Innovative Electrochemical Screening Allows Transketolase Inhibitors to Be Identified.

Transketolases (TKs) are ubiquitous thiamine pyrophosphate (TPP)-dependent enzymes of the nonoxidative branch of the pentose phosphate pathway. They are considered as interesting therapeutic targets in numerous diseases and infections (e.g., cancer, tuberculosis, malaria), for which it is important to find specific and efficient inhibitors. Current TK assays require important amounts of enzyme, are time-consuming, and are not specific. Here, we report a new high throughput electrochemical assay based on the oxidative trapping of the TK-TPP intermediate. After electrode characterization, the enzyme loading, electrochemical protocol, and substrate concentration were optimized. Finally, 96 electrochemical assays could be performed in parallel in only 7 min, which allows a rapid screening of TK inhibitors. Then, 1360 molecules of an in-house chemical library were screened and one early lead compound was identified to inhibit TK from E. coli with an IC50 of 63 µM and an inhibition constant ( KI) of 3.4 µM. The electrochemical assay was also used to propose an inhibition mechanism.

Interactions between Biological Cells and Layered Double Hydroxides: Towards Functional Materials.

This review highlights the current research on the interactions between biological cells and Layered Double Hydroxides (LDH). The as-prepared biohybrid materials appear extremely attractive in diverse fields of application relating to health care, environment and energy production. We describe how thanks to the main features of biological cells and LDH layers, various strategies of assemblies can be carried out for constructing smart biofunctional materials. The interactions between the two components are described with a peculiar attention to the adsorption, biocompatibilization, LDH layer internalization, antifouling and antimicrobial properties. The most significant achievements including authors' results, involving biological cells and LDH assemblies in waste water treatment, bioremediation and bioenergy generation are specifically addressed.

Assessment of the Fe(III)-EDDS complex in Fenton-like processes: from the radical formation to the degradation of bisphenol A.

The present work describes, for the first time, the use of a new and strong complexing agent, ethylenediamine-N,N'-disuccinic acid (EDDS) in the homogeneous Fenton process. The effect of H(2)O(2) concentration, Fe(III)-EDDS concentration, pH value, and oxygen concentration on the homogeneous Fenton degradation of bisphenol A (BPA) used as a model pollutant, was investigated. Surprisingly, the performance of BPA oxidation in an EDDS-driven Fenton reaction was found to be much higher at near neutral or basic pH than at acidic pH. Inhibition and probe studies were conducted to ascertain the role of several radicals (e.g., (•)OH, HO(2)(•)/O(2)(•-)) on BPA degradation. This unexpected effect of pH on Fenton reaction efficiency could be due to the formation of HO(2)(•) or O(2)(•-) radicals and to the presence of different forms of the complex Fe(III)-EDDS as a function of pH. Indeed, the reduction of Fe(III)-EDDS to Fe(II)-EDDS is a crucial step that governs the formation of hydroxyl radical, mainly responsible for BPA degradation. In addition to its ability to maintain iron in soluble form, EDDS acts as a superoxide radical-promoting agent, enhancing the generation of Fe(II) (the rate limiting step) and therefore the production of (•)OH radicals. These results are very promising because they offer an important new treatment option at higher range of pH values and more particularly at pHs encountered in natural conditions.

Hybrid and biohybrid layered double hydroxides for electrochemical analysis.

Layered double hydroxides (LDH) are lamellar materials that have been extensively used as electrode modifiers. Nanostructured organic-inorganic materials can be designed by intercalation of organic or metallic complexes within the interlayer space of these materials or by the formation of composite materials based on biopolymers (alginate or chitosan) or biomolecules, such as enzymes. These hybrid or biohybrid materials have interesting properties applicable in electroanalytical devices. From an exhaustive review of the literature, the relevance of these hybrid and biohybrid LDH materials as electrode materials for electrochemical detection of species with an environmental or health impact is evaluated. The analytical characteristics (sensitivity and detection limit) of LDH-based amperometric sensors or biosensors are scrutinized.

Synthesis route to supported gold nanoparticle layered double hydroxides as efficient catalysts in the electrooxidation of methanol.

This work describes a new one-step method for the preparation of AuNP/LDH nanocomposites via the polyol route. The novelty of this facile, simple synthesis is the absence of additional reactants such as reductive agents or stabilizer, which gives the possibility to obtain phase-pure systems free of undesiderable effect. The AuNP formation is confirmed by SEM, TEM, PXRD, and XAS; moreover, the electrochemical characterization is also reported. The electrocatalytic behavior of AuNP/LDH nanocomposites has been investigated with respect to the oxidation of methanol in basic media and compared with that of pristine NiAl-Ac. The 4-fold highest catalytic efficiency observed with AuNP/LDH nanocomposites suggests the presence of a synergic effect between Ni and AuNP sites. The combination of these experimental findings with the low-cost synthesis procedure paves the way for the exploitation of the presented nanocomposites materials as catalysts for methanol fuel cells.

Characterization of hemoglobin immobilized in MgAl-layered double hydroxides by the coprecipitation method.

Hemoglobin was immobilized in Mg(2)Al-Layered Double Hydroxides (LDH) by coprecipation method at pH 9.0. Interactions between Hb and LDH particles were investigated by X-ray diffraction patterns, FTIR, UV-vis, circular dichroism, and fluorescence spectroscopies. Morphology and porosity of Mg(2)Al-Hb(cop) biohybrid are analyzed from SEM and TEM images and permeability measurement. The direct electron transfer of immobilized Hb was studied by cyclic voltammetry, and the electrocatalytic activity was evaluated at glassy carbon modified with this Mg(2)Al-Hb(cop) biohybrid. Even though the percentage of electroactive Hb was less than 2%, this bioelectrode showed a low detection limit (1.5 x 10(-8) M) and a very high sensitivity (37 A/M cm(2)) for the amperometric detection of H(2)O(2).

Biosensing applications of clay-modified electrodes: a review.

Two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs), also defined as anionic clays, have open structures which are favourable for interactions with enzymes and which intercalate redox mediators. This review aims to show the interest in clays and LDHs as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. It is meant to provide an overview of the various types of electrochemical biosensors that have been developed with these 2D layered materials, along with significant advances over the last several years. The different biosensor configurations and their specific transduction procedures are discussed.

Confined Growth of NiAl-Layered Double Hydroxide Nanoparticles Within Alginate Gel: Influence on Electrochemical Properties.

NiAl Layered Double Hydroxide (LDH) alginate bionanocomposites were synthesized by confined coprecipitation within alginate beads. The NiAl based bionanocomposites were prepared either by impregnation by divalent and trivalent metal cations of pre-formed calcium cross-linked alginate beads or by using the metal cations (Ni2+, Al3+) as crosslinking cationic agents for the biopolymer network. The impregnation step was systematically followed by a soaking in NaOH solution to induce the LDH coprecipitation. Powder x-ray diffraction (PXRD), infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), thermogravimetry analysis (TGA), electron microscopies (SEM and TEM) confirmed the biotemplated coprecipitation of LDH nanoparticles ranging from 75 to 150 nm for both strategies. The drying of the LDH@alginate beads by supercritical CO2 drying process led to porous bionanocomposite aerogels when Ca2+ cross-linked alginate beads were used. Such confined preparation of NiAl LDH was extended to bionanocomposite films leading to similar results. The permeability and the electrochemical behavior of these NiAl@alginate bionanocomposites, as thin films coated on indium tin oxide (ITO) electrodes, were investigated by cyclic voltammetry, demonstrating an efficient diffusion of the K4Fe(CN)6 redox probe through the LDH@alginate based films and the improvement of the electrochemical accessibility of the Ni sites.

Assembly of nitroreductase and layered double hydroxides toward functional biohybrid materials.

The development of new multifunctional materials integrating catalytically active and selective biomolecules, such as enzymes, as well as easily removable and robust inorganic supports that allow their use and reuse, is a subject of ongoing attention. In this work, the nitroreductase NfrA2/YncD (NR) from Bacillus megaterium Mes11 strain was successfully immobilized by adsorption and coprecipitation on layered double hydroxide (LDH) materials with different compositions (MgAl-LDH and ZnAl-LDH), particle sizes and morphologies, and using different enzyme/LDH mass ratios (Q). The materials were characterized and the immobilization and catalytic performance of the biohybrids were studied and optimized. The nitroreductase-immobilized on the nanosized MgAl-LDH displayed the best catalytic performance with 42-46% of catalytic retention and>80% of immobilization yield at saturation values of enzyme loading Cs ≈ 0.6 g NR/g LDH (Q = 0.8). The adsorption process displayed high enzyme-LDH affinity interactions yielding to a stable biohybrid material. The increase in the amount of enzyme loading favoured the catalytic performance of the biohybrid due to the better preservation of the native conformation. The biohybrid was reused several times with partial activity retention after 4 cycles. In addition, the biohybrid was successfully dried maintaining the catalytic activity for several weeks when it was stored in its dry form. Finally, thin films of NR@LDH biohybrid deposited on glassy carbon electrodes were evaluated as a modified electrode applied for nitro-compound detection. The results show that these biohybrids can be used in biotechnology applications to efficiently detect compounds such as dinitrotoluene. The search for new non-hazardous chemical designs preventing or reducing the use of aggressive chemical processes for human being and the environment is the common philosophy within sustainable chemistry.

Spongy gel-like layered double hydroxide-alkaline phosphatase nanohybrid as a biosensing material.

Formation of new bio-nanohybrid material was obtained by immobilization of alkaline phosphatase within a Mg(2)Al LDH by "soft chemistry" coprecipitation synthesis, resulting in an original spongy gel-like morphology allowing the preservation of the enzyme structure and activity even at low pH values thanks to the buffering property of the basic host structure.

Laccase immobilization in redox active layered double hydroxides: a reagentless amperometric biosensor.

This paper describes a new system for amperometric determination of dissolved oxygen and its application for the detection of anionic toxic substances, which are known as enzyme inhibitors. This biosensor is based on the co-immobilization of laccase from Trametes versicolor and a redox active layered double hydroxide [Zn-Cr-ABTS] on a glassy carbon electrode. The electrochemical transduction step corresponds to the electrocatalytic reduction of O2 at 0.2V by laccase as catalyst and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as mediator. Such device provides a fast and a sensitive response for dissolved oxygen determination between 6 x 10(-8) and 4 x 10(-6)M and very low detection limits for azide (5.5 nM), fluoride (6.9 nM) and cyanide (6.2 nM).

Thiamine biosensor based on oxidative trapping of enzyme-substrate intermediate.

In the present work, we describe a new thiamine amperometric biosensor based on thiamine pyrophosphate (ThDP)-dependent transketolase (TK)-catalyzed reaction, followed by the oxidative trapping of TK intermediate α,ß-dihydroxyethylthiamine diphosphate (DHEThDP) within the enzymatic active site. For the biosensor design purpose, TK from Escherichia coli (TKec) was immobilized in Mg2Al-NO3 Layered Double Hydroxides (LDH) and the electrochemical detection was achieved with the TKec/LDH modified glassy carbon electrode (GCE). The transduction process was based on the ability of Fe(CN)63- to oxidize DHEThDP to glycolic acid along with ThDP regeneration. The released Fe(CN)64- was re-oxidized at +0.5V vs Ag-AgCl and the reaction was followed by chronoamperometry. The TKec/LDH/GCE biosensor was optimized using the best TK donor substrates, namely l-erythrulose and d-fructose-6-phosphate. ThDP was assayed with great sensitivity (3831mAM-1cm-2) over 20-400nM linear range.

Design of Laccase-Metal Organic Framework-Based Bioelectrodes for Biocatalytic Oxygen Reduction Reaction.

Laccase in combination with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator is a well-known bioelectrocatalyst for the 4-electron oxygen reduction reactions (ORR). The present work deals with the first exploitation of mesoporous iron(III) trimesate-based metal organic frameworks (MOF) MIL-100(Fe) (MIL stands for materials from Institut Lavoisier) as a new and efficient immobilization matrix of laccase for the building up of biocathodes for ORR. First, the immobilization of ABTS in the pores of the MOF was studied by combining micro-Raman spectroscopy, X-ray powder diffraction (XRPD), and N2 porosimetry. The ABTS-MIL-100(Fe)-based modified electrode presents excellent properties in terms of charge transfer kinetics and ionic conductivity as well as a very stable and reproducible electrochemical response, showing that MIL-100(Fe) provides a suitable and stabilizing microenvironment for electroactive ABTS molecules. In a second step, laccase was further immobilized on the MIL-100(Fe)-ABTS matrix. The Lac-ABTS-MIL-100(Fe)-CIE bioelectrode presents a high electrocatalytic current density of oxygen reduction and a reproducible electrochemical response characterized by a high stability over a long period of time (3 weeks). These results constitute a significant advance in the field of laccase-based bioelectrocatalysts for ORR. According to our work, it appears that the high catalytic efficiency of Lac-ABTS-MIL-100(Fe) for ORR may result from a synergy of chemical and catalytic properties of MIL-100(Fe) and laccase.

Thin bacteria/Layered Double Hydroxide films using a layer-by-layer approach.

This paper reports the design of thin bacteria/Layered Double Hydroxides (LDH) films in which bacterial cells of Pseudomonas sp. strain ADP were assembled alternatively with Mg2Al-NO3 LDH nanosheets by a layer-by-layer deposition method. The UV-Vis spectroscopy was used to monitor the assembly process, showing a progressive increase in immobilized bacteria amount upon deposited cycles. The {ADP/LDH}n film was characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy and atomic force microscopy. The metabolic activity of immobilized bacteria was determined using chronoamperometry by measuring the biochemical oxygen demand in presence of glucose using an artificial electron acceptor (Fe(CN)6(3-)) at 0.5V/Ag-AgCl. A steady current of 0.250µAcm(-2) was reached in about 30s after the addition of 5mM glucose.

Bacteria encapsulated in layered double hydroxides: towards an efficient bionanohybrid for pollutant degradation.

A soft chemical process was successfully used to immobilize Pseudomonas sp. strain ADP (ADP), a well-known atrazine (herbicide) degrading bacterium, within a Mg2Al-layered double hydroxide host matrix. This approach is based on a simple, quick and ecofriendly direct coprecipitation of metal salts in the presence of a colloidal suspension of bacteria in water. It must be stressed that by this process the mass ratio between inorganic and biological components was easily tuned ranging from 2 to 40. This ratio strongly influenced the biological activity of the bacteria towards atrazine degradation. The better results were obtained for ratios of 10 or lower, leading to an enhanced atrazine degradation rate and percentage compared to free cells. Moreover the biohybrid material maintained this biodegradative activity after four cycles of reutilization and 3 weeks storage at 4°C. The ADP@MgAl-LDH bionanohybrid materials were completely characterized by X-ray diffraction (XRD), FTIR spectroscopy, thermogravimetric analysis and scanning and transmission electronic microscopy (SEM and TEM) evidencing the successful immobilization of ADP within the inorganic matrix. This synthetic approach could be readily extended to other microbial whole-cell immobilization of interest for new developments in biotechnological systems.

HRP/[Zn-Cr-ABTS] redox clay-based biosensor: design and optimization for cyanide detection.

A novel inexpensive and simple amperometric biosensor, based on the immobilization of HRP into redox active [Zn-Cr-ABTS] layered double hydroxide, is applied to the determination of cyanide. The electrochemical transduction step corresponds to the reduction at 0.0 V of ABTS+* enzymatically formed in the presence of H2O2. The biosensor has a fast response to H2O2 (8s) with a linear range of 1.7 x 10(-9) to 2.1 x 10(-6) M and a sensitivity of 875 mA M(-1) cm(-2). The apparent Michaelis-Menten constant (KMapp) is 12 microM. The detection of cyanide is performed via its non competitive inhibiting action on the HRP/[Zn-Cr-ABTS] electrode. The concentration range of the linear response and the apparent inhibition constant (ki) are 5 x 10(-9) to 4 x 10(-8) and 1.4 x 10 (-7) M, respectively.

An efficient amperometric transketolase assay: towards inhibitor screening.

This paper describes an innovative amperometric biosensor for the in vitro determination of activity of transketolase from Escherichia coli (TKec) using commercially available TK substrates, namely d-fructose-6-phosphate a physiological donor and glycolaldehyde the best non-phosphorylated acceptor. A galactose oxidase (GAOx) biosensor, based on the immobilization of this enzyme within laponite clay, allows amperometric detection of L-erythrulose released upon TK-catalyzed reaction. A calibration curve has been established from 0.01 to 0.1 U ml(-1) TKec concentration in solution. These data are comparable to that obtained by a fluorometric method. In order to ensure a higher sensitivity and re-usability of the system, an original bienzymatic sensing system was further developed based on apoenzyme TKec and GAOx separately immobilized on the electrode surface. The inner sensing layer contains GAOx@laponite and the outer layer TKec@layered double hydroxide biohybrid. The biosensor response was validated by the determination of KD(app) for thiamine diphosphate, the TK cofactor and the inhibition action of two commercially available products, pyrophosphate, a TK cofactor analog and d-arabinose-5-phosphate, a substrate analog.

Optimized immobilization of transketolase from E. coli in MgAl-layered double hydroxides.

Immobilization of TK from Escherichia coli (TKec) on MgAl-NO3 layered double hydroxides (LDH) was carried out by two processes: adsorption and coprecipitation. As a comparison, the adsorption method was realized either at pH 7.5 in buffered solutions (MOPS and Gly-Gly) or in pure water. For the coprecipitation method, the formation of the inorganic LDH support was realized directly in the presence of TKec solubilized in Gly-Gly. The prepared biohybrids, called respectively TKec@LDHads and TKec@LDHcop, were characterized by powder X-ray diffraction, FTIR spectroscopy in comparison with TKec free reference products, i.e. MgAl-NO3, MgAl-Gly-Gly. The enzymatic activities of the various TKec@LDH biohybrids as well as their stabilities over time were investigated by UV-vis assay. A maximum of activity (12 U/mg of solid) was reached for TKec@MgAl-Gly-Gly biohybrid prepared by coprecipitation. Finally, thin films were prepared through a one-step deposition on a polished support. The enzymatic activity of the resulting TKec@MgAl-Gly-Glycop film was tested over four recycling processes with a reproducible activity of 2.7 U/mg cm(2).

Electrochemical determination of mesotrione at organoclay modified glassy carbon electrodes.

A natural Cameroonian smectite-type clay (SaNa) was exchanged with cationic surfactants, namely cetyltrimethylammonium (CTA) and didodecyldimethyl ammonium (DDA) modifying its physico-chemical properties. The resulting organoclays that have higher adsorption capacity for mesotrione than the pristine SaNa clay, have been used as modifiers of glassy carbon electrode for the electrochemical detection of this herbicide by square wave voltammetry. The stripping performances of SaNa, SaCTA and SaDDA modified electrodes were therefore evaluated and the experimental parameters were optimized. SaDDA gives the best results in deoxygenated acetate buffer solution (pH 6.0) after 2 min accumulation under open circuit conditions. Under optimal conditions, the reduction current is proportional to mesotrione concentration in the range from 0.25 to 2.5 µM with a detection limit of 0.26 µM. The fabricated electrode was also applied for the commercial formulation CALLISTO, used in European maize market.

LDHs as electrode materials for electrochemical detection and energy storage: supercapacitor, battery and (bio)-sensor.

From an exhaustive overview based on applicative academic literature and patent domain, the relevance of Layered Double Hydroxide (LDHs) as electrode materials for electrochemical detection of organic molecules having environmental or health impact and energy storage is evaluated. Specifically the focus is driven on their application as supercapacitor, alkaline or lithium battery and (bio)-sensor. Inherent to the high versatility of their chemical composition, charge density, anion exchange capability, LDH-based materials are extensively studied and their performances for such applications are reported. Indeed the analytical characteristics (sensitivity and detection limit) of LDH-based electrodes are scrutinized, and their specific capacity or capacitance as electrode battery or supercapacitor materials, are detailed.