Synthesis of cyclooctapeptides: constraints analogues of the peptidic neurotoxin, omega-agatoxine IVB-an experimental point of view.

omega-AGA IVB is an important lead structure when considering the design of effectors of glutamate release inducting P/Q-type calcium channels. The best route to achieve the analogues possessing the three-dimensional arrangement corresponding to the native binding loop was the introduction of constraint by ring formation via side chain to side chain lactamization for suitably protected Lys and Glu residues. Since tryptophane residue located at position 14 of this neuropeptide has been suggested as essential for binding, analogues in which this amino acid was replaced by aza-tryptophane and alanine were synthesized. The synthesis was carried out on various acid-labile resins (BARLOS chlorotrityl, Rink amide, PEG-based or Wang resins), by Fmoc strategy. In this paper, we describe optimization of the peptide cyclization with various protecting groups, and on resin or in solution cyclization experimental parameters.

Mode of biosorption of chromium(III) by Spirulina species cells from aqueous solutions.

The ability of commercial Spirulina species to remove chromium(III) [Cr(III)] from an aqueous environment was studied under photoautotrophic conditions. Biomass displayed high adsorptive capacity, with recorded sorption rates up to 99% at a concentration range of 0.02 to 0.18 mg chromium ions/mL of medium. Using isolated cell wall preparations, it was shown that Cr(III) is mainly sorbed onto the surface of cell walls and that the sorption capacity of the walls is enormously high. Living cells of cyanobacteria show the tendency to form multilayer sorption systems, as indicated electron microscopy.