9 research outputs found
Coordinationâcageâcatalysed hydrolysis of organophosphates : cavityâ or surfaceâbased?
The hydrophobic central cavity of a waterâsoluble M8L12 cubic coordination cage can accommodate a range of phosphoâdiester and phosphoâtriester guests such as the insecticide âdichlorvosâ (2,2âdichlorovinyl dimethyl phosphate) and the chemical warfare agent analogue di(isopropyl) chlorophosphate. The accumulation of hydroxide ions around the cationic cage surface due to ionâpairing in solution generates a high local pH around the cage, resulting in catalysed hydrolysis of the phosphoâtriester guests. A series of control experiments unexpectedly demonstrates thatâin marked contrast to previous casesâit is not necessary for the phosphoâtriester substrates to be bound inside the cavity for catalysed hydrolysis to occur. This suggests that catalysis can occur on the exterior surface of the cage as well as the interior surface, with the exteriorâbinding catalysis pathway dominating here because of the small binding constants for these phosphoâtriester substrates in the cage cavity. These observations suggest that cationic but hydrophobic surfaces could act as quite general catalysts in water by bringing substrates into contact with the surface (via the hydrophobic effect) where there is also a high local concentration of anions (due to ion pairing/electrostatic effects)
A regional water quality model designed for a range of users and for retrofit and re-use
We discuss the motivations for, and software design concepts underpinning, the development of a regional water quality model. The Environmental Management Support System (EMSS) was developed to predict daily fluxes of runoff, total suspended sediment, total nitrogen and total phosphorous through a large-scale river network. It was built using a custom environmental modelling framework called Tarsier, founded on the Borland C++ Builder rapid application development environment. Three autonomous models are integrated within the EMSS, but are loosely coupled so that alternative models could be retrofitted into the system if desired. The three models share common data handling and visualisation routines resident in the Tarsier modelling environment and used in other modelling applications. The EMSS was designed for use by a range of stakeholders with varying levels of computer and technical proficiency. To satisfy their varying needs, we built three different interfaces, suited to âexpertâ, âintermediateâ and âbasicâ users. The interfaces for the latter two groups were developed using interface prototyping methods, resulting in software that suited the user requirements. The object-oriented design employed in the coding of the EMSS has enhanced the extendibility and re-useability of the software. The EMSS development was part of a larger hydrologic modelling initiative aimed at reducing duplication in model building and standardising approaches to model design and delivery. The lessons learned during development of the EMSS have informed our future model development strategy