Waveguide fabrication in lithium-niobo-phosphate glasses by high repetition rate femtosecond laser:route to non-equilibrium material’s states

We study waveguide fabrication in lithium-niobo-phosphate glass, aiming at a practical method of single-stage fabrication of nonlinear integrated-optics devices. We observed chemical transformations or material redistribution during the course of high repetition rate femtosecond laser inscription. We believe that the laser-induced ultrafast heating and cooling followed by elements diffusion on a microscopic scale opens the way toward the engineering non-equilibrium sates of matter and thus can further enhance Refractive Index (RI) contrasts by virtue of changing glass composition in and around the fs tracks. © 2014 Optical Society of America.

Inhibition of iron-catalysed hydroxyl radical formation by inositol polyphosphates: a possible physiological function for myo-inositol hexakisphosphate

1. The ability of myo-inositol polyphosphates to inhibit iron-catalysed hydroxyl radical formation was studied in a hypoxanthine/xanthine oxidase system [Graf, Empson and Eaton (1987) J. Biol. Chem. 262, 11647-11650]. Fe3+ present in the assay reagents supported some radical formation, and a standard assay, with 5 microM Fe3+ added, was used to investigate the specificity of compounds which could inhibit radical generation. 2. InsP6 (phytic acid) was able to inhibit radical formation in this assay completely. In this respect it was similar to the effects of the high affinity Fe3+ chelator Desferral, and dissimilar to the effects of EDTA which, even at high concentrations, still allowed detectable radical formation to take place. 3. The six isomers of InsP5 were purified from an alkaline hydrolysate of InsP6 (four of them as two enantiomeric mixtures) and they were compared with InsP6 in this assay. Ins(1,2,3,4,6)P5 and D/L-Ins(1,2,3,4,5)P5 were similar to InsP6 in that they caused a complete inhibition of iron-catalysed radical formation at > 30 microM. Ins(1,3,4,5,6)P5 and D/L-Ins(1,2,4,5,6)P5, however, were markedly less potent than InsP6, and did not inhibit radical formation completely; even when Ins(1,3,4,5,6)P5 was added up to 600 microM, significant radical formation was still detected. Thus InsP5s lacking 2 or 1/3 phosphates are in this respect qualitatively different from InsP6 and the other InsP5s. 4. scyllo-Inositol hexakisphosphate was also tested, and although it caused a greater inhibition than Ins(1,3,4,5,6)P5, it too still allowed detectable free radical formation even at 600 microM. 5. We conclude that the 1,2,3 (equatorial-axial-equatorial) phosphate grouping in InsP6 has a conformation that uniquely provides a specific interaction with iron to inhibit totally its ability to catalyse hydroxyl radical formation; we suggest that a physiological function of InsP6 might be to act as a 'safe' binding site for iron during its transport through the cytosol or cellular organelles

Synthesis, crystallography and biological activity of myo-inositol phosphates

The antioxidant property of myo-inositol hexakisphosphate is important in the prevention of hydroxyl radical formation which may allow it to act as a 'safe' carrier of iron within the cell. Here, the hypothesis that the recently discovered natural product, myo-inositol 1,2,3-trisphosphate represents the simplest structure to mimic phytate's antioxidant activity has been tested. The first synthesis of myo-inositol 1,2,3-trisphosphate has been completed, along with its X-ray structure determination and that of key synthetic intermediates. Iron binding studies of myo-inositol 1,2,3-trisphosphate demonstrated that phosphate groups with the equatorial-axial-equatorial conformation are required for complete inhibition of hydroxyl radical formation. myo-Inositol monophosphatase is a key enzyme in recycling myo-inositol from its monophosphates in the brain and its inhibition is implicated in lithium's antimanic properties. Current synthetic strategies require inositol compounds to be protected (often with more than one group), resolved, phosphorylated and deprotected to produce the desired optically active myo-inositol phosphates. Here, the synthesis of myo-inositol 3-phosphate has been achieved in only 4 steps from myo-inositol. The stereoselective addition of the chiral phosphorylating agent (2R,4S,5R)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidin-2-one to a protected inositol intermediate allowed separation of diastereoisomers and easy deprotection to myo-inositol 3-phosphate. This strategy also allows the possible introduction of labels of oxygen and sulphur to give a thiophosphate of known stereochemistry at phosphorus which would be useful for the analysis of the stereochemical course of phosphate hydrolysis catalysed by inositol monophosphatase.