Our studies of the radiation chemistry of aqueous solutions of aliphatic phosphates have revealed details which might shed some light on the chemical mechanisms of radiation induced strand breaks in DNA and related compounds.SCHOLES and WEISS have shown that during Y-radiolysis of aqueous solutions of nucleic acids 1 and of dihydrogen ethyl phosphate 2 in the presence of oxygen, labile phosphates are formed whidi readily hydrolyse. WILKINSON and WILLIAMS 3 found inorganic phosphate after y-radiolysis of disodium alkyl phosphates also in the absence of oxygen. They 3 proposed the reaction sequence (1) and (2), leading to labile phosphates. RCH20P03-~ + • OHRCHOPO3-" + HoO (1)Our results show that this medianism can be disregarded for kinetic reasons. Using pulse radiolysis techniques we measured the rate constant of OH attack on trimethyl phosphate (I), cf. reaction (3). and on sodium dimethyl phosphate (II) in N20-saturated solutions in competition with OH attack on CNS" (k = 7.5 xl0 9 l mole -1 s -1 , cf. ref. 4 ) and found £; = 8xl0 7 1 mole -1 s -1 for both phosphates.(CH,0)3P0 + -0H->CH20(CH30)2P0 + HoO (3)These data reveal stationary concentrations of OH radicals at dose rate levels attainable with 60 Co y-radiation which are much too low to render reaction (2) competitive with reaction (1). The radical -CH20 (CH30)2P0 shows u.v. end absorption with £ = 480 1 mole -1 cm -1 at = 220 nm, and decays with a second order rate constant of k = 2 x 10 9 1 mole -1 s -1
Americium / Mixed solvent / Stability constant / Monofluoride complex / Solvation number SummaryThe stability constant (/?,) of AmF 2+ in the mixed solvent system of dimethyl sulfoxide and water with 0.1 moldm -3 ionic strength was determined using a solvent extraction technique to compare with Nd(III) bearing similar chemical properties to Am(III). The value of In ß, was nearly constant when the mole fraction of DMSO in the bulk solution (X s ) was less than 0.04 and it increased with an increase in X a in the range of 0.04 < X s < 0.25. The variation of In β, with X x is obviously different from the result of Nd(III). The difference between the variations of In β, of Am(III) and Nd(III) with X, could be associated with (1) the cation solvation effect (containing the variation effect of the solvation number in the primary solvation sphere of tripositive cation) and (2) the variation effect of interionic distance between tripositive cation and fluoride ion. The variation of In β, of Am(IIl) in 0.04 < X, < 0.25 of the DMS0-H 2 0 system is considerably influenced by both effects due to the variation of solvation number in the primary solvation sphere and the variation of interionic distance, but that of Nd(III) in X, < 0.28 hardly contains those effects.
Europium / Mixed solvent / Stability constant / Monofluoride complex / Variation in solvation number SummaryThe stability constants (/?,) of the monofluoride complex of Eu(IlI) have been determined in mixed solvents of methanol and water at a 0.10 Μ ionic strength using a solvent extraction technique. The values of In /?, increase as the mole fraction of methanol in the mixed solvent system increases. The variation in the stability constants can be correlated with both the large effect due to the solvation of F" and the small effect due to both (1) the solvation of cations in connection with complexation and (2) the electrostatic attraction between Eu lT and F . Based on the variation in the sum of (1) and (2) in water and the mixed solvent solutions, it was determined that the coordination number (CN) of Eu(III) varied from a mixture of CN = 9 and 8 to CN = 8 at about a 0.03 mole fraction of methanol in the mixed solvent.
A series of neutral technetium-99m )?-diketonate radiopharmaceuticals containing the Tc = N group has been prepared in which the substituent of the ^-diketone ligand is varied to cause chemical changes in the resultant complexes. Analyses by TLC, HPLC, and paper electrophoresis show that the complexes are neutral, lipidsoluble tracers. Their in-vitro properties, evaluated by means of octanol-water and cyclohexane-water partition coefficients and protein binding determination, show a high lipophilic character which may give them potential as a brain imaging agent.
The photoreaction of the enone (I) with cyclopentene gave the radical coupling products, (VII) and (VIII), along with the hydrogen abstraction product (VI), but not [2π+2π] photocycloadduct. On the other hand, the photoreaction of I with cyclohexene proceeded in somewhat different manner to give the [2π+2π] photocycloadduct (V) other than the hydrogen abstraction product (VI) and the radical coupling product (IX).
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