How to make a polypeptide chain \”snake walk \’?
From side to side to avoid attacks by snakeskin walk is an advanced operating skills DOTA and other competitive multiplayer online tactical game. You can be thought of this technique in addition gamers can grasp, the condensation formed by a plurality of amino acids of the polypeptide (peptide) chain can also show? Department of Chemistry, Virginia Tech John B. Matson TF and TF Liu Guoliang cooperation, reported in JACS polypeptide formed by nano tetrapeptides with a method of self-assembly nano-helix. To the polypeptide by introducing Ag nanoribbons system + , and polystyrene sulfonate sodium (PSSS) polypeptide can nanoribbons \”snake walk\”, forming nano-helix. Furthermore, by reducing the Ag + Preparation of helical polypeptide nano – silver metal complexes may be enhanced Raman scattering (SERS) substrate as a surface. 
First, the authors synthesized two of the same amino acid composition but a different arrangement order of the supramolecular polymer tetrapeptide isomers (KSC\’EKS and C\’EKSKS, FIGS. 1A and B). TEM shows two tetrapeptide showed nanoribbons morphology (Fig. 1C and D) in phosphate buffer. However, when AgNO3 was added to the buffer and PSSS, KSC\’EKS morphology from nanoribbons turned into nano-helix (FIG. 1E), while no change C\’EKSKS morphology (FIG. 1F). Polypeptide chain \”snake walk\” off the inorganic salt solution in water and the positive ions related to glutamate KSC\’EKS shield position and a carboxyl group in the chain of KS. AgNO3 was added and PSSS increases hydrophobic interaction between KSC\’EKS molecules, nano-helix formation induced, but not significantly change the C\’EKSKS force between molecules, so that the latter remains unchanged morphology.
Subsequently, the authors reduction of silver ions by sodium borohydride, found Ag nanoparticle attached to the polypeptide chain. This phenomenon indicates that Ag + does have adsorbed on the polypeptide chain. Ag nanoparticle growth in two steps: the first step having an average diameter of 2.8 nanometers, seed silver nanoparticles adhered to the polypeptide chain (Figure 2A and B). Step continue to introduce Ag + and a reducing agent to the system, before the step using the generated Ag particles having an average diameter as a growth nucleus of 7.6 nm silver nanoparticles (Fig. 2C and D). Transmission electron microscopy showed that the morphology C\’EKSKS nano strip remains unchanged before and after the growth of Ag, and the pitch of the helix KSC\’EKS nano widened. Further, Ag particles tends to be deposited in a recess KSC\’EKS helix (FIG. 2C inset), and C\’EKSKS nano Ag particles are mostly attached to the strip at the edge of the polypeptide, more random arrangement (FIG. 2D illustration).
growth of Ag nanoparticle position – affects the physical properties of metallic silver composite. The authors explored synthesized polypeptide – silver composite performance as SERS substrate. Rhodamine B red dye molecule to be detected. The results show (FIG. 3), attached KSC\’EKS Ag nano-particles exhibit significant helical Raman signal enhancement. C\’EKSKS adhered with Ag nano-particles is comparable with other silver-containing group SERS performance. Ag particles contain two polypeptides had no significant signal enhancement properties. The results show that spiral nano structure is the key to enhance performance SERS. Using 2,2\’-bipyridine having the same tendency as the SERS enhancement was detected. The authors speculated that excellent performance Ag- SERS nano composite coil position thanks to the growth of Ag particles: Ag particles spiral pits located at more stable than the polypeptide chain of Ag particles are located surface, and the spiral space is conducive to increased silver particles distribution density such that adjacent silver particles from the more recent, good reinforcing effect. Compared to other conventional SERS substrates, such as pure metal particles or a metal array of photolithography, the work reported in the present Ag- polypeptide substrate having a unique spatial arrangement of particles, easilyDissolved in water, better biocompatibility advantages.
Original: https: //pubs.acs.org/doi/pdf/10.1021/jacs.0c03672
