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Nonionic Surfactant Blends to Control the Size of Microgels and Their Catalytic Performance during Glycoside Hydrolyses

In a proof of concept
study, a series of nonionic surfactant blends
derived from Tween 80 and Span 80 were used to prepare catalytic microgels
from stabilized droplets in miniemulsions. The goal of this study
is to optimize the catalytic efficiency of microgels by decreasing
their particle size with surfactants that are custom-made for the
respective prepolymerization mixture. The effectiveness of the approach
is examined by evaluating the catalytic efficiency of the resulting
microgels in comparison to their counterparts made in the presence
of ionic sodium dodecyl sulfate (SDS) solution. Spherical particles
with hydrophilic–lipophilic balance (HLB) value dependent mean
hydrodynamic diameters between 99 and 200 nm are obtained. Addition
of Cu­(II) ions and selected other transition metal ions activated
the dormant catalysts for cleavage of glycosidic bonds in 2-[4-(2-hydroxyethyl)­piperazin-1-yl]­ethanesulfonic
acid (HEPES) buffer at pH 7.00 and 37 °C using a fluorescent
model substrate. The highest proficiency for the catalytic hydrolysis
was observed for Cu­(II)-containing microgels (kcat/KM × knon = 870 000) with the lowest diameter indicating
an almost twofold better stabilization of the transition state compared
to a microgel prepared in the presence of ionic SDS solution. The
study establishes a correlation of the HLB value of the nonionic surfactant
blend used during material synthesis to the particle size and catalytic
performance of the resulting microgels.