The electrochemical properties of LiMn2O4 and LiMyMn2−yO4 false(M=normalTi,normalGe,normalFe,normalZn,normalor Nifalse) were studied for different conditions of sample preparation and different degrees of cation substitution false(yfalse) . In the voltage range 3.5–4.5 V, cells of either spinel LiMn2O4 or λ‐MnO2 (made by leaching the Li from LiMn2O4 ) reversibly insert 0.4 Li per Mn at an average voltage of 4.1 V, leading to an energy density of 480 Wh/kg of cathode. Cells cycled 50 times lost less than 10% of their initial capacity, suggesting that this material could be used instead of LiCoO2 or LiNiO2 as the cathode in the new generation of “rocking chair batteries.” Replacing Mn with cations of valence 2 (Ni, Zn) or 3 (Fe) reduces the amount of Mn+3 and correspondingly reduces the capacity of the cells at 4.1 V, but does not affect their cycling performance.

No abstract

Understanding the formation of sulfate particles in the troposphere is critical because of their health effects and their direct and indirect effects on radiative forcing, and hence on climate. Laboratory studies of the chemical and physical changes in sodium chloride, the major component of sea-salt particles, show that sodium hydroxide is generated upon reaction of deliquesced sodium chloride particles with gas-phase hydroxide. The increase in alkalinity will lead to an increase in the uptake and oxidation of sulfur dioxide to sulfate in sea-salt particles. This chemistry is missing from current models but is consistent with a number of previously unexplained field study observations.

The flow of information through the epidermal growth factor receptor (EGFR) is shaped by molecular interactions in the plasma membrane. The EGFR is associated with lipid rafts, but their role in modulating receptor mobility and subsequent interactions is unclear. To investigate the role of nanoscale rafts in EGFR dynamics, we used single-molecule fluorescence imaging to track individual receptors and their dimerization partner, human epidermal growth factor receptor 2 (HER2), in the membrane of human mammary epithelial cells. We found that the motion of both receptors was interrupted by dwellings within nanodomains. EGFR was significantly less mobile than HER2. This difference was likely due to F-actin because its depolymerization led to similar diffusion patterns between the EGFR and HER2. Manipulations of membrane cholesterol content dramatically altered the diffusion pattern of both receptors. Cholesterol depletion led to almost complete confinement of the receptors, whereas cholesterol enrichment extended the boundaries of the restricted areas. Interestingly, F-actin depolymerization partially restored receptor mobility in cholesterol-depleted membranes. Our observations suggest that membrane cholesterol provides a dynamic environment that facilitates the free motion of EGFR and HER2, possibly by modulating the dynamic state of F-actin. The association of the receptors with lipid rafts could therefore promote their rapid interactions only upon ligand stimulation.

Two-photon, two-color (1+1′) zero-kinetic-energy (ZEKE) photoelectron spectra are presented for the 1:1 phenol-water complex, a prototype system for hydrogen bonding between an aromatic molecule and a simple solvent. ZEKE spectra via different (intermolecular) vibrational intermediate S1 levels of the fully protonated complex (C6H5OH–H2O, h3) as well as the ZEKE spectrum via the vibrationless S1 state of the threefold deuterated complex (C6H5OD–D2O, d3) have been recorded. The spectra are rich in structure, which is mainly attributable to intermolecular vibrations of the ionic complex. Progressions of the intermolecular stretch vibration (240 cm−1) in combination with different intermolecular and intramolecular vibrational levels are the dominant feature of all ZEKE spectra obtained and indicate a large change in the complex geometry along the hydrogen-bond coordinate on ionization. Comparison between the spectrum of the d3 complex and the spectra via different intermediate intermolecular levels of the h3 complex has allowed a more detailed analysis of the intermolecular features compared to previously reported results. Finally, the vibrational assignments obtained are compared with ab initio results for the phenol-water cation reported in the following paper in this issue.

by reaction 2 with a rate constant value5 of k2 -1.3 X 10"m cm3 molecule"1 s"1. The rate constants for the pertaining C2H2-HC-COand CH2('A,) reactions were taken from the current literature;1"9 k values for the less important singlet CH2 removal processes by O and H atoms were estimated to be 1.3 X 10"m and 2.5 X 10"10 cm3 molecule"1 s"1, respectively. The model predicts [CH2('A1)] 4.3 X 109 molecules cm"3 at its t = 2 ms maximum, i.e., nearly equal to the (approximate) measurement.An important additional observation is that at short reaction times (<2 ms) the CH2(1A1) signals vanish upon removing hydrogen from the reaction mixture; this lends support to the proposed singlet CH2 formation reaction 2 and rules out direct formation by the primary C2H2 + O reaction.As anticipated above, the likely mechanism of reaction 2 is an HCCO + H combination process leading to vibrationally excited ketene in the singlet ground state which then rapidly fragments into CH2('A,) + CO. Thus, the mechanism is quite similar to that for ketene photodissociation at 308 nm,18 where CH2 is formed solely in the singlet state.16 There is, however, a difference in the vibrational energy content of the CH^O^'A,) molecule: in the 308-nm photolysis process it is 93 kcal/mol whereas in the chemical activation reaction 2 it is about 105 kcal/mol, using A//f(HCCO) = 42 kcal/mol19 and Ai/f(CH2CO) = -11 kcal/ mol.20 Thus in the latter case the lifetime for fragmentation will be even shorter and hence singlet -triplet intersystem crossing even less probable. Also, the excess energy available to the fragments is only 7 kcal/mol in the 308-nm photolysis,16,17 whereas it is 19 kcal/mol for reaction 2; as a consequence, in the latter process a smaller fraction of the singlet CH2 will arise in the (0,0,0) vibrational ground state.

Pumpprobe photoionization in a supersonic free jet has been used to determine quantum yields and rates of intersystem crossing from the SI state of phenol, phenol-H20, indole, indole-H20, and a variety of substituted indoles. Refined data analysis plus a more complete accounting of photofragmentation has resulted in lower intersystem-crossing quantum yields in phenol and phenol-H20 than previously reported. Intersystem-crossing quantum yields of all the indole compounds studied were found to be similar except for 2,3-dimethylindole for which evidence is presented for the existence of predissociation of the 'Lb origin level.The role of phenyl torsion in the excited-state dynamics of 3-hydroxyflavone (3HF) has been studied by use of time-resolved and static emission spectroscopies. 3HF, 2'-Me-3HF, 4'-Me3HF, and 3-hydroxychromone were studied in aprotic solvents and in 10 K argon matrices. The results show that in all cases excited-state proton transfer occurs very rapidly (

We studied the structure and bonding of a series of silicon oxide clusters, Si 3 O y ͑ y 1 6͒, using anion photoelectron spectroscopy and ab initio calculations. For y 1 3 the clusters represent the sequential oxidation of Si 3 , and provide structural models for the oxidation of silicon surfaces. For y 4 6, the clusters contain a central Si in a tetrahedral bonding environment, suggesting the onset of the bulklike structure. Evidence is presented that suggests the Si 3 O 4 cluster ͑D 2d ͒ may provide a structural model for oxygen-deficient defect sites in bulk SiO 2 materials.