Nuclear resonance studies of local structure in RBa2Cu3O6+x compounds

http://www.ester.ee/record=b4329298~S58*es

Õunamahla kvaliteeti ja mükotoksiini patuliini teket mõjutvad tegurid

A thesis for applying for the degree of Doctor of Philosophy in Agriculture.The aim was to find out the effect of cultivation system (organic- and conventional-), apple preprocessing storage temperature (+3°C and +9°C) and juice pressing technology (rack-and-frame press, water press and belt press) on juice mineral elements, polyphenol content, sensory properties and mycotoxin patulin content. Additionally, an experiment was conducted to find out if the apples with physiological disorders (bitter pit and superficial scald) are more susceptible to blue mould rot and if the juice pressed from these apples contains more patulin. Nine studied apple juices out of 53 were contaminated with patulin. The most important outcome of the doctoral thesis was that patulin formation in disordered apples may occur even if visual signs of fungal infection are not present. To reduce the risk of patulin contamination, it is important to press the disordered apples into juice as soon as possible. Rainfall during two weeks before harvest may increase the risk of patulin contamination in apple juice, therefore it is important to inspect apple cores for detection any fungal diseases in rainy years. Organic apple juice pressed from apples harvested from old low-maintenance orchards contained more P, K and Mg compared to the conventional juices or organic apple juices pressed from apples harvested from young well-maintained orchards. Organic apple juices tended to contain more polyphenols, but the effect was not uniform among all cultivars. Polyphenols in organic apples were more prone to degradation if apples were kept at higher than optimal storage temperatures before juice processing. Therefore, the apples for juice pressing should not be stored at higher temperature than 3±2 °C. Rack-and-frame press juices had the lowest and belt-press juices the highest content of polyphenols. Belt press juice had the poorest sensory properties characterized as less sweet, more sour, bitter and astringent compared to other juices. Water press juices had a fresher aroma and flavour and were the most yellow and brightest. The results indicate, that water press juices would be preferred by the consumers, therefore the small-scale juice producers can be advised to implement water press instead of rack-and-frame press. In further research, it would be important to study patulin formation in visually non-spoiled apples.Doktoritöö eesmärgiks oli välja selgitada viljelusviisi (mahe- ja tava-), õunte pressimiseelse säilitustemperatuuri (+3°C ja +9°C) ja pressimistehnoloogia (pakkpress, vesipress ja lintpress) mõju mahla mineraalelementide- ja polüfenoolide sisaldusele, sensoorsetele omadustele ning mükotoksiini patuliini sisaldusele, mis on tervisele ohtlik. Lisaks uuriti, kas füsioloogiliste häiretega (kaltsiumipuuduse laigud ja koore pruunistumine) õunad on vastuvõtlikumad rohehallitusele ja kas nendest õuntest pressitud mahl sisaldab rohkem patuliini. Kokku uuriti katsetes 53 erinevat mahla, millest üheksa sisaldasid patuliini. Doktoritöö kõige olulisem tulemus oli avastus, et füsioloogiliste häiretega õuntes võib patuliin tekkida ka siis, kui õuntel puuduvad silmaga nähtavad seenhaigustesse nakatumise tunnused. Füsioloogiliste häiretega õunad tuleks pressida mahlaks esimesel võimalusel, et vähendada õunamahla patuliiniga saastumise riski. Nendel aastatel, kui õunte koristuseelsel perioodil sajab palju vihma, on patuliini esinemise tõenäosus mahlas suurem ja tuleks kontrollida hallitustunnuseid õunte südamikes. Vanadest vähese hooldusega maheaedade õuntest pressitud mahlad sisaldasid rohkem P, K ja Mg võrreldes tava-aedadest või noortest ja hästi hooldatud maheaedadest korjatud õuntest pressitud mahladega. Maheõuntest pressitud mahladel oli ka tendents kõrgemale polüfenoolide sisaldusele, kuigi sorditi oli mõju erinev. Kui õunu säilitati enne mahla pressimist optimaalsest kõrgemal temperatuuril, vähenes maheõuntes polüfenoolide sisaldus enam kui tavaõuntes. Seetõttu ei tohiks mahla pressimiseks mõeldud õunu säilitada kõrgemal temperatuuril kui 3±2 °C. Pakkpressi mahlades oli kõige madalam ja lintpressi mahlades kõige kõrgem polüfenoolide sisaldus. Samas olid lintpressi mahlad vähem magusad, enam hapud ja kibedad ning esines kootavat toimet. Vesipressi mahladel oli kõige värskem aroom ja maitse ning mahla värvus oli kõige säravam. Nimetatud omadused lubavad eeldada, et vesipressi mahlad oleksid tarbijate poolt enam eelistatud, seega võiks väiketootjatele soovitada vesipressi kasutamist pakkpressi asemel tootmaks tervislikku ja maitsvat õunamahla. Edaspidi on eelkõige oluline uurida patuliini teket ilma visuaalsete seenhaiguste tunnusteta õuntes.Publication of this thesis is supported by the Estonian University of Life Sciences. This research was supported by Core Organic Plus Cofund project FaVOR-DeNonDe 2015–2018, Estonian Ministry of Rural Affairs and The Enterprise Estonia project EU50282

Molecular orientational dynamics of the endohedral fullerene Sc3_{3}N@C80_{80} as probed by 13^{13}C and 45^{45}Sc NMR

We measure 13C and 45Sc NMR lineshapes and spin-lattice relaxation times (T1) to probe the orientational dynamics of the endohedral metallofullerene Sc3N@C80. The measurements show an activated behavior for molecular reorientations over the full temperature range with a similar behavior for the temperature dependence of the 13C and 45Sc data. Combined with spectral data from Magic Angle Spinning (MAS) NMR, the measurements can be interpreted to mean the motion of the encapsulated Sc3N molecule is independent of that of the C80 cage, although this requires the similar temperature dependence of the 13C and 45Sc spin-lattice relaxation times to be coincidental. For the Sc3N to be fixed to the C80 cage, one must overcome the symmetry breaking effect this has on the Sc3N@C80 system since this would result in more than the observed two 13C lines.Comment: 6 pages, 5 figure

Jahn-Teller orbital glass state in the expanded fcc Cs3C60 fulleride

The most expanded fcc-structured alkali fulleride, Cs3C60, is a Mott insulator at ambient pressure because of the weak overlap between the frontier t1u molecular orbitals of the C603− anions. It has a severely disordered antiferromagnetic ground state that becomes a superconductor with a high critical temperature, Tc of 35 K upon compression. The effect of the localised t1u3 electronic configuration on the properties of the material is not well-understood. Here we study the relationship between the intrinsic crystallographic C603− orientational disorder and the molecular Jahn–Teller (JT) effect dynamics in the Mott insulating state. The high-resolution 13C magic-angle-spinning (MAS) NMR spectrum at room temperature comprises three peaks in the intensity ratio 1:2:2 consistent with the presence of three crystallographically-inequivalent carbon sites in the fcc unit cell and revealing that the JT-effect dynamics are fast on the NMR time-scale of 10−5 s despite the presence of the frozen-in C603− merohedral disorder disclosed by the 133Cs MAS NMR fine splitting of the tetrahedral and octahedral 133Cs resonances. Cooling to sub-liquid-nitrogen temperatures leads to severe broadening of both the 13C and 133Cs MAS NMR multiplets, which provides the signature of an increased number of inequivalent 13C and 133Cs sites. This is attributed to the freezing out of the C603− JT dynamics and the development of a t1u electronic orbital glass state guided by the merohedral disorder of the fcc structure. The observation of the dynamic and static JT effect in the Mott insulating state of the metrically cubic but merohedrally disordered Cs3C60 fulleride in different temperature ranges reveals the intimate relation between charge localization, magnetic ground state, lifting of electronic degeneracy, and orientational disorder in these strongly-correlated systems

Two-dimensional tetramer-cuprate Na5RbCu4(AsO4)4Cl2: phase transitions and AFMorder as seen by 87Rb NMR

We report the Rb nuclear magnetic resonance (NMR) results in a recently synthesized Na5RbCu4(AsO4)Cl2. This complex novel two-dimensional (2D) cuprate is an unique magnetic material, which contains layers of coupled Cu4O4 tetramers. In zero applied magnetic field, it orders antiferromagnetically via a second-order low-entropy phase transition at TN = 15(1) K. We characterise the ordered state by 87Rb NMR, and suggest for it a noncollinear rather than collinear arrangement of spins. We discuss the properties of Rb nuclear site and point out the new structural phase transition(s) around 74 K and 110 K.Comment: 2 pages, 2 figures, Proceedings of SCES'05, Vienna 200

Physiological disorders affect apple susceptibility to Penicillium expansum infection and increase probability for mycotoxin patulin occurrence in apple juice

ArticlePenicillium expansum infection of apples and mycotoxin patulin (PAT) production has previously been associated with many pre- and postharvest factors other than physiological disorders. In the current study, ‘Antei’ and ‘Krameri tuviõun’ apples with and without bitter pit (BP) symptoms and ‘Talvenauding’ apples with and without superficial scald (SS) symptoms were used in order to determine if the named physiological disorders may influence susceptibility to P. expansum infection and PAT production. Apples were inoculated with 10 μL P. expansum spore suspension with the concentration of 1×105 conidia mL-1 and stored at 24 °C with relative humidity (RH) 80%. After 7 and 11 days, lesion diameters were measured, and apples were pressed into juice. PAT content was determined in pasteurized juice. Two cultivars out of three showed that in fruit with physiological disorders, Penicilllium infection and PAT production proceeded significantly faster compared to apples, which did not have physiological disorders. SS increased the risk for PAT occurrence in juice more than BP: while the juice pressed from BP–affected apples with no visual signs of fungal diseases did not contain PAT, juice pressed from apples with SS contained PAT three times above legislative limits defined by the World Health Organization (50 μg L-1)

Study of oxygen ordering in htc superconductors by magnetic resonance of different nuclei

NMR of 169Tm and NQR/NMR of 63/65Cu was applied to investigate the order of oxygen in the HTC superconductors of the type RBa2Cu301. From the spectra of three different lattice sites, one for Tm and two for Cu, it is evident, that three ordered structures exist: Tetra for x = 6.0, ortho-II for x = 6.5 and ortho-I for x = 7.0. No other ordered structures could be detected. A coexistence of ortho-I and -II is evident in a wide region between 6.6 and 6.8. The existence of extended domains of ortho-II is essential for the onset of superconductivity. In the tetragonal region below 6.3 we find mainly insulated oxygen ions in the Cu(1) plane; in superconducting samples of the 60 K plateau oxygen is ordered in chains of a mean length of about 12 oxygen ions. In the region of the 90 K plateau the chains become very long and the oxygen vacancies are clustered in empty fragments of chains. © 1993 IOP Publishing Ltd