WorldWideScience

Sample records for allotropy

  1. UV inactivation of enzymes in supramolecular complexes of biological membranes. The phenomenon of photochemical allotropy

    International Nuclear Information System (INIS)

    The photosensitivity of erythrocyte acetylcholinesterase (AChE) is different in its free and membrane-bound states. The modification of the structure of membraneous lipids by phospholipases A2, C and D or by cholesterol depletion is accompanied by a change in AChE photosensitivity. UV light was demonstrated to induce cooperative structural transitions in the erythrocyte membrane. This follows from the data obtained by circular dichroism and solubilization in detergents. In contrast to free AChE, UV light acts on the membraneous enzyme as a mixed inhibitor (simultaneous change in Vsub(max) and Ksub(m)). The anomalous behaviour of membrane-bound enzyme, termed the phenomenon of photochemical allotropy, is associated with a modification of the structure within the microenvironment of the residual AChE. The phenomenon depends on membrane integrity, and disappears after treatment of erythrocyte ghosts with ultrasound, trypsin, phospholipases and neuraminidase and remains unchanged in cholesterol-depleted membranes. The nature and localization of events responsible for this phenomenon are discussed. (author)

  2. Oana Salişteanu Cristea, Prestito latino - Elemento ereditario nel lessico della lingua italiana - Doppioni e varianti, Istituto di Studi Romanzi, Facoltà di Lettere, Università Carolina Praga; Praga 2000, pp. 199

    Directory of Open Access Journals (Sweden)

    Pavao Tekavčić

    2005-12-01

    Full Text Available La ricchezza del lessico italiano dall'antichità ad oggi e la sua complicata stratificazione sono oggetto dell'interesse dei linguisti da più di un secolo e mezzo; eppure, c'è una serie di problemi non studiati a fondo, tuttora aperti e promettenti. Uno di tali temi è la coesistenza di due (o più riflessi di una sola base latina, cioè gli allotropi e doppioni (franc. doublets. Dai tempi di Ugo Angelo Canello (anni 70 dell'Ottocento questo settore del vocabolario non cessa di preoccupare gli studiosi ed il più recente contributo -- importantissimo, diciamolo subito-- che riassume, discute, sistematizza e in gran parte completa quanto fatto finora, è il recentissimo volume della professoressa Oana Sălişteanu Cristea, docente di linguistica italiana (storia della lingua, filologia e dialettologia all'Università di Bucarest. Questo libro è l'oggetto della presente recensione.

  3. Carbon nanoribbons and nanotubes based on δ-graphyne: A first-principles study

    Science.gov (United States)

    Zhou, Hongcai; Lu, Shuangwen; Li, Feng; Qu, Yuanyuan

    2016-04-01

    As a stable allotropy of two-dimensional (2D) carbon materials, δ-graphyne has been predicted to be superior to graphene in many aspects. Using first-principles calculations, we investigated the electronic properties of carbon nanoribbons (CNRs) and nanotubes (CNTs) formed by δ-graphyne. It is found that the electronic band structures of CNRs depend on the edge structure and the ribbon width. The CNRs with zigzag edges (Z-CNRs) have spin-polarized edge states with ferromagnetic (FM) ordering along each edge and anti-ferromagnetic (AFM) ordering between two edges. The CNRs with armchair edges (A-CNRs), however, are semiconductors with the band gap oscillating with the ribbon width. For the CNTs built by rolling up δ-graphyne with different chirality, the electronic properties are closely related to the chirality of the CNTs. Armchair (n, n) CNTs are metallic while zigzag (n, 0) CNTs are semiconducting or metallic. These interesting properties are quite crucial for applications in δ-graphyne-based nanoscale devices.