Flow-Injection Chemiluminescence Determination of Aspartic Acid in Tea Leaves Using Tris (2,2′-bipyridyl) Ruthenium (II)–Ce(IV) System

A flow injection chemiluminescence (CL) determination of aspartic acid is described. In this work, it was observed that aspartic acid could enhance the chemiluminescence (CL) emission of Ru(bipy)3(2+)-Ce(IV) system and this enhancement effect was dependent on the concentration of aspartic acid, based on which, CL system was established for the determination of aspartic acid. Under the optimum experimental conditions, the linear range and detection limit are 2 x 10(-7)-1.3 x 10(-5) M and 1.5 x 10-(8) M, respectively. The R.S.D. is 1.75%. (n = 10). The proposed method has been applied to detect the content of aspartic acid in tea leaves with satisfactory results. The possible mechanism of the CL reaction was discussed.     

Spectroscopic Determination of Mebendazole Using a 1,10 Phenanthroline–Iron Complex

Journal of Applied Spectroscopy - Simple, rapid, and sensitive spectroscopic methods have been proposed to determine the antifungal drug mebendazole. These methods adapted the reduction of ferric...     

Viscosity and Temperature Effects on the Rate of Oxygen Quenching of Tris-(2,2′-bipyridine)ruthenium(II)

We compare the bimolecular quenching rate constant (k₂) of luminescent tris(2,2′-bipyridine)ruthenium(II) by oxygen in water, ethylene glycol and glycerol as a function of temperature and viscosity to several theoretical models. The Smoluchowski equation with experimentally determined diffusion coefficients produced calculated values that were in the best agreement with experiment. For the less viscous solvent, water, this equation produced a value that was approximately an order of magnitude larger than the experimental value. With an increase in solvent viscosity, the Smoluchowski value approached the experimental value. Using the Smoluchowski equation with calculated diffusion coefficients based on the known radii of the reacting species produced deviations an order of magnitude larger in water and a factor of two or three lower in ethylene glycol and glycerol. If an assumption is made that the radii of both molecules are equal, we have the Stokes Einstein equation, and the only parameters become temperature and viscosity. Using this relationship, the calculated values for water are about a factor of two larger and with ethylene glycol and glycerol about a factor of 6 smaller than experimental data. These results show that bimolecular quenching is a more complex process affected by many parameters such as solvent cage effects in addition to viscosity and temperature.     

Theoretical studies on the geometrical and electronic structures of supramolecule bis(2,2′-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II)/functionalized SWCNT dyads

Functionalization of carbon nanotube (CNT) with multiple redox and photo active entities is one of the extensive processes due to its importance in building molecular or supramolecular electronic devices, solar energy storage and conversion systems. Thus, to have better understanding about structural aspects and correct electronic structure of these large systems, the quantum studies have gained increased popularity. In present study, we have investigated the structural and electronic properties of functionalized CNTs (fCNTs) with [Ru(bpy)₂(5-NH₂-1,10-phen)]⁺², (Ru-bpy-phen)⁺², supramolecule based on DFT calculations. Main attention has been applied to obtain stable configuration, binding energies and effect of functionalization on electronic behavior of the selected supramolcule. We also evaluate the effect of nanotube’s diameter and chirality on electronic properties of considered supramolecule. Calculated binding energies show that interaction between the (Ru-bpy-phen)⁺² and the host CNTs depends on the tube diameter while the chirality doesn’t affect significantly on the binding nature of respected complex. We have also investigated the influence of non-local dispersion interactions (vdW) and temperature on the stability and electronic structure of the considered system. Results obtained from the ab initio MD simulations showed that increasing the temperature can affect the distance between C and N atoms in the linkage position. The charge analysis indicates the existence of remarkable charge transfer between (Ru-bpy-phen)⁺² as donor and fCNTs as acceptor moieties in the isolated molecule. In the presence of vdW forces and at higher temperature, the charge transfer was decreased but the direction of transferred charge remains unchanged.     

Determination of iodide in urine based on chemiluminescence system of cerium (IV)–tween 40–iodide

In acidic medium, the oxidation reaction of cerium (IV) with iodide can produce strong chemiluminescence (CL) in the presence of surfactant tween 40 as an enhancer. On this basis, a flow injection method with CL detection was established for the determination of iodide. The method is simple, rapid and effective to determine iodide in the range of 8.0×10^?8–5.0×10^?5 mol/L with a determination limit of 5.0×10^?8 mol/L. The relative standard deviation is 2.7% for the determination of 5.0×10^?6 mol/L iodide (n=11). The method has been applied to determine the content of iodide in urine with satisfactory results. Furthermore, it is suggested that the light emission from cerium (IV)–tween 40 reaction is probably because of the formation of singlet oxygen ¹O₂^? and the emitter is excited oxygen molecular pairs O₂(¹Δ_g)O₂(¹∑_g^?).     

Electronic and Resonance Raman Spectra of the μ-tris(Bipyrazine)ruthenium(II)-Hexaquis{ruthenium(II)EDTA} Supramolecular Complex

Abstract

Resonance Raman and electronic spectra of the μ-tris(bipyrazine)ruthenium(II)-hexaquis{ruthenium(II)EDTA} supramolecular complex are reported in this paper. Excitation in the 457–676 nm range leads to the selective enhancement of the Ru-bipyrazine vibrational peaks according to distinct patterns, supporting the assignment of the absorption bands at 670 and 490 nm as charge-transfer (MLCT) transitions from the [Ru^IIEDTA] d_π orbitals to the π₁? and π₂? LUMO levels of the bipyrazine ligand. A vibronic coupling mechanism involving the two excited states is suggested for the excitation at 490 nm. The occurrence of MLCT transitions in the [Ru(bpz)₃]²⁺ central unity, around 440 nm, is supported by the Raman and fluorescence excitation profiles.     

Determination of Selenium (IV) in Natural Waters by HG‐AAS Using an Integrated Reaction Chamber Gas–Liquid Separator

Abstract

A simple online sequential insertion manifold coupled to a hydride generation atomic absorption spectrometer (HG‐AAS) has been developed for selective inorganic Se(IV) determination. The online method is based on the sequential insertion of sample and reagents in the integrated reaction chamber gas–liquid separator (RC‐GLS), which operates initially as reaction chamber for various sample volumes (up to 20 mL) and subsequently as gas–liquid separator with limited dead volume. The generated hydride from a large sample volume is trapped in the RC‐GLS for a short time and then it is flashed in the atomic absorption cell. The HCl and the NaBH₄ concentration was optimized for selective inorganic Se(IV) determination. For 8‐mL and 16‐mL sample consumption, the sampling frequency is 40 h^?1 and 24 h^?1, while the detection limit is 0.04 µg L^?1 and 0.03 µg L^?1, respectively. The precision (relative standard deviation) for 2.0 µg L^?1 Se(IV) (n=10) is 2.6% and 2.8% for 8 mL and 16 mL sample volumes, respectively. The accuracy of the proposed method was evaluated by analyzing the certified reference material, NIST CRM 1643d, and also by analyzing spiked natural water.     

Excitation and Detection of a Nonlinear Resonance of Oscillations of a Spring–Mass System Using Electromagnetic Induction

Technical Physics - Nonlinear oscillations and resonances of a spring–mass system are experimentally and theoretically studied. A unified method for excitation, dissipation, and detection of...     

Synthesis and Reactivity of Mg(II)–Fe(II)–Fe(III) Hydroxycarbonates

Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)₂ in carbonate-containing aqueous media obeying to [Fe^II _4(1–x)Mg^II _4x Fe^III ₂(OH)₁₂]²⁺ [CO₃ ^2– nH₂O]^–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms^–1 (with respect to -iron at room temperature) and quadrupole splitting E _Q=2.76 mms^–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms^–1 and E _Q=0.44 mms^–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O₂. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.     

Europium-sensitized Chemiluminescence of System Tetracycline–H<Subscript>2</Subscript>O<Subscript>2</Subscript>–Fe(II)/(III) and Its Application to the Determination of Tetracycline

Chemiluminescence (CL) of the reaction system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III) was used for the determination of tetracycline hydrochloride in water, pharmaceutical preparations, and honey. The CL spectrum registered for this system shows emission bands typical of Eu(III) ions, with a maximum at λ ∼ 600 nm, corresponding to the electronic transitions of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂. A strong chemiluminescence intensity characteristic of europium(III) ions in the system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III), as contrasted to the emission of the system tetracycline–H₂O₂–Fe(II)/(III) without Eu(III), proves that the Eu(III) ion plays the role of a chemiluminescence sensitizer, accompanying tetracycline oxidation in the Fenton system (H₂O₂–Fe(II)/(III)). A linear dependence was observed for the integrated CL light intensity on the tetracycline concentration in the range of 2 × 10⁻⁷ to 3 × 10⁻⁵ mol l⁻¹ with the detection limit of 5 × 10⁻⁸ mol l⁻¹ in aqueous solution.     

Photophysics of mixed ligand complexes of ruthenium(II) with 2,2′-bipyridyl and phosphines

Luminescence of mixed ligand complexes of ruthenium(II) of the types cis-Ru(bpy)₂X₂(I), cis-[Ru(bpy)₂(PPh₃)X](BF₄)(II), and cis-Ru(bpy)(PP)X₂(III) (X = CN, NO₂, PPh₃ is triphenyl phosphine; PP is 1,2-bis(diphenylphospino)ethane (dppe) and cis-,2-bis(diphenylphosphino)ethylene (dppene)) is studied in alcohol matrices (EtOH/MeOH, 4:1) frozen at 77 K. A sequence of complexes I–III exhibits an additive (in the number of phosphorous atoms) blue shift of the absorption and luminescence bands and an increase in the quantum yield of luminescence and in the excited-state lifetime. The rate constant of nonradiative deactivation of the excited state decreases more than by an order of magnitude in the sequence I–III of cyano complexes and only by three times in a sequence of nitro complexes. This is assumed to be caused by a specific (in the hydrogen bond type) interaction of nitro groups of complexes with a proton solvent.     

Using a 1,8-diamino naphthalene–copper (II) system as a turn-on fluorescence probe for detecting Sudan I

An easy-to-use fluorescence probe for detecting Sudan I was developed. The probe detects Sudan I because Sudan I and 1,8-diamino naphthalene competitively interact with copper (II). Copper (II) effectively quenches the fluorescence of 1,8-diamino naphthalene because the 1,8-diamino naphthalene interacts with copper (II) and forms a 1,8-diamino naphthalene–copper (II) complex. Adding Sudan I causes the fluorescence of the system to be recovered because the Sudan I removes copper (II) from the 1,8-diamino naphthalene–copper (II) complex, liberating the 1,8-diamino naphthalene. The displacement of 1,8-diamino naphthalene by Sudan I gives a high fluorescence recovery efficiency. Under optimal conditions, the fluorescence intensity F achieved when Sudan I was added had a good linear relationship (R²?=?0.999) with the Sudan I concentration over the range 0–4.6?µM. The Sudan I detection limit was 0.032?µM. The method offers a new way of quantitatively determining Sudan I.     

Spectral Analysis of Methylene Blue–Mediated Photodynamic Inactivation of Bacteria Using a 635-nm Diode Laser System

In this paper we assess the efficacy of a laser system, emitting at 635 nm, in methylene blue–mediated photodynamic inactivation of Pseudomonas aeruginosa that contaminates wounds, using diffuse reflectance spectrometry. The spectral plots of the contaminated wounds were recorded before and after laser irradiation, and the refractive index and extinction coefficient were determined by Kramers-Kronig analysis of reflectance spectra. The changes in optical parameter values after the treatment were corroborated with bacterial counts determined by bacteriological examination. The results revealed that the combined treatment 635-nm laser–methylene blue is an efficient way to destroy the bacteria that contaminate the wounds.     

Synthesis,phase stability and oxide ion conductivity of Ce(IV)–Cd(II) double substituted bismuth vanadate

Bi₄V₂O_11-δ has been doped with Ce and Cd to study double substitution. The system with various dopant concentrations (0.07 ≤ x ≤ 0.30) was prepared by the standard solid-state reaction method. The correlation between the polymorphism and oxide ion performance was well investigated as a function of temperature and composition with the help of thermal analysis, X-ray diffraction (XRD) and AC impedance spectroscopy. From XRD results it is seen that the high oxide ion conducting tetragonal γ-phase is stabilized for x = 0.17. For the compositions x ≤ 0.10, monoclinic α-phase is retained at room temperature with clear evidence for two successive phase transitions α ? β and β ? γ. For x = 0.13, β ? γ phase transition is seen. However, the existence of order–disorder, γ' ? γ transition was confirmed for x = 0.17. It is seen that the highest low-temperature ionic conductivity at 320 °C is 3.19 × 10^?4 S cm^?1 which was observed for x = 0.17.     

Laboratory Intercomparison on the Determination of the Fe(II)/Fe(III) Ratio in Glass Using Mössbauer Spectroscopy

A Perturbed Angular Correlation (PAC) study was performed on the system that presents a rich variety of structural and magnetic phase transitions as a function of the oxygen content (δ) or as a function of temperature (T). The PAC signal at room temperature allowed the determination of the Electrical Field Gradient (EFG) parameters and to correlate them with the lattice average symmetry namely the orthorhombic (O′ or O*) Pbnm and rhombohedral (R) phases measured by X-ray diffraction.     

Solid-phase total synthesis of (–)-Phenylhistine and (–)-Aurantiamine. Synthesis of a diverse dehydro-2,5-diketopiperazine library. Part II

The preparation of solid supported glycine phosphonate and its utilization for the total synthesis of two natural products is presented. The proposed protocol combines diversity with accessibility and speed, which makes this scaffold suitable for automated parallel synthesis and combinatorial chemistry. The preparation of a small library of dehydro-2,5-diketopiperazines, combining several natural amino acids with diverse heterocycles (including thiazoles, pyridines, indoles and imidazoles), is also demonstrated.