Understanding Performance Degradation in Cation‐Disordered Rock‐Salt Oxide Cathodes

The collective redox activities of transition‐metal (TM) cations and oxygen anions have been shown to increase charge storage capacity in both Li‐rich layered and cation‐disordered rock‐salt cathodes. Repeated cycling involving anionic redox is known to trigger TM migration and phase transformation in layered Li‐ and Mn‐rich (LMR) oxides, however, detailed mechanistic understanding on the recently discovered Li‐rich rock‐salt cathodes is largely missing. The present study systematically investigates the effect of oxygen redox on a Li_1.3Nb_0.3Mn_0.4O₂ cathode and demonstrates that performance deterioration is directly correlated to the extent of oxygen redox. It is shown that voltage fade and hysteresis begin only after initiating anionic redox at high voltages, which grows progressively with either deeper oxidation of oxygen at higher potential or extended cycling. In contrast to what is reported on layered LMR oxides, extensive TM reduction is observed but phase transition is not detected in the cycled oxide. A densification/degradation mechanism is proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation‐disordered rock‐salts can lead to performance degradation in these newer cathodes with 3D Li migration pathways. Design strategies to achieve balanced capacity and stability are also discussed.     

Electrooptical analysis of blue and of cation-regenerated bacteriorhodopsin

Blue bacteriorhodopsin was prepared by electrodialysis, cation-exchange chromatography and acidification. The electrooptical properties of these preparations compared to those of the native purple bacteriorhodopsin suggest that the blue bacteriorhodopsin has a smaller induced dipole moment than the native purple bacteriorhodopsin and that bound cations in the native bacteriorhodopsin stabilize the protein conformation in the membrane.Purple bacteriorhodopsin was regenerated by addition of potassium, magnesium or ferric ions to blue bacteriorhodopsin. Both spectrscopically and electrooptically the potassium- and ferric-regenerated samples are different from the native purple state. Although the magnesium-regenerated sample is spectroscopically similar to the native purple bacteriorhodopsin, the electrooptical properties are rather similar to those of the cation-depleted blue sample, suggesting that it is very difficult to re-stabilize protein structures once cations are depleted.     

Ionic balance,proton efflux,nitrate reductase activity and growth ofHippophaë rhamnoides L. ssp.rhamnoides as influenced by combined-N nutrition or N2 fixation

Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N₂ fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH ₄ ⁺ , a mixture of NH ₄ ⁺ and NO ₃ ^? producing the highest yields. Growth was severely reduced when solely dependent on N₂ fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N₂-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO ₃ ^? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO ₃ ^? and NH ₄ ⁺ , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH ₄ ⁺ , NO ₃ ^? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO ₃ ^? +NH ₄ ⁺ plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH ₄ ⁺ plants than in the NO ₃ ^? plants. Measured extrusions of H⁺ or OH^? (HCO ₃ ^? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N₂ fixation amounted to 0.45–0.55 meq H⁺. (mmol N_org)^?1. Without acidity control and in the presence of NH ₄ ⁺ , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N₂-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.     

Chick brain glutamine synthetase and Mn2+−Mg2+ interactions

Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg²⁺ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca²⁺, Co²⁺, Fe²⁺, Li⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺) only Co²⁺, Mg²⁺ and Mn²⁺ supported GS activity; the order of activatory ability was Mg²⁺>Co²⁺>Mn²⁺. The maximum activating effect of Mn²⁺ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn²⁺, modulates the Mg²⁺ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis.     

Salinity and germination of annual Melilotus from the Guadalquivir delta (SW Spain)

The germination response to NaCl treatments has been studied in Melilotus seed populations collected from saline and non-saline soils in the Guadalquivir delta. The rank orders for salt tolerance and seed weight were the same in the threeMelilotus species living in this area:Melilotus messanensis>M. segetalis>M. indica. Within the species, differences in germination response to salinity were found inM. indica (6 populations) andM. segetalis (8 populations). The relationship between salt tolerance during germination and salinity of maternal habitat is discussed.     

Roles of proteins in cation/membrane interactions of isolated rat cardiac sarcolemmal vesicles

To ascertain the roles of the membrane proteins in cation/sarcolemmal membrane binding, isolated rat cardiac sarcolemmal vesicles were extensively treated with Protease (S. aureus strain V.8). SDS-gel electrophoresis, protein and phosphate analysis confirmed that at least 20–22% of the protein, but none of the phospholipid, was solubilized by this procedure, and that the remaining membrane proteins were extensively hydrolyzed into small fragments. The cation binding properties of the treated vesicles were then examined by analyzing their aggregation behavior. The results demonstrate that this procedure had no effect on the selectivity series for di- and trivalent cation binding, or the divalent cation-induced aggregation behavior of the sarcolemmal vesicles at different pHs, indicating that proteins are probably not involved in these interactions and cannot be the low affinity cation binding sites previously observed [21, 22]. It did, however, change the pH at which protons induced sarcolemmal vesicle aggregation, suggesting a possible role for proteins in these processes. Protease treatment also modified the effects of fluorescamine labelling on divalent cation-induced vesicle aggregation, indicating that the NH, groups being labelled with fluorescamine are located on the sarcolemmal proteins. Together, these results support the hypothesis that di- and trivalent cation binding to the sarcolemmal membrane is largely determined by lipid/lipid and/or lipid/carbohydrate interactions within the plane of the sarcolemmal membrane, and that membrane proteins may exert an influence on these interactions, but only under very specialized conditions.Abbreviations MES 2-(N-morpholino)ethanesulfonic acid - MOPS 3-(N-morpholino) propanesulfonic acid - HEPES N-2-Hydroxyethylpiperizine-N-2- ethanesulfonic acid - CHES 2(N-Cyclohexylamino) ethanesulfonic acid - DTT DL-Dithiothreitol - PMSF Phenylmethyl-sulfonyl fluoride     

Calcium ion transport across discs of the cortical flesh of apple fruit in relation to fruit development

Transport of Ca²⁺ through discs of apple fruit tissue was examined in tissue taken at different stages of fruit development. Transport rates decreased with fruit development when cation exchange was the predominant influence on transport (with 10⁻⁶ M ⁴⁵CaCl₂ as the source solution). This decrease was associated with a reduction in relative cell wall surface area, cation exchange capacity and cell wall yield that occurred during fruit growth. When diffusion was the major transport force, and when transport was influenced by solution infiltration of the tissue disc (10⁻² M ⁴⁵CaCl₂ in the source solution), transport rates increased during fruit growth. This increment was related to increases in air space of the tissue. Ca²⁺ transport through apple fruit tissue is influenced by the extent and nature of the cell wall, changing proportions of air space and Ca²⁺ concentration in the extracellular solution.     

Voltage-dependent channels permeable to K+ and Na+ in the membrane ofAcer pseudoplatanus vacuoles

Summary The patch-clamp technique in whole-cell configuration was used to study the electrical properties of the tonoplast in isolated vacuoles fromAcer pseudoplatanus cultured cells. In symmetrical KCl or K₂ malate solutions, voltage- and time-dependent inward currents were elicited by hyperpolarizing the tonoplast (inside negative), while in the positive range of potential the conductance was very small. The specific conductance of the tonoplast at –100 mV, in 100mm symmetrical KCl was about 160 S/cm². The reversal potentials (E _rev) of the current, measured in symmetrical or asymmetrical ion concentrations (cation, anion or both) were very close to the values of the K⁺ equilibrium potential. Experiments performed in symmetrical or asymmetrical NaCl indicate that Na⁺ too can flow through the channels. NeitherE _rev nor amplitude and kinetics of the current changed by replacing NaCl with KCl in the external solution. These results indicate the presence of hyperpolarization-activated channels in tonoplasts, which are permeable to K⁺ as well as to Na⁺. Anions such as Cl^– or malate seem to contribute little to the channel current.     

Acclimatation sur la côte d'azur et en corse deSerangium parcesetosum [Col.: Coccinellidae] prédateur de l'aleurode des citrus,Dialeurodes citri [Hom.: Aleyrodidae]

Résumé La CoccinelleSerangium parcesetosum Sicard originaire de l'Inde a été importée en France en 1985 de Géorgie soviétique où elle avait été introduite pour lutter contre l'Aleurode des CitrusDialeurodes citri Ashmead. Les premiers lachers ont été effectués sur la C?te d'Azur et en Corse où elle semble désormais bien acclimatée.      

Paradise lost: Mitochondrial eve refuted

Being based solely on neontological data, all «unique parent» evolutionary hypotheses, of which «Mitochondrial Eve» is one, fall into the category ofscala naturae. Mathematical treatment of neontological data bases, using cladistic approaches does not confer the status of scientific hypotheses onto such scenarios. Apart from these fundamental problems, such hypotheses are flawed on a number of other bases, including the fact that there is a proportion of parental contribution to mitochondrial lineages, despite widely publicised statements that mithocondrial DNA in mammals is «strictly» maternally inherited. Other weaknesses of «unique mother» hypotheses on that their proponents endeavour to describe the evolution of diploid organisms on the basis of variability in extant haploid organelles, the evolution of which is delinked from that of the diploid organism. A further difficulty is that it is not possible to reconstruct interspecific relationships on the basis of intraspecific variability. There is a general ignorance among proponents of «unique mother» hypotheses regarding the distribution of biological variability on the surface of the globe, a fact which renders the molecular clock inaccurate, and which upsets the simplistic proposal that molecular diversity equates with time. «Unique mother» scenarios are also invalidated by the presence of shared chromosome and other polymorphisms in african great apes and humans at similar percentages in the different lineages, a fact which indicates that these evolving populations did not experience «bottlenecks». These and other difficulties effectively refute the «Mitochondrial Eve» hypothesis, which in any case much resembles creationism of a special kind, in which the offspring of a breeding pair are visualised as belonging to a species different from its parents. Such extreme examples of the punctuational mode of evolution are highly likely to be incorrect.