Papers by Egle Molotokaite
Metadata of "Incorporating a molecular antenna in diatom microalgae cells enhances photosynt... more Metadata of "Incorporating a molecular antenna in diatom microalgae cells enhances photosynthesis"
Advanced Science, 2020
In this regard, light-responsive systems offer the possibility to employ light as a clean, non-in... more In this regard, light-responsive systems offer the possibility to employ light as a clean, non-invasive, and spatio-temporally precise tool for controlling a variety of biological signals both in vitro and in vivo. [4-9] A plethora of photochromic systems allowing modulation of molecular responses in a reversible fashion have been developed. [10,11] Among them, azobenzenes [12] are widely employed as versatile photoresponsive element for conferring reversible sensitivity to bio(inspired) targets and drugs, such as artificial membranes, [13-15] peptides, [16,17] nucleic acids, [18,19] ion channels, [20,21] living organisms, [22] and antibacterial molecules. [23-25] These studies have demonstrated that effective and reversible photomodulation can be achieved both in vitro and in vivo, by the covalent binding of the azobenzene unit to the selected target. Alternatively, one can exploit non-covalent interactions to assist the incorporation of photoactive molecules in bio-systems. [26-30] Although this method is less specific than the covalent approach, the relatively weak non-covalent interactions still allow for driving affinity to various bio-interfaces, while ensuring full The non-covalent affinity of photoresponsive molecules to biotargets represents an attractive tool for achieving effective cell photo-stimulation. Here, an amphiphilic azobenzene that preferentially dwells within the plasma membrane is studied. In particular, its isomerization dynamics in different media is investigated. It is found that in molecular aggregates formed in water, the isomerization reaction is hindered, while radiative deactivation is favored. However, once protected by a lipid shell, the photochromic molecule reacquires its ultrafast photoisomerization capacity. This behavior is explained considering collective excited states that may form in aggregates, locking the conformational dynamics and redistributing the oscillator strength. By applying the pump probe technique in different media, an isomerization time in the order of 10 ps is identified and the deactivation in the aggregate in water is also characterized. Finally, it is demonstrated that the reversible modu lation of membrane potential of HEK293 cells via illumination with visible light can be indeed related to the recovered trans→cis photoreaction in lipid membrane. These data fully account for the recently reported experiments in neurons, showing that the amphiphilic azobenzenes, once partitioned in the cell membrane, are effective light actuators for the modification of the electrical state of the membrane.
Photosynthesis Research, 2020
The kinetics of excited state energy migration were investigated by femtosecond transient absorpt... more The kinetics of excited state energy migration were investigated by femtosecond transient absorption in the isolated Photosystem I-Light Harvesting Complex I (PSI-LHCI) supercomplex and in the isolated PSI core complex of spinach under conditions in which the terminal electron donor P700 is chemically pre-oxidised. It is shown that under these conditions the relaxation of the excited state is characterised by lifetimes of about 0.4 ps, 4.5 ps, 15 ps, 35 ps and 65 ps in PSI-LHCI and 0.15 ps, 0.3 ps, 6 ps and 16 ps in the PSI core complex. Compartmental spectral-kinetic modelling indicates that the most likely mechanism to explain the absence of long-lived (ns) excited states is the photochemical population of a radical pair state, which cannot be further stabilised and decays nonradiatively to the ground state with time constants in the order of 6-8 ps.
The Journal of Physical Chemistry B, 2017
The dynamics of excited state equilibration and primary photochemical trapping have been investig... more The dynamics of excited state equilibration and primary photochemical trapping have been investigated in the Photosystem I-Light Harvesting Complex I isolated from spinach, by the complementary time-resolved fluorescence and transient absorption approaches. The combined analysis of the experimental data indicates that the excited state decay is described by lifetimes in the ranges of 12-16 ps, 32-36 ps and 64-77 ps, for both detection methods, whereas faster components, having lifetimes of 550-780 fs and 4.2-5.2 ps, are resolved only by transient absorption. A unified model capable of describing both the fluorescence and the absorption dynamics has been developed. From this model it appears that the majority of excited state equilibration between the bulk of the antenna pigments and the reaction center occurs in less than 2 ps, that the primary charge separated state is populated in ~4 ps and that the charge stabilisation by electron transfer is completed in ~70 ps. Energy equilibration dynamics associated with the long wavelength absorbing/emitting forms harbored by the PSI external antenna are also characterized by a time mean lifetime of ~75 ps, thus overlapping with radical pair charge stabilization reactions. Even in the presence of a kinetic bottleneck for energy equilibration, the excited state dynamics are shown to be principally trap-limited. However, direct excitation of the low energy chlorophyll forms is predicted to lengthen significantly (~2-folds) the average trapping time.
Nanoscale, 2012
This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe... more This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state.
Journal of Laser Micro/Nanoengineering, 2010
Interfering laser beams with the high pulse energy provide an opportunity of direct laser pattern... more Interfering laser beams with the high pulse energy provide an opportunity of direct laser patterning of materials in a predetermined way. This study reports results of the laser beam interference ablation of thin metal films on the glass substrate irradiated with the picosecond laser. Gratings and grids consisting of metal wires of several hundred nanometers were produced in a chromium film. A matrix of nanodots was obtained after irradiation of a aluminum film. The period of structures caused by interference was close to 2 μm.
Scientific Reports
Diatom microalgae have great industrial potential as next-generation sources of biomaterials and ... more Diatom microalgae have great industrial potential as next-generation sources of biomaterials and biofuels. Effective scale-up of their production can be pursued by enhancing the efficiency of their photosynthetic process in a way that increases the solar-to-biomass conversion yield. A proof-of-concept demonstration is given of the possibility of enhancing the light absorption of algae and of increasing their efficiency in photosynthesis by in vivo incorporation of an organic dye which acts as an antenna and enhances cells’ growth and biomass production without resorting to genetic modification. A molecular dye (Cy5) is incorporated in Thalassiosira weissflogii diatom cells by simply adding it to the culture medium and thus filling the orange gap that limits their absorption of sunlight. Cy5 enhances diatoms’ photosynthetic oxygen production and cell density by 49% and 40%, respectively. Cy5 incorporation also increases by 12% the algal lipid free fatty acid (FFA) production versus t...
Nanoscale, 2012
This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe... more This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state.
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Papers by Egle Molotokaite