Soluble Mn(III) in suboxic zones

Soluble manganese(III) [Mn(III)] has been thought to disproportionate to soluble Mn(II) and particulate Mn(IV)O2 in natural waters, although it persists as complexes in laboratory solutions. We report that, in the Black Sea, soluble Mn(III) concentrations were as high as 5 micromolar and constituted up to 100% of the total dissolved Mn pool. Depth profiles indicated that soluble Mn(III) was produced at the top of the suboxic zone by Mn(II) oxidation and at the bottom of the suboxic zone by Mn(IV)O2 reduction, then stabilized in each case by unknown natural ligands. We also found micromolar concentrations of dissolved Mn(III) in the Chesapeake Bay. Dissolved Mn(III) can maintain the existence of suboxic zones because it can act as either an electron acceptor or donor. Our data indicate that Mn(III) should be ubiquitous at all water column and sediment oxic/anoxic interfaces in the environment.     

Interstitial nitrate profiles and oxidation of sedimentary organic matter in the eastern equatorial atlantic

Pore-water nitrate concentrations in six pelagic eastern equatorial Atlantic cores increase from bottom water values (22 micromolar) to 40 micromolar at a depth of about 5 centimeters, then decrease to undetectable levels at depths as shallow as 40 centimeters. These nitrate concentrations and concentration gradients reflect zones of oxygen reduction, nitrate reduction, and sulfate reduction in the sediments. The estimated benthic flux of nitrate to the ocean from our data is much less than the total globalflux of nitrate to deep waters, even though these equatorial sediments underlie a productive upwelling zone. The estimated denitrification rate in our study area suggests that pelagic sediments may be important sites of marine denitrification.     

Micromolar affinity benzodiazepine receptors: identification and characterization in central nervous system

Receptors that selectively bind micromolar concentrations of benzodiazepines are present in rat brain membrane. These micromolar receptors exhibit saturable, stereospecific binding, and the potency of benzodiazepine binding to these receptors is correlated with the ability of the benzodiazepines to inhibit maximum electric shock-induced convulsions. Benzodiazepine receptors with nanomolar affinity differ from the micromolar receptors in their binding, kinetic, and pharmacologic characteristics. The micromolar receptors also bind phenytoin, a non-benzodiazepine anticonvulsant. These results provide evidence for a distinct class of clinically relevant benzodiazepine receptors that may regulate neuronal excitability and anticonvulsant activity.     

Simulating the self-assembly of gemini (dimeric) surfactants

The morphologies and dynamics of aggregates formed by surfactant molecules are known to influence strongly performance properties spanning biology, household cleaning, and soil cleanup. Molecular dynamics simulations were used to investigate the morphology and dynamics of a class of surfactants, the gemini or dimeric surfactants, that are of potential importance in several industrial applications. Simulation results show that these surfactants form structures and have dynamic properties that are drastically different from those of single-chain surfactants. At the same weight fraction, single-chain surfactants form spherical micelles whereas gemini surfactants, whose two head groups are coupled by a short hydrophobic spacer, form thread-like micelles. Simulations at different surfactant concentrations indicate the formation of various structures, suggesting an alternative explanation for the unexpected viscosity behavior of gemini surfactants.     

Biotin enhances guanylate cyclase activity

Biotin and its analog, (+)-biotin-p-nitrophenyl ester enhanced guanylate cyclase activity two- to threefold in rat liver, kidney, colon, cerebellum, and heart. Dose-response relationships revealed that at concentrations as low as 1 micromolar, both biotin and its analog caused maximal augmentation of guanylate cyclase activity. These data suggest a role for the activation of guanylate cyclase in the mechanism of action of this vitamin.     

Directional dynamics in the photodissociation of oriented molecules

We observed directional dynamics in the photodissociation of an oriented molecule. When a laser dissociated hexapole-oriented carbonyl sulfide molecules, the three-dimensional recoil of carbon monoxide fragments, which we measured with ion imaging, was strongly asymmetric. We obtained a microscopic view of molecular bond breaking that revealed both the sign and the magnitude of the deflection angle of the fragment in the molecular frame. This experimental approach can be applied to study and control the three-dimensional dynamics of photoinitiated reactions of fixed molecules or molecules oriented by emerging techniques.     

RNA-mediated metal-metal bond formation in the synthesis of hexagonal palladium nanoparticles

RNA sequences have been discovered that mediate the growth of hexagonal palladium nanoparticles. In vitro selection techniques were used to evolve an initial library of approximately 10(14) unique RNA sequences through eight cycles of selection to yield several active sequence families. Of the five families, all representative members could form crystalline hexagonal palladium platelets. The palladium particle growth occurred in aqueous solution at ambient temperature, without any endogenous reducing agent, and at low concentrations of metal precursor (100 micromolar). Relative to metal precursor, the RNA concentration was significantly lower (1 micromolar), yet micrometer-size crystalline hexagonal palladium particles were formed rapidly (7.5 to 1 minutes).     

Dynamics of water molecules in aqueous solvation shells

We report on the direct measurement of the dynamics of water molecules in the solvation shell of an ion in aqueous solution. The hydrogen-bond dynamics of water molecules solvating a Cl-, Br-, or I- anion is slow compared with neat liquid water, indicating that the aqueous solvation shells of these ions are rigid. This rigidity can play an important role in the overall dynamics of chemical reactions in aqueous solution. The experiments were performed with femtosecond midinfrared nonlinear spectroscopy, because this technique allows the spectral response of the water molecules in the solvation shell to be distinguished clearly from that of the other water molecules in the solution.     

The multielectron ionization dynamics underlying attosecond strong-field spectroscopies

Subcycle strong-field ionization (SFI) underlies many emerging spectroscopic probes of atomic or molecular attosecond electronic dynamics. Extending methods such as attosecond high harmonic generation spectroscopy to complex polyatomic molecules requires an understanding of multielectronic excitations, already hinted at by theoretical modeling of experiments on atoms, diatomics, and triatomics. Here, we present a direct method which, independent of theory, experimentally probes the participation of multiple electronic continua in the SFI dynamics of polyatomic molecules. We use saturated (n-butane) and unsaturated (1,3-butadiene) linear hydrocarbons to show how subcycle SFI of polyatomics can be directly resolved into its distinct electronic-continuum channels by above-threshold ionization photoelectron spectroscopy. Our approach makes use of photoelectron-photofragment coincidences, suiting broad classes of polyatomic molecules.     

Calcium sensitivity of glutamate release in a calyx-type terminal

Synaptic efficacy critically depends on the presynaptic intracellular calcium concentration ([Ca2+]i). We measured the calcium sensitivity of glutamate release in a rat auditory brainstem synapse by laser photolysis of caged calcium. A rise in [Ca2+]i to 1 micromolar readily evoked release. An increase to >30 micromolar depleted the releasable vesicle pool in <0.5 millisecond. A comparison with action potential-evoked release suggested that a brief increase of [Ca2+]i to approximately 10 micromolar would be sufficient to reproduce the physiological release pattern. Thus, the calcium sensitivity of release at this synapse is high, and the distinction between phasic and delayed release is less pronounced than previously thought.     

Nicotine is chemotactic for neutrophils and enhances neutrophil responsiveness to chemotactic peptides

Neutrophils contribute to chronic bronchitis and pulmonary emphysema associated with cigarette smoking. Nicotine was found to be chemotactic for human neutrophils but not monocytes, with a peak activity at approximately 31 micromolar. In lower concentrations (comparable to those in smokers' plasma), nicotine enhanced the response of neutrophils to two chemotactic peptides. In contrast to most other chemoattractants for neutrophils, however, nicotine did not affect degranulation or superoxide production. Nicotine thus may promote inflammation and consequent lung injury in smokers.     

A synthetic HIV-1 protease inhibitor with antiviral activity arrests HIV-like particle maturation

A synthetic peptidemimetic substrate of the human immunodeficiency virus 1 (HIV-1) protease with a nonhydrolyzable pseudodipeptidyl insert at the protease cleavage site was prepared. The peptide U-81749 inhibited recombinant HIV-1 protease in vitro (inhibition constant Ki of 70 nanomolar) and HIV-1 replication in human peripheral blood lymphocytes (inhibitory concentration IC50 of 0.1 to 1 micromolar). Moreover, 10 micromolar concentrations of U-81749 significantly inhibited proteolysis of the HIV-1 gag polyprotein (p55) to the mature viral structural proteins p24 and p17 in cells infected with a recombinant vaccinia virus expressing the HIV-1 gag-pol genes. The HIV-1 like particles released from inhibitor-treated cells contained almost exclusively p55 and other gag precursors, but not p24. Incubation of HIV-like particles recovered from drug-treated cultures in drug-free medium indicated that inhibition of p55 proteolysis was at least partially reversible, suggesting that U-81749 was present within the particles.     

Chemotaxis of Rhizobium spp. to a Glycoprotein Produced by Birdsfoot Trefoil Roots

Rhizobium spp. show chemotaxis to plant root exudates. A glycoprotein has been isolated from the root exudates of birdsfoot trefoil, Lotus corniculatus, which, at micromolar concentrations, attracts six strains of rhizobia. This glycoprotein has been given the trivial name trefoil chemotactin and contains approximately twice as much protein as carbohydrate. Gel filtration of trefoil chemotactin on a Bio-Gel A-1.5m column gave a molecular weight of approximately 60,000. Trefoil chemotactin represents a new class of chemoattractants for bacteria.     

Inhibition of leishmanias but not host macrophages by the antitubulin herbicide trifluralin

The dinitroaniline herbicide trifluralin (alpha, alpha, alpha-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine), at micromolar concentrations, selectively inhibited both proliferation and differentiation of the parasitic protozoan Leishmania mexicana amazonensis. In vitro, radioactive trifluralin showed specific binding to leishmania tubulin but not to mammalian tubulin. Because herbicides such as trifluralin are economical and are considered safe for man and domesticated animals, they may serve as useful sources of potential antiparasitic agents.     

Time-resolved dynamics in N2O4 probed using high harmonic generation

The attosecond time-scale electron-recollision process that underlies high harmonic generation has uncovered extremely rapid electronic dynamics in atoms and diatomics. We showed that high harmonic generation can reveal coupled electronic and nuclear dynamics in polyatomic molecules. By exciting large amplitude vibrations in dinitrogen tetraoxide, we showed that tunnel ionization accesses the ground state of the ion at the outer turning point of the vibration but populates the first excited state at the inner turning point. This state-switching mechanism is manifested as bursts of high harmonic light that is emitted mostly at the outer turning point. Theoretical calculations attribute the large modulation to suppressed emission from the first excited state of the ion. More broadly, these results show that high harmonic generation and strong-field ionization in polyatomic molecules undergoing bonding or configurational changes involve the participation of multiple molecular orbitals.     

Nanoribbon waveguides for subwavelength photonics integration

Although the electrical integration of chemically synthesized nanowires has been achieved with lithography, optical integration, which promises high speeds and greater device versatility, remains unexplored. We describe the properties and functions of individual crystalline oxide nanoribbons that act as subwavelength optical waveguides and assess their applicability as nanoscale photonic elements. The length, flexibility, and strength of these structures enable their manipulation on surfaces, including the optical linking of nanoribbon waveguides and other nanowire elements to form networks and device components. We demonstrate the assembly of ribbon waveguides with nanowire light sources and detectors as a first step toward building nanowire photonic circuitry.     

Small-molecule inhibition of TNF-alpha

We have identified a small-molecule inhibitor of tumor necrosis factor alpha (TNF-alpha) that promotes subunit disassembly of this trimeric cytokine family member. The compound inhibits TNF-alpha activity in biochemical and cell-based assays with median inhibitory concentrations of 22 and 4.6 micromolar, respectively. Formation of an intermediate complex between the compound and the intact trimer results in a 600-fold accelerated subunit dissociation rate that leads to trimer dissociation. A structure solved by x-ray crystallography reveals that a single compound molecule displaces a subunit of the trimer to form a complex with a dimer of TNF-alpha subunits.     

Probing proton dynamics in molecules on an attosecond time scale

We demonstrate a technique that uses high-order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on a subfemtosecond time scale. The chirped nature of the electron wavepacket produced by laser ionization in a strong field gives rise to a similar chirp in the photons emitted upon electron-ion recombination. Use of this chirp in the emitted light allows information about nuclear dynamics to be gained with 100-attosecond temporal resolution, from excitation by an 8-femtosecond pulse, in a single laser shot. Measurements on molecular hydrogen and deuterium agreed well with calculations of ultrafast nuclear dynamics in the H2+ molecule, confirming the validity of the method. We then measured harmonic spectra from CH4 and CD4 to demonstrate a few-femtosecond time scale for the onset of proton rearrangement in methane upon ionization.     

Preparation of a pure molecular quantum gas

An ultracold molecular quantum gas is created by application of a magnetic field sweep across a Feshbach resonance to a Bose-Einstein condensate of cesium atoms. The ability to separate the molecules from the atoms permits direct imaging of the pure molecular sample. Magnetic levitation enables study of the dynamics of the ensemble on extended time scales. We measured ultralow expansion energies in the range of a few nanokelvin for a sample of 3000 molecules. Our observations are consistent with the presence of a macroscopic molecular matter wave.     

Fluidity of bound hydration layers

We have measured the shear forces between solid surfaces sliding past each other across aqueous salt solutions, at pressures and concentrations typical of naturally occurring systems. In such systems the surface-attached hydration layers keep the compressed surfaces apart as a result of strongly repulsive hydration forces. We find, however, that the bound water molecules retain a shear fluidity characteristic of the bulk liquid, even when compressed down to films 1.0 +/- 0.3 nanometer thick. We attribute this to the ready exchange (as opposed to loss) of water molecules within the hydration layers as they rub past each other under strong compression.