Search results for "Titration"

Methylation as an effective way to generate SOD-activity in copper complexes of scorpiand-like azamacrocyclic receptors

2018

Abstract Methylation of the secondary amine groups of a scorpiand-type ligand consisting of a pyridine spacer connected through methylene groups to a tris(2-aminomethyl) unit with the pendant arm further functionalised with a 3-pyridine unit leads to a ligand whose Cu(II) complex exhibits threefold enhanced SOD activity with respect to the non-methylated ligand. Potentiometric studies indicate the formation of [CuL] 2+ species with a stability three orders of magnitude lower than that formed with the related non-methylated ligand. Kinetic studies indicate that methylation of the secondary nitrogens causes a deceleration of both the complex formation and the acid-induced dissociation of the …

Syntheses, structures and physical characterization of two new three-dimensional mixed-valence hexadecavanadate derivatives

2007

Abstract Two new hexadecavanadate derivatives, (bpy)[Zn(4,4′-bpy)2]2[H4ClV16O38]·6H2O 1 and (bpy)[Co(4,4′-bpy)2]2[H4ClV16O38]·6H2O 2 (bpy = 4,4′-bipyridine), were synthesized under the hydrothermal conditions and structurally characterized by IR, XPS and EPR spectroscopy, redox titration and single-crystal X-ray diffraction. The two compounds are isostructural and crystallize in the tetragonal non-centrosymmetric space group P-4n2 (No. 118) with a = 17.124(2), b = 17.124(2), c = 14.724(3) A, V = 4317.5(12) A3 and Z = 1 for the compound 1, and a = 17.038(2), b = 17.038(2), c = 14.754(3) A, V = 4282.9(12) A3 and Z = 1 for the compound 2. Compounds 1 and 2 were constructed from 4-connected {H4…

Portlandite solubility and Ca 2+ activity in presence of gluconate and hexitols

2021

The current paper investigates the impact of gluconate, D-sorbitol, D-mannitol and D-galactitol on calcium speciation at high pH values by i) solubility measurements of portlandite (Ca(OH)2) and ii) potentiometric titration measurements of calcium salt solutions. Thermodynamic modeling was used to fit the chemical activities of Ca2+ and OH- ions and thus to determine the strength and kind of the different Ca-organic-hydroxide complexes. The strength of complex formation with Ca decreases in the order gluconate >> sorbitol > mannitol > galactitol, which follows the same order as sorption on portlandite. Heteropolynuclear gluconate complexes with calcium and hydroxide dominate the…

Structural and hydrogenation study on the ball milled TiH2–Mg–Ni

2015

International audience; With the aim of further understanding for TieNieMg alloys and their hydrogenation behavior, powders of TiH2, Mg and Ni with the molar ratio of 3:1:2 have been mechanically milled for 10 h, 20 h, 30 h, 40 h according to the stoichiometry (TiH2)1.5Mg0.5Ni. Microstructures of the milled sample were analyzed and their hydrogenation properties as negative electrodes for Ni-MH batteries were studied. Phase change with milling time revealed the fast formation of the Ti-Mg-H FCC phase. The alloying priority among Ti, Mg and Ni was demonstrated by comparing phase compositions in different milling time. Hydrogen capacities evaluated by both solidegas reaction and electrochemic…

Chiral hemicucurbit[8]uril as an anion receptor: selectivity to size, shape and charge distribution

2017

A novel eight-membered macrocycle of the hemicucurbit[n]uril family, chiral (all-R)-cyclohexanohemicucurbit[8]uril (cycHC[8]) binds anions in a purely protic solvent with remarkable selectivity. The cycHC[8] portals open and close to fully encapsulate anions in a 1 : 1 ratio, resembling a molecular Pac-Man™. Comprehensive gas, solution and solid phase studies prove that the binding is governed by the size, shape and charge distribution of the bound anion. Gas phase studies show an order of SbF6− ≈ PF6− > ReO4− > ClO4− > SCN− > BF4− > HSO4− > CF3SO3− for anion complexation strength. An extensive crystallographic study reveals the preferred orientations of the anions within the octahedral cav…

Oligoamide Foldamers as Helical Chloride Receptors-the Influence of Electron-Withdrawing Substituents on Anion-Binding Interactions.

2019

The anion-binding properties of three closely related oligoamide foldamers were studied using NMR spectroscopy, isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1 H NMR spectra of the foldamers in [D6 ]acetone solution revealed partial preorganization by intramolecular hydrogen bonding, which creates a suitable cavity for anion binding. The limited size of the cavity, however, enabled efficient binding by the inner amide protons only for the chloride anion resulting in the formation of a thermodynamically stable 1:1 complex. All 1:1 chloride complexes displayed a significant favourable contribution of the entropy term. Most likely, this is due to the …

Dipeptides of S-Substituted Dehydrocysteine as Artzyme Building Blocks: Synthesis, Complexing Abilities and Antiproliferative Properties †

2021

Background: Dehydropeptides are analogs of peptides containing at least one conjugate double bond between α,β-carbon atoms. Its presence provides unique structural properties and reaction centre for chemical modification. In this study, the series of new class of dipeptides containing S-substituted dehydrocysteine with variety of heterocyclic moieties was prepared. The compounds were designed as the building blocks for the construction of artificial metalloenzymes (artzymes). Therefore, the complexing properties of representative compounds were also evaluated. Furthermore, the acknowledged biological activity of natural dehydropeptides was the reason to extend the study for antiproliferativ…

Thermodynamic analysis of the interactions between human ACE2 and spike RBD of Betacoronaviruses (SARS-CoV-1 and SARS-CoV-2)

2023

There are many scientific reports on the interaction of the SARS-CoV-2 virus S protein (and its RBD) with the human ACE2 receptor protein. However, there are no reliable data on how this interaction differs from the interaction of the receptor binding domain of SARS-CoV-1 with ACE2, in terms of binding strength and changes in reaction enthalpy and entropy. Our studies have revealed these differences and the impact of zinc ions on this interaction. Intriguingly, the binding affinity of both RBDs (of SARS-CoV-1 and of SARS-CoV-2) to the ACE2 receptor protein is almost identical; however, there are some differences in the entropic and enthalpic contributions to these interactions.

Urate as effector for crustacean hemocyanins.

2004

Polyaminocyclodextrin nanosponges: synthesis, characterization and pH-responsive sequestration abilities

2016

New pH-responsive nanosponges were obtained by reacting four different polyaminocyclodextrins with heptakis-(6-bromo)-(6-deoxy)-β-cyclodextrin. The materials obtained were characterized by various techniques (FT-IR, potentiometric titration, differential scanning calorimetry (DSC), porosimetry (BET), 13C{1H} CP-MAS NMR). Their adsorption abilities at different pH values were verified towards a suitable set of model guests, and seem mainly controlled by electrostatic interactions, as a function of the protonation/charge status of the polymer matrix. By contrast, data positively point out a lesser importance assumed by the induced-fit effect, important in affecting the formation of host–guest…