CURRENT RESEARCH PROJECTS

MEASURING NON-COVALENT ARENE-ARENE INTERACTIONS: The conformationally switchable systems have also been used a molecular torsional balances to measure face to face arene-arene interactions. A new molecular balance is presented based on an bicyclic N-aryl succinimide that adopts two distinct folded and unfolded conformations due to the presence of restricted rotation about a Caryl-Nimide single bond. In the folded conformer, a phenyl ether arm is positioned over an aromatic shelf in face to face stacking geometry. In the unfolded conformer, the phenyl ether arm is far from the aromatic self and cannot form an intramolecular arene-arene interactions. Due to the rigidity of the bicyclic framework of the balance, the folded conformer is constrained to this face to face geometry to the exclusion of other geometries such as edge to face. This has been confirmed by the x-ray crystallographic and molecular modeling studies of the balances. Thus, measurement of the folded/unfolded ratio yields an accurate measure of the face to face arene-arene interaction. The balance also has other attractive features such as 1) an efficient modular synthesis that allows rapid study of the influence of different aromatic surfaces and 2) excellent solubility in a wide range of organic solvents which allowed study of the influence of solvents on the arene-arene interactions.

PREVIOUS RESEARCH PROJECTS

The general focus of our research is the templated synthesis of small molecules, molecular devices, and polymers. Areas of interest include: molecular recognition, molecular devices, molecularly imprinted polymers, sensing, supramolecular chemistry, non-covalent interactions, and physical organic chemistry.

INTRODUCTION: The three-dimensional shape of molecules and polymers are a key variable in determining their physical properties including: polarity, dipole moments, refractive index, viscosity, chirality, and recognition properties. The traditional method of manipulating the shape and configuration is via chemical synthesis. We have been investigating new methods that utilize molecular templates (Fig 1). The molecular template can be used to assist in the synthesis or conformational folding of small molecule molecular receptors (Fig 1a and b) or molecularly imprinted polymers (Fig 1c).

SHAPE ADAPTABLE MOLECULES/POLYMERS VIA RESTRICTED ROTATION:  We have developed a new class of compounds that can be thermally molded or shaped with a molecular template. These are based on rigid molecular frameworks containing connected together by C(aryl)-N(imide) single bonds that display restricted rotation at room temperature. As a consequence, the molecules and oligomers are conformationally flexible at elevated temperatures and thus can be molded and shaped into different conformations. On cooling to room temperature, the new shapes are “locked in” as restricted rotation is reinstated even when removed from the promoting environment. We have demonstrated examples of molecules that can be shaped in response to metal ions, pH, solvent polarity, and hydrogen bonding chiral guest molecules; and that the resulting conformational changes can be “saved” using stable conformational rotamers. These compounds have applications as molecular memory devices, reprogrammable separation materials, and sensors.

MOLECULARLY IMPRINTED POLYMERS: Polymers can be imprinted with a template molecule to form complementary cavities. These polymers have found applications as easily tailored separation supports, chemical sensors, and catalysts. The methodology is highly attractive due to the ease and flexibility with which selective materials can be produced. These characteristics are offset by relatively low binding affinities and heterogeneity of the newly formed cavities. We address both of these issues by selectively inactivating the low affinity sites. The resulting polymer will have greater utility due to enhanced binding properties and homogeneity. A key to this site-selective chemical modification strategy is the ability to quantitatively measure shifts in the distribution of binding sites, which we are able to do by the measurement of affinity distribution spectra that plots the number of binding sites with respect to association constants.