Denise Rooney

Slow delivery of a nitrification inhibitor (dicyandiamide) to soil using a biodegradable hydrogel of chitosan.

Using chemical inhibitors to reduce soil nitrification decreases emissions of environmental damaging nitrate and nitrous oxide and improves nitrogen use efficiency in agricultural systems. The efficacy of nitrification inhibitors such as dicyandiamide (DCD) is limited in soil due to biodegradation. This study investigated if the persistence of DCD could be sustained in soil by slow release from a chitosan hydrogel. DCD was encapsulated in glyoxal-crosslinked chitosan beads where excess glyoxal was (i) partly removed (C beads) or (ii) allowed to dry (CG beads). The beads were tested in water and in soil. The beads contained two fractions of DCD: one which was quickly released in water, and one which was not. A large DCD fraction within C beads was readily available: 84% of total DCD bead content was released after 9h immersion in water, while between 74% and 98% was released after 7d in soil under low to high moisture conditions. A lower percentage of encapsulated DCD was readily released from CG beads: 19% after 9h in water, and 33% after 7d in soil under high rainfall conditions. Kinetic analysis indicated that the release in water occurred by quasi-Fickian diffusion. The results also suggest that DCD release was controlled by bead erosion and the leaching of glyoxal derivatives, predominantly a glyoxal-DCD adduct whose release was positively correlated with that of DCD (R(2)=0.99, p⩽0.0001). Therefore, novel chitosan/glyoxal composite beads show a promising slow-release potential in soil for agrochemicals like DCD.

Selective aliphatic/aromatic organogelation controlled by the side chain of serine amphiphiles

The influence of two structural features of N-Fmoc-L-serine lipoamino acids on organogel formation were investigated. These were (i) the nature of the group on the serine side chain (hydroxyl compared to O-tert-butyl) and (ii) the length of the aliphatic chain (C-14 compared to C-18). O-tert-Butylated derivatives preferentially gelled saturated hydrocarbon solvents, while compounds with the hydroxyl group in the side chain promoted the highly unusual gelation of solely aromatic solvents. Extension of the chain length of the lipoamino acid (from C-14 to C-18) decreased the selectivity observed for the shorter chain homologues. Spectroscopic analyses of these systems indicated that H-bonds, aromatic π–π stacking and van der Waals interactions are involved in the gelation processes. Rheological characterization of the gels revealed the aromatic solvent gels to be more stable than their aliphatic counterparts. Scanning Electron Microscopy (SEM) imaging of the xerogels showed that the structure of gels formed in aromatic solvents differs significantly from those formed in aliphatic ones. The different self-assembly modes of the gelator molecules could be induced by steric effects which depend on the functional groups on the side chain. The organogels obtained were thermoresponsive, moldable and capable of self-healing. In addition, the lipoamino acids studied were phase selective gelators in biphasic mixtures of water/organic solvent and efficiently removed water soluble polluting dye rhodamine B from the aqueous phase.