Morphology of Ion-Containing Polymers: Correlations Between Structure, Dynamics, and Ion Conduction

Ion-containing polymers are of intense interest for applications in energy storage and conversion devices. The conductivities of these polymers are determined by both the ion mobility and the total number of mobile charge carriers, which in turn depend on the chemical structure and morphology. To rationally design ion-containing polymers with high conductivity, a comprehensive understanding of their multi-scale structure is essential. The morphologies of several ion-containing polymers have been explored as a function of material chemistry and external stimuli by X-ray scattering, scanning transmission electron microscopy, and various types of spectroscopy. The fundamental structure-property relationships in ion-containing polymers are discussed. Two classes of ion-containing polymers with very different aggregation behaviors have been studied. The first class is the polystyrene-based ionomers, where there are unfavorable interactions between the polymer matrix and ionic groups. The ionic functional groups in these hydrocarbon-based ionomers self-assemble into ionic aggregates, due to the strong electrostatic interactions in the low dielectric constant matrix and the lack of any solvation interactions between ions and hydrocarbons. The effects of acid content, neutralization level, and cation type on the size, number density, and composition of ionic aggregates were explored. The morphological findings provide a framework for interpreting the dielectric relaxation behaviors of the same ionomers, so as to establish correlations between structure and dynamics. The second class is poly(alkyl oxide)-based ionomers. The ionic groups have favorable interactions with the polymer matrix in poly(ethylene oxide) (PEO)-based polyester ionomers or urethane groups in poly(tetramethylene oxide)-based polyurethane ionomers. The states of ions are highly dependent on the PEO length, cation size and temperature in PEO-based ionomers. Decreasing cation size from Cs to Li results in a transition of ionic states from isolated ion pairs to aggregated ion pairs. As the temperature increases, these ionomers exhibit greater microphase separation of the ionic groups due to the decreased ability of PEO to solvate the ions. These findings combine to greatly advance our understanding of the interplay between morphology and ion conduction in single-ion conductors

Analysis of ADP-glucose pyrophosphorylase expression during turion formation induced by abscisic acid in Spirodela polyrhiza (greater duckweed)

<p>Abstract</p> <p>Background</p> <p>Aquatic plants differ in their development from terrestrial plants in their morphology and physiology, but little is known about the molecular basis of the major phases of their life cycle. Interestingly, in place of seeds of terrestrial plants their dormant phase is represented by turions, which circumvents sexual reproduction. However, like seeds turions provide energy storage for starting the next growing season.</p> <p>Results</p> <p>To begin a characterization of the transition from the growth to the dormant phase we used abscisic acid (ABA), a plant hormone, to induce controlled turion formation in <it>Spirodela polyrhiza </it>and investigated their differentiation from fronds, representing their growth phase, into turions with respect to morphological, ultra-structural characteristics, and starch content. Turions were rich in anthocyanin pigmentation and had a density that submerged them to the bottom of liquid medium. Transmission electron microscopy (TEM) of turions showed in comparison to fronds shrunken vacuoles, smaller intercellular space, and abundant starch granules surrounded by thylakoid membranes. Turions accumulated more than 60% starch in dry mass after two weeks of ABA treatment. To further understand the mechanism of the developmental switch from fronds to turions, we cloned and sequenced the genes of three large-subunit ADP-glucose pyrophosphorylases (<it>APLs</it>). All three putative protein and exon sequences were conserved, but the corresponding genomic sequences were extremely variable mainly due to the invasion of miniature inverted-repeat transposable elements (MITEs) into introns. A molecular three-dimensional model of the SpAPLs was consistent with their regulatory mechanism in the interaction with the substrate (ATP) and allosteric activator (3-PGA) to permit conformational changes of its structure. Gene expression analysis revealed that each gene was associated with distinct temporal expression during turion formation. <it>APL</it>2 and <it>APL</it>3 were highly expressed in earlier stages of turion development, while <it>APL</it>1 expression was reduced throughout turion development.</p> <p>Conclusions</p> <p>These results suggest that the differential expression of <it>APL</it>s could be used to enhance energy flow from photosynthesis to storage of carbon in aquatic plants, making duckweeds a useful alternative biofuel feedstock.</p

Structures and Dynamics in Live Bacteria Revealed by Super-Resolution Fluorescence Microscopy

Light microscopy, in particular fluorescence microscopy, is a widely used imaging method in biological research due to its noninvasive nature and molecular specificity. The resolution of conventional fluorescence microscopy is limited to a few hundred nanometers by the diffraction of light, leaving many biological structures too small to be optically resolved. Stochastic Optical Reconstruction Microscopy (STORM) technique overcomes this limit by localizing single photoswitchable fluorophores separated in time. We further extended the then two-dimensional capability to three-dimensional (3D) STORM by determining both axial and lateral positions of individual fluorophores with nanometer accuracy using optical astigmatism. Iterative, stochastic activation of photo-switchable probes enables high-precision 3D localization of each probe and thus the construction of a 3D image without scanning the sample. We achieved an image resolution of 20 - 30 nm in the lateral dimensions and 50 - 60 nm in the axial dimension. This development allowed us to resolve the 3D morphology of nanoscopic cellular structures. Enabled by the super-resolution imaging capability, we used 3D STORM in conjunction with biochemical assays to study structures and dynamics in live bacteria. Bacterial chromosomes are confined in submicron-sized nucleoids. Chromosome organization is facilitated by nucleoid-associated proteins (NAPs), but the structure of the chromosome and the molecular mechanisms underlying its organization are poorly understood, in part due to the lack of appropriate tools for visualizing the chromosome in vivo. Using STORM, we found that four NAPs, HU, Fis, IHF, and StpA, were largely scattered throughout the E. coli nucleoid. In contrast, H-NS, a global transcriptional silencer, formed two compact clusters per chromosome driven by oligomerization of DNA-bound H-NS, through their N-terminal domain interactions. H-NS sequestered the regulated operons into these clusters and juxtaposed numerous DNA segments broadly distributed throughout the chromosome. Deleting H-NS led to substantial chromosome reorganization. These observations demonstrate that H-NS plays a key role in global chromosome organization in E. coli. Finally, we describe the use of the same sub-diffraction localization for single-particle tracking to study MreB paralogs (actin-like proteins in bacteria) in B. subtilis. We found that MreB and the elongation machinery moved circumferentially around the cell, perpendicular to its length, with nearby synthesis complexes and MreB filaments moving independently in both directions. Inhibition of cell wall synthesis by various methods blocked the movement of MreB. Thus, bacteria elongate by the uncoordinated, circumferential movements of synthetic complexes that insert radial hoops of new peptidoglycan during their transit, possibly driving the motion of the underlying MreB filaments.Physic

The Operculum-Plug Area and Membranous Structure of the Eggs of Trichuris Trichiura

Eggs of Trichuris trichiura were prepared for scanning electron microscopy (SEM) by the dimethylsulfoxide freeze-cracking method. The egg-shell and oocyte were examined by SEM. The egg has a chitinous shell which consists of more than 10 layers of dense lamellae. The shell is bordered by a limiting membrane. An operculum and a collar made of chitinous shell together form the opercular area. The operculum is an empty cavity. The chitinous fibers of the egg-shell in this area are diffuse and loose, with numerous micropores or spaces. The egg-shell in this area therefore appears to form a fine tubular network. The oocyte is an undifferentiated cell with a biconcave drum-like shape. The perivitelline space is conspicuous at both ends of the cell

Long-term Orbital Period Variation of Hot Jupiters from Transiting Time Analysis using TESS Survey Data

Many hot Jupiters may experience orbital decays, which are manifested as long-term transit timing variations. We have analyzed 7068 transits from the Transiting Exoplanet Survey Satellite (TESS) for a sample of 326 hot Jupiters. These new mid-transit time data allow us to update ephemerides for these systems. By combining the new TESS transit timing data with archival data, we search for possible long-term orbital period variations in these hot Jupiters using a linear and a quadratic ephemeris model. We identified 26 candidates that exhibit possible long-term orbital period variations, including 18 candidates with decreasing orbital periods and 8 candidates with increasing orbital periods. Among them, 12 candidates have failed in our leave-one-out cross-validation (LOOCV) test and thus should be considered as marginal candidates. In addition to tidal interaction, alternative mechanisms such as apsidal precession, R{\o}mer effect, and Applegate effect could also contribute to the observed period variations. The ephemerides derived in this work are useful for scheduling follow-up observations for these hot Jupiters in the future. The Python code used to generate the ephemerides is made available online.Comment: Accepted for publication in ApJ

Balancing of sulfur storage in maize seed

Abstract Background A balanced composition of amino acids in seed flour is critical because of the demand on essential amino acids for nutrition. However, seed proteins in cereals like maize, the crop with the highest yield, are low in lysine, tryptophan, and methionine. Although supplementation with legumes like soybean can compensate lysine deficiency, both crops are also relatively low in methionine. Therefore, understanding the mechanism of methionine accumulation in the seed could be a basis for breeding cultivars with superior nutritional quality. Results In maize (Zea mays), the 22- and 19-kDa α-zeins are the most prominent storage proteins, nearly devoid of lysine and methionine. Although silencing synthesis of these proteins through RNA interference (RNAi) raises lysine levels in the seed, it fails to do so for methionine. Computational analysis of annotated gene models suggests that about 57% of all proteins exhibit a lysine content of more than 4%, whereas the percentage of proteins with methionine above 4% is only around 8%. To compensate for this low representation, maize seeds produce specialized storage proteins, the 15-kDa β-, 18-kDa and 10-kDa δ-zeins, rich in methionine. However, they are expressed at variant levels in different inbred lines. A654, an inbred with null δ-zein alleles, methionine levels are significantly lower than when the two intact δ-zein alleles are introgressed. Further silencing of β-zein results in dramatic reduction in methionine levels, indicating that β- and δ-zeins are the main sink of methionine in maize seed. Overexpression of the 10-kDa δ-zein can increase the methionine level, but protein analysis by SDS-PAGE shows that the increased methionine levels occur at least in part at the expense of cysteines present in β- and γ-zeins. The reverse is true when β- and γ-zein expression is silenced through RNAi, then 10-kDa δ-zein accumulates to higher levels. Conclusions Because methionine receives the sulfur moiety from cysteine, it appears that when seed protein synthesis of cysteine-rich proteins is blocked, the synthesis of methionine-rich seed proteins is induced, probably at the translational level. The same is true, when methionine-rich proteins are overexpressed, synthesis of cysteine-rich proteins is reduced, probably also at the translational level. Although we only hypothesize a translational control of protein synthesis at this time, there are well known paradigms of how amino acid concentration can play a role in differential gene expression. The latter we think is largely controlled by the flux of reduced sulfur during plant growth.</p

Apoptosis of human tongue squamous cell carcinoma cell (CAL-27) induced by Lactobacillus sp. A-2 metabolites

Objective: To study the effect of Lactobacillus sp. A-2 metabolites on viability of CAL-27 cells and apoptosis in CAL-27 cells. Methods: Lactobacillus sp. A-2 metabolites 1 and 2 (LM1 and LM2) were obtained by culturing Lactobacillus sp. A-2 in reconstituted whey medium and whey-inulin medium; the cultured CAL-27 cells were treated with different concentrations of LM1 and LM2 (0, 3, 6, 12, 24, 48 mg/mL) and assayed by methyl thiazolyltetrazolium (MTT) method; morphological changes of apoptotic cell were observed under fluorescence microscopy by acridine orange (Ao) fluorescent staining; flow cytometry method (FCM) and agarose gel electrophoresis were used to detect the apoptosis of CAL-27 cells treated LM1 and LM2. Results: The different concentrations of LM1 and LM2 could restrain the growth of CAL-27 cells, and in a dose-dependent manner; the apoptosis of CAL-27 cells was obviously induced and was time-dependent. Conclusions: Viability of CAL-27 cells was inhibited by Lactobacillus sp. A-2 metabolites; Lactobacillus sp. A-2 metabolites could induce CAL-27 cells apoptosis; study on the bioactive compounds in the Lactobacillus sp. A-2 metabolites and their molecular mechanism is in progress

The multivalent adhesion molecule SSO1327 plays a key role in Shigella sonnei pathogenesis : SSO1327 is an adhesin required for S. sonnei pathogenesis

Shigella sonnei is a bacterial pathogen and causative agent of bacillary dysentery. It deploys a type III secretion system to inject effector proteins into host epithelial cells and macrophages, an essential step for tissue invasion and immune evasion. Although the arsenal of bacterial effectors and their cellular targets have been studied extensively, little is known about the prerequisites for deployment of type III secreted proteins during infection. Here, we describe a novel S. sonnei adhesin, SSO1327 which is a Multivalent Adhesion Molecule (MAM) required for invasion of epithelial cells and macrophages and for infection in vivo. The S. sonnei MAM mediates intimate attachment to host cells, which is required for efficient translocation of type III effectors into host cells. SSO1327 is non-redundant to IcsA; its activity is independent of type III secretion. In contrast to the up-regulation of IcsA-dependent and independent attachment and invasion by deoxycholate in S. flexneri, deoxycholate negatively regulates IcsA and MAM in S. sonnei resulting in reduction in attachment and invasion and virulence attenuation in vivo. A strain deficient for SSO1327 is avirulent in vivo but still elicits a host immune response