Preparation and Electrochemical Analysis of Several Solvent Reorganization Energy Probes

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Weak interactions in ligand-receptor pairs are important in biological systems. However, the energetics of these interactions are often difficult to quantify for ligandreceptor pairs. Weak interactions are a part of reorganization energy, which plays a role in electron transfer reactions. Under certain conditions the rate of electron transfer can be measured using electrochemistry (cyclic voltammetry). Therefore, electron transfer can be used to study binding. The premise is that when protein binds to a ligand, it changes the dielectric constant of the medium surrounding the metal complex, resulting in a shift in electrochemical potential. For the work presented here, the biotin-avidin system was chosen because it has been extensively studied and can be easily modified. Two different types of these solvent reorganization energy probes are being investigated in this system — solution probes and solid-state probes — which differ mainly in the method by which electron transfer is measured. Synthetic methods for solution probes to modify biotin with iron are discussed — specifically, 5-BMB and 5-BPB. The syntheses of the ligands were carried out. The synthesis of the iron complex is under way. For the solid-state probes, a synthetic method is described for a biotinylated thiol. This thiol is combined with a ruthenium complex and functionalized alkane-thiols, namely 11-mercapto-1- undecanol, 11-mercaptoundecanoic acid, and octadecanethiol, to form mixed monolayers on a gold electrode. The analysis of these monolayers in the presence and absence of avidin using cyclic voltammetry is discussed. For the monolayer incorporating 11-mercapto-1-undecanol, a potential shift of 21 mV was observed in the absence of biotin upon addition of avidin, and a potential shift of 29 mV was observed in the presence of biotin upon addition of avidin. For the monolayers incorporating 11-mercaptoundecanoic acid and octadecanethiol, no significant shift in potential was observed upon avidin addition.

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  • 07/17/2018
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