sodium-dodecyl-sulfate and indole

Motional properties are important for understanding protein function and are accessible to NMR relaxation measurements. The goal of this study is to investigate the internal dynamics occurring in gramicidin A (gA) channels in order to provide benchmark experimental data for comparison with the results of molecular dynamics simulations. We therefore synthesized several (15)N isotope-enriched gA samples, covering all backbone residues as well as the Trp indole side chains for NMR relaxation experiments. On the basis of the (15)N NMR spectra for labeled gA samples incorporated in sodium dodecylsulfate (SDS) micelles, we determined T(1), T(2), and heteronuclear NOE values for backbone and indole (15)NH groups. The results indicate that the SDS-incorporated gA channel is a constrained structure without an especially "floppy" region. The NMR observables, particularly those for backbone groups, are predicted well by the molecular dynamics simulations in the accompanying article (DOI 10.1021/jp200904d ).

Topics: Amino Acid Sequence; Dimerization; Gramicidin; Indoles; Micelles; Molecular Dynamics Simulation; Nuclear Magnetic Resonance, Biomolecular; Sodium Dodecyl Sulfate

The photoinduced reaction of thioxanthone (TX) with various indolic and phenolic derivatives and amino acids like tryptophan and tyrosine has been monitored in sodium dodecyl sulfate micellar medium. Laser flash photolysis and magnetic field effect (MFE) experiments have been used to study the dynamics of the radical pairs. The quenching rate constant with different quenchers in SDS micellar solution has been measured. For indoles the electron-transfer reaction has been found to be followed by proton transfer from the donor molecule, which gives rise to the TX ketyl radical. On the other hand, the electron-transfer reaction in the case of phenols is preceded with formation of a hydrogen-bonded exciplex. The extent of the MFE and magnitude of the magnetic field corresponding to one-half of the saturation value of MFE ( B 1/2) support the fact that hyperfine mechanism plays the primary role. Quenching of MFE in the presence of gadolinium ions confirms that the radical pair is located near the micellar interface. MFE study has been further extended to protein-like bovine serum albumin in micellar solution. The results indicate loss in mobililty of radical pairs in the protein surfactant complex.

Topics: Absorption; Amino Acids; Animals; Cattle; Electron Transport; Indoles; Magnetics; Micelles; Phenol; Photochemical Processes; Protein Binding; Serum Albumin, Bovine; Sodium Dodecyl Sulfate; Surface-Active Agents; Thioxanthenes; Time Factors; Xanthones

The absorption and fluorescence spectral characteristics of some biologically active indoles have been studied as a function of acidity and basicity (H_/pH/H(o)) in cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecylsulphate, SDS) and aqueous phases at a given surfactant concentration. The prototropic equilibrium reactions of these probes have been studied in aqueous and micellar phases and apparent excited state acidity constant (pK(a)(*)) values are calculated. The probes show formation of different species on changing pH. Various species present in water, CTAB and SDS have been identified and the equilibrium constants have been determined by Fluorimetric Titration method. The fluorescence spectral data suggest the formation of oxonium ion through the excited state proton transfer reaction in highly acidic media and formation of photoproducts due to the base catalyzed auto-oxidative reaction in basic aqueous solutions. Variations in the apparent pK(a)(*) value have been observed in different media. The change in the apparent pK(a) values depends upon the solubilising power of the micelles, as well as on the location of the protonating site in the molecule. The observation about increase in pK(a)(*) values in SDS and decrease in CTAB compared to pure water for various equilibria is consistent with the pseudophase ion-exchange (PIE) model.

Topics: 5-Methoxytryptamine; Cetrimonium; Cetrimonium Compounds; Hydrogen-Ion Concentration; Hydroxyindoleacetic Acid; Indoles; Light; Methoxydimethyltryptamines; Micelles; Molecular Probes; Oxidation-Reduction; Photolysis; Protons; Sodium Dodecyl Sulfate; Spectrometry, Fluorescence; Surface-Active Agents; Titrimetry; Water