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The CH(2)I+O(2) reaction has been studied using laser flash photolysis followed by absorption spectroscopy, laser-induced fluorescence spectroscopy and mass spectrometry. The rates of formation of IO and CH(2)O were found to be dependent upon the concentration of CH(2)I(2) under pseudo-first-order conditions ([O(2)]≫[CH(2)I(2)]), demonstrating that IO and CH(2)O are not formed directly from the title reaction, in contrast to recent investigations by Enami et al. It is proposed that the reaction proceeds via the formation of the peroxy radical species CH(2)IO(2), which undergoes self-reaction to form CH(2)IO, and which decomposes to CH(2)O+I, and that in laboratory systems IO is formed via the reaction I+CH(2)IO(2). The absorption spectrum of a species assigned to CH(2)IO(2) was observed in the range 310-400 nm with a maximum absorption at 327.2 nm of σ≥1.7×10(-18) cm(2) molecule(-1). A modelling study enabled the room temperature rate coefficients for the CH(2)IO(2)+CH(2)IO(2) self-reaction and the I+CH(2)IO(2) reaction to be confined within the ranges (6-12)×10(-11) cm(3) molecule(-1) s(-1), and (1-2)×10(-11) cm(3) molecule(-1) s(-1), respectively. In the atmosphere, CH(2)IO(2) will slowly react with other radicals to release iodine atoms, which can then form IO via reaction with ozone. Slow formation of IO means that lower concentrations are formed, which leads to a lower propensity to form particles as the precursor molecule OIO forms at a rate which is dependent on the square of the IO concentration.

Methods are described for detecting precipitation of ionisable drugs under conditions of changing pH, estimating kinetic solubility from the onset of precipitation, and measuring solubility by chasing equilibrium. Definitions are presented for kinetic, equilibrium, and intrinsic solubility of ionisable drugs, supersaturation and subsaturation, and for chasers and non-chasers, which are two classes of ionisable drug with significantly different solubility properties. The use of Bjerrum Curves and Neutral-Species Concentration Profiles to depict solubility properties are described and illustrated with case studies showing super-dissolving behaviour, conversion between crystalline forms and enhancement of solubility through supersaturation, and the use of additives and simulated gastrointestinal fluids.

The temperature and pressure dependence of the rate coefficient for the reaction of iodine monoxide radicals with dimethyl sulfide (DMS), IO + DMS --> I + DMSO (1), was studied using laser induced fluorescence (LIF) to monitor the temporal profile of IO following 351 nm photolysis of RI/DMS/NO2/He (RI = CH3I/CF3I) mixtures. The study was performed over the range T = 296-468 K yielding a positive activation energy and k1 = (9.6 +/- 8.8) x 10(12) exp{-(1816 +/- 397)/T}. No dependence was observed on total pressure between 5-300 Torr. The rate coefficient at 296 K was determined as (2.0 +/- (0.6)(0.4)) x 10(-14) cm3 molecule(-1) s(-1), more than an order of magnitude smaller than a recent study but in reasonable agreement with the previous literature.

This paper describes a low volume, in vitro apparatus for investigating the dissolution and precipitation behaviour of active pharmaceutical ingredients (APIs) under a wide range of experimental conditions and dissolution media. The apparatus has automated and dynamic pH control, allowing the simulated passage of drugs through the gastrointestinal tract (GIT). Experiments can be performed in the presence of biorelevant media and excipients, providing information related to the predicted behaviour of APIs under physiological conditions. The technique is described in detail and results are presented for a number of neutral, basic, acidic and ampholytic drug compounds.

Laser-induced fluorescence from the CH3I-Cl and ICH2I-Cl adducts formed in association reactions between chlorine atoms and CH3I and CH2I2 has been observed for the first time. The LIF excitation and dispersed fluorescence spectra have been measured in the range 345-375 nm and 380-480 nm, respectively, at 204 and 296 K. The excitation spectra exhibit vibrational fine structure, and a semiquantitative analysis of the spectra yields a similar binding energy for both adducts of approximately 60 kJ mol(-1). The adduct fluorescence is efficiently quenched by N2 and exhibits a zero-pressure lifetime of approximately 25-30 ns. Using LIF excited from the CH3I-Cl and ICH2I-Cl adducts, the kinetics of the reactions of atomic chlorine with methyl iodide and diiodomethane have been investigated, the results showing that both reactions proceed via two independent channels, an association reaction to form the adduct and a bimolecular abstraction reaction. At T approximately 200 K, the association reaction is predominant, and CH3I-Cl formation is irreversible, with rate coefficients for adduct formation found to be pressure-dependent and in reasonable agreement with the literature. At approximately 200 K, removal of the adduct is dominated by reaction with radical species (CH3 and ClSO) and by self-reaction, which proceed at close to the gas kinetic limit. At 296 K, CH3I-Cl formation is reversible, and the equilibrium constant, K(p) = (70.9 +/- 27.4) x 10(3) atm(-1), was determined, which is in excellent agreement with the literature, and the adduct does not significantly react with CH3I. The uncertainty is at the 95% confidence level (2sigma) and includes systematic errors. At approximately 200 K, the ICH2I-Cl adduct is again stabilized, with pressure-dependent rate coefficients reaching the high pressure limit at lower pressures than for the Cl + CH3I reaction. At room temperature, the ICH2I-Cl adduct is removed via an additional unimolecular decomposition channel, which dominates over the reversible decomposition channel to reform Cl + CH2I2. Neither adduct was observed to undergo significant reaction with molecular oxygen at approximately 200 or 296 K, with an upper limit rate coefficient determined as k < 10(-16) cm(3) molecule(-1) s(-1).

The dispersed fluorescence spectra originating from the v' = 2 and v' = 0 levels of the A(2)Pi(3/2) state of iodine monoxide (IO) have been recorded for the first time after laser induced fluorescence (LIF) excitation in the A(2)Pi(3/2)<-- X(2)Pi(3/2) electronic transition. The results are used to obtain relative Franck-Condon factors for various v'-->v'' transitions in the A(2)Pi(3/2)--> X(2)Pi(3/2) system up to v'' = 12 and compared with theoretical predictions. A fluorescence quenching study of the A(2)Pi(3/2) state of IO has also been performed, revealing that collisional quenching and rotational energy transfer (RET) are rapid in the A(2)Pi(3/2) state of IO. The J'-dependence to fluorescence quenching of the A(2)Pi(3/2) (v' = 2) state of IO by N(2) suggests a collisional predissociation mechanism.