Use of Gd sup (3+) Fluorescence to Measure Vibrational Spectra.

Coupling between the narrow fluorescence transition of Gd sup (3+) at 311 nm and the vibrational transitions of its inner- sphere ligands gives rise to the emission of vibronic photons between 320 and 350 nm. The energy difference between the fluorescence and vibronic transitions is equal to that of the vibrational transitions of the molecular group coordinated to Gd sup (3+). Because this method is sensitive exclusively to the vibrational modes of the ligating molecule, the IR spectrum of the ligand can be measured in the presence of other molecules absorbing in the IR. The vibronic spectra of Gd sup (3+) ligated to 20 different organic, and inorganic molecules is shown to accurately measure the IR spectrum of the ligand. Application of this technique to measure the vibrational spectrum of a metal-binding site in a protein and the solvent environment surrounding polynucleotides was not successful. Suggestions for improvements to overcome these problems are presented.