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Coloration in biology
Coloration in biology
Photos of birds with rhodoxanthin in portions of their plumage: (A) Black-necked Cotinga, Phoenicircus nigricollis (close relative of Ph. carnifex), (B) Jambu fruit dove, Ptilinopus jambu, (C) Beautiful fruit dove, Ptilinopus pulchellus (D) Wompoo pigeon, Ptilinopus magnificus (E) Yellow-bibbed fruit-dove, Ptilinopus solomonensis. (Figure from Berg et al., 2013; Photo credits: (A) Wim de Groot; (B and C) T. Friedel/VIREO; (D) W. Peckover/VIREO; (E) Mehd Halaouate.
Vibrational and electronic spectroscopy of the retro-carotenoid rhodoxanthin in avian plumage, solid-state films, and solution
C.J. Berg, A.M. LaFountain, R.O. Prum, H.A. Frank and M.J.Tauber Archives of Biochemistry and Biophysics, 2013
Despite varied colors exhibited by the neotropical birds illustrated to the left, the red/pink/purple feathers all contain a carotenoid known as rhodoxanthin. This molecule is one of very few retro-carotenoids in nature. We hypothesized that the different colors could result from intermolecular electronic coupling. Resonance Raman spectra acquired by M.S. student Chris Berg at room temperature and 77 K, absorption and reflection spectra, and DFT calculations were utilized to probe the feathers and extracts of rhodoxanthin. Though the findings did not prove or disprove the role of intermolecular electronic coupling, nevertheless other structural insights were gained from this spectroscopic study.
Our lab acquired and analyzed resonance Raman spectra for another study of broadbills, led by collaborators Richard Prum, Amy LaFountain, and Harry Frank: Mechanism of carotenoid coloration in the brightly colored plumages of broadbills (Eurylaimidae) R.O. Prum, A.M. LaFountain, C.J. Berg, M.J. Tauber, and Harry A. Frank J. Comp. Physiol .B, 2014
Recently (2024) I have revived studies of coloration in biology with an investigation of an insect. As before, vibrational (resonance Raman) and electronic (reflection) spectroscopy are utilized in tandem. These findings will be summarized in this website as the year unfolds.
Electrical properties of rocks at high pressures and temperatures using impedance spectroscopy
Electrical properties of rocks at high pressures and temperatures using impedance spectroscopy
Multi-anvil press in the Pommier lab at the Carnegie Institution for Science.
Dunite from San Carlos, AZ showing olivine crystals.
Electrical properties of iron sulfides in mantle xenoliths
Electrical properties of iron sulfides in mantle xenoliths
M.J. Tauber, S. Saxena, E.S. Bullock, H. Ginestet, & A. Pommier; American Mineralogist, 2023.
S. Saxena, A. Pommier, & M.J. Tauber; JGR-Solid Earth, 2021.
Funded by the NSF.
The detection and quantification of metal sulfides in host rocks have long been motivated by mineral prospecting, fundamental interest in the mantle, and other reasons. A specific motivation for our recent studies has been to understand some exceptionally conductive regions in the Earth's upper mantle. Could the anomalous conductivity be the result of iron-sulfur compounds?
In Saxena et al., 2021 (JGR), we tested this hypothesis by performing electrical experiments under pressure and temperature on natural and synthetic mantle rocks. The amount of iron-sulfur compound was varied to understand its effect on the electrical properties. Subsequently (Tauber et al., 2023), we reanalyzed electrical data for a dunite host with added FeS or Fe-S-Ni, and reported additional experimental runs along with electron microprobe analyses. Relatively low levels of iron sulfide were found to establish an electrical path through the silicate host, even below the melting point of the metal sulfide. At the threshold levels, we found that the conductivity was sensitive to annealing conditions, as well as the addition of metals which affected the redox environment.
Backscattered-electron (BSE) image illustrating metal sulfides in a host glass having a composition analogous to some Mercury lavas.
Experimental investigation of the role of sulfur in highly reduced silicate glasses and melts
Experimental investigation of the role of sulfur in highly reduced silicate glasses and melts
A. Pommier, M.J. Tauber, H. Pirotte, G. D. Cody, A. Steele, E.S. Bullock, B. Charlier, and B.O. Mysen; Geochimica et Cosmochimica Acta, 2023.
Funding: NSF and Carnegie endowment.
This study focused on sulfur-bearing samples synthesized under highly reduced conditions relevant to the planet Mercury. Multiple spectroscopic methods were utilized to probe the speciation and bonding of sulfur, and elucidate the impact of this element on transport properties of the glasses or melts. In situ impedance spectroscopy was used to probe the samples in a multi-anvil press under 2 - 4 GPa pressures and 475 - 1738 K temperatures. Samples at ambient conditions were also probed with 29Si NMR spectroscopy, Raman spectroscopy, and electron microscopy. An unexpected finding was that sulfide bonds not only with alkaline-earth atoms (Ca, Mg) as was previously known, but also with Si, i.e., directly to the silicate framework of the glass.
A subsequent study probed pure alkaline-earth sulfides by electrical impedance and Raman spectroscopy, as well as other techniques. This work has been submitted for review (2024).
Vibrational spectroscopy of triplet excited states
Vibrational spectroscopy of triplet excited states
As part of our previous work on singlet exciton fission, our group developed a special interest in the vibrational/vibronic properties of triplet excited states. Highlight coming soon!
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