We describe here the covalent modification of a glassy carbon electrode with toluidine blue (TB) diazonium salt, which is generated in situ from the reaction between the aromatic amino phenyl group of TB and sodium nitrite. TB is attached directly to the electrode surface without any cross‐linking agent or complex matrices. The resulting TB films exhibit excellent electrocatalytic behavior toward NADH oxidation. Low potential detection of NADH is performed at 0.15 V vs. Ag/AgCl. Furthermore, an ethanol biosensor is developed using the TB modified electrode and alcohol dehydrogenase. The great stability and reusability, excellent electrochemical reversibility, technically simple preparation and short preparation time make this method suitable for low‐cost bioelectronical devices.
The glucose oxidation cascade is fascinating; although
oxidation
products have high economic value, they can manipulate the biological
activity through posttranslational modification such as glycosylation
of proteins, lipids, and nucleic acids. The concept of this work is
based on the ability of reactive species induced by cold atmospheric
plasma (CAP) in aqueous liquids and the corresponding gas–liquid
interface to oxidize biomolecules under ambient conditions. Here,
we report the oxidation of glucose by an argon-based dielectric barrier
discharge plasma jet (kINPen) with a special emphasis on examining
the reaction pathway to pinpoint the most prominent reactive species
engaged in the observed oxidative transformation. Employing
d
-glucose and
d
-glucose-
13
C
6
solutions
and high-resolution mass spectrometry and ESI-tandem MS/MS spectrometry
techniques, the occurrence of glucose oxidation products, for example,
aldonic acids and aldaric acids, glucono- and glucaro-lactones, as
well as less abundant sugar acids including ribonic acid, arabinuronic
acid, oxoadipic acid, 3-deoxy-ribose, glutaconic acid, and glucic
acid were surveyed. The findings provide deep insights into CAP chemistry,
reflecting a switch of reactive species generation with the feed gas
modulation (Ar or Ar/O
2
with N
2
curtain gas).
Depending on the gas phase composition, a combination of oxygen-derived
short-lived hydroxyl (
•
OH)/atomic oxygen [O(
3
P)] radicals was found responsible for the glucose oxidation
cascade. The results further illustrate that the presence of carbohydrates
in cell culture media, gel formulations (agar), or other liquid targets
(juices) modulate the availability of CAP-generated species
in vitro
. In addition, a glycocalyx is attached to many
mammalian proteins, which is essential for the respective physiologic
role. It might be questioned if its oxidation plays a role in CAP
activity.
A Mo
IV
mono-oxido bis-dithiolene complex, [MoO(mohdt)
2
]
2−
(mohdt = 1-methoxy-1-oxo-4-hydroxy-but-2-ene-2,3-bis-thiolate) was synthesized as a structural and functional model for molybdenum oxidoreductase enzymes of the DMSO reductase family. It was comprehensively characterized by
inter alia
various spectroscopic methods and employed as an oxygen atom transfer (OAT) catalyst. The ligand precursor of mohdt was readily prepared by a three-step synthesis starting from dimethyl-but-2-ynedioate. Crystallographic and
13
C-NMR data support the rationale that by asymmetric substitution the electronic structure of the ene-dithio moiety can be fine-tuned. The Mo
IV
O bis-dithiolene complex was obtained by
in situ
reaction of the de-protected ligand with the metal precursor complex
trans
-[MoO
2
(CN)
4
]
4−
. The catalytic oxygen atom transfer mediated by the complex was investigated by the model OAT reaction from DMSO to triphenylphosphine with the substrate transformation being monitored by
31
P NMR spectroscopy. [MoO(mohdt)
2
]
2−
was found to be catalytically active reaching 93% conversion, albeit with a rather low reaction rate (reaction time 56 h). The observed overall catalytic activity is comparable to those of related complexes with aromatic dithiolene ligands despite the novel ligand being aliphatic in nature and originally perceived to perform more swiftly. The respective results are rationalized with respect to a potential intermolecular interaction between the hydroxyl and ester functions together with the electron-withdrawing functional groups of the dithiolene ligands of the molybdenum mono-oxido complex and equilibrium between the active monomeric Mo
IV
O and Mo
VI
O
2
and the unreactive dimeric M
O
3
species.
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