Search results for "ionic strength"
showing 10 items of 198 documents
The solution behavior of dopamine in the presence of mono and divalent cations: A thermodynamic investigation in different experimental conditions
2021
The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop-)] with methylmercury(II) (CH3Hg+), magnesium(II), calcium(II), and tin(II) were studied in NaCl(aq) at different ionic strengths and temperatures. Different speciation models were obtained, mainly characterized by mononuclear species. Only for Sn2+ we observed the formation of binuclear complexes (M2L2 and M2LOH (charge omitted for simplicity)
Conformational Changes in the Nucleosome Followed by the Selective Accessibility of Histone Glutamines in the Transglutaminase Reaction: Effects of …
2001
Transglutaminases, the enzymes that catalyze the acyl-transfer reaction between glutamine and primary amines, have been used to introduce probes into proteins in order to perform structural studies using physical techniques. Here we use an original approach in which the increasing accessibility of the glutamines of core histones to TGase is used to monitor the salt-induced conformational changes of the nucleosome. The rationale of this strategy is that the accessibility of a glutamine to transglutaminase depends on the blockage due to the presence of either other histones or DNA. At low ionic strength, only glutamines on the N-terminal tails of H2B and H3 are labeled with monodansylcadaveri…
NMR study of hexanucleotide d(CCGCGG)2 containing two triplet repeats of fragile X syndrome
2003
Abstract Long repeated stretches of d(CCG) and tri-nucleotide are crucial mutations that cause hereditary forms of mental retardation (fragile X-syndrome). Moreover, the alternating (CG) di-nucleotide is one of the candidates for Z-DNA conformation. Solution NMR structure of d(CCGCGG) 2 has been solved and is discussed. The determined NMR solution structure is a distorted highly bent B-DNA conformation with increased flexibility in both terminal residues. This conformation differs significantly from the Z-DNA tetramer structure reported for the same hexamer in the crystal state at similar ionic strength by Malinina and co-workers. Crystal structure of d(CCGCGG) 2 at high salt concentration …
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 )…
Molecular characterization of α,β-poly[( N -hydroxyethyl)- dl –aspartamide] by light scattering and viscometry studies
2000
Abstract α,β-poly[(N-hydroxyethyl)- dl -aspartamide] (PHEA) is a new synthetic polymer which is of interest in biomedical applications. In this paper, the molecular characterization of PHEA by multi-angle laser light scattering and viscometry off-line and on-line to a size exclusion chromatography system is reported. These techniques furnish an exhaustive and consistent characterization of the PHEA polymer. The fractionation of the PHEA macromolecules was relatively simple. Using an aqueous mobile phase of medium ionic strength, the elution was substantially regular and the macromolecules were not aggregate. The molar mass M of four PHEA samples approximately ranges from 46 to 53 K g/mol, t…
Apparent Molar Mass of a Polyelectrolyte in an Organic Solvent in the Low Ionic Strength Limit As Revealed by Light Scattering
2013
The apparent molar mass of a partially quaternized poly-2-vinylpyridines (degree of quaternization 4.3% < Q < 35%) in 1-propanol is measured by light scattering at low ionic strength (10–6 M < cs < 10–3 M) as a function of polyion repeat unit concentration (7 × 10–5 monomol/L < cm,p < 4 × 10–2 monomol/L). No dialysis was applied prior to measurements. The apparent molar mass under “salt-free” conditions is smaller than the true molar mass by an order of magnitude, while approaching the true value at higher ionic strength. Concomitant data on the dependence of scattering intensity on scattering wave vector show that the dilute polyelectrolyte solutions are strongly correlated. A recent theor…
A Trinuclear Copper(II) Cryptate and Its μ3-CO3 Cascade Complex: Thermodynamics, Structural and Magnetic Properties
2011
The 2,4,6-triethylbenzene-capped hexaamine macrobicycle with pyridyl spacers (pyr) was able to coordinate three copper(II) ions within its cavity. Potentiometric studies performed at 298.2 K in MeOH/H(2)O (50:50 v/v) and at ionic strength 0.10 mol dm(-3) in KNO(3) revealed that trinuclear species predominate in solution from pH 5.0, the hydroxo complexes being the main species, which start forming at unusual very low pH values. The single-crystal X-ray determination of the trinuclear complex showed that the three copper centres have square-planar geometry, arranged in an almost equilateral triangle, and have carbonate bridging the three metal centres. The presence of carbonate resulted from…
Reactivity of Neutral Mo(S2C6H4)3 in Aqueous Media: an Alternative Functional Model of Sulfite Oxidase.
2009
The kinetics of the reaction of neutral [Mo(S2C6H4)3] with hydrogen sulfite to produce the anionic Mo(V) complex, [Mo(S2C6H4)3]-, and sulfate have been investigated. It has been shown that [Mo(S2C6H4)3] acts as the electron-proton sink in the oxygenation reaction of HSO3(-) by water. Reaction rates, monitored by UV/vis stopped-flow spectrometry, were studied in THF/water media as a function of the concentration of HSO3(-) and molybdenum complex, pH, ionic strength, and temperature. The reaction exhibits pH-dependent HSO3(-) saturation kinetics, and it is first-order in complex concentration. The kinetic data and MS-ESI spectra are consistent with the formation of [Mo O(S2C6H4)2(S2C6H5)]- (1…
Sedimentation of halloysite nanotubes from different deposits in aqueous media at variable ionic strengths
2019
Abstract Halloysite clay is a natural nanomaterial that is attracting a growing interest in colloidal science. The halloysite aqueous dispersion stability is a key aspect for the configuration of a purification protocol as well as to establish the durability of a formulation. A physico-chemical study demonstrated the role of ionic strength and nanotube characteristic sizes on the sedimentation behavior. We highlighted the importance of the electrostatic repulsions exercised between the particles in the settling process. A protocol for image analysis has been proposed to provide robust information from time resolved optical images on the suspensions. In conclusion, we managed to correlate mi…
Modelling of natural and synthetic polyelectrolyte interactions in natural waters.
2006
In this paper SIT and Pitzer models are used for the first time to describe the interactions of natural and synthetic polyelectrolytes in natural waters. Measurements were made potentiometrically at 25 °C in single electrolyte media, such as Et4NI and NaCl (for fulvic acid 0.1 < I /mol L− 1 < 0.75), and in a multi-component medium simulating the composition of natural waters at a wide range of salinities (for fulvic and alginic acids: 5 < S < 45) with particular reference to sea water [Synthetic Sea Water for Equilibrium studies, SSWE]. In order to simplify calculations, SSWE was considered to be a “single salt” BA, with cation B and anion A representing all the major cations (Na+, K+, Mg2+…