Thermal lens studies of the reaction of iron (II) with 1,10-phenanthroline at the nanogram level

The determination of iron(II) with 1,10-phenanthroline in aqueous solutions was carried out exemplarily by thermal lens spectrometry. The peculiarities of analytical reactions at the nanogram level of reactants can be studied using this method. Under the conditions of the competing reaction of ligand protonation, the overall stability constant for iron(II) chelate with 1,10-phenanthroline was determined at a level of n x 10(-7) mol L(-1), logbeta3 = 21.3+/-0.1. The rates of formation and dissociation of iron(II) tris-(1,10-phenanthrolinate) at a level of n x 10(-8) mol L(-1) were found to be (2.05+/-0.05) x 10(-2) min(-1) and (3.0+/-0.1) x 10(-3) min(-1), respectively. The conditions for the determination of iron(II) with 1,10-phenanthroline by thermal lensing were reconsidered, and ascorbic acid was shown to be the best reducing agent, which provided minimum and reproducible sample pretreatment. Changes in the conditions at the nanogram level improved both the selectivity and sensitivity of determination. The optimum measurement conditions for thermal lensing were determined not only by the absorption of the analyte and reagents, but also by the background absorption of the solvent. The limits of detection and quantification of iron(II) at 488.0 nm (excitation beam power 140 mW) are 1 x 10(-9) and 6 x 10(-9) mol L(-1), respectively; the reproducibility RSD for the range n x 10(-8)-n x 10(-6) mol L(-1) is 2-5%.     

Thermal lensing spectrophotometric analysis with ion-pair solvent extraction

Thermal lensing spectrophotometry is applied to the determination of iron(II) with 4,7-diphenyl-1,10-phenanthroline disulfonic acid in aqueous solution, and in chloroform by ion-pair extraction with trioctylmethylammonium chloride. A phase-sensitive detection system with digital processing was used, the optimum modulation frequency being 5–10 Hz. A baseline drift of 0–03% was achieved. In water, the enhancement factor (sensitivity relative to conventional spectrophotometry) was 70 at an exciting power of 800 mW, and 2 × 10^-9 M iron(II) was determined. In chloroform 2 × 10^-10 M iron(II)—complex could be detected, the enhancement factor being 1200.     

Electrochemical behavior of 5-amino-1,10-phenanthroline and oxidative electropolymerization of tris[5-amino-1,10-phenanthroline]iron(II)

The electrochemical behavior of 5-amino-1,10-phenanthroline and tris[5-amino-1,10-phenanthroline]-iron(II) at carbon paste, glassy carbon, and platinum electrodes is reported. The iron complex undergoes electrochemically induced oxidative polymerization from acetonitrile solutions and the resulting polymers are very stable. Charge transport through the polymer films occurs with a charge transfer diffusion coefficient, D_ct, equal to 3.1 × 10⁻⁸ cm² s⁻¹ corresponding to an electron self-exchange rate of 5.2×10⁷M⁻¹ s⁻¹. The activation energy and the entropy change for the charge transfer diffusion process are (approximate values) 32.0 ± 0.12 kJ mol⁻¹ and −24.7 ± 0.4 J K⁻¹ mol⁻¹, respectively.     

Investigation of adsorption of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) on glasses and silica by thermal lens spectrometry

Thermal lens spectrometry is used for studying adsorption equilibria in aqueous solutions at the level of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) as a model system. The kinetics of the sorption of the chelate on silica is studied and adsorption isotherms are built. Thermal lensing is used as a method for direct determination of the chelate concentration adsorbed on a quartz surface. The detected amount is 4.1×10⁻¹⁵ mol at the area irradiated by the excitation beam. The adsorption of iron(II) tris-(1,10-phenanthrolinate) on laboratory glassware at the nanogram level is characterised by measuring the residual concentration of the sorbate in solution. A procedure for handling and cleaning the laboratory glassware for determining nanogram amounts of iron in aqueous solutions is proposed. The sensitivity of thermal lensing both in measuring adsorption on silica and glass and quartz surfaces is 100-fold higher than diffuse-reflectance measurements under the same conditions.     

Fluorescence enhancement assay for trace iron(II) using Pyr-tempo as a spin label fluorescent probe

Pyrene-tetramethylpiperidinyl (Pyr-Tempo) as a spin label fluorescent probe for iron(II) was synthesized. It exhibited weak fluorescence (λ_exc/λ_em = 346/399 nm) in aqueous solution due to an intramolecular quenching pathway. A method for determination of iron(II) was proposed based on the fluorescence enhancement of the probe in the presence of iron(II) in acidic medium. Under optimum conditions, the fluorescence enhancement of Pyr-Tempo is linearly proportional to the iron(II) concentration range of 6.0 × 10⁻⁸ to 9.6 × 10⁻⁶ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁹ mol L⁻¹. The relative standard deviation (RSD) of six replicate measurements is 1.95% for 3.0 × 10⁻⁷ mol L⁻¹ iron(II). The developed spin label fluorescence probe is found to be rapidly and sensitively responsive to iron(II) with high selectivity compared to existing fluorescence methods. The proposed method was successfully applied to iron(II) detection in five real samples with satisfactory results obtained by manual UV/Vis spectrophotometry (standard method) with 1,10-phenanthroline.     

Ruthenium(II) complexes: synthesis,cytotoxicity in vitro,apoptosis, DNA-binding,photocleavage, and antioxidant activity studies

Two new ruthenium(II) complexes, [Ru(dmp)₂(APIP)](ClO₄)₂ (1) (APIP?=?2-(2-aminophenylimidazo[4,5-f][1,10]phenanthroline), dmp?=?2,9-dimethyl-1,10-phenanthroline) and [Ru(dmp)₂(HAPIP)](ClO₄)₂ (2) (HAPIP?=?2-(2-hydroxyl-5-aminophenyl)imidazo[4,5-f][1,10]phenanthroline), were synthesized and characterized. The DNA-binding properties of these complexes were investigated by absorption titration, viscosity measurements, and photoactivated cleavage. The DNA-binding constants for 1 and 2 have been determined to be 2.3 (±?0.3)?×?10⁴ (mol?L^?1)^?1 and 3.3 (±?0.4)?×?10⁴ (mol?L^?1)^?1. The results indicate that 1 and 2 interact with DNA through intercalative mode. The cytotoxicities of 1 and 2 were assessed against BEL-7402, HepG-2 and MCF-7 cell lines using standard MTT assay. The apoptosis induced by these complexes was studied with the acridine orange/ethidium bromide staining method. The antioxidant activity on hydroxyl radical was also investigated.     

In-Capillary Derivatization and Preconcentration for CE of Metal Ions as Their Phenanthroline Complexes

A simple and automated method involving in-capillary derivatization and in-capillary preconcentration was developed for the simultaneous determination of metal ions by capillary zone electrophoresis. Fe(II), Zn(II), Cu(II) and Cd(II) were derivatized using 1,10-phenanthroline as the derivatizing agent. The in-capillary derivatization and in-capillary preconcentration via large volume injection were performed sequentially as follows: 60 mmol L^?1 1,10-phenanthroline was first hydrodynamically injected (0.2 psi) for 2 s; metal ions were introduced by hydrodynamic injection (0.5 psi) for 60 s; 0.2 mol L^?1 acetate pH 5.5 containing 20 % methanol was used as the running buffer. Four metal ions can be determined within 8 min using 16 kV. The resulting preconcentration factors were in the range 12–21. Good linearity was obtained for concentrations of 0.1–8.0 mg L^?1 (r ² > 0.990). The mean recoveries of the metal ions evaluated by fortification of wine samples were in the range 90–102 %. The limits of detection ranged from 0.05 to 0.2 mg L^?1. The proposed method can be applied for directly determining metal ions in wine samples.     

Determination of Adsorbates on the Surface of Polymer with Low Absorption Capacity by Thermal Lens Spectrometry

Thermal lens spectrometry in a coaxial configuration is used for the direct determination of adsorbates on a planar surface of polyethylene terephthalate (PET). A possibility of the direct measurement of the rate of adsorption from solutions and the determination of the parameters of the adsorbed layer is demonstrated by the example of an investigation of the adsorption of iron(II) tris(1,10-phenantrolinate) on a PET surface. The adsorption isotherm of iron(II) tris(1,10-phenantrolinate) on the PET surface is described by the Langmuir equation and is linear in the concentration range in solution from 0.02 to 0.7 mM. The method for calculating the thermal perturbation in surface-absorbing solids was used to interpret the results of the adsorption study, and a possibility of determining iron(II) tris(1,10-phenantrolinate) on the surface at a level smaller than a monolayer was shown. Thermal lens spectrometry enables the determination of the absorption of the surface layer at a level up to 5 × 10^–5 absorbance units, which corresponds to the surface concentration of iron(II) tris(1,10-phenanthrolinate) 2 × 10^–13 mol/cm². Using the example of the adsorption of 4-(2-pyridylazo) resorcinol on the PET surface, it is demonstrated that, in the case of strong absorption of the surface layer, the thermal destruction of substance and the deformation of the substrate may occur. A local increase in temperature in the layer is also confirmed by theoretical calculations.     

Application of Dipon, (1,4,8,11-Tetraazacyclotetradecane-4,11-bis(methylphosphonic acid) as Selective Complexing Agent for Determination of Copper(II)

A new macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid)(dipon), is selective complexing agent for copper(II) over other transition metal ions. The ligand was tested for analytical applications of copper(II) determination. Spectrophotometric determination under optimal experimental conditions (?log [H⁺]= 5.5, c _L≈ 5 × 10^?4 mol L^?1, λ= 310 nm) is valid in dynamic range (5–200)× 10^?6 mol L^?1 with detection limit 2.2 × 10^?6 mol L^?1, i.e. 0.14 μg ml^?1. Volumetric determination of copper(II) with standardized dipon solution was used for copper(II) determination at micromolar concentration level without any necessity to sequester interfering metal ions. A sharp end point of titration was detected by UV/VIS spectrophotometry. Both methods were tested on artificial and real samples (spiked mineral water, alloys) and gave satisfactory results without any systematic error. The advantage of both methods is their simplicity, rapidity and no sensitivity to the presence of other metal ions.     

Thermal lens determination of cytochrome c and its NO complex

Spectrophotometric and thermal lens measurements showed that cw laser beam (450–530 nm, up to 100 mW) does not affect the absorption band of cytochrome c. Therefore, thermal lensing is used for determining cytochrome c (III) (c _min = 1 × 10^?7 mol/L at λ = 488.0 nm; c _min = 3 × 10^?8 mol/L at λ = 514.5 nm) and its active form, cytochrome c (II) (c _min = 1 × 10^?8 mol/L at λ = 514.5 nm). The enhancement of the sensitivity of determination of these species as compared with conventional spectrophotometry is more than two orders of magnitude. The optimal conditions for the formation of the NO complex of cytochrome c for its photometric determination were selected: the molar ratio of dodecyl sulfate (a modifying agent) to cytochrome c is 1: 30 at a working wavelength of 560 nm. When exposed to laser radiation, the nitrosyl complex of cytochrome c dissociates to form cytochrome c (III). The decomposition of this complex can be monitored by thermal lensing (514.5 nm) down to a level of 1 × 10^?7 mol/L.     

Construction and analytical application of a biosensor based on stearic acid-graphite powder modified with sweet potato tissue in organic solvents

A biosensor based on stearic acid-graphite powder modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as peroxidase source was constructed and applied in organic solvents. Several parameters were studied to evaluate the performance of this biosensor such as stearic acid-graphite powder and tissue composition, type and concentration of supporting electrolyte, organic solvents, water/organic solvent ratio (% v/v) and hydrogen peroxide concentration. After selection of the best conditions, the biosensor was applied for the determination of hydroquinone in cosmetic creams in methanol. At the peroxidase electrode hydroquinone is oxidized in the presence of hydrogen peroxide and the radical formed was reduced back electrochemically at –180 mV vs Ag/AgCl (3.0 mol L^–1 KCl). The reduction current obtained was proportional to the concentration of hydroquinone from 6.2 × 10^–5 to 1.5 × 10^–3 mol L^–1 (r = 0.9990) with a detection limit of 8.5 × 10^–6 mol L^–1. The recovery of hydroquinone from two samples ranged from 98.8 to 104.1% and an RSD lower than 1.0% for a solution containing ¶7.3 × 10^–4 mol L^–1 hydroquinone and 1.0 × 10^–3 mol L^–1 hydrogen peroxide in 0.10 mol L^–1 tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n = 10) was obtained.     

Construction and Performance Characterization of Ion‐Selective Electrodes for Potentiometric Determination of Paroxetine Hydrochloride in Pharmaceutical Preparations and Biological Fluids

Three types of ion‐selective electrodes: PVC membrane, modified carbon paste (CPE), and coated graphite electrodes (CGE) have been constructed for determining paroxetine hydrochloride (Prx). The electrodes are based on the ion pair of paroxetine with sodium tetraphenylborate (NaTPB) using dibutyl phthalate as plasticizing solvent. Fast, stable and potentiometric response was obtained over the concentration range of 1.1×10^?5–1×10^?2 mol L^?1 with low detection limit of 6.9×10^?6 mol L^?1 and slope of a 56.7±0.3mV decade^?1 for PVC membrane electrode, the concentration range of 2×10^?5–1×10^?2 mol L^?1 with low detection limit of 1.2×10^?5 mol L^?1 and slope of a 57.7±0.6 mV decade^?1 for CPE, and the concentration range of 2×10^?5–1×10^?2 mol L^?1 with low detection limit of 8.9×10^?6 mol L^?1 and slope of a 56.1±0.1 mV decade^?1 for CGE. The proposed electrodes display good selectivity for paroxetine with respect to a number of common inorganic and organic species. The electrodes were successfully applied to the potentiometric determination of paroxetine hydrochloride in its pure state, its pharmaceutical preparation, human urine and plasma.     

Physicochemical properties of compounds of alkyl sulfates and cationic copper(II) complexes with some organic reagents

Compounds of alkyl sulfates and cationic copper(II) complexes with some organic reagents (pyridine, 1,10-phenanthroline, 2,2'-dipyridyl) were prepared, and their physicochemical characteristics (composition, thermal stability, solubility) were determined. The synthesized compounds are poorly soluble (solubility product K_S = n×10^–20–n×10^–22) and thermally stable (90–260°С). An effect of the hydrophobilicity of alkyl sulfates on the UV characteristics of the copper(II)–organic reagent systems and on the solubility of the studied compounds was evaluated.     

Investigation of the reaction of copper(I) with 2,9-dimethyl-1,10-phenanthroline at trace level by thermal lensing

The stability constants for copper(I) chelate with 2,9-dimethyl-1,10-phenanthroline are determined by thermal lensing, and the advantages over spectrophotometric determination of stability constants are shown. Changes in the photometric reaction when moving from the microgram to the nanogram level of reactants are discussed. The conditions for the thermal-lens determination of copper are optimized. The limit of detection of copper is 3x10(-8) mol dm(-3), and the linear calibration range 1x10(-7)-1x10(-5) mol dm(-3).     

THE KINETICS OF ELECTRON TRANSFER FOR A SERIES OF IRON(II) CYCLIDENE COMPLEXES

Abstract

The kinetics of oxidation of a series of iron(II) cyclidene complexes by tris(1,10-phenanthroline)cobalt(III) in methanol have been measured by stopped flow spectrophotometry. The reactions obey a first order rate law when the cobalt(III) complex is present in large excess. The corresponding second order rate constants fall in the range 5.0–130 × 10⁵ M^?1s^?1 (25°C). A linear correlation between the logarithm of the rate constant and the iron(III)/(II) redox potential indicates that the reactions behave as simple outer-sphere electron transfer processes. The self-exchange rate constants for the iron cyclidene complexes have been estimated from the Marcus equation and found to vary between 0.7 × 10⁷ M¹s¹ and 9 × 10⁷ M¹s¹. The dependence of the self-exchange rate constant on ligand structure is discussed.     

Spectroscopy studies on DNA binding of two ruthenium complexes [Ru(MeIm)4(L)]2+ (L = iip and tip)

Two ruthenium(II) complexes [Ru(MeIm)₄(L)]²⁺ (L?=?2-(imidazo-4-group)-1H-imidazo-[4,5-f][1,10]phenanthroline, 2-(thiophene-2-group)-1H-imidazo[4,5-f][1,10]phenanthroline, MeIm?=?1-methylimidazole) have been synthesized according to literature and structurally characterized. The interaction of the complexes with calf thymus DNA has been explored using electronic absorption titration, competitive binding experiment, circular dichroism, thermal denaturation, and viscosity measurements. The results show that both complexes could bind DNA in a intercalation mode and the DNA-binding affinity of [Ru(MeIm)₄(tip)]²⁺ (K _b?=?(7.2?±?0.3)?×?10⁵?(mol?L^?1)^?1) is greater than that of [Ru(MeIm)₄(iip)]²⁺ (K _b?=?(6.1?±?0.2)?×?10⁵?(mol?L^?1)^?1).     

Optimization of a sensitive method for the “switch-on” determination of mercury(II) in waters using Rhodamine B capped gold nanoparticles as a fluorescence sensor

Monodisperse and “naked” gold nanoparticles (GNPs) were modified with thioglycolic acid (TGA). The fluorescence of rhodamine B (RB) is quenched completely by the gold NPs surface with negative charge mainly as a result of fluorescence resonance energy transition (FRET) and collision. The quenching mechanism can be described by a Langmuir isotherm, which was systematically investigated by steady-state fluorescence spectrometry and absorption spectrometry. Hg(II) ion disrupts the GNPs–RB pair, producing a large “switch-on” fluorescence. A low background, highly sensitive and reproducible fluorescence assay for Hg(II) is presented. Under the optimum conditions, the restoration fluorescence intensity is proportional to the concentration of Hg(II). The calibration graphs are linear over the range of 1.0?×?10^?9 to 3.1?×?10^?8 mol L^?1 with a detection limit of 4.0?×?10^?10 mol L^?1. The relative standard deviation was 1.2% for a 5.0?×?10^?9 mol L^?1 Hg(II) solution (N?=?6). This method was applied to the analysis of Hg(II) in environmental water samples, and the results were consistent with those of atomic absorption spectroscopy (AAS).     

Flow injection spectrophotometry followed by atomic Absorption spectrometry for the determination of iron(II) and total iron

In the flow system described, iron(II) is measured spectrophotometrically with 1,10-phenanthroline, and total iron is determined in the same flow line by atomic absorption spectrometry. Linear calibration ranges are 0.1–35 and 0.1–10 μg ml^?1 for iron(II) and total iron, respectively.     

Determination of Trace of Cobalt in Complex Matrices by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of cobalt in a complex matrices at an in situ plated lead film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–nioxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. The calibration graph was linear from 5×10^?10 to 2×10^?8 mol L^?1 and from 1×10^?10 to 1×10^?9 mol L^?1 for the accumulation times 120 and 600 s, respectively. The detection limit (based on the 3 σ criterion) for Co(II) following accumulation time of 600 s was 1.1×10^?11 mol L^?1. The interference of high concentrations of foreign ions and surfactants was studied.     

Spectrofluorimetric determination of thiols by use of N-[P-(2-benzoxazolyl)- phenyl]maleimide

The weak fluorescence of N-[P-2-benzoxazolyl)phenyl]maleimide (BOPM) can be greatly enhanced by thiol-containing compounds. A sensitive and simple spectrofluorimetric method based on the use of BOPM has been developed for the determination of thiols such as cysteine (Cys) and reduced glutathione (GSH). Calibration plots were linear in the concentration range from 0 to 1.6 × 10^–7 mol L^–1 for Cys and 0 to 1.7 × 10^–7 mol L^–1 for GSH. The detection limits (3σ) were 2.36 × 10^–10 mol L^–1 for Cys and 1.49 × 10^–10 mol L^–1 for GSH. Many other amino acids (present at 100-fold greater concentrations) did not interfere with the determination. The proposed method has been used for the determination of Cys in protein hydrolysate and cystine electrolyte or GSH in serum, with recoveries of 95.4–103.7%.