Interaction and protection mechanism between Li@C(60) and nucleic acid bases (NABs): performance of PM6-DH2 on noncovalent interaction of NABs-Li@C60

To discuss the protection mechanism of DNA from radiation as well as assess the performance of PM6-DH2 on noncovalent interactions, the interaction of four nucleic acid bases (NABs) such as adenine (A), cytosine (C), guanine (G), and thymine (T), with Li@C(60) was extensively investigated with the-state-of-art theoretical methods describing noncovalent systems, like M06-2x, PBE-D, and PM6-DH2 methods. In the gas phase, the binding strength of NABs to Li@C(60) from M06-2x decreases in the sequence, G>C>A>T. As dispersion was explicitly included, PBE-D relatively enhances the binding of A and T and corrects the sequence to, G>A>C～T. PM6-DH2 predicted similar binding energies to those from PBE-D within 0.5 kcal/mol and the same binding sequence, suggesting that the PM6-DH2 method is promising for nano-scale systems. In the aqueous solution, binding of NABs-Li@C(60) is considerably decreased, and the M06-2X and PM6-D methods yield a different sequence from the gas phase, G>A>T>C. The encapsulation of Li atom results in a lower IP for Li@C(60) than those of NABs, and the dominant localization of single-occupied molecular orbital on Li@C(60) moiety of the complexes NABs-Li@C(60) further indicates that an electron would be ejected from Li@C(60) upon radiation and Li@C(60) is therefore able to protect DNA bases from radiation. In addition, it was revealed that Li prefers coordination with the hexagonal ring at Li@C(60) , which clarifies the existing controversy in this respect. Finally, Yang's reduced density gradient approach clearly shows that the weak and strong noncovalent interaction regions in the complexes, NABs-Li@C(60) and (NABs-Li@C(60) )(+).     

Theoretical characterization of thioepoxidated single wall carbon nanotubes

We have studied the external addition of sulfur to the walls of the (5,5) and (10,0) SWCNTs forming a cyclic thioepoxide. The binding energies are close to 32 kcal/mol, but they can be increased to 41 kcal/mol if the sulfur atoms are added forming a line along the axis of the (10,0) SWCNT. The addition of sulfur atoms to the (5,5) SWCNT alters the DOS but the tubes remains metallic. However, for the (10,0) SWCNT the exothermic addition of sulfur atoms can induce strong changes in the DOS, depending on the amount of sulfur atoms added. When we included one sulfur per 120 carbons, the (10,0) SWCNT showed metallic properties.     

Dynamics of local chirality during SWCNT growth: armchair versus zigzag nanotubes

We present an analysis of the dynamics of single-walled carbon nanotube (SWCNT) chirality during growth, using the recently developed local chirality index (LOCI) method [ Kim et al. Phys. Rev. Lett. 2011 , 107 , 175505 ] in conjunction with quantum chemical molecular dynamics (QM/MD) simulations. Using (5,5) and (8,0) SWCNT fragments attached to an Fe(38) catalyst nanoparticle, growth was induced by periodically placing carbon atoms at the edge of the SWCNT. For both armchair and zigzag SWCNTs, QM/MD simulations indicate that defect healing-the process of defect removal during growth-is a necessary, but not sufficient, condition for chirality-controlled SWCNT growth. Time-evolution LOCI analysis shows that healing, while restoring the pristine hexagon structure of the growing SWCNT, also leads to changes in the local chirality of the SWCNT edge region and thus of the entire SWCNT itself. In this respect, we show that zigzag SWCNTs are significantly inferior in maintaining their chirality during growth compared to armchair SWCNTs.     

Improvement of SWCNT transparent conductive films via transition metal doping

To realize transparent conductive films based on single-walled carbon nanotubes (SWCNTs), we applied a spray coating process with transition metal doping to SWCNT networks. Schottky contacts between metallic and semiconducting SWCNTs changed to Ohmic contacts due to the reduction of metals on the SWCNT surfaces via direct conversion from solution.     

On the applicability of cluster models to study the chemical reactivity of carbon nanotubes

We have performed a comparative study on the reactivity of metallic and semiconducting nanotubes using infinite and finite models. Infinite models were created using periodic boundary conditions while finite ones were constructed by means of hydrogen terminated nanotubes sections. Cluster models systematically underestimate the reactivity of metallic single wall carbon nanotube (SWCNT)s. We have confirmed that metallic nanotubes are more reactive than semiconducting species, in disagreement with previous works. The differences can be attributed to the presence of an instability in the singlet ground state of the wavefunction corresponding to semiconducting nanotubes clusters. When lower electronic states of the pristine cluster are considered, semiconducting nanotubes become less reactive as compared with metallic SWCNTs. Particularly, if an antiferromagnetic solution is considered for the semiconducting (10,0) SWCNT cluster, it becomes less reactive than the (5,5) SWCNT, as observed for infinite models. Because semiconducting nanotubes are less reactive than metallic counterparts, their reaction energies converge faster to the values observed for graphene. For a 1.6-nm diameter semiconducting nanotube, the addition energy is comparable with graphene. Thus, semiconducting nanotubes with diameters larger than 1.6 nm are going to be as reactive as graphene and the effects of curvature will be unimportant.     

A dispersion-corrected density functional theory study of the noncovalent interactions between nucleobases and carbon nanotube models containing stone–wales defects

The noncovalent bonding between nucleobases (NBs) and Stone–Wales (SW) defect-containing closed-end single-walled carbon nanotubes (SWNTs) was theoretically studied in the framework of density function theory using a dispersion-corrected functional PBE-G06/DNP. The models employed in this study were armchair nanotube (ANT) (5,5) and zigzag nanotube (ZNT) (10,0), which incorporated SW defects in different orientations. In one of them, the (7,7) junction is tilted with respect to SWNT axis (ANT-t and ZNT-t), whereas in ANT-p and ZNT-p models the (7,7) junction is parallel and perpendicular to the axis, respectively. The binding energies for uracil, thymine, cytosine, 5-methylcytosine, adenine, and guanine interacting with the defect-containing nanotube models were compared to the values previously obtained with the same calculation technique for the case of defect-free SWNTs, both in the gas phase (vacuum) and in aqueous medium. For most models, the interaction strength tends to be higher for purine than for pyrimidine complexes, with a clear exception of the systems including ZNT-p, both in vacuum and in aqueous medium. As it could be expected, the binding strength in the latter case is lower as compared to that in vacuum, roughly by 2–4 kcal/mol, due to the implicit inclusion of a medium (i.e., water) via the conductor-like screening model model. The closest contacts between NBs and SWNT models, frontier orbital distribution, and highest-occupied molecular orbital–lowest-unoccupied molecular orbital gap energies are analyzed as well. © 2019 Wiley Periodicals, Inc.     

Simultaneous purification and spectrophotometric determination of nickel present in as-prepared single-walled carbon nanotubes (SWCNT)

The quality of single-walled nanotubes (SWCNT) is usually assessed by means of electron microscopic techniques or Raman spectroscopy. However, these sophisticated techniques are not widely available and do not reliably estimate the impurities in highly heterogeneous samples containing metal particles, fullerenes and other carbonaceous materials. We have developed a simple, inexpensive and convenient spectrophotometric method to assess the purity of arc-discharge grown as-prepared SWCNT. Purification process consists of initial gas phase oxidation and refluxing with nitric acid at the optimal conditions including short time period during acid refluxing. We have shown that this method could remove the metal particles effectively with a good yield of high quality SWCNTs, as shown by the spectrophotometric and scanning tunneling microscope studies described here. The extent of removal of the nickel present in as-prepared carbon nanotube sample is followed by spectrophotometeric analysis of the dissolved nickel analyte. The composition of nickel in the SWCNT sample is found to be 17.56%. The method is based on the chelating of Ni²⁺ with dimethylglyoxime in ammoniacal citrate medium to form nickel dimethylglyoxime complex. A second stage purification of SWCNT eliminates the residual metal particles. The purified SWCNT has been studied using scanning tunneling microscopy which shows clearly resolved individual carbon nanotubes.     

A new analytical approach based on asymmetrical flow field-flow fractionation coupled to ultraviolet spectrometry and light scattering detection for SWCNT aqueous dispersion studies

This work demonstrates the potential of asymmetrical flow field-flow fractionation (A4F) coupled to Ultraviolet spectrometry (UV) and multi-angle light scattering (MALS) for the study of single-walled carbon nanotube (SWCNT) dispersion in aqueous solutions containing a surfactant. The results indicate that this technique is a powerful analytical tool that is able to evaluate SWCNT dispersion states in aqueous media and, more importantly, determine the presence or absence of aggregates, the numbers and sizes of different SWCNT populations and the SWCNT size distribution. Dynamic light scattering was employed to complete and demonstrate the relevance of the data that were obtained via A4F-UV-MALS. Two different anionic surfactants that are used to disperse SWCNTs were then studied. The dispersing powers of the surfactants were experimentally evaluated based on their structural organizations. This study demonstrates that surfactant concentration and sonication energy are key parameters that control the SWCNT dispersion state and SWCNT structural integrity therein.     

Chemically assisted directed assembly of carbon nanotubes for the fabrication of large-scale device arrays

We report the directed assembly of single-walled carbon nanotubes (SWCNTs) at lithographically defined positions on gate oxide surfaces, allowing for the high yield ( approximately 90%) and parallel fabrication of SWCNT device arrays. SWCNTs were first chemically functionalized through diazonium chemistry with a hydroxamic acid end group that both renders the SWCNTs water-soluble and discriminately binds the SWCNTs to basic metal oxide surfaces (i.e., hafnium oxide (HfO2)). The functionalized SWCNTs are then assembled from an aqueous solution into narrow trenches etched into SiO2 films with HfO2 at the bottom. The side walls of the patterned trenches induce alignment of the SWCNTs along the length of the trenches. Heating the structures to 600 degrees C removes the organic moieties, leaving pristine SWCNTs as evidenced by Raman spectroscopy and electrical measurements. Palladium source-drain electrodes deposited perpendicular to the trench length readily contact the ends of the aligned SWCNTs. The resultant devices exhibit the electrical performance expected for SWCNT devices, with no performance deterioration as a result of the placement process. This technique allows for the directed assembly and alignment of SWCNTs over a large area and results in a high yield of working devices, presenting a promising path toward large-scale SWCNT device integration.     

一维碳纳米管/二维二硫化钼混合维度异质结的原位制备及其电荷转移性能

一维(1D)材料与二维(2D)材料的结合可形成独特的混合维度异质结,其在继承2D/2D范德瓦尔斯异质结的独特物性之外,还具有丰富的堆叠构型,为进一步调控异质结的结构及性能提供了新的可操控自由度。p型1D单壁碳纳米管(SWCNT)与n型2D二硫化钼(MoS₂)的结合,为调控异质结的能带结构及器件性能提供了丰富的选择。本文直接在高密度、手性窄分布的SWCNT定向阵列及无序薄膜表面原位生长MoS₂,制备出高质量1D SWCNT/2D MoS₂混合维度异质结。深入分析形核点的表面形貌与结构,提出了“吸附-扩散-吸附”生长机制,用于解释混合维度异质结的生长。利用拉曼光谱分析,证实SWCNT与MoS₂间存在显著的电荷转移作用,载流子可在界面处快速传输,为后续基于此类1D/2D异质结的新型电子及光电器件的设计与制备提供了新思路。     

Diameter Selection of Carbon Nanotubes in Polymer/SWCNT Nanowire Arrays Fabricated by Template Wetting

Arrays of polymer/SWCNT (single‐wall carbon nanotube) nanowires supported on a residual nanocomposite film are prepared by melt wetting using porous anodic aluminum oxide (AAO) as a template. The aggregation parameter of SWCNTs extracted from the analysis of their Raman radial breathing modes gives the highest value for native SWCNTs, indicating that they tend to organize into bundles giving rise to a high degree of aggregation. However, the lowest value achieved at the interface between the nanocomposite film and the nanoarray is explained considering that the forces acting during infiltration are able to disrupt the SWCNT bundles inducing nanotube dispersion. In addition, scanning the nanoarrays along the nanowires length by Raman microscopy has shown a diameter selection of SWCNTs by the AAO membrane. The results reported in this work reveal that it is possible to fabricate arrays of nanowires with homogeneous SWCNT distribution along tens of microns, optimizing nanotube dispersion.     

Hydrogen adsorption on Ce/SWCNT systems: a DFT study

The adsorption of H(2) on Ce doped single-walled carbon nanotubes (SWCNT) and graphene are investigated by using density functional theory. For both systems, it is found that Ce preferentially occupies the hollow site on the outside. The results indicate that Ce/SWCNT system is a good candidate for hydrogen storage where six H(2) per Ce can be adsorbed and 5.14 wt% H(2) can be stored in the Ce(3)/SWCNT system. Among metal-doped SWCNTs, Ce exhibits the most favorable hydrogen adsorption characteristics in terms of the adsorption energy and the uptake capacity. The hybridization of the Ce-4f and Ce-5d orbitals with the H orbital contributes to the H(2) binding where Ce-4f electrons participate in the hybridization due to the instability of the 4f state. The interaction between H(2) and Ce/SWCNT is balanced by the electronic hybridization and electrostatic interactions. Curvature of SWCNT changes the size of the binding energy of Ce and C and the adsorption energy of H(2) on Ce.     

A comparison of the effect of nanotube chirality and electronic properties on the π–π interaction of single‐wall carbon nanotubes with pyrazinamide antitubercular drug

Theoretical investigation on local electronic structure and stability of the π–π stacking interaction of pyrazinamide (PZA) with armchair (5,5) and zigzag (9,0) single‐walled carbon nanotubes (SWCNTs) is performed using density functional theory (DFT). PZA is physisorbed onto nanotube sidewall through interaction of π orbitals of PZA and SWCNT and the enhanced structural stability of PZA/SWCNT systems is due to weak side‐on rather than the head‐on π‐interactions. The physisorption of PZA onto SWCNT sidewall is thermodynamically favored; as a consequence, it modulates the electronic properties of pristine nanotube in the vicinity of Fermi region and π–π stacked interactions is stronger in (9,0) SWCNT compared to (5,5) SWCNT. The density of states (DOS) analysis show that PZA contributes toward the enhancement of electronic states. Projected DOS and frontier orbital analysis in the vicinity of Fermi level region suggest the electronic states to be contributed from SWCNT rather than PZA. In addition, hybrid DFT calculation which includes the dispersion correction is employed to explain the non‐covalent π–π stacking interaction between PZA and SWCNT. The local density approximation and GGA results are compared with DFT‐D to explain near about accurately the weak nonbonded van der Waals interactions between PZA and SWCNTs. © 2012 Wiley Periodicals, Inc.     

Carbon chains and the (5,5) single-walled nanotube: structure and energetics versus length

Reliable thermochemistry is computed for infinite stretches of pure-carbon materials including acetylenic and cumulenic carbon chains, graphene sheet, and single-walled carbon nanotubes (SWCNTs) by connection to the properties of finite size molecules that grow into the infinitely long systems. Using ab initio G3 theory, the infinite cumulenic chain (:C[double bond]C[double bond]C[double bond]C:) is found to be 1.9+/-0.4 kcal/mol per carbon less stable in free energy at room temperature than the acetylenic chain (.C[triple bond]C-C[triple bond]C.) which is 24.0 kcal/mol less stable than graphite. The difference between carbon-carbon triple, double, and single bond lengths (1.257, 1.279, and 1.333 A, respectively) in infinite chains is evident but much less than with small hydrocarbon molecules. These results are used to evaluate the efficacy of similar calculations with the less rigorous PM3 semiempirical method on the (5,5) SWCNT, which is too large to be studied with high-level ab initio methods. The equilibrium electronic energy change for C(g)-->C[infinite (5,5) SWCNT] is -166.7 kcal/mol, while the corresponding free energy change at room temperature is -153.3 kcal/mol (6.7 kcal/mol less stable than graphite). A threefold alternation (6.866, 6.866, and 6.823 A) in the ring diameter of the equilibrium structure of infinitely long (5,5) SWCNT is apparent, although the stability of this structure over the constant diameter structure is small compared to the zero point energy of the nanotube. In general, different (n,m) SWCNTs have different infinite tube energetics, as well as very different energetic trends that vary significantly with length, diameter, and capping.     

Adsorption of DNA/RNA nucleobases on hexagonal boron nitride sheet: an ab initio study

Our ab initio calculations indicate that the interaction of deoxyribonucleic/ribonucleic acid (DNA/RNA) nucleobases [guanine (G), adenine (A), thymine (T), cytosine (C), and uracil (U)] with the hexagonal boron nitride (h-BN) sheet, a polar but chemically inert surface, is governed by mutual polarization. Unlike the case of graphene, all nucleobases exhibit the same stacking arrangement on the h-BN sheet due to polarization effects: the anions (N and O atoms) of nucleobases prefer to stay on top of cations (B) of the substrate as far as possible, regardless of the biological properties of nucleobases. The adsorption energies, ranging from 0.5 eV to 0.69 eV, increase in the order of U, C, T, A and G, which can be attributed to different side groups or atoms of nucleobases. The fundamental nature of DNA/RNA nucleobases and h-BN sheet remains unchanged upon adsorption, suggesting that the h-BN sheet is a promising template for DNA/RNA-related research, such as self-assembly.     

Poly(γ‐benzyl‐L‐glutamate)‐functionalized single‐walled carbon nanotubes from surface‐initiated ring‐opening polymerizations of N‐carboxylanhydride

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate) (PBLG) by ring‐opening polymerizations of γ‐benzyl‐L ‐glutamic acid‐based N‐carboxylanhydrides (NCA‐BLG) using amino‐functionalized SWCNTs (SWCNT‐NH₂) as initiators. The SWCNT functionalization has been verified by FTIR spectroscopy and transmission electron microscopy. The FTIR study reveals that surface‐attached PBLGs adopt random‐coil conformations in contrast to the physically absorbed or bulk PBLGs, which exhibit α‐helical conformations. Raman spectroscopic analysis reveals a significant alteration of the electronic structure of SWCNTs as a result of PBLG functionalization. The PBLG‐functionalized SWCNTs (SWCNT‐PBLG) exhibit enhanced solubility in DMF. Stable DMF solutions of SWCNT‐PBLG/PBLG with a maximum SWCNTs concentration of 259 mg L^?1 can be readily obtained. SWCNT‐PBLG/PBLG solid composites have been characterized by differential scanning calorimetry, thermogravimetric analysis, wide/small‐angle X‐ray scattering (W/SAXS), scanning electron microscopy, and polarized optical microscopy for their thermal or morphological properties. Microfibers containing SWCNT‐PBLG and PBLG can also be prepared via electrospinning. WAXS characterization reveals that SWCNTs are evenly distributed among PBLG rods in solution and in the solid state where PBLGs form a short‐range nematic phase interspersed with amorphous domains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2340–2350, 2010     

Intrinsic lifetimes of the excited state of DNA and RNA bases

The lifetimes of the excited state of free nucleobases were measured in the gas phase for the first time. They are, respectively, 1.0 and 0.8 ps for the purine bases adenine (shown above) and guanine and 3.2, 2.4, and 6.4 ps for the pyrimidine bases cytosine, uracil, and thymine at 267 nm. The longer lifetimes of the pyrimidine bases may be associated with their higher propensity toward photodegradation, especially in the case of thymine. The ultrashort lifetime of nucleobases conventionally known in solution was found to be an intrinsic molecular property due to extremely facile internal conversion, and therefore the lifetime should be largely independent of the medium at this energy, that is, whether in vacuo, in solution, or in vivo. The evolutionary selection of nucleobases as the durable carriers of genetic information is suggested to be due to their inherent immunity from photochemical reactions.     

Carbon nanotube field effect transistors for the fast and selective detection of human immunoglobulin G

We report a field effect transistor (FET) based on a network of single-walled carbon nanotubes (SWCNTs) which can selectively detect human immunoglobulin G (HIgG). HIgG antibodies, which are strongly adsorbed onto the walls of the SWCNTs, are the basic elements of the recognition layer. The non-specific binding of proteins and the effects of other interferences are avoided by covering the non-adsorbed areas of the SWCNTs with Tween 20. The selectivity of the sensor has been tested against bovine serum albumin (BSA), the most abundant protein in plasma. HIgG in aqueous solution with concentrations from 1.25 mg L(-1) (8 nM) can be readily detected with response times of about 10 min. The SWCNT networks that form the basis of the sensor are easily grown by chemical vapour deposition. Silver screen-printed electrodes make the sensor quick to build. The sensitivity obtained with this sensor is similar to other FET devices based on SWCNTs built using much more complicated lithography processes. Moreover, the sensor is a reagentless device that does not need labels to detect HIgG.     

Supramolecular Surface Modification and Solubilization of Single‐Walled Carbon Nanotubes with Cyclodextrin Complexation

A novel approach to solubilize single‐walled carbon nanotubes (SWCNTs) in the aqueous phase is described by employing supramolecular surface modification. We use cyclodextrin complexes of synthetic molecules that contain a planar pyrene moiety or a bent, shape‐fitted triptycene moiety as a binding group connected through a spacer to an adamantane moiety that is accommodated in the cyclodextrin cavity. The binding groups attach to the sidewalls of SWCNTs through a π–π stacking interaction to yield a supramolecular system that allows the SWCNTs to dissolve in the aqueous phase through the formed hydrophilic cyclodextrin shell. The black aqueous SWCNT solutions obtained are stable over a period of months. They are characterized through absorbance, static, and time‐resolved fluorescence spectroscopy as well as Raman spectroscopy, TEM, and fluorescence‐decay measurements. Furthermore, the shape‐fitted triptycene‐based system shows a pronounced selectivity for SWCNTs with a diameter of 1.0 nm.     

Quantum chemical investigation on structures of pyrrolic amides functionalized (5,5) single-walled carbon nanotube and their binding with halide ions

The structures of mono- and di-podal pyrrolic amides functionalized (5,5) single-walled carbon nanotubes (SWCNTs) and their complexes with fluoride, chloride, and bromide ions were obtained using the two-layered ONIOM(MO:MO) and density functional theory (DFT) methods. The binding energies between halide ions and all the receptors and their charge transfers were obtained using DFT method. The computational results indicate that the pyrrolic amide functionalized on the SWCNT affects to the density of state and energy gap of SWCNT. All the free receptors, mono-, di-podal pyrrolic amides and the functionalized SWCNT forming the strongest complexes were found.