Synthesis of l-cystine nanotubes by alkalinization of l-cysteine in the presence of gallium nitride

The alkaline oxidation of l-cysteine (l-Cys) was conducted in aqueous media forming the insoluble l-cystine dimer as confirmed by X-ray diffraction. In another experiment, a gallium nitride film was added to the l-Cys solution and the l-cystine crystals presented a preferential growth. The transmission electron microscopy images showed the formation of single- and multi-wall l-cystine nanotubes. The infrared and high resolution electron microscopy data suggested that the growth of the tubes resulted from the successive staking of l-cystine dimers onto the (0 0 1) family of planes, which was a consequence of the ionic assembly between l-cystine over a layer of l-Cys molecules previously grafted to the gallium nitride particles.