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.     

Ultra-lightweight paper foams: processing and properties

A methodology for producing a low density cellulose-based foam has been developed by combining a surfactant with pulp, mixing at high velocity to entrain air, and then drying in a non-restrained fashion. The structure of the foam, characterized through optical microscopy and X-ray computed tomographic microscopy, consists of pulp fibres in random orientations surrounding air bubbles along with large void spaces. Through careful design of experiments, the effect of fibre type, length distribution, surfactant, and air content on the mechanical behavior and permeability of the foam material was investigated. The results indicate that foamed cellulose materials can be produced at a strength of one-half the tensile strength of a standard handsheet, but having a relative density of only one percent. No chemical additives were used to enhance the strength of these samples as the properties of the foam material are enhanced simply through variation of the process parameters. Thus, a strong cellulose-based foam, with a density as low as 10 mg/cm³, can be fabricated using standard papermaking infrastructure and hence at low cost.     

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.     

Simultaneous Q-switching and mode-locking in the CW Nd: YAG laser

The theory of transient mode-locking for an active modulator in a laser with a homogeneously broadened line is presented. The theory is applied to simultaneously Q-switched and mode-locked Nd:YAG lasers and good agreement between theory and experiment is obtained. The main conclusion is that under usual Q-switched operating conditions the mode-locking process does not have sufficient time to build up to steady-state conditions. We also present a method to overcome this problem by allowing the laser to prelase before the Q-switch is opened. Mode-locked pulses whose width approaches the steady-state value are obtained. The transient mode-locking theory presented here also applies to actively mode-locking TEA CO₂ lasers and to other types of simultaneously pulsed and mode-locked lasers.     

A crown ether,template-driven,macrolide closure

Macrolide formation from reactive crown ether $\text{1}$ is driven by the proximate binding of alkoxide and thioester functionalities.