Exhaustive radiolysis of 11 mM aqueous benzene solutions: effect of added oxygen

The gamma radiolysis of aqueous benzene solutions was studied under various conditions (oxygenated, aerated and anoxic) to ascertain the role that oxygen plays in the destruction of benzene. For the oxygenated and aerated systems, phenol and biphenyl were the major quantified products. For the anoxic system, phenol was the sole quantified product. Benzene was initially consumed with approximately the same yield in each of the three systems; G(–benzene) was 0.49 μmol J^–1. Initial yields of phenol, G(phenol), were found to be 0.12, 0.060 and 0.030 μmol J^–1 for the oxygenated, aerated and anoxic systems, respectively. Biphenyl was initially formed with G=0.028 and 0.019 μmol J^–1 in the oxygenated and aerated systems, respectively. The percent conversion of benzene to CO₂ after an absorbed dose of 2500 kGy was 55.1%, 30.5% and 12.5%, respectively, for the oxygenated, aerated and anoxic systems. The last traces of benzene disappeared by a dose of ca. 60 kGy in all three systems. A mechanism was proposed for each system that depended upon the presence or absence of O₂. The total solution toxicity for each system was calculated by summing the individual toxicities of benzene and each quantified product. For the oxygenated and aerated systems, the total solution toxicity was found to go through a maximum at a dose of 22 kGy and then decrease to a value below that of the original solution. The total solution toxicity of the anoxic system was found to decrease from the onset of irradiation.     

Dissociative ionization of 1,4-bis(2,5-phenyloxazolyl)benzene

Dissociative ionization of 1,4-bis(2,5-phenyloxazolyl)benzene (POPOP) molecule by electron impact in gaseous phase is studied. Potentials of appearance of some fragments of the molecule under study are determined from the experimentally measured dependences of ionization cross-section on the ionizing electron energy. A new ion with m/z = 144 [C₉H₆ON]⁺ is detected in the mass spectrum of the POPOP molecule, being complementary to the fragment with m/z = 220 [C₁₅H₁₀ON]⁺. The threshold of appearance of this ion is determined (E_ap = 9.51 eV) as well as the first ionization potential of the POPOP molecule and fragment ion appearance potentials.     

ATP- and redox-induced conformational changes in the activator of the radical enzyme 2-hydroxyisocaproyl-CoA dehydratase

A [4Fe–4S]¹⁺ cluster-containing protein activates 2-hydroxyisocaproyl-CoA dehydratase by an ATP-driven electron transfer. The activator has been proposed to change its conformation by MgATP similarly to nitrogenase Fe-protein. Iron chelation by bathophenanthroline removed the reduced [4Fe–4S]¹⁺ cluster from the activator in an ATP-dependent manner (rate, v = 0.128 ± 0.004 min⁻¹; K_m = 21 ± 1 μM); with ADP no chelation was observed (v < 0.001 min⁻¹). Chelation of the oxidised [4Fe–4S]²⁺ cluster occurred faster with ADP (v = 0.34 ± 0.05 min⁻¹) than with ATP (v = 0.132 ± 0.005 min⁻¹). The data indicate that reduction of the activator and binding of ATP induce conformational changes necessary to transfer the electron to the dehydratase. Interaction of both proteins promotes ATP hydrolysis (K_m = 0.5 ± 0.1 μM).     

Potential energy surface and rate constant of the inversion substitution reactions CH3X + O2 → CH3O2• + X• (X = SH,NO2)

The temperature dependence of the rate constant of the inversion substitution reactions CH₃X + O₂ → CH₃O₂^? + X^? (X = SH, NO₂), can be expressed as k = 6.8 × 10^–12(T/1000)^1.49exp(–62816 cal mol^–1/RT) cm³ s^–1 (X = SH) and k = 6.8 × 10^–12(T/1000)^1.26 × × exp(–61319 cal mol^–1/RT) cm³ s^–1 (X = NO₂), as found with the use of high-level quantum chemical methods and the transition state theory.     

DFT study of group 8 catalysts for the hydrophenylation of ethylene: Influence of ancillary ligands and metal identity

Computational methods are used to investigate catalytic hydrophenylation of ethylene using complexes of the type [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ [Y = Mp, n = 1; Y = Tp, n = 0; M = Ru or Os; L = PMe₃, PF₃, or CO; Mp = tris(pyrazolyl)methane; Tp = hydrido-tris(pyrazolyl)borate]. The conversion of ethylene and benzene to ethylbenzene with [(Y)M(L)(Ph)]ⁿ⁺ as catalyst involves four steps: (1) ethylene coordination, (2) ethylene insertion into the M–Ph bond, (3) benzene coordination, and (4) benzene C–H activation. DFT calculations form the basis to compare stoichiometric benzene C–H activation by [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ complexes to yield methane and [(Y)M(L)(Ph)(NCMe)]ⁿ⁺. In addition, starting from the 16-electron species [(Y)M(L)(Ph)]ⁿ⁺, potential energy surfaces for the formation of ethylbenzene are calculated to reveal the impact of modifications to the scorpionate ligand (Mp or Tp), co-ligand (L) and metal center (M).     

Measurements of Stark widths and shifts of Ne I lines using degenerate four-wave mixing and Thomson scattering methods

We report on measurements of Stark widths and shifts of four prominent Ne I lines of the 3s,3s′-3p transition arrays. The measurements were performed in an atmospheric-pressure arc discharge operated in argon–neon gas mixture.Sub-Doppler degenerate four-wave mixing technique was used to measure the line profiles, while Thomson scattering yielded the plasma parameters: electron density, n_e = (0.53–1.33) × 10²³ m^− 3, and electron temperature, T_e = 10,200–20,900 K. The measured profiles are symmetric within the uncertainty limits. The experimental Stark widths and shifts are compared with results of other experiments and theoretical calculations.     

A novel design of a temperature-controlled FT-ICR cell for low-temperature black-body infrared radiative dissociation (BIRD) studies of hydrated ions

A novel design for a temperature-controlled ICR cell is described for use in black-body infrared radiative dissociation (BIRD) studies of weakly bound systems like water clusters. Due to several improved design features, it provides a very uniform black-body radiation environment, and at the same time maintains efficient pumping for a low collision rate on the order of 10^?2 s^?1. At the lowest temperatures reached, nominally 89 K cell plate temperature, water evaporation effectively ceases, while intracluster reactions in V⁺(H₂O)_n with a small activation energy are still observed. BIRD rate constants for Ag⁺(H₂O)_n, n = 4–6, are shown in the temperature range T = 160–320 K. For n = 6, a linear Arrhenius plot with R² = 0.9943 is obtained without any calibration, confirming the suitability of the cell for quantitative BIRD studies.     

Adsorptive removal of phenol by bagasse fly ash and activated carbon: Equilibrium,kinetics and thermodynamics

Present study deals with the adsorption of phenol on carbon rich bagasse fly ash (BFA) and activated carbon-commercial grade (ACC) and laboratory grade (ACL). BFA is a solid waste obtained from the particulate collection equipment attached to the flue gas line of the bagasse-fired boilers of cane sugar mills. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH₀), contact time, adsorbent dose and initial concentration (C₀) on the removal of phenol. C₀ varied from 75 to 300 mg/l for the adsorption isotherm studies and the effect of temperature on adsorption. Optimum conditions for phenol removal were found to be pH₀ ≈ 6.5, adsorbent dose ≈10 g/l of solution and equilibrium time ≈5 h. Adsorption of phenol followed pseudo-second order kinetics with the initial sorption rate for adsorption on ACL being the highest followed by those on BFA and ACC. The effective diffusion coefficient of phenol is of the order of 10⁻¹⁰ m²/s. Equilibrium isotherms for the adsorption of phenol on BFA, ACC and ACL were analysed by Freundlich, Langmuir, Temkin, Redlich–Peterson, Radke–Prausnitz and Toth isotherm models using non-linear regression technique. Redlich–Peterson isotherm was found to best represent the data for phenol adsorption on all the adsorbents. The change in entropy (ΔS°) and heat of adsorption (ΔH°) for phenol adsorption on BFA were estimated as 1.8 MJ/kg K and 0.5 MJ/kg, respectively. The high negative value of change in Gibbs free energy (ΔG°) indicates the feasible and spontaneous adsorption of phenol on BFA. The values of isosteric heat of adsorption varied with the surface loading of phenol.     

Structure,chemical bonding,and 45Sc solid state NMR of Sc2RuSi2

The silicide Sc₂RuSi₂ was synthesized from the elements by arc-melting. The structure was refined on the basis of single crystal X-ray diffractometer data: Zr₂CoSi₂ type, C2/m, a = 1004.7 (2), b = 406.8 (1), c = 946.6 (2) pm, β = 117.95 (2), wR2 = 0.0230, 743 F² values, and 32 variables. The structure consists of a rigid three-dimensional [RuSi₂] network in which the two crystallographically independent scandium atoms fill larger cages of coordination numbers 16 and 15, respectively. The [RuSi₂] network shows short Ru–Si distances (234–247 pm) and two different Si₂ pairs: Si1–Si1 at 247 and Si2–Si2 at 243 pm. Each silicon atom has trigonal prismatic Sc₆ (for Si2) or Sc₄Ru₂ (for Si1) coordination. These building units are condensed via common edges and faces. The various Sc–Sc distances between the prisms range from 327 to 361 pm. From electronic structure investigation within DFT, chemical bonding shows a major role of Ru–Si bonding and the presence of strong electron localization around Si–Si pairs pointing to a polyanionic silicide network [RuSi₂]^δ?. The ⁴⁵Sc MAS-NMR spectra recorded at 11.7 and 9.4 T clearly resolve the two distinct scandium sites. The large electric field gradients present at both scandium sites result in typical line shapes arising from second-order quadrupole perturbation effects.     

Crystal structure and ionic conductivity of AgCr2(PO4)(P2O7)

Single crystals of a new phosphate AgCr₂(PO₄)(P₂O₇) have been prepared by the flux method and its structural and the infrared spectrum have been investigated. This compound crystallizes in the monoclinic system with the space group C2/c and the parameters are, a = 11.493 (3) Å, b = 8.486 (3) Å, c = 8.791 (2) Å, β = 114.56 (2)°, V = 779.8 (3) ųand Z = 4. Its structure consists of CrO₆ octahedra sharing corners with P₂O₇ units to form undulating chains extending infinitely along the [110] direction. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the Ag⁺ ions are located. The infrared spectrum of this compound was interpreted on the basis of P₂O₇^4? and PO₄^3? vibrations. The appearance of ν_sP–O–P in the spectrum suggests a bent P–O–P bridge for the P₂O₇^4? ions in the compound, which is in agreement with the X-ray data. The electrical measurements allow us to obtain the activation energy of (1.36 eV) and the conductivity measurements suggest that the charge carriers through the structure are the silver captions.     

Characterization of a new magnesium hydrogen orthophosphate salt,Mg3.5H2(PO4)3, synthesized in supercritical water

Beige crystals of a new magnesium hydrogen orthophosphate salt, Mg_3.5H₂(PO₄)₃, as well as nanoparticles of an amorphous, non-Mg-containing phosphate material, Fe_1−yK_yPO₄ (0 < y < 1), have been produced by hydrothermal reactions in supercritical water (SCW) of equivalent quantities of aqueous MgCl₂·6H₂O (2 M), and K₄P₂O₇ (1 M) in concentrated HCl in a stainless-steel batch reactor at 400–450 °C and 25–32 MPa. The new salt has been characterized by single-crystal X-ray diffraction and IR and Raman spectroscopies. It crystallizes in the triclinic space group Pī, Z = 2 with the following unit-cell parameters: a = 6.438(1), b = 7.856(1), c = 9.438(1) Å; α = 104.57(1), β = 108.61(1), γ = 101.28(1)°, V = 739.99 Å³. The effects of the SCW conditions on the nature of the products and their yields and morphologies have been studied by IR and Raman spectroscopies, X-ray powder diffraction, X-ray energy dispersive analysis, scanning electron microscopy, transmission electron microscopy and inductively coupled plasma analysis.     

Doping effect of nonmagnetic impurity on the spin-Peierls-like transition in the quasi-one-dimensional (quasi-1D) spin system of 1-(4′-nitrobenzyl)pyridinium bis(maleonitriledithiolato)nickelate

A nonmagnetic compound, [NO₂BzPy][Cu(mnt)₂] (mnt^2? = maleonitriledithiolate; NO₂BzPy⁺ = 1-(4′-nitrobenzyl)pyridinium), is isostructural with [NO₂BzPy][Ni(mnt)₂], which is a quasi-1D spin system and exhibits a spin-Peierls-like transition with J = 192 K in the gapless state and spin energy gap = 738 K in the dimerization state, respectively. Further, five nonmagnetic impurity doped compounds [NO₂BzPy][Cu_xNi_1?x(mnt)₂] (x = 0.04–0.74) were prepared, and their crystal structures as well as magnetic properties were investigated. The nonmagnetic doping causes the suppression of the spin transition with an average rate of 139(13) K/percentage of dopant concentration, and the transition collapse is estimated at around x > 0.5.     

Effects of electron beam irradiation on the photoelectrochemical properties of TiO2 film for DSSCs

TiO₂ has been widely utilized for various industrial applications such as photochemical cells, photocatalysts, and electrochromic devices. The crystallinity and morphology of TiO₂ films play a significant role in determining the overall efficiency of dye-sensitized solar cells (DSSCs). In this study, the preparation of nanostructured TiO₂ films by electron beam irradiation and their characterization were investigated for the application of DSSCs. TiO₂ films were exposed to 20–100 kGy of electron beam irradiation using 1.14 MeV energy acceleration with a 7.46 mA beam current and 10 kGy/pass dose rates. These samples were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) analysis. After irradiation, each TiO₂ film was tested as a DSSC. At low doses of electron beam irradiation (20 kGy), the energy conversion efficiency of the film was approximately 4.0% under illumination of simulated sunlight with AM 1.5 G (100 mW/cm²). We found that electron beam irradiation resulted in surface modification of the TiO₂ films, which could explain the observed increase in the conversion efficiency in irradiated versus non-irradiated films.     

Long-distance electronic interaction in a molecular wire consisting of a ferrocenyl–ethynyl unit bridging two [(η5-C5H5)(dppe)M] metal centers

Several multinuclear ferrocenyl–ethynyl complexes of formula [(η⁵-C₅H₅)(dppe)M^II?CC–(fc)_n–CC–M^II(dppe)(η⁵-C₅H₅)] (fc = ferrocenyl; dppe = Ph₂PCH₂CH₂PPh₂; 1: M^II = Ru²⁺, n = 1; 2: M^II = Ru²⁺, n = 2; 3: M^II = Ru²⁺, n = 3; 4: M^II = Fe²⁺, n = 2; 5: M^II = Fe²⁺, n = 3) were studied. Structural determinations of 2 and 4 confirm the ferrocenyl group directly linked to the ethynyl linkage which is linked to the pseudo-octahedral [(η⁵-C₅H₅)(dppe)M] metal center. Complexes of 1–5 undergo sequential reversible oxidation events from 0.0 V to 1.0 V referred to the Ag/AgCl electrode in anhydrous CH₂Cl₂ solution and the low-potential waves have been assigned to the end-capped metallic centers. The solid-state and solution-state electronic configurations in the resulting oxidation products of [1]⁺ and [2]²⁺ were characterized by IR, X-band EPR spectroscopy, and UV–Vis at room temperature and 77 K. In [1]⁺ and [2]²⁺, broad intervalence transition band near 1600 nm is assigned to the intervalence transition involving photo-induced electron transfer between the Ru³⁺ and Fe²⁺ metal centers, indicating the existence of strong metal-to-metal interaction. Application of Hush’s theoretical analysis of intervalence transition band to determine the nature and magnitude of the electronic coupling between the metal sites in complexes [1]⁺ and [2]²⁺ is also reported. Computational calculations reveal that the ferrocenyl–ethynyl-based orbitals do mix significantly with the (η⁵-C₅H₅)(dppe)Ru metallic orbitals. It clearly appears from this work that the ferrocenyl–ethynyl spacers strongly contribute in propagating electron delocalization.     

Luminescence properties of yttrium gadolinium orthovanadate nanophosphors and efficient energy transfer from VO43− to Sm3+ via Gd3+ ions

In this paper, luminescence properties of orthovanadates, Y_1−x−yGd_xVO₄:ySm³⁺ (where x = 0.05–0.50, y = 0.01–0.05), and the energy transfer mechanism from VO₄³⁻ to Sm³⁺ via Gd³⁺ ions were investigated in detail. X-ray diffraction (XRD) analysis confirmed the crystalline phase for synthesized nanophosphor in a tetragonal structure with I41/amd space group. The average crystallite size estimated from XRD was ∼28 nm. Field-emission scanning electron microscopy coupled with energy dispersive X-ray analysis revealed oval shaped morphology and composition of the nanophosphor, respectively. From high-resolution transmission electron microscopy observations, the particle sizes were found to be in the range 10–80 nm. The photoluminescence studies of Y_0.77Gd_0.20VO₄:0.03Sm³⁺ nanophosphor under 311 nm excitation exhibits dominant emission peak at 598 nm corresponding to ⁴G_5/2 → ⁶H_7/2 transition. The energy transfer occurs from VO₄³⁻ to Sm³⁺ via Gd³⁺ ions was confirmed by applying Dexter and Reisfeld’s theory and Inokuti-Hirayama model. Moreover, the energy transfer efficiencies and probabilities were calculated from the decay curves. Furthermore, Commission Internationale de l’Eclairage (CIE) color coordinate (0.59, 0.37) has been observed to be in the orange-red (598 nm) region for Y_0.77Gd_0.20VO₄:0.03Sm³⁺ nanophosphor. These results perfectly established the suitability of these nanophosphors in improving the efficiency of silicon solar cells, light emitting diodes, semiconductor photophysics, and nanodevices.     

On oxoacidic properties and solubilities of beryllium and magnesium oxides in molten (CsCs + KCl + NaCl) eutectic at T = 783 K

Reactions of Be²⁺ and Mg²⁺ with O^2– in molten eutectic mixture (CsCs + KCl + NaCl) (0.455:0.245:0.30) at T = 783 K were studied by a potentiometric method using Pt(O₂)|ZrO₂(Y₂O₃) indicator electrode. Addition of O^2– ions to the melt containing Mg²⁺ results in precipitation of MgO (pK_s,MgO = 11.89 ± 0.3, molality) whereas interaction of Be²⁺ with O^2– is accompanied with sequential formation of Be₂O²⁺ (pK = 15.68 ± 0.5, molality) and precipitation of BeO (pK_s,BeO = 9.62 ± 0.3, molality). On the basis of the obtained and known data pK_s,MgO–T⁻¹ dependence in molten (CsCs + KCl + NaCl) eutectic is constructed. The slope of the said dependence in T/K = (from 583 to 1073) range is in good agreement with the value predicted by the Shreder equation, that extends the range of use of the Shreder equation for predictions of metal oxide solubilities in molten halides.     

Experimental and computational thermochemistry of 1,4-benzodioxan and its 2-R derivatives

The standard molar energies of combustion, at T = 298.15 K, of crystalline 1,4-benzodioxan-2-carboxylic acid and 1,4-benzodioxan-2-hydroxymethyl were measured by static bomb calorimetry in an oxygen atmosphere. The standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in the gas phase at T = 298.15 K: 1,4-benzodioxan-2-carboxylic acid ?(547.7 ± 3.0) kJ · mol^?1 and 1,4-benzodioxan-2-hydroxymethyl ?(374.2 ± 2.3) kJ · mol^?1.In addition, density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets, 6-311G⁷ and cc-pVTZ, have been performed for the compounds studied. We have also tested two more accurate computational procedures involving multiple levels of electron structure theory in order to get reliable estimates of the thermochemical parameters of the compounds studied. The agreement between experiment and theory gives confidence to estimate the enthalpies of formation of other 2-R derivatives of 1,4-benzodioxan (R = –CH₂COOH, –OH, –COCH₃, –CHO, –CH₃, –CN, and –NO₂).     

Diazenyl schiff bases: Synthesis,spectral analysis,antimicrobial studies and cytotoxic activity on human colorectal carcinoma cell line (HCT-116)

A series of diazenyl schiff bases have been synthesized by reaction of salicylaldehyde containing azo dyes with various substituted aniline derivatives in the presence of acetic acid as catalyst. The structures of diazenyl derivatives were determined by FTIR, UV–vis, ¹H NMR, ¹³C NMR, CHN analysis, fluorimetric and mass spectroscopic studies. The synthesized derivatives were screened for their in vitro antimicrobial activity against various Gram-positive (S. aureus, B. subtilis, B. cereus), Gram-negative (S. typhi, S. enterica, E. coli, P. aeruginosa) bacterial and fungal (C. albicans, A. niger and A. fumigatus) strains, using cefadroxil (antibacterial) and fluconazole (antifungal) as standard drugs. The diazenyl schiff bases were also screened for their cytotoxicity against human colorectal carcinoma cell line (HCT-116) using 5-fluorouracil as standard drug by Sulforhodamine-B Stain (SRB) assay. The schiff bases exhibited significant activity toward both Gram-positive, Gram-negative bacterial and fungal strains. Most of the synthesized derivatives showed high activity against S. enterica. 4-((2,5-Dichlorophenyl)diazenyl)-2-((3-bromophenylimino)methyl)phenol (SBN-40) was found to be very active against S. aureus, B. cereus and E. coli, with MIC = 0.69 (µM/ml × 10²). The compound 4-((2-bromophenyl)diazenyl)-2-((4-nitrophenylimino)methyl)phenol (SBN-13) possessed comparable activity (IC₅₀ = 7.5 µg/ml) to the standard drug 5-fluorouracil (IC₅₀ = 3.0 µg/ml) against human colorectal carcinoma cell line (HCT-116).     

Spectroscopic properties of RBiBO4 (R = Ca,Sr) glasses doped with TiO2

Transparent glasses, melt quenching derived, containing 10RO·20Bi₂O₃·(70 ? x)B₂O₃·xTiO₂ [R = Ca, Sr] with x = 0, 0.5, 1.0 wt% were characterized by X-ray powder diffraction. Physical and spectroscopic properties viz., density, absorption, emission, electron paramagnetic resonance (EPR) and FTIR were investigated. The absorption band around 823 nm in pure glass samples is attributed to the electronic transition of ³P₀ to ³P₂ of Bi⁺ radicals. A small absorption hump centered around 609 nm is found in all doped glasses due to ²T_2g to ²E_g transition of octahedral Ti³⁺ ions. The emission results revealed that all the samples exhibit a broad emission band covering entire visible-light range, with λ_ex = 360 nm, centered 470–520 nm corresponds to electronic transition of ³P₁ to ¹S₀ of Bi³⁺ ions, therefore the present materials can be potentially used as tunable or full-color display systems. And a strong emission around 706 nm with λ_ex = 514 nm due to transition of ²P_3/2 to ²P_1/2 of Bi²⁺ ions. In SrO mixed glasses Ti⁴⁺ ions effect the environment of Bi³⁺ ion symmetry units from C₂ to C_3i. A small EPR signal (at room temperature) is observed in titanium doped glasses due to Ti³⁺ ions. In both the series with increase of TiO₂ concentration BO₄ units are gradually converted into BO₃ units and new cross linkages are formed, like B–O–Ti, Bi–O–Ti at the expense of B–O–B bonds.     

Real structure of SrSi2O2N2

SrSi₂O₂N₂ is an important host lattice for Eu²⁺ doped phosphors. Its crystal structure (space group P1, a = 7.0802(2) Å, b = 7.2306(2) Å, c = 7.2554(2) Å, α = 88.767(3)°, β = 84.733(2)°, γ = 75.905(2)° and V = 358.73(2) Å³, Z = 4) is isotypic with EuSi₂O₂N₂: highly condensed silicate layers are separated by Sr²⁺. The samples are characterized by pronounced real structure effects owing to pseudosymmetry of partial structures. Polysynthetic twinning with domains of various sizes is ubiquitous and oriented intergrowth of domains with different orientations has also been observed and analysed in detail by means of electron diffraction and high-resolution electron microscopy. These effects also affect the X-ray powder pattern and were taken into account in a Rietveld refinement.