Estimation of medium effect on dissociation constant of ammonium ion and formation constants of silver(I)-ammine complexes in aqueous solution

Acidity constants of ammine complexes of tetravalent platinum in aqueous solutions have been determined by a spectrophotometric method at very low ionic strengths and extrapolated to zero ionic strength. Temperature variations of pK-values (25 °C and 50 °C) yield thermodynamic parameters for two successive deprotonation steps of hexaammineplatinum(IV), pentaamminechloroplatinum(IV), and tris(ethylenediamine)pla- tinum(IV) complexes and for the deprotonation of pentaammineaquacobalt(III) ion.The enthalpy changes for the first and second steps are similar and range from 50 to 75 kJ/mole while for the aqua ligand of Co(III) 33 kJ/mole are found. The very large difference in the entropy changes (about 70 to 80 J/K mole for the first step and -10 to + 20 J/K mole for the second step) is interpreted by a model of solvation change. The primary hydration sphere of strongly oriented and immobilized water dipoles around the highly charged complex cation is transformed to a hydrogen-bonded solvation sheath when the electric field of the complex is weakened upon release of the first proton.

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ChemInform Abstract: DISSOCIATION CONSTANT OF COPPER SULFATE IN AQUEOUS SOLUTION FROM EMF DATA

Chemischer Informationsdienst ◽

10.1002/chin.198441013 ◽

1984 ◽

Vol 15 (41) ◽

Author(s):

S. N. PRASAD ◽

J. C. GHOSH

Keyword(s):

Aqueous Solution ◽

Dissociation Constant ◽

Copper Sulfate

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Fluorescence of the Complexes of 2-Methylnaphthoate and 2-Hydroxypropyl-α-, -β-, and -γ-Cyclodextrins in Aqueous Solution

Applied Spectroscopy ◽

10.1366/000370202321115841 ◽

2002 ◽

Vol 56 (12) ◽

pp. 1579-1587 ◽

Cited By ~ 20

Author(s):

Antonio Di Marino ◽

Franscisco Mendicuti

Keyword(s):

Aqueous Solution ◽

Fluorescence Anisotropy ◽

Intensity Ratio ◽

Driving Forces ◽

Emission Spectra ◽

Formation Constants ◽

Dielectric Constants ◽

Additional Information ◽

Fluorescence Techniques ◽

Naturally Occurring

Fluorescence techniques were employed to study the inclusion complexes of 2-methylnaphthoate (MN) with 2-hydroxypropyl-α-cyclodextrin (αHPCD), 2-hydroxypropyl-β-cyclodextrin (βHPCD), and 2-hydroxypropyl-γ-cyclodextrin (γHPCD). Emission spectra of MN show two vibronic bands whose intensity ratio R is very sensitive to the polarity of the medium. The stoichiometry and formation constants of these complexes were investigated by obtaining R as a function of the cyclodextrin (CD) concentration. Results showed identical stoichiometry (1/1) for the three MN/αHPCD, MN/β-HPCD, and MN/γHPCD complexes. Formation constants at 25 °C were 780 ± 15, 2700 ± 130, and 165 ± 10 M−1, respectively. ΔH0 and ΔS0 were obtained from linear van't Hoff plots. Results reveal that the complexation of MN with αHPCD is enthalpy driven. With βHPCD, both the entropy and enthalpy terms favor the process, whereas the formation of the complex with γHPCD is entropically governed. The extrapolation of R at infinite CD concentration allows us to estimate the effective dielectric constants of the inner CD cavities, which are around 50, but which differ from their counterparts, the naturally occurring α-, β-, and γ-CDs. Fluorescence anisotropy, quencher lifetimes, and average lifetimes can also give additional information about the structure and driving forces accompanying the formation of such complexes.

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