Cage-like structure

The hydrophobic effect. Water molecules around a non-polar solute form a cage-like structure, which ices the entropy. When two non-polar groups associate, water molecules are liberated, increasing the entropy. 

Analysis This cage-like structure contains 6, 5 and 4-membered rings we are most interested in the 4, and can disconnect this in two ways ... 

Unusual heterocyclic systems can be obtained by photodimerizations and for five-membered heterocycles with two or more heteroatoms such dimerizations need be effected on their ring-fused derivatives. Cyclobutanes are usually obtained as in the photodimerization of the s-triazolo[4,3-a]pyridine (540) to the head-to-head dimer (541). These thermally labile photodimers were formed by dimerization of the 5,6-double bond in one molecule with the 7,8-double bond in another (77T1247). Irradiation of the bis( 1,2,4-triazolo[4,3-a]pyridyl)ethane (542) at 300 nm gave the CK0ifused cyclobutane dimer (543). At 254 nm the cage-like structure (544) was formed (77T1253). 

Boron Compounds with Cage-Like Structures... 

Crossley (89) described the self-assembly of a spherical cage-like structure made up of two zinc porphyrin dimers bound to a tetramine ligand. The 2 1 complex is stable at 10-6m concentrations, but addition of excess of ligand causes dissociation of the capsule with formation of a 1 1 complex. 

This is possible only because further attack by Br , on the first-formed intermediate (14), is prevented completely by the extremely bulky, cage-like structures at each end of the original double bond completion of normal, overall addition of Br2 thus cannot occur. 

Although it is probable that only four bonds are formed in many complexes, the cage-like structures effectively prevent the formation of complexes other than those with 1 1 stoichiometry (Chapter 3). This feature is of considerable analytical importance. 

EDTA forms stable complexes with a wide range of metal ions. The exceptional stability is conferred by the large number of donor groups and the subsequent isolation of the metal ion in the cage-like structure. It is clear from the foregoing section that complex formation will be pH dependent and may be represented by different equations depending on the pH and the ionic form of the EDTA. However, for purposes of comparison it is best to use the equilibrium... 

Dinuclear rhodium(II) carboxylate complexes with cage-like structures 46, in which carboxylate groups bridge the two metals and a... 

Clathrin-mediated endocytosis involves the internalization of transmembrane receptor-ligand complexes stimulating the formation of a coated pit that eventually buds off the membrane to form an intracellular endocy-totic vesicle. This process is dependent on the protein clathrin that is recruited to the membrane and forms a cage-like structure around the forming pit. Internalization via clathrin-dependent pathway allows the uptake of particles approximately 120nm in size (63-65). Once internalized, the clathrin coating disassociates from the endosome to be recycled and to allow the endosome to fuse with an intracellular compartment, usually a... 

The size of these macrocycles and their cage-like structure renders them suitable to serve as host molecules or artificial receptors for small molecules, in addition to having possible biological activity. 

Diamines with a cage-like structure in which the nitrogen atoms are separated by a three carbon chain, form radical-cations where the non-bonding orbital from one nitrogen atom interacts with the radical-cation on the other nitrogen atom to form a three-electron bond [76]. Cyclic voltammetry of 16 in acetonitrile shows two reversible waves with E° = 0.11 and 0.72 V vs. see. The second wave is due to the formation of a dication with a tw o-electron bond between the nitrogen atoms. 

The unusual cage-like structure of S4N4 (7) has evoked continued debate over its electronic structure. The possible existence of bonding interactions between trans-annular sulfur atoms has received particular attention. Extended Huckel CNDO... 

Ultramarines are three-dimensional cage-like structures. They differ from feldspars and zeolites because of the large spaces within the structures that can contain cations and anions but not water, illustrating a natural buckeyball-like structure and cavity, and a diversity of environment between the internal and external cages. Ultramarines can act as ion-exchangers for both anions and cations. The blue color of ultramarines is due to the presence of the ion although a yellow ion S2 also exists in the same structure. 

Cage-like structures containing phosphorus have been assigned on the basis of NMR spectra. For instance, in B10H10CHP, identified as a... 

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