RESUMO
The conformational changes of 3,5,3'-triiodo L-thyronine induced by interaction with phospholipids were analyzed by Raman spectroscopy. The spectra were interpreted in terms of two conformers of this hormone in equilibrium in the lipid medium, depending on the orientation of the 3'-iodine with respect to the ring alpha. Theoretical geometry optimizations on both conformers in vacuo and in different solvents, together with the respective calculated energies support the experimental results. The presence of only one iodine atom in the phenolic ring allows assumption of a higher flexibility of 3,5,3'-triiodo L-thyronine and a better accommodation into the lipid medium compared to 3,5,3',5'-tetraiodo L-thyronine. The possible physiological implications of structural differences that appear in membrane models between 3,5,3'-triiodo L-thyronine and 3,5,3',5'-tetraiodo L-thyronine are discussed.
Assuntos
Tri-Iodotironina/química , Animais , Gema de Ovo/química , Fosfatidilcolinas/química , Conformação Proteica , Espectrofotometria Infravermelho , Análise Espectral Raman , Tiroxina/química , Tiroxina/fisiologia , Tri-Iodotironina/fisiologiaRESUMO
The Raman spectrum of liquid N-(fluorosulfonyl)imidosulfurous difluoride FSO2N = SF2 and the IR spectrum of its vapour phase were recorded. The observed features in combination with the theoretical studies indicate the existence at room temperature of only one conformer. In accord with previous results obtained by electron-diffraction analysis, this single conformer possesses C1 symmetry in which the SF2 group is oriented syn with respect to the N-S single bond. Theoretical vibrational spectra were also determined using ab initio and density functional theory (DFT) calculations at different levels of approximation. For all except one of the torsional modes, experimental wavenumbers were obtained. A subsequent normal coordinate analysis was performed using a torsional wavenumber calculated by theoretical methods.