Protein adsorption and activity on carbon xerogels with narrow pore size distributions covering a wide mesoporous range

Luis A Ramírez-Montoya,Alejandro Concheso,Isabel D Alonso-Buenaposada,Héctor García,J Angel Menéndez,Ana Arenillas,Miguel A Montes-Morán

doi:10.1016/j.carbon.2017.04.009

Abstract

Four carbon xerogels (CXs) were used to study the effect of the average pore size (APS) on the adsorption and activity of cytochrome c (cyt c). Pore size distributions of the CXs were relatively narrow with APSs covering the whole mesoporosity range (5, 15, 30 and 55 nm), as determined by mercury porosimetry. Selected techniques verified that all carbons were identical in terms of composition and surface chemistry. The best APS for cyt c adsorption (in terms of capacity) was 30 nm, with loadings of 180 mg of protein (g of support)−1. The CX with APS of 15 nm also hosted high amounts of cyt c, followed by the material with 55 nm. The CX with 5 nm APS did not adsorb cyt c. The pH of adsorption had little effect on the final amount adsorbed, thus stressing the hydrophobic nature of the protein/carbon surface interaction. The activity of the resulting materials towards the ABTS oxidation was similar regardless the amount of cyt c adsorbed on their surface/pores. Their performance in successive cycles of re-use was different depending on the carbon support; xerogels bearing APSs ≥15 nm presented an increasing activity with increasing the number of cycles.

Highlights

The interaction of proteins with porous substrates is crucial for a number of applications [1,2]
This very same argument should be valid for the adsorption of cyt c on nanostructured mesoporous carbons, since they are virtually pure carbon materials with hydrophobic surfaces [8,9,13]
The synthesis of carbon xerogels with narrow pore size distributions (PSDs) and the control of their average pore size over the whole mesopores range provide an ideal set of materials for studying the interaction of carbon surfaces with proteins

Summary

Introduction

The interaction of proteins with porous substrates is crucial for a number of applications [1,2]. Due to the size of most biomolecules of interest, microporosity seems not relevant [3,4] This situation could be reverted as an increasing interest on protein/porous carbons systems is steadily shown [5,6]. Most studies on the interaction of proteins with mesoporous materials concentrate in a rather narrow range, normally below 20 nm of average pore size. This work studies the effect of the pore size on the protein loading and activity using four carbon xerogels with relatively narrow PSD. The maxima of such PSD cover the whole range of mesoporosity (from 5 nm to 55 nm). Factors that are known to affect the adsorption process and the activity of the supported cyt c have been considered

Experimental

Results and discussion

Activity of the supported cyt c

Conclusions