Experimental and calculated infrared spectra of disubstituted naphthoquinones

Calculated vibrational properties of pigments in protein binding sites 2: Semiquinones in photosynthetic proteins

[Q_A^- - Q_A] Fourier transform infrared difference spectra have previously been obtained using purple bacterial reaction centers from Rhodobacter sphaeroides with unlabeled, ¹⁸O and ¹³C isotope labeled phylloquinone (PhQ, also known as vitamin K₁) incorporated into the Q_A protein binding site (Breton, (1997), Proc. Natl. Acad. Sci. USA94 11318-11323). The nature of the bands in these spectra and the isotope induced band shifts are poorly understood, especially for the phyllosemiquinone anion (PhQ^-) state. To aid in the interpretation of the bands in these experimental spectra, ONIOM type QM/MM vibrational frequency calculations were undertaken. Calculations were also undertaken for PhQ^- in solution. Surprisingly, both sets of calculated spectra are similar and agree well with the experimental spectra. This similarity suggests pigment-protein interactions do not perturb the electronic structure of the semiquinone in the Q_A binding site. This is not found to be the case for the neutral PhQ species in the same protein binding site. PhQ also occupies the A₁ protein binding site in photosystem I, and the vibrational properties of PhQ^- in the Q_A and A₁ binding sites are compared and shown to exhibit considerable differences. These differences probably arise because of changes in the degree of asymmetry of hydrogen bonding of PhQ^- in the A₁ and Q_A binding sites.

Effects of endogenous and exogenous reductants in lung fluid on the bioaccessible metal concentration and oxidative potential of ultrafine particles

Health risk posed by ultrafine particles (UFPs) is potentially increased by reducing substances present in lung fluid, although knowledge of the underlying mechanisms is insufficient. Here, UFPs mainly consisting of metals and quinones were prepared. The reducing substances examined included lung endogenous and exogenous reductants. UFPs were extracted in simulated lung fluid containing reductants. Extracts were used to analyze metrics relevant to health effects, including the bioaccessible metal concentration (Me_BA) and oxidative potential (OP^DTT). The Me_BA of Mn (974.5-9896.9 μg L^-1) was higher than those of Cu (155.0-599.6 μg L^-1) and Fe (79.9-500.9 μg L^-1). Correspondingly, UFPs containing Mn had higher OP^DTT (2.07-12.0 pmol min^-1 μg^-1) than those containing Cu (2.03-7.11 pmol min^-1 μg^-1) and Fe (1.63-5.34 pmol min^-1 μg^-1). Endogenous and exogenous reductants can increase Me_BA and OP^DTT, and the increments were generally higher for composite than pure UFPs. Positive correlations between OP^DTT and Me_BA of UFPs in the presence of most reductants emphasized the importance of the bioaccessible metal fraction in UFPs for inducing oxidative stress by reactive oxygen species (ROS)-generating reactions between quinones, metals, and lung reductants. Present findings provide novel insight into the toxicity and health risks of UFPs.