Progress in magnetoelectric materials is hindered by apparently contradictory requirements for time-reversal symmetry broken and polar ferroelectric electronic structure in common ferromagnets and antiferromagnets. Alternative routes can be provided by recent discoveries of a time-reversal symmetry breaking anomalous Hall effect (AHE) in noncollinear magnets and altermagnets, but hitherto reported bulk materials are not polar. Here, the authors report the observation of a spontaneous AHE in doped AgCrSe2 , a layered polar semiconductor with an antiferromagnetic coupling between Cr spins in adjacent layers. The anomalous Hall resistivity 3 μ Ω c m $\mu \Omega \, \textnormal {cm}$ is comparable to the largest observed in compensated magnetic systems to date, and is rapidly switched off when the angle of an applied magnetic field is rotated to ≈80° from the crystalline c-axis. The ionic gating experiments show that the anomalous Hall conductivity magnitude can be enhanced by modulating the p-type carrier density. They also present theoretical results that suggest the AHE is driven by Berry curvature due to noncollinear antiferromagnetic correlations among Cr spins, which are consistent with the previously suggested magnetic ordering in AgCrSe2 . The results open the possibility to study the interplay of magnetic and ferroelectric-like responses in this fascinating class of materials.

• Keywords
• Berry curvature, anomalous Hall effect, ionic gating, magnetism, polar structure,
• Publication type
• Journal Article MeSH

Humic substances (HS) in soil are widely distributed in cold environments and account for a significant fraction of soil's organic carbon. Bacterial strains (n = 281) were isolated at 15 °C using medium containing humic acids (HA), a principal component of HS, from a variety of polar soil samples: 217 from the Antarctic and 64 from the Arctic. We identified 73 potential HA-degrading bacteria based on 16S rRNA sequence similarity, and these sequences were affiliated with phyla Proteobacteria (73.9%), Actinobacteria (20.5%), and Bacteroidetes (5.5%). HA-degrading strains were further classified into the genera Pseudomonas (51 strains), Rhodococcus (10 strains), or others (12 strains). Most strains degraded HA between 10 and 25 °C, but not above 30 °C, indicating cold-adapted degradation. Thirty unique laccase-like multicopper oxidase (LMCO) gene fragments were PCR-amplified from 71% of the 73 HA-degrading bacterial strains, all of which included conserved copper-binding regions (CBR) I and II, both essential for laccase activity. Bacterial LMCO sequences differed from known fungal laccases; for example, a cysteine residue between CBR I and CBR II in fungal laccases was not detected in bacterial LMCOs. This suggests a bacterial biomarker role for LMCO to predict changes in HS-degradation rates in tundra regions as global climate changes. Computer-aided molecular modeling showed these LMCOs contain a highly-conserved copper-dependent active site formed by three histidine residues between CBR I and CBR II. Phylogenetic- and modeling-based methods confirmed the wide occurrence of LMCO genes in HA-degrading polar soil bacteria and linked their putative gene functions with initial HS-degradation processes.

• MeSH
• Bacteria * enzymology   genetics   MeSH
• Phylogeny MeSH
• Humic Substances * microbiology   MeSH
• Laccase * genetics   metabolism   MeSH
• Soil MeSH
• Soil Microbiology * MeSH
• RNA, Ribosomal, 16S genetics   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Humic Substances * MeSH
• Laccase * MeSH
• Soil MeSH
• RNA, Ribosomal, 16S MeSH

Chlorella and Stichococcus are morphologically simple airborne microalgae, omnipresent in terrestrial and aquatic habitats. The minute cell size and resistance against environmental stress facilitate their long-distance dispersal. However, the actual distribution of Chlorella- and Stichococcus-like species has so far been inferred only from ambiguous morphology-based evidence. Here we contribute a phylogenetic analysis of an expanded SSU and ITS2 rDNA sequence dataset representing Chlorella- and Stichococcus-like species from terrestrial habitats of polar, temperate and tropical regions. We aim to uncover biogeographical patterns at low taxonomic levels. We found that psychrotolerant strains of Chlorella and Stichococcus are closely related with strains originating from the temperate zone. Species closely related to Chlorella vulgaris and Muriella terrestris, and recovered from extreme terrestrial environments of polar regions and hot deserts, are particularly widespread. Stichococcus strains from the temperate zone, with their closest relatives in the tropics, differ from strains with the closest relatives being from the polar regions. Our data suggest that terrestrial Chlorella and Stichococcus might be capable of intercontinental dispersal; however, their actual distributions exhibit biogeographical patterns.

• Keywords
• Chlorella, SSU/ITS2, Stichococcus, biogeography, green algae, polar strains,
• MeSH
• Biofilms classification   MeSH
• Chlorella vulgaris classification   genetics   growth & development   MeSH
• Chlorophyta classification   genetics   growth & development   MeSH
• Ecosystem MeSH
• Phylogeny MeSH
• Phylogeography MeSH
• DNA, Ribosomal Spacer genetics   MeSH
• Cold Climate * MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Antarctic Regions MeSH
• Arctic Regions MeSH
• Names of Substances
• DNA, Ribosomal Spacer MeSH

PURPOSE: The tear film lipid layer (TFLL) covers the tear film, stabilizing it and providing a protective barrier against the environment. The TFLL is divided into polar and non-polar sublayers, but the interplay between lipid classes in these sublayers and the structure-function relationship of the TFLL remains poorly characterized. This study aims to provide insight into TFLL function by elucidating the interactions between polar and non-polar TFLL lipids at the molecular level. METHODS: Mixed films of polar O-acyl-ω-hydroxy fatty acids (OAHFA) or phospholipids and non-polar cholesteryl esters (CE) were used as a model of the TFLL. The organization of the films was studied by using a combination of Brewster angle and fluorescence microscopy in a Langmuir trough system. In addition, the evaporation resistance of the lipid films was evaluated. RESULTS: Phospholipids and OAHFAs induced the formation of a stable multilamellar CE film. The formation of this film was driven by the interdigitation of acyl chains between the monolayer of polar lipids and the CE multilayer lamellae. Surprisingly, the multilayer structure was destabilized by both low and high concentrations of polar lipids. In addition, the CE multilayer was no more effective in resisting the evaporation of water than a polar lipid monolayer. CONCLUSIONS: Formation of multilamellar films by major tear film lipids suggest that the TFLL may have a similar structure. Moreover, in contrast to the current understanding, polar TFLL lipids may not mainly act by stabilizing the non-polar TFLL sublayer, but through a direct evaporation resistant effect.

• Keywords
• Cholesteryl ester, Dry eye, Evaporation, Lipid multilayer, O-Acyl-ω-hydroxy fatty acid, Phospholipid, Tear film lipid layer,
• MeSH
• Cholesterol Esters MeSH
• Lipids MeSH
• Fatty Acids MeSH
• Tears * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cholesterol Esters MeSH
• Lipids MeSH
• Fatty Acids MeSH

Long-range intermolecular forces are able to steer polar molecules submerged in superfluid helium nanodroplets into highly polar metastable configurations. We demonstrate that the presence of such special structures can be identified, in a direct and determinative way, by electrostatic deflection of the doped nanodroplet beam. The measurement also establishes the structures' electric dipole moments. In consequence, the introduced approach is complementary to spectroscopic studies of low-temperature molecular assembly reactions. It is enabled by the fact that within the cold superfluid matrix the molecular dipoles become nearly completely oriented by the applied electric field. As a result, the massive (tens of thousands of helium atoms) nanodroplets undergo significant deflections. The method is illustrated here by an application to dimers and trimers of dimethyl sulfoxide (DMSO) molecules. We interpret the experimental results with ab initio theory, mapping the potential energy surface of DMSO complexes and simulating their low temperature aggregation dynamics.

• Publication type
• Journal Article MeSH

Membrane proteins are a large, diverse group of proteins, serving a multitude of cellular functions. They are difficult to study because of their requirement of a lipid membrane for function. Here we show that two-photon polarization microscopy can take advantage of the cell membrane requirement to yield insights into membrane protein structure and function, in living cells and organisms. The technique allows sensitive imaging of G-protein activation, changes in intracellular calcium concentration and other processes, and is not limited to membrane proteins. Conveniently, many suitable probes for two-photon polarization microscopy already exist.

• MeSH
• Cell Membrane metabolism   ultrastructure   MeSH
• Protein Conformation MeSH
• Membrane Proteins metabolism   ultrastructure   MeSH
• Microscopy, Fluorescence, Multiphoton methods   MeSH
• Microscopy, Polarization methods   MeSH
• Structure-Activity Relationship MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Membrane Proteins MeSH

A novel class of chiral superbases derived from the 2,2'-bipyridyl-N,N'-dioxide skeleton are presented. Combined experimental and theoretical data reveal that their proton affinities are on the order of 1050 kJ mol(-1), with protonation occurring at the oxygen atoms in a chelating manner. In the free bases, the oxygen atoms form a strongly polar binding site hidden in a hydrophobic envelope formed by the hydrocarbon backbone of the superbases. This chiral molecular structure can entrap polar intermediates or polarized transition structures and stabilize them in nonpolar solvents. Specifically, this mode of catalysis is shown for the coupling of benzaldehyde and allyltrichlorosilane.

• MeSH
• 2,2'-Dipyridyl analogs & derivatives   chemistry   MeSH
• Oxygen chemistry   MeSH
• Molecular Structure MeSH
• Solvents chemistry   MeSH
• Stereoisomerism MeSH
• Thermodynamics MeSH
• Binding Sites MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 2,2'-bipyridyl-N,N'-dioxide MeSH Browser
• 2,2'-Dipyridyl MeSH
• Oxygen MeSH
• Solvents MeSH

Detoxification of heme in Plasmodium depends on its crystallization into hemozoin. This pathway is a major target of antimalarial drugs. The crystalline structure of hemozoin was established by X-ray powder diffraction using a synthetic analog, β-hematin. Here, we apply emerging methods of in situ cryo-electron tomography and 3D electron diffraction to obtain a definitive structure of hemozoin directly from ruptured parasite cells. Biogenic hemozoin crystals take a striking polar morphology. Like β-hematin, the unit cell contains a heme dimer, which may form four distinct stereoisomers: two centrosymmetric and two chiral enantiomers. Diffraction analysis, supported by density functional theory analysis, reveals a selective mixture in the hemozoin lattice of one centrosymmetric and one chiral dimer. Absolute configuration has been determined by morphological analysis and confirmed by a novel method of exit-wave reconstruction from a focal series. Atomic disorder appears on specific facets asymmetrically, and the polar morphology can be understood in light of water binding. Structural modeling of the heme detoxification protein suggests a function as a chiral agent to bias the dimer formation in favor of rapid growth of a single crystalline phase. The refined structure of hemozoin should serve as a guide to new drug development.

• Publication type
• Journal Article MeSH

Four phenyl-bonded stationary phases, differing in polar embedded group between spacer and phenyl ring, were used for the separation of flavonoids in reversed-phase conditions. In addition, the work was focused on the comparison of these stationary phases in terms of retention and nature of interactions between flavonoid solutes and both, mobile and stationary phases. The differences and similarities between the columns and between individual flavonoids were evaluated by a statistical analysis. The retention over the wider range of mobile phase composition was described using well known model suggested for partition chromatographic systems. Due to differences in polarity of flavonoids, gradient elution had to be applied to achieve appropriate conditions for the successful separation. A chromatographic optimization software was employed for establish the appropriate profiles of gradient separations using UV detection at 275 nm. The most appropriate conditions for the separation of flavonoids were apparent on the phenyl and phenoxy columns.

• Keywords
• Flavonoid, Glycoside, Linear free energy relationship, Phenyl-bonded phases,
• MeSH
• Chemistry Techniques, Analytical methods   standards   MeSH
• Chromatography, Liquid * MeSH
• Flavonoids analysis   chemistry   MeSH
• Indicators and Reagents chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Flavonoids MeSH
• Indicators and Reagents MeSH

A variety of health benefits has been documented to be associated with the consumption of probiotic bacteria, namely bifidobacteria and lactobacilli. Thanks to the scientific advances in recent years we are beginning to understand the molecular mechanisms by which bacteria in general and probiotic bacteria in particular act as host physiology and immune system modulators. More recently, the focus has shifted from live bacteria towards bacteria-derived defined molecules, so called postbiotics. These molecules may represent safer alternative compared to the live bacteria while retaining the desired effects on the host. The excellent source of effector macromolecules is the bacterial envelope. It contains compounds that are pivotal in the adhesion phenomenon, provide direct bacteria-to-host signaling capacity and the associated physiological impact and immunomodulatory properties of bacteria. Here we comprehensively review the structure and biological role of Bifidobacterium surface and cell wall molecules: exopolysaccharides, cell wall polysaccharides, lipoteichoic acids, polar lipids, peptidoglycans and proteins. We discuss their involvement in direct signaling to the host cells and their described immunomodulatory effects.

• Keywords
• Bacterial antigens, Bifidobacterium, Exopolysaccharide, Lipoteichoic acid, Peptidoglycan, Probiotics,
• MeSH
• Polysaccharides, Bacterial chemistry   MeSH
• Bacterial Proteins chemistry   MeSH
• Bifidobacterium chemistry   MeSH
• Cell Wall chemistry   MeSH
• Teichoic Acids chemistry   MeSH
• Lipids chemistry   MeSH
• Lipopolysaccharides chemistry   MeSH
• Peptidoglycan chemistry   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Polysaccharides, Bacterial MeSH
• Bacterial Proteins MeSH
• Teichoic Acids MeSH
• Lipids MeSH
• Lipopolysaccharides MeSH
• lipoteichoic acid MeSH Browser
• Peptidoglycan MeSH