Biomimetic synthesis of struvite with biogenic morphology and implication for pathological biomineralization

published_or_final_versio

Insolation triggered abrupt weakening of Atlantic circulation at the end of interglacials.

Abrupt cooling is observed at the end of interglacials in many paleoclimate records, but the mechanism responsible remains unclear. Using model simulations, we demonstrate that there exists a threshold in the level of astronomically induced insolation below which abrupt changes at the end of interglacials of the past 800,000 years occur. When decreasing insolation reaches the critical value, it triggers a strong, abrupt weakening of the Atlantic meridional overturning circulation and a cooler mean climate state accompanied by high-amplitude variations lasting for several thousand years. The mechanism involves sea ice feedbacks in the Nordic and Labrador Seas. The ubiquity of this threshold suggests its fundamental role in terminating the warm climate conditions at the end of interglacials

Imaging Oxygen Distribution in Marine Sediments. The Importance of Bioturbation and Sediment Heterogeneity

The influence of sediment oxygen heterogeneity, due to bioturbation, on diffusive oxygen flux was investigated. Laboratory experiments were carried out with 3 macrobenthic species presenting different bioturbation behaviour patterns:the polychaetes Nereis diversicolor and Nereis virens, both constructing ventilated galleries in the sediment column, and the gastropod Cyclope neritea, a burrowing species which does not build any structure. Oxygen two-dimensional distribution in sediments was quantified by means of the optical planar optode technique. Diffusive oxygen fluxes (mean and integrated) and a variability index were calculated on the captured oxygen images. All species increased sediment oxygen heterogeneity compared to the controls without animals. This was particularly noticeable with the polychaetes because of the construction of more or less complex burrows. Integrated diffusive oxygen flux increased with oxygen heterogeneity due to the production of interface available for solute exchanges between overlying water and sediments. This work shows that sediment heterogeneity is an important feature of the control of oxygen exchanges at the sediment–water interface

High energy emission from microquasars

The microquasar phenomenon is associated with the production of jets by X-ray binaries and, as such, may be associated with the majority of such systems. In this chapter we briefly outline the associations, definite, probable, possible, and speculative, between such jets and X-ray, gamma-ray and particle emission.Comment: Contributing chapter to the book Cosmic Gamma-Ray Sources, K.S. Cheng and G.E. Romero (eds.), to be published by Kluwer Academic Publishers, Dordrecht, 2004. (19 pages

Study on fluorometric determination of hydrogen peroxide catalyzed by iron(III)-tetrasulfonato-phthalocyanine with thiamine hydrochloride as a substrate

Iron(III)-tetrasulfonatophthalocyanine(FeTSPc) has been used as a mimetic enzyme in the determination of hydrogen peroxide with thiamine hydrochloride as a fluorogenic substrate. The determinations were carried out in both acidic and basic environments, with different limits of detection and linear ranges. In acidic condition, the linear calibration graph was obtained from 5.0x10(-8) mol/L to 8.0x10(-6) mol/L, with a detection limit of 2.1x10(-8) mol/L H2O2 when Na2HPO4-citric buffer solution (pH 2.8) was used as the reaction medium. It was also found that using one of the three polybasic carboxylic acids such as citric acid, tartaric acid and malonic acid as the catalytic reaction medium can lead to particularly sensitive systems, permitting a detection limit as low as 3.5x10(-9) mol/L H2O2; whereas in basic reaction medium (Na2CO3-NaHCO3 buffer solution, pH = 10.0), the linear range of the calibration graph was from 5.0x10(-8) mol/L to 2.0x10(6) mol/L H2O2 with a detection limit of 1.4x10(-8) mol/L. The applicability of the method to the determination of glucose in human serum was demonstrated by investigating the recovery of the known glucose added to human serum

A new red-region substrate, tetra-substituted amino aluminium phthalocyanine, for the fluorimetric determination of H2O2 catalyzed by mimetic peroxidases

A new red-region fluorogenic substrate, tetra-substituted amino aluminium phthalocyanine, was developed for the selective determination of H2O2 based on the catalytic effect of mimetic peroxidases, viz., hemin or iron tetrasulfonatophthalocyanine (FeTSPc). Under the optimum conditions, the linearity of the calibration graph for the determination of H2O2 with hemin (or FeTSPc) as the catalyst was in the range from 0.0 to 3.0 X 10(-7) mol L-1 (or from 0.0 to 2.0 x 10(-6) mol L-1). The detection limits were 3.7 X 10(-9) and 4.9 x 10(-9) mol L-1 H2O2, respectively. The relative standard deviation (n = 7) was within 1.5% in the middle of the linear range. The peroxidase activity of the mimetic enzymes hemin and FeTSPc, the effects of some experimental conditions and the influence of foreign substances were investigated. With this substrate, 0.0-7.5 x 10(-8) mol L-1 hemin and 0.0-2.0 x 10(-6) mol L-1 FeTSPc can be determined with an accuracy and precision of about 1.3%. The potential application of the reagent was tested by the determination of H2O2 in rainwater

Sensitive fluorimetric determination of formaldehyde by the co-quenching effect of formaldehyde and sulfite on the fluorescence of tetra-substituted amino aluminium phthalocyanine

A novel and sensitive fluorimetric method was developed for the determination of formaldehyde based on the co-quenching effect of formaldehyde and sulfite on the fluorescence of tetra-substituted amino aluminium phthalocyanine. Formaldehyde in the concentration range 0.040-1.19 mug ml(-1) can be determined with a limit of detection of 7.5 ng ml(-1). The relative standard deviation for nine replicate measurements of 80.0 ng ml(-1) formaldehyde is 1.8%. The method was applied to the analysis of real samples with satisfactory results

Novel spectrofluorimetric method for the determination of thiamine with iron(III) tetrasulfonatophthalocyanine as a catalyst

A sensitive, selective and rapid spectrofluorimetric method is proposed for the determination of thiamine by using mimetic enzyme iron(iii) tetrasulfonatophthalocynanine (FeTSPc) as a catalyst for the oxidation reaction between thiamine and hydrogen peroxide. It is based on the oxidation of thiamine in alkaline medium to give an intensively fluorescent compound, which has an excitation wavelength of 375 nm and an emission wavelength of 440 nm. The determination was found to be activated by fluorogenic substrates with a p-hydroxyphenyl structure such as L-tyrosine, tyramine and p-hydroxyphenylpropionic acid. Under optimum conditions, the responses for thiamine were linear from 1.0 x 10(-8) to 1.0 x 10(-4)mol L-1, with a detection limit of 4.3 x 10(-9) mol L-1. The relative standard deviation was 2.2% for 2.0 X 10(-7) mol L-1 thiamine (n = 6). The activation of the p-hydroxyphenyl substrates, the effects of some experimental conditions and the influence of foreign substances were investigated. The potential application of the method was tested by selectively determining thiamine in commercial vitamin B-1, vitamin B complex and rice