National Institute Of Materials Physics - Romania

The present study brings developments in the area of tissue engineering of heart valves, with the design and application of a new 2D model for human heart valve. This model contains valvular interstitial cells (VIC) encapsulated in gold covered electrospun polycaprolactone (PCL/Au) fibers, the latter serving also as an electrochemical sensor that enables the monitoring of oxygen levels of cellular media. The biocompatibility of PCL and PCL/Au with VIC was evaluated after the encapsulation of VIC in both scaffolds using the lactate dehydrogenase assay. Fluorescence microscopy of the encapsulated cells was used for the investigation of cell morphology, by employing phalloidin labelled F-actin (red) and DAPI nuclear staining (blue). The electrochemical techniques allowed to investigate the effect of cell encapsulation within the PCL/Au 2D constructs and to quantify the dissolved oxygen levels in cell culture media at both PCL/Au and PCL/Au with encapsulated cells (PCL/ Au/cells). Experiments were performed in a hypoxistation, which allowed a fine control on the cellular media oxygenation. Electrochemical impedance spectroscopy (EIS) was used to evaluate the electrochemical behavior of the 2D constructs, PCL/Au and PCL/Au/cells, in cellular media at different O-2 concentration. Results were analyzed and both impedance values at a fixed frequency and values of the equivalent circuit elements were used to construct calibration curves for dissolved O-2 determination. The second electrochemical technique used to monitor the levels of O-2 at PCL/Au and PCL/Au/cells in the cellular media was square wave voltammetry with sensitivities of 1.5 and 2.5 mu A cm(-2) mu M-1, for PCL/Au and PCL/Au/cells, respectively.

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

A nanostructured samarium oxide electrode was constructed by electrodeposition onto the surface of a gold electrode on SiO2/Si wafer. The samarium oxides electrode's surface morphology was investigated by scanning electron microcopy showing a quasi-monodispersed nanoplatelets like structure. X-rays diffraction analysis demonstrated a mixture of monoclinic and hexagonal phases while the X-rays photoelectron spectroscopy indicated the co-existence of both Sm2+ and Sm3+ species in a 1:3 proportion. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the charge transfer processes at the surface of the samarium oxide electrode in the absence and in the presence of redox probes. A roughness factor of 2.5 was determined from the samarium oxide electrode while the charge transfer constant was almost double when compared to the planar gold electrode. Then, the samarium oxide electrode was used for the H2O2 detection by fixed potential amperometry at -0.20 V (vs. Ag/AgCl) with a linear region between 0.01 and 1.00 mM, a sensitivity of 153 mu A cm(-2) mM(-1) and a LoD = 2.70 mu M. Glucose oxidase was used as a model enzyme in order to test the capacity of the samarium oxides electrode for biosensing. The enzyme was immobilized by physical adsorption and the optimum conditions for glucose analysis investigated. The biosensor showed a linear range for glucose detection between 0.10 and 1.20 mM with a sensitivity of 8.40 mu A cm(-2) mM(-1) and a LoD = 8.00 mu M. Selectivity was tested toward common interfering species, and the results revealed the lack of biosensor response. The glucose biosensor on samarium oxides was tested for glucose detection in serum samples with a recovery factor of 90%, and the result validated with a commercial glucometer. (C) 2021 Elsevier Ltd. All rights reserved.

The reactions between [CuX(PPh3)](4) or [CuX(PPh3)(3)], X = Cl or Br, and N-benzoyl-N'-(4-methoxyphenyl)thio-urea (BTU-OMe), N-benzoyl-N'-(4-methylphenyl)thiourea (BTU-Me) in toluene gave new four-coordinated tetrahedral copper(I) complexes of two types: [CuX(BTU)(PPh3)(2)] (1, 2) and [CuX(BTU)(2)(PPh3)] (3,4) [BTU = N-benzoyl-N'-(4-methoxy/methyl phenyl)thiourea derivatives, X = Cl (a) and Br (b)]. These complexes were fully characterized by several analytical and spectroscopic (IR, UV/VIS, H-1, C-13 and P-31 NMR) techniques. The molecular structure of a representative complex, [Cu(BTU-OMe)(PPh3)(2)Cl] (3a), was determined by the single crystal X-ray diffraction method which reveals a distorted tetrahedral geometry where the Cu(I) ion is surrounded by one BTU ligand molecule, two PPh3 groups and one chloride anion. These eight heteroleptic complexes were found to emit in solid state with lifetimes in the 12-99 mu s range and with the highest quantum yield of 4.0% for 3b. The reaction between [CuBr(PPh3)](4) and N-benzoyl-N',N'-(di-n-butyl)thiourea (BTU-Bu-2) ligand gave the simple [CuBr(BTU-Bu-2)(3)] complex (5), when the PPh3 molecules were completely removed by the BTU derivative. The spectroscopic data indicated a distorted tetrahedral geometry produced by three BTU ligand molecules and one bromide anion. Complex 5 has the highest quantum yield (11%) with the lifetime of 29 mu s in solid-state.

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.

To enhance the spectral response of solar cells, an experimental study on LaPO4:0.01Ce(3+)/xNd(3+) (x = 0, 2, 4 mol%) was carried out, where structural and morphological properties of the prepared samples were well characterized by the means of X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electronic microscope. Additionally, the photoluminescence behavior of phosphors in ultraviolet-visible (UV-VIS) and Near-infrared (NIR) regions were investigated to confirm the energy transfer (ET) from Ce3+ to Nd3+. Moreover, the quantum efficiency of Ce3+/Nd3+-co-doped samples was estimated as high as similar to 172% and the possible ET process was described. Accordingly, the LaPO4:Ce3+/Nd3+ phosphors can convert the UV light (275 nm) into NIR photons (approx. 1059 nm) through the possible two-pathway energy transfer processes from Ce3+ sensitizer ions to Nd3+ activators. Obtained NIR down-conversion emissions are suitable for improving the conversion efficiency of c-Si solar cells.

We describe herein synthesis of novel hydroxy-bis-2,5-disubstituted-1,3,4-oxadiazoles and their ability to emit green light, through ESIPT mechanism. Unlike previous reports, our compounds exhibit very good quantum yields, most likely avoiding the presumed intramolecular fluorescence quenching in presence of the second oxadiazole moiety. Studies regarding behaviour of the compounds in polar and non-polar solvents are also described, indicating the possibility to modulate the emission according to the environment. The solid-state structural analysis, corroborated with fluorescence data, suggest the importance of the tert-butyl group in preservation of the luminescent properties. The corresponding benzyl-protected compounds, precursors to the target hydroxy-bis-2,5-disubstituted-1,3,4-oxadiazoles were also investigated for their optical properties and found to display very intense blue emission, with quantum yields values in dichloromethane (between 0.423 and 0.499) almost equal to the standard quinine sulfate.

In this study curcumin was immobilized in a silica matrix to overcome its poor aqueous solubility and rapid degradation profile. Two kinds of sol-gel powders based on colloidal silica were synthesized and characterized, one prepared with an ethanolic solution of curcumin and the other using cethyltrimethylammonium bromide (CTAB) to solubilize the dye. The successful integration of curcumin in the matrix as well as the interaction with the components of the composite powders was validated by different analysis methods (DSC, FTIR). The samples morphology was evaluated by SEM. UV-Vis and fluorescence studies showed that curcumin was stable, in its enol configuration in both matrices. The sensitivity to ammonia was proved by exposing the powders to NH3 vapors in a sealed vessel. Color changes were measured with a colorimeter. UV-Vis spectra showed that the enol form of the dye in EtOH/CTAB based SiO2 matrices was energetically stable under NH3 atmosphere, even after being kept a few days at low temperature. A fluorescence quenching of both samples was noticed due to interaction curcumin-ammonia. Both samples have antimicrobial properties, the CTAB containing one being more efficient. The EtOH/CTAB based SiO2 powders may represent a novel signaling and antimicrobial system, useful for food or pharmaceutical applications. [GRAPHICS] .

The performances of 3.5 at.% Nd:LGSB bifunctional laser and nonlinear optical (NLO) crystal were investigated. A high-quality single crystal with incongruent melting, having dimensions of about 12 mm in diameter and 35 mm in length, was grown along the c-axis by the Czochralski technique. The phase-matching curve for type I second harmonic generation (SHG) was determined. Efficient laser emission at 1062 nm, along the phase-matching direction for SHG of 1062 nm radiation, was obtained under the pump at 807 nm with a fiber-coupled laser diode. The Nd:LGSB laser operated with a high slope efficiency of eta(sa) = 0.56 (with respect to the absorbed pump power), delivering the highest output power of 2.1 W for 4.04 W of absorbed pump power. Preliminary SFD experiments resulted in achieving a maximum green output power of 48 mW at 3.94 W absorbed pump power.

Microporous graphitic carbons obtained by pyrolysis of a-cyclodextrin have been conveniently doped with N and P elements by performing the thermal graphitization adding urea or phosphoric acid as source of these elements. Electron microscopy shows that doping does not influence the structure and dimensions of the micropores, while XPS reveals the distribution of these dopant elements in two main families corresponding to pyridinic and pryrrolic N atoms and to triphenylphosphine and triphenylphosphine oxide for P doping. Thermo-programmed desorption of H2, CO2 and NH3 indicates that the presence of dopant element is responsible for chemisorption of these gases and introduces basic and acid sites. These desorption measurements agree with the catalytic performance of the series of carbons for the chemo and stereo selective hydrogenation of internal aliphatic and aromatic alkynes to cis configured alkenes. N/P doped microporous carbons were found to be stable under the reaction conditions, according to the constant TOF values and XRD and XPS characterization of the materials after their use as catalysts. In addition microporosity appears to play a positive effect by comparing the activity of microporous carbons with the performance of analogous N/P-doped graphenes. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).