Metrical Theorems on Restricted Diophantine Approximations to Points on a Curve

We investigate rational approximations (r/p,q/p) or (r/p,q/r) to points on the curve (α,α^τ) for almost all α>0, where p,q,r are all primes. We immediately obtain corollaries on making p,[αp], [α^τp] simultaneously prime.     

Self-assembled monolayers of alkanethiolates on palladium are good etch resists

This paper describes microcontact printing (muCP) of long-chain alkanethiolates on palladium, followed by solution-phase etching with an iron(III)-based etchant, to make patterned structures. The commonly used soft-lithographic procedure for fabricating microstructures-muCP of SAMs on gold-has three shortcomings: a significant surface density of pinhole defects, substantial edge roughness, and incompatibility with processes used in CMOS fabrication. Microcontact printing on palladium gives fewer defects and smaller edge roughness than on gold, and is compatible with CMOS. The mechanism by which etch-resistant patterns are formed is different for palladium and gold. The Pd/S interfacial layer formed by the reaction of palladium films with sulfur-containing compounds provides good resistance to etches independently of the barrier to access the surface provided by the film of (CH2)n groups in the long-chain SAMs. This barrier is the basis of the etch resistance of SAMs on gold, but only supplements the etch resistance of the sulfur-containing interfacial layer on palladium. Characterization of the SAM formed from hexadecanethiol on palladium is described.     

PRIMARY PROCESSES IN THE LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS OF l-EPHEDRINE

Abstract— Transient absorption spectra produced by laser flash-photolysis of an aqueous solution of ephedrine have been measured under a variety of conditions. Ephedrine was found to photoionise via a biphotonic process. The apparent yield of photoionisation increases with lowering of pH, a value of 8.8 being found for the p K _a associated with this change. The cation radical absorption spectrum has been determined using the techniques of both pulse radiolysis and laser flash photolysis. The extinction coefficient of the cation at 295 nm was determined to be 1.37 × 10⁴ dm³ mol^-1 cm^-1 and 1.2 × 10⁴ dm³ mol-¹cm-¹ by the two techniques, respectively, at pH 11. It is also shown that the rate constant for electron abstraction by the azide radical to form the ephedrine cation is controlled by protonation of the amine group in the side chain. The ephedrine anion radical spectrum and its extinction coefficient at 305 nm were also determined. The excited states responsible for photoionisation and photodegradation are discussed.     

Kinetics of nucleophilic attack on coordinated organic moieties : VI. Mechanism of addition of tri-n-butylphosphine to [(C7H7)M(CO)3]BF4 (M = Cr, Mo, W) and related cations

Phosphonium adduct formation via attack of tri-n-butylphosphine on the cations [(C₇H₇)M(CO)₃]⁺ (M = Cr, Mo, W) obeys the rate law, Rate = k [complex] [PBu₃]. The very similar rate constants for the Cr, Mo and W complexes confirm the similar electrophilicities of the tropylium rings in these cations, and also support the view that there is direct addition to the rings. The related complexes [(C₆H₇)Fe(CO)₃]BF₄ and [(C₆H₆)Mn(CO)₃]BF₄ also form adducts with PBu₃, and the quantitative reactivity order [(C₆H₇)Fe(CO)₃]⁺ > [(C₇H₇)Cr(CO)₃]⁺ » [(C₆H₆)Mn(CO)₃]⁺ (160:60:1) has been established.     

Chromatographic,spectroscopic, topographic,and X-ray crystallographic studies of the solid solution formed by racemic 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (3-carboxy-proxyl)

The solid solution formed by the title compound, C₉H₁₆NO₃, has been examined by a variety of techniques and shown to be an equi-molecular mixture of the two enantiomers. Refinement of the disordered structure was based on the orthorhombic space groupPnma witha=8.023(2),b=10.030(3), andc=12.352(2)Å, finalR=0.055. The oxygens of the carboxyl group are disordered and both enantiomers can occupy the same, rather than alternate, crystallographic sites. Results from studies involving IR, GC-MS, and chiral chromatography are also presented. In addition we report on the use of synchrotron X-ray topography to investigate strain in crystals of the solid solution.     

Photodimerization of Coumarin Functionalized Poly(alkyl Acrylate) and Poly(alkyl Methacrylate) Random Copolymers: Influence of Copolymer Composition on Photocrosslinking

Coumarin‐containing poly(alkyl (meth)acrylates) were prepared via 70–80% esterification of hydroxy‐containing acrylic copolymers, then solution cast into thin films and photocrosslinked via the dimerization of coumarin derivatives with UVA light. The coumarin‐modified polymers crosslinked upon exposure and exhibited gel fractions between 74 and 99%. Coumarin dimerization efficiency increased with higher polymer mobility at the irradiation temperature. The effects of light intensity and irradiation time in photo‐dimerized systems followed the Bunsen‐Roscoe reciprocity law indicating that coumarin photodimerization depended only on dose. Thus, low intensities are overcome with longer times. This is an important advantage over photoinitiated free radical crosslinking which depends on irradiation intensity to the ½ power.     

Synthesis of Acetophenone Azine

Conditions for preparing acetophenone azine via the oxidative dimerization of acetophenone imine anion are investigated.     

Oxidation of Alcohols by Bromine on Alumina

Bromine adsorbed on neutral alumina is an effective reagent for the oxidation of secondary alcohols to ketones.