Towards greener and more sustainable batteries for electrical energy storage.

Ever-growing energy needs and depleting fossil-fuel resources demand the pursuit of sustainable energy alternatives, including both renewable energy sources and sustainable storage technologies. It is therefore essential to incorporate material abundance, eco-efficient synthetic processes and life-cycle analysis into the design of new electrochemical storage systems. At present, a few existing technologies address these issues, but in each case, fundamental and technological hurdles remain to be overcome. Here we provide an overview of the current state of energy storage from a sustainability perspective. We introduce the notion of sustainability through discussion of the energy and environmental costs of state-of-the-art lithium-ion batteries, considering elemental abundance, toxicity, synthetic methods and scalability. With the same themes in mind, we also highlight current and future electrochemical storage systems beyond lithium-ion batteries. The complexity and importance of recycling battery materials is also discussed.

Conformational forces affecting the folding pathways of dendrotoxins I and K from black mamba venom.

The conformations of the major intermediates trapped during the folding of dendrotoxins I and K from venom of black mamba snakes, have been investigated by circular-dichroism spectroscopy. Local alterations to the native, folded conformations are observed in toxins I and K and in a protein of similar sequence, bovine pancreatic trypsin inhibitor. The inability of intermediates (30-51, 14-38) to complete refolding by forming directly the 5-55 disulphide bond is explained. The following observations on the role of secondary structure in the folding of the three proteins are of interest. 1. It is not necessary for the three proteins to acquire elements of secondary structure at the same stage of folding in order to attain similar three-dimensional conformations. 2. The stability of the final folded state is not directly correlated to an early appearance of secondary structure. 3. The degree of secondary structure already present in intermediates (30-51) seems to determine the pathway of refolding preferred by the corresponding protein.

The structure of the abortive nicotinamide adenine dinucleotide-pyruvate-lactate dehydrogenase complex as determined by circular dichroism.

Both ternary complexes consisting of lactate dehydrogenase-NAD+ and pyruvate or alpha ketobutyrate were compared, by means of circular dichroism spectra, with the corresponding binary complexes formed between lactate dehydrogenase and both NAD-pyruvate and NAD-alpha ketobutyrate adducts. Strong differences were observed. They disappeared when the ternary complexes were dissociated by addition of urea. This behaviour is explained by assuming the existence, in the abortive ternary complexes of a NAD+ activated transient form having a partial carbonium ion at position 4. Such a structure may account for the abortive and for the evolutive ternary complexes of the dehydrogenases as well as for the chemical synthesis mechanism of adducts.

Binding of adducts of NAD(P) and enolizable ketones to NAD(P)-dependent dehydrogenases.

Carbonyl compounds such as alpha-ketoglutarate, pyruvate, oxaloacetate, butyraldehyde, acetaldehyde or acetone react with NAD or NADP to give adducts. Binding studies of adducts to dehydrogenases are performed by means of ultraviolet differential spectroscopy, circular dichroism and spectrofluorimetry. The dehydrogenases show a high degree of binding specificity toward the adducts which contain their specific oxidized substrate and their specific coenzyme. The high selectivity of the dehydrogenases for adducts is evidenced by binding studies of NAD(P)-pyruvate and NAD(P)-alpha-ketoglutarate adducts on glutamate dehydrogenase at pH 7.6 and 8.9. Evidence is presented showing that adducts bind to the active site of the enzymes.

Studies of covalent adducts of NAD(P) and enolizable ketones as specific glutamate dehydrogenase inhibitors.

Structural analogues of the reduced coenzymes, NADH or NADPH, of dehydrogenases are prepared by addition of carbonyl compounds including: pyruvate, alpha ketoglutarate, oxaloacetate, butyraldehyde, acetaldehyde and acetone, to the oxidized coenzymes NAD(P). Some of the adducts obtained are specific inhibitors of the glutamate dehydrogenase. The specificity is related to the carbonyl compound used. The high selectivity of the dehydrogenases for adducts is evidenced by inhibition studies of NAD(P)-pyruvate and NAD(P)-alpha ketoglutarate adducts on both activities of glutamate dehydrogenase. The inhibitions are competitive with the reduced coenzymes and the oxidized substrates: adducts could be considered as structures closely related to the ternary complexes of the dehydrogenase.