DOI: 10.1021/la901448a A Langmuir XXXX, XXX(XX), XXX–XXX pubs.acs.org/Langmuir © XXXX American Chemical Society Structure and Catalytic Behavior of Myoglobin Adsorbed onto Nanosized Hydrotalcites Francesca Bellezza, Antonio Cipiciani,* Loredana Latterini, Tamara Posati, and Paola Sassi Dipartimento di Chimica, Universit  a di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy, and “Centro di Eccellenza Materiali Innovativi Nanostrutturati” (CEMIN), Universit  a di Perugia, via Elce di Sotto 10, 06123 Perugia, Italy Received April 23, 2009. Revised Manuscript Received June 24, 2009 The adsorption of myoglobin (Mb) onto nanosized nickel aluminum hydrotalcite (NiAl-HTlc) surface was studied, and the structural properties of the resulting protein layer were analyzed by using FT-IR, Raman, and fluorescence spectroscopies. Upon adsorption onto the nanoparticle surface, the protein molecules maintained their secondary structure, while the tertiary structure was altered. The fluorescence spectra and anisotropy values of adsorbed Mb revealed that the emitting amino acid residues are affected by different microenvironments when compared to the native protein behavior. Moreover, the decrease of fluorescence decay times of tryptophan indicated the occurrence of interactions among the fluorophores and the constituents of the nanoparticles, such as the metal cations, which can take place when conformational changes of Mb occur. Raman spectra indicated that the interaction of Mb molecules with NiAl-HTlc nanoparticles modified the porphyrin core, changing the spin state of the heme iron from high spin (HS) to low spin (LS). The enzymatic activity of the nanostructured biocomposite was evaluated in the oxidation of 2-methoxyphenol by hydrogen peroxide and discussed on the basis of structural properties of adsorbed myoglobin. Introduction During the last few decades, the interfacial behavior and the adsorption of biomacromolecule such as proteins on solid inorganic surfaces have attracted much attention. 1 The adsorp- tion of a protein onto a nonbiological solid surface is an impor- tant phenomenon not only from a fundamental point of view but also because it is the key to several important applications such as artificial implants, protein-purification strategies, biosensors, drug delivery systems, catalysts, and catalyst supports. 2 Protein adsorption is a complex process involving many events such as conformational changes, hydrogen bonding, and/or hydrophobic and electrostatic interactions. Although surface- protein interactions are not well understood, surface chemistry has been shown to play a fundamental role in protein adsorption. 3,4 Proteins adsorb in different quantities, conformations, and orientations, depending on the chemical and physical characteri- stics of both protein and support surfaces. In the biomaterials field, much research has been devoted to methods that modify the size and textural surface of existing materials in order to achieve more desirable biological integration. 5 The exposure of a solid surface to biological fluids normally leads to the adsorption of proteins, and the adsorbed protein layer can further mediate additional responses, such as cell attachment and activation, and can create unpredicted perturbations to device operations. 6 Studies on both natural and synthetic clay minerals including hydrotalcite-like compounds (HTlc’s) have been extensively carried out because of their low toxicity, good biocompatibility, and possible use in pharmaceutical, cosmetic, and biomedical applications. 7,8 HTlc’s are layered solids with positively charged layers and interlayered charge balancing anions. Their structure is similar to that of brucite, the naturally occurring Mg(OH) 2 , in which the Mg atoms are octahedrically coordinated by six OH groups; each OH group is shared by three octahedral cations and points to the interlayer space. The general formula of synthetic HTlc is [M(II) 1-x M(III) x (OH) 2 ] x+ [A n- x/n ] x- 3 mH 2 0, where M(II) is a divalent cation (Mg, Zn, Ni,..), M(III) is a trivalent metal cation (Al, Fe, Cr,...), A n- is an anion of charge n, and m is the molar amount of cointercalated water. 9 HTlc’s are widely applicable not only to build various supra- molecular structures and heterogeneous hybrid systems but also to stabilize and protect biomolecules (DNA, enzymes, oligo- nucleotides, etc.), and to develop drug delivery systems. 10 Although HTlc’s present structures and intercalation properties similar to cationic clays, these materials have been scarcely exploited for the adsorption of biological macromolecules such as proteins and enzymes at the solid-liquid interface. For this reason, a more in-depth knowledge of the properties of protein adsorption of HTlc could be useful to improve their biocompatibility. Many researchers have indicated that an important factor in determining the biological response of solid materials is the *Corresponding author. Tel: 075/5855540. Fax: 075/5855560. E-mail: cipan@unipg.it. (1) Gray, J. J. Curr. Opin. Struct. Biol. 2004, 14, 110. (2) (a) He, L.; Dexter, A. F.; Middelberg, A. P. J. Chem. Eng. Sci. 2006, 61, 989. (b) Sels, B. F.; De Vos, D. E.; Jacobs, P. A. Catal. Rev.;Sci. Eng. 2001, 43, 443. (c) Martinez Martinez, V.; De Cremer, G.; Roeffaers, M B. J.; Sliwa, M.; Baruah, M.; De Vos, D. E.; Hofkens, J.; Sels, B. F. J. Am. Chem. Soc. 2008, 130, 13192. (3) (a) Bellezza, F.; Cipiciani, A.; Costantino, U.; Negozio, M. E. Langmuir 2002, 18, 8737. (b) Bellezza, F.; Cipiciani, A.; Costantino, U.; Marmottini, F. Langmuir 2006, 22, 5064. (4) (a) Nath, N.; Hyun, J.; Ma, H.; Chilkoti, A. Surf. Sci. 2004, 570, 98. (b) Roach, P.; Farrar, D.; Perry, C. C. J. Am. Chem. Soc. 2005, 127, 8168. (5) Caruso, F. Adv. Mater. 2001, 13, 11. (6) Bajpai, A. Polym. Int. 2005, 54, 304. (7) Choy, J. H.; Choi, S. J.; Oh, J. M.; Park, T. Appl. Clay Sci. 2007, 36, 122. (8) Costantino, U.; Ambrogi, V.; Nocchetti, M.; Perioli, L. Microporous Mesoporous Mater. 2008, 107, 149. (9) Rives, V. Layered Double Hydroxides: Present and Future; Nova Science Publishers: New York, 2001. (10) Kwak, S. Y.; Jeong, Y. J.; Park, J. S.; Choy, J. H. Solid State Sci. 2002, 151, 229. Downloaded by CIBER CONSORTIA ITALY on July 16, 2009 Published on July 13, 2009 on http://pubs.acs.org | doi: 10.1021/la901448a