Reactions of dichloride anion radicals with pyrimidine and its derivatives.
Rate constants for the reactions of dichloride anion radicals with pyrimidine and its derivatives were determined by a conventional flash photolysis. Kinetic treatment was carried out by assuming that second-order self decay of the anion radicals and the reaction with a substrate proceed simultaneously. Values of the rate constants were found within 1.1 × 107 to 4.1 × 109 M-1 s-1; the lowest reactivity was observed for pyrimidine and the highest for 2, 4, 6triaminopyrimidine. Comparison of the rate constants with those for hydroxyl radicals suggests that the dichloride anion radicals undergo a different reaction with pyrimidine bases from that of the hydroxyl radicals. A transient absorption due to an intermediate produced in the reaction with the anion radicals was observed for 5-aminouracil. This is only a case where relatively long-lived absorption was observed. The absorption was used to determine the rate constants for the reactions with the anion radicals.
Ultraviolet photoelectron studies of the ground-state electronic structure and gas-phase tautomerism of purine and adenine
Ultraviolet photoelectron spectroscopy has been employed to study electronic structure and tautomerism in adenine and purine and in various methyl-substituted derivatives of these molecules. The assignment of the photoelectron spectra has been aided by results from HAM^ molecular orbital calculations which are empirically parameterized to provide orbital ionization potentials. The calculations predict that the lone-pair orbitals in purine and adenine are similar in spacial distribution and have similar ionization potentials. This conclusion is supported by the spectroscopic data which indicate that in purine the three highest occupied lone-pair orbitals have ionization potentials of -9.6, - 10.6, and - 11.7 eV. In adenine these orbitals have ionization potentials of -9.6, - 10.5, and 11.39 eV. The planar exocyclic amino group in adenine causes the A structure of this molecule to be significantly different than that in purine. In adenine the ionization potentials of the five highest occupied A orbitals are 8.48, -9.6, -10.5, 12.10, and 13.21 eV. In purine the ionization potentials of the four highest occupied a orbitals are -9.6, -10.2, -11.9, and 13.10 eV. The band arising from the fifth highest occupied A orbital in purine has an ionization potential greater than 13.5 eV and is not resolved. A comparison of the photoelectron spectra of purine, adenine, and their 7- and 9-methyl-substituted derivatives indicates that the spectra of purine and adenine are much more similar to the spectra of their 9-methyl derivatives than to the spectra of their 7-methyl derivatives. This observation supports the conclusion that in an isolated environment the N(9)H tautomers of both purine and adenine are more stable than the N(7)H tautomers.
Enhancement of surface properties on Low Density Polyethylene packaging films using various fluorination routes
Nowadays, packaging market deployment requires an important attention. Influence of treatment with molecular (F2) or atomic (Fradical dot) fluorine on properties of Low Density Polyethylene (LDPE) films was investigated. The films were treated using direct fluorination conditions with F2 or a specific reagent XeF2, which releases atomic fluorine Fradical dot. Changes of LDPE chemical composition were investigated by FTIR and solid state NMR. Surface morphology was studied by several microscopy techniques (SEM and AFM). Finally to further characterize film properties after treatments, surface energy measurements and electron paramagnetic resonance (EPR) analyses were also carried out. An upper fluorinated layer, which contains mainly high amount of single bondCF2single bond, was formed during the direct fluorination conditions (F2). For the process performed with XeF2, specific groups single bondCHFsingle bond were detected not only on the polymer surface but also in the bulk. The final CHF/CF2 ratio depended on the fluorination route. Treatment with Fradical dot (originated from XeF2 decomposition) resulted in single bondCHFsingle bond groups in bulk prevailing formation whereas F2 formed mainly single bondCF2single bond groups. Regardless to the reactive species, radicals (dangling bonds) appeared during the fluorination and reacted with oxygen during the exposition to air after the treatment. Such a process resulted in oxygenated polar groups formation and consequently in the surface energy increase.