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1.
The complexation of trivalent lanthanides with aliphatic dicarboxylic acids (malonic, succinic, glutaric and adipic) were studied at 25°C and 0.1 M (NaClO4) ionic strength by luminescence and absorption spectroscopy and luminescence lifetime measurements. The luminescence spectra and decay constants indicate that ML and ML2 complexes were formed. The stability constants of Eu(III) complexes with the dicarboxylic acids were calculated from the changes of the 5D07F0 excitation spectra of Eu(III). For the four dicarboxylic acids studied, both the stability constant and the number of water molecules released from the inner sphere of Eu(III) upon complexation decrease from malonate to adipate for both the ML and ML2 complexes. The results are interpreted as reflecting an increasing tendency from chelation to monodentation as the carbon chain length increases between carboxylate groups. The trend in the oscillator strength in the hypersensitive transition of the Nd(III)and Ho(III) complexes is the same as that in the ligand basicity.  相似文献   

2.
The reactions of cadmium halides with the 15-membered macrocyclic crown ethers, 15-crown-5 and benzo-15-crown-5, have been carried out and six new complexes have been isolated and structurally characterized. Metal to ligand stoichiometries of 1:1, 2:1, 3:1 and 3:2 have been observed with a variety of different formulations. Examples of charge separated ion pairs ([(NH4)(benzo-15-crown-5)2]2[Cd2I6]), halogen bridged monomers, dimers or polymers ([Cd(15-crown-5)(OHMe)(μ-Br)CdBr3], [Cd(15-crown-5)(μ-Br)2CdBr(μ-Br)]2(isolated from the same reaction mixture) and [(CdCl2)2CdCl2(15-crown-5)]n), and hydrogen bonded finite chains or polymers ([(Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN and [CdI2(OH2)2(THF)]·benzo-15-crown-5) have been isolated. Three different types of 15-crown-5 coordination modes have been observed in these complexes. In-cavity coordination resulting in pentagonal bipyramidal geometries about Cd2+ was observed in [(CdCl2)2CdCl2(15-crown-5)]n, [Cd(15-crown-5)(OHMe)(μ-Br)CdBr3], and [Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN, [Cd(15-crown-5)(μ-Br)2CdBr(μ-Br)]2 displays out-of-cavity coordination with one etheric donor distorted into an axial position of a distorted pentagonal bipyramid. The third coordination mode is secondary sphere coordination via hydrogen bonding which is observed for [Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN. The good fit of Cd2+ within the cavity of 15-crown-5 results in shorter bonding contacts and a more narrow distribution in Cd---O values (2.273(7)-2.344(6) Å) than observed for cadmium halide complexes of 18-crown-6 (Cd---O = 2.69(1)–2.81(1) Å).  相似文献   

3.
Reaction of LaCl3·7H2O containing small amounts of La(NO3)3·7H2O as an impurity with 12-crown-4 or 18-crown-6 in 3:1 CH3CN:CH3OH resulted in the isolation of the mixed anion complexes [LaCl2(NO3)(12-crown-4)]2, [La(NO3)(OH2)4(12-crown-4)]Cl2·CH3CN and [LaCl2(NO3)(18-crown-6)]. The nine-coordinate dimer, [LaCl2(NO3)(12-crown-4)]2, has all of the anions in the inner coordination sphere and La3+ has a capped square antiprismatic geometry. It crystallizes in the orthorhombic space group Pbca with (at −150 °C) a = 12.938(6), B = 15.704(3), C = 13.962(2) Å, and Dcalc = 2.08 g cm−3 for Z = 4. The second complex isolated from the same reaction, [La(NO3)(OH2)4(12-crown-4)]Cl2·CH3CN, has the bidentate nitrate anion in the inner coordination sphere but the two chloride anions are in a hydrogen bonded outer sphere. This complex is ten-coordinate 4A,6B-expanded dodecahedral and crystallizes in the monoclinic space group P21 with (at 20 °C) A = 7.651(2), B = 11.704(7), C = 11.608(4) Å, β = 95.11(2)°, and Dcalc = 1.80 g cm−3 for Z = 2. The 18-crown-6 complex, [LaCl2(NO3)(18-crown-6)], has all inner sphere anions and has ten-coordinate 4A,6B-expanded dodecahedral La3+ centers. It crystallizes in the orthorhombic space group Pbca with (at 20 °C) a = 14.122(7), B = 13.563(5), C = 19.311(9) Å, and Dcalc = 1.89 g cm−3 for Z = 8.  相似文献   

4.
Near-infrared absorption spectra of A2CoX4 (A = Cs, ethyl4N; X = Cl, Br) single crystals and from KBr pellets at low temperature are recorded by the Fourier transform technique. At 2 K a rich fine structure of v1(4A24T2) and v2(4A24T1) ligand field spectra is detected which can be assigned to low symmetry level splittings due to actual site symmetries superimposed by vibrational fine structure. Comparison of fundamental frequencies obtained from far-infrared spectra allows an assignment of all peaks measured in the vibronic spectra to vibrational modes of the MX4 complex. Zero-phonon bands are identified using the assistance of angular overlap calculations.  相似文献   

5.
The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H2L and Ln(NO3)3 · 6H2O give rise to three mononuclear lanthanide complexes Ln(H2L)(NO3)3 [H2L = N,N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N,N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O2O2 set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac)2 · H2O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO3)3 · H2O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N2O2 cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes.  相似文献   

6.
The cyclopentadienyl osmium(II) complexes [(η5-C5H5)Os(PPh3)2X] [X = Br (1), CH3CN (2)] reacts with sodium azide (NaN3) to yield the corresponding azido complex [(η5-C5H5)Os(PPh3)2N3] (3). This undergoes [3+2] dipolar cycloaddition reaction with activated alkynes like dimethyl and diethyl acetylenedicarboxylate to yield triazolato complexes [(η5-C5H5)Os(PPh3)2{N3C2(CO2R)2}] [R = –CH2CH3 (4) and –CH3 (5)]. The complex 3 also reacts with nitriles such as tetracyanoethylene (TCE), fumaronitrile and p-nitrobenzonitrile to yield complexes of the type [(η5-C5H5)Os(PPh3)2{N4C2(CN)C(CN)2}] (6), [(η5-C5H5)Os(PPh3)2{N3C2HCN}] (7) and [(η5-C5H5)Os(PPh3)2{N4C(C6H4p-NO2)}] (8). These complexes were fully characterized on the basis of microanalyses, FT-IR and NMR spectroscopic data. The molecular structure of the representative complex [(η5-C5H5)Os(PPh3)2{N3C2(CO2CH2CH3)2}] (4) was determined by single crystal X-ray analysis.  相似文献   

7.
The complex C60Pt[P(OPh)3]2 displays C60 ππ* intraligand bands in the UV-Vis region and a long-wavelength absorption at λmax = 770 nm which is assigned to a metal-to-ligand charge transfer (MLCT) transition from platinum to fullerene. The irradiation of the complex leads to the population of the reactive MLCT state and subsequently to the dissociation (C60Pt[P(OPh)3]2 → C60 + Pt[P(OPh)3]2) in the primary photochemical step. Product formation takes place by the interception of Pt[P(OPh)3]2 with suitable scavengers such as CHCl3 or O2.  相似文献   

8.
Reactions of Cr(CO)36-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)2Re(THF), where Cp′ = η5-C5H5 or η5-C5Me5, give the products Cp′(CO)2Re(η262-BT)Cr(CO)3 in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)2Re(η262-BT)Cr(CO)3 (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)2Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η2) or the sulfur (η1(S)). Thus, the electron-withdrawing Cr(CO)3 group in 3 stabilizes the 2,3-η2 mode of BT coordination to the Cp′(CO)2Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group .  相似文献   

9.
The chloro complexes trans-[Pt(Me)(Cl)(PPh3)2], after treatment with AgBF4, react with 1-alkynes HC---C---R in the presence of NEt3 to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh3)2] (R = p-tolyl (1), Ph (2), C(CH3)3 (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH2)nCl (n = 2, 3) in the presence of 1 equiv. of HBF4 to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH2)nCl](CH2R) } (PPh3)2][BF4] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)2(PMe2Ph)2] with 2 equiv. HBF4 and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH2CH2CH2Cl)(CH2Ph) } (PMe2Ph)2][BF4] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH2CH2Cl)(CH2Ph) } (PPh3)2][BF4] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh3)2], after treatment with AgBF4 in HOCH2CH2Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe2Ph)]2 with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl2{C(OCH2CH2CH2Cl)(CH2C6H4-p-Me}(PMe2Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna21, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) Å3 and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.  相似文献   

10.
With exposure to trace amounts of air and moisture, the Cr2(II, II) complex Cr2(μ-3,5Cl2-form)4, where 3,5Cl2-form is [(3,5-Cl2C6H3)NC(H)N(3,5-Cl2C6H3)], undergoes an oxidative addition reaction. Structural information from the X-ray crystal structure of the edge-sharing bioctahedral (ESBO) Cr2(III, III) product Cr2(μ-OH)2(μ-3,5Cl2-form)22-3,5Cl2-form)2 (1) indicates 1 has a significantly longer Cr–Cr distance [2.732(2) Å] than Cr2(μ-3,5Cl2-form)4 [1.9162(10) Å], but the shortest Cr–Cr distance in an ESBO Cr2(III, III) complex recorded to date.  相似文献   

11.
The dialkyl-μ-ethylidene-μ-methylene-bis (pentamethylcyclopentadienyl)-dirhodium complexes [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe) (R)2] (4, P=Me; 5, Et; 6, n-Bu; 7, CH=CH2; and 8, Z-CH=CHMe) have been prepared from RMgBr and [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe)(X)2] (2, X=Cl; 3, X=Br). Structures deduced from the NMR spectra show that the dialkyl complexes can exist in one trans and two cis forms. The decomposition of the dimethyl complex 4 is compared with that of the related di-μ-methylene complex; it reacts readily (30°C, MeCN solution) in the presence of one-electron oxidisers to give propene and methane and a little ethene and some butenes. Mass-spectrometric analysis of the 13C labelling in the organics originating from [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe) (13CH3)2] shows that methane derives from the Rh---Me, ethene half from the ethylidene and half from coupling of Rh-methyl and a bridging methylene, while the propene arises almost entirely from the ethylidene and a rhodium methyl. The butenes come from coupling of ethylidene, methylene and a Rh-methyl, but only quite small amounts are formed; thus C+C coupling is the major decomposition path for the μ-ethylidenes, in contrast to the di-μ-methylene complexes where C+C+C coupling predominates. The divinyl complex [{(C5Me5)Rh}2(μ-CH2)(μ-CHMe) (CH=CH2)2] also underwent internal C+C coupling on reaction with AgBF4 in MeCN to give a mixture of the allyl and methylallyl cations [(C5Me5)Rh(η3-CH2CHCHR)(MeCN)]+(10, R=H; 11, R=Me).  相似文献   

12.
New partially N-hydroxyethylated 14-membered tetraaza macrocycles 1,8-bis(2-hydroxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L2) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L3) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L1) with 2-hydroxyethyl bromide. The complexes [NiL3]2+, [CuL2]2+, and [CuL3]2+ have been prepared and characterized. The complex [CuL2](ClO4)2 has a square-pyramidal coordination geometry with one apical oxygen atom; only one of the two hydroxyethyl groups is coordinated to the metal ion. Electronic absorption spectra of [CuL3](ClO4)2 containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL2](ClO4)2. Unexpectedly, the nickel(II) complex [NiL3](ClO4)2 has a severely distorted trigonal bipyramidal coordination geometry with the oxygen atom of the pendant arm at the equatorial position. The Ni---O bond distance of the nickel(II) complex is shorter, or not longer, than the Ni---N bond distances. The ligand in [CuL2]2+ is in the RRSS (trans-III) configuration, as usual, whereas that in [NiL3]2+ has the RRRR (trans-V) conformation. The coordination geometry and properties of [NiL3]2+ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.  相似文献   

13.
Myometrial low speed supernatant prepared from non-pregnant rhesus uteri was incubated with 3H-Prostaglandin (PG) E1 with or without addition of unlabelled prostaglandins. The uptake of 3H-PGE1 was inhibited in a dose dependent fashion by PGE2>PGE1>PGA1>PGF2=PGA1>PGB1=PGB2≥PGD2. PGE1 metabolites inhibited 3H-PGE1 binding in the following order: 13,14-dihydro-PGE1>13,14-dihydro-15-keto-PGE1=15-keto-PGE1. The specific binding of 3H-PGE1 and 3H-PGF2 was similarly affected by the temperature and time of incubation. Equilibrium binding constants determined using rhesus uteri obtained during the luteal phase of the menstrual cycle indicate the presence of high affinity PGE1 binding sites with an average (n=3) apparent dissociation constant of 2.2 × 10−9M and a lower affinity PGE1 binding site with a Kd 1 × 10−8M. No high affinity — low capacity 3H-PGF2 sites could be demonstrated.

Relative uterine stimulating potencies of some natural prostaglandins and prostaglandin analogs tested after acute intravenous administration in mid-pregnant rhesus monkeys corresponded with the PGE1 binding inhibition of the respective compound. The uterine stimulating potencies of the prostaglandin analogs tested were: (15S)-15-methyl-PGE2=16,16-dimethyl-PGE2>17-phenyl-18,19,20-trinor-P GE2>16 phenoxy-17,18,19,20-tetranor-PGE2=PGE2=PGE1=(15S)-15-methyl-PGE2>PGF2.  相似文献   


14.
The reaction of TiCl4 with Li2[(SiMe2)25-C5H3)2] in toluene at room temperature afforded a mixture of cis- and trans-[(TiCl3)2{(SiMe2)25-C5H3)2}] in a molar ratio of 1/2 after recrystallization. The complex trans-[(TiCl3)2{(SiMe2)25-C5H3)2}] was hydrolyzed immediately by the addition of water to THF solutions to give trans-[(TiCl2)2(μ-O){(SiMe2)25-C5H3)2}] as a solid insoluble in all organic solvents, whereas hydrolysis of cis-[(TiCl3)2{(SiMe2)25-C5H3)2}] under different conditions led to the dinuclear μ-oxo complex cis-[(TiCl2)2)(μ-O){(SiMe2)25-C5H3)2}] and two oxo complexes of the same stoichiometry [(TiCl)2(μ-O){(SiMe2)25-C5H3)2}]2(μ-O)2 as crystalline solids. Alkylation of cis- and trans-[(TiCl3)2{(SiMe2)25-C5H3)2}] with MgCIMe led respectively to the partially alkylated cis-[(TiMe2Cl)2{(SiMe2)25-C5H3)2}] and the totally alkylated trans-[(TiMe3)2{(SiMe2)25-C5H3)2}] compounds. The crystal and molecular structure of the tetranuclear oxo complex [(TiCl)2(μ-O){(SiMe2)25-C5H3)2}]2(μ-O)2 was determined by X-ray diffraction.  相似文献   

15.
The reaction of the title complex with DNA has been examined. Addition of [(bpy)2(OH2)RuORu(OH2) (bpy)2]4+ to DNA leads to the reduction of the complex to Ru(bpy)2(OH2)22+, as indicated by absorption spectroscopy and cyclic voltammetry. The reaction is accelerated by Mg2+. The combined evidence points to a mechanism where the oxo-bridged dimer is hydrolyzed to a monomeric Ru(III) complex that is capable of oxidizing DNA to effect strand scission. Gel electrophoresis demonstrates nicking of supercoiled /gfX174 DNA by [(bpy)2(OH2)RuORu(OH2) (bpy)2]4+, and double-stranded cleavage is observed in the presence of Mg2+. Linearization of the plasmid prior to treatment with the complex does not lead to further fragmentation, suggesting that supercoiling is required to realize double-stranded cleavage.  相似文献   

16.
In a synthetic route that varies from the standard procedure requiring irradiation, the (η6-C6H5Cl)Cr(CO)2PPh3 complex is obtained upon reacting (η6-C6H5Cl)Cr(CO)3 with tetrakis(triphenylphosphine)palladium(0), CuI, and trimethylsilylphenylacetylene in triethylamine. The X-ray crystal structure of the yellow–orange crystals of (η6-C6H5Cl)Cr(CO)2PPh3 allows structural comparisons to related (arene)Cr(CO)2PR3 complexes.  相似文献   

17.
Electrospray mass spectrometry (ESMS) has been used to investigate the relative ligand properties of the triphenylpnictogen ligands EPh3 (E=P, As, Sb and Bi) towards silver(I) and copper(I) ions. It is found that the preferred species formed increase in coordination number from two for PPh3 in [Ag(PPh3)2]+ to four for SbPh3 in [Ag(SbPh3)4]+, consistent with the decreasing donor ligand ability and increasing metal –E bond length in the series PPh3–AsPh3–SbPh3. With BiPh3, the spectra were complex, suggesting considerable decomposition. These studies also suggest that silver(I) and copper(I) ions will have widespread utility in the characterisation of tertiary stibine ligands, as has been described previously for phosphines and arsines. These studies demonstrate the power of the ESMS technique in determining the donor properties of a related series of ligands, and this information is of significance in coordination chemistry.  相似文献   

18.
Two ruthenium(II) complexes with polypyridyl, Ru(bipy)2(phen)](ClO4)2·H2O (1) and [Ru(bipy)2(Me-phen)](ClO4)2 (2), (phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, Me-phen = 5-methyl-1,10-phenanthroline), were synthesized and characterized by IR, MS and NMR spectra. Their structures were determined by single crystal X-ray diffraction techniques. The strong steric interaction between the polypyridyl ligands was relieved neither by the elongation of the Ru---N bonds nor increase of the N---Ru---N bite angles. The coordination sphere was distorted to relieve the ligand interaction by forming specific angles (δ) between the polypyridyl ligand planes and coordination planes (N---Ru---N), and forming larger twisted angles between the two pyridine rings for each bipy. The bond distances of Ru---N(bipy) and Ru---N(phen) were virtually identical with experimental error, as expected of π back-bonding interactions which statistically involve each of the ligands present in the coordination sphere.  相似文献   

19.
The syntheses and characterization of two new tetradentate hemilabile ligands 1,2-bis(2-diphenylphosphinoethoxy)benzene (5) and 2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene (10) are reported. Ligands 5 and 10 were synthesized as models to test the suitability of specific phosphinoether coordination environments for complexing Rh(I) in high surface area thiophene-based, redox-active polymeric systems. Ligands 5 and 10 react with the product formed from the reaction between (bicyclo[2.2.1]hepta-2,5-diene)rhodium(I) chloride dimer and AgBF4 to form [η2-(1,2-bis(2-diphenylphosphinoethoxy)benzene) η4-norbornadiene rhodium(I)] tetrafluoroborate (6) and [η2-(2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene) η4-norbornadiene rhodium(I)] tetrafluoroborate (11), respectively. Complexes 6 and 11 react with H2 in CD2Cl2 to form the two new square-planar cis-phosphine, cis-ether Rh(I) complexes 7 and 12, respectively. Compound 7, which could be characterized on the basis of its 31P NMR spectrum, is extremely reactive and decomposes in CD2Cl2. In THF compounds 6 and 11 react with H2 to form the dihydride, bis-THF adducts 8 and 16, respectively, which upon removal of solvent form 7 and 12, respectively. Compound 12 is a stable, isolable complex that reacts with acetonitrile to form a cis-phosphine, cis-acetonitrile adduct 15. Removal of solvent from 15 leads to the quantitative reformation of 12. Compound 12 does not react to a detectable extent with gross excesses of benzene or even thiophene, demonstrating the suitability of this ligand environment for implementation into a thiophene-based polymeric system. Compound 12 does catalyze the hydrogenation of cyclohexene to form cyclohexane, and mechanistic implications of such a transformation are discussed.  相似文献   

20.
Reaction of sodium or potassium molybdate and excess malic acid in a wide range of pH values (pH 4.0–7.0) resulted in the isolation of two cis-dioxo-bis(malato)-Mo(VI) complexes, viz. Na3[MoO2H(S-mal)2] and K3[MoO2H(S-mal)2]·H2O (H3mal=malic acid). The sodium complex is also characterized by an X-ray structure analysis, showing that the mononuclear Mo units are linked together via very strong symmetric CO2···H··· O2C-hydrogen bond [2.432(5) Å], forming a polymeric chain. The molybdenum atoms are quasi-octahedrally coordinated by two cis-oxo groups and two bidentate malate ligands via its alkoxy and -carboxyl groups, while the β-carboxylic and carboxylate groups remain uncomplexed, as the coordination of vicinal carboxylate and alkoxide of homocitrate in FeMo cofactor of nitrogenase. The absolute configuration of the metal center in this S-malato complex is assigned as Λ and the homochirality within the chain is established as a homochiral form ···ΛS–ΛS–ΛS–ΛS···. It is proposed that the chiral configuration of the metal center in wild-type FeMo-co biosynthesis might be induced by the early coordination of the chiral R-homocitric acid, while a mixture of raceme might be obtained in the biosynthesis of NifV FeMo-cofactor. The absolute configuration of wild-type FeMo-cofactor is assigned as ΔR.  相似文献   

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