A step towards mobile arsenic measurement for surface waters.

Surface modified quantum dots (QDs) are studied using a bio-inspired cysteine rich ligand (glutathione, GSH) and their quenching response and selectivity to arsenic examined. As predicted from As(3+) binding with highly crosslinked phytochelatin-(PCn)-like molecules, better arsenic selectivity is obtained for a thicker more 3-dimensional GSH surface layer, with exposed sulfhydryl groups. A detection limit of at least 10 µM can be achieved using CdSe/ZnS core-shell QDs capped with this GSH structure. The system is also demonstrated using a mobile phone camera to record the measurement, producing a detection limit of 5 µM. However, copper remains the main interferent of concern. Water-soluble CdTe QDs show little sensitivity to As(3+) even with a GSH surface, but they remain sensitive to Cu(2+), allowing a copper baseline to be established from the CdTe measurement. Despite anticipating that spectrally non overlapping fluorescence would be required from the two types of QDs to achieve this, a method is demonstrated using RGB channels from a mobile phone and processing the raw data for CdTe QDs, with an emission wavelength of 600 nm, and CdSe/ZnS QDs, with emission maximum of 630 nm. It is shown that As(3+) measurement remains feasible at the WHO guideline value of 10 µg L(-1) up to a copper concentration of around 0.3 µM Cu(2+), which corresponds to the highest recorded level in a selection of large rivers world-wide.

Phylogenetic relationships, character evolution and biogeography of southern African members of Zygophyllum (Zygophyllaceae) based on three plastid regions.

The plastid coding rbcL and non-coding trnLF regions of 53 of 55 southern African Zygophyllum species were sequenced and used to evaluate the phylogenetic relationships within the southern African representatives of the genus. Published sequences of the same gene regions of Australian, Asian and North African Zygophyllum species were included to assess the relationships of the species from these regions to the southern African species. The addition of Z. stapffii from Namibia, found to be conspecific with Z. orbiculatum from Angola, lead to a greatly resolved tree. The molecular results were largely congruent with a recent sectional classification of the southern African species and supported their subdivision into subgenera Agrophyllum and Zygophyllum. Reconstruction of the character evolution of capsule dehiscence, seed attachment and seed mucilage showed that these characters allowed a division of southern African species into the two subgenera but that this could not be applied to species occurring elsewhere. Other morphological characters were found to vary and unique character combinations, rather than unique characters, were found to be of systematic value in sectional delimitation. The study suggests that repeated radiations from the horn of Africa to southern Africa and Asia and back lead to the present distribution of the taxa in the subfamily Zygophylloideae. Although this study supports some of the recent taxonomic changes in the group, the unresolved relationships between the proposed genera Tetraena and Roepera and those retained as Zygophyllum species suggest that changes to the taxonomy may have been premature.

The effect of cytochrome b5 on progesterone metabolism in the ovine adrenal.

The production of glucocorticoids and mineralocorticoids in the endoplasmic reticulum (ER) of the mammalian adrenal cortex are, to a great extent, regulated by the relative activities of the steroid 21-hydroxylase (P450c21) and steroid 17 alpha-hydroxylase (P450c17) enzymes. Progesterone can be 17 alpha-hydroxylated to yield 17 alpha-hydroxyprogesterone which, under certain conditions and in certain species, can be further lyased to adrostenedione by the same enzyme. P450c21 can 21-hydroxylate 17 alpha-hydroxyprogesterone to yield cortisol but also converts progesterone to corticosterone. Cytochrome b5 (cyt b5) can also participate in the regulation of adrenal microsomal steroid hydroxylase activities by changing the rates of the P450c21 and P450c17 reactions or by affecting the 17 alpha-hydroxylation:17,20-lyase ratio of progesterone, by P450c17. We investigated the metabolism of progesterone by sheep adrenal microsomes to identify the products of the different steroid hydroxylase activities in the ER and to investigate the influence of cyt b5 on progesterone metabolism using purified ovine cyt b5 and anti-cyt b5. The P450c17-activity in sheep adrenal microsomes is inhibited by the addition of purified cyt b5 while anti-cyt b5 IgG stimulates the 17 alpha-hydroxylation of progesterone. No 17,21-lyase-activity towards progesterone could be detected in sheep adrenal microsomes.