7].     

Intramolecular Charge Transfer Reaction in Solutions of Low to High Electrolyte Concentrations: Interplay between Friction and Solvation

Fluorescence emission spectroscopy have been used to investigate the effects of electrolytes on the excited state intramolecular charge transfer (ICT) reaction in 4-(1-azetidinyl)benzonitrile (P4C) in very dilute to concentrated electrolyte solutions of ethyl acetate (EA), acetonitrile (AN) and ethanol (EtOH). In the limit of very low electrolyte concentrations, the reaction rate (=1/τ _rxn, τ _rxn being the reaction time) is found to decrease with increasing electrolyte concentration, the extent of decrease being the maximum in EA and the minimum in AN. At moderate to higher electrolyte concentrations, however, the rate increases upon further addition of electrolyte. The observed non-monotonic electrolyte concentration dependence of rate is believed to occur due to a novel interplay between friction and solvation experienced by the photo-excited reactant in solution. Moreover, the long time decay constant and amplitude of the bi-exponential decay of the time resolved fluorescence emission intensity also show a significant electrolyte concentration dependence which corroborates the relevant steady-state results. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Synthesis,crystal structures and luminescent properties of phenylmercury(II) complexes with thiohydrazone ligands having weak Hg····π and Hg····Hg interactions

The Reaction of phenylmercury(II) acetate with salicylaldehyde morpholine N-thiohydrazone (H₂smth) and 2-hydroxyacetophenone morpholine N-thiohydrazone (H₂apmth) in dry ethanol under gentle refluxing condition form light yellow complexes [PhHg(Hsmth)] (1) and [PhHg(Hapmth)] (2) involving formation of Hg-S bond from the thiol form of the ligands after deprotonation of the SH proton. The structures of the complexes as determined by X-ray crystallography shows that the complex (1) has a distorted T-shaped geometry while the complex (2) adopts familiar linear coordination geometry. Complex (2) has two independent molecules comprising the asymmetric unit. Both the complexes form two-dimensional supramolecular assemblies due to a combination of weak intermolecular Hg····π and Hg····Hg interactions. The Hg····π and Hg····Hg distances are 3.937 and 4.0216(10) Å, respectively, possibly indicating weak mercuriophilic interactions. The luminescent properties of the complexes in solution and in the solid state at room temperature are also described.     

Small noise asymptotics for invariant densities for a class of diffusions: A control theoretic view

We consider multi-dimensional nondegenerate diffusions with invariant densities, with the diffusion matrix scaled by a small >0. The o.d.e. limit corresponding to =0 is assumed to have the origin as its unique globally asymptotically stable equilibrium. Using control theoretic methods, we show that in the ↓0 limit, the invariant density has the form ≈exp(−W(x)/²), where the W is characterized as the optimal cost of a deterministic control problem. This generalizes an earlier work of Sheu. Extension to multiple equilibria is also given.     

On the fundamental group-scheme

We show that the fundamental group-scheme of a separably rationally connected variety defined over an algebraically closed field is trivial. Let X be a geometrically irreducible smooth projective variety defined over a finite field k admitting a k-rational point. Let {En,σn}_n?0 be a flat principal G-bundle over X, where G is a reductive linear algebraic group defined over k. We show that there is a positive integer a such that the principal G-bundle is isomorphic to E₀, where FX is the absolute Frobenius morphism of X. From this it follows that E₀ is given by a representation of the fundamental group-scheme of X in G.     

Indigenous development of a 2 kW RF-excited fast axial flow CO<Subscript>2</Subscript> laser

RF-excited fast axial flow CO₂ lasers in kilowatt regime are presently being used for various new scientific applications in addition to laser material processing because of its versatility and superior beam quality. We have indigenously developed a compact 2 kW RF-excited fast axial flow CO₂ laser with moderate beam quality. In this paper the key design features of the laser and the associated high power capacitively coupled RF excitation technique are discussed in detail. Operational characteristics of this system are described along with the experimental findings.