Synthesis and characterization of amino acid functionalized oligo/poly-thiophenes

The development of new methods for the immobilization of biomolecules onto solid conducting surfaces is important in the advancement of spectro-electrochemical sensors. To prevent the problems that occur during the direct adsorption of modified biomolecules onto the surface of a bare electrode, we suggest that layers of conductive materials be used as an interface to fix and protect the biomolecule probes at 'the surface of the electrode. Polythiophenes appear to be ideal for such purposes due to their excellent adhesion properties to the surface of electrodes, their stability in both the doped and de-doped states, and their ability to carry functionalities that can be exploited for biomolecule immobilization. Other advantages of using thiophenes relate to their well-established synthesis and electrochemical oxidation of its monomers.;The ability of the amino acid functionalized films to form hydrogen bonds with an amino acid that is free in solution was examined using CV and NMR experiments. Hydrogen bond formation was shown to decrease the capacitive current of the films and cause their oxidation peak potential to shift to more oxidative values. It was also seen that the interactions could be monitored using the chemical shift of amide protons in the 1H NMR of amino acid functionalized monomers.;The second method of immobilization required the synthesis of a benzotriazole ester functionalized terthiophene, which when electrochemically oxidized results in a polythiophene modified electrode that bears easily exploitable functionalities. It was found that amine containing molecules can be grafted to the modified electrode simply through incubation in a solution containing the molecule of interest. Using ATR-FTIR we were able to confirm the adsorption of amino acids and peptides onto the surface of the electrode.;In this study we have developed two different methods for the immobilization of biomolecules, specifically amino acids, onto the surface of a polythiophene modified electrode. The first method required the synthesis of a variety of alanine and leucine functionalized mono- and terthiophenes. Using the carboxylic acids in both thiophene-3-carboxylic acid and acetic acid, we were able to form an amide linkage between the thiophenes and the amino acids, through a benzotriazole ester intermediate. The corresponding ter-thiophene monomers were obtained via the Stille cross-coupling reaction of a 2,5-dibrominated amino acid functionalized thiophene monomer with 2-tributyl- stannyl-thiophene. All of the newly synthesized monomers were characterized using 1H and 13C NMR, IR, UV/Vis, and HRMS. The polymers which were formed through the electrochemical oxidation of the monomers were characterized electrochemically using cyclic voltammetry and optically using ATR-FTIR and UV/Vis spectroscopy. Starting with two different thiophene monomers also allowed for us to examine the effects the linker size has on the properties of the resulting material.