Adsorption and catalytic activity of trinitro-fluorenone derivatives towards NADH oxidation on different electrode materials
Introduction
The electrochemical regeneration of oxidized nicotinamide adenine dinucleotide (NAD+) at high rate constants is an important step in the development of reagentless dehydrogenase based sensors. On bare electrodes this reaction is however often severely inhibited and therefore numerous redox mediators have been suggested in the literature in order to overcome this problem [1], [2], [3], [4]. Only few of them meet simultaneously the criteria of high rate constants, low overpotentials and reasonable lifetime. In this context we have recently proposed a new family of mediators, nitrofluorenones, that seems to be very competitive with those reported by other authors [5]. Their redox chemistry is based on the two-electron/two-proton transfer involved in the switching from a nitrosogroup to a hydroxylamine group located on a fluorenone skeleton. This completely reversible process catalyses the reoxidation of NADH and a comparative study allowed us to select one particularly efficient molecule, 2,4,7-trinitro-9-fluorenone (TNF). When this species is adsorbed as a monolayer on glassy carbon catalytic rate constants of up to have been measured at potentials close to 0 V vs. Ag/AgCl. The excellent stability of the monolayer in this case is most likely due to π–π interactions between the aromatic parts of the mediator and the carbon substrate.
However when using electrode materials other than carbon, as it might be necessary for some applications, only weak or no π–π interactions are possible, and therefore we were not able to obtain a stable adsorption of TNF. In this communication, we report about new molecules out of the nitrofluorenone family, obtained by the introduction of specific side groups into TNF, that not only form stable layers on platinum and gold, but also show a catalytic activity comparable to the one measured for TNF on glassy carbon.
Section snippets
Materials
2,4,7-trinitro-9-fluorenone (TNF) and (2,4,7-trinitro-9-fluorenylidene)-malononitrile (TNFM) were obtained from Aldrich and used as received.
4-(N-allylamido)-2,5,7-trinitro-9-fluorenone (TNFA) has been synthesized by refluxing equivalent amounts of freshly distilled allylamine and 2,5,7-trinitro-9-fluorenone-4-carboxylic acid chloride in dry toluene overnight (81% yield). The latter compound was obtained by a literature procedure [6]. The purity and the structure of the final product have been
Results and discussion
Modified electrodes were obtained as previously described [7] by dipping the polished electrode in a 0.5 mM solution of the nitro compound in THF for a few minutes. Then the electrode is rinsed with ultrapure water. This results in an adsorbed layer of the water insoluble organic catalyst. Choosing the right negative potential limit during the first scan in pure supporting electrolyte the nitro groups can be individually transformed into hydroxylamine substituents. In Fig. 1(A) this is
Conclusion
We were able to adapt the molecular structure of the present nitrofluorenone system in order to ensure good adsorption on different electrode materials. Furthermore all molecules show a satisfying activity towards NADH oxidation and this will allow us to build up enzyme electrodes not only with glassy carbon [11] but also using gold or platinum. A considerable extension of the possible applications of this new family of redox mediators can therefore be anticipated, for example their adsorption
References (11)
- et al.
J. Electroanal. Chem.
(1995) - et al.
J. Electroanal. Chem.
(1999) - et al.
J. Electroanal. Chem.
(2001) - et al.
J. Electroanal. Chem.
(1978) - et al.
Mikrochim. Acta
(1997)
Cited by (33)
Carbon nanodots modified-electrode for peroxide-free cholesterol biosensing and biofuel cell design
2023, Sensors and Actuators B: ChemicalCitation Excerpt :NADH can be oxidized by using electrocatalysts that lower the oxidation overpotential at carbon electrode surfaces and therefore minimize the interferences from compounds present in biological samples, whereas H2O2 detection methods are prone to interferences [14]. Various NADH oxidation catalysts, such as quinone derivatives, phenazines, phenothiazines, nitro-fluorenone and catechol, have been extensively studied [15–18] due to the ubiquity of the enzymatic reactions involving NADH as a cofactor and therefore the relevance of NADH detection. Furthermore, the grafting of phenazines and phenothiazines on screen printed electrodes for NADH oxidation has been reported [18–20].
Photoelectrocatalytic detection of NADH on n-type silicon semiconductors facilitated by carbon nanotube fibers
2021, Electrochimica ActaCitation Excerpt :Fouling of the electrode surface due to the adsorption of oxidation products, which leads to electrode passivation and therefore irreproducibility of the analytical signal, has also been observed [1,27]. To overcome the problems of bare electrodes, the modification of the electrode surface with redox mediators (e.g. quinone derivatives, phenazine, phenoxazine and phenothiazine dyes, nitro-fluorenone and catechol) which catalyze the oxidation of NADH [17,28,29], polymers [3], and nanomaterials, such as carbon nanotubes and graphene sheets [16], have been widely considered. Physical adsorption, electropolymerized films, and to a lesser extent, covalent attachment have been used for the electrode modification with redox mediators to obtain a stable immobilization.
Nitrofluorene derivatives trapped within MWCNTs for electrocatalysis of NADH: Substituent effects on π-π stacking interaction strength
2020, Electrochemistry CommunicationsCitation Excerpt :The total charge of the oxidation signal centred at 20 mV (154.5 μC) is essentially the same as the sum of the signals corresponding to both the oxidation of the redox mediator on MWCNT/GCE (dashed line, Fig. 6D) and the oxidation of NADH (dot-dashed line, Fig. 6D). These kinds of results have been seen previously by other researchers [14,20,23,24]. It has been postulated that the electrocatalytic mechanism for this type of redox mediator (organic 2 electron-proton acceptor) with NADH involves an intermediate charge transfer complex [25].
5,5-Dithiobis(2-nitrobenzoic acid) pyrene derivative-carbon nanotube electrodes for NADH electrooxidation and oriented immobilization of multicopper oxidases for the development of glucose/O<inf>2</inf> biofuel cells
2017, Biosensors and BioelectronicsCitation Excerpt :Nitroaromatics are a class of catalytically active compounds for NADH oxidation and were proposed as electrocatalysts for NAD+ regeneration fifteen years ago (Casero et al., 1999; Mano and Kuhn, 1999). Mano et al. performed extensive studies on mono- and multi substituted nitroaromatics to determine the effect of the number and position of NO2 substituents in the catalyst molecules on NADH electrooxidation (Mano et al., 2001; Munteanu et al., 2004). They showed it was possible to tailor the catalytic currents and formal potentials of the catalysts depending upon number and position of the NO2.
Increasing amperometric biosensor sensitivity by length fractionated single-walled carbon nanotubes
2008, Biosensors and BioelectronicsImproved enzyme immobilization for enhanced bioelectrocatalytic activity of porous electrodes
2007, Electrochemistry Communications