Protein structures evolved through a complex interplay of cooperative interactions and it is still very challenging to design new protein folds de novo. Here, we present a strategy to design self-assembling polypeptide nanostructured polyhedra, based on modularization using orthogonal dimerizing segments. We designed end experimentally demonstrated formation of the tetrahedron that self-assembles from a single polypeptide chain comprising 12 concatenated coiled-coil-forming segments separated by flexible peptide hinges. Path of the polypeptide chain is guided by the defined order of segments that traverse each of the 6 edges of the tetrahedron exactly twice, forming coiled-coil dimers with their corresponding partners. Coincidence of the polypeptide termini in the same vertex is demonstrated by reconstitution of the split fluorescent protein by the polypeptide with the correct tetrahedral topology, while polypeptides with a deleted or scrambled segment order fail to self-assemble correctly. This design platform provides the basis for construction of new topological polypeptide folds based on the set of orthogonal interacting polypeptide segments.

We report on a new highly reproducible route to recognitive self-assembly of molecular-scale circuits using sulfur-terminated subnanometer diameter Mo6S9-xIx (MoSIx) molecular nanowires. We demonstrate solution-processed attachment of MoSIx connecting leads to gold nanoparticles (GNPs). We also show that naked nanowires have the potential to bind thiolated proteins such as green fluorescent protein directly, thus providing a universal construct to which almost any protein could be attached. We further demonstrate three-terminal branched circuits with GNPs, opening a self-assembly route to multiscale complex molecular-scale architectures at the single-molecule level.

No abstract

Sedimentation measurements have been performed on dispersions of Mo 6 S 3 I 6 nanowires in a range of common solvents. By far the best solvents were N , N-dimethylformamide ͑DMF͒ and acetone. Stable dispersions of purified Mo 6 S 3 I 6 nanowires in DMF, with concentrations as high as 0.06 g l −1 , could be produced. Detailed analysis of the sedimentation curves showed that the material consisted of three phases, two insoluble phases and one which could be stably dispersed. We associate the insoluble phases with pseudospherical impurities and insoluble nanowires. The sedimenting nanowires tend to be in the form of large diameter bundles, in contrast to the dispersed phase which consists of nanowires arranged in smaller bundles. The average diameters of the nanowire bundles stably suspended in DMF are 12± 14 nm. The measured sedimentation time constants of the insoluble nanowires agree very well with theory allowing us to calculate the solid-fluid interaction parameter, ␤, to be very close to 10 5 Pa. The material could be purified by controlled sedimentation hence the identification of the various phases was confirmed by x-ray photoelectron spectroscopy and scanning electron microscopy.

Flat panel display technology seems to be an ever-expanding fi eld developing into a multibillion dollar market. A set of technical solutions involve a transparent conducting fi lm (TCF) that is today still dominated by indiumtinoxide (ITO). In a race to fi nd alternatives that would avoid the indium pitfalls, mainly due to its increasing price and limited natural availablity, replacement materials have been extensively investigated. This work demonstrates that by exploiting basic principles of crystal growth in geometrically constrained conditions, zinc oxide (ZnO) could easily be utilized for this purpose. ZnO layers were grown on inexpensive glass substrates via lowtemperature citrateassisted hydrothermal (HT) method. It was shown that in the nucleation stage the crystal growth can be effi ciently controlled by spatially confi ned oriented growth (SCOG) mechanism to produce smooth and dense (0001) oriented polycrystalline ZnO fi lms with superb optical properties. Our products show optical transparency of 82% and surprisingly low sheet resistance for undoped ZnO, only in the order of few 100 Ω sq − 1 . We believe that a very high degree of selforganization between the ZnO crystals in our polycrystalline fi lms grown under controlled SCOG conditions is main reason for the highest so far reported transparency to conductivity ratio for undoped ZnO thin fi lm ceramics.conductivity which meet the high standards for many photonic and/or electronic applications.