Structure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length
were performed at B3LYP/6-31G* level of theory. From 1 to 9 COOH groups were added at the end of the nanotube. The differences
in structure and energetics of partially and fully functionalized SWCNTs at one end of the nanotube are observed. Up to nine
COOH groups could be added at one end of (9,0) zigzag SWCNT in case of full functionalization. However, for (5,5) armchair
SWCNT, the full functionalization was impossible due to steric crowding and rim deformation. The dependence of substituent
attachment energy on the number of substituents at the carbon nanotube rim was observed. 相似文献
The geometric structures of perfect ZnTe, that with Zn vacancy (Zn0.875Te), and Cu-doped ZnTe (Zn0.875Cu0.125Te) were optimized using the pseudopotential plane wave (PP-PW) method based on the density functional theory (DFT) within generalized gradient approximation (GGA). The cohesive energy, band structure, density of states, and Mulliken populations were calculated and discussed in detail. On the other hand, an accurate calculation of linear optical functions (the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectrum) was performed. The results demonstrated that compared to the perfect ZnTe, the lattice parameters of Zn0.875Te and Zn0.875Cu0.125Te were changed and the cell volumes decreased to some extent due to the vacancy and introduction of impurity. A vacancy acceptor level and an acceptor impurity level were produced in Zn0.875Te and Zn0.875Cu0.125Te, respectively. By comparison, Cu doping in the ZnTe system is relatively stable while the monovacancy system is not. 相似文献
The structural, optical and magnetic properties of Cu, Ag, Au-doped Si7 Clusters have been systematically investigated using density functional theory calculations. The global optimized structures of Cu, Ag, Au-doped Si clusters are predicted to have a lower HOMO–LUMO gap and higher magnetic moment. M-doping (M?=?Cu, Ag, Au) in Si cluster widens a range of adsorption wavelength, especially Au-doping. The characteristics in electronic density of states (DOSs) show that C5v-Si6Cu has a big asymmetrical spin-up and spin-down. The average atomic moment is 0.428 mμB per atom for the Si6Cu cluster with C5v symmetry, while the average paramagnetic moment is 0.143 mμB per atom for other M-doped (M?=?Cu, Ag, Au) Si7 clusters. 相似文献
Low dimensional materials have attracted great research interest from both theoretical and experimental point of views. These materials exhibit novel physical and chemical properties due to the confinement effect in low dimensions. The experimental observations of graphene open a new platform to study the physical properties of materials restricted to two dimensions. This featured article provides a review on the novel properties of quasi one-dimensional (1D) material known as graphene nanoribbon. Graphene nanoribbons can be obtained by unzipping carbon nanotubes (CNT) or cutting the graphene sheet. Alternatively, it is also called the finite termination of graphene edges. It gives rise to different edge geometries, namely zigzag and armchair, among others. There are various physical and chemical techniques to realize these materials. Depending on the edge type termination, these are called the zigzag and armchair graphene nanoribbons (ZGNR and AGNR). These edges play an important role in controlling the properties of graphene nanoribbons. The present review article provides an overview of the electronic, transport, optical, and magnetic properties of graphene nanoribbons. However, there are different ways to tune these properties for device applications. Here, some of them, such as external perturbations and chemical modifications, are highlighted. Few applications of graphene nanoribbon have also been briefly discussed. 相似文献
Meldola's blue (MB) functionalized carbon nanotubes (CNT) nanocomposite film (MB/CNT) electrode was prepared by non-covalent adsorbing MB on the surface of a carbon nanotubes modified glassy carbon electrode (CNT/GCE). Electrochemical behaviors of the resulting electrode were investigated thoroughly with cyclic voltammetry in the potential range of -0.6 to 0.2V, and two well-defined redox couples were clearly visualized. We also studied the electron transfer kinetics of MB loaded on CNT (MB/CNT) in comparison with that of MB on conventional graphite powder (MB/GP). The heterogeneous electron transfer rate constant (k(s)) of MB/CNT was calculated to be about three times larger than that of MB/GP. The accelerated electron transfer kinetics was attributed to the unique electrical and nanostructural properties of CNT supports as well as the interaction between MB and CNT. In connection with the oxidation of nicotinamide adenine dinucleotide (NADH), excellent electrocatalytic activities were observed at MB/CNT/GCE compared with MB/GP modified glassy carbon electrode (MB/GP/GCE). Based on the results, a new NADH sensor was successfully established using the MB/CNT/GCE. Under a lower operation potential of -0.1V, NADH could be detected linearly up to a concentration of 500 microM with an extremely lower detection limit of 0.048+/-0.02 microM estimated at a signal-to-noise ratio of 3. Sensitivity, selectivity, reproducibility and stability of the NADH sensor were also investigated and the main analytical data were also compared with those obtained with the MB/GP/GCE. 相似文献
Magnetic carbon nanotubes (MCNTs) with necklace-like nanostructures was prepared via hydrothermal method, and hyperbranched
poly(amidoamine) (PAMAM) was grafted on the surface of MCNTs on the basis of the Michael addition of methyl acrylate and the
amidation of the resulting ester with a large excess of ethylenediamine (EDA), which could achieve generational growth under
such uniform stepwise reactions. The terminal –NH2 groups from the dendritic PAMAM were reacted with differently functionalized groups to form functionalized MCNTs. Subsequently,
enzyme was immobilized on the functionalized MCNTs through adsorption, covalent bond, and metal-ion affinity interactions.
The immobilization of glucoamylase, hereby chosen as model enzyme, onto the differently functionalized MCNTs is further demonstrated
and assessed based on its activity, thermal stability, as well as reusability. Besides ease in recovery by magnetic separation,
the immobilized glucoamylase on functionalized MCNTs offers superior stability and reusability, without compromising the substrate
specificity of free glucoamylase. Furthermore, the results indicate that the metal-chelate dendrimer offers an efficient route
to immobilize enzymes via metal-ion affinity interactions. The applicability of the regenerated supports in the current study
is relevant for the conjugation of other enzymes beyond glucoamylase. 相似文献
We investigate properties of a reported new mechanism for cell–cell interactions, tunneling nanotubes (TNT’s). TNT’s mediate
actin-based transfer of vesicles and organelles and they allow signal transmission between cells. The effects of lateral pulling
with polystyrene beads trapped by optical tweezers on TNT’s linking separate U-87 MG human glioblastoma cells in culture are
described. This cell line was chosen for handling ease and possible pathology implications of TNT persistence in communication
between cancerous cells. Observed nanotubes are shown to have the characteristic features of TNT’s. We find that pulling induces
two different types of TNT bifurcations. In one of them, termed V-Y bifurcation, the TNT is first distorted into a V-shaped
form, following which a new branch emerges from the apex. In the other one, termed I-D bifurcation, the pulled TNT is bent
into a curved arc of increasingly broader span. Curves showing the variation of pulling force with displacement are obtained.
Results yield information on TNT structure and elastic properties.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Mediated biosensors consisting of an oxidase and peroxidase (POx) have attracted increasing attention because of their wider applicability. This work presents a novel approach to fabricate nanobiocomposite bienzymatic biosensor based on functionalized multiwalled carbon nanotubes (MWNTs) with the aim of evaluating their ability as sensing elements in amperometric transducers. Electrochemical behavior of the bienzymatic nanobiocomposite biosensor is investigated by Faradaic impedance spectroscopy and cyclic voltammetry. The results indicate that glucose oxidase (GOD) and horseradish peroxidase (HRP) are strongly adsorbed on the surface of the thionin (TH) functionalized MWNTs and demonstrate a facile electron transfer between immobilized GOD/HRP and the electrode via the functionalized MWNTs in a Nafion film. The functionalized carbon nanotubes act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centres of enzymes through TH. Linear ranges for these electrodes are from 10 nM to 10 mM for glucose and 17 nM to 56 mM for hydrogen peroxide with the detection limit of 3 and 6 nM, respectively. A remarkable feature of the bienzyme electrode is the possibility to determine glucose and hydrogen peroxide at a very low applied potential where the noise level and interferences from other electroactive compounds are minimal. Performance of the biosensor is evaluated with respect to response time, detection limit, selectivity, temperature and pH as well as operating and storage stability. 相似文献
The performance of a new glucose biosensor based on the combination of biocatalytic activity of glucose oxidase (GOx) with the electrocatalytic properties of CNTs and neutral red (NR) for the determination of glucose is described. This sensor is comprised of a multiwalled carbon nanotubes (MWNTs) conduit functionalized with NR and Nafion (Nf) as a binder and glucose oxidase as a biocatalyst. Neutral red was covalently immobilized on carboxylic acid groups of the CNTs via carbodiimide reaction. The functionalized MWNTs were characterized by microscopic, spectroscopic and thermal methods. The MWNT-NR-GOx-Nf nanobiocomposite was prepared by mixing the GOx solution with NR functionalized CNTs followed by mixing homogeneously with Nafion. The performance of the MWNT-NR-GOx-Nf nanobiocomposite modified electrode was examined by electrochemical impedance spectroscopy and cyclic voltammetry. The catalytic reduction of hydrogen peroxide liberated from the enzymatic reaction of glucose oxidase upon glucose with NR functionalized CNTs leads to the selective detection of glucose. The excellent electrocatalytic activity and the influence of nanobiocomposite film result in good characteristics such as low potential detection of glucose with a large determination range from 1 x 10(-8) to 1 x 10(-3)M with a detection limit of 3 x 10(-9)M glucose, a short response time (with 4s), good stability and anti-interferent ability. The improved electrocatalytic activity and stability made the MWNT-NR-GOx-Nf nanobiocomposite biosensor system a potential platform to immobilize different enzymes for other bioelectrochemical applications. 相似文献
The geometrical structures, electrical properties, and nonlinear optical (NLO) properties of AlNNT–Li and BNNT–Li nanotube systems were investigated by means of the density functional theory (DFT) method. Frontier molecular orbitals and density of states analyses show that adsorption of the Li atom can significantly narrow the wide HOMO–LUMO gaps of pure AlNNT and BNNT. The results reveal that AlNNT–Li and BNNT–Li systems containing diffuse excess electrons can be regarded as inorganic electrides. The formation of diffuse excess electrons leads to a decrease in transition energies, thereby increasing the first hyperpolarizabilities (β0) of AlNNT–Li and BNNT–Li. This work may contribute to the development of potential high-performance NLO materials.
Graphical abstract The structural characteristics and nonlinear optical properties of the AlNNT–Li and BNNT–Li systems were studied by means of density functional theory. Introduction of Li atoms greatly enhances the static first hyperpolarizabilities of AlNNT–Li and BNNT–Li
Chitosan fibres were grafted with flavonoids using tyrosinase to produce reactive o-quinones which subsequently react with primary amino groups of the chitosan. The reaction mechanism using chemically different flavonoids (flavanols, flavonols, flavone, flavanone, isoflavone) was followed by UV/vis spectroscopy and the successful grafting was demonstrated by ATR-IR spectroscopy, pH potentiometric titration and reflectance measurements. An increase of antioxidant activity of functionalized chitosan fibres using well established methods was found depending on the type of the flavonoid used. In addition, some flavonoids increased antimicrobial activity of chitosan against Bacillus subtillis and Pseudomonas aeruginosa. 相似文献
Diversely substituted 2-pyrrolines have been prepared by a novel multicomponent process involving a reaction of various N-(aryl- and alkylsulfonamido)-acetophenones with aldehydes and malononitrile. While the reaction is highly regioselective, it is not stereoselective, generating a mixture of cis and trans 2-pyrrolines. A number of analogs from both cis and trans 2-pyrroline libraries were found to have antiproliferative activity in human cancer cell lines. 相似文献
Because of the potential importance of carbon nanotubes (CNT) in renewable energy and other fields, molecular orbital ab initio calculations are used to study the relation between mechanical and electronic properties of such structures. We estimate a modulus of elasticity of 1.3 TPa and find out that the mechanism of CNT structure deformation is dependent on their chirality. Armchair and chiral nanotubes have ductile deformation fracture while zigzag have both ductile and brittle; on the other hand armchair nanotubes fracture and form two caps while chiral nanotubes adopt a helical-structure conformation. In addition, the energy gap between occupied and unoccupied molecular orbitals increases when nanotubes are under plastic deformation. This strong coupling between mechanical and electrical properties can be used to tune CNT mechanically to specific electronic bandgaps, affecting directly their electromagnetic absorption properties. 相似文献
An enormous length of DNA is packaged in the nuclei of eukaryotic cells. This is achieved through several intermediate levels of compaction, ranging from the double helix to the chromosome. The nucleosome is now firmly established as the first level of chromatin structure. Next it appears that the nucleosomes are themselves stacked in a two-track array, with a dinucleosome repeat. Several winding patterns of DNA are compatible with such a structure. It is shown here that, compared to other feasible DNA paths, the observed winding pattern has remarkable topological properties. The possible biological significance of this peculiarity is discussed. 相似文献
Bioprocess and Biosystems Engineering - Long-term and excessive use of monocrotophos (MPs) pesticide leads to an accumulation of MPs residues in agricultural products. Electrochemical biosensor... 相似文献
A novel and highly stable biomimetic oxidase sensor system was designed for catehol detection. FePP used as biomimetic horseradish peroxidase (HRP) was immobilized onto modified multi-walled carbon nanotubes (MWCNTs). Functional groups such as –OH, –NH2 and –COOH were introduced onto the surface of MWCNTs to provide biomimetic microenvironment for iron porphyrins (FePP). Stable biomimetic enzyme electrode has been developed to detect catechol as a simple, economical and efficient method. At optimal condition, the detection limit of OH-MWCNTs/FePP/Nafion was 3.754 × 10− 6 M. After stored at − 4 °C for 35 days, the oxidation current value still maintained 98.3% of initial activity. In repetitive nature test, relative standard deviation (RSD) of oxidation current remained within 1.0% after ten consecutive measurements in the same concentration of catechol solution, while most of reported oxidase sensor was within 2.0% under the same condition.