Simulation of the interface between titanium oxide and amino acids in solution by first principles MD Walter Langel * , Lars Menken 1 Institut f€ ur Chemie und Biochemie, Universit€ at Greifswald, Soldmannstrasse 23, Greifswald D-17489, Germany Received 15 January 2003; accepted for publication 22 April 2003 Abstract Theadsorptionofglycine,methionine,serine,andcysteineonpartiallyhydroxylatedrutile(100)and(110)surfaces wassimulatedbyfirstprinciplesmoleculardynamics.Perfectsurfacesandwellknowndefectssuchasoxygenvacancies and facets were modelled. In most runs the simulation cell was filled with H 2 O molecules up to standard density. BindingofthecarboxylgroupstothesurfacethroughhydrogenbondsandTi–Ointeractionisweakinallcases.The adsorbate–substrate interactions do not seem to be significantly stronger than adsorbate–adsorbate hydrogen bonds. TheNH þ 3 -groupofthezwitterionshowedonlyweakinteractionwiththesurfaceoxygenatomsandrotatedaroundits figure axis. More stable configurations are attained by ester condensation of the carboxyl group and a basic surface hydroxyl group and by the formation of a bond between a deprotonated hydroxyl or thiol group of serine or cysteine, respec- tively, and a surface Ti. Calculations suggest that these groups bind to the perfect surface rather than inserting into oxygen vacancies. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Titanium oxide; Biological molecules – proteins; Ab initio quantum chemical methods and calculations; Molecular dynamics; Models of surface chemical reactions 1. Introduction Favourable mechanic properties make titanium a widely used material for medical implants. It is one of the least toxic metals, and is accepted by livingtissue,butcellgrowtharoundtheimplanted metalisverysensitivetoitssurfacestructure[1].In biological system titanium is passivated by a thin oxide layer, which is in contact with an aqueous solutionorwithwatervapourinair.Anyexposure to H 2 O leads to at least partial hydroxylation, whereas complete dehydroxylation affords clean- ing procedures at very high temperatures in UHV systems [2]. Biological cells are often immobilized by at- taching them to peptides with special amino acid sequences such as RGDS [3,4]. Connecting pep- tides to an oxide surface is not straightforward, * Corresponding author. Tel./fax: +49-3834-86-4423. E-mail address: langel@uni-greifswald.de (W. Langel). URL: http://www.chemie.uni-greifswald.de/~plasma. 1 Present address: Department of Chemical Engineering, University College London, London, UK. 0039-6028/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0039-6028(03)00723-4 Surface Science 538 (2003) 1–9 www.elsevier.com/locate/susc