PubMed · 13606090
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D KIRMAN, S W MORGENSTERN, D FELDMAN. 1958. A modified microtechnic for determining chloride.. https://doi.org/10.1093/ajcp%2F30.6_ts.564
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Chloride ions are essential for proper function of the photosynthetic oxygen-evolving complex (OEC) of Photosystem II (PS II). Although proposed to be directly ligated to the Mn cluster of the OEC, the specific structural and mechanistic roles of chloride remain unresolved. This study utilizes X-ray absorption spectroscopy (XAS) to characterize the Mn-Cl interaction in inorganic compounds that contain structural motifs similar to those proposed for the OEC. Three sets of model compounds are examined; they possess core structures Mn(IV)(3)O(4)X (X=Cl, F, or OH) that contain a di-micro-oxo and two mono-micro-oxo bridges or Mn(IV)(2)O(2)X (X=Cl, F, OH, OAc) that contain a di-micro-oxo bridge. Each set of compounds is examined for changes in the XAS spectra that are attributable to the replacement of a terminal OH or F ligand, or bridging OAc ligand, by a terminal Cl ligand. The X-ray absorption near edge structure (XANES) shows changes in the spectra on replacement of OH, OAc, or F by Cl ligands that are indicative of the overall charge of the metal atom and are consistent with the electronegativity of the ligand atom. Fourier transforms (FTs) of the extended X-ray absorption fine structure (EXAFS) spectra reveal a feature that is present only in compounds where chloride is directly ligated to Mn. These FT features were simulated using various calculated Mn-X interactions (X=O, N, Cl, F), and the best fits were found when a Mn-Cl interaction at a 2.2-2.3 A bond distance was included. There are very few high-valent Mn halide complexes that have been synthesized, and it is important to make such a comparative study of the XANES and EXAFS spectra because they have the potential for providing information about the possible presence or absence of halide ligation to the Mn cluster in PS II.
Human red blood cells (RBC) can be studied by means of whole-cell and nystatin-perforated patch-clamp techniques. In 85% of the whole-cell experiments (n=86) and 69% of the perforated-patch recordings (n=13), steps to positive potentials, from a holding potential of 0 mV, induced a slow-activating non-inactivating persistent outward current which reverted at about 0 mV. The current activation phase fitted well with a two-component exponential curve. Half-maximal conductance was reached at about 42 mV. Na+ and K+ carried this current, which was not affected by 20 nM charybdotoxin or 20 mM TEA, but was reduced following a partial substitution of extracellular Cl- by tartrate. This current has characteristics similar to the single-channel currents already described in RBC and may be involved in the rapid adaptations of these cells in the circulation.
The nature of coagulant species formed in the system ferric chloride/municipal sewage was explored with Transmission Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (TEM-EDXS) and Fe K-edge X-ray Absorption spectroscopy. Jar-test data combined with chemical analysis of supernatant (dissolved organic carbon, iron, and phosphorus) and Fourier-Transform-Infrared spectroscopy (FTIR) of freeze-dried sediment, provided a detailed description of sewage clarification. The results showed that the nature of coagulant species evolves with Fe concentration. Up to the optimum turbidity removal, mainly iron dimers linked with one phosphate anion are detected. At higher dosages, polymers of hydrolyzed Fe appear even though PO(4) still participates in the formation of coagulant species. TEM observation of freeze-dried sediments corroborates such an evolution of Fe speciation. EDXS analyses reveal that minute amounts of sulfur, silicon, aluminum, and calcium, are associated with the coagulant species. Even though the coagulant species change with Fe concentration, the destabilization mechanism, inferred from electrophoretic mobility of aggregates and the evolution of floc size under cyclic changes of stirring conditions, is equivalent with a charge neutralization of sewage colloids in the whole range of coagulant concentration.