Lithium-Oxygen Batteries and Related Systems: Potential, Status, and Future.

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation.

Locating intercalants within lipid bilayers using fluorescence quenching by bromophospholipids and iodophospholipids.

In previous work, we have been able to determine the depth of intercalated molecules within the lipid bilayer using the solvent polarity sensitivity of three spectroscopic techniques: the C NMR chemical shift (δ); the fluorescence emission wavelength (λ), and the ESR β-H splitting constants (a). In the present paper, we use the quenching by a heavy atom (Br or I), situated at a known location along a phospholipid chain, as a probe of the location of a fluorescent moiety. We have synthesized various phospholipids with bromine (or iodine) atoms substituted at various locations along the lipid chain.

Shedding Light on the Oxygen Reduction Reaction Mechanism in Ether-Based Electrolyte Solutions: A Study Using Operando UV-Vis Spectroscopy.

Using UV-vis spectroscopy in conjunction with various electrochemical techniques, we have developed a new effective operando methodology for investigating the oxygen reduction reactions (ORRs) and their mechanisms in nonaqueous solutions. We can follow the in situ formation and presence of superoxide moieties during ORR as a function of solvent, cations, anions, and additives in the solution. Thus, using operando UV-vis spectroscopy, we found evidence for the formation of superoxide radical anions during oxygen reduction in LiTFSI/diglyme electrolyte solutions.

2,4-Dimethoxy-2,4-dimethylpentan-3-one: An Aprotic Solvent Designed for Stability in Li-O Cells.

In this study, we present a new aprotic solvent, 2,4-dimethoxy-2,4-dimethylpentan-3-one (DMDMP), which is designed to resist nucleophilic attack and hydrogen abstraction by reduced oxygen species. Li-O cells using DMDMP solutions were successfully cycled. By various analytical measurements, we showed that even after prolonged cycling only a negligible amount of DMDMP was degraded.

The importance of solvent selection in Li-O cells.

We have examined the effect of glyme selection on the cycling behavior of Li-O cells. We conclude that diglyme is the optimal solvent for prolonged cycling. We have also focused on the effect of electrolyte solution instability as compared to other cell components.

Feasibility of Full (Li-Ion)-O Cells Comprised of Hard Carbon Anodes.

Aprotic Li-O battery is an exciting concept. The enormous theoretical energy density and cell assembly simplicity make this technology very appealing. Nevertheless, the instability of the cell components, such as cathode, anode, and electrolyte solution during cycling, does not allow this technology to be fully commercialized.

Mechanistic Role of Li⁺ Dissociation Level in Aprotic Li-O₂ Battery.

The kinetics and thermodynamics of oxygen reduction reactions (ORR) in aprotic Li electrolyte were shown to be highly dependent on the surrounding chemical environment and electrochemical conditions. Numerous reports have demonstrated the importance of high donor number (DN) solvents for enhanced ORR, and attributed this phenomenon to the stabilizing interactions between the reduced oxygen species and the solvent molecules. We focus herein on the often overlooked effect of the Li salt used in the electrolyte solution.

Catalytic Behavior of Lithium Nitrate in Li-O2 Cells.

The development of a successful Li-O2 battery depends to a large extent on the discovery of electrolyte solutions that remain chemically stable through the reduction and oxidation reactions that occur during cell operations. The influence of the electrolyte anions on the behavior of Li-O2 cells was thought to be negligible. However, it has recently been suggested that specific anions can have a dramatic effect on the chemistry of a Li-O2 cell.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer. Part V: a comparison of liposomes, bioliposomes and erythrocyte ghosts.

Afri et al. (2014a,b) have recently reported their mapping of DMPC liposomes using (13)C NMR in conjunction with a wide range of difunctional intercalants: n-ketoesters, n-ketoacids and n-ketophosphatidylcholines. The present study initiates a comparable study of bioliposomes and erythrocyte ghosts.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer: Part III: studies on keto esters and acids.

The development of "molecular rulers" would allow one to quantitatively locate the penetration depth of intercalants within lipid bilayers. To this end, an attempt was made to correlate the (13)C NMR chemical shift of polarizable "reporter" carbons (e.g.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer. Part IV: studies on ketophospholipids.

In our companion paper, we described the preparation and intercalation of two homologous series of dicarbonyl compounds, methyl n-oxooctadecanoates and the corresponding n-oxooctadecanoic acids (n=4-16), into DMPC liposomes. (13)C NMR chemical shift of the various carbonyls was analyzed using an E(T)(30) solvent polarity-chemical shift correlation table and the corresponding calculated penetration depth (in Å). An iterative best fit analysis of the data points revealed an exponential correlation between E(T)(30) micropolarity and the penetration depth (in Å) into the liposomal bilayer.

On the Challenge of Electrolyte Solutions for Li-Air Batteries: Monitoring Oxygen Reduction and Related Reactions in Polyether Solutions by Spectroscopy and EQCM.

Polyether solvents are considered interesting and important candidates for Li-O2 battery systems. Discharge of Li-O2 battery systems forms Li oxides. Their mechanism of formation is complex.

1,1-diamino-2,2-dinitroethylenes are always zwitterions.

The nitration of tetraiodoethylene (7) yields 1,1-diiodo-2,2-dinitroethylene (8). The latter reacts with alkylamines 9 or alkyldiamines 11 to give the corresponding acyclic 1,1-diamino-2,2-dinitroethylenes 10 or their cyclic analogs 12, respectively. On the basis of liquid and solid-state (13)C and (15)N NMR data, x-ray analysis and ab initio calculations, we suggest that the title compounds are always zwitterionic and that the C(A)-C(N) bond is not a true double bond.

The effect of intercalants on the host liposome.

When phospholipids are vigorously dispersed in water, liposomes are formed. In the present study, we have explored the effect of intercalant concentration on various properties of unilamellar liposomes. Liposomes were sonically intercalated with vitamin E acetate (VitEAc) and hypericin (Hy) until no difference in light transmission was observed, which reflects the formation of liposomes of minimal diameter.

Using fluorescence to locate intercalants within the lipid bilayer of liposomes, bioliposomes and erythrocyte ghosts.

In previous work, we have shown the utility of the "NMR technique" in locating intercalants within the lipid bilayer. We describe herein the development of a more sensitive and complementary "fluorescence technique" for this purpose and its application to liposomes, bioliposomes and erythrocyte ghosts. This technique is based on the observation in selected compounds of an excellent correlation between the emission wavelength (λ(em)) and Dimroth-Reichardt E(T)(30) polarity parameter for the solvent in which the fluorescence emission spectrum was obtained.

A reinvestigation of the reaction of coumarins with superoxide in the liposomal bilayer: correlation between depth and reactivity.

Afri et al. reported in this journal (Free Radic. Biol.

A simple, safe and efficient synthesis of Tyrian purple (6,6'-dibromoindigo).

6,6'-Dibromoindigo is a major component of the historic pigment Tyrian purple, arguably the most famous dye of antiquity. Over the last century, chemists have been interested in developing practical syntheses of the compound We describe herein a new, reasonably simple and efficient synthesis of Tyrian purple which opens the way to the production of large quantities of the dye with minimal hazards and at low cost.

Preparation of Tyrian purple (6,6'-dibromoindigo): past and present.

Over the past century, various synthetic approaches have been suggested to the most famous dye of antiquity, Tyrian purple (6,6'-dibromoindigo). These synthetic routes have been exhaustively surveyed and critically evaluated from the perspective of convenience, cost, safety and yield.

Determining radical penetration into membranes using ESR splitting constants.

Determination of the depth of radical penetration into a lipid membrane is critical to the understanding of the role membranes play in radical attack. We have previously studied radical penetration into lipid bilayers using novel lipophilic spin traps and a combination of NMR and ESR techniques. We now focus on erythrocyte ghost (EG) membranes.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer Part II. The preparation of a molecular ruler.

We have previously shown how the location of an intercalant within the lipid bilayer can be qualitatively determined by using the excellent correlation that exists between the 13C NMR chemical shift of a polarizable carbon (e.g., the carbonyl or nitronyl carbon) and the polarity (using the Dimroth-Reichardt's ET(30) parameter) of the microenvironment in which that carbon resides.

Aggregate formation in the intercalation of long-chain fatty acid esters into liposomes.

Various hydrophobic benzenediacetic esters, the corresponding benzenedipropionic esters, and branched alkyl esters were intercalated into DMPC liposomes, where the molar ratio (n/n) of ester:DMPC was 1:5. In the case of the very long-chain derivatives, double carbonyl peaks were observed in the 13C NMR spectrum. This doubling phenomenon was observed only for the carbonyl peaks, whose chemical shift is most sensitive to solvent polarity, and disappeared when the ester:DMPC molar ratio drops below 1:15.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer Part I. Discovering the guidelines.

The development of "molecular rulers" would allow one to quantitatively locate intercalants within the liposomal bilayer. To this end, we have attempted to correlate the 13C NMR chemical shift of a polarizable "reporter" carbon (e.g.

Determining radical penetration of lipid bilayers with new lipophilic spin traps.

Predicting the susceptibility of lipid moieties to radical attack requires a determination of the depth of radical penetration into a lipid membrane. We thus synthesized three homologous series of lipophilic spin traps--DMPO analogs 2-alkanoyl-2-methyl-1-pyrroline N-oxides (11) and PBN derivatives 4-alkoxyphenyl N-tert-butylnitrones (18) and 4-alkoxyphenyl N-admantylnitrones (20). The intercalation depth of these spin traps within the liposomal bilayer was determined via the previously reported NMR technique, which correlates the chemical shift and the micropolarity (measured in ET(30) units) experienced by the pivotal nitronyl carbon.

Porphyrin depth in lipid bilayers as determined by iodide and parallax fluorescence quenching methods and its effect on photosensitizing efficiency.

Photosensitization by porphyrins and other tetrapyrrole chromophores is used in biology and medicine to kill cells. This light-triggered generation of singlet oxygen is used to eradicate cancer cells in a process dubbed "photodynamic therapy," or PDT. Most photosensitizers are of amphiphilic character and they partition into cellular lipid membranes.

Active oxygen chemistry within the liposomal bilayer. Part IV: Locating 2',7'-dichlorofluorescein (DCF), 2',7'-dichlorodihydrofluorescein (DCFH) and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) in the lipid bilayer.

2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) is commonly used to detect the generation of reactive oxygen intermediates and for assessing the overall oxidative stress in toxicological phenomenon. It has been suggested that DCFH-DA crosses the cell membrane, subsequently undergoing deacetylation by intracellular esterases. The resulting 2',7'-dichlorodihydrofluorescein (DCFH) is proposed to react with intracellular hydrogen peroxide or other oxidizing ROS to give the fluorescent 2',7'-dichlorofluorescein (DCF).