Purification of octyl β- d-glucopyranoside and re-estimation of its micellar size

Abstract

The commercial non-ionic detergent octyl β- d-glucopyranoside is often contaminated by significant amounts of UV absorbing and/or ionic compounds that can associate with membrane proteins. Such impurities can be monitored by several techniques (i.e., spectrophotometry, size exclusion chromatography, and pH, conductivity, and surface tension measurements) and can be removed using mixed-bed ion exchange chromatography. High performance of size exclusion chromatography, dynamic light scattering, and ultracentrifugation have been used to re-estimate the size of micelles of octyl β- d_glucopyranoside since previously published data varied over a wide range. Aggregation numbers were 27 to 100 for micellar molecular weights 8000 to 29 000. Direct physical methods that do not perturbate the sample indicated a large size for the micelles (hydrodynamic radius 23 ± 3 A ̊ ; M r 22 000 ± 3000; aggregation number 75 ± 10 for a 34 mM aqueous solution). In contrast the chromatographic micellar size appeared to be smaller (hydrodynamic radius 15 ± 1 A ̊ ; M r 8000 ± 1000; aggregation number 27). This underestimation may be the result of adsorption and/or alteration of the micelles.