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Sponge-Like Ionic Liquids for Clean Biocatalytic Processes
Published in Pedro Lozano, Sustainable Catalysis in Ionic Liquids, 2018
Susana Nieto-Cerón, Elena Álvarez-González, Juana M. Bernal, Antonio Donaire, Pedro Lozano
In this sense, the imidazolium cation provides the enzyme with an additional stabilization compared with the reaction performed in conventional organic solvents. Indeed, our group demonstrated that free lipase B from Candida antarctica provided substantially higher yields for the synthesis of butyl butyrate when four hydrophobic ILs, comprising dialkylimidazolium cations and perfluorinated or bis(trifluoromethyl)sulfonyl amide anions, were used compared with those obtained in 1-butanol or hexane. The stabilizing effect of the imidazolium cation and the protective effect of the ILs on the enzyme were maintained even after seven operation cycles [126]. Simultaneously, the effect of the nature of both cation and anion was checked in the synthesis of N-acetyl-L-tyrosine propyl ester [126] by using alpha-chymotrypsin as biocatalyst. An extended length of the side chain of the imidazolim cations also contributed to the efficiency of the reaction, as did the anion size. Taking all the aforementioned together, it is concluded that highly apolar ILs present a high degree of protection to the enzyme.
Lipase-Catalyzed Reactions in Nonaqueous Media
Published in Sulaiman Al-Zuhair, Hanifa Taher, Supercritical Fluids Technology in Lipase Catalyzed Processes, 2016
Sulaiman Al-Zuhair, Hanifa Taher
The activity (Dang et al., 2007; de los Ríos et al., 2008; Eckstein et al., 2002; Lozano et al., 2002, 2003a, b; van Rantwijk and Sheldon, 2007), stability (Dang et al., 2007; Kaar et al., 2003; Klahn et al., 2011; Lozano et al., 2001, 2003a), and behavior (Madeira Lau et al., 2000) of many lipases in different ILs were found comparable to those in organic solvents. Madeira Lau et al. (2000) tested the use of C. antarctica lipase B in [bmim][PF6] and [bmim][BF4] in alcoholysis, ammoniolysis, and perhydrolysis reactions, and found comparable reaction rates to those in tert-butanol. Lozano et al. (2003a) tested ester synthesis using lipase in ILs based on dialkylimidazolium or quaternary ammonium cations associated with perfluorinated or bis(trifluoromethylsulfonyl)amide anions, and found that the activity of the lipase was enhanced when compared to that in organic solvents. de los Ríos, Hernández-Fernández, Martinez et al. (2007b) studied the transesterification of vinyl butyrate with 1-butanol catalyzed by C. antarctica lipase B for the synthesis of butyl butyrate in different imidazolium-based ILs. The activity and selectivity of the lipase in the water-immiscible ILs ([bmim][PF6], [bdmim][PF6], [hmim][PF6], [omim][PF6], [emim][NTf2], [bmim][NTf2], [hmim][NTf2] and [omim][NTf2]) were found to be higher than those obtained in n-hexane. P. cepacia lipase and Candida rugosa lipase also performed better than organic solvents. The ability of these two enzymes in [bmim][PF6] were found to be better than in dichloromethane (Nara et al., 2002) and chloroform (Kim et al., 2003), respectively. Sheldon et al. (2002) studied the stability of C. antarctica lipase B in [bmim][PF6] and found that both free and immobilized forms of the enzyme were stable. Similar results were also reported by Lozano et al. (2001).
Chemistry of hydroperoxycarbonyls in secondary organic aerosol
Published in Aerosol Science and Technology, 2018
Demetrios Pagonis, Paul J. Ziemann
Two studies of the decomposition of organic hydroperoxides in the presence of aldehydes (Durham, Wurster, and Mosher 1958) and strong acid (Griesbaum and Neumeister 1982) reported in the synthetic organic chemistry literature are also relevant to the current work, even though they were conducted in bulk solutions instead of SOA. In particular, they are informative since they establish that AHPA cyclize to CPHA, and they point to the importance of peroxyhemiacetals as key intermediates in decomposition reactions. In their study of the decomposition of n-butyl hydroperoxide in the presence of butanal, Durham, Wurster and Mosher (1958) observed a high yield (0.52) of gaseous H2, and experiments with deuterated peroxide showed that the source of H2 was the alkyl chains of the hydroperoxide and aldehyde. The primary products in solution were butyric acid, butyraldehyde, butyl butyrate, butyl alcohol, and a small amount of butyl formate, indicating that decomposition did not proceed by a single pathway under these conditions. And when Griesbaum and Neumeister (1982) investigated the decomposition of 6-methoxy-6-hydroperoxyhexanal (an AHPA similar to ours) in methanol in the presence of strong acid, they observed a 1:2:1 yield ratio of diester, acetal ester, and diacetal, and proposed a simpler decomposition mechanism in which a peroxyacetal intermediate decomposed to give these products. These results have been incorporated into Figure 3 as the concerted elimination and strong acid decomposition pathways for CHPA, respectively. Knowing then that CPHA and peroxyacetals are likely to be key intermediates in AHPA decomposition in SOA, we set out to characterize the cyclization reaction of AHPA and identify decomposition products with and without strong acid present to determine which of these pathways are likely applicable to HOMs.