REGULAR ARTICLE Adsorption of catechol on a wet silica surface: density functional theory study Shabeer Ahmad Mian • Xingfa Gao • Shigeru Nagase • Joonkyung Jang Received: 19 February 2011 / Accepted: 18 June 2011 / Published online: 30 June 2011 Ó Springer-Verlag 2011 Abstract Marine mussel proteins adhere permanently to diverse wet surfaces via their catechol (1, 2-dihydroxy- benzene) functionality. To elucidate the molecular mech- anism underlying this water-resistant adhesion, we performed density functional theory calculations for the competitive adsorption of catechol and water on a wet silica surface. Results show the energetic spontaneity of the reaction; catechol displaces water molecules and adheres directly to the surface. This result was subsequently cor- roborated by our molecular dynamics simulation. Keywords Mussel adhesion  Catechol  Silica  Water  Density functional theory 1 Introduction An adhesive that is capable of sticking to wet surfaces has numerous potential applications including surgical tissue adhesives, dental cement, ship building, and underwater construction [1]. The synthesis of a moisture-resistant adhesive is elusive because of the water layers blocking direct contact with the surface. However, marine mussels naturally overcome this obstruction and adhere to virtually any wet surface, even under saline and tidal conditions [2–4]. This fact has triggered extensive efforts to elucidate the mussel adhesion mechanism. Mussel adhesive proteins (MAPs) are known to have an unusually high content of 3,4-dihydroxy-L-phenylalanine (L-DOPA) [5–7]. The con- sensus view is that the catechol functionalities (1, 2-dihy- droxybenzene) of L-DOPA anchor MAPs on the surface to which they adhere to [8, 9]. The oxidized catechol (quinone) is responsible for the subsequent cross-linking of MAPs (curing) necessary to form a matrix of adhesion [10, 11]. It remains unclear how catechol displaces the pre- adsorbed water molecules and establishes firm adhesion, especially onto a hydrophilic surface that has strong affinity for water. We recently calculated the binding energy of catechol on an amorphous silica using density functional theory (DFT) [12]. Catechol adhered to the silica more strongly than water. The versatility of catechol adhesion is attributable to the torsion of its hydroxyls (OHs); the OHs and the phenylene ring of catechol, respectively, contributed to adhesion via hydrogen (H) bonds and dispersion interactions. The displacement of the pre-adsorbed water molecules by catechol was not studied in our previous work. A geometry optimization showed that the binding of catechol to the silica surface remains intact after adding water molecules around the Dedicated to Professor Shigeru Nagase on the occasion of his 65th birthday and published as part of the Nagase Festschrift Issue. Electronic supplementary material The online version of this article (doi:10.1007/s00214-011-0982-0) contains supplementary material, which is available to authorized users. S. A. Mian  J. Jang (&) Department of Nanomaterials Engineering, Pusan National University, Miryang 627-706, Republic of Korea e-mail: jkjang@pusan.ac.kr X. Gao Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, USA S. Nagase Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan 123 Theor Chem Acc (2011) 130:333–339 DOI 10.1007/s00214-011-0982-0