Spheroidal molecule

A somewhat different approach to providing tailored cavities for metal cations was taken by the groups of Cram and Lehn °. Graf and Lehn prepared the spheroidal molecule 21 which has an interesting molecular architecture. The molecule has ten coordination sites within it, six which form an octahedral array and four which are in a tetrahedral arrangement. This remarkable compound is soluble in all solvents from petroleum... 

Abstract The present paper discusses classification of nano-objects, which is based on their size, morphology and chemical nature. The subject of nanochemistry includes those nano-objects whose chemical properties depend on size and morphology, such as spheroidal molecules, anisotropic (2D) and isotropic (ID) nanoparticles, nano-clusters and nanophases. Nanophase is a nano-dimensional part of the microphase whose properties depend on its size. The potential health hazards of nano-objects are associated with their capability of penetrating the body through inhalation, digestion or the skin. 

At the end of the twentieth century, in the area of physics, and later in the area of chemistry extraordinarily important experimental results were produced, which gave rise to a new concept of nano-world. Development of high resolution electron microscopes allows detection of not only nano-dimensional particles but also large molecules. New types of matter such as spheroidal molecules with a hollow core (fullerenes and nanotubes), nanosized phases formed by a few atoms of metals... 

The first thing that attracts attention is a stable tendency to energy decrease with an increase of the number of atoms and therefore the size of a fullerene cage (Fig. 1). It is obvious that it reflects the overall decrease of a molecular strain of spheroid molecules going from C6o to higher fullerenes. 

X, measures the energy barrier involved as the solvent dipoles change. For spheroidal molecules, the following expression was first used by Marcus... 

Half-generation starburst polyamidoamines were hydrolyzed by the author by reacting with NaOH in methyl alcohol. This generated spheroidal molecules with negative charges dispersed on the periphery. Counterions consisted of Na", K+, Cs" or Rb . Other examples are described (1,2,3). 

Molecular globularity is defined as with surface area of a sphere of volume V, where S and Vare the molecular surface and volume described above, respectively. Globularity is 1.0 for perfect spherical molecules. It assumes values greater than 1.0 for real spheroidal molecules. Globularity is also related to molecular flexibility. 

We started this section with a reference to the ancient perception about the elements of Perfection and their role in the Universe. Here it seems timely to remember that the highest symbol of the Harmony and Unity in the World had been always represented in the shape of the Sphere. The repercussions of these beliefs can be found in all religions, very ancient and rather modern. Therefore it is hardly surprising to observe that the preparation of a nearly perfect spheroidal molecule, buckminsterfullerene 59, besides its overwhelming scientific importance, elicits a special excitement due simply to the intrinsic beauty of this structure and its appeal to the common perception of Harmony. 

The Rieske-protein fragment is an oblate spheroidal molecule measuring 40x45x25 A. As shown in the stereogram in Fig. 4 (C), the molecule consists of three sheets of anti-parallel P-strands, with P-sheet-1 consisting of P-1, -9 and -10 strands P-sheet-2 of p-2, -3, and -4 strands, and P-sheet-3 of p-5, -6, -7, and -8 strands. The p-sheets and strands may be visualized from the stereogram of the three-dimensional Ca structure shown in Fig. 4 (C). A front view of two Rieske ISPs, one from bovine-heart mitochondria and one from spinach chloroplasts, are shown in Color Plate 14 (A) and (B), where the three layers of antiparallel P-sheets can be seen even more easily. 

Heme electronic structures can depend sensitively and selectively on molecular structure details, that very subtle aspects of the heme environment may be elucidated by their influences on hyperfine shifts. " " Myoglobin (Mb) is a monomeric b-type haemoprotein of 17k Da and its protein moiety consists of eight helices, A-H, that are linked by short polypeptide segments to form an oblate spheroid molecule (Fig. 2). Lecomte and La Mar reported that... 

Macropore and film diffusion are relatively well understood and are therefore not discussed in any detail in this voliune. In contrast, despite intensive study over the last 30 years, our imderstanding of micropore diffusion is still far from complete. At the micropore scale diffusive transport is largely controlled by steric interactions which are dominated by repulsive forces. The relative diameter of the micropore and the diffusing molecifie is clearly a critical variable. For small spherical or spheroidal molecules there is a clear... 

Both dodecahedrane, (CH)2o, and buckminsterfullerene, Qo, appear to thwart entropy by folding 20 atoms and 60 atoms, respectively, into spheroid molecules of icosahedral symmetry. Unlike C o, dodecahedrane... 

It should be noted that metal clusters can also be formed in fiillerenes or nanotubes. Endohedral complexes Mn C6o, in which metal clusters are localized in the inner cavities of the spheroidal molecule Ceo, and organometallic polymers of the type CeoPdn are known. Nanocomposite materials are also formed upon evaporation of... 

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