Ultraviolet radiation-induced limitation to epilithic microbial growth in arid deserts--dosimetric experiments in the hyperarid core of the Atacama Desert

Experiments were conducted during November 2003 in the dry core of the Atacama Desert, Yungay, Chile to test the hypothesis that UV radiation, in environments where liquid water is not available, and thus enzymatic repair of UV-induced damage is inhibited, can prevent epilithic colonization. Novel dosimeters made from the cryptoendolithic, desiccation and radiation-resistant cyanobacterium Chroococcidiopsis sp. isolated from the dry Negev desert, Israel, showed that monolayers of this organism were killed within one day. The diurnal profile of microbial loss of viability was investigated with dosimeters of Bacillus subtilis, which similarly showed cell death within one day. Soil grains obtained from south of Yungay where liquid water is more abundant and transported to the hyperarid core showed killing of indigenous vegetative organisms within one day. Gypsum and mineral grain coverings of 1mm were sufficient to prevent measurable UV-induced damage of Chroococcidiopsis and B. subtilis after 8d exposure. These results show that under extreme desiccation and an ambient UV flux the surface of rocks can potentially be rendered sterile, but that millimetre thick mineral coverings can protect organisms from UV-induced killing, consistent with the observed patterns of lithophytic colonization in the Atacama Desert. These data further show that UV radiation can be an important limiting factor in surface biological rock weathering in arid regions.     

Programmable fluidic production of microparticles with configurable anisotropy

We report a technique for continuous production of microparticles of variable size with new forms of anisotropy including alternating bond angles, configurable patchiness, and uniform roughness. The sequence and shape of the anisotropic particles are configured by exploiting a combination of confinement effects and microfluidics to pack precursor colloids with different properties into a narrow, terminal channel. The width and length of the channel relative to the particle size fully specify the configuration of the anisotropic particle that will be produced. The precursor spheres packed in the production zone are then permanently bonded into particles by thermal fusing. The flow in the production zone is reversed to release the particles for collection and use. Particles produced have linear chain structure with precisely configured, repeatable bond angles. With software programmable microfluidics, sequence and shape anisotropy are combined to yield synthesized homogeneous (type "A"), surfactantlike (type "A-B") or triblock (type "A-B-A") internal sequences in a single device. By controlling the dimensions of the microfluidic production zone, triangular prisms and particles with controlled roughness and patchiness are produced. The fabrication method is performed with precursors spheres with diameter as small as 3.0 microm.     

Differentiable Distance Spaces

The distance function \({\varrho(p, q) ({\rm or} d(p, q))}\) of a distance space (general metric space) is not differentiable in general. We investigate such distance spaces over \({\mathbb{R}^n}\), whose distance functions are differentiable like in case of Finsler spaces. These spaces have several good properties, yet they are not Finsler spaces (which are special distance spaces). They are situated between general metric spaces (distance spaces) and Finsler spaces. We will investigate such curves of differentiable distance spaces, which possess the same properties as geodesics do in Finsler spaces. So these curves can be considered as forerunners of Finsler geodesics. They are in greater plenitude than Finsler geodesics, but they become geodesics in a Finsler space. We show some properties of these curves, as well as some relations between differentiable distance spaces and Finsler spaces. We arrive to these curves and to our results by using distance spheres, and using no variational calculus. We often apply direct geometric considerations.     

Towards nitrogen transfer catalysis: reactive lattice nitrogen in cobalt molybdenum nitride

Lattice nitrogen within the catalyst Co(3)Mo(3)N is both reactive and likely highly mobile, enabling potential novel nitrogen transfer pathways; evidence suggests that loss and subsequent regain of lattice nitrogen in the system reversibly cycles through the previously unknown nitride, Co(6)Mo(6)N.     

Asymptotic enumeration of tournaments with a given score sequence containing a specified digraph

This paper studies the probability that a random tournament with specified score sequence contains a specified subgraph. The exact asymptotic value is found in the case that the scores are not too far from regular and the subgraph is not too large. An n‐dimensional saddle‐point method is used. As a sample application, we prove that almost all tournaments with a given score sequence (not too far from regular) have a trivial automorphism group. ©2000 John Wiley & Sons, Inc. Random Struct. Alg., 16: 47–57, 2000     

Studies of multicomponent Kinugasa reactions in aqueous media

Micelle-promoted, copper-catalyzed multicomponent Kinugasa reactions were studied in aqueous media. Reactions were performed in a ‘single pot’ for a series of in situ generated C,N-diphenylnitrones with Cu(I) phenylacetylide providing β-lactams in yields of 45-85%. Substituents affect the reaction by either accelerating cycloaddition or minimizing side reactions.     

Sulfur fixation on bagasse activated carbon by chemical treatment and its effect on acid dye adsorption

Heteroatoms are known to introduce specific surface functionalities that can enhance the adsorption properties of carbons. Sulfur fixation on bagasse-activated carbon was conducted by a low temperature chemical treatment with sulfuric acid followed by physical activation with CO₂ at 900?°C. The effect of sulfur fixation on the surface chemical properties of bagasse-activated carbons were investigated and on their subsequent acid dye removal (CIBA AB80) behavior. Surface chemical development were examined and followed using Fourier transform infrared spectroscopy (FTIR), heteroatom analysis and carbon surface acidity. Functional group stability with thermal treatment was also investigated. The textural properties of the activated carbons were characterized by nitrogen adsorption. Chemical pre-treatment and gasification was able to fix up to 0.2 wt% of sulfur on the activated carbon. Although the sulfur fixed by chemical treatment is low, this method introduced several advantages in comparison to fixation by thermal methods. The chemical method did not interfere with the textural development of the carbon, as found in thermal methods. In addition, the surface chemistry generated by these levels of sulfur groups was sufficient to increase the uptake of acid blue dyes by more than 700% based on adsorption capacities normalized by the surface area of the carbon.     

Low valent and hydride complexes of NHC coordinated gallium and indium

The reactions of the N-heterocyclic carbene 1,3-dimesitylimidazol-2-ylidene (IMes) with Ga[GaCl(4)], "GaI", InCl(2) and GaBr(3) have been examined. All reactions using a low valent gallium or indium starting material led to species of the form [{MX(2)(IMes)}(2)], where M = Ga, X = Cl (1), I (2); M = In, X = Cl (3), with disproportionation and loss of gallium metal in the case of 2. Reaction of IMes with gallium tribromide yields the air and moisture stable complex [GaBr(3)(IMes)] (4), which has been used as a precursor to the mixed bromohydrides [GaBrH(2)(IMes)] (5) and [GaBr(2)H(IMes)] (6) by (i) ligand redistribution with [GaH(3)(IMes)], (ii) hydride-bromide exchange with triethylsilane, and (iii) alkylation with (n)butyllithium followed by β-hydride elimination (6 only). Attempts to prepare 1, or monovalent analogues such as [{GaCl(IMes)}(n)], by thermally induced reductive elimination of dihydrogen from the chlorohydride congeners of 5 and 6 resulted in isolation of the known compounds [IMesCl][Cl] (IMesCl = 1,3-dimesityl-2-chloroimidazolium), and/or 1,3-dimesityl-2-dihydroimidazole, and gallium metal. Preliminary photochemical NMR spectroscopy and catalytic studies of 5 and 6 aimed at reductive dehydrogenation under milder conditions are reported. Compounds 1 and 4 have been characterised by single crystal X-ray structure determination.     

Interplay between Cationic and Neutral Species in the Rhodium‐Catalyzed Hydroaminomethylation Reaction

The reactivity of [Rh(CO)₂{(R,R)‐Ph? BPE}]BF₄ ( 2 ) toward amine, CO and/or H₂ was examined by high‐pressure NMR and IR spectroscopy. The two cationic pentacoordinated species [Rh(CO)₃{(R,R)‐Ph? BPE}]BF₄ ( 4 ) and [Rh(CO)₂(NHC₅H₁₀){(R,R)‐Ph‐BPE}]BF₄ ( 8 ) were identified. The transformation of 2 into the neutral complex [RhH(CO)₂{(R,R)‐Ph? BPE}] ( 3 ) under hydroaminomethylation conditions (CO/H₂, amine) was investigated. The full mechanisms related to the formation of 3 , 4 and 8 starting from 2 are supported by DFT calculations. In particular, the pathway from 2 to 3 revealed the deprotonation by the amine of the dihydride species [Rh(H)₂(CO)₂{(R,R)‐Ph? BPE}]BF₄ ( 6 ), resulting from the oxidative addition of H₂ on 2 .