Multi-walled carbon nanotubes applied through seed-priming influence early germination, root hair, growth and yield of bread wheat (Triticum aestivum L.).

BACKGROUND: Reports of multi-walled carbon nanotubes (MWCNTs) incorporated into plants have indicated better yield and productivity, yet the phenomena need in-depth understanding especially when agricultural crops are tested. We primed wheat seeds with MWCNTs to understand the effects on germination, growth, anatomy, physiology and yield. RESULT: This study, carried out in field conditions, is a step forward over the previous reports. Early germination, excessive root hair, denser stomata and larger root length result in faster growth and higher yield of wheat plants. Denser root hair facilitated the uptake of both water and essential minerals such as phosphorus (P) and potassium (K), which boosted the crop yield by significantly improving grain yield per plant from 1.53 to 2.5 g, a 63% increase. Increase in cell elongation by 80% was recorded, while xylem and phloem sizes dilated to almost 83% and 85% of control, thus enhancing their capacity to conduct water and nutrients. CONCLUSION: Augmented growth of MWCNT-primed wheat, enhancement in grain number, biomass, stomatal density, xylem-phloem size, epidermal cells, and water uptake is observed while finding no DNA damage. This opens up an entirely new aspect to using cost-effective nanomaterials (the MWCNTs were produced in-house) for enhancing the performance of crop plants. © 2017 Society of Chemical Industry.

The structural and electronic properties of tubular gold clusters with a spinal support.

Scalar relativistic density functional theory (DFT) is used to investigate the structural and electronic properties of an endohedrally doped hollow tube of gold with a hexagonal cross-section, X(M)Au(N) (X = Si, Al and Au, M = 3, 6, 9 and N = 24, 42, 60). Only Si as a dopant can be encapsulated to provide a stable backbone to the parent tubular Au(N) whereas structures containing an Al or Au backbone are distorted into non-cage like structures as the size increases. The dopant atoms increase the electron density around the Fermi level and shift the d-energy levels to deeper energy levels, thus reducing the HOMO­LUMO gap of the AuN tube. The effect is more pronounced in the Si doped Au(N) than the Al or Au doped Au(N) tubes. The Si9Au60 structure, though stable, shows a slight bending which can be corrected by removing one Si atom from the backbone which provides it with the correct amount of space. It can be concluded that Si and Al atoms can form long chains within the Au nanotube if a gap is present after every 4­6 layers of Au atoms to accommodate the size mismatch between the Si­Si and Al­Al bonds and the Au layers. Si doping within the Au(N) tube is more compatible than Al doping, as confirmed by Mulliken charge analysis.

Structural evolution and stability of hydrogenated Li(n) (n = 1-30) clusters: a density functional study.

The structure and electronic and optical properties of hydrogenated lithium clusters Li(n)H(m) (n = 1-30, m ≤ n) have been investigated by density functional theory (DFT). The structural optimizations are performed with the Becke 3 Lee-Yang-Parr (B3LYP) exchange-correlation functional with 6-311G++(d, p) basis set. The reliability of the method employed has been established by excellent agreement with computational and experimental data, wherever available. The turn over from two- to three-dimensional geometry in Li(n)H(m) clusters is found to occur at size n = 4 and m = 3. Interestingly, a rock-salt-like face-centered cubic structure is seen in Li(13)H(14). The sequential addition of hydrogen to small-sized Li clusters predicted regions of regular lattice in saturated hydrogenated clusters. This led us to focus on large-sized saturated clusters rather than to increase the number of hydrogen atoms monotonically. The lattice constants of Li(9)H(9), Li(18)H(18), Li(20)H(20), and Li(30)H(30) calculated at their optimized geometry are found to gradually approach the corresponding bulk values of 4.083. The sequential addition of hydrogen stabilizes the cluster, irrespective of the cluster size. A significant increase in stability is seen in the case of completely hydrogenated clusters, i.e., when the number of hydrogen atoms equals Li atoms. The enhanced stability has been interpreted in terms of various electronic and optical properties like adiabatic and vertical ionization potential, HOMO-LUMO gap, and polarizability.

Structural, electronic, and vibrational properties of C(60-n)Nn (n = 1-12).

Ab initio investigation of structural, electronic and vibrational properties of nitrogen-doped fullerenes (C(60-n)Nn, for n = 1-12) has been performed using numerical atomic orbital density functional theory. We have obtained the ground-state structures for C(60-n)Nn for n = 1-12, which show higher stability with a single nitrogen in a pentagon and two nonadjacent nitrogen atoms in a hexagon. Nitrogen doping leads to structural deformation, with the diameter showing variation from (7.14 - 0.24) to (7.14 + 0.10) A. The average diameter of C(60-n)Nn shows a small decrease for n > or = 5, with a minimum value of 7.06 A for n = 12. The change in the average diameter signifies the volume contraction, which is also maximum for C48N12. The binding energy per atom is found to decrease as a function of the number of N atoms. The HOMO-LUMO gap is found to decrease with an increase in substitutional nitrogen atoms; however, no systematic pattern could be observed. The Mulliken charge analysis performed on all optimized geometries shows a charge transfer of -0.3 to -0.45 (or 0.3-0.45 electrons) from nitrogen to carbon atoms, resulting in nitrogen atoms behaving as electrophilic sites. The harmonic vibrational frequency analysis shows the absence of any imaginary mode. The vibrational frequencies are found to decrease with an increase in the number of nitrogen atoms in C(60-n)Nn. The results obtained are consistent with available theoretical and experimental results.

Controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes.

A facile method for controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes is demonstrated. Nitric acid based oxidation was carried out to create carboxylic groups exclusively at the ends of carbon nanotubes, whereas oxidation using a mixture of nitric and sulfuric acid with varied reaction time was carried out to control the population of carboxylic groups on the side walls of nanotubes. In turn, 4-aminothiophenol modified gold nanoparticles were covalently interfaced to these carboxylated multi-walled carbon nanotubes in the presence of a zero length cross-linker, 1-ethylene-3-(3-dimethylaminopropyl) carbodiimide. Raman spectroscopic results showed increase in height of disorder band with each of these successive steps, indicating the increase in degree of functionalization of the carbon nanotubes. Fourier transformed infrared spectroscopic analysis affirmed the functionalization of nanostructures and the formation of nanohybrid. Transmission electron and field emission scanning electron microscopic analysis ascertained the attachment of gold nanoparticles to the ends and side walls of the multi-walled carbon nanotubes. The new hybrid nanostructures may find applications in electronic, optoelectronic, and sensing devices.

Transition metal induced magnetism in smaller fullerenes (Cn for n≤36).

The magnetic properties of 3d transition metals (TM) encapsulated inside smaller fullerenes ranging from C20 to C36 have been investigated using spin polarized density functional theory. The TM impurities stabilize asymmetrically at an off-center position for n≥28. The total magnetic moment (MM) of TM@Cn complexes are largely contributed by TMs and a small amount of MM of 0.12-0.50 µB is induced on the cage carbon atoms. The 3d TM atoms interact with C atoms of C20 and C28 cage ferromagnetically (FM) except for Ni@C28 which shows antiferromagnetic (AFM) interaction. The magnetic interactions change from FM to AFM in C32 cage for Ti, V, Cr and Mn. The MM gets quenched in Ni@Cn for n≥32. The total MM of Mn@Cn does not show any change although the nature of magnetic interactions changes from FM to AFM at n=32. Ti and V are the only TMs which show positive cohesive energy in all fullerenes considered. The smallest fullerene which can encapsulate all 3d TM are Cn for n≥32, consistent with available experimental and theoretical results.