metaphosphoric-acid and phosphoric-acid

Abundant neutral losses of 98 Da are often observed upon ion trap CID-MS/MS of protonated phosphopeptide ions. Two competing fragmentation pathways are involved in this process, namely, the direct loss of H3PO4 from the phosphorylated residue and the combined losses of HPO3 and H2O from the phosphorylation site and from an additional site within the peptide, respectively. These competing pathways produce product ions with different structures but the same m/z values, potentially limiting the utility of CID-MS(3) for phosphorylation site localization. To quantify the relative contributions of these pathways and to determine the conditions under which each pathway predominates, we have examined the ion trap CID-MS/MS fragmentation of a series of regioselective (18)O-phosphate ester labeled phosphopeptides prepared using novel solution-phase amino acid synthesis and solid-phase peptide synthesis methodologies. By comparing the intensity of the -100 Da (-H3PO3 (18)O) versus -98 Da (-[HPO3 + H2O]) neutral loss product ions formed upon MS/MS, quantification of the two pathways was achieved. Factors that affect the extent of formation of the competing neutral losses were investigated, with the combined loss pathway predominantly occurring under conditions of limited proton mobility, and with increased combined losses observed for phosphothreonine compared with phosphoserine-containing peptides. The combined loss pathway was found to be less dominant under ion activation conditions associated with HCD-MS/MS. Finally, the contribution of carboxylic acid functional groups and backbone amide bonds to the water loss in the combined loss fragmentation pathway was determined via methyl esterification and by examination of a phosphopeptide lacking side-chain hydroxyl groups.

Topics: Amino Acid Sequence; Isotope Labeling; Molecular Sequence Data; Oxygen Isotopes; Peptide Fragments; Phosphopeptides; Phosphoric Acids; Phosphorous Acids; Stereoisomerism; Tandem Mass Spectrometry; Water

To compare the effects of two etching procedures using meta-phosphoric (MPA) or ortho-phosphoric acid (OPA) on dentine demineralisation, resin-dentine bonds durability and interface nanoleakage/ultra-morphology.. Middle-dentine specimens were etched using 37% OPA (15s) or 40% MPA (60s) and submitted to infrared spectroscopy (FTIR) or ultra-morphology dye-assisted (calcium-staining) confocal microscopy (Ca-CLSM). A three-step etch-and-rinse adhesive was formulated, applied onto dentine and light-cured for 30s before composite build-up. After 24h, the dentine-bonded specimens were cut into 1mm(2) beams; half were immediately submitted to microtensile bond strength (μTBS) and half stored in DW for six months. The μTBS results were analysed with repeated-measures ANOVA and Tukey's test (p<0.05). Further teeth were bonded and prepared for interface nanoleakage/ultra-morphology confocal evaluation.. FTIR and Ca-CLSM analyses showed dicalcium phosphate dihydrate (Brushite) precipitation in MPA-etched dentine and on the bottom (front of demineralisation) of the OPA-etched dentine. Statistical analysis showed similar μTBS for both etching procedures after 24h. The μTBS of specimens in OPA-group dropped significantly (p<0.05) after six month; the specimens in the MPA group showed no statistically difference (p>0.05). CLSM depicted no evident sign of nanoleakage within the resin-dentine interface of the MPA-treated specimens, while the specimens in OPA-group presented intense nanoleakage and interface degradation.. The use of MPA (60s) as an alternative dentine conditioning agent in etch-and-rinse bonding procedures may be a suitable strategy to create more durable resin-dentine bonds.

Topics: Acid Etching, Dental; Adult; Calcium Phosphates; Chemical Precipitation; Dental Bonding; Dental Leakage; Dental Stress Analysis; Dentin; Dentin-Bonding Agents; Fluorescein-5-isothiocyanate; Fluorescent Dyes; Humans; Light-Curing of Dental Adhesives; Materials Testing; Methacrylates; Microscopy, Confocal; Phenols; Phosphoric Acids; Phosphorous Acids; Polyethylene Glycols; Polymethacrylic Acids; Spectroscopy, Fourier Transform Infrared; Stress, Mechanical; Sulfoxides; Surface Properties; Tensile Strength; Young Adult

A new, highly sensitive and simple kinetic method for the determination of thyroxine was proposed. The method was based on the catalytic effect of thyroxine on the oxidation of As(III) by Mn(III) metaphosphate. The kinetics of the reaction was studied in the presence of orthophosphoric acid. The reaction rate was followed spectrophotometrically at 516 nm. It was established that orthophosphoric acid increased the reaction rate and that the extent of the non-catalytic reaction was extremely small. A kinetic equation was postulated and the apparent rate constant was calculated. The dependence of the reaction rate on temperature was investigated and the energy of activation and other kinetic parameters were determined. Thyroxine was determined under the optimal experimental conditions in the range 7.0 x 10(-9) to 3.0 x 10(-8) mol L(-1) with a relative standard deviation up to 6.7% and a detection limit of 2.7 x 10(-9) molL(-1). In the presence of 0.08 mol L(-1) chloride, the detection limit decreased to 6.6 x 10(-10) mol L(-1). The proposed method was applied for the determination of thyroxine in tablets. The accuracy of the method was evaluated by comparison with the HPLC method.

Topics: Arsenic; Catalysis; Kinetics; Manganese; Phosphoric Acids; Phosphorous Acids; Spectrum Analysis; Tablets; Temperature; Thyroxine