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.     

Manganese pentacarbonyl bromide as candidate for a molecular qubit system operated in the infrared regime

Our concept for a quantum computational system is based on qubits encoded in vibrational normal modes of polyatomic molecules. The quantum gates are implemented by shaped femtosecond laser pulses. We adopt this concept to the new species manganese pentacarbonyl bromide [MnBr(CO)5] and show that it is a promising candidate in the mid-infrared (IR) frequency range to connect theory and experiment. As direct reference for the ab initio calculations we evaluated experimentally the absorption bands of MnBr(CO)5 in the mid-IR as well as the related transition dipole moments. The two-dimensional potential-energy surface spanned by the two strongest IR active modes and the dipole vector surfaces are calculated with density-functional theory. The vibrational eigenstates representing the qubit system are determined. Laser pulses are optimized by multitarget optimal control theory to form a set of global quantum gates: NOT, CNOT, Pi, and Hadamard. For all of them simply structured pulses with low pulse energies around 1 microJ could be obtained. Exemplarily for the CNOT gate we investigated the possible transfer to experimental shaping, based on the mask function for pulse shaping in the frequency regime as well as decomposition into a train of subpulses.     

Multiwavelength Q-switched CO2 laser with continuous discharge

A low-pressure (20 mbar) CO₂ laser allows to extract pulses at several selected wavelengths simultaneously from the same active medium. We demonstrated this, using an industrial laser modified by a Q-switch and a resonator with two branches. In one branch the wavelengths are spatially separated, whereas in the other they oscillate in one common transverse mode. We designed a multi-wavelength resonator which requires a single additional reflector compared to usual laser cavities. It provided tunable oscillation at six wavelength simultaneously.     

New TEA-lasers based onD′→A′ transitions in halogen monofluoride compounds: ClF (284.4 nm), BrF (354.5 nm), IF (490.8 nm)

As an outcome of a systematic study of excitation kinetics and fluorescence spectra concerning theD′(3π_2u )→A′(3π_2g ) transitions in homonuclear diatomic halogens and corresponding transitions in interhalogen molecules [1], this paper describes, for the first time, TEA laser action in the three halogen monofluorides ClF, BrF, and IF. Output energies in the mJ range were demonstrated in a fast TEA discharge arrangement at the wavelengths of 284.4, 354.5, and 490.8 nm for ClF, BrF, and IF, respectively. The results suggest parameter scalability and wavelength tunability.     

The semantics of knowledge attributions

The basic idea of conversational contextualism is that knowledge attributions are context sensitive in that a given knowledge attribution may be true if made in one context but false if made in another, owing to differences in the attributors’ conversational contexts. Moreover, the context sensitivity involved is traced back to the context sensitivity of the word “know,” which, in turn, is commonly modelled on the case either of genuine indexicals such as “I” or “here” or of comparative adjectives such as “tall” or “rich.” But contextualism faces various problems. I argue that in order to solve these problems we need to look for another account of the context sensitivity involved in knowledge attributions and I sketch an alternative proposal.     

Macroscopic enrichment of12C by a high-power mechanically Q-switched CO2 laser

The isotope-selective multiphoton dissociation of CHClF₂ in a multipass refocusing Herriott cell was used to enrich more than 4 moles of chlorodifluoromethane to 99.99% of¹²C isotopic purity. It is the largest isotope quantity ever separated by a laser process. A cw excited mechanically Q-switched CO₂ laser, which delivers 16 mJ pulses at 5 kHz was used. The enrichment controlled by a mass-spectrometer and guided by a PC was run with a rate of 25 g¹²C per 24 h.     

Investigation of UV-laser induced metallization: Platinum from Pt (PF3)4

We have measured the Pt deposition yields on various substrate materials from Pt(PF₃)₄ in the case where a KrF laser irradiates the solid surface. The data imply that an ample amount of electrons is produced by the laser surface interaction and dissociative electron capture initiates the metal deposition. The metal atom release is completed by a concerted surface reaction at a reduced energy demand. This is evidenced by thermochemical considerations. A simple criterion is derived to estimate the attainable spatial resolution. Sudden melting and evaporation beyond a certain layer thickness interferes with the deposition process. This is in accord to a model given, based on a poor thermal contact at the platinum substrate interface. The results may help to optimize uv laser induced metal deposition with respect to purity, adherence and structure.     

Vibrational heating in the v2 mode of ammonia by a CO2 laser

Various levels of the v₂ mode of ammonia have been pumped by a pulsed CO₂ laser. In mixtures of NH₃ with a large excess of Ar the 1 v₂ (+), 1 v₂ (?), and 2 v₂ (?) levels could be appreciably populated. The level populations were monitored by absorption spectroscopy in the ultraviolet using appropriate vibronic transitions of the ùA^″₂←X?¹A₁ absorption band . The energy balance was examined by comparing the number of molecules removed from the ground state with the number densities in the vibrationally excited levels and with the number of photons absorbed during the laser pulse. While the ground-state depletion corresponds well to the excited-state populations only a fraction of the photons deposited can be accounted for in the excited molecules. This is consistent with the assumption of very fast V-T relaxation.