Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P39060 (endostatin)
 2,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The influence of [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) on solutions containing lead(II) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP). The readings were taken at fixed total TAPS to total lead(II) concentration ratios and various pH values, at 25.0+/-0.1 degrees C and ionic strength 0.1M KNO(3). Due to the basic pK(a) of the ligand, which occurs in the pH range where large amount of lead polynuclear species are formed, and the occurrence of ligand adsorption, that disabled the use of high concentrations of TAPS on DCP experiments, GEP and DCP experimental conditions were put to the limit in order to provide the correct Pb-TAPS-OH model and reliable stability constants. The proposed final model is: PbL, PbL(2), PbL(2)(OH) and PbL(2)(OH)(2) with overall stability constants values, as logbeta, 3.27+/-0.06, 6.5+/-0.1, 12.7+/-0.1 and 17.27+/-0.06, respectively. A comparative analysis of the strength of complexation of TAPS and a structural related buffer, 2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid (TAPSO), with lead is also discussed.
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PMID:Modelling of Pb-(TAPS)(x)-(OH)(y) system and refinement of stability constants in the region of lead hydrolysis and lead hydroxide precipitation. 1907 53

This work describes the application of polarography, a technique scarcely used for modelling and optimisation of stability constants, in the study of copper complexes with [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS). Direct current polarography (DCP), using low total copper ion and large total ligand to total copper concentration, enabled the full characterization of Cu-(TAPS)(x)-(OH)(y) system, whose complexation occurs in the pH range of copper hydrolysis and Cu(OH)(2) precipitation. Cu-(TAPS)(x)-(OH)(y) system was studied by DCP and glass electrode potentiometry (GEP) in aqueous solution at fixed total ligand to total metal concentrations ratios and varied pH values (25.0 degrees C; I=0.1M, KNO(3)). The predicted model, as well as the overall stability constants values, are (as logbeta): CuL(+)=4.2, CuL(2)=7.8, CuL(2)(OH)(-)=13.9 and CuL(2)(OH)(2)(2-)=18.94. GEP only allowed confirming the stability constants for CuL(+) and CuL(2) and was used to determine the pK(a) of TAPS, 8.342. Finally, a briefly comparative analysis between TAPS and other structural related buffers was done. Evaluation based on logbeta(CuL) versus pK(a) revealed that TES, TRIS, TAPS and AMPSO coordinated via amino and hydroxymethylgroups forming a five-membered chelate ring. For BIS-TRIS and TAPSO, and possibly DIPSO, one or more five-membered chelate rings involving additional hydroxyl groups are also likely formed.
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PMID:Challenges in modelling and optimisation of stability constants in the study of Cu-(TAPS)(x)-(OH)(y) system by polarography. 1907 57