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“Background At the forefront of many lines of research in drug delivery are the endless possibilities of gold nanoparticles (AuNPs) [1–4]. These molecules are selleck kinase inhibitor readily taken up by cells, and they therefore provide a valuable means for drug delivery, with reports of efficient transport across the blood–brain barrier in mice [5] and nuclear penetration in the human HeLa cell line [6]. At nanoscale, the properties conferred upon such an otherwise inert metal in its bulk form are surprising. It is precisely these unique properties that offer potential KPT-8602 mouse in fields as diverse as diagnostics, anti-cancer therapies, catalysts and fuel cells. One avenue that has been

studied exhaustively in recent years is the use of coatings and capping agents in the rational design of NPs, both to stabilise and functionalise these nanoparticles. Specific capping agents can lead to the self-assembly of NPs into ordered ‘superstructures’ creating different shapes [7], and by altering the capping structure, different arrangements can be achieved. In terms of biocompatibility, when using a polyvinyl alcohol capping agent, AuNPs do not show toxicity in zebrafish, despite being taken up into embryos and evidence of bioaccumulation [8]. These observations highlight INK1197 mouse the

use of capping agents as an approach to achieve safer NPs. We recently proposed the use of peptide-biphenyl hybrid (PBH) ligands as capping agents [9]. PBHs have a biphenyl system and two amino acid/peptide fragments, and they present key characteristics, such as dynamic

properties in solution [10], ordered structures in the solid phase [11] and biological activity as calpain inhibitors [12]. Some of these properties arise from the presence of amino acid residues, as well as aromatic rings, that are able to participate in a variety of non-covalent bonds, including hydrogen bonds [13, 14] and arene interactions [15, 16]. In addition, the conformational flexibility around the aryl-aryl single bond allows the PBH to adopt its structure in order to obtain the most favourable interactions with other chemical Tryptophan synthase species, thus achieving high biological activity [17]. In peptidomimetics, this approach is considered a novel way to tailor NPs to have desired physico-chemical properties, which could contribute, for example, to advances in biomedical applications for AuNPs as drug delivery systems. A molecule can be designed in such a way as to benefit from structure-activity relationships and to attain higher levels of stability and/or biocompatibility. In a study on the design of peptide capping ligands for AuNPs, Lévy et al. [18] reported that peptide chain length, hydrophobicity and charge strongly influence NP stability. Here, we capped AuNPs with various PBH ligands and studied how the ligand structures influence the stability and the physico-chemical properties of the AuNPs under cell culture conditions and how they affect the biological response.