Self-assembly of conjugated polymers and ds-oligonucleotides directed fractal-like aggregates

Highly ordered nanostructures between conjugated polymers and ds-oligonucleotides have been first fabricated by simply controlling the self-assembly processes, which shows a novel concept for fabricating fractal-like structures. The formation of polymer/DNA fractal-like aggregates is a diffusion-limited aggregation (DLA) process. The fractal dimension is independent of the polymer/DNA concentration but only related to the polymer/DNA charge ratio. More interestingly, the different fluorescent resonance energy transfer (FRET) behavior between the polymer and the DNA can be used to distinguish dsDNA from ssDNA.     

Size‐Dependent Charge Transfer in Blends of PbS Quantum Dots with a Low‐Gap Silicon‐Bridged Copolymer

The photophysics of bulk heterojunctions of a high‐performance, low‐gap silicon‐bridged dithiophene polymer with oleic acid capped PbS quantum dots (QDs) are studied to assess the material potential for light harvesting in the visible‐ and IR‐light ranges. By employing a wide range of nanocrystal sizes, systematic dependences of electron and hole transfer on quantum‐dot size are established for the first time on a low‐gap polymer–dot system. The studied system exhibits type II band offsets for dot sizes up to ca. 4 nm, whch allow fast hole transfer from the quantum dots to the polymer that competes favorably with the intrinsic QD recombination. Electron transfer from the polymer is also observed although it is less competitive with the fast polymer exciton recombination for most QD sizes studied. The incorporation of a fullerene derivative provides efficient electron‐quenching sites that improve interfacial polymer‐exciton dissociation in ternary polymer–fullerene–QD blends. The study indicates that programmable band offsets that allow both electron and hole extraction can be produced for efficient light harvesting based on this low‐gap polymer‐PbS QD composite.     

Ab-initio study of anisotropic and chemical surface modifications of β-SiC nanowires

The electronic band structure and electronic density of states of cubic SiC nanowires (SiCNWs) in the directions [001], [111], and [112] were studied by means of Density Functional Theory (DFT) based on the generalized gradient approximation and the supercell technique. The surface dangling bonds were passivated using hydrogen (H) atoms and OH radicals in order to study the effects of this passivation on the electronic states of the SiCNWs. The calculations show a clear dependence of the electronic properties of the SiCNWs on the quantum confinement, orientation, and chemical passivation of the surface. In general, surface passivation with either H or OH radicals removes the dangling bond states from the band gap, and OH saturation appears to produce a smaller band gap than H passivation. An analysis of the atom-resolved density of states showed that there is substantial charge transfer between the Si and O atoms in the OH-terminated case, which reduces the band gap compared to the H-terminated case, in which charge transfer mainly occurs between the Si and C atoms.     

Molecular design and theoretical investigation on the thieno[3,2-b]thienobis(silolothiophene)-based low band gap donor polymers for efficient polymer solar cell

Donor–acceptor (D–A) copolymers have been proved to be excellent candidates for efficient polymer solar cells. In this paper, a series of D–A polymers with the same donor unit of Si4T and different acceptor units are theoretically designed. Two novel strategies (extending the length of π-conjugation and using the electron-deficient groups) have been considered for the conjugated polymer design. The energy levels and band gaps are theoretically investigated using the confirmed density functional theory/time-dependent density functional theory method. The results show that, compared with two original polymers, the newly designed D–A polymers have better predicted performances with smaller band gaps and lower highest occupied molecular orbital energy levels. When combined with fullerene derivatives (PCBM) for organic solar cells, these polymers can produce power conversion efficiencies as high as ～10%, estimated by Scharber diagrams.     

A DFT study of the effects of donor-to-acceptor ratio on the electronic properties of copolymers based on tricyclic non-classical thiophene

The geometries and electronic properties of the 1D polymers composed of thieno[3,2-b]thiophene (TT), thiophene (T), pyrrole (P), furan (F) and tricyclic non-classical thiophenes ([1,2,5]thiadiazolo[3,4-b]thieno-[3,4-e]pyrazine, TTP) are investigated systematically by the density functional theory method at the B3LYP level with 6-31G(d) basis set. The theoretical study suggests that the ratio of donor-to-acceptor (D-A ratio) plays a crucial role in the geometric and electronic properties for the alternating donor–acceptor polymers. The increase in the D-A ratio leads to an increase in the bridge bond length and an inverse change in the bond-length alternation. Furthermore, the increase in the portion of donor units can lead to an obvious reduction in band gap for these studied polymers. The TT-containing polymer possessing the D-A ratio of 2:1 (p-BTTTTP) that is predicted to have a small band gap of 0.25 eV and a relatively small effective mass of carriers is a good candidate for an intrinsic conducting polymer. Therefore, the tricyclic non-classical thiophenes (TTP) and TT are good building blocks that can lead to small band gap polymers.     

Electronic structure of siloxene model compounds

The electronic structures of one-dimensional and two-dimensional siloxene (Si₆O₃H₆) model compounds have been examined theoretically, using the semiempirical tight-binding self-consistent field crystal orbital (SCF-CO) method. These compounds are formed by silicon-based chain and planar structures containing a regular array of oxygen atoms. Results show that the two-dimensional polysilane in which OH groups are substituted for H atoms possesses a relatively smaller direct gap than other siloxenes. It is assumed that the electronic structures of siloxenes are affected not only by the dimensionality of Si-Si -conjugational networks due to an array of oxygen atoms, but also by the diminishing of the electron population in the Si-Si bonding orbitals caused by oxygen atoms with large electronegativity.     

Carbon doped boron phosphide nanotubes: A computational study

A computational study based on density functional theory (DFT) calculations has been performed to investigate the properties of the electronic structure of carbon doped boron phosphide nanotube (C-doped BPNT). Pristine and the C-doped structures of two representative (6,0) zigzag and (4,4) armchair BPNTs have been investigated. At first, the geometries of the structures have been allowed to relax by optimization. Subsequently, NMR parameters have been calculated in the optimized structures. The results indicated that the influence of C-doping was more significant on the geometries of the zigzag model than the armchair one. The difference of band gap energies between the pristine and C-doped armchair BPNT was larger than the zigzag model. Significant differences of NMR parameters of those nuclei directly contributed to the C-doping atoms have been observed.     

Electronic Structure Analysis of a New Quinoid Conjugated Polymer

The low lying unoccupied orbitals of oligomers of 4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b'] dithiophene (CDM) are not delocalized over the whole molecule. Is such electron localization in the conduction band of poly-CDM responsible for its low n-type conductivity? Are polymers of the tricyclic thioketone (TCT) with more delocalized unoccupied orbitals a better alternative for stable n-dopable conducting polymers? Monomer through tetramer of TCT have been optimized with density functional theory. IP, EA, energy gap, and band width of the corresponding polymer were obtained by extrapolation. Comparison with data for oligomers of 4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b'] dithiophene and of thiophene indicates that the novel polymer would have a small band gap and would fulfil the conditions for n-dopability and high mobility of n-type carriers.     

Recent Development of Quinoxaline Based Polymers/Small Molecules for Organic Photovoltaics

Among the various molecular designs developed for the synthesis of conjugated polymers and small molecules for optoelectronic applications, the donor: acceptor (D–A) approach is the most widely explored method over the past decades. Through the covalent linkage of electron‐rich and electron‐deficient units, a plethora of medium‐low band gap materials has been developed and tested in organic photovoltaic devices. In particular, the quinoxaline aromatic structure and its derivatives are among the most studied electron deficient aromatic units used in D–A structures. Quinoxaline based materials are endowed with characteristics that are useful for large scale production in real world applications, such as easy synthetic procedures and excellent stability in air. Moreover, the use of quinoxaline based polymers/small molecules in bulk heterojunction (BHJ) devices led to power conversion efficiencies over 9%. Considering the potential of quinoxaline based materials, this review gathers together quinoxaline based polymers and small molecules reported in the literature during the last 5 years, summarizing and discussing the structure‐properties relationships for this class of organic semiconductors, aiming to serve as a background and to promote efforts for the further development of new quinoxaline derivatives with improved and advanced properties for future applications.     

Computational investigation of double nitrogen doping on graphene

Density functional theory (DFT) calculations were performed to study doping of two nitrogen atoms at different positions on a finite-sized graphene model of C₈₂H₂₄. We examined 21 structures of double nitrogen doped graphene to calculate their relative stabilities. The structure with two nitrogen atoms located apart is the most stable among the positional isomers considered in this study. For double nitrogen doping within a six-membered ring, the 1,4-position is more preferred than 1,3- or 1,2-positions for the finite-sized single layer graphene sheet. Our computational study supports the experimental observation of two nitrogen atoms at the 1,3- and 1,4-positions in a single six-membered ring of graphene. Furthermore, the structures with N-N bond are the least stable among two nitrogen doped graphene structures. The effects of nitrogen doping and the positions of two nitrogen atoms on the HOMO-LUMO energy gap of pristine graphene were analyzed.     

Synthesis, crystal and band structures, and optical and magnetic properties of a 1D copper coordination polymer with chelidamic acid ligand

A 1D coordination polymer, {[Cu₃(C₇H₂NO₅)₂(H₂O)₇]·2(H₂O)}_n (1), has been synthesized and characterized by X-ray single-crystal diffraction. The crystal structure of 1 features that distorted square-pyramidal coordination polyhedra composed of Cu atoms and chelidamic acid ligands are interlinked into a 1D polymer, further linked by hydrogen bonds into a 3D network. The optical properties were investigated in terms of diffuse reflectance and fluorescent spectra, which exhibit strong luminescence. The electronic band structure along with the density of states (DOSs) calculated by the DFT method indicate that compound 1 pose an energy band gap of 1.89 eV and that the origin of the emission band may be mainly ascribed to metal-to-ligand charge transfer (MLCT) where the electrons are transferred from the Cu-3d to O-2p and C-2p states.     

The effects of electron-acceptor strength and donor-to-acceptor ratio on the electronic properties of thieno[3,2-b]thiophene-based donor–acceptor copolymers

Theoretical analysis on the geometries and electronic properties of thieno[3,2-b]thiophene (TT)-based alternating donor–acceptor conjugated polymers of donor and acceptor unit with the ratio of 1:1 and 2:1, as well as their corresponding monomers, is reported. The theoretical results suggest that both the electron-acceptor strength and the mole ratio of donor to acceptor (D/A ratio) contribute significantly to the electronic properties of alternating donor–acceptor conjugated copolymers. However, the impact of D/A ratio on the geometrical and electronic properties of the donor–acceptor copolymers is more marked compared with that of the acceptor strength. The increase in the portion of TT unit can significantly decrease the bond length alternation, strengthen the π-electron delocalisation and narrow the band gap. In addition, the mole ratio of donor-to-acceptor unit also has an impact on the bandwidth. The copolymers possessing a D/A ratio of 2:1, i.e. p-TTP-DTT, p-DTP-DTT and p-TBT-DTT, may be good candidates for conduction materials due to their very narrow band gap ( < 0.72 eV), relatively small effective mass of carriers and relatively large bandwidth.     

Theoretical investigation of cyromazine tautomerism using density functional theory and Møller–Plesset perturbation theory methods

A computational chemistry analysis of six unique tautomers of cyromazine, a pesticide used for fly control, was performed with density functional theory (DFT) and canonical second-order Møller–Plesset perturbation theory (MP2) methods to gain insight into the contributions of molecular structure to detection properties. Full geometry optimisation using the 6-311++G** basis set provided energetic properties, natural charges, frontier orbitals and vibrational modes. Excitation energies were obtained using time-dependent DFT. Hydrogen location and bond order contribute significantly to the electronic properties. The common cyromazine tautomer possesses the lowest energy, highest band gap energy and highest excitation energy. B3LYP/6-31G** dynamics simulations indicate each tautomer possesses a stable structure with limited rotation about the single bonds. Tautomerisation involving intramolecular hydrogen transfer influences the natural charges of neighbouring atoms and the frontier orbital properties. The excitation energies are highly correlated with band gap energies of the frontier orbitals. The calculated infrared and Raman spectra are suitable for vibrational assignments associated with the chemical structure. The tautomeric forms of cyromazine possess similar spatial properties and significant variation in electronic properties.     

The arthropod gap junction and pseudo-gap junction: Isolation and preliminary biochemical analysis

Summary The hepatopancreas of the crayfish, Procambarus clarkii, contains an unusual abundance of gap junctions, suggesting that this tissue might provide an ideal source from which to isolate the arthropod-type of gap junction. A membrane fraction obtained by subcellular fractionation of this organ contained smooth septate junctions, zonulae adhaerentes, gap junctions and pentalaminar membrane structures (pseudo-gap junctions) as determined by electron microscopy. A further enrichment of plasma membranes and gap junctions was achieved by the use of linear sucrose gradients and extraction with 5 mM NaOH. The enrichment of gap junctions correlated with the enrichment of a 31 Kd protein band on polyacrylamide gels. Extraction with 20 mM NaOH or 0.5% (w/v) Sarkosyl NL97 resulted in the disruption and/or solubilization of gap junctions. Negative staining revealed a uniform population of 9.6 nm diameter subunits within the gap junctions with an apparent sixfold symmetry. Using antisera to the major gap junctional protein of rat liver (32 Kd) and to the lens membrane protein (MP 26), we failed to detect any homologous antigenic components in the arthropod material by immunoblotting-enriched gap junction fractions or by immunofluorescence on tissue sections. The enrichment of another membrane structure (pseudo-gap junctions), closely resembling a gap junction, correlated with the enrichment of two protein bands, 17 and 16Kd, on polyacrylamide gels. These structures appeared to have originated from intracellular myelin-like figures in phagolysosomal structures. They could be distinguished from gap junctions on the basis of their thickness, detergent-alkali insolubility, and lack of association with other plasma membrane structures, such as the septate junction. Pseudo-gap junctions may be related to a class of pentalaminar contacts among membranes involved in intracellular fusion in many eukaryotic cell types. We conclude that pseudo-gap junctions and gap junctions are different cellular structures, and that gap junctions from this arthropod tissue are uniquely different from mammalian gap junctions of rat liver in their detergentalkali solubility, equilibrium density on sucrose gradients, and protein content (antigenic properties).     

Spectrophotometric assay of long-chain unsaturated and hydroxy fatty acids in concentrated sulfuric acid

A spectrophotometric method has been developed for the determination of long-chain unsaturated and hydroxy fatty acids in concentrated sulfuric acid. The assay is based on the absorbance produced in the 290 to 300-nm range from their reaction with sulfuric acid at 100°C. α,β-Unsaturated aliphatic acids give absorption bands at 235–240 nm and thus can be easily differentiated from unsaturated fatty acids having the double bond(s) at positions not conjugated with the carboxyl group. A certain minimum chain length is required for full development of the absorption band at 300 nm. Position and intensity of the so-formed absorption band is independent on the position and number of the double bonds or hydroxyl groups. Carboxyl groups are not essential, as unsaturated hydrocarbons and higher alcohols likewise react with sulfuric acid to produce the absorbing species at 300 nm, providing a minimum chain length of 5 carbon atoms is present. The nature of the absorbing species at 300 nm is discussed.     

Optoelectronic properties of naphtho[2, 1-b:6, 5-b′]difuran derivatives for photovoltaic application: a computational study

Some important optoelectronic properties of naphtho[2,1-b:6,5-b′]difuran (DPNDF) and its two derivatives have been limelighted by applying the density functional theory (DFT). Due to their low cost, high stability and earth abundance, the DPNDF and its derivatives are considered as potential organic semiconductor materials for their optoelectronics applications. Highly proficient derivatives are obtained systematically by attaching –CN (cyanide) to DPNDF at various sites. Our calculations indicate that DPNDF has a wide and direct band gap with an energy gap of 3.157 eV. Whereas the band gaps of its derivatives are found to be decreased by 88 meV for derivative “a” and 300 meV for derivative “b” as a consequence of p orbitals present in C and N atoms in derivative structures. The narrowing of the energy gap and density of states for the derivatives of DPNDF in the present investigation suggest that energy gap can be engineered for desirable optoelectronic applications via derivatives designing. Furthermore, their obtained results for optical parameters such as the dielectric and conductivity functions, reflectivity, refractive index, and the extinction coefficients endorses their aptness for optoelectronic applications.

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Graphical Abstract Real part of dielectric function for derivative “b”

     

Curious results with palladium- and platinum-carrying polymers in mass cytometry bioassays and an unexpected application as a dead cell stain

We describe the synthesis of metal-chelating polymers (MCPs) with four different pendant polyaminocarboxylate ligands (EDTA, DTPA, TTHA, DOTA) and an orthogonal end-group, either a fluorescein molecule or a bismaleimide linker for antibody attachment. Polymer characterization by a combination of (1)H NMR, UV/vis absorption measurements, and thermal gravimetric analysis (TGA) indicated that each chain of the fluorescein-terminated polymers contained one dye molecule. These polymer samples were loaded with three different types of lanthanide ions as well as palladium and platinum ions. The numbers of metal atoms per chain were determined by a combination of UV/vis and conventional ICP-MS measurements. The experiments with lanthanide ions demonstrated that a net anionic charge on the polymer is important for water solubility. These experiments also showed that at least one type of lanthanide ion (La(3+)) is capable of forming a bimetallic complex with pendant DTPA groups. Conditions were developed for loading these polymers with palladium and platinum ions. While these polymers could be conjugated to antibodies, the presence of Pd or Pt ions in the polymer interfered with the ability of the antibody to recognize its antigen. For example, a goat anti-mouse (secondary) antibody labeled with polymers that contain Pd or Pt no longer recognized a primary antibody in a sandwich assay. In mass cytometry assays, these Pd- or Pt-containing MCPs were very effective in recognizing dead cells and provide a new and robust assay for distinguishing live cells from dead cells.     

SYNTHESIS OF NOVEL POLYDIAMIDOPROPANOATE DENDRIMER PNA-PEPTIDE CHIMERAS FOR NON-INVASIVE MAGNETIC RESONANCE IMAGING OF CANCER

A variety of dendrimers can be conjugated to oligonucleotides to increase the number of contrast paramagnetic atoms (e.g., gadolinium or dysprosium) per probe. Thus, it was of interest to test a route for assembly of chelating dendrimer branches directly on the N-termini of peptide nucleic acid (PNA)-peptide chimeras by continuous solid-phase coupling on polymer supports. Dendrimer-PNA-peptides complementary to 12 nt of mutant KRAS mRNA have been prepared with a C-terminal insulin-like growth factor 1 (IGF1) analog d(Cys-Ser-Lys-Cys) and N-terminal polydiamidopropanoate (PDAP) dendrimers with different numbers of diaminopropanoate residues. 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelating moieties were then coupled to PDAP dendrimer-PNA-peptide chimeras before cleavage from the polymer supports. The DOTA-PDAP-PNA-peptide probes with 1, 2, 4, 8, or 16 amino (or DOTA) moieties were cleaved, purified by RP-HPLC, and characterized by MALDI-TOF mass spectroscopy.     

DFT calculation of the electronic properties of fluorene-1,3,4-thiadiazole oligomers

Thiadiazole derivatives have been widely employed in the areas of pharmaceutical, agricultural, industrial, and polymer chemistry. The electronic and molecular structures of thiadiazoles are of interest because they have an equal number of valence electrons and similar molecular structures to thiophenes, which are currently used in the construction of organic solar cells due to their relatively high hole mobilities and good light-harvesting properties. For this reason, the electronic properties of fluorene-1,3,4-thiadiazole oligomers warrant investigation. In the present work, the structure of fluorene-1,3,4-thiadiazole with one thiadiazole unit in the structure was analyzed. This molecule was then expanded until there were 10 thiadiazole units in the structure. The band gap, HOMO and LUMO distributions, and absorption spectrum were analyzed for each molecule. All calculations were performed by applying the B3LYP/6-31G(d) chemical model in the Gaussian 03W and GaussView software packages. The electronic properties were observed to significantly enhance as the number of monomeric units increased, which also caused the gap energy to decrease from 3.51 eV in the oligomer with just one thiadiazole ring to 2.33 eV in the oligomer with 10 units. The HOMO and LUMO regions were well defined and separated for oligomers with at least 5 monomer units of thiadiazole.

Electronic structure and molecular design of simplified polyimide systems

The electronic structures of newly designed polyimide systems (ethenetetracarboxylic 1,2:1,2-dianhydride-diaminoethyne (PI-A) and ethenetetracarboxylic 1,1:2,2-dianhydride-diaminoethyne(PI-B)) are studied in detail with respect to their optimized geometries on the basis of the one-dimensional tight-binding self-consistent field crystal-orbital method. The computational results have revealed that PI-B shows intriguing properties such as a very small band gap and a wide bandwidth near the frontier level, compared with PI-A and other polyimides. Since PI-B would be a promising candidate for a new electric conducting material, a reaction diagram for this polymer is also proposed.Also affiliated to Central Research Laboratories, Matsushita Electric Industrial Co., Moriguchi 570, Japan.