Atmospheric chemistry of t-CF3CH=CHCl: products and mechanisms of the gas-phase reactions with chlorine atoms and hydroxyl radicals

FTIR-smog chamber techniques were used to study the products and mechanisms of the Cl atom and OH radical initiated oxidation of trans-3,3,3-trifluoro-1-chloro-propene, t-CF(3)CH=CHCl, in 700 Torr of air or N(2)/O(2) diluent at 296 ± 2 K. The reactions of Cl atoms and OH radicals with t-CF(3)CH=CHCl occur via addition to the >C=C< double bond; chlorine atoms add 15 ± 5% at the terminal carbon and 85 ± 5% at the central carbon, OH radicals add approximately 40% at the terminal carbon and 60% at the central carbon. The major products in the Cl atom initiated oxidation of t-CF(3)CH=CHCl were CF(3)CHClCHO and CF(3)C(O)CHCl(2), minor products were CF(3)CHO, HCOCl and CF(3)COCl. The yields of CF(3)C(O)CHCl(2), CF(3)CHClCOCl and CF(3)COCl increased at the expense of CF(3)CHO, HCOCl and CF(3)CHClCHO as the O(2) partial pressure was increased over the range 10-700 Torr. Chemical activation plays a significant role in the fate of CF(3)CH(O)CHCl(2) and CF(3)CClHCHClO radicals. In addition to reaction with O(2) to yield CF(3)COCl and HO(2) the major competing fate of CF(3)CHClO is Cl elimination to give CF(3)CHO (not C-C bond scission as previously thought). As part of this study k(Cl + CF(3)C(O)CHCl(2)) = (2.3 ± 0.3) × 10(-14) and k(Cl + CF(3)CHClCHO) = (7.5 ± 2.0) × 10(-12) cm(3) molecule(-1) s(-1) were determined using relative rate techniques. Reaction with OH radicals is the major atmospheric sink for t-CF(3)CH=CHCl. Chlorine atom elimination giving the enol CF(3)CH=CHOH appears to be the sole atmospheric fate of the CF(3)CHCHClOH radicals. The yield of CF(3)COOH in the atmospheric oxidation of t-CF(3)CH=CHCl will be negligible (<2%). The results are discussed with respect to the atmospheric chemistry and environmental impact of t-CF(3)CH=CHCl.     

$\mathfrak{D}$ -Differentiation in Hilbert Space and the Structure of Quantum Mechanics

An appropriate kind of curved Hilbert space is developed in such a manner that it admits operators of - and -differentiation, which are the analogues of the familiar covariant and D-differentiation available in a manifold. These tools are then employed to shed light on the space-time structure of Quantum Mechanics, from the points of view of the Feynman ‘path integral’ and of canonical quantisation. (The latter contains, as a special case, quantisation in arbitrary curvilinear coordinates when space is flat.) The influence of curvature is emphasised throughout, with an illustration provided by the Aharonov-Bohm effect.     

A Unified Framework for Relativity and Curvilinear-Time Newtonian Mechanics

Classical mechanics is presented so as to render the new formulation valid for an arbitrary temporal variable, as opposed to Newton’s Absolute Time only. Newton’s theory then becomes formally identical (in a precise sense) to relativity, albeit in a three-dimensional manifold. (The ultimate difference between the two dynamics is traced to the existence of the relativistic ‘mass-shell’ condition.) A classical Lagrangian is provided for our formulation of the equations of motion and it is related to one of the known forms of the corresponding relativistic Lagrangian, which is the analogue of the Polyakov Lagrangian of string theory. Dedicated to Emeritus Professor D. Speiser (Université Catholique de Louvain, Belgium) who provided the inspiration for this article.     

A tabu search algorithm for frequency assignment

This paper presents the application of a tabu search algorithm for solving the frequency assignment problem. This problem, known to be NP-hard, is to find an assignment of frequencies for a number of communication links, which satisfy various constraints. We report on our computational experiments in terms of computational efficiency and quality of the solutions obtained for realistic, computer-generated problem instances. The method is efficient, robust and stable and gives solutions which compare more favourably than ones obtained using a genetic algorithm.     

Algebraic study of a class of relativistic wave equations

First-order relativistic wave equations are considered whose irreducible matrix coefficients satisfy the simplest (except for the Dirac algebra) unique mass condition, (β · p)³ = p²(β · p), which is also sufficient to guarantee causality in a minimally coupled external electromagnetic field. All of the associated representations of SL(2, ©) are classified and studied up to and including those which are the direct sum of four irreducible components, (n, m), with either n or m less than two. A large number of families of representations are found which permit the algebraic condition to be satisfied. These are tabulated according to whether a Hermitian choice for β⁰ is possible and their spin content is given. If a unique spin is described, then the only possible representations are

$\text{(1) (}\text{n}\text{,0) ⊕ (}\text{n}\text{? 1/2, 1/2)}$

$\text{(2) (}\text{n}\text{,0) ⊕ (}\text{n}\text{+ 1/2, 1/2)}$

$\text{(3) (}\text{n}\text{+ 1/2, 1/2) ⊕ (}\text{n}\text{,0) ⊕ (}\text{n}\text{? 1/2, 1/2)}$

$\text{(4) (1,0) ⊕ (1/2, 1/2) ⊕ (0,1)}$

and their conjugates. If, in addition, the representation is assumed to be self-conjugate, then only the Dirac and Petiau-Duffin-Kemmer equations survive.     

Poly(arylene sulfides) with pendant cyano groups as high-temperature laminating resins

Poly(phenylene sulfides) were synthesized from m-benzenedithiol and aromatic dibromides in a basic medium of potassium carbonate in dimethylformamide or dimethylacetamide. The products obtained were slightly off-white with relatively low melting ranges and had inherent viscosities in the 0.2–0.4 dl/g range in hexamethylphosphoric triamide. Similar poly(phenylene sulfides) containing pendant cyano groups along the polymer chains were obtained by the use of 5 mole-% of either 2,4-dichlorobenzonitrile or 3,5-dichlorobenzonitrile. The products were similar to the pure polyphenylene sulfides, except that they showed lower melting ranges and gave insoluble products when heated alone or in the presence of zinc chloride.     

Accessing DNA by low voltage alternating current Joule effect heating

A DNA release sample preparation method based on the use of low voltage alternating currents (LVACs) to generate Joule effect heating (JEH) is reported. This is a simple cell disruption strategy that offers internal, homogenous, rapid and low power consumption heating for the access of analytical grade DNA in seconds.A 100 μL JEH microreactor with a parallel and symmetric two electrode arrangement for uniform field generation was fabricated by machining and used to characterise JEH and DNA release from human epithelia, yeast (Saccharomyces cerevisiae) and Gram-positive bacteria (Enterococcus faecium) cell types. A 1 kHz sinusoidal low voltage (e.g. 10 Vrms) alternating current was used to reduce electrode:sample interactions. Following 96 °C JEH treatment, effective DNA release was identified by PicoGreen^® quantification for all three cell types. The JEH treated sample material was further successfully used, without purification, as a PCR template. Exposure to JEH-mediated 96 °C temperatures for a 1 s duration was used to provide PCR-grade DNA template material from S. cerevisiae and E. faecium cells, and a 10 s duration was used for human epithelia cells. However, prolonged (>1 min) exposure to 96 °C JEH-mediated temperatures resulted in diminished DNA returns and the production of components that interfered with the PCR reaction.Further miniaturisation of the LVAC JEH cell by microfabrication was considered, and a JEH microreactor designs were evaluated by FLOTHERM v3.2 thermal modelling. Thermal isolation, using a free-standing cavity structure was identified as an excellent means to enable rapid heating (220 °C s⁻¹) with low power consumption (0.2 W).     

New thermally stable polymer with a graphite-type structure

A new thermally stable polymer with a structure resembling that of graphite has been synthesized by the condensation of 1,4,5,8-tetraaminoanthraquinone and 1,3,6,8-tetraketo-1,2,3,6,7,8-hexahydropyrene (naphthalene-1,8,4,5-diindandione). Prepolymers, with an open structure, were soluble to some extent in concentrated sulfuric acid but were more completely solubilized by methanesulfonic acid. The final polymer with a closed-ring structure, which was obtained by heating the prepolymer having an inherent viscosity of 0.4, was completely insoluble in these acids. Elemental analysis indicated that a high degree of cyclization was achieved, and the final polymer showed good thermal stability. Prepolymers with inherent viscosities in the range 0.11–1.58 have been obtained but, usually, a high viscosity was accompanied by a low acid solubility. Prepolymers with an inherent viscosity of 0.4, which were very soluble (>90%) in strong acids, were solubilized to a high degree by reduction with sodium dithionite in alkaline, aqueous dimethylacetamide. The highest molecular weight prepolymer (inherent viscosity of 1.30–1.58) was solubilized to a greater extent in this base mixture than in methanesulfonic acid. However, it was not completely soluble, under the conditions employed. The propolymers of higher molecular weight showed some fiber- and film-forming properties.     

Large steric effect in the substitution reaction of amines with phosphoimidazolide-activated nucleosides

Aliphatic amines react with phosphoimidazolide-activated derivatives of guanosine and cytidine (ImpN) by replacing the imidazole group. The kinetics of reaction of guanosine 5'-phospho-2-methylimidazolide (2-MeImpG) with glycine ethyl ester, glycinamide, 2-methoxyethylamine, n-butylamine, morpholine, dimethylamine (Me2NH), ethylmethylamine (EtNHMe), diethylamine (Et2NH), pyrrolidine, and piperidine were determined in water at 37 degrees C. With primary amines, a plot of the logarithm of the rate constant for attack by the amine on the protonated substrate, log kSH(A), versus the pKa of the amine exhibits a good linear correlation with a Bronsted slope, beta nuc = 0.48. Most of the secondary amines tested react with slightly higher reactivity than primary amines of similar pKa. Interestingly, some secondary amines show substantially lower reactivity than might be expected: EtNHMe reacts about eight times, and Et2NH at least 100 times, more slowly than Me2NH although all three amines are of similar basicity. For comparison, the kinetics of reaction of guanosine 5'-phosphoimidazolide (ImpG) and cytidine 5'-phosphoimidazolide (ImpC) were determined with Me2NH, EtNHMe, and Et2NH, and similar results were obtained. These results establish that the increased steric hindrance observed with the successive addition of ethyl groups are not due to any special steric requirements imposed by the guanosine or the methyl on the 2-methylimidazole leaving group of 2-MeImpG. It is concluded that addition of ethyl and, perhaps, groups larger than ethyl dramatically increases the kinetic barrier for addition of aliphatic secondary amines to the P-N bond of ImpN. This study supports the observation that the primary amino groups on the natural polyamines are at least 2 orders of magnitude more reactive than the secondary amino groups in the reaction with ImpN.     

Nanopatterning of alkynes on hydrogen-terminated silicon surfaces by scanning probe-induced cathodic electrografting

The electrochemical cathodic electrografting reaction, previously demonstrated on bulk silicon surfaces, can be patterned on the nanoscale utilizing conducting probe atomic force microscopy (CP-AFM). Alkyne electrografting is a particularly useful chemical technique since it leads to direct covalent attachment of conjugated alkynes to silicon. In addition, application of a forward bias during the reaction renders the surface less sensitive to oxidation and the resulting monolayers are very stable in air and basic aqueous solution. Alkyne monolayer lines can be drawn down to 40 nm resolution using a Pt-coated AFM tip, and the heights of the monolayers scale with the molecular length of the alkyne. The tip is biased (+) and the surface is biased (-) to drive the cathodic electrografting reaction under ambient conditions. The resistance of the monolayers to fluoride, as well as friction force microscopy, indicate that the alkynes are covalently bonded to the surface, not oxide-based, and hydrophobic. The reaction does not work with alkenes, and therefore hydrosilylation is not the primary mode of reaction. Wider lines (300 nm) can be produced using broadened Pt-coated AFM tips. This reaction could be important for the interfacing of conjugated molecules directly to silicon in a spatially controlled fashion.