Effect of counterion

Table 43.2. Effect of counterions on the deactivation of Jacobsen s Co-salen catalyst...

Thus, effects of the surfaces can be studied in detail, separately from effects of counterions or solutes. In addition, individual layers of interfacial water can be analyzed as a function of distance from the surface and directional anisotropy in various properties can be studied. Finally, one computer experiment can often yield information on several water properties, some of which would be time-consuming or even impossible to obtain by experimentation. Examples of interfacial water properties which can be computed via the MD simulations but not via experiment include the number of hydrogen bonds per molecule, velocity autocorrelation functions, and radial distribution functions. 

Landis, F A. and Moore, R. B. 2000. Blends of a perfluorosulfonate ionomer with poly(vinylidene fluoride) Effect of counterion type on phase separation and crystal morphology. Macromolecules 33 6031-6041. 

It is generally accepted that there is little effect of counterion on reactivity of ion pairs since the ion pairs in cationic polymerization are loose ion pairs. However, there is essentially no experimental data to unequivocally prove this point. There is no study where polymerizations of a monomer using different counterions have been performed under reaction conditions in which the identities and concentrations of propagating species are well established. (Contrary to the situation in cationic polymerization, such experiments have been performed in anionic polymerization and an effect of counterion on propagation is observed see Sec. 5-3e-2.)... 

TABLE 5-11 Effect of Counterion on Anionic Polymerization of Styrene" ... 

The stereoselective polymerization of various acrylates and methacrylates has been studied using initiators such as atkyllithium [Bywater, 1989 Pasquon et al., 1989 Quirk, 1995, 2002]. Table 8-12 illustrates the effects of counterion, solvent, and temperature on the stereochemistry of the anionic polymerization of methyl methacrylate (MMA). In polar solvents (pyridine and THF versus toluene), the counterion is removed from the vicinity of the propagating center and does not exert an influence on entry of the next monomer unit. The tendency is toward syndiotactic placement via chain end control. The extent of syndiotacticity... 

TABLE 8-12 Effect of Counterion, Solvent, and Temperature of Polymerization of Methyl Methacrylate... 

To evaluate the effect of counterion screening on the chemical potential of the chosen solute ions, we first multiply (S8.6-12) by the appropriate prefactor for ions of charge Q (= ze) in a medium of dielectric constant k ... 

Table 12. Effect of counterion on the molecular weight of poly- N-vinylcarbazole) (/5)a...

Figure 4. Effect of counterion upon fragmentation observed in SIMS.

We first describe the NMR parameters for the duplex to strand transition of the synthetic DNA poly(dA-dT) (18) with occasional reference to poly(dA-dU) (24) and poly(dA- brdU) and the corresponding synthetic RNA poly(A-U) (24). This is followed by a comparison of the NMR parameters of the synthetic DNA in the presence of 1 M Na ion and 1 M tetramethylammonium ion in an attempt to investigate the effect of counterion on the conformation and stability of DNA. We next outline structural and dynamical aspects of the complexes of poly(dA-dT) with the mutagen proflavine (25) and the anti-tumor agent daunomycin (26) which intercalate between base pairs and the peptide antibiotic netropsin (27) which binds in the groove of DNA. 

The effect of counterion on the synthetic DNA conformation has been probed by comparing the NMR parameters in high salt sodium and tetramethylammonium solutions. We observe a specific change at one of the two glycosidic torsion angles and at one of the two phosphodiester linkages for poly(dA-dT) on proceeding from Na+ to TMA+ solutions. 

Of course, these relationships do not take into account the variations in SO4 chemical shift due to the effects of counterions, pH, concentration and temperature. It has not been possible to adopt the IUPAC chemical shift scale exactly, because that would require measuring the chemical shifts of all secondary references reported in the literature with respect to the standard suggested by IUPAC. 

Mah et al. demonstrated the effect of counterions on the cationic polymerization of styrene [35-37]. The radiation-induced polymerization is much more sensitive to impurities than the catalytic polymerization, as the former involves the cationic species in a free ion state. Thus, one can expect, in the presence of stable anions, the promotion of the cationic polymerization because of the ion-pair formation between the dimer cation and the counterion. The effect was... 

Table I. Effect of Counterion Species on Contact Angle, Series B Films...

Kadirov MK, Bosnjakovic A, Schlick S (2005) Membrane-derived fluorinated radicals detected by electron spin resonance in UV-irradiated Nation and Dow ionomers effect of counterions and H202. J Phys Chem B 109(16) 7664-70... 

---