Reversible Structural Changes Research Articles

Reversible autoinhibitory regulation of Escherichia coli metallopeptidase BepA for selective β-barrel protein degradation

Escherichia coli periplasmic zinc-metallopeptidase BepA normally functions by promoting maturation of LptD, a β-barrel outer-membrane protein involved in biogenesis of lipopolysaccharides, but degrades it when its membrane assembly is hampered. These processes should be properly regulated to ensure normal biogenesis of LptD. The underlying mechanism of regulation, however, remains to be elucidated. A recently solved BepA structure has revealed unique features: In particular, the active site is buried in the protease domain and conceivably inaccessible for substrate degradation. Additionally, the His-246 residue in the loop region containing helix α9 (α9/H246 loop), which has potential flexibility and covers the active site, coordinates the zinc ion as the fourth ligand to exclude a catalytic water molecule, thereby suggesting that the crystal structure of BepA represents a latent form. To examine the roles of the α9/H246 loop in the regulation of BepA activity, we constructed BepA mutants with a His-246 mutation or a deletion of the α9/H246 loop and analyzed their activities in vivo and in vitro. These mutants exhibited an elevated protease activity and, unlike the wild-type BepA, degraded LptD that is in the normal assembly pathway. In contrast, tethering of the α9/H246 loop repressed the LptD degradation, which suggests that the flexibility of this loop is important to the exhibition of protease activity. Based on these results, we propose that the α9/H246 loop undergoes a reversible structural change that enables His-246-mediated switching (histidine switch) of its protease activity, which is important for regulated degradation of stalled/misassembled LptD.

Photochromism of Copper(I) and Silver (I) complexes of 1-alkyl-2-(arylazo)imidazoles in miceller media

Photochromism, a reversible structural change of distinctive absorption feature of each isomer upon irradiation of light, is largely influenced by external environment such as polarity of media, existence of noncovalent interactions, hydrogen bonding etc. In this work, the Photochromism of [Cu(RaaiR/)2]ClO4 and [Ag(RaaiR/)2]NO3 complexes (RaaiR/ = 1-alkyl-2-(arylazo)imidazole) have been examined in the micelle media in MeOH using Triton-X-100, CTAB and SDS. 1-Alkyl-2-(arylazo)imidazole undergoes trans-to-cis isomerization about –N=N- bond upon light irradiation. The quantum yield (ft®c) of the photoisomerization follows the sequence nonionic micelle (Triton-X-100) > Cationic micelle (CTAB) > no micelle > anioic micelle (SDS). Although the cis-to-trans isomerization is also carried out photochemically but thermal process is faster and is followed. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature (298 – 313 K) experiment. Triton-X-100 and CTAB amplify the activation energy (Ea) of cis ® trans thermal isomerization while in presence of SDS it is decreased.

Reversible structural phase transition, dielectric switches and photoluminescence based on hexathiocyanate Thulium(III) anions

Thulium(III) chloride hydrate with potassium thiocyanate and tetrabutylammonium chloride formed a novel compound [((nBu)4N)3][Tm(SCN)6] (1), (nBu = CH3CH2CH2CH2) in the ratio 1:6:1. Differential scanning calorimetry (DSC) measurements show a pair of reversible peaks at 204.6 K (heating) and 188.7 K (cooling) with a heat hysteresis about 15.9 K, indicating the compound 1 undergoes a reversible structural phase change. Dielectric measurement further confirms the phase transition. X-ray single crystal diffraction analysis shows that the compound 1 belongs to triclinic crystal system in P−1 space group at temperatures of 140 K and 300 K, suggesting the phase transition is isosymmetric Zhang et al. (2013) [1]. The analysis of structure reveals that the disorder of the [(nBu)4N]+ cation, leading to the reversible structural phase transition. The results of solid-state fluorescence show that the emission peak of compound 1 is 458 nm, and which is of great significance to the development the fluorescence materials of the rare earth organometallic compounds.

Structural changes associated to orthokeratology: A systematic review

PurposeTo summarize the peer-reviewed literature on corneal structural changes after orthokeratology (OK) and to analyze the quality of the studies published. MethodsAn exhaustive search was carried out in the databases Pubmed MEDLINE, Web of Science and Scopus. Original studies in English, with a cohort or experimental design and analyzing the cellular and structural changes of the cornea after OK fitting for myopia correction were selected. The NewCastle-Ottawa Assessment Scale (NOS) tool was used to analyze the quality of the studies selected. ResultsThe search provided a total of 1837 articles, of which 12 were selected following the inclusion and exclusion criteria. All studies had good quality according to the NOS tool (mean 7.58 ± 1.31). The mean ± standard deviation follow-up period of lens wear in the studies evaluated was 19.27 ± 33.97 months. The following reversible changes after OK have been reported: reduction in central epithelial basal cells, an increase in height and especially in width of superficial epithelial cells, as well as an increase in central stromal thickness and in the number of active keratocytes. Concerning corneal endothelium, only changes in terms of polymegathism were reported that were compatible with those observed for other types of contact lens wear. In relation to corneal sensitivity, there was a reduction during the use of OK, as well as in the nervous density of the sub-basal plexus at the central level, with some contradictory outcomes concerning the reversibility of these changes. ConclusionOK produces reversible structural changes in the central epithelium and central anterior corneal stroma, as well as a decrease in the nerve density of the sub-basal plexus and corneal sensitivity. The quality of published studies evaluating these aspects is good, although more studies are needed to evaluate longer follow-up changes.

On the Promotion of Catalytic Reactions by Surface Acoustic Waves.

Surface acoustic waves (SAW) allow to manipulate surfaces with potential applications in catalysis, sensor and nanotechnology. SAWs were shown to cause a strong increase in catalytic activity and selectivity in many oxidation and decomposition reactions on metallic and oxidic catalysts. However, the promotion mechanism has not been unambiguously identified. Using stroboscopic X‐ray photoelectron spectro‐microscopy, we were able to evidence a sub‐nanosecond work function change during propagation of 500 MHz SAWs on a 9 nm thick platinum film. We quantify the work function change to 455 μeV. Such a small variation rules out that electronic effects due to elastic deformation (strain) play a major role in the SAW‐induced promotion of catalysis. In a second set of experiments, SAW‐induced intermixing of a five monolayers thick Rh film on top of polycrystalline platinum was demonstrated to be due to enhanced thermal diffusion caused by an increase of the surface temperature by about 75 K when SAWs were excited. Reversible surface structural changes are suggested to be a major cause for catalytic promotion.

Dynamic Porous Pattern through Controlling Noncovalent Interactions in Polyelectrolyte Film for Sequential and Regional Encapsulation.

Inspired by nature, many functional surfaces have been developed with special structures in biology, chemistry, and materials. Many research studies have been focused on the preparation of surfaces with static structure. Achieving dynamical manipulation of surface structure is desired but still a great challenge. Herein, a polyelectrolyte film capable of regional and reversible changes in the microporous structure is presented. Our proposal is based on the combination of azobenzene (Azo) π-π stacking and electrostatic interaction, which could be affected respectively by ultraviolet (UV) irradiation and water plasticization, to tune the mobility of polyelectrolyte chains. The porous patterns can be obtained after regional ultraviolet irradiation and acid treatment. Owing to the reversibility of Azo π-π stacking and electrostatic interaction, the patterns can be repeatedly created and erased in the polyelectrolyte film made by layer-by-layer (LbL) self-assembly of poly(ethyleneimine)-azo and poly(acrylic acid). Furthermore, through two rounds of porous pattern formation and erasure, different functional species can be loaded separately and confined regionally within the film, showing potential applications in the functional surface. This work highlights the coordination of two noncovalent interactions in thin films for regional and reversible controlling its structure, opening a window for more in-depth development of functional surfaces.

Engineering Mesoporous Structure in Amorphous Carbon Boosts Potassium Storage with High Initial Coulombic Efficiency

HighlightsA facile self-etching strategy was used to obtain mesoporous carbon (meso-C) nanowires with zinc-catalyzed short-range ordered structure.Meso-C anode showed high initial Coulombic efficiency (76.7%) and excellent cycling stability (1000 cycles) for potassium-ion batteries.In/ex situ characterizations revealed the reversible structural changes, and the kinetic analyses revealed the rapid K+ diffusion in electrode.

Reversible Changes in the Grain Structure and Conductivity in a Block Copolymer Electrolyte

We study the phase behavior of a triblock organic–inorganic hybrid copolymer, poly(polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-b-poly(polyhedral oligomeric silsesquioxane) (POSS-PE...

Redox Chemistry and Reversible Structural Changes in Rhombohedral VO2F Cathode during Li Intercalation.

Metal oxyfluorides are currently attracting much attention for next-generation rechargeable batteries because of their high theoretical capacity and resulting high energy density. Rhombohedral VO2F is promising because it allows two-electron transfer during electrochemical lithium cycling, with a theoretical capacity of 526 mAh g-1. However, the chemical changes it undergoes during operation are not clearly understood. In this work, a combination of synchrotron X-ray and neutron diffraction was employed to accurately describe the crystal structure of both pristine and lithiated VO2F, using samples with high crystallinity to overcome challenges in previous studies. The mechanism and reversibility of the lithium insertion was monitored in real time by high angular synchrotron diffraction measurements, performed in operando on a lithium battery in the high-voltage range: 3.9-2.3 V vs Li+/Li. Insertion of up to one lithium ion proceeds through a solid-solution reaction, while Rietveld refinements of neutron powder diffraction data revealed that the lithiated states adopt the noncentrosymmetric R3c framework, uncovering an octahedral Li-(O/F)6 coordination with reasonable Li-O/F bond lengths. This work further evaluates the redox changes of VO2F upon Li intercalation. By a comparison of changes in electronic states of all the elements in the compound, it clarifies the critical role of both anions, O and F, in the charge compensation through their covalent interactions with the 3d states of V. The clear evidence of participation of F challenges existing assumptions that its high electronegativity renders this anion largely a spectator in the redox reaction.

Water-Pillared Sodium Vanadium Bronze Nanowires for Enhanced Rechargeable Magnesium Ion Storage.

Owing to the advantages of high safety, low cost, high theoretical volumetric capacities, and environmental friendliness, magnesium-ion batteries (MIBs) have more feasibility for large-scale energy storage compared to lithium-ion batteries. However, lack of suitable cathode materials due to sluggish kinetics of magnesium ion is one of the biggest challenges. Herein, water-pillared sodium vanadium bronze nanowires (Na2 V6 O16 ·1.63H2 O) are reported as cathode material for MIBs, which display high performance in magnesium storage. The hydrated sodium ions provide excellent structural stability. The charge shielding effect of lattice water enables fast Mg2+ diffusion. It exhibits high specific capacity of 175 mAh g-1 , long cycle life (450 cycles), and high coulombic efficiency (≈100%). At high current density of 200 mA g-1 , the capacity retention is up to 71% even after 450 cycles (compared to the highest capacity), demonstrating excellent long-term cycling performance. The nature of charge storage kinetics is explored. Furthermore, a highly reversible structure change during the electrochemical process is proved by comprehensive electrochemical analysis. The remarkable electrochemical performance makes Na2 V6 O16 ·1.63H2 O a promising cathode material for low-cost and safe MIBs.

Combining optical microscopy, turbidimetry, and DSC to study structural transformations in the mixtures of semicrystalline polymers with low-molar-mass crystallizable substances

The phase behavior of low-density polyethylene mixtures with 1,2,4,5 – tetrachlorobenzene and camphor is investigated by optical methods and differential scanning calorimetry. The use of a photoconductive cell integrated into an optical microscope equipped with a heating stage, allows us, for the first time, to combine turbidimetry with visual observations to detect crystallization of a low-molar-mass substance from the amorphous regions of a semicrystalline polymer. Crystallization in the restrained conditions of an apparently solid polymer matrix leads to crystals much smaller than the low-molar-mass crystals formed in a mixture with the melted polymer. We discuss the details of reversible structural changes taking place to the binary mixtures of crystallizable components in the course of their heating and cooling. Constructed phase diagrams provide important information for developing technologies based on thermally induced phase separation in such systems.

P0454MORPHODENSITOMETRIC FEATURES OF PERIPHERAL BLOOD LYMPHOCYTES IN PATIENTS WITH PRIMARY GLOMERULONEPHRITIS

Abstract Background and Aims Lymphocytes play an important role in the development of glomerulonephritis (GN). Their subpopulations are activated under the influence of certain cytokines that act on the activation factors of transcription of these cells, leading to the corresponding regulation of gene expression. However, in addition, in the regulatory processes of lymphocyte functions, epigenetic modifications of the degree of nuclear chromatin compaction are important. The morphological manifestation of the latter may be the state of the optical density of the nuclei and the range of its variability due to the ratio of chromatin condensation/decondensation. The study of the features of potentially reversible changes in chromatin structure in somatic cells becomes actual. One of the convenient objects for studying the epigenetic mechanisms of the genome functioning regulation are interphase nuclei of peripheral blood lymphocytes. Morphodensitometric study permits to establish compensatory changes at the cellular level and to evaluate the functional state of the hereditary apparatus. The aim of the research was to study the morphodensitometric features of genome status of peripheral blood lymphocytes in patients with primary GN. Method We examined 119 patients (76 men and 43 women) with primary GN. The average age of patients was (39.65±14.16) years. The patients underwent a renal biopsy to verify the morphological form of the disease. For comparison, a survey of 30 healthy individuals was conducted. Chromatin of nuclei and its changes were studied using an image analyzer based on the programm Image Tool for Windows (v. 3.0). The advantage of this method is the possibility of a combined assessment of morphometric (area, perimeter), spectrometric (optical and integral density) data with the analysis of the microanatomy of isolated chromatin blocks and the chromatin function at the same time. The study of the morphodensitometric characteristics of peripheral blood lymphocytes is an informative and accessible method for assessing the general state of the function and structure of the hereditary apparatus of the organism. Results The sexual characteristics of the morphometric and optical parameters of lymphocytes nuclei of patients were established. So, in all patients and especially women, a decrease in the perimeter of lymphocytes nuclei was registered in 1.25 and 1.31 times, respectively (p <0.05). The area of these cells nuclei also naturally decreased in 1.22 times in all patients (in 1.08 and 1.34 times in men and women, respectively) compared to the control (p<0.05). A significant decrease in the area of lymphocytes nuclei with an unchanged density of chromatin packing in these nuclei limits the space inside the nucleus for the interaction of individual chromosome loci in this space. Such limitations can be a serious obstacle to the normal functioning of the genome and its repairing processes. Meanwhile, differences in the optical density parameter of lymphocytes nuclei in both groups were defined. The minimum and maximum optical density were higher in the group of patients, and the range of optical density variability showed wider borders of functional heterogeneity of cells compared to the control. Conclusion Comparative analysis of morphodensitometric features of peripheral blood lymphocytes in patients with primary GN detected the changes in the ratio of chromatin condensation/decondensation and normal structure of nuclei, that may indicate functional disorders of the genotype due to exo- and endogenous factors.

Stimuli-Responsive Molecule Modification to Locally Functionalized Single-Walled Carbon Nanotubes for Wavelength Switching of Near Infrared Photoluminescence

Single-walled carbon nanotubes (SWNTs) with semiconducting features show near infrared (NIR) photoluminescence (PL). Defect doping to the SWNTs has been found to enhance the PL properties, which is achieved by local chemical modification.[1-9] It allows us to functionalize various molecules on the doped sites and such locally functionalized SWNTs (lf-SWNTs) show PL property changes depending on the modified molecules. For example; electronic property difference in the modified aryl groups induced PL shifts.[3] Moreover, protonation of amine groups[6] and molecular recognition at the doped sites[7,8] can be used for wavelength tuning. Therefore, stimuli responsiveness in the NIR PL properties could be designed in the lf-SWNTs through molecular approaches. In this presentation, we report reversible wavelength modulation based on molecular structure changes occurring at the doped sites by external stimuli. Molecular binding through covalent bond formation and photo-induced structural changes are used for the wavelength switching processes.Imine chemistry is based on a condensation reaction of aldehyde and amine groups that occurs just by mixing the corresponding compounds. Owing to the reversibility of this reaction system, multistep wavelength switching of the NIR PL was conducted by imine bond formation, exchange or dissociation reactions of the imine bond, and Kabachnik-Fields reactions at the doped sites of the lf-SWNTs.[9] Photo-induced switching of the NIR PL was performed by creating the doped sites functionalized with photochromic molecules that showed color changes (= electronic property changes) by light irradiation. The photo-induced reversible structural changes of the modified molecules on the lf-SWNTs were observed by absorption spectroscopy, which accompanies spectral shifts of the NIR PL of the lf-SWNTs. Details including the relationship between PL shifts and molecular structure changes will be discussed at the meeting.[1] B. Weisman et al. Science, 330, 1656 (2010). [2] Y. Miyauchi et al. Nat. Photon., 7, 715 (2013). [3] Y. Wang et al. Nat. Chem., 5, 840 (2013). [4] S. Doorn et al. Nat. Photon., 11, 577 (2017). [5] T. Shiraki et al. Sci. Rep., 6, 28393 (2016). [6] Y. Wang et al. J. Phys. Chem. C, 119, 3733 (2015) [7] T. Shiraki et al. Chem. Commun., 52, 12972 (2016). [8] T. Shiraki et al. Chem. Eur. J., 24, 9393 (2018). [9] T. Shiraki et al. Chem. Eur. J., 24, 19162 (2018). Figure 1

Operando Surface X-Ray Diffraction Studies of Structurally-Defined Oxygen Evolution Electrocatalysts Based on Electrodeposited Epitaxial Transition Metal Oxide Films

Iron-group oxides are among the best precious-metal-free catalyst for the oxygen evolution reaction (OER) in alkaline media [1] and thus of great interest for large-scale electrochemical water splitting into O2 and H2. A wide variety of different catalysts, based on oxides of Co, Fe, and Ni, have been synthesized and studied, exhibiting rather diverse nanoscale morphologies and usually an unknown surface structure. This makes it difficult to compare their reactivity and correlate it with ab initio theoretical studies, which hinders the development of clear structure-reactivity relationships and unambiguous determination of the OER reaction mechanism.In this work we report in situ and operando surface x-ray diffraction (SXRD) studies of well-defined Co3O4 and b-CoOOH electrocatalysts [2]. Ultrathin epitaxial films (10-20 nm thickness) of these materials were electrodeposited on Au single crystals from a dilute Co(II) tartrate solution of pH 14, using a modified version of the procedure described in Ref. [3]. Characterization by SXRD and AFM revealed that epitaxial Co3O4(111) and β-CoOOH(001) deposits were obtained in 2 M and 5 M NaOH, respectively. The film orientation is independent of the substrate and in the surface plane aligned with the Au(111) and Au(001) substrate lattice. The β-CoOOH(001) film deposits were found to be smooth with clearly visible atomic steps. The Co3O4 films exhibits a more island-like morphology, which can be controlled by the deposition parameters.The potential-dependent structure of these model oxide electrocatalysts during cyclic voltammograms was studied at pH values between 7 and 13 over a wide potential range up to OER current densities of 150 mA/cm2. For this, a custom designed electrochemical cell was used that allows high-resolution SXRD characterization together with electrochemical and optical reflectivity measurements while gas evolution proceeds. The two oxide materials show very different behavior. The CoOOH(001) samples were perfectly stable over a wide potential range. In the case of Co3O4(111), fast and fully reversible structural changes are observed, in good agreement with a previous operando study of polycrystalline Co3O4 catalysts [4]. Specifically, the near surface region of Co3O4(111) is converted to a new phase, which is assigned to highly disordered CoOOH. This restructuring starts at potentials 300 mV negative of the onset of the OER, indicating that the process is related to the thermodynamically predicted Co3O4 / β-CoOOH(001) transition rather than to the catalytic reaction. The formed skin layer is of defined thickness, which changes linearly with applied potential. In addition, continuous changes of the Co3O4 unit cell volume are found over a wide potential range, which are assigned to changes in the oxide bulk, related to the pseudo-capacitive charging current in the pre-OER potential range. The kinetics of these structural changes is fast and highly reversible. Furthermore, systematic studies of Co3O4(111) films with different morphology show a smaller skin layer thickness and lower magnitude of the bulk oxide changes for smoother deposits, suggesting an important role of more open oxide facets for the structural conversion.Surprisingly, the catalytic activity of the skin layer covered Co3O4(111) and that of the smooth β-CoOOH(001) are almost identical, if the true microscopic surface area is taken into account. This indicates that the number of OER active sites on the two oxides is similar, despite the very different defect density, and is at variance with previous suggestions that di-µ-oxo bridged Co cations are exclusively responsible for the OER activity of Co oxides. For the smooth β-CoOOH(001) a turnover frequency of 4.2 s-1 per surface atom is determined at an overpotential of 400 mV, which exceeds that estimated in most studies of polycrystalline Co oxide electrocatalysts.[1] C. C. L. McCrory et al., Journal of the American Chemical Society 2015, 137, 4347.[2] F. Reikowski, et al., ACS Catalysis, 2019, 9, 3811[3] J. A. Koza et al., Chem. Mat. 2012, 24, 3567.[4] A. Bergmann, et al., Nature Communications, 2015, 6, 8625. Figure 1

Structural changes in noble metal nanoparticles during CO oxidation and their impact on catalyst activity

The dynamical structure of a catalyst determines the availability of active sites on its surface. However, how nanoparticle (NP) catalysts re-structure under reaction conditions and how these changes associate with catalytic activity remains poorly understood. Using operando transmission electron microscopy, we show that Pd NPs exhibit reversible structural and activity changes during heating and cooling in mixed gas environments containing O2 and CO. Below 400 °C, the NPs form flat low index facets and are inactive towards CO oxidation. Above 400 °C, the NPs become rounder, and conversion of CO to CO2 increases significantly. This behavior reverses when the temperature is later reduced. Pt and Rh NPs under similar conditions do not exhibit such reversible transformations. We propose that adsorbed CO molecules suppress the activity of Pd NPs at lower temperatures by stabilizing low index facets and reducing the number of active sites. This hypothesis is supported by thermodynamic calculations.

Raman spectroscopy and X‐ray diffraction of pressure‐induced reversible structure change in K2OsO2(OH)4

AbstractHigh‐pressure structural evolution of K2OsO2(OH)4, a potassium osmate dihydrate, has been studied by high‐pressure Raman spectroscopy and angle dispersive X‐ray diffraction. A pressure‐induced reversible structure change is observed at approximately 8 GPa, evidenced by the splitting of Raman modes and the addition of X‐ray diffraction peaks. The splitting of phonon generally occurs in the Raman modes with smaller Grüneisen parameters. The pressure‐induced structural change is correlated with the relatively isolated arrangement of Os–O polyhedron. In addition, the zero‐pressure bulk modulus B0 = 46(1) GPa and zero‐pressure Grüneisen parameters γ of K2OsO2(OH)4 are given and discussed.

Optically tunable microresonator using an azobenzene monolayer

Photoswitchable organic molecules can undergo reversible structural changes with an external light stimulus. These optically controlled molecules have been used in the development of “smart” polymers, optical writing of grating films, and even controllable in vivo drug release. Being the simplest class of photoswitches in terms of structure, azobenzenes have become the most ubiquitous, well-characterized, and implemented organic molecular switches. Given their predictable response, they are ideally suited to create an all-optically controlled switch. However, fabricating a monolithic optical device comprised solely of azobenzene while maintaining the photoswitching functionality is challenging. In this work, we combine integrated photonics with optically switchable organic molecules to create an optically controlled integrated device. A silica toroidal resonant cavity is functionalized with a monolayer of an azobenzene derivative. After functionalization, the loaded cavity Q is above 105. When 450 nm light is coupled into cavity resonance, the azobenzene isomerizes from trans isomer to cis isomer, inducing a refractive index change. Because the resonant wavelength of the cavity is governed by the index, the resonant wavelength changes in parallel. At a probe wavelength of 1300 nm, the wavelength shift is determined by the duration and intensity of the 450 nm light and the density of azobenzene functional groups on the device surface, providing multiple control mechanisms. Using this photoswitchable device, resonance frequency tuning as far as 60% of the cavity’s free spectral range in the near-IR is demonstrated. The kinetics of the tuning are in agreement with spectroscopic and ellipsometry measurements coupled with finite element method calculations.

High-Pressure Raman and Infrared Spectroscopic Study of Prehnite

High-pressure Raman and infrared spectra of a natural sample of prehnite, with a chemical composition of Ca2(Al0.74,Fe0.26)2Si3O10(OH)2, are presented. Analyses of the spectra indicate that prehnite undergoes a reversible structural change between 6 and 8 GPa that is most likely associated with a subtle alteration in the orientation and/or deformation of the polyhedra comprising the framework of the structure. At pressures in excess of ~11 GPa, the high-pressure spectra indicate that prehnite undergoes a reversible phase transition involving the collapse of the framework structure.

Reversible laser-assisted structural modification of the surface of As-rich nanolayers for active photonics media

Reversible structural changes of As-rich As–Se nanolayers occurring during in situ thermal annealing and above-bandgap laser illumination were studied by synchrotron radiation photoelectron spectroscopy. It was found that the first thermal annealing of As56Se44 nanolayers led to a decrease of the concentration of As that can be connected with evaporation of more volatile As-rich fractions from the surface. This process is accompanied by structural rearrangements in the nanolayers. In situ green laser illumination of annealed samples causes an increase in the concentration of homopolar As–As bonds associated with As-Se2As s.u., while the opposite effect was detected during further thermal treatment. These processes appeared to be reversible for three sequences of annealing and illumination. The observed effect of the reversible photoinduced structural modification is discussed in detail, and possible applications as an active optical medium for photonics are proposed.

Chaperone function of Arabidopsis NPR1

To cope with diverse environmental stresses, the sessile organisms of plants have evolved diverse defense molecules and signaling systems to transfer the stress signals into downstream metabolic cascades and induce the expression of defense-associated genes. Among the defense systems, the Arabidopsis nonexpressor of pathogenesis-related protein 1 (AtNPR1) playing a key role in a plant systemic acquired immune responses has been shown to have multiple functions. The molecular structure of AtNPR1 has two domains, BTB/POZ and ANK repeat, that are involved in protein–protein interactions. Despite the function of its salicylic acid-induced defense activity in nucleus, the biochemical property of its cytosolic oligomers has not been elucidated. Based on the results that the reversible structural change of redox proteins is a typical property of molecular chaperones, we investigated the biochemical characteristics of AtNPR1 after expressing it in E. coli and purifying the protein. From the study, the recombinant AtNPR1 functions as a protein chaperone to protect plants from heat stress through its structural switching by its oligomer form. Under heat-induced (43 °C) condition, the AtNPR1 protein prevents from aggregation of substrate, MDH. And the structural change was regulated upon the redox changes, such as DTT treatment dissociated its structure to monomer and reduced its chaperone activity, suggesting that the heat-induced chaperone activity of AtNPR1 is dependent on its redox status. In summary, the cytosolic AtNPR1 oligomer performs the important function of molecular chaperone to protect plants from heat stress that can be applied to the preparation of heat shock-tolerant useful crops.