In Situ Measurements of Aggregation and Disaggregation of Cu(II) Complex at Liquid/Liquid Interface

• Published in: Analytical chemistry (Washington) Vol. 80; no. 21; pp. 8348 - 8352
• Main Authors: Watarai, Hitoshi, Oyama, Hiroko
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.11.2008
• Subjects: Analytical chemistry; Aqueous chemistry; Chemical compounds; Chemistry; Copper; Exact sciences and technology; Membranes; Scientific imaging; Spectrometric and optical methods; Water; Fluid mechanics; Adenine; Hydrophobic compound; Liquid membrane; Heptane; Guanine; Aggregation; Measurement in situ; Phenol; Copper II Complexes; Liquid liquid interface; Molecular recognition; Bathochromism; Mass spectrometry; Microfluidics; Ultraviolet visible spectrometry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac8008719

Aggregation of Cu(II)−5-(octadecyloxy)-2-(2-thiazolylazo)phenol (TARC18) complex at the heptane/water interface was measured directly by a centrifugal liquid membrane spectrometry and a two-phase microflow API-MS method. When the pH of an aqueous phase was increased from 4 to 6, the 1:1 complex of Cu(II)−TARC18, which was formed as a positively charged complex at the interface, formed further an aggregate, accompanied by the change of spectra suggesting its aggregation. The MS spectra of the interfacial species indicated the formation of 2:3 complex for Cu(II) and TARC18 under the conditions that the aggregate was formed. This observation allowed us to analyze the interfacial aggregation stoichiometrically: the aggregate of the 2:3 complex was formed from a 1:1 complex at the interface. The addition of purine base of adenine or guanine into the system resulted in the disruption of the aggregate by the formation of a new three-element complex of 1:1:1 for Cu(II), TARC18, and the base, showing a bathochromic shift in the spectra. Thus, the disaggregation experiment showed an interfacial molecular recognition ability of the Cu(II)−TARC18 aggregate for hydrophobic bases.