Effect coordinatively-active

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

As described previously, lipophilic monoimidazole ligands form 2 1 complexes with the Zn2 + ion (n = 2 in Scheme 2) as active catalysts except for some sterically hindered ligands (Table 3, 5, 7), and bisimidazole ligands form 1 1 complexes (n = 1 in Scheme 2, Table 5). In this chiral system, the latter 1 1 complex accords with kinetic analyses for both L-47 and L,L-49 ligands as shown in Fig. 12 and Table 11. These conclusions seem to be reasonable since monoimidazole derivatives have only one imidazole nitrogen, while the other bisimidazole and chiral ligands have more than two nitrogen atoms which can effectively coordinate to the Zn2 + ion. 

R. Hoppe, Effective coordination numbers and mean Active ionic radii. Z Kristallogr. 150 (1979) 23. 

Reactions in solution proceed in a similar manner, by elementary steps, to those in the gas phase. Many of the concepts, such as reaction coordinates and energy barriers, are the same. The two theories for elementary reactions have also been extended to liquid-phase reactions. The TST naturally extends to the liquid phase, since the transition state is treated as a thermodynamic entity. Features not present in gas-phase reactions, such as solvent effects and activity coefficients of ionic species in polar media, are treated as for stable species. Molecules in a liquid are in an almost constant state of collision so that the collision-based rate theories require modification to be used quantitatively. The energy distributions in the jostling motion in a liquid are similar to those in gas-phase collisions, but any reaction trajectory is modified by interaction with neighboring molecules. Furthermore, the frequency with which reaction partners approach each other is governed by diffusion rather than by random collisions, and, once together, multiple encounters between a reactant pair occur in this molecular traffic jam. This can modify the rate constants for individual reaction steps significantly. Thus, several aspects of reaction in a condensed phase differ from those in the gas phase ... 

The reaction of cyclic nitrone with phenyl isothiocyanate <2003MI253>, isocyanate <1974JOC568>, or cyano-esters <1995JP11417> has been reported. The beneficial effect of activation of the dipolarophile by coordination on a platinum complex and focused microwave irradiation has been described (Scheme 15) <2003JCD2540>. 

It should be mentioned that donor substitution of the phenylene backbone of the salphen ligand was shown to have a decreasing effect on activity [103], which explains the overall lower productivity compared with halogen-substituted chromium salphens. However, experiments clearly proved an increased activity upon dimerization. Whereas the monomeric complex m = 4) converts about 30% of p-BL in 24 h, producing a molecular weight of 25,000 g/mol, the corresponding dimer yields up to 99% conversion with > 100,000 g/mol. Moreover, the smaller polydispersity (PD < 2) shows the better polymerization control, which is attributed to the decreased rate of polymer chain termination. This behavior is caused by the stabilization of the coordinated chain end by the neighboring metal center, as recently reported for dual-site copolymerizations of CO2 with epoxides [104-106]. The polymeric products feature an atactic microstructure since the... 

Communicate regularly Clear and ongoing communication within the transition team and with management is essential to effectively coordinate plan activities, report progress, resolve issues, and identify evolving resource needs. 

A discussion of the indirect dissipation mechanism is more pertinent to the present topic of incoherent tunneling reactions. In this mechanism, the reaction coordinate is coupled to one or several active modes that characterize the reaction complex. These modes are damped because of coupling to a continuous bath. The overall effect of active oscillators and bath may be represented by an effective spectral density 7eff(o>). For instance, in the case of one harmonic active oscillator with frequency friction coefficient 17, 7eff(w) is proportional to the imaginary part of its susceptibility and equals [Garg et al., 1985]... 

Besides the intrinsic value of the identification of a new, selective and high yield method to synthesise silsesquioxane Bu2Si20(0H)4, this experiment proved that tert-butyl silsesquioxane a2bA is a suitable precursor for titanium catalysts. Thus, silsesquioxane structures different from the known precursor silsesquioxane alb i [R7Si709(0H)3] [25, 26, 28] can effectively coordinate titanium centres to yield almost equally active epoxidation catalysts. 

By evaluating the character of influence of an R1-substituent on the stereochemistry of ICC of azomethinic ligands of type 868, the following two effects are usually emphasized spatial, related to volume, and coordinatively-active, caused by the presence of additional donor centers. The first one causes, in the majority of cases, distortions of tetracoordinated polyhedra the second one increases the coordination number of a metal complex-former from 4 to 5 and later to 6. Guided by these considerations, it is possible to carry out the controlled synthesis of metal complexes with a programmed geometry of the coordination unit. 

A study of the influence of coordinatively-active R1-substituent nature on the structure of complexes of type 868 was begun in the 1960s and continues to be of interest at present [100,134]. The effect of such substituents is related mainly to an increase of coordination number of the central atom of chelates 868, i.e., it provides a transition from square-planar or tetrahedral polyhedra to penta- or hexacoordi-nated ones. This circumstance allows us to carry out a programmed synthesis of ICC of the azomethinic series with pyramidal or octahedral structures. 

These observations clearly emphasize how the NMF is critical for maintaining physical properties of the SC. However, as our understanding of the terminal differentiation and SC maturation process has increased, it has become clear that by maintaining free water in the SC, the NMF also facilitates critical biochemical events. As indicated earlier the coordinated activity of specific proteases and lipases is essential for optimum SC function, and these hydrolytic processes can only function in the presence of water that is effectively maintained by the water-retaining capacity of the NMF. Perhaps the most striking example of this is the regulation of a number of intracellular proteases within the corneocyte that, as we discuss in the next section, are ultimately responsible for the generation of the major elements of the NMF itself. 

Blocking either the 2- or 4-position allows lithiation at the other LDA or BuLi can be used to 4-lithiate the 2-blocked 3-fluoropyridines 319,284 320285 and 321,286 287 and BuLi 2-lithiates the 4-blocked 3-fluoropyridine 322.284 288 289 Note the selectivity for removal of the acidified pyridine protons in 321 and 322 over the coordination-activated ones adjacent to the pivalanilide group. A double orthodirecting effect ensures 4-lithiation of 323.290... 

Synchronizing activities is the hallmark of coordination. Within a department, many functions take place simultaneously or in sequence to accomplish an objective. The function of the manager in this respect is to bring these activities together in an efficient and effective manner to produce the desired output. Coordinating activities include corrective actions, in which adjustments to a process need to be made to bring about the outcome preventative actions, which prevent problems from occurring and... 

The use of Al(III) complexes as catalysts in Lewis acid mediated reactions has been known for years. However, recent years have witnessed interesting developments in this area with the use of ingeiuously designed neutral tri-coordinate Al(lll) chelates. Representative examples involving such chelates as catalysts include (1) asymmetric acyl halide-aldehyde cyclocondensations, " (2) asymmetric Meerwein-Schmidt-Ponndorf-Verley reduction of prochiral ketones, (3) aldol transfer reactions and (4) asymmetric rearrangement of a-amino aldehydes to access optically active a-hydroxy ketones. It is important to point out that, in most cases, the use of a chelating ligand appears critical for effective catalytic activity and enantioselectivity. 

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