Publications

Although the DPPH (2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) radical is known for its indefinite stability, both in solid and in solution, and therefore no dimerization reaction occurs, the DPPH-dimer has been obtained by an alternative synthesis. Oxidation of the DPPH-dimer led to the corresponding DPPH-diradical, practically exhibiting all of the known properties of the simple DPPH radical. The structures were confirmed using 1H and 13C NMR, IR, UV-vis, HR-MS, and electron spin resonance (for the diradical) analyses. Additionally, cyclic voltammetry and superconducting quantum interference device (SQUID) measurements were performed to investigate the electrochemical and magnetic properties of the DPPH-diradical. DFT calculations revealed that the ground state was an open-shell singlet. The diradical character y of the ground state and vertical S-T gap were 0.279 and -5.81 kcal mol-1, respectively.

This study aimed to develop and characterise novel hydrogels based on natural bioactive compounds for topical antimicrobial applications. Four gel systems were formulated using different polymers, namely polyacrylic acid (Carbopol 940, CBP-G), chitosan with high and medium molecular weights (CTH-G and CTM-G), and sodium alginate (ALG-G), incorporating tinctures of Verbena officinalis and Aloysia triphylla, Laurus nobilis essential oil, and a beta-cyclodextrin-clove essential oil complex. All gels displayed a homogeneous macroscopic appearance and maintained stability for over 90 days. Rheological studies demonstrated gel-like behaviour for CBP-G and ALG-G, with well-defined linear viscoelastic regions and distinct yield points, while CTM-G exhibited viscoelastic liquid-like properties. SEM imaging confirmed uniform and continuous matrices, supporting controlled active compound distribution. Thermogravimetric analysis (TG-DTA) revealed a two-step degradation profile for all gels, characterised by high thermal stability up to 230 degrees C and near-total decomposition by 500 degrees C. FTIR spectra confirmed the incorporation of bioactive compounds and products and highlighted varying interaction strengths with polymer matrices, which were stronger in CBP-G and CTH-G. Antimicrobial evaluation demonstrated that chitosan-based gels exhibited the most potent inhibitory and antibiofilm effects (MIC = 2.34 mg/mL) and a cytocompatibility assessment on HaCaT keratinocytes showed enhanced cell viability for chitosan gels and dose-dependent cytotoxicity for alginate formulations at high concentrations. Overall, chitosan-based gels displayed the most favourable combination of stability, antimicrobial activity, and biocompatibility, suggesting their potential for topical pharmaceutical use.

We investigate the energy spectrum and transport properties of a diatomic square lattice model that manifest antichiral characteristics. The emergence of antichiral edge states is primarily governed by the relative sign of the next-nearest-neighbor hopping parameters on the two sublattices. However, in finite systems, the atomic structure at the boundaries plays a crucial role in determining whether the system exhibits chiral/antichiral behavior. Using both analytical and numerical methods, we reveal the presence of antichiral edge states in ribbon geometries and emphasize the importance of atomic connectivity at the edges. Extending our analysis, we simulate various finite size geometries to identify which configuration supports antichiral behavior. The transport properties are studied in the Landauer-B & uuml;ttiker approach for a Hall device with four leads. We study the transmittance coefficients, transverse (Hall), and longitudinal resistance by comparing the antichiral versus chiral situations. In particular, the antichiral case shows a vanishing Hall effect and negative longitudinal resistance. The presence of the bulk currents is proved by calculating explicitly the currents on the plaquette and the local density of states in the system with leads. Additionally, we investigate the influence of Anderson disorder on the transmittance coefficients to highlight the reduced robustness of antichiral systems.

This study describes the development of a pyruvate kinase (PyK)-biosensor for the evaluation of PyK activity, as a diagnostic tool for early cancer screening and detection of kinase inhibitors used in cancer treatment, with the evaluation of the inhibition mechanism. The biosensor was constructed by co-immobilizing the enzymes PyK and pyruvate oxidase (PyOx) on Au film electrodes by crosslinking with glutaraldehyde (GA) and evaluated electrochemically by cyclic voltammetry (CV) and fixed potential amperometry (CA). First, the experimental conditions were optimized in terms of applied potential, enzyme ratio PyK:PyOx and enzyme substrate concentration: phosphoenolpyruvate (PEP) and adenosine diphosphate (ADP). The biosensor sensitivity towards PEP detection was 2.11 +/- 0.08 mu A mM- 1 cm- 2, with very high reproducibility and repeatability, which made it suitable for inhibition studies of PyK inhibitor. The inhibition mechanism of shikonin was determined in relation to both PEP and ADP, with the calculation of IC50 values and binding constants (Ki). Detection of shikonin was possible at very low concentrations in the linear range of 0.1-4.0 pM. The electrochemical results were validated by UV-Vis spectrophotometry. The developed biosensor is a valuable tool for drug screening by enabling enzyme catalytic function examination with applicability to identify inhibitors, estimate their affinity, inhibition mechanism linked to their molecular mechanisms of action and evaluate selectivity, of great interest in both pharmaceutical and medical domains.

The present paper concerns a formalism aimed to describe the behavior and trajectories of complex scalar waves with space-varying amplitude in media characterized by variable refractive index. The classical wave equation is transformed into an eikonal-type equation, without imposing the geometrical optics limit, satisfied by an effective refractive index. The effective index combines the refractive properties of the medium with self-refraction phenomena generated by the space dependence of the wave amplitude. It also induces wave packet dispersion, leading to relations between the group and phase velocities that are particularly relevant in the context of de Broglie waves. The equations of motion are provided, and it is shown that the self-refraction term bends the trajectory of the wave and changes its velocity. The dynamics is dictated by the curvature of the trajectory expressed in terms of the gradient of the effective refractive index. The uncovered findings point toward a possible generalization of geometrical optics with relevant implications for its relation to quantum mechanics, general relativity and transformation optics.

Integrating two-dimensional transition-metal dichalcogenides with graphene is attractive for low-power memory and neuromorphic hardware, yet sequential wet transfer leaves polymer residues and high contact resistance. We demonstrate a complementary metal-oxide-semiconductor (CMOS)-compatible, transfer-free route in which an atomically thin amorphous MoS2 precursor is RF-sputtered directly onto chemical vapor-deposited few-layer graphene and crystallized by confined-space sulfurization at 800 degrees C. Grazing-incidence X-ray reflectivity, Raman spectroscopy, and X-ray photoelectron spectroscopy confirm the formation of residue-free, three-to-four-layer 2H-MoS2 (roughness: 0.8-0.9 nm) over 1.5 cm x 2 cm coupons. Lateral MoS2/graphene devices exhibit reproducible non-volatile resistive switching with a set transition (SET) near +6 V and an analogue ON/OFF approximate to 2.1, attributable to vacancy-induced Schottky-barrier modulation. The single-furnace magnetron sputtering + sulfurization sequence avoids toxic H2S, polymer transfer steps, and high-resistance contacts, offering a cost-effective pathway toward wafer-scale 2D memristors compatible with back-end CMOS temperatures.

Pnictogen chalcohalide semiconductors are emerging materials with broad potential in energy-related applications, including solar cells, photocatalysis, photodetectors, batteries, supercapacitors, thermoelectric and piezoelectric generators. Their compositional flexibility allows fine tuning of structural and optoelectronic properties. In this study, microcrystalline powders of Sb1-xBixSeI (x = 0-1) were synthesized from binary precursors by a solid-state method in evacuated quartz ampoules. Energy dispersive spectroscopy confirmed the successful substitution of Sb with Bi in Sb1-xBixSeI. The formation of solid solutions was also supported by Raman spectroscopy and X-ray diffraction (XRD). All materials exhibited needle-shaped crystal morphologies and orthorhombic crystal structure (Pnma), regardless of the Bi/Sb ratio. XRD patterns shifted toward smaller angles with increasing Bi content, indicating lattice expansion. Calculated lattice parameters (b and c) increased linearly with Bi incorporation, while the lattice parameter (a) remained constant. Raman spectra exhibited characteristic peaks at 182 cm- 1 for Bi-Se vibration and 209 cm- 1 for Sb-Se vibration, with intensity ratios reflecting Bi content. UV-Vis-NIR diffuse reflectance spectroscopy revealed a direct band gap that decreased from 1.7 eV (SbSeI) to 1.29 eV (BiSeI). Room-temperature photoluminescence measurements exhibited a single emission band, shifting from 1.75 eV to 1.41 eV with increasing Bi content. Ultraviolet photoelectron spectroscopy indicated a shift in the valence band maximum from 0.44 eV (SbSeI) to 1.1 eV (BiSeI). These findings highlight the tunability of Sb1-xBixSeI compounds, offering pathways for optimizing their properties for specific optoelectronic applications.

This study explores the optimization of multi-walled carbon nanotube (MWCNT) concentration in nylon-based nanocomposites to enhance the performance of triboelectric nanogenerators (TENGs). Nylon/MWCNT nanocomposite films were fabricated using the spin-coating method, and their electrical output was systematically evaluated as a function of MWCNT concentration. Results show that the open-circuit voltage (Voc) and short-circuit current (Isc) increase with MWCNT loading up to 0.05 wt%, reaching a peak of 29.7 V and 3.0 mu A, respectively, compared to 17.5 V and 1.8 mu A for pristine nylon-based TENGs. However, a decline in output was observed at 0.1 wt% due to MWCNT agglomeration, which disrupts charge transfer and introduces charge leakage. The enhancement at optimal concentration is attributed to improved charge trapping and increased dielectric constant, while excessive CNT loading reduces the effective contact area and limits triboelectric charge generation. These findings underscore the crucial role of nanomaterial dispersion in optimizing TENG performance and offer valuable insights for the development of high-efficiency triboelectric energy harvesting systems.

A facile and versatile strategy to obtain NPs@ZnAlO nanocomposite materials, comprising controlled-size nanoparticles (NPs) within a ZnAlO matrix is reported. The mono-(Au, Ni) and bimetallic (Ni-Au) NPs serving as an active phase were prepared by the polyol-alkaline method, while the ZnAlO support was obtained via the thermal decomposition of its corresponding layered double hydroxide (LDH) precursors. X-ray diffraction (XRD) patterns confirmed the successful fabrication of the nanocomposites, including the synthesis of the metallic NPs, the formation of LDH-like structure, and the subsequent transformation to ZnO phase upon LDH calcination. The obtained nanostructures confirmed the nanoplate-like morphology inherited from the original LDH precursors, which tended to aggregate after the addition of gold NPs. According to the UV-Vis spectroscopy, loading NPs onto the ZnAlO support enhanced the light absorption and reduced the band gap energy. ATR-DRIFT spectroscopy, H2-TPR measurements, and XPS analysis provided information about the functional groups, surface composition, and reducibility of the materials. The catalytic performance of the developed nanostructures was evaluated by the photodegradation of bisphenol A (BPA), under simulated solar irradiation. The conversion of BPA over the bimetallic Ni-Au@ZnAlO reached up to 95% after 180 min of irradiation, exceeding the monometallic Ni@ZnAlO and Au@ZnAlO catalysts. Its enhanced activity was correlated with good dispersion of the bimetals, narrower band gap, and efficient charge carrier separation of the photo-induced e-/h+ pairs.

This study investigates the influence of different aromatic side groups on the 2D-benzodithiophene (BDT) unit in donor-acceptor conjugated polymers for organic solar cell (OSC) applications. Three new polymers, P1, P2, and P3, featuring phenyl, thienyl, and thienothienyl side chains on the 2D-BDT backbone, respectively, were synthesized using the Stille cross-coupling reaction. The benzotriazole (BTz) unit served as the electron acceptor with a selenophene it-bridge to enhance electronic interactions. The optical band gaps were determined to be 1.79 eV, 1.74 eV, and 1.73 eV for P1, P2, and P3, respectively. OSCs fabricated using these polymers and PC71BM as the acceptor showed the best performance for the thienyl-substituted polymer (P2), achieving a PCE of 4.34 % with a JSC of 10.08 mA/cm2, an VOC of 0.67 V, and a FF of 64 %. Compared to P1 and P3, the P2-based blend exhibited a more defined interpenetrating network with PC71BM, enhancing charge transport and promoting exciton dissociation due to its thinner active layer and optimized morphology. These findings highlight the importance of side-chain engineering in improving the optoelectronic properties, morphology, and photovoltaic performance of OSCs. This study highlights the critical role of side-chain engineering in tuning the optoelectronic properties, morphology, and performance of OSCs. The findings emphasize that thienyl side chains in P2 facilitate better it-it stacking and molecular organization, resulting in superior device performance compared to phenyl and thienothienyl-substituted counterparts.