Mirror image forms of snow flea antifreeze protein prepared by total chemical synthesis have identical antifreeze activities

The recently discovered glycine-rich snow flea antifreeze protein (sfAFP) has no sequence homology with any known proteins. No experimental structure has been reported for this interesting protein molecule. Here we report the total chemical synthesis of the mirror image forms of sfAFP (i.e., L-sfAFP, the native protein, and D-sfAFP, the native protein's enantiomer). The predicted 81 amino acid residue polypeptide chain of sfAFP contains Cys residues at positions 1, 13, 28, and 43 and was prepared from four synthetic peptide segments by sequential native chemical ligation. After purification, the full-length synthetic polypeptide was folded at 4 degrees C to form the sfAFP protein containing two disulfides. Chemically synthesized sfAFP had the expected antifreeze activity in an ice recrystallization inhibition assay. Mirror image D-sfAFP protein was prepared by the same synthetic strategy, using peptide segments made from d-amino acids, and had an identical but opposite-sign CD spectrum. As expected, D-sfAFP displays the same antifreeze properties as L-sfAFP, because ice presents an achiral surface for sfAFP binding. Facile synthetic access to sfAFP will enable determination of its molecular structure and systematic elucidation of the molecular basis of the antifreeze properties of this unique protein.     

pH-programmable DNAzyme nanostructures

Two engineered DNA nanostructures consisting of a nucleic acid functional hairpin and a DNA "tweezers" assembly act as pH-switchable devices for the "ON-OFF" activation/deactivation of the horseradish-peroxidase-mimicking DNAzyme.     

Diblock copolymer nanostructures

Polystyrene-block-poly(2-cinnamoylethyl methacrylate) (PS-b-PCEMA) and poly(acrylic acid)-block-poly(2-cinnamoylethyl methacrylate) (PAA-b-PCEMA) were synthesized. These polymers formed micelles with PCEMA as the core in solvents poor for the PCEMA block but good for the other blocks. When the PS block was much longer than the PCEMA block, star micelles were prepared. The PCEMA cores of these micelles were then photo-crosslinked to yield PS star polymers. Nanospheres of PCEMA were obtained by photolyzing crew-cut micelles of PAA-b-PCEMA, in which the water-soluble PAA block was much shorter than the water-insoluble PCEMA block. PS-b-PCEMA self-assembled at silica and their THF/cyclopentane micellar solution interfaces to form diblock monolayers called polymer brushes, in which the insoluble PCEMA block spread like a melt on the silica surface and the chains of the soluble PS block stretched into the solution phase like bristles of a brush. By tuning the relative composition, PCEMA in bulk formed cylindrical micro-domains dispersed in the continuous PS matrix. Irradiation of the PS-b-PCEMA brushes enabled our preparation of crosslinked PS-b-PCEMA monolayers. Nanofibers were prepared by dissolving in THF the irradiated PS-b-PCEMA films with crosslinked cylindrical PCEMA micro-domains.     

Silica-metal core-shell nanostructures

Silica-metal nanostructures consisting of silica cores and metal nanoshells attract a lot of attention because of their unique properties and potential applications ranging from catalysis and biosensing to optical devices and medicine. The important feature of these nanostructures is the possibility of controlling their properties by the variation of their geometry, shell morphology and shell material. This review is devoted to silica-noble metal core-shell nanostructures; specifically, it outlines the main methods used for the preparation and surface modification of silica particles and presents the major strategies for the formation of metal nanoshells on the modified silica particles. A special emphasis is given to the St?ber method, which is relatively simple, effective and well verified for the synthesis of large and highly uniform silica particles (with diameters from 100 nm to a few microns). Next, the surface chemistry of these particles is discussed with a special focus on the attachment of specific organic groups such as aminopropyl or mercaptopropyl groups, which interact strongly with metal species. Finally, the synthesis, characterization and application of various silica-metal core-shell nanostructures are reviewed, especially in relation to the siliceous cores with gold or silver nanoshells. Nowadays, gold is most often used metal for the formation of nanoshells due to its beneficial properties for many applications. However, other metals such as silver, platinum, palladium, nickel and copper were also used for fabrication of core-shell nanostructures. Silica-metal nanostructures can be prepared using various methods, for instance, (i) growth of metal nanoshells on the siliceous cores with deposited metal nanoparticles, (ii) reduction of metal species accompanied by precipitation of metal nanoparticles on the modified silica cores, and (iii) formation of metal nanoshells under ultrasonic conditions. A special emphasis is given to the seed-mediated growth, where metal nanoshells are formed on the modified silica cores with deposited metal nanoparticles. This strategy assures a good control of the nanoshell thickness as well as its surface properties.     

Mirror image supramolecular helical tapes formed by the enantiomeric-depsipeptide derivatives of the amyloidogenic peptide amylin(20-29)

Factors that determine the chirality of supramolecular helical tapes formed by a backbone-modified amylin(20-29) depsipeptide and inverso-depsipeptide, were studied by Fourier transform infrared spectroscopy, circular dichroism and transmission electron microscopy. Although β-sheet propensity was absent in both peptides, it was found that the l-depsipeptide formed left-handed and the enantiomeric d-depsipeptide right-handed helical tapes. Moreover, the backbone-modified depsipeptides, showed a certain degree of cross-recognition between both enantiomers, which might have implications in designing amyloid formation inhibitors.     

Polyvalent nucleic acid nanostructures

Polyvalent oligonucleotide-nanoparticle conjugates possess several unique emergent properties, including enhanced cellular uptake, high antisense bioactivity, and nuclease resistance, which hypothetically originate from the dense packing and orientation of oligonucleotides on the surface of the nanoparticle. In this Communication, we describe a new class of polyvalent nucleic acid nanostructures (PNANs), which are comprised of only cross-linked and oriented nucleic acids. We demonstrate that these particles are capable of effecting high cellular uptake and gene regulation without the need of a cationic polymer co-carrier. The PNANs also exhibit cooperative binding behavior and nuclease resistance properties.     

Photonics of supramolecular nanostructures

The results of studying optical and photochemical properties of organic supramolecular nanostructures capable of self-organizing due to specific intermolecular interactions are generalized in the review. The linear and nonlnear optical properties of supramolecular nanostructures of the guest—host type based on cyclodextrins, intramolecular and intermolecular complexes of crown-containing styryl dyes with metal cations, and aggregates of carbocyanine dyes are described. Photolysis reactions in supramolecular nanostructures, including photoisomerization, photocycloaddition, and formation of excimeric and charge-transfer complexes are presented. A possibility of controlling photochemical transformations in these systems by the light and cations of metal salts is shown.     

DNA-programmed assembly of nanostructures

DNA is a unique material for nanotechnology since it is possible to use base sequences to encode instructions for assembly in a predetermined fashion at the nanometre scale. Synthetic oligonucleotides are readily obtained by automated synthesis and numerous techniques have been developed for conjugating DNA with other materials. The exact spatial positioning of materials is crucial for the future development of complex nanodevices and the emerging field of DNA-nanotechnology is now exploring DNA-programmed processes for the assembly of organic compounds, biomolecules, and inorganic materials.     

Self-assembly of magnetic nanostructures

We use Monte Carlo and quaternion molecular dynamics simulations to study the self-assembly of intriguing structures which form in colloidal suspensions of small magnetite particles. We show that the only stable isomers with few particles, a ring and a chain, can be efficiently interconverted using a magnetizable tip. We propose to use the oscillating dipole field of the tip to locally anneal the aggregates to either a ring in zero field or a chain in nonzero applied field.     

Towards chemical analysis of nanostructures in biofilms I: imaging of biological nanostructures

Due to their direct influence on the stability of bacterial biofilms, a better insight into the nanoscopic spatial arrangement of the different extracellular polymeric substances (EPS), e.g., polysaccharides and proteins, is important for the improvement of biocides and for process optimization in wastewater treatment and biofiltration. Here, the first application of a combination of confocal laser-scanning microscopy (CLSM) and atomic force microscopy (AFM) to the investigation of river-water biofilms and related biopolymers is presented. AFM images collected at selected areas of CLS micrographs dramatically demonstrate the heterogeneity of biofilms at the nanometer scale and the need for a chemical imaging method with nanoscale resolution. The nanostructures (e.g., pili, flagella, hydrocolloids, and EPS) found in the extracellular matrix are classified according to shape and size, which is typically 50–150 nm in width and 1–10 nm in thickness, and sets the demands regarding spatial resolution of a potential chemical imaging method. Additionally, thin layers of the polysaccharide alginate were investigated. We demonstrate that calcium alginate is a good model for the EPS architecture at the nanometer scale, because of its similar network-like structure. Figure CLSM-AFM allows imaging of nanometer-sized extracellular structures     

Olefin metathesis on nanostructures

Alkene metathesis processes on nanostructures can proceed via radial or lateral pathways. Radial metathesis installs new functionalities on the surface of a nanostructure through outward growth from its core. Lateral metathesis involves successive crosslinking of neighboring alkenes on the nanostructure and creates a polymer shell around the particle.     

Conjugated-carbon nanostructures: Emergences

General emergent features of conjugated-carbon nanostructures are sought. Here, “general” indicates applicability over a broad class of such structures, including graphene and buckytubes, possibly with boundaries or other sorts of defects or decorations, or rather general substructures of graphene or of buckytubes. In addition, “emergent” means that different characteristics and properties are novel and are evidenced from different models, for example, from resonance theory and Hückel theory, preferably with evidence that the features persist upon elaboration. One robust emergent feature is “Dirac cones” in the band structure of graphene and some related materials. Another interesting feature is novel “blended” boundary orbitals that are delocalized longitudinally along the boundary direction while being variably localized in the transverse direction. Furthermore, defects at the ends of polymer chains may be localized or delocalized depending on local features—although the ideas apply more widely to different conjugated-carbon structures including molecules. Explicit formulas are derived to elucidate the asymptotic behavior of unpaired electron density at the ends of selected benzenoid polymers and its relation to the associated HOMO-LUMO gap. Our approach offers a general framework to understand ab initio results, which may, at first sight, appear to be unconventional or counterintuitive to some common ideas of bonding patterns in conjugated carbon nanostructures.     

Bi-phasic nanostructures for functional applications

Biphasic solid state composites of the type metal/metal oxide or element/element oxide can be synthesized in one pot chemical reactions using so called molecular "single source precursors". Due to their singular genesis these composites show peculiar hetero-structures based on core-shell hierarchies such as superlattices and composite nanospheres or nanowires. They exhibit superior or new functional properties compared to their individual constituent compounds. In the current work, we review in particular the synthetical and mechanistical approach of bi-phasic (Al/Al(2)O(3)) nanostructures such as nanospheres, nanowires and nanoloops using a single source precursor. Other bi-phasic materials of the general formula M/MO(x) (for example M = Ge, Sn, Pb) are addressed for comparison. The impact of different synthetical conditions as well as of modification of surfaces by laser techniques and their technological relevance are presented briefly. Additionally, functional applications of the prepared surfaces are explained with some outstanding case studies. These case studies are primarily concerned with their use as biomaterials and their application in medicine as well as with their use as thin films for optics and functional surfaces.     

Cation-dependent switching of DNA nanostructures

DNA is a versatile building material for nanoconstruction because of its remarkable molecular-recognition capability and well-predicted duplex conformation. A number of DNA motifs have been engineered, which can assemble into well-defined nanostructures in Mg(2+)-containing buffer solution. XRD studies reveal that the DNA conformation is slightly influenced by divalent cations (such as Mg(2+) or Ca(2+)). This phenomenon can be utilized in DNA self-assembly for regulating self-assembled DNA nanostructures. As an initial step, a symmetric cross motif forms flat, periodic, 2D lattices in Mg(2+)-containing solutions, but long nanofibers in Ca(2+)-containing solutions. The obtained DNA fibers can serve as templates to fabricate CaCO(3) nanotubes and nanowires.     

Synthesis of fullerene@gold core-shell nanostructures

A "direct encapsulation" method was developed for the synthesis of highly stable water-soluble fullerene@gold core-shell nanostructures, with gold nanoshells showing either closed or porous morphology. This gold nano-shell coating formed a "nano-oven", capable of decomposing encapsulated fullerene molecules rapidly when irradiated by laser. We envisaged this being a useful tool for chemical reactions as well as a novel scaffold for nano-material synthesis.     

Amphiphilic nanostructures in foam films

The revised articles outline the potential of microscopic foam film instrumentation as an investigation tool in studying the amphiphilic nanostructures in aqueous surfactant solutions. The impact of amphiphilic nanostructures on the drainage behaviour and stability of foam films is traced for surfactant solutions of concentrations orders of magnitude above CMC (micellar solutions) to about two orders of magnitude lower than CMC (premicellar solutions). It is found that in the high-concentration domain the micellar entities affect mainly the stability of the films. In the low-concentration domain, the presence of smaller crumbly aggregates (premicelles), plays a significant role for the kinetic stability of the films. Through the mechanism of Marangoni effect, an enhanced coupling of the specific film hydrodynamics and the mass transfer of the surfactant is obtained. The result is a sharp rise in the kinetic stability of the foam films. The importance of this trend of research is related to providing better insight into the self-assembling phenomena and into the factors that determine the drainage and the stability of thin liquid films. The results have potential and actual applications in food, cosmetic and pharmaceutical industries, as well as in biology and medicine.