Spatial arrangements, typical

The three dimensional analogue of a BLM is a vesicle, Fig. 1. Like the bilayer, the wall thickness of a vesicle is typically about 50 A and the vesicle itself may be 300 to 1000 A in diameter. This spatial arrangement makes possible the formation of two phases inside and outside the wall with different chemical compositions. Although the permeability of a typical membrane by water is relatively high (ca. 10 2 cm/sec), that of ions and small neutral molecules is much lower (Na+ ... 

Many polymers have the capability to crystallize. This capability basically depends on the structure and regularity of the chains and on the interactions between them. The term sernicrystalline state should be used rather than crystalline state, because regions in which the chains or part of them have an ordered and regular spatial arrangement coexist with disordered regions typical of the amorphous state. X-ray diffraction studies of samples of polymers crystallized from the melt reveal diffuse zones, char-... 

Another typical secondary structure is the p-sheet. Tertiary structure describes the spatial arrangement of amino acid residues that are far apart (such as folding of parts of the protein connected by disulfidic bonds). 

Pyrolysis of nylon 6 generates a significant proportion of caprolactam, which can be considered the monomer. The cleavage of the peptide bond explains easily the formation of the monomer. The molecules of polymers have a spatial arrangement and do not have a linear form as typically indicated with planar chemical formulas (see also Section 1.3). The idealized spatial form for the molecule of nylon 6 is suggested below ... 

In Figure 1 examples of structure of some zeolites are given to picture some typical spatial arrangements of channels, cavities, etc. 

Protein structure is typically classified as consisting of four levels primary (1°), secondary (11°), tertiary (III°), and quaternary (IV°). Primary structure is the sequence of amino acids in the protein. Secondary structure is the local three-dimensional spatial arrangement of amino acids that are close to one another in the primary sequence. a-Helices and P-sheets compose the majority of secondary structures in all known proteins. Tertiary structure is the spatial arrangement of amino acid residues that are far apart in the linear primary sequence of a single polypeptide chain, and it includes disulfide bonds and noncovalent forces. These noncovalent forces include hydrogen bonding, which is also the primary stabilization force for the formation of a-helices and P-sheets, electrostatic interactions, van der Waals forces, and hydrophobic effects. Quaternary structure is the manner in which subunits of a multi-subunit protein are arranged with respect to one another. 

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