Single-walled Carbon Nanotubes Complexes Research Articles

Interactions of phospholipid monolayer with single-walled carbon nanotube wrapped by lysophospholipid

In this study, we prepared single-walled carbon nanotubes (SWNTs) wrapped by 1-stearoyl-2-hydroxy-sn-glycero-3-phospho-(1′-rac-glycerol) (LPG), leading to a complex of SWNT–LPG. In an attempt to investigate the interactions of SWNT–LPG with a mimicked cell surface, SWNT–LPG solution was injected into the sub-phase of Langmuir trough to form a mixed monolayer with dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG), respectively. In addition to the measurement of typical surface pressure–area isotherms under compression mode, area changes occurring during insertion of SWNT–LPG into the monolayer were recorded at various surface pressures. Changes in surface potential were also measured for evident tracing of the degree of interactions between sub-phase and monolayer. A systematic comparison of relaxation patterns and insertion behavior along with surface potential data provided a rational basis to distinguish the degree of interactions between SWNT–LPG and the designated monolayer. The observed tendencies were found to be in accordance with the surface topography as revealed by the tapping mode atomic force microscopy. It was consistently observed that SWNT–LPG interacted with DPPC to a greater extent than with DPPG, when the sufficient coverage of nanotube surface by LPG molecules was assured.

Hydrogen transport in single-walled carbon nanotubes encapsulated by palladium

Hydrogen transport and loading into single-walled carbon nanotubes (SWCNT) encapsulated by thin Pd layers onto a massive Pd substrate were studied using a complex of vacuum thermal desorption, cyclic voltammetry and ESR methods. By adding SWCNT the hydrogen capacity of the Pd–SWCNT composite under electrochemical loading increases as much as 25% relative to Palladium metal alone. This provides moderate growth in the gravimetric capacity of the total composite based on a massive Pd substrate. The hydrogen binding energy in the SWCNT (eH=0.075eV/H-atom), estimated by studies of hydrogen transport in the Pd–SWCNT composite was lower than predicted for the Pd–SWCNT complex, but higher than the physisorption on the bare SWCNT. Using ESR we established that the Pd–Cx e-complexes formed at the wall of nanotube could be considered as hydrogen adsorption site, providing both high net gravimetric capacity and low hydrogen binding energy in the Pd encapsulated SWCNT. The results obtained provide an opportunity to probe a condensed hydrogen phase of nanometer scale confined in SWCNT, encapsulated by transition metals.

Density functional calculations on adsorption of 2-methylheptylisonicotinate antitubercular drug onto functionalized carbon nanotube

The interaction of 2-methylheptylisonicotinate (MHI) drug with (5,5) armchair single-wall carbon nanotube (SWNT) of finite length is studied using density functional theory. Carbon nanotubes can act as a suitable drug delivery vehicle for internalization of MHI within biological systems. DFT-PW91/DNP calculations reveal that the binding energies are negative for MHI–SWNT system and decreases with increase in functionalization, suggesting thermodynamic favorability for covalent attachment of functional moieties onto nanotube sidewall. Global reactivity descriptors determined from energies of frontier orbital help to understand the properties and reactivity of the drug–SWNT complex. Solvation studies indicate the enhanced solubility of MHI drug in presence of carbon nanotube support. These results are extremely relevant in order to identify the potential applications of functionalized carbon nanotubes as drug delivery systems.

Hierarchical polymer assemblies constructed by the mutual template effect of cationic polymer complex and anionic supramolecular nanofiber

Creation of higher-ordered polymeric architectures composed of alternative assemblies of single-walled carbon nanotubes (SWNTs) and fibrous porphyrin J-aggregates can be easily achieved utilizing the cationic semi-artificial polysaccharide which can act not only as a tubular host for SWNTs but also as a one-dimensional template for porphyrin molecules. This new class of hierarchical polymer assembly is formed, for the first time, by the mutual template effect of two components, i.e., the cationic SWNT complexes and the anionic porphyrin supramolecular nanofibers. In the present system, the self-assembling behaviors of the SWNT complexes as well as the final properties of the SWNT nanoarchitectures are strongly affected by the packing mode of porphyrin molecules on the cationic semi-artificial polysaccharide. Furthermore, we have confirmed that the light energy captured by the porphyrin J-aggregates is effectively transferred to SWNTs.

Supramolecular complexes of single walled carbon nanotubes with conjugated polymers

We have synthesized a series of conjugated polymers, including poly[(2,7-(9,9-dioctylfluorene)-alt-2,7-(9,9-didodecylfluorene)] (PF), poly[(2,7-(9,9-dioctylfluorene)-alt-2,5-(3-dodecylthiophene)] (PFT), and poly(3-dodecylthiophene) (PT). Non-covalent functionalization of single walled carbon nanotubes (SWNTs) with these polymers can impart good solubility to nanotubes in a number of organic solvents, including THF, dichlorobenzene, chloroform, and toluene. Solution and solid-state characterization of the resulting polymer–SWNT composites are described, including UV-Vis absorption and Raman spectroscopy. It was found that the UV-Vis absorption maximum of the polymers was red-shifted in their corresponding composites due to the planarization of the polymer backbone following adsorption upon the SWNT surface. Polymer–SWNT complexes also exhibited good solution stability at elevated temperature in THF and dichlorobenzene, with no significant SWNT sedimentation observed at elevated temperatures. Both UV-Vis absorption and Raman spectroscopy results indicated that the interaction of PT with the nanotubes was different from those of PF and PFT, suggesting that the choice of aromatic ring in the polymer structures plays an important role in the supramolecular complex formation with carbon nanotubes.

A pH-responsive carboxylic β-1,3-glucan polysaccharide for complexation with polymeric guests

The helix-forming nature of β-1,3-glucan polysaccharides is a characteristic that has potential for producing gene carriers, bio-nanomaterials and other chiral nanowires. Herein, carboxylic curdlan (CurCOOH) bearing the β-1,3-polyglucuronic acid structure was successfully prepared from β-1,3-glucan polysaccharide curdlan (Cur) by one-step oxidation using a 4-acetamido-TEMPO/NaClO/NaClO(2) system as the oxidant. The resulting high-molecular-weight CurCOOH was proved to bear the 6-COOH group in 100% purity. The optical rotatory dispersion (ORD) spectra indicated that the obtained CurCOOH behaves as a water-soluble single-strand in various pH aqueous media. This advantage has allowed us to use CurCOOH as a polymeric host to form various macromolecular complexes. For example, complexation of CurCOOH with single-walled carbon nanotubes (SWNTs) resulted in a water-soluble one-dimensional architecture, which formed a dispersion in aqueous solution that was stable for several months, and much more stable than SWNTs complexes of the similar negatively-charged polyacrylic acid (PAA) and polymethacrylic acid (PMAA). It was shown that in the complex, SWNTs are effectively wrapped by a small amount of CurCOOH, enabling them to avoid electrostatic repulsion. This pH-responsive CurCOOH formed a very stable complex with cationic water-soluble polythiophenes (PT-1), which was stabilized not only by the hydrophobic interaction but also by the electrostatic attraction between trimethylammonium cations in PT-1 and dissociated anionic COO(-) groups in CurCOOH. The included PT-1 became CD-active only in the neutral to basic pH region, and the positive Cotton effect suggested that the conjugated main chain is twisted in the right-handed direction. We also found that CurCOOH can interact with polycytidylic acid (poly(C)) only under high NaCl concentrations, the binding and release of which could be controlled by a change in the salt concentration. We believe, therefore, that CurCOOH bearing a dissociable COOH group can act as a new potential polymeric host to construct novel polymeric complexes applicable for gene carriers, biosensors, chiral polymer assemblies, etc.

The effect of molecular weight on the supramolecular interaction between a conjugated polymer and single-walled carbon nanotubes

The synthesis and fractionation of poly[2,7-(9,9-dioctylfluorene)-alt-2,5-(3-dodecylthiophene)] resulted in the isolation of eight different molecular weight (Mw) samples ranging from Mn of 5 to 85 kg mol−1. These individual polymer samples were fully characterized by Gel Permeation Chromatography, Nuclear Magnetic Resonance, as well as absorption and fluorescence spectroscopy. Each sample was separately mixed and ultrasonicated with single-walled carbon nanotubes (SWNTs) in tetrahydrofuran, and the nanotube concentration within the resulting solutions was measured. It was found that the solubility of the polymer–SWNT complexes strongly depends on the Mw of the conjugated polymer, with a maximum concentration reached when Mw ranged between 10 and 35 kg mol−1. Higher and lower Mws resulted in substantially reduced nanotube concentrations.

Improved selectivity in discriminating handedness and diameter of single-walled carbon nanotubes with N-substituted 3,6-carbazolylene-bridged chiral diporphyrin nanotweezers

Chiral diporphyrin nanotweezers 1 consisting of two chiral porphyrins with N-substituted 3,6-carbazolylene in between have been studied for the separation of single-walled carbon nanotubes (SWNTs). As compared to the analogous nanotweezers 2 without an N-substitutent, nanotweezers 1 with the N-octylcarbazolylene spacer exhibit much higher extraction ability and better selectivity for SWNTs. A narrower diameter range of SWNTs, from 0.88 to 0.92 nm, was selectively extracted with nanotweezers 1. In addition, only (7,6)-SWNTs of 0.90 nm diameter were optically enriched through extraction with 1, while SWNTs extracted with 2 showed lower optical purity of (7,6)-SWNTs. These enhanced extraction and discrimination abilities of 1 can be attributed to the formation of a more stable SWNT complex of 1 than of 2 in methanol.

Adsorption of M Species and M2 Dimers (M = Cu, Ag, and Au) on the Pristine and Defective Single-Walled Carbon Nanotubes: A Density Functional Theory Study

We studied the adsorption of neutral M, charged M, and M2 dimers (M = Cu, Ag, Au) on the pristine single-walled carbon nanotubes (SWNTs) as well as on the Stone−Wales and vacancy sites by means of the B3LYP/6-31G (d,p) hybrid density functional method. Our results for neutral metal atoms on the pristine and defective SWNTs agree very well with previous periodic calculations. The binding affinity trend of metal species toward the pristine and defective SWNTs is in the order of M+ > M− > M. This implies that the transfer of electron density between metal species and the nanotubes, the electrostatic attraction, and the Pauli repulsion play an important role in the M−SWNT system. From the Mulliken population analysis, the transfer of electron density induces a positive charge of the metal species and a negative charge of the carbon atoms of nanotubes. As far as the adsorption energy is concerned, the metal species are likely to deposit on the defect site, particularly on the vacancy site, rather than on the pristine tube. To explore the reactivity of the M−SWNT complexes which can serve as a gas sensor as well as a catalyst, the interaction between a CO molecule and a metal atom deposited on the atomic vacancy was also examined. We also found that the adsorption energy per atom decreases from the metal atom to metal dimers in line with the fact that metal−metal cohesion dominates over metal−SWNT interaction. Finally, based on calculated interaction energies, dimerization of adsorbed atoms on the defect sites is not particularly favored compared to dimerization on the pristine tube except for that of Ag and Au atoms on the vacancy site.

Covalent linking of ethylene amine functionalized single-walled carbon nanotubes to cobalt (II) tetracarboxyl-phthalocyanines for use in electrocatalysis

In this paper, we report on the use of ethylene amine (EA) side-wall functionalized single-walled carbon nanotubes (SWCNT) in the synthesis of covalently linked cobalt (II) tetracarboxyl-phthalocyanine complex (CoTCPc–EA–SWCNT(linked)), the characterization of the linked complex and the application of this complex in the electrocatalytic oxidation of amitrole. UV–vis, FTIR, TEM, Raman and XRD spectroscopies were used in characterization of CoTCPc–EA–SWCNT complex, while cyclic voltammetry, rotating disc electrode (RDE) voltammetry, chronoamperometry and electrochemical impedance spectroscopy were used during the characterization of amitrole on the modified glassy carbon electrode. Thermogravimetric analysis (TGA) was used to confirm the extend of functionalisation of of SWCNTs. The catalytic rate constant was 1.2 × 10 3 M −1 s −1 and the apparent electron rate transfer constant was 3.0 × 10 −5 cm s −1. The linear dynamic range was 1.0 × 10 −5–1.6 × 10 −4 M, with a sensitivity of ∼0.76 A mol −1L cm −2 and a limit of detection of 0.1 μM using the 3δ notation.

Coordination chemistry on the surface of single-walled carbon nanotubes

A facile method to coordinate transition metal complexes (TMCs) on single-walled carbon nanotubes (SWNTs) has been developed. Reaction of Zn(OAc) 2 with carboxylic acid functionalized SWNTs (SWNT-COOH) affords SWNT complexes ‘zipped-together’ by zinc carboxylate units (termed SWNT-TMC- 1 herein). Reactions of SWNT-TMC- 1 with 2,2′-bipyridine or 4,4′-bipyridine gave two new SWNT-TMCs, the former being ‘unzipped’ (SWNT-TMC- 2), and the latter involving an additional ligand bridge between the zinc ions (SWNT-TMC- 3). Inclusion of 2,2′-bipyridine and 4,4′-bipyridine into the SWNT-TMCs was confirmed by IR spectroscopy. The microstructures of SWNT-TMC- 2 and SWNT-TMC- 3 were investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (Xps), elemental mapping and linear profiles analysis.

Benzonitrile Adsorption on Fe-Doped Carbon Nanostructures

In this work we report a first principles study of benzonitrile (BZN) interaction with pristine and Fe-doped single-walled carbon nanotubes (SWNTs), graphene, and C60. The results show that the BZN molecule weakly adsorbs on SWNTs, graphene, and C60 through π−π aromatic ring stacking. This interaction can be considerably strengthened by the inclusion of Fe atoms, which leads to a strong π−3d−π covalent bond linking the BZN to the carbon nanostructure. The calculated binding energy values suggest that the BZN molecule adsorption with Fe atoms is much stronger than those for Fe−SWNT, Fe−C60, or Fe−graphene interaction. Indeed, the BZN−Fe stability on each carbon nanostructure surface was studied and the SWNTs complexes are more stable than those of C60 and graphene.

Enrichment of (8,4) Single‐Walled Carbon Nanotubes Through Coextraction with Heparin

Heparin sodium salt is investigated as a dispersant for dispersing single-walled carbon nanotubes (SWNTs). Photoluminescence excitation (PLE) spectroscopy is used for identification and abundance estimation of the chiral species. It is found that heparin sodium salt preferentially disperses larger-diameter Hipco SWNTs. When used to disperse CoMoCAT nanotube samples, heparin has a strong preference for (8,4) tubes, which have larger diameter than the predominant (6,5) in pristine CoMoCAT samples. PLE intensity due to (8,4) tubes increases from 7% to 60% of the total after threefold extractions. Computer modeling verifies that the complex of (8,4) SWNTs and heparin has the lowest binding energy amongst the four semiconducting species present in CoMoCAT. Network field-effect transistors are successfully made with CoMoCAT/heparin and CoMoCAT/sodium dodecylbenzene sulfonate (SDBS)-heparin (x3), confirming the easy removability of heparin.

Molecular modeling of dissociative and non-dissociative chemisorption of nitrosamine on close-ended and open-ended pristine and Stone-Wales defective (5,5) armchair single-walled carbon nanotubes

The nitrosamine adsorbed on close-ended and open-ended pristine and Stone-Wales defective (5,5) armchair single-walled carbon nanotubes (SWCNTs) was studied using the B3LYP/6-31G(d) method. Structure optimization of all possible adsorption configurations based on the combination of two nitrosamine (amino- and imino-) isomers and four types of nanotubes was carried out. The most stable configuration for the nitrosamine adsorbed on the (5,5) armchair SWCNTs was found to be dissociative chemisorption. The adsorption energies of the most stable structures of the adsorption complexes of close-ended and open-ended pristine SWCNTs with the imino isomer of nitrosamine were -127.15 and -137.14 kcal mol(-1), respectively.

Organization of single-walled carbon nanotubes wrapped with liquid-crystalline π-conjugated oligomers

Two oligo(phenylenevinylene)s with cyanobiphenyl terminates were synthesized as non-covalent modifiers of single walled carbon nanotubes (SWNTs). The wrapping of SWNTs with synthesized oligomers enhanced the dispersibility in CHCl3 by the dissociation of SWNT bundle structures. It was found that the addition of oligomers caused self-organized precipitation from a homogeneous dispersed solution of SWNT complexes. The self-organized precipitates exhibited thermotropic liquid-crystalline properties.

The ionic liquid-associated synthesis of a cellulose/SWCNT complex and its remarkable biocompatibility

Single-walled carbon nanotubes (SWCNTs) wrapped with cellulose have been successfully prepared by the treatment of SWCNTs with a cellulose solution in the ionic liquid 1-butyl-3-methylimidazolium bromide. The obtained SWCNT complex can be dispersed in water, forming a stable solution with excellent biocompatibility. It was found that long cellulose/SWCNT scaffolds could promote the growth of HeLa cells. In suspensions, short cellulose/SWCNTs complexes tend to enter HeLa cells and show little affect on cell proliferation. Therefore, the complexes have potential applications in biomaterial scaffolds and intracellular drug delivery systems.

Stiffness- and Conformation-Dependent Polymer Wrapping onto Single-Walled Carbon Nanotubes

This work reports the effect of stiffness and conformation of chain-like polymers on wrapping behaviors around single-walled carbon nanotubes (SWNT). As a model of chain-like polymers, three kinds of poly(dialkylsilane) (PSi)s with random-coiled, flexible, and semiflexible main chains were employed. Complexes of PSi and SWNT were prepared using mechanochemical high-speed vibration milling (HSVM). Stiffness-dependent polymer wrapping behaviors were investigated using combinational analyses with a differential scanning calorimeter, transmission electron microscopy, and atomic force microscopy. Furthermore, the conformational behaviors of the PSi's wrapped onto SWNTs were characterized spectroscopically with ordinary UV spectroscopy. Random-coiled and flexible PSi's were successfully wrapped onto small bundles of SWNTs, in which their conformations were changed to fit the surface curvatures of the SWNTs. However, semiflexible PSi could not form a complex with SWNTs, and its conformation remained unchanged even after the same HSVM process. Knowledge gained from this study may lead to a new approach to molecular design of chain-like polymers for efficient wrapping materials for SWNTs.

A Facile Strategy for Preparation of Fluorescent SWNT Complexes with High Quantum Yields Based on Ion Exchange

AbstractThe fluorescent imidazolium salt (1,3‐bis(9‐anthracenylmethyl)imidazolium chloride, [bamim]Cl) has been grafted onto the surfaces of single‐walled carbon nanotubes (SWNTs) using an ion exchange strategy based on metathesis of the K+ ion in CO2K derivatized SWNTs with [bamim]+. The resulting SWNT‐[bamim] complex has been characterized with high‐resolution transmission electron microscopy (HR‐TEM), X‐ray photoelectron spectroscopy (XPS), elemental mapping, and elemental linear profiles analysis. A blue light emission can be observed at 392, 414 and 438 nm for SWNT‐[bamim] upon being excited at 254 nm. The quantum yield (QY) of the SWNT‐[bamim] complex (0.40) is much higher than that of SWNT/[bamim]Cl (0.02), used as a control, and prepared using a π‐π stacking method, indicating that ion exchange is a far more effective strategy for retaining a high QY. Additionally, UV‐Vis‐NIR and Raman spectroscopy show that the SWNT‐[bamim] complex can maintain the one‐dimensional electronic states of SWNTs. Other imidazolium salts have also been successfully grafted onto SWNTs via the same strategy, indicating that the ion exchange process can serve as a universal strategy for the functionalization of SWNTs.

Au–carbon nanotube composites from self-reduction of Au3+ upon poly(ethylene imine) functionalized SWNT thin films

The combination of single-walled carbon nanotubes (SWNTs) with metal nanoparticles has been an area of recent interest due to the attractive electronic, mechanical, catalytic, and photonic properties of such materials. Although complexes of SWNTs and nanoparticles are known, macroscopic samples in which nanoparticles are uniformly dispersed in high density throughout the nanotube substrate have not been reported. Here, a simple method for the production of carbon nanotube thin films containing Au nanoparticles is described. SWNTs functionalized with highly branched poly(ethylene imine) (Mn = 10 kDa) were found to exhibit impressive aqueous solubility (180 mg L−1), allowing for the formation of homogeneous thin films by vacuum filtration. These films were subsequently functionalized with Au nanoparticle clusters by in-situreduction of HAuCl4 under mild conditions in the absence of additional reducing agents. Using thermogravimetric analysis, it was determined that poly(ethylene imine) functionalized SWNTs contained 17 wt% polymer, which amounts to one polymer chain for every 2600 carbon atoms within the nanotubes. Incubating these films in aqueous HAuCl4 solutions resulted in a high density, uniform distribution of Au nanoparticle clusters along the film surface. In addition, using transmission electron microscopy (TEM) and focused ion beam (FIB) milling within a scanning electron microscope (SEM), nanoparticles were found to be embedded at various depths throughout the film. SEM was employed to determine Au nanoparticle diameter and distribution. The average diameter of the Au clusters could be controlled in the range of 50 to 550 nm.

Efficient photosensitized energy transfer and near-IR fluorescence from porphyrin–SWNT complexes

Energy transfer from photoexcited porphyrin molecules to single-walled carbon nanotubes (SWNTs) has been experimentally detected for samples in aqueous Triton X-100 micellar suspensions. Addition of SWNTs to micelle-suspended porphyrin results in strong quenching of porphyrin fluorescence. Measurements of concentration-dependent quenching and spectra suggest that this process arises from formation of ground state non-covalent complexes between porphyrins and SWNTs. Optical excitation of the porphyrin generates characteristic near-IR emission from the SWNTs, indicating efficient energy transfer within the complexes. This energy transfer is deduced to occur through a Dexter-type electron exchange mechanism. Complexation of SWNTs with organic photosensitizers provides a novel way of uniformly exciting a wide range of nanotube structural species in polydisperse samples using only a single excitation wavelength.