α,ω-Alkanedibromides Form Low Conductance Chemisorbed Junctions with Silver Electrodes.

Chemical groups capable of connecting molecules physically and electrically between electrodes are of critical importance in molecular-scale electronics, influencing junction conductance, variability, and function. While the development of such linkage chemistries has focused on interactions at gold, the distinct reactivity and electronic structure of other electrode metals provides underexplored opportunities to characterize and exploit new binding motifs. In this work we show that α,ω-alkanedibromides spontaneously form well-defined junctions using silver, but not gold, electrodes through application of the glovebox-based scanning tunneling microscope-based break junction method.

Resolving molecular frontier orbitals in molecular junctions with kHz resolution.

Designing and building single-molecule circuits with tailored functionalities requires a detailed knowledge of the junction electronic structure. The energy of frontier molecular orbitals and their electronic coupling with the electrodes play a key role in determining the conductance of nanoscale molecular circuits. Here, we developed a method for measuring the current-voltage (-) characteristics of single-molecule junctions with a time resolution that is two orders of magnitude higher than previously achieved.

Investigation of machine learning algorithms for taxonomic classification of marine metagenomes.

Taxonomic profiling of microbial communities is essential to model microbial interactions and inform habitat conservation. This work develops approaches in constructing training/testing data sets from publicly available marine metagenomes and evaluates the performance of machine learning (ML) approaches in read-based taxonomic classification of marine metagenomes. Predictions from two models are used to test accuracy in metagenomic classification and to guide improvements in ML approaches.

Cooperative Self-Assembly of Dimer Junctions Driven by π Stacking Leads to Conductance Enhancement.

We demonstrate enhanced electronic transport through dimer molecular junctions, which self-assemble between two gold electrodes in π-π stabilized binding configurations. Single molecule junction conductance measurements show that benzimidazole molecules assemble into dimer junctions with a per-molecule conductance that is higher than that in monomer junctions. Density functional theory calculations reveal that parallel stacking of two benzimidazoles between electrodes is the most energetically favorable due to the large π system.

Studies on the Regioselective Rearrangement of Azanorbornanic Aminyl Radicals into 2,8-Diazabicyclo[3.2.1]oct-2-ene Systems.

Aminyl radicals are nitrogen-centered radicals of interest in synthetic strategies involving C-N bond formation due to their high reactivity. These intermediate radicals are generated by the reaction of an organic azide with tributyltin hydride (BuSnH) in the presence of substoichiometric amounts of azobisisobutyronitrile (AIBN). In this work, we report the regioselective rearrangement of azanorbornanic ([2.

Controlled masking and targeted release of redox-cycling ortho-quinones via a C-C bond-cleaving 1,6-elimination.

Natural products that contain ortho-quinones show great potential as anticancer agents but have been largely discarded from clinical development because their redox-cycling behaviour results in general systemic toxicity. Here we report conjugation of ortho-quinones to a carrier, which simultaneously masks their underlying redox activity. C-benzylation at a quinone carbonyl forms a redox-inactive benzyl ketol.

Cyclopropenylidenes as Strong Carbene Anchoring Groups on Au Surfaces.

The creation of stable molecular monolayers on metallic surfaces is a fundamental challenge of surface chemistry. N-Heterocyclic carbenes (NHCs) were recently shown to form self-assembled monolayers that are significantly more stable than the traditional thiols on Au system. Here we theoretically and experimentally demonstrate that the smallest cyclic carbene, cyclopropenylidene, binds even more strongly than NHCs to Au surfaces without altering the surface structure.

Diverse nitrogen cycling pathways across a marine oxygen gradient indicate nitrogen loss coupled to chemoautotrophic activity.

Genetic markers and geochemical assays of microbial nitrogen cycling processes, including autotrophic and heterotrophic denitrification, anammox, ammonia oxidation, and nitrite oxidation, were examined across the oxycline, suboxic, and anoxic zones of the Cariaco Basin, Venezuela. Ammonia and nitrite oxidation genes were expressed through the entire gradient. Transcripts associated with autotrophic and heterotrophic denitrifiers were mostly confined to the suboxic zone and below but were also present in particles in the oxycline.

Environmental DNA reveals seasonal shifts and potential interactions in a marine community.

Environmental DNA (eDNA) analysis allows the simultaneous examination of organisms across multiple trophic levels and domains of life, providing critical information about the complex biotic interactions related to ecosystem change. Here we used multilocus amplicon sequencing of eDNA to survey biodiversity from an eighteen-month (2015-2016) time-series of seawater samples from Monterey Bay, California. The resulting dataset encompasses 663 taxonomic groups (at Family or higher taxonomic rank) ranging from microorganisms to mammals.

Identifying the molecular adsorption site of a single molecule junction through combined Raman and conductance studies.

Single-molecule junctions are ideal test beds for investigating the fundamentals of charge transport at the nanoscale. Conducting properties are strongly dependent on the metal-molecule interface geometry, which, however, is very poorly characterized due to numerous experimental challenges. We report on a new methodology for characterizing the adsorption site of single-molecule junctions through the combination of surface enhanced Raman scattering (SERS), current-voltage (-) curve measurements, and density functional theory simulations.

High-Performance Field-Effect Transistors Based on αP and βP.

The electronic properties of black and blue phosphorus nanoribbons are investigated, which enables the proposal of junction-free field-effect transistors that comprise metallic armchair nanoribbons as electrodes and, in between, a semiconducting zigzag nanoribbon as channel material (cut out of a single sheet of monolayer black or blue phosphorus). Using first-principles calculations and the nonequilibrium Green's function method, the proposed field-effect transistors are characterized. It is found that it is possible to achieve outstanding performance, with high on/off ratios, low subthreshold swings, and high transconductances.

Crossover in the inelastic electron tunneling spectra of conjugated molecules with direct Au-C links.

We use inelastic electron tunneling spectroscopy (IETS) first-principles simulations to identify and characterize the different vibrational modes of single conjugated molecules bonded to Au metal electrodes. The molecules are polyphenyls (with 1 to 4 benzene units) bonded to Au via highly conducting direct Au-C bonds. The short molecule shows near resonant elastic transmission, with a crossover to tunneling for the longer backbones.

In Situ Formation of N-Heterocyclic Carbene-Bound Single-Molecule Junctions.

Self-assembled monolayers (SAMs) formed using N-heterocyclic carbenes (NHCs) have recently emerged as thermally and chemically ultrastable alternatives to those formed from thiols. The rich chemistry and strong σ-donating ability of NHCs offer unique prospects for applications in nanoelectronics, sensing, and electrochemistry. Although stable in SAMs, free carbenes are notoriously reactive, making their electronic characterization challenging.

Evaluation of marine zooplankton community structure through environmental DNA metabarcoding.

Zooplankton dominate the abundance and biomass of multicellular animals in pelagic marine environments; however, traditional methods to characterize zooplankton communities are invasive and laborious. This study compares zooplankton taxonomic composition revealed through metabarcoding of the cytochrome oxidase I (COI) and 18S rRNA genes to traditional morphological identification by microscopy. Triplicates of three different sample types were collected from three coral reef sites in the Florida Keys National Marine Sanctuary: (1) 1 L surface seawater samples prefiltered through 3 m filters and subsequently collected on 0.

The Scientific Legacy of the CARIACO Ocean Time-Series Program.

The CARIACO (Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.50°N, 64.66°W, observed biogeochemical and ecological processes in the Cariaco Basin of the southwestern Caribbean Sea from November 1995 to January 2017.

Salinity induction of recycling Crassulacean acid metabolism and salt tolerance in plants of Talinum triangulare.

Background And Aims: Crassulacean acid metabolism (CAM) can be induced by salinity, thus conferring the plant higher water-use efficiency. Talinum triangulare does not frequently encounter salt in its natural habitat but is cultivated in soils that may become salinized. Here we examined whether plants of T.

What is the potential for dark CO2 fixation in the facultative crassulacean acid metabolism species Talinum triangulare?

In obligate Crassulacean acid metabolism (CAM) plants, dark CO2 fixation is almost the sole route of CO2 fixation and, under drought, continues for long periods. In contrast, in plants of the facultative CAM species Talinum triangulare under experimental drought, dark CO2 fixation provides a small proportion of the daily assimilation observed in watered plants and occurs only for a few days, after which almost nil CO2 fixation is observed. Under field conditions, with a practically unlimited substrate volume, drought-induced CAM might operate for a longer period and make a higher contribution to daily CO2 fixation.

Left hemicranial hypoplasia in 2 patients with primary progressive aphasia.

Background: Primary progressive aphasia (PPA) leads to a gradual and relatively isolated dissolution of language function. The factors that determine the selectivity of the disease process remain unknown. We had speculated that PPA may occasionally arise as a tardive manifestation of genetic or acquired vulnerabilities involving the language network of the brain.