Coupling Fluid and Solute Dynamics Within the Ocular Surface Tear Film: A Modelling Study of Black Line Osmolarity

We present a mathematical model describing the spatial distribution of tear film osmolarity across the ocular surface of a human eye during one blink cycle, incorporating detailed fluid and solute dynamics. Based on the lubrication approximation, our model comprises three coupled equations tracking the depth of the aqueous layer of the tear film, the concentration of the polar lipid, and the concentration of physiological salts contained in the aqueous layer. Diffusive boundary layers in the salt concentration occur at the thinnest regions of the tear film, the black lines. Thus, despite large Peclet numbers, diffusion ameliorates osmolarity around the black lines, but nonetheless is insufficient to eliminate the build-up of solute in these regions. More generally, a heterogeneous distribution of solute concentration is predicted across the ocular surface, indicating that measurements of lower meniscus osmolarity are not globally representative, especially in the presence of dry eye.Vertical saccadic eyelid motion can reduce osmolarity at the lower black line, raising the prospect that select eyeball motions more generally can assist in alleviating tear film hyperosmolarity. Finally, our results indicate that measured evaporative rates will induce excessive hyperosmolarity at the black lines, even for the healthy eye. This suggests that further evaporative retardation at the black lines, for instance due to the cellular glycocalyx at the ocular surface or increasing concentrations of mucus, will be important for controlling hyperosmolarity as the black line thins.     

Internal and External Influences on Near-Surface Microbial Community Structure in the Vicinity of the Cape Verde Islands

Microbial community structure in the subtropical north-east Atlantic Ocean was compared between 2 years and variation attributed to environmental variables. Surface seawater communities were analysed by flow cytometry and fluorescence in situ hybridisation. Probes specific to Alphaproteobacteria, Cyanobacteria, Gammaproteobacteria and Bacteroidetes identified 67–100% of cells. Due to natural variation in the study region due to the occurrence of major currents and islands, data could not be pooled but were instead divided between distinct water masses. Community structure did not differ greatly around the Cape Verde Islands between sampling periods but varied substantially in the open ocean, suggesting different environmental perturbations favour specific bacterial groups. Wind speed varied significantly between years, with moderate to strong breeze in winter 2008 and gales in winter 2006 (8.9 ± 0.2 ms⁻¹ and 16.0 ± 0.4 ms⁻¹, respectively). Enhanced wind-driven turbulence was associated with domination by the SAR11 clade of Alphaproteobacteria, which were present at 2.4-fold in the abundance of Prochlorococcus (41.8 ± 1.6% cells, compared to 17.7 ± 7.1%). Conversely, the calmer conditions of 2008 seemed to favour Prochlorococcus (40.0 ± 1.2% cells). Prochlorococcus high-light adapted clade HLI were only numerous during wind-driven turbulence, whereas oligotrophic-adapted clade HLII dominated under calm conditions. Bacteroidetes were most prominent in turbulent conditions (9.5 ± 1.3% cells as opposed to 4.7 ± 0.3%), as were Synechococcus. In 2008, a considerable dust deposition event occurred in the region, which may have led to the substantial Gammaproteobacteria population (22.5 ± 4.0% cells compared to 4.6 ± 0.6% in 2006). Wind-driven turbulence may have a significant impact on microbial community structure in the surface ocean. Therefore, community change following dust storm events may be linked to associated wind in addition to dust-derived nutrients.     

New iridium bis‐terpyridine complexes: synthesis,characterization, antibiofilm and anticancer potentials

BioMetals - This study represents synthesis, characterization, screening of antibiofilm efficacy, and cytotoxicity of iridium bis-terpyridine complexes. The complexes were characterized by NMR, MS,...     

Evaluation of the efficiency of metabolism of dinoflagellate phosphorus and carbon by a planktonic ciliate

The trophic transfer of nutrients through the microbial food web is a key top-down control in aquatic ecosystems which is notoriously difficult to evaluate, particularly for planktonic protists. In this study, a sensitive dual-radioactive tracer technique was developed to simultaneously assess the ingestion rate, and carbon- and phosphorus-specific assimilation efficiencies, of the marine planktonic ciliate Strobilidium neptuni feeding on the autotrophic dinoflagellate Heterocapsa triquetra. Dinoflagellate prey were simultaneously 16 h pulse labelled with NaH¹⁴CO₃ and H₃³³PO₄ before being fed to the ciliate, and radioactive labels were traced into ciliate biomass and the experimental medium, as well as being monitored in the prey cells. Rates measured in short-term (10 min) incubations, as commonly used to estimate protist uptake of fluorescently labelled prey, were approximately 6 times higher and 3–6 times more variable than rates measured in longer 3–5 h incubations. The efficiency of accumulation of prey carbon (54±9%) by ciliates was lower than that of prey phosphorus (68±3%) suggesting that the phosphorus to carbon ratio in the ciliates was 1.3 times higher than in the labelled dinoflagellate biomass. Rates of phosphorus accumulation and release were combined to reveal that ciliates consumed 3.2±0.6 dinoflagellates cell^?1 h^?1. The assessment of carbon tracer release by ciliates was less reliable due to ¹⁴CO₂ exchange between the experimental media and air. The study concludes that the dual phosphorus–carbon radioactive tracer labelling of algal prey allowed the quantification of protist herbivory and nutrient remineralisation in laboratory experiments, thereby providing a potential technique for studying planktonic microbial trophic interactions in situ.     

A simple synthesis of 8-(methoxycarbonyl)octyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside and derivatives and their use in the preparation of neoglycoconjugates.

8-(Methoxycarbonyl)octyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (10) was synthesized in 54% yield by regioselective diglycosylation of unprotected mannoside 4, employing the trichloroacetimidate donor 1, followed by debenzoylation. Derivatives of compounds 4 and 10 were used to prepare conjugates containing fluorochromes for the study of carbohydrate-lectin interactions, as well as conjugates with phospholipids for the preparation of liposomes.     

Changes in the Architectonics and Morphometric Characteristics of Erythocytes under the Influence of Magnetite Nanoparticles

A new high-precision technique for calculating the ratio of the erythrocyte area/volume using atomic-force microscopy has been developed. The method was tested on erythrocytes of healthy donors. Scanning electron microscopy, atomic-force microscopy, and X-ray microanalysis revealed that magnetite nanoparticles can interact with erythrocyte membranes in vitro. This interaction resulted in the development of a pathology of erythrocytes typical for poikilocytosis and anisocytosis. When the magnetite was incubated with erythrocytes in a serum-free medium, nanoparticles aggregated.     

Circular dichroism calculation for random-coil polypeptide chains

A method of calculation of the circular dichroism (CD) of random-coil polypeptides has been developed by means of a Monte-Carlo approach to the treatment of statistical systems and exciton theory of optical activity of polymers. The contribution of π–π^* and n–π^* amide transitions to the CD has been taken into account. The π–π^* transition gives rise to two CD bands: a negative short-wavelength band and a weak positive long-wavelength one. The n –π^* transition gives rise to one negative CD band.     

Structure of O-specific polysaccharide from Yersinia pseudotuberculosis of serotype VI lipopolysaccharide

Using methylation studies, partial hydrolysis and 13C NMR spectroscopy data, the following structure of O-specific polysaccharide from lipopolysaccharide of Yersinia pseudotuberculosis VI serovar has been proposed: (Formula: see text).     

Structure of the O-specific polysaccharide chain of the lipopolysaccharide from Yersinia intermedia serotype O:4.33

O-specific polysaccharide has been isolated on autohydrolysis of lipopolysaccharide from Yersinia intermedia O: 4.33 (strain 1476) and shown to consist of the yersiniose B (3.6-dideoxy-4-C-(1-hydroxyethyl)-xylo-hexose) and 2-acetamido-2-deoxy-D-galactose residues in a molar ratio of 1 : 2. Acid hydrolysis, methylation. solvolysis with anhydrous hydrogen fluoride. and 13C-NMR studies indicate the polysaccharide to be composed of trisaccharide repeating units of the following structure: (Formula: see text).