Effect of pH on the Redox and Sorption Properties of Native and Phosphorylated Starches.

Starch is a common biopolymer that can be used for removing heavy metal ions from aqueous solutions. A valuable property of starch is its functional diversity, which can be enhanced by chemical modification. Hydroxyl groups enclosed in the starch and formed during hydrolysis act as reducing agents of Cr(VI). The sorption properties of native starch depend mainly on the presence of carboxyl groups formed during redox processes and basic centers created during acid hydrolysis, while the superiority of phosphorylated starch is related to the presence of phosphate groups binding Cr(III) ions. The effectiveness of starch depends on a series of equilibria established in its aqueous suspension and chromate ions solution, where the pH is the driving force for these processes. In this article, a systematic discussion of pH changes being the consequence of chemical reactions unraveling the extraordinary functionalities of starch was given. It also explained the influence of establishing equilibria and chemical modifications of starch on the efficiency of chromium ion removal. This allowed for the development of a comprehensive mechanism for the interaction of Cr(VI) and Cr(III) ions with native and phosphorylated starch.

Pandemic resilient cities: Possibilities of repairing Polish towns and cities during COVID-19 pandemic.

Cities, due to population density and the complexity of human interactions, experience specific problems arising from their functioning in the era of the Covid-19 pandemic. Many scientists who publish their findings in contemporary literature agree on the need to shape pandemic resilient cities by making changes to the functional-spatial structure and preparing cities for rapid revitalization [regeneration] in the post-pandemic period. The main objective of the research is to identify the most important problems regarding service infrastructure deficiencies in the nine medium-sized Polish cities selected for research located in the Warsaw agglomeration, which are well connected with Warsaw. The research was based on: analysis of selected GIS spatial data, demographic data from the Polish Central Statistical Office, surveys among residents, on their needs during pandemic constraints. The focus was on three important aspects of development in the era of the pandemic: access to first-need services, access to greenery and active recreation areas, accessibility and transport efficiency problems. The research revealed changes in the way people travel and do their essential shopping, inadequate cycling infrastructure and problems with the availability of essential services close to where they live. The research programme varies, although the diagnosis and the possibility of transforming the functional-spatial structure of the cities studied as typical medium-sized cities in the impact zone of a large centre dominate. The conclusions provide examples of proposals for tactical urbanism planning solutions that could rapidly improve the quality of residence in a low-budget way. Finally, the proposals and guidelines for creating sustainable pandemic resilient cities are described. The article investigates the aspect of urban resilience related to transport, services, relaxation, while using the method of tactical urbanism as a remedy for cities' pandemic problems.

Thermal properties and free radicals generation in starch isolated from pumpkin fruits.

The selected thermal and rheological properties of pumpkin starches were compared with values evaluated for corn and potato starch. The pumpkin starches had lower pasting temperatures (by near 3°C and 24°C than potato or corn starch respectively), the peak viscosity (nearly 2300mPas lower than potato starch) and higher final viscosities (by 80-120mPas than those for potato starch and by 1700mPas in relation to corn starch). The thermal profile of pumpkin starches examined by the DSC method were quite similar to those of potato starch but lower than those of corn. The retrogradation degree of pumpkin starch was lower by 5-26% than that for corn or potato starches. The thermal treatment of starches led to the formation of radicals. Pumpkin starches were less susceptible to the formation of radicals than potato starch and had less about 0.3-1.3×1015radicals/g than potato starch.

Effect of thermal treatment on potato starch evidenced by EPR, XRD and molecular weight distribution.

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification.

Thermally generated radicals as indicators of the starch modification studied by EPR spectroscopy: a review.

The results compiled and discussed in the present review have been published by the research group of the Chemistry Faculty, Jagiellonian University or by other Authors, as given in References. Relatively stable and short-lived radicals generated thermally in starches of various botanic origin were used as indicators of the changes in the starch structure and properties occurring upon chemical and physical modifications. The number of radicals was determined by electron paramagnetic resonance (EPR) spectroscopy. Distribution of water and accessibility of different zones in the starch granule for reagents were tested by using paramagnetic Cu(2+) ions as a probe molecule. Relatively stable radicals generated in starch at 300°C revealed protective properties against ionizing radiation. Thermally induced short-lived radicals exhibited sensitivity to the degree of the starch structure ordering.

Optical nonlinearity and electric conductivity origin study on sucrose crystal by using IR, Raman, INS, NMR, and EPR spectroscopies.

The supposed importance of hydrogen bonds toward the origin of second harmonic generation (SHG) and electric conductivity in crystalline sucrose was investigated by IR (4000-10cm(-1)), INS (2000-10cm(-1), at 35K), polarized Raman (3600-50cm(-1)) spectra, and (1)H NMR second moment line records in the temperature range 450-80K. The temperature dependence of NIR (7000-5500cm(-1)) polarized spectra gave information about -CH2 motions complementary to NMR results concerning -CH2OH group rearrangements. The EPR spectra were applied to study the generation of radical ions by exposure to NIR radiation. Density functional theory quantum chemical calculations were performed to reproduce the vibrational spectra in order to complete as far as possible the assignments of bands observed by us and in the literature in sucrose crystals, and to throw more light on the possible reasons of sucrose electric conductivity and optical nonlinearity by the knowledge of theoretical values of dipole moments, polarizabilities, first order hyperpolarizabilities of sucrose molecule and clusters as well as ionization energy and electron affinity. The proton transfer in one specific hydrogen bond parallel to the helical axis b is proposed to be the most important in SHG and conductivity origin.

Interactions of chromium ions with starch granules in an aqueous environment.

In this study, interactions of dichromate ions with potato starch granules in highly acidic aqueous solutions and at different temperatures were investigated. It was found that the process underwent a reduction of Cr(2)O(7)(2-) to Cr(3+) accompanied by the formation of intermediate Cr(5+) ions detected by electron paramagnetic resonance (EPR) spectroscopy. The reactions took place after the attachment of dichromate anions to the granules and resulted in a lowering of the Cr(2)O(7)(2-) initial content in the solution. The newly formed Cr(3+) ions were both accumulated by the granules or remained in the solution. It was observed for the first time that the quantity of such ions taken by the granules from the solution was noticeably higher than that delivered by trivalent chromium salt solution. It was revealed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) that the chromium ions were not only adsorbed on the granule surface but also introduced into the granule interior and evenly distributed there. An activation energy of the reduction reaction equal to 65 kJ·mol(-1) and the optimal parameters of the process were established. The proposed mechanism could be useful for the bioremediation of industrial effluents polluted by hexavalent chromium compounds.

EPR spectroscopy as a tool for investigation of differences in radical status in wheat plants of various tolerances to osmotic stress induced by NaCl and PEG-treatment.

Two kinds of wheat genotypes with different tolerance to osmotic stress (NaCl and PEG-treatment) were investigated with biochemical analyses, including the measurements of total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, reducing power and starch content. The results were compared with electron paramagnetic resonance (EPR) data concerning the nature and amounts of stable long lived radicals present in the control and stressed plants. In addition, the changes in manganese content upon stress conditions were monitored. Different mechanisms of protection against PEG stress in sensitive and tolerant wheat genotypes were postulated. In sensitive genotypes, electrons were created in excess in stress conditions, and were stabilized by polysaccharide molecules, whereas in tolerant genotypes, protection by antioxidants dominated. Moreover, the quinone-semiquinone balance shifted towards semiquinone, which became the place of electron trapping. NaCl-treatment yielded significant effects mainly in sensitive genotypes and was connected with the changes of water structure, leading to inactivation of reactive oxygen species by water molecules.

Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations.

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.

Selenium-induced protection of photosynthesis activity in rape (Brassica napus) seedlings subjected to cadmium stress. Fluorescence and EPR measurements.

Fluorescence and electron paramagnetic resonance measurements were used to study selenium influence on photosystem activity in rape seedlings affected by Cd stress. Water cultures containing Hoagland nutrients were supplemented with 400 microM of CdCl(2), 2 microM of Na(2)SeO(4) and a mixture of both CdCl(2) and Na(2)SeO(4). The seedlings were cultured till the first leaf reached about 1 cm in length. Cadmium-induced changes in the activity of both photosystems were partly diminished by Se presence in the nutrient medium. Electron microscopy photographs confirmed less degradation in chloroplasts of plants cultured on media containing Se. It is suggested that sucrose groups of starch, which is deposited in greater amounts in Cd-stressed plants, may act as traps for free radicals produced under those conditions.

Electron paramagnetic resonance study of water distribution in starch granules.

An electron paramagnetic resonance (EPR) study was performed for potato and wheat starch containing Cu2+ ions as a paramagnetic probe. Distribution of water in the starch granules as well as the interactions between the copper and starch matrix of different crystalline structures were determined. EPR spectra of the native starches consisted of two different centers of Cu2+. One of them, giving at 293 and 77 K an EPR signal of axial symmetry with a well-resolved hyperfine structure (HFS), was assigned to the Cu2+ -starch complex in which Cu2+ ions strongly interacted with oxygen atoms of the starch matrix. Another Cu2+ species, exhibiting an isotropic signal at 293 K and an axial signal with resolved HFS at 77 K, was attributed to a [Cu(H2O)6]2+ complex freely rotating at room temperature and immobilized at low temperatures. Interaction of Cu2+ with the starch matrix and the relative number of the particular copper species depended on the crystallographic type of starch. Dehydration at 393 K resulted in elimination of the rotating complex signal and decrease of the total intensity of the EPR spectrum caused by clustering of the Cu2+ ions. Freezing at 77 K and thawing led to restoring of the spectrum intensity and reappearing of the signal of the [Cu(H2O)6]2+ complex. This effect, related to liberation of water molecules from the granule semicrystalline growth rings on freezing/thawing, was especially visible for wheat starch, indicating differences in the water retention ability of starch granules of different crystallographic structure.

Phosphate positioning and availability in the starch granule matrix as studied by EPR.

Cu(2+) was introduced as an EPR probe into the starch granules isolated from different starch crop genotypes including transgenically modified potatoes generated for extreme amylose and starch phosphate monoester concentrations. Several discrete copper adducts bound to the starch matrix with different strength was revealed. It was found that phosphate has a significant influence on the type of these species, their number, location in the structure, and strength of binding. Well dispersed Cu(2+) complexes with axial symmetry are formed in the semicrystalline part of the starch linked through O-P- bonds in the phosphorylated starches. In the amorphous part of the starch, freely rotating hexaaqua complexes of Cu(2+) and complexes coupled antiferromagnetically are formed. The amount of the former increases with content of phosphate indicating enhanced binding of water in the granules. The results complement previous experimental data and molecular models for the starch granule with respect to the location and effects of phosphate and crystalline matter.

Catalytic activity of MCM-48-, SBA-15-, MCF-, and MSU-type mesoporous silicas modified with Fe3+ species in the oxidative dehydrogenation of ethylbenzene in the presence of N2O.

MCM-48, SBA-15, MCF, and MSU mesoporous silicas were used as supports for a deposition of Fe oxide species. Iron was introduced using two different methods: the wetness impregnation and the molecular designed dispersion (MDD). The obtained catalysts were characterized with respect to their textural parameters (BET), chemical composition (electron microprobe analysis), and reducibility (TPR). The coordination environment of Fe was determined using EPR and UV-vis/DRS. The samples were tested as catalysts in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of N(2)O. An influence of Fe dispersion and reducibility on the catalytic activity was discussed. Isolated Fe(3+) species appeared to be more selective in the styrene formation, whereas iron oxide clusters showed a higher selectivity in total oxidation of aromatic hydrocarbons. The reaction system was well described by the Mars- van Krevellen mechanism.