Modelling and measurement of diffusion to and across bio-membranes and interfaces

Background Syngenta Group is the world's largest Agroscience company. Core to the biological effects of the products they sell is understanding and predicting the movement of chemicals across bio-membranes such as leaf surfaces and how this competes with available loss mechanisms. This is envisaged to become increasingly important as precision applications grow. The project will bring together the two key areas of measuring and modelling the desired and undesired processes to develop scientific insight and methodologies for quantitatively describing, simulating, and predicting transport under realistic conditions.
The Compton Group have extensive expertise in the modelling of interfacial processes allowing for coupled mass transport, adsorption/desorption and homo- and heterogeneous chemical kinetics both in nano-scale and macro-scale experiments. Moreover, the Compton group are experts in using electrochemistry and fluorescence spectroscopy to study interfacial processes. All three methodologies will be used in the project.

Project The bio-membranes studied will be based on a model 'waxy layer'. Model active ingredients (Ai's) that are electroactive and/or fluorescent will be used from two possible starting points, namely from a nano-particle in an aqueous solution or from a saturated aqueous solution.
In the first case how the nano-particle moves to the waxy layer, dissolves and is then transported across the membrane will be studied and modelled. This project will study the impact of parameters such as the size and shape of the particle, the role of poly-dispersity, the particle's diffusion coefficient, the rate of dissolution at the particle/solution interface (with the limits of kinetic vs solubility control), the diffusion coefficient and solution chemistry of the released molecule, and the rate of interfacial uptake of the released molecule (with limits between kinetic and thermodynamic control).
Simulation will be performed via student coded finite difference methods and COMSOL. Electrochemical methods will be used to study the detection and loss of single nano-particles in the vicinity of a model leaf via so-called 'nano-impact' experiments, which will characterise the diffusion of the particles, noting that the finite size of the particles leads to hindered diffusion near interfaces. Second a fluorescence microscope will allow fluorescent nano-particles arriving at interfaces to be monitored simultaneously with monitoring the uptake of fluorescent molecules by the model 'waxy layer' to give insight into the interfacial dynamics at the water/waxy layer interface system developed by Syngenta to mimic leaf surfaces.
For the second case the same type of study will be performed but crystallisation of the Ai system will compete with the uptake across the membrane. With successful description of these two cases, two directions of increasing complexity would be followed. First is repeating the analysis with a second model Ai system to allow investigation of the mixed system when both Ai's are present, addressing the question as to if this leads to differential uptake and how to describe this. Second is analysis of the impact of the addition of a formulation additive, thought to disrupt the characteristics of the waxy layer, and investigating if this alters the dissolution/precipitation of the model Ai as well as the uptake. In all cases theory would synergise with experiments.

Alignment The proposed project requires the application of fundamental physics and chemistry in the area of biological systems. This project falls within the EPSRC 'Biophysics and Soft Matter Physics' research area within the 'Physical Sciences' theme. The fundamental information and capability generated is potentially transformative in the area of chemical uptake and transport in plants, an area at the very heart of Syngenta's interests.