Probing the Transition State-to-Intermediate Continuum: Mechanistic Distinction between a Dry versus Wet Perepoxide in the Singlet Oxygen "Ene" Reaction at the Air-Water Interface.

A mechanistic study is reported for the reactions of singlet oxygen (O) with alkene surfactants of tunable properties. Singlet oxygen was generated either top-down (photochemically) by delivery as a gas to an air-water interface bottom-up (chemically) by transport to the air-water interface as a solvated species. In both cases, reactions were carried out in the presence of 7-carbon (7C), 9-carbon (9C), or 11-carbon (11C) prenylsurfactants [(CH)C═CH(CH)SO Na ( = 4, 6, 8)].

Dark-Binding Process Relevant to Preventing Photosensitized Oxidation: Conformation-Dependent Light and Dark Mechanisms by a Dual-Functioning Diketone.

Few photosensitizers function in both light and dark processes as they usually have no function when the lights are turned off. We hypothesized that light and dark mechanisms in an α-diketone will be decoupled by dihedral rotation in a conformation-dependent binding process. Successful decoupling of these two functions is now shown.

Alkane Chain-extended Pterin Through a Pendent Carboxylic Acid Acts as Triple Functioning Fluorophore, O Sensitizer and Membrane Binder.

In order to develop a new long alkane chain pterin that leaves the pterin core largely unperturbed, we synthesized and photochemically characterized decyl pterin-6-carboxyl ester (CapC) that preserves the pterin amide group. CapC contains a decyl-chain at the carboxylic acid position and a condensed DMF molecule at the N2 position. Occupation of the long alkane chain on the pendent carboxylic acid group retains the acid-base equilibrium of the pterin headgroup due to its somewhat remote location.

S,S-Chiral Linker Induced U Shape with a Syn-facial Sensitizer and Photocleavable Ethene Group.

There is a major need for light-activated materials for the release of sensitizers and drugs. Considering the success of chiral columns for the separation of enantiomer drugs, we synthesized an S,S-chiral linker system covalently attached to silica with a sensitizer ethene near the silica surface. First, the silica surface was modified to be aromatic rich, by replacing 70% of the surface groups with (3-phenoxypropyl)silane.

Kinetic Control in the Regioselective Alkylation of Pterin Sensitizers: A Synthetic, Photochemical, and Theoretical Study.

Alkylation patterns and excited-state properties of pterins were examined both experimentally and theoretically. 2D NMR spectroscopy was used to characterize the pterin derivatives, revealing undoubtedly that the decyl chains were coupled to either the O4 or N3 sites on the pterin. At a temperature of 70°C, the pterin alkylation regioselectively favored the O4 over the N3.

Lipophilic Decyl Chain-Pterin Conjugates with Sensitizer Properties.

A new series of decyl chain [-(CH)CH] pterin conjugates have been investigated by photochemical and photophysical methods, and with theoretical solubility calculations. To synthesize the pterins, a nucleophilic substitution (S2) reaction was used for the regioselective coupling of the alkyl chain to the O site over the N site. However, the O-alkylated pterin converts to N-alkylated pterin under basic conditions, pointing to a kinetic product in the former and a thermodynamic product in the latter.

"Ene" Reactions of Singlet Oxygen at the Air-Water Interface.

Prenylsurfactants [(CH3)2C═CH(CH2)nSO3(-) Na(+) (n = 4, 6, or 8)] were designed to probe the "ene" reaction mechanism of singlet oxygen at the air-water interface. Increasing the number of carbon atoms in the hydrophobic chain caused an increase in the regioselectivity for a secondary rather than tertiary surfactant hydroperoxide, arguing for an orthogonal alkene on water. The use of water, deuterium oxide, and H2O/D2O mixtures helped to distinguish mechanistic alternatives to homogeneous solution conditions that include dewetting of the π bond and an unsymmetrical perepoxide transition state in the hydroperoxide-forming step.

Photoactive chitosan: a step toward a green strategy for pollutant degradation.

This article is a highlight of the paper by Ferrari et al. in this issue of Photochemistry and Photobiology. It describes the innovative use of rose bengal-conjugated chitosan as a reusable green catalyst that photo-degrades phenolic compounds in aqueous media, and thereby has decontamination potential of polluted waters.