1. Department of Bioengineering, Rice University, P.O. Box 1892, MS 142, Houston, Texas 77251-1892;
2. Department of Neurological Surgery, Case Western Reserve University, and The Research Institute, University Hospitals of Cleveland, 11100 Euclid Avenue, Cleveland, Ohio 44106-5012;
3. Department of Chemistry, Rice University, P.O. Box 1892, MS 60, Houston, Texas 77251-1892;
4. Department of Chemical Engineering, Rice University, P.O. Box 1892, MS 362, Houston, Texas 77251-1892;