National Institute Of Materials Physics - Romania

This paper presents the synthesis, physico-chemical and biological properties of four new coordination compounds with mixed ligands: acrylate ion (acr) and benzimidazole/benzimidazole derivatives with the general formula [Co(L)(2)(acr)(2)]center dot nH(2)O [(1) L: benzimidazole (HBzIm), n: 0.5; (2) L: 2-methylbenzimidazole (2-MeBzIm), n: 0.5; (3) L: 5-methylbenzimidazole (5-MeBzIm), n: 0; (4) L: 5,6-dimethylbenzimidazole (5,6-Me(2)BzIm), n: 0]. Their chemical formulae were achieved correlating the chemical analysis with mass spectrometry data, the ligands coordination modes were assigned by Fourier transform-infrared measurements, and the trigonal bipyramidal geometry of cobalt ion in complexes was assigned by data correlation of UV-Vis-NIR spectra and magnetic moments measurements. Single-crystal X-ray diffraction reveals a mononuclear structure with a pentacoordinated cobalt (II) ion, connected to two acrylato coordinated in different modes and two unidentate 5,6-dimethylbenzimidazole ligands for compound (4). The biological tests were performed against several microbial strains, the cytotoxicity was evaluated on HCT8 cellular lines and the cell cycle analysis was performed on HT29 cellular lines. Microbiological assays indicated that Co (II) complexes present a very good to good activity against Candida albicans 1760, Enterococcus faecium E5, Bacillus subtilis ATCC 6683 and Escherichia coli ATCC 25922. Predictive pharmacokinetic (ADME), toxicity and drug-likeness profiles were evaluated for Co (II) complexes. Our results highlight that Co (II) complexes depicted in the present study are suitable to be used as efficient pharmacological agents.

Nano-size and shape of fluorescent silver nanostructures are important for a wide range of bio-applications, especially as drug delivery systems, imaging and sensing. The aim of the work is to develop a fluorescent silver nano-structured system, synthesized by chemical reduction of aqueous AgNO3 solution by Tryptophan using Dextran 70 as stabilizing agent (SNPs(FL)). The formed fluorescent nano-system was analyzed by UV-Vis absorption, DLS, SEM, TEM, AFM, steady-state and time resolved fluorescence spectroscopy. TEM analysis showed multi-twined nanoparticle, with the size within 15-40 nm. SNPs(FL) shows the fluorescence emission at 346 nm, the fluorescence quantum yield, phi = 0.034 and the integrated fluorescence lifetime, = 1.82 ns. Riboflavin fluorescence behaviour in the RF/SNPs(FL) system, has been also studied. The results have relevance in using SNPs(FL) as a potential marker/emissive system to solve various biological barriers in humans, like drug release and protein structure.

Multi-layered structures, composed of thin films from materials with different compositions or physical properties, represents a way to obtain enhanced properties or even new functionalities. In this work, lead zirconate titanate PbZrxTi1-xO3 (PZT; x = 0.20, 0.52, 0.80) multilayers were grown by pulsed laser deposition (PLD) on a single crystal strontium titanate (SrTiO3, STO) substrate, using a strontium ruthenate (SrRuO3, SRO) film as buffer layer for epitaxial growth, and also as back electrode. Up and down multi-layers were grown and their physical and structural properties were compared, up being the structure in which Zr concentration was varied from 20% near the STO substrate to 80% at the surface, while down is for the structure in which the Zr concentration starts with 80% near the substrate and ends with 20% at the surface. It was found that the electric and pyroelectric properties of the two graded structures are significantly different. The up structure presents electric properties that are comparable with those of single composition PZT films while the properties of the down structure are deteriorated, especially in terms of the leakage current magnitude. Pyroelectric signal could be measured only for the up structure. These differences were attributed to larger density of structural defects in the down structure compared to the up one. This is due to the different growth sequence: Lop structure starts with tetragonal PZT on cubic substrate (lower lattice mismatch, 1.1%) while down structure starts with rhombohedral PZT on cubic substrate (larger lattice mismatch, almost 5%).

The paper deals with a study of composites based on poly(p-phenylenevinylene) (PPV) and reduced graphene oxide (RGO) in terms of photoconductivity and photocurrent (PC) dynamics in charge-discharge cyclic processes. The explanation for the photoconductive behavior is built with the support of DeVore and Onsager theories. Scanning samples in both directions involves charge transport, to and from, available energy states called defect centers. The existence of these centers is confirmed by a decrease in the composite bandgap caused by the RGO localized states which are situated slightly above the first HOMO level in the PPV bandgap. The contribution of RGO to the photoconductive properties of PPV is revealed through a photocurrent value with two orders of magnitude higher than for PPV.

The influence of the Gd3+ co-dopant on the structure, morphology and up-conversion luminescence/magnetic properties of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals was investigated and compared to those of Gd-free samples. Electron microscopy has indicated an inhibiting effect of the agglomeration and collapsing process of the nanocrystals compared to the Gd-free powder samples. The surface analysis of nanocrystals have not shown oxygen-metal bonds related to the metal oxidation within the surface nanometric layer. The paramagnetic properties are related to the magnetic moment of the Gd3+ ions. The up-conversion luminescence of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals is about six times stronger than in LiYF4:Yb3+/Er3+ nanocrystals; the enhancement effect is most probably due to the lattice distortion induced by the Gd co-doping.

Up-conversion luminescence and thermoluminescence properties of LaF3 nanocrystals, with sizes of about 20 nm, were studied and discussed in relation to -size and surface related effects. XPS spectra have evidenced the presence of oxidized Er and La ions within a thin layer (of about 1 nm thickness) at the nanocrystals surface, as well as Yb ions bonded with fluorine ions. The green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion emissions of Er3+ ions are influenced by the relative dominance of Erions that reside within the thin oxidized layer. The broad thermoluminescence curves are assigned to the recombination of trap defects associated with surface states and within the oxidized surface layer. (C) 2019 Elsevier B.V. All rights reserved.

A critical discussion on the presently available models for the relaxation time of magnetic nanoparticles approaching the superparamagnetic regime in the presence of interparticle dipolar interactions is considered. The direct implications of such interactions for magnetic fluid hyperthermia therapy through susceptibility loss mechanisms give rise to an indirect method for their study via specific absorption rate measurements performed on ferrofluids of different volume fractions. The theoretical support for the specific evolution of the relaxation time constant and the anisotropy energy barrier versus the interparticle interactions in a perturbation approach of the simple Neel expression for the relaxation time is provided via static and time-dependent micromagnetic simulations.

The work describes the development of a flexible, hydrogel embedded pH-sensor that can be integrated in inexpensive wearable and non-invasive devices at epidermal level for electrochemical quantification of H+ ions in sweat. Such a device can be useful for swift, real time diagnosis and for monitoring specific conditions. The sensors' working electrodes are flexible poly(methyl methacrylate) electrospun fibers coated with a thin gold layer and electrochemically functionalized with nanostructured palladium/palladium oxide. The response to H+ ions is investigated by cyclic voltammetry and electrochemical impedance spectroscopy while open circuit potential measurements show a sensitivity of aprox. -59 mV per pH unit. The modification of the sensing interface upon basic and acid treatment is characterized by scanning and transmission electron microscopy and the chemical composition by X-ray photoelectron spectroscopy. In order to demonstrate the functionality of the pH-sensor at epidermal level, as a wearable device, the palladium/palladium oxide working electrode and silver/silver chloride reference electrode are embedded within a pad of polyacrylamide hydrogel and measurements in artificial sweat over a broad pH range were performed. Sensitivity up to -28 mV/pH unit, response time below 30 s, temperature dependence of approx. 1 mV/degrees C as well as the minimum volume to which the sensor responses of 250 nanoliters were obtained for this device. The proposed configuration represents a viable alternative making use of low-cost and fast fabrication processes and materials.

Devices developed for the aeronautic or space industries must be able to operate in harsh environments. In order to protect devices such as microstrip antennae, various coatings have to be used. Herein, we present the results of obtaining YSZ/Al2O3 heterostructures by Pulsed Laser Deposition (PLD) for the protection of planar monopole antennas without changing their performances after the deposition process. The theoretical SRIM-TRIM simulation code results on the effects of ionized radiations incident on a YSZ/Al2O3 heterostructure, as well as the physical properties of the YSZ/Al2O3 thin films obtained by the PLD technique are also presented. The SRIM studies show that at the same energy range the proton penetration depth is higher than the alpha penetration depth, giving insights about the penetration depth of proton and alpha particles in the studied targets. Our goal is to obtain a multilayer structure able to enhance the endurance of the antenna and microwave circuitry in harsh space environment without reducing the performances under nominal operation conditions.