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Nowadays, the demand for food packaging that maintains the safety and quality of products has become one of the leading challenges. It can be solved by developing functional materials based on biodegradable polymers, such as poly(lactic acid) (PLA). In order to develop PLA-based functional materials with antibacterial activity, silver nanoparticles (AgNPs) were introduced. In the present study, AgNPs stabilized by a copolymer of ethylene and maleic acid were used. Under the joint action of shear deformations and high temperature, the biocomposites of PLA with poly(ethylene glycol) and AgNPs were produced. Their mechanical and thermal characteristics, water absorption, and structure were investigated using modern methods (DSC, FTIR, Raman spectroscopy, SEM). The effect of AgNP concentration on the characteristics of PLA-based biocomposites was detected. Based on the results of antibacterial activity tests (against Gram-positive and Gram-negative bacteria, along with yeast) it is assumed that these systems have potential as materials for extending the storage of food products. At the same time, PLA-PEG biocomposites with AgNPs possess biodegradability.

The exciton interaction of four chlorophyll a (Chl a) molecules in a symmetrical tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP was analyzed in the pH range of 3-11. Exciton splitting ΔE = 232 ± 2 cm -1 of the Q y band of Chl a into two subcomponents with relative intensities of 78.1 ± 0.7 % and 21.9 ± 0.7 % was determined by a joint decomposition of the absorption and circular dichroism spectra into Gaussian functions. The exciton coupling parameters were calculated based on the BoWSCP atomic structure in three approximations: the point dipole model, the distributed atomic monopoles, and direct ab initio calculations in the TDDFT/PCM approximation. The Coulomb interactions of monomers were calculated within the continuum model using three values of optical permittivity. The models based on the properties of free Chl a in solution suffer from significant errors both in estimating the absolute value of the exciton interaction and in the relative intensity of exciton transitions. Calculations within the TDDFT/PCM approximation reproduce the experimentally determined parameters of the exciton splitting and the relative intensities of the exciton bands. The following factors of pigment-protein and pigment-pigment interactions were examined: deviation of the macrocycle geometry from the planar conformation of free Chl; the formation of hydrogen bonds between the macrocycle and water molecules; the overlap of wave functions of monomers at close distances. The most significant factor is the geometrical deformation of the porphyrin macrocycle, which leads to an increase in the dipole moment of Chl monomer from 5.5 to 6.9 D and to a rotation of the dipole moment by 15° towards the cyclopentane ring. The contributions of resonant charge-transfer states to the wave functions of the Chl dimer were determined and the transition dipole moments of the symmetric and antisymmetric charge-transfer states were estimated., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In nature, carotenoids are present as trans - and cis -isomers. Various physical and chemical factors like light, heat, acids, catalytic agents, and photosensitizers can contribute to the isomerization of carotenoids. Living organisms in the process of evolution have developed different mechanisms of adaptation to light stress, which can also involve isomeric forms of carotenoids. Particularly, light stress conditions can enhance isomerization processes. The purpose of this work is to review the recent studies on cis/trans isomerization of carotenoids as well as the role of carotenoid isomers for the light capture, energy transfer, photoprotection in light-harvesting complexes, and reaction centers of the photosynthetic apparatus of plants and other photosynthetic organisms. The review also presents recent studies of carotenoid isomers for the biomedical aspects, showing cis- and trans- isomers differ in bioavailability, antioxidant activity and biological activity, which can be used for therapeutic and prophylactic purposes., Competing Interests: Conflict of interestThe authors declare no competing interests., (© International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature 2023. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)

The paper reports on the absorption dynamics of chlorophyll a in a symmetric tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP. It was measured by a broadband femtosecond laser pump-probe spectroscopy within the range from 400 to 750 nm and with a time resolution of 20 fs-200 ps. When BoWSCP was excited in the region of the Soret band at a wavelength of 430 nm, nonradiative intramolecular conversion S 3 →S 1 was observed with a characteristic time of 83 ± 9 fs. When the complex was excited in the region of the Q y band at 670 nm, relaxation transition between two excitonic states of the chlorophyll dimer was observed in the range of 105 ± 10 fs. Absorption spectra of the excited singlet states S 1 and S 3 of chlorophyll a were obtained. The delocalization of the excited state between exciton-coupled Chl molecules in BoWSCP tetramer changed in time and depended on the excitation energy. When BoWSCP is excited in the Soret band region, an ultrafast photochemical reaction is observed. This could result from the reduction of tryptophan in the vicinity of chlorophyll.

It is known that during the process of aging, there is a significant decrease in the number of melanosomes in the retinal pigment epithelium (RPE) cells in the human eye. Melanosomes act as screening pigments in RPE cells and are fundamentally important for protection against the free radicals generated by light. A loss or change in the quality of melanin in melanosomes can lead to the development of senile pathologies and aggravation in the development of various retinal diseases. We have previously shown that the interaction between melanin melanosomes and superoxide radicals results in oxidative degradation with the formation of water-soluble fluorescent products. In the present study, we show, using fluorescence analysis, HPLC, and mass spectrometry, that visible light irradiation on melanolipofuscin granules isolated from RPE cells in the human eye results in the formation of water-soluble fluorescent products from oxidative degradation of melanin, which was in contrast to lipofuscin granules and melanosomes irradiation. The formation of these products occurs as a result of the oxidative degradation of melanin by superoxide radicals, which are generated by the lipofuscin part of the melanolipofuscin granule. We identified these products both in the composition of melanolipofuscin granules irradiated with visible light and in the composition of melanosomes that were not irradiated but were, instead, oxidized by superoxide radicals. In the melanolipofuscin granules irradiated by visible light, ions that could be associated with melanin oxidative degradation products were identified by applying the principal component analysis of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) data. Degradation of the intact melanosomes by visible light is also possible; however, this requires significantly higher irradiation intensities than for melanolipofuscin granules. It is concluded that the decrease in the concentration of melanin in RPE cells in the human eye with age is due to its oxidative degradation by reactive oxygen species generated by lipofuscin, as part of the melanolipofuscin granules, under the action of light.

Photosystem I (PSI) of the cyanobacterium Acaryochloris marina is capable of performing an efficient photoelectrochemical conversion of far-red light due to its unique suite of cofactors. Chlorophyll d (Chl-d) has been long known as the major antenna pigment in the PSI from A. marina, while the exact cofactor composition of the reaction centre (RC) was established only recently by cryo-electron microscopy. The RC consists of four Chl-d molecules, and, surprisingly, two molecules of pheophytin a (Pheo-a), which provide a unique opportunity to resolve, spectrally and kinetically, the primary electron transfer reactions. Femtosecond transient absorption spectroscopy was here employed to observe absorption changes in the 400-860 nm spectral window occurring in the 0.1-500 ps timescale upon unselective antenna excitation and selective excitation of the Chl-d special pair P 740 in the RC. A numerical decomposition of the absorption changes, including principal component analysis, allowed the identification of P 740 (+) Chl d2 (-) as the primary charge separated state and P 740 (+) Pheo a3 (-) as the successive, secondary, radical pair. A remarkable feature of the electron transfer reaction between Chl d2 and Pheo a3 is the fast, kinetically unresolved, equilibrium with an estimated ratio of 1:3. The energy level of the stabilised ion-radical state P 740 (+) Pheo a3 (-) was determined to be ~60 meV below that of the RC excited state. In this regard, the energetics and the structural implications of the presence of Pheo-a in the electron transfer chain of PSI from A. marina are discussed, also in comparison with those of the most diffused Chl-a binding RC., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to declare., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Surface-enhanced Raman scattering (SERS) is considered an efficient technique providing high sensitivity and fingerprint specificity for the detection of pesticide residues. Recent developments in SERS-based detection aim to create flexible plasmonic substrates that meet the requirements for non-destructive analysis of contaminants on curved surfaces by simply wrapping or wiping. Herein, we reported a flexible SERS substrate based on cellulose fiber (CF) modified with silver nanostructures (AgNS). A silver film was fabricated on the membrane surface with an in situ silver mirror reaction leading to the formation of a AgNS-CF substrate. Then, the substrate was decorated through in situ synthesis of raspberry-like silver nanostructures (rAgNS). The SERS performance of the prepared substrate was tested using 4-mercaptobenzoic acid (4-MBA) as a Raman probe and compared with that of the CF-based plasmonic substrates. The sensitivity of the rAgNS/AgNS-CF substrate was evaluated by determining the detection limit of 4-MBA and an analytical enhancement factor, which were 10 nM and ~10 7 , respectively. Further, the proposed flexible rAgNS/AgNS-CF substrate was applied for SERS detection of malathion. The detection limit for malathion reached 0.15 mg/L, which meets the requirements about its maximum residue level in food. Thus, the characteristics of the rAgNS/AgNS-CF substrate demonstrate the potential of its application as a label-free and ready-to-use sensing platform for the SERS detection of trace hazardous substances.

Transient absorption dynamics of chlorophylls a and d dissolved in tetrahydrofuran was measured by the broadband femtosecond laser pump-probe spectroscopy in a spectral range from 400 to 870 nm. The absorption spectra of the excited S 1 singlet states of chlorophylls a and d were recorded, and the dynamics of the of the Q y band shift of the stimulated emission (Stokes shift of fluorescence) was determined in a time range from 60 fs to 4 ps. The kinetics of the intramolecular conversion Q x →Q y (electronic transition S 2 →S 1 ) was measured; the characteristic relaxation time was 54 ± 3 and 45 ± 9 fs for chlorophylls a and d, respectively.

This review analyzes new data on the mechanism of ultrafast reactions of primary charge separation in photosystem I (PS I) of cyanobacteria obtained in the last decade by methods of femtosecond absorption spectroscopy. Cyanobacterial PS I from many species harbours 96 chlorophyll a (Chl a ) molecules, including six specialized Chls denoted Chl 1A /Chl 1B (dimer P 700 , or P A P B ), Chl 2A /Chl 2B , and Chl 3A /Chl 3B arranged in two branches, which participate in electron transfer reactions. The current data indicate that the primary charge separation occurs in a symmetric exciplex, where the special pair P 700 is electronically coupled to the symmetrically located monomers Chl 2A and Chl 2B , which can be considered together as a symmetric exciplex Chl 2A P A P B Chl 2B with the mixed excited (Chl 2A P A P B Chl 2B ) * and two charge-transfer states P 700 + Chl 2A - and P 700 + Chl 2B - . The redistribution of electrons between the branches in favor of the A -branch occurs after reduction of the Chl 2A and Chl 2B monomers. The formation of charge-transfer states and the symmetry breaking mechanisms were clarified by measuring the electrochromic Stark shift of β-carotene and the absorption dynamics of PS I complexes with the genetically altered Chl 2B or Chl 2A monomers. The review gives a brief description of the main methods for analyzing data obtained using femtosecond absorption spectroscopy. The energy levels of excited and charge-transfer intermediates arising in the cyanobacterial PS I are critically analyzed., Competing Interests: Conflict of interestThe authors have no relevant financial or non-financial interests to disclose., (© International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature 2022, Springer Nature or its licensor holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)

Background: Despite the introduction of direct oral anticoagulants, the search for new oral anticoagulants remains an urgent task., Objective: By using docking and scoring, based on physical methods, simple chemical rules, methods of synthesis, and activity measurement, develop new low-molecular-weight inhibitors of factor Xa, which are potential anticoagulants., Methods: The development of leads was based on chemical synthesis and structure-based drug design methods. The basic idea was to combine the two approaches: one based on predictive modeling and the other based on the experimental data., Results: In this study, we developed some nanomolar leads. Further chemical modification improved the inhibition constant by more than one order., Discussion: The method proposed in this paper, as well as other methods, includes virtual screening, chemical synthesis, and activity measurement. However, the most time-consuming process in this method (chemical synthesis) was simplified, and the cost was reduced to the extent that was allowed; a very simple chemical reaction was chosen, i.e., the formation of an amide bond., Conclusion: In this work, we demonstrated how using simple chemical rules based on the structurebased drug design, substances with a nanomolar concentration of activity can be developed., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

In Photosystem I (PS I), the role of the accessory chlorophyll (Chl) molecules, Chl 2A and Chl 2B (also termed A -1A and A -1B ), which are directly adjacent to the special pair P 700 and fork into the A- and B-branches of electron carriers, is incompletely understood. In this work, the Chl 2A and Chl 2B transient absorption ΔA 0 (λ) at a time delay of 100 fs was identified by ultrafast pump-probe spectroscopy in three pairs of PS I complexes from Synechocystis sp. PCC 6803 with residues PsaA-N600 or PsaB-N582 (which ligate Chl 2B or Chl 2A through a H 2 O molecule) substituted by Met, His, and Leu. The ΔA 0 (λ) spectra were quantified using principal component analysis, the main component of which was interpreted as a mutation-induced shift of the equilibrium between the excited state of primary donor P 700 ⁎ and the primary charge-separated state P 700 + Chl 2 - . This equilibrium is shifted to the charge-separated state in wild-type PS I and to the excited P 700 in the PS I complexes with the substituted ligands to the Chl 2A and Chl 2B monomers. The results can be rationalized within the framework of an adiabatic model in which the P 700 is electronically coupled with the symmetrically arranged monomers Chl 2A and Chl 2B ; such a structure can be considered a symmetric tetrameric exciplex Chl 2A P A P B Chl 2B , in which the excited state (Chl 2A P A P B Chl 2B )* is mixed with two charge-transfer states P 700 + Chl 2A - and P 700 + Chl 2B - . The electron redistribution between the two branches in favor of the A-branch apparently takes place in the picosecond time scale after reduction of the Chl 2A and Chl 2B monomers., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The energy and charge-transfer processes in photosystem I (PS I) complexes isolated from cyanobacteria Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 were investigated by pump-to-probe femtosecond spectroscopy. The formation of charge-transfer (CT) states in excitonically coupled chlorophyll a complexes (exciplexes) was monitored by measuring the electrochromic shift of β-carotene in the spectral range 500-510 nm. The excitation of high-energy chlorophyll in light-harvesting antenna of both species was not accompanied by immediate appearance of an electrochromic shift. In PS I from T. elongatus, the excitation of long-wavelength chlorophyll (LWC) caused a pronounced electrochromic effect at 502 nm assigned to the appearance of CT states of chlorophyll exciplexes. The formation of ion-radical pair P 700 + A 1 - at 40 ps was limited by energy transfer from LWC to the primary donor P 700 and accompanied by carotenoid bleach at 498 nm. In PS I from Synechocystis 6803, the excitation at 720 nm produced an immediate bidentate bleach at 690/704 nm and synchronous carotenoid response at 508 nm. The bidentate bleach was assigned to the formation of primary ion-radical state P B + Chl 2B - , where negative charge is localized predominantly at the accessory chlorophyll molecule in the branch B, Chl 2B . The following decrease of carotenoid signal at ~ 5 ps was ascribed to electron transfer to the more distant molecule Chl 3B . The reduction of phylloquinone in the sites A 1A and A 1B was accompanied by a synchronous blue-shift of the carotenoid response to 498 nm, pointing to fast redistribution of unpaired electron between two branches in favor of the state P B + A 1A - .

The Photosystem I (PSI) reaction center in cyanobacteria is comprised of ~96 chlorophyll (Chl) molecules, including six specialized Chl molecules denoted Chl1A/Chl1B (P 700 ), Chl2A/Chl2B, and Chl3A/Chl3B that are arranged in two branches and function in primary charge separation. It has recently been proposed that PSI from Chroococcidiopsis thermalis (Nürnberg et al. (2018) Science 360, 1210-1213) and Fischerella thermalis PCC 7521 (Hastings et al. (2019) Biochim. Biophys. Acta 1860, 452-460) contain Chl f in the positions Chl2A/Chl2B. We tested this proposal by exciting RCs from white-light grown (WL-PSI) and far-red light grown (FRL-PSI) F. thermalis PCC 7521 with femtosecond pulses and analyzing the optical dynamics. If Chl f were in the position Chl2A/Chl2B in FRL-PSI, excitation at 740 nm should have produced the charge-separated state P 700 + A 0 - followed by electron transfer to A 1 with a τ of ≤25 ps. Instead, it takes ~230 ps for the charge-separated state to develop because the excitation migrates uphill from Chl f in the antenna to the trapping center. Further, we observe a strong electrochromic shift at 685 nm in the final P 700 + A 1 - spectrum that can only be explained if Chl a is in the positions Chl2A/Chl2B. Similar arguments rule out the presence of Chl f in the positions Chl3A/Chl3B; hence, Chl f is likely to function solely as an antenna pigment in FRL-PSI. We additionally report the presence of an excitonically coupled homo- or heterodimer of Chl f absorbing around 790 nm that is kinetically independent of the Chl f population that absorbs around 740 nm., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Photosystem I (PSI) is a Type-I reaction center and is the largest photosynthetic complex to be characterized. In cyanobacteria, PSI is organized as a trimer with a three-fold axis of symmetry. Recently, a tetrameric form of PSI has been identified in cyanobacteria. Plastids in plants and algae only contain monomeric PSI, suggesting that tetrameric PSI may be key in the transition from ancestral cyanobacterial trimeric PSI to plant/algal monomeric PSI. We have investigated the kinetics of electron transfer to the initial acceptor in PSI tetramer isolated from Chroococcidiopsis TS-821. Using a pump-probe technique with 25 fs low-energy, 720 nm pump pulses, we measure the ultrafast (<100 fs) conversion of a delocalized exciton into a charge-separated state between the primary donor P 700 and the primary acceptor A 0 . Comparison with previous pump-probe analysis of the trimeric PSI complexes from Synechocystis sp PCC 6803 (Shelaev et al. [2010] Biochim Biophys Acta, 1797, 1410-1420) reveals that the tetrameric (PSI) complexes from Chroococcidiopsis sp TS-821 are quite similar. The transfer of an electron from the A 0 to the following acceptor A1 (phylloquinone) takes place in a time frame of about 30 ps, which is slightly longer compared to PSI trimeric complex (~24 ps). The slight spectral differences between trimeric and tetrameric PSI complexes are discussed., (© 2018 The American Society of Photobiology.)

Background: Factor Xa (FXa) is known to play a central role in blood coagulation cascade and considered to be one of the most attractive targets for oral anticoagulants of new generation., Objective: Our approach for the development of directly acting oral anticoagulants (DOAC), FXa inhibitors was demonstrated in this work., Method: Chemical synthesis is the base of our approach for the development of potential inhibitors. In this work, the substances like R1-(CONH)-R2-(CONH)-R3 are being developed, using previously described docking and screening methods, where R1, R2 and R3 are some chemical groups and (CONH) are amide bonds connecting R1, R2 and R3. The direction of amide bond (CONH) could be arbitrary for R1, R2 and R2, R3., Results: Chemical modifications were made in the frame of the results, taking into account the structure of FXa, chemical synthesis capabilities, as well as patentability of the target compounds. Subnanomolar potency of several developed compounds was achieved. Several analyzers and various testing-suites have been used to measure the concentration that doubled the prothrombin time (PTx2). Moreover, in human plasma the PTx2 concentration of the compound 217 (DD217) turned out to be 80±20 nM. The compound efficacy has proved by in vivo assays including oral administrations in rats, rabbits and monkeys., Conclusion: The pharmacodynamic profile of DD217 for oral administration in cynomolgus monkeys proves the efficacy of the compound, which makes it promising for the future preclinical trials., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

The ultrafast primary charge separation in Photosystem I (PS I) excited by femtosecond pulses centered at 720 and 760nm was studied by pump-to-probe laser spectroscopy. The absorbance in the red edge of PS I absorption spectrum has an unusual exponential dependence on wavelength. The cutoff of short wavelength components of 760nm pulse allows direct excitation of reaction center chlorophyll molecules without involvement of light-harvesting antenna. The transient spectrum manifests the features of the primary ion-radical pair P 700 + A 0 - at time delay <180fs, followed by formation of the secondary pair P 700 + A 1 - with a characteristic time of 26ps. The obtained data are rationalized in the framework of adiabatic three-state model that includes the chlorophyll dimer P 700 and two symmetrically arranged nearest chlorophyll molecules of A 0 . The arrangement of chlorophylls results in strong electronic coupling between P 700 and A 0 . Excitation in the maximum of P 700 absorption generates electronic states with the highest contribution from P 700 *, whereas excitation in the far-red edge predominantly generates charge transfer state P 700 + A 0 - in both branches of redox-cofactors. The three-level model accounts for a flat-bottomed potential surface of the excited state and adiabatic character of electron transfer between P 700 and A 0 , providing a microscopic explanation of the ultrafast formation of P 700 + A 0 - and exponential decline of PS I absorption., (Copyright © 2017 Elsevier B.V. All rights reserved.)