Tandabany C. Dinadayalane

Advancing risk assessment of engineered nanomaterials: Application of computational approaches

Nanotechnology that develops novel materials at size of 100nm or less has become one of the most promising areas of human endeavor. Because of their intrinsic properties, nanoparticles are commonly employed in electronics, photovoltaic, catalysis, environmental and space engineering, cosmetic industry and - finally - in medicine and pharmacy. In that sense, nanotechnology creates great opportunities for the progress of modern medicine. However, recent studies have shown evident toxicity of some nanoparticles to living organisms (toxicity), and their potentially negative impact on environmental ecosystems (ecotoxicity). Lack of available data and low adequacy of experimental protocols prevent comprehensive risk assessment. The purpose of this review is to present the current state of knowledge related to the risks of the engineered nanoparticles and to assess the potential of efficient expansion and development of new approaches, which are offered by application of theoretical and computational methods, applicable for evaluation of nanomaterials.

Toward selection of efficient density functionals for van der Waals molecular complexes: comparative study of C-H···π and N-H···π interactions.

We have evaluated the performance of two of the recently developed density functionals (M06-2X and B2PLYP-D), which are widely used, by considering three important prototype systems, including benzene-acetylene, benzene-methane, and benzene-ammonia, possessing C-H···π or N-H···π interactions. Computational results are compared with the available experimental data. Considered density functionals are from two different classes: hybrid meta density functional (M06-2X) and double hybrid density functional (B2PLYP-D). The performance of a range of basis sets (6-31G(d), 6-31+G(d), 6-31+G(d,p), 6-311G(d,p), 6-311+G(d,p), aug-cc-pVXZ (X = D, T, Q)) with the above-mentioned two density functionals was evaluated. Comparison of the results includes Poples basis sets versus Dunnings correlation consistent basis sets with the M06-2X and B2PLYP-D functionals considered in this study. The basis set effect on geometrical parameters, dissociation energies, and selected vibrational frequency shifts was thoroughly analyzed. We have addressed whether the counterpoise corrections with geometry optimizations and vibrational frequencies are important. Our computational study reveals that calculations carried out with smaller basis sets very well reproduce the reported experimental values of dissociation energies. The present study also shows that using the very large Dunnings correlation consistent basis set worsens the results. The necessity of including counterpoise correction for binding energies depends on the system and the type of method used. In general, vibrational frequency calculations using these DFT functionals generate characteristic red shifts for the C-H···π or N-H···π interactions in the complexes.

Fundamental Structural, Electronic, and Chemical Properties of Carbon Nanostructures: Graphene, Fullerenes, Carbon Nanotubes, and Their Derivatives

This chapter provides information on various carbon allotropes and in-depth details of structural, electronic, and chemical properties of graphene, fullerenes, and single-walled carbon nanotubes (SWCNTs). We have written an overview of different computational methods that were employed to understand various properties of carbon nanostructures. Importance of application of computational methods in exploring different sizes of fullerenes and their isomers is given. The concept of isolated pentagon rule (IPR) in fullerene chemistry has been revealed. The computational and experimental studies involving Stone–Wales (SW) and vacancy defects in fullerene structures are discussed in this chapter. The relationship between the local curvature and the reactivity of the defect-free and defective fullerene and single-walled carbon nanotubes has been revealed. We reviewed the influence of different defects in graphene on hydrogen addition. The viability of hydrogen and fluorine atom additions on the external surface of the SWCNTs is revealed using computational techniques. We have briefly pointed out the current utilization of carbon nanostructures and their potential applications. Introduction to Carbon Nanostructures Carbon is one of the first few elements known in antiquity. The pure forms of this element include diamond and graphite, which have been known for few thousand years (http://www.nndc.bnl.gov/content/elements.html; Pierson 1993; Wikipedia – http://en.wikipedia.org/wiki/Carbon). Both of these materials are of immense importance in industry and in everyday life. Diamond and graphite are termed as giant structures since, by means of a powerful microscope, one could see millions and millions of atoms, all connected together in a regular array. Diamond would appear as a rigid and rather complex system like some enormous scaffolding construction. Carbon is also the major atomic building block for life. All lifeforms on Earth have carbon central to their composition. More than 10 million carbon-containing compounds are known. Compounds containing only carbon atoms, particularly nano-sized materials, are intriguing and attract attention of scientists working in various disciplines. Before 1985, scientists deemed that there were only three allotropes of carbon, namely, diamond, graphite, and amorphous carbon such as soot and charcoal. Soccer ball-shaped molecule comprising of 60 carbon atoms, C60 buckyball named fullerene, was discovered in 1985, and it is another interesting carbon allotrope (Kroto et al. 1985). Carbon nanotubes (CNTs), a spin-off product of fullerene, were reported in 1991 by Iijima (1991). Important well-known carbon materials are depicted in Fig. 1. The publication of transmission Fundamental Structural, Electronic, and Chemical Properties of Carbon. . . 3

Chapter 7 Toward nanomaterials: Structural, energetic and reactivity aspects of single-walled carbon nanotubes

Publisher Summary This chapter reviews the theoretical and experimental investigations on the chemistry of single-walled C nanotubes (SWNTs) and presents the classification of C nanotubes, sidewall functionalization of SWNTs, and detailed theoretical investigations of Stone–Wales (SW) defects in the (5,5) armchair nanotube. The structures and relative stabilities of the SW defect at different positions and orientations of the (5,5) armchair SWNT are examined, using the Hartree–Fock (HF) and Moller–Plesset perturbation theory through second order (MP2) methods and the Becke, three-parameter, Lee-Yang-Parr (B3LYP) functional. The local curvature is evaluated using the pyramidalization angle at the C sites of the SW defect region and the reactivity is explained based on the pyramidalization angle. The C–C bond shared by two 7-membered rings in the SW defect of SWNT need not always be less reactive than the corresponding bond in the pristine structure. The pyramidalization angles explain the reactivity of different bonds of the SW defect nanotubes. The C–C bonds that are in the 5–7, 5–6, and 7–7 ring fusions of SW defect region are highly reactive compared to defect-free structures because of the high local strain at these sites.

Mechanical properties of silicon nanowires

Silicon nanowires (SiNWs) are at the top of the list of materials used in conventional electromechanical devices as well as in strained nanotechnology. Both experimental and theoretical studies showed the size‐dependent character of mechanical properties of SiNWs. However, the surface contaminations, local surface strains, ‘boundary conditions’, native oxide, equipment‐induced errors, and the errors caused by postprocessing of results lead to softening of Youngs modulus and extension of the region where the size dependency is seen by experimentalists. Application of improved potentials or advanced theoretical modeling such as inclusion of explicit treatment of temperature and quantum‐mechanical effects allows to show specificity of Youngs modulus to the size and shape in case of small (width <4 nm) nanowires. The ductile‐brittle transitions of SiNWs at different temperatures are revealed. Some suggestions on postprocessing techniques are discussed.

Modelling of the Stabilization of the Complex of a Single Walled (5,5) Carbon Nanotube C60H20 with Cumulenic or Acetylenic Chain

Model calculations have been carried out for a (5,5) single walled carbon nanotube (SWNT) C60H20 and cumulene C2nH4 or acetylene C2nH2 (n = 1–4) chains and for their complexes obtained by insertion of a respective chain into the nanotube to check whether the theoretical simulation can (a) reproduce the stabilization of such supramolecular system and (b) propose which structure, i. e. acetylenic or cumulenic one, forms more stable complexes with SWNTs on the basis of quantum chemical calculations. In agreement with expectations, the calculations have revealed that the supramolecular systems are not stabilized at the DFT and HF level but, interestingly, reveal stabilization at the MP2/6‐31G* level. Practically the same HOMO and LUMO energy gaps and very small charge transfer between the SWNT and chains have been found.

Toward Understanding of Hydrogen Storage in Single-Walled Carbon Nanotubes by Investigations of Chemisorption Mechanism

We provide an overview of experimental and theoretical studies on hydrogen storage in single-walled carbon nanotubes (SWNTs) via chemisorption mechanism. The atomic hydrogens that are generated by dissociation of H2 molecules bind with carbon atoms of nanotubes, leading to strong C–H bonds in the chemisorption process. Recent experimental study indicates that 5.1 ± 1.2 wt% hydrogen storage could be achieved by hydrogenation (chemisorption process) of SWNTs. Our computational study shows that chemisorptions of one and two hydrogen atoms on the external surface of (3, 3), (4, 4), (5, 5), and (6, 6) armchair SWNTs are highly exothermic processes. Furthermore, two hydrogen atoms favor to bind at adjacent positions rather than at alternate carbon sites. This is different from the results reported on zigzag nanotubes. The chemisorptions of one and two hydrogen atoms significantly alter the C–C bond lengths of SWNTs in the vicinity of hydrogen addition due to the change of hybridization of carbon atom(s) from sp2 to sp3 at the chemisorption site(s). The effect of increasing the length of SWNTs on the geometries and the reaction energies of hydrogen chemisorption has also been explored. The high exothermicity of the chemisorption of hydrogen atoms on the surface of SWNTs explains the reason for the requirement of high temperature to remove hydrogen from hydrogenated SWNTs.

Binding of Alkali Metal Ions with 1,3,5-Tri(phenyl)benzene and 1,3,5-Tri(naphthyl)benzene: The Effect of Phenyl and Naphthyl Ring Substitution on Cation−π Interactions Revealed by DFT Study

The effect of substitution of phenyl and naphthyl rings to benzene was examined to elucidate the cation-π interactions involving alkali metal ions with 1,3,5-tri(phenyl)benzene (TPB) and 1,3,5-tri(naphthyl)benzene (TNB). Benzene, TPB, and four TNB isomers (with ααα, ααβ, αββ, and βββ types of fusion) and their complexes with Li+, Na+, K+, Rb+, and Cs+ were optimized using DFT approach with B3LYP and M06-2X functionals in conjunction with the def2-QZVP basis set. Higher relative stability of β,β,β-TNB over α,α,α-TNB can be attributed to peri repulsion, which is defined as the nonbonding repulsive interaction between substituents in the 1- and the 8-positions on the naphthalene core. Binding energies, distances between ring centroid and the metal ions, and the distance to metal ions from the center of other six-membered rings were compared for all complexes. Our computational study reveals that the binding affinity of alkali metal cations increases significantly with the 1,3,5-trisubstitution of phenyl and naphthyl rings to benzene. The detailed computational analyses of geometries, partial charges, binding energies, and ligand organization energies reveal the possibility of favorable C-H···M+ interactions when a α-naphthyl group exists in complexes of TNB structures. Like benzene-alkali metal ion complexes, the binding affinity of metal ions follows the order: Li+ > Na+ > K+ > Rb+ > Cs+ for any considered 1,3,5-trisubstituted benzene systems. In case of TNB, we found that the strength of interactions increases as the fusion point changes from α to β position of naphthalene.

Advances in In Silico Research on Nerve Agents

Nerve-agents (NAs) are toxic environment contaminants causing massive health hazard to the plant, animal, and civilian populations. Moreover, these materials have the properties of adsorption on various artificial surfaces which include cement, paints, metal oxides and clay minerals. These adsorption properties also threaten long-lasting toxic after-effects of NA exposure to the environment. Modeling these diverse NA-exposure characteristics through computational techniques has been always of great importance because of the restrictions in using such materials directly in the experiments due to their high toxicity. The present review discusses the recent advancements in the in silico research of NA, which include their conformational, biological and surface-occlusion properties. There are some positive sides of NA-adsorption also. The adsorption properties of NAs on oxide surfaces are used as binder to remove and subsequently deactivate them through chemical treatments. Moreover, NA adsorption on various surfaces is also useful to design materials to detect those agents using spectroscopic techniques. The present review also discusses the theoretical advancements in these directions in details. All of these discussions are mostly based on the results of the state of the art quantum-chemical computations. Related experimental results are also discussed to validate the results from such theoretical approaches.

Chapter 1:Graphene: Properties, Biomedical Applications and Toxicity

Among numerous commercial endeavors, nanotechnology is regarded as the key technology of the 21st century. It provides novel products and facilitates applications of innovative techniques in medicine, pharmacy, computer technology, and sensing. Therefore, it holds promise for potential global socio-...