Dark signal characteristics

Treatment of the photolysate with methanol gave two diastereomeric methoxysilanes in about 3 1 proportions, consistent with methanol addition being a nonstereospecific process. During extended photolysis (8 hours) to convert all of 25 to 26 it was observed that the concentration of 26 decreased, and a set of signals characteristic of a different silene grew in (no change of relative proportions occurred in the dark). The chemical... 

Fig. 8.16 Fe Mossbauer spectra of [Fe2 (PMAT)2](BF4)4-DMF at selected temperatures. At 298 K, the only quadrupole doublet is characteristic of iron(II) in the HS state. SCO from HS to LS occurs at one Fe(II) site of the dinuclear complex at ca. 225 K. The second Fe(II) site remains in the HS state, but feels the spin state conversion of the neighboring atom by local distortions communicated through the rigid bridging ligand, giving rise to a new quadrupole doublet (dark gray), i.e., HS in [HS-LS], in the Mossbauer spectrum. The intensity ratio of the resonance signals of HS in [HS-LS] to that of LS (black) in [HS-LS] is close to 1 1 at all temperatures (from [32])...

For implementations that rely upon d.c. signal detection, such as the LCTF NIR imaging system, subtraction of the so-called dark response is critical. There are two components of this response, one that is wavelength independent, the detector response when no photons are impinging on the array, a characteristic of the... 

The resolved complex is composed of two fractions, a soluble part, which comprises about 15% of complex I proteins, and a water-insoluble part consisting of the rest of the protein and the bulk of complex I lipids. The soluble fraction is easily separated from the insoluble material by centrifugation. Upon fractionation with ammonium sulfate, it yields a soluble flavoprotein containing iron and labile sulfide and a dark brown protein, which contains large amounts of iron and labile sulfide but no flavin. The latter appears to be an iron-sulfur protein and exhibits an EPR signal which is characteristic of iron-sulfur center 2 of intact complex I (46). Its absorption spectrum is shown in Fig. 8. The insoluble fraction also contains equimolar amounts of iron and labile sulfide and little or no flavin. 

The cytochrome is normally in its reduced state in intact dark-adapted material but is very sensitive to changes in its environment, changing from its high-potential form ( n, 380 mV) to its low-potential form ( ,n=80 mV). The redox state of the cytochrome seems to have no direct relationship to the function of the 02-evolving enzyme (e.g. Ref. 190). The oxidized Cyt 6-559 gives rise to characteristic low-spin haem EPR signals [191]. 

Schematic map of the global ridge crest showing active hydrothermal vents that have been discovered (dark circles) and those that are known to exist because of characteristic signals in the overlying water column (dark triangles). From German and Von Damm (2003).

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