%0 Journal Article
%T Controlled Release Kinetics in Hydroxy Double Salts: Effect of Host Anion Structure
%A Stephen Majoni
%A Jeanne M. Hossenlopp
%J Advances in Physical Chemistry
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/710487
%X Nanodimensional layered metal hydroxides such as layered double hydroxides (LDHs) and hydroxy double salts (HDSs) can undergo anion exchange reactions releasing intercalated anions. Because of this, these metal hydroxides have found applications in controlled release delivery of bioactive species such as drugs and pesticides. In this work, isomers of hydroxycinnamate were used as model compounds to systematically explore the effects of anion structure on the rate and extent of anion release in HDSs. Following intercalation and subsequent release of the isomers, it has been demonstrated that the nature and position of substituent groups on intercalated anions have profound effects on the rate and extent of release. The extent of release was correlated with the magnitude of dipole moments while the rate of reaction showed strong dependence on the extent of hydrogen bonding within the layers. The orthoisomer showed a more sustained and complete release as compared to the other isomers. 1. Introduction Nanodimensional layered double hydroxides (LDHs) and hydroxy double salts (HDSs) have been shown to undergo ion exchange reactions with a variety of inorganic and organic ions [1¨C3]. This ion exchange capability, coupled with the ability to vary the intralayer metal ions, has enabled fine-tuning of these materials for different applications which range from catalysis to isomer separation [3¨C6]. LDHs and HDSs have a brucite type layer structure in which magnesium ions are surrounded by six hydroxide ions in an approximately octahedral geometry with exchangeable anions occupying the interlayer region [7]. LDHs have a general formula and HDSs can be represented as where M2+ and Me2+ represent different divalent metal ions. In both LDHs and HDSs, is an exchangeable anion which balances the charge and controls the interlayer separation and -spacing. Anion exchange ability, potential for sustained release, and biocompatibility of the LDHs and HDSs have made them useful in the uptake, storage, and controlled release of bioactive materials such as drugs and plant growth regulators [8¨C11]. The rate of release of stored drugs and pesticides depends on the intralayer metal composition of the host materials and the size of the intercalated drugs and pesticides [10, 12]. In addition to the effect of the layer metal ion composition and size of intercalated drugs, the structure of the intercalated drugs is expected to significantly affect their rates of release. In studies involving intercalation reactions, it has been observed that LDHs and HDSs exhibit selectivity when
%U http://www.hindawi.com/journals/apc/2014/710487/