Layer guided-acoustic plate mode biosensors for monitoring MHC-peptide interactions

The transduction signals from the immobilisation of a class I heavy chain, HLA-A2, on a layer guided acoustic plate mode device, followed by binding of beta(2)-microglobulin and subsequent selective binding of a target peptide are reported

Quantification of Nitric Acid Using Photolysis Induced Fluorescence for use in Chemical Kinetic Studies

Previous laboratory investigations have predominantly relied on UV absorption measurement of [HNO_3]. Whilst direct, this measurement is difficult at temperatures <298 K, where heterogeneous loss to cold surfaces is significant. Single and two photon photodissociation of HNO_3 was studied in N_2 and He at 193 and 248 nm, and a unique HNO_3 detection method was established using two photons at 248 nm, with good reproducibility and limit of detection (∼1.25 × 10^(14) cm^(-3)). Emissions from excited products have been identified spectroscopically, over a range of pressures and laser energies to support the HNO_3 quantification method

Pressure and Temperature Dependencies of Rate Coefficients for the Reaction OH + NO₂ + M → Products

The OH + NO₂ reaction is a critically important process for radical chain termination in the atmosphere with a major impact on the ozone budgets of the troposphere and stratosphere. Rate constants for the reaction of OH + NO₂ + M → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a laser photolysis–laser-induced fluorescence (LP-LIF) technique augmented by in situ optical spectroscopy for quantification of [NO₂]. The experiments are carried out over the temperature range of 230–293 K and the pressure range 50–750 Torr of N₂ and air and as a function of [O₂]. The observed rate coefficients in N₂ agree with the newest experimental literature data sets and are within experimental uncertainty of current recommended literature values at 293 K but are systematically higher by up to 22% at 700 Torr and 230 K. The efficacy of different falloff parametrizations has been examined and compared to those in literature sources. The collisional quenching efficiency of O₂ was found to be in excellent agreement with current literature sources, and rate coefficients determined in air at 293 and 245 K were observed to be within uncertainty of the rate coefficients measured in N₂ bath gas. This work has improved confidence in the literature rate coefficients under conditions of the lower troposphere (∼760 Torr, 280–310 K) toward the stratosphere (10–100 Torr, 220–250 K)

Pressure and Temperature Dependencies of Rate Coefficients for the Reaction OH + NO₂ + M → Products

The OH + NO₂ reaction is a critically important process for radical chain termination in the atmosphere with a major impact on the ozone budgets of the troposphere and stratosphere. Rate constants for the reaction of OH + NO₂ + M → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a laser photolysis–laser-induced fluorescence (LP-LIF) technique augmented by in situ optical spectroscopy for quantification of [NO₂]. The experiments are carried out over the temperature range of 230–293 K and the pressure range 50–750 Torr of N₂ and air and as a function of [O₂]. The observed rate coefficients in N₂ agree with the newest experimental literature data sets and are within experimental uncertainty of current recommended literature values at 293 K but are systematically higher by up to 22% at 700 Torr and 230 K. The efficacy of different falloff parametrizations has been examined and compared to those in literature sources. The collisional quenching efficiency of O₂ was found to be in excellent agreement with current literature sources, and rate coefficients determined in air at 293 and 245 K were observed to be within uncertainty of the rate coefficients measured in N₂ bath gas. This work has improved confidence in the literature rate coefficients under conditions of the lower troposphere (∼760 Torr, 280–310 K) toward the stratosphere (10–100 Torr, 220–250 K)

Abundance of NO3 derived organo-nitrates and their importance in the atmosphere

The chemistry of the nitrate radical and its contribution to organo-nitrate formation in the troposphere has been investigated using a mesoscale 3-D chemistry and transport model, WRF-Chem-CRI. The model-measurement comparisons of NO2, ozone and night-time N2O5 mixing ratios show good agreement supporting the model’s ability to represent nitrate (NO3) chemistry reasonably. Thirty-nine organo-nitrates in the model are formed exclusively either from the reaction of RO2 with NO or by the reaction of NO3 with alkenes. Temporal analysis highlighted a significant contribution of NO3-derived organo-nitrates, even during daylight hours. Night-time NO3-derived organo-nitrates were found to be 3-fold higher than that in the daytime. The reactivity of daytime NO3 could be more competitive than previously thought, with losses due to reaction with VOCs (and subsequent organo-nitrate formation) likely to be just as important as photolysis. This has highlighted the significance of NO3 in daytime organo-nitrate formation, with potential implications for air quality, climate and human health. Estimated atmospheric lifetimes of organo-nitrates showed that the organo-nitrates act as NOx reservoirs, with particularly short-lived species impacting on air quality as contributors to downwind ozone formation

Quantification of Nitric Acid Using Photolysis Induced Fluorescence for use in Chemical Kinetic Studies

Previous laboratory investigations have predominantly relied on UV absorption measurement of [HNO_3]. Whilst direct, this measurement is difficult at temperatures <298 K, where heterogeneous loss to cold surfaces is significant. Single and two photon photodissociation of HNO_3 was studied in N_2 and He at 193 and 248 nm, and a unique HNO_3 detection method was established using two photons at 248 nm, with good reproducibility and limit of detection (∼1.25 × 10^(14) cm^(-3)). Emissions from excited products have been identified spectroscopically, over a range of pressures and laser energies to support the HNO_3 quantification method