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

先正达集团是全球最大的农业科技公司。他们销售的产品的生物效应的核心是理解和预测化学物质在生物膜（如叶子表面）上的运动，以及这种运动如何与现有的损失机制竞争。随着精密应用的增长，这将变得越来越重要。该项目将把测量和模拟理想和不理想过程的两个关键领域结合起来，为定量描述、模拟和预测现实条件下的运输发展科学见解和方法。康普顿集团在界面过程建模方面拥有丰富的专业知识，可以在纳米尺度和宏观尺度实验中实现耦合质量传递、吸附/解吸以及同质和非均质化学动力学。此外，康普顿小组是使用电化学和荧光光谱研究界面过程的专家。这三种方法都将在项目中使用。研究的生物膜将基于“蜡层”模型。具有电活性和/或荧光的模型活性成分（Ai）将从两个可能的起点开始使用，即水溶液中的纳米颗粒或饱和水溶液。在第一种情况下，纳米粒子如何移动到蜡质层，溶解，然后通过膜运输，将被研究和模拟。该项目将研究参数的影响，如颗粒的大小和形状、多分散性的作用、颗粒的扩散系数、颗粒/溶液界面的溶解速率（以动力学控制和溶解度控制为限）、释放分子的扩散系数和溶液化学，以及释放分子的界面摄取速率（以动力学控制和热力学控制为限）。模拟将通过学生编码的有限差分方法和COMSOL进行。通过所谓的“纳米冲击”实验，电化学方法将用于研究模型叶片附近单个纳米颗粒的检测和损失，这将表征颗粒的扩散，注意到颗粒的有限尺寸导致界面附近的扩散受阻。其次，荧光显微镜可以监测到达界面的荧光纳米颗粒，同时监测模型“蜡层”对荧光分子的吸收，从而深入了解先正达开发的模拟叶片表面的水/蜡层界面系统的界面动力学。对于第二种情况，将进行相同类型的研究，但Ai系统的结晶将与跨膜吸收竞争。成功地描述了这两种情况后，将遵循两个增加复杂性的方向。首先是用第二个模型Ai系统重复分析，以便在两个Ai都存在的情况下对混合系统进行调查，解决这是否会导致差异吸收以及如何描述这一问题。其次是分析添加配方添加剂的影响，该添加剂被认为会破坏蜡质层的特性，并研究这是否会改变模型Ai的溶解/沉淀以及吸收。在任何情况下，理论都会与实验相结合。拟议的项目需要在生物系统领域应用基础物理和化学。该项目属于EPSRC“物理科学”主题下的“生物物理学和软物质物理学”研究领域。所产生的基本信息和能力在植物的化学吸收和运输领域具有潜在的变革性，这是先正达感兴趣的核心领域。

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.