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Spectroscopic studies of proton-transfer and metal-ion binding of a solution-phase model for silica-immobilized 8-hydroxyquinoline

Journal Article · · Analytica Chimica Acta
 [1];  [1]
  1. University of Utah, Salt Lake City, UT (United States)

The proton-transfer and stepwise metal-ion complex formation reactions of the water-soluble 8HQ ligand, 5-(p-sulfophenylazo)-8-hydroxyquinoline, are investigated in order to understand the interfacial reactivity of the analogous ligand immobilized to silica by a phenylazo linker on the 5-position on the quinoline ring. Raman spectra of the ligand are acquired to determine whether the same tautomerization equilibrium exists for the solution-phase model compound as for the silica-immobilized ligand. UV-vis absorption spectra of aqueous solutions of the ligand are acquired as a function of pH and metal-ion concentration. The stepwise reactions are monitored, equilibrium constants are determined, and component spectra are resolved using multivariable least-squares methods. These methods were shown to be capable of resolving component spectra made up of broad bands that differ by only a 3-nm band shift. The acid dissociation constants of the ligand were determined to be: pKA1 of 3.78 ± 0.3 and pKA2 of 7.94 ± 0.4. The equilibrium constants for ligand binding to Cu2+ were also measured and found to be K1 = 1.4 (±0.3) x 1010 and K2 = 2.0 (±0.5) x 107. The first ligand binding constant was compared to the complexation of the silica-immobilized 8HQ ligand. The formation constant for the 1:1 ligand:Cu2+ solution complex was ~30-times greater than that of the silica-immobilized 8HQ ligand. This is likely due to interactions of the immobilized ligand with the nearby silica surface that change its affinity for metal-ion binding.

Research Organization:
University of Utah, Salt Lake City, UT (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)
Grant/Contract Number:
FG03-93ER14333
OSTI ID:
2480723
Alternate ID(s):
OSTI ID: 20870098
Journal Information:
Analytica Chimica Acta, Journal Name: Analytica Chimica Acta Journal Issue: 1-2 Vol. 494; ISSN 0003-2670
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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