The formation of low-dimensional inorganic nanotube crystallites in carbon nanotubes

The filling of carbon nanotubes, which vary in diameter and morphology, is directly observed by molecular dynamics computer simulation with a potential model which thermodynamically favors a four-coordinate bulk crystal structure. Inorganic nanotube (INT) structures form which are based on percolating hexagonal nets. For small carbon nanotube diameters the filling is shown to proceed via an "internal wetting" mechanism, which depends on the internal carbon nanotube area rather than the free volume. Both single- and double-walled INTs are predicted to form. The atomistic formation mechanisms are discussed and an intermediate structure identified. The INT structures, including the observed intermediate, are discussed by reference to a simple energy landscape. The formation energetics are discussed in terms of a simple analytical model which combines the INT strain energy and the tube-tube interactions. An effective phase diagram, which predicts the INT morphologies as a function of carbon nanotube diameter, is derived and discussed with respect to the analytical model.     

Controlling reversible elastic deformation of carbon nanotube rings

We show that bundles of carbon nanotubes can be coiled into ring structures by controlling the contraction of their polymer shells. With the robust carbon nanotubes, we demonstrate their reversible transformation between circular and compressed rings in a colloid.     

Deuterium structural effects in inorganic and bioinorganic aggregates

Deuterium kinetic isotope effects are widely used in chemical and biological research. Deuterium thermodynamic effects on the aqueous synthesis of inorganic materials, however, seem not to have been recognized. Here we report that the simple replacement of H(2)O with D(2)O in the synthesis of a solid-state manganese complex results in a new structurally and magnetically distinct phase. When iron oxides are synthesized, the relative amount of the mineral phases obtained in H(2)O vs D(2)O is different. The morphology and magnetic properties of the iron core of the iron storage protein ferritin are likewise different when mineralization is carried out in heavy water. The formation of extra inorganic solids, change in the ratio of two phases or alteration of a single phase morphology in D(2)O suggest that new inorganic and bioinorganic metal complexes might be obtained by using the thermodynamic isotope effect.     

Chemical and structural characterization of carbon nanotube surfaces

To utilize carbon nanotubes (CNTs) in various commercial and scientific applications, the graphene sheets that comprise CNT surfaces are often modified to tailor properties, such as dispersion. In this article, we provide a critical review of the techniques used to explore the chemical and structural characteristics of CNTs modified by covalent surface modification strategies that involve the direct incorporation of specific elements and inorganic or organic functional groups into the graphene sidewalls. Using examples from the literature, we discuss not only the popular techniques such as TEM, XPS, IR, and Raman spectroscopy but also more specialized techniques such as chemical derivatization, Boehm titrations, EELS, NEXAFS, TPD, and TGA. The chemical or structural information provided by each technique discussed, as well as their strengths and limitations. Particular emphasis is placed on XPS and the application of chemical derivatization in conjunction with XPS to quantify functional groups on CNT surfaces in situations where spectral deconvolution of XPS lineshapes is ambiguous.      

Application of symmetry operation measures in structural inorganic chemistry

This paper presents an application of the recently proposed symmetry operation measures to the determination of the effective symmetry point group of coordination polyhedra in inorganic solids. Several structure types based on octahedra are found to present distinct distortion patterns each, not strictly attached to the crystallographic site symmetry. These include the (NH4)2[CuCl4], CdI2 (brucite), FeS2 (pyrite), TiO2 (rutile), CaCl2, GdFeO3, PbTiO3,LiNbO3, BiI3, CrCl3, Al2O3, and NiWO4 structures. It is shown that a similar analysis can be applied to the Bailar and tetragonal Jahn-Teller distortions of molecular transition metal complexes, as well as to solids based on tetrahedra, such as the ZnCl2, FeS, BeCl2, SiS2, and KFeS2 structure types.     

Potential-induced structural deformation at electrode surfaces

The atomic structure on the metal side of the electrochemical interface depends on the applied electric potential and the nature of the adsorbing species in the electrolyte solution. In this short article, we review some recent results probing surface stress and surface relaxation effects in single-crystal metal electrodes that are driven by potential changes. Both the potential and the structure in the electrolyte layers at the interface alter the metal electronic structure so that the surface in the electrochemical environment is strongly modified from the ultra-high vacuum counterpart. A methodology for linking experimental and theoretical approaches for a fundamental understanding of electrochemical reactions is proposed.     

Tensile deformation induced structural rearrangement in amorphous silicon nitride

Silicon nitride exhibits good mechanical properties and thermal stability at high temperatures. Since experiments have limitations in nanoscale characterization of the chemical structure and related properties, atomistic simulation is a proper way to investigate the mechanism of this unique feature. In this paper, the melt-quench method is used to generate the amorphous structure of silicon nitride; then the structural properties of silicon nitride under tensile deformation were studied by angular pair distribution functions. The corresponding mechanism of tensile stress induced structure rearrangement is explored.     

Size dependent structural and electronic properties of MgO nanotube clusters

MgO nanotube clusters which cross sections are composed of two‐, three‐, four‐, and five‐membered rings are constructed and studied by the density functional theory at B3LYP/6‐31G(d) level. The variations of bond length present anisotropic effect. Three‐membered ring nanotube cluster is the most stable tube among these MgO isomers. Mixed covalent and ionic bonding always exists in MgO nanotube clusters. With increasing length of MgO nanotube clusters, the averaged atomic charge increases, and converge to 1.227; the s‐p separation of O bands decreases; whereas energy gap nearby frontier orbitals present dramatic difference corresponding to various structure family. It is possible that MgO nanotube clusters show electronic properties of semiconductor. An interpretation for MgO nanotube clusters fabricated by simply thermal methods is proposed. The structural and electronic properties of MgO nanotube clusters are discussed systematically in details. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Hydration-dependent structural deformation of guanine in the electronic singlet excited state

Theoretical study was performed to investigate how the degree of hydration affects the structures and properties of the canonical form (keto-N9H) of guanine in the ground and lowest singlet pipi* excited state. This work is the continuation of our earlier work where we have studied the hydration of guanine in the first solvation shell with one, three, five, and six water molecules. In the present investigation, we have considered 7-13 water molecules in hydrating guanine. Ground-state geometries were optimized at the Hartree-Fock level, whereas the configuration interaction-singles (CIS) method was used for the excited-state geometry optimization. The 6-311G(d,p) basis set was used in all calculations. The harmonic vibrational frequency analysis was used to determine the nature of the optimized ground- and excited-state potential energy surfaces; all geometries were found to be minima at the respective potential surfaces. It was found that the degree of hydration has a significant influence on the excited-state structural nonplanarity of guanine. It is expected that excited-state dynamics of guanine will depend on the degree of hydration. Ground- and excited-state geometries of selected hydrated species were also optimized in the bulk water solution using the polarizable continuum model (PCM). It was found that bulk water solution generally does not have significant influence on the structure of the hydrated species. Effects of hydration on different stretching vibrations in the ground and excited states are also discussed.     

Single-walled carbon nanotube as an effective quencher

Over the past few years, single-walled carbon nanotubes (SWNTs) have been the focus of intense research motivated by their unique physical and chemical properties. This review specifically summarizes recent progress in the development of fluorescence biosensors that integrate the quenching property of SWNTs and the recognition property of functional nucleic acids. SWNTs are substantially different from organic quenchers, showing superior quenching efficiency for a variety of fluorophores, with low background and high signal-to-noise ratio, as well as other advantages derived from the nanomaterial itself. As the second key component of biosensors, functional nucleic acids can bind to either their complementary DNA or a target molecule with the ability to recognize a broad range of targets from metal ions to organic molecules, proteins, and even live cells. By taking advantage of the strengths and properties of both SWNTs and nucleic acid based aptamers, a series of fluorescence biosensors have been designed and fabricated for the detection of a broad range of analytes with high selectivity and sensitivity.     

Initial structural studies of charged receptors that bind to inorganic phosphate anion and to an anionic phospholipid found in bacterial membranes

ITC titration studies of a family of bis-ammonium receptors based upon a scaffold of two bis-linked phenol rings show that several of the receptors bind to both dihydrogenphosphate and phosphatidylglycerol anions in a similar binding motif. Thermodynamic properties determined from ITC show that anion binding is entropy driven. Job plots determined from (1)H NMR clearly demonstrate that anion-receptor binding stoichiometry is dependent on the receptor's length of its bis-amine linkage.     

Demonstrating Linear Regression and Error Using an Experiment with a Microwave Oven

To provide an application for the method of linear least squares to data collected in a laboratory, a beaker with water is heated in a microwave oven, and the water temperature is measured as a function of heating variables (time and oven setting). This procedure enables a student to obtain a regression line for each oven setting, and to evaluate the intercept and slope of this line and compare them with the initial temperature of the water and the heating versus oven setting relationship described in the microwaves manufacturers manual. They also are asked to identify any sources of errors observed in this experiment.     

Influence of iron ions on the structural properties of some inorganic glasses

The effects of iron on the structural properties of Zn-borosilicate glass and Pb-metaphosphate glass were studied using X-ray diffraction,⁵⁷Fe Mössbauer spectroscopy and IR spectroscopy. Zn-borosilicate glass was prepared with varying amounts of Fe₂O₃ (up to 30% wt.). It was found that the chemical form of added iron (-FeOOH, -Fe₂O₃ or Fe₃O₄) affects the Fe³⁺/Fe²⁺ ratio, as well as the distribution of iron ions at different coordination sites. At high concentration of iron the crystallization of zinc ferrite in the glass matrix takes place. X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy showed that the amount of zinc ferrite in Zn-borosilicate glass decreases with the following order of addition: -FeOOH-Fe₂O₃Fe₃O₄. In Pb-metaphosphate glass doped with high concentration of -Fe₂O₃, the crystallization of Fe₃(PO₄)₂ is pronounced. The assignments of IR band positions and the corresponding interpretation are given. The importance of this study for the technology of vitrification of high-level radioactive wastes is emphasized.     

Understanding the geometric diversity of inorganic and hybrid frameworks through structural coarse-graining

Much of our understanding of complex structures is based on simplification: for example, metal–organic frameworks are often discussed in the context of “nodes” and “linkers”, allowing for a qualitative comparison with simpler inorganic structures. Here we show how such an understanding can be obtained in a systematic and quantitative framework, combining atom-density based similarity (kernel) functions and unsupervised machine learning with the long-standing idea of “coarse-graining” atomic structure. We demonstrate how the latter enables a comparison of vastly different chemical systems, and we use it to create a unified, two-dimensional structure map of experimentally known tetrahedral AB₂ networks – including clathrate hydrates, zeolitic imidazolate frameworks (ZIFs), and diverse inorganic phases. The structural relationships that emerge can then be linked to microscopic properties of interest, which we exemplify for structural heterogeneity and tetrahedral density.

A coarse-graining approach enables structural comparisons across vastly different chemical spaces, from inorganic polymorphs to hybrid framework materials.     

Zirconium vanadophosphate as an inorganic ion exchanger

Zirconium vanadophosphate was characterized as a stable inorganic ion exchager. The ion-exchange capacity was measured as 1.75 meq. H⁺ g^?1 at room temperature and it is stable up to 300°C. The exchanger is selective for devalent cations and the order of sorption of cations was found to be M²⁺ > M⁺ > M³⁺ M⁴⁺. Separations of Co²⁺?Ni²⁺, Cu²⁺?Hg²⁺ and Cr(VI)?Cr³⁺ were achieved on a column containing the ion exchanger. Copper could be separated from other base metals in geochemical samples. Differential thermal analysis showed an endothermic peak in the range of 65–420°C due to the dehydration of the ion exchanger with a low activation energy of 7.79 kcal mol^?1, which follows first-order kinetics. The ion exchanger did not show any further decomposition up to 1000°C. Infrared studies confirmed the presence of

groups which act as exchange sites for the cations. X-ray diffraction studies revealed that the compound is crystalline, with a crystal structure resembling that of the mineral muscovite.     

Investigation of structural changes in semi-crystalline polymers during deformation by synchrotron X-ray scattering

The mechanical behavior of polymer materials is strongly dependent on polymer structure and morphology of the material. The latter is determined mainly by processing and thermal history. Temperature-dependent on-line X-ray scattering during deformation enables the investigation of deformation processes, fatigue and failure of polymers. As an example, investigations on polypropylene are presented. By on-line X-ray scattering with synchrotron radiation, a time resolution in the order of seconds and a spatial resolution in the order of microns can be achieved. The characterization of the crystalline and amorphous phases as well as the study of cavitation processes were performed by simultaneous SAXS and WAXS. The results of scattering experiments are complemented by DSC measurements and SEM investigations. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1574–1586, 2010