Porphyrin Aerogel Catalysts for Oxygen Reduction Reaction in Anion-Exchange Membrane Fuel Cells

Platinum group metal (PGM)-free catalysts for oxygen reduction reaction have shown high oxygen reduction reaction activity in alkaline media. In order to further increase the power density of anion-exchange membrane fuel cells (AEMFCs), PGM-free catalysts need to have a high site density to reach high current densities. Herein, synthesis, characterization, and utilization of heat-treated iron porphyrin aerogels are reported as cathode catalysts in AEMFCs. The heat treatment effect is thoroughly studied and characterized using several techniques, and the best performing aerogel is studied in AEMFC, showing excellent performance, reaching a peak power density of 580 mW cm⁻² and a limiting current density of as high as 2.0 A cm⁻², which can be considered the state-of-the-art for PGM-free based AEMFCs.     

The primary,secondary, and structures of higher levels of pectin polysaccharides

Pectin is a heteropolysaccharide abundant in the cell wall of plants and is obtained mainly from fruit (citrus and apple), thus its properties are particularly prone to changes occurring during ripening process. Properties of pectin depend on the string-like structure (conformation, stiffness) of the molecules that determines their mutual interaction and with the surrounding environment. Therefore, in this review the primary, secondary, and structures of higher levels of pectin chains are discussed in relation to external factors including crosslinking mechanisms. The review shows that the primary structure of pectin is relatively well known, however, we still know little about the conformation and properties of the more realistic systems of higher orders involving side chains, functional groups, and complexes of pectin domains. In particular, there is lack of knowledge on the influence of postharvest changes and extraction method on the primary and secondary structure of pectin that would affect conformation in a given environment and assembly to higher structural levels. Exploring the above-mentioned issues will allow to improve our understanding of pectin functionality and will help to tailor new functionalities for the food industry based on natural but often biologically variable source. The review also demonstrates that atomic force microscopy is a very convenient and adequate tool for the evaluation of pectin conformation since it allows for the relatively straightforward stretching of the pectin molecule in order to measure the force-extension curve which is directly related to its stiffness or flexibility.     

A Proposed Molecular Mechanism of High-Dose Vitamin D3 Supplementation in Prevention and Treatment of Preeclampsia

A randomized prospective clinical study performed on a group of 74 pregnant women (43 presenting with severe preeclampsia) proved that urinary levels of 15-F_2t-isoprostane were significantly higher in preeclamptic patients relative to the control (3.05 vs. 2.00 ng/mg creatinine). Surprisingly enough, plasma levels of 25-hydroxyvitamin D₃ in both study groups were below the clinical reference range with no significant difference between the groups. In vitro study performed on isolated placental mitochondria and placental cell line showed that suicidal self-oxidation of cytochrome P450scc may lead to structural disintegration of heme, potentially contributing to enhancement of oxidative stress phenomena in the course of preeclampsia. As placental cytochrome P450scc pleiotropic activity is implicated in the metabolism of free radical mediated arachidonic acid derivatives as well as multiple Vitamin D₃ hydroxylations and progesterone synthesis, we propose that Vitamin D₃ might act as a competitive inhibitor of placental cytochrome P450scc preventing the production of lipid peroxides or excess progesterone synthesis, both of which may contribute to the etiopathogenesis of preeclampsia. The proposed molecular mechanism is in accord with the preliminary clinical observations on the surprisingly high efficacy of high-dose Vitamin D₃ supplementation in prevention and treatment of preeclampsia.     

Synthesis of tailored nanogels by means of two-stage irradiation

A new method allowing to synthesize polymeric nanogels of independently chosen weight-average molecular weight (M_w) and dimensions in an additive-free system consisting only of linear macromolecules and water is described and tested. This approach, based on generation of free radicals using ionizing radiation in oxygen-free polymer solutions, consists of two steps. In the first step, semi-concentrated polymer solution is irradiated at a moderate dose rate, so that in the stationary state the average number of radicals per chain is <1. This promotes intermolecular cross-linking with increase in M_w and coil dimensions. When the desired M_w is reached, in the second step intra-molecular recombination is induced by pulse irradiation of dilute solution (with the average number of radicals per chain >1 after each pulse), leading to a decrease in nanogel diameter while keeping M_w nearly constant. Experimental data on a model polymer – poly(N-vinylpyrrolidone) – confirm that the proposed method allows synthesizing nanogels of desired properties (independently chosen molecular weight and radius of gyration) in a pure polymer-water system, eliminating the use of monomers, cross-linking agents, or other auxiliary substances.     

Impact of Pre-Ozonation on Mechanical Properties of Selected Genotypes of Cucumber Fruits During the Souring Process

Cucumber souring is a process mediated by a microorganisms present on the surface of cucumber fruits. Sour pickles are fresh cucumbers that have been poured over with a sodium chloride solution and various types of spices. In the present research, pre-ozonated and control cucumber fruits were subjected to the souring processes. It was observed that ozone treatment had no negative impact on the quality of the fruit before the souring process. Moreover, sour pickles after pre-ozonation had better mechanic and sensory properties than the control.     

Transmission electron microscopy studies of the Pd–C films obtained by physical and chemical vapor deposition

Transmission Electron Microscopy (TEM) analysis of carbonaceous films that contain palladium nanoparticles were carried out. These layers will be used in next-generation hydrogen sensors. The investigated films were obtained in Physical Vapor Deposition (PVD) and followed in Chemical Vapor Deposition (CVD) processes. For TEM analysis, cross-sections specimen (lamella) of both samples (i.e. PVD and PVD/CVD) were prepared with the usage of Focus Ion Beam (FIB). TEM analysis of the cross-sections determined the films' thickness, which were ∼200 nm and ∼300 nm for PVD and PVD/CVD films respectively. The greater thickness of the PVD/CVD films was associated with xylene decomposition and consecutive formation of porous structure. Our studies allowed to obtain some information about the distribution of palladium crystallites and porous carbon in the both layers of Pd–C.