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CAMP Senior University Professor Richard Partch uses NMR to monitor receptor-toxin interactions. Changes in the numerical values of proton or carbon chemical shifts are known to occur when some organic receptor molecules are exposed to donor molecules. The physical basis for this phenomenon is a change in the electronic and magnetic environment near the atoms in question as the two molecules approach each other. Such shifts are being measured by Professor Richard Partch and graduate student Evon Powell, to determine how well several receptor molecules having electron deficient aromatic rings bind to electron rich aromatic rings of some therapeutics (Fig.1) and other bioactive molecules, including cocaine, that are lethal when overdosed. Figure 2 shows how the two rings share p electron density in the charge-transfer mode.

Powell, with synthesis assistance from Research Associate Dr. Sudha Rani and undergraduates Allison Jacques and Heather Stokes, prepared several dinitrobenzene derivatives having powerful charge-transfer acceptor properties. They have carboxamide and sulfonamide functionalities and are designed for subsequent covalent attachment to biocompatible, injectable carrier nanoparticles for use in emergency remediation of overdoses

The NMR spectrum of the aromatic protons in one receptor example, N-ethyl-3,5-dinitrobenzene carboxamide, appear as a triplet centered at 9.1755 ppm and a doublet centered at 9.9575 ppm. The peaks in both the doublet and triplet retain the same splitting when a donor like bupivacaine is added. However, all of the peaks in the multiplets shift by amounts shown in Table 1. Such shifts can be used to calculate binding energies of the acceptor-donor complexes, which are believed to relate to the efficiency of removal of a toxin from blood. This type of binding depends on relative p electron density of aromatic ring systems and is not influenced by water or other components such as carbohydrates, cholesterol or proteins in blood.

Figure 1

Figure 2

Figure 3

Table1

Table 2

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