Formamidopyrimidines as major products in the low- and high-intensity UV irradiation of guanine derivatives

Two major UV-induced transformation products of guanosine (Guo) in oxygen-free aqueous solution were isolated and characterized using reverse-phase HPLC-ESI-MS and UV absorption spectrophotometric techniques. These products were identified as two different sugar isomers of 2,6-diamino-4-hydroxy-5-formamidopyrimidine ribonucleosides, FapyGuo. A formation quantum yield of the order of 10(-3) for these products was obtained at a 75 microM concentration of Guo, while an increase in the ground state concentration of Guo from 10(-5) to 10(-4) M decreased their formation yield by a factor of ten. The formation of FapydGuo was also observed in the 254 nm photolysis of 2'-deoxyguanosine. In addition, the formation FapyGua was identified in the UV photolysis of all the guanine derivatives investigated. A formation quantum yield of the order of 10(-4) was obtained for the latter product, except in the photolysis of Gua in which a higher formation yield (10(-3)) was determined. These results suggest that hydration of the radical cation of guanine, followed by opening of the imidazole ring to form Fapy products, is one of the main low-intensity UV radiation-induced photo-transformation pathway of the guanine derivatives in oxygen-free aqueous solutions. Furthermore, the formation of the Fapy products and base release occurs through a similar photo-transformation pathways using a high-intensity UV radiation source.     

Photoionization of DNA and RNA bases,nucleosides and nucleotides through a combination of one- and two-photon pathways upon 266 nm nanosecond laser excitation

The 266 nm nanosecond laser photolysis of various purine and pyrimidine derivatives results in their photoionization (PI) as one of the primary photochemical pathways. Electron photoejection occurs through a combination of one- and two-photon mechanisms. The PI values depend on the substituents attached to the chromophore of the base. The net PI of the purine bases at 266 nm are of the same order of magnitude (10(-2)) as those of the pyrimidine bases under similar experimental conditions. The monophotonic component is approximately one-third of the net PI yield of the bases. A nonrelaxed singlet excited state intermediate is tentatively proposed for this pathway. It is proposed that this state is significantly stabilized by water solvation, transforming it into a charge transfer to solvent state from which the hydrated electron evolves.     

Double bond shifts induced by reaction of hex-5-en-2-one with triosmium clusters

Carbon---hydrogen bond cleavage at the terminal 6-position occurs when hex-5-en-2-one (CH₂=CHCH₂CH₂COMe) oxidatively adds to [Os₃(CO)₁₀(MeCN)₂] to give [Os₃H(μ-CH=CHCH₂CH₂COMe)(CO)₁₀], which is completely analogous to the simple vinyl complex [Os₃H(μ-CH=CH₂)(CO)₁₀]. A minor product from the reaction is [Os₃(CH₃CH=CHCH₂COMe)(CO)₁₀], an isomer in which double-bond migration has occurred to give the βγ-unsaturated ketone; stabilisation occurs through chelation and ketone coordination. [Os₃H₂(CO)₁₀] reacts with CH₂=CHCH₂CH₂COMe in refluxing cyclohexane to give a third isomer, [Os₃H(CH₃CH₂C=CHCOMe)(CO)₁₀], in which further double bond migration has occurred to give the β-unsaturated ketone. Metallation at the β-site gives an Os---C bond as part of a 5-membered chelate ring. Thermolysis of each of the three isomeric decarbonyl species in refluxing cyclohexane or heptane leads to the elimination of an Os(CO)₄ group to give the dinuclear compound [Os₂H(EtC=CHCOMe)(CO)₆] in varying yield. Pathways from γδ to the βγ and finally the β unsaturated ketones may be mapped out.     

Disproportionation kinetics of N ? Cl-n-propylamine and N ? Cl-isopropylamine

The kinetics of the disproportionation of N ? Cl-n-propylamine and N – Cl-isopropylamine to the corresponding N, N-dichloramines were found to be a second order with respect to the N-chloramine. The influence of amine concentration, pH, buffers, ionic strength, and temperature were also studied. The observed influence of pH supports a reaction mechanism which allowed estimation of the protonation constants of the chloramines studied. The influence of buffers, which was studied for both the above chloramines and N ? Cl-3-aminopropanol, reflects general acid catalysis, for which a mechanism is proposed. Bronsted's equation was fitted to the catalytic constants obtained therefrom so as to estimate the values of the parameter α for these three N-chloramines. © John Wiley & Sons, Inc.     

Use of basic amphiprotic organic solvents containing neutral-surfactant aggregates as pseudostationary phase in non-aqueous capillary electrophoresis

A new approach to non-aqueous capillary electrophoresis based on the addition of anionic carboxylic surfactants to the basic amphiprotic organic solvent in which form neutral-surfactant aggregates was developed with a view to improving the electrophoretic resolution of charged substances. These aggregates acts as a new pseudostationary phase. The presence of these aggregates allows the effective separation of four tetracyclines with increased selectivity. The efficiency of sodium caprylate, sodium laurate and sodium palmitate as surfactants was examined. The latter two proved more effective than the former as they provided migration times reproducible to within 7% or better in all cases. The additional use of an alcohol allows peak shape to be controlled, which expands the potential of this electrophoretic technique even further. The proposed method was used to determine tetracyclines in water samples. The sensitivity of the determination was improved by using a flow manifold coupled at-line to the capillary electrophoresis system in order to preconcentrate the analytes. The limits of detection thus achieved ranged from 50 to 90 μg/l. Under optimal operating conditions, recoveries ranged from 97 to 104%, and precision from 5.4 to 7.0%.     

Preservation of bone collagen from the late Cretaceous period studied by immunological techniques and atomic force microscopy

Late Cretaceous avian bone tissues from Argentina demonstrate exceptional preservation. Skeletal elements are preserved in partial articulation and suspended in three dimensions in a medium-grained sandstone matrix, indicating unusual perimortem taphonomic conditions. Preservation extends to the microstructural and molecular levels. Bone tissues respond to collagenase digestion and histochemical stains. In situ immunohistochemistry localizes binding sites for avian collagen antibodies in fossil tissues. Immunohistochemical studies do not, however, guarantee the preservation of molecular integrity. A protein may retain sufficient antigenicity for antibody binding even though degradation may render it incapable of original function. Therefore, we have applied atomic force microscopy to address the integrity and functionality of retained organic structures. Collagen pull-off measurements not only support immunochemical evidence for collagen preservation for antibody recognition but also imply preservation of the whole molecular integrity. No appreciable differences in collagen pull-off properties were measured between fossil and extant bone samples under physiological conditions.     

Use of Physical Properties for Compositional Analysis of Ternary Mixtures. Application to Mixtures of 2-Methoxy-2-methylbutane, Methanol, and 2,2,4-Trimethylpentane or Methylcyclohexane

Two ternary systems comprising gasoline components were characterized by determining their refractive indexes, densities, sound transmission speeds, and isentropic compressibilities at 25°C and 1 atm pressure. These data were then correlated with composition using a polynomial. Single measurements of the refractive index and density of fully miscible mixtures of the system 2-methoxy-2-methylbutane (TAME) + methanol + 2,2,4-trimethylpentane allowed estimation of its composition with precision better than ±0.002 mole fraction. However, it was shown that this approach to compositional analysis of homogeneous mixtures of TAME + methanol + methylcyclohexane would not give reliable results.     

Use of eosin as a fluorophore in capillary electrophoresis with laser detection.

Eosin has been used to generate the background signal for indirect fluorimetric detection of inorganic and organic ions, simultaneously separated by capillary zone electrophoresis (CZE). This reagent provides constant fluorescence over the pH range of 5-10 and is compatible with the excitation by an argon ion laser at 488 nm with emission at 520 nm. The use of esosine as fluorophore, H3BO3, and Na2B4O7 as electrolyte and diethylentriamine as modifier of the electroosmotic flow in CZE were optimised. The analytical potential of the studied buffer was tested on a group of 12 anions, used as model compounds. Both, hydrodynamic and electrokinetic injection mode were optimised. The detection limits determined by the last injection mode, were in the range 0.008-0.037 mg l(-1). By using this method, the quantitation of the common anions in tap and mineral water has been carried out successfully.     

The effect of 2-hydroxypropyl-β-cyclodextrin on the excited triplet state of promazine and chlorpromazine

Chlorpromazine hydrochloride (CPZ) is a widely used anti-psychotic drug that induces skin photosensitization and photoallergy response after systematic use or topical applications. The photoallergic mechanism is still unknown. However, it has been proposed that the triplet excited state (³CPZ*) could participate in the photodamaging effects. In this work, we report the photophysical properties of the triplet excited state of CPZ and its parent derivative promazine hydrochloride (PZ) in the presence of 2-hydroxypropyl-β-cyclodextrin (HPC). Absorption measurements indicate that PZ and CPZ form an inclusion complex with HPC through a 1:1 stoichiometry. The equilibrium constant at 25 °C is (2.55 ± 0.09) × 10³ M⁻¹ and (3.27 ± 0.07) × 10³ M⁻¹ for PZ and CPZ, respectively. The CPZ and PZ triplet excited state properties changed in the presence of HPC. The triplet lifetime increases with HPC concentration that is related to the amount of drug bound. In addition, the triplet intersystem crossing quantum yield was determined to be 0.45 and 0.17 for PZ and CPZ, respectively, when more than 95% of the drug molecules are bound to HPC. Altogether, these results suggest that the microenvironment plays a crucial role in the ³CPZ* and ³PZ* properties and thus it can modulate their photosensitizing effects.