Affiliation: | a Department of Chemistry, Texas A&M University, Spence and Ross Streets, P.O. Box 300012, College Station, TX 77843-3255, USA b Department of Biochemistry and Biophysics, Texas A&M University, P.O. Box 300012, College Station, TX 77843-3255, USA c Department of Mathematics, University of Houston, Houston, TX 77204-3008, USA |