Application of a laser produced plasma: Experimental Stark widths of single ionized lead lines

The optical emission spectroscopy from laser produced plasma generated by a 10,640 Å radiation, with an irradiance of 1.4 × 10¹⁰ W cm^− 2 on several lead targets, in vacuum and in an atmosphere of argon, was recorded and analyzed between 1900 and 7000 Å. The Local Thermodynamic Equilibrium conditions and plasma homogeneity have been checked. Stark widths for 31 lines of Pb II have been measured. These lines measured in this work correspond to the transitions 7s → 6p, n(n = 8, 9, 10)s → 7p, n(n = 7, 8)p → 7s, n(n = 7, 8)p → 6p², n(n = 7, 8)d → 7p, n(n = 5, 6)f → 6d, n(n = 5, 6)f → 6p². The population level distribution and the corresponding temperatures were obtained using Boltzmann plots. The plasma electron densities were determined using well-known Stark broadening parameters of spectral lines. Special attention was dedicated to the possible self-absorption of the different transitions. Temporal evolution of the plasma parameters was studied between 0.1 and 9 μs. Stark broadening parameters of the spectral lines were measured at 2.5 μs where the electron temperature was close to 11,300 K and the electron density to 0.8 × 10¹⁶ cm^− 3. The experimental results obtained have been compared with the experimental and theoretical values given by other authors. A systematic trend of this parameter versus temperature of 4244.9 Å Pb II line has been presented.     

Pharmacoinformatics study of Piperolactam A from Piper betle root as new lead for non steroidal anti fertility drug development

Fertility control is a burning problem all over the world to regulate population overflow and maintain ecological balance. This study is an in-silico approach to explore a non-steroidal lead as contraceptive agent in order to avoid several contraindications generated by steroidal analogues. Piperolactam A, an aristolactam isolated from Piper betle Linn. showed binding affinity towards estrogen and progesterone receptor as −8.9 and −9.0 Kcal/mol (inhibition constant K_i = 0.294 μM and 0.249 μM) respectively which is even larger than that of reported antagonists such as Rohitukine and OrgC (binding affinity −8.7 and −8.4 Kcal/mol; K_i 0.443 μM and 0.685 μM respectively). The binding site exploration displayed more hydrogen bonding of Piperolactam A (His 524, Leu 346, Thr 347) than Rohitukine and OrgC (Leu 718) with associated receptors which was further confirmed by molecular dynamics simulations. The drug-likeliness of the compound has been proved from its tally with Lipinsky’s Rule of Five and lowered toxicity such as cardiac toxicity, liver toxicity, mutagenicity and ecological toxicity. Endocrine disruptome and later docking guided molecular simulations revealed that Piperolactam A has weaker binding affinity and/or lower probability of binding with nuclear receptors especially hERG and cytochrome P450. The high Caco-2 permeability suggested more bioavailability hence more therapeutic efficacy of the drug.     

3D-QSAR,docking, molecular dynamics simulation and free energy calculation studies of some pyrimidine derivatives as novel JAK3 inhibitors

Janus kinase 3 (JAK3) is a promising drug target for the treatment of inflammatory diseases, autoimmune disorders, organ transplant rejection and various cancers. In the present study, 3D-QSAR, docking, MD simulation and MM/PBSA studies were performed on a series of pyrimidine-based JAK3 inhibitors. A reliable COMSIA (q² = 0.717 and r² = 0.986) model was developed and validated using external validation test set, bootstrapping, progressive scrambling and r_m² metrics analyses. Structural requirements identified through contour maps of the model were strategically utilized to computationally design 170 novel JAK3 inhibitors with improved potency. Docking studies were performed on the selected data set and newly designed compounds to show their binding mode and to identify important interacting residues inside the active site of JAK3. In addition, docking results of the selected designed compounds inside the active sites of JAK1, JAK2 and TYK2 indicated their JAK3 selectivity. MD simulation (100 ns) on the docked complex of compound 28 (one of highly active compounds of the data set) assisted in the further exploration of the binding interactions. Some crucial residues like Lys830 (glycine-rich loop), Val836, Ala853, Leu905 (hinge region), Cys909, Asn954, Leu956 and Ala966 were identified. Hydrogen bond interactions with hinge residue Leu905 were critical for the binding of JAK3 inhibitors. Additionally, MM/PBSA calculation provided the binding free energy of the compound 28. Newly designed molecules showed promising results in the preliminary in silico ADMET evaluations. Outcomes of the study can further be exploited to develop potent JAK3 inhibitors.     

Free NH3 quantum rotations in Hofmann clathrates: structure factors and line widths studied by inelastic neutron scattering

Quantum rotations of NH₃ groups in Hofmann clathrates Ni–Ni–C₆H₆ and Ni–Ni–C₁₂H₁₀ have been studied using inelastic neutron scattering. Calculations of the dynamical structure factor for a free uniaxial quantum rotor reproduce the neutron scattering data with respect to their Q- and T-dependence as well as the relative intensities for the 0 → 1, 0 → 2 and 1 → 2 transitions. Though the effective NH₃ rotation constant is different from the gas phase value, the effective radius of rotation (i.e., the average distance of protons from the rotation axis) is equal or very close to the geometrical value r = 0.94 Å for a NH₃ group. Comparing the experimental data with the calculated dynamical structure factor for the 0 → 3 transition it could be shown, that the corresponding transition line, in contrast to transitions between j = 0,1,2 levels measured so far, has a finite width at T = 0 K.     

Exploration of interaction zones of β-tubulin colchicine binding domain of helminths and binding mechanism of anthelmintics

Numerous studies postulated the possible modes of anthelmintic activity by targeting alternate or extended regions of colchicine binding domain of helminth β-tubulin. We present three interaction zones (zones vide −1 to −3) in the colchicine binding domain of Haemonchus contortus (a helminth) β-tubulin homology model and developed zone-wise structure-based pharmacophore models coupled with molecular docking technique to unveil the binding hypotheses. The resulted ten structure-based hypotheses were then refined to essential three point pharmacophore features that captured recurring and crucial non-covalent receptor contacts and proposed three characteristics necessary for optimal zone-2 binding: a conserved pair of H bond acceptor (HBA to form H bond with Asn226 residue) and an aliphatic moiety of molecule separated by 3.75 ± 0.44 Å. Further, an aliphatic or a heterocyclic group distant (11.75 ± 1.14 Å) to the conserved aliphatic site formed the third feature component in the zone-2 specific anthelmintic pharmacophore model. Alternatively, an additional HBA can be substituted as a third component to establish H bonding with Asn204. We discern that selective zone-2 anthelmintics can be designed effectively by closely adapting the pharmacophore feature patterns and its geometrical constraints.     

Photolysis of glyoxal in air

The photolysis of glyoxal in synthetic air was investigated in a quartz cell at 298 K using three types of UV sources (TL/12 lamps (275–380 nm), TL/03 lamps (390–470 nm) and mercury lamps (254 nm)) and products were identified and quantitatively analyzed using long-path FTIR spectroscopy. For all light sources, the observed products were CO, HCHO and HCOOH. Absolute quantum yields were determined using Cl₂ and Br₂ as actinometers. Photolysis in the first absorption band of glyoxal, using TL/12 lamps, provided an overall quantum yield of Φ_T = 0.97 ± 0.05, independent of total pressure ranging from 100 to 700 Torr air. The absolute quantum yields obtained with the TL/03 lamps, covering the second absorption band of glyoxal, showed dependency on total pressure, ranging from Φ_T = 0.12 at 100 Torr to Φ_T = 0.042 at 700 Torr, which can be expressed as a Stern–Volmer-type equation 1/Φ_T = (6.80 + 251.8) × 10⁻⁴ × P (Torr).By combining the product yields with literature data, we deduced the detailed picture of glyoxal photolysis, including the dependency of the quantum yield of each particular channel: CHOCHO + hν → 2HCO (Φ₁); CHOCHO + hν → H₂ + 2CO (Φ₂); CHOCHO + hν → H₂CO + CO (Φ₃) on the applied wavelength. The product quantum yields indicate that dissociation into two HCO radicals is the most important pathway under atmospheric conditions. The mean photolysis rate was measured under solar radiation in the EUPHORE outdoor chamber to be J_obs = 1.04 ± 0.10 × 10⁻⁴ s⁻¹, corresponding to a mean effective quantum yield ϕ_eff = 0.035 ± 0.007. Although glyoxal has a very low effective quantum yield, photolysis remains an important removal path in the atmosphere.     

Kinetics and mechanism of the chromic oxidation of 3-O-methyl-d-glucopyranose

The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by Cr^VI in acid medium yields Cr^III, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over Cr^VI is used. The redox reaction takes place through the combination of Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III pathways. Intermediacy of free radicals and Cr^II in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO₂²⁺ formed by reaction of Cr^II with O₂. Intermediate oxo-Cr^V–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO₄, intermediate Cr^V rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate Cr^V bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with Cr^VI distinguishes this derivative from glucose, which is oxidized to gluconic acid.     

Substitution reactions of thorium(IV) acetate to synthesize nano-sized carboxylate complexes

Some mixed-ligand thorium(IV) complexes with the general formula [Th(OOCCH₃)_4?nL_n] (L = anions of myristic, palmitic or stearic acid and n = 1–4) have been synthesized by the stepwise substitution of acetate ions of thorium(IV) acetate with straight chain carboxylic acids in toluene under reflux. The complexes were characterized by elemental analyses, spectral (electronic, infrared, NMR and powder XRD) studies, electrical conductance and magnetic susceptibility measurements. Doubly and triply bridged coordination modes of the ligands were established by their infrared spectra and nano-size of the complexes by powder XRD. Room temperature magnetic susceptibility measurements revealed diamagnetic nature of the complexes. Electronic absorption spectra of the complexes showed π → π*, n → π* and charge transfer transitions. Molar conductance values indicated the complex to be non-electrolytes. These are a new type of mixed-ligand thorium(IV) complexes for which a nano-sized, oxygen bridged polymeric structure has been established on the basis of physico-chemical studies.     

Photo-luminescence studies of strontium barium niobate crystals doped with Cr3+ ions

This paper reports the photo-luminescence spectroscopic results of Strontium–Barium–Niobate, Sr_x,Ba_1−xNb₂O₅ (SBN, x = 0.61 for near congruent composition) crystals doped with Cr₂O, at cryogenic temperature (20 K). The experimental results reveal the need of re-assignment of the Cr³⁺ ions defect centres in this material. For first time, a broad emission band in the near infrared region centred at ca. 950 nm is reported. This emission band has micro-seconds decaytime constant and a FWHM band-width > 1700 cm⁻¹ and has been ascribed to the vibronically assisted ⁴T₂ → ⁴A₂ transition. A much narrower emission band centred at ca. 764 nm with milli-seconds decaytime constant and a FWHM band-width of ca. 170 cm⁻¹ is correlated to the ²E → ⁴A₂ radiative transition (R-line).     

Structural characterization,molecular dynamics,dielectric and spectroscopic properties of tetrakis(pyrazolium) bis(μ2-bromo-tetrabromobismuthate(III)) dihydrate, [C3N2H5]4[Bi2Br10]·2H2O

The structure of [C₃N₂H₅]₄[Bi₂Br₁₀]·2H₂O, (PBB) was determined by single crystal X-ray diffraction at 100 K. It crystallizes in the monoclinic space group C2/m, with a = 12.992(4) Å, b = 16.326(5) Å, c = 8.255(3) Å, β = 108.56°(3), V = 1659.9(9) Å³ and Z = 2. The structure consists of discrete binuclear [Bi₂Br₁₀]⁴⁻ anions, ordered pyrazolium cations and water molecules. The crystal packing is governed by strong N–H⋯O and weak O–H⋯Br hydrogen bonds. A sequence of structural phase transitions in PBB was established on the basis of differential scanning calorimetry and dilatometric studies. Two reversible first-order phase transitions were found: (I → II) at 381/371 K (on heating/cooling) and (II → III) at 348/338 K. Dielectric response near both phase transitions is characteristic of crystals with the “plastic-like” phases. Over the phase III a low frequency dielectric relaxator is disclosed. The possible molecular motions in the PBB compound are characterized by the ¹H NMR studies. The infrared spectra of polycrystalline compound in the temperature range 300–380 K are reported for the region 4000–400 cm⁻¹. The observed spectral changes through the structural phase transition III → II are attributed to an onset of motion both of the pyrazolium cations and water molecules.     

Direct mass analysis of neutral molecules by superconductivity

Dissociation related to ion collision reactions produces neutral fragments in addition to ionic fragments, and the ability to analyze both neutral and ionic fragments is crucial for fully understanding chemical reactions in the gas phase. However, conventional mass spectroscopy (MS) instruments are unable to directly analyze multiple neutral fragments without reionization. This inability is called “neutral loss.” We report the first tandem MS instrument realized by a kinetic-energy-sensitive cryodetector (a superconducting tunnel junction operated in the Giaever mode) as the second mass separation (KEMS) to quantitatively analyze multiple fragment molecules, either neutral or ionic, in a keV kinetic energy range. The performance of the MS/KEMS instrument was examined using the collisions of singly charged acetone or acetyl precursors with a Xe target. These singly charged ions undergo either collisionally activated dissociation (CAD) or electron transfer dissociation (ETD), including a dissociation path of ABA⁺ + e → ABA* → A + B + A or AB + A, which produces neutral fragments only. Our approach is able to determine the branching ratios of the competing CAD and ETD processes and may provide a method to overcome the neutral loss.     

Kinetics and mechanism of the reduction of colloidal MnO2 by glycyl-leucine in the absence and presence of surfactants

The kinetics of the reduction of water-soluble colloidal manganese dioxide by glycyl-leucine (Gly-Leu) has been investigated in the presence of perchloric acid both in aqueous as well as micellar media at 35 °C. The study was carried out as functions of [MnO₂], [Gly-Leu] and [HClO₄]. The first-order-rate is observed with respect to [MnO₂], whereas fractional-order-rates are determined in both [Gly-Leu] and [HClO₄]. Addition of sodium pyrophosphate and sodium fluoride enhanced the rate of the reaction. Further, the use of surfactant micelles is highlighted as, in favourable cases, the micelles help the redox reactions by bringing the reactants into a close proximity due to hydrogen bonding. While the ionic surfactants SDS and CTAB have not shown any effect on the reaction rate, the nonionic surfactant TX-100 has catalytic effect which is explained in terms of the mathematical model proposed by Tuncay et al. (1999). The Arrhenius and Eyring equations are valid for the reaction over the range of temperatures used and different activation parameters (E_a, ΔH^#, ΔS^# and ΔG^#) have been evaluated. Kinetic studies show that the redox reaction between MnO₂ and Gly-Leu proceeds through a mechanism combining one- and two-electron pathways: Mn(IV) → Mn(III) → Mn(II) and Mn(IV) → Mn(II). On the basis of the observed results, a possible mechanism has been proposed and discussed.     

Identifying spectator bonds in modeling reactions: OH + CO → H + CO2

An adiabatic quantum dynamical model is introduced to solve a paradox with respect to the role of the CO vibration in the OH + CO(v) → H + CO₂ reaction. The previous agreement of five-dimensional diabatic with six-dimensional results for CO(v = 0), which erroneously suggested that the CO bond acts as a spectator, is due to a compensation of effects. For CO(v = 1), the reduced dimensionality adiabatic model approximates better the full-dimensional results. Whether AB acts as a spectator in a reaction with X cannot be decided on the basis of a diabatic calculation for AB(v = 0) + X only.     

Operando soft x-ray emission spectroscopy of LiMn2O4 thin film involving Li–ion extraction/insertion reaction

We developed an electrochemical in situ cell for soft x-ray emission spectroscopy (XES) to accurately investigate the redox reaction and electronic structure of transition metals in the cathode materials for Li–ion battery. The in situ cell consists of a Li–metal counter electrode, an organic electrolyte solution, and a cathode on a membrane window which separates the liquid electrolyte from high vacuum and can pass the incoming and emitted photons. In this study, the Mn 3d electronic structure of LiMn₂O₄ thin-film electrode was clarified by the operando XES. At the charged state, the XES spectrum changed significantly from the open-circuit-voltage (OCV) state, suggesting oxidation of the Mn^3 + component through Li–ion extraction. Upon discharge up to 3.0 V vs. Li/Li⁺, the XES spectrum almost returned to its profile at the OCV state with small difference, indicating the valence change of Mn: Mn^3.6 + → Mn^4 + → Mn^3.3 + corresponding to the OCV, charged, and discharged states.     

Thermodynamic properties of metal amides determined by ammonia pressure-composition isotherms

Thermodynamic properties of Mg(NH₂)₂ and LiNH₂ were investigated by measurements of NH₃ pressure-composition isotherms (PCI). Van’t Hoff plot of plateau pressures of PCI for decomposition of Mg(NH₂)₂ indicated the standard enthalpy and entropy change of the reactions were ΔH° = (120 ± 11) kJ · mol^?1 (per unit amount of NH₃) and ΔS° = (182 ± 19) J · mol^?1 · K^?1 for the reaction: Mg(NH₂)₂ → MgNH + NH₃, and ΔH° = 112 kJ · mol^?1 and ΔS^o = 157 J · mol^?1 · K^?1 for the reaction: MgNH → (1/3)Mg₃N₂ + (1/3)NH₃. PCI measurements for formation of LiNH₂ were carried out, and temperature dependence of plateau pressures indicated ΔH° = (?108 ± 15) kJ · mol^?1 and ΔS° = (?143 ± 25) J · mol^?1 · K^?1 for the reaction: Li₂NH + NH₃ → 2LiNH₂.     

Optical and dielectric properties of isothermally crystallized nano-KNbO3 in Er3+-doped K2O–Nb2O5–SiO2 glasses

Precursor glass of composition 25K₂O–25Nb₂O₅–50SiO₂ (mol%) doped with Er₂O₃ (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO₃ nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO₃ estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO₃ phase. The measured visible photoluminescence spectra have exhibited green emission transitions of ²H_11/2, ⁴S_3/2 → ⁴I_15/2 upon excitation at 377 nm (⁴I_15/2 → ⁴G_11/2) absorption band of Er³⁺ ions. The near infrared (NIR) emission transition ⁴I_13/2 → ⁴I_15/2 is detected around 1550 nm on excitation at 980 nm (⁴I_15/2 → ⁴I_11/2) of absorption bands of Er³⁺ ions. It is observed that photoluminescent intensity at 526 nm (²H_11/2 → ⁴I_15/2), 550 nm (⁴S_3/2 → ⁴I_15/2) and 1550 nm (⁴I_13/2 → ⁴I_15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (τ_f) of the ⁴I_13/2 → ⁴I_15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er³⁺ ions gradually enter into the KNbO₃ nanocrystals.     

Quantum efficiency improvement of a cesium based resonance fluorescence detector by helium-induced collisional excitation energy transfer

Quantum efficiency improvement of a cesium based resonance fluorescence detector (RFD) was achieved by enhancing the transfer in a particular channel of the RFD excitation scheme with noble gas-induced collisional excitation energy transfer (CEET). The influence of Cs–Ar and Cs–He collisional mixing between the 6D and 7P states in cesium on the quantum efficiency of the 6S → 6D → 7P → 6S excitation scheme was investigated by fluorescence measurements at relevant transitions. Ar-induced CEET was found to have little effect on the fluorescence response and quantum efficiency of the Cs RFD excitation scheme. However, a 35 fold quantum efficiency increase in the cesium resonance fluorescence detector response at only moderate He pressures was observed.     

A time-dependent wave packet study of the H4 four-center reaction

A quantum model based on the time-dependent initial state selected wave packet approach was developed to study the four-center (4C) reaction, A₂ + B₂ → 2AB, and the competing collision induced dissociation (CID), A₂ + B₂ → A + B₂ + A, as applied to the H₂(v₁) + H₂(v₂) system important in combustion. A reduced three-dimensional model of the reaction with the atoms constrained to an isosceles trapezium and a realistic global potential energy surface of Aguado et al. [J. Chem. Phys. 101 (1994) 2742], following Hernández and Clary [J. Chem. Phys. 104 (1996) 8413], was used. A method to analyse the reaction flux for 4C and CID reaction probabilities is presented. The initial A₂ vibrational excitation is not only more efficient than translational energy in facilitating the 4C and CID processes, it also reduces the threshold energy. Both the 4C and CID processes exhibit similar threshold energy behavior. For low vibrational excitation in the A₂ diatom, the 4C process is dominant; as the A₂ diatom becomes highly excited the CID process becomes more important at low collision energies with B₂, but as the collision energy increases the 4C process is favored again.     

Excited state properties of [Pd0(NHC)(quinone)]2 with NHC = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene and quinone = 1,4-naphthoquinone

The carbene complex [Pd⁰(NHC)(quinone)]₂with NHC = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene and quinone = 1,4-naphthoquinone shows two long-wavelength absorptions at 312 and 399 nm which are assigned to (NHC→quinone) LLCT and (Pd⁰ → quinone) MLCT transitions. The MLCT state is not reactive, but emissive (λ_max = 564 nm at 77 K). At r.t., the complex undergoes a photoredox decomposition which is initiated by the LLCT state.     

Diffusion coefficients of bolaform alkane-1,n-bis(trimethylammonium bromide) surfactants

Mutual diffusion coefficients of alkane-1,n-bis(trimethylammonium bromide), C_nMe₆Br₂ (n = 8, 10, 12), surfactants have been measured using the Taylor dispersion technique, at T = 298.15 K, at concentrations from (0.000 to 0.0380) mol · dm⁻³. The dependence of mutual diffusion coefficients on the concentration has been discussed in the framework of Onsager–Fuoss and Pikal models. On the basis of this discussion, it is suggested that these surfactants behave as associated electrolytes. From limiting mutual diffusion coefficient values, extrapolated from experimental values for c → 0, limiting ionic conductance, tracer diffusion coefficients, and hydration radii of alkane-1,n-bistrymethyl ammonium ions have been estimated. For the case of dodecane-1,12-bis(trimethylammonium bromide), no aggregation has been noticed up to 0.04 mol · dm⁻³.