Mild, Solvent-Free ω-Hydroxy Acid Polycondensations Catalyzed by <i>Candida </i><i>a</i><i>ntarctica</i> Lipase B

Immobilized Candida antarctica Lipase B (Novozyme-435) was studied for bulk polyesterifications of linear aliphatic hydroxyacids of variable chain length. The products formed were not fractionated by precipitation. The relative reactivity of the hydroxyacids was l6-hydroxyhexadecanoic acid ≈ 12-hydroxydodecanoic acid ≈ 10-hydroxydecanoic acid (DPavg ≅ 120, Mw/Mn ≤ 1.5, 48 h, 90 °C) > 6-hydroxyhexanoic acid (DPavg ≅ 80, Mw/Mn ≤ 1.5, 48 h, 90 °C). Remarkable improvements in molecular-weight buildup resulted from leaving water in the reaction. By 4 h, without application of vacuum, the DPavg for 12- and 16-carbon hydroxyacids was about 90. In contrast, with identical substrates and water removal, the DPavg at 4 h was about 23. Large differences in the molecular-weight build up of 12-hydroxydodecanoic acid were observed for catalyst concentrations (%-by-wt relative to monomer) of 0.1, 0.5, 1, and 10. Nevertheless, by 24 h, with 1% catalyst containing 0.1% lipase, poly(12-hydroxydodecanoic acid) with Mn 17 600 was formed. For 12-hydroxydodecanoic acid polymerization at 90 °C, the catalyst activity decreased by 7, 18, and 25% at reaction times of 4, 24, and 48 h, respectively. Furthermore, the retention of catalyst activity was invariable as a function of the substrates used

Lipase-Catalyzed Polycondensations: Effect of Substrates and Solvent on Chain Formation, Dispersity, and End-Group Structure

The effects of substrates and solvent on polymer formation, number-average molecular weight (Mn), polydispersity, and end-group structure for lipase-catalyzed polycondensations were investigated. Diphenyl ether was found to be the preferred solvent for the polyesterification of adipic acid and 1,8-octanediol giving a Mnof 28 500 (48 h, 70 °C). The effect of varying the alkylene chain length of diols and diacids on the molecular weight distribution and the polymer end-group structure was assessed. A series of diacids (succinic, glutaric, adipic, and sebacic acid) and diols (1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol) were polymerized in solution and in bulk. It was found that reactions involving monomers having longer alkylene chain lengths of diacids (sebacic and adipic acid) and diols (1,8-octanediol and 1,6-hexanediol) give a higher reactivity than reactions of shorter chain-length diacids (succinic and glutaric acid) and 1,4-butanediol. The bulk lipase-catalyzed condensation reactions were feasible, but the use of diphenyl ether gave higher Mn values (42 400 g/mol in 3 days at 70 °C). The polydispersity varied little over the conditions studied giving values ≤2. No specific trend with respect to end-group structure as a function of time was observed. At 70 °C, the retention of catalyst activity in the bulk was independent of substrate structure but was higher when reactions were conducted in diphenyl ether than in bulk

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

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 (−OH SAM) were formed on 316L SS, and lipase catalysis 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