“Ene” Reactions of Singlet Oxygen at the Air–Water Interface

Prenylsurfactants [(CH₃)₂CCH­(CH₂)_<i>n</i>SO₃^– Na⁺ (<i>n</i> = 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. The prenylsurfactants and a photoreactor technique allowed a certain degree of interfacial control of the hydroperoxidation reaction on a liquid support, where the oxidant (airborne ¹O₂) is delivered as a gas

Photoactive Fluoropolymer Surfaces That Release Sensitizer Drug Molecules

We describe a physical–organic study of two fluoropolymers bearing a photoreleasable PEGylated photosensitizer that generates ¹O₂(¹Δ_g) [chlorin e₆ methoxy tri­(ethylene glycol) triester]. The surfaces are Teflon/poly­(vinyl alcohol) (PVA) nanocomposite and fluorinated silica. The relative efficiency of these surfaces to photorelease the PEGylated sensitizer [shown previously to be phototoxic to ovarian cancer cells (Kimani, S. et al. <i>J. Org. Chem</i> <b>2012</b>, <i>77</i>, 10638)] was slightly higher for the nanocomposite. In the presence of red light and O₂, ¹O₂ is formed, which cleaves an ethene linkage to liberate the sensitizer in 68–92% yield. The fluoropolymers were designed to deal with multiple problems. Namely, their success relied not only on high O₂ solubility and drug repellency but also on the C–F bonds, which physically quench little ¹O₂, for singlet oxygen’s productive use away from the surface. The results obtained here indicate that Teflon-like surfaces have potential uses in delivering sensitizer and singlet oxygen for applications in tissue repair and photodynamic therapy (PDT)

Mechanism of Photochemical O‑Atom Exchange in Nitrosamines with Molecular Oxygen

The detection of an oxygen-atom photoexchange process of <i>N-</i>nitrosamines is reported. The photolysis of four nitrosamines (<i>N</i>-nitrosodiphenylamine <b>1</b>, <i>N</i>-nitroso-<i>N</i>-methylaniline <b>2</b>, <i>N</i>-butyl-<i>N</i>-(4-hydroxy­butyl)­nitrosamine <b>3</b>, and <i>N</i>-nitroso­diethylamine <b>4</b>) with ultraviolet light was examined in an ¹⁸O₂-enriched atmosphere in solution. HPLC/MS and HPLC-MS/MS data show that ¹⁸O-labeled nitrosamines were generated for <b>1</b> and <b>2</b>. In contrast, nitrosamines <b>3</b> and <b>4</b> do not exchange the ¹⁸O label and instead decomposed to amines and/or imines under the conditions. For <b>1</b> and <b>2</b>, the ¹⁸O atom was found not to be introduced by moisture or by singlet oxygen [¹⁸(¹O₂ ¹Δ_g)] produced thermally by ¹⁸O–¹⁸O labeled endoperoxide of <i>N,N</i>′-di­(2,3-hydroxy­propyl)-1,4-naphthalene dipropanamide (DHPN¹⁸O₂) or by visible-light sensitization. A density functional theory study of the structures and energetics of peroxy intermediates arising from reaction of nitrosamines with O₂ is also presented. A reversible head-to-tail dimerization of the <i>O-</i>nitrooxide to the 1,2,3,5,6,7-hexaoxa­diazocane (30 kcal/mol barrier) with extrusion of O¹⁸O accounts for exchange of the oxygen atom label. The unimolecular cyclization of <i>O-</i>nitrooxide to 1,2,3,4-trioxazetidine (46 kcal/mol barrier) followed by a retro [2 + 2] reaction is an alternative, but higher energy process. Both pathways would require the photoexcitation of the nitrooxide

Experimental and DFT Computational Insight into Nitrosamine PhotochemistryOxygen Matters

A nitrosamine photooxidation reaction is shown to generate a peroxy intermediate by experimental physical-organic methods. The irradiation of phenyl and methyl-substituted nitrosamines in the presence of isotopically labeled 18-oxygen revealed that an O atom was trapped from a peroxy intermediate to trimethylphosphite or triphenylphosphine, or by nitrosamine itself, forming two moles of nitramine. The unstable peroxy intermediate can be trapped at low temperature in postphotolyzed solution in the dark. Chemiluminescence was also observed upon thermal decomposition of the peroxy intermediate, that is, when a postphotolysis low-temperature solution is brought up to room temperature. A DFT study provides tentative information for cyclic nitrogen peroxide species on the reaction surface