Silver nanoparticles (AgNPs) are becoming increasingly important for manifold applications in, for example, imaging, catalysis, electronics, and the development of antimicrobial coatings. [1][2][3] The formation of AgNPs is typically accomplished by chemical reduction or irradiation of Ag + ions with visible light in the presence of additives, such as polymers or surfactants, which induce the formation of AgNPs and stabilize the NPs. [1,2] Recently, peptides bearing functional groups that coordinate to Ag + ions have become popular as additives. [4][5][6][7][8] Their large structural and functional diversity also renders peptides attractive for the controlled formation of AgNPs of defined sizes, which still presents a challenge to date. Since the rational design of peptides that induce metal NP formation is difficult, combinatorial approaches are attractive for the identification of suitable peptides. [7,8] We envisaged that colorimetric on-bead screening of split-andmix libraries could be a particularly powerful tool that would allow the testing of diverse libraries, which contain both natural and unnatural amino acids. [9] The typical size-and shape-dependent coloration of AgNPs [1] was anticipated to allow for a facile identification of active library members.Herein, we introduce the use of combinatorial split-andmix libraries for the identification of peptides that are capable of inducing the formation of AgNPs. In conjunction with scanning electron microscopy (SEM) studies, we also demonstrate that the method allows for the identification of certain types of peptides that induce the formation of AgNPs of specific sizes.We started our investigations by testing the members of peptide library 1 for their ability to induce AgNP formation in the presence of either light or the chemical reducing agent sodium ascorbate (Figure 1 a). Within the library, the amino acids serine (Ser), aspartic acid (Asp), histidine (His), and tyrosine (Tyr), bearing functional groups that were envisaged for Ag + ion coordination, were employed in positions AA1 and AA2 (Figure 1). Tyr was included in the library as it is a well-known photoactive residue. [6] Linkers of varying flexibility and geometry were used to connect the amino acids in order to allow for diverse spatial arrangements of their sidechain functional groups. trans-2-Aminohexanoic acid (Achc), Pro-Aib (Aib = aminoisobutyric acid) and Pro-Gly were chosen as turn-inducing linkers, and 6-aminohexanoic acid (Ahx) and b-alanine as flexible linkers. The library was prepared by encoded [10] split-and-mix synthesis [11] on TentaGel resin by utilizing seven different linkers and seven different l-and d-amino acids in positions AA1 and AA2, hence the library consisted maximally of 7 3 = 343 different peptides (Figure 1 a). Amino acid couplings were performed by following the standard Fmoc/tBu protocol for peptide synthesis using HBTU/iPr 2 NEt as the coupling reagent and piperidine for Fmoc deprotections (Fmoc = 9-fluorenylmethyloxycarbonyl, HBTU = O-(benzotriazol-l-yl)-N,N,N'...

Split‐and‐mix‐Bibliotheken sind ein ausgezeichnetes Hilfsmittel zur Identifizierung von Peptiden, die die Bildung von Ag‐Nanopartikeln aus Ag+‐Ionen unter Bestrahlung oder in Gegenwart von Natriumascorbat als Reduktionsmittel vermitteln. In kolorimetrischen Screenings wurden strukturell unterschiedliche Peptide identifiziert, die die Bildung von unterschiedlich großen Ag‐Nanopartikeln induzieren, was durch SEM‐Studien und Röntgenpulverbeugungsexperimente bestätigt wurde.magnified image

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