Hervé Vezin

Conjugated dicarboxylate anodes for Li-ion batteries.

Present Li-ion batteries for portable electronics are based on inorganic electrodes. For upcoming large-scale applications the notion of materials sustainability produced by materials made through eco-efficient processes, such as renewable organic electrodes, is crucial. We here report on two organic salts, Li(2)C(8)H(4)O(4) (Li terephthalate) and Li(2)C(6)H(4)O(4)(Li trans-trans-muconate), with carboxylate groups conjugated within the molecular core, which are respectively capable of reacting with two and one extra Li per formula unit at potentials of 0.8 and 1.4 V, giving reversible capacities of 300 and 150 mA h g(-1). The activity is maintained at 80 degrees C with polyethyleneoxide-based electrolytes. A noteworthy advantage of the Li(2)C(8)H(4)O(4) and Li(2)C(6)H(4)O(4) negative electrodes is their enhanced thermal stability over carbon electrodes in 1 M LiPF(6) ethylene carbonate-dimethyl carbonate electrolytes, which should result in safer Li-ion cells. Moreover, as bio-inspired materials, both compounds are the metabolites of aromatic hydrocarbon oxidation, and terephthalic acid is available in abundance from the recycling of polyethylene terephthalate.

Reversible anionic redox chemistry in high-capacity layered-oxide electrodes

Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li(1+x)Ni(y)Co(z)Mn(1-x-y-z)O₂) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li₂Ru(1-y)Sn(y)O₃ materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g(-1). Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M(n+)→M((n+1)+)) and anionic (O(2-)→O₂(2-)) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li₂MO₃ is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials.

2,5-Bis(n-methoxyphenyl)-1,3,4-oxadiazoles used as corrosion inhibitors in acidic media: correlation between inhibition efficiency and chemical structure

Abstract The efficiency of 2,5-bis( n -methoxyphenyl)-1,3,4-oxadiazoles ( n -MOX), as corrosion inhibitors for mild steel in 1 M HCl and 0.5 M H 2 SO 4 have been determined by weight loss measurements and electrochemical studies. The results showed that these inhibitors revealed a good corrosion inhibition even at very low concentrations. Comparison of results among those obtained by the studied oxadiazoles showed that 2-MOX was the best inhibitor. It is found to behave better in 1 M HCl than in 0.5 M H 2 SO 4 . Polarisation curves indicate that 2-MOX is a mixed inhibitor in 1 M HCl, but in 0.5 M H 2 SO 4 , the inhibition mode of 2-MOX depends on the electrode potential and acts essentially as a cathodic inhibitor. The inhibition efficiency slightly increases with temperature in the range from 25 to 60 °C, the associated activation energy have been determined. The addition of 2-MOX leads to decrease this activation energy. The adsorption of 2-MOX on the mild steel surface in both acidic media follows a Langmuir isotherm model. Significant correlations are obtained between inhibition efficiency with the calculated chemical indexes, indicating that variation of inhibition with structure of the inhibitors may be explained in terms of electronic properties.

Low-potential sodium insertion in a nasicon-type structure through the Ti(III)/Ti(II) redox couple

We report the direct synthesis of powder Na3Ti2(PO4)3 together with its low-potential electrochemical performance and crystal structure elucidation for the reduced and oxidized phases. First-principles calculations at the density functional theory level have been performed to gain further insight into the electrochemistry of Ti(IV)/Ti(III) and Ti(III)/Ti(II) redox couples in these sodium superionic conductor (NASICON) compounds. Finally, we have validated the concept of full-titanium-based sodium ion cells through the assembly of symmetric cells involving Na3Ti2(PO4)3 as both positive and negative electrode materials operating at an average potential of 1.7 V.

The antimalarial ferroquine: role of the metal and intramolecular hydrogen bond in activity and resistance.

Inhibition of hemozoin biocrystallization is considered the main mechanism of action of 4-aminoquinoline antimalarials including chloroquine (CQ) but cannot fully explain the activity of ferroquine (FQ) which has been related to redox properties and intramolecular hydrogen bonding. Analogues of FQ, methylferroquine (Me-FQ), ruthenoquine (RQ), and methylruthenoquine (Me-RQ), were prepared. Combination of physicochemical and molecular modeling methods showed that FQ and RQ favor intramolecular hydrogen bonding between the 4-aminoquinoline NH group and the terminal amino group in the absence of water, suggesting that this structure may enhance its passage through the membrane. This was further supported by the use of Me-FQ and Me-RQ where the intramolecular hydrogen bond cannot be formed. Docking studies suggest that FQ can interact specifically with the {0,0,1} and {1,0,0} faces of hemozoin, blocking crystal growth. With respect to the structure-activity relationship, the antimalarial activity on 15 different P. falciparum strains showed that the activity of FQ and RQ were correlated with each other but not with CQ, confirming lack of cross resistance. Conversely, Me-FQ and Me-RQ showed significant cross-resistance with CQ. Mutations or copy number of pfcrt, pfmrp, pfmdr1, pfmdr2, or pfnhe-1 did not exhibit significant correlations with the IC(50) of FQ or RQ. We next showed that FQ and Me-FQ were able to generate hydroxyl radicals, whereas RQ and me-RQ did not. Ultrastructural studies revealed that FQ and Me-FQ but not RQ or Me-RQ break down the parasite digestive vacuole membrane, which could be related to the ability of the former to generate hydroxyl radicals.

Investigation of the inhibitive effect of substituted oxadiazoles on the corrosion of mild steel in HCl medium

Abstract The influence of 2,5-bis(4-nitrophenyl)-1,3,4-oxadiazole (PNOX) and 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (PAOX) on the corrosion of mild steel in hydrochloric acid was studied in relation to the concentration of oxadiazoles using various electrochemical techniques and weight loss measurements. The results showed that PAOX inhibited the corrosion of mild steel in 1 M HCl whereas PNOX accelerated it. PAOX suppressed both cathodic and anodic processes of steel corrosion in 1 M HCl by its chemisorption on the surface via sharing electrons between nitrogen or oxygen and iron atoms. PAOX was adsorbed on the mild steel surface according to a Langmuir isotherm adsorption model. The electronic properties of PNOX and PAOX obtained by using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies.

Linear resistance model of the inhibition mechanism of steel in HCl by triazole and oxadiazole derivatives: structure–activity correlations

A quantum chemical study of the corrosion inhibition efficiency of triazole and oxadiazole derivatives, at the mild steel electrode, in molar hydrochloric acid (1 M HCl) was carried out. The correlation between the molecular structure and inhibition efficiency of these heterocyclic compounds was investigated using a linear model encompassing the charge transfer resistance (Rt). The linear resistance model was optimised with the semi-empirical quantitative structure–activity relationships approach. Regression equations, with multiple correlation coefficients superior at 0.90, were derived between 1/Rt and molecular descriptors. These significant correlations indicated that the variation of the corrosion inhibition with the structure of the inhibitors may be explained in terms of electronic properties.

Electrochemical characterization of lithium 4,4′-tolane-dicarboxylate for use as a negative electrode in Li-ion batteries

Lithium 4,4′-tolane-dicarboxylate has been synthesized and examined for use as a negative electrode material in lithium ion batteries. Cycling studies in Swagelok cells, using lithium as a counter electrode, show a reversible capacity of ∼200 mAh g−1 at ∼0.65 V and minimal discharge/charge polarization (∼15 mV). XRD and SEM analyses reveal that the material crystallizes in two different ways depending on the type of solvent used in the synthesis. The changes in structural packing with methanol or ethanol dramatically affect the capacity of the material leading to electrodes that are able to intercalate almost two vs. one Li per unit formula, respectively.

Beyond the silica surface by direct silicon-29 dynamic nuclear polarization

Buried truth: High-field magic angle spinning dynamic nuclear polarization (MAS DNP) enhances the sensitivity of solid-state NMR spectroscopy, but only for protonated surfaces. Direct 29 Si DNP using the biradical TOTAPOL (see picture) circumvents this limitation by producing a 30-fold enhancement of subsurface 29 Si NMR signals in mesoporous silica, a material with applications in photonics, nanotechnology and catalysis.

Magnesium Chelating 2-Hydroxyisoquinoline-1,3(2H,4H)-diones, as Inhibitors of HIV-1 Integrase and/or the HIV-1 Reverse Transcriptase Ribonuclease H Domain: Discovery of a Novel Selective Inhibitor of the Ribonuclease H Function

2-Hydroxyisoquinoline-1,3(2H,4H)-dione was recently discovered as a scaffold for the inhibition of HIV-1 integrase and the ribonuclease H function of HIV-1 reverse transcriptase. First, we investigate its interaction with Mg(2+) and Mn(2+) using different spectroscopic techniques and report that 2-hydroxyisoquinoline-1,3(2H,4H)-dione forms a 1:1 complex with Mg(2+) but a 1:2 complex with Mn(2+). The complex formation requires enolization of the ligand. ESR spectroscopy shows a redox reaction between the ligand and Mn(2+) producing superoxide anions. Second, 2-hydroxyisoquinoline-1,3(2H,4H)-dione, its magnesium complex, and its 4-methyl and 2-hydroxy-4-methoxycarbonylisoquinoline-1,3(2H,4H)-diones were tested as inhibitors of HIV-1 integrase, reverse transcriptase ribonuclease H, and DNA polymerase functions. Their antiviral activities were evaluated and 2-hydroxy-4-methoxycarbonyl-isoquinoline-1,3(2H,4H)-dione was found to inhibit the viral replication of HIV-1 in MT-4 cells. Cross-resistance was measured for this compound on three different viral strains. Experimental data suggest that the antiviral activity of 2-hydroxy-4-methoxycarbonylisoquinoline-1,3(2H,4H)-dione is probably due to the RNase H inhibition.