Photodynamic activity rather than drilling causes membrane damage by a light-powered molecular nanomotor.

The chase toward endowing chemical compounds with machine-like functions mimicking those of biological molecular machineries has yielded a variety of artificial molecular motors (AMMs). Pharmaceutical applications of photoexcited monomolecular unidirectionally-rotating AMMs have been envisioned in view of their ability to permeabilize biological membranes. Nonetheless, the mechanical properties of lipid membranes render the proposed drilling activity of AMMs doubtful. Here, we show that singlet oxygen released by a photoexcited "molecular drill" oxidized unsaturated lipids composing giant unilamellar vesicles. In contrast, giant liposomes built of saturated lipids were inert to AMM photoactuation. The AMM did not mechanically destroy gramicidin A ion channels in planar bilayer lipid membranes but instead photoinactivated them. Sodium azide, a singlet oxygen quencher, reduced both AMM-mediated light-induced dye release from unsaturated large unilamellar vesicles and protected gramicidin A from photoinactivation. Upon additional consideration of the underlying bilayer mechanics, we conclude that AMMs' envisioned therapeutic and pharmaceutical applications rely on their photodynamic activity rather than their nanomechanical drilling abilities.

ζ-Carotene: Generation and Quenching of Singlet Oxygen, Comparison with Phytofluene.

It is known that C40 carotenoids with a short chain of conjugated double bonds (CDB) (5 and 7, respectively) are universal precursors in the biosynthesis of colored carotenoids in plant cells. Previously, using mainly stationary measurements of photosensitized phosphorescence of singlet oxygen (1O2), we discovered that phytofluene efficiently generates 1O2 in aerated solution and therefore, can serve as a source of the UV photodynamic stress in living cells [Ashikhmin et al., Biochemistry (Moscow), 2020, 85, 773]. In the present paper, by using novel pulsed light emitting diodes (LEDs), aerated hexafluorobenzene as a solvent and time-resolved measurements of 1O2 phosphorescence we confirmed that phytofluene efficiently photosensitizes 1O2 formation. The quantum yield of this process according to the novel experiments is about 0.4. An ability to generate 1O2 was also found in aerated solutions of ζ-carotene although the quantum yield of this process is 30-fold lower that in phytofluene solutions. Both carotenoids were found to quench 1O2 in the dark with the quenching rate constants equal to (3.6 ± 0.9)×107 and (2.1 ± 0.2)×108 M-1s-1, respectively. To our knowledge, the rate constant of 1O2 quenching by ζ-carotene has been reported in the present paper for the first time. It follows from the data obtained that the rate constants of 1O2 quenching by both carotenoids are much (by 2-3 orders of magnitude) smaller than the rate constant of the diffusion-limited biomolecular reactions. Hence, both carotenoids are weak protectors against 1O2 oxidative activity. It is more likely that they are potential promoters of photodynamic stress in living cells.

In memory of Vladimir Anatolievich Shuvalov (1943-2022): an outstanding biophysicist.

We present here a tribute to one of the foremost biophysicists of our time, Vladimir Anatolievich Shuvalov, who made important contributions in bioenergetics, especially on the primary steps of conversion of light energy into charge-separated states in both anoxygenic and oxygenic photosynthesis. For this, he and his research team exploited pico- and femtosecond transient absorption spectroscopy, photodichroism & circular dichroism spectroscopy, light-induced FTIR (Fourier-transform infrared) spectroscopy, and hole-burning spectroscopy. We remember him for his outstanding leadership and for being a wonderful mentor to many scientists in this area. Reminiscences by many [Suleyman Allakhverdiev (Russia); Robert Blankenship (USA); Richard Cogdell (UK); Arvi Freiberg (Estonia); Govindjee Govindjee (USA); Alexander Krasnovsky, jr, (Russia); William Parson (USA); Andrei Razjivin (Russia); Jian- Ren Shen (Japan); Sergei Shuvalov (Russia); Lyudmilla Vasilieva (Russia); and Andrei Yakovlev (Russia)] have included not only his wonderful personal character, but his outstanding scientific research.

"Fundamental principles of photodynamic, laser and PUVA therapy": a session of the Russian Photobiology Society 9th Congress (Shepsi, Krasnodar region, Russia; September, 12-19, 2021).

At the section "Fundamentals of photodynamic, laser and PUVA therapy," 32 reports were presented in full-time and on-line format. Representatives of various scientific schools reported on the results of fundamental and applied research on the processes occurring at the cellular and organismal levels upon irradiation with low-intensity red light and upon the introduction of photosensitizers of various nature, followed by laser irradiation. Scientific reports proposed new photosensitizers, as well as their conjugates with biologically active molecules for fluorescent diagnostics and photodynamic therapy of oncological diseases. Plenary reports were presented by Professor Mikhail Grin "Natural chlorins as a promising platform for creating drugs with photoinduced antitumor and antimicrobial activity," Professor Alexander Krasnovsky "Laser activation of dissolved oxygen in natural conditions," and Professor Elena Filonenko "Photodynamic therapy in the treatment of demodicosis of the facial skin with topical application of a gel based on 5-ALA." At the poster section, young scientists presented 18 posters, which describe in detail the research voiced in the section reports.

Chlorin Endogenous to the North Pacific Brittle Star Ophiura sarsii for Photodynamic Therapy Applications in Breast Cancer and Glioblastoma Models.

Photodynamic therapy (PDT) represents a powerful avenue for anticancer treatment. PDT relies on the use of photosensitizers-compounds accumulating in the tumor and converted from benign to cytotoxic upon targeted photoactivation. We here describe (3S,4S)-14-Ethyl-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (ETPA) as a major metabolite of the North Pacific brittle stars Ophiura sarsii. As a chlorin, ETPA efficiently produces singlet oxygen upon red-light photoactivation and exerts powerful sub-micromolar phototoxicity against a panel of cancer cell lines in vitro. In a mouse model of glioblastoma, intravenous ETPA injection combined with targeted red laser irradiation induced strong necrotic ablation of the brain tumor. Along with the straightforward ETPA purification protocol and abundance of O. sarsii, these studies pave the way for the development of ETPA as a novel natural product-based photodynamic therapeutic.

Remembering Navasard V. Karapetyan (1936-2015).

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.

Characterization of the low-temperature triplet state of chlorophyll in photosystem II core complexes: Application of phosphorescence measurements and Fourier transform infrared spectroscopy.

Phosphorescence measurements at 77 K and light-induced FTIR difference spectroscopy at 95 K were applied to study of the triplet state of chlorophyll a ((3)Chl) in photosystem II (PSII) core complexes isolated from spinach. Using both methods, (3)Chl was observed in the core preparations with doubly reduced primary quinone acceptor QA. The spectral parameters of Chl phosphorescence resemble those in the isolated PSII reaction centers (RCs). The main spectral maximum and the lifetime of the phosphorescence corresponded to 955±1 nm and of 1.65±0.05 ms respectively; in the excitation spectrum, the absorption maxima of all core complex pigments (Chl, pheophytin a (Pheo), and ß-carotene) were observed. The differential signal at 1667(-)/1628(+)cm(-1) reflecting a downshift of the stretching frequency of the 13(1)-keto C=O group of Chl was found to dominate in the triplet-minus-singlet FTIR difference spectrum of core complexes. Based on FTIR results and literature data, it is proposed that (3)Chl is mostly localized on the accessory chlorophyll that is in triplet equilibrium with P680. Analysis of the data suggests that the Chl triplet state responsible for the phosphorescence and the FTIR difference spectrum is mainly generated due to charge recombination in the reaction center radical pair P680(+)PheoD1(-), and the energy and temporal parameters of this triplet state as well as the molecular environment and interactions of the triplet-bearing Chl molecule are similar in the PSII core complexes and isolated PSII RCs.

Low-temperature (77 K) phosphorescence of triplet chlorophyll in isolated reaction centers of photosystem II.

Phosphorescence characterized by the main emission band at 952 ± 1 nm (1.30 eV), the lifetime of 1.5 ± 0.1 ms and the quantum yield nearly equal to that for monomeric chlorophyll a in aqueous detergent dispersions, has been detected in isolated reaction centers (RCs) of spinach photosystem II at 77 K. The excitation spectrum shows maxima corresponding to absorption bands of chlorophyll a, pheophytin a, and ß-carotene. The phosphorescence intensity strongly depends upon the redox state of RCs. The data suggest that the phosphorescence signal originates from the chlorophyll triplet state populated via charge recombination in the radical pair [Formula: see text].

Phosphorescence study of chlorophyll d photophysics. Determination of the energy and lifetime of the photo-excited triplet state. Evidence of singlet oxygen photosensitization.

Chlorophyll d (Chl d) is the major pigment in both photosystems (PSI and II) of the cyanobacterium Acaryochloris marina, whose pigment composition represents an interesting alternative in oxygenic photosynthesis. While abundant information is available relative to photophysical properties of Chl a , the understanding of Chl d photophysics is still incomplete. In this paper, we present for the first time a characterization of Chl d phosphorescence, which accompanies radiative deactivation of the photoexcited triplet state of this pigment. Reliable information was obtained on the energy and lifetime of the Chl d triplet state in frozen solutions at 77 K using diethyl ether and aqueous dispersions of Triton X100 as solvents. It is shown that triplet Chl d is effectively populated upon photoexcitation of pigment molecules and efficiently sensitizes singlet oxygen phosphorescence in aerobic solutions under ambient conditions. The data obtained are compared with the previous results of the phosphorescence studies of Chl a and Pheo a, and their possible biological implications are discussed.

Chlorophyll isolation, structure and function: major landmarks of the early history of research in the Russian Empire and the Soviet Union.

This paper covers major events of the early history of chlorophyll research in the Russian Empire and the Soviet Union from 1771 until 1952, when the modern period of studies on photosynthesis began in full swing. Short biographical sketches of key scientists, reviews of their major research contributions and some selected photographs are included.