Specific Chirality Research Articles

Recognition Ability of DNA for Carbon Nanotubes Correlates with Their Binding Affinity

The ability to sort mixtures of carbon nanotubes (CNTs) based on chirality has recently been demonstrated using special short DNA sequences that recognize certain matching CNTs of specific chirality. In this work, we report on a study of the relationship between recognition sequences and the strength of their binding to the recognized CNT. We have chosen the (6,5) CNT and its corresponding DNA recognition sequences for investigation in this study. Binding strength is quantified by studying the kinetics of DNA replacement by a surfactant, which is monitored by following shifts in the absorption spectrum. We find that recognition ability correlates strongly with binding strength thus measured; addition or subtraction of just one base from the recognition sequence can enhance the kinetics of DNA displacement some 20-fold. The surfactant displaces DNA in two steps: a rapid first stage lasting less than a few seconds, followed by progressive removal lasting tens of minutes. The kinetics of the second stage is analyzed to extract activation energies. Fluorescence studies support the finding that the DNA sequence that recognizes the (6,5)-CNT forms a more stable hybrid than its close relatives.

Violation of the Condon Approximation in Semiconducting Carbon Nanotubes

The Condon approximation is widely applied in molecular and condensed matter spectroscopy and states that electronic transition dipoles are independent of nuclear positions. This approximation is related to the Franck-Condon principle, which in its simplest form holds that electronic transitions are instantaneous on the time scale of nuclear motion. The Condon approximation leads to a long-held assumption in Raman spectroscopy of carbon nanotubes: intensities arising from resonance with incident and scattered photons are equal. Direct testing of this assumption has not been possible due to the lack of homogeneous populations of specific carbon nanotube chiralities. Here, we present the first complete Raman excitation profiles (REPs) for the nanotube G band for 10 pure semiconducting chiralities. In contrast to expectations, a strong asymmetry is observed in the REPs for all chiralities, with the scattered resonance always appearing weaker than the incident resonance. The observed behavior results from violation of the Condon approximation and originates in changes in the electronic transition dipole due to nuclear motion (non-Condon effect), as confirmed by our quantum chemical calculations. The agreement of our calculations with the experimental REP asymmetries and observed trends in family dependence indicates the behavior is intrinsic.

Charge Transfer between Metal Clusters and Growing Carbon Structures in Chirality-Controlled Single-Walled Carbon Nanotube Growth

Synthesis of single-walled carbon nanotubes (SWCNTs) with specific chirality has been a great challenge. The detailed role of catalyst clusters in chirality-selective growth of SWCNTs is still unclear. We studied armchair (5,5), chiral (6,5), and zigzag (9,0) nanotube growths on a relaxed Ni55 cluster. Although adhesion energies and chemical potentials of growing carbon structures only show small differences, charges are evidently transferred (or redistributed) from Ni atoms to the growing end edges of nanotubes, which enhance the reactivity of carbon edges. Different chiral nanotubes exhibit distinct reaction active sites. (5,5) has five identical double-carbon active sites, while (9,0) has nine single-carbon active sites. (6,5) has a kink site with the highest reaction activity. These findings imply that the structures of metal clusters strongly correlate with nanotube growth sites through charge transfer (or redistribution). Potential opportunities exist in enabling (n,m) selective growth by engineerin...

Rational Concept To Recognize/Extract Single-Walled Carbon Nanotubes with a Specific Chirality

Single-walled carbon nanotubes (SWNTs) have remarkable and unique electronic, mechanical, and thermal properties, which are closely related to their chiralities; thus, the chirality-selective recognition/extraction of the SWNTs is one of the central issues in nanotube science. However, any rational materials design enabling one to efficiently extract/solubilize pure SWNT with a desired chirality has yet not been demonstrated. Herein we report that certain chiral polyfluorene copolymers can well-recognize SWNTs with a certain chirality preferentially, leading to solubilization of specific chiral SWNTs. The chiral copolymers were prepared by the Ni(0)-catalyzed Yamamoto coupling reaction of 2,7-dibromo-9,9-di-n-decylfluorene and 2,7-dibromo-9,9-bis[(S)-(+)-2-methylbutyl]fluorene comonomers. The selectivity of the SWNT chirality was mainly determined by the relative fraction of the achiral and chiral side groups. By a molecular mechanics simulation, the cooperative interaction between the fluorene moiety, alkyl side chain, and graphene wall were responsible for the recognition/dissolution ability of SWNT chirality. This is a first example describing the rational design and synthesis of novel fluorene-based copolymers toward the recognition/extraction of targeted (n, m) chirality of the SWNTs.

Growth Position and Chirality Control of Single-Walled Carbon Nanotubes

We propose a novel technique to grow the single-walled carbon nanotubes (SWNTs) with specific chirality at the desired position using free electron laser (FEL) irradiation during growth and surface treatment. As a result, only the semiconducting SWNTs grew at the area between triangle electrodes, where the ozone treatment was done to be hydrophilic when an alcohol chemical vapor deposition (ACCVD) process was carried out with the 800nm FEL irradiation. Although the number of possible chiral index is 22 in the SWNTs grown without the FEL irradiation, the number is much reduced to be 8 by the FEL.

Orbital Specific Chirality and Homochiral Self-Assembly of Achiral Molecules Induced by Charge Transfer and Spontaneous Symmetry Breaking

We study the electronic mechanisms underlying the induction and propagation of chirality in achiral molecules deposited on surfaces. Combined scanning tunneling microscopy and ab initio electronic structure calculations of Cu-phthalocyanines adsorbed on Ag(100) reveal the formation of chiral molecular orbitals in structurally undistorted molecules. This effect shows that chirality can be manifest exclusively at the electronic level due to asymmetric charge transfer between molecules and substrate. Single molecule chirality correlates with attractive van der Waals interactions, leading to the propagation of chirality at the supramolecular level. Ostwald ripening provides an efficient pathway for complete symmetry breaking and self-assembly of homochiral supramolecular layers.

Tight-binding model for carbon nanotubes from ab initio calculations

Here we present a parametrized tight-binding (TB) model to calculate the band structureof single-wall carbon nanotubes (SWNTs). On the basis of ab initio calculations we fit theband structure of nanotubes of different radii with results obtained with an orthogonal TBmodel to third neighbors, which includes the effects of orbital hybridization by means of areduced set of parameters. The functional form for the dependence of these parameters onthe radius of the tubes can be used to interpolate appropriate TB parametersfor different SWNTs and to study the effects of curvature on their electronicproperties. Additionally, we have shown that the model gives an appropriatedescription of the optical spectra of SWNTs, which can be useful for a properassignation of SWNTs’ specific chirality from optical absorption experiments.

Effect of Chirality by the Free Electron Laser Irradiation

We attempt to control a chirality of a single-walled nanotube (SWNT) using free electron laser (FEL) irradiation during its growth. It is expected that the FEL irradiation with a wavelength corresponding to an optical absorption of SWNT with a specific chirality promotes the growth of the specific SWNT. The specific SWNT reveals an optical absorption corresponding to the each own chirality. CNTs were grown using alcohol catalytic chemical vapor deposition (ACCVD) method with ethanol. The FEL was in-situ irradiated during ACCVD. The FEL used in this work is featured by the variable wavelength and the very sharp pulse width approximately 500 ps. The FEL with the wavelength of 1300 ∼ 1450 nm was irradiated to grow semiconductive SWNTs with the diameter of ca. 1.1 nm. In the SWNTs grown without FEL irradiation and/or with 1350 nm FEL irradiation, radial breathing modes (RBM) peaks were observed. From the RBM peak value the diameter of the SWNTs was estimated ca. 1.1 nm. Also those SWNTs were thought to be metallic from Kataura plot and resonance Raman effects. On the other hand, it was confirmed that 1300, 1400 and 1450 nm FEL irradiations resulted in the change of SWNT chilality, where no RBM peak appeared.

Some Remarks on Applying Homogenization Theory to Modeling the Constitutive Response of Carbon Nanotubes

An approach is described for constructing (using molecular dynamics simulations at the atomic scale) a mathematical model for the constitutive behavior of a carbon nanotube. The method is based on applying homogenization theory to a hexagonal array of carbon atoms with a specific chirality vector. The molecular dynamics simulations generate a set of periodic, rapidly varying, elastic constants for the nanotube. An example is presented to illustrate the technique for a specific array on a nanotube surface.

Preferential Growth of Single-Walled Carbon Nanotubes with Metallic Conductivity

Single-walled carbon nanotubes can be classified as either metallic or semiconducting, depending on their conductivity, which is determined by their chirality. Existing synthesis methods cannot controllably grow nanotubes with a specific type of conductivity. By varying the noble gas ambient during thermal annealing of the catalyst, and in combination with oxidative and reductive species, we altered the fraction of tubes with metallic conductivity from one-third of the population to a maximum of 91%. In situ transmission electron microscopy studies reveal that this variation leads to differences in both morphology and coarsening behavior of the nanoparticles that we used to nucleate nanotubes. These catalyst rearrangements demonstrate that there are correlations between catalyst morphology and resulting nanotube electronic structure and indicate that chiral-selective growth may be possible.

Quantum Electronic Stability in Selective Enrichment of Carbon Nanotubes

We have studied the structural and electronic stability of a helical ribbon of flavin mononucleotide wrapping around single-walled carbon nanotubes using first-principles density-functional calculations. The helical ribbon is formed through hydrogen bonding between adjacent uracil moieties of the isoalloxazine ring and stabilized through concentric pi-pi interactions. The electronic structure calculations reveal quantum electronic stability associated with lattice registry and band alignment between the helical assembly and the (8,6) nanotube. The electronic stability plays an essential role in the experimentally observed highly selective enrichment of specific chirality tubes.

Optical Characterizations and Electronic Devices of Nearly Pure (10,5) Single-Walled Carbon Nanotubes

It remains an elusive goal to achieve high-performance single-walled carbon nanotube (SWNT) field-effect transistors (FETs) composed of only single-chirality SWNTs. Many separation mechanisms have been devised and various degrees of separation demonstrated, yet it is still difficult to reach the goal of total fractionation of a given nanotube mixture into its single-chirality components. Chromatography has been reported to separate small SWNTs (diameter < or = 0.9 nm) according to their diameter, chirality, and length. The separation efficiency decreased with increasing tube diameter when the ssDNA sequence d(GT)(n) (n = 10-45) was used. Here we report our results on the separation of single-chirality (10,5) SWNTs (diameter = 1.03 nm) from HiPco tubes using ion-exchange chromatography. The separation efficiency was improved by using the new DNA sequence (TTTA)(3)T, which can recognize SWNTs with the specific chirality (10,5). The chirality of the separated tubes was examined by optical absorption, Raman, photoluminescence excitation/emission, and electrical transport measurements. All of the spectroscopic methods gave a single peak of (10,5) tubes. The purity was 99% according to the electrical measurement. The FETs composed of separated SWNTs in parallel gave an I(on)/I(off) ratio up to 10(6) due to the single-chirality-enriched (10,5) tubes. This is the first time that SWNT FETs with single-chirality SWNTs have been achieved. The chromatography method has the potential to separate even larger diameter semiconducting SWNTs from other starting materials to further improve the performance of the SWNT FETs.

A strategy to control the chirality of single-walled carbon nanotubes

We present a strategy to control the chirality of single-walled carbon nanotubes synthesized by chemical vapor deposition (CVD) over crystalline catalyst nanoparticles. Atomic-resolution imaging of nucleation points makes it possible to explore the structural correlation between the catalysts and the corresponding nanotubes. The formation of nanotubes with specific chirality could be associated with the angle of the step edge on (1 1 1) plane of the particle with respect to the growth direction of nanotubes. The result shows the potential in promoting some experimental advances in synthesis of nanotubes with the desired structure.

A DNA-based approach to the carbon nanotube sorting problem

Carbon nanotube sorting, i.e., the separation of a mixture of tubes into different electronic types and further into species with a specific chirality, is a fascinating problem of both scientific and technological importance. It is one of those problems that are easy to describe but difficult to solve. Single-stranded DNA forms stable complexes with carbon nanotubes and disperses them effectively in water. A particular DNA sequence of alternating guanine (G) and thymine (T) nucleotides ((GT) n , with n = 10 to 45) self-assembles into an ordered supramolecular structure around an individual nanotube, in such a way that the electrostatic properties of the DNA-carbon nanotube hybrid depend on tube structure, enabling nanotube separation by anion-exchange chromatography. This review provides a summary of the separation of metallic and semiconducting tubes, and purification of single (n, m) tubes using the DNA-wrapping approach. We will present our current understanding of the DNA-carbon nanotube hybrid structure and separation mechanisms, and predict future developments of the DNA-based approach.

Effect of Nanotube Cap on the Aromaticity of Single-Wall Carbon Nanotubes

The aromaticity properties of single-wall carbon nanotubes are investigated using density functional theory to determine the nucleus independent chemical shift at the open end of one-end-closed nanotubes and two-ends-open nanotubes. Two chiralities: near-arm-chair (6,5) and near-zigzag (9,1) nanotubes of identical diameter and each one having a unique cap compatible with their structure are examined for a comparison of their aromatic properties and the influence of the presence of the cap on such properties. The influence of the cap structure is also analyzed on the (8,3) nanotube having a larger diameter and being compatible with three different caps. We conclude that the presence of the cap and the specific chirality provide distinct aromaticity and reactivity properties to single-wall carbon nanotubes, whereas for a given chirality the particular nature of the cap seems to be of no relevance for these properties.

Transition State Chirality and Role of the Vicinal Hydroxyl in the Ribosomal Peptidyl Transferase Reaction

The ribosomal peptidyl transferase is a biologically essential catalyst responsible for protein synthesis. The reaction is expected to proceed through a transition state approaching tetrahedral geometry with a specific chirality. To establish that stereospecificity, we synthesized two diastereomers of a transition state inhibitor with mimics for each of the four ligands around the reactive chiral center. Preferential binding of the inhibitor that mimics a transition state with S chirality establishes the spatial position of the nascent peptide and the oxyanion and places the amine near the critical A76 2'-OH group on the P-site tRNA. Another inhibitor series with 2'-NH 2 and 2'-SH substitutions at the critical 2'-OH group was used to test the neutrality of the 2'-OH group as predicted if the hydroxyl functions as a proton shuttle in the transition state. The lack of significant pH-dependent binding by these inhibitors argues that the 2'-OH group remains neutral in the transition state. Both of these observations are consistent with a proton shuttle mechanism for the peptidyl transferase reaction.

Selection of carbon nanotubes with specific chiralities using helical assemblies of flavin mononucleotide

The chirality of single-walled carbon nanotubes affects many of their physical and electronic properties. Current production methods result in nanotubes of mixed chiralities, so facile extraction of specific chiralities of single-walled carbon nanotubes is an important step in their effective utilization. Here we show that the flavin mononucleotide, a common redox cofactor, wraps around single-walled carbon nanotubes in a helical pattern that imparts efficient individualization and chirality selection. The cooperative hydrogen bonding between adjacent flavin moieties results in the formation of a helical ribbon, which organizes around single-walled carbon nanotubes through concentric pi-pi interactions between the flavin mononucleotide and the underlying graphene wall. The strength of the helical flavin mononucleotide assembly is strongly dependent on nanotube chirality. In the presence of a surfactant, the flavin mononucleotide assembly is disrupted and replaced without precipitation by a surfactant micelle. The significantly higher affinity of the flavin mononucleotide assembly for (8,6)-single-walled carbon nanotubes results in an 85% chirality enrichment from a nanotube sample with broad diameter distribution.

Temperature Dependence of Raman Scattering from Single-Walled Carbon Nanotubes: Undefined Radial Breathing Mode Peaks at High Temperatures

We measured the Raman scatterings from various single-walled carbon nanotube (SWNT) samples over a wide temperature range (4–1000 K). The G-band peaks showed a clear temperature dependence, namely, decrease in the Raman shift frequency and broadening of the peak width as temperature increases. The main G-band peak (G+ peak) showed universal temperature dependence in Raman shift for the various SWNT samples and for the three excitation laser wavelengths (488.0, 514.5, and 632.8 nm), although the G-band features changed depending on the SWNT samples and excitation laser wavelengths owing to the resonance Raman effects. The Raman shift, peak width, and intensity of the radial breathing mode (RBM) peaks also exhibited temperature dependence. At high temperatures, undefined RBM peaks appeared, which could not be assigned to specific chiralities, and showed opposite temperature dependence in their intensities. The intensities of the RBM peaks are strongly enhanced by the resonance Raman effects, and the temperature may change the resonance Raman conditions.

Curvature effects on theE33andE44exciton transitions in semiconducting single-walled carbon nanotubes

The ${E}_{33}$ and ${E}_{44}$ optical transitions of small diameter $(0.7--1.2\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ semiconducting single-walled carbon nanotubes are probed using deep blue $(415--465\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ resonance Raman spectroscopy and photoluminescence excitation spectroscopy in the UV and blue regions $(280--488\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$. Individual radial breathing mode features, as well as Raman and photoluminescence excitation maxima, are assigned to specific nanotube chiralities. The chiral angle dependence of Raman intensity within a given $2n+m$ branch is found to continue, as does the trend toward increased excitation linewidths and weaker Raman intensities as higher lying transitions are accessed. The semiconducting ${E}_{33}$ and ${E}_{44}$ transition energies obtained for the largest observed diameters confirm recent results [P. T. Araujo et al., Phys. Rev. Lett. 98, 067401 (2007)] that show that these transitions reside on a blueshifted scaling-law line, separate from that describing ${E}_{11}$ and ${E}_{22}$ behaviors. Energies for nanotubes with diameter less than $0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, however, are not explained by any previous scaling-law fits. This behavior at small diameters is interpreted in terms of both a crossing over of the ${E}_{33}$ and ${E}_{44}$ energy trend lines for a given $2n+m$ branch and a chirality dependence in the many-body exciton effects that becomes significant at high curvatures.

Effect of Nanotube Length on the Aromaticity of Single-Wall Carbon Nanotubes

The aromaticity properties of single-wall carbon nanotubes are investigated using density functional theory to determine the nucleus independent chemical shift at the open end of one-end-closed nanotubes and two-ends-open nanotubes. Two chiralities: near-arm-chair (6,5) and near-zigzag (9,1) nanotubes of identical diameter and each one having a unique cap compatible with their structure are examined for a comparison of their aromatic properties and the influence of the presence of the cap on such properties. The influence of the cap structure is also analyzed on the (8,3) nanotube having a larger diameter and being compatible with three different caps. We conclude that the presence of the cap and the specific chirality provide distinct aromaticity and reactivity properties to single-wall carbon nanotubes, whereas for a given chirality the particular nature of the cap seems to be of no relevance for these properties.