Photogeneration of singlet molecular oxygen (1O2, 1Δ g ) using monomeric and aggregated forms of copper tetra-4-(morpholine-4-yl)-tetra-5-(2-naphthoxy)phthalocyanine in organic solvents

Luminescence and chemical acceptors methods were used to study the photosensitized formation of singlet molecular oxygen (¹O₂, ¹?? _g ) by monomer and aggregated forms of copper tetra-4-(morpholine-4-yl)-tetra-5-(2-naphthoxy)phthalocyanine in benzene, benzene-d ₆, acetone, DMF, and pyridine. The values of ¹O₂ quantum yield were determined. The effectiveness of the ¹O₂ photoproduction was shown to be reduced due mainly to the aggregation of the copper phthalocyanine molecules.     

Equilibrium between the hydroperoxyl and 1-hydroxycyclohexylperoxyl radicals—Chain carriers in cyclohexanol oxidation with molecular oxygen

The equilibrium constant K ₂ for the dissociation of the 1-hydroxycyclohexylperoxyl radical to cyclohexanone and the hydroperoxyl radical was determined by the selective inhibition method using nitrobenzene. For cyclohexanol oxidation initiated by cumyl peroxide, (1.6 ± 0.2) × 10^?4 mol/L (373 K, ortho-dichlorobenzene).     

Kinetics and mechanism of reactions of bis(biguanide)copper(II) ion with glycine and α-alanine in aqueous media

Summary The kinetics of the reaction of [Cu(bigH)₂]²⁺ (bigH = biguanide) with an excess of amino acid (LH), namely glycine or -alanine, in aqueous solution in the 7.6–9.0 pH range at different temperatures (30–40° C) have been followed by stopped-flow spectrophotometry. The ligand replacement process has been found to pass through intermediate formation of a ternary complex, [Cu(bigH)L]⁺ at the slower step, followed by rapid transformation into the binary complex, [CuL₂]. The overall ligand replacement process has a ligand dependent (k ₁) path which is first order with respect to the incoming ligand (L^-), and a ligand independent (k ₀) path. Under pseudo-first order conditions containing excess amino acid, the experimental observations conform to the rate law k _obs = k ₀ + k ₁ K _a[L]_T/([H⁼] + K _a), where [L]_T stands for the total concentration of amino acid and K _a gives the deprotonation constant of LH. The solvent assisted dissociation (i.e. k ₀ path) leads to a copper(II) mono-biguanide complex followed by rapid nucleophilic substitution; the k ₁ path is in agreement with an associative mechanism. The activation parameters (H , S ) for each step have been determined.     

Specific features of oxidation of ferrocenylacetic acid with molecular oxygen in the absence and in the presence of Brønsted acids

Comparative analysis of the specific features of autooxidation of ferrocenylacetic acid (FcCH₂COOH) in organic solvents at 30–50°C in the absence and in the presence of trifluoroacetic acid (processes 1 and 2 respectively) was carried out. It was shown that both reactions proceed as a sequence of two macrostages, the molecular and the chain radical oxidation of the metal complex. Introduction of acid (HX) in the reaction mixture leads to a significant increase in the rate of the process, in the amount of oxygen per one mole of metal complex absorbed by the reaction mixture, and to the change in the yields of main reaction products like hydroxymethylferrocene, formylferrocene, ferrocenylpyruvic acid, and CO₂. On the basis of results of the investigation performed, the kinetic and thermodynamic analysis of primary reactions of the process probable mechanisms of both macrostages in both processes were suggested. The significant effect of approach and orientation on the rate of the molecular oxidation of complex as the bifunctional reagent was noted. An assumption was made that the acid takes place in the molecular oxidation of FcCH₂COOH according to two alternative mechanisms differing by the way of its coordination with O₂ and the metal complex in the prereactional intermediates. The oxidative transformation of these intermediates leads to the generation of radicals of different nature, Fc^+·CH₂C(O)OO^· and HO₂^· which initiate the chain radical oxidation of the metal complex.     

Thermodynamic aspects of the Ru(III)—EDTA—ascorbate—molecular oxygen system for the oxidation of saturated and unsaturated organic compounds

The activation and thermodynamic parameters corresponding to rate and equilibrium constants, respectively, for the homogeneous oxidation of the saturated substrates, cyclohexane to cyclohexanol, cyclohexanol to cis-1,3-cyclohexane diol and olefin, cyclohexene to epoxide by Ru(III)—EDTA—ascorbateO₂ system were determined by measuring the various rates and equilibrium constants at four different temperatures in the range 288–313 K and μ = 0.1 M KNO₃ in a 50% (V/V) mixture of 1,4-dioxane and water in acidic medium. The kinetics of the oxidation of these substrates at each particular temperature was studied as a function of the concentration, the substrates, hydrogen ion, catalyst, ascorbic acid and molecular oxygen. The orders of the reaction in cyclohexanol and cyclohexene concentrations are one, and those in cyclohexane and hydrogen ion concentration are fractional and inverse first-order, respectively. For all substrates the reaction is first order with respect to the concentrations of molecular oxygen, ascorbic acid and catalyst. The source of the oxygen atom transferred to the substrates was confirmed by ¹⁸O₂ isotope studies in which the ¹⁸O was incorporated in the oxidized products. The kinetics and solvent isotope effect were studied for the oxidation of C₆H₁₂, C₆D₁₂, C₆H₁₁OH and C₆D₁₁OD. The order of the reactivity observed in the oxidation of the substrates studied is cyclohexene > cyclohexanol > cyclohexane. A comparison of the rates of oxidation of the substrates and the corresponding activation parameters with the catalytic systems Ru(III)—EDTAO₂ and Ru(III)—EDTA—ascorbateH₂O₂ indicated that activation parameters become more favourable in the presence of ascorbic acid, where the system acts as a mono-oxygenase and the activation energies are drastically reduced. Highly negative entropies are associated with all oxygen atom transfer reactions, indicating that the oxidation process is associative in nature.     

Kinetics of oxidation of 4,4′-biphenyldiol and of 4,4′-biphenoquinone by metal ions in aqueous perchlorate media: Reactions with Mn(III), Ce(IV) and Ag(II)

The kinetics and mechanisms of the oxidation of 4,4′-biphenyldiol ([1,1′-biphenyl]-4,4′-diol, I) to 4,4-biphenoquinone ([bi-2,5-cycloexadiene-(1,1′-cycloexadiene-(1,1′-ylidene)]-4,4′-dione, II) as well as the oxidative decomposition of II by means of some metal ions (Mn^III, Ce^IV and Ag^II) have been investigated in aqueous perchlorate media at different temperatures and acidities. The oxidation of I follows the empirical rate law: $\text{−}\text{d[I}\text{]}\text{d}\text{t}\text{= k[}\text{I][M}\text{]f([}\text{H}{}^{\mathrm{+}}\text{])}$, where M represents the oxidizing metal ion, and the decomposition of II: $\text{−}\text{d[II]}\text{d}\text{t}\text{= k′[}\text{II}\text{][}\text{M}\text{]}{}^{\mathrm{a}}\text{f′([}\text{H}{}^{\mathrm{+}}\text{])}$, where a = 1 for Ag^II and a = 0 for Ce^IV and Mn^III. The reaction mechanisms are proposed.     

Collision induced absorption in the a1Δ(v = 2) ← X3Σg(-)(v = 0) band of molecular oxygen

Using cavity ring-down spectroscopy we measured the collision induced absorption spectrum associated with the a(1)Δ(v = 2) ←X(3)Σ(g)(-)(v = 0) band of oxygen near 922 nm both in pure oxygen and in mixtures of oxygen and nitrogen. For pure oxygen, we report for this band an integrated absorption of (1.56 - 0.04/+0.40) × 10(-5) cm(-2) amg(-2). We find that collisions between oxygen and nitrogen do not result in any measurable CIA signal. At 1 bar of oxygen, this collision induced transition is much stronger than the allowed magnetic dipole and electric quadrupole transitions.     

Kinetics of aquation of trans-dichlorobis(N,N′-dimethylethylenediamine)cobalt(III) ion in water–methanol in water–propan-2-ol media

The complex trans-[Co(dmen)2Cl2]Cl (dmen=N,N-dimethylethylenediamine) has been prepared and characterized by elemental analysis, u.v.-vis. and i.r. spectra. The kinetics of the primary aquation of trans-[Co(dmen)2Cl2] in H2O, H2O–MeOH and H2O–i-PrOH have been examined over a wide range of solvent compositions and temperatures (40–55°C). Plots of rate constants (log k) versus the reciprocal of the dielectric constant of the medium (Ds–1) and Grunwald–Winstein values of the solvent (Y) were found to be non-linear. The variation of enthalpies (H) and entropies (S) of activation with solvent composition has been determined. Plots of H or S versus the mole fraction of each solvent exhibit extrema at x2=ca. 0.16 and 0.27 for MeOH and at x2=ca. 0.03 and 0.14 for i-PrOH. Furthermore, the cycle relating the free energy of activation in H2O to that in H2O–co-solvent shows that the stabilizing influence of the changes in the solvent structure is greater on the emergent five-coordinate cation in the transition state than that on the complex ion in the initial state, with the difference becoming greater as the mole fraction of the co-solvent increases.     

Kinetics of oxidation of phenylhydrazine by a μ-oxo diiron(III,III) complex in acidic aqueous media

Phenylhydrazine (R) quantitatively reduces [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) (phen?=?1,10-phenanthroline) and its conjugate base [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) to [Fe(phen)₃]²⁺ in presence of excess 1,10-phenanthroline in the pH range 4.12–5.55. Oxidation products of phenylhydrazine are dinitrogen and phenol. The reaction proceeds through two parallel paths: 1?+?R?→?products (k ₁), 2?+?R?→?products (k ₂); neither RH⁺ nor the doubly deprotonated conjugate base of the oxidant, [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3) is kinetically reactive though both are present in the reaction media. At 25.0°C, I?=?1.0?M (NaNO₃), the rate constants are k ₁?=?425?±?10?M^?1?s^?1 and k ₂?=?103?±?5?M^?1?s^?1. An inner-sphere, one-electron, rate-limiting step is proposed.     

Temperature dependence of the relaxation rate constants of the a 1Δg and b 1Σ +g states of oxygen isotopes

The relaxation rate constants of the low-lying electronic singlet states, a ¹Δ_g and b ¹Σ⁺_g , of gaseous natural O₂ and of the isotope ¹⁸O₂ were investigated as a function of temperature from 100 to 295 K. The measured increase of the rate constants with temperature is in good agreement with a theory of electronic-to-vibrational-translational energy transfer. The significant effects of the different electronic states and of the isotope masses on the absolute values of the relaxation rate constants, which range from 1.0× 10⁻²⁰ to 3.9× 10⁻¹⁷ s⁻¹ molecule⁻¹ cm³ at 295 K, are discussed.     

Complexes of β-cyclodextrin with chloronitrobenzenes and with solvents in water + organic solvent mixtures

Inclusion complexes of chloronitrobenzenes with -cyclodextrin in aqueous 0.1 M phosphate buffer solutions containing various concentrations of ethanol, dimethylsulfoxide, dimethylformamide, acetone and acetonitrile have been studied by a polarographic method. The diffusion coefficients and the stability constants of the corresponding complexes have been determined. Using an equation derived by us which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the solvent, both stability constants have been calculated. The influence of solvent on the stability constant of chloronitrobenzenes is discussed     

Formation constants and oxidation of bis(1,10-phenanthroline)-copper(I) perchlorate and bis(2,2′-bipyridine)copper(I) perchlorate by molecular oxygen in formamide

Summary A study was made of the slow oxidation with molecular oxygen in formamide of the cuprous complexes Cu(1,10-phenanthroline)₂ ⁺ and Cu(2,2-bipyridine)₂ ⁺, and of Cu(MeCN)₄ClO₄ with and without complexing agents. The two formation constants were calculated from the kinetic data. Both complexes reacted with a rate constant of 0.001 with respect to the value obtained in solvent water. A catalytic effect of the water molecules is proposed to explain this difference. The cupric complexes formed were isolated and identified as [CuL₂ formate]ClO₄ and [CuL₂ cyanate]ClO₄.     

Change of intensity of a1Δg → X3Σ g − transition in oxygen molecule upon interaction with H2, N2, and CS2

The semiempirical MINDO/3 CI method has been used to calculate collision complexes of the oxygen molecule with certain diamagnetic molecules, simulating the effect of solvents in increasing the intensity of the a¹_g X³ _g ^– transition in the oxygen molecule.Cherkassy Engineering Technology Institute, 460 Shevchenko Street, Cherkassy 257006, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 143–146, May–June, 1996. Original article submitted July 12, 1995.     

Characterization of O2 (1Δg)-derived oxidation products of tryptophan: A combination of tandem mass spectrometry analyses and isotopic labeling studies

The fragmentation mechanisms of singlet oxygen [O(2) ((1)Delta(g))]-derived oxidation products of tryptophan (W) were analyzed using collision-induced dissociation coupled with (18)O-isotopic labeling experiments and accurate mass measurements. The five identified oxidized products, namely two isomeric alcohols (trans and cis WOH), two isomeric hydroperoxides (trans and cis WOOH), and N-formylkynurenine (FMK), were shown to share some common fragment ions and losses of small neutral molecules. Conversely, each oxidation product has its own fragmentation mechanism and intermediates, which were confirmed by (18)O-labeling studies. Isomeric WOH lost mainly H(2)O + CO, while WOOH showed preferential elimination of C(2)H(5)NO(3) by two distinct mechanisms. Differences in the spatial arrangement of the two isomeric WOHs led to differences in the intensities of the fragment ions. The same behavior was also found for trans and cis WOOH. FMK was shown to dissociate by a diverse range of mechanisms, with the loss of ammonia the most favored route. MS/MS analyses, (18)O-labeling, and H(2)(18)O experiments demonstrated the ability of FMK to exchange its oxygen atoms with water. Moreover, this approach also revealed that the carbonyl group has more pronounced oxygen exchange ability compared with the formyl group. The understanding of fragmentation mechanisms involved in O(2) ((1)Delta(g))-mediated oxidation of W provides a useful step toward the structural characterization of oxidized peptides and proteins.     

High resolution spectral analysis of oxygen. II. Rotational spectra of a(1)Δ(g) O2 isotopologues

As part of a comprehensive review on molecular oxygen spectroscopy, we have measured rotational spectra of isotopic forms of molecular oxygen in its a(1)Δ(g) electronic state with high-resolution terahertz spectroscopy. The data are recorded in close proximity to predicted positions. Due to the high resolution and good signal-to-noise ratio, the fundamental hyperfine parameters eQq and C(I) are determinable for (17)O-substituted species for the first time. A refined nuclear spin orbit coupling constant, a = -211.9328(283) MHz, was determined, and is roughly two orders of magnitude more precise than values determined from near infrared spectroscopy or electron spin resonance studies. Vibrationally excited oxygen in the a(1)Δ(g) electronic state was also observable with small signal levels for many of the rotational transitions.