Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.     

Structural and Spectral Analyses of 2-[(2-Benzothiazolylmethyl)thio]-benzenamine and 2-[(2-Benzothiazolylmethyl)thio]-benzenamine hydrobromide

Abstract  

2-[2-benzothiazoylmethyl)thio]-benzenamine, which was first reported in 1898, was isolated from the reaction of bromoacetyl bromide and 2-aminothiophenol [1]. The product crystallized from an aqueous methanol solution of the reaction mixture to which nickel(II) acetate had been added. 2-[(2-benzothiazolylmethyl)thio]-benzenamine crystallized in the monoclinic system, in space group C2/c, with cell dimensions of a = 27.392 (19) ?, b = 4.730 (3) ?, and c = 23.686 (16) ?, β = 122.465 (6)°, V = 2589(3) ?³, Z = 8 and refined to R = 0.0343 and R _w  = 0.0844. Crystallization from methanol yielded the product as the hydrobromide salt in the monoclinic space group Cc, with cell dimensions of a = 10.488 (3) ?, b = 33.404 (9) ?, c = 5.2578 (14) ?, β = 116.769(2)°, V = 1644.7(8) ?³, Z = 4 and refined to R = 0.0296 and R _w  = 0.0600. Mass spectral and NMR analyses confirmed that the bulk and crystalline compound were all 2-[(2-benzothiazolylmethyl)thio]-benzenamine.     

Computational studies of ethynyl- and diethynyl-expanded tetrahedranes, prismanes, cubanes, and adamantanes

B3LYP/6-31+G(d) and MP2/6-31+G(d) computations were performed on a series of ethynyl- and diethynyl-expanded tetrahedranes, prismanes, cubanes and adamantanes. Every ethynyl expansion reduces the ring strain energy of the cage. The deprotonation energies of the cage poly-ynes are exceptionally low; we estimate that the gas-phase deprotonation energy of the diethynyl-expanded cubane is about 309 kcal mol(-1). The ring and cage poly-ynes can serve as effective hosts of either lithium or sodium cation, where the best host maximizes the number of interactions of alkynyl groups with the cation at an ideal distance. Last, the vertical excitation energies of the poly-ynes and their conjugate bases suggest that the alkynyl groups are interacting through space. The poly-ynes express a broad range of absorption energies, indicating that these molecules are potential targets in expressly designed optical applications.