Structure and magnetic properties of Ca14MnP11

The compound Ca₁₄MnP₁₁ crystallizes in the Ca₁₄AlSb₁₁ structure type with the tetragonal space group I4₁/acd (Z=8) and lattice parameters of , c=20.7565(9) at 90 K. The structure consists of MnP₄⁹⁻ tetrahedron, P₃⁷⁻ trimer, 4 P³⁻ isolated anions and 14 Ca²⁺ cations. Similar to other compounds of this structure type containing phosphorous, the P₃⁷⁻ trimer has a central P atom that is best modeled in the structure as being equally split between two sites. In addition, there is no additional distortion of the manganese-containing tetrahedron compared with the main group analog, Ca₁₄GaP₁₁, suggesting that the Mn oxidation state is Mn²⁺. Temperature-dependent magnetic susceptibility shows that the compound is paramagnetic over the entire temperature range measured (2-300 K). The data can be fit with a modified Curie-Weiss law and provide an effective magnetic moment of 5.80 (2) B.M. with a Weiss constant of −2.13(2) K and . This moment is significantly higher than those measured for any of the Mn-containing analogs and is consistent with Mn²⁺. This result will be discussed in light of the electron counting scheme for Mn compounds of the Ca₁₄AlSb₁₁ structure-type.     

Synthesis of the fungal natural product (−)-xylariamide A

The first synthesis of the fungal natural product (−)-xylariamide A 1 is reported. N,O-Bis(trimethylsilyl)acetamide induced coupling of d-tyrosine with (E)-but-2-enedioic acid 2,5-dioxo-pyrrolidin-1-yl ester methyl ester 5 produced the dechloro natural product 6, which was subsequently monochlorinated using oxone and KCl to yield synthetic 1. (−)-Xylariamide A 1, (+)-xylariamide A 2 and (−)-dechloroxylariamide A 6 displayed no cytotoxic or antimicrobial activity.     

A facile sulfonylation method enabling direct syntheses of per(2-O-sulfonyl)-β-cyclodextrins

Cs₂CO₃ was found to efficiently catalyze the reaction of β-cyclodextrin and N-tosylimidazole. Stirring β-cyclodextrin and N-tosylimidazole in 1/1.2 molar ratio in DMF in the presence of catalytic amount of Cs₂CO₃ at rt for 1.5 h afforded 2^A-mono(O-tosyl)-β-cyclodextrin in 32% yield. The 2^A,2^B-, 2^A,2^C- and 2^A,2^D-ditosylates were isolated in ca. 6-7% yields, respectively, when β-cyclodextrin and N-tosylimidazole were used in 1/2.5 molar ratio. The charge of excess (10 equiv) of N-tosylimidazole ensured a one-step direct (protection-free) synthesis of the per(2-O-tosyl)-β-cyclodextrin in 5% isolated yield. N-(m-Nitrobenzenesulfonyl)imidazole even allowed a much faster access to the corresponding persulfonate in only 1 h reaction.     

Effect of Sulfate on an Iron Manganese Catalyst for Fischer-Tropsch Synthesis

The effect of sulfate on Fischer-Tropsch synthesis performance was investigated in a slurry- phase continuously stirred tank reactor(CSTR)over a Fe-Mn catalyst.The physiochemical properties of the catalyst impregnated with different levels of sulfate were characterized by N_2 physisorption,X-ray photoelectron spectroscopy(XPS),H_2(or CO)temperature-programmed reduction(TPR),Mφssbauer spectroscopy,and CO_2 temperature-programmed desorption(TPD).The characterization results indicated that the impregnated sulfate slightly decreased the BET surface area and pore volume of the catalyst, suppressed the catalyst reduction and carburization in CO and syngas,and decreased the catalyst surface basicity.At the same time,the addition of small amounts of sulfate improved the activities of Fischer- Tropseh synthesis(FTS)and water gas shift(WGS),shifted the product to light hydrocarbons(C_1-C_(11)) and suppressed the formation of heavy products(C_(12 )).Addition of SO_4~(2-)to the catalyst improved the FTS activity at a sulfur loading of 0.05-0.80 g per 100 g Fe,and S-05 catalyst gave the highest CO conversion(62.3%),and beyond this sulfur level the activity of the catalyst decreased.     

A stable carbonyl-pyrazine-metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

Pentacarbonylpyrazinetungsten(0), (CO)₅W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)₅W(pyz)W(CO)₅ plus free pyrazine. These three species exist at equilibrium. Using the quantitative ¹H NMR spectroscopy, the equilibrium constant could be determined to be K_eq = (5.9 ± 0.8) × 10⁻² at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)₄(pyz)₂ was found to be less stable than W(CO)₅(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)₄[P(OCH₃)₃](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)₄[P(OCH₃)₃](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, ¹H, ¹³C, and ³¹P NMR spectroscopy.     

Synthesis of trimethyl (2S,3R)- and (2R,3R)-[2-H1]-homocitrates and the corresponding dimethyl ester lactones—towards elucidating the stereochemistry of the reaction catalysed by homocitrate synthase and by the Nif-V protein

Trimethyl (2S,3R)- and (2R,3R)-[2-²H₁]-homocitrates, 10b and 10c respectively, and dimethyl (2S,3R)- and (2R,3R)-[2-²H₁]-homocitric lactones, 11b and 11c respectively, have been synthesised from shikimic acid and [2-²H]-shikimic acid by a route which defines the stereochemistry of the two chiral centres in each compound. The NMR spectra of these products will enable the stereochemistry of the biological reaction catalysed by homocitrate synthase and by the protein from the nifV gene to be elucidated.     

Synthesis and Visible Spectral Behaviour of Some New N‐Bridgehead Heterocyclic Cyanine Dyes Incorporating Pyrazolo (4,5‐b) Indolizine (Benzoindolizine)

The new unsymmetrical N‐bridgehead, apo (zeromethine), mono‐methine, dimethine, meso substituted tetramethine and styryl cyanine dyes incorporating pyrazolo (4,5‐b) indolizine (benzoindolizine) nuclei were prepared. Structural confirmation was carried out by elemental analyses, IR, H‐NMR, mass spectra and ¹³C‐NMR with the aid of carbon DEPT spectral data. The visible absorption spectra for the newly synthesized cyanines were examined in 95% ethanol.     

Synthesis and Structure Determination of Some New N‐Glycosides of 4,5‐Disubstituted‐1,2,4‐Triazole‐3‐Thiones

Some new N‐glycosides of 4‐(2‐phenylethyl)‐5‐pyridyl‐1,2,4‐triazole‐3‐thiones were synthesised by the coupling reaction of halo sugar with 4,5‐disubstituted 3H‐1,2,4‐triazole‐3‐thiones in the presence of mercuric cyanide and dry nitromethane as solvent, followed by deprotection using dry ammonia in methanol. All of the above compounds were fully characterized by means of infrared, ¹H NMR spectroscopy, mass spectroscopy and elemental analysis.     

Methane production from synthesis gas using a mixed culture ofR. rubrum M. barkeri,and M. formicicum

The components of synthesis gas, CO, H₂, and CO₂, may be converted into CH₄ biologically through either acetate or H₂/CO₂ as intermediates. Of these two routes, conversion through H₂/CO₂ is preferred. This paper presents results of mixed-culture studies employing the photosynthetic bacteriumR. rubrum for converting CO to CO₂ and H₂ by the water gas shift reaction and two methanogens,M. formicicum andM. barkeri, for converting CO₂ and H₂ into CH₄. Results are presented for triculture operation in two types of reactors, the packed bubble column and the trickle-bed reactor.     

SYNTHESIS AND CHARACTERIZATION OF PHTHALAZINONE POLY(ARYL ETHER SULFONE KETONE)WITH CARBONYL GROUP*

A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K_2CO_3 to produce high molecular weight polymers which can be dissolved in some polarsolvents such as chloroform and nitrobenzene at room temperature and can be easily can into flexible, yellowish andtransparent films. PPESK is an amorphous polymer having a decomposition temperature above 400℃, which indicates that ithas high thermal stability. At the same time, the thermal properties of PPESKs with dicyandiamide (DICY) as curing agentindicated that the heat-resistance properties of the PPESKs are improved after curing. The apparent activation energy (ΔE) ofthe cross-linking reaction and the reaction order (n) of PPESK/DICY were found to be 52.2 kJ/mol and ca. 1.0, respectively.Therefore, the cross-linking reaction is approximately a first order reaction.