Kinetic stability shape

In contrast to the above-described kinetic stability, colloids may also be thermodynamically stable. A stable macromolecular solution is an example we have already discussed. Formation of micelles beyond the critical micelle concentration is another example of the formation of a thermodynamically stable colloidal phase. However, when the concentration of the (say, initially spherical) micelles increases with addition of surfactants to the system, the spherical micelles may become thermodynamically unstable and may form other forms of (thermodynamically stable) surfactant assemblies of more complex shapes (such as cylindrical micelles, liquid-crystalline phases, bilayers, etc.). 

Myers (1960) recognized two kinds of stability, viz., inherent stability as a function of time, and induced stability as a function of stimuli. Induced kinetic stability necessitates the expenditure of work exceeding .12 Acceptance of a stabilization role for water has not been universal Jirgensons (1946) argued against it, enunciating instead the influence of particle shape and the mutual chemical affinity between atomic groups at the solid-liquid interface. 

So, NMR spectra of 4,4 -bipyridyl, pyrazine, and ethylenediamine coordinated to undecatungstocobalto(III)silicate and -borate anions. Identification of 1 1 and dumbbell-shaped 12 complexes, Bull. Korean Chem. Soc, 14 759 (1993) (c) J.L. Samonte and M.T. Pope, Derivatization of polyoxotungstates in aqueous solution. Exploration of the kinetic stability ofcobalt(II)- and cobalt(III) derivatives of lacunary anions with pyridine and pyridine-type ligands. Can. J. Chem.. In press... 

A template approach has been invoked by Stack et al. to immobilize a metastable [Fe"(OTf)2(phen )2] (phen , substituted 9,10-phenanthroline) complex 12 in a preformed binding pocket shaped by a thermodynamically stable [Cu(phen )2] template. After replacing Cu+ by Fe +, the iron(II)-containing polymer 12 was obtained. A [Fe (OTf)2(phen )2] intermediate is unstable in a homogeneous solution and rapidly leads to the tris(chelate) [Fe(phen )3] + complex and Fe + ions [21]. Thus, the matrix prevents ligand scrambling and again kinetically stabilizes a metastable species by site isolation. 

Mechanically bonded complexes that undergo no dissociation have the same kinetic stability as covalent molecules, whereas their supramolecular structures generate a variety of dynamic and responsive functions. Use of such supramolecular motifs may prove a useful approach to construction of the cavity-shaped frameworks that are more relevant to the modeling of enzymes. 

Thus, the shape and orientation of the NHCs may dictate the selectivity. It is also well established that large ligands kinetically stabilize transition metal complexes and support reductive eliminations. Conversely, it is assumed that the steric hindrance is detrimental to oxidative addition steps. In contradiction with this common belief, Organ and Holland showed that the... 

This reaction has been reexamined using optical, IR and NMR spectroscopic methods to probe NO reactions with Fe(TPP)(NO) and the more soluble Fe(TmTP)(NO) (92). These studies confirmed the formation of Fe(Por)(NO)2 in toluene-dg at low temperature (Eq. (43)). NMR line shape analysis was used to calculate K43 = 23 M-1 at 253 K (3100 M-1 at 179 K, AH° = —28kJmol 1) (92). The failure of the Fen(Por) complexes to promote NO disproportionation, in contrast to the behavior of the respective Ru(II) and Os(II) analogs, may find its origin partly in the relatively low stability of the dinitrosyl intermediate (K52 estimated to be 2.8 M-1 at 298 K) and unfavorable kinetics of subsequent reaction of this species with NO. 

The function f(it) can be given in a concrete expression as "S"-shape nonlinear function, schematically shown on the left in Figure 8A. For the convenience of analysis we take the approximation to express the "S"-shape characteristics with the combination of two straight lines as shown on the right in Figure 8A. The third term of Equation 2-2 means the increment of [D] with compression at the air/water interface. To simplify the analysis, we further assume kj k i. This assumption is consistent with the observed stability of the bilayers formed at the zero surface pressure point. The kinetics of [D] can be then expressed as... 

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