Covalent Hybrid Research Articles

Covalent hybridization of CNT by thymine and uracil: A computational study

We have investigated the electronic and structural properties of covalent functionalization of the tip of (5,0) carbon nanotube (CNT) by di-keto and keto-enol forms of thymine (T) and uracil (U) nucleobases. Density functional theory (DFT) calculations have been performed to optimize the investigated structures and to calculate the properties such as dipole moment, bond length, band gap, total energy, binding energy and quadrupole coupling constant. The results indicated that, due to the functionalization of CNT by T and U, the hybrids exhibit new properties in which they are similar in both types of CNT-T and CNT-U hybrids.

Theory of ferroelectricity in Bi‐based multiferroics

AbstractAn electron‐phonon (vibronic) theory of the Bi‐based multiferroics is developed. It is shown that the electron‐lattice covalency hybridization between the Bi 6s2 lone electron pair and empty oxygen 2p states causes instability of R25 and R15 polar vibrations in the reference cubic phase. The cubic perovskite structure is distorted by displacements of oxygen ions corresponding to the condensation of the R25 mode at the boundary point R = π /a (1, 1, 1) of the Brillouin zone (a is the cell constant of the cubic phase). These oxygen displacements correspond to the rotation of the FeO6 octahedron in BiFeO3 about the cube space diagonal. The triply degenerate mode Γ1u participates in the s‐p mixing of Bi lone electron pair states and 2p oxygen states. The ferroelectric instability holds in the R $ \bar 3 $c phase and the observed ferroelectric transition R $ \bar 3 $c → R 3c is connected with the softening of the A2u mode. The Γ1u mode in the R $ \bar 3 $c phase splits in Eu and A2u modes. We have calculated the spontaneous polarization Ps = 30–40 μC/cm2 (Ps = 1.5 μC/cm2 is also possible), Tc = 1105 K and dielectric constants. It is shown that the phase transition of the first order is in agreement with the experiment. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

AN ELECTRON-PHONON THEORY OF THE Bi-BASED MAGNETIC-FERROELECTRIC PEROVSKITES

ABSTRACT It is shown that the electron-lattice covalency hybridization between the Bi 6s2 lone electron pair and empty oxygen 2p states causes instability of R25 and R15 polar vibrations in the reference cubic phase. The cubic perovskite structure is distorted by displacements of oxygen ions corresponding to the condensation of the R25 mode at the boundary point R=π/a(1, 1, 1) of the Brillouin zone (a is the cell constant). The ferroelectric instability holds in the phase and the observed ferroelectric transition is connected with the softening of the A2u mode. The Γ1u mode in the phase splits in Eu and A2u modes. We have calculated the spontaneous polarization Ps =30−40 μC/cm2 (Ps =1.5 μC/cm2 is also possible), Tc = 1105 K and dielectric constants.

Transient electronic structure of the photoinduced phase ofPr0.7Ca0.3MnO3probed with soft x-ray pulses

We use time-resolved x-ray absorption near-edge structure spectroscopy to investigate the electronic dynamics associated with the photoinduced insulator-to-metal phase transition in the colossal magnetoresistive manganite Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}. Absorption changes at the O K and Mn L edges directly monitor the evolution of the density of unoccupied states in the transient photoinduced phase. We show that the electronic structure of the photoinduced phase is remarkably similar to that of the ferromagnetic metallic phase reached in related manganites upon cooling below the Curie temperature.

A π‐stacked and conjugated hybrid based on poly(N‐vinylcarbazole) postfunctionalized with terfluorene for stable deep‐blue hole‐transporting materials

AbstractThe combination of π‐stacked with π‐conjugated building blocks offers an essential strategy to construct multifunctional organic semiconductors (MOSs) with the unique optoelectrical properties. Covalent hybrids can efficiently avoid the intrinsic phase‐separation defects in corresponding blend system. In this contribution, poly(vinylcarbazole) tethered with terfluorene, PVK‐TF, as a double‐channeled π‐stacked and π‐conjugated hybrid (SCH), has been constructed via Friedal‐Crafts click postmodification (FCCP). The chemical structure and optoelectrical property were determined by GPC, UV–vis, PL, TGA, DSC, and CV. Its PL spectra in the annealing thin film at N2 atmosphere without low‐energy emission bands centered at the 530 nm indicates that no π‐stacks between carbazole and TF or among TFs dominate the whole condensed phase, which is in agreement with the intrachain T‐shaped π‐pitched motifs in molecular modeling simulation due to steric hindrance effect in complicated diarylfluorenes (CDAFs). A supporting prototype stable deep‐blue PLED was successfully obtained with an Internationale de l'Eclairage (CIE) coordinates of (0.20, 0.10) and a width at half maximum (FWHM) of about 60 nm at high current density of 100 mA/cm2 (35 V). Deep‐blue PVK‐TF is a promising MOS for hole‐transporting and host materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5221–5229, 2009

Synthesis and characterization of cellulose/silica hybrid materials with chemical crosslinking

The cellulose/silica hybrid biomaterials are prepared by sol–gel covalent crosslinking process. The tetraethoxysilane (TEOS) as precursor, γ-aminopropyltriethoxylsilane (APTES) as couple agent, and 2,4,6-tri[(2-epihydrin-3-bimethyl-ammonium)propyl]-1,3,5-triazine chloride (Tri-EBAC) as crosslinking agent, are used in the sol–gel crosslinking process. The chemical and morphological structures of cellulose/silica covalent crosslinking hybrids are investigated with micro-FT-IR spectra, nitrogen element analysis, X-ray diffraction, SEM, AFM, and DSC. The results show that the cellulose/silica hybrids form new macromolecular structures. In sol–gel process, inorganic particles are dispersed at the nanometer scale in the cellulose host matrix, bounding to the cellulose through covalent bonds. The cellulose/silica covalent crosslinking hybrid can form good and smooth film on the cellulose. The thermal properties of organic/inorganic hybrids are improved.

Disterolphospholipids: Nonexchangeable Lipids and Their Application to Liposomal Drug Delivery

Extreme makeover of cholesterol: Cholesterol exchange is a major reason for the instability of liposomes in blood. The formation of a covalent hybrid between cholesterol and glycerophosphocholine preserves the bilayer-stabilizing effect of free cholesterol but prevents its transfer from the bilayer. Thus, disterolphospholipids (e.g. 1) are valuable new components for liposome formulation.

3D diamond‐containing nanocomposites based on hybrid polyurethane–poly(2‐hydroxyethyl methacrylate) semi‐IPNs: Composition‐nanostructure‐segmental dynamics‐elastic properties relationships

AbstractNanostructure, glass transition dynamics and elastic properties were studied in the 3D nanodiamond‐containing composites based on polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks (PU‐PHEMA semi‐IPNs), neat PU or PHEMA matrices. Nanodiamond (ND) content in the nanocomposites varied from 0.25 to 3 wt %. Combined differential scanning calorimetry/ laser‐interferometric creep rate spectroscopy/atomic force microscopy approach was utilized. A large impact of small 3D ND additives on PU‐PHEMA networks' dynamics and properties was revealed under conditions when an average inter‐particle distance L exceeds by far gyration radius Rg. The pronounced heterogeneity of glass transitions' dynamics and two opposite effects were observed. The main effect was a strong suppression of PHEMA glass transition dynamics at 90–180 °C, with the enhancement of creep resistance and threefold to sixfold increasing modulus of elasticity. The peculiarly crosslinked structure of nanocomposites, due to double covalent hybridization, resulted in low rheological percolation threshold, and a synergistic effect in dynamics was observed. Less pronounced effect of accelerating dynamics in the temperature region between β‐ and α‐transitions in PHEMA was associated with dynamics in domains with loosened molecular packing. The distinct physical limit for “anomalous” decreasing Tg is predicted in terms of the notion of the common segmental nature of α‐ and β‐relaxations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1696–1712, 2008

Covalency effects on the magnetism ofEuRh2P2

In experiments, the ternary Eu pnictideEuRh2P2 shows an unusual coexistence of a non-integral Eu valence of about 2.2 and arather high Néel temperature of 50 K. In this paper, we present a model whichexplains the non-integral Eu valence via covalent bonding of the Eu 4f-orbitals toP2 molecular orbitals. In contrast to intermediate valence models where the hybridization withdelocalized conduction band electrons is known to suppress magnetic orderingtemperatures to at most a few kelvin, covalent hybridization to the localizedP2 orbitals avoids this suppression. Using perturbation theory we calculate the valence, thehigh-temperature susceptibility, the Eu single-ion anisotropy and the superexchangecouplings of nearest and next-nearest neighbouring Eu ions. The model predicts atetragonal anisotropy of the Curie constants. We suggest an experimental investigation ofthis anisotropy using single crystals. From experimental values of the valence and the twoCurie constants, the three free parameters of our model can be determined.

An atomic force microscopy study of DNA hairpin probes monolabelled with gold nanoparticle: Grafting and hybridization on oxide thin films

First and original results are reported regarding the surface evolution of two kinds of oxide film after covalent grafting and hybridization of hairpin oligonucleotide probes. These hairpin probes were monolabelled with a 1.4 nm gold nanoparticle. One kind of oxide film was rough Sb doped SnO 2 oxide film and the other kind was smooth SiO 2 film. Same process of covalent grafting, involving a silanization step, was performed on both oxide surfaces. Atomic force microscopy (AFM) was used to study the evolution of each oxide surface after different steps of the process: functionalization, probe grafting and hybridization. In the case of rough SnO 2 films, a slight decrease of the roughness was observed after each step whereas in the case of smooth SiO 2 films, a maximum of roughness was obtained after probe grafting. Step height measurements of grafted probes could be performed on SiO 2 leading to an apparent thickness of around 3.7 ± 1.0 nm. After hybridization, on the granular surface of SnO 2, by coupling AFM with SEM FEG analyses, dispersed and well-resolved groups of gold nanoparticles linked to DNA duplexes could be observed. Their density varied from 6.6 ± 0.3 × 10 10 to 2.3 ± 0.3 × 10 11 dots cm −2. On the contrary, on smooth SiO 2 surface, the DNA duplexes behave like a dense carpet of globular structures with a density of 2.9 ± 0.5 × 10 11 globular structures cm −2.

Ab-initio investigation of electronic properties and magnetism of half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In)

The electronic structures and magnetism of the half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In) have been investigated to search for new candidate half-metallic materials. Here, we predict that NiCrAl, and NiCrGa and NiCrIn are possible half-metals with an energy gap in the minority spin and a completely spin polarization at the Fermi level. The energy gap can be attributed to the covalent hybridization between the d states of the Ni and Cr atoms, which leads to the formation of bonding and antibonding peaks with a gap in between them. Their total magnetic moments are 1 μ B per unit cell; agree with the Slater–Pauling rule. The partial moment of Cr is largest in NiCrZ alloys and moments of Ni and Al are in antiferromagnetic alignment with Cr. Meanwhile, it is also found that FeCrAl is a normal ferromagnetic metal with a magnetic moment of 0.25 μ B per unit cell and CoCrAl is a semi-metal and non-magnetic.

Optical biosensor microsystems based on the integration of highly sensitive Mach–Zehnder interferometer devices

We present highly sensitive optical biosensors able to be fully integrated in lab-on-a-chip microsystems using standard CMOS compatible processes. These optical biosensors are based on integrated Mach–Zehnder interferometers, which have been designed to have high surface sensitivity and monomode behaviour. As a biosensing application of the devices we show the real-time detection of the covalent immobilization and hybridization of DNA strands without labelling. In order to achieve a lab-on-a-chip portable microsystem, we present the integration of the sensor with a CMOS compatible microfluidic system using SU-8 photolithography patterned layers.

Increasing the operation temperature of polymer electrolyte membranes for fuel cells: From nanocomposites to hybrids

Among the possible systems investigated for energy production with low environmental impact, polymeric electrolyte membrane fuel cells (PEMFCs) are very promising as electrochemical power sources for application in portable technology and electric vehicles. For practical applications, operating FCs at temperatures above 100 °C is desired, both for hydrogen and methanol fuelled cells. When hydrogen is used as fuel, an increase of the cell temperature produces enhanced CO tolerance, faster reaction kinetics, easier water management and reduced heat exchanger requirement. The use of methanol instead of hydrogen as a fuel for vehicles has several practical benefits such as easy transport and storage, but the slow oxidation kinetics of methanol needs operating direct methanol fuel cells (DMFCs) at intermediate temperatures. For this reason, new membranes are required. Our strategy to achieve the goal of operating at temperatures above 120 °C is to develop organic/inorganic hybrid membranes. The first approach was the use of nanocomposite class I hybrids where nanocrystalline ceramic oxides were added to Nafion. Nanocomposite membranes showed enhanced characteristics, hence allowing their operation up to 130 °C when the cell was fuelled with hydrogen and up to 145 °C in DMFCs, reaching power densities of 350 mW cm −2. The second approach was to prepare Class II hybrids via the formation of covalent bonds between totally aromatic polymers and inorganic clusters. The properties of such covalent hybrids can be modulated by modifying the ratio between organic and inorganic groups and the nature of the chemical components allowing to reach high and stable conductivity values up to 6.4 × 10 −2 S cm −1 at 120 °C.

The fabrication of rare earth covalent luminescent hybrid materials with potential molecular bridge by in situ sol–gel process

1,2,4-Benzenetricar boxylic acid (abbreviated as TMA) was modified to achieve a functional molecular bridge (TMA-APMES) with double reactivity by the reaction with a cross-linking molecule (3-aminopropyl-methyl-diethoxylsiliane, APMES). The modified functional ligand further behaves as a bridge both coordinates to Ln 3+ through oxygen atom and occurs in situ sol–gel process with matrix precursor (tetraethoxysilane, TEOS) through co-hydrolysis and co-polycondensation reaction. Then a novel molecular hybrid material (named as hybrid Ln 3+) with double chemical bond (Tb O coordination bond and Si O covalent bond) resulted. Ultraviolet absorption, phosphorescence, and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The strong luminescence of Tb 3+ substantiates optimum energy couple and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb 3+.

Proton-conducting methacrylate–silica sol–gel membranes containing tungstophosphoric acid

The increase of the operation temperature in proton-exchange membrane fuel cell (PEMFC) above 100 °C is a great concern for the application of this type of cells in electric vehicles. Hybrid organic–inorganic membranes with nano-sized interfaces can combine the main properties to meet this objective. Methacrylate–silica covalent hybrid membranes have been synthesised by polymerization of 2-hydroxyethyl methacrylate and 3-methacryloxypropyl trimethoxysilane, and hydrolysis–polycondensation of alkoxide radicals. Tungstophosphoric acid hydrate was incorporated to endow the membranes with proton conductivity. The composition and synthesis conditions to promote organic polymerisation and sol–gel condensation avoiding phase separation have been optimised. The structural analysis shows homogeneous membranes without phase separation. The water retention properties provided by SiO 2 and tungstophosphoric acid leads to high proton conductivity (maximum values around 3 × 10 −2 S cm −1) at 100–150 °C. A 0.5 M % of Tungstophosphoric acid (PWA) is enough to build well-connected paths for proton conduction.

Polydipyrrole- and polydicarbazole-nanorods as new nanosized supports for DNA hybridization

Novel functional polydipyrrole- and polydicarbazole nanorods have been AAO template-synthesized from COOH-dipyrrole/-dicarbazole monomers using Vapor Deposition and Liquid Phase Polymerizations (VDP and LPP). They were tested as insoluble supports for covalent DNA attachment and hybridization.

Off-center displacements of Ti ions in oxide ferroelectrics and a gigantic photo-induced dielectric constant of quantum paraelectric perovskite oxides in the electron-lattice theory

In this work we investigate the coupling of the F1u vibrations with the actual electronic states of BO6n− cluster in ABO3 ferrorelectric-oxides. This coupling leads to the dynamical covalency hybridization of B(Ti,Ta,Nb) and oxygen electronic states. It is shown that at fulfilment of definite criteria the free energy at T = 0, the adiabatic potential of BO6n− cluster have the following configurations: (1) one maximum at x0 = y0 = z0 = 0 (ferroelectric instability); (2) eight minima in the points |x0| = |y0| = |z0| = y0; (3) twelve saddle points at |p| = |q| ≠ 0, r = 0 (p, q, r = x, y, z) with a maximum in the r cross-section and minima along p and q. We show that the photo-induced changes of local ferroelectric distortions can take place. A gigantic enhancement of the dielectric constant by UV-light illumination is calculated in the electron-lattice theory in quantum paraelectrics of perovskite oxides, such as SrTiO3 and KTaO3, under a weak DC electric field. The temperature dependence of the gigantic real part of the dielectric constant ϵUVDC of SrTi16O3 under both UV-light and DC electric fields is calculated in satisfactory agreement with the experiment.

Covalent attachment and hybridization of DNA oligonucleotides on patterned single-walled carbon nanotube films.

DNA oligonucleotides were covalently immobilized to prepatterned single-walled carbon nanotube (SWNT) multilayer films by amidation. SWNT multilayer films were constructed via consecutive condensation reactions creating stacks of functionalized SWNT layers linked together by 4,4'-oxydianiline. Aminated- or carboxylated-DNA oligonucleotides were covalently immobilized to the respective carboxylated or aminated SWNT multilayer films through amide bond formation using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. UV-vis-NIR spectroscopic analysis indicated that the SWNT film surface density increased uniformly according to the number of reaction cycles. Scanning electron microscopy and contact angle measurements of the SWNT multilayer film revealed a uniform coverage over the substrate surface. The covalent attachment of DNA oligonucleotides to the SWNT multilayer films and their subsequent hybridization with complementary oligonucleotides were verified using X-ray photoelectron spectroscopy and fluorescence-based measurements. This is the first report demonstrating that DNA oligonucleotides can be covalently attached to immobilized SWNT multilayer films. The anchored DNA oligonucleotides were shown to exhibit excellent specificity, realizing their potential in future biosensor applications.

Synthesis and characterisation of proton conducting styrene-co-methacrylate–silica sol–gel membranes containing tungstophosphoric acid

The increase of the operation temperature in proton exchange membrane fuel cell (PEMFC) above 100 °C is a great concern for the application of this type of cells in electric vehicles. Hybrid organic–inorganic membranes with nanosized interfaces can combine the main properties to meet this objective. Poly (styrene-co-methacrylate)–silica covalent hybrid membranes have been synthesised by copolymerization of monomers (styrene (STY) and 2-hydroxyethyl methacrylate (HEMA)), with formation of covalent bonds between hydroxyl group from the latter and pre-hydrolyzed tetraethoxysilane. Tungstophosphoric acid hydrate was incorporated to endow the membranes of proton conductivity. The optimal composition and synthesis conditions to promote organic polymerization and sol–gel condensation avoiding phase separation are important issues of this work. The structural analysis shows homogeneous membranes without phase separation. The combination of water uptake and water retention properties provided by SiO 2 and tungstophosphoric acid leads to high proton conductivity (maximum values around 1 S/cm) at 120 °C.

Hybrid Organic/Inorganic Sol-Gel Materials for Proton Conducting Membranes

One important application of hybrid organic-inorganic materials with nano-sized interfaces is the preparation of membranes for Proton Exchange Membrane Fuel Cells (PEMFC) operating at high temperature. Poly (styrene-co-methacrylate)--silica covalent hybrid membranes have been synthesised by copolymerization of monomers (styrene and 2-hydroxyethyl methacrylate), with formation of covalent bonds between hydroxyl group of HEMA and pre-hydrolysed tetraethoxysilane (TEOS). Sulfonation of benzyl groups was applied to endow the membranes of proton conductivity. The incorporation of an inorganic component to a polymeric one modifies properties like thermal, chemical and mechanical stability, and proton conductivity. A compromise between these properties has to be achieved to produce adequate proton conducting membranes with application in PEMFC. The hybrid membrane with 25% SiO2 combines these properties being a promising candidate for application in PEMFC.