RUI: Thermodynamics and NMR Crystallography of Organic Crystal Forms

In this project, funded by the Chemical Structure Dynamics and Mechanisms-A (CSDM-A) program of the Chemistry Division, Professor Manish Mehta of Oberlin College is using experimental methods of physical chemistry to study the stability of organic co-crystals, the molecular basis of plastic and elastic crystals, and the creation of crystals that will allow existing techniques to determine their structures to a new level of accuracy. Co-crystals have proved to be a useful formulation for some medicinal compounds, one that allows control over factors such as solubility and biological effectiveness, yet their stability is poorly understood.

The PI and his research team are building two custom instruments that will enable measurements of physical properties to determine that stability. His team is also investigating the structural characteristics of an unusual class of bendable organic crystals. If success, these studies will add to our understanding of the connection between structure and stability, and this will inform the design of new compounds.

The research is being performed by college students as part of a course taught by the PI. Undergraduate participants in this research are gaining hands-on experience with modern experimental methods, acquiring skills in written and oral communication, and eventually are expected be undergraduate coauthors on peer-reviewed publications.

This project concerns organic crystal forms and is divided into two main thrust areas. The first goal is to determine three key thermodynamic quantities necessary to understand the relative stability of crystal forms: the enthalpy of formation via bomb calorimetry, standard molar entropy via heat capacities using low-temperature calorimetry, and the enthalpy of sublimation via the Knudsen effusion mass-loss method.

These three quantities are being combined to yield the Gibbs energy of formation, which determines overall thermodynamic stability. The study focuses a set of molecular targets chosen for their structural homology; included are common functional groups and ubiquitous supramolecular synthons. This course-based undergraduate research is being performed as part of a thermodynamics course taught by the PI.

In the second thrust area, the PI and his research team are investigating elastic and plastic molecular crystals by using solid-state NMR to detect subtle changes when the crystals are subjected to mechanical strain. The team will attempt to detect the effects of isotope substitution on organic crystalline structure. Students are gaining hands-on experience with cutting-edge techniques which will prepare them for advanced study in the chemical sciences.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.