Improving stability of zinc nanoparticles in chitosan solution with a nanosecond pulsed laser

A green method is presented to fabricate zinc nanoparticles using laser ablation synthesis in a natural polymer solution. The main aims are to reduce the zinc nanoparticles size and to increase their stability by using different ablation times in a chitosan solution as a natural polymer stabilizer. A Nd:YAG pulsed laser (532 nm) of energy 60 mJ/pulse, with a pulse duration of 10 ns was used to ablate a zinc plate immersed in chitosan solution from which the nanoparticles were produced. The average particle sizes as well as the volume fraction of the zinc nanoparticles in the solution were measured at 5, 10, 15, 30 min of ablation time. The results showed that the particle size decreased from 9.43 to 5.04 nm with spherical morphology and its volume fraction increased from 0.24 × 10−7 to 8.5 × 10−7 as the ablation time progressed from 5 to 30 min respectively. As a comparative study, a reasonable decrease was observed in the particle size for chitosan than distilled water. It was also noted that the stability and dispersion of zinc nanoparticles were much higher in the chitosan solution compared to water. In addition, the COSMO (conductor-like screening model) solvation model was used to compare the enthalpies of Zn-NPs in different media. Obtained results confirmed their stability was higher when merged in a natural polymer compared to water

Structural Transition-Induced Raman Enhancement in Bioinspired Diphenylalanine Peptide Nanotubes

Semiconducting materials are increasingly proposed as alternatives to noble metal nanomaterials to enhance Raman scattering. We demonstrate that bioinspired semiconducting diphenylalanine peptide nanotubes annealed through a reported structural transition can support Raman detection of 10-7 M concentrations for a range of molecules including mononucleotides. The enhancement is attributed to the introduction of electronic states below the conduction band that facilitate charge transfer to the analyte molecule. These results show that organic semiconductor-based materials can serve as platforms for enhanced Raman scattering for chemical sensing. As the sensor is metal-free, the enhancement is achieved without the introduction of electromagnetic surface-enhanced Raman spectroscopy.Science Foundation IrelandUCD School of PhysicsSustainable Energy Authority of Ireland (SEAI

Thermally-controlled spherical peptide gel architectures prepared using the pH switch method

Self-assembling nanostructured peptide gels are promising materials for sensing, drug delivery, and energy harvesting. Of particular interest are short diphenylalanine (FF) peptides modified with 9-fluorenylmethyloxycarbonyl (Fmoc), which promotes the association of the peptide building blocks. Fmoc-FF gels generally form fibrous networks and while other structures have been demonstrated, further control of the gelation and resulting ordered three-dimensional structures potentially offers new possibilities in tissue engineering, sensing, and drug release applications. Herein, we report that the structure tunability of Fmoc-FF gels can be achieved by controlling the water content and the temperature. We further explore the incorporation of metal nanoparticles in the formation of the gel to enable optical sensing applications based on hybrid Fmoc-FF-nanoparticle microspheres. Finally, fluorescence lifetime imaging microscopy reveals a correlation between lifetime and reduced bandgap, in support of a semiconductor-induced charge transfer mechanism that might also increase the stability of an excited state of a probe molecule. The observations potentially further widen the use of these peptide materials in bioimaging and sensing applications.Science Foundation IrelandEuropean Commission Horizon 2020Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Saudi ArabiaMinistry of Higher Education of Saudi Arabia under the King Abdullah Scholarship Progra

Experimental and DFT study of GO-decorated CaO quantum dots for catalytic dye degradation and bactericidal potential

This research lays the groundwork for preparing graphene oxide (GO)-doped CaO nanocomposites for efficient antibacterial potential and dye degradation. The study aimed to reduce the recombination rate of the electron hole (e−/h+) of CaO and improve charge transfer. This issue can be minimized by doping high-surface area GO into CaO quantum dots (QDs). Herein, the one-pot co-precipitation technique has prepared various concentrations (1, 3, and 5 wt%) of GO-doped CaO. Characterization techniques were used to investigate optical, elemental analysis, microstructural, functional, and morphological properties. The addition of GO into QDs showed excellent catalytic activity (CA) to control sample CaO against methylene blue (MB) in basic and acidic media compared to the neutral media. The synergistic effect of morphological alternation attributed to an increase in the mechanism of CA upon doping. Various concentrations of GO to QDs promised remarkable bactericidal potency against Escherichia coli

Novel 3-chloro-6-nitro-1H-indazole derivatives as promising antileishmanial candidates: synthesis, biological activity, and molecular modelling studies

An efficient pathway was disclosed for the synthesis of 3-chloro-6-nitro-1H-indazole derivatives by 1,3-dipolar cycloaddition on dipolarophile compounds 2 and 3. Faced the problem of separation of two regioisomers, a click chemistry method has allowed us to obtain regioisomers of triazole-1,4 with good yields from 82 to 90% were employed. Also, the antileishmanial biological potency of the compounds was achieved using an MTT assay that reported compound 13 as a promising growth inhibitor of Leishmania major. Molecular docking demonstrated highly stable binding with the Leishmania trypanothione reductase enzyme and produced a network of hydrophobic and hydrophilic interactions. Molecular dynamics simulations were performed for TryR-13 complex to understand its structural and intermolecular affinity stability in a biological environment. The studied complex remained in good equilibrium with a structure deviation of ∼1–3 Å. MM/GBSA binding free energies illustrated the high stability of TryR-13 complex. The studied compounds are promising leads for structural optimisation to enhance the antileishmanial activity

Probing Optoelectronic and Thermoelectric Properties of Lead-Free Perovskite SnTiO3: HSE06 and Boltzmann Transport Calculations

In order to develop a useful material for the optoelectronic sector with a variety of uses in thermoelectric and optical properties at a reasonable price, we researched SnTiO3, a Pb-free and Sn-based perovskite. We used the most recent density functional theory (DFT) methods, such as the gradient approximation (GGA) approach and the screened hybrid functional (HSE06). The calculated electronic structure yields to an indirect band gap of 2.204 eV along with two different K-points such as (X-Γ) using HSE06. The accomplished optical properties have been examined by dispersion, absorption, reflection, optical conductivity, and loss function against photon energy. The thermoelectric properties and electronic fitness function (EFF) were predicted DFT along with the Boltzmann transport theory. The Seebeck coefficient (S) and related thermoelectric properties such as electronic/thermal conductivity and the Hall coefficient were calculated as a function of chemical potential and carrier density (electrons and holes concentration) for room temperature. It was established that the temperature increases the Seebeck coefficient (S) at every hole carrier concentration. SnTiO3 has good EFF at 300, 500, and 800 K as well. The discovered EFF suggests that this material’s thermoelectric performance rises with temperature and can also be improved through doping. These findings demonstrated the potential of SnTiO3 as an n-type or p-type thermoelectric material depending on the doping

Contribution à l'étude de la formation des images optiques en microscopie champ proche optique: effet de la sonde en deux dimensions

This work consists in the development of a theoretical tool for the purpose to undertake numerical simulations able to take into account the coupling between the probe and the object. The first part, concerns the combination of the differential method and the algorithms T and S, to overcome numerical problems which appear in the cases where the size of system (probe - object) is more realistic. The developed global model is two-dimensional and applied in polarization TE under the normal diffraction condition. We have used the developed model to study the formation of optical image by monomodes and multimodes probes. The obtained optical images at constant height, have allowed us to study the installation of guided modes, and then to study the influence of the apex shape and size. By calculating the transfer functions in the case of monomodes probes we have observed that this function of transfer can exist only in particular cases ( e.g. of size of objects, distance probe-object, incidence angle etc...) and that in general a pseudo-function of transfer remains accessible. To validate our results, we have studied more complicated (structured) probes, possessing a core, a sheath and possibly a metallic coating. With a very good qualitative agreement with experimental results recorded at constant intensity mode, it is interesting to observe that the attacked probe is more efficient than the etched probe. By extending our study to the infrared near-field, the study of spectroscopy map about the detection of an absorbent object embedded in a dielectric layer confirms the former results : the probe modify slightly the spectroscopic signature. This application shows the pertinence of the theoretical model and its large applications in any spectral domain.Ce travail est relatif à la contribution d'un modèle théorique pour représenter un PSTM. L'approche est globale et veut pouvoir prendre en considération des objets de tailles inférieures à la longueur d'onde mis en présence de sondes de tailles réalistes. Le modèle développé est bi-dimensionnel et dans cette thèse son application est limité à la polarisation S (TE) en diffraction normale et à hauteur constante. Nous exposons d'abord les bases du modèle mis en oeuvre qui repose sur la méthode différentielle à laquelle sont combinés des algorithmes matriciels. Pour éviter tout problème numérique lorsque le système sonde-objet a des dimensions réalistes (beaucoup supérieure à la longueur d'onde) nous avons utilisé l'algorithme matriciel S. Après avoir défini les critères à satisfaire strictement pour obtenir des performances sûres nous avons appliqué ce modèle aux différents cas suivant : - Sonde monomodes - Sondes multimodes - Sondes structurées (gaine, coeur et éventuellement revêtement métallique externe sont pris en compte). - Spectroscopie d'un objet absorbant inséré dans un couche diélectrique uniforme en proche IR. Tous nos résultats sont cohérents et ouvrent des voies sûres pour l'interprétation des images puisque nous avons montrés que nos calculs étaient en accord qualitatif correct avec des résultats expérimentaux obtenus antérieurement sur des systèmes tests. Dans tous les cas étudiés nous avons montré que la présence de la sonde, quelle que soit sa nature et sa structure, perturbait la distribution du champ électromagnétique rayonné par l'objet. Ceci nous conduit à définir une nouvelles approche de la fonction de transfert en microscopie de champ proche. L'étude encore limitée aux sondes monomodes, montre que la fonction de transfert n'est pas définie dans le cas général. Ce premier travail ouvre des perspectives intéressantes puisque pour la première fois des sondes de formes réelles (incluant apex et taper) et de grandes tailles (jusqu'à 70µm pour la partie guidante) éventuellement métallisées, ont été prises en compte dans un modèle numérique. Il permet aussi d'aborder de façon nouvelle le problème de la fonction de transfert et des images spectroscopiques, y compris en IR. Il est aussi adaptable à la polarisation P (TM

Magnetic and electronic properties of Neptunium chalcogenides from GGA U SOC and DFT investigations

Pro zkoumání strukturních, elektronických a magnetických vlastností chalcogenidů Neptunia (Np2X5, X = S, Se a Te) byly použity techniky prvo principiálních výpočtů. V literatuře nebyly dříve popsány experimentální nebo teoretické studie jejich fyzikálních vlastností. Přítomnost vysoce lokalizovaných f stavů vyžadovala využití spirálové vazby a přístupu GGA + U, aby bylo správně popsáno spojení f-f. Np2X5 byl nalezen kovový charakter s vysokým magnetickým momentem kvůli přítomnosti Neptunia. Fermi povrchy Np2Te5 vykazovaly větší elektrickou vodivost ve srovnání s Np2Se5 a Np2S5. Bylo zjištěno, že magnetický moment je mezi 13,24 a 13,92 μB, vyvolaný hlavně Npf a d-orbitály, stejně jako spinpolarizace chalcogenů (Te, Se, S) indukovaných Np. Chalkogenidy Neptunia vykazují zajímavé magnetické vlastnosti a měly by být manipulovány s opatrností kvůli jejich radioaktivním vlastnostem.First-principles calculations techniques were employed to explore the structural, electronic and magnetic properties of Neptunium chalcogenides (Np2X5, X = S, Se and Te). No experimental or theoretical studies of their physical properties have been previously reported in the literature. The presence of highly localized f states has requested the employment of the spin orbit coupling and GGA + U approach in order to describe correctly the f–f coupling. Np2X5 was found metallic with high magnetic character due to the Neptunium presence. Fermi surfaces of Np2Te5 have shown a greater electrical conductivity compared to Np2Se5 and Np2S5. The magnetic moment was found to be between 13.24 and 13.92 μB, principally induced by Np f and d-orbitals as well as the spin-polarization of the chalcogenes (Te, Se, S) induced by Np. Neptunium chalcogenides have shown interesting magnetic properties and should be manipulated with precaution due to their radioactive properties