Coordination induced fluorescence enhancement and construction of a Zn3 constellation through hydrolysis of ligand imine arms

The phenoxido and alkoxido bridged neutral Zn(3) complex [Zn(3)(μ-H(2)bemp)(2)(μ(3)-emp)(2)] (1), with an angular Zn(3)(μ-OPh)(2)(μ-OEt)(2) core and capping nitrogen donors, was synthesized via simultaneous chelation-cum-bridging of the parent and hydrolysed ligands. Zinc(II) coordination triggered the solution phase imine (C=N) bond hydrolysis of H(3)bemp (2,6-bis-[(2-hydroxyethylimino)methyl]-4-methylphenol) and yielded the unexpected angular trinuclear Zn(II) complex 1, having structural similarity with the Zn(3) active site of P1 nuclease. H(3)bemp also displays a zinc(II) selective chelation-enhanced fluorescence response from strong metal ion coordination. Complexation of zinc(II) with H(3)bpmp (2,6-bis-[(3-hydroxypropylimino)methyl]-4-methylphenol), a close analogue of H(3)bemp, instead provides only mononuclear [Zn(H(2)bpmpH(N))(2)](ClO(4))(2)·2H(2)O (2·2H(2)O) (H(N) is the proton attached to an imine nitrogen atom) of two zwitterionic ligands, generated through a kind of coordination driven acid-base reaction, without showing any aggregation reaction. As the sole metal-organic precursor, both the complexes under pyrolytic conditions give ZnO nano structures of two morphologies.     

M-estimation of wavelet variance

The wavelet variance provides a scale-based decomposition of the process variance for a time series or a random field and has been used to analyze various multiscale processes. Examples of such processes include atmospheric pressure, deviations in time as kept by atomic clocks, soil properties in agricultural plots, snow fields in the polar regions and brightness temperature maps of South Pacific clouds. In practice, data collected in the form of a time series or a random field often suffer from contamination that is unrelated to the process of interest. This paper introduces a scale-based contamination model and describes robust estimation of the wavelet variance that can guard against such contamination. A new M-estimation procedure that works for both time series and random fields is proposed, and its large sample theory is deduced. As an example, the robust procedure is applied to cloud data obtained from a satellite.     

Tetranuclear Cu(II) complex supported by a central mu4-1,1,3,3 azide bridge

The new cluster [Cu4L2(N3)]Cl.16H2O has been synthesized and characterized; it features a unique mu4-1,1,3,3 bridging mode for azide, whose capacity to mediate magnetic coupling has been examined through bulk magnetic measurements and numeric fitting procedures.     

Tl(I), Fe(II), and Co(II) complexes supported by a monoanionic N,N,N'-heteroscorpionate ligand bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr (Ar = 2,6-iPr2C6H3)

The lithium salt (L)Li(THF) (L- = bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr, Ar = 2,6-iPr2C6H3) can be readily prepared from lithium bis(3,5-di-tertbutylpyrazol-1-yl)methide and the N-methyleneaniline H2C=NAr. This N,N,N'-heteroscorpionate lithium reagent can be transmetalated with Tl(OTf), FeCl2(THF)(1.5), and CoCl2 to yield the (L)Tl, (L)FeCl, and (L)CoCl complexes, respectively. Single crystal structural data for compounds (L)Li(THF), (L)Tl, (L)FeCl, and (L)CoCl reveal in each case the hapticity of the sterically demanding, monoanionic L- ligand to be kappa3-N3.     

Study of Kinetics of Iron Minerals in Coal by 57Fe Mössbauer and FT-IR Spectroscopy During Natural Burning

The process of burning of sulphur rich coal from Jaipur mine in North-Eastern India was carried out at a temperature of (675 ± 5) °C for different time intervals. ⁵⁷Fe Mössbauer spectroscopy was applied to study the reaction products of iron compounds in each step of thermal treatment. The transformation of Szomolnokite (FeSO_4·H₂O) and Pyrite (FeS₂) in the as received coal sample finally transformed to γ-Fe₂O₃ and α-Fe₂O₃. Other clay minerals produce some low spin silicate ash. Fourier Transmission Infrared (FT-IR) spectroscopy gives the ratio of several structural parameters such as H _ar/H _al and H _ar/C _ar. DTA analysis of the coal sample gives the exothermic reaction at different temperatures. TGA and TG analysis of the coal sample in an inert atmosphere shows the weight loss of the coal sample in different temperature ranges.     

Synthesis of dragmacidin D via direct C-H couplings

Dragmacidin D, an emerging biologically active marine natural product, has attracted attention as a lead compound for treating Parkinson's and Alzheimer's diseases. Prominent structural features of this compound are the two indole-pyrazinone bonds and the presence of a polar aminoimidazole unit. We have established a concise total synthesis of dragmacidin D using direct C-H coupling reactions. Methodological developments include (i) Pd-catalyzed thiophene-indole C-H/C-I coupling, (ii) Pd-catalyzed indole-pyrazine N-oxide C-H/C-H coupling, and (iii) acid-catalyzed indole-pyrazinone C-H/C-H coupling. These regioselective catalytic C-H couplings enabled us to rapidly assemble simple building blocks to construct the core structure of dragmacidin D in a step-economical fashion.     

An analytical approach to the effect of finite-sized end reservoirs on electroosmotic transport through narrow confinements

The presence of end reservoirs often alters the electrical potential distributions inside narrow fluidic confinements of electrokinetically actuated miniaturized devices to a significant extent. This paper examines the influence of finite size effect of the end reservoirs on the concerned potential distribution analytically, using the Schwarz-Christoffel conformal mapping. The effective electric field directly acting across the channel is accordingly represented by a calibration curve, which sums up the role of the key geometric parameters (reservoir-to-channel height and length ratios) on the potential distribution. The analytical model is further augmented to assess the flow characteristics through the channel. The results indicate that the alterations in the flow characteristics due to alterations in the effective electric field on account of the finite size effects of the end reservoirs can turn out to be significantly more prominent than the corresponding alterations due to the axial pressure gradients induced by the sudden contraction and expansion effects associated with the end reservoirs. The derived results can be further utilized to facilitate the practical design of miniaturized fluidic devices, using conveniently tractable analytical tools.     

Salen complexes of zirconium and hafnium: synthesis, structural characterization, controlled hydrolysis, and solvent-free ring-opening polymerization of cyclic esters and lactides

Dinuclear salen compounds of zirconium and hafnium are efficient initiators for the solvent-free ring-opening polymerization of cyclic ester monomers and lactides. There is a correlation between the theoretical and experimental number-average molecular weights (M(n)'s) in these polymerizations. Polymerization of β-butyrolactone gives poly(3-hydroxybutyrate) with a good M(n) and molecular weight distribution.