Magnetic orientation of carbon nanotubes at temperatures of 231 K and 314 K

Carbon nanotubes were placed in magnetic fields of  80.0 kOe at temperatures of 231 K and 314 K. Scanning electron microscopy showed that nanotubes were oriented with the tube axis parallel to the fields. It was also observed that the probability of the orientation became higher, when the temperature was raised from 231 K to 314 K. The anisotropy in the susceptibilities parallel X∥ and perpendicular X _⊥ to the tube axis is suggested to increase with rise in temperature: X∥ ? X⊥ = (4 ± 2) × 10^?6 emu mol^?1 (per mol of carbon atoms) at 231 K and X∥ ? X⊥ = (45 ± 27) × 10^?6 emu mol^?1 at 314 K.     

A theoretical investigation of the interaction between fluorinated dimethyl ethers and molecular chlorine

Halogen bonds have received a great deal of attention in recent years. In this work, the interaction between fluorinated dimethyl ethers (n_F = 0–4) and molecular chlorine has been investigated by the theoretical methods. The two molecules are bonded together by an O···Cl?Cl halogen bond and the interaction energies calculated at the MP2/aug-cc-pVDZ level range between ?15.5 (n_F = 0) and ?6.1 (n_F = 4) kJ mol^?1. The correlations between interaction energies and proton affinity or ionisation potential of the ethers are discussed. The interaction between the molecules results in a small contraction of the CH bond of ethers and an elongation of the Cl?Cl bond. The data are analysed by a natural bond orbital analysis carried out at the wB97XD/6-311++G(d,p) level. The charge transfer from the ethers to Cl₂ is weak, ranges between 0.044 and 0.008 e and occurs mainly to the external Cl atom. The elongation of the Cl?Cl bond is related to the occupation of the σ^*(Cl?Cl) orbital and to the intermolecular hyperconjugation interaction between LP(O) and σ^*(Cl?Cl) orbitals. The interaction between the ethers and chlorine induces an enhancement of the infrared intensity and Raman scattering activity of the ν(Cl?Cl) vibration.     

Zerfallsschema und Matrixelemente für denβ-Übergang Ag110m→Cd110

Theβ decay Ag^110m→Cd¹¹⁰ has been investigated with a double lens spectrometer and aβ-γ circular-polarization correlation setup. The shape of the 6⁺→6⁺ β spectrum withE ₀=529 keV was found to be allowed, in disagreement with earlier work. The constantA of theβ-γ circular-polarization correlation was measured to beA=0·07±0·02. This implies a ratioX of Fermi to Gamow-Teller contribution to the decay ofX ₁=?0·02±0·03 orX ₂=?10·3 _?4·1 ^+2·3 . Qualitative shell model considerations favor the valueX ₁. Additional information is given for the disintegration schemes of Ag^110m and Ag¹¹⁰.     

A new study of the ν 2(A 1) infrared band of phosphorus trifluoride

The high-resolution Fourier transform infrared spectrum of phosphorus trifluoride (PF₃) has been reinvestigated in the v_2?=?1 vibrational excited state near 487?cm^?1 (at a resolution of 3?×?10^–3?cm^–1). Thanks to our new accurate rotational ground-state C ₀ value, 0.159970436(69)?cm^–1, and to recent pure rotational measurements, 318 new infrared transitions of the ν ₂ fundamental band have been assigned, extending the rotational quantum number values up to K _max?=?71 and J _max?=?72. A merge, for the first time, of 135 reported microwave data (K _max?=?42 and J _max?=?49) within the v_2?=?1 excited level and 2860 rovibrational transitions yielded improved constants of ν ₂. Parameters of this band have been obtained, up to sextic centrifugal distortion constants, by least-squares fits, σ _IR?=?3.60?×?10^–4?cm^–1 and σ _MW?=?5.53?×?10^–6?cm^–1 (166?kHz). Comparison of these constants with those measured previously by infrared spectroscopy reveals orders of magnitude higher accuracy of these new values.     

The concentration dependence of the proton chemical shift and the deuterium quadrupole coupling parameter for binary solutions of ethanol

Concentration dependent experimental measurements of the ethanol hydroxyl proton chemical shift σ_H for binary solutions were carried out. The solvents used were carbon tetrachloride (CCl₄), benzene, chloroform, acetonitrile, acetone and dimethylsulphoxide (DMSO). The chemical shift values range from 0.69 ppm (relative to TMS) for dilute ethanol (extrapolated to infinite dilution) in CCl₄ to 5.34 ppm for neat liquid ethanol. Ab initio calculations of the ethanol-solvent hydrogen bond energies show a correlation with the values for the chemical shift. The hydrogen bond energies for ethanol-solvent dimers range from 0.63 kcal mol^?1 for ethanol-CCl₄ to 9.34 kcal mol^?1 for ethanol-DMSO. Theoretical calculations show a linear correlation between the deuterium quadrupole coupling parameter XD ^ar d the isotropic proton chemical shift σ_H: X_D(kHz) = 291.48 ? 14.96 σ_H, where σ_H is the proton chemical shift in ppm relative to TMS (R ² = 0.99). Using the concentration dependent chemical shift data and this equation, X_D ia observed to range from 280 kHz for very dilute concentrations in CCl₄, where the primary species is ethanol monomer, to 210 kHz for the neat liquid that is comprised primarily of cyclic pentamers.     

Radical chemistry of glucosamine naphthalene acetic acid and naphthalene acetic acid: a pulse radiolysis study

Free radical‐induced oxidation reactions of glucosamine naphthalene acetic acid (GNaa) and naphthalene acetic acid (Naa) have been studied using pulse radiolysis. GNaa was synthesized by covalently attaching Naa on glucosamine. Hydroxyl adduct (from the reaction of hydroxyl radicals (^●OH) at the naphthalene ring) was identified as the major transient intermediate (suggesting that the ^●OH reaction is on the naphthalene ring) and is characterized by its absorption maxima of 340 and 400 nm. Both GNaa and Naa undergo similar reaction pattern. The bimolecular rate constants determined for the reactions are 4.8 × 10⁹ and 8.9 × 10⁹ dm³ mol^?1 s^?1 for GNaa and Naa respectively. The mechanism of reaction of ^●OH with GNaa was further confirmed using steady‐state method. Radical cation of GNaa was detected as an intermediate during the reaction of sulfate radical (SO₄^●?) with GNaa (k₂ = 4.52 × 10⁹ dm³ mol^?1 s^?1). This radical cation transforms to a ^●OH adduct at higher pH. The radical cation of GNaa is comparatively long lived, and a cyclic transition state by neighboring group participation accounts for its stability. The oxy radical anion (O^●?) reacts with GNaa (k₂ = 1.12 × 10⁹ dm³ mol^?1 s^?1) mainly by one‐electron transfer mechanism. The reduction potential values of Naa and GNaa were determined using cyclic voltammetric technique, and these are 1.39 V versus NHE for Naa and 1.60 V versus NHE for GNaa. Copyright © 2014 John Wiley & Sons, Ltd.     

Theoretical studies on structure and performance of [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine‐based derivatives

Based on energetic compound [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine, a series of functionalized derivatives were designed and first reported. Afterwards, the relationship between their structure and performance was systematically explored by density functional theory at B3LYP/6‐311 g (d, p) level. Results show that the bond dissociation energies of the weakest bond (N–O bond) vary from 157.530 to 189.411 kJ · mol^?1. The bond dissociation energies of these compounds are superior to that of HMX (N–NO_2, 154.905 kJ · mol^?1). In addition, H1, H2, H4, I2, I3, C1, C2, and D1 possess high density (1.818–1.997 g · cm^?3) and good detonation performance (detonation velocities, 8.29–9.46 km · s^?1; detonation pressures, 30.87–42.12 GPa), which may be potential explosives compared with RDX (8.81 km · s^?1, 34.47 GPa ) and HMX (9.19 km · s^?1, 38.45 GPa). Finally, allowing for the explosive performance and molecular stability, three compounds may be suggested as good potential candidates for high‐energy density materials. Copyright © 2016 John Wiley & Sons, Ltd.     

The B 2Σ+–X 2Σ+ Transition of 12C17O+: The 2‐υ″ Progression

Abstract

Three new bands of the B ²Σ⁺–X ²Σ⁺ system of ¹²C¹⁷O⁺ have been investigated using conventional spectroscopic techniques. The spectra were observed in a graphite hollow‐cathode lamp by discharging molecular oxygen (enriched in about 45% of the ¹⁷O₂ isotope) under 1.0 Torr pressure. The rotational analysis of the 2–4, 2–5, and 2–6 bands was performed with the effective Hamiltonian of Brown (Brown et al., J. Mol. Spectrosc. 1979; 74: 294–318). Molecular constants were derived from a merge calculation, including both the current wavenumbers and the spectroscopic data published by the authors previously. The principal equilibrium constants for the ground state of ¹²C¹⁷O⁺ are ω_e=2185.9658(84), ω_e x _e = 14.7674(11), B _e=1.927001(38), α_e=1.8236(22)×10^?2, γ_e=?0.331(28)×10^?4, D _e=6.041(12)×10^?6, β_e=0.100(31)×10^?7 cm^?1, and the equilibrium constants for the excited state are σ_e=45876.499(15), ω_e=1712.201(12), ω_e x _e=27.3528(39), B _e=1.754109(35), α_e=2.8706(57)×10^?2, γ_e = ?1.15(19)×10^?4, D _e=7.491(20)×10^?6, β_e=2.13(12)×10^?7, γ_e = 2.0953(97)×10^?2, and α_γe=?9.46(59)×10^?4 cm^?1, respectively. Rydberg–Klein–Rees potential energy curves were constructed for the B ²Σ⁺ and X ²Σ⁺ states of this molecule, and Franck–Condon factors were calculated for the vibrational bands of the B–X system.     

Cooperativity between the hydrogen bonding and halogen bonding in F3CX ··· NCH(CNH) ··· NCH(CNH) complexes (X=Cl,Br)

MP2 calculations with the cc-pVTZ basis set were used to analyse the intermolecular interactions in F₃CX?···?NCH(CNH)?···?NCH(CNH) triads (X=Cl, Br), which are connected via hydrogen and halogen bonds. Molecular geometries, binding energies, and infrared spectra of the dyads and triads were investigated at the MP2/cc-pVTZ computational level. Particular attention was given to parameters such as the cooperative energies, cooperative dipole moments, and many-body interaction energies. All studied complexes, with the simultaneous presence of a halogen bond and a hydrogen bond, show cooperativity with energy values ranging between ?1.32 and ?2.88?kJ?mol^?1. The electronic properties of the complexes were analysed using the Molecular Electrostatic Potential (MEP), electron density shift maps and the parameters derived from the Atoms in Molecules (AIM) methodology.     

Diffusion of chromium and manganese in γ-TiAl

The γ-TiAl intermetallic compound with suitable alloying additions has shown considerable promise as a material for high-temperature applications. Diffusion studies in this alloy system are useful in assessment of their creep behaviour and structural stability in service conditions. Tracer diffusion coefficients of ⁵¹Cr and ⁵⁴Mn in a γ-TiAl intermetallic compound containing 54.1 at. % aluminium were determined in the temperature range from 1095 to 1470?K. The temperature dependence of both the diffusing species follows a linear Arrhenius behaviour and can be expressed as D _Cr?=?4.4?×?10^?3exp(?350?kJ?mol^?1/RT)?m^2?s^?1 and D _Mn?=?1.2?×?10^?3?×exp(?326?kJ?mol^?1/RT)?m^2?s^?1. The data are analysed on the basis of empirical correlations between the diffusion and melting parameters applicable for conventional mono-vacancy diffusion mechanism in metals. It is concluded that impurity diffusion in γ-TiAl occurs through the migration of thermal vacancies via nearest-neighbour or next-nearest neighbour jumps.     

Interatomic force constants studies of AMF3perovskite-type crystals (A = K,Rb; M = Mg,Ni, Co,Zn, Mn)

A simple model involving only three force constants allows us to evaluate the short range interactions in perovskite fluorides from the experimental values of the elastic constants and the lattice parameters of these compounds. The results indicate that the A-F bonds are quite central in character whereas the M-F bonds are axially symmetric; thus the short range A-F interactions are assumed to have the Born-Mayer form:ZZZZZBy studying the variations of the force constants with respect to the lattice parameter r, it is determined that ρ = 0·232 , λ = 2·8 × 10^?8 ergs for K⁺-F^?; ρ = 0·232 , λ = 4·1 × 10^?8 ergs for Rb⁺-F^?; λ₂, ρ₂ and ρ₂ are respectively 6·9 × 10^?10 ergs, 0·34 , 0·98for Co²⁺-F^? and 2·9 × 10^?10 ergs, 0·46 , 1·40for Mn²⁺-F^?. Taking into account both the short range repulsive potential and the long range electrostatic potential we can study the variations of the lattice energy as a function of r near the equilibrium position and deduce a theoretical value of the lattice distance. In spite of the simplicity of the model, the discrepancy between the experimental and the theoretical values is less than 10 per cent for all the compounds.     

Effect of protonation on individual hydrogen bonds in the 8-oxoguanine-cytosine base pair: NMR,NBO and AIM analyses

Protonation increases the total binding energy of the 8-oxoguanine-cytosine (8OG:C) base pair by 60–70% at the B3LYP/6-311++G(d,?p) level of theory. It changes the individual H-bond energies, estimated from electron charge densities at bond critical points, by 1.16 to ?16.41?kcal?mol^?1. The individual H-bond energies and the two bond X–Y spin–spin coupling constants (^2hJ_X–Y) increase with protonation where 8OG behaves as an H-bond donor; the reverse is true for the H-bonds in which the 8OG unit acts as an H-bond acceptor. Similar to ^2hJ_X–Y, the value of ^1hJ_O–H (a one-bond H?···?Y spin–spin coupling constant) is distance dependent and in linear correlation with the O?···?H distance, but the ^1hJ_N–H values are independent of the N–H distance and the PSO term is the predominant portion in it. The ¹J_X–H spin–spin coupling constant is dominated by the negative FC term for all hydrogen bonds, although the PSO term is the best to investigate the behaviour of ¹J_X–H across the X–H?·?Y H-bond.     

Relationship between cation–π and anion–π interactions: individual binding energies in the π–Mz+–π–X−–π system

The mutual influence of cation–π and anion–π interactions in the π–M^z+–π–X^?–π system (M^z+ = Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺ and X^? = F^?, Cl^?) has been studied by quantum mechanical calculations. Both geometric parameters and energy data reveal that cation–π and anion–π interactions enhance each other in the π–M^z+–π–X^?–π system. Individual binding energies (E_ion···π) have been estimated in the quintuplet system using a simple new method from electron charge densities calculated at the bond critical points (BCPs) of the ion···π interaction by the atoms in molecules (AIM) method at the M062X/6-31+G(d) level of theory. With respect to the obtained individual binding energies, the strength of an ion···π interaction depends on the cooperative effects of other components.     

A Spectral Study of the Interaction Between Chelerythrine Chloride and Adenosine

Abstract

The possible anticancer mechanisms of chelerythrine (CHE) and its interactions with adenosine were investigated by UV‐visible spectrophotometric and spectrofluorimetric measurements and by thermodynamic calculations. The binding of CHE to adenosine could be characterized by the hypochromic and bathochromic effects in the absorption bands and the quenching of fluorescence intensity. The spectral data were fitted by linear analysis, yielding a binding constant of 8.68×10⁴ L · mol^?1 at 25°C of CHE with adenosine, and a van't Hoff enthalpy of 92.8 kJ/mol for the endothermic interactions. In addition, with ΔG=?28.2 kJ/mol and ΔS=406 J/mol · K, the interactions should be entropy‐driven.     

Computational study on structures,thermochemical properties,and bond energies of disulfide oxygen (S–S–O)‐bridged CH3SSOH and CH3SS(=O)H and radicals

Cleavage of disulfide bonds is a common method used in linking peptides to proteins in biochemical reactions. The structures, internal rotor potentials, bond energies, and thermochemical properties (Δ_fH°, S°, and Cp(T)) of the S–S bridge molecules CH₃SSOH and CH₃SS(=O)H and the radicals CH₃SS?=O and C?H₂SSOH that correspond to H‐atom loss are determined by computational chemistry. Structure and thermochemical parameters (S° and Cp(T)) are determined using density functional Becke, three‐parameter, Lee–Yang–Parr (B3LYP)/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p). The enthalpies of formation for stable species are calculated using the total energies at B3LYP/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p), and the higher level composite CBS–QB3 levels with work reactions that are close to isodesmic in most cases. The enthalpies of formation for CH₃SSOH, CH₃SS(=O)H are ?38.3 and ?16.6 kcal mol^?1, respectively, where the difference is in enthalpy RSO–H versus RS(=O)–H bonding. The C–H bond energy of CH₃SSOH is 99.2 kcal mol^?1, and the O–H bond energy is weaker at 76.9 kcal mol^?1. Cleavage of the weak O–H bond in CH₃SSOH results in an electron rearrangement upon loss of the CH₃SSO–H hydrogen atom; the radical rearranges to form the more stable CH₃SS· = O radical structure. Cleavage of the C–H bond in CH₃SS(=O)H results in an unstable [CH₂SS(=O)H]* intermediate, which decomposes exothermically to lower energy CH₂ = S + HSO. The CH₃SS(=O)–H bond energy is quite weak at 54.8 kcal mol^?1 with the H–C bond estimated at between 91 and 98 kcal mol^?1. Disulfide bond energies for CH₃S–SOH and CH3S–S(=O)H are low: 67.1 and 39.2 kcal mol^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

On difference of properties between organic fluorine hydrogen bond C–H···F–C and conventional hydrogen bond

The existence of C–H···F–C hydrogen bonds in the complexes of trifluoromethane and cyclic molecule (oxirane, cyclobutanone, dioxane, and pyridine) has been experimentally proven by Caminati and co-workers. This study presents a theoretical investigation on these C–H···F–C hydrogen bonds at B97D/6-311++G^** and MP2/6-311++G^** levels, in terms of C–H vibrational frequency shifts, atoms in molecules characteristics, and the bonding feature of C–H···F–C hydrogen bonds. It is found that in three important aspects, there are significant differences in properties between C–H···F–C and conventional hydrogen bonds. The C–H···F–C hydrogen bonds show a blueshift in the C–H vibrational frequencies, instead of the X–H normal redshift in X–H···Y conventional hydrogen bonds. The natural bond orbital (NBO) analyses show that σ and p types of lone pair orbitals of the F atom to an antibonding σ^*_H–C orbital form a dual C–H···F–C hydrogen bond. Such a dual hydrogen bonding leads to the proton acceptor directionality of the C–H···F–C hydrogen bond softer. Our studies also show that the Laplacian of the electron density (▽²ρ_BCP) is not always a good criterion for hydrogen bonds. Therefore, we should not recommend the use of the Laplacian of the electron density as a criterion for C–H···F–C hydrogen bonds.     

Interplay and competition between the lithium bonding and halogen bonding: R3C···XCN···LiCN and R3C···LiCN···XCN as a working model (R = H,CH3; X = Cl,Br)

UMP2 calculations with aug-cc-pVDZ basis set were used to analyse intermolecular interactions in R₃C···XCN···LiCN and R₃C···LiCN···XCN triads (R = H, CH₃; X = Cl, Br) which are connected via lithium bond and halogen bond. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries and binding energies of dyads, and triads are investigated at the UMP2/aug-cc-pVDZ computational level. Particular attention is paid to parameters such as cooperative energies, and many-body interaction energies. All studied complexes, with the simultaneous presence of a lithium bond and a halogen bond, show cooperativity with energy values ranging between ?1.20 and ?7.71 kJ mol^?1. A linear correlation was found between the interaction energies and magnitude of the product of most positive and negative electrostatic potentials (V_S,maxV_S,min). The electronic properties of the complexes are analysed using parameters derived from the atoms in molecules (AIM) methodology. According to energy decomposition analysis, it is revealed that the electrostatic interactions are the major source of the attraction in the title complexes.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Pulse radiolysis studies of 2‐ and 3‐hydroxybenzyl alcohols: inhibition of dehydration of ·OH‐(hydroxybenzyl alcohols) adducts by H2PO4− ions

Reactions of ·OH/O ^.? radicals and H‐atoms as well as specific oxidants such as Cl₂^.? and N₃· radicals have been studied with 2‐ and 3‐hydroxybenzyl alcohols (2‐ and 3‐HBA) at various pH using pulse radiolysis technique. At pH 6.8, ·OH radicals were found to react quite fast with both the HBAs (k = 7.8 × 10⁹ dm³ mol^?1 s^?1 with 2‐HBA and 2 × 10⁹ dm³ mol^?1 s^?1 with 3‐HBA) mainly by adduct formation and to a minor extent by H‐abstraction from ? CH₂OH groups. ·OH‐(HBA) adduct were found to undergo decay to give phenoxyl type radicals in a pH dependent way and it was also very much dependent on buffer‐ion concentrations. It was seen that ·OH‐(2‐HBA) and ·OH‐(3‐HBA) adducts react with HPO₄^2? ions (k = 2.1 × 10⁷ and 2.8 × 10⁷ dm³ mol^?1 s^?1 at pH 6.8, respectively) giving the phenoxyl type radicals of HBAs. At the same time, this reaction is very much hindered in the presence of H₂PO ions indicating the role of phosphate ion concentration in determining the reaction pathway of ·OH adduct decay to final stable product. In the acidic region adducts were found to react with H⁺ ions. At pH 1, reaction of ·OH radicals with HBAs gave exclusively phenoxyl type radicals. Proportion of the reducing radicals formed by H‐abstraction pathway in ·OH/O ^.? reactions with HBAs was determined following electron transfer to methyl viologen. H‐atom abstraction is the major pathway in O ^.? reaction with HBAs compared to ·OH radical reaction. H‐atom reaction with 2‐ and 3‐HBA gave transient species which were found to transfer electron to methyl viologen quantitatively. Copyright © 2010 John Wiley & Sons, Ltd.     

Quasi-elastic neutron scattering of benzene in Na-mordenite

The rotational and translational dynamics of benzene adsorbed in Na-mordenite have been studied by incoherent quasi-elastic neutron scattering. The measurements were performed at two benzene coverages at 300, 400 and 450 K. The observed quasi-elastic broadenings are described by a uniaxial rotational model about the six-fold axis of benzene. The mean time between successive jumps, at 300 K, is τ=1.45 × 10^?12 s at low coverage and 2.05×10^?12 s at high coverage. The correlation times follow an Arrhenius law with E_A=4.51 kJ mol^?1, at both coverages. The translational diffusion coefficient has been measured at 300 K and was found to be 0.67 × 10^?6 cm²s^?1.