Time Resolved CW-EPR Spectroscopy of Powdered Samples:  Electron Spin Polarization of a Nitroxyl Radical Adsorbed on NaY Zeolite, Generated by the Quenching of Excited Triplet Ketones

Jockusch, Steffen; Liu, Zhiqiang; Ottaviani, M. Francesca; Turro, Nicholas J.

doi:10.1021/jp0110861

Cited by 8 publications

(4 citation statements)

References 29 publications

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“…5,10,15,20-Tetraphenyl-21 H ,23 H -porphine (Aldrich) was used without further purification. The 15 N isotope labeled O-TEMPO (4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy) ( 15 N-O-TEMPO) was synthesized as described previously . In all other experiments, where the nitrogen isotope is not specified, 14 N in its natural isotopic ratio was used.…”

Section: Methodsmentioning

confidence: 99%

Chemically Induced Dynamic Electron Polarization Generated through the Interaction between Singlet Molecular Oxygen and Nitroxide Radicals

et al. 2005

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An absorptive chemically induced dynamic electron polarization (CIDEP) was generated by the quenching of singlet oxygen by nitroxide radicals (TEMPO derivatives). The spin polarization decay time of the nitroxide (measured by time-resolved EPR) correlates with the lifetime of singlet oxygen (measured by singlet oxygen phosphorescence spectroscopy). In addition, a deuterium isotope effect on the spin polarization decay time was observed, a signature of singlet oxygen involvement. With use of isotope labeled nitroxides ( 15 N, 14 N), the relative spin polarization efficiencies of TEMPO, 4-oxo-TEMPO, and 4-hydroxy-TEMPO by singlet oxygen were determined. The relative spin polarization efficiencies (per quenching event) decrease in the order 4-hydroxy-TEMPO > TEMPO > 4-oxo-TEMPO, whereas an opposite trend was observed for the total quenching rate constants of singlet oxygen by the nitroxides where the order is 4-hydroxy-TEMPO < TEMPO < 4-oxo-TEMPO.

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Section: Methodsmentioning

confidence: 99%

Chemically Induced Dynamic Electron Polarization Generated through the Interaction between Singlet Molecular Oxygen and Nitroxide Radicals

et al. 2005

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“…It has been known for some time that water interactions play an important structural role in proteins and there have been many studies of these interactions using a variety of methods. − In particular, small peptides have received a lot of attention because of their experimental tractability and relative simplicity. Recent advances in experimental techniques have afforded some exciting new views, − including detailed information about the interaction of individual water molecules with amino acids and small peptides isolated in the gas phase. − Small peptides are also particularly well suited for theoretical treatment and many studies have been conducted using Monte Carlo, , molecular dynamics, − and quantum chemistry calculations. − Dipeptides, tripeptides, and larger peptides, − have been investigated by both theoretical and experimental means.…”

Section: Introductionmentioning

confidence: 99%

Water Molecule Adsorption on Protonated Dipeptides

2004

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Equilibrium constants for the adsorption of the first water molecule on six protonated dipeptides (Gly-Gly+H(+), Gly-Ala+H(+), Ala-Gly+H(+), Ala-Ala+H(+), Pro-Gly+H(+), and Gly-Trp+H(+)) have been measured as a function of temperature, and DeltaH(o) and DeltaS(o) determined. Density functional theory calculations were performed for both the unsolvated peptides and the peptide water complexes at the B3LYP/6-311++G level. MP2/6-311++G** calculations were also carried out for Gly/Ala peptides. The calculations suggest that adsorption of a water molecule by these simple dipeptides is a complex process, both the unsolvated peptide and the peptide-water complexes have multiple conformations with similar free energies. Average DeltaH(o) and DeltaS(o) values derived from the calculations are in reasonable agreement with the experimental results. According to the calculations, the dominant water adsorption process involves a significant conformational change to accommodate a bridging water molecule. DeltaH(o) is diminished for Pro-Gly+H(+) mainly because the water interacts with a secondary amine, whereas for Gly-Trp+H(+), DeltaH(o) is significantly decreased by the loss of cation-pi interactions upon water adsorption. For unsolvated peptides the proton affinities of the N-terminus and the backbone carbonyl groups are known to be similar. Addition of a single water molecule causes a significant stabilization of the N-terminus protonation site.

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“…A similar methodology has been previously employed in studies of chemically induced dynamic electron polarization of nitroxides using time-resolved electron paramagnetic resonance. 24 The high viscosity of this polymer allows the zeolite particles to remain suspended over long periods of time, and it has high transparency at wavelengths greater than 240 nm. The samples of NaY in the polymethylhydrosiloxane dispersant were prepared at a concentration of 2.5 mg mL Ϫ1 ; under these conditions, the samples transmittance was 65%.…”

Section: Resultsmentioning

confidence: 99%

Monitoring photodecomposition of dibenzyl ketone within NaY zeolite with a pre-fluorescent nitroxide compound

Aspée

Maretti

Scaiano

2003

Photochem Photobiol Sci

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Benzyl radicals derived from photodecomposition of dibenzyl ketone have been monitored in NaY zeolite using the pre-fluorescent probe 4-(3-hydroxy-2-methyl-4-quinolinoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxyl free radical (QT). The steady-state and time-resolved fluorescence show a strong interaction of QT within the zeolite cavities. Furthermore, the increase in the fluorescence with the irradiation time reveals the efficient trapping of benzyl radicals by QT under vacuum. Dispersion of the zeolite composites in liquid polymers results in an improvement in the fluorescence measurement and faster kinetics in comparison with the solid samples. These results are interpreted in terms of partial refractive index matching as a consequence of polymer reptation into the zeolite cavities. Analysis of the fluorescence lifetime distribution shows the presence of different fluorescence ensembles with different fluorescence quantum yields, depending on the microenvironment within the zeolite particle. Pre-fluorescent probes offer a novel and useful methodology for studying radical processes in zeolites.

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Time Resolved CW-EPR Spectroscopy of Powdered Samples: Electron Spin Polarization of a Nitroxyl Radical Adsorbed on NaY Zeolite, Generated by the Quenching of Excited Triplet Ketones

Cited by 8 publications

References 29 publications

Chemically Induced Dynamic Electron Polarization Generated through the Interaction between Singlet Molecular Oxygen and Nitroxide Radicals

Chemically Induced Dynamic Electron Polarization Generated through the Interaction between Singlet Molecular Oxygen and Nitroxide Radicals

Water Molecule Adsorption on Protonated Dipeptides

Monitoring photodecomposition of dibenzyl ketone within NaY zeolite with a pre-fluorescent nitroxide compound

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