Analysis of copper complex lability using -equilibration techniques and free-ion selective radiotracer extraction

Marine Exopolysaccharide Complexed With Scandium Aimed as Theranostic Agents

(1) Background: Exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium, showed anti-metastatic properties. They may represent a new class of ligands to be combined with theranostic radionuclides, such as ⁴⁷Sc/⁴⁴Sc. The goal of this work was to investigate the feasibility of such coupling. (2) Methods: EPSs, as well as heparin used as a drug reference, were characterized in terms of molar mass and dispersity using Asymmetrical Flow Field-Flow Fractionation coupled to Multi-Angle Light Scattering (AF4-MALS). The intrinsic viscosity of EPSs at different ionic strengths were measured in order to establish the conformation. To determine the stability constants of Sc with EPS and heparin, a Free-ion selective radiotracer extraction (FISRE) method has been used. (3) Results: AF4-MALS showed that radical depolymerization produces monodisperse EPSs, suitable for therapeutic use. EPS conformation exhibited a lower hydrodynamic volume for the highest ionic strengths. The resulting random-coiled conformation could affect the complexation with metal for high concentration. The LogK of Sc-EPS complexes have been determined and showing that they are comparable to the Sc-Hep. (4) Conclusions: EPSs are very promising to be coupled with the theranostic pair of scandium for Nuclear Medicine.

Reversed phase free ion selective radiotracer extraction (RP-FISRE): a new tool to assess the dynamic stabilities of metal (-organic) complexes, for complex half-lives spanning six orders of magnitude

This paper introduces reversed phase free ion selective radiotracer extraction (RP-FISRE) as a new tool to assess the stability of metal complexes, as illustrated by the assessment of the stability of [(177)Lu]Lu-DOTA-octreotate. To this end, the TUDelft-developed FISRE, where the released metal is column-retained and the complex eluted, was changed into RP-FISRE, where the complex is column-retained and the released metal is eluted. This change in the approach allows for studies to be performed with high stability complexes. This paper presents RP-FISRE, the strength of the radiotracer approach, and the first-ever kd data on the release of (177)Lu from [(177)Lu]Lu-DOTA-octreotate.

Effects of lability of metal complex on free ion measurement using DMT

Very low concentrations of free metal ion in natural samples can be measured using the Donnan membrane technique (DMT) based on ion transport kinetics. In this paper, the possible effects of slow dissociation of metal complexes on the interpretation of kinetic DMT are investigated both theoretically and experimentally. The expressions of the lability parameter, Lgrangian , were derived for DMT. Analysis of new experimental studies using synthetic solution containing NTA as the ligand and Cu(2+) ions shows that when the ionic strength is low (<or=0.2 mM Ca(NO(3))(2)) the dissociation rate of NTACu becomes the limiting step in Cu transport of the DMT measurement. In natural waters, dissolved organic matter (DOM) is the most important source of ligands that complex metals. By comparing the fraction of labile species measured using other dynamic sensors (DGT, GIME) in several freshwaters, it is concluded that in most waters ion transport in DMT is controlled by diffusion in the membrane. Only in very soft waters (<0.7 mM Ca+Mg), the dissociation rate of natural metal complex may influence ion transport in DMT. In this case, neglecting this effect may lead to an underestimation of the free metal ion concentration measured.

An exchange method to investigate the kinetics of Cd complexation in soil solutions

Knowledge of the dynamic speciation of metals in soil solution is necessary for soil-plant transfer models. The lability of a metal in a given context partly depends on the kinetics of interconversion between the free ion (M) and one complex (ML), governed by the association (c(k)a) and dissociation (c(k)d) rate constants of the reaction of formation of ML If only one single complex is assumed to be present in solution, a single kinetic experiment will enable estimation of ckd and cka', that is, the product of cka by the concentration of free ligand in solution. The method consists of the measurements over time of the radioactive metal remaining in solution after the labeling of a Ca resin--solution system in balanceforthe nonlabeled metal initially present. The method is described for Cd and was applied on four soil solution extracts. The order of magnitude of the estimated c(k)a'- and c(k)d-values was about 10(-3) s(-1). The advantages and drawbacks of the method are discussed.

Mass spectrometric analysis of nitroxyl-mediated protein modification: comparison of products formed with free and protein-based cysteines

Although biologically active, nitroxyl (HNO) remains one of the most poorly studied NO(x). Protein-based thiols are suspected targets of HNO, forming either a disulfide or sulfinamide (RSONH2) through an N-hydroxysulfenamide (RSNHOH) addition product. Electrospray ionization mass spectrometry (ESI-MS) is used here to examine the products formed during incubation of thiol proteins with the HNO donor, Angeli's salt (AS; Na2N2O3). Only the disulfide, cystine, was formed in incubates of 15 mM free Cys with equimolar AS at pH 7.0-7.4. In contrast, the thiol proteins (120-180 microM), human calbindin D(28k) (HCalB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and bovine serum albumin (BSA) gave four distinct types of derivatives in incubates containing 0.9-2.5 mM AS. Ions at M + n x 31 units were detected in the ESI mass spectra of intact HCalB (n = 1-5) and GAPDH (n = 2), indicating conversion of thiol groups on these proteins to RSONH2 (+31 units). An ion at M + 14 dominated the mass spectrum of BSA, and intramolecular sulfinamide cross-linking of Cys34 to one of its neighboring Lys or Arg residues would account for this mass increase. Low abundant M + 14 adducts were observed for HCalB, which additionally formed mixed disulfides when free Cys was present in the AS incubates. Cys149 and Cys153 formed an intramolecular disulfide in the AS/GAPDH incubates. Since AS also produces nitrite above pH 5 (HN2O3(-) --> HNO + NO2(-)), incubation with NaNO2 served to confirm that protein modification was HNO-mediated, and prior blocking with the thiol-specific reagent, N-ethylmaleimide, demonstrated that thiols are the targets of HNO. The results provide the first systematic characterization of HNO-mediated derivatization of protein thiols.