Synthesis and structure of a novel supramolecular Zn3Co8 assembly containing a linear Zn3 core

Reaction of Zn(OAc)(2).2H2O (OAc = acetate) with LH2 in THF followed by reaction with Co2(CO)8 yields the novel supramolecular assembly Zn3L2(OAc)2[Co2(CO)6](4).0.5CH2Cl2, which was characterized by X-ray diffraction (LH2 = (CH2)3(N=CH-2-OH-5-C identical to CSiMe3C6H3)2 or N,N'-propylenebis(2-hydroxy-5-trimethylsilylethynl-1-aldimine).     

Facile syntheses of quater-, penta-, and sexipyrroles

alpha,alpha-Linked oligopyrroles are attractive precursors for both expanded porphyrin and conducting polymer chemistry. We demonstrate facile methods for synthesizing quater-, penta-, and sexipyrroles from more readily available bi- and terpyrrole intermediates. These products demonstrate stability in their brightly colored oxidized forms, while reduction using borohydride reagents gives the corresponding all-pyrrole oligomers, which oxidize readily in air. The oxidized quater- and sexipyrroles were characterized by single-crystal X-ray diffraction analysis.     

Trinuclear copper(II) complex showing high selectivity for the hydrolysis of 2'-5' over 3'-5' for UpU and 3'-5' over 2'-5' for ApA ribonucleotides

The cooperative action of multiple Cu(II) nuclear centers is shown to be effective and selective in the hydrolysis of 2'-5' and 3'-5' ribonucleotides. Reported herein is the specific catalysis by two trinuclear Cu(II) complexes of L3A and L3B. Pseudo first-order kinetic studies reveal that the L3A trinuclear Cu(II) complex effects hydrolysis of Up(2'-5')U with a rate constant of 28 x 10(-)(4) min(-)(1) and Up(3'-5')U with a rate constant of 0.5 x 10(-)(4) min(-)(1). The hydrolyses of Ap(3'-5')A and Ap(2'-5')A proceed with rate constants of 24 x 10(-)(4) min(-)(1) and 0.5 x 10(-)(4) min(-)(1) respectively. The L3A trinuclear Cu(II) complex demonstrates high specificity for Up(2'-5')U and Ap(3'-5')A. Similar studies with the more rigid L3B trinuclear Cu(II) complex shows no selectivity and yields lower rate constants for hydrolysis. The selectivity observed with the L3A ligand is attributed to the geometry of the ligand-bound diribonucleotide which ultimately dictates the proximity of the attacking hydroxyl and the phosphoester to a Cu(II) center for activation and subsequent hydrolysis.     

Crystal and molecular structures of (η-xanthene)- (η-cyclopentadienyl)iron(II) hexafluorophosphate and (η-2-methylthianthrene)(η-cyclopentadienyl)iron(II) hexafluorophosphate

The neutral complexes (η⁵-C₅H₅NiXL (X = Cl, L = PPh₃ (I); L = PCy₃ (II); X = Br, L = PPh₃ (III); L = PCy₃ (IV); X = I, L = PPh₃ (V); L = PCy₃ (VI)) have been obtained by treating NiX₂L₂ with thallium cyclopentadienide. The same reaction in the presence of TlBF₄ gives cationic derivatives [(η⁵-C₅H₅)NiL₂]BF₄ (L = 2PPh₂Me (VII); L = dppe (VIII)), whereas mononuclear complexes containing two different ligands (L₂ = PPh₃ + PCy₃ (IX)) or dinuclear [(η⁵-C₅H₅)Ni(PPh₃)]₂dppe(BF₄)₂ (X) are obtained from the reaction of III with TlBF₄ in the presence of a different ligand. Reduction of cationic complexes with Na/Hg gives very unstable nickel(I) derivatives (η⁵-C₅H₅)NiL₂, which could not be isolated purely. Similar reduction of neutral complexes under CO gives a mixture of decomposition products containing [(η⁵-C₅H₅)Ni(CO)]₂ and nickel(o) carbonyls, whereas in the presence of acetylenes, dinuclear [(η⁵-C₅H₅)Ni]₂(RCCR′) (R = R′ = Ph; R = Ph, R′ = H) are obtained.     

Synthesis of 1-(1,1-dimethylethyl)-1H-pyrazole-4-carboxylate ester derivatives

Attempts to prepare ethyl 5-cyano-1-(1,1-dimethylethyl)-1H-pyrazole-4-carboxylate ( 7 ) by the reaction of the corresponding 5-chloro derivative 1b with cyanide ion were unsuccessful. The chloro ester was synthesized from the corresponding amino ester la utilizing nonaqueous diazotization with nitrosyl chloride. An alternate process was developed which allowed the preparation of 7 from the corresponding 5-methyl ester 3 in four steps. The structure of the N-methylamide 8 synthesized from 7 was confirmed by X-ray diffraction analysis.     

Controlled composting of straw

Production of composts on the farm from surplus straw might provide a low-cost biotechnological approach for increasing the value of this lignocellulosic waste. Successful composting depends on the conversion of the polysaccharides (cellulose and hemicelluloses) of straw by inoculated microorganisms to products that can promote plant growth when applied to the land. None of the potentially useful products we have identified are produced by cellulolytic organisms. We have therefore studied mixed populations in which noncellulolytic bacteria depend for growth on the products of fungal cellulolysis. The nature and yield of bacterial products depends not only on conditions within the compost, but also on the microbial inoculants used. Under defined laboratory conditions, using pure cellulose, N₂ is fixed by the anaerobic bacteriumClostridium butyricum in association with a cellulolytic fungus such asTrichoderma sp. A similar association has been achieved on straw withPenicillium corylophilum as the cellulolytic fungus. Cellulolytic fungi can also provide available substrates for the production of bacterial polysaccharides that can improve the structure of unstable soils. The yield of polysaccharide and its efficacy in soil aggregate stabilization again varies with the inoculants used. Such composts can thus contribute to plant nutrition and to soil structure. The adoption ofTrichoderma spp. as the cellulolytic inoculants would further extend the potential value of the compost to include the biocontrol of plant pathogens.