Spherical complex

The dissolution of quartz is accelerated by bi- or multidentate ligands such as oxalate or citrate at neutral pH-values. The effect is due to surface complex formation of these ligands to the Si02-surface (Bennett, 1991). In the higher pH-range the dissolution of quartz is increased by alkali cations (Bennett, 1991). Most likely these cations can form inner-spheric complexes with the =SiO groups. Such a complex formation is accompanied by a deprotonation of the oxygen atoms in the surface lattice (see Examples 2.4 and 5.1). This increase in C H leads to an increase in dissolution rate (see Fig. 5.9c). 

Of the neutral ligands described in Section 2, the macrotetrolides and the macroheterobicyclic ligands form nearly spherical complexes and the depsipeptides valinomycin and enniatin B approximately cylindrical ones (Table l)6). Calculations of AGk-values for both kinds of complex show that the discrimination between mono- and divalent cations is dependent not only on the coordination number but also on the overall size and shape of the complexed ligand, because the electrostatic interaction of the complex with the surrounding medium (term AGs in Eq. 

Fig. 14. Calculated influence of dimensions of complexes on the preference of K+ over Baa+ with other parameters constant. Left spherical complex, cubic coordination. Right cylindrical complex, octahedral coordination (The circles on the calculated curves are at dimensions determined by X-ray analysis)...

Figure 6.10 View of the half-shell of the spherical complex 6.30 showing the five-membered P5 and six-membered P4CU2 rings.

In a similar manner, the reaction of 6.28 with CuCl in CH2CI2-CH3CN produces the spherical complex [ Cp Ta(CO)2(t " -P4) 6 CuCl g] (6.31). The tantalum complex 6.31 is comprised of 32 core atoms forming four-membered P4 rings and six-membered P4CU2 rings in an extended cubic arrangement with... 

Apolipoproteins ( apo designates the protein in its lipid-free form) combine with lipids to form several classes of lipoprotein particles, spherical complexes with hydrophobic lipids in the core and hydrophilic amino acid side chains at the surface (Fig. 21-39a). Different combinations of lipids and proteins produce particles of different densities, ranging from chylomicrons to high-density lipoproteins. These particles can be separated by ultracentrifugation (Table 21-2) and visualized by electron microscopy (Fig. 21-39b). 

Fig. 16 Typical TEM pictures of a dried dispersion on a copper grid. (a) At lower resolution spherical complex particles are shown surrounded hy a halo consisting of block copolymers (scale bar=500 nm). (b) At higher resolution, the internal structure of the particle is revealed to be tart-like (scale bar=200 nm). Reprinted with permission from [142], Copyright 2000 American Chemical Society...

A tennis-ball-shaped molecular aggregate can be constructed by the self-assembly of curved molecule I. Tetrameric assembly of II generates a pseudo-spherical capsule. Dimeric assembly of III can be induced by the encapsulation of smaller molecules of appropriate size and shape at the center of a spherical complex. 

Hydrophobic lipids (triacylglycerols and cholesteryl esters) are virtually completely insoluble in water they are solubilized for transport in plasma by incorporation into lipoproteins. Lipoproteins are spherical complexes containing triacylglycerol (triglyceride) and cholesteryl ester surrounded by a layer containing phospholipids, unesterified cholesterol, and specific apolipoproteins. 

In Table 4 there are presented data, concerning the specific adsorption of the ions at the silica/aqueous electrolyte interface. Metal ions may adsorb with formation of inner-sphere complexes, hydrocarbon clusters (for example Cu2+) or outer-spherical complexes as for example Mn2+ [105]. The determination of the adequate adsorption mechanism is possible with in situ spectroscopy method (Table 4). 

For two spherical complex ions of radii r, and r2 the free energy change required to rearrange the solvent shells of the two ions from the reactant state to the transition state is estimated (Marcus, 1956) from a classical dielectric continuum model of the solvent, giving (51) and (52), in which all quantities... 

Similar to solution complexation, surface complexation can be distinguished between inner-spherical complexes (e.g. phosphate, fluoride, copper), where the ion is directly bound to the surface, and outer-spherical (e g. sodium, chloride) complexes where the ion is covered by a hydration sleeve with the attraction working only electrostatically. The inner-sphere complex is much stronger and not dependent on electrostatic attraction, i.e. a cation can also be sorbed on a positively charged surface (Drever 1997). 

The exciplex or CIP is treated as a dipole of radius q and dipole moment p. The last term in Eq. (15) describes the energy of this dipole, based on the Kirkwood-Onsager model (assuming formation of a spherical complex) [14]. Thus, an exciplex or CIP is stabilized by Coulombic interactions and by solvation. The solvation energy is expected to be favored by increasing solvent polarity and a large dipole... 

Example 6.6. Kinetics of Complex Fonnation of Co with F Estimate the rate of inner-spheric complex formation of a 10 M F solution with Co(H20). The following simplifying assumption is made [Co(II)] > [F ]... 

Highly stable, 1 1 non-covalent, spherical complexes, e.g. (377), are formed from l,3,5-tris(methyl phosphonomethyl)benzene and triammonium compounds. ... 

Meissner, R.S. Rebek. J.. Jr. de Mendoza. J. Autoencapsulation through intermolecular forces A synthetic selfassembling spherical complex. Science 1995. 270 (5241). 1485-1488. 

Lysozyme Poly(styrenesulfonate) Spherical complexes, dense globules [120]... 

To obtain the extended structures from cages in the light of molecular size and weight, intense efforts have been paid to construct symmetric spherical complexes composed of a large number of building blocks. In a sphere molecule, many weak interactions to construct the skeleton are... 

GIANT SELF-ASSEMBLED MnL2n SPHERICAL COMPLEXES... 

Another member of this giant spherical complex is 72-component M24L4g rhombicuboctahedra, which can form from self-assembly of square planar Pd ions and bent ligands with a bend angle of 135° (Fig. 9.40) [48,52]. It is noteworthy that switching between two spherical complexes of M24L4g and M12L24... 

Another example of polymerization in self-assembled spherical complexes is related to polymerization of an anionic monomer within the nanocavity of a highly cationic M12L24 coordination sphere with 24 ammonium cations on its interior surface [60]. The highly cationic nanoenvironment of this nanocage was exploited for controlling radical polymerization of anionic sodium p-styrenesulphonates. It was demonstrated that a cationic sphere can have electrostatic interactions with anionic guests and encapsulate them within its cationic interior. 

Harris K, Fujita D, Fujita M. Giant hollow MnL2n spherical complexes structure, function-aUsation and applications. Chem Commun 2013 49 6703-12. 

Meissner RS, Rebek J Jr, de Mendoza J (1995) Autoencapsulation through intermolecular forces a synthetic self-assembhng spherical complex. Science 270(5241) 1485-1488... 

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