Electronic characterization techniques circular dichroism

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

The magnetic and electronic properties of the D. gigas Fdll [3Fe-4S] center were revealed by different and complementary spectroscopic techniques EPR 89), Mossbauer 90, 91), resonance Raman (RR) 92), magnetic circular dichroism MCD) 93), EXAFS 94), saturation magnetization (95), electrochemistry 96), and NMR (97, 98). The [4Fe-4S] center is also well characterized and surprising information has been obtained in relation to cluster interconversions and noncysteinyl coordination, as illustrated for D. gigas Fdl and D. africanus Fdlll, as well as the possibility of generating unusual reduced states. 

Due to the fundamental importance of the adsorbed protein film, many methods have been used to characterize its nature. These methods include ellipsometry (3,A), Fourier transform infrared spectroscopy (FTIR) (5,6), multiple attenuated internal reflection spectroscopy (MAIR) (7,8) immunological labeling techniques (9), radioisotope labeled binding studies (j ), calorimetric adsorption studies (jj ), circular dichroism spectroscopy (CDS) (12), electrophoresis (j ), electron spectroscopy for chemical analysis (ESCA) (1 ), scanning electron microscopy (SEM) (15,16,9), and transmission electron microscopy (TEM) (17-19). 

A combination of circular dichroism, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, chemical crosslinking, and analytical ultracentrifugation studies showed that both the apo- and metallated derivatives of H21(31-mer) form two-stranded a-helical coiled coils in aqueous solution. Further characterization of these derivatives by EPR spin-label experiments helped to determine its three-dimensional backbone structure. In these studies, a Cys-21 mutant of the 31-mer coiled coil, H21/C21(31-mer), was prepared and labeled with a thiol-specific nltroxide spin label (MTSL = l-oxyl-2,2,5,5-tetramethyl-A -pyrroline-3-methyl-methanethiosulfonate) at position 21 of the peptide sequence which is the site of metal substitution in the ET heterodimer. Comparison of the low-temperature, dipolar-broadened spectrum of the spin-labeled dimer with those of magnetically dilute peptide samples yielded a backbone-to-backbone distance that was nearly identical to that of the GCN4 homodimer. Based on these results, computer modeling studies provided an estimate of the metal-to-metal distance in the ET heterodimer of m-m > 25 A. The electron-transfo properties of this system are now being studied by a combination of laser flash-quench and pulse radiolysis techniques. 

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