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.     

A study of the overall heat transfer coefficient of greenhouse cladding materials with thermal screens using the hot box method

A laboratory guarded hot box was designed and constructed to investigate the overall heat transfer coefficient, U (W m^?2 K^?1), of different greenhouse polyethylene plastic films with or without thermal screens. Tests were made on plastic films, in both dry and wet (in the presence of condensation) states, with or without thermal screens, as functions of wind velocity and temperature difference. It was found that the overall heat transfer coefficient U increases with increase in temperature difference. For a given temperature difference, the U value increases as the wind velocity increases. The condensation phenomena favored the plastic film, since its U value was always less than that of the corresponding dry film. It was found that using a thermal screen would reduce the U value by about 30%, an energy saving of about 30%.     

Gold clusters: reactions and deuterium uptake

We have examined the reactivity and saturation of small gold clusters (cations, neutrals and anions) towards several molecules and find that specific small gold clusters exhibit a pronounced variation in their reactivity towards hydrogen, methane and oxygen. The reactivity not only depends strongly on cluster size but also on the cluster charge state. For example, small (n<15) gold cations react readily with D₂, but no evidence of reaction is observed for the anions under our experimental conditions. Similar behavior is seen for methane. With oxygen only even atom (odd electron) anions are reactive, and Au ₁₀ ⁺ is the only cation which exhibits evidence of reaction. The global features (small cluster cations reactive towards H₂, CH₄, but large ones not reactive, odd electron anions reactive towards O₂) are qualitatively explained by appealing to a simple frontier orbital picture. The uptake of deuterium and methane on gold clusters also exhibits a pronounced size dependence with D/Au varying from a high of 3 for the dimer to zero for clusters containing more than 15 Au atoms. Comparison of the methane and deuterium saturation behavior leads us to suggest that methane is dissociated and bound as CH₃ and H.     

Adsorption and decomposition of triethylsilane on Si(1 0 0)

The adsorption and decomposition of triethylsilane (TES) on Si(1 0 0) were studied using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), electron stimulated desorption (ESD), and X-ray photoelectron spectroscopy (XPS). TPD and HREELS data indicate that carbon is thermally removed from the TES-dosed Si(1 0 0) surface via a β-hydride elimination process. At high exposures, TPD data shows the presence of physisorbed TES on the surface. These species are characterized by desorption of TES fragments at 160 K. Non-thermal decomposition of TES was studied at 100 K by irradiating the surface with 600 eV electrons. ESD of mass 27 strongly suggests that a β-hydride elimination process is a channel for non-thermal desorption of ethylene. TPD data indicated that electron irradiation of physisorbed TES species resulted in decomposition of the parent molecule and deposition of methyl groups on the surface that desorbed thermally at about 900 K. Without electron irradiation, mass 15 was not detected in the TPD spectra, indicating that the production of methyl groups in the TPD spectra was a direct result of electron irradiation. XPS data also showed that following electron irradiation of TES adsorbed on Si(1 0 0), carbon was deposited on the surface and could not be removed thermally.     

Atomic qubit manipulations with an electro-optic modulator

We report new techniques for driving high-fidelity stimulated Raman transitions in trapped-ion qubits. An electro-optic modulator induces sidebands on an optical source, and interference between the sidebands allows coherent Rabi transitions to be efficiently driven between hyperfine ground states separated by 14.53 GHz in a single trapped 111Cd+ ion.     

Enhancing Teaching Assistants' (TAs') Inquiry Teaching by Means of Teaching Observations and Reflective Discourse

Recent education reform efforts advocate teaching the process of science (inquiry) in undergraduate lecture and laboratory classes. To meet this challenge, professional development for the graduate student instructors (teaching assistants, or TAs) often assigned to teach these classes is needed. This study explored the implementation of an observation protocol designed to support peer observation and reflection among TAs teaching inquiry‐based undergraduate biology laboratories. The researchers of this study and TA‐peers who are experienced in teaching inquiry used the protocol to observe novice TAs at the beginning, mid‐point, and end of a semester‐long teaching assignment. Novice TAs used a modified version of this protocol to observe an experienced and a novice TA. Analysis of post‐semester interview data indicated engaging in both sets of observations and post‐observation discussions facilitated by the protocol gave novice TAs new ways to teach content, guidance on implementing pedagogical theory, and means to improve communications with students and classroom management skills. Researchers also used quantitative data collected from the observations to document frequency of teaching and student behaviors associated with teaching inquiry and how these frequencies changed during the semester. Considerations for how to use both sets of data to inform changes in TA professional development are discussed.     

Influence of agrochemicals on greenhouse cladding materials

A test chamber for investigation of the influence of agrochemicals (sulfur vapor) on the condensation and mechanical properties of greenhouse cladding materials was designed and constructed. The roof of the test chamber was covered by three types of polyethylene films. The exterior surfaces of the films were exposed to sun while the interior surfaces were exposed to sulfur vapor as used in rose greenhouses. At four dates, 3, 6, 9 and 12 weeks from the start of experiments, samples of the three types plastic film were tested for their mechanical (elongation at break) and anti-drop properties. It was observed that after 3 weeks of sulfur evaporation the anti-drop plastic film had lost it anti-drop properties. It was found that, after twelve weeks of sulfur evaporation the elongation at break of plastic films, were reduced to about 35% of their original value.     

Kinetics and mechanism of iron(III) dissociation from the dihydroxamate siderophores alcaligin and rhodotorulic acid

The kinetics and mechanism of siderophore ligand dissociation from their fully chelated Fe(III) complexes is described for the highly preorganized cyclic tetradentate alcaligin and random linear tetradentate rhodotorulic acid in aqueous solution at 25 degrees C (Fe2L3 + 6H+ reversible 2 Fe3+ aq + 3 H2L). At siderophore:Fe(III) ratios where Fe(III) is hexacoordinated, kinetic data for the H(+)-driven ligand dissociation from the Fe2L3 species is consistent with a singly ligand bridged structure for both the alcaligin and rhodotorulic acid complexes. Proton-driven ligand dissociation is found to proceed via parallel reaction paths for rhodotorulic acid, in contrast with the single path previously observed for the linear trihydroxamate siderophore ferrioxamine B. Parallel paths are also available for ligand dissociation from Fe2(alcaligin)3, although the efficiency of one path is greatly diminished and dissociation of the bis coordinated complex Fe(alcaligin)(OH2)2+ is extremely slow (k = 10(-5) M-1 s-1) due to the high degree of preorganization in the alcaligin siderophore. Mechanistic interpretations were further confirmed by investigating the kinetics of ligand dissociation from the ternary complexes Fe(alcaligin)(L) in aqueous acid where L = N-methylacetohydroxamic acid and glycine hydroxamic acid. The existence of multiple ligand dissociation paths is discussed in the context of siderophore mediated microbial iron transport.