Spectrocoulometric study of the hydrolysis of the tris (1,10-phenanthroline)iron(III) complex ion

The spectrocoulometric technique reported earlier is applied to verify the mechanism and to evaluate the contributions k_Bi of the individual bases to the total rate constant k of the hydrolysis of the tris (1,10-phenanthroline) iron(III) complex, Fe (phen)³⁺₃. Both normal and “open-circuit” spectrocoulometric experiments are used. Partial rate constants for four bases in the acetate-buffered solutions are k_H2O=(3.4±1.2) × 10^?4s^?1 (k_H2O includes the H₂O concentration), k_OH=(1.20±0.06)×10⁷ mol^?1dm³s^?1, k_phen=(1.4±0.2) mol^?1dm³s^?1, k_Ac=(3.8±0.3)×10^?2 mol^?1dm³s^?1, at 25°C and ionic strength 0.5 mol dm^?3. The Fe(phen)³⁺³ hydrolysis, with (phen)₂ (H₂O) Fe-O-Fe (H₂O) (phen)⁴⁺² formation, is first order with respect to Fe (phen)³⁺³ and the bases present in the solution. The rate-determining step in the hydrolysis is the entry of a base to the coordinating sphere of the complex, as in the hydrolysis of the analogous 2,2′-bipyridyl complex.     

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 × 10^–7 mol L^–1, logβ ₃ = 21.3 ± 0.1. The rates of formation and dissociation of iron(II) tris-(1,10-phenanthrolinate) at a level of n × 10^–8 mol L^–1 were found to be (2.05 ± 0.05) × 10^–2 min^–1 and (3.0 ± 0.1) × 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 × 10^–9 and 6 × 10^–9 mol L^–1, respectively; the reproducibility RSD for the range n × 10^–8–n × 10^–6 mol L^–1 is 2–5%.     

Antiradical activity of 5-amino-1,3,6-trimethyluracil in the radical chain oxidation of ethylbenzene as the model system

The antiradical activity of 5-amino-1,3,6-trimethyluracil was quantitatively measured in the initiated radical chain oxidation of ethylbenzene as the model system. The rate constant of the reaction of 5-amino-1,3,6-trimethyluracil with the ethylbenzene peroxyl radical at 333 K was found: k ₇ = (2.1 ± 0.3) × 10⁵ L mol^?1 s^?1. The kinetics of 5-amino-1,3,6-trimethyluracil consumption in the course of the radical chain oxidation of ethylbenzene was studied. The stoichiometric inhibition factor was determined to be f = 2.     

Spectral and kinetic evidence for attack at coordinated phenanthroline in the reaction between aliphatic amines and transition metal complexes of 5-nitro-1,10-phenanthroline

Various transition metal complexes of 5-nitro-1,10-phenanthroline react with aliphatic amines in dipolar aprotic solvents to give deeply coloured species. The spectral changes, which can be reversed upon addition of acid or of the appropriate protonated amine, do not depend either on the nature of the metal and the ancillary ligands or on the geometry of the complexes; this has been taken as evidence that the colour forming process is due to a specific interaction of aliphatic amines with coordinated phenanthroline. While the rate of reaction of [Pt(5-NO₂phen)Cl₂] and [Pd(5-NO₂phen)Cl₂] with Br^?, which is known to displace Cl^? in the substrates, depends strongly on the nature of the central atom, the second order rate constant at 25°C being 3.2 × 10^?4 dm³mol^?1s^?1 and 1.35 dm³mol^?1s^?1 for the platinum and the palladium derivative respectively, the rate of reaction with n-propylamine has a comparable value for both substrates. This is further evidence that amines attack the coordinated phenanthroline, rather than the central atom. On the basis of the spectral features and the reaction stoicheiometry, the adducts of metal complexes of 5-NO₂phen and aliphatic amines are presumably Meisenheimer-like complexes.     

Synthesis of some novel heteroarylene ethynylene polymers containing 1,10-phenanthroline in the polymer backbone

Palladium-catalyzed polycondensation between 3,8-dibromo-1,10-phenanthroline and substituted phenyl-1,4-diacetylenes in the presence of diisopropylamine produced the soluble π-conjugated poly(heteroarylene ethynylene)s 7a and 7b . The polymers were obtained in high yields (86–92%) and had molecular weights of M̄_n = 8700 g · mol⁻¹ ( 7a ; vapor pressure osmometry) and 6900 g · mol⁻¹ ( 7b ; vapor pressure osmometry). The low molecular model compounds 6a and 6b were prepared to analyze the connection between the primary structure and spectroscopic properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4442–4448, 1999     

Spectrokinetic study of SF5 and SF5O2 radicals and the reaction of SF5O2 with NO

UV spectra of SF₅ and SF₅O₂ radicals in the gas phase at 295 K have been quantified using a pulse radiolysis UV absorption technique. The absorption spectrum of SF₅ was quantified from 220 to 240 nm. The absorption cross section at 220 nm was (5.5 ± 1.7) × 10⁻¹⁹ cm². When SF₅ was produced in the presence of O₂ an equilibrium between SF₅, O₂, and SF₅O₂ was established. The rate constant for the reaction of SF₅ radicals with O₂ was (8 ± 2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The decomposition rate constant for SF₅O₂ was (1.0 ± 0.5) × 10⁵ s⁻¹, giving an equilibrium constant of K_eq = [SF₅O₂]/[SF₅][O₂] = (8.0 ± 4.5) × 10⁻¹⁸ cm³ molecule⁻¹. The SF₅ O₂ bond strength is (13.7 ± 2.0) kcal mol⁻¹. The SF₅O₂ spectrum was broad with no fine structure and similar to the UV spectra of alkyl peroxy radicals. The absorption cross section at 230 nm was found to (3.7 ± 0.9) × 10⁻¹⁸ cm². The rate constant of the reaction of SF₅O₂ with NO was measured to (1.1 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ by monitoring the kinetics of NO₂ formation at 400 nm. The rate constant for the reaction of F atoms with SF₄ was measured by two relative methods to be (1.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1994 John Wiley & Sons, Inc.     

Preconcentration of molybdenum(VI) on polymeric adsorbents and its photometric determination with bis(2,3,4-trihydroxyphenylazo)benzidine in the presence of 1,10-phenanthroline

The complexation of molybdenum(VI) with bis(2,3,4-trihydroxyphenylazo)benzidine (H₆L) is studied in the presence of 1,10-phenanthroline. A mixed-ligand complex formed with a molar component ratio of 2: 2: 4. The maximum absorbances of the binary and mixed-ligand complexes are observed at 437 and 426 nm, and their molar absorbance coefficients are (9.02 ± 0.02) × 10⁴ and (10.01 ± 0.01) × 10⁴, respectively. It is found that 1,10-phenanthroline affects H₆L and improves the complexation characteristics. A procedure is developed for the photometric determination of molybdenum(VI) in seawater after preconcentration.     

Inhibiting effect of 5-amino-5-methyluracil and its derivatives on the free-radical oxidation of 1,4-dioxane

The antiradical activity of 5-amino-6-methyluracil in the initiated radical-chain oxidation of 1,4-dioxane as a model system was studied quantitatively. The rate constant k ₇ of its reaction with the peroxyl radical of 1,4-dioxane was measured to be (5.6 ± 1.8) × 10⁵ L mol^?1 s^?1 at 333 K. The effect of the methyl substituents in the 1- and 3-positions of the uracil ring and in the amino group on the rate constant of inhibition was studied. The strengths of all N-H bonds in the 5-amino-6-methyluracil and its derivatives were calculated in the G3MP2B3 approximation and were compared with the measured rate constants of inhibition. By the example of the reaction of 5-amino-6-uracil with i-PrO ₂ ^?? , different attack pathways of the peroxyl radical at the N-H bonds of uracil were analyzed in the UB3LYP/6-311+G(d,p) approximation. The lowest activation barrier (5.8 kJ/mol) was observed for peroxyl radical attack on the (C⁵)N-H bonds. The site responsible for the inhibition activity of the compound is the amino group.     

Extraction—spectrophotometric determination of cadmium with diphenylcarbazone in the presence of 1,10-phenanthroline

The addition of 1,10-phenanthroline improves both the extraction and the spectrophotometric sensitivity of the determination of cadmium with diphenylcarbazone. Slope analysis suggests the formation of a 1:2:2 extracted species. The molar absorptivity is 9.4 × 10⁴ l cm^-1 mol^-1 at 536 nm and extraction is maximal at pH 8.2–9.8. Extraction is rapid and absorbances remain constant at room temperature for 48 h. Various divalent metal ions interfere.     

Role of Mononuclear Rare Earth Metal Complexes in Promoting the Hydrolysis of 2-Hydroxypropyl p-Nitrophenyl Phosphate

Two long-chain multidentate ligands： 2,9-di-（n-2＇,5＇,8＇-triazanonyl）-1,10-phenanthroline （L^1） and 2,9-di- （n-4＇,7＇,10＇-triazaundecyl）-1,10-phenanthroline （L^2） were synthesized. The hydrolytic kinetics of 2-hydroxypropyl p-nitrophenyl phosphate （HPNP） catalyzed by the complexes of L^1 or L^2 with La（Ⅲ） or Gd（Ⅲ） have been studied in aqueous solution at （298.2±0.1） K, I=0.10 mol·dm^-3 KNO3 in pH 7.5-9.1, respectively, finding that the catalytic effect of GdL^1 was the best among the four complexes for hydrolysis of HPNP. Its kLnLH-1, kLnLand pKa are 0.047 mol^-1·L·s^-1, 0.000074 mol^-1·L·s^-1 and 8.90, respectively. This paper expounded the studied result with the structure of the ligands and the properties of the metal ions, and deduced the catalysis mechanism.     

Electrochemistry of Tris(1,10-phenanthroline)iron(II) inside a polymeric hydrogel. Coupled chemical reactions and migration effects

The retention, release, and detection of metallic complexes in polymeric hydrogels are of interest in drug delivery, analytical chemistry, and water remediation. The electrochemistry of the redox complexes inside the hydrogel could be affected by the viscoelastic properties of the gel, local ionic force and pH, and interactions (e.g., hydrophobic) between the complex and the polymer chains. In this work, it is shown that a simple setup, consisting of a disk electrode pressed on the hydrogel, allows to perform electrochemistry of a redox couple: Tris(1,10-phenanthroline)iron(II) (Fe(phen)₃ ²⁺) inside a hydrogel matrix. The behavior is compared with the same couple in solution, and it is found that the electrochemical properties of the redox couple are strongly affected by the presence of the hydrogel matrix. The cyclic voltammogram of the hydrogel loaded with complex shows a response, which suggests electrochemical-chemical mechanism. The chemical step is likely linked to a catalytic oxidation of free hydrated Fe²⁺ ions present inside the hydrogel together with the redox complex. Since Fe²⁺ ions have small charge transfer constants on the glassy carbon electrodes, only the catalytic current is observed. Indeed, when excess ligand (phenanthroline) is absorbed inside the hydrogel, the measured cyclic voltammograms show a single reversible oxidation/reduction step. It seems that the complexation equilibrium shifts toward the complex, making the free iron concentration negligible. Accordingly, the cyclic voltammetry shape and peak potential difference agree with a reversible oxidation/reduction. Additionally, the peak currents of the cyclic voltammograms show a linear dependence with the square root of time, as predicted by a Randles-Sevcik equation. However, the measured currents are smaller than the simulated ones. The differences are in agreement with simulations of the cyclic voltammograms where the migration of the redox species is considered. Chronoamperometry is used to measure the mass transport of redox species inside the hydrogel. It is found that the current transients still obey Cottrell’s equation, but the diffusion coefficients obtained from the slopes of Cottrell’s plots have to be corrected for migration effects. The effective diffusion coefficient of Fe(phen)₃ ²⁺ measured inside the hydrogel (D _Red-hydrogel = 5.5 (±0.5) × 10^?8 cm² s^?1) is ca. 80 times smaller than the one measured in solution (D _Red-solution = 4.4 (±0.5) × 10^?6 cm² s^?1). The simple setup has a true semi-infinite boundary condition, which allows characterizing the hydrogel in the same condition as the bulk material and easily changing both the redox species and the hydrogel structure.     

Spectral properties and analytical application of the ternary complex of lanthanum(III) with 1,10-phenanthroline and eosin

The pink lanthanum—(1,10-phenanthroline)₂—(eosin)₂ complex is used to determine 0.5–10 × 10^-5 M lanthanum, either in aqueous solution or chloroform. In the presence of EDTA, only aluminium and cyanide interfere.     

Determination of Astaxanthin and Canthaxanthin Triplet Properties in Different Polarities of the Solvent by Laser Flash Photolysis

Triplet‐triplet extinction coefficients for astaxanthin ( I ) and canthaxanthin ( II ) in different deaerated polarity solutions of MeCN and benzene were evaluated by laser flash photolysis at 298 K in the spectral region from 350 to 650 nm by energy transfer method, employing 2‐acetonaphthone as sensitizer. The triplet‐triplet extinction coefficients in MeCN and benzene were different in terms of the carotenoid present. The maximum triplet‐triplet extinction coefficient was 0.1–1.7×10⁵ L·mol⁻¹·cm⁻¹ in different solvents. The rate constants of triplet decay were I : 1.25×10¹⁰ L·mol⁻¹·s⁻¹, II : 1.12×10¹⁰ L·mol⁻¹·s⁻¹ in MeCN; and I : 1.75×10¹⁰ L·mol⁻¹·cm⁻¹, II : 3.27×10¹⁰ L·mol⁻¹·s⁻¹ in benzene. The bimolecular rate constants of energy transfer from triplet excited 2‐acetonaphthone to carotenoids were determined from the linear regression of the decay rate constant of 2‐acetonaphthone triplet at varying carotenoid concentrations. The triplet lifetimes of ³AST* and ³CAN* in different solvents were also determined. The results indicated that triplet energy transfer was nearly diffusion‐controlled.     

Photocurrent kinetics at the electron emission from a metal into electrolyte solution: Part II. Solutions without acceptors and solutions of N2O,NO2−, NO3−

A method of measuring the kinetics of currents arising at the electron photoemission from a metal into electrolyte solution when affected by the u.v. laser pulses for 10^?8 s at the frequency of repetitions 10–25 Hz is described. Measurements have been taken in solutions without acceptors and in those containing N₂O and NO₂^?, NO₃^? ions as electron acceptors. The rate constants of capture of the solvated electrons by N₂O ((6±1)×0⁹ mol^?1 s^?1) and NO₂^? ((4.5±1)×10⁹ mol^?1 s^?1) and the diffusion coefficients of OH-radicals ((1.0±0.3)×10^?5 cm² s^?1) and of NO ((1.2±0.3)×10^?5 cm² s^?1) are found. The oxidation rate of NO₃^2? has been shown to decrease from 40 cm s^?1 in the range of potentials ?0.55 to ?1.0 V. The rate constant of bimolecular recombination of the solvated electrons ((1.3±0.4)×10¹⁰ mol^?1 s^?1) has been found from the dependence of the emitted charge on the light intensity.     

Chemical and pharmacological aspects of novel hetero MLB complexes derived from NO2 type Schiff base and N2 type 1,10-phenanthroline ligands

A series of hetero ligand MLB complexes (1–5) were synthesised from tridentate NO₂ type Schiff base [H₂L: (E)-2-((2-hydroxy-4-methoxyphenyl)(phenyl)methyleneamino)benzoic acid; derived from 2-hydroxy-4-methoxybenzophenone and 2-aminobenzoic acid] and bidentate N₂ type 1,10-phenanthroline (B: phen) ligands. The structural characterization of the synthesised MLB complexes were carried out via analytical as well as various spectral studies. Additionally, the low molar conductance values (Λ_m = 14–22 Ω⁻¹ cm² mol⁻¹) imply that the complexes (1–5) are non-electrolytes. The obtained results reinforce that stoichiometry of the mononuclear hetero ligand complexes can be represented as [M(II)-Schiff base(L)-phen(B)·H₂O] and both H₂L and (B) ligands can act as tri and bidentates respectively. Moreover, both the ligands bind with metal(II) ions to build a stable six, six, five membered chelate rings with octahedral geometry. The existing solvent water molecule is confirmed from thermal as well as vibrational analysis. Their microcrystalline nature and uniform surface morphology were confirmed by both powder XRD and SEM studies. 3D molecular modeling and analysis of NiLB and CuLB complexes (3 and 4) were also studied. Mn(II), Ni(II) and Cu(II) complexes (1, 3 and 4) strongly interact with DNA through intercalation binding with strong binding constant values. The obtained K_app values were 5.23, 4.98, 6.36, 7.21 and 4.86 × 10⁵ mol⁻¹ for MLB complexes (1–5) respectively and the negative Δ³G values shown that all the complexes are strongly interact with DNA in a spontaneous manner. Further, remarkable biological, antioxidant and DNA activities were remarkably exhibited by MnLB, NiLB and CuLB complexes.     

Synthesis,characterization, photophysical,and redox properties of three trinuclear Ru(II) polypyridyl complexes possessing 5-amino-1,10-phenanthroline ligands

Three ruthenium(II) polypyridyl complexes with 5-amino-1,10-phenanthroline ligands have been successfully designed and synthesized. They have been fully characterized by ESI-MS, ESI-HRMS, ¹H NMR, and elemental analyses. The photophysical and electrochemical properties of the three complexes have been investigated in organic solvent. The geometrical configuration and the electron density distribution in the frontier molecular orbitals of the three complexes have been studied. The three complexes show metal-to-ligand charge transfer (¹MLCT) absorption at 445 nm, and intense triplet metal-to-ligand (³MLCT) emission at around 619 nm in fluid solution at 298 K and 580 nm in low-temperature glass. Electrochemical studies of the three complexes are consistent with one Ru^III/II reversible couple at around 1.31 V accompanied by three ligand-centered reduction couples.

     

Kinetics and mechanisms of the reactions of aluminium(III) with β-diketones in aqueous solution

The kinetics and mechanisms of the reactions of aluminium(III) with pentane-2,4-dione (Hpd), 1,1,1-trifluoro pentane-2,4-dione (Htfpd) and heptane-3,5-dione (Hhptd) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm⁻³ sodium perchlorate. The kinetic data are consistent with a mechanism in which aluminium(III) reacts with the β-diketones by two pathways, one of which is acid independent while the second exhibits a second-order inverse-acid dependence. The acid-independent pathway is ascribed to a mechanism in which [Al(H₂O)₆]³⁺ reacts with the enol tautomers of Hpd, Htfpd, and Hhptd with rate constants of 1.7(±1.3)×10⁻², 0.79(±0.21), and 7.5(±1.6)×10⁻³ dm³ mol⁻¹ s⁻¹, respectively. The inverse acid pathway is consistent with a mechanism in which [Al(H₂O)₅(OH)]²⁺ reacts with the enolate ions of Hpd, Htfpd, and Hhptd with rate constants of 4.32(±0.18)×10⁶, 5.84(±0.24)×10³, and 1.67(±0.05)×10⁷ dm³ mol⁻¹ s⁻¹, respectively. An alternative formulation involves a pathway in which [Al(H₂O)₄(OH)₂]⁺ reacts with the protonated enol tautomers of the ligands. This gives rate constants of 2.79(±0.12)×10⁴, 3.86(±0.16)×10⁵, and 8.98(±0.25)×10³ dm³ mol⁻¹ s⁻¹ for reaction with Hpd, Htfpd, and Hhptd, respectively. Consideration of the kinetic data reported here together with data from the literature, suggest that [Al(H₂O)₅(OH)]²⁺ reacts by an associative or associative-interchange mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 257–266, 1998.     

Spectroscopy study of 5-amino-1,10-phenanthroline

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH = 5-Aphen + H+ (-log K = 5.78 +/= 0.03) and 5-AphenH2 = 5-AphenH2 = 5-Aphen + 2H+ (-log K = 6.89 +/= 0.07). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.     

Kinetics of peroxidase redox conversion on viologen-modified gold electrodes

The electrochemical conversions of horseradish peroxidase on methyl viologen- and benzyl viologen-modified gold electrodes have been studied. The formal heterogeneous rate constants, k^o′_s,h, of the peroxidase redox reactions (ferri/ferro forms) equal 8.4(±0.25)×10⁻⁴ and 1.3(±0.8)×10⁻⁵ cm s⁻¹, and the transfer coefficients, α, are 0.31(±0.06) and 0.71(±0.14) on benzyl viologen- and methyl viologen-modified electrodes, respectively. The participation of the peroxidase active centre in these processes was determined spectroelectrochemically.     

5-氨基-1,10-菲咯啉：可异构化杂环螯合荧光载体作为比例计量型锌离子荧光探针的一种原型

5-amino-l,10-phenanthroline （5-AP）, as a tautomeric heterocyclic aromatic chelating fluorophore （THACF）, can sense Zn^2＋ selectively by shifting emission from 495 to 564 nm upon Zn^2＋ addition in ethanol. The ratiometric fluorescent sensing behavior has been correlated to the tautomerization of 5-AP affected by solvents and metal chelation. The strategy using THACF as ratiometric fluorescent sensor for Zn^2＋ not only simplifies the synthetic procedure but also gives a promising alternative for Zn^2＋ ratiometric fluorescent sensor design.