Optical activity in mixed-ligand terbium complexes containing 5-sulfosalicyclic acid and chiral hydroxycarboxylic acids

The optical activity associated with the f-f; emission bands of Tb(III) complexes which contain chiral hydroxycarboxylic acids has been studied by means of circularly polarized luminescence (CPL) spectroscopy. Complexes having the general formula Tb(SSA)₂(L) were studied (where SSA signifies 5-sulphosalicylic acid), with the chiral ligand (L) being L-lactic acid, L-mandelic acid, L-aspartic acid, and L-malic acid. The CPL spectra were found to be sensitive to the mode of bonding between the metal and the chiral ligand and therefore allowed predictions to be made regarding how the hydroxycarboxylic acid ligands attach to the Tb(III) ion. Also, the degree of optical activity varied systematically with the concentration of chiral ligand, and we have used this dependence to calculate formation constants for the addition of a hydroxycarboxylic acid ligand to the Tb/SSA complex. Finally, the line shape and magnitudes of the CPL spectra provide information regarding the type of chirality experienced by the Tb(III) ion.     

The trousers problem revisited

Anderson and DeWitt considered the quantization of a massless scalar field in a spacetime whose spacelike hypersurfaces change topology and concluded that the topology change gives rise to infinite particle and energy production. We show here that their calculations are insufficient and that their propagation rule is unphysical. However, our results using a more general propagation rule support their conclusion.     

A study of the alkene-ozone reactions, 2,3-dimethyl 2-butene + O3 and 2-methyl propene + O3, with photoelectron spectroscopy: measurement of product branching ratios and atmospheric implications

The reactions of ozone with the alkenes 2,3-dimethyl 2-butene (DMB) and 2-methyl propene (2MP) have been investigated using a flow-tube interfaced to a u.v. photoelectron spectrometer. These reactions were studied at low pressure at different reagent partial pressures, both with the alkene in excess and ozone in excess. In each case, photoelectron spectra recorded as a function of time have been used to estimate partial pressures of the reagents and products as a function of time using photoionization cross-sections of selected photoelectron bands of the reagents and products, which were measured separately. The yields of all the main products have been determined, some of which have been measured in previous studies. For each reaction, oxygen was observed as a product for the first time and its yield was measured. Kinetics simulations were performed using reaction schemes which were developed for these reactions, which are consistent with that used earlier for the ozone-ethene reaction, in order to determine the main reactions for production of the products. The experimental product yields have been used in a global model to estimate their global annual emissions in the atmosphere. For example, for the reaction of O(3) with 2MP the formaldehyde, formic acid and acetone global annual emissions are calculated as 0.4 Tg, 25.0 Gg and 0.16 Tg respectively, which are estimated as 0.02, 0.3 and 0.2% of the total annual emission respectively. For the reaction of O(3) with DMB, the acetone yield is higher at 0.9 Tg which is approximately 1% of the total annual estimated emission.     

Laser-induced fluorescence detection of singlet CH2 in low-pressure methane/oxygen flames

Methylene, CH₂, is a chemically important intermediate in hydrocarbon combustion but has previously eluded optical detection in a combustion environment. The CH₂ signal as a function of height above the burner surface in a premixed, laminar, methane/oxygen flame (5.6 Torr and fuel equivalence ratio 1.05) is measured by laser-induced fluorescence (LIF) in the B ₁ – ã¹ A ₁ electronic system. The ã state which lies 3165 cm^–1 above the ground state is populated at the high temperatures of the flame (800–1800 K). Although less than one photon for each laser pulse is detected, we can unambiguously attribute the LIF features in the region 450 to 650 nm to CH₂ by both scanning the excitation laser and dispersing fluorescence. LIF temperatures and CH and OH LIF concentration profiles are also obtained for the flame. The CH₂ radical concentration maximum occurs closer to the burner than that of either OH or CH, as expected from models of methane combustion chemistry.     

Towards dynamic coating of glass microchip chambers for amplifying DNA via the polymerase chain reaction

As microchip technology evolves to allow for the integration of more complex processes, particularly the polymerase chain reaction (PCR), it will become necessary to define simple approaches for minimizing the effects of surfaces on the chemistry/processes to be performed. We have explored alternatives to silanization of the glass surface with the use of additives that either dynamically coat or adsorb to the glass surface. Polyethylene glycol, polyvinylpyrrolidone (PVP), and hydroxyethylcellulose (HEC) have been explored as potential dynamic coatings and epoxy (poly)dimethylacrylamide (EPDMA) evaluated as an adsorbed coating. By carrying out analysis of the PCR products generated under different conditions via microchip electrophoresis, we demonstrate that these coating agents adequately passivate the glass surface in a manner that prevents interference with the subsequent PCR process. While several of the agents tested allowed for PCR amplification of DNA in glass, the EPDMA was clearly superior with respect to ease of preparation. However, more efficient PCR (larger mass of amplified product) could be obtained by silanizing the glass surface.     

A study of the ethene-ozone reaction with photoelectron spectroscopy: measurement of product branching ratios and atmospheric implications

The ozone-ethene reaction has been investigated at low pressure in a flow-tube interfaced to a u.v. photoelectron spectrometer. Photoelectron spectra recorded as a function of reaction time have been used to estimate partial pressures of the reagents and products, using photoionization cross-sections for selected photoelectron bands of the reagents and products, which have been measured separately. Product yields compare favourably with results of other studies, and the production of oxygen and acetaldehyde have been measured as a function of time for the first time. A reaction scheme developed for the ozone-ethene reaction has been used to simulate the reagents and products as a function of time. The results obtained are in good agreement with the experimental measurements. For each of the observed products, the simulations allow the main reaction (or reactions) for production of that product to be established. The product yields have been used in a global model to estimate their global annual emissions in the atmosphere. Of particular interest are the calculated global annual emissions of formaldehyde (0.96 ± 0.10 Tg) and formic acid, (0.05 ± 0.01 Tg) which are estimated as 0.04% and 0.7% of the total annual emission respectively.