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<jats:p>Nonequilibrium fluctuations, whether generated externally or by a chemical reaction far from equilibrium, can bias the Brownian motion of a particle in an anisotropic medium without thermal gradients, a net force such as gravity, or a macroscopic electric field. Fluctuation-driven transport is one mechanism by which chemical energy can directly drive the motion of particles and macromolecules and may find application in a wide variety of fields, including particle separation and the design of molecular motors and pumps.</jats:p>

<jats:p>Mesoporous silica materials containing functionalized organic monolayers have been synthesized. Solid-state nuclear magnetic resonance suggests that a cross-linked monolayer of mercaptopropylsilane was covalently bound to mesoporous silica and closely packed on the surface. The relative surface coverage of the monolayers can be systematically varied up to 76 percent. These materials are extremely efficient in removing mercury and other heavy metals from both aqueous and nonaqueous waste streams, with distribution coefficients up to 340,000. The stability of these materials and the potential to regenerate and reuse them have also been demonstrated. The surface modification scheme reported here enables rational design of the surface properties of tailored porous materials and may lead to the synthesis of more sophisticated functionalized composites for environmental and industrial applications.</jats:p>

<jats:p> Hexagonal and cubic phases of manganese oxide mesoporous structures (MOMS) have been prepared by means of the oxidation of Mn(OH) <jats:sub>2</jats:sub> . The hexagonal MOMS materials form a hexagonal array of pores with an open porous structure, thick walls (1.7 nanometers), and exceptional thermal stability (1000°C). The walls of the mesopores are composed of microcrystallites of dense phases of Mn <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> and Mn <jats:sub>3</jats:sub> O <jats:sub>4</jats:sub> , with MnO <jats:sub>6</jats:sub> octahedra as the primary building blocks. The calcined hexagonal MOMS have an electrical conductivity of 8.13 × 10 <jats:sup>−6</jats:sup> per ohm·centimeter, an average manganese oxidation state of 3.55, and a band gap of 2.46 electron volts. Catalytic oxidations of cyclohexane and <jats:italic>n</jats:italic> -hexane in aqueous solutions in a batch reactor show conversions of ∼10 and ∼8 percent, respectively. Characterization and catalytic data suggest that MOMS systems show significant enhancement in thermal stability with respect to octahedral molecular sieve materials. </jats:p>

<jats:p>Large dynamic nuclear polarization signal enhancements (up to a factor of 100) were obtained in the solid-state magic-angle spinning nuclear magnetic resonance (NMR) spectra of arginine and the protein T4 lysozyme in frozen glycerol-water solutions with the use of dynamic nuclear polarization. Polarization was transferred from the unpaired electrons of nitroxide free radicals to nuclear spins through microwave irradiation near the electron paramagnetic resonance frequency. This approach may be a generally applicable signal enhancement scheme for the high-resolution solid-state NMR spectroscopy of biomolecules.</jats:p>

<jats:p> Squash seeds, peduncles, and fruit rind fragments from Archaic period stratigraphic zones of Guilá Naquitz cave in Oaxaca, Mexico, are assigned to <jats:italic>Cucurbita pepo</jats:italic> on the basis of diagnostic morphological characters and identified as representing a domesticated plant on the basis of increased seed length and peduncle diameter, as well as changes in fruit shape and color, in comparison to wild <jats:italic>Cucurbita</jats:italic> gourds. Nine accelerator mass spectrometer radiocarbon dates on these specimens document the cultivation of <jats:italic>C. pepo</jats:italic> by the inhabitants of Guilá Naquitz cave between 10,000 to 8000 calendar years ago (9000 to 7000 carbon-14 years before the present), which predates maize, beans, and other directly dated domesticates in the Americas by more than 4000 years. </jats:p>

<jats:p>Ice discharge from north and northeast Greenland calculated from satellite radar interferometry data of 14 outlet glaciers is 3.5 times that estimated from iceberg production. The satellite estimates, obtained at the grounding line of the outlet glaciers, differ from those obtained at the glacier front, because basal melting is extensive at the underside of the floating glacier sections. The results suggest that the north and northeast parts of the Greenland ice sheet may be thinning and contributing positively to sea-level rise.</jats:p>

<jats:p> The 1.42- to 2.40-micrometer spectrum of Kuiper belt object 1993SC was measured at the Keck Observatory in October 1996. It shows a strongly red continuum reflectance and several prominent infrared absorption features. The strongest absorptions in 1993SC’s spectrum occur near 1.62, 1.79, 1.95, 2.20, and 2.32 micrometers in wavelength. Features near the same wavelengths in the spectra of Pluto and Neptune’s satellite Triton are due to CH <jats:sub>4</jats:sub> on their surfaces, suggesting the presence of a simple hydrocarbon ice such as CH <jats:sub>4</jats:sub> , C <jats:sub>2</jats:sub> H <jats:sub>6</jats:sub> , C <jats:sub>2</jats:sub> H <jats:sub>4</jats:sub> , or C <jats:sub>2</jats:sub> H <jats:sub>2</jats:sub> on 1993SC. In addition, the red continuum reflectance of 1993SC suggests the presence of more complex hydrocarbons. </jats:p>

<jats:p>X-ray emission was discovered in comet Hyakutake (C/1996 B2) by the Röntgen satellite in 1996, and these emissions were attributed to the excitation of high charge state solar wind ions due to electron capture from cometary molecules or atoms. Using the plasma flow in the coma of Hyakutake calculated by a three-dimensional adaptive magnetohydrodynamic model, the density distribution of solar wind ions in the coma and the resulting x-ray emission were computed. The calculated High Resolution Imager count rate of 4.4 per second and the spatial distribution of the x-ray emission agree with the observations. A detailed energy spectrum of cometary x-rays is predicted in the 80 to 2000 electronvolt energy range. Cometary x-rays present a sensitive tool to monitor cometary activity and solar wind ion composition.</jats:p>

<jats:p> A mechanism is proposed to explain the activity of orotidine 5′-monophosphate decarboxylase (ODCase). This enzyme is the one of the most proficient known, with a catalytic proficiency ( <jats:italic>k</jats:italic> <jats:sub>cat</jats:sub> / <jats:italic>K</jats:italic> <jats:sub>m</jats:sub> )/ <jats:italic>k</jats:italic> <jats:sub>non</jats:sub> = 10 <jats:sup>23</jats:sup> M <jats:sup>−1</jats:sup> . Quantum mechanical calculations predict a mechanism involving a stabilized carbene intermediate, which represents a previously unrecognized mode of enzymatic activity for ODCase. The proposed mechanism involves proton transfer from a weak acid (p <jats:italic>K</jats:italic> <jats:sub>a</jats:sub> = 7, where <jats:italic>K</jats:italic> <jats:sub>a</jats:sub> is the acid constant) concerted with decarboxylation, in a nonpolar enzyme environment. Such a mechanism makes possible different approaches to the design of ODCase inhibitors. Furthermore, the prediction that general acid catalysis may only be effective in low dielectric media is of general significance for understanding the activity of many enzymes. </jats:p>

<jats:p> The compound <jats:italic>N</jats:italic> -(17-hydroxylinolenoyl)- <jats:sc>l</jats:sc> -glutamine (named here volicitin) was isolated from oral secretions of beet armyworm caterpillars. When applied to damaged leaves of corn seedlings, volicitin induces the seedlings to emit volatile compounds that attract parasitic wasps, natural enemies of the caterpillars. Mechanical damage of the leaves, without application of this compound, did not trigger release of the same blend of volatiles. Volicitin is a key component in a chain of chemical signals and biochemical processes that regulate tritrophic interactions among plants, insect herbivores, and natural enemies of the herbivores. </jats:p>