Analysis of the Visual Spectrum of Methyl Orange in Solvents and in Hydrophobic Binding Sites
| Autor: | Mary S. Maggio, Richard L. Reeves, Edward A. Sylvestre, William H. Lawton, Robert S. Kaiser |
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| Rok vydání: | 1973 |
| Předmět: | |
| Zdroj: | Canadian Journal of Chemistry. 51:628-635 |
| ISSN: | 1480-3291 0008-4042 |
| DOI: | 10.1139/v73-095 |
| Popis: | The absorption curves of methyl orange (MO) and analogous p-aminophenylazobenzenes in organic and aqueous organic solvents are shown to consist of two severely overlapping bands. The curves have been resolved into two skewed component bands using a regression method. The blue shift of the absorption maximum obtained when organic solvents are added to aqueous solutions of MO, or when MO is bound to bovine serum albumin or a surfactant micelle, is the result of a change in relative intensities of the component bands. The low-frequency component is assigned to a π1 → π1* transition of a solvate in which there is specific hydrogen-bonding interaction between solvent and the azo nitrogens, and the high-frequency component to a π1 → π1* transition of a solvate in which the interaction is absent. The low-frequency component is favored by aqueous solvent compositions and by low temperatures. The free energies of interconversion of the species in various hydrogen-bonding solvents are correlated by the solvent surface tension but not by the dielectric constant. The results show that the shift in absorption maximum accompanying binding to a protein or micelle should be interpreted as a shift in an equilibrium rather than as a shift in transition energy. |
| Databáze: | OpenAIRE |
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