Hugo E. Gottlieb

Electrolyte Solutions with a Wide Electrochemical Window for Rechargeable Magnesium Batteries

Electrolyte solutions for rechargeable Mg batteries were developed, based on reaction products of phenyl magnesium chloride (PhMgCl) Lewis base and Alcl 3 Lewis acid in ethers. The transmetallation of these ligands forms solutions with Mg x Cl + y and AlCl 4-n Ph n - ions as the major ionic species, as analyzed by multinuclei nuclear magnetic resonance spectroscopy. Tetrahydrofuran (THF) solutions of (PhMgCl) 2 -Alcl 3 exhibit optimal properties: highly reversible Mg deposition (100% cycling efficiency) with low overvoltage: <0.2 V and electrochemical windows wider than 3 V. A specific conductivity of 2-5 X 10 -3 Ω -1 cm -1 could be measured between -10 and 30°C for these solutions, similar to that of standard electrolyte solutions for Li batteries. Mg ions intercalate reversibly with Chevrel phase (Mg x Mo 6 S 8 ) cathodes in these solutions. These systems exhibit high thermal stability. The solutions may enable the use of high voltage, high-capacity Mg insertion materials as cathodes and hence open the door for research and development of high-energy density, rechargeable Mg batteries.

The antioxidant activity of aqueous spinach extract: chemical identification of active fractions

In previous studies we have elucidated the presence of powerful, natural antioxidants (NAO) in water extracts of spinach leaves and demonstrated their biological activity in both in vitro and in vivo systems. In the present study, the chemical identity of several of these antioxidant components is presented. Spinach leaves were extracted with water and the 20,000 g supernatant which contained the antioxidant activity was extracted with a water:acetone (1:9) solution. The 20,000 g supernatant obtained was further purified on reverse phase HPLC using C-8 semi-preparative column. Elution with 0.1% TFA resulted in five hydrophilic peaks. Elution with acetonitrile in TFA resulted in seven additional hydrophobic peaks. All the peaks were detected at 250 nm. All the fractions obtained showed antioxidant activity when tested using three different assays. Based on 1H and 13C NMR spectroscopy four of the hydrophobic fractions were identified as glucuronic acid derivatives of flavonoids and three additional fractions as trans and cis isomers of p-coumaric acid and others as meso-tartarate derivatives of p-coumaric acid. The present study demonstrates for the first time the presence of both flavonoids and p-coumaric acid derivatives as antioxidant components of the aqueous extract of spinach leaves.

Carbon-13 nuclear magnetic resonance spectroscopy of flavonoid and isoflavonoid compounds

Abstract The 13 C NMR spectra of 15 flavonoid and 9 isoflavonoid substances of various ring C oxidiation states were analyzed and their carbon shifts assigned. In the case of 3 terpenic flavones and two glycoflavones linewidths were related qualitatively to molecular segmental motion.

The electrochemical behavior of selected polar aprotic systems

The present work involves a rigorous study of the cathodic reactions of selected polar aprotic solvents including tetrahydrofuran (THF), dimethyxyethane (DME), propylene carbonate (PC) and γ-butyrolactone (BL) on gold electrodes using tetrabutylammonium perchlorate (TBAP) as an electrolyte. Under these conditions, passivation does not occur, therefore a rigorous product analysis could be carried out. 1H NMR, 13C NMR, FT-ir and GCMS in conjuctions with cyclic voltammetry and bulk electrolysis were used in order to study the reduction products and their mechanisms of formation. The reduction pattern of the ethereal systems involves mostly cation (TBA*) reduction to tributylamine butene and butane, PC solutions are reduced mostly to propene and propylene dicarbonate di-anion CH3CH(OCO2−)CH2(OCO2−). BL is reduced to an anion of cyclic β-keto ester. The influence of water contamination was also rigorously studied and found to have a pronounced effect on these reactions. Mechanisms of electroreduction of the above systems are discussed.

13C NMR spectroscopy of neolignans

Abstract The 13 C NMR spectra of 15 neolignans of several structural types and two lignans were analyzed and their carbon shifts assigned. The shifts of pyrogallol ether and ethyl phenyl carbinyl ether models were used in this connection. The stereochemistry of a dimeric sideproduct in the preparation of the latter models was determined by 13 C NMR analysis.

A Detailed Investigation of the Thermal Reactions of LiPF6 Solution in Organic Carbonates Using ARC and DSC

The thermal stability of 1 M LiPF 6 solutions in mixtures of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in the temperature range of 40 to 350°C was studied by accelerating rate calorimeters (ARC) and differential scanning calorimeters (DSC). Nuclear magnetic resonance (NMR) was used to analyze the condensed reaction products at different reaction stages. Studies by DSC and pressure measurements during ARC experiments with LiPF 6 solutions detected a gas-releasing endothermic reaction starting at ∼170°C, involving diethyl carbonate which occurs before a number of exothermic reactions, which follow as the temperature increases. Fluoride ions are released and react with the alkyl carbonate molecules both as bases and as nucleophiles. The bulk analysis by NMR shows that HO-CH 2 -CH 2 -OH, FCH 2 CH 2 -OH, F-CH 2 CH 2 -F, and polymer are major products. Gas analysis by NMR and Fourier transform infrared spectroscopy shows PF 5 , CO 2 , CH 3 F, CH 3 CH 2 F, and H 2 O as major gaseous products of the thermal reaction of these solutions.

5-(12-heptadecenyl)-resorcinol, the major component of the antifungal activity in the peel of mango fruit

Abstract A mixture of5-(12- cis -heptadecenyl)- and 5-pentadecyl-resorcinol was isolated from the peel of mango fruit; it acts as a preformed agent against Alternaria alternata , a fungus responsible for the black spot disease of mango fruits in Israel. The chemical characterization was done by 1 HNMR, 13 CNMR and MS.

Improved Electrolyte Solutions for Rechargeable Magnesium Batteries

Electrolyte solutions of magnesium organo-halo-aluminates in ethers are suitable for rechargeable magnesium batteries as they enable highly reversible electrodeposition for magnesium while they possess a wide electrochemical window (>2.2 V). Adding LiCI or tetrabutylammonium chloride to these solutions considerably improves their ionic conductivity, the kinetics of the Mg deposition-dissolution processes, and the intercalation behavior of Mg x MO 6 S 8 Chevrel cathodes. The dissolution of both salts in the electrolytic solutions involves acid-base reactions with complex species. Multinuclei nuclear magnetic resonance and Raman spectroscopy were used in conjunction with electrochemical techniques to study these systems. The nature of these reactions, their products, and the way they influence the various properties of these solutions, are discussed herein.

The use of accelerating rate calorimetry (ARC) for the study of the thermal reactions of Li-ion battery electrolyte solutions

The thermal stability of 1M LiPF6, LiClO4, LiN(SO2CF2CF3)2 (LiBETI) and LiPF3(CF2CF3)3 (LiFAP) solutions in mixtures of ethylene carbonate, diethyl carbonate and dimethyl carbonate in the temperature range 40–350 8C was studied by ARC and DSC. NMR was used to analyze the reaction products at different reaction stages. The least thermally stable are LiClO4 solutions. LiPF3(CF2CF3)3 solutions showed higher thermal stability than LiPF6 solutions. The highest thermal stability was found for LiN(SO2CF2CF3)2 solutions. Studies by DSC and pressure measurements during ARC experiments with LiPF6 and LiFAP solutions detected an endothermic reaction, which occurs before a number of exothermic reactions as the temperature increases. Fluoride ions are formed and react with the alkyl carbonate molecules both as bases and as nucleophiles. # 2003 Elsevier Science B.V. All rights reserved.

Accumulation of Secondary Carotenoids in Chlorella zofingiensis

Summary We have previously found that in Chlorella emersonii , grown under synergistic conditions of high irradiance and low nitrogen, chlorophyll and primary carotenoids were degraded, whereas secondary carotenoids were produced. In this study Chlorella zofingiensis was cultivated under similar conditions. Maximal growth was achieved in a culture growing under light irradiance of 150 μmol quanta m -2 s -1 and a nitrogen concentration of 0.5 mg/mL of KNO 3 . Higher nitrogen concentrations or higher irradiance inhibited cell division. The secondary carotenoids produced were identified as canthaxanthin (about 30 %) and astaxanthin (about 70 %) in the form of mono- and diesters. Maximal accumulation occurred in cells starved of nitrogen and grown at a light irradiance of 300 μLmol m -2 s -1 . Exposure of a thin layer of algal cells to sunlight resulted in de-esterification of the astaxanthin esters. It is suggested that secondary carotenoids have a photo-protective role, that is, under high light conditions they protect chlorophyll and other photosynthetic pigments against damage.