Active Biocatalysts Based on Pepsin Immobilized in Short Channeled Zr-Ce-SBA-15

doi:10.3724/SP.J.1077.2012.00185

Abstract

Abstract:

Short channeled Zr-Ce-SBA-15 (ZCS) mesoporous materials with hexagonal platelet morphologies were synthesized through a hydrothermal route without addition of mineral acids. Porcine pepsin was immobilized inside ZCS and conventional SBA-15 through physical adsorption. A grafting step with [1-(2-amino-ethyl)-3-aminopropryl] trimethoxysilane (AAPTS) was performed to reduce the pore openings of the host material in order to minimize the enzyme leaching. The hybrid materials were characterized by X-ray diffraction, scanning electron microscope, transmission microscope, N₂ adsorption/desorption and Fourier-transform infrared spectroscope. The results confirmed that pepsin is located inside the channels of the mesoporous materials and the grafting process does not affect the mesoporous structure. The immobilization of pepsin into ZCS and SBA-15 were compared. The results demonstrate that the ZCS materials have higher adsorption rates and adsorption capacities (the maximum adsorption capacity is 257.9 mg/g) compared with SBA-15. The ZCS materials with short channels are superior to conventional SBA-15 facilitating molecular diffusion. The catalytic activity of the hybrid bioinorganic material was tested with hemoglobin. The immobilized pepsin has maintained the necessary degree of freedom to fulfill its catalytic activity.

Key words: short channeled, mesoporous materials, porcine pepsin, enzyme immobilization, catalysis

CLC Number:

O629
Q814

WANG Fang, LI Jian-Sheng, RAN Dong-Qin, DUAN Meng-Shan, SUN Xiu-Yun, WANG Lian-Jun. Active Biocatalysts Based on Pepsin Immobilized in Short Channeled Zr-Ce-SBA-15[J]. Journal of Inorganic Materials, 2012, 27(2): 185-190.

Figures/Tables 8

Fig. 1 Low-angle XRD patterns of SBA-15(a), PEP/SBA-15 (b), PEP/SBA-15/AAPTS (c), ZCS (d), PEP/ZCS (e) and PEP/ZCS/AAPTS (f)

Fig. 2 SEM and TEM images of ZCS and SBA-15

Fig. 3 N2 adsorption-desorption isotherms (A) and pore size distributions (B) of SBA-15 (a), PEP/SBA-15 (b), PEP/ SBA-15/AAPTS (c), ZCS (d), PEP/ZCS (e) and PEP/ZCS/ AAPTS (f)

Table 1 Textural properties of samples

Sample	S_BET/(m²·g^-1)	D/nm	V/(cm³·g^-1)
SBA-15	847	9.6	1.16
PEP/SBA-15	577	7.5	0.99
PEP/SBA-15/AAPTS	241	6.2	0.39
ZCS	805	9.2	1.03
PEP/ZCS	547	8.4	0.80
PEP/ZCS/AAPTS	129	7.3	0.22

Fig. 4 FTIR spectra of SBA-15 (a), PEP/SBA-15 (b), PEP/ SBA-15/AAPTS (c), ZCS (d), PEP/ZCS (e) and PEP/ZCS/ AAPTS (f)

Fig. 5 Adsorption curves of the amount of adsorbed pepsin within SBA-15 and ZCS

Table 2 Leakage of adsorbed enzyme

Sample	Relative enzyme leaching amount/%
PEP/SBA-15	20.7
PEP/ZCS	21.4
PEP/SBA-15/AAPTS	7.7
PEP/ZCS/AAPTS	7.2

Table 3 Catalytic activity test for peptic hydrolysis

Sample	Enzyme activity / (U·mg^-1)		Relative enzyme activity/%
Sample	Initial	After 4 cycles	Initial	After 4 cycles
Free pepsin	28.71	—	100%	—
PEP/SBA-15	7.34	3.06	25.6%	10.6%
PEP/ZCS	9.65	2.76	33.6%	9.6%
PEP/SBA-15/AAPTS	4.88	4.75	17.0%	16.5%
PEP/ZCS/AAPTS	6.23	6.00	21.7%	20.9%

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