Effect of counterion on the

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

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

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. 

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... 

Effect of Counterions on the Hydrovinylation. In the hydrovinylation of styrene using a ligand with a hemilabile atom... 

Table 2 Effect of counterions on the hydrovinylation of styrene using hemilabile ligand...

Table II. Effect of Counterion on the Rate of Anionic Homopolymerization of Styrene in Tetrahydrofuran at 25 C.

The partition behavior of compounds between aqueous phases and octanol is now a routine measurement or calculation used in life sciences research as a model for membrane transport, particularly across the blood-brain barrier. The effect of counterions on the partition of saccharin has been extensively studied to investigate permeation of, and solubility in, lipid membranes <89PHA66, 90PHA191). 

The work of Allen et al. was extended simultaneously by Bhattacharyya et al.272 and by Dainton, Ivin and their students274. Both groups investigated the effect of counterions on the propagation constant. Bhattacharyya et al. monitored the progress of the reaction by a spectrophotometric technique and confirmed the independence of the bimolecular propagation constant of the concentration of sodium polystyryl varied by a factor of 24. The absence of free ions was demonstrated by the lack of conductance of the... 

Neglect the effect of counterions on the conformation of charged chains ... 

The effect of counterions on the Si shift is of some interest, since such effects might give useful information on the geometric relationship of Si s and nearby counterions. Many expected that interaction with cations would be deshielding, based on... 

Fig. 12. Effect of counterion on the sample concentration dependence of the distribution coefficients in MgX2-BaX2 (a) and BaXa-MgXa (b) systems.

K.-I. Izutsu, Y. Fujimaki, A. Kuwabara, and N. Aoyagi, Effect of Counterions on the Physical Properties of 1-Arginine in Frozen Solutions and Freeze-Dried Solids, Int.. Pharm., 301,161 (2005). 

Consideration of the effect of counterion on the p value for addition of poly(styryl)carbanions to DPE is also instructive. The p value increases as the size of the counterion increases, i.e., as the electrostatic interaction of the counterion with the negative charge decreases. This effect would be expected for any transition state structure, since the small lithium cation would be expected to minimize delocalization into the phenyl rings (see Sect. 2.2 of this review and Chap. 1 of [3]). Thus, with the cesium counterion, for any degree of charge transfer onto the 1,1-diphenylcarbon in the transition state, this charge would be more delocalized than for the corresponding lithium system. It would also be predicted that the p value for addition of butyllithium to styrene... 

To model reactions in. solution, other workers have included the effects of counterions on the potential eneigy surface. For example, LiNHi has been used to model the synthetically important reactions of lithium amides with carbon acids such as aldehydes and acetylenes. When carbonyls are involved (i.e., aldehydes), precoordination of the carbonyl oxygen to the metal ion plays an important role and must be incorporated for a realistic description of the condensed phase system. To date, efforts to model counterion effects generally have neglected solvent and it appears that a QM/MM or related approach could be valuable for future studies of ion-paired proton transfers. 

Biihl M, Schreckenbach G, Sieffert N, Wipff G. Effect of Counterions on the Structure and Stability of Aqueous Uranyl(VI) Complexes. A First-Principles Molecular Dynamics Study. Inorg Chem. 2009 48 9977-9979. 

Buhl M, Schreckenbach G, Sieffert N and Wipff G 2009 Effect of counterions on the structure and stability of aqueous uranyl(vi) complexes, a first-principles molecular dynamics study. Inorganic Chemistry mil), 9977-9979. PMID 19780567. 

The effect of counterions on the phase behavior of perfluoropolyether car-boxylates (Cl-PFPE-X, where X = Na, K, or NH4) of the general structure... 

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