Interaction of Biological Molecules with Clay Minerals: A Combined Spectroscopic and Sorption Study of Lysozyme on Saponite

Cliff T. Johnston, Birck Nanotechnology Center, Purdue University
Gnanasiri S. Premachandra, Birck Nanotechnology Center, Purdue University
Tamas Szabo, Szeged University
Joyce Lok, Birck Nanotechnology Center, Purdue University
Robert A. Schoonheydt, Katholieke Universiteit Leuven

Date of this Version



Langmuir, 2012, 28 (1), pp 611–619


The interaction of hen egg white lysozyme (HEWL) with Na- and Cs-exchanged saponite was investigated using sorption, structural, and spectroscopic methods as a model system to study clay protein interactions. HEWL sorption to Na- and Cs-saponite was determined using the bicinchoninic acid (BCA) assay, thermogravimetric analysis, and C and N analysis. For Na-saponite, the TGA and elemental analysis-derived sorption maximum was 600 mg/g corresponding to a surface coverage of 0.85 ng/mm(2) with HEWL occupying 526 m(2)/g based on a cross-sectional area of 13.5 nm(2)/molecule. HEWL sorption on Na-saponite was accompanied by the release of 9.5 Na+ ions for every molecule of HEWL sorbed consistent with an ion exchange mechanism between the positively charged HEWL (IEP 11) and the negatively charged saponite surface. The d-spacing of the HEWL Na-saponite complex increased to a value of 4.4 nm consistent with the crystallographic dimensions of HEWL of 3 x 3 x 4.5 nm. In the case of Cs-saponite, there was no evidence of interlayer sorption; however, sorption of HEWL to the "external" surface of Cs-saponite showed a high affinity isotherm. FTIR and Raman analysis of the amide I region of the HEWL saponite films prepared from water and D2O showed little perturbation to the secondary structure of the protein. The overall hydrophilic nature of the HEWL-Na-saponite complex was determined by water vapor sorption measurements. The clay retained its hydrophilic character with a water content of 18% at high humidity corresponding to 240 H2O molecules per molecule of HEWL.


Nanoscience and Nanotechnology