Synthesis and Crystal Structure of the Hydrogen Polyphosphide Bis(Tetraphenylphosphonium) hydrogenheptaphosphide‐ammonia(1/3) (PPh4)2HP7 · 3NH3

(PPh₄)₂HP₇ · 3NH₃ was prepared by the reaction of K₃P₇ with a proton‐charged ion exchange resin in the presence of (PPh₄)Br in liquid ammonia, and characterized by low temperature X‐ray structure analysis. The thermally very unstable compound contains the hydrogenheptaphosphide anion HPequation/tex2gif-stack-1.gif, the nortricyclane‐like cage of which is slightly distorted by the attachment of the hydrogen atom.     

Gel electrophoresis as a means of detecting ternary complex formation of thymidylate synthetase

Polyacrylamide gel electrophoresis was used to resolve as many as three protein components from incubation mixtures containing the inhibitor, 5-fluoro-2′-deoxyuridylate, the cofactor, 5,10-methylene tetrahydrofolate, and thymidylate synthetase. In a series of mixtures containing excess 5,10-methylenetetrahydrofolate and constant levels of thymidylate synthetase, the relative amounts of the protein components were shown to be dependent on the concentration of the inhibitor. Evidence is presented which suggests that the three protein components correspond to (1) native enzyme, (2) an inhibitor-cofactor-enzyme complex in a 1:1:1 molar ratio, and (3) an inhibitorcofactorenzyme complex in a 2:2:1 molar ratio, respectively. Ternary complexes of thymidylate synthetase are stable to gel filtration and are shown to undergo a relatively slow rate of breakdown on storage at 25 °C.     

Carbon Monoxide and Cyanide Ligands in a Classical Organometallic Complex Model for Fe-Only Hydrogenase

The Fe(I) organometallic complex [(μ-SCH(2)CH(2)CH(2)S)Fe(2)(CO)(6)] provides a structural model for the cyano-carbonyl diiron site of Fe-only hydrogenase as characterized by X-ray crystallography (the picture shows the structure (black) of the model overlaid with that of the Fe-Fe dimetallic site in the hydrogenase isolated from Desulfovibrio desulfuricans). Cyanide substitution of CO occurs readily and provides spectroscopic references for the active site.     

Effects of viscosity on droplet formation and mixing in microfluidic channels

This paper characterizes the conditions required to form nanoliter-sized droplets (plugs) of viscous aqueous reagents in flows of immiscible carrier fluid within microfluidic channels. For both non-viscous (viscosity of 2.0 mPa s) and viscous (viscosity of 18 mPa s) aqueous solutions, plugs formed reliably in a flow of water-immiscible carrier fluid for Capillary number less than 0.01, although plugs were able to form at higher Capillary numbers at lower ratios of the aqueous phase flow rate to the flow rate of the carrier fluid (in all the experiments performed, the Reynolds number was less than 1). The paper also shows that combining viscous and non-viscous reagents can enhance mixing in droplets moving through straight microchannels by providing a nearly ideal initial distribution of reagents within each droplet. The study should facilitate the use of this droplet-based microfluidic platform for investigation of protein crystallization, kinetics, and assays.     

As12Se44—: ein neuartiges Selenoarsenatanion mit einem Polyarsenkäfig in der Verbindung [Co(NH3)6]2As12Se4 · 12 NH3

As₁₂Se₄^4—: a New Selenoarsenate Anion with a Polyarsenic Cage in the Compound [Co(NH₃)₆]₂As₁₂Se₄ · 12 NH₃ Orange coloured crystals of [Co(NH₃)₆]₂As₁₂Se₄ · 12 NH₃ were prepared by the reduction of As₄Se₄ with a solution of sodium in liquid ammonia and subsequent precipitation with CoBr₂. The X‐ray structure determination shows them to contain the selenoarsenate anion As₁₂Se₄^4—, which consists of a central As₁₂‐cage with four exo‐bonded, formally negatively charged Se atoms. The structure of the As₁₂‐cage is equivalent to the main polyphosphorus building unit of a known organopolyphosphane and of tubular P₁₂ in the compound (CuI)₃P₁₂.     

Surface second-harmonic generation: A novel technique for ps-pulse duration measurements

Second-harmonic generation from dye adsorbates has been successfully used to measure the duration of ps pulses. In the red and in the blue-green spectral range pulse durations of 2.4 and 6.1 ps—in agreement with streak camera measurements — have been obtained from collinear, slow autocorrelation traces.     

Resonance ionization spectroscopy: How a new field expands

A scientometric study of communication and growth of a new development of physics, resonance ionization spectroscopy, has been made. Formal (journal publications) and informal (talks, lecures) communication patterns have been studied. Self citation dominates in early publications, but drops off as the field expands. Informal communication leads formal only by about a year in time, but is much larger in number.