Interaction of lead atom with atmospheric dioxygen and ozone: quantic study of the structure and the stability of resulting Pb(On) (n=1,2,3) compounds

Lead reaction with oxygen and ozone molecules is of a great importance for the study of the impact of this metal in the atmosphere medium. Stable species, intermediates, and transition states of possible resulting complexes have been studied with the three parameter hybrid B3LYP exchange-correlation DFT method, and coupled cluster with single, double, and triple excitation methods. Geometry, and spectroscopic and thermodynamic properties obtained for the different species are presented, discussed, and compared to available experimental data. On the basis of the knowledge of the thermal dissociation enthalpies and the absorbed wave length edges calculated for each species, we have drawn the most probable oxygenated complexes present in the atmosphere.     

Ionic Liquids for and by Analytical Spectroscopy

Abstract

In this mini‐review we highlight two aspects of ionic liquids that to date have either no or limited studies. They are (1) exploitation of unique features of ionic liquids to develop novel spectroscopic methods and (2) development of novel spectroscopic methods, for the sensitive and accurate determination of thermal physical properties of ionic liquids. In the first category, we will describe several novel methods which were developed utilizing unique properties of ionic liquids for measurements which are not possible otherwise. They include the sensitive and accurate method to determine enantiomeric compositions of a variety of pharmaceutical products with different size, shape, and functional groups. This method is based on the use of a chiral IL which serves both as a solvent and also as a chiral selector. Ionic liquids have also been successfully used to substantially enhance the sensitivity of thermal lens measurements. In the second category, we will describe recent development in which transient grating technique and thermal lens technique have been successfully used for the sensitive, accurate, nondestructive determination of thermal physical properties of ILs.     

Guanine Substitutions Prevent Conformational Switch from Antiparallel to Parallel G-Quadruplex

Guanine quadruplexes, recently reported to form in vivo, represent a broad spectrum of non-canonical conformations of nucleic acids. The actual conformation might differ between water solutions and crowding or dehydrating solutions that better reflect the conditions in the cell. Here we show, using spectroscopic techniques, that most guanine substitutions prevent the conformational switch from antiparallel or hybrid forms to parallel ones when induced by dehydrating agents. The inhibitory effect does not depend on the position of the substitution, but, interestingly, on the type of substitution and, to some extent, on its destabilising potential. A parallel form might be induced in some cases by ligands such as N-methyl mesoporphyrin IX and even this ligand-induced switch is inhibited by guanine substitution. The ability or inability to have a conformation switch, based on actual conditions, might significantly influence potential conformation-dependent quadruplex interactions.     

Spectroscopic properties of molecular anions of astrophysical and laboratory interest

Spectroscopic constants and molecular properties of the selected six diatomic anions of astrophysical and laboratory interest namely, FO⁻, CCl⁻, NS⁻, ClO⁻, ClF⁻ and AlS⁻ in their ground state have been studied in detail using hybrid HF/DF B3LYP method. The effect of basis set on spectroscopic properties has been studied with systematic improvement of basis set from aug-cc-pVDZ to aug-cc-pV5Z. The values of the spectroscopic constants and molecular properties obtained with these basis sets have been extrapolated to the complete basis set (CBS) limit. The spectroscopic properties calculated with the aug-cc-pV5Z basis set are very close to those at the CBS limit and these values agree very well with the theoretical and experimental results wherever available. Many of the spectroscopic constants and molecular properties of these anions are new and in particular those for ClF⁻ and AlS⁻ are first reported.     

Energetic polymers as binders in composite propellants and explosives

The principles behind the use of polymeric binders in composite propellants and explosives are described with emphasis on the properties which they should possess in order to satisfy the requirements for inclusion in a composition. The desirability of using energetic polymers as binders in terms of both performance and safety, and the problems associated with their preparation and properties, are discussed. The contributions of chemical synthesis within DRA to overcome these problems will be shown. Preparation of energetic polymers both by polymer modification and by polymerization of an energetic monomer is described. We have developed three energetic polymers: poly-3-nitratomethyl-3-methyloxetane (polyNIMMO), polyglycidyl nitrate (polyG-LYN) and nitrated hydroxy-terminated polybutadiene (NHTPB). Two of these (polyNIMMO and polyGLYN) have shown excellent properties in propellant and explosive formulations and proved that low-vulnerability, high-performance compositions are possible. The properties of the products from our work are compared with those of other groups and a glimpse of the future in this area is given to show the potential for new energetic polymers.     

Nitrification Progress of Nitrogen-Rich Heterocyclic Energetic Compounds: A Review

As a momentous energetic group, a nitro group widely exists in high-energy-density materials (HEDMs), such as trinitrotoluene (TNT), 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), etc. The nitro group has a significant effect on improving the oxygen balance and detonation performances of energetic materials (EMs). Moreover, the nitro group is a strong electron-withdrawing group, and it can increase the acidity of the acidic hydrogen-containing nitrogen-rich energetic compounds to facilitate the construction of energetic ionic salts. Thus, it is possible to design nitro-nitrogen-rich energetic compounds with adjustable properties. In this paper, the nitration methods of azoles, including imidazole, pyrazole, triazole, tetrazole, and oxadiazole, as well as azines, including pyrazine, pyridazine, triazine, and tetrazine, have been concluded. Furthermore, the prospect of the future development of nitrogen-rich heterocyclic energetic compounds has been stated, so as to provide references for researchers who are engaged in the synthesis of EMs.     

Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. I. Structure and energetics

The structural and energetic properties of purely siliceous, proton-, and Cu- and Co-exchanged chabazite have been studied using periodic density-functional (DFT) calculations with both conventional gradient-corrected exchange-correlation functionals and hybrid functionals mixing exact (i.e., Hartree-Fock) and DFT exchange. Spin-polarized and fixed-moment calculations have been performed to determine the equilibrium and excited spin-configurations of the metal-exchanged chabazites. For the purely siliceous chabazite, hybrid functionals predict a slightly more accurate cell volume and lattice geometry. For isolated Al/Si substitution sites, gradient-corrected functionals predict that the lattice distortion induced by the substitution preserves the local tetrahedral symmetry, whereas hybrid functionals lead to a distorted Al coordination with two short and two long Al-O bonds. Hybrid functionals yield a stronger cation-framework binding that conventional functionals in metal-exchanged zeolites, they favor shorter cation-oxygen bonds and eventually also a higher coordination of the cation. Both types of functionals predict the same spin in the ground-state. The structural optimization of the excited spin-states shows that the formation of a high-spin configuration leads to a strong lattice relaxation and a weaker cation-framework bonding. For both Cu- and Co-exchanged chabazite, the prediction of a preferred location of the cation in a six-membered ring of the zeolite agrees with experiment, but the energy differences between possible cation locations and the lattice distortion induced by the Al/Si substitution and the bonding of the cation depends quite significantly on the choice of the functional. All functionals predict similar energy differences for excited spin states. Spin-excitations are shown to be accompanied by significant changes in the cation coordination, which are more pronounced with hybrid functionals. The consequences of electronic spectra and chemical reactivity are analyzed in the following papers.     

四唑互变异构反应的密度泛函理论(DFT)研究

运用11种密度泛函理论方法对四唑互变异构反应进行了计算研究。结果表明,B3LYP-DFT法与从头算的优化几何和能量最为吻合;在6-31^*基组下B3LYP计算的IR频率与MP2/6-311G^*^*计算结果相差很小;用未经校正的B3LYP计算频率求得的产物(2H-四唑)的热力学性质与实测结果也完全一致;由此推荐B3LYP-DFT法适合于对四唑化合物作系统研究。     

Theoretical investigation of the coexistence of α and β-nitric acid trihydrates (NAT) molecular conformations

In this letter we document the possibility of the existence of a second molecular configuration for nitric acid trihydrates. Density functional theory (DFT) methods have been used for studying the nitric acid trihydrates α and β-NAT conformations, their spectroscopic and thermodynamics properties and dipole moments have been calculated. This study describes the gas–solid phase transition of the NAT and provides two possible pathways for the molecular structure transformation between α and β-NAT.     

Little Thermodynamic Penalty for the Synthesis of Ultraporous Metal Organic Frameworks

Many metal–organic frameworks (MOFs) of ultrahigh porosity (with molar volumes more than ten times greater than those of the corresponding dense phases) have been synthesized. However, the number of possible structures far exceeds those that have been made. It is logical to ask if there are energetic barriers to the stability of ultraporous MOFs or whether there is little thermodynamic penalty to their formation. Herein, we show that although the molar volumes of MOF‐177 and UMCM‐1 reach ultrahigh values, their energetic metastability is in the same range (of 7–36 kJ mol^?1) as that seen previously for other porous materials. These findings suggest that there is little thermodynamic penalty for the synthesis of structures with varying porosity, and hence, ultraporous frameworks are energetically accessible. Therefore, innovative synthesis methods have the possibility to overcome the drawbacks of conventional approaches and greatly extend the number, porosity, and properties of new framework materials.     

Spectroscopic constants and molecular properties of CN−, SiH−, PO−, SO−, SF−, and SiS−: Density functional study

Spectroscopic constants and molecular properties of selected diatomic anions namely CN^?, SiH^?, PO^?, SO^?, SF^?, and SiS^? in their ground states have been studied in detail using the hybrid HF/DF B3LYP method. The consistency of the calculated values has been verified with four different basis sets, with improved quality. The spectroscopic constants and molecular properties calculated with the aug‐cc‐pVTZ basis set agree very well with the experimental and theoretical values wherever available. Most of the spectroscopic constants and molecular properties of the selected diatomic anions, particularly the spectroscopic constants and molecular properties of SO^? and SiS^? are reported for the first time. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Energetic materials based on poly furazan and furoxan structures

Furazan and furoxan represent fascinating explosophoric units with intriguing structures and unique properties. Compared with other nitrogen-rich heterocycles, most poly furazan and furoxan-based heterocycles demonstrate superior energetic performances due to the higher enthalpy of formation and density levels. A large variety of advanced energetic materials have been achieved based on the combination of furazan and furoxan moieties with different kinds of linkers and this review provides an overview of the development of energetic poly furazan and furoxan structures during the past decades, with their physical properties and detonation characteristics summarized and compared with traditional energetic materials. Various synthetic strategies towards these compact energetic structures are highlighted by covering the most important cyclization methods for construction of the hetercyclic scaffolds and the following modifications such as nitrations and oxidations. Given the synthetic availabilities and outstanding properties, energetic materials based on poly furazan and furoxan structures are undoubtedly listed as a promising candidate for the development of new-generation explosives, propellants and pyrotechnics.     

Specific quantum mechanical/molecular mechanical capping-potentials for biomolecular functional groups

We present a series of capping-potentials designed as link atoms to saturate dangling bonds at the quantum/classical interface within density functional theory-based hybrid QM/MM calculations. We aim at imitating the properties of different carbon-carbon bonds by means of monovalent analytic pseudopotentials. These effective potentials are optimized such that the perturbations of the quantum electronic density are minimized. This optimization is based on a stochastic scheme, which helps to avoid local minima trapping. For a series of common biomolecular groups, we find capping-potentials that outperform the more common hydrogen-capping in view of structural and spectroscopic properties. To demonstrate the transferability to complex systems, we also benchmark our potentials with a hydrogen-bonded dimer, yielding systematic improvements in structural and spectroscopic parameters.     

Spontaneous segregation on a hybrid chiral surface

Segregation of enantiomers in two-dimensional adsorbed layers is a process that is usually controlled by anisotropic directional interactions between adsorbed molecules. In this contribution, we propose a simple theoretical model in which the chiral segregation occurs even though the lateral interactions are neglected. In particular, we consider a solid surface composed of two domains with different patterns of active sites being mirror images of each other. The domains of opposite handedness represent crystal facets of a composite chiral material which are adjoined to form a heterochiral adsorbing surface. To explore equilibrium properties of the system, we use Canonical Ensemble Monte Carlo method for a square lattice. The influence of factors such as energetic properties of the surface and density of the adsorbed layer on the extent of separation is examined. The obtained results indicate that effective two-dimensional separation on the hybrid chiral surface assumed in our model can be achieved only at sufficiently low adsorbate densities. The results also suggest that the segregation on the hybrid surface would be a promising method of enantiodiscrimination for those chiral molecules which do not exhibit strong lateral interactions.     

Mechanical properties of hybrid inorganic-organic framework materials: establishing fundamental structure-property relationships

The mechanical properties of hybrid framework materials, including both nanoporous metal-organic frameworks (MOFs) and dense inorganic-organic frameworks, are discussed in this critical review. Although there are relatively few studies of this kind in the literature, major recent advances in this area are beginning to shed light on the fundamental structure-mechanical property relationships. Indeed research into the mechanical behavior of this important new class of solid-state materials is central to the design and optimal performance of a multitude of technological applications envisaged. In this review, we examine the elasticity of hybrid frameworks by considering their Young's modulus, Poisson's ratio, bulk modulus and shear modulus. This is followed by discussions of their hardness, plasticity, yield strength and fracture behavior. Our focus is on both experimental and computational approaches. Experimental work on single crystals and amorphized monoliths involved primarily the application of nanoindentation and atomic force microscopy to determine the elastic moduli and hardness properties. The compressibility and bulk moduli of single crystals and polycrystalline powders were studied by high-pressure X-ray crystallography in the diamond anvil cell, while in one instance spectroscopic ellipsometry has also been used to estimate the elastic moduli of MOF nanoparticles and deposited films. Theoretical studies, on the other hand, encompassed the application of first principles density-functional calculations and finite-temperature molecular dynamics simulations. Finally, by virtue of the diverse mechanical properties achievable in hybrid framework materials, we propose that a new domain be established in the materials selection map to define this emerging class of materials (137 references).     

Electronic peculiarities of the excited states of [RuN5C]+ vs. [RuN6]2+ polypyridine complexes: insight from theory

The ground state, oxidized ground state, (3)MLCT and (3)MC excited states have been studied by DFT and TDDFT for two Ru(II) complexes bearing an N(6) or N(5)C coordination sphere. The effect of replacing one Ru-N dative bond by one Ru-C covalent bond have been studied and quantified on their ground state by the means of geometry optimization, NBO analysis and calculation of their IR vibrations. IR fingerprints of the Ru-C bond have been found at 945 and 1113 cm(-1). In addition, this study confirmed and quantified the effects of N→C(-) substitution on the spectroscopic properties of the [RuN(5)C](+) complex: a broader and bathochromically-shifted absorption spectrum, a smaller ground-(3)MLCT energy gap and a highly energetic (3)MC state are the major characteristics of the carbon-containing monocationic complex.     

Spectroscopic units in conjugated polymers: a quantum chemically founded concept?

In conjugated polymers the concept of spectroscopic units belonging to different spatial segments of the chain, which are responsible for the spectroscopic properties of the polymer, has been used to explain the spectral heterogeneity and the excitation migration by (F?rster type) hopping transfer. In the present work we study the possible mechanism of segmentation of polythiophene into spectroscopic units by using quantum-chemical methods (ZINDO). We found that static geometric defects such as kinks or torsions do not result in a significant localization of the excited states to a certain segment. Hence, we propose that a dynamic localization of excitation due to the interaction between the nuclear and electronic degrees of freedom is responsible for the formation of the spectroscopic units.     

Quantum chemical modeling of the addition reactions of 1‐n‐phenylpropyl radicals to C60 fullerene

Modeling of the addition of various radicals to C₆₀ fullerene is currently an active research area. However, the radicals considered are not able to adequately model polymeric radicals. In this work, we have performed a theoretical study of the possible reactions of C₆₀ fullerene with 1‐n‐phenylpropyl radicals, which are used to model polystyrene radicals. Several possible ways of subsequent addition of up to four 1‐phenylpropyl radicals to C₆₀ have been analyzed, the structures of the intermediates have been defined and thermal properties, such as the activation enthalpies of the corresponding reactions, have been calculated using density functional theory with the approximation of PBE/3z. It is shown that the topology of the spin density distribution on the fullerenyl radical causes regioselectivity for further radical addition. According to the energetic characteristics of the reactions, we assume the possibility of formation of products of one‐, two‐, three‐, and four‐ addition of the growth radical to the fullerene core in radical polymerization of styrene in the presence of C₆₀ fullerene. © 2016 Wiley Periodicals, Inc.     

Halogen bonds between 2,2,6,6-tetramethylpiperidine-N-oxyl radical and CxHyFzI species: DFT calculations of physicochemical properties and comparison with hydrogen bonded adducts

Structural, thermodynamic, and magnetic properties of adducts between the 2,2,6,6-tetramethylpiperidine-N-oxyl radical and representative hydrogen and halogen bond donors in solution have been investigated by an integrated computational tool including hybrid density functionals and discrete-continuum solvent models. From a quantitative point of view, the computed values show a fair agreement with experiment when environmental effects are taken into the proper account. From a more general point of view, our analysis points out a number of analogies, but also some difference, between hydrogen and halogen bond, which have been interpreted in terms of the various effects tuning thermodynamic and spectroscopic parameters.     

Photoluminescence Properties of Graphene Oxide in Non-Aqueous Solvents

Detailed attention to the interaction between graphene oxide (GO) and various organic fluorophores has been documented in literature as a result of which the impact of GO on the photophysical properties of the fluorophores is well known to the scientific community. However, the photoluminescence (PL) properties of GO in polar aprotic solvents are yet to be established. In this article, the PL properties of GO in polar aprotic solvents using various spectroscopic techniques have been reported. n-π* transition due to the C=O bonds in the sp³ hybrid regions and π-π* transition due to C=C bonds in the sp² hybrid are prominent in GO. The presence of quasi-molecules within sp²-sp³ domains acts as PL centers located in the sp³ matrixes of GO are responsible for the PL properties. This study showcases the presence of multiple emissive states of GO in polar aprotic solvents and conveys the fact that the PL properties of GO are very much wavelength-dependent.