(451e) Effects of the Surface Chemistry and the Pore Geometry of Mesoporous SBA-15 On the Catalytic Activity of Adsorbed Proteins

    
 When a protein adsorbs on the surface of a material that is curved on the
nanoscale, the structure and function of the adsorbed protein can be markedly
changed. For example, when proteins are adsorbed on silica nanoparticles and
carbon nanotubes, which have a positive, convex curvature, changes in secondary
structure of the protein have been noted, which result in a decrease in
catalytic activity^1,2. However, when proteins adsorb on nanoporous
materials with a negative, concave local surface geometry, the behavior is
different: we have noted a relative increase in enzymatic activity of adsorbed
lysozyme and myoglobin on nanoporous SBA-15 with controlled pore sizes. This
suggests a distinct interaction mechanism between these proteins and the
nanopore surface.

   
  Our preliminary studies of the enhanced catalytic activity of the
adsorbed lysozyme and myoglobin on SBA-15, reported at the AIChE meeting in
2009, illustrated that confinement of mesopores can stabilize protein
structures. Ordered mesoporous SBA-15 with carefully controlled surface
geometries and different surface chemical properties were introduced to study
the effects of the local surface geometry and surface chemistry on the
conformation of the adsorbed protein. A decrease in catalytic activity of the
same adsorbed proteins on SBA-15, of which the pore surface is modified with
hydrophobic moieties, but which has a similar pore size to the original SBA-15,
for which a remarkable increase in activity was noted, reveals that local surface
chemistry also plays an important role on the function of the adsorbed
proteins. Liquid phase ATR-FTIR spectroscopy with Fourier self-deconvolution
and mathematical analysis were introduced to analyze the nature and the changes
of the secondary structures of free and adsorbed protein molecules on mesopores
with different pore sizes and surface properties³. Our studies show
that the protein structures are perturbed to a different extent, depending on
the surface interactions.

     
The results show that the activity and stability of adsorbed proteins inside
the pores of SBA-15 are strongly correlated with the local geometry and the
surface properties of the nanoporous materials. Strong surface interactions,
and a confined space of the right geometry are essential to enhance the
activity and stability of the adsorbed proteins.  

References:

(1) Vertegel, A. A.;
Siegel, R. W.; Dordick, J. S. Langmuir 2004, 20,
6800-6807.

(2) Asuri, P.; Bale,
S. S.; Karajanagi, S. S.; Kane, R. S. Current Opinion in Biotechnology 2006,
17, 562-568.

(3) Dong, A.; Malecki,
J. M.; Lee, L.; Carpenter, J. F.; Lee, J. C. Biochemistry 2002, 41,
6660-6667.