Morphology icosahedral

Virus symmetry The nucleocapsids of viruses are constructed in highly symmetrical ways. Symmetry refers to the way in which the protein morphological units are arranged in the virus shell. When a symmetrical structure is rotated around an axis, the same form is seen again after a certain number of degrees of rotation. Two kinds of symmetry are recognized in viruses which correspond to the two primary shapes, rod and spherical. Rod-shaped viruses have helical symmetry and spherical viruses have icosahedral symmetry. 

The two groups of viruses, RNA and DNA, are further divided according to size, morphology, and biological and chemical properties. Thus, the icosahedral RNA viruses that are ether stable are divided into the picornaviruses and the reoviruses. The name picornavirus comes from pico... 

Clathrins, first observed by Pearse, are structures with pentagonal and hexagonal faces that can form three dimensional structures with the same truncated icosahedral morphology as a C6o molecule or a soccer ball [1], The vertices of the clathrin coating are formed by three intertwined proteins composed of heavy and light chains that emanate from a central hub in a structure known as a triskelion, shown in Fig. 3.1. 

An excellent example where a capsid virus has been given a new supramolecular application can be found in the work of Nolte who took an icosahedral capsid virus, cowpea chloritic mottle virus (CCMV) and used it as a nanoreactor for polymer synthesis [30], Natural CCMV spontaneously assembles in acidic aqueous solution and disassembles in basic solution. The capsid contains pores open at pH 5 to release RNA into the host. Once the RNA leaves, the empty capsule is left. The Nolte group was able to assemble the subunits around polystyrene sulfonate with a mass of 9.9 kDa but the resulting structure had a different morphology to the natural system. Indeed, capsules formed around polymers with masses between 2 and 85 kDa but not around those with masses above 100 kDa. This raised the question of the potential for polymers to form within a capsid but to test the possibility a mixture of botanical, biological and chemical approaches was needed. 

At the morphological level, one observes in axially symmetric proteins linear and planar crystallographic scalings, whereas 3-dimensional scaling occurs in icosahedral viruses. 

For Au NPs supported on the MgO(lOO) surface TEM has shown that even very small clusters are well faceted and fee ordered (36). This is explained by the strong adhesion and small lattice mismatch ( 3%) between Au and MgO, which favors epitaxial Wulf-Kaischew-Iike morphologies. For larger lattice mismatch (e.g. Pd/MgO) NPs may be significantly strained and contain dislocations. To model these effects theoretically requires carefiil treatment of the metal-substrate interaction (37). In contrast for weakly interacting supports, such as graphite, strained decahedral and icosahedral clusters have been observed by TEM (33). 

Fullerenes are carbon allotropes discovered in 1985 by Harold W. Kroto, Robert E Curl and Richard E. Smalley. These carbon nanostructures possess icosahedral symmetry and are sp hybridized. Fullerenes have a closed cage-like structure and are examples for zero-dimensional CNMs. Depending on the number of carbon atoms that a cluster possesses, these are named (contains 60 carbon atoms), C (contains 70 carbon atoms), Cg (contains 84 carbon atoms), etc. The unique morphology of these CNMs possess large surface area to volume ratio and is suitable for a wide variety of applications. Synthesis methods of fullerenes are well developed [7-9]. 

Icosahedral nanoparticles were also made recently. This morphology is composed of 20 tetrahedral subunits with 30 twinned plates, and one icosahedral nanocluster is bound with 20 111 facets. Ag, An, and Pd are among the metals that can form... 

This represents the solution for the kissing problem in three dimensions and is valid for icosahedral and cuboctahedral morphologies. For other shapes, the reader may refer to a paper from the group of Martin [29]. Particles possessing the above number of atoms are said to be in a closed-shell configuration. The number of atoms required to fill up coordination shell completely, nx, of a particular shell, is given by... 

On the basis of the evidence in fig. 106 for the thermodynamic stability of the icosahedral phase, we conclude that it should be possible to obtain large icosahedral grains by slow cooling fix)m the melt. Figure 107 shows the solidification morphology observed... 

The growth morphology of the stable decagonal quasi crystals Al-Ni-Co or Al-Mn-Pd shows that they grow as decaprismaic (ten prism faces with the tenfold axis as rotation axis). Al-Cu-Fe quasi crystals, which are icosahedral quasi crystals, grow with triacontahedral shape, which exhibit 30 rhombic faces perpendicular to the twofold rotation axes. Though the interpretation of the patterns involves more mathematical complexicity, the experimental... 

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