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od 2020-09-20 |
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UV cross-linked polyvinylpyrrolidone electrospun fibres as antibacterial surfaces Many bacteria become progressively more resistant to antibiotics and it remains a challenging task to control their overall levels. Polymers combined with active biomolecules come to the forefront for the design of antibacterial materials that can address this encounter. In this work, we investigated the photo-crosslinking approach of UV-sensitive benzophenone molecule (BP) with polyvinylpyrrolidone (PVP) polymer within electrospun fibres. The BP and PVP solutions allowed fabricating polymer mats that were subsequently functionalised with antibacterial lysozyme. The physical properties of the crosslinked electrospun fibres were investigated by scanning electron microscopy and atomic force microscopy. The average diameter of the obtained fibres decreased from 290 ± 50 nm to 270 ± 70 nm upon the addition of the crosslinking molecules and then to 240 ± 80 nm and 180 ± 90 nm after subsequent crosslinking reaction at an increasing time: 3 and 5 h, respectively. The peak force quantitative nanomechanical mapping (PF-QNM) indicated the increase of DMT modulus of obtained cross-linked fibres from 4.1 ± 0.8 GPa to 7.2 ± 0.5 GPa. Furthermore, the successful crosslinking reaction of PVP and BP solution into hydrogels was investigated in terms of examining photo-crosslinking mechanism and was confirmed by rheology, Raman, Fourier transform infrared and nuclear magnetic resonance. Finally, lysozyme was successfully encapsulated within cross-linked PVP-BP hydrogels and these were successfully electrospun into mats which were found to be as effective antibacterial agents as pure lysozyme molecules. The dissolution rate of photo cross-linked PVP mats was observed to increase in comparison to pure PVP electrospun mats which opened a potential route for their use as antibacterial, on-demand, dissolvable coatings for various biomedical applications.
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Science and Technology of Advanced Materials, 20(1), 979-991, (2019) |
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Structural studies on the stereoisomerism of a natural dye miraxanthin I The chemical structure of a yellow dye present in Mirabilis jalapa L., miraxanthin I, was characterized by NMR spectroscopy. The extract of M. jalapa was analysed by a high-performance liquid chromatographic system (LC-DAD-FL-ESI-MS/MS) and the presence of miraxanthin I among other betaxanthins was confirmed. This dye was synthesized from previously generated methionine-betaxanthin by oxidation with 10% H2O2. The E/Z stereoisomers of miraxanthin I were found by NMR analysis to occur in a 50 : 33 : 10 : 7 ratio in aqueous solution (7E,9E : 7Z,9E : 7E,9Z : 7Z,9Z configurations, respectively). Comparison of NMR data with chemical shifts obtained from quantum chemical calculations strongly suggests the presence of intramolecular hydrogen bonds which may favour a more rigid structure of the dye. This explains the highest fluorescence quantum yield among betaxanthins. The observed changes in the H-1 NMR spectra during the measurements indicate on miraxanthin I hydrolysis for which a mechanism is proposed. The first step during the hydrolysis process is protonation of the nitrogen atom within the central bridge bond system which is observed in the ZE stereoisomer by NMR.
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New Journal of Chemistry, 43(46), 18165-18174, (2019) |
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Single-walled carbon nanotube/sulfanyl porphyrazine hybrids deposited on glassy carbon electrode for sensitive determination of nitrites The metallation reaction of 2-[2-(3,5-dibutoxycarbonylphenoxy)ethoxy]ethylsulfanyl-substituted porphyrazine with manganese and nickel salts led to novel porhyrazine derivatives with d-block metal ions in the core. Voltammetric studies of nickel(II) porphyrazine in organic electrolyte revealed the existence of well-defined one-electron ligand-based reductions and ligand-based one-electron oxidation redox pairs. Manganese porphyrazine however, presented both metal-based and ligand-based reductions and oxidation processes. The glassy carbon electrode with deposited single-walled carbon nanotube/sulfanyl porphyrazine hybrids was examined for the electrocatalytic oxidation of nitrites. The results indicated that when nickel(II) porphyrazine is present, it significantly contributes to the promotion of the electrocatalytic current for nitrites oxidation. The response of the proposed modified electrode was linear considering the nitrites concentration in the range of 5-200 mu M and with a detection limit (LOD) and quantitation limit (LOQ) equal to 1.08 and 3.60 mu M, respectively. The proposed voltammetric sensor was also applied for the determination of nitrites in tap water and mineral water samples.
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Dyes and Pigments, 171, 107660, (2019) |
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Structural and dynamic study of block copolymer - Nanoparticles nanocomposites Nanocomposites based on block copolymer (BCP) and gold nanoparticles (NPs) filler were measured in terms of their structure and polymer chain molecular dynamics. NPs were functionalized in order to gain selective affinity to one specific type of BCP domain. BCP directed NPs assembly was monitored using atomic force microscopy. Thin nanocomposite films were fabricated via spin-coating technique, annealed and subsequently subjected to reactive ion etching in order to expose inorganic NPs location within the BCP matrix. Selective NPs incorporation was confirmed. Furthermore, interesting NPs distribution in quasi-2D crystallites was revealed. Spectroscopic methods (nuclear magnetic resonance and dielectric spectroscopy) enabled investigation of polymer chain reorientations and estimation of the impact of nano-filler on polymer dynamics. Nanocomposite crystallinity was assessed via thermal analysis and supported by spectroscopic techniques.
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Polymer, 167, 130-137, (2019) |
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NMR relaxometry in the investigation of the kinetics of the recrystallization of felodipine The method of Nuclear Magnetic Resonance (NMR) relaxometry is proposed to be applied to investigate the kinetics of the recrystallization of a substance from the amorphous phase. The method is based on the determination and analysis of nuclear magnetization recovery M-z obtained from spin-lattice T-l relaxation time measurements as a function of time since sample amorphization. The formation of a biphasic (crystalline and amorphous) system in the process of recrystallization implies that the magnetization recovery M-z is biexponential and that the amplitudes of its components are proportional to the number of spins (protons) in the crystalline and amorphous phases, and, thus, also to the volume occupied by the phases. The method was tested for amorphous felodipine samples with grain sizes close to 0.1 or 1 mm, and the recrystallization process was confirmed by using Powder X-ray Diffraction (PXRD) and Fourier-Transform Infrared (FTIR) methods. Qualitative comparison of the results obtained with the data obtained earlier by PXRD and Raman methods for felodipine samples with grain sizes of 0.2 and 0.6 mm [U. S. Kestur, I. Ivanesivic, D. E. Alonzo, L S. Taylor, Influence of particle size on the crystallization kinetics of amorphous felodipine powders, Powder Technology 236 (2013) 197-204] showed reasonable agreement The method is fully extensive and can be applied to amorphous samples prepared in different ways, such as grinding, milling or melting, as well as for co-amorphous or amorphous solid dispersion samples. (C) 2019 Elsevier B.V. All rights reserved.
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Powder Technology, 347, 35-41, (2019) |
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Zaktualizowano: podstrony 2021-06-21 / bazę danych: 2024-11-02 by Webmaster: Zbigniew Fojud