Streamlined Gelator Discovery Through the Analysis of Intermolecular Interactions in the Solid State.

Abstract

Low molecular weight gels are self-assembled materials comprised of a fiberous structure that is able to immobilize a liquid phase. Gels can be triggered by an external stimulus, which gives rise to proposed applications such as sensing. The causes for gelation are not well understood. It is hypothesized that one dimensional (1D) intermolecular interactions cause aggregation into a fiber-like structure. This thesis details our efforts to understand how intermolecular interactions in the solid state can be used to predict new gelators and how those gels can be used for practical applications.

Chapter 2 describes the discovery of a new Hg-containing gelator (Hg(2-(1H)-quinoxalinone)2) by identifying prominent 1D intermolecular interactions in solid state packing structures accessed from Cambridge Structural Database. This gelator has potential for application in sensing and environmental remediation. The gel can be triggered selectively by the addition of mercury ions, but is unstable to chloride.

Chapter 3 details a structure-property relationship study on five gelators and four nongelators obtained by structural modification of Hg(2-(1H)-quinoxalinone)2,. These compounds exhibit multiple solid-state forms. It has been demonstrated that dissolution enthalpies are higher for gelators than nongelators. The influence of multiple forms on dissolution enthalpy was investigated, but we concluded that dissolution enthalpies must be measured on forms matching the gel to have meaningful results. Nevertheless, a new chloride-tolerant gelator was discovered that gelled a solution of river water.

Chapter 4 illustrates the development of a widely-applicable method to identify new gelators using information in solid-state packing structures. Morphologies of Pb2+-containing CIF files were predicted using the attachment energy theory. We hypothesized that high predicted aspect ratios would be the result of 1D intermolecular interactions and could lead to classes of molecules that contain gelators. Two gelators were identified from the top 5% of aspect ratios. The influence geometry optimization parameters and other factors on the computational model were thoroughly investigated.

This work represents an investigation of how intermolecular interactions direct self-assembly and how this information can be used to identify new gelators.