Werner‐type metal complexes of potato starch

Abstract

It was shown that potato starch formed Werner-type complexes. In these complexes a metal atom is ligated by the lone electron pairs of hydroxyl groups from d-glucose units and phosphate groups in starch. Acetate, chloride and nitrate were counter-ions to the transition metal atoms. The metal cations bound preferentially to the phosphoric acid moiety of amylopectin, but secondarily they were co-ordinated by the hydroxyl groups of the d-glucose units. This resulted in the formation of clathrate cages in which a significant number of the water molecules were trapped. Such structures were able to co-ordinate further metal cations. Only Mn(II) and Co(II) ions, with acetate counter-ions, neither formed clathrate cages nor were co-ordinated by the hydroxyl groups of the d-glucose of starch.

Starch–metal complexes and their rheology

“…Our former EPR studies [16][17][18][19][20] showed that complexes of starches with all metal acetates, iron(III) chloride and all Ni(II) salts had tetrahedral inner coordination spheres. Cu(II) nitrate and chloride formed complexes of the square planar inner coordination spheres whereas Co(II) salts, except acetate had octahedral inner coordination spheres.…”

“…Consequently, also polysaccharides are capable as O-ligate metal ions [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Particular attention has been paid to starch as the ligand of metal ions.…”

“…Thus, anions penetrate granular starch suspended in aqueous solutions of salts of metals of the first non-transition group [25]. In contrast to that, cations of the metals from higher non-transition [26] and transition groups [20] bound in granules by coordination as proven by EPR and thermal studies [13][14][15][16][17][18][19][20]. Starch gels more efficiently coordinate to metal ions and amylopectin more efficiently coordinate to metal ions than amylose [17].…”

“…Starch gels more efficiently coordinate to metal ions and amylopectin more efficiently coordinate to metal ions than amylose [17]. Potato starch (PS) and amylopectin additionally coordinate metal ions to the phosphate groups [19,48].…”

“…Although formation of the Werner-type complexes of metal salts with starches [16][17][18][19][20] has been proven and structures of inner coordination spheres of those complexes, enthalpies of their formation, and thermal stabilities have been reported, neither macrostructure of such complexes nor capacity of starches in coordinating metal ions was recognized. In this paper the problem is approached quantitatively involving conductivity and rheological measurements of starch pastes on addition of metal salts.…”