Icosahedral nucleus

The arrangement of 22 spherons around an inner tetrahedron of four spherons shown in Fig. 7 involves icosahedral packing each of the four inner spherons is surrounded by an icosahedron of 12, three of which are the three other inner spherons. This structure (26 spherons, 52 neutrons) with one spheron missing may be assigned to magic number 50. The complete structure, with 26 spherons, corresponds to the stable nucleus as discussed in the following section. 

The non-enveloped human viruses all have icosahedral capsids. The structural proteins undergo a self-assembly process to form capsids into which the viral nucleic acid is packaged. Most non-enveloped viruses accumulate within the cytoplasm or nucleus and are only released when the cell lyses. 

The existence of icosahedral Ar clusters is essentially due to the stability of the icosahedral nuclei produced in the free jet expansion. Similarly, a small metallic cluster showing an icosahedral shape in micrographs must have been grown from a nucleus with identical shape. This does not mean, however, that this cluster is actually stable. In effect, a metastable cluster may survive if its temperature is low enough. It may even grow very rapidly while preserving its shape since an MIC layer possesses the remarkable property of needing only one nucleation to fill up a new layer, contrary to an fee cluster, which would need one nucleation on each face. ... 

Fig. 29. Calculated central transition spectra48 for a single spin-3/2 nucleus undergoing (a) four-site tetrahedral jumps and (b) 12-site icosahedral jumps between equally populated sites in each case. The motional correlation times are given in the figure in seconds for each lineshape. The quadrupole coupling constant (axially symmetric) used in the simulations was 3 MHz.

The building block of each layer of 10 is the spherical icosahedral giant oxidized cluster cage of the Mo72Fe3o type but which now has a reduced metal-oxide-based cluster - the tetrahedral two-electron reduced Keggin [H2PM012040] ion-as nucleus (Figure 8). Like in the layer compound 8, each of the cluster-cluster composites is linked to four others via Fe-O-Fe bonds to form a layer structure. 

Adenoviruses consist of a large double-stranded DNA genome (about 36 kilobase pairs long) packaged within a nonenveloped icosahedral capsid that is primarily composed of three virus-encoded proteins (hexon, pen ton base, and fiber proteins) [39]. The fiber proteins protrude fi om the surface of the virus and mediate its attachment to target cells via a high affinity interaction with the cellular receptor CAR (coxsackievirus and adenovirus receptor) [40]. The virus is then internahzed into endosomal vesicles via specific interactions between the penton base proteins and ofy integrins [41]. Adenoviruses escape these vesicles by an acid-induced endosomolytic activity and are transported to the nucleus, into which they enter via pores in the nuclear membrane [42]. 

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