Gazzaz HA, Ember E, Zahl A, van Eldik R (2009)
Publication Type: Journal article, Original article
Publication year: 2009
Original Authors: Gazzaz H.A., Ember E., Zahl A., Van Eldik R.
Publisher: Royal Society of Chemistry
Pages Range: 9486-9495
Journal Issue: 43
DOI: 10.1039/b912911a
Rate and activation parameters for the complex-formation reaction of Ni with 4-(2-pyridylazo)-N,N-dimethyl aniline (PADA) were studied as a function of pH in different buffers in both aqueous and sodium dodecyl sulfate (SDS) micelle solutions. In aqueous Tris buffer solution, the forward and backward rate constants increased with increasing pH, while the complex-formation constant decreased due to a larger increase in the backward rate constant. The activation entropy, ΔS, and activation volume, ΔV, changed with increasing pH from positive to negative values, suggesting an apparent changeover from a dissociative to a more associative mechanism. Complex-formation reactions with 2,2′-bipyridine in Tris buffer showed almost no increase in the forward and backward rate constants on increasing the pH, but the ΔS and ΔV values became more negative. N-ethylmorpholine buffer showed no pH effect on the rate constants and activation parameters. Water exchange reactions of aquated Ni were also studied as a function of pH under the same conditions. The reported rate and activation parameters for water exchange in Tris and N-ethylmorpholine buffers are consistent with those found for the complex-formation reactions of Ni with PADA. The observed pH and buffer effects for both the complex-formation and water exchange reactions of aquated Ni can be accounted for in terms of the formation of a Ni-Tris complex in Tris buffer and general base catalysis by the buffer components. In SDS micelle solution, the complex-formation reaction with PADA was much faster than in aqueous solution, but the increase in rate constant with increasing pH was less significant, while ΔS and ΔV became more positive, pointing to a more dissociative mechanism. For SDS micelle solutions there was no effect on the water exchange rate constant or activation volume. Mechanistic interpretations are offered for all observed pH, buffer and medium effects. © The Royal Society of Chemistry 2009.
APA:
Gazzaz, H.A., Ember, E., Zahl, A., & van Eldik, R. (2009). Mechanistic information from volume profiles for water exchange and complex-formation reactions of aquated Ni(II). pH, buffer and medium effects. Dalton Transactions, 43, 9486-9495. https://doi.org/10.1039/b912911a
MLA:
Gazzaz, Hanaa Asaad, et al. "Mechanistic information from volume profiles for water exchange and complex-formation reactions of aquated Ni(II). pH, buffer and medium effects." Dalton Transactions 43 (2009): 9486-9495.
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