Search results for "Potentiometry"

Oxaaza cyclophanes in the recognition of nucleotides. The role of oxygen and electron-rich aromatic rings

2007

Dioxapolyaza cyclophanes derived from resorcinol and different polyamine chains have been studied in aqueous solution as abiotic receptors for nucleotides. The presence of the additional ethyleneoxy subunits is reflected in a higher basicity and in a significant increase in the log K values for the interaction with nucleotides relative to that of related polyazacyclophanes.

A thermodynamic insight into the recognition of hydrophilic and hydrophobic amino acids in pure water by aza-scorpiand type receptors.

2014

Interactions of different hydrophilic (His, Asp, Glu,) and hydrophobic (Ala, Phe, Tyr, Trp) amino acids in water with a scorpiand aza-macrocycle (L1) containing a pyridine group in the ring and its derivative (L2) bearing a naphthalene group in the tail have been analysed by potentiometric and calorimetric measurements. Theoretical calculations corroborate that major attractive forces that hold the adduct together are hydrogen bonds and salt-bridges, even though other interactions such as π-stacking or NH(+)⋯π may contribute in the case of hydrophobic amino acids and L2. Calorimetric measurements indicate that the interactions between L1 and the different amino acids are principally driven …

Hydrogen and copper ion-induced molecular reorganizations in scorpionand-like ligands. A potentiometric, mechanistic, and solid-state study.

2007

Two aza scorpionand-like macrocycles (L2 and L3) have been prepared. L2 consists of a tren amine with two of its arms cyclizized with a 2,6-bis(bromomethyl)pyridine. In L3, the remaining pendant arm has been further functionalized with a fluorophoric naphthalene group. X-ray data on the compounds [H(L3)]ClO4.H2O (1) and [H3(L3)](H2PO4)3.H2O (2) as well as solution studies (pH-metry, UV-vis, and fluorescence data) show the movement of the pendant arm as a result of the protonation degree of the macrocycles and of the formation of intramolecular hydrogen bonds. X-ray data on the complexes [Cu(L2)](ClO4)2]2.H2O (3) and [Cu(L3)](ClO4)2 (4) and solution studies on Cu2+ coordination show the impl…

Reaction of 3-Amino-1,2,4-Triazole with Diethyl Phosphite and Triethyl Orthoformate: Acid-Base Properties and Antiosteoporotic Activities of the Prod…

2017

The reaction of diethyl phosphite with triethyl orthoformate and a primary amine followed by hydrolysis is presented, and the reaction was suitable for the preparation of (aminomethylene)bisphosphonates. 3-Amino-1,2,4-triazole was chosen as an interesting substrate for this reaction because it possesses multiple groups that can serve as the amino component in the reaction-namely, the side-chain and triazole amines. This substrate readily forms 1,2,4-triazolyl-3-yl-aminomethylenebisphosphonic acid (compound 1) as a major product, along with N-ethylated bisphosphonates as side products. The in vitro antiproliferative effects of the synthesized aminomethylenebisphosphonic acids against J774E m…

Thermodynamic studies of actinide complexes. 1. A reappraisal of the solution equilibria between plutonium(IV) and ethylenediaminetetraacetic acid (E…

2007

Abstract A detailed reevaluation of the complexation equilibria of plutonium(IV) with the polyaminocarboxylic sequestering agent EDTA4− has been performed in 1 M (H,K)NO3 media at 298 K by means of visible absorption spectrophotometry and glass-electrode potentiometry at millimolar concentration levels. The high binding affinity even under strongly acidic conditions supports the exclusive formation of the neutral Pu(EDTA) complex over the range 0.01 ≤ [H+] ≤ 0.9 M with an apparent formation constant of log β110 = 25.8(1) at 0.9 M HNO3. Extrapolation to zero ionic strength using the SIT approach provides the first ever-reported NEA–TDB compliant estimate of β 110 0 ( log β 110 0 = 32.2 ( 3 )…

Binding of fluoride and carbonate by open chain polyammonium cations

2004

The formation of open chain polyammonium cation-fluoride and -carbonate complexes was studied by potentiometric and calorimetric techniques at t=25 degrees C. Several species of H(i)AL (A=amine; L=F(-), CO(3)(2-)) are formed in both systems with a mean stability log K=1.0zeta (zeta=|z(anion)xz(cation)|) and log K=2.0zeta for fluoride and carbonate, respectively. The comparison with analogous systems (chloride and acetate for fluoride and hydrogenphosphate, sulfate and malonate for carbonate) showed that fluoride and carbonate form the most stable species with open chain polyammonium cations, among low molecular weight anions. The N-alkyl substitution does not play negligible role in the sta…

A Comparative Study on Nickel Binding to Hpn-like Polypeptides from Two Helicobacter pylori Strains

2021

Combined potentiometric titration and isothermal titration calorimetry (ITC) methods were used to study the interactions of nickel(II) ions with the N-terminal fragments and histidine-rich fragments of Hpn-like protein from two Helicobacter pylori strains (11637 and 26695). The ITC measurements were performed at various temperatures and buffers in order to extract proton-independent reaction enthalpies of nickel binding to each of the studied protein fragments. We bring up the problem of ITC results of nickel binding to the Hpn-like protein being not always compatible with those from potentiometry and MS regarding the stoichiometry and affinity. The roles of the ATCUN motif and multiple His…

Risedronate complexes with Mg2+, Zn2+, Pb2+, and Cu2+: Species thermodynamics and sequestering ability in NaCl(aq) at different ionic strengths and a…

2021

Abstract In this paper, potentiometry and calorimetry were used to determine the thermodynamics of interaction between risedronate and four bivalent metal cations, namely: Mg2+, Zn2+, Pb2+, and Cu2+ in aqueous NaCl solutions at different ionic strengths and at T = 298.15 K. The data analysis allowed us to ascertain that the main species formed were the MLH2, MLH, ML and M2L; however scarcely soluble species precipitated at acidic pH values, between 4 and 7 depending on the metal cation involved, probably due to the formation of the neutral M2L(s) species. Comparison of the stability constants with other similar ligands suggests that metal complexation occurs through the phosphonate with an …

Acid-base properties of halloysite clay nanotubes in NaCl medium

2014

Thermodynamics of interaction between risedronic acid and metal cations: investigations in solution and in the solid state

2019

Risedronic acid (see Figure 1) belongs to the class of biphosphonates (BP), widely used in the medical field to treat bone disorders. Bisphosphonates (BPs, e.g., alendronate, risedronate, and ibandronate) help to maintain bone mass, to inhibit osteoclast-mediated bone resorption, and to reduce the risk of both vertebral and non-vertebral fractures. The clinical efficacy of BPs is mainly based on two key properties: their capacity to strongly bind hydroxyapatite crystals of bone, and their inhibitory effects on osteoclast precursors and mature osteoclasts. Interaction of risedronate with metal cations is poorly investigated. Qualitatively, it is indicated that adsorption of risedronate is in…