Coordination chemistry umpolung: a gallane ligand on a phosphine lewis acceptor.

Pentaphenylphosphinophosphonium trifluoromethanesulfonate reacts with amino-iminogall(I)ane to effect quantitative substitution of Ph3P and formation of the first complex of a gallium Lewis base on a phosphine Lewis acid.     

Phosphorus-nitrogen-phosphorus ligands: cooperative effects between nitrogen and phosphorus substituents on catalytic activity

A new generation of PNP compounds bearing different diarylphosphine groups were prepared and used as ligands in palladium-catalysed Suzuki cross-coupling reactions. Rates of oxidative addition of iodobenzene to (PNP)Pd[0] complexes were measured using UV spectroscopy. Synergistic effects between the N- and P- substituents were identified and correlated in redox and catalytic chemistry.     

Cellulose synthesis in the Arabidopsis secondary cell wall

The identification of genes responsible for cellulose synthesis has led to a significant advance in our understanding of the synthesis of this important polymer. The identification of these genes has arisen from the identification of cellulose deficient mutants. The irregular xylem (irx) mutants of Arabidopsis are caused by a severe reduction in cellulose synthesis in the secondary cell wall. Three irx mutants deficient in secondary cell wall cellulose are the result of mutations in three different members of the cellulose synthase catalytic subunit (CesA) gene family. The three proteins encoded by these genes all associate within the same membrane bound complex, and the presence of all three, but not their activity, is required for correct assembly and targeting of this complex. The knowledge that these three proteins associate provides a good opportunity to purify the cellulose synthase complex, and recent results working towards this goal are discussed.     

MONOADDITION OF DICTAMNINE TO SYNTHETIC DOUBLE-STRANDED POLYDEOXYRIBONUCLEOTIDES IN UVA AND THE EFFECT OF PHOTOMODIFIED DNA ON TEMPLATE ACTIVITY

Abstract— The photoreactivity of dictamnine, a furoquinoline alkaloid, towards different synthetic DNAs has been studied. The ratio of the photobinding of [₃H]-dictamnine to poly(dA-dT) poly(dA-dT): poly(dG-dC) poly(dG-dC): poly(dA-dU) poly(dA-dU): poly(dA) poly(dT), in relation to that of calf thymus DNA, is 18:1:0.5:0.3. Prior treatment of calf thymus DNA with dictamnine in light inhibits the subsequent incorporation of 8-methoxypsoralen (8-MOP). These results suggest that the sites in DNA for the photobinding of dictamnine are probably identical with those for monoad-ducts of 8-MOP. Furthermore, the template activity of photomodified DNA in the RNA polymerase reaction is considerably inhibited for poly(dA-dT)poly(dA-dT), to a lesser extent for calf thymus DNA, but almost not affected for the linear copolymer, poly(dA)-poly(dT).     

Laser spectroscopic studies of interactions of UVI with bacterial phosphate species

We have investigated the interactions of UVI with two bacterial phosphate-containing species: Gram-positive Bacillus sphaericus and Gram-negative Pseudomonas aeruginosa. The Gram-positive B. sphaericus was investigated by using Raman spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). We found that living cells, spores, and intact heat-killed cells complexed UVI (pH 4.5) through phosphate groups bound to their surfaces, while decomposed cells released H2PO4- and precipitated UVI as UO2(H2PO4)2. TRLFS of UVI showed that Gram-negative P. aeruginosa--genetically engineered to accumulate polyphosphate, subsequently degrade it, and secrete phosphate--precipitated UVI quantitatively at pH 4.5. The same bacterial strain, not induced to secrete phosphate, sorbed only a small amount of UVI.     

Determination of psilocin and psilocybin using flow injection analysis with acidic potassium permanganate and tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence detection respectively

A simple, rapid and sensitive method for the determination of psilocin and psilocybin is described. This is the first report on the determination of psilocin and psilocybin using flow injection analysis with acidic potassium permanganate and tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence. The limits of detection (signal-to-noise ratio = 3) are 9 × 10⁻¹⁰ M and 3 × 10⁻¹⁰ M for psilocin and psilocybin, respectively.A concise synthetic route for psilocin in three steps from readily available starting materials is also described. The structures were elucidated on the basis of spectroscopic data.     

Nitrogen ligands on phosphorus(III) Lewis acceptors: A versatile new synthetic approach to unusual N-P structural arrangements

A series of Lewis acid-base adducts of phosphines with amines or pyridines have been prepared and structurally characterized, demonstrating the importance of Lewis acceptor behavior in the chemistry of electron-rich (lone-pair-bearing) centers. The neutral and cationic complexes all contain examples of N-P coordinate bonds that are void of N-P pi-bonding and therefore represent definitive N-P single bonds. The structures are examples of N-P topologies that are rare or have not previously been observed, highlighting the synthetic viability of Lewis acid-base coupling in the still developing field of nitrogen-phosphorus chemistry.     

A unique new multiband molecular conductor: [BDTA][Ni(dmit)2]2

A new molecular conducting material, [BDTA][Ni(dmit)2]2, with a novel multiband electronic structure has been prepared by simple mixing of precursor salts of the components.     

Monte Carlo simulation of segregation in ceramic thin films

A Monte Carlo exchange technique is used to study segregation in thin ceramic films with application to MgO/MnO. The approach is not restricted to the dilute limit. Surface concentrations as a function of temperature and film composition are determined directly from the simulations. For all compositions studied (Mn(chi)Mg(1-chi)O, 0 < or = chi < or = 1) the (001) surface is Mn(2+) rich; the occupancy of sites by Mn(2+) decreases rapidly with depth. The ratio of the number of Mn(2+) to Mg(2+) ions at the surface decreases as a function of temperature. The calculated enthalpies of segregation of Mn(2+) for the thin film are strongly dependent on the total Mn(2+) concentration at small Mn(2+) concentrations, with the enthalpy of segregation varying by a factor of two with surface coverage.