Journal of Inorganic Biochemistry 95 (2003) 55–63 www.elsevier.com / locate / jinorgbio Formation of spherical iron(III) oxyhydroxide nanoparticles sterically stabilized by chitosan in aqueous solutions a,b, c d e b * ´ ´ ´ Pal Sipos , Otto Berkesi , Etelka Tombacz , Tim G. St. Pierre , John Webb a Department of Inorganic and Analytical Chemistry, University of Szeged, P .O. Box 440, H-6701 Szeged, Hungary b Department of Chemistry, Murdoch University, Murdoch, WA 6150, Australia c Department of Physical Chemistry, University of Szeged, Szeged, Hungary d Department Colloidal Chemistry University of Szeged, Szeged, Hungary e Department of Physics, University of Western Australia, Nedlands, WA 6160, Australia Received 7 October 2002; received in revised form 3 February 2003; accepted 10 February 2003 ´ ´ The authors wish to dedicate this publication to the memory of Professor Kalman Burger (1929–2000) Abstract The interactions between the cationic polymer chitosan (Chit) and iron(III) were investigated. The solution properties were studied by pH-metry, viscometry and dynamic light scattering. Solid state iron(III)–Chit samples were also prepared and characterized by IR spectroscopy and electron microscopy. In aqueous solutions, the precipitation pH of the iron(III) oxyhydroxide (FeOOH) is significantly shifted towards the higher pH values in the presence of Chit indicating that some interaction takes place between the iron(III) and the polymer. However, the additivity of the pH-metric titration curves, the lack of variation both in the viscometric and IR spectra of Chit in the presence and absence of iron(III), indicate the lack of direct complexation between the Chit and ferric ions. Isolated FeOOH nanospheres of 5–10 nm diameter were observed on the transmission electron microscopic pictures of samples obtained from solutions containing iron(III) and Chit, while from DLS measurements hydrodynamic units with a few hundred nm in diameter were identified. Our data support that Chit acts as steric stabilizer and inhibits the macroscopic aggregation of the subcolloidal FeOOH particles. Thus the iron(III)–Chit interactions offer a simple and economic way to fabricate nanometric size FeOOH spheres, morphologically similar to the core of iron(III)-storage protein, ferritin.  2003 Elsevier Science Inc. All rights reserved. Keywords: Iron(III); Chitosan; Ferritin; Polysaccharides; Nanostructure; pH-potentiometry; Viscometry; Dynamic light scattering; Electron microscopy; IR spectroscopy 1. Introduction recent review see Ref. [4]). Chit is able to ‘‘collect’’ transition metal ions selectively [2,5,6], and can be com- Chitosan (Chit), one of the most abundant glycans, is a bined with metal ions through ion-exchange, sorption and b-(1→4)-linked polymer consisting of D-glucosamine and chelation. Several examples can be found in the literature N-acetyl-D-glucosamine monomeric units, and can be for each mode of interaction [1,2,5,6]. considered as mostly or completely deacetylated chitin Recently the iron(III)–Chit interactions received consi- [1,2]. While chitin is practically insoluble in water, Chit is derable attention. The interaction of iron(III) with Chit is soluble at pH#7, due to the protonation of its sugar-amino used for the treatment of iron overload [7] or for the groups (the pK of D-glucosamine is 7.52 [3]). removal of iron(III) (and other metal ions) from natural- or a Both mono- and polysaccharides are known to form wastewaters [8–10]. Catalytic activity in various redox stable complexes with transition metal ions (for the most reactions of iron(III) immobilised to Chit [11,12] and a potential application of iron(III)–Chit as support for immobilized metal affinity chromatography [13] have also *Corresponding author. Department of Inorganic and Analytical been reported. More recently an iron(III)–Chit complex Chemistry, University of Szeged, P.O. Box 440, H-6701 Szeged, Hun- was successfully utilized for the treatment of hyperphos- gary. Tel.: 136-62-544-054; fax: 136-62-420-505. E-mail address: sipos@chem.u-szeged.hu (P. Sipos). phataemia [14–16]. 0162-0134 / 03 / $ – see front matter  2003 Elsevier Science Inc. All rights reserved. doi:10.1016 / S0162-0134(03)00068-0