SPIN-TRAPPING AND ESR STUDIES OF THE DIRECT PHOTOLYSIS OF AROMATIC AMINO ACIDS, DIPEPTIDES, TRIPEPTIDES AND POLYPEPTIDES IN AQUEOUS SOLUTIONS—I. PHENYLALANINE AND RELATED COMPOUNDS

Abstract— The direct UV photolysis of l -Phe and peptides containing l -Phe in aqueous solutions has been investigated at room temperature. The short-lived free radicals formed during photolysis were spin-trapped by t -nitrosobutane and identified by electron spin resonance. During the photolysis of l -Phe the decarboxylation and the deamination radicals were spin-trapped. For N-formyl and N-acetyl- l -Phe the decarboxylation radicals were observed. For dipeptides containing Phe the decarboxylation radicals were observed and in some cases the deamination radicals from the N-terminal residue were found. For the tripeptides Gly- l -Phe- l -Ala and Gly-Gly- l -Phe, the C-terminal decarboxylation radical was spin trapped; for l -Phe-Gly-Gly only the deamination radical of the N-terminal residue could be detected. However, for Gly- l -Phe-Gly, five different radicals were identified. The results of the spin-trapping experiments of the 260 nm photolysis of RNase-S-peptide, containing 20 amino acid residues, was interpreted in terms of a chain scission between the alpha carbon of the Phe residue and the adjacent carbonyl group.     

A STUDY OF AQUEOUS SOLUTIONS OF NUCLEIC ACID CONSTITUENTS EXPOSED TO MONOCHROMATIC 160 nm VACUUM-UV LIGHT BY SPIN-TRAPPING METHOD

Spin-trapping technique was employed to detect and identify free radical intermediates produced in aqueous solutions of nucleic acid constituents (pyrimidine bases and pyrimidine nucleosides) after irradiation by monochromatic 160 nm vacuum-UV light from the electron storage ring. Short-lived free radicals produced in the molecules were converted into relatively long-lived free radicals (spin-adducts) by the reaction with MNP used as a spin trap. The resulting nitroxide radicals were subsequently analysed by esr.
The esr measurements were made after irradiating H₂O solution containing sample and the spin trap and once freeze-drying it and re-dissolving the residual powder in D₂O to get the spectrum with a well-resolved hyperfine structure. Thus, clear evidence that most of the radicals were not formed by H-addition but formed by OH-addition at the C5 position of the 5, 6 double bond were obtained for pyrimidine bases. For pyrimidine nucleosides, although the effect of H₂O-D₂O exchange was not recognized on resolution improvement of the hyperfine structure of the esr spectra, careful analysis of the hyperfine structure made it possible to identify the radical structures; OH-addition radicals at the C6 of the double bond of the base moiety in addition to the OH-addition radicals at the C5 position for all except for 2-deoxycytidine. Evidence for the formation of free radicals at the sugar moiety was not clear.     

Cloud condensation nuclei (CCN) activity and oxygen-to-carbon elemental ratios following thermodenuder treatment of organic particles grown by α-pinene ozonolysis

The effects of thermodenuder treatment on the cloud condensation nuclei (CCN) activity and elemental composition of organic particles grown by α-pinene ozonolysis were investigated. The secondary organic material (SOM) was produced in a continuous-flow chamber, with steady-state organic particle mass concentrations M(org) ranging from 1.4 to 37 μg m(-3). Particles exiting in the outflow were heated to temperatures T of up to 100 °C in a thermodenuder. The oxygen-to-carbon (O:C) and hydrogen-to-carbon (H:C) ratios were measured by on-line mass spectrometry. The observed elemental ratios were fit by a linear function, given by (H:C) = -0.8 (O:C) +1.8 for 0.38 < O:C < 0.50. This fit included the dependence on both M(org) and T, meaning that the single variable of post-thermodenuder M(org) was sufficient as an accurate predictor for O:C(M(org)(T)) and H:C(M(org)(T)). This result suggests that equilibrium partitioning theory largely governed the initial volatilization in the thermodenuder. By comparison, the CCN activity had a different dependence on thermodenuder treatment. At 25 °C, the CCN activity was independent of M(org), having an effective hygroscopicity parameter κ(org) of 0.103 ± 0.002. At 100 °C, however, κ(org) varied from 0.105 for M(org) = 1.4 μg m(-3) to 0.079 for M(org) = 37 μg m(-3), indicating that for high mass concentration the CCN activity decreased with heat treatment. The interpretation is that the oligomer fraction of the SOM increased at elevated T, both because of particle-phase reactions that produced oligomers under those conditions and because of the relative enrichment of lower-volatility oligomers in the SOM accompanying the evaporation of higher-volatility monomers from the SOM. Oligomers have high effective molecular weights and thereby significantly influence CCN activity. The production rates of different types of oligomers depend on the types and concentrations of functional groups present in the SOM, which in turn are strongly influenced by M(org). We conclude with a hypothesis, which is supported by a detailed molecular kinetic model, that the changes in κ(org) at high T were more significant at high compared to low M(org) because particle-phase SOM at high M(org) contained a mix of functional groups favorable to oligomerization, such as carbonyl groups.     

SPIN-TRAPPING and ESR STUDIES OF THE DIRECT PHOTOLYSIS OF AROMATIC AMINO ACIDS, DIPEPTIDES, TRIPEPTIDES and POLYPEPTIDES IN AQUEOUS SOLUTIONS—III. TRYPTOPHAN and RELATED COMPOUNDS

Abstract— The UV photolysis of tryptophan (Trp) and Trp-containing peptides in aerated aqueous solutions has been studied by ESR and spin-trapping techniques using f-nitrosobutane as the spin-trap. The photolysis of Trp alone at 290 nm gave rise to the addition of the spin-trap to carbon 3 of the indole ring. A large ESR signal from the hydronitroxide spin-adduct was also observed revealing the formation of hydrated electrons. Generally, the photolysis of Trp-containing dipeptides generated the deamination radical of the N-terminal amino acid followed by addition to the spin-trap. In the case of lysyl-Trp, a deamination radical from the side chain of lysine was proposed. A sensitization experiment with Trp as sensitizer and glycine (Gly) as substrate led to the generation of the deamination radical of Gly. Most of the observed free radicals resulting from the photolysis of Trp-containing peptides can be explained in terms of hydrated electrons reacting with the carbonyl group followed by deamination of the N-terminus.     

Intense laser-induced decomposition of mass-selected 2-, 3-, and 4-methylaniline cations

Photodecomposition processes of 2-, 3-, and 4-methylaniline cations induced by a moderately intense (10¹¹ W/cm²) visible nanosecond laser field and an intense (10¹⁵ W/cm²) UV femtosecond laser field have been investigated using a tandem mass spectrometer. Highly unsaturated fragment cations such as and are dominantly produced by the nanosecond laser, while less unsaturated smaller fragment cations such as , and are produced mainly by the femtosecond laser. Ab initio calculations have also been performed to estimate the stable geometrical structures of and and those of possible intermediate ring compounds for discussing the photodecomposition pathways in intense laser fields.     

SPIN-TRAPPING and ESR STUDIES OF THE DIRECT PHOTOLYSIS OF AROMATIC AMINO ACIDS, DIPEPTIDES, TRIPEPTIDES and POLYPEPTIDES IN AQUEOUS SOLUTIONS—II. TYROSINE and RELATED COMPOUNDS

Abstract— The UV-photolysis of peptides containing tyrosine (Tyr) was investigated in aqueous solutions at room temperature at 220 and 265 nm. The short-lived free radicals formed during photolysis were spin-trapped by t-nitrosobutane and identified by electron spin resonance. For N-acetyl- and N-formyl-L-Tyr and for peptides containing L-Tyr as the middle residue, photolysis at 265 nm under neutral conditions produced mainly spin-adducts due to the scission between the alpha carbon and the methylene group attached to the aromatic ring, while at 220 nm decarboxylation radicals were spin-trapped. Photolysis of di- and tripeptides at 275 nm in alkaline solutions predominantly generated deamination radicals. The radicals produced in the photolysis of the oxidized A chain of insulin were tentatively characterized by comparison with the results for di- and tripeptides.     

Ca(2+)-dependent and caspase-3-independent apoptosis caused by damage in Golgi apparatus due to 2,4,5,7-tetrabromorhodamine 123 bromide-induced photodynamic effects

To clarify the role of the Golgi apparatus in photodynamic therapy-induced apoptosis, its signaling pathway was studied after photodynamic treatment of human cervix carcinoma cell line HeLa, in which a photosensitizer, 2,4,5,7-tetrabromorhodamine 123 bromide (TBR), was incorporated into the Golgi apparatus. Laser scanning microscopic analysis of TBR-loaded HeLa cells confirmed that TBR was exclusively located in the Golgi apparatus. HeLa cells incubated with TBR for 1 h were then exposed to visible light using an Xe lamp. Light of wavelength below 670 nm was eliminated with a filter. Morphological observation of nuclei stained with Hoechst 33342 revealed that apoptosis of cells was induced by exposure to light. Electron spin resonance spectrometry showed that light-exposed TBR produced both singlet oxygen (1O2) and superoxide anion (O2-). Apoptosis induction by TBR was inhibited by pyrrolidine dithiocarbamate, an O2- scavenger, but not by NaN3, a quencher of 1O2. Furthermore, TBR-induced apoptosis was inhibited by aurintricarboxylic acid and ZnCl2, which are known as inhibitors of deoxyribonuclease (DNase) gamma, and (acetoxymethyl)-1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, a chelator of Ca2+, but not by acetyl Asp-Glu-Val-Asp-aldehyde, an inhibitor of caspase-3. These results suggested that O2- was responsible for TBR-induced apoptosis, and Ca(2+)-dependent and caspase-3-independent nuclease such as DNase gamma played an important role in apoptotic signaling triggered by Golgi dysfunction.