The Orthodox Dry Seeds Are Alive: A Clear Example of Desiccation Tolerance

To survive in the dry state, orthodox seeds acquire desiccation tolerance. As maturation progresses, the seeds gradually acquire longevity, which is the total timespan during which the dry seeds remain viable. The desiccation-tolerance mechanism(s) allow seeds to remain dry without losing their ability to germinate. This adaptive trait has played a key role in the evolution of land plants. Understanding the mechanisms for seed survival after desiccation is one of the central goals still unsolved. That is, the cellular protection during dry state and cell repair during rewatering involves a not entirely known molecular network(s). Although desiccation tolerance is retained in seeds of higher plants, resurrection plants belonging to different plant lineages keep the ability to survive desiccation in vegetative tissue. Abscisic acid (ABA) is involved in desiccation tolerance through tight control of the synthesis of unstructured late embryogenesis abundant (LEA) proteins, heat shock thermostable proteins (sHSPs), and non-reducing oligosaccharides. During seed maturation, the progressive loss of water induces the formation of a so-called cellular “glass state”. This glassy matrix consists of soluble sugars, which immobilize macromolecules offering protection to membranes and proteins. In this way, the secondary structure of proteins in dry viable seeds is very stable and remains preserved. ABA insensitive-3 (ABI3), highly conserved from bryophytes to Angiosperms, is essential for seed maturation and is the only transcription factor (TF) required for the acquisition of desiccation tolerance and its re-induction in germinated seeds. It is noteworthy that chlorophyll breakdown during the last step of seed maturation is controlled by ABI3. This update contains some current results directly related to the physiological, genetic, and molecular mechanisms involved in survival to desiccation in orthodox seeds. In other words, the mechanisms that facilitate that an orthodox dry seed is a living entity.

Holographic Optical Lenses Recorded on a Glassy Matrix-Based Photopolymer for Solar Concentrators

Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a half is enough to meet the world’s electricity consumption for a complete year. Generally, solar concentrators are used to collect the solar radiation and to concentrate it at a single focal point. These devices consist in a set of mirrors or mechanical structures to reduce the area of a photovoltaic cell, which is typically very expensive. Volume transmission phase holographic optical elements could be opportunely designed and realized to obtain a simple, lightweight, compact and inexpensive planar solar concentrator. With the aim of bringing scientific attention to this still developing topic, in this work we critically report a complete investigation on a new photopolymeric material obtained by sol-gel reactions used as possible recording material for volume holographic solar concentrators; as a proof of concept, both terrestrial and extreme environments, such as space, are considered as potential applications.

Raman spectra of MCl-Ga2S3-GeS2 (M = Na, K, Rb) glasses

Raman spectra of (MY) x (Ga2S3)0.2−0.2x (GeS2)0.8−0.8x pseudo-ternary glassy systems (M = Na, K, Rb; Y = Cl, Br, I) were investigated systematically as a function of MY nature and alkali content. Raman spectroscopy of the Ga3S3-GeS2 glassy matrix shows a complicated local structure: corner-sharing CS- and edge-sharing ES-GeS4/2 tetrahedra, Ga-S triclusters and ETH-Ga2S6/2 ethane-like units. The Ga2S6/2 population decreases with increasing x related to a substitution of some bridging sulfur atoms around central Ga by terminal Y species with a respective decrease of the network rigidity. The formation of mixed Ga-(S,Y) environment is affected by the M+ ion size and the MY concentration.

Electrochemical Properties of Pristine and Vanadium Doped LiFePO4 Nanocrystallized Glasses

In our recent papers, it was shown that the thermal nanocrystallization of glassy analogs of selected cathode materials led to a substantial increase in electrical conductivity. The advantage of this technique is the lack of carbon additive during synthesis. In this paper, the electrochemical performance of nanocrystalline LiFePO4 (LFP) and LiFe0.88V0.08PO4 (LFVP) cathode materials was studied and compared with commercially purchased high-performance LiFePO4 (C-LFP). The structure of the nanocrystalline materials was confirmed using X-ray diffractometry. The laboratory cells were tested at a wide variety of loads ranging from 0.1 to 3 C-rate. Their performance is discussed with reference to their microstructure and electrical conductivity. LFP exhibited a modest electrochemical performance, while the gravimetric capacity of LFVP reached ca. 100 mAh/g. This value is lower than the theoretical capacity, probably due to the residual glassy matrix in which the nanocrystallites are embedded, and thus does not play a significant role in the electrochemistry of the material. The relative capacity fade at high loads was, however, comparable to that of the commercially purchased high-performance LFP. Further optimization of the crystallites-to-matrix ratio could possibly result in further improvement of the electrochemical performance of nanocrystallized LFVP glasses.

Preparation of Luminescent Glass Aggregates from Soda-Lime Waste Glass

This research studied the preparation of luminescent glass aggregates prepared from soda-lime waste glass and strontium aluminate-based phosphors. The properties of the samples were determined by means of X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), Archimedes’ method, and photoluminescence (PL) spectroscopy. It was found that the pore characteristics, density, and formation of crystallite phases in the glassy matrix depended on the phosphor content. The addition of fine phosphor powder tended to inhibit the glass crystallization and to reduce the apparent porosity of the aggregates. In general, the disadvantage of phosphors is their luminescent degradation under thermal attacks, which limits their use in applications involving high-temperature annealing. The phosphors, however, still had good luminescent properties and long-term stability with the sintering temperature as high as 750°C. The results indicated that the phosphors could be composited with glasses at high processing temperatures, enabling their widespread application.

Effect of varying phosphate content on the structure and properties of sol-gel derived SiO2-CaO-P2O5 bio-glass

In this work, biocompatible glass (bioglass) particles were prepared by low temperature, acid catalysed sol-gel method. The effect of varying phosphate (P2O5) content (10, 15 and 20 mol %) in the sol-gel derived glass composition were studied. The sol-gel derived bioglass particles were compacted into cylindrical pellets via hydraulic press machine and sintered at 600°C for 3 hours. The bioglass particulates were analysed by x-ray fluorescence (XRF), Fourier Transformed Infrared (FTIR), X-Ray Diffraction (XRD) and nitrogen gas adsorption. Meanwhile, the sintered bioglass pellets were analysed by FTIR, XRD and FESEM-EDX. Furthermore, in vitro bioactivity analysis was performed by immersion in simulated body fluid (SBF) for 14 days. Bioglass particulates with high glassy phase, high surface area and high porosities were obtained for all compositions. Increasing of phosphate content to 20 mol% particularly reduced the porous characteristics of the bioglass particulates. Furthermore, leads to higher bridging oxygen (BO) atoms, higher amorphous silicate networks, lower glass crystallinity and higher number of phosphate crystallites within the amorphous glassy matrix. Increased to 20 mol% of phosphate also reduced the ability of the bioglass surface to induce carbonated apatite formation when immersed in simulated body fluid (SBF) solution.

Facile and reproducible method of stabilizing $$\hbox {Bi}_2\hbox {O}_3$$ phases confined in nanocrystallites embedded in amorphous matrix

Bismuth sesquioxide ($$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 ) draws much attention due to wide variety of phases in which it exists depending on the temperature. Among them, $$\delta$$ δ phase is specially interesting because of its high oxide ion conductivity and prospects of applications as an electrolyte in fuel cells. Unfortunately, it is stable only in a narrow temperature range ca. 730–830 $$^{\circ }$$ ∘ C. Our group has developed a facile and reproducible two-stage method of stabilizing $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 crystalline phases confined in nanocrystallites embedded in amorphous matrix. In the first stage, glassy materials were obtained by a routine melt-quenching method: pure $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 powders were melted in porcelain crucibles and fast-cooled down to room temperature. In the second step, the materials were appropriately heat-treated to induce formation of crystallites of $$\beta$$ β , $$\delta$$ δ or $$\gamma$$ γ $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 phases confined in a glassy matrix, depending on the process conditions. It was found out that the vitrification of the initial $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 and the subsequent nanocrystallization were unexpectedly possible due to the presence of some Al, and Si impurities from the crucibles. Systematic DTA, XRD, optical, Raman and SEM/EDS studies were carried out to investigate the influence of the syntheses processes and allowed us to determine conditions under which the particular phases appear and remain stable down to room temperature.

Kinetics Investigation of the Formation of a Gas-Resistant Glass-Forming Layer during the Oxidation of ZrB2-MoSi2-Y2O3-Al Coatings in the Air Atmosphere

In this article, the coatings of ZrB2-xMoSi2-Y2O3-yAl (x = 24, 35, 45 wt %; y = 10, 15, 20 wt %) were applied to the surface of a carbon/carbon composite to protect against high-temperature oxidation using a multi-chamber detonation accelerator. The kinetic analysis of the formation processes of a glass-forming layer during the oxidation of the initial components of the system ZrB2-MoSi2-Y2O3-Al in an air atmosphere at a temperature of 1400 °C was carried out and the kinetically significant stages of the heterogeneous reaction were determined. It is shown that the speed and density of the formation of a glassy matrix can be adjusted by fine-tuning the ratio of components in the initial powder.

Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

The three complexes [M(Me2dpb)Cl] (M = Ni, Pd, Pt) containing the tridentate N,C,N-cyclometalating 3,5-dimethyl-1,5-dipyridyl-phenide ligand (Me2dpb−) were synthesised using a base-assisted C‒H activation method. Oxidation potentials from cyclic voltammetry increased along the series Pt < Ni < Pd from 0.15 to 0.74 V. DFT calculations confirmed the essentially ligand-centred π*-type character of the lowest unoccupied molecular orbital (LUMO) for all three complexes in agreement with the invariant reduction processes. For the highest occupied molecular orbitals (HOMO), contributions from metal dyz, phenyl C4, C2, C1, and C6, and Cl pz orbitals were found. As expected, the dz2 (HOMO-1 for Ni) is stabilised for the Pd and Pt derivatives, while the antibonding dx2−y2 orbital is de-stabilised for Pt and Pd compared with Ni. The long-wavelength UV-vis absorption band energies increase along the series Ni < Pt < Pd. The lowest-energy TD-DFT-calculated state for the Ni complex has a pronounced dz2-type contribution to the overall metal-to-ligand charge transfer (MLCT) character. For Pt and Pd, the dz2 orbital is energetically not available and a strongly mixed Cl-to-π*/phenyl-to-π*/M(dyz)-to-π* (XLCT/ILCT/MLCT) character is found. The complex [Pd(Me2dpb)Cl] showed a structured emission band in a frozen glassy matrix at 77 K, peaking at 468 nm with a quantum yield of almost unity as observed for the previously reported Pt derivative. No emission was observed from the Ni complex at 77 or 298 K. The TD-DFT-calculated states using the TPSSh functional were in excellent agreement with the observed absorption energies and also clearly assessed the nature of the so-called “dark”, i.e., d‒d*, excited configurations to lie low for the Ni complex (≥3.18 eV), promoting rapid radiationless relaxation. For the Pd(II) and Pt(II) derivatives, the “dark” states are markedly higher in energy with ≥4.41 eV (Pd) and ≥4.86 eV (Pt), which is in perfect agreement with the similar photophysical behaviour of the two complexes at low temperatures.