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Crystallites and Electric Fields in Solid Ammonia

ABSTRACT: Abstract Absorption spectra of vacuum?deposited films of ammonia have been obtained in the range 115?nm to 310?nm for a set of 15 deposition temperatures, Td, between 20?K and 80?K. Results focus upon the region 115?nm to 130?nm in overlapping D, E, F and G?X Rydberg transitions involving Wannier?Mott excitons. We identify two phases of ammonia, showing the solid to be polymorphic. Peak absorption wavelengths in the region of interest are found to shift to the red by 299?cm?1, for Td between 20?K to 50?K, and 1380?cm?1 for Td between 55?K to 80?K. Shifts provide evidence for the presence of spontaneously generated electric fields in these films, of values in excess of 108?V?m?1 for Td of 20?K to 50?K to a few times 107?V?m?1 for 55?K to 80?K. Results enable us to place a lower limit of 1.58?nm on the size of crystallites in the low temperature regime. This dimension represents 16 unit cells or 64 species, giving a more quantitative description than the nebulous term amorphous, as applied to solid ammonia. We also determine that crystallites formed in the high temperature regime contain, within ±20?%, 1688, 756 and 236 molecules of ammonia, respectively at Td of 65?K, 60?K and 55?K. What do we mean when we describe a film of vacuum?deposited material as amorphous and what by crystalline? In this study of spontaneously electrical solid ammonia, we show that the so?called “amorphous” phase, prepared between 20–50?K, is a crystalline material composed of crystallites containing >64 molecules. More broadly, we introduce a technique to quantify the size of crystallites in nanoscale films.

SUBMITTER: Cassidy A

PROVIDER: S-EPMC7528761 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Project description:Glioblastoma multiforme (GBM), is the most common form of adult malignant brain tumor, highly heterogeneous and relatively resistant to therapy with a poor prognosis. As other cancers, GBM starts from a relatively small fraction of poorly differentiated and particularly aggressive cancer stem cells (CSCs), responsible for aberrant proliferation and invasion, rapidly spreading the tumor growth in the other parts of the central nervous system. Due to the extreme tumor heterogeneity, standard therapies (i.e., surgery, chemotherapy and radiotherapy) provide poor positive outcomes and cancers usually recur. Therefore, alternative approaches, possibly targeting CSCs, are necessary for searching effective therapeutic strategies against GBM. Among many emerging new therapeutic strategies, ultra-short pulsed electric fields (PEF) are considered extremely promising in cancer therapy and our previous results demonstrated the capability of a specific electric pulse protocol, characterized by a high pulse amplitude and a short duration, to selectively affect medulloblastoma CSCs preserving normal cells. Here, we tested the same exposure protocol to investigate the response of U87 GBM cells, and of U87-derived neurospheres. By analyzing different in vitro biological endpoints and taking advantage of transcriptomic and bioinformatics analyses, we found that, independently of CSCs content, PEF exposure affected cell proliferation and differentially regulated hypoxia, inflammation and P53/cell cycle checkpoints. PEF exposure also significantly reduced the clonogenic potential, reducing the ability to form new neurospheres, and inhibited the invasion potential. Importantly, exclusively in U87 neurospheres, PEF exposure changed the expression of stemness/differentiation genes. Our results, confirm this physical stimulus as a promising treatment to destabilize the extreme intra-tumoral GBM heterogeneity opening up the possibility to develop future therapeutic strategies mediated by PEF exposure.

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Crystallites and Electric Fields in Solid Ammonia

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