Mixed Pentele-Chalcogen Cationic Chains from Aluminum and Gallium Halide Melts

The reactions of tellurium or selenium with bismuth or antimony in chloridogallate and iodidoaluminate melts in the presence of group 15 trihalides as weak oxidants yielded the compounds (Sb₂Te₂)­[GaCl₄] (<b>1</b>), (Sb₂Te₂)­I­[AlI₄] (<b>2</b>), (Bi₂Te₂)­Cl­[GaCl₄] (<b>3a</b>), (Bi₂Se₂)­Cl­[GaCl₄] (<b>3b</b>), (Sb₃Te₄)­[GaCl₄] (<b>4</b>), and (SbTe₄)­[Ga₂Cl₇] (<b>5</b>). In the crystal structures one-dimensional polymeric cations (Sb₂Te₂⁺)_<i>n</i> (<b>1</b>), (Sb₂Te₂²⁺)<i>_n</i> (<b>2</b>), (Bi₂Te₂²⁺)<i>_n</i> (<b>3a</b>), (Bi₂Se₂²⁺)_<i>n</i> (<b>3b</b>), (Sb₃Te₄⁺)_<i>n</i> (<b>4</b>), and (SbTe₄⁺)_<i>n</i> (<b>5</b>) are present. The polymeric cationic strands in <b>2</b>, <b>3a</b>, <b>3b</b>, and <b>4</b> consist of pentele/chalcogen dumbbells, which are connected to ladder-shaped bands. The strands in <b>1</b> and <b>5</b> consist of condensed rings that involve four-membered Sb₂Te₂ rings for <b>1</b>, and five-membered SbTe₄ rings for <b>5</b>. The counteranions are the weakly coordinating [GaCl₄]⁻, [AlI₄]⁻, and [Ga₂Cl₇]⁻ in addition to Cl^– and I^– anions, which are coordinated to the atoms of the cations. The crystal structures of <b>1</b>–<b>4</b> are characterized by a statistical disorder in the anions with alternatively occupied positions for the Al and Ga atoms. For <b>4</b> superstructure reflections appear in the diffractions patterns, indicating a partial order. A correct assignment of the Sb and Te positions in the cation of <b>5</b> was achieved by periodic quantum-chemical calculations, which were performed via a Hartree–Fock density functional theory hybrid method. A clear preference of the 4-fold coordinated site was obtained for Sb

Biofilm and Diatom Succession on Polyethylene (PE) and Biodegradable Plastic Bags in Two Marine Habitats: Early Signs of Degradation in the Pelagic and Benthic Zone?

<div><p>The production of biodegradable plastic is increasing. Given the augmented littering of these products an increasing input into the sea is expected. Previous laboratory experiments have shown that degradation of plastic starts within days to weeks. Little is known about the early composition and activity of biofilms found on biodegradable and conventional plastic debris and its correlation to degradation in the marine environment. In this study we investigated the early formation of biofilms on plastic shopper bags and its consequences for the degradation of plastic. Samples of polyethylene and biodegradable plastic were tested in the Mediterranean Sea for 15 and 33 days. The samples were distributed equally to a shallow benthic (sedimentary seafloor at 6 m water depth) and a pelagic habitat (3 m water depth) to compare the impact of these different environments on fouling and degradation. The amount of biofilm increased on both plastic types and in both habitats. The diatom abundance and diversity differed significantly between the habitats and the plastic types. Diatoms were more abundant on samples from the pelagic zone. We anticipate that specific surface properties of the polymer types induced different biofilm communities on both plastic types. Additionally, different environmental conditions between the benthic and pelagic experimental site such as light intensity and shear forces may have influenced unequal colonisation between these habitats. The oxygen production rate was negative for all samples, indicating that the initial biofilm on marine plastic litter consumes oxygen, regardless of the plastic type or if exposed in the pelagic or the benthic zone. Mechanical tests did not reveal degradation within one month of exposure. However, scanning electron microscopy (SEM) analysis displayed potential signs of degradation on the plastic surface, which differed between both plastic types. This study indicates that the early biofilm formation and composition are affected by the plastic type and habitat. Further, it reveals that already within two weeks biodegradable plastic shows signs of degradation in the benthic and pelagic habitat.</p></div

Oxygen production rate.

<p>Amount of oxygen (µmol) produced per day per square centimetre of plastic surface (white for PE, grey for biodegradable plastic) after 15 days and after 33 days of the experiment. Time 0 represents the polymer without biofilm. The error bars indicate the standard error. (A) Results of benthic samples (6 m water depth). (B) Results of pelagic samples (3 m water depth).</p

SEM pictures of the plastic surface of PE samples following removal of the biofilm.

<p>Each sample is displayed in two magnifications. (A) and (B) show untreated PE; (C) and (D) PE after 15 days; (E) and (F) PE after 33 days. Arrows in (F) mark fissures close to remains of the biofilm.</p

Biofilm amount in relation to plastic type, site and exposure time.

<p>^a likelihood ratio of <i>Chi</i>² value</p><p>^b degrees of freedom</p><p>^c probability value</p><p>Biofilm amount in relation to plastic type, site and exposure time.</p

Detrended correspondence analysis (DCA) for the diatom community on PE and biodegradable plastic in the benthic (A) and in the pelagic zone (B).

<p>Diatoms were categorised by morphology. Each data point represents a plastic sample, the distance between the data points shows the similarity of the diatom composition found on the sample. The smaller the distance, the more similar the composition was between the samples. Different symbols were used to group the samples by plastic type and sampling time. Around the centroid of all data points for these groups an ellipse indicating the 95% confidence interval of their standard error was drawn. If these ellipses do not overlap the groups are assumed to be significantly different (P ≤ 0.05).</p

Biofilm development over time.

<p>The relative amount of biofilm found on PE (white) and biodegradable plastic (grey) after 15 and after 33 days of the experiment. Time 0 represents the polymer without biofilm. The error bars indicate the standard error. (A) Results of benthic samples (6 m water depth). (B) Results of pelagic samples (3 m water depth).</p

Photo of representatives for each diatom group based on morphological features.

<p>No example is shown for group G13 (i.e. unknown diatoms) in this figure. Image source for G2: [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137201#pone.0137201.ref033" target="_blank">33</a>] modified, and for G11: [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137201#pone.0137201.ref034" target="_blank">34</a>] modified.</p

Diatom groups based on morphological features.

<p>Diatom groups based on morphological features.</p

Tensile properties (sigma and epsilon) for each treatment.

<p>^a standard error</p><p>Tensile properties (sigma and epsilon) for each treatment.</p