Sugar fatty acid ester surfactants: Base‐catalyzed hydrolysis

Abstract

Rate constants for the base-catalyzed hydrolysis of sucrose laurate, sucrose α-sulfonyl laurate, and sucrose α-ethyl laurate were measured at several temperatures in pH 11 buffer. Activation energies and Arrhenius factors for the hydrolysis reactions were determined. At 27°C, sucrose laurate hydrolyzed fastest and sucrose α-ethyl laurate slowest. Activation energies and Arrhenius factors showed that both steric and electronic factors affect the rates of ester hydrolysis. Other work has shown that bacterial hydrolysis of sugar fatty acid esters is inhibited in the presence of either α-sulfonyl or α-alkyl groups. A kinetic study of base-catalyzed ester hydrolysis has revealed reasons for the inhibition of bacterial hydrolysis and provided information regarding ester stability at elevated pH.Biodegradation of sugar fatty acid esters by initial hydrolysis was found to be inhibited by the presence of α-alkyl or α-sulfonyl substituents adjacent to the ester bond (1,2). Lipases catalyze bacterial hydrolysis by a nucleophilic process involving a negatively charged tetrahedral intermediate (3-6). The essence of this enzymatic process is similar to the base-catalyzed hydrolysis of esters by hydroxide. This occurs almost universally by a bimolecular nucleophilic mechanism that also involves the formation of a negatively charged tetrahedral intermediate. Both processes are therefore expected to be subject to some of the same steric and electronic influences.Although there is a negatively charged residue in the active site of lipases, it is unlikely that electrostatic repulsion with sulfonyl groups inhibits hydrolysis since this is not observed in the case of other negatively charged substrates (6). On the other hand, the presence of alkyl groups adjacent to the carbonyl carbon of esters is known to reduce the rate of hydrolysis considerably (7). By determining the importance of steric and electronic factors in controlling the kinetics of base-catalyzed hydrolysis of sucrose esters, deductions can be made regarding factors affecting the corresponding enzymatic process.In addition, many cleaning formulations in which these surfactants may be applied have an elevated pH. However, stability of sugar esters to hydrolysis under these conditions is not well understood. It is therefore useful to investigate the factors influencing base hydrolysis of sugar esters from the point of view of formulation stability.In the current study, high-performance liquid chromatography (HPLC) was used to measure base hydrolysis rates of three key sugar esters: sucrose laurate, sucrose α-ethyl laurate, and sucrose α-sulfonyl laurate. The general structure of these surfactants is shown in Scheme 1; R=H in the case of sucrose laurate, SO 3 − Na + in the case of sucrose α-sulfonyl laurate, and CH 2 CH 3 in the case of sucrose α-ethyl laurate. Second-order rate constants for hydrolysis at elevated pH were determined at several different temperatures. This allowed energies of activation and Arrhenius factors to be determined in each case. The relative inf...

Stability of Sucrose Fatty Acid Esters under Acidic and Basic Conditions

“…3.2.1 Identification of hydrolysates generated under basic conditions Sucrose and fatty acids, but neither monosaccharides nor monosaccharide esters, were detected in the hydrolysate by GC-MS; that is, no evidence for hydrolysis of the glycosidic bond was found. In agreement with a previous study 17 , the base hydrolysis occurred exclusively at the ester bond. …”

“…Baker et al have already studied the base hydrolysis of sucrose monoesters in detail 17 . They found that the ester hydrolysis in buffer solution followed pseudo first-order kinetics because the concentration of hydroxide ions remained constant during hydrolysis.…”

“…showed that base hydrolysis occurred exclusively at the ester bond, and they determined the kinetic parameters for the ester hydrolysis of 6-O-monoesters at pH 11 17 .…”

Sugar fatty acid ester surfactants: Structure and ultimate aerobic biodegradability

“…The different electronic properties of these subtsituents may also affect biodegradability. Reasons for biodegradability differences were the subject of considerable further investigation described in separate publications (39,40).…”

Practical Production of 6-O-Octanoyl-D-allose and Its Biological Activity on Plant Growth

“…5) We have reported the enzymatic synthesis of D-allose fatty acid esters via lipasecatalyzed transesterification 6) because we expected that the introduction of unbranched alkyl chains to D-allose would provide not only good surface activity and enhanced membrane permeability, but also higher biological activity than that of D-allose itself on the basis of biosurfactant research on sugar fatty acid esters. 7,8) Moreover, they are also non-ionic and biodegradable 9) and, therefore, could be widely used in the food, cosmetic, and pharmaceutical industries. Although the same regioselective acylation of the C-6 primary hydroxy group as D-glucose was observed in that of Dallose, irrespective of the different configuration of the hydroxy group at C-3 of D-allose, a drawback in this process is the use of toxic acetonitrile which may not be compatible with food industrial purposes.…”