Counterions structure

Evans, and later j0rgensen, studied the counterion effect of these Cj-symmetric bis(oxa-zoline)/Cu(II) complexes, and found that the counterion structure dramatically affected the catalytic efficiency, and SbFg- was the best among the anions examined (SbF6>PF6>OTf>BF4) [27,28] (Eq. 8A.15). This cationic bis(oxazoline)/Cu(II) catalyst has been successfully applied to asymmetric synthesis of enr-A1 -tetrahydrocannabinol [29] and enf-shikimic acid [30]. 

The extent of aggregation observed by small-angle neutron scattering Is very dependent on concentration In agreement with light scattering and solution viscosity studies. These measurements on SPS solutions are expected to apply In general to Ionomer solutions In low polarity solvents with appropriate considerations for polymer architecture and counterion structure. 

Effect of Counterion Structure on Ionomer Properties Quaternary Phosphonium Counterions in Sulfonated EPDM... 

Bijma, K., Rank, E., and Engberts, J. B. F. N., Effect of counterion structure on micellar growth of alkylp5n idinium surfactants in aqueous solution, J. Colloid Interface Sci., 205, 245—256 (1998). 

With isotopic labelling experiments, not only the polyion-polyion structure factor, but also other partial structure factors such as counterion-counterion structure factors, have been determined [137, 138]. First experiments provide evidence that the counterion-counterion structure factor also exhibits a peak at nearly the same position as the peak in the polyion-polyion structure factor. This is interpreted to originate from condensation of counterions onto the polyions. A similar observation was also made using SAXS by studying poly-potassiumstyrenesulphonate (KPSS) and NaPSS [139], where the scattering curve is mostly determined by the distribution of counterions because of their high contrast factor. 

Biomimetic systems based on cationic surfactants composed of an isosteviol moiety and different counterions, namely bromide (SI) and tosylate (S2), have been designed. The counterion structure was shown to play a crucial role in the surfactant association. A number of methods used provide evidence that only one type of aggregate, i.e., micelles were observed in the S2 systems, while a concentration-dependent association occurred in the case of SI. The DLS and fluorescence anisotropy measurements showed that the micelle-vesicle-micelle transitions probably occur with the SI system. The occurrence of small aggregates near the CMC with radii of 2.5 nm is supported by NMR self-diffusion data. ... 

When the ionic (ions and ion pairs of equal reactivity, without regard for the counterion structure) and covalent species operate simultaneously, such that the apparent rate constant (kp) is a resultant of the absolute rate constants kj, and kp and proportions of ionic (P) and covalent species (1-P) ... 

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