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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2023)

The photo-oxidative degradation of two novel covalent xanthophyll dimers: X(Z,Z) and X(Z,Z)X were measured in aromatic solvents and quantified using quantum yields of decayed (QY). X(Z,Z) is comprised of two cofacial oriented zeaxanthin molecules (Z,Z) bound at one end by a xanthene (X) molecule, where X(Z,Z)X is bound by two xanthene molecules, one at either end of the molecules’ the long axis. X(Z,Z), X(Z,Z)X, and zeaxanthin were subjected to environmental stressor such as oxygen and light. The reaction of the xanthophyll series with 0 %, 20 %, 40 %, 70 % and 100 % partial pressures of dissolved oxygen (pO2) were compared in a time course study. The decay of X(Z,Z) and zeaxanthin are described as bi-modal, with a fast initial decay period (at irradiation times, t ≤ 5 minutes) followed by a slow linear decay period (t > 5 minutes). Across all oxygen concentrations, X(Z,Z) has the largest the quantum yields of decay, followed closely by zeaxanthin. The rigid, X(Z,Z)X molecule was the most stable carotenoid against photobleaching across all pO2. Zeaxanthin photo-oxidation products were identified as 9-cis zeaxanthin, 13-cis zeaxanthin, zeaxanthin 5,6-epoxide, and zeaxanthin 5,8-epoxide using high-pressure liquid chromatography (HPLC-DAD) and mass spectrometry (MS). UV-Resonance Raman spectra probed at 370 nm identified two X(Z,Z) isomers namely, X(9-cis ,Z)X and X(13-cis, Z)X Triplet excited state parameters of X(Z,Z) and X(Z,Z)X were measured via sensitization with 1,4,8,11,15,18,22,25-octa-n-butoxyphthalocyanine, ( PdPc(OBu)8). The ground state quenching rate constant, kSQ and the intrinsic decay lifetime kT, were determined using Stern-Volmer quenching. The kSQ of the dimers are both diffusion limited and equal to, kSQ = 1.0 x 10^10 M^-1s^-1, over 2x the rate constant reported for zeaxanthin self-quenching. The second order energy transfer rate constant kET, from the triplet excited PdPc(OBu)8 sensitizer to the ground state xanthophyll dimers were also determined. Lastly, the intrinsic lifetimes of X(Z,Z) and X(Z,Z)X were 27 μs and 24 μs, respectively.

    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2014)
    Background: Optical access to a travelling ion packet is required in many ion beamexperiments that study ion-photon interactions.Methods: An approach is described for carrying out direct infrared excitation of a fastion beam that uses an optical-quality reflective beam blocker to illuminate a counterpropagating pulsed ion beam in a collinear configuration. This arrangement providesoptical access along the axis of ion beam propagation by placing a mirror in the beampath at a 25 degree angle. The ion packet is bumped over the mirror, which is alsoused to block fast neutral particles produced during ion beam acceleration that alsopropagate along the beam path.Results: The efficiency of this setup is demonstrated in a photodetachment experimenton NO− anions, where a photoinduced depletion of up to 90% of the beam is achievedin a single laser shot. To demonstrate the application of this configuration, the relativephotodetachment cross section for NO− has been measured in the range of 2800 –7200 cm-1. The measured relative cross section shows a set of sharp peaks that areidentified as vibrational autodetachment resonances.Conclusion: The new setup paves the way for future experiments where parentanionic species are vibrationally excited via direct infrared excitation first andundergo photodetachment/photodissociation in a subsequent step.
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