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A Model for Enhanced Nucleation of Protein Crystals on a Fractal Porous Substrate

S. Stolyarova ^*, E. Saridakis  , N. E. Chayen  and Y. Nemirovsky ^*

^* Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel; Biological Structure and Function Section, Division of Biomedical Sciences, Faculty of Medicine, Imperial College, London SW7 2AZ, United Kingdom; and Laboratory of Structural and Supramolecular Chemistry, Institute of Physical Chemistry, National Centre for Scientific Research ‘Demokritos’, Aghia Paraskevi, 15310 Athens, Greece

Correspondence: Address reprint requests to S. Stolyarova, Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel. Tel.: 972-4-8293797; Fax: 972-4-8235107; E-mail: ssstolya{at}tx.technion.ac.il.

The phenomenon of enhanced nucleation and crystallization of proteins on porous silicon (PS) is theoretically studied and explained. The PS layer is treated as a fractal structure, and a new mechanism of local supersaturation associated with the fractality is proposed. It is shown that the number of adsorbed molecules on a fragment with a fractal surface significantly exceeds that on one with flat surfaces. For a fractal PS surface, a local concentration of molecules that is sufficient for nucleation is possible inside and in the close vicinity of the pores, even when the average conditions in the bulk of the solution correspond to metastability. The wide distribution of fractal pore size is favorable for the crystallization of a wide range of macromolecules using the same sample. In addition, the PS technology is very flexible, allowing tailoring the pore size and concentration as well as the fractal properties to specific proteins by changing the fabrication conditions.