Fibre-optic fluorosensor for sulphur dioxide

A fibre-optic sensor for continuous measurement of sulphur dioxide is described. It is based on the dynamic quenching of the fluorescence of a polynuclear aromatic hydrocarbon [benzo(b)fluoranthene] which is immobilized in silicone polymer. Sulphur dioxide is shown to be an efficient quencher; Stern-Volmer graphs are given which describe the relation between SO₂ concentration and relative fluorescence. Detection limits are about 0.01% (v/v) SO₂ in air; the useful range is from 0.01–6% (v/v). Other gases likely to occur in air were found to be inert, except for oxygen which also acts as a dynamic quencher. Its interference is negligible for SO₂ levels below 6% in air at constant oxygen pressure, because the quenching efficiency of SO₂ is about 26 times higher than that of oxygen. For varying oxygen levels, a two-sensor technique is suggested.     

Nicotinamidoxime as an analytical reagent

Summary Uranium (VI) has been found to give a yellow colour with nicotinamidoxime in alkaline medium which is highly satisfactory for the spectrophotometric estimation of the metal. The optimumph for development of the colour is 10.9–11.5 in presence of a large excess of the reagent, at 10–40C. The colour intensity is measured at 400 m. Sensitivity is 0.045 g uranium per cm², with a visual identification limit of 5 g uranium per ml. Beer's law is obeyed in the range of 5–40 ppm of the metal with an optimum range of 8–40 ppm. The colour is stable for at least one hour. All the common anions are without effect, excepting however, phosphate, carbonate, and cyanide which are tolerated only in traces. Use of tartrate or EDTA helps to mask effectively all the interfering cations excepting copper, iron and vanadium.     

Mechanism of iridium(III) catalysis in the oxidation of diols by N-bromoacetamide

Summary The kinetics of iridium(III)-catalysed oxidation of 1,2-ethanediol and 1,4-butanediol by N-bromoacetamide (NBA) in HClO₄ in the presence of [Hg(OAc)₂] as a scavenger for Br^– have been investigated. The reactions are zero-order with respect to both diols, and first-order in NBA at low NBA concentrations, tending to zero order at high concentrations. The order in Ir^III decreases from unity to zero at high iridium(III) concentrations. A positive effect on the oxidation rate is observed for [H⁺] and [Hg^II] whereas a negative effect is observed for acetamide and [Cl^–]. Ionic strength does not influence the oxidation rate. (H₂OBr)⁺ is postulated as the oxidizing species. A mechanism consistent with the observed kinetic data is proposed.     

Anisotropic electronic intracule densities for diatomics

The electronic intracule density, a three-dimensional contraction of the spinless electron pair density, is the probability density function for an interelectronic vector. A computationally efficient algorithm for the evaluation of the basic two-electron intracule integral for GTO s is presented. In order to provide an initial understanding of the topography of intracule distributions, anisotropic intracule densities for the X¹Σ ground states of the H₂ and N₂ molecules are reported and analyzed.     

Nickel nitrosyl complexes with the diphenylphosphinoethane ligand

Summary Four-coordinate nickel nitrosyl complexes of the general formula Ni(NO)X(Dppe) (Dppe=Ph₂PCH₂CH₂PPh₂) have been prepared byin situ formation of Ni(NO₂)X(Dppe), (X= Cl, Br, I or SCN) followed by reduction with triphenylphosphine, or carbon monoxide, and/or DMF. Oxygenation of the nitrosyl complexes gives the corresponding nitro products and as indicated by u.v.-vis spectroscopy involves formation of an intermediate. The oxygenation rate increases markedly in the presence of light or of a catalytic amount of benzoyl peroxide and a tentative explanation is offered for these observations. Ionic adducts are formed in reactions between the nitrosyl complexes and donor molecules.Paper presented in part at the XXth ICCC Conference.     

Enzymatic fabrication of DNA nanostructures: extension of a self-assembled oligonucleotide monolayer on gold arrays

Nucleic acid nanostructures are useful as templates for bionanofabrication of composite molecular nanostructures in materials science, molecular electronics, and biosensing. Here, we demonstrate that terminal deoxynucleotidyl transferase, which repetitively adds mononucleotides to the 3' end of a short DNA initiator, can be used to rapidly fabricate DNA nanostructures up to 121 nm high with lateral dimensions from 0.1 to 4 mum in 2 h. These programmable scaffolds can potentially be employed to build more complex nanostructures consisting of natural or unnatural nucleotides with selective docking sites along the single-stranded DNA.     

A study of equilibrium between cadmium cyanide and alkali halides and thiocyanate by solubility measurements

Summary A study of the Cd(CN)₂ +x X^– [Cd(CN)₂X _x ] ^x– equilibrium (where X = Cl, Br or CNS) has been carried out at 18° and 38° by measuring the solubility of cadmium cyanide in potassium chloride, bromide and thiocyanate at various concentrations, and at a high ionic strength (6 M) maintained with sodium perchlorate to minimise the effect of activity coefficients. Equilibrium constants forx = 1 and 2 have been calculated and clearly favour the situation wherex = 1. H values for the dissociation of [Cd(CN)₂X]^– have also been calculated.     

A highly diastereoselective synthesis of (E)-B-2-(1-cyclopropyl-1-alkenyl)-1,3,2-dioxaborinanes. Isolation and oxidation to alkyl cyclopropyl ketones

A convenient, novel synthesis of alkyl cyclopropyl ketones based on Z-1-bromo-1-alkenylboronate esters is developed. α-Bromo-(Z)-1-alkenylboronate esters readily available from literature procedures smoothly undergo a reaction with cyclopropylmagnesium bromide in tetrahydrofuran to provide the corresponding ‘ate’ complexes. These ‘ate’ complexes undergo intramolecular nucleophilic substitution reactions to provide the corresponding (E)-1-alkenylboronate esters containing cylcopropyl moiety for the first time in good isolated yields (68-82%). The carbon skeleton present in these intermediates is confirmed by oxidation with hydrogen peroxide and sodium acetate to afford the corresponding alkyl cyclopropyl ketones in good yields (72-85%).     

Synthesis,characterisation and solid state thermal behaviour of nickel(II) diamine complexes

Summary [NiL₂X₂] (L =N,N-dimethyl-1,2-ethanediamine; X = Cl^–, CF₃CO ₂ ^– , CC1₃CO ₂ ^– and CBr₃CO ₂ ^– ), [NiL₂C₂O₄] · H₂O and [NiL₂X₂] · 2 H₂O (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^– ) have been synthesised and their thermal studies carried out. Thermally induced phase transition phenomena are noticed in [NiL₂X₂] (X = CF₃CO ₂ ^– and CCl₃CO ₂ ^– ) and their probable mechanisms are described. [NiL₂X₂] (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^2– ) and [NiLX₂] (X = Cl^–, 0.5 C₂O ₄ ^2– and 0.5 SO ₄ ^2– ) have been prepared by solid state pyrolysis from the respective parent diamine complexes. [NiL₂X₂] have been made in solid state by temperature arrest technique from [NiL₂(CX₃CO₂)₂] (X = Cl^– and Br^–).     

Adhesion and debonding of soft elastic films: crack patterns, metastable pathways, and forces

We study the phenomenon of debonding in a thin soft elastic film sandwiched between two rigid plates as one of the plates is brought into intimate contact and then pulled away from contact proximity by application of a normal force. Nonlinear simulations based on minimization of total energy (composed of stabilizing elastic strain energy and destabilizing adhesive interaction energy) are employed to address the problems of contact hysteresis, cavitation, crack morphology, variation of contact area, snap-off distance, pull-off force, work done, and energy loss. Below a critical distance (d(c)) upon approach, simulations show the formation of columnar structures and nonrandom, regularly arranged nanocavities at the soft interface at a length scale of approximately 3h (h being the thickness of the film). The persistence of such instability upon withdrawal (distance >d(c)) indicates a contact hysteresis, which is caused by an energy barrier that separates the metastable states of the patterned configuration and the global minimum state of the flat film. The energy and the pull-off force are found to be nonequilibrium and nonunique properties depending on the initial contact, defects, noise, etc. Three broad pathways of debonding leading to adhesive failure of the interface, depending on the stiffness of the film, step size of withdrawal, and the imposed noise, are identified: a catastrophic column collapse mode, a peeling mode involving a continuous decrease in the contact area, and a column splitting mode. The first two modes are caused by a very high stress concentration near the cavity edges. These metastable patterned configurations engender pull-off forces that are orders of magnitude smaller than that required to separate two flat surfaces from contact.