National Institute Of Materials Physics - Romania

Publications

5675 articles found

221. On the electrochemical oxidation of methionine residues of proteins

Authors: Bunea, MC; Oprescu, C; Enache, TA

Published: FEB 15 2023, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 931, 117209, DOI: 10.1016/j.jelechem.2023.117209

The oxidation of methionine side chain residues in proteins provides a great diversity of possible oxidation mechanisms dictated, among others, by the oxidizing species, solvent properties, and protein structure. The oxidation behavior of a series of short acetylated synthetic peptides, Ac-GMG, Ac-GGMGG and Ac-GGGMGGG, was investigated by differential pulse and square wave voltammetry, in a wide pH range, at glassy carbon electrode. It was found that always the first oxidation step represents the one-electron oxidation of thioether moiety with the formation of a radical cation. Following this, depending on the experimental condi-tions and side chain position of methionine, the radical is stabilized by the nucleophilic attack of water or by catalytic support of the neighboring carbonyl and amide groups in an intermediate structure, finally converted in methionine sulfoxide which can be further oxidized, at more positive potential, into methionine sulfone. For Ac-GGGMGGG, at pH 8.0, the amino and amide groups are active involved in the oxidation process and the electrode reaction takes place with proton transfer

222. The influence of the synthesis method on Gd2O3 morpho-structural properties and sensitivity to CO2 under in-field conditions

Authors: Simion, CE; Vlaicu, ID; Iacoban, AC; Mihalcea, CG; Ghica, C; Stanoiu, A

Published: FEB 15 2023, MATERIALS CHEMISTRY AND PHYSICS, 296, 127354, DOI: 10.1016/j.matchemphys.2023.127354

In this study, we report the implications of the synthesis method on Gd2O3 sensitivity to CO2. The rare-earth oxide was prepared by wet chemical co-precipitation and by hydrothermal method. The obtained powders labelled Gd2O3-CoP and Gd2O3-HT were deposited as thick films over commercial Al2O3 substrates provided with Pt electrodes and a back-side heater. Both powders consist of the same crystallographic phase, with a significant difference appearing in selected area electron diffraction patterns, transmission electron microscopy images at higher magnification and X-ray diffraction spectra, with respect to the crystallization degree. The associated role in sensing properties is revealed via electrical resistance variations determined by CO2 concen-trations in the range between 400 and 3000 ppm and variable relative humidity between 0 and 50%RH, similar to the in-field atmosphere. The proposed CO2 interaction mechanism is based on phenomenological in-vestigations which highlight the electronic affinity variation as the effect of dipoles induced by the in-field conditions on the Gd2O3 surface.

223. Hydrogen Production Mechanism in Low-Temperature Methanol Decomposition Catalyzed by Ni3Sn4 Intermetallic Compound: A Combined Operando and Density Functional Theory Investigation

Authors: Mauri, S; D'Olimpio, G; Ghica, C; Braglia, L; Kuo, CN; Istrate, MC; Lue, CS; Ottaviano, L; Klimczuk, T; Boukhvalov, DW; Politano, A; Torelli, P

Published: FEB 9 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 14, DOI: 10.1021/acs.jpclett.2c03471

Hydrogen production from methanol decomposition to syngas (H2 + CO) is a promising alternative route for clean energy transition. One major challenge is related to the quest for stable, cost-effective, and selective catalysts operating below 400 degrees C. We illustrate an investigation of the surface reactivity of a Ni3Sn4 catalyst working at 250 degrees C, by combining density functional theory, operando X-ray absorption spectroscopy, and high-resolution transmission electron microscopy. We discovered that the catalytic reaction is driven by surface tin-oxide phases, which protects the underlying Ni atoms from irreversible chemical modifications, increasing the catalyst durability. Moreover, we found that Sn content plays a key role in enhancing the H2 selectivity, with respect to secondary products such as CO2. These findings open new perspectives for the engineering of scalable and low-cost catalysts for hydrogen production.

224. Up-conversion emission in transition metal and lanthanide co-doped systems: dimer sensitization revisited

Authors: Avram, D; Colbea, C; Patrascu, AA; Istrate, MC; Teodorescu, V; Tiseanu, C

Published: FEB 7 2023, SCIENTIFIC REPORTS, 13, 2165, DOI: 10.1038/s41598-023-28583-3

Lanthanide (Ln) co-doped transition metal (TM) upconversion (UC) co-doped systems are being intensively investigated for their exciting applications in photonics, bioimaging, and luminescence thermometry. The presence of TM, such as Mo6 + /W6 +, Mn2 +, or Fe3 + determines significant changes in Ln UC emission, such as intensity enhancement, colour modulation, and even the alteration of the photon order. The current mechanism assumes a ground-state absorption/excited-state absorption (ESA/GSA) in TM-Yb dimer followed by direct energy transfer to Er/Tm excited states. We revisit this mechanism by addressing two issues that remain ignored: a dynamical approach to the investigation of the upconversion mechanism and the intrinsic chemical complexity of co-doped TM, Ln systems. To this aim, we employ a pulsed, excitation variable laser across a complete set of UC measurements, such as the emission and excitation spectra and emission decays and analyze multiple grains with transmission electron microscopy (TEM). In the Mo co-doped garnet, the results sustain the co-existence of Mo-free garnet and Mo oxide impurity. In this Mo oxide, the Er upconversion emission properties are fully explained by a relatively efficient sequential Yb to Er upconversion process, with no contribution from Yb-Mo dimer sensitization.

225. Temperature dependent magnetic properties of Ni_xCo_1-xFe₂O₄: Single- and multidomain particles

Authors: Msomi, JZ; Nhlapo, TA; Stanciu, A; Greculeasa, S; Kuncser, V; Moyo, T

Published: FEB 1 2023, PHYSICA B-CONDENSED MATTER, 650, 414595, DOI: 10.1016/j.physb.2022.414595

In the present work, nanocrystalline NixCo1-xFe2O4 oxides with average crystallite size between 11 nm and 111 nm have been analyzed by Mossbauer spectroscopy, hysteresis loops, field cooled (FC) and zero field cooled (ZFC) magnetization measurements. A core-shell model has been proposed. Accordingly, the Mossbauer spectra evidence a ferrimagnetic core and a disordered shell (spin-glass), the latter increasing with Ni concentration. Hysteresis curves reveal the ferromagnetic nature of the investigated compounds and transformation from single- to multi-domain behaviour at a critical particle size dependent on Ni2+ ion concentration. The magnetic properties of finest powders (average crystallite size similar to 11 nm) are the most sensitive to the Ni2+ ions content. A general increase in the coercive field, H-C, with reducing temperature according to the modified Kneller's formula H-c(T) = H-c(0)[1-(T/T-B)(beta) where beta = 0.45 occurs. A high saturation magnetization of about 90 emu/g and an increase in H-C from about 0.3 kOe at 300 K to 7 kOe at 10 K have been observed for the sample Ni0.1Co0.9Fe2O4 (x = 0.1). Increasing magnetization and coercive field with reducing temperature are also explained within the core shell model. FC and ZFC data show strong dependence of the magnetic properties on crystallite size and concentration of Ni2+ ions.

226. Temperature dependent magnetic properties of NixCo1-xFe2O4: Single- and multidomain particles

Authors: Msomi, JZ; Nhlapo, TA; Stanciu, A; Greculeasa, S; Kuncser, V; Moyo, T

Published: FEB 1 2023, PHYSICA B-CONDENSED MATTER, 650, 414595, DOI: 10.1016/j.physb.2022.414595

227. Effects of mechanochemical activation on the structural, magnetic and optical properties of yttrium iron garnet-graphene nanoparticles

Authors: Glasser, S; Tolea, F; Craig, AJ; Sofronie, M; Aitken, JA; Sorescu, M

Published: FEB 1 2023, PHYSICA B-CONDENSED MATTER, 650, 414501, DOI: 10.1016/j.physb.2022.414501

Yttrium iron garnet nanoparticles were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h, with and without graphene nanoparticles. The samples were subsequently characterized by Mo center dot ssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflec-tance spectroscopy. Examination of the quadrupole doublet's abundance as function of ball milling time indi-cated that graphene slowed down the precipitation of the yttrium iron perovskite (yttrium orthoferrite) phase. The increased linewidth of the doublet showed that the carbon from graphene preferentially entered the lattice of the yttrium orthoferrite. The saturation magnetization decreased with decreasing particle size for prolonged milling due to the occurrence of the antiferromagnetic hematite phase. The enhanced absorption in the infrared region could be associated with the incorporation of carbon from graphene in the lattice of the yttrium ortho-ferrite. The results are interesting for sensing and microwave applications.

228. Synthetic peptide array on gold for the electrochemical assessment of the 20S proteasome activity and effect of inhibitory compounds

Authors: Barsan, MM; Serban, A; Onea, M; Wysocka, M; Lesner, A; Diculescu, VC

Published: FEB 1 2023, APPLIED SURFACE SCIENCE, 610, 155620, DOI: 10.1016/j.apsusc.2022.155620

A sensor for the enzymatic activity and inhibition of the 20S proteasome was developed by immobilizing the synthetic peptide ABZ-VVSYAMG-(O2Oc)2-OH at Au electrodes. The detection principle is based on the elec-troactivity of ABZ, part of the ABZ-VVSY-OH moiety released from the peptide upon 20S proteasome chymo-trypsin action. The peptide was immobilized on a para-amino thiophenol (PATP) self-assembled monolayer on Au electrode by cross-linking its amino group to the -(O2Oc)2-OH moiety of the peptide (Au/PATP/peptide). The immobilization of the peptide and its interaction with 20S proteasome was investigated by SEM, QCM, SPR, ATR-FTIR and electrochemistry. The activity of 20S proteasome was assessed electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) after the immersion Au/PATP/peptide in 20S proteasome solution. CV study showed a decrease in both capacitive and faradaic currents corresponding to the ABZ-VVSY-OH removal, allowing the quantification of the 20S proteasome activity. The EIS study revealed that the resis-tance corresponding to charge transfer reactions at the peptide/solution interface correlated to the ABZ redox reaction, decreased linearly with increasing the incubation time in 20S proteasome solution. The perfected assay was applied for the investigation of the inhibitory effect of one synthetic, bortezomib, and two naturally occurring, epoxomicin, and lactacystin inhibitors.

229. Multi-Parametric Exploration of a Selection of Piezoceramic Materials for Bone Graft Substitute Applications

Authors: Nedelcu, L; Ferreira, JMF; Popa, AC; Amarande, L; Nan, B; Balescu, LM; Geambasu, CD; Cioangher, MC; Leonat, L; Grigoroscuta, M; Cristea, D; Stroescu, H; Ciocoiu, RC; Stan, GE

Published: FEB 2023, MATERIALS, 16, 901, DOI: 10.3390/ma16030901

This work was devoted to the first multi-parametric unitary comparative analysis of a selection of sintered piezoceramic materials synthesised by solid-state reactions, aiming to delineate the most promising biocompatible piezoelectric material, to be further implemented into macro-porous ceramic scaffolds fabricated by 3D printing technologies. The piezoceramics under scrutiny were: KNbO3, LiNbO3, LiTaO3, BaTiO3, Zr-doped BaTiO3, and the (Ba0.85Ca0.15)(Ti0.9Zr0.1)O-3 solid solution (BCTZ). The XRD analysis revealed the high crystallinity of all sintered ceramics, while the best densification was achieved for the BaTiO3-based materials via conventional sintering. Conjunctively, BCTZ yielded the best combination of functional properties-piezoelectric response (in terms of longitudinal piezoelectric constant and planar electromechanical coupling factor) and mechanical and in vitro osteoblast cell compatibility. The selected piezoceramic was further used as a base material for the robocasting fabrication of 3D macro-porous scaffolds (porosity of similar to 50%), which yielded a promising compressive strength of similar to 20 MPa (higher than that of trabecular bone), excellent cell colonization capability, and noteworthy cytocompatibility in osteoblast cell cultures, analogous to the biological control. Thereby, good prospects for the possible development of a new generation of synthetic bone graft substitutes endowed with the piezoelectric effect as a stimulus for the enhancement of osteogenic capacity were settled.

230. Chiral and Catalytic Effects of Site-Specific Molecular Adsorption

Authors: Borca, B; Michnowicz, T; Aguilar-Galindo, F; Petuya, R; Pristl, M; Schendel, V; Pentegov, I; Kraft, U; Klauk, H; Wahl, P; Arnau, A; Schlickum, U

Published: 2023 FEB 17 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, DOI: 10.1021/acs.jpclett.2c03575

The changes of properties and preferential interactions based on subtle energetic differences are important characteristics of organic molecules, particularly for their functionalities in biological systems. Only slightly energetically favored interactions are important for the molecular adsorption and bonding to surfaces, which define their properties for further technological applications. Here, prochiral tetracenothiophene molecules are adsorbed on the Cu(111) surface. The chiral adsorption configurations are determined by Scanning Tunneling Microscopy studies and confirmed by first-principles calculations. Remarkably, the selection of the adsorption sites by chemically different moieties of the molecules is dictated by the arrangement of the atoms in the first and second surface layers. Furthermore, we have investigated the thermal effects on the direct desulfurization reaction that occurs under the catalytic activity of the Cu substrate. This reaction leads to a product that is covalently bound to the surface in chiral configurations.