Lysine-Capped Silica Nanoparticles: A Solid-State NMR Spectroscopy Study
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Lysine-Capped Silica Nanoparticles: A Solid-State NMR Spectroscopy Study Chengchen Guo1, Gregory P. Holland2, Jeffery L. Yarger1 1
School of Molecular Sciences, Magnetic Resonance Research Center, Arizona State University, Tempe, Arizona, 85287-1604, USA Department of Chemistry and Biochemistry, San Diego State University, San Diego, California, 92182-1030, United States
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ABSTRACT To achieve the goal of biocompatibility in nano-based materials we must first obtain a fundamental understanding of the physical and chemical behavior of biomolecules at the interfaces of nanomaterials. A first step towards understanding protein interactions with nanomaterials is to understand how individual amino acids interact at the interfaces. In this paper, we investigated the lysine adsorption behavior on fumed silica nanoparticles by solid-state NMR spectroscopy. We use 1H, 13C and 15N solid-state magic angle spinning (MAS) NMR techniques to elucidate how lysine is adsorbed on silica nanoparticles surfaces via strong hydrogen-bonding interaction between the protonated side-chain amine group and silanol group on silica nanoparticles surfaces.* INTRODUCTION Silica nanoparticles (SiO2 NPs) are one of the most common biocompatible inorganic oxide nanomaterials with wide applications ranging from structural materials to catalysis and as a medium for drug delivery.1-4 Due to their wide application in biological systems, a fundamental understanding of the physical and chemical behavior of biomolecules at SiO2 NP interfaces is necessary.5-7 Among all the biomolecule-SiO2 NP systems, the amino acid-SiO2 NP system is the simplest and most practical system and constitutes the first step in understanding more complicated bioinorganic systems such as peptide-SiO2 NP and protein-SiO2 NP systems. NMR spectroscopy is an atomic/molecular level characterization technique providing details about the chemical environments of atoms and molecules in solution and in the solid state. This feature makes NMR spectroscopy a premiere technique for investigating ultra-small systems including nanoscale systems with high chemical and spatial resolutions.8-10 There have been several solid-state NMR methods and techniques developed and applied to studying the interaction between amino acids and silica surfaces.11-18 In the present work, the adsorption behavior of lysine on silica nanoparticles is investigated by solid-state NMR spectroscopy. Lysine (Lys) was chosen in this study because of its unique structure, where there is only a single side-chain amine group. It is this side-chain amine group that makes lysine the simplest basic amino acid compared with the other two basic amino acids, arginine and histidine. Because of this, lysine has been used in synthesizing a range of nanomaterials.19,20 Recently, Yokoi et al.20 illustrated that lysine is a good ligand in synthesizing ultrasmall silica nanoparticles (
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