The macrocycles L(1)-L(3) incorporating N(2)S(3)-, N(2)S(2)O-, and N(2)S(2)-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as Pb(II), Cd(II), and Hg(II) to give 1:1 ML, 1:2 ML(2), and 2:1 M(2)L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 degrees C were determined from fluorescence vs M(II)/L molar ratio data. The complexes [Pb(L(1))][ClO(4)](2).(1)/(2)H(2)O (1), [Pb(L(2))][ClO(4)](2).MeNO(2) (1a), [Pb(L(3))(2)][ClO(4)](2).2MeCN (1b), and [Cd(L(3))][NO(3)](2) (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L(1)-L(3) in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacting with counteranion units and solvent molecules. On the contrary, the 1:2 complex 1b shows Pb(II) sandwiched between two symmetry-related molecules of L(3) reaching an overall [4N + 4S] eight-coordination.

Abstract:A new 2-pyrrolidinone with a polyunsaturated side chain has been identified from the cyanobacterium Fischerella muscicola (Thuret). Its structure was elucidated by UV, NMR and mass spectroscopy. Derivatisation of the natural product and stereocontrolled synthesis of the derivative allowed the determination of the absolute configuration by means of chiral gas chromatography. The new compound, fischerellin B, shows algicidal properties. Copyright © 1996 Elsevier Science Ltd Recently the isolation of an algicide, fischerellin A, from the cyanobacterium Fischerella muscicola (Thuret) has been reported.! Here we wish to report the isolation and structure determination of another algicide from this species, which could be isolated as a minor component and bioassayed as described previously. 2 This new compound, which we like to call fischerellin B, is found in crude extracts in smaller quantities than fischerellin A. Similar to fischerellin A, fischerellin B is also present in F. ambigua (N~ig.). 2The cyanobacteria were cultured and harvested as described earlier. 2 Methanolic extracts of 70 g of lyophylised cyanobacteria were repeatedly subjected to RP-18-HPLC (H20/MeOH) followed by silica gel column chromatography (Et20). The resulting yellowish solid (about 1 mg) was homogeneous by TLC, HPLC and GC. The compound was identified to be (3R,5S)-3-methyl-5-((5E)-pentadec-5-ene-7,9-diynyl)-pyrrolidin-2-one (1). The identification procedure is described below. Konstanzer Online-Publikations-System (KOPS) URL: http://www.ub.uni-konstanz.de/kops/volltexte/2008/4850/ URN: http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-48508 First publ. in: Tetrahedron Letters 38 (1997 The mass spectrum obtained by GC-MS (Fisons MD 800 instrument) showed a molecular ion at m/z = 299. High resolution MS (Fisons VG 250 SE instrument) revealed the elemental composition to be C20H29NO. The base peak of the spectrum at m/z = 98 (CsHsNO) suggested a methylated pyrrolidinone ring)The UV spectrum (MeOH) showed a characteristic series of sharp absorptions at 240, 252, 267 and 283 nm indicating the presence of an enediyne chromophor. 4Further information was obtained by one and two dimensional NMR spectroscopy. The results are summarised in Table 1

Heme d1 plays an important role in denitrification as the essential cofactor of the cytochrome cd1 nitrite reductase NirS. At present, the biosynthesis of heme d1 is only partially understood. The last step of heme d1 biosynthesis requires a so far unknown enzyme that catalyzes the introduction of a double bond into one of the propionate side chains of the tetrapyrrole yielding the corresponding acrylate side chain. In this study, we show that a Pseudomonas aeruginosa PAO1 strain lacking the NirN protein does not produce heme d1. Instead, the NirS purified from this strain contains the heme d1 precursor dihydro-heme d1 lacking the acrylic double bond, as indicated by UV-visible absorption spectroscopy and resonance Raman spectroscopy. Furthermore, the dihydro-heme d1 was extracted from purified NirS and characterized by UV-visible absorption spectroscopy and finally identified by high-resolution electrospray ionization mass spectrometry. Moreover, we show that purified NirN from P. aeruginosa binds the dihydro-heme d1 and catalyzes the introduction of the acrylic double bond in vitro. Strikingly, NirN uses an electron bifurcation mechanism for the two-electron oxidation reaction, during which one electron ends up on its heme c cofactor and the second electron reduces the substrate/product from the ferric to the ferrous state. On the basis of our results, we propose novel roles for the proteins NirN and NirF during the biosynthesis of heme d1.