173 research outputs found
Large tunable image-charge effects in single-molecule junctions
The characteristics of molecular electronic devices are critically determined
by metal-organic interfaces, which influence the arrangement of the orbital
levels that participate in charge transport. Studies on self-assembled
monolayers (SAMs) show (molecule-dependent) level shifts as well as
transport-gap renormalization, suggesting that polarization effects in the
metal substrate play a key role in the level alignment with respect to the
metal's Fermi energy. Here, we provide direct evidence for an electrode-induced
gap renormalization in single-molecule junctions. We study charge transport in
single porphyrin-type molecules using electrically gateable break junctions. In
this set-up, the position of the occupied and unoccupied levels can be followed
in situ and with simultaneous mechanical control. When increasing the electrode
separation, we observe a substantial increase in the transport gap with level
shifts as high as several hundreds of meV for displacements of a few \aa
ngstroms. Analysis of this large and tunable gap renormalization with
image-charge calculations based on atomic charges obtained from density
functional theory confirms and clarifies the dominant role of image-charge
effects in single-molecule junctions
Continuous combined microwave and hot air treatment of apples for fruit fly (Bactrocera tryoni and B. jarvisi) disinfestation
Apples at 24 ± 2 °C were heated in a pilot scale hot air assisted (40 °C) continuous pentagonal microwave system, to evaluate the effectiveness of this treatment on insect mortality (variety Mutsu) and fruit quality (variety Granny Smith). An average temperature of 53.4 ± 1.3 °C at core, bottom and flesh of the apple was recorded at the end of the treatment. One hundred percent mortality of the most tolerant stage of Queensland fruit fly (Bactrocera tryoni, Froggatt) and Jarvis's fruit fly (Bactrocera jarvisi, Tryon), were observed when the Mortality value (M52, equivalent time of isothermal treatment at 52 °C) at the slowest heating point applicable for each experiment was ≥ 50 min and ≥ 37 min, respectively. Results showed that microwave heat treatment is effective for insect disinfestation without any adverse impact on total soluble solids, flesh or peel firmness of the treated apples. The treated apples recorded a significantly higher pH and lower ion leakage than the untreated apples after 3 or 4 weeks. Therefore, the microwave heat treatment has the potential to be developed as an alternative chemical free quarantine treatment against economically significant insect pests. Industrial relevance Hot air assisted microwave heating of fruits and vegetables, is more cost effective compared to vapour heat treatment and ionising radiation for disinfestation of insects. Microwave treatment is environmentally friendly compared to fumigation and chemical treatments. Hot air assisted microwave disinfestation can be performed at farms or centralised pack houses since the capital cost would be comparatively lower than vapour heat or ionising radiation treatments
Gelation Landscape Engineering Using a Multi-Reaction Supramolecular Hydrogelator System
Simultaneous control of the kinetics and
thermodynamics of two different types of covalent
chemistry allows pathway selectivity in the formation of
hydrogelating molecules from a complex reaction network.
This can lead to a range of hydrogel materials with vastly
different properties, starting from a set of simple starting
compounds and reaction conditions. Chemical reaction
between a trialdehyde and the tuberculosis drug isoniazid
can form one, two, or three hydrazone connectivity
products, meaning kinetic gelation pathways can be
addressed. Simultaneously, thermodynamics control the
formation of either a keto or an enol tautomer of the
products, again resulting in vastly different materials.
Overall, this shows that careful navigation of a reaction
landscape using both kinetic and thermodynamic
selectivity can be used to control material selection from
a complex reaction network
An autonomous chemically fuelled small-molecule motor
Molecular machines are among the most complex of all functional molecules and lie at the heart of nearly every biological process. A number of synthetic small-molecule machines have been developed, including molecular muscles, synthesizers, pumps, walkers, transporters and light-driven and electrically driven rotary motors. However, although biological molecular motors are powered by chemical gradients or the hydrolysis of adenosine triphosphate (ATP), so far there are no synthetic small-molecule motors that can operate autonomously using chemical energy (that is, the components move with net directionality as long as a chemical fuel is present). Here we describe a system in which a small molecular ring (macrocycle) is continuously transported directionally around a cyclic molecular track when powered by irreversible reactions of a chemical fuel, 9-fluorenylmethoxycarbonyl chloride. Key to the design is that the rate of reaction of this fuel with reactive sites on the cyclic track is faster when the macrocycle is far from the reactive site than when it is near to it. We find that a bulky pyridine-based catalyst promotes carbonate-forming reactions that ratchet the displacement of the macrocycle away from the reactive sites on the track. Under reaction conditions where both attachment and cleavage of the 9-fluorenylmethoxycarbonyl groups occur through different processes, and the cleavage reaction occurs at a rate independent of macrocycle location, net directional rotation of the molecular motor continues for as long as unreacted fuel remains. We anticipate that autonomous chemically fuelled molecular motors will find application as engines in molecular nanotechnology.</p
Nano-electronic switches: Light-induced switching of the conductance of molecular systems
The emerging landscape of single-molecule protein sequencing technologies
Single-cell profiling methods have had a profound impact on the understanding of cellular heterogeneity. While genomes and transcriptomes can be explored at the single-cell level, single-cell profiling of proteomes is not yet established. Here we describe new single-molecule protein sequencing and identification technologies alongside innovations in mass spectrometry that will eventually enable broad sequence coverage in single-cell profiling. These technologies will in turn facilitate biological discovery and open new avenues for ultrasensitive disease diagnostics.This Perspective describes new single-molecule protein sequencing and identification technologies alongside innovations in mass spectrometry that will eventually enable broad sequence coverage in single-cell proteomics.</p
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