CBET-EPSRC Molecular Engineering of Inhibitors to Self-Assembly: Fundamental structure informing in silico design

多环芳烃(PAHs)是一类复杂的有机分子，其分子结构中含有多个碳环。日常生活中的例子包括萘和一些家用溶剂，但它们更常见的是作为化学原料和材料。在化学上，这些化合物在物理性质和与其他化合物相互作用的方式方面都是独一无二的。多环芳烃具有强烈的自缔合倾向，必须谨慎控制以获得最佳材料性能，或适当抑制以避免不必要的行为。问题的关键在于，多环芳烃在有机溶剂混合物中的缔合是当代一系列工程挑战的核心，包括有机光伏电池的制造、高性能盘状液晶的设计以及防止石油沥青质聚集和结垢。我们面临的问题是，多环芳烃的关联被误解了。这是一个复杂的问题，不仅涉及分子的化学性质，而且涉及从溶液形成固体结构的分子的集体行为。我们处于研究这个问题的独特位置，因为我们将从X射线和中子实验中获得详细的信息，在这些实验中，高能束从这些分子的对和星团中散射，给我们关于形成的星团的类型、形状和大小的直接信息。同时，我们将通过分子模拟来研究这些系统，在形成分子的原子水平上，我们用数值方法求解流体模型的时间演化。这些模拟密切依赖于分子间力的描述，我们将通过散射实验来验证这一点。石油沥青质的无序(而不是结晶)多尺度结构(4-8个分子的芳香聚集体和半径~5-20 nm的扩散团簇)将作为基准情况。它们的结合是由一系列相互作用驱动的，包括但可能不限于，a)由于分子和周围溶剂之间平均分子尺寸的巨大差异而导致的相分离，b)形成分子重要部分的多环芳烃核心之间的增强相互作用，以及c)由于杂原子(S、N、O等)的存在而产生的极性相互作用。在这三种贡献中，后者的研究要少得多，也是本研究的重点。在我们综合方法的最后阶段，我们将考虑粗粒度模拟，其中分子由更大的单元(每个单元由几个原子组成)建模。我们将根据严格的实验和细粒度的模拟来微调这一策略，这将使我们能够进行极大的模拟，并探索与多环芳烃的关联相关的时间尺度。我们的最终目标是开发一套指导方针，为计算机设计自组装抑制剂提供信息。这将打开一个令人难以置信的强大的研究领域，人们可以在计算机上设想工程分子来满足工业需求。

Polyaromatic hydrocarbons (PAHs) are complex organic molecules which have the unique trait of including in their molecular structure more than one carbon rings. Everyday examples include naphthalene and some household solvents, however they are more common as chemical feedstocks and materials. Chemically, these compounds are unique both in terms of the physical properties and in terms of the way they interact with other compounds. PAHs have a strong propensity to self-associate, which must be either carefully controlled to obtain optimum material properties or appropriately inhibited to avoid unwarranted behaviour. The crux of the matter is that the association of PAHs in mixtures of organic solvents is central to a diverse range of contemporary engineering challenges including the fabrication of organic photovoltaics, design of high-performance discotic liquid crystals, and prevention of petroleum asphaltene aggregation and fouling. The problem faced by us is that the association of PAH's is misunderstood. It is a complex problem that involves not only the chemical nature of the molecules but the collective behaviour of molecules forming solid structures from solution. We are uniquely placed to study this problem, as we will obtain detailed information from X-ray and neutron experiments, where high energy beams scatter off pairs and clusters of these molecules giving us direct information on the type, shape and size of the clusters formed. In parallel, we will study these systems through molecular simulations, where we solve by numerical methods the time evolution of a model of the fluid at the level of the atoms forming the molecules. These simulations intimately depend on the description of the intermolecular forces, which we will validate against the scattering experiments. The disordered (as opposed to crystalline) multiscale structure of petroleum asphaltenes (aromatic aggregates of 4-8 molecules and diffuse clusters of radii ~5-20 nm) will serve as a benchmark case. Their association is driven by a collection of interactions, including, but possibly not limited to, a) phase separation due to the large difference in average molecular size between molecules and the surrounding solvents, b) enhanced interactions between the cores of the PAH cores that form a significant part of the molecules and c) polar interactions arising from the presence of heteroatoms (S, N, O, etc.). Of these three contributions, the latter is much less studied and is the focus of this study. In a final stage of our integrated approach we will consider coarse-grained simulations, where molecules are modelled by larger units (of several atoms each). This strategy, which we will fine tune to our rigorous experiments and fine-grained simulations, will allow us to perform extremely large simulations and explore time scales that are relevant to the association of PAH's. Our ultimate objective is to develop a set of guidelines that could inform the computer design of inhibitors to self-assembly. This will open an incredibly powerful research area where one could envision engineering molecules on a computer to satisfy industrial requirements.