Coherent spin dynamics of electrons and holes in CsPbBr3_3 perovskite crystals

The lead halide perovskites demonstrate huge potential for optoelectronic applications, high energy radiation detectors, light emitting devices and solar energy harvesting. Those materials exhibit strong spin-orbit coupling enabling efficient optical orientation of carrier spins in perovskite-based devices with performance controlled by a magnetic field. Perovskites are promising for spintronics due to substantial bulk and structure inversion asymmetry, however, their spin properties are not studied in detail. Here we show that elaborated time-resolved spectroscopy involving strong magnetic fields can be successfully used for perovskites. We perform a comprehensive study of high-quality CsPbBr$_3$ crystals by measuring the exciton and charge carrier $g$-factors, spin relaxation times and hyperfine interaction of carrier and nuclear spins by means of coherent spin dynamics. Owing to their "inverted" band structure, perovskites represent appealing model systems for semiconductor spintronics exploiting the valence band hole spins, while in conventional semiconductors the conduction band electrons are considered for spin functionality.Comment: 8 pages, 3 figures + supplementary informatio

The effect of molecular structure of chlorin photosensitizers on photo-bleaching of 1,3-diphenylisobenzofuran—the possible evidence of iodine reactive species formation

In this short communication, we focus on the ability of chlorin e$_{6}$ photosensitizers (PSs) with one, two or three cationic groups to generate singlet oxygen species ($^{1}$O$_{2}$) in an apolar model medium, viz. 1-octanol (OctOH). The quantum yield of $^{1}$O$_{2}$ ($\Phi _{\Delta }$) is determined indirectly by the chemical method for seven synthesized PSs using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen trap. The $\Phi _{\Delta }$ values of four PSs with one or two cationic groups occupying opposite positions in the macrocycle are equal to 0.6, which is nearly identical to the values obtained by the time-resolved fluorescence spectroscopy method. In contrast, three PSs containing a 3(1),3(2)-bis-(N,N,N-trimethylaminomethylvinyl) iodide fragment with two adjacent cationic groups have an abnormally high quantum yield reaching 0.8. It is apparent that this phenomenon results from faster trap oxidation induced by radical reactions leading to molecular iodine formation

The effect of molecular structure of chlorin photosensitizers on photo-bleaching of 1,3-diphenylisobenzofuran—the possible evidence of iodine reactive species formation

In this short communication, we focus on the ability of chlorin e$_{6}$ photosensitizers (PSs) with one, two or three cationic groups to generate singlet oxygen species ($^{1}$O$_{2}$) in an apolar model medium, viz. 1-octanol (OctOH). The quantum yield of $^{1}$O$_{2}$ ($\Phi _{\Delta }$) is determined indirectly by the chemical method for seven synthesized PSs using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen trap. The $\Phi _{\Delta }$ values of four PSs with one or two cationic groups occupying opposite positions in the macrocycle are equal to 0.6, which is nearly identical to the values obtained by the time-resolved fluorescence spectroscopy method. In contrast, three PSs containing a 3(1),3(2)-bis-(N,N,N-trimethylaminomethylvinyl) iodide fragment with two adjacent cationic groups have an abnormally high quantum yield reaching 0.8. It is apparent that this phenomenon results from faster trap oxidation induced by radical reactions leading to molecular iodine formation

Volumetric ultrasound imaging: modeling of waveform inversion

Ultrasound imaging is widely used in medicine and nondestructive testing. Medical ultrasound volumetric imaging can be considered as a competitive method to X-ray CT and MRI. Recent results in breast ultrasound tomography provide spatial distribution of sound speed and attenuation coefficient based on inverse problem solution in frequency domain. Breast tissue can be characterized as relatively homogeneous medium with possible number of small diagnostically important target inhomogeneities (lesions). This paper is focused on numerical model of complex structure with objects of different sizes and properties that can be met in medicine or in various industrial or scientific cases. High resolution ultrasound imaging is sensitive to a number of effects such as reverberation, diffraction and attenuation that can degrade image quality and cause the artifacts. Those effects are investigated and eliminated by iterative waveform inversion performed in time domain for volumetric visualization of objects’ structure and acoustic properties

Radioresistance, DNA Damage and DNA Repair in Cells With Moderate Overexpression of RPA1

International audienceMolecular responses to genotoxic stress, such as ionizing radiation, are intricately complex and involve hundreds of genes. Whether targeted overexpression of an endogenous gene can enhance resistance to ionizing radiation remains to be explored. In the present study we take an advantage of the CRISPR/dCas9 technology to moderately overexpress the RPA1 gene that encodes a key functional subunit of the replication protein A (RPA). RPA is a highly conserved heterotrimeric single-stranded DNA-binding protein complex involved in DNA replication, recombination, and repair. Dysfunction of RPA1 is detrimental for cells and organisms and can lead to diminished resistance to many stress factors. We demonstrate that HEK293T cells overexpressing RPA1 exhibit enhanced resistance to cell killing by gamma-radiation. Using the alkali comet assay, we show a remarkable acceleration of DNA breaks rejoining after gammairradiation in RPA1 overexpressing cells. However, the spontaneous rate of DNA damage was also higher in the presence of RPA1 overexpression, suggesting alterations in the processing of replication errors due to elevated activity of the RPA protein. Additionally, the analysis of the distributions of cells with different levels of DNA damage showed a link between the RPA1 overexpression and the kinetics of DNA repair within differentially damaged cell subpopulations. Our results provide knew knowledge on DNA damage stress responses and indicate that the concept of enhancing radioresistance by targeted alteration of the expression of a single gene is feasible, however undesired consequences should be considered and evaluated

Dark and Photoinduced Cytotoxic Activity of the New Chlorophyll-a Derivatives with Oligoethylene Glycol Substituents on the Periphery of Their Macrocycles

In the present work, we investigated the dark and photoinduced cytotoxic activity of the new chlorophyll-a derivatives which contain the substituents of oligoethylene glycol on the periphery of their macrocycles. These compounds were tested using human cell lines to estimate their potential as photosensitizers for photodynamic therapy of cancer. It was shown that all the tested compounds have expressed photoinduced cytotoxic activity in vitro. Detailed study of the biological activity of one of the most perspective compound in this series—pyropheophorbide-a 17-diethylene glycol ester (Compound 21) was performed. This new compound is characterized by lower dark cytotoxicity and higher photoinduced cytotoxicity than previously described in a similar compound (DH-I-180-3) and clinically used PhotolonTM. Using fluorescent microscopy, it was shown that Compound 21 quickly penetrates the cells. Analysis of caspase-3 activity indicated an apoptosis induction 40 min after exposure to red light (λ = 660 nm). The induction of DNA damages and apoptosis was shown using Comet assay. The results of expression analysis of the stress-response genes indicate an activation of the genes which control the cell cycle and detoxification of the free radicals after an exposure of HeLa cells to Compound 21 and to red light. High photodynamic activity of this compound and the ability to oxidize biomolecules was demonstrated on nuclear-free mice erythrocytes. In addition, it was shown that Compound 21 is effectively activated with low energy 700 nm light, which can penetrate deep into the tissue. Thus, Compound 21 is a prospective substance for development of the new drugs for photodynamic therapy of cancer

Acoplanarity, Aromaticity, Chirality, and Helical Twisting Power of Chlorin e6 13(N)-Methylamide-15,17-dimethyl Ester Complexes: Effect of a Metal

The experimental and theoretical study of the influence of metal complexing on geometry, aromaticity, chirality, and the ability to twist the nematic phase by complexes based on modified natural chlorin e6 was carried out. The geometry optimization of the chlorin e6 13(N)-methylamide-15,17-dimethyl ester (MADMECl) and its Zn, Cu, and Ni complexes by DFT (CAM-B3LYP/6–31 G(d,p) functional) method was performed. Based on these calculations, the acoplanarity degree of the macrocyclic ligand and the distortion energy of its dianion were estimated, which allowed the arrangement of the MADMECl complexes in the series Ni > Cu > Zn. Aromaticity was evaluated using the NICS criterion (nuclear independent chemical shift). An increase in the degree of aromaticity of the macrocycle upon complex formation was established. At the same time, the aromaticity of the inner conjugation contour corresponds to the same series as the acoplanarity, while the outer π-delocalization is characterized by the reverse sequence. An experimental evaluation of the electron circular dichroism of the Soret and the Q-bands, as well as the g-factor of dissymmetry, was carried out. The growth of these parameters with an increase in the degree of acoplanarity and aromaticity of the internal conjugation contour was determined. The induction of helical phases in mixtures of nematic liquid crystals (LCs) based on cyanobiphenyls and MADMECl macrocyclic metal complexes was studied by polarization microscopy, and the clearance temperatures and helix pitch of the mesophases were measured. A strong effect of the metal on the phase transition temperature and helical twisting power was established

Solvation, Cancer Cell Photoinactivation and the Interaction of Chlorin Photosensitizers with a Potential Passive Carrier Non-Ionic Surfactant Tween 80

Cancer and drug-resistant superinfections are common and serious problems afflicting millions worldwide. Photodynamic therapy (PDT) is a successful and clinically approved modality used for the management of many neoplastic and nonmalignant diseases. The combination of the light-activated molecules, so-called photosensitizers (PSs), with an appropriate carrier, is proved to enhance PDT efficacy both in vitro and in vivo. In this paper, we focus on the solvation of several potential chlorin PSs in the 1-octanol/phosphate saline buffer biphasic system, their interaction with non-ionic surfactant Tween 80 and photoinactivation of cancer cells. The chlorin conjugates containing d-galactose and l-arginine fragments are found to have a much stronger affinity towards a lipid-like environment compared to ionic chlorins and form molecular complexes with Tween 80 micelles in water with two modes of binding. The charged macrocyclic PSs are located in the periphery of surfactant micelles near hydrophilic head groups, whereas the d-galactose and l-arginine conjugates are deeper incorporated into the micelle structure occupying positions around the first carbon atoms of the hydrophobic surfactant residue. Our results indicate that both PSs have a pronounced affinity toward the lipid-like environment, leading to their preferential binding to low-density lipoproteins. This and the conjugation of chlorin e6 with the tumor-targeting molecules are found to enhance their accumulation in cancer cells and PDT efficacy

Oxidative Damage Induced by Phototoxic Pheophorbide a 17-Diethylene Glycol Ester Encapsulated in PLGA Nanoparticles

Pheophorbide a 17-diethylene glycol ester (XL-8), is a promising high-active derivative of known photosensitizer chlorin e6 used in photodynamic therapy. However, high lipophilicity and poor tumor accumulation limit XL-8 therapeutic application. We developed a novel XL-8 loaded with poly(D,L-lactide-co-glycolide) nanoparticles using the single emulsion-solvent evaporation method. The nanoparticles possessed high XL-8 loading content (4.6%) and encapsulation efficiency (87.7%) and a small size (182 ± 19 nm), and negative surface charge (−22.2 ± 3.8 mV) contributed to a specific intracellular accumulation. Sustained biphasic XL-8 release from nanoparticles enhanced the photosensitizer photostability upon irradiation that could potentially reduce the quantity of the drug applied. Additionally, the encapsulation of XL-8 in the polymer matrix preserved phototoxic activity of the payload. The nanoparticles displayed enhanced cellular internalization. Flow cytometry and confocal laser-scanning microscopy studies revealed rapid XL-8 loaded nanoparticles distribution throughout the cell and initiation of DNA damage, glutathione depletion, and lipid peroxidation via reactive oxygen species formation. The novel nanoformulated XL-8 simultaneously revealed a significant phototoxicity accompanied with enhanced photostability, in contrast with traditional photosensitizers, and demonstrated a great potential for further in vivo studies

Author Correction: Coherent spin dynamics of electrons and holes in CsPbBr3 perovskite crystals (vol 10, 673, 2019)

Correction to: Nature Communications https://doi.org/10.1038/s41467-019-08625-z, published online 08 February 2019 The original version of this Article contained an error in Fig. 2c, in which the numbers on the y-axis were given in the wrong order: ‘800’ at the bottom through to ‘0’ at the top. This has been corrected in both the PDF and HTML versions of the Article. Also, the Source Data file initially published online was corrupted and was replaced.ISSN:2041-172