Marcin Jarek

Origin of spontaneous polarization and reconstructive phase transition in guanidinium iodide

Structural determinations as a function of temperature allowed us to model the polar properties of guanidinium iodide, C(NH)2I, in its hexagonal P63mc-symmetric phase. These results have been compared with the experimental data of the pyroelectric measurements. It has been shown that the crystal lattice polarization, arising from the ionic displacements, increases with temperature and abruptly vanishes at the first-order phase transition to the high-temperature phase of monoclinic space group P21/m. Thus, this transition non-typically lowers the crystal symmetry when temperature is increased. Moreover, the polar–non-polar symmetry change, accompanied by the crystal polarization loss, does not occur as a ferroelectric–paraelectric phase transition. This is rather uncommon, but can be rationalized by the reconstructive character of the transition and by the structural hindrances for the polarization reversal in the low-temperature phase. The reconstructive nature of the structural changes and the 3% decrease in the crystal volume can explain a large temperature hysteresis of the transition point, a strong sensitivity to the thermal history of the sample, and the metastable features of the high-temperature phase.

Preparation and characterization of Au/Pd modified-tio 2 photocatalysts for phenol and toluene degradation under visible light—: the effect of calcination temperature

Rutile loaded with Au/Pd nanoparticles was prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane followed by calcination. The effect of calcination temperature (from 350 to 700°C) on the structure of Au/Pd nanoparticles deposited at rutile matrix and the photocatalytic properties of Au/Pd-TiO2 was investigated in two model reactions (toluene degradation in gas phase and phenol degradation in aqueous phase). Toluene was irradiated over Au/Pd-TiO2 using light emitting diodes (LEDs, λmax = 415 nm). The sample 0.5 mol% Pd/TiO2 exhibited the highest activity under visible light irradiation in gas and aqueous phase reaction among all photocatalysts calcined at 350°C, while the sample modified only with gold nanoparticles showed the lowest activity. The Au/Pd-TiO2 sample calcinated at 350°C possesses the highest photocatalytic activity when degrading phenol under visible light, which is 14 times higher than that of the one calcinated at 450°C. It was observed that increasing temperature from 350 to 700°C during calcination step caused segregation of metals and finally resulted in photoactivity drop.

Synthesis and characterization of magnetite/silver/antibiotic nanocomposites for targeted antimicrobial therapy

The article is devoted to preparation and characterization of magnetite/silver/antibiotic nanocomposites for targeted antimicrobial therapy. Magnetite nanopowder was produced by thermochemical technique; silver was deposited on the magnetite nanoparticles in the form of silver clusters. Magnetite/silver nanocomposite was investigated by XRD, SEM, TEM, AFM, XPS, EDX techniques. Adsorptivity of magnetite/silver nanocomposite towards seven antibiotics from five different groups was investigated. It was shown that rifampicin, doxycycline, ceftriaxone, cefotaxime and doxycycline may be attached by physical adsorption to magnetite/silver nanocomposite. Electrostatic surfaces of antibiotics were modeled and possible mechanism of antibiotic attachment is considered in this article. Raman spectra of magnetite, magnetite/silver and magnetite/silver/antibiotic were collected. It was found that it is difficult to detect the bands related to antibiotics in the magnetite/silver/antibiotic nanocomposite spectra due to their overlap by the broad carbon bands of magnetite nanopowder. Magnetic measurements revealed that magnetic saturation of the magnetite/silver/antibiotic nanocomposites decreased on 6-19 % in comparison with initial magnetite nanopowder. Pilot study of antimicrobial properties of the magnetite/silver/antibiotic nanocomposites were performed towards Bacillus pumilus.

Mesoporous drug carrier systems for enhanced delivery rate of poorly water-soluble drug: nimodipine

Two mesoporous silica materials: MCM-41 and SBA-15 were applied as potential nanocarriers for poorly soluble drug—nimodipine. Drug incorporation was performed using modified adsorption from the solution method and loaded samples before and after washing procedure were studied. The physical properties were verified by: differential scanning calorimetry, X-ray powder diffraction, electron microscopies (SEM/TEM) and Fourier-transform infrared spectroscopy (FT-IR). FT-IR results for bulk nimodipine were interpreted on the basis of first principles calculations (DFT). As a result of encapsulation process, in both matrices nimodipine appeared simultaneously in two forms: crystalline and amorphous, but the first one turned out to be easily removable during washing procedure. The in vitro dissolution and release tests were performed with ultra pure water under supersaturating conditions. The release rate of the amorphous nimodipine from mesoporous silica materials was at least 70 times higher than dissolution rate of bulk drug, thus revealed a potential usefulness of such carrier in future pharmaceutical applications in terms of delivery of poorly soluble drugs.

Antimicrobial electrospun poly(ε-caprolactone) scaffolds for gingival fibroblast growth

This study discusses the value of polymer electrospun materials in three-dimensional (3D) scaffolds and antibacterial wound dressings for potential dental applications. Polycaprolactone (PCL) and polyvinylpyrrolidone (PVP) nanofibers were used as bases for gingival fibroblast (HGF-1 cell line) growth. HGF-1 cells cultured on both types of nanofibers were found to have normal morphology and growth by selective staining of the nuclei and cytoskeleton. The nanofibers were synthesized on different collectors to obtain a random or parallel alignment. Cell growth was observed along the nanofibers. In addition, antibiotics were incorporated within the nanofibers and studied by means of Raman spectroscopy and differential scanning calorimetry. The release profile of the antibiotics was determined by broad band dielectric measurements. The drug was found to be released by Fickian diffusion. The WST-1 test found PCL and PCL/ampicillin nanofibers to have minimal cytotoxicity. The antibacterial activity of materials containing ampicillin was evaluated by zone inhibition against a selected oral strain of Streptococcus sanguinis. The bacterial growth was inhibited by antibiotic release from PCL/ampicillin mats.

Green synthesis of rifampicin-loaded copper nanoparticles with enhanced antimicrobial activity

The antimicrobial properties of copper and rifampicin-loaded copper nanoparticles were investigated using four strains: Staphylococcus aureus, Escherichia coli, Bacillus pumilis and Pseudomonas fluorescens. Spherical-shaped copper nanoparticles were synthesized via green reduction method from the peppermint extract. It was found that adsorption of rifampicin on the copper nanosurface enhances its biological activity and prevents the development of resistance. The interactions between rifampicin-copper nanoparticles and bacteria cells were monitored using atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). It was proven that loaded with rifampicin copper nanoparticles were able to damage the S. aureus cell membrane and facilitate the bacteria biofilm matrix disintegration. Moreover, the DNA decomposition of S. aureus treated with copper and rifampicin-copper nanoparticles was confirmed by agarose gel electrophoresis. The results obtained indicate that adsorption of rifampicin on the copper nanoparticles surface might provide the reduction of antibiotic dosage and prevent its adverse side effects.Graphical Abstract

Influence of silver content on rifampicin adsorptivity for magnetite/Ag/rifampicin nanoparticles

Magnetite nanoparticles (NPs) decorated with silver (magnetite/Ag) are intensively investigated due to their application in the biomedical field. We demonstrate that the increase of silver content on the surface of nanoparticles improves the adsorptivity of antibiotic rifampicin as well as antibacterial properties. The use of ginger extract allowed to improve the silver nucleation on the magnetite surface that resulted in an increase of silver content. Physicochemical and functional characterization of magnetite/Ag NPs was performed. Our results show that 5%-10% of silver content in magnetite/Ag NPs is already sufficient for antimicrobial properties against Streptococcus salivarius and Staphylococcus aureus. The rifampicin molecules on the magnetite/Ag NPs surface made the spectrum of antimicrobial activity wider. Cytotoxicity evaluation of the magnetite/Ag/rifampicin NPs showed no harmful action towards normal human fibroblasts, whereas the effect on human embryonic kidney cell viability was time and dose dependent.

Synthesis, structure, EPR studies and up-conversion luminescence of ZnO:Er3+–Yb3+@Gd2O3 nanostructures

ZnO:Er3+–Yb3+@Gd2O3 nanostructures were obtained by “wet” chemistry methods – the sol–gel technique for the preparation of ZnO and ZnO:Er3+–Yb3+ nanoparticles (NPs), and the seed deposition method for obtaining Gd2O3. The crystal structure, morphology, phase and elemental composition, resonant microwave absorption of rare earth ions, point defects in the ZnO:Er3+–Yb3+@Gd2O3 crystal structure and up-conversion luminescence were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, and optical spectroscopy. The crystallization temperature (600 °C) of the Gd2O3 phase on the ZnO surface was found. As-obtained ZnO:Er3+–Yb3+ NPs (with size ∼7 nm) are highly crystalline and monodispersed. ZnO:Er3+–Yb3+ NPs annealing at 900 °C leads to the formation of highly polydispersed ZnO:Er3+–Yb3+ NPs, covered by a Gd2O3 shell. The process of the incorporation of the rare earth ions into the ZnO structure, as well as the effect of Gd2O3 content on the morphology and visible up-conversion (UC) luminescence in ZnO:Er3+–Yb3+ matrices were studied.

In search of the mutual relationship between the structure, solid-state spectroscopy and molecular dynamics in selected calcium channel blockers

Three isostructural 1,4-dihydropyridines (DHPs), namely, nifedipine, nitrendipine and nimodipine were selected to characterize their structure, intermolecular interactions and molecular dynamics. The studied samples were analyzed using powder X-ray diffraction (XRD), neutron (INS) and infrared spectroscopy (FT-IR) as well as solid-state nuclear magnetic resonance (NMR), where each technique was supported by the state-of-the-art theoretical calculations for solid-state. By combining multiple experimental techniques with advanced theoretical calculations we were able to shed light on the mutual relation between the structure, stabilizing intermolecular interactions and their spectral response. For the first time, unambiguous computationally-supported assignment of the most prominent spectral features in DHPs is presented to give a valuable support for polymorph screening and drug control. Molecular motions were interpreted in details, revealing that a dynamic reservoir of each compound is dominated by intra-molecular reorientations of methyl groups and large-amplitude oscillations in terminal chains. Our study successfully validates the realm of applicability of first-principles solid-state calculations in search of the mutual relation between the structure and spectroscopy in this important class of drugs. Such approach gives a first necessary step to gather combined structure-dynamics data on functionalized DHPs, which are of importance to better understand crystallization and binding tendency. The NMR relaxation experiments reveal that nitro groups significantly hinder the reorientation of methyl rotors and provide the first evidence of low-temperature methyl-group tunneling in DHPs, an intriguing quantum-effect which is to be further explored.

Experimental and solid-state computational study of structural and dynamic properties in the equilibrium form of temazepam.

Structural properties and rotational dynamics of methyl groups in the most stable form of temazepam were investigated by means of (13)C CP MAS NMR, quasielastic neutron scattering (QENS), and (1)H NMR spin-lattice relaxation methods. The QENS and (1)H NMR studies reveal the inequivalency of methyl groups, delivering their activation parameters. The structural properties of the system were explored in frame of periodic density functional theory (DFT) computations, giving insight into the reorientational barriers and providing understanding of the solid-state NMR results. The theoretical computations are shedding light on the intermolecular interactions along their relation with particular asymmetric structural units.