Threonine and Polythreonine Accelerate Calcium Carbonate Formation

Acidic macromolecules are considered to be critical to calcium carbonate formation in organisms and have been chosen as a model chemical for modifying biomineralization. Here, this view is challenged, and it is found that low-charge amino acid threonine (Thr) and its polymer poly-Thr can accelerate calcium carbonate formation by increasing nucleation. In contrast to aspartic acid (Asp) and poly-Asp, Thr and poly-Thr did not affect the morphology of product crystals but accelerated the formation of crystal nucleation rapidly. This effect may be partially attributed to the negative charges of these chemicals that interact with calcium. This finding provides novel insights into the mechanisms of biomineralization that involve diverse chemistry control not limited to acidic macromolecules and may inspire the synthesis of calcium carbonate in a short time

Viscoelastic Properties of Water Suspensions of Polymer Nanofibers Synthesized via RAFT-Mediated Emulsion Polymerization

We report on the rheological properties of water suspensions of poly­(methacrylic acid<i>-<i>co</i>-</i>poly­(ethylene oxide) methyl ether methacrylate)<i>-<i>b</i>-</i>polystyrene and poly­(methacrylic acid<i>-<i>co</i>-</i>poly­(ethylene oxide) methyl ether methacrylate)<i>-<i>b</i>-</i>poly­(methyl methacrylate) self-assembled amphiphilic block copolymer nanofibers, synthesized via RAFT-mediated aqueous emulsion polymerization. The viscoelastic properties were studied over a range of nanofiber concentrations spanning the transition from the dilute to semidilute regimes. From the measured viscoelastic parameters, two sets of suspensions could be differentiated depending on their aspect ratio (length/diameter ≈70 and ≈54) and the average length of the nanofibers was calculated in the 2.4 μm – 3.8 μm range. The viscoelastic properties appeared to depend mainly on the aspect ratio of the fibers rather than on their nature and composition. As expected the zero shear viscosity was observed to scale with the volume fraction ϕ as η₀ ∝ ϕ¹ and η₀ ∝ ϕ³ for dilute and semidilute regime, respectively. However, the deviation of the scaling law in semidilute regime at higher concentrations and the slowdown of the rotary diffusion can be related to different mechanisms. While a Brownian motion of nanofibers is the dominant mechanism of relaxation, it was also concluded that clustering phenomenon and broad length distribution of nanofibers implies that some large nanofibers could be non Brownian

Explanation of the Source of Very Large Errors in Many Exchange–Correlation Functionals for Vanadium Dimer

Vanadium dimer is a notoriously difficult case for Kohn–Sham (KS) density functional theory with currently available approximations to the exchange–correlation (xc) functionals, and many approximate xc functionals yield an exceedingly large error in the calculated bond energy. In this paper, we first test the bond energies estimated by 43 xc functionals and the Hartree–Fock (HF) method. The results further confirm the large errors and show that, with the experimental bond energy being 64.2 kcal/mol, the KS calculations give predictions all over the map with errors ranging from −61.5 to +60.5 kcal/mol, and the HF method performs much worse with an error of −124.4 kcal/mol! The reason for these very large errors is examined in this article by analyzing the atomic and molecular orbital energies calculated by various xc functionals. The results show that the errors in estimates of the bond energy of vanadium dimer can primarily be related to the calculated energy gap between the 4s and 3d_z2 atomic orbitals of the vanadium atom and especially to the 3d_z2 orbital energy. This interesting relation between the errors in the calculated bond energy and the magnitudes of the single-particle orbital energies provides a constructive alternative to the common but more sterile explanation that it is the static correlation energy due to multicenter left–right correlation that makes the vanadium dimer and many other transition metal compounds so difficult for Kohn–Sham calculations. One of the most important factors in determining the critical atomic orbital energy is the amount of nonlocal HF exchange that is included in the xc functional, but it is still difficult to explain why different local functionals (functionals with no HF exchange) yield quite different results. We conclude that improving calculations of orbital energies of atoms may provide a route to improving the accuracy of theoretical predictions of molecular bond energies for systems containing metal atoms

Determining Microeukaryotic Plankton Community around Xiamen Island, Southeast China, Using Illumina MiSeq and PCR-DGGE Techniques

<div><p>Microeukaryotic plankton are important components of aquatic environments and play key roles in marine microbial food webs; however, little is known about their genetic diversity in subtropical offshore areas. Here we examined the community composition and genetic diversity of the microeukaryotic plankton in Xiamen offshore water by PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis), clone-based sequencing and Illumina based sequencing. The Illumina MiSeq sequencing revealed a much (approximately two orders of magnitude) higher species richness of the microeukaryotic community than DGGE, but there were no significant difference in species richness and diversity among the northern, eastern, southern or western stations based on both methods. In this study, Copepoda, Ciliophora, Chlorophyta, Dinophyceae, Cryptophyta and Bacillariophyta (diatoms) were the dominant groups even though diatoms were not detected by DGGE. Our Illumina based results indicated that two northern communities (sites N2 and N3) were significantly different from others in having more protozoa and fewer diatoms. Redundancy analysis (RDA) showed that both temperature and salinity were the significant environmental factors influencing dominant species communities, whereas the full microeukaryotic community appeared to be affected by a complex of environmental factors. Our results suggested that extensive sampling combined with more deep sequencing are needed to obtain the complete diversity of the microeukaryotic community, and different diversity patterns for both abundant and rare taxa may be important in evaluating the marine ecosystem health.</p></div

Schematic life cycle of <i>Aurelia</i>.

<p>Normal development traits and stages were presented with black illustrates and arrows, whereas modifications of the typical life cycle were drawn with colored objects (Red: process described in this study; others: process published with references herein). I: direct development of planula; II: production of elongated stolons, podocysts, and free-swimming propagules from scyphistoma; III: reverse development of ephyra; IV: direct polyp formation from degenerating juvenile medusa and medusa tissue fragments; V: direct polyp formation from living medusa; VI: polyp colony release from medusa-polyp complex.</p

Direct polyp formation from degenerating juvenile <i>Aurelia</i> sp.1 medusae.

<p>A-D: normal development from ephyrae to juvenile medusae, showing individuals of newly released (A), 5-day (B), 10-day (C) and 20-day (D) old, respectively. E, F: aboral (E) and oral (F) view of a 25-day old medusa after 5 days post settlement. G-L: juvenile medusae during reverse transformation. Scale bars = 0.2 mm (A, B); 0.5 mm (C-L). Arrows showed degeneration of medusa tentacles (E), occurrence of polyp stolon (G), development of polyp tentacles (H), and remains of medusa rhopalia (I and J).</p

Map of Xiamen offshore sea area showing the locations of twelve sampling sites.

<p>Map of Xiamen offshore sea area showing the locations of twelve sampling sites.</p

Direct polyp formation from living <i>Aurelia</i> sp.1 medusae.

<p>A, D: 3-month old medusae. B, C: the same individual as (A) after 75 days, showing the thickened layers and projecting pointed ends at different scales. E-G: the same individual as (D) after 75 days, showing the derived colonies (E and F) and thickened layers (G) at different scales. H-L: proportions of living medusae at different stages of direct polyp formation. Scale bars = 1 cm (A, B, D, E); 5 mm (C, F, G-L). Arrows showed transformation process at different stages.</p

Species information of <i>Aurelia</i> sp.1 in Xiamen Bay, East China Sea.

<p>A: sampling location for <i>Aurelia</i> sp.1 from Xiamen Bay, which was indicated as the red dot in the map. B and C: Neighbor-Joining cladogram of <i>Aurelia</i> based on mitochondrial COI (B) and nuclear ITS (C) sequences, bootstrap values higher than 70 were shown close to each branch node, number of sequences belonging to the same species were indicated in the bracket following the species name, and sequences of <i>Aurelia</i> sp.1 obtained in this study were highlighted.</p

Percentage of sequences in all OTUs classified by major taxonomic groups of twelve sampling sites<b>,</b> as revealed by (A) DGGE and clone based sequencing and (B) Illumina Miseq sequencing.

<p>Percentage of sequences in all OTUs classified by major taxonomic groups of twelve sampling sites<b>,</b> as revealed by (A) DGGE and clone based sequencing and (B) Illumina Miseq sequencing.</p