Density Functional Theory calculations and Molecular Dynamics Simulations of the Interaction of Bio-molecules with Hydro
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1131-Y01-06
Density Functional Theory calculations and Molecular Dynamics Simulations of the Interaction of Bio-molecules with Hydroxyapatite Surfaces in an Aqueous Environment Neyvis Almora-Barrios1 and Nora H. de Leeuw*1,2 1
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. 2 Institute of Orthopaedics and Musculoskeletal Science, University College London, Brockley Hill, Stanmore HA7 4LP, Middlesex, UK [email protected], [email protected]
ABSTRACT In view of the importance of the hydroxyapatite/collagen composite of both natural bone tissue and synthetic biomaterials for hard tissue replacement, we have employed a combination of electronic structure calculations based on the Density Functional Theory and molecular dynamics simulations to investigate the adsorption of three major collagen I amino acids, as well as a complete peptide strand, at two hydroxyapatite surfaces, both in vacuo and in a liquid water environment. The free amino acids as well as the peptide form multiple interactions with the surfaces and bind more strongly to the (01 1 0) surface than the (0001) surface, in agreement with experiment, which has found that in natural bone the (01 1 0) surface grows preferentially from a collagen matrix. INTRODUCTION Apatites Ca10(PO4)6(F,Cl,OH)2 are a complex and diverse class of materials, which are becoming increasingly important as candidates for use as bio-materials. In the geological environment, they are the most abundant phosphorus-bearing minerals, found extensively in igneous, metamorphic and sedimentary rocks [1]. More recently, hydroxyapatite (HA) has gained additional prominence owing to its biological rôle as one of the main constituents of mammalian bones and teeth [2]. Natural bone is a highly hierarchical collagen-mineral composite, containing nano-sized mineral platelets - essentially carbonated hydroxyapatite Ca10(PO4)6(OH)2 [3] - a protein matrix and water [4]. The protein in bone is predominantly type I collagen, the structure of which is complex, and which self-assembles in a multi-step process [5]. In summary, a triple helix is formed from three polypeptide chains with a highly repetitive amino acid sequence with glycine (NH2-CH2-COOH) in every third position [GLY-X-Y]n, where X and Y are commonly proline (NH-C4H7-COOH) and hydroxyproline (NH-C4H6(OH)-COOH), respectively. Experimental studies have demonstrated that the growth process of HA is controlled by the interaction between the organic matrix and the HA crystal [6-10], which determines the eventual morphology of the HA platelets in the bone. The apatite platelets are very thin indeed, typically 2-4 nm [4], and these crystals are arranged in an ordered fashion within and around the collagen strands to form mineralised collagen fibrils. The apatite mineral is aligned with its caxis, the [0001] direction, along the fibril, which makes the (01 1 0) surface one of the major planes that interact with the collagen functional groups. These mineralized fibrils are then 1
arranged in paralle
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