Effect of mass of pristine carbon nanotubes on the photolysis of phenylalanine

Photolyses at 254 nm of aqueous solutions of phenylalanine (Phe) were carried out at 25 degrees C in the absence and presence of multiwalled carbon nanotubes (CNT). The photolyses were performed in distilled, deoxygenated water and inert Ar atmosphere or in distilled water and air atmosphere. Kinetics of the photolyses were followed by UV spectrophotometry at 220 nm. Initial rates were obtained from the plot of Delta A versus Delta t, both in the presence of CNT (Delta A/Delta t = p*) and in their absence (Delta A/Delta t = p(o)*). The ratio p*/p(o)* gave the ratio k*/k(o)* of the rate constants of the photolysis in the presence and in the absence of nanotubes, respectively. The mass of nanotubes produced an exponential attenuation of the photolytic decomposition of Phe with minor formation of tyrosine and an attenuation constant kappa of the shielding effect of the nanotubes against the photolytic degradation of the amino acid. The results show the effects of CNT on the photolysis of Phe and support the previously observed attenuation effect of carbons on the denaturalizatoion of amino acids and proteins. It is concluded that carbons produce a shielding effect on the photolysis, absorbing the photons and decreasing substantially their denaturalization while at the same time excites the active sites of the carbon for the insertion reaction of the organic moiety.