Photoreactivity of biologically active compounds. XIX: Excited states and free radicals from the antimalarial drug primaquine

The formation and reactivity of excited states and free radicals from primaquine was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (< 50 ns) and with a triplet energy < 250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms 1O2 by laser flash photolysis (PQΦΔ = 0.025). Primaquine photoionises by a biphotonic process and also forms the monoprotonated cation radical (PQH2+•) by one electron oxidation by OH• (kq = 6.6•109 M-1s-1) and Br2•- (kq = 4.7•109 M-1s-1) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k2 = 7.4•108 M-1s-1). PQH2+• is scavenged by O2, although at a limited rate (kq = 1.0•106 M-1s-1). The reduction potential (E°) of PQH2+• / PQH+ is < +1015 mV. Primaquine also forms PQH2+• at pH 2.4, by one electron oxidation by Br2•- and proton loss (kq = 2.7•109 M-1s-1). The non-protonated cation radical (PQ+•) is formed during one electron oxidation with Br2•- at alkaline conditions (kq = 4.2•109 M-1s-1 at pH 10.8). The estimated pKa-value of PQH2+•/ PQ+• is pKa ~ 7-8. Primaquine is not a scavenger of O2•- at physiological pH. Thus self-sensitization by O2•- is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the 1O2 quencher sodium azide. Photosensitized degradation by formation of 1O2 is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of PQH2+• is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium

The contribution of free radicals in paracetamol degradation by UV/NaClO

UV/Chlorine is an emerging advanced oxidation process which forms several reactive species including •OH, •Cl, •OCl. This study investigated the contribution of three main free radicals: •OH, •Cl, •OCl on Paracetamol degradation under different conditions. Benzoic acid (BA), Nitro benzene (NB) and DMOB were used as probe compounds. The second rate constant of •OH, •Cl, •OCl with PRC were determined: 4.19 (±0.15) ×109 M-1s-1; 3.71 1010 M-1s-1; 3.532×109 M-1s-1, respectively. The formation of free radicals depends on pH. In particular, at pH 5: the contribution of •OH and     (-•OCl, •Cl) are 45 %, 41 %, respectively, at pH 8.5, the contribution of free radicals increases up to 63 %. Keywords. Paracetamol, UV/Chlorine process, reactive species

Allopurinol and oxypurinol are hydroxyl radical scavengers

AbstractAllopurinol is a scavenger of the highly reactive hydroxyl radical (k2 approx. 109 M−1s−1). One product of attack of hydroxyl radical upon allopurinol is oxypurinol, which is a major metabolite of allopurinol. Oxypurinol is a better hydroxyl radical scavenger than is allopurinol (k2 approx. 4 × 109 M−1s−1) and it also reacts with the myeloperoxidase-derived oxidant hypochlorous acid. Hence the protective actions of allopurinol against reperfusion damage after hypoxia need not be entirely due to xanthine oxidase inhibition

The ρ(1S,2S)\rho(1S,2S), ψ(1S,2S)\psi(1S,2S), Υ(1S,2S)\Upsilon(1S,2S) and ψt(1S,2S)\psi_t(1S,2S) mesons in a double pole QCD Sum Rule

We use the method of double pole QCD sum rule which is basically a fit with two exponentials of the correlation function, where we can extract the masses and decay constants of mesons as a function of the Borel mass. We apply this method to study the mesons: $\rho(1S,2S)$, $\psi(1S,2S)$, $\Upsilon(1S,2S)$ and $\psi_t(1S,2S)$. We also present predictions for the toponiuns masses $\psi_t(1S,2S)$ of m(1S)=357 GeV and m(2S)=374 GeV.Comment: 14 pages, 11 figures in Braz J Phys (2016

Публікації Я. Новицького на сторінках «Катеринославських губернських відомостей»

Pulsed-field-gradient nuclear magnetic resonance (NMR) combined with time-resolved chemically induced dynamic nuclear polarization (TR-CIDNP) was applied to study the reduction of guanosyl radicals in reactions with the proteins hen egg white lysozyme (HEWL) and bovine a-lactalbumin (BLA) in their native state.Guanosyl radicalswere generated photochemically in the reaction of guanosine-50-monophosphate with photosensitizer, triplet-excited 2,20-dipyridyl. In this reaction, at pH 5 guanosyl cation radical is formed, which deprotonates to yield the neutral guanosyl radical. To minimize the contribution of the cation radical, phosphate buffer was added, which accelerates the deprotonation of guanosyl cation radical. From model simulations of CIDNP kinetics the rate constants of the reduction were found to be (3.1 ± 0.5) 9 107 M-1s-1 for HEWL and (1.6 ± 0.4) 9 107 M-1s-1 for BLA. Also, experiments were carried out at the conditions for denatured HEWL, i.e., at 50 C in the presence of 10 M urea-d4. The rate constant of the reduction of guanosyl radical in this case was (3.6 ± 0.5) 9 108 M-1s-1

Review:Oksigen Singlet (1O2) dan Efek Fotooksidasi pada Produk Pangan

Dari sejumlah penelitian yang dilakukan secara intensif, terungkap oksigen singlet menjadi ancaman baru keamanan pangan. Oksigen singlet, yang merupakan komponen bukan radikal, bereaksi langsung dengan nonradikal, dan komponen kaya elektron dengan ikatan rangkap tanpa pembentukan radikal bebas. Reaksi fotoksidasi yang didorong oleh oksigen singlet sangat cepat pada makanan akibat rendahnya energi aktivasi yang dibutuhkan untuk terjadinya reaksi kimia. Secara berurutan, laju reaksi oksigen singlet dan oksigen triplet (3O2) dengan asam linoleat adalah 1,3 x 105 M-1S-1 dan 8,9 x 101 M-1S-. Dengan demikian, laju reaksi oksigen singlet dengan asam linoleat sekitar 1450 kali lebih cepat dibandingkan oksigen triplet dengan asam linoleat. Pentingnya peran oksigen singlet terhadap penurunan kualitas makanan telah banyak diketahui belakangan ini, terutama menyangkut oksidasi lemak, vitamin dan protein, yang sensitif terhadap kerusakan oksidatif.&nbsp

Potent Antioxidant and Anti-Tyrosinase Activity of Butein and Homobutein Probed by Molecular Kinetic and Mechanistic Studies †

Butein (BU) and homobutein (HB) are bioactive polyhydroxylated chalcones widespread in dietary plants, whose antioxidant properties require mechanistic definition. They were investigated by inhibited autoxidation kinetic studies of methyl linoleate in TritonTM X-100 micelles at pH 7.4, 37 °C. Butein had kinh = (3.0 ± 0.9) × 104 M−1s−1 showing a chain-breaking mechanism with higher antioxidant activity than reference α-tocopherol (kinh = (2.2 ± 0.6) × 104 M−1s−1), particularly concerning the stoichiometry or peroxyl radical trapping n = 3.7 ± 1.1 vs. 2.0 for tocopherol. Homobutein had kinh = (2.8 ± 0.9) × 103 M−1s−1, pairing the relative BDEOH measured by radical equilibration EPR as 78.4 ± 0.2 kcal/mol for BU and estimated as 82.6 kcal/mol for HB. The inhibition of mushroom tyrosinase (mTYR) by HB and BU was also investigated. BU gives a reversible uncompetitive inhibition of monophenolase reaction with KI′ = 9.95 ± 2.69 μM and mixed-type diphenolase inhibition with KI = 3.30 ± 0.75 μM and KI′ = 18.75 ± 5.15 μM, while HB was nearly competitive toward both mono- and diphenolase with respective KI of 2.76 ± 0.70 μM and 2.50 ± 1.56 μM. IC50 values (monophenolase/diphenolase at 1 mM substrate) were 10.88 ± 2.19 μM/15.20 ± 1.25 μM, 14.78 ± 1.05 μM/12.36 ± 2.00 μM, and 33.14 ± 5.03 μM/18.27 ± 3.42 μM, respectively, for BU, HB, and reference kojic acid. Molecular docking studies confirmed the mechanism. Results indicate very potent antioxidant activity for BU and potent anti-tyrosinase activity for both chalcones, which is discussed in relation to bioactivity toward protection from skin disorders and food oxidative spoilage

Reaction kinetics of carbon dioxide with aqueous solutions of l-Arginine, Glycine & Sarcosine using the stopped flow technique

The use of amino acids as potential solvents for carbon dioxide (CO2) capture has been considered by a number of researchers. However, very little is known about the kinetics and mechanism of amino acids-CO2 reactions. In this work, we investigate the reactions of three amino acids (l-Arginine, Glycine and Sarcosine) with CO2 in aqueous media using stopped-flow conductivity technique. The experiments were performed at temperatures between 293 and 313K and amino acids concentrations were in the range of 0.05–0.2 molar. The overall rate constants (kov) was found to increase with increased amino acid concentration and solution temperature. Both zwitterion and termolecular mechanisms were used to model and interpret the data. However, the Zwitterion mechanism was found to be the preferred one. From the stopped-flow results at pH around 6, we found that neutral l-Arginine, Glycine and Sarcosine react with CO2(aq) with k(M−1s−1)=2.81×1010exp(−4482.9T(K)), k(M−1s−1)=3.29×1013exp(−8143.7T(K)) and k(M−1s−1)=3.90×1013exp(−7991.0T(K)) respectively. The corresponding activation energies are 37.28kJmol−1, 67.71kJmol−1 And 66.44kJmol−1 respectively. A comparison between the kinetics of the three amino acids showed that Arginine exhibits highest reaction rate with CO2 followed by Sarcosine and then Glycine. The technique and results obtained from this work can be used as strong tools in the development of efficient new solvents for the removal of CO2 from flue and industrial gases.This paper was made possible by an NPRP Grant # 7-1154-2-433 from the Qatar National Research Fund (a member of Qatar Foundation)

Quenching of the Fluorescence of Tris (2 2-Bipyridine) Ruthenium(II) [Ru(bipy)3]2+ by a Dimeric Copper(II) Complex.

The quenching of the [Ru(bipy)3]2+ by Cu2L2+ was studied and the data were plotted with the Stern-Volmer equation. The plot showed a break and was divided into 2 regions, \u3c0.5 and \u3e0.5 Cu2L2+: [Ru(bipy)3]2+ molar ratio. Quenching above the 0.5 Cu2L2+: [Ru(bipy)3]2+ molar ratio was slower (330 x 10-6 M-1s-1) than the quenching rate reaction below 0.5 ratio (387 x 10-6 M-1s-1). With Cu2L2+ being a dimeric complex the break and differences in the quenching reaction rates can be explained in terms of the stoichiometry. When the Cu2L2+: [Ru(bipy)3]2+ ratio is \u3c 0.5, then each [Ru(bipy)3]2+ can interact with 1 Cu2L2+ dimer. At 0.5 then there is exactly a 1:1 ratio RuII : CuII. Above the 0.5 ratio the [Ru(bipy)3]2+ can interact with maybe only one of the Cu2L2+\u27s in the dimer, or with a [Ru(bipy)3]2+: Cu2L2+ unit, so the quenching is less efficient

Nitro-Triarylmethyl Radical as Dual Oxygen and Superoxide Probe

Superoxide radical is involved in numerous physiological and pathophysiological processes. Tetrathiatriarylmethyl (TAM) radicals are knows to react with superoxide allowing measurement of superoxide production in biological media. We report the synthesis of a Nitro conjugated TAM radical showing a rate constant of 7 × 105 M−1s−1 which is two order of magnitude higher than other TAMs allowing high sensitivity measurement of superoxid