thanks to the high surface area open framework. Tryp adsorption
is further proved by the presence of the trypsin characteristic
vibrational bands (amide I and II bands in the 1700–1450 cmÀ1
region) in the FTIR spectrum (see ESIw). However, as the
PXRD pattern is unmodified, we must consider that adsorption
occurs at the surface of crystallites.
Moreover, activity of Mg2Al-CO3SC–Tryp toward hydrolysis
of N-benzoyl-L-arginine-p-nitroanilide was enhanced compared to
that of Tryp immobilized on classic Mg2Al-CO3. It was measured
to be more than 2 times higher, respectively, 2.74 Â
10À6 mol minÀ1 mgÀ1 compared to 1.22 Â 10À6 mol minÀ1 mgÀ1
.
In summary, aerogels of various LDH compositions displaying
the highest surface area reported so far were prepared by
combining fast precipitation and supercritical CO2 drying. Based
on the preliminary adsorption results, it is our belief that this
general approach which easily provides an LDH open porous
framework with an extremely high inner surface area will be of
great interest for the subsequent development of functionalized
LDH materials with enhanced properties in many fields of
application such as adsorption and catalysis.
Fig. 3 (A) PXRD pattern and (B) TEM image of the Mg2Al-DDSSC
phase.
Notes and references
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Fig. 4 Adsorption isotherms of trypsin by Mg2Al-CO3 (’) and
Mg2Al-CO3SC (K) LDH.
to form a 3D framework as previously observed (Fig. 3B).
Nevertheless, such behavior provides an excellent opportunity
to produce in a simple way high surface area LDH intercalated
with various functional anionic species.
Finally in order to evaluate the surface properties of LDH
aerogels, we investigated the adsorption capacity of Mg2Al-CO3SC
toward trypsin (Tryp) which is a pancreatic serine protease.
Immobilization of Tryp is of great interest for many industrial
applications18 such as protein detection or separation, biocatalysis,
food industry. Note that concerning enzyme immobilization
techniques, there is a real need for supports with higher surface
area leading to enhanced adsorption capacity. Fig. 4 shows
the adsorption isotherms obtained for Mg2Al-CO3SC and
for Mg2Al-CO3 conventionally prepared by a constant pH
method, in comparison. Both LDH display L-type isotherms,
which can be described satisfactorily by the Freundlich
equations (Cs = kfCn). The results of the fit are reported in
the inset of Fig. 4. The adsorption capacity (kf) of the aerogel
is considerably higher (nearly 20 times) than that for the
conventional MgAl-CO3 matrix. It is strikingly clear therefore
that the enzyme adsorption is greatly enhanced at the surface
of the nanostructured LDH. It is noteworthy that this value is
also greatly higher than the reported19 Tryp immobilization
rates involving for instance mesoporous silica (117 mg gÀ1) or
carbon nanotubes (420 mg gÀ1). This trend could be easily
explained by an increase of the porosity of the LDH aerogel which
enhances the diffusion of the enzyme into the adsorption sites,
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c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 7197–7199 7199