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1Author    Hermann Esterbauer, Helmward Zöllner, N. Orbert ScholzRequires cookie*
 Title    Reaction of Glutathione with Conjugated Carbonyls  
 Abstract    1. GSH reacts with conjugated carbonyls according to the equation: G S H + R —C H = C H — COR R —CH(SG) —CH2—COR. The forward reaction follows second order, the reverse reaction first order kinetics. It is assumed that this reaction reflects best the ability of conjugated carbonyls to inactivate SH groups in biological systems. 2. The rate of forward reaction increases with pH approx. parallel with asH • Besides OH" ions also proton donors (e. g. buffers) increase the rate. The catalytic effect of pH and buffer is inter­ preted in view of the reaction mechanism. 3. The equilibrium constants as well as the rate constants for forward (k t) and reverse reaction show an extreme variation depending on the carbonyl structure. Acrolein and methyl vinyl ketone (k t = 120 and 32 mol-1 sec-1 , resp.) react more rapidly than any other carbonyl to give very stable adducts (half-lives for reverse reaction 4.6 and 60.7 days, resp.). Somewhat less reactive are 4-hydroxy-2-alkenals and 4-ketopentenoic acid (k t between 1 and 3 mol-1 sec-1), but they also form very stable adducts showing half-lives between 3.4 and 19 days. All other carbonyl studied react either very slowly (e. g. citral, ethly crotonate, mesityl oxide, acrylic acid) or form very labile adducts (crotonal, pentenal, hexenal, 3-methyl-butenone). Comparing biological activities of con­ jugated carbonyls their reactivity towards HS (/cj) and the stability of the adducts must be con­ sidered. 
  Reference    (Z. Naturforsch. 30c, 466—473 [1975]; received January 17/April 11975) 
  Published    1975 
  Keywords    Glutathione, Conjugated Carbonyls, Rate Constant, Equilibrium Constant 
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 TEI-XML for    default:Reihe_C/30/ZNC-1975-30c-0466.pdf 
 Identifier    ZNC-1975-30c-0466 
 Volume    30 
2Author    HansE. Wilhelm, Horst Gebert, Wolfgang RegensteinRequires cookie*
 Title    Effect of Substituents on the Viscosity Dependence of Fluorescence and on the S l -T l Energy Gap of Donor-Acceptor Substituted Trans-Stilbenes  
 Abstract    The dependence of fluorescence quantum yields and Sj-lifetimes of donor-acceptor substituted trans-stilbenes on temperature was measured in the temperature range from 298 to 100 K, using solutions of stilbenes in 3-methylpentane (3-MP). Measurements of fluorescence and phosphores-cence spectra show that the triplet energy is almost independent of the acceptor. The S[-energy and the S r Ti energy gap decrease with increasing acceptor strength. For all compounds intersystem crossing (ISC) S, —» T, is negligible. 
  Reference    Z. Naturforsch. 52a, 837—842 (1997); received November 18 1997 
  Published    1997 
  Keywords    Stilbenes, Fluorescence, Phosphorescence, Singlet-Triplet Energy Gap, Rate Constants 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0837.pdf 
 Identifier    ZNA-1997-52a-0837 
 Volume    52 
3Author    W. A. Prütz, S. VogelRequires cookie*
 Title    Specific Rate Constants of Hydroxyl Radical and Hydrated Electron Reactions Determined by the RCL Method  
 Abstract    Relative rate constants of OH radical and eaq~ reactions have been determined by comparing, under steady x-irradiation, the effect of various solutes upon the radiation-induced chemiluminescence (RCL) of aqueous dye (DH) solutions, [DH + -OH] + eaq --> DH* + OH -. The results abundantly confirm other published data. RCL changes upon addition of phosphates indicate prototropic reactions with the oxidized dye, D'-f^PO^ ^ DH-+ + HPO4 2-, promoting or inhibiting the formation of semioxidized dye (DH-+) as the most efficient RCL precursor. The RCL enhancement commonly observed upon addition of halides and pseudo halides is discussed at some length on the base of previous and present results in order to focus attention to the possible correlation between such RCL enhancement and the effect of halogen-sensitization in radiobiology. RCL results suggest that the halide transients formed from OH radicals, X -+ -OH X 1 -f OH -, are very powerful oxidizing agents reacting with aromatics by electron-abstraction rather than by addition or H-abstraction. The common application of I -and SCN -as competitors for the estimation of OH radical reactivities is being commented in the context. 
  Reference    (Z. Naturforsch. 31b, 1501—1510 [1976]; received July 12 1976) 
  Published    1976 
  Keywords    Hydrated Electron, Hydroxyl Radical, Luminescence, Radiation Chemistry, Rate Constants 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-1501.pdf 
 Identifier    ZNB-1976-31b-1501 
 Volume    31 
4Author    Eberhard Bothe, G. Ali, Ureshi, D. Ietrich, S. Ch, Lte-F Ro, H. Lin DRequires cookie*
 Title    Rate of OH Radical Induced Strand Break Formation in Single Stranded DNA under Anoxic Conditions. An Investigation in Aqueous Solutions Using Conductivity Methods  
 Abstract    Single stranded D N A (ssD N A) in aqueous N 20-satu rated solution was pulse-irradiated with electrons or irradiated under steady-state conditions with 60Co-y rays. The conductivity increase after irradiation was measured as a function o f concentration, pH, temperature, metal cation content and additives. The conductivity increase could be shown to be due to the release o f associated counterions (N a+ or H+) as a result o f the formation o f chain breaks. At 28 mg I-1 D N A ~ 8 sodium ions are liberated per 100 eV absorbed energy (G (N a +) = 8.3). On the basis o f G value for single-strand breaks (ssb) o f G(ssb) = 0.55, it is calculated that 8.3/0.55 = 15 sodium ions per strand break are set free. The release o f N a+ monitored by 23N a-N M R at pH 7 as a function o f dose corresponds to that o f the conductivity increase. The rate o f the conductivity increase does not depend on d ose/p u lse (range 2 -2 0 J kg-1) and shows at least two components. The rate constant o f the fast and dom inant com ponent is constant above pH 8.5 (A: = 38 s— 1, 20 °C) and increases linearly with proton concentration below pH 7. Values o f 13kcal/m ol for the activation energy and 5 x 10" s_1 for the frequency factor were obtained at pH 7.3. Addition o f p-benzoquinone (pBQ) increases the rate constant o f the fast component proportionally to the concentration o f pBQ. From these results the rate-determining step o f the fast conductivity increase is concluded to be the splitting o f D N A radicals. The pH dependence and the m agnitude o f the activation energy agree with results from low molecular weight model com pounds for the C-4' m echanism ; this m echanism involves a heterolytic splitting o f the phosphoric acid ester bond starting from the 4' radical o f D N A . 
  Reference    Z. Naturforsch. 38c, 1030—1042 (1983); received Septem ber 19 1983 
  Published    1983 
  Keywords    DNA, Formation o f Strand Breaks, Electrical Conductivity, Pulse R adiolysis, Rate Constants 
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 TEI-XML for    default:Reihe_C/38/ZNC-1983-38c-1030.pdf 
 Identifier    ZNC-1983-38c-1030 
 Volume    38