An accurately measured equilibrium acid dissociation constant (pKa) is essential for understanding and predicting the fate of perfluorocarboxylic acids (PFCAs) in the environment. The aqueous pKa of perfluorooctanoic acid (PFOA) has been determined potentiometrically using a standard water-methanol mixed solvent approach and was found to be 3.8 +/- 0.1. The acidity of PFOA is thus considerably weaker than its shorter-chain PFCA homologues. This was attributed to differences in molecular and electronic structure, coupled with solvation effects. The pKa of PFOA was suppressed to approximately 2.3 at higher concentrations because of the aggregation of perfluorooctanoate (PFO). Often, PFCA partion coefficients are determined at concentrations above those found in the environment. Thus, it was suggested that a pKa correction factor, which accounts for this concentration-dependent shift in acid/base equilibrium, should be applied to PFCA partition efficients before they are implemented in environmental fate models. A pKa of 3.8 +/- 0.1 suggests that a considerable concentration of the PFCA exists as the neutral species in the aqueous environment for example, in typical Ontario rainwater, it is approximately 17%. Transport, fate, and partitioning models have often ignored the presence this species completely. The environmental dissemination of PFCAs could, in part, be explained by considering the role of the neutral species.

We have designed and synthesized a water-soluble, sulfonated version of an azobenzene-based thiol-reactive cross-linker that can be introduced into peptides and proteins and act as a conformational photoswitch. The sulfonated compound is shown to effect a similar degree of conformational control on a model peptide helix system, as its nonsulfonated counterpart but can be introduced without the need for any organic cosolvent. The sulfonated azobenzene cross-linker thus expands the range of proteins to which photocontrol can be applied.

The gateway to morphine biosynthesis in opium poppy (Papaver somniferum) is the stereochemical inversion of (S)-reticuline since the enzyme yielding the first committed intermediate salutaridine is specific for (R)-reticuline. A fusion between a cytochrome P450 (CYP) and an aldo-keto reductase (AKR) catalyzes the S-to-R epimerization of reticuline via 1,2-dehydroreticuline. The reticuline epimerase (REPI) fusion was detected in opium poppy and in Papaver bracteatum, which accumulates thebaine. In contrast, orthologs encoding independent CYP and AKR enzymes catalyzing the respective synthesis and reduction of 1,2-dehydroreticuline were isolated from Papaver rhoeas, which does not accumulate morphinan alkaloids. An ancestral relationship between these enzymes is supported by a conservation of introns in the gene fusions and independent orthologs. Suppression of REPI transcripts using virus-induced gene silencing in opium poppy reduced levels of (R)-reticuline and morphinan alkaloids and increased the overall abundance of (S)-reticuline and its O-methylated derivatives. Discovery of REPI completes the isolation of genes responsible for known steps of morphine biosynthesis.

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