Surface Modification of Functional Self-Assembled Monolayers on 316L Stainless Steel Via Lipase Catalysis

Author(s): Mahapatro, Anil, David M. Johnson, Devang N. Patel, Marc D. Feldman, Arturo A. Ayon, C. Mauli Agrawal

Journal: Langmuir (2006) 22: 901-905.

Abstract:
Lipase catalyzed esterification of therapeutic drugs to functional self-assembled monolayers (SAMs) on 316L stainless steel (SS) after assembly has been demonstrated. SAMs of 16-mercaptohexadecanoic acid (-COOH SAM) and 11-mercapto-1-undecanol (-OHSAM) were formed on 316L SS, and lipase  atalysis was used to attach therapeutic drugs, perphenazine and ibuprofen, respectively, on these SAMs. The reaction was carried out in toluene at 60 °C
for 5 h using Novozyme-435 as the biocatalyst. The FTIR spectra after surface modification of -OH SAMs showed the presence of the C=O stretching bands at 1745 cm^-1, which was absent in the FTIR spectra of -OH SAMs. Similarly, the FTIR spectra after the reaction of the -COOH SAM with perphenazine showed two peaks in the carbonyl region, a peak at 1764 cm^-1, which is the  representative peak for the C=O stretching for esters. The second peak at 1681 cm^-1 is assigned to the C=O stretching of the remaining unreacted terminal COOH. XPS spectra after lipase catalysis with ibuprofen showed a photoelectron peak evolving at 288.5 eV which arises from the carbon (C=O) of the carboxylic acid of the drug (ibuprofen). Similarly for -COOH SAMs, after esterifiation we see a small, photoelectron peak evolving at 286.5 eV which corresponds to the C in the methylene groups adjacent to the oxygen (C-O), which should evolve only after the esterification of perphenazine with the -COOH SAM. Thus, lipase catalysis provides an alternate synthetic methodology for surface modification of functional SAMs after assembly.