Photolytic insertion of albumin on activated carbon modified with ozone.

254nm photolyses of bovine serum albumin [BSA] in aqueous solutions, were carried out in the presence of activated carbons modified by reaction with ozone. The photolyses were monitored by fluorescence spectroscopy and UV spectrophotometry, and the products were characterized by elemental analysis, FTIR, TGA, total organic carbon analyses [TOC], and XPS. The ozonation reaction was carried out at room temperature with O3 under dry and wet conditions. The carbon characterization showed that the reaction increased the amount of epoxide and carbonyl groups on the carbon matrix. The activated carbon modified with dry O3 exhibited higher concentration of oxidized groups in its surface, smaller surface area and lower thermal stability. Characterization of the photolysis of ozonized carbons pointed to a small release of carbon organic groups during the reaction with elimination of epoxide groups and increase of carbonyl groups without change of thermal stability. Photolysis of BSA in aqueous solution occurred with fluorescence quenching due to changes of the local microenvironment and/or macromolecular conformational changes. Absorbance increase of the UV spectrum indicated a hyperchromic effect due to albumin structure modifications during photolysis. TGA analysis of the photolysed activated carbons in the presence of BSA suggested that ozonized carbon samples underwent insertion of BSA upon photolysis, in particular the sample ozonized under dry conditions. The changes observed for the FTIR and elemental analysis agreed with this conclusion, which was further supported by 13C SS-NMR, fluorescence emission and XPS.

1-(3-Chloro-4-fluoro-phen-yl)-5-(2-diazo-acet-yl)-4-phenyl-pyrrolidin-2-one.

In the title compound, C(18)H(13)ClFN(3)O(2), the pyrrolidine ring adopts an envelope conformation and the planar part is rotated by 4.3 (6)° from the plane of the benzene ring and is almost perperdicular both to the diazo-acetyl unit [dihedral angle = 78.93 (7)°] and the phenyl ring [dihedral angle = 86.07 (7)°]. In the crystal, mol-ecules are linked into a three-dimensional framework by C-H⋯O inter-actions. The mol-ecular conformation is stabilized by an intra-molecular C-H⋯O hydrogen bond.

Diethyl 1-(4-methyl-phen-yl)-3-phenyl-5-oxopyrrolidine-2,2-dicarboxyl-ate.

In the title compound, C(23)H(25)NO(5), the lactam ring adopts an envelope conformation and both eth-oxy-carbonyl side chains show an s-cis conformation: one is nearly planar, the dihedral angle between CO(2) and OCH(2)CH(3) groups being 7.95 (14)° and the other is almost orthogonal, the C-O-C-C torsion angle being 85.33 (9)°. Dimers related by inversion symmetry are stabilized by C-H⋯O hydrogen bonds. The crystal structure is consolidated by weak intermolecular C-H⋯O inter-actions. Weak intra-molecular inter-actions of the same kind also occur.

Diethyl 1-(4-fluorophenyl)-3-(2-furyl)-5-oxopyrrolidine-2,2-dicarboxylate and diethyl 1-(3,4-dichlorophenyl)-3-(2-furyl)-5-oxopyrrolidine-2,2-dicarboxylate.

The title compounds, C20H20FNO6 and C20H19Cl2NO6, respectively, may exhibit bioactivity. In these compounds, the pyrrolidine ring adopts a conformation intermediate between envelope and half-chair. Only one of the two ethoxycarbonyl side chains is nearly planar. Centrosymmetric pairs are formed, and the crystal structure is stabilized by weak C-H.O hydrogen bonds and van der Waals interactions.

On the kinetics and energetics of one-electron oxidation of 1,3,5-triazines.

One-electron oxidation of 1,3,5-triazines is observed with both excited uranyl ion (*UO2(2+)) and sulfate radical anion (SO4.-) in aqueous solution, but not with Tl2+, indicating that the standard reduction potentials E degree of 1,3,5-triazine radical cations are = 2.3 +/- 0.1 V vs. NHE, consistent with theoretical calculations; this suggests that if triazines inhibit electron transfer during photosynthesis, they would need to act on the reductive part of the electron transport chain.

Reaction pathways and mechanisms of photodegradation of pesticides.

The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.

Intracellular oxidation of dipeptides. Base-promoted elimination from N-halodipeptides to 2-[N-alkyl-N-(2-N-alkylimino-2-alkyl-ethanoyl)amino]-2,2-dialkylethanoic acids.

One of the possible ways of intracellular oxidation of peptides is via the formation of the corresponding (N-X)-dipeptides, that then undergo base-promoted elimination to yield intermediate 2-[N-alkyl-N-(2-N-alkylimino-2-alkylethanoyl)amino]-2,2-dialkylethanoic acids, which subsequently hydrolyze. Such an elimination process is general-base catalyzed, with Brønsted beta values ranging from 0.26 to 0.31, which suggests an essentially constant degree of proton transfer at the TS. For (N-X)-dipeptides, the ratio k(N-Br)/k(N-Cl) ranges from 2.5 to 15, suggesting a structural dependence of the degree of N-X bond breaking at the TS. The values of beta and k(N-Br)/k(N-Cl) support a concerted asynchronous A(xh)D(H)D(N) mechanism, its TS changing from reactant-like to slightly nitrenium-like depending on the structure of the starting dipeptide. As a consequence of the antiperiplanarity requirements of the reaction, the steric interaction between the leaving group and the substituent on the C bearing the H to be eliminated controls the reaction rate. Such steric interaction is rather important, as indicated by the steric crossed-interaction coefficient (p(ssy') = 0.33). Semiempirical calculations show that bulky substituents in the vicinity of the reaction center imply additional energy requirements for the system to achieve the antiperiplanarity needed at the TS for the reaction to proceed. From the observations reported it follows that (N-X)-dipeptides lose their oxidizing power more readily than analogous (N-X)-amino acids or (N-X)-amines, opening a possible pathway to lessen intracellular halogen-based oxidative stress.

CONSEL, a least-squares program for estimating stability constants from polarographic data.

This article describes CONSEL, a least-squares linear-regression program which, when applied to polarographic data, provides estimates of stability constants suitable for priming non-linear optimization programs. The use of CONSEL avoids the need for recourse to traditional graphical methods. The results of its application to three systems are presented.