A mechanistic study of sialic acid mutarotation: implications for mutarotase enzymes

The mutarotation of N-acetylneuraminic acid (Neu5Ac) proceeds by four kinetically distinct pathways: (i) the acid-catalyzed reaction of neutral Neu5Ac; (ii) the spontaneous reaction of the carboxylic acid (the kinetically equivalent acid-catalyzed reaction on the anion being ruled out by the solvent deuterium kinetic isotope effect of 3.74 ± 0.68); (iii) a spontaneous, water-catalyzed, reaction of the anion; and (iv) a specific-base catalyzed reaction of the anion. The magnitude of the solvent kinetic isotope effect, k(H2O)/k(D2O) = 4.48 ± 0.74 is consistent with a ring-opening transition state in which a water molecule is deprotonating the anomeric hydroxyl group in concert with strengthening solvation of the ring oxygen atom. The mechanistic implications for Neu5Ac mutarotases are discussed.     

Experimental and analytical comparisons of failure in thermoplastic composite laminates

Failure characteristics of Gr/PEEK were studied, using an experimental investigation and a fully nonlinear ply-by-ply finite-element technique. The stacking sequence of the laminates (with centrally located holes) investigated were: 0, 90, ±45 deg, (0/45/90/−45 deg)_2s and (0±45/90 deg)_2s. The [0 deg] laminate failure was characterized by splitting at the extremities of the hole and along the fibers. The [90 deg] laminates failed in the transverse direction, whereas the [±45 deg] laminates exhibited considerable elongation to failure. In the case of the quasi-isotropic laminates, the failure progression appeared to be due dominantly to matrix cracking followed by fiber failure. Analytical predictions of the failure process showed reasonably good correlation with the experimentally determined data.     

High-throughput bioscreening system utilizing high-performance affinity magnetic carriers exhibiting minimal non-specific protein binding

For affinity purification of drug target protein we have developed magnetic carriers, narrow in size distribution (184±9 nm), which exhibit minimal non-specific binding of unwanted proteins. The carriers were highly dispersed in aqueous solutions and highly resistant to organic solvents, which enabled immobilization of various hydrophobic chemicals as probes on the carrier surfaces. Utilizing the carriers we have automated the process of separation and purification of the target proteins that had been done by manual operation previously.     

Polarization in K+n charge exchange scattering between 0.851 GeV/c and 1.351 GeV/c

The polarization parameter for K⁺n charge exchange scattering has been measured at five momenta between 0.851 GeV/c and 1.351 GeV/c for centre of mass angles $\text{?0.8 <}\text{cos}\text{θ}{}^1\text{< 0.8}$. Results from a phase shift analysis incorporating these results are presented. No Z¹ resonances are observed.     

Organotin(IV) derivatives of mercaptosuccinic and thiodiacetic acids

Di- and tri-organotin(IV) complexes of general formula R₂SnAH, (R₃Sn)₂AH, R₂SnB, (R₃Sn)₂B (A=dianion of mercaptosuccinic acid; B=dianion of thiodiacetic acid; R=Me, Et, nPr, nBu, nOct in R₂Sn and nBu in R₃Sn) have been synthesized and characterized by elemental analysis, IR and ¹H and ¹³C NMR spectroscopy. These data support the preferential binding of sulphur over carboxylate by tin(IV) in R₂SnAH and (R₃Sn)₂AH. R₂SnAH complexes are assigned pentacoordinated bridged polymeric trigonal bipyramidal geometry whereas (R₃Sn)₂AH complexes are monomeric with trigonal bipyramidal geometry at tin arising from a bidentate carboxylate group at one tin atom and from weak bonding via Sn←O?C at the other tin atom. In R₂SnB and (R₃Sn)₂B, tin(IV) binds to two carboxylate groups in a unidentate and a bidentate manner respectively, resulting in tetracoordinated and pentacoordinated structures. Potential uses of these compounds are discussed.     

Mössbauer studies of solid state photolysis of barium and strontium tris(oxalato) ferrates (III)

Solid state photolysis of strontium and barium tris(oxalato) ferrate(III) was done under a medium pressure lamp and investigated with Mössbauer spectroscopy. The product [Fe^II(C₂O₄) (H₂O)₂]^2? formed during photolysis is found to be quite stable and does not convert to ferric state on long standing in air.     

Pyrimidine analogues. Reaction of 1,3-dimethyl-6-hydroxylaminopyrimidine-2,4-dione with nitrophenyl isothiocyanates

Reaction between 6-hydroxylaminouracil and nitrophenylisothiocyanates gave new purines which could be of biological interest.     

Controlling coherent and incoherent plasma emissions: the role of electron plasma waves

We present results of our two-pulse time resolved measurements of second harmonic and hard X-ray generation in the interaction of an intense (10¹⁶ Wcm^-2, 100 fs, 800 nm) laser with a preplasma generated on a solid surface. The time-resolved study as a function of both plasma scale length and laser polarization brings out interesting features of electron plasma wave dynamics. The harmonic and X-ray emission show contrary behavior and we interpret the results in terms of Resonance Absorption and Wave-Breaking mechanisms. Simple optimization of the scale length of the preplasma and the polarization parameters of the main pulse results in significant enhancements, up to a factor of 100 for X-rays and 10 for the second harmonic respectively. These results can help us understand the governing mechanisms for higher harmonic generation and for fast particle generation, aiding the development of more efficient sources. PACS 52.35.Fp; 42.65.Ky; 52.38.Ph