π‐Aryl/heteroaryl conjugated coumarin‐thiazoles: Synthesis,optical spectral and nonlinear optic properties

A series of π‐aryl/heteroaryl conjugated coumarin‐thiazole systems 8a‐f has been synthesized by using Hantzsch thiazole protocol and Wittig olefination as the keys. In the UV‐Visible spectra of 8a‐f , a main absorption band associated with a dominant π‐π* transition is observed in the region of 338 to 390 nm. Qualitatively, the values of λ_max have been found to correlate satisfactory with the donor/acceptor characteristics of the π‐attached chromophores. Marked changes observed in the absorption maxima of 8a under acidic conditions are rationalized on the basis of mono‐or bis‐protonation and modification of the donor/acceptor properties of chromophores undergoing protonation. The emission spectra of 8a‐f , obtained by exciting the molecules at their main absorption bands showed emission maxima in the region of 429 nm to 537 nm, with relatively high Stokes shifts of 145 and 171 nm being observed for 8a and 8e , carrying a π‐donor, dimethylaminophenyl and a π‐acceptor, p‐nitrophenyl chromophore, respectively. Although, the first hyperpolarisability β, measured by the hyper‐Reileigh scattering (HRS) technique are modest (12 to 23 × 10^?30 esu), all the compounds exhibited complete transparency in the frequency doubling region at 532 nm and showed high thermal stability (T_d from 330 to 365 °C).     

Estimation of tungsten in complex matrices using toluene 3,4-dithiol and thiocyanate

 A rapid less labour-intensive procedure for complete decomposition of tungsten bearing complex matrices by potassium pyrosulphate and its determination using toluene 3,4-dithiol and thiocyanate is reported. The analytical results of various standard reference materials are presented (Jasperoid GXR-1, Deposit GXR-3, copper mill head GXR-4, tin-tungsten ore IGS-26, Mo-W ore IGS-27, tungsten concentrate SRM-277, scheelite ore SRM-2430, reference tungsten ore TLG-1, CT-1, BH-1 and Mo-W ore MP-2) along with two manganese nodules (GSPN-2 and GSPN-3) recently introduced by the Chinese Academy of Geological Sciences and one Polish soil sample (SRM-2710). For most of the samples the agreement between the observed value and the published data have been found to be extremely good. Derivations have been noted in some samples where published concentrations are indicative values only, indicating that more data are still required to upgrade the status from proposed/unspecified to the certified level. Results of various statistical analyses (intermethod comparison, F-test and regression analysis) reveal that the methods are matrix dependent. Separation of tungsten from molybdenum is straightforward, hence can be used for a quality control programme and in the evaluation of reference materials. Received: 30 December 1996 / Revised: 12 March 1997 / Accepted: 15 March 1997     

Synthesis and Evaluation of Some Quinoline Schiff Bases as a Corrosion Inhibitor for Mild Steel in 1 N HCl

This article has been retracted.     

Diastereoselective synthesis of functionalized 2-methyltetrahydropyran-4-ones

A simple procedure for the synthesis of functionalized 2-methyl-2,3-dihydropyran-4-ones, based on the Maitland-Japp reaction, and their diastereoselective conversion into functionalized 2-methyltetrahydropyran-4-ones has been developed. This allows access to a structural unit present in a large number of biologically active natural products, and has been successfully applied to the synthesis of the molecule found in Civet cat secretion.     

Micellisation of triblock copolymers of ethylene oxide and 1,2-butylene oxide: effect of B-block length

We have used pyrene fluorescence spectroscopy and isothermal titration calorimetry (ITC) to investigate the effect of hydrophobic-block length on values of the critical micelle concentration (cmc) for aqueous solutions of triblock poly(butylene oxide)-poly(ethylene oxide)-poly(butylene oxide) block copolymers (B(n)E(m)B(n), where m and n denote the respective block lengths) with hydrophobic block lengths in the range n=12-21. Combined with results from previous work on B(n)E(m)B(n) copolymers with shorter B blocks, plots of log(10)(cmc) (cmc in molar units and reduced to a common E-block length) against total number of B units (n(t)=n for diblock or n(t)=2n for triblock copolymers) display transitions in the slopes of the two plots, which indicate changes in the micellisation equilibrium. These occur at values of n(t)which can be assigned to the onset and completion of collapse of the hydrophobic B blocks, an effect not previously observed for reverse triblock copolymers. The results are compared with related data for diblock E(m)B(n) copolymers.     

Experimental Validation of a Two-Dimensional Model of the Transient and Steady-State Characteristics of a Wicked Heat Pipe

Abstract

The transient behavior of a copper-water wicked (80 mesh SS-304 screen) heat pipe during start-up is studied. The transient axial temperature distributions are measured and successfully compared for all the three sections of the heat pipe with the numerical solution of a developed two-dimensional model that utilizes the concept of a growing thermal layer in the wall and the wick region and takes into account axial conduction during transient operation. Steady-state temperature profiles are obtained as a limiting case. The experimental and theoretically predicted time required to attain steady state are in close agreement as well.     

Calcium Hydride Catalysts for Olefin Hydrofunctionalization: Ring-Size Effect of Macrocyclic Ligands on Activity

The fifteen-membered NNNNN macrocycle Me₅PACP (Me₅PACP=1,4,7,10,13-pentamethyl-1,4,7,10,13-pentaazacyclopentadecane) stabilized the [CaH]⁺ fragment as a dimer with a distorted pentagonal bipyramidal coordination geometry at calcium. The hydride complex was prepared by protonolysis of calcium dibenzyl with the conjugate acid of Me₅PACP followed by hydrogenolysis or treating with ⁿOctSiH₃ of the intermediate calcium benzyl cation. The calcium hydride catalyzed the hydrogenation and hydrosilylation of unactivated olefins faster than the analogous calcium complex stabilized by the twelve-membered NNNN macrocycle Me₄TACD (Me₄TACD=1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Kinetic investigations indicate that higher catalytic efficiency for the Me₅PACP stabilized calcium hydride is due to easier dissociation of the dimer in solution when compared to the Me₄TACD analogue.     

Electron transport through molecular wires based on a face-shared bioctahedral motif

Density functional theory in conjunction with non-equilibrium Green's functions is used to explore the electron transport properties of a series of molecules based on the face-shared bioctahedral (M₂Cl₉) motif. The metal-metal bond orders in the chosen molecules, [Rh₂Cl₉]^3–, [Ru₂Cl₉]^3– and [Mo₂Cl₉]^3– vary from 0 (Rh) to 1 (Ru) and 3 (Mo), and the calculations indicate that there is a direct correlation between conductance and bond order. The [Mo₂Cl₉]^3– case is particularly interesting as it is well known from crystallographic studies to be very flexible, the Mo–Mo bond length varying over a range of ～0.35 Å depending on cation. The upper limit of this range marks the point where homolytic cleavage of the δ_π components of the triple bond is complete, and this has a marked impact on electron transport. The localization of the metal-based orbitals means that those on the left (source) and right (drain) sides respond very differently to applied bias, giving rise to resonance effects at particular bias voltages, and hence to negative differential resistance effects.     

Improved measurement of /V(cb)/ using B-->D*l nu decays

We determine the weak coupling /V(cb)/ between the b and c quarks using a sample of 3 x 10(6) BB; events in the CLEO detector at the Cornell Electron Storage Ring. We determine the yield of reconstructed B-->D*l nu; decays as a function of w, the boost of the D* in the B rest frame, and from this we obtain the differential decay rate d Gamma/dw. By extrapolating d Gamma/dw to w=1, the kinematic end point at which the D* is at rest relative to the B, we extract the product /V(cb)/F(1), where F(1) is the form factor at w=1. Combined with theoretical results for F(1) we determine /V(cb)/=0.0469+/-0.0014(stat)+/-0.0020(syst)+/-0.0018(theor).