Ferrocytochrome c and deoxyhemoglobin in the reaction with the iron cysteamine nitrosyl complex {Fe2[S(CH2)2NH3]2(NO)4}SO4·2.5H2O

By an example of the iron cysteamine nitrosyl complex {Fe₂[S(CH₂)₂NH₃]₂(NO)₄}SO₄··2.5H₂O (CAC), it was shown for the first time that the hydrolysis of this NO donor in the presence of ferrocytochrome c (cyt c ²⁺) affords the iron nitrosyl complex NO-cyt c ²⁺, which serves as the NO depot. The rate constant of NO release from CAC was determined from the kinetics of the formation of NO-cyt c ²⁺. At pH 3.0 the rate constant is (2.7±0.1)·10⁻³ s⁻¹. Ferrocytochrome c produces a less stabilizing effect on CAC than deoxyhemoglobin (Hb). Thus in the presence of cyt c ²⁺, the reaction is completed in 1 h, whereas NO is released from a solution of CAC (2·10⁻⁴ mol L⁻¹) in the presence of Hb during 40 h. The previously unknown stabilization of iron nitrosyl complexes by hemoglobin was found.     

Formation of nitrosothiols by the reaction of different forms of hemoglobin with (tetranitrosyl)bis(pyrimidin-2-ylthio)diiron

The reaction of hemoglobin (Hb), oxyhemoglobin (HbO₂), and methemoglobin (metHb) with the tetranitrosyl iron complex of the fu₂-S type [Fe₂(SC₄H₃N₂)₂(NO)₄] (1) was studied. The reaction results in the nitrosylation of the free SH group of 93-β-cysteine in these forms of hemoglobin. The change in the Hb, HbO₂, and metHb concentrations was monitored by spectrophotometry, recording the difference absorption spectra of the experimental systems with these forms of hemoglobin and the buffer containing complex 1 in the same concentration. The absorption spectra were processed to obtain the components using the MATHCAD method. The nitrosothiol concentration was determined by the Saville reaction. In a protic medium containing 3.3% DMSO, complex 1 spontaneously generates NO due to hydrolysis (k = 3.7 · 10^-4 s^-1). Oxyhemoglobin reacts with evolved NO to form metHb. Complex 1 reduces metHb with a high rate to yield Hb (k = 6.7 · 10^-3 s^-1) followed by the formation of HbNO (k = 6.5 · 10^-3 s^-1). Oxidized complex 1 yields NO with a higher rate than the starting complex does. The reaction of HbO₂ and metHb (0.02 mmo1 L^-1) with complex 1 affords nitrosothiols in micromolar concentration during 5 min, and no nitrosothiol is formed in the case of Hb.     

Photochromic transformations in solutions of 8,8′-diquinolyl disulfide and di(mercaptoquinolinato)nickel(<Emphasis Type="SmallCaps">II</Emphasis>)

The nature of intermediate species and their reactions were studied by laser pulse photolysis for a photochromic system consisting of 8,8′-diquinolyl disulfide (RSSR) and a planar Ni^II complex di(mercaptoquinolinato)nickel(II) (Ni(SR)₂) in toluene and benzene solutions. Under exposure to laser radiation, disulfide RSSR dissociates to two RS^· radicals, whose spectrum has an intense absorption band with a maximum at λ = 400 nm (ε = 8400 L mol⁻¹ cm⁻¹). The radicals disappear by recombination (2k _rec = 4.6 · 10⁹ L mol⁻¹ s⁻¹). In the presence of the Ni(SR)₂ complex, coordination of the radical (k _coord = 4.4 · 10⁹ L mol⁻¹ s⁻¹) competes with recombination to form a radical complex RS^· Ni(SR)₂ having an intense absorption band with a maximum at 460 nm (ε = 16 600 L mol⁻¹ cm⁻¹). This species decays in the second-order reaction (2k = 4.6 · 10⁴ L mol⁻¹ s⁻¹). Since the photochromic system returns to the initial state, the reaction of two radical complexes is assumed to produce radical recombination and reduction of the disulfide and Ni(SR)₂ complex. Analysis of the kinetic data showed that some RS^· radicals decay in the microsecond time interval due to the reaction with the RS^· Ni(SR)₂ radical complex (k = 3.1 · 10⁹ L mol⁻¹ s⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2291–2300, October, 2005.     

Kinetics of protonation of tungsten hydrides WH(CO)2(NO)L2 by weak OH-acids

The kinetics of protonation of tungsten hydrides WH(CO)₂(NO)L₂ (1, L = PMe₃, PEt₃, P(OPri)₃, PPh₃) by weak OH-acids (PhOH, (CF₃)₂CHOH, (CF₃)₃COH) in hexane was studied by IR spectroscopy. The study of the reactions of compounds 1 with OH-acids at 190–270 K revealed that the first step involves the formation of dihydrogen-bonded W(CO)₂(NO)L₂(H)...HOR complexes. When the temperature increases to ambient, the proton transfer and evolution of molecular hydrogen occur, affording the final products: organyloxy derivatives W(OR)(CO)₂(NO)L₂. The study of the kinetics at 298 K found that the proton transfer is the rate-determining step. The rate constants k _app are 2.2·10⁻⁵–6.3·10⁻⁴ s⁻¹, and the free activation energies are ΔG ^≠ _298K = 22–23 kcal mol⁻¹. The rate constants depend on the proton-accepting properties of the hydride and the acidic properties of the OH-proton donor and increase in the same order as the enthalpy of hydrogen bond formation. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 837–841, May, 2007.     

Radical scavenging reactions of chlorogenic acid: A pulse radiolysis study

At near neutral pH (approx. 5.5), the OH-adduct of chlorogenic acid (CGA), formed on pulse radiolysis of N₂O-saturated aqueous CGA solutions (λ _max = 400 and 450 nm) with k = 9 × 10⁹ dm³ mol⁻¹ s⁻¹, rapidly eliminates water (k = 1 × 10³ s⁻¹) to give a resonance-stabilized phenoxyl type of radical. Oxygen rapidly adds to the OH-adduct of CGA (pH 5.5) to form a peroxyl type of radical (k = 6 × 10⁷ dm³ mol⁻¹ s⁻¹). At pH 10.5, where both the hydroxyl groups of CGA are deprotonated, the rate of reaction of · OH radicals with CGA was essentially the same as at pH 5.5, although there was a marked shift in the absorption maximum to approx. 500 nm. The CGA phenoxyl radical formed with more specific one-electron oxidants, viz., Br ₂ ^·− and N ₃ ^· radicals show an absorption maximum at 385 and 500 nm, k ranging from 1–5.5 × 10⁹ dm³ mol⁻¹ s⁻¹. Reactions of other one-electron oxidants, viz., NO ₂ ^· , NO^· and CCl₃OO^· radicals, are also discussed. Repair rates of thymidine, cytidine and guanosine radicals generated pulse radiolytically at pH 9.5 by CGA are in the range of (0.7–3) × 10⁹ dm³ mol⁻¹ s⁻¹.     

Pulse radiolysis study of the oxidation of the I<Superscript>−</Superscript> ions with the radical anions Br<Subscript>2</Subscript><Superscript>·−</Superscript> in an aqueous solution: formation and properties of the radical anion BrI<Superscript>·−</Superscript>

The radiation chemical redox transformations in solutions of bromides in the presence of minor additives of iodides were studied by pulse radiolysis. The change in the concentrations of the Br⁻ and I⁻ ions changes the ratio of the formed short-lived radical anions Br₂ ^·−, BrI^·−, and I₂ ^·−. The spectrum of the mixed radical anion BrI^·− contains a broad optical band at 370 nm with ɛ₃₇₀ = 9650 L mol⁻¹ cm⁻¹. The reduction potential of the BrI^·−/Br⁻, I⁻ pair is 1.25 V. The rate constants for the forward and backward reactions Br₂ ^·− + I⁻ ⇌ BrI^·− + Br⁻ are k _f = 4.3·10⁹ and k _r = 1.0·10⁵ L mol⁻¹ s⁻¹, respectively; for the reactions BrI^·− ⇌ Br⁻ + I^·, k _f = 5.7·10⁸ s⁻¹ and k _r = 1.0·10¹⁰ L mol⁻¹ s⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1787–1792, September, 2008.     

Revealing of the cation-binding sites on the surface of hemoglobin in its reaction with the NO donor, the nitrosyl iron complex {Fe2[S(CH2)2NH3]2(NO)4}SO4·2.5H2O

Deoxyhemoglobin (Hb) stabilizes the cationic nitrosyl iron complex with cysteamine {Fe₂[S(CH₂)₂NH₃]₂(NO)₄}SO₄·2.5H₂O (CysAm), by slowing down its hydrolysis. In the absence of Hb, the electrochemical detection of NO release in the course of the hydrolysis using a sensor electrode gave the rate constant of (5.2±0.2)·10^?5 s^?1. The release of NO is a reversible process, and the amount of released NO is 1.4% of the CysAm concentration. In the presence of Hb, NO is released much more slowly, and the reaction is more intense than that in the absence of Hb. The adsorption of CysAm by an Hb molecule results in NO release from the CysAm-Hb complex with a rate constant of 1·10^?8 s^?1. The analysis of the Hb surface revealed the possible location of the cation-binding sites, which reversibly bind the cationic CysAm complex. The kinetic parameters of NO release from CysAm in the absence and in the presence of Hb were studied by the kinetic modeling.     

Preparation and reactivity of metal-containing monomers

The thermal decomposition of iron (III) acrylate, [Fe₃O(CH₂=CHCOO)₆ · 3H₂O]OH (FeAcr), a monomer with a complex cluster cation, has been studied at 200–370 °C. Thermal transformations of FeAcr occur in two temperature regions. The rates of gas evolution in the low temperature region (200–300 °C) and the high temperature region (300–370 °C) are described by first-order equations withk=4.2 · 10²¹exp[−59000/(RT)] s⁻¹ andk=1.3 · 10⁶exp[−30500/(RT)] s⁻¹, respectively. A study of the qualitative and quantitative composition of the products of FeAcr thermolysis was carried out. The thermal transformation of FeAcr is a complex process of dehydration, degradation, and polymerization in the solid phase followed by decarboxylation of the metal-carboxyl groups of the polymer. for part 33 see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1743–1750, October, 1993.     

Kinetics of the radical reactions in pulse radiolyzed RHF — CO2(SF6)-O2-NO gaseous mixtures; RHF = CH3CH2F, CH3CHF2, CH3CF3, CH2FCF3

The kinetics of the peroxy radicals RHFO₂ reactions with NO has been studied by using pulse radiolysis and UV absorption spectroscopy. The rate constants of interaction of oxygen atoms with NO − k ₂ = 2.2±0.2·10⁻¹² cm³·s⁻¹ and NO₂ − k ₃ = 2.1±0.2·10⁻¹¹ cm³·s⁻¹ were found in agreement with the literature values. The bath gases (SF₆ or CO₂) have got minor effect on the rate constants of RHFO₂+NO→NO₂+prod. reactions; RHFO₂ = CH₃CH₂O₂, CH₃CHFO₂, CH₃CF₂O₂, CF₃CH₂O₂, CF₃CHFO₂. The obtained rate coefficients are in the scope of the literature values, although they are lower than those recommended in NIST database. The reasons are discussed.     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

A new amperometric H<Subscript>2</Subscript>O<Subscript>2</Subscript> biosensor based on nanocomposite films of chitosan–MWNTs,hemoglobin, and silver nanoparticles

A new H₂O₂ biosensor was fabricated on the basis of nanocomposite films of hemoglobin (Hb), silver nanoparticles (AgNPs), and multiwalled carbon nanotubes (MWNTs)–chitosan (Chit) dispersed solution immobilized on glassy carbon electrode (GCE). The immobilized Hb displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ′) of −22.5 mV in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) in the Chit–MWNTs film was evaluated as 2.58 s⁻¹ according to Laviron’s equation. The surface concentration (Γ*) of the electroactive Hb in the Chit–MWNTs film was estimated to be (2.48 ± 0.25) × 10⁻⁹ mol cm⁻². Meanwhile, the Chit–MWNTs/Hb/AgNPs/GCE demonstrated excellently electrocatalytical ability to H₂O₂. Its apparent Michaelis–Menten constant (K _M^app) for H₂O₂ was 0.0032 mM, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H₂O₂ ranging from 6.25 × 10⁻⁶ to 9.30 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.47 × 10⁻⁷ mol L⁻¹ (S/N = 3). Furthermore, the biosensor possessed rapid response to H₂O₂ and good stability, selectivity, and reproducibility.     

Pulse radiolytic investigation of the reaction of hydroxyl radicals with gentamycin

Hydroxyl radicals were generated radiolytically in N₂O-saturated aqueous solutions of the aminoglycoside antibiotic, gentamycin. Using the pulse radiolysis technique, the rate constant of OH radicals with gentamycin determined was 1.2·10⁹ dm³·mol⁻¹·s⁻¹. Upon^.OH attack a transient species with an absorption maximum at 270 nm is observed which decays by second-order kinetics within the solute concentration range of 3.2·10⁻⁵ to 1·10⁻³mol·dm⁻³. Transient species undergoes transformation to a permanent product absorbing between 260 and 340 nm with maximum absorption at 300 nm. Rate constant of the reaction of bimolecular decay of gentamycin radicals, k (Gen^.+Gen^.) was found to be ≈ 1.4·10⁷ dm³·mol⁻¹·s⁻¹.     

Neutral thallium clusters in aqueous solutions. Pulse radiolysis study

The formation of neutral Tl₂ (λ_max = 390 nm) and Tl₄ (λ_max = 360 nm) clusters in dilute aqueous solutions of Tl₂SO₄ containing formate ions was found by pulse radiolysis. The rate constants for the recombination of Tl⁰ atoms and Tl₂ clusters are equal to 1.5·10¹⁰ L mol⁻¹ s⁻¹ and 1.0·10¹⁰Lmol⁻¹ s⁻¹ (±30%), respectively, and the extinction coefficient of Tl₂ at 390 nm is −6.0·10³ L mol⁻¹ cm⁻¹ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2367–2369, December, 1999.     

Extraction and DFT study on the complexation of the cesium cation with a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs⁺(aq) + A⁻(aq) + 1(nb) ⇆ 1·Cs⁺(nb) + A⁻ (nb) taking part in the two-phase water–nitrobenzene system (A⁻ = picrate, 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, A⁻) = 2.8 ± 0.1. Further, the stability constant of the hexaarylbenzene-based receptor·Cs⁺ complex (abbrev. 1·Cs⁺) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Cs⁺) = 4.7 ± 0.1. By using quantum mechanical DFT calculations, the most probable structure of the 1·Cs⁺ complex species was solved. In this complex having C ₃ symmetry, the cation Cs⁺ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation–π interaction. Finally, the calculated binding energy of the resulting complex 1·Cs⁺ is −220.0 kJ/mol, confirming relatively high stability of the considered cationic complex species.     

Decay kinetics of benzophenone oxide in the liquid phase

The kinetics of self-termination of benzophenone oxide (BPO) in the liquid phase was studied by flash photolysis. The extinction coefficient of BPO (ε) was found to be virtually independent of the solvent nature, ε=(1.9±0.1)·10³ L mol⁻¹ cm⁻¹. The rate constant of the BPO self-temination increases from 1.8·10⁷ (MeCN) and 7.4·10⁷ (C₆H₆) to 1.5·10⁹ (n-decane) and 2.0·10⁹ L mol⁻¹ s⁻¹ (n-pentane) at 293±2 K. Solvation of BPO promotes a polar state of the molecule in MeCN and C₆H₆. In nonpolar hydrocarbons, a great contribution is made by the biradical structure resulting in an increase in the rate constant and a shift of the absorption maximum to the long-wave region (from 410 nm in MeCN to 425 nm inn-pentane). In solutions of benzene and acetonitrile, benzophenone oxide reacts with the parent diazo compound with a rate constant of (2–4)·10⁵ L mol⁻¹ s⁻¹ (293±2 K) along with the self-termination. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1329–1332, July, 1998.     

Kinetics of the peroxy RFO2 radical formation in the RHF-O2-CO2 gaseous mixtures

The kinetic data on the molecular oxygen activity of CH₃CH^·, CH₃CF₂ ^· and CF₃CHF^· radicals are reported. In laboratory, these radicals were generated by pulsed (12 ns) electron beam interaction with the gaseous RHF-O₂-CO₂ mixtures containing large excess of carbon dioxide (RHF = CH₃CH₂F, CH₃CHF₂ or CH₂FCF₃). The transient product (O₃ or RFO₂ ^·) formation was monitored by the UV absorptions at 250 nm and the rate constants of Reactions (4) and (9) were obtained. The values of k ₉ diminished with increasing number of fluorine atoms in RHF molecule. For CH₃CH₂F and CH₃CHF₂ the k ₉’s were equal to (8.8–10.2)^·10⁻¹⁴cm^{3 ·}s⁻¹ and (7.3–8.4)^·10⁻¹⁴cm^{3 ·}s⁻¹, respectively, and seem to be determined for the first time. In the case of CH₂FCF₃ the obtained value of k _CF3CHF+O2 = 5.20±0.76^·10⁻¹⁴cm^{3 ·}s⁻¹ is much higher than the value published in the literature.⁴ The other determined rate constant data are comparable to the literature values.     

Syntheses,weak interactions, 3D network structures and magnetic properties of two salts based on bis(maleonitriledithiolate)copper(II) anion and substituted triphenylphosphonium cation

Two new salts, [BzTPP]₂[Cu(mnt)₂] (1) and [4NO₂BzTPP]₂[Cu(mnt)₂] (2) (BzTPP⁺ = benzyltriphenylphosphonium and mnt²⁻ = maleonitriledithiolate) have been prepared and characterized by elemental analyses, UV, IR, molar conductivity and single-crystal X-ray diffraction. The single-crystal structure analysis shows that 1 crystallizes in the monoclinic space group P2₁/n, while 2 crystallizes in the triclinic space group P−1. The effects of weak intramolecular interactions such as C–H···O, C–H···S, C–H···N, C–H···Cu hydrogen bonds and p···π, π···π stacking interactions in the solids generate a 3D network structure. It is noted that the change in the molecular topology of the counteraction when the 4-substituted group in the benzyl ring is changed from H to NO₂ results in differences in the crystal system, space group, weak interactions and the stacking mode of the cations and anions of 1 and 2. The magnetic susceptibilities of these salts measured in the temperature range 2.0 to 300 K show weak ferromagnetic coupling features with θ = 2.05 × 10⁻² K for 1 and 5.13 × 10⁻³ K for 2.     

Experimental and theoretical study on the complexation of the cesium cation with dibenzo-30-crown-10

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs⁺ (aq) + A⁻ (aq) + 1(nb) \rightleftarrows \rightleftarrows 1·Cs⁺(nb) + A⁻(nb) taking place in the two-phase water–nitrobenzene system (A⁻ = picrate, 1 = dibenzo-30-crown-10; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, A⁻) = 4.0 ± 0.1. Further, the stability constant of the 1·Cs⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Cs⁺) = 5.9 ± 0.1. Finally, by using quantum–mechanical DFT calculations, the most probable structure of the resulting cationic complex species 1·Cs⁺ was derived.     

Photochemical and photophysical properties ofmeso-tetraferrocenylporphyrin. Quenching ofmeso-tetraphenylporphyrin by ferrocene

It was found that the quantum yield of the fluorescence ofmeso-tetraferrocenylporphyrin (TFcP) is at most 3.0·10⁻⁵, and that of the triplet state of FTcP is at least 200 times lower than the quantum yield ofmeso-tetraphenylporphyrin (TPP). Excitation of TFcP in CCl₄ by light with λ>410 nm results in the oxidation of TFcP. The singlet and triplet excited states of TPP in toluene and acetonitrile are quenched by ferrocene with rate constants of 1.2·10¹⁰ and 1.7·10¹⁰, (4.6±0.5)·10⁸ and (1.37±0.21)·10⁹ L mol⁻¹ s⁻¹, respectively. The quenching mechanisms are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1924–1927, October, 1999.     

Kinetics of hydrated electron reactions with phosphate anions: a laser photolysis study

The decay kinetics of hydrated electron (e_aq ⁻) formed upon photolysis of aqueous solutions of sodium pyrene-1,3,6,8-tetrasulfonate at λ = 337 nm in the presence of phosphate anions (up to 2 mol L⁻¹) was studied by nanosecond laser-pulse photolysis in a wide range of pH (3.5–10) and ionic strength (I, up to 2 mol L⁻¹) values. At high pH values, where the HPO₄ ²⁻ ions dominate, the e_aq ⁻ decay kinetics depends only slightly on phosphate concentration (rate constant for the reaction is at most 2·10⁵ L mol⁻¹ s⁻¹). The H₂PO₄ ⁻ ions react with e_aq ⁻ at a rate constant of 2.8·10⁶ L mol⁻¹ s⁻¹ (I = 0), which increases linearly with the parameter in accordance with the Debye-Hückel theory. The rate constant for quenching of e_aq ⁻ by H₃PO₄ at pH ≤ 4 decreases linearly with the parameter due to the secondary salt effect and equals 1.6·10⁹ L mol⁻¹ s⁻¹ at I = 0. The logarithm of the rate constant for quenching of e_aq ⁻ by phosphates is linearly related to the number of the O-H bonds in the phosphate molecule. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1277–1280, July, 2007.