Hydroxamic acid polymers

Abstract

A polymer bearing hydroxamic acid groups and having a high affinity for iron(III) was prepared through the following procedure. Acryloylalanine (III), prepared by the reaction of acryloyl chloride with alanine, was treated with N‐hydroxysuccinimide in the presence of dicyclohexylcarbodiimide to give the N‐hydroxysuccinimide ester (IV). The ester IV was polymerized by using AIBN in dioxane to give polymer V. Treatment of polymer V with methylhydroxylamine in DMF gave the hydroxamic acid polymer II. The water‐soluble polymer II was purified by dialysis or by gel‐permeation chromatography (GPC) on Sephadex G‐25. Analytical GPC on Sephadex G‐200 and Sepharose 4B indicate that the average molecular weight of the polymer is in the range of 5 × 105 to 1 × 106. The presence of hydroxamic acid groups is confirmed by the intense red‐brown color produced by the addition of iron(III) to a 50% aqueous DMF solution of the polymer under acidic conditions. In pure water the polymer‐iron complex precipitates as a tan solid. Iron‐binding studies of the polymer reveal that the iron(III) trihydroxamic acid complex FeA3 forms at low concentrations of iron. At higher iron levels a lower order of stability is apparent, which can be accounted for by the conversion of FeA3 to FeA2+. In contrast, the FeA3 complex of the trihydroxamic acid deferoxamine‐B is stable at all iron levels. These results are consistent with the polymer structure, which for steric reasons would favor a stable complex, FeA2+, between iron and two adjacent hydroxamic acid groups. An FeA3 complex would be expected to have a lower stability as a result of either bond angle strain and atomic compression, or a lower probability in bringing a third hydroxamic acid into position to form the octahedral complex.

Synthesis and chelating properties of some poly(amidoxime‐hydroxamic acid) resins toward some trivalent lanthanide metal ions

“…A variety of methods are known for the preparation of hydroxamic acids;2, 25–31 perhaps the most common methods involve the acylation of an acid derivative, such as an ester or acid chloride, with hydroxylamine and its derivatives. The syntheses of poly(hydroxamic acid) ion‐exchange resins have been achieved through the treatment of copoly(acrylamide‐divinylbenzene) with hydroxylamine hydrochloride in the presence of KOH and from the reaction between acryl hydroxamic acid with divinylbenzene by a free‐radical solution polymerization 32.…”

Beyond Biological Chelation: Coordination of f‐Block Elements by Polyhydroxamate Ligands

“…However, this route allowed for the presence of the carboxylate compound in the final product due to incomplete conversion to the acid chloride intermediate. An alternative route included the conversion of polyesters to polyhydroxamic acids in the presence of strong base . The full conversion of these polymers through multiple reactions is the downfall for these materials.…”

“…This resin was modeled after the structure of DFOB. The authors determined that the spacing of the hydroxamic acid units was instrumental in the formation of strong iron(III) chelates, with the optimal spacing of nine atoms between units . The DFOB framework was further investigated by Winston et al, who further investigated the effects of spacing of the hydroxamic acid units and their chelation efficiency for iron(III).…”

“…An alternative route included the conversion of polyesters to polyhydroxamic acids in the presenceo fstrong base. [94,95] The full [67].…”

“…Thisr esin was modeled after the structure of DFOB.T he authors determined that the spacingo ft he hydroxamic acid units was instrumental in the formationo fs trong iron(III)c helates, with the optimal spacingo fn ine atoms between units. [95,97] The DFOB framework was further investigated by Winston et al, who further investigated the effects of spacing of the hydroxamic acidu nits and their chelation efficiency for iron(III). Ap olymer containing hydroxamic acids side by side, HAP-1 (Figure 4), had ap oor performance compared to DFOB due to the inability for units so close to keep iron(III) chelated in an octahedral geometry.H owever, the use of b-alanine in place of alaninea llowed for 11-atom spacingb etween the units, HAP-II ( Figure 4).…”