Crown ether-like octanuclear molybdenum(V) clusters for cation binding and gas adsorption.

Octanuclear polyoxomolybdenum-based porous materials, Na8[Mo8O8(µ2-O)8(µ2-OH)8(3-apz)4]2·26H2O (1, 3-Hapz = 3-aminopyrazole), K8[Mo8O8(µ2-O)8(µ2-OH)8(3-apz)4]2·7H2O (2) and (NH4)4[Mo8O8(µ2-O)8(µ2-OH)4(3-apz)8]·20.5H2O (3), have been successfully synthesized by a hydrothermal method and fully characterized. X-ray structural analyses show that microporous materials 1-3 contain round pores formed by octanuclear molybdenum-oxygen groups connected sequentially with pore sizes of 4.0, 4.0, and 4.8 Å, respectively. Both 1 and 2 are composed of two {Mo8} rings, which are connected by strong intramolecular hydrogen bonds between bridging hydroxy groups and oxygen atoms to form dimeric structures. The central pores in 1 and 2 are occupied by Na+ and K+, respectively, while they are empty in 3. This reflects the structural expansion and contraction effects induced by different cations. Through intermolecular stacking, 1-3 also exhibit channels with sizes of 14.0 × 6.4, 4.6 × 2.6, and 5.4 × 5.4 Å, respectively, which were used for the studies of gas adsorption. The results show that 1-3 can selectively adsorb CO2 and O2, including the empty hole in 3, while they show little or no affinity for gases H2, N2, and CH4. Moreover, an additional polyoxomolybdenum-based species (Mo8O26)n·4n(3-H2apz) (4) has been obtained with protonated 3-aminopyrazole in the absence of a reducing agent, which can serve as an intermediate for the polyoxomolybdenum-based porous products.

Radiological insights into rheumatoid meningitis - a rare central nervous system manifestation of rheumatoid arthritis: a retrospective review of six cases.

BACKGROUND: The objective is to analyze and review the clinical, laboratory, and neuroimaging characteristics of rheumatoid meningitis (RM) in six patients with known rheumatoid arthritis (RA). METHODS: We performed a retrospective review of patients diagnosed with RM from August 2012 to June 2023. To identify the cases, we used medical term search engines and the hospital´s radiology case database. Clinical information and laboratory findings were gathered from the medical records. A neuroradiologist with five years of experience reviewed and analyzed the RM to determine the characteristics findings of RM. RESULTS: Six patients with RM are included. Seizures along with headaches were among the clinical signs that were documented. All the patients had high levels of rheumatoid factor (RF) and anti-cyclic citrullinated peptides (ACPA) in the peripheral blood. Biopsy in two cases confirmed typical rheumatoid nodules. Leptomeningeal enhancement was found bilaterally in all cases and was predominantly found in the frontoparietal region. "Mismatch DWI/FLAIR" was found in five patients. Bilateral subdural collections could be found in two patients. Brain PET scan revealed increased metabolism in two cases. CONCLUSION: Rheumatoid meningitis is a rare complication of rheumatoid arthritis (RA) with challenging clinical diagnosis due to non-specific symptoms. This study highlights the importance of MR in detecting characteristic neuroimaging patterns, including "mismatch DWI/FLAIR", to aid in early diagnosis. Increased awareness of this condition may facilitate timely intervention and improve prognosis. These results still need to be verified by large studies.

Genome Mining of Cinnamoyl-Containing Nonribosomal Peptide Gene Clusters Directs the Production of Malacinnamycin.

Cinnamoyl-containing nonribosomal peptides (CCNPs) constitute a unique family of actinobacterial secondary metabolites that display a broad spectrum of biological activities. Here, we present a genome mining approach targeting cyclase and is isomerase to discover new CCNPs, which led to the identification of 207 putative CCNP gene clusters from public bacterial genome databases. After strain prioritization, a novel class of CCNP-type glycopeptides named malacinnamycin was identified. A plausible biosynthetic pathway for malacinnamycin was deduced by bioinformatics analysis.

Octa- and Tetradecanuclear Mixed-Valent Vanadium(III/IV) Malates with Triazoles: Gas Adsorptions, Chiral Interface Recognition, and In Situ Decarboxylation.

Spontaneous resolution has been found for a pair of cage-like octanuclear mixed-valent vanadium(III/IV) malate enantiomers [Δ-VIII4VIV4O5(R-mal)6(Hdatrz)6]·44.5H2O (ΔR-1) and [Λ-VIII4VIV4O5(S-mal)6(Hdatrz)6]·38.5H2O (ΛS-1, H3mal = malic acid; Hdatrz = 3,5-diamino-1,2,4-triazole). Their racemic reduced product K7[VIII5VIV3O5(R,S-mal)6(trz)6]·17H2O (2) and tetradecanuclear species K11[VIII3VIV11O11(R,S-mal)12(atrz)6]·45.5H2O (3) (Htrz = 1,2,3-triazole, Hatrz = 3-amino-1,2,4-triazole) have also been obtained. In situ decarboxylation happens for 3-amino-1,2,4-triazole-5-carboxylic acid (H2atrzc) to yield 3-amino-1,2,4-triazole under hydrothermal conditions. Both 1 and 2 show an interesting bicapped-triangular-prismatic {V8O5(mal)6} building block, which further decorates symmetrically with three [VIV2O2(R,S-mal)2]2- units to construct a pinwheel-like {V14}-cluster, 3. Bond valence calculation sum (BVS) analyses manifest that the oxidation states of bicapped V atoms are +3 in 1-3, while the other V atoms in the {V6O5} core are ambiguous between +3 and +4 states with strong electron delocalization. Intriguingly, the triple helical chains in 1 associate in parallel to generate an amine-functionalized chiral polyoxovanadate (POV)-based supramolecular open-framework. The diameter of the interior channel is 13.6 Å, showing preferential adsorption of CO2 over gases N2, H2, and CH4. Importantly, homochiral framework ΔR-1 is capable of performing chiral interface recognition for R-1,3-butanediol (R-BDO) through host-guest interactions, as confirmed by the structural analysis of the host-guest complex ΔR-1·3(R-BDO). There are six R-BDO molecules in the channel of ΔR-1.

Crown ether-like discrete clusters for sodium binding and gas adsorption.

Hexanuclear polyoxomolybdenum-based discrete supermolecules Nax[MoV6O6(µ2-O)9(Htrz)6-x(trz)x]·nH2O (x = 0, n = 15, 1; x = 1, n = 12, 2; x = 2, n = 10, 3; x = 2, n = 49, 4; Htrz = 1H-1,2,3-triazole) have been prepared and fully characterized with different amounts of sodium cations inside and outside the intrinsic holes. Structural analyses demonstrate that they all exist a triangular channel constructed by six molybdenum-oxygen groups with inner diameters of 2.86 (1), 2.48 (2), and 3.04 (3/4) Å, respectively. Zero, one, or two univalent enthetic guest Na+ have been hosted around the structural centers, which reflect the expansion and contraction effects at microscopic level. Water-soluble species can serve as crown ether-like metallacycles before and after the sodium binding. Diverse nanoscale pores are further formed through intermolecular accumulations with hydrogen bonding. Gas adsorption studies indicate that 2-4 can selectively adsorb CO2 and O2 but have little or even no affinities toward H2, N2, and CH4. Theoretical calculations corroborate the roles of Na+ and auxiliary ligand with different states in bond distances, molecular orbitals, electrostatic potentials, and lattice energies in these discrete clusters. The binding orders of sodium cations in 2-4 are similar with the classical crown ethers, where 2 is the strongest one with 2.226(4)av Å for sodium cation bonded to six O atoms.

Statistical analyses of the oxidized P-clusters in MoFe proteins using the bond-valence method: towards their electron transfer in nitrogenases.

26 well selected oxidized P-clusters (P2+) from the crystallographic data deposited in the Protein Data Bank have been analysed statistically by the bond-valence sum method with weighting schemes for MoFe proteins at different resolutions. Interestingly, the oxidation states of P2+ clusters correspond to Fe23+Fe62+ with high electron delocalization, showing the same oxidation states as the resting states of P-clusters (PN) in nitrogenases. The previously uncertain reduction of P2+ to PN clusters by two electrons was assigned as a double protonation of P2+, in which decoordination of the serine residue and the peptide chain of cysteine take place, in MoFe proteins. This is further supported by the obviously shorter α-alkoxy C-O bond (average of 1.398 Å) in P2+ clusters and longer α-hydroxy C-O bond (average of 1.422 Å) in PN clusters, while no change is observed in the electronic structures of Fe8S7 Fe atoms in P-clusters. Spatially, the calculations show that Fe3 and Fe6, the most oxidized and most reduced Fe atoms, have the shortest distances of 9.329 Šfrom the homocitrate in the FeMo cofactor and 14.947 Šfrom the [Fe4S4] cluster, respectively, and may well function as important electron-transport sites.

The Synergistic Effects between Sulfobetaine and Hydrophobically Modified Polyacrylamide on Properties Related to Enhanced Oil Recovery.

In order to explore the mechanism responsible for the interactions in the surfactant-polymer composite flooding and broaden the application range of the binary system in heterogeneous oil reservoirs, in this paper, the influences of different surfactants on the viscosity of two polymers with similar molecular weights, partially hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM), were studied at different reservoir environments. In addition, the relationship between the surfactant-polymer synergistic effects and oil displacement efficiency was also investigated. The experimental results show that for HPAM, surfactants mainly act as an electrolyte to reduce its viscosity. For HMPAM, SDBS and TX-100 will form aggregates with the hydrophobic blocks of polymer molecules, reducing the bulk viscosity. However, zwitterionic surfactant aralkyl substituted alkyl sulfobetaine BSB molecules can build "bridges" between different polymer molecules through hydrogen bonding and electrostatic interaction. After forming aggregates with HMPAM molecules, the viscosity will increase. The presence of two polymers all weakened the surfactant oil-water interfacial membrane strength to a certain extent, but had little effect on the interfacial tension. The synergistic effect of the "bridge" between HMPAM and BSB under macroscopic conditions also occurs in the microscopic pores of the core, which has a beneficial effect on improving oil recovery.

m5C-dependent cross-regulation between nuclear reader ALYREF and writer NSUN2 promotes urothelial bladder cancer malignancy through facilitating RABL6/TK1 mRNAs splicing and stabilization.

The significance of 5-methylcytosine (m5C) methylation in human malignancies has become an increasing focus of investigation. Here, we show that m5C regulators including writers, readers and erasers, are predominantly upregulated in urothelial carcinoma of the bladder (UCB) derived from Sun Yat-sen University Cancer Center and The Cancer Genome Atlas cohort. In addition, NOP2/Sun RNA methyltransferase family member 2 (NSUN2) as a methyltransferase and Aly/REF export factor (ALYREF) as a nuclear m5C reader, are frequently coexpressed in UCB. By applying patient-derived organoids model and orthotopic xenograft mice model, we demonstrate that ALYREF enhances proliferation and invasion of UCB cells in an m5C-dependent manner. Integration of tanscriptome-wide RNA bisulphite sequencing (BisSeq), RNA-sequencing (RNA-seq) and RNA Immunoprecipitation (RIP)-seq analysis revealed that ALYREF specifically binds to hypermethylated m5C site in RAB, member RAS oncogene family like 6 (RABL6) and thymidine kinase 1 (TK1) mRNA via its K171 domain. ALYREF controls UCB malignancies through promoting hypermethylated RABL6 and TK1 mRNA for splicing and stabilization. Moreover, ALYREF recognizes hypermethylated m5C site of NSUN2, resulting in NSUN2 upregulation in UCB. Clinically, the patients with high coexpression of ALYREF/RABL6/TK1 axis had the poorest overall survival. Our study unveils an m5C dependent cross-regulation between nuclear reader ALYREF and m5C writer NSUN2 in activation of hypermethylated m5C oncogenic RNA through promoting splicing and maintaining stabilization, consequently leading to tumor progression, which provides profound insights into therapeutic strategy for UCB.

Successive constructions of regular tetra-, hexa- and octanuclear microporous polyoxovanadates(III) for gas adsorption.

Pyrazole-assisted tetranuclear microporous polyoxovanadates(III) (POVs) (NH4)2K2[V4(µ2-OH)4(ox)4(pz)4]·9H2O (1, ox = oxalate and pz = pyrazole) and (NH4)2Na2[V4(µ2-OH)4(ox)4(4-mpz)4]·7H2O (2, 4-mpz = 4-methylpyrazole) have been constructed in reduced media, along with their triazole neutral hexa- and octanuclear products K2[V6(µ2-OH)6(ox)6(Hdatrz)6]Cl2·29.5H2O (3) and [V8(µ2-OH)8(SO3)8(Hdatrz)8]·38H2O (4, Hdatrz = 1H-1,2,4-triazole-3,5-diamine) successively. Both polyanionic structures of 1 and 2 share similar inorganic building blocks that consist of regular {V4(µ2-OH)4} skeletons with an inner diameter of 2.8 Å, while a paddle wheel-shaped cluster 3 contains a {V6(µ2-OH)6} skeleton with two chlorides encapsulated around the center of the ring, occupying a hole of 3.7 Å. An interesting isolated intrinsic polyoxometalate-based metal-organic framework (POMOF) 4 exists as an octanuclear petaloid-like skeleton {V8(µ2-OH)8(SO3)8} with an inner diameter of 5.2 Å. Bond valence sum calculations manifest that all V ions have severely reduced +3 oxidation states in 1-4, which are supported by charge balance, structural and magnetic data. Moreover, gas adsorptions indicate that 1, 2 and 4 can adsorb CO2 and O2 more favorably than N2, CH4 and H2 gases. Compared with 1 and 2, due to the functionalization of microchannels with Lewis base amino and hydroxy groups and uncoordinated azolate N-donors inside POMOF 4, it should have notable affinities toward CO2 adsorption.

Single-cell transcriptomics reveals a low CD8+ T cell infiltrating state mediated by fibroblasts in recurrent renal cell carcinoma.

PURPOSE: Recurrent renal cell carcinoma(reRCC) is associated with poor prognosis and the underlying mechanism is not yet clear. A comprehensive understanding of tumor microenvironment (TME) of reRCC may aid in designing effective anticancer therapies, including immunotherapies. Single-cell transcriptomics holds great promise for investigating the TME, however, this technique has not been used in reRCC. Here, we aimed to explore the difference in the TME and gene expression pattern between primary RCC (pRCC) and reRCC at single-cell level. EXPERIMENTAL DESIGN: We performed single-cell RNA sequencing analyses of 32,073 cells from 2 pRCC, 2 reRCC, and 3 adjacent normal kidney samples. 41 pairs of pRCC and reRCC samples were collected as a validation cohort to assess differences observed in single-cell sequencing. The prognostic significance of related cells and markers were studied in 47 RCC patients underwent immunotherapy. The function of related cells and markers were validated via in vitro and in vivo experiments. RESULTS: reRCC had reduced CD8+ T cells but increased cancer-associated fibroblasts (CAFs) infiltration compared with pRCC. Reduced CD8+ T cells and increased CAFs infiltration were significantly associated with a worse response from immunotherapy. Remarkably, CAFs showed substantial expression of LGALS1 (Gal1). In vitro, CAFs could induce CD8+ T cells apoptosis via Gal1. In vivo, knockdown of Gal1 in CAFs suppressed tumor growth, increased CD8+ T cells infiltration, reduced the proportion of apoptotic CD8+ T cells and enhanced the efficacy of immunotherapy. CONCLUSIONS: We delineated the heterogeneity of reRCC and highlighted an innovative mechanism that CAFs acted as a suppressor of CD8+ T cells via Gal1. Targeting Gal1 combined with anti-PD1 showed promising efficacy in treating RCC.

Intrinsic Molybdenum-Based POMOFs with Impressive Gas Adsorptions and Photochromism.

Novel molybdenum(VI/V) POM-based self-constructed frameworks [MoVI 12 O24 (µ2 -O)12 (trz)6 (H2 O)6 ] ⋅ 6Hma ⋅ 18H2 O (1, Htrz=1H-1,2,3-triazole, ma=methylamine), [MoVI 7 O14 (µ2 -O)8 (trz)5 (H2 O)] ⋅ 7Hma ⋅ 5H2 O (2), Na3 [MoV 6 O6 (µ2 -O)9 (Htrz)3 (trz)3 ] ⋅ 7.5H2 O (3) and [MoV 8 O8 (µ2 -O)12 (Htrz)8 ] ⋅ 30H2 O (4) have been covalently decorated with tri-coordinated deprotonated/protonated 1,2,3-triazoles. Channels with an inner diameter of 7.5 Šwere found in 1, whereas a tunnel composed of stacking molecules with an inner diameter of 4.1 Šalong the b-axis exists in 2; it is occupied by free disordered methylamines, showing selective adsorption of O2 and CO2 at 25 °C. Obvious downfield shifts were observed by 13 C NMR spectroscopies for methylamines inside the confined channels in 1 and 2. There are diversified pores in 3 and 4, which are formed by the molecules themselves and intermolecular accumulations. Adsorption tests indicate that 3 and 4 are fine adsorption materials for CH4 and CO2 under low pressure that rely on the environments built by the POMs. Correspondingly, 1 and 2 display reversible photoresponsive thermochromism that is subtlety influenced by the channels. The polyoxometalate organic frameworks (POMOFs) with multiple functional adsorptions are easy to assemble. Their photo-/thermoresponse properties offer a new pathway for the self-constructions of one-off hybrid materials that possess the good properties of both POMs and MOFs.

Isolated Mixed-Valence Iron Vanadium Malate and Its Metal Hydrates (M = Fe2+, Cu2+, Zn2+) with Reversible and Irreversible Adsorptions for Oxygen.

Isolated octanuclear iron-vanadium malate (NH4)3(CH3NH3)3[FeIII2VIV2VV4O11(mal)6]·7.5H2O (1; H3mal = malic acid) and its family of metal hydrates M'3n[MII(H2O)2]1.5n[FeIII2VIV2VV4O11(mal)6]n·xnH2O (2 or 2-Fe, M' = NH4+, M = Fe, x = 7.5; 3 or 3-Cu, M' = K+, M = Cu, x = 10; 4 or 4-Zn, M' = K+, M = Zn, x = 6.5) have been obtained by self-assembly in water. The cluster anion [Fe2V6O11(mal)6]6- (1a) shows an interesting iron bicapped-triangular-prismatic structure, which is bridged by M2+ hydrates (M = Fe, Cu, Zn) to construct isostructural metal organic frameworks (MOFs) 2-4. The mixed-valence vanadium systems in 1-4 were determined by theoretical bond valence calculations (BVS) and charge balance. The magnetic susceptibilities are further elucidated as high spin for Fe3+ in 1a and bridging Fe2+ in 2-Fe, respectively. A strong ferromagnetic interaction was also observed for 2-Fe at 3 K. 2-Fe, 3-Cu, and 4-Zn have similar hydrophilic channels with diameters of 6.8, 6.5, and 6.6 Å, respectively, which show obvious affinity for O2 in comparison with no adsorption of N2, H2, CO2, and CH4 at room temperature under different pressures. Moreover, 2-Fe and 4-Zn exhibit irreversible O2 absorptions, which may be attributed to charge transfer between O2 and open metal sites (OMSs) formed during vacuum heating pretreatment. UV-vis and EPR spectra show a change in electronic structure of 2-Fe after O2 adsorption. The reversible adsorption observed in 3-Cu suggests a weak interaction between O2 and Cu2+ due to the Jahn-Teller effect. The properties of gas adsorption provide an insight into the performances of small molecules in the channels constructed by synthetic octanuclear model compounds, which are related to the interactions between the gas substrate and the heterometal cluster in biology.

Bond-valence analyses of the crystal structures of FeMo/V cofactors in FeMo/V proteins.

The bond-valence method has been used for valence calculations of FeMo/V cofactors in FeMo/V proteins using 51 crystallographic data sets of FeMo/V proteins from the Protein Data Bank. The calculations show molybdenum(III) to be present in MoFe7S9C(Cys)(HHis)[R-(H)homocit] (where H4homocit is homocitric acid, HCys is cysteine and HHis is histidine) in FeMo cofactors, while vanadium(III) with a more reduced iron complement is obtained for FeV cofactors. Using an error analysis of the calculated valences, it was found that in FeMo cofactors Fe1, Fe6 and Fe7 can be unambiguously assigned as iron(III), while Fe2, Fe3, Fe4 and Fe5 show different degrees of mixed valences for the individual Fe atoms. For the FeV cofactors in PDB entry 5n6y, Fe4, Fe5 and Fe6 correspond to iron(II), iron(II) and iron(III), respectively, while Fe1, Fe2, Fe3 and Fe7 exhibit strongly mixed valences. Special situations such as CO-bound and selenium-substituted FeMo cofactors and O(N)H-bridged FeV cofactors are also discussed and suggest rearrangement of the electron configuration on the substitution of the bridging S atoms.

Gas Adsorption of Mixed-Valence Trinuclear Oxothiomolybdenum Glycolates.

Trinuclear oxothiomolybdenum(IV) glycolates (H2glyc, glycolic acid) with 2-methylimidazole (2-mim), 4-methylimidazole (4-mim), and sulfite, Na2[MoIV3(µ3-S)(µ2-O)3(glyc)3(2-mim)3]·1.5H2O (1), (4-Hmim)6[MoIV3(µ3-S)(µ2-O)3(glyc)3(4-mim)3]2[MoVIO2(glyc)2] (2), and Na3(4-Hmim)[MoIV3(µ3-S)(µ2-O)3(SO3)(glyc)3(4-mim)]·8H2O (3), have been isolated in reduced media, where 4-methylimidazole trinuclear oxothiomolybdenum(IV) glycolates in 2 coprecipitate with dioxomolybdenum(VI) glycolate, exhibiting unusual mixed valences of 4+ and 6+. Large downfield shifts of glycolates have been observed in solid-state and solution 13C (1H) NMR spectra with coordination to Mo, indicating obvious dissociation of soluble 1 and 3 in solution. Investigations of the coordination modes and conversions among the three complexes give insight into the reactivities of trinuclear oxothiomolybdenum(IV) complexes. Channels with 3.1 × 7.0 Å2 diameters exist in 2, showing reversible O2 absorption of 65.03 mg at 29.9 bar compared with little or no adsorption of N2, H2, CO2, and CH4 at room temperature, respectively. Moreover, trinuclear 2- or 4-methylimidazole oxothiomolybdenum(IV) glycolates 1 and 3 show only a few adsorptions for O2 under the same conditions.

[Clinical analysis on arthroscopic debridement for the treatment of early infection after total knee replacement].

OBJECTIVE: To compare the clinical effects of arthroscopic debridement versus open debridement on controlling and treatment of infection after total knee replacement. METHODS: From October 2009 to September 2016 in three hospitals, 11 patients with 11 joints which were infected after total knee replacement were randomly divided into two groups:5 cases in arthroscopy group and 6 cases in routine group. Patients in arthroscopy group were treated with arthroscopic debridement to remove the necrotic tissues, then closed-type irrigation with sensitive antibiotics by using two sebific ducts were performed continuously for 2 or 3 weeks until the flushing fluid became clear for 3 or 5 days;other 6 patients in routine group were treated with open surgical debridement and the following procedures in keeping with those in the arthroscopy group. Operation time, blood loss and incision length were recorded during the operation, and pain scores were recorded on the 1st, 3rd and 7th day after the operation. The curative effects were evaluated according to the Hospital for Special Surgery score system. RESULTS: The local and general symptoms of the 11 patients disappeared, and the test outcomes of biochemistry, blood and synovial fluid were normal. All patients were followed up, and the duration ranged from 6 to 18 months. Infection recurrences were observed in 1 case of arthroscopy group and 2 cases of routine group 3 months later after operation, and all these patients who underwent the second time operation with arthroscopic debridement were cured. According to the Hospital for Special Surgery score system, 3 cases obtained excellent result, 2 good, no poor and bad cases in arthroscopy group;3 cases obtained excellent result, 1 good, 1 poor and 1 bad in routine group. CONCLUSIONS: If the sensitive antibiotics can be found for the infected joints without obvious destruction of bone and no prosthesis loosening, it has a better therapeutic effect by using arthroscopic debridement combined with continuous drainage and irrigation. The method has a better curative effect with smaller trauma.

α-Hydroxy coordination of mononuclear vanadyl citrate, malate and S-citramalate with N-heterocycle ligand, implying a new protonation pathway of iron-vanadium cofactor in nitrogenase.

Unlike the most of α-alkoxy coordination in α-hydroxycarboxylates to vanadium, novel α-hydroxy coordination to vanadium(IV) has been observed for a series of chiral and achiral monomeric α-hydroxycarboxylato vanadyl complexes [VO(H2cit)(bpy)]·2H2O (1), [VO(Hmal)(bpy)]·H2O (2), [VO(H2cit)(phen)]·1.5H2O (3), [VO(Hmal)(phen)]·H2O (4), and [(Δ)VO(S-Hcitmal)(bpy)]·2H2O (5), [VO(H2cit)(phen)]2·6.5H2O (6), which were isolated from the reactions of vanadyl sulfate with α-hydroxycarboxylates and N-heterocycle ligands in acidic solution. The complexes feature a tridentate citrate, malate or citramalate that chelates to vanadium atom through their α-hydroxy, α-carboxy and ß-carboxy groups; while the other ß-carboxylic acidic group of citrate is free to participate strong hydrogen bonds with lattice water molecule. The neutral α-hydroxy group also forms strong intermolecular hydrogen bonds with water molecule and the negatively-charged α-carboxy group in the environment. The inclusion of a hydrogen ion in α-alkoxy group results in the formation of a series of neutral complexes with one less positive charge. There are two different configurations of citrate with respect to the trans-position of axial oxo group, where the complex with trans-hydroxy configuration seems more stable with less hindrance. The average bond distances of V-Ohydroxy and V-Oα-carboxy are 2.196 and 2.003Å respectively, which are comparable to the VO distance (2.15Å) of homocitrate in FeV-cofactor of V-nitrogenase. A new structural model is suggested for R-homocitrato iron vanadium cofactor as VFe7S9C(R-Hhomocit) (H4homocit=homocitric acid) with one more proton in homocitrate ligand.

Synthesis and characterization of homochiral polymeric S-malato molybdate(VI): toward the potentially stereospecific formation and absolute configuration of iron-molybdenum cofactor in nitrogenase.

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. Na(3)[MoO(2)H(S-mal)(2)] and K(3)[MoO(2)H(S-mal)(2)].H(2)O (H(3)mal=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 CO(2)...H... O(2)C-hydrogen bond [2.432(5) A], 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 alpha-carboxyl groups, while the beta-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 Lambda and the homochirality within the chain is established as a homochiral form ...Lambda(S)-Lambda(S)-Lambda(S)-Lambda(S)... . 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 Delta(R).