Brilmayer, Robert ; Kübelbeck, Sonja ; Khalil, Adnan ; Brodrecht, Martin ; Kunz, Ulrike ; Kleebe, Hans-Joachim ; Buntkowsky, Gerd ; Baier, Grit ; Andrieu‐Brunsen, Annette (2021):
Influence of Nanoconfinement on the pKa of Polyelectrolyte Functionalized Silica Mesopores. (Publisher's Version)
In: Advanced Materials Interfaces, 7 (7), Wiley, ISSN 2196-7350,
DOI: 10.26083/tuprints-00019915,
[Article]

Abstract

Functionalized ordered mesoporous materials are relevant in technologies, such as drug release, sensing, and separation. To design functionality, the silica framework can be functionalized with responsive molecules or polymers. Often, the pH value in those hybrid materials determines performance. Even though pH/pKa differences between polymers in bulk solutions and nanoscale confinement have been observed, the influence of confinement on pH- and pore filling dependent polyelectrolyte oligomer chain charge has yet not been investigated systematically. Here, mesoporous silica films are functionalized with (2-dimethylamino)ethyl methacrylate) (DMAEMA) and 2-(methacryloyloxy)ethyl phosphate (MEP) oligomers using photoiniferter initiated polymerization. This approach allows a controlled and environmentally friendly mesopore functionalization in water. The obtained oligomer functionalized pores are tunable with respect to pore filling. For both, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(2-(methacryloxy)ethyl phosphate) (PMEP), the charge generation inside mesopore confinement is significantly delayed toward harsher pH conditions resulting in pKa shifts of 1–2 pH units. Polymer amount and ionic strength show to further influence the pKa of PDMAEMA in mesopores. The technological importance of the pH value in confinement and its effect on enzyme stabilization is demonstrated. Lipase from Aspergillus oryzae loses its activity upon encapsulation in silica nanoparticles at pH values where the enzyme is stable in bulk solution.

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