Design of High-Relaxivity Polyelectrolyte Nanocapsules Based on Citrate Complexes of Gadolinium(III) of Unusual Composition.

Evgenia Burilova,Alexander Solodov,Darya Shurtakova,Julia Shayimova,Ruslan Kashapov,Lucia Zakharova,Rustem Amirov,Julia Zhuravleva,Vladimir Evtjugin,Elena Zhiltsova

doi:10.3390/ijms222111590

Abstract

Through nuclear magnetic relaxation and pH-metry, the details of the complexation of gadolinium(III) ions with citric acid (H4L) in water and aqueous solutions of cationic polyelectrolytes are established. It is shown that the presence of poly(ethylene imine) (PEI) in solution affects magnetic relaxation behavior of gadolinium(III) complexes with citric acid (Cit) to a greater extent than polydiallyldimethylammonium chloride (PDDC). A large increase in relaxivity (up to 50 mM−1s−1) in the broad pH range (4–8) is revealed for the gadolinium(III)–citric acid–PEI system, which is particularly strong in the case of PEI with the molecular weight of 25 and 60 kDa. In weakly acidic medium (pH 3–7), the presence of PEI results in the formation of two tris-ligand associates [Gd(H2L)3]3− and [Gd(H2L)2(HL)]4−, which do not exist in aqueous medium. In weakly alkaline medium (pH 7–10), formation of ternary complexes Gd(III)–Cit–PEI with the Gd(III)–to–Cit ratio of 1:2 is evidenced. Using transmission electron microscopy (TEM) and dynamic light scattering techniques (DLS), the formation of the particles with the size of 50–100 nm possessing narrow molecular-mass distribution (PDI 0.08) is determined in the solution containing associate of PEI with tris-ligand complex [Gd(H2L)2(HL)]4−.

Highlights

Investigation of complexation reactions of metal ions in polymer solutions is of great practical importance for ecology, medicine, and other fields of science
PEUF is based on the formation of stable complexes of water-soluble polymers with heavy metal cations, which are separated from low-molecularweight components of solution through filtration using chemically inert solid membranes
The relaxation curve of gadolinium aqua-ions [Gd(H2 O)8 ]3+ in water (Figure 1) preserves constant R2 values up to neutral medium (15.5 ± 0.5 mM−1 s−1 ) and there is a decay of relaxivity after pH 6, which is caused by a gradual hydrolysis of gadolinium(III) resulting in the precipitation of insoluble hydroxide [Gd(OH)3 ]

Summary

Introduction

Investigation of complexation reactions of metal ions in polymer solutions is of great practical importance for ecology, medicine, and other fields of science. Anionic polymers are usually employed (polyacrylic acid, polystyrene sulfonate, etc.) [1,5,6,7] In this case, both direct coordination of functional groups with the cations of Cu(II), Ni(II), Zn(II), and Pb(II) and electrostatic binding of anionic metal complexes with protonated or quaternized groups of polyelectrolytes, as well as combination of the mentioned approaches are possible for polyamines. Both direct coordination of functional groups with the cations of Cu(II), Ni(II), Zn(II), and Pb(II) and electrostatic binding of anionic metal complexes with protonated or quaternized groups of polyelectrolytes, as well as combination of the mentioned approaches are possible for polyamines The latter variant was demonstrated on the example of the reaction of PEI with copper(II) through the formation of coordination bonds with nitrogen atoms of amino groups and simultaneously with the [Cr(CN) (NO)]3− complex, which is electrostatically attracted to protonated ammonium groups of polymer [8]

Methods

Results

Conclusion