Methylammonium bismuth (III) iodide single crystals and films have been developed and investigated. We have further presented the first demonstration of using this organic–inorganic bismuth-based ...material to replace lead/tin-based perovskite materials in solution-processable solar cells. The organic–inorganic bismuth-based material has advantages of non-toxicity, ambient stability, and low-temperature solution-processability, which provides a promising solution to address the toxicity and stability challenges in organolead- and organotin-based perovskite solar cells. We also demonstrated that trivalent metal cation-based organic–inorganic hybrid materials can exhibit photovoltaic effect, which may inspire more research work on developing and applying organic-inorganic hybrid materials beyond divalent metal cations (Pb (II) and Sn (II)) for solar energy applications.
The intersection between Cu-catalyzed atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP) has been recently shown to be a result of competition ...between the CuI and CuII complexes of polyamine ligands for the same organic free radical. The tetradentate ligands N,N′-bis-2′-pyridylmethyl-ethane-1,2-diamine (L1) and N,N′-dimethyl-N,N′-bis-2′-pyridylmethyl-ethane-1,2-diamine (L2) form stable Cu complexes which, depending on their oxidation state, can either liberate or complex organic radicals. Herein, we show that this process may be affected by subtle changes to the ligand system. Switching from a tertiary amine (L2) to a secondary amine (L1) retains ATRP and OMRP activity through a series of cyclic voltammetry measurements in the presence of the initiator bromoacetonitrile.
•A fungal nitrate reductase (NR) catalyses the reduction of nitrate to nitrite.•NR may be immobilised on a glassy carbon electrode with the biopolymer chitosan.•Electrocatalytic nitrate reduction can ...be achieved with NR mediated by anthraquinone sulfonate.•High selectivity and exceptional sensitivity for nitrate is found.•The NR enzyme electrode is stable for at least 3 months.
We report an electrochemical nitrate biosensor incorporating the enzyme nitrate reductase (NR) from the fungus Neurospora crassa entrapped within a polymeric chitosan matrix on a glassy carbon (GC) electrode. The artificial electron mediator anthraquinone sulfonate (AQ) is utilized as an electron transfer partner (co-substrate) for NR. The NR enzyme was effectively immobilized within the chitosan matrix without the need for a dialysis membrane, and exhibited high sensitivity and selectivity for nitrate using either rotating disk cyclic voltammetry or constant potential amperometry methods. A particular feature was the longevity of the biosensor which retained more than 70% activity over a period of 3 months. The practical application of the biosensor was demonstrated by the determination of nitrate concentrations in lake and river water samples without any pre-treatment, and the results were validated with a reliable spectroscopic assay.
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The bacterial molybdenum (Mo)-containing formate dehydrogenase (FdsDABG) from Cupriavidus necator is a soluble NAD+-dependent enzyme belonging to the DMSO reductase family. The holoenzyme is complex ...and possesses nine redox-active cofactors including a bis(molybdopterin guanine dinucleotide) (bis-MGD) active site, seven iron–sulfur clusters, and 1 equiv of flavin mononucleotide (FMN). FdsDABG catalyzes the two-electron oxidation of HCOO– (formate) to CO2 and reversibly reduces CO2 to HCOO– under physiological conditions close to its thermodynamic redox potential. Here we develop an electrocatalytically active formate oxidation/CO2 reduction system by immobilizing FdsDABG on a glassy carbon electrode in the presence of coadsorbents such as chitosan and glutaraldehyde. The reversible enzymatic interconversion between HCOO– and CO2 by FdsDABG has been realized with cyclic voltammetry using a range of artificial electron transfer mediators, with methylene blue (MB) and phenazine methosulfate (PMS) being particularly effective as electron acceptors for FdsDABG in formate oxidation. Methyl viologen (MV) acts as both an electron acceptor (MV2+) in formate oxidation and an electron donor (MV+•) for CO2 reduction. The catalytic voltammetry was reproduced by electrochemical simulation across a range of sweep rates and concentrations of formate and mediators to provide new insights into the kinetics of the FdsDABG catalytic mechanism.
The cubane phenyl ring bioisostere paradigm was further explored in an extensive study covering a wide range of pharmaceutical and agrochemical templates, which included antibiotics (cefaclor, ...penicillin G) and antihistamine (diphenhydramine), a smooth muscle relaxant (alverine), an anaesthetic (ketamine), an agrochemical instecticide (triflumuron), an antiparasitic (benznidazole) and an anticancer agent (tamibarotene). This investigation highlights the scope and limitations of incorporating cubane into bioactive molecule discovery, both in terms of synthetic compatibility and physical property matching. Cubane maintained bioisosterism in the case of the Chagas disease antiparasitic benznidazole, although it was less active in the case of the anticancer agent (tamibarotenne). Application of the cyclooctatetraene (COT) (bio)motif complement was found to optimize benznidazole relative to the benzene parent, and augmented anticancer activity relative to the cubane analogue in the case of tamibarotene. Like all bioisosteres, scaffolds and biomotifs, however, there are limitations (e.g. synthetic implementation), and these have been specifically highlighted herein using failed examples. A summary of all templates prepared to date by our group that were biologically evaluated strongly supports the concept that cubane is a valuable tool in bioactive molecule discovery and COT is a viable complement.
This study showcases the application of an integrated workflow of molecular networking chemical profiling (GNPS), together with miniaturized microbioreactor cultivation profiling (MATRIX) to ...successfully detect, dereplicate, prioritize, optimize the production, isolate, characterize, and identify a diverse selection of new chemically labile natural products from the Queensland sheep pasture soil-derived fungus
sp. CMB-MRF324. More specifically, we report the new tryptamine enamino tripeptide aspergillamides E-F (
-
), dihydroquinoline-2-one aflaquinolones H-I (
-
), and prenylated phenylbutyrolactone aspulvinone Y (
), along with an array of known co-metabolites, including asterriquinones SU5228 (
) and CT5 (
), terrecyclic acid A (
), and aspulvinones N-CR (
), B (
), D (
), and H (
). Structure elucidation was achieved by a combination of detailed spectroscopic and chemical analysis, biosynthetic considerations, and in the case of
an X-ray crystallographic analysis.
Nitrate reductase (NR) from the fungus Neurospora crassa is a complex homodimeric metallo-flavoenzyme, where each protomer contains three distinct domains; the catalytically active terminal ...molybdopterin cofactor, a central heme-containing domain, and an FAD domain which binds with the natural electron donor NADPH. Here, we demonstrate the catalytic voltammetry of variants of N. crassa NRs on a modified Au electrode with the electrochemically reduced forms of benzyl viologen (BV2+) and anthraquinone sulfonate (AQS−) acting as artificial electron donors. The biopolymer chitosan used to entrap NR on the electrode non-covalently and the enzyme film was both stable and highly active. Electrochemistry was conducted on two distinct forms; one lacking the FAD cofactor and the other lacking both the FAD and heme cofactors. While both enzymes showed catalytic nitrate reductase activity, removal of the heme cofactor resulted in a more significant effect on the rate of nitrate reduction. Electrochemical simulation was carried out to enable kinetic characterisation of both the NR:nitrate and NR:mediator reactions.
•Electrocatalytic nitrate reduction with a fungal nitrate reductase•Activity demonstrated with two enzyme forms that lack specific redox cofactors•Electrochemical simulation reveals rate limiting electron transfer with synthetic electron transfer partners
Molybdenum-dependent enzymes that can reduce N-hydroxylated substrates (e.g. N-hydroxyl-purines, amidoximes) are found in bacteria, plants and vertebrates. They are involved in the conversion of a ...wide range of N-hydroxylated organic compounds into their corresponding amines, and utilize various redox proteins (cytochrome b5, cyt b5 reductase, flavin reductase) to deliver reducing equivalents to the catalytic centre. Here we present catalytic electrochemistry of the bacterial enzyme YcbX from Escherichia coli utilizing the synthetic electron transfer mediator methyl viologen (MV2+). The electrochemically reduced form (MV+.) acts as an effective electron donor for YcbX. To immobilize YcbX on a glassy carbon electrode, a facile protein crosslinking approach was used with the crosslinker glutaraldehyde (GTA). The YcbX-modified electrode showed a catalytic response for the reduction of a broad range of N-hydroxylated substrates. The catalytic activity of YcbX was examined at different pH values exhibiting an optimum at pH 7.5 and a bell-shaped pH profile with deactivation through deprotonation (pKa1 9.1) or protonation (pKa2 6.1). Electrochemical simulation was employed to obtain new biochemical data for YcbX, in its reaction with methyl viologen and the organic substrates 6-N-hydroxylaminopurine (6-HAP) and benzamidoxime (BA).
•Substrate activity for electrocatalytic reduction of N-hydroxylated organic compounds•EPR characterization of 2Fe—2S cluster active site and redox potential•In depth electrochemical simulation of experimental data to obtain kinetic information
Multidrug resistance (MDR) mediated by P-glycoprotein (Pgp) represents a significant impediment to successful cancer treatment. The compound, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone ...(Dp44mT), has been shown to induce greater cytotoxicity against resistant cells than their nonresistant counterparts. Herein, the structure–activity relationships of selected thiosemicarbazones are explored and the novel mechanism underlying their ability to overcome resistance is further elucidated. Only thiosemicarbazones with electron-withdrawing substituents at the imine carbon mediated Pgp-dependent potentiated cytotoxicity, which was reversed by Pgp inhibition. Treatment of resistant cells with these thiosemicarbazones resulted in Pgp-dependent lysosomal membrane permeabilization (LMP) that relied on copper (Cu) chelation, reactive oxygen species generation, and increased relative lipophilicity. Hence, this study is the first to demonstrate the structural requirements of these thiosemicarbazones necessary to overcome MDR. We also demonstrate the mechanism that enables the targeting of resistant tumors, whereby thiosemicarbazones “hijack” lysosomal Pgp and form redox-active Cu complexes that mediate LMP and potentiate cytotoxicity.
A chemical investigation of Australian soil-derived bacteria Actinomadura sp. S4S-00069B08 yielded eight new benzenoid ansamycins, goondansamycins A–H. Goondansamycins feature rare ...1,4-benzoxazin-3-one or o-diamino-p-benzoquinone moieties and can exist as both aglycones or 9-O-α-glycosides of either d-rhodinose or d-amicetose. Structures were solved on the basis of detailed spectroscopy, including X-ray analysis.
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