3 research outputs found
Symmetric Bis-benzimidazoles Are Potent Anti-Staphylococcal Agents with Dual Inhibitory Mechanisms against DNA Gyrase
Various bis-benzimidazole derivatives have been reported
to possess
activity against Gram-positive pathogens. No mechanism of action has
been elucidated to fully account for the antibacterial activity of
this class of compounds. A group of symmetric bis-benzimidazoles (BBZ)
designed as anticancer agents have previously been shown to possess
moderate antiproliferative activity. We sought to assess the antibacterial
activity and mechanism of action of BBZ compounds against <i>Staphylococcus aureus</i>. Antibacterial activities were assessed
by determination of minimal inhibitory concentrations (MICs), time-kill
curves, and scanning electron microscopy. Transcriptional responses
to BBZ treatment were determined using whole genome microarrays. Activities
against bacterial type II topoisomerases were investigated using in
vitro supercoiling, decatenation, DNA binding, and DNA cleavage inhibition
assays. MICs for EMRSA-16 were between 0.03 and 0.5 μg/mL. The
compounds showed concentration-dependent bactericidal activity and
induced cell swelling and lysis. Transcriptional responses to BBZ
were consistent with topoisomerase inhibition and DNA damage. A subset
of BBZ compounds inhibited <i>S. aureus</i> DNA gyrase supercoiling
activity with IC<sub>50</sub> values in the range of 5–10 μM.
This inhibition was subsequently shown to operate through both inhibition
of binding of DNA gyrase to DNA and accumulation of single-stranded
DNA breaks. We conclude that BBZ compounds are potent anti-staphylococcal
agents and operate at least in part through DNA gyrase inhibition,
leading to the accumulation of single-stranded DNA breaks, and by
preventing the binding of gyrase to DNA
Superlinear Composition-Dependent Photocurrent in CVD-Grown Monolayer MoS<sub>2(1–<i>x</i>)</sub>Se<sub>2<i>x</i></sub> Alloy Devices
Transition
metal dichalcogenides (TMDs) have emerged as a new class of two-dimensional
materials that are promising for electronics and photonics. To date,
optoelectronic measurements in these materials have shown the conventional
behavior expected from photoconductors such as a linear or sublinear
dependence of the photocurrent on light intensity. Here, we report
the observation of a new regime of operation where the photocurrent
depends superlinearly on light intensity. We use spatially resolved
photocurrent measurements on devices consisting of CVD-grown monolayers
of TMD alloys spanning MoS<sub>2</sub> to MoSe<sub>2</sub> to show
the photoconductive nature of the photoresponse, with the photocurrent
dominated by recombination and field-induced carrier separation in
the channel. Time-dependent photoconductivity measurements show the
presence of persistent photoconductivity for the S-rich alloys, while
photocurrent measurements at fixed wavelength for devices of different
alloy compositions show a systematic decrease of the responsivity
with increasing Se content associated with increased linearity of
the current–voltage characteristics. A model based on the presence
of different types of recombination centers is presented to explain
the origin of the superlinear dependence on light intensity, which
emerges when the nonequilibrium occupancy of initially empty fast
recombination centers becomes comparable to that of slow recombination
centers
Postgrowth Tuning of the Bandgap of Single-Layer Molybdenum Disulfide Films by Sulfur/Selenium Exchange
We demonstrate bandgap tuning of a single-layer MoS<sub>2</sub> film on SiO<sub>2</sub>/Si <i>via</i> substitution of its sulfur atoms by selenium through a process of gentle sputtering, exposure to a selenium precursor, and annealing. We characterize the substitution process both for S/S and S/Se replacement. Photoluminescence and, in the latter case, X-ray photoelectron spectroscopy provide direct evidence of optical band gap shift and selenium incorporation, respectively. We discuss our experimental observations, including the limit of the achievable bandgap shift, in terms of the role of stress in the film as elucidated by computational studies, based on density functional theory. The resultant films are stable in vacuum, but deteriorate under optical excitation in air