Two new lithiated phases of V6O13 were formed by carefully tuning the temperature of electrochemical lithiation in a 'coffee-bag' type Li-ion battery at 2.78 V versus Li/Li+. These were studied by single-crystal X-ray diffraction. A phase with the composition Li-2/3 V6O13 was obtained at 308 K with a unit cell three times the volume of the original V6O13 cell. A single crystal discharged at ambient temperature was shown to be LiV6O13 and twice the unit-cell volume of the original V6O13 cell. On lithiation, the structures retain their basic V6O13 structure of alternating single and double layers of VO6 octahedra. The lithium ions occupy chemically equivalent sites, where they coordinate fivefold to O atoms, and associate with the single layers of VO6 octahedra. The insertion of lithium causes a significant elongation of one of the V-O bonds in each structure, which expands from 1.65 to 1.89 Angstrom; this is due to the charge reduction of a specific V atom.

Lithium manganese oxide crystals with composition (Li(0.91)Mn(0.09))Mn(2)O(4) were synthesized by a flux method. The crystals have a structure closely related to that of the cubic spinel LiMn(2)O(4), but 9% of the lithium ions in the tetrahedral 4a site are substituted by Mn(2+) ions. This substitution lowers the average Mn oxidation state below 3.5+, resulting in a Jahn-Teller distortion of the MnO(6) octahedron.

The interdisciplinary area of science and engineering dealing with solid electrolytes and mixed conductors is frequently known as solid-state ionics. It concerns materials that show rapid ionic motion with or without electronic conductivity, from basic science through application. Interest in solid-state ionic materials has continued for the past few decades due to several important, promising applications, such as fuel cells, batteries, sensors, and electrochemical pumps. The principle behind these applications is simply either the Nernst law (as exemplified by Equation 1 in the article by Singhal in this issue) or Faraday's laws of electrochemistry (which connect current flow to mass flow), as applied to a cell consisting of an electrolyte and two electrodes. However, the technological issues are complex, and demands on materials can be very diverse, as illustrated by the five articles in this issue. These articles are based, in part, on the invited talks presented at a symposium in April 1999 on the same subject at Lehigh University to commemorate G.C. Farrington's inauguration as its president.

IntroductionMixed conductors show significant mobility of both electronic and ionic species and were the subject of an earlier review in MRS Bulletin.1 The current review is restricted to those mixed conductors of interest for use in lithium batteries, with an emphasis on commercialization. The first lithium batteries were primary cells using pure lithium anodes and carbon monofluoride or manganese oxide as the cathode. Both were developed in Japan, the former for use in fishing floats and the latter for calculators and similar small devices. Such primary cells based mainly on MnO2 or FeS2 cathodes are still extensively used in watches, cameras, and so on. Lithium primary cells are also the main power source for many medical devices, such as pacemakers. In some of these applications, silver vanadate is the cathode.

We have studied the structme and conductivity of perovskite-type Lao.sSro.2Gao.ssMgo.Js02.825. the new, supe1ior oxygen ion conductor (1, 2) for use as electrolyte in high temperatme solid oxide fuel cells.Since the transpmt prope1ties of substitutionally disordered and oxygen deficient matelials are largely determined by their local structure, which may differ in symmetry from the average long range Clystalline symmetry, we studied the local and average structures of Lao.sSli).2Gao.ssMgo.Js02.825using powderneutr•on and electr•on diffraction and high resolution lattice imaging in TEM.Despite the macroscopic cubic symmetr)' revealed by neuu•on powder diffraction, Lao.sSro.2Gao.ssMgo.Js02.825exhibits a lower symmetry shmt range order evidenced by, firstly, weak and sharp superstr11ctme reflections and, secondly, str•eaks of diffuse scatte1ing in the electr•on diffraction patterns.Neutron powder profile refinement shows that tl1e oxygen nuclei are displaced from tl1e sites of cubic symmetry in a manner similar to tl1at in perovskite-related layered structme of brmvnmille1ite.Them1al stability of the local structmes was studied by high temperature electron diffraction and will be discussed in relation witl1 the conductivity measurements.Modeling of the oxygen mobility was perfmmed using the bond valence method (3).

The structure of a mixed-ion Ba2+-K+ beta-ferrite, Ba0.39K0.39Fe11O17.03, has been determined by X-ray diffraction, and refined in the hexagonal space-group P6(3)/mmc, R(F)=3.4%, R(W)(F-2)=5.9%. At least two possible charge compensation mechanisms could be identified: (i) a Frenkel defect of Fe3+ ions indicating an extra oxygen ion in the conduction plane, and (ii) Fe2+ ions and/or vacancies at Fe3+ ion sites in the spinel block. The K+ ions and most of the Ba2+ ions in the conduction plane are found at a 6(h) site near the 2(d) (Beevers-Ross) site; the remainder of the Ba2+ ions are at a 6(h) site at x approximate to 0.88, y=-x.

A kinetic study of the initial step of the nitrosation of synephrine, N-acetylsynephrine and ephedrine by sodium nitrite has been carried out in acid medium at 31 0 K and ionic strength 0.36 mol dm-3. In order to simplify the reaction, [nitrite] > [amine] has been used. The absorbance changes at 300 nm (synephrine and N-acetylsynephrine) and at 332/323 nm (ephedrine). were measured and then analysed according to the initial rate procedure. The results are interpreted on the basis of a simultaneous nitrosation of the amine and phenolic groups in synephrine. Unlike the early reports the global constants for N-nitrosation (0.142 dm6 mol-2 s-1) and C-nitrosation (3.6 x 10(-4) dm3 mol-1 s-1) obtained at pH 3 in unbuffered medium indicate that the rate of nitrosation of the amino group is one order of magnitude larger than that for the phenolic group.

The transport of proteins into the nucleus requires the recognition of a nuclear localization signal sequence. Several proteins that interact with these sequences have been identified, including one of about 66 kDa. We have prepared antibodies that recognize the 66-kDa nuclear localization signal binding protein (NLSBP) and inhibit nuclear localization in vitro. By immunofluorescence, it is seen that the NLSBP is predominantly cytoplasmic and is distributed peripherally around the nucleus and the microtubule organizing center. There is also a weak punctate staining of the surface of the nucleus. Methanol-fixed cells can also be stained directly with fluorescently labeled karyophilic proteins. These stains reveal the same cytoplasmic structures as anti-NLSBP. The expression of the NLSBP is growth dependent. When cells grown to confluence are examined, the cytoplasmic staining is greatly reduced, leaving the punctate nuclear staining as the predominant feature. In serum-starved cells, very little staining of either the cytoplasm or the nucleus can be seen. Upon simulation by the addition of serum, the original cytoplasmic and nuclear envelope staining is restored. Cells grown in the presence of colchicine or taxol have an altered NLSBP distribution but apparently normal cytoplasmic nuclear transport.

We have isolated a cytoplasmic chaperonin based on its ability to catalyze the folding of denatured beta-actin. The cytoplasmic chaperonin is organized as a multisubunit toroid and requires Mg2+ and ATP for activity. The folding reaction proceeds via the rapid ATP-independent formation of a binary complex, followed by a slower ATP-dependent release of the native product. Electron microscopic observations reveal a striking structural change that occurs upon addition of Mg2+ and ATP. The eukaryotic cytoplasm thus contains a chaperonin that is functionally analagous to its prokaryotic, mitochondrial, and chloroplastic counterparts.

The major components of heterogeneous nuclear ribonucleoprotein (hnRNP) complexes are transcripts of RNA polymerase II and small nuclear (sn) RNAs. The sizes of the complexes and their shapes as judged from electron micrographs depend to a large degree on the method used for their preparation. The principle of this approach is to examine the structures formed between proteins and nucleic acids of defined lengths. Changes in the size and shape of the complexes as the lengths of the nucleic acids increase can be related to a stepwise buildup of the complexes and will reflect their structure and the way in which they are assembled. RNAs of defined lengths and sequences can be easily obtained by in vitro transcription. Homopolymers are useful for reconstitution because they provide simplified model systems that are homogeneous in composition and secondary structure. To obtain defined sizes of homopolymers, a partially hydrolyzed mixture can be separated by electrophoresing through a polyacrylamide gel, cutting the gel, and eluting the fragments of the desired sizes.

Through a series of label transfer experiments, we have identified a HeLa cell nuclear protein that interacts with nuclear localization signals (NLSs). The protein has a molecular weight of 66,000 and an isoelectric point of approximately 6. It associates with a synthetic peptide that contains the SV-40 T antigen NLS peptide but not with an analogous peptide in which an asparagine is substituted for an essential lysine (un-NLS peptide). In addition to these peptides, several proteins have been tested as label donors. With the proteins, there is a correlation between nuclear localization (assayed with lysolecithin-permeabilized cells) and label transfer to the 66-kD protein. The NLS peptide (but not the un-NLS peptide) competes with the proteins in label transfer experiments, but neither wheat germ agglutinin nor ATP has an effect. These results suggest that the 66-kD protein functions as an NLS receptor in the first step of nuclear localization. In the course of this work, we have observed that the Staphylococcus aureus protein A is a strongly karyophilic protein. Its dramatic nuclear localization properties suggest that it may have multiple copies of an NLS.

A cDNA clone which expresses a protein that cross-reacts immunologically with the human C1 and C2 hnRNP core proteins has been isolated. The clone was selected by a sensitive immunochemical assay employing an avidin-biotin complex for detection, and identified as a clone for the hnRNP C proteins by a highly sensitive antibody select assay that is described here. The clone contains 677 nucleotides, and, as shown by northern blotting, is derived from a 1.5 Kb poly(A)+ mRNA. There are regions of strong homology between the human and mouse genes, weak homology is seen with chicken DNA, and very little, if any, homology can be detected with Drosophila, Artemia, sea urchin, or yeast DNAs. Two peptides (a total of 24 amino acids) of the calf thymus single-stranded DNA binding protein UP2 show perfect homology with the deduced amino acid sequence of the clone, suggesting that UP2 is related to the hnRNP C proteins. There is also a region that has a sequence very similar to two regions of the single-stranded DNA binding protein UP1 that contain proposed DNA binding sites.

Using immunochemical techniques, we have examined the macromolecular state of association of the major heterogeneous nuclear ribonucleoprotein (hnRNP) core proteins in mitotic HeLa cells. We find that these proteins are not free but are associated with high-molecular-weight RNA in the form of particles that sediment as a broad band between 80 and 200 S. We have termed these complexes MhnRNP for mitotic hnRNP protein-containing particles. Their quantity, composition, sedimentation coefficients, buoyant density, and sensitivity to dissociating conditions suggest that they are closely related to the hnRNP complexes of interphase cells and may represent hnRNP complexes containing unprocessed or partially processed heterogeneous nuclear RNA that have been released into the cytoplasm during mitosis. Exogenously added RNA does not associate with the MhnRNP nor does it compete for the major MhnRNP proteins. The MhnRNP remain distinct from other ribonucleoprotein complexes and do not associate with ribosomes even though these structures are not separated by a nuclear envelope during mitosis.

This chapter presents a discussion on ribonucleic acid (RNA)-helix-destabilizing proteins. The chapter outlines some aspects of RNA metabolism where the need for helix-destabilizing proteins appears to be evident. The chapter focuses on ribosomal protein S1 from E. coli and protein HD40 from the brine shrimp Artemia salina, a major component of heterogeneous nuclear ribonucleoprotein (hnRNP) particles. In both cases, the in vitro unwinding activity of these proteins can be correlated with their respective functions. The chapter describes the nucleic acid binding and helix-destabilizing properties of protein S1 and HD40. While comparative investigations of analogous proteins from other eukaryotes are needed, HD40 may prove to be a good model for in vitro studies on the structure and function of hnRNP; its physical properties appear to be representative of the glycine-rich core proteins, and it can be purified in relatively large amounts. In contrast to helix-destabilizing proteins participating in dynamic processes that appear to exercise a transient effect on the conformation of the nucleic acid, HD40 is a component of an isolatable nucleoprotein in which the single-stranded RNA is maintained in an unfolded state owing to its interaction with the protein. The chapter recommends the need for in vitro investigations involving purified individual hnRNP proteins and messenger ribonucleic acid (mRNA) precursors along with the development of specific methods for the isolation of native hnRNP.

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Glycine-rich core hnRNP proteins purified from wheat bind tightly to single-stranded but not to double-stranded nucleic acids with a preference for natural RNA over single-stranded DNA. Binding results in i) a progressive disruption of the residual secondary structure of the polynucleotide and the formation of an extended nucleoprotein filament until a protein to polynucleotide weight ratio of about 5:1 is attained. As more protein is added, this is followed by ii) the formation of globular structures along the polynucleotide chain with a concomitant reduction in the contour length of the nucleoprotein complex. These two features of the interaction--unwinding and condensation into beads--are analogous to the previously described behavior of the major glycine-rich core hnRNP protein from Artemia salina (Thomas et al. (1981) Proc. Natl. Acad. Sci. USA 78, 2888) and may represent the basic functional properties of this relatively well conserved group of nuclear proteins.