Epitaxial Electrodeposition of Chiral Films Using Chiral Precursors

Abstract

Chiral drugs have played an important role in driving the market for past few decades. Currently, more than half of the drugs marketed are chiral. [1-4] It is well established that chiral drugs often differ in their pharmacological, toxicological and pharmacokinetic properties. Historically, the pharmaceutical industry has relied on using enzymatic reactions to produce enantiospecific molecules. The chiral drugs are often synthesized in the racemic form, and are then resolved into pure enantiomer. [5] From an Industry perspective, the process is neither cost effective nor completely safe. The enantiomer should be characterized in detail in order to develop a safe and reliable formulation. One way to get around that would be to develop enantiospecific catalyst that can be reused. Chiral surfaces offer this possibility. They have been produced by decorating the surfaces of achiral substrates by chiral molecules, or by introducing defects in the single crystals which exposes chiral kink sites. [6-17] It was shown that chiral surfaces can also be produced by electrodeposition technique. [18, 19] Unlike other vacuum techniques, electrodeposition is cheaper and can be carried out at ambient conditions. [20, 21] In this method, chiral molecules present in the electrodeposition solution determine the final Chirality of the electrodeposited thin film. In this regard, electrodeposition resembles biomineralization, where organic molecules adsorbed on surface, reduce the symmetry of surfaces, resulting in chiral crystal habits. [22-28] Crystals like calcite and gypsum which crystallize in achiral space group can be transformed to chiral space group by treating calcite with chiral etchants or by crystallizing calcite in the presence of amino acids. Chiral morphologies of calcites can also be deposited electrochemically. [29]