Nonspecific binding of small molecules to proteins influences transdermal permeation and intestinal absorption, yet understanding of the molecular and thermodynamic basis is still limited. In this study, we report all-atom, fully solvated molecular dynamics simulations of the thermodynamic characteristics of epigallocatechin-3-gallate (EGCG) binding keratin. Experimental validation is reported in Part II. Herein, 18 mu s of simulation sampling was calculated. We show that the binding process is a combination of hydrophobic interaction, hydrogen bonding and aromatic interaction. The umbrella sampling technique was used to calculate the binding free energy of EGCG with keratin segments. By extracting EGCG from the keratin-EGCG complex using steered molecular dynamics, the rupture force was observed to be linearly related to the binding free energy. Multilayer binding of EGCG clusters to keratin has been shown. The binding free energy of -6.2 kcal mol(-1) obtained from the simulations was in excellent agreement with the experimental Part II. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 4816-4823, 2013