Pyrophosphate | EPFL Graph Search

vignette|Anion pyrophosphate ou PPi. Les pyrophosphates (appelés aussi « diphosphates ») sont l'anion (base conjuguée), les sels et les esters de l'acide pyrophosphorique. Les pyrophosphates sont constitués de deux molécules de phosphate condensées. Ils sont constitués autour d'une liaison P-O-P de type anhydride d'acide (formule semi-développée (O3P)–O–(PO3)4−). Les esters sont constitués autour d'une liaison de type C–O–P (formule semi-développée R–O–(PO2)–O–(PO3)3−). Synthèse Les pyrophosphates sont formés en chauffant des phosphates (hydrogénophosphates) ; ils tirent ainsi leur nom de cette origine (le préfixe pyro en grec signifiant feu). :\mathrm{2\ HPO_4^{2-} \longrightarrow (P_2O_7)^{4-} + H_2O} Exemples Rôle biochimique Les pyrophosphates ont un rôle majeur dans les processus de transfert d'énergie dans les cellules vivantes. Les anions pyrophosphates inorganiques HP2O, abrégés en PPi à l'instar des phosphates inorganiq

Propriétés physico-chimiques et ostéogéniques d'un biociment hydraulique à base de phosphates de calcium

Biocements made from β-TCP - H3PO4 - H2O and β-TCP - MCPM - H2O mixtures were studied in order to obtain a better control of their setting time and mechanical strength (β-TCP = Ca3(PO4)2; MCPM = Ca(H2PO4)2.H2O). The effects of factors like the purity of the β-TCP powder, its particle size distribution, the carnet composition or the presence of additives were investigated. More fundamental studies were also done on the reactions controlling the setting time, i.e. β-TP dissolution and DCPD (CaHPO4.2H2O) precipitation. The influence of additives on the kinetics of these controlling reactions were studied in order to establish how they influenced the setting time. To complete these experiments, cements made from β-TCP - MCPM - CSH - H2O mixtures were implanted in rabbit tibias (CSH = CaSO4.l/2H2O). The aging behavior in vivo and in vitro were compared. Results show that many factors affect the physico-chemical properties of the cements, particularly setting time and tensile strength. However, these factors have only a very limited number of pathways in which they can act. For example, setting time can only change when either β-TCP dissolution rate, DCPD germination rate or interparticular free volume are modified. Tensile strength only depends on DCPD weight fraction (binder for β-TCP powder), porosity and microstructure. Sulfate, pyrophosphate and citrate ions delay the cement's setting time in the following order: sulfate < citrate < pyrophosphate. These three ions inhibit DCPD crystal growth in the same order. Therefore, these results suggest that all the ions which inhibit DCPD crystal growth are potential setting time delaying additives. The concentration range in which sulfate ions act on setting time is limited between 0 and 0.1 M; beyond this concentration sulfate ions precipitate as CSD (CaSO4.2H2O). As DCPD and CSD structures are nearly identical, the presence of CSD crystals speeds up the setting reaction by acting as seeds for DCPD crystals. This phenomenon provokes a decrease in the setting time and a refinement of the microstructure with a consequent increase in the tensile strength. Accurate control of the cement composition is very important, i.e. volume and concentration of the phosphoric acid solution. Results show that an excess of phosphoric acid provokes the recrystallization of DCPD into DCP, a process which strongly decreases tensile strength. A modification of the microstructure is also observed when initial β-TCP specific surface area is changed. An increase in the surface area gives an increase in the tensile strength and a decrease in the setting time. In our experiments, a fivefold increase of specific surface area decreases the setting time by a factor of three and doubles the tensile strength. These results show that β-TCP particle size distribution has a very strong effect on the physico-chemical properties of our cements. The comparison between in vitro and in vivo tests prove that in vivo results cannot be anticipated by in vitro experiments. However, in vivo results are extremely positive: our cement is biocompatible, bioresorbable and osteoconductive. These results show that after one month, our cements are closely bonded to living bone, and after four months, our cements are nearly completely resorbed and replaced by new bone (except for dense and large β-TCP particles).

EPFL1993

Metal-based chemosensors for amino acids, peptides, and nucleotides

Andrey Buryak

An organometallic 4d transition metal complex [CpRhCl2]2, together with commercially available dyes, was used to construct indicator displacement assays (IDAs) for the detection of peptides, amino acids, and nucleotides. The combination of the CpRh complex with the dye azophloxine was found to form a chemosensing ensemble for the sequence-selective detection of histidine- and methionine-containing peptides in water at neutral pH. A strong interaction of the rhodium complex with peptides bearing histidine or methionine residue in the position 1 or 2 allowed to detect these peptides down to a concentration of 0.3 µM. The same organometallic complex and three commercially available dyes were employed to compose an array of IDA chemosensors for the detection of natural amino acids. We found that the variation of the pH can effectively be used to modulate the selectivity of an IDA sensor. An excellent discrimination of 20 amino acids was achieved. The combination of [Cp*RhCl2]2 with the dyes gallocyanine, evans blue, and mordant yellow 10 forms a multicomponent indicator displacement assay (MIDA), which can be used to sense low millimolar concentrations of nucleotides and the pyrophosphate anion in buffered aqueous solution. Moreover, the MIDA allows to simultaneously determine the concentrations of adenosine triphosphate and pyrophosphate/cyclic adenosine monophosphate with a single UV-Vis measurement. In the second part of our work we investigated whether dynamic combinatorial libraries (DCLs) can be used for sensing purposes. We found that the dyes arsenazo I, methylcalcein blue, and glycine cresol red, in combination with the metal salts CuCl2 and NiCl2, form a DCL of differently colored metal-dye complexes. The addition of an analyte able to interact with a member(s) of such a library, results in a re-equilibraion easily detectable by UV-Vis spectroscopy. Using dipeptides as analytes we demonstrated that this way of sensing is very effective – even closely related peptides such as regio- (Ala-Phe vs. Phe-Ala) and stereo- (Phe-Ala vs. D-Phe-Ala) isomers can easily be discriminated. Additionally, we found that the identity of the best sensor depends on the problem to be addressed.

EPFL2007

A Fluorescent Sensor for Pyrophosphate Based on a Pd(II) Complex

Jie Gao, Rosario Scopelliti, Kay Severin

A mixture of the Pd(II) complex [Pd(NO3)2(bipy)] (bipy = 2,2-bipyridine) and the fluorescent dye Methylcalcein blue (MCB) constitutes a chemosensing ensemble which can be used for the detection of pyrophosphate (PPi) by fluorescence spectroscopy. The sensor operates in buffered aqueous solution at neutral pH, and allows sensing PPi at low to mid micromolar concentrations with very good selectivity over other anions such as phosphate, acetate, nitrate, sulfate, chloride, and bicarbonate.

Royal Society of Chemistry2010

Metal-based chemosensors for amino acids, peptides, and nucleotides

Andrey Buryak

EPFL2007

Propriétés physico-chimiques et ostéogéniques d'un biociment hydraulique à base de phosphates de calcium

EPFL1993