Navasard Vaganovich Karapetyan (September 6, 1936-March 6, 2015) began his scientific career at the Bach Institute of Biochemistry of the Russian Academy of Sciences, Moscow, and was associated with this institute for over 56 years. He worked in the area of biochemistry and biophysics of photosynthesis and was especially known for his studies on chlorophyll a fluorescence in higher plants and cyanobacteria, molecular organization of Photosystem I, photoprotective energy dissipation, and dynamics of energy migration in the two photosystems. We present here a brief biography and comments on the work of Navasard Karapetyan. We remember him as an enthusiastic person who had an unflagging curiosity, energy and profound sincere interest in many aspects of photosynthesis research.
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Red chlorophyll excitation dynamics in Arthrospira platensis photosystem I trimeric complexes as studied by femtosecond transient absorption spectroscopy.
FEBS Lett
September 2014
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia.
Femtosecond absorption spectroscopy was applied to study for the first time excitation dynamics in isolated photosystem I trimers from Arthrospira platensis, which display extremely long-wavelength absorption peaks. Pump-probe spectra observed at 77K in the timescale of dozens of picoseconds upon 70-fs excitation revealed two maxima near 710 and 730 nm, which correspond to red chlorophyll forms. Bleaching at 680 nm developed in ∼ 200 fs, whereas the bleaching kinetics at 710 and 730 nm exhibited two components with time constants of 1 and 5.
View Article and Find Full Text PDFManipulating the excitation transfer in Photosystem I using a Fabry-Perot metal resonator with optical subwavelength dimensions.
Phys Chem Chem Phys
April 2014
Institut für Physikalische und Theoretische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
We demonstrate controlled modification of the fluorescence and energy transfer properties of Photosystem I (PSI) - one of the most important light harvesting systems - by using a newly developed approach to produce optical subwavelength microcavities for cryogenic temperature issues. The experiments were carried out on PSI from the cyanobacterium Arthrospira platensis as it shows a broad and structured fluorescence emission. By changing the distance between the cavity forming mirrors, the electromagnetic field mode structure around PSI is varied affecting the emission and energy transfer properties, which allows us to selectively enhance signals of resonant emitters and suppress off-resonant emission.
View Article and Find Full Text PDFLong-wavelength limit of photochemical energy conversion in Photosystem I.
J Am Chem Soc
March 2014
Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.
In Photosystem I (PS I) long-wavelength chlorophylls (LWC) of the core antenna are known to extend the spectral region up to 750 nm for absorbance of light that drives photochemistry. Here we present clear evidence that even far-red light with wavelengths beyond 800 nm, clearly outside the LWC absorption bands, can still induce photochemical charge separation in PS I throughout the full temperature range from 295 to 5 K. At room temperature, the photoaccumulation of P700(+•) was followed by the absorbance increase at 826 nm.
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