No abstract

The dehydropolymerization of BunnSnH2, catalysed by [Zr(C5H5)(C5Me5){Si(SiMe3)3}Me], produces cyclic (SnBun2), oligomers and long H(SnBun2),H polystannane chains (MJM, = 17 500/7800), which exhibit a long-wavelength electronic absorption (Amax = 382 nm) and emit green light (Amax = 505 nm; 337.1 nm excitation).The recent discovery and rapid development of polysilane high polymers can be attributed largely to the interesting electronic properties which these materials possess. 1 Polysilanes exhibit a strong near-UV absorption that results from o-conjugation along the silicon backbone. The radiation-sensitivity associated with excitation of this transition makes these polymers suitable for applications in microlithography .Also, owing to their delocalized electronic structure and relatively narrow band gap (ca. 4 eV), polysilanes provide a new class of photoconducting and charge-transporting poly-

No abstract

No abstract

No abstract

The non-enzymic transamination reaction of a-amino acids with a-keto acids was investigated in aqueous media at 30.0 "C. The functionalised single-walled co-vesicle composed of a synthetic peptide lipid, hexanoyl] -L-histidinamide bromide, and a hydrophobic pyridoxal derivative, 1 -(NN-di hexadecylcarbamoylmethyl) -2-methyl -3hydroxy-4-formyl-5hydroxymet hy I pyridi n iu m chloride, effectively catalysed am i no-group transfer from L-p henylalanine to pyruvic acid in the presence of copper(ii) ions, showing turnover behaviour. The catalytic activity of the vesicular system was much higher than those of 1,2-dimethyl-3-hydroxy-4-formyl-5-hydroxymethylpyridinium chloride and pyridoxal examined in aqueous media containing copper( ii) ions. The ratedetermining step involved in the catalytic cycle performed with the vesicular catalyst is primarily assigned t o the product-releasing process, the hydrolysis of the copper(i1) chelate of the aldimine Schiff's base to afford alanine.Vitamin B,-dependent transaminases catalyse the amino-group transfer from a-amino acids (AA) to a-keto acids (KA') and take part in amino-acid metabolism.' It is well known that the catalytic cycle is completed by the sequential reactions in the enzymic system shown in the Scheme: (i) formation of the aldimine Schiffs base (ASB) of AA with the coenzyme, pyridoxal 5'-phosphate (PLP), which is tightly bound to the apoprotein (step A); (ii) isomerization of ASB to the ketimine Schiffs base (KSB) (step B); (iii) hydrolysis of KSB to give an aketo acid (KA) and pyridoxamine 5'-phosphate (PMP) (step C); (iv) reversal of this sequence of reactions, starting with P M P and another a-keto acid (KA'), to afford PLP and the corresponding a-amino acid (AA') uiu formation of the ketimine and aldimine Schiff s bases (KSB' and ASB', respectively) (steps D -E -F). Although the half-transamination reactions (A -B C; D -E -F) proceed in non-enzymic

The copper(II)-catalyzed transamination of 2-methyl-3-hydroxy-4-aminomethyl-5-(dodecylthiomethyl)pyridine (C12SPM) with sodium pyruvate was investigated in an aqueous medium at pH 6.8, μ 0.10 (KCl), and 30.0±0.1 °C in the presence of molecular aggregates of N,N-ditetradecyl-Nα-[6-(trimethylammonio)hexanoyl]-l-alaninamide bromide (N+C5Ala2C14), N,N-ditetradecyl-Nα-[6-(trimethylammonio)hexanoyl]-l-histidinamide bromide (N+C5His2C14), or hexadecyltrimethylammonium bromide (CTAB). The reaction afforded the corresponding pyridoxal analogue (C12SPL) and alanine as the final products upon addition of edta which liberates the copper(II) ion from the coordination sites of the aldimine Schiff-base. The coordination interaction between the copper(II) ion and C12SPM, which takes place prior to the transamination, was clarified by electronic spectroscopy. The reactivity of the 2:1 (ketimine:CuII) complex was found to be much larger than that of the 1:1 complex in the molecular assemblies of N+C5Ala2C14 and CTAB, and the formation of the former species was more pronounced in the N+C5Ala2C14 vesicle. The bilayer vesicle formed with N+C5His2C14 allowed the formation of the 1:1 complex in preference to that of the 2:1 complex, and the coordination-free imidazolyl group of the amphiphile effectively catalyzed the isomerization as a general base.

High-purity InP layers have been successfully grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylphosphine (TBP) as a phosphorus source. The highest quality InP layer, which was grown at a V/III ratio of 36, a growth temperature of 600 °C and a growth pressure of 760 Torr, exhibited electron mobility as high as 167 000 cm2/V s and carrier concentrations as low as 1.8×1014 cm−3 at 77 K. The film quality strongly depended on the silicon content as an impurity in TBP. Electron mobility at 77 K was dependent on the silicon content, changing its value from 10 100 cm2/V s (Si content; 0.8 ppm) to 167 000 cm2/V s (Si content; <0.03 ppm). The low-temperature (4.2 K) optical properties were also affected by silicon content as a impurity. It was found that electron mobility of 167 000 cm2/V s was the highest ever reported for InP grown by MOCVD using TBP as a phosphorus source. The quality of InP grown using TBP was equivalent to that of InP grown using phosphine (PH3).