Synthesis of DNA triangles with vertexes of bis(terpyridine)iron(II) complexes

The synthesis of the terpyridine derivative 1 tethered to a DNA oligonucleotide and its use for the preparation of two-way branched metal-organic modules capable of self-assembling into DNA triangles are described.     

Controlled self-assembly of amphiphilic oligopeptides into shape-specific nanoarchitectures

Here, we report a novel, programmable, molecular self-assembling system to fabricate shape-specific, three-dimensional nanoarchitectures. Three types of simple 16-mer peptides consisting of hydrophobic Leu and hydrophilic Lys, LKL16, KLK16, and LK16, were prepared as building blocks for nanofabrications. A detailed analysis of the conformation and self-assembling mechanism was performed by using circular dichroism (CD), FTIR spectroscopy, and atomic force microscopy (AFM). A wide variety of self-assembled nanoarchitectures, such as beta-sheet-plates, beta-sheet-fibers, alpha-helix-particles, and alpha-helix-plates, could be fabricated by tuning the peptide sequence, reaction time, and solution pH. The ability to control the self-assembled nanostructures should provide a simple and/or essential insight into the mechanism of peptide aggregation, including amyloid formation, and it should be useful for the design of novel bio-related nanomaterials.     

Helical rosette nanotubes with tunable stability and hierarchy

The design of nanostructured materials with tunable dimensions and properties that maintain their structural integrity under physiological conditions is a major challenge in biomedical engineering and nanomedicine. Helical rosette nanotubes (HRN) are a new class of materials produced through a hierarchical self-assembly process of low molecular weight synthetic organic modules in water. Here, we describe a synthetic strategy to tune their stability and hierarchy by preorganization of the self-assembling units, control of net charge per unit of nanotube surface area, amphiphilicity, and number of H-bonds per self-assembling module, and through peripheral steric (de)compression. Using these criteria, HRNs with tunable stability and hierarchical architecture were produced from self-assembling modules that (a) persist as individual molecules in solution, (b) self-assemble into HRN but denature at high temperature (<85 degrees C), (c) self-assemble into HRN whose structural integrity persists even in boiling water (>95 degrees C), and (d) self-assemble into well-dispersed short nanotubes, long nanotubes, ribbons, or superhelices. Given the biocompatibility, synthetic accessibility, and chemical and physical tunability of these materials, numerous applications in biomedical engineering, materials science, and nanoscience and technology are envisioned.     

Dynamic decomposition/recombination of hydrogen bonds in molecular duplex strands

Dynamic decomposition/recombination of hydrogen bonds in the hydrazide based molecular duplex strands was explored by variable-temperature 1H NMR experiments. A shuttle-like dynamic process of the two constituent molecules of the duplex strands between two degenerate states was observed.     

Design and Synthesis of a Highly Stable Six-hydrogen-bonded Self-assembly Yellowish Green Electroluminescent Molecular Duplex

Since the first fabrication of thin-layer organic electroluminescent(OEL)device in1987by C.W.Tang et al1.,OEL materials had been of ever increasing interest2,3.While up to now,full-color display has been commercialized with small molecules having different structures.In general,host-dopant systems are often employed in RGB OLEDs.This procedure,however,would lead to relatively poor performance for OEL devices,because of the easy aggregation and crystallization of the dopants,which would…     

Doubly N‐Confused [36]Octaphyrin(1.1.1.1.1.1.1.1): Isomerization,Bis‐Metal Coordination,and Topological Chirality

A novel [36]octaphyrin analogue embedding two N‐confused pyrrole units demonstrated unique prototropy‐coupled isomerization between the Figure‐of‐eight and dumbbell conformers. Upon bis‐metal coordination, fixation of fully π‐conjugated Figure‐of‐eight structures was achieved as referred from the X‐ray crystal structure. Chirogenesis of the helical enantiomers was proved by intense circular dichroism (CD) response in the near infrared (NIR) region.     

DNA-programmed modular assembly of cyclic and linear nanoarrays for the synthesis of two-dimensional conducting polymers

Nanometer-scale arrays of conducting polymers were prepared on scaffolds of self-assembling DNA modules. A series of DNA oligomers was prepared, each containing six 2,5-bis(2-thienyl)pyrrole (SNS) monomer units linked covalently to N4 atoms of alternating cytosines placed between leading and trailing 12-nucleobase recognition sequences. These DNA modules were encoded so the recognition sequences would uniquely associate through Watson-Crick assembly to form closed-cycle or linear arrays of aligned SNS monomers. The melting behavior and electrophoretic migration of these assemblies showed cooperative formation of multicomponent arrays containing two to five DNA modules (i.e., 12-30 SNS monomers). The treatment of these arrays with horseradish peroxidase and H(2)O(2) resulted in oxidative polymerization of the SNS monomers with concomitant ligation of the DNA modules. The resulting cyclic and linear arrays exhibited chemical and optical properties typical of conducting thiophene-like polymers, with a red-end absorption beyond 1250 nm. AFM images of the cyclic array containing 18 SNS units revealed highly regular 10 nm diameter objects.     

Novel heteroaromatic-based multi-branched dyes with enhanced two-photon absorption activity

The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 x 10(-50) cm4 s photon(-1) molecule(-1), measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.     

Modification of fluorophore photophysics through peptide-driven self-assembly

We describe the formation of self-assembling nanoscale fibrillar aggregates from a hybrid system comprising a short polypeptide conjugated to the fluorophore fluorene. The fibrils are typically unbranched, approximately 7 nm in diameter, and many microns in length. A range of techniques are used to demonstrate that the spectroscopic nature of the fluorophore is significantly altered in the fibrillar environment. Time-resolved fluorescence spectroscopy reveals changes in the guest fluorophore, consistent with energy migration and excimer formation within the fibrils. We thus demonstrate the use of self-assembling peptides to drive the assembly of a guest moiety, in which novel characteristics are observed as a consequence. We suggest that this method could be used to drive the assembly of a wide range of guests, offering the development of a variety of useful, smart nanomaterials that are able to self-assemble in a controllable and robust fashion.     

Doubly N‐Confused [36]Octaphyrin(1.1.1.1.1.1.1.1): Isomerization,Bis‐Metal Coordination,and Topological Chirality

A novel [36]octaphyrin analogue embedding two N‐confused pyrrole units demonstrated unique prototropy‐coupled isomerization between the Figure‐of‐eight and dumbbell conformers. Upon bis‐metal coordination, fixation of fully π‐conjugated Figure‐of‐eight structures was achieved as referred from the X‐ray crystal structure. Chirogenesis of the helical enantiomers was proved by intense circular dichroism (CD) response in the near infrared (NIR) region.     

Recent advances in photoresponsive supramolecular self-assemblies

Construction of supramolecular self-assemblies whose self-assembling process and self-assembled architectures can be controlled by external stimuli is a fascinating and challenging topic for supramolecular chemists. The modification of photochromic molecules with noncovalent interaction sites or the incorporation of photochromic molecules into self-assembling modules makes light an ideal external input, providing high-performance photoresponsive multicomponent self-assemblies. Among such systems, in this tutorial review we deal with several photoresponsive supramolecular self-assemblies showing a unique mechanism and/or type of photoresponse. These examples illustrate that we would be able to produce further new photoresponsive molecular ensembles if one can elaborately hybridize photochromic molecules to specifically-designed supramolecular self-assemblies. We believe that the accumulation of insight into the construction principle, mechanism and concept of such smart supramolecular self-assemblies should realize practical smart functional materials.     

In vitro corrosion resistance and cytocompatibility of minerals substituted apatite/biopolymers duplex coatings on anodized Ti for orthopedic implant applications

In this work, strategies for the formation of duplex coatings with enhanced bioactivity, mechanical properties and corrosion resistance have been focused. TiO₂ arrays were fabricated on Ti alloy were carried out in a single step using suitable electrolyte by anodization method. Here, we have synthesized a novel bioactive material, minerals incorporated Hydroxyapatite (La/Tb-HAP)-chitosan-casein duplex coatings on anodized Ti via electrodeposition method. The fabricated novel composite coatings were characterized by FT-IR, XRD, FESEM and EDAX analyses. Also, the mechanical properties of duplex coatings were scrutinized by Dermitron thickness and microhardness tester. The corrosion resistance of the as-developed duplex coatings was studied by electrochemical techniques using Ringers solution as the electrolyte. In addition, the antibacterial activity, cell viability, live and dead staining were executed to substantiate the biocompatibility of TNT/CS-CA@M-HAP duplex coatings. From the overall summary of this work, it is proved that the resultant CS-CA@M-HAP coatings on TNT exhibit excellent bioactivity and improved corrosion resistance over pure Ti and serve as a potential candidate for orthopedic applications.     

Influence of small rings on the thermodynamics of equilibrium self-assembly

The competition between the formation of linear chain clusters and ring structures in an equilibrium self-assembling system is reexamined by developing a new Flory-Huggins type theory that combines an estimate for the loss of configurational entropy ΔS(ring) upon ring formation with the standard treatment of the free energy of a polydisperse solution of linear chains. The excess entropy of ring formation ΔS(ring) is obtained from an analytical fit to exact enumeration data for self-avoiding chains and rings with 30 or fewer steps on a cubic lattice. Illustrative calculations of the spinodal curves and the extent and the average degree of self-assembly highlight the physical conditions for which the cyclic structures impact the thermodynamic characterization of equilibrium self-assembling systems.     

A genetic toolbox for creating reversible Ca2+-sensitive materials

A major goal of polymer science is to develop "smart" materials that sense specific chemical signals in complex environments and respond with predictable changes in their mechanical properties. Here, we describe a genetic toolbox of natural and engineered protein modules that can be rationally combined in manifold ways to create reversible self-assembling materials that vary in their composition, architecture, and mechanical properties. Using this toolbox, we produced several materials that reversibly self-assemble in the presence of Ca2+ and characterized these materials using particle-tracking microrheology. The properties of these materials could be predicted from the dilute solution behavior of their component modules, suggesting that this toolbox may be generally useful for creating new stimuli-sensitive materials.     

Fluorescence and electrochemical detection of pyrimidine/purine transversion by a ferrocenyl aminonaphthyridine derivative

A novel hydrogen bond-forming ligand for pyrimidine/purine transversion, which contains both a fluorescent naphthyridine moiety and a ferrocenyl group as an electrochemical indicator, is described. Hydrogen bond-mediated recognition for a target nucleobase at an abasic site in a DNA duplex is confirmed by both fluorescence and electrochemical measurements. The analysis by fluorescence titration reveals that the ligand shows significant fluorescent quenching upon formation of a 1 : 1 complex with the target nucleobase opposite the abasic site, and the selectivity is in the order of cytosine > thymine > adenine, guanine, reflecting the stability of the hydrogen bond formation.     

Detection of a single DNA base-pair mismatch using an anthracene-tagged fluorescent probe

A novel anthracene-tagged oligonucleotide can discriminate between a fully-matched DNA target sequence and one with a single mismatching base-pair through a remarkable difference in fluorescence emission intensity upon duplex formation.     

FORMATION OF FLOWER-LIKE AGGREGATES FROM SELF-ASSEMBLING OF MICELLES WITH PEO SHELLS AND CROSS-LINKED POLYACRYLAMIDE CORES

Amphiphilic block copolymers,poly(ethylene oxide)-b-poly(N-acryloxysuccinimide) (PEO-b-PNAS) with various molecular weights have been successfully synthesized by atom transfer radical polymerization (ATRP) of NAS using functionalized PEO (PEO-Br) as ATRP macroinitiator.The self-assembling of the block copolymers in water,which is a good solvent for PEO and a non-solvent for PNAS.yielded spherical core-shell micelles with PNAS as core and PEO as shell.The cross-linked reaction of oxysuccinimide in PNAS ch...     

Versatile and self-assembling urea-linked neosaccharides from sugar aminoalcohols

The increasing interest in urea compounds as self-assembling molecules, ion transporters and organocatalysts prompted several efforts towards synthetic urea-linked glycomimetics. In this frame we studied in details a novel two steps dimerization reaction of sugar vicinal aminoalcohol building blocks, opening a synthetic path to a series of urea-linked neosaccharides. Glucosamine neodisaccharide possessing an oxazolidinone–urea–oxazolidinone system could be transformed into both cyclic and higher linear neosaccharides. Furthermore, a series of six urea-linked glucosamine and galactosamine neodisaccharides was tested for self-assembling properties by measuring NMR spectra at different temperatures and concentrations as well as by gelation of several organic solvents.     

Role of alkylated residues in the tetrapeptide self-assembly—A molecular dynamics study

Designing peptide sequences that self-assemble into well-defined nanostructures can open a new venue for the development of novel drug carriers and molecular contrast agents. Current approaches are often based on a linear block-design of amphiphilic peptides where a hydrophilic peptide chain is terminated by a hydrophobic tail. Here, a new template for a self-assembling tetrapeptide (YXKX, Y = tyrosine, X = alkylated tyrosine, K = lysine) is proposed with two distinct sides relative to the peptide's backbone: alkylated hydrophobic residues on one side and hydrophilic residues on the other side. Using all-atom molecular dynamics simulations, the self-assembly pathway of the tetrapeptide is analyzed for two different concentrations. At both concentrations, tetrapeptides self-assembled into a nanosphere structure. The alkylated tyrosines initialize the self-assembly process via a strong hydrophobic effect and to reduce exposure to the aqueous solvent, they formed a hydrophobic core. The hydrophilic residues occupied the surface of the self-assembled nanosphere. Ordered arrangement of tetrapeptides within the nanosphere with the backbone hydrogen bonding led to a beta sheet formation. Alkyl chain length constrained the size and shape of the nanosphere. This study provides foundation for further exploration of self-assembling structures that are based on peptides with hydrophobic and hydrophilic moieties located on the opposite sides of a peptide backbone.     

Electrochemical charge transfer mediated by metal nanoparticles and quantum dots

Electron transfer processes mediated by nanostructured materials assembled at electrode surfaces underpin fundamental processes in novel electrochemical sensors, light energy conversion systems and molecular electronics. Functionalisation of electrode surfaces with hierarchical architectures incorporating self-assembling molecular systems and materials, such as metal nanostructures, quantum dots, carbon nanotubes, graphene or biomolecules have been intensively studied over the last 20 years. Important steps have been made towards the rationalisation of the charge transfer dynamics from redox species in solution across molecular self-assembling systems to electrode surfaces. For instance, a unified picture has emerged describing the factors which determine the rate constant for electron transfer processes across rigid self-assembling molecular barriers. An increasing bulk of evidence has recently shown that the incorporation of nanomaterials into self-assembling monolayers leads to an entirely different electrochemical behaviour. This perspective rationalises some of the key observations associated with nanoparticle mediated charge transfer, such as the apparent distance independent charge transfer resistance observed for redox species in solution. This behaviour only manifests itself clearly in the case where the probability of direct charge transfer from the redox probe to the electrode is strongly attenuated by self-assembling molecular barriers. Here we will highlight specific issues concerning self-assembled monolayers as blocking barriers prior to discussing the effect of nanoparticles on the electrochemical response of the system. Selected examples will provide conclusive evidence that the extent of charge transfer mediation is determined by the overlap between the density of states of the nanostructures and the energy levels of redox species in solution. Only in the case where a strong overlap exists between the energy levels of the two components, the nanostructures behave as "electron launchers", allowing efficient charge transfer across insulating molecular layers.