A highly specific and catalytic oxidation of water occurs when using a dinuclear Mn complex of a mononegative carboxylate‐containing pentadentate ligand (see scheme). Isotope‐labeling experiments coupled with membrane inlet mass spectrometry show that one oxygen atom in the evolved O2 molecule is derived from water and the other from the oxidant.

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lron(ii) complexes of the pentadentate ligand N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-l,2diamine ( L2) and the potentially hexadentate ligand N.N'-bis(6-methyl-2-pyridylmethyl) -N,N'-bis(2pyridylmethyl)ethane-1,2-diamine (L') have been isolated. Both ligands behave as pentadentate ligands in their iron(ii) complexes with the general formulation [FeL(X)]"+ (L = L' or L2, n = 1 or 2) with the sixth co-ordination site (X) occupied by an auxiliary ligand e.g. H20, CI, SCN or CN. The crystal structure of [FeL1(H,0)][PF,],=H20 1 shows that the nitrogen atom of one of the 6-methyl-2pyridylmethyl groups of the formally hexadentate ligand is not co-ordinated to the iron atom. Instead a water molecu_le occupies the sixth co-ordination position. Complex 1 crystallizes in the triclinic space group P1, with a = 10.485(2), b = 13.161 (5), c = 14.853(6) A, a = 69.31 (4), p = 74.42(3), y = 66.37(3)O and Z = 2. The structure refined to a final R value of 0.052 for 2531 reflections. The complexes show peroxidase activity, the availability of a labile site on the relatively stable iron(I1) complexes, along with no apparent tendency to form 0x0-bridged diiron(ll1) species, which are likely to be crucial factors in the mechanism of the oxidation reactions. Efforts to isolate a complex with a co-ordinated peroxide in the sixth position were unsuccessful. However, we have spectroscopic evidence that peroxide reacts with the iron(I1) complexes to form an unstable species, probably of the form [Fe"'L(OOR)]2+ ( L = L1 or L2, R = H or But). The peroxide ligand in this iron(ll1) complex is likely to be forced into an 'end-on' co-ordination mode.

Background: Arsenic-containing carbohydrates (arsenosugars) are common constituents of marine algae, including those species used as human food. The toxicology of these compounds has not been fully evaluated. Methods: Arsenic metabolites in human urine were monitored over a 4-day period after ingestion of a synthetic specimen of arsenosugar. The metabolites were determined by HPLC-inductively coupled plasma mass spectrometry, and structural assignments were confirmed with liquid chromatography-electrospray ionization mass spectrometry. Results: Approximately 80% of the total ingested arsenic was excreted in the urine during the 4 days of the experiment. There was a lag-period of ∼13 h before substantial quantities of arsenic appeared in the urine, and the excretion rate peaked between 22 and 31 h. At least 12 arsenic metabolites were detected, only 3 of which could be positively identified. Dimethylarsinate (DMA) was the major metabolite, constituting 67% of the total arsenicals excreted. A new urinary arsenic metabolite, dimethylarsinoylethanol, represented 5% of the total arsenicals, whereas trimethylarsine oxide was present as a trace (0.5%) constituent. One other significant metabolite cochromatographed with a reduced DMA standard, and hence was possibly dimethylarsinous acid. The second most abundant metabolite in the urine (20% of the total arsenic) remained unidentified, whereas the rest of the excreted arsenic was made up of several trace metabolites and small amounts of unchanged arsenosugar. Conclusions: Arsenosugars are biotransformed by humans to at least 12 arsenic metabolites, the toxicologies of which are currently unknown.

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