A spin label (4-amino-2,2,6,6-tetramethylpiperidine 1-oxide, TEMPO) and a fluorescence dye (1-pyrenylbutyl, Py) were attached randomly along the same poly(N4sopropylacrylamide) chain (PNIPAM-Py-T, Mv 2.3 X 106, Py content 1.9 X 10-5 mol g-l), and their interactions in solutions of the polymer were studied using electron paramagnetic resonance (EPR), 13C nuclear magnetic resonance (13C NMR), and fluorescence spectroscopy. The thermoreversible phase transition of aqueous solutions of the polymer was examined by these three techniques.EPR spectra of solutions of PNIPAM-Py-T (3 g L-I) were recorded as a function of temperature (20-35 "C) and analyzed in terms of the isotropic hyperfine coupling constant and the correlation time for the reorientation motion. The temperature dependence of the simulated spectra. The fluorescence of PNIPAM-Py-T in cold water (1 g L-*) displayed contributions from isolated excited pyrenes (Py*, monomer emission) and from preassociated pyrenes ("excimer" emission). This excimer emission decreased at the phase transition temperature while the monomer emission increased. Quantum yield determinations and fluorescence lifetime measurements are interpreted in termsof two competing temperature-induced effects: (1) a disruption of the pyrene preassociation and (2) an increase in the efficiency of the quenching of Py* by the TEMPO nitroxide radicals. Supporting evidence was obtained by fluorescence measurements carried out with solutions of PNIPAM-Py-T in methanol and by intermolecular fluorescence quenching experiments using a singly labeled polymer (PNIPAM-Py, M, 2.6 X lo6, Py content 4.2 X mol g-l) and either TEMPO or a TEMPO-labeled polymer (PNIPAM-T, Mv 2.9 X 106, TEMPO content 1 X mol g-l).

Our knowledge about the metabolism of alkylcyclobutanones (2-ACBs) is limited, and the lack of literature on the metabolism of 2-ACBs causes consumers to doubt the safety of irradiated foods. The objectives of this study were to evaluate the metabolism of 2-dodecylcyclobutanone (2-DCB) and identify any possible metabolite. The 2-DCB was mixed with rat S9 (postmitochondrial supernatant fraction) and beta-nicotinamide adenine dinucleotide phosphate (NADPH) in phosphate buffer (pH 7.4) and incubated for 2 h at 37 degrees C. Then, the incubation mixture was mixed with sodium sulfate and extracted with n-hexane by using a Soxhlet apparatus. The hexane extract was concentrated under nitrogen and injected into the gas chromatography-mass spectrometry (GC-MS) machine running in selective ion monitoring mode (SIM) to measure 2-DCB concentration. The hexane extract from the in vitro and in vivo studies was also derivatized with a silylation reagent and injected into a GC-MS running in full scan mode. The average percentage of 2-DCB recovered from the test incubations was 23%, compared with 50% from the controls. The GC-MS chromatograms of the derivatized samples showed a unique peak in the in vitro test incubations and in the hexane extract of the rat feces that were given 2-DCB. This peak was later identified as 2-doecylcyclobutanol.