Iron and zinc porphyrin linked MoO(dithiolene) complexes in relevance to electron transfer between Mo-cofactor and cytochrome b5 in sulfite oxidase.

Oxo-molybdenum (dithiolene) complexes covalently linked individually to iron and zinc porphyrin have been synthesized to show an electron transfer between the two metal centres in relevance to electron transfer from Mo-cofactor to cytochrome b5 domains in the oxidative half of the catalytic cycle of native sulfite oxidase. This association has been investigated by electrochemical, EPR measurement and X-ray absorbance spectroscopy techniques.

Stepwise oxidations of a nickel(ii)-iron(iii) heterobimetallic porphyrin dimer: structure, spectroscopic and theoretical investigation.

We have reported here the synthesis, structure and spectroscopic properties of the NiII-FeIII heterobimetallic ethene-bridged porphyrin dimer and investigate the effect upon step-wise one- and two-electron oxidations to produce a mixed-valence π-cation radical dimer and a dication diradical complex, respectively. We then investigate their electronic structure and spin coupling model and compare them with the corresponding homobimetallic analog. Detailed UV-vis-NIR, IR, and variable temperature magnetic studies and EPR and NMR spectroscopic investigations along with X-ray structure determination of the 2e-oxidized complex have demonstrated strong electronic communications through the bridge between two porphyrin π-cation radicals. The structure and geometrical parameters revealed the stabilization of the high-spin state of iron and the low-spin state of nickel in the 2e-oxidized complex. The extensive conjugation between the two porphyrin π-cation radicals has also altered the bridge from an ethylene to an exo-methylene moiety. Variable temperature magnetic studies of the 2e-oxidized complex revealed stronger antiferromagnetic coupling between two π-cation radical spins (Jr1-r2) of the NiII-FeIII heterodimer which is in sharp contrast to its diiron(iii) analog where the porphyrin π-cation radical undergoes stronger antiferromagnetic coupling predominantly with the corresponding Fe(iii) unpaired spin (JFe-r). The experimental observations are also strongly supported by DFT calculations.

Preparation of Iron-Sulfur Cubane Nanoclusters and Their Immobilization on Functionalized Carbon Nanotubes.

With large surface area and versatile electronic behaviour, the composites of Fe4S4(SRS)4 nanoclusters and functionalized carbon nanotubes (f-CNTs), are expected to catalyze the conversion of protons to hydrogen gas at lower electro-potentials with higher output than a platinum electrode. In search of a non-noble metal based catalytic material, we report for the first time, the isolation of unimolecular iron-sulfur cubane cluster, [Fe4(µ-S)4(mnt)4], (1) (mnt = maleonitriledithiolate) as nanocubes (63×85×120 nm) in MeCN-EtOH (MeCN is acetonitrile, while EtOH is ethanol) solvents and bimolecular [NBu4]4[Fe4(µ-S)4(mnt)4] as nanocuboctahedra (120×121×125 nm) in pure EtOH. The cubic shape of the nanocrystal reminds its geometrical relationship with a molecular cube and one of sides of the nanocube and nanocuboctahedron matches at 120 nm. The nanocubes of Fe4S4(SRS)4 have been immobilized on f-CNTs and characterized by SEM and TEM methods which indicate that clusters of Fe4S4 of diameter (8-9 nm) interact with surfaces, sidewalls and tip of the f-CNTs. A ferrocene type of interaction could not be observed with f-CNTs, because nanoparticles are not found in CNT-inner cavity. The interaction could be either adsorption or hydrogen bonding interactions between -COOH/-OH groups of f-CNTs and N≡C terminals of iron-sulphur nanoclusters leading to immobilization of an iron-sulfur nanocluster on a single CNT molecule or the iron-sulfur nanoclusters can be entrapped between two CNT molecules.

One electron reduced square planar bis(benzene-1,2-dithiolato) copper dianionic complex and redox switch by O2/HO(-).

The complex [Ph4P]2[Cu(bdt)2] (1(red)) was synthesized by the reaction of [Ph4P]2[S2MoS2CuCl] with H2bdt (bdt = benzene-1,2-dithiolate) in basic medium. 1(red) is highly susceptible toward dioxygen, affording the one electron oxidized diamagnetic compound [Ph4P][Cu(bdt)2] (1(ox)). The interconversion between these two oxidation states can be switched by addition of O2 or base (Et4NOH = tetraethylammonium hydroxide), as demonstrated by cyclic voltammetry and UV-visible and EPR spectroscopies. Thiomolybdates, in free or complex forms with copper ions, play an important role in the stability of 1(red) during its synthesis, since in its absence, 1(ox) is isolated. Both 1(red) and 1(ox) were structurally characterized by X-ray crystallography. EPR experiments showed that 1(red) is a Cu(II)-sulfur complex and revealed strong covalency on the copper-sulfur bonds. DFT calculations confirmed the spin density delocalization over the four sulfur atoms (76%) and copper (24%) atom, suggesting that 1(red) has a "thiyl radical character". Time dependent DFT calculations identified such ligand to ligand charge transfer transitions. Accordingly, 1(red) is better described by the two isoelectronic structures [Cu(I)(bdt2, 4S(3-,)*)](2-) ↔ [Cu(II)(bdt2, 4S(4-))](2-). On thermodynamic grounds, oxidation of 1(red) (doublet state) leads to 1(ox) singlet state, [Cu(III)(bdt2, 4S(4-))](1-).

Electronic structure of monodithiolated iron-oxotungsten heterometallic complexes: integer-spin Fe-W assembly.

Fe-W heterometallic complexes, in which an FeX2 (X = Cl, SPh) moiety is attached to monodithiolene oxotungsten through a sulfide bridge, that is, [Ph4P]2[Cl2Fe(S)2WOS2] (1), [Ph4P]2[Cl2Fe(S)2WOS2(DMED)] (2, DMED = dimethylethylenedicarboxylate), [Ph4P]2[Cl2Fe(S)2WO(tdt)] (3, tdt = toluenedithiolate), [Ph4P]2[(SPh)2Fe(S)2WO(tdt)] (4), and [Ph4P]2[Cl2Fe(S)2WO(edt)] (5, edt = ethanedithiolate), are reported. Mössbauer and EPR spectroscopy, magnetism, electrochemistry, and electronic structural analysis based on DFT and TD-DFT calculations show the transfer of electron from the iron center to the tungsten center, thus resulting in a ferromagnetically coupled Fe(III) W(V) unit, along with antiferromagnetic intermolecular interactions, from the starting Fe(II) and W(VI) compounds. A net spin of a S = 3 ground state, which arises from ferromagnetically coupled Fe(III) and W(V) atoms, displays a rare X-band EPR in normal mode at g ≈ 7 in the solid state.

Oxomolybdenum monodithiolene complexes linked with sulfur bridged iron: antiferromagnetically coupled Fe(III)Mo(V) systems.

Mo-Fe heterometallic complexes with Fe(X)(2) (X = Cl, SPh) moiety attached to monodithiolene oxomolybdenum via sulfur bridge, viz., [Ph(4)P](2)[Cl(2)FeS(2)MoOS(2)(DMED)] (2) (DMED, dimethylethylenedicarboxylate), [Ph(4)P](2)[Cl(2)FeS(2)MoO(tdt)] (3) (tdt, toluenedithiolate) and [Ph(4)P](2)[(SPh)(2)FeS(2)MoO(tdt)] (4) are reported. Mossbauer spectroscopy, magnetism, EPR, electrochemistry and electronic structure based on DFT and TD-DFT calculation show the transfer of electron from iron to molybdenum centre resulting antiferromagnetically coupled Fe(III)Mo(V) unit from the starting Fe(II) and Mo(VI) compounds. A net spin of S = 2 ground state arising from antiferromagnetically coupled Fe(III) and Mo(V) shows a rare X-band EPR in normal mode at g ~ 12 in the solid state. In addition, Mossbauer studies show that electron drifting is more pronounced upon substitution of the chloride ligand by thiophenolate. The changes in dithiolene periphery electronically affect the charge distribution between Mo-Fe in {OMo(µS)(2)Fe} core. DFT calculations indicate that the increasing stability of dative Fe → Mo hetero metal-metal bond in these complexes from 3 to 2 to 4 is related to the extent of electron transfer from the iron to molybdenum centre.

Nitrous-acid-mediated synthesis of iron-nitrosyl-porphyrin: pH-dependent release of nitric oxide.

Two iron-nitrosyl-porphyrins, nitrosyl[meso-tetrakis(3,4,5-trimethoxyphenylporphyrin]iron(II) acetic acid solvate (3) and nitrosyl[meso-tetrakis(4-methoxyphenylporphyrin]iron(II) CH(2)Cl(2) solvate (4), were synthesized in quantitative yield by using a modified procedure with nitrous acid, followed by oxygen-atom abstraction by triphenylphosphine under an argon atmosphere. These nitrosyl porphyrins are in the {FeNO}(7) class. Under an argon atmosphere, these compounds are relatively stable over a broad range of pH values (4-8) but, under aerobic conditions, they release nitric oxide faster at high pH values than that at low pH values. The generated nitric-oxide-free iron(III)-porphyrin can be re-nitrosylated by using nitrous acid and triphenylphosphine. The rapid release of NO from these Fe(II) complexes at high pH values seems to be similar to that in nitrophorin, a nitric-oxide-transport protein, which formally possesses Fe(III). However, because the release of NO occurs from ferrous-nitrosyl-porphyrin under aerobic conditions, these compounds are more closely related to nitrobindin, a recently discovered heme protein.

Relation of soya bean meal level to the concentration of plasma free amino acids and body growth in white rats.

Amino acid (AA) levels in plasma and body growth were determined in rats (n20) fed diets with different soya bean meal levels. Free AA in plasma was determined by reversed-phase high-pressure liquid chromatography. We have used four levels of protein diets like 8%, 15%, 23% and 35% in this trial. Rats which were fed the low-protein (8%) diet with low percentage of soya bean meal were found to be growth-retarded. The body weight gain of high protein group (35%) was lower than that of the 23% groups. In the rats fed with the low-soya bean meal diet, some nonessential AA (NEAA) in plasma like asparagine, aspartic acid, cysteine, glutamic acid and serine increased, whereas the essential AA (EAA), with the exception of arginine, methionine and valine decreased. Here, plasma EAA-to-NEAA ratios were not correlated to growth and experimental diet. We hypothesize that AA metabolism is associated to changes in growth in rats on different protein intake. This study has showed the sensitivity of body mass gain, feed intake, feed conversion rate of rats to four levels of protein in the diet under controlled experimental conditions.

Comparative study between omentopexy and omental plugging in treatment of giant peptic perforation.

Giant peptic perforation is a life threatening surgical emergency with high mortality.. This study aims to compare the success rate between omental plugging and standard omentopexy in the emergency management of giant perforations. A prospective non-randomized study of 23 patients with giant peptic perforation (≥2 cm in diameter) was carried out over a period of 18 months. The highest incidence was seen in the age group of 41-50 years. Intestinal fistula occurred in 23.08% of the omentopexy group compared to none in the omental plugging group. The mean hospital stay was slightly higher in the omentopexy group. Three patients died in the omentopexy group post operatively after 24 h compared to none in the omental plugging group and this was statistically significant (p < 0.05). Omental plugging is associated with lesser morbidity and mortality compared to omentopexy in the management of giant peptic perforations.

*NO2-mediated meso-hydroxylation of iron(III) porphyrin.

(*)NO(2) generated from (*)NO and air add to iron(III) porphyrin upon nitration, which isomerized spontaneously to hydrolysis, yielding a meso-hydroxylated cation that seized by the end oxidation product, a nitrate ion, through extensive hydrogen bonding.

Direct incorporation of a ferric ion in the porphyrinogen core: tetrakis(cyclohexyl)iron porphyrinogen anion with different conformers and its reaction with iodine.

Et(4)N[L' 'Fe(III)].3DCM (1) is directly synthesized by adding ferric chloride into a solution of a lithium salt of tetrakis(cyclohexyl)porphyrinogen (L' '). [L' '](4-) is a good chelating ligand for both Fe(III) and Fe(II) ions. It is an avid proton scavenger but not a reducing agent. 1 showed a magnetic moment (mu(eff)) of 4.3 micro(B) in the solid, which changed to 6.0 micro(B) in solution. This change in spin state is common for all iron porphrinogens. 1 showed polymorphism, and with pyridine in the lattice, it changed to Et(4)N[L' 'Fe(III)].DCM(0.5)Py(1.5) (2), possessing two different conformers. Calculation of these conformers at the density functional theory level showed the relative energies of all d orbital changes in three conformers, highlighting the influence of the disposition of a peripheral ligand. Iodine oxidation of 1 yielded [L' '(DeltaDelta)Fe(II)I][I(3).I(2)(+).I(3)(-)] (3) with the introduction of two C(alpha)-C(alpha) bonds with concomitant reduction of Fe(III) to Fe(II). Its mu(eff) (5.4 mu(B)) in the solid changed to 4.8 micro(B) in solution, suggesting a high spin state (S = 2) for Fe(II).

Structural and functional analogue of the active site of polysulfide reductase from Wolinella succinogenes.

Synthesis of [PPh4]2[Mo(SPh)2(S2C2(CN)2)2] (2) from [PPh4]2[MoO(S2C2(CN)2)2] (1) has been achieved to mimic the postulated [Mo(S)6] core of polysulfide reductase with two thiolates and two bis(ene-dithiolate) ligands. Compound 2 reacts with polysulfide to yield H2S, modeling the function of polysulfide reductase. The facile conversion of 2 back to 1 in moist solvent suggests that the interconversion of the [MoIV = O] and [MoIV - X] (X = O-Ser, S-Cys, Se-Cys) moieties might occur in the DMSO reductase class of enzymes under appropriate hydrophobic/hydrophilic conditions.