chlorophyll-a and sodium-bromide

Glancing angle laser-induced fluorescence was used to follow the kinetics of chlorophyll loss at the air-salt water interface under the influence of visible radiation. Aqueous solutions of NaCl, NaBr, NaI, KNO(3), and NaNO(2) in a range of concentrations up to approximately 1 M were used as substrates. The first-order reaction rate depends linearly on salt concentration for the halide salts but does not vary with concentration for nitrate or nitrite salts. At the same salt concentration, the chlorophyll loss rate is greatest for the bromide-containing solutions, followed by those containing chloride and then iodide. The results are consistent with a mechanism in which photoproduced chlorophyll cations are reduced by halide anions and subsequently react with the halogen atoms thus produced. This mechanism gives a novel route for gas-phase halogenated species, and possibly nitrogen oxides, to be released to the marine boundary layer.

Topics: Air; Bromides; Chlorophyll; Halogens; Kinetics; Nitrates; Nitrites; Oxidation-Reduction; Photochemistry; Potassium Compounds; Salts; Sodium Chloride; Sodium Compounds; Sodium Iodide; Water

The intact Photosystem I core protein, containing the psaA and psaB polypeptides, and electron transfer components P-700 through FX, was isolated from cyanobacterial and higher plant Photosystem I complexes with chaotropic agents followed by sucrose density ultracentrifugation. The concentrations of NaClO4, NaSCN, NaI, NaBr or urea required for the functional removal of the 8.9 kDa, FA/FB polypeptide was shown to be inversely related to the strength of the chaotrope. The Photosystem I core protein, which was purified to homogeniety, contains 4 mol of acid-labile sulfide and has the following properties: (i) the FX-containing core consists of the 82 and 83 kDa reaction center polypeptides but is totally devoid of the low-molecular-mass polypeptides; (ii) methyl viologen and other bipyridilium dyes have the ability to accept electrons directly from FX; (iii) the difference spectrum of FX from 400 to 900 nm is characteristic of an iron-sulfur cluster; (iv) the midpoint potential of FX, determined optically at room temperature, is 60 mV more positive than in the control; (v) there is indication by ESR spectroscopy of low-temperature heterogeneity within FX; and (vi) the heterogeneity is seen by optical spectroscopy as inefficiency in low-temperature electron flow to FX. The constraints imposed by the amount of non-heme iron and labile sulfide in the Photosystem I core protein, the cysteine content of the psaA and psaB polypeptides, and the stoichiometry of high-molecular-mass polypeptides, cause us to re-examine the possibility that FX is a [4Fe-4S] rather than a [2Fe-2S] cluster ligated by homologous cysteine residues on the psaA and psaB heterodimer.

Topics: Bromides; Centrifugation, Density Gradient; Chlorates; Chlorophyll; Cold Temperature; Cross-Linking Reagents; Cyanobacteria; Digitonin; Electron Spin Resonance Spectroscopy; Electron Transport; Glutaral; Kinetics; Light-Harvesting Protein Complexes; Molecular Weight; Octoxynol; Oxidation-Reduction; Photochemistry; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Plant Proteins; Polyethylene Glycols; Sodium; Sodium Compounds; Sodium Iodide; Spectrophotometry; Thiocyanates; Urea