Isostructural second-order phase transition of b-Bi2O3 at high pressures: an experimental and theoretical study

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp507826jWe report a joint experimental and theoretical study of the structural and vibrational properties of synthetic sphaerobismoite (beta-Bi2O3) at high pressures in which room-temperature angle-dispersive X-ray diffraction (XRD) and Raman scattering measurements have been complemented with ab initio total energy and lattice dynamics calculations. Striking changes in Raman spectra were observed around 2 GPa, whereas X-ray diffraction measurements evidence no change in the tetragonal symmetry of the compound up to 20 GPa; however, a significant change exists in the compressibility when increasing pressure above 2 GPa. These features have been understood by means of theoretical calculations, which show that beta-Bi2O3 undergoes a pressure-induced isostructural phase transition near 2 GPa. In the new isostructural beta' phase, the Bi3+ and O2- environments become more regular than those in the original beta phase because of the strong decrease in the activity of the lone electron pair of Bi above 2 GPa. Raman measurements and theoretical calculations provide evidence of the second-order nature of the pressure-induced isostructural transition. Above 20 GPa, XRD measurements suggest a partial amorphization of the sample despite Raman measurements still show weak peaks, probably related to a new unknown phase which remains up to 27 GPa. On pressure release, XRD patterns and Raman spectra below 2 GPa correspond to elemental Bi-I, thus evidencing a pressure-induced decomposition of the sample during downstroke.Financial support from the Spanish Consolider Ingenio 2010 Program (MALTA Project CSD2007-00045) is acknowledged. This work was also supported by Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) under Project 201050/2012-9, Spanish MICINN under Projects MAT2010-21270-004-01/03/04 and MAT2013-46649-C4-2/3/4-P, Spanish MINECO under Project CTQ2012-36253-C03-02, and from Vicerrectorado de Investigacion de la Universitat Politecnica de Valencia under Projects UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11. Supercomputer time has been provided by the Red Espanola de Supercomputacion (RES) and the MALTA cluster. JAS. acknowledges Juan de la Cierva fellowship program for financial support.Pereira, ALJ.; Sans Tresserras, JÁ.; Vilaplana Cerda, RI.; Gomis, O.; Manjón Herrera, FJ.; Rodriguez-Hernandez, P.; Muñoz, A.... (2014). Isostructural second-order phase transition of b-Bi2O3 at high pressures: an experimental and theoretical study. Journal of Physical Chemistry C. 118(40):23189-23201. https://doi.org/10.1021/jp507826jS23189232011184

Toksikološka svojstva citrinina

Citrinin (CTN) is a nephrotoxic mycotoxin produced by several fungal strains belonging to the genera Penicillium, Aspergillus, and Monascus. It contaminates various commodities of plant origin, cereals in particular, and is usually found together with another nephrotoxic mycotoxin, ochratoxin A (OTA). These two mycotoxins are believed to be involved in the aetiology of endemic nephropathy. In addition to nephrotoxicity, CTN is also embryocidal and fetotoxic. The genotoxic properties of CTN have been demonstrated with the micronuleus test (MN), but not with single-cell gel electrophoresis. The mechanism of CTN toxicity is not fully understood, especially not whether CTN toxicity and genotoxicity are the consequence of oxidative stress or of increased permeability of mitochondrial membranes. CTN requires complex cellular biotransformation to exert mutagenicity. Compared with other mycotoxins, CTN contamination of food and feed is rather scarce. However, it is reasonable to believe that humans are much more frequently exposed to CTN than generally accepted, because it is produced by the same moulds as OTA, which is a common contaminant of human food all over the world. At present, there are no specifi c regulations either in Croatia or in the European Union concerning CTN in any kind of commodity.Citrinin (CTN) nefrotoksičan je mikotoksin koji proizvode različiti sojevi plijesni iz rodova Penicillium, Aspergillus i Monascus. CTN se može naći u različitim namirnicama biljnog podrijetla, osobito u žitaricama i obično se nalazi zajedno s drugim nefrotoksičnim mikotoksinom, okratoksinom A (OTA). Pretpostavlja se da je izloženost ovim mikotoksinima povezana s nastankom endemske nefropatije. Osim što je nefrotoksičan, CTN je još i embricidan i fetotoksičan. Na genotoksičnost citrinina upućuje pozitivan mikronukleusni test na različitim vrstama staničnih kultura, iako je kometski test negativan. Mutagenost CTN-a očituje se na različitim vrstama stanica samo ako se pridodaju stanični aktivatori kao npr. S9-mix. Mehanizam toksičnosti CTN-a nije potpuno razjašnjen pa još uvijek traje znanstvena rasprava je li njegova toksičnost i genotoksičnost posljedica oksidacijskog stresa ili povećane permeabilnosti mitohondrijskih membrana. U dostupnoj literaturi podaci o kontaminiranosti hrane i krmiva ovim mikotoksinom mnogo su rjeđi od onih za druge mikotoksine. Može se pretpostaviti da su ljudi često izloženi ovom mikotoksinu zato što ga proizvode iste plijesni koje proizvode i OTA, a one kontaminiraju hranu po cijelom svijetu. U Hrvatskoj i u zemljama Europske Unije ne postoje zakonske odredbe o dopuštenim granicama CTN-a u bilo kojoj vrsti hrane