Boris Sket

Crystal Structures and Emission Properties of the BF2 Complex 1-Phenyl-3-(3,5-dimethoxyphenyl)-propane-1,3-dione: Multiple Chromisms, Aggregation- or Crystallization-Induced Emission, and the Self-Assembly Effect

It is known that electron donating groups have quite a different effect on the π-delocalization of a conjugate system when bonded at ortho and para as compared to meta positions in the phenyl ring. In the present work, the BF2 complex of 1-phenyl-3-(3,5-dimethoxyphenyl)-propane-1,3-dione (1), a molecule with two methoxy groups in one of the phenyl rings at meta positions, was prepared. Compound 1 exists as two polymorphs having different mutual orientations of the two methoxy groups: in polymorph A away from each other (termed anti), while in polymorph B one methoxy group is oriented toward the other (syn-anti). In both crystals, the molecules which are antiparallel (the subPh rings as well as dioxaborine are on opposite sides) form stacks through face-to-face π-π interactions, while in polymorph A the crystal packing is further stabilized by intermolecular C(phenyl)-H···F and C(methoxy)-H···F hydrogen bonds. Solid A possesses numerous chromic effects, including mechano-, thermo-, and chronochromism, though the latter to a lesser extent, as well as the effect of rearrangement of the amorphous phase into a more stable crystalline phase A, associated with crystallization-induced emission enhancement (CIEE). The solid-state emission can be repeatedly switched regarding its color and efficiency with excellent reversibility by external stimuli. On the other hand, crystalline solid B undergoes thermal interconversion of syn-anti to the anti conformer. Compound 1 shows a solvatochromic effect (SE), is aggregation-induced emission (AIE) active, and through the sublimation process displays self-assembling crystalline platelike microstructures or microfibers that reveal an obvious optical waveguide effect.

Global diversity of amphipods (Amphipoda; Crustacea) in freshwater

Amphipods are brooding peracaridan crustaceans whose young undergo direct development, with no independent larval dispersal stage. Most species are epibenthic, benthic, or subterranean. There are some 1,870 amphipod species and subspecies recognized from fresh or inland waters worldwide at the end of 2005. This accounts for 20% of the total known amphipod diversity. The actual diversity may still be several-fold. Amphipods are most abundant in cool and temperate environments; they are particularly diversified in subterranean environments and in running waters (fragmented habitats), and in temperate ancient lakes, but are notably rare in the tropics. Of the described freshwater taxa 70% are Palearctic, 13% Nearctic, 7% Neotropical, 6% Australasian and 3% Afrotropical. Approximately 45% of the taxa are subterranean; subterranean diversity is highest in the karst landscapes of Central and Southern Europe (e.g., Niphargidae), North America (Crangonyctidae), and Australia (Paramelitidae). The majority of Palearctic epigean amphipods are in the superfamily Gammaroidea, whereas talitroid amphipods (Hyalella) account for all Neotropic and much of the Nearctic epigean fauna. Major concentrations of endemic species diversity occur in Southern Europe, Lake Baikal, the Ponto-Caspian basin, Southern Australia (including Tasmania), and the south-eastern USA. Endemic family diversity is similarly centered in the Western Palearctic and Lake Baikal. Freshwater amphipods are greatly polyphyletic, continental invasions have taken place repeatedly in different time frames and regions of the world. In the recent decades, human mediated invasions of Ponto-Caspian amphipods have had great impacts on European fluvial ecosystems.

The nature of biodiversity in hypogean waters and how it is endangered

The specialised aquatic hypogean, i.e. stygobiotic, fauna has been recognised in some regions moderately rich. Slovenia, the broader Dinaric region, and Europe are particularly rich with about 7–8% of all Metazoa and about 40% of Crustacea species being stygobionts. The hypogean biotic diversity is in general predominantly a crustacean diversity. The high number of stygobiont Crustacea–Malacostraca species can be explained by the near absence of Insecta as well as by their high endemicity and sometimes additional specialisation, i.e. the spatial and ecological partition of the environment by the species. Although one cave system may exceptionally shelter up to 40 stygobiont species, they are distributed there into separate associations. Among more than 2000 described stygobiontic Malacostraca species, which include close to 950 Amphipoda, the species numbers within some genera are very high (e.g. Niphargus with 275 spp.). With 10 orders represented the higher taxonomic diversity of stygobiont Malacostraca matches that of fresh waters or the sea. Comparison of some faunas shows that the limiting factors for biodiversity might be the lower ecological diversity of habitats and restricted food resources underground, both brought about to a high degree by the darkness and absence of plants. Being K-strategists, stygobionts are endangered by any sudden changes in their environment. In the case of an increased food input by modest organic pollution, they can be outcompeted by energetically demanding but competitively stronger recent immigrants from surface.

The colonization of Europe by the freshwater crustacean Asellus aquaticus (Crustacea: Isopoda) proceeded from ancient refugia and was directed by habitat connectivity.

Recent continental‐scale phylogeographic studies have demonstrated that not all freshwater fauna colonized Europe from the classic Mediterranean peninsular refugia, and that northern or central parts of the continent were occupied before, and remained inhabited throughout the Pleistocene. The colonization history of the ubiquitous aquatic isopod crustacean Asellus aquaticus was assessed using mitochondrial COI and a variable part of nuclear 28S rDNA sequences. Phylogeographic analysis of the former suggested that dispersion proceeded possibly during late Miocene from the western part of the Pannonian basin. Several areas colonized from here have served as secondary refugia and/or origins of dispersion, well before the beginning of the Pleistocene. Postglacial large‐scale range expansion was coupled with numerous separate local dispersions from different refugial areas. Connectivity of the freshwater habitat has played an important role in shaping the current distribution of genetic diversity, which was highest in large rivers. The importance of hydrographic connections for the maintenance of genetic contact was underscored by a discordant pattern of mtDNA and nuclear rDNA differentiation. Individuals from all over Europe, differing in their mtDNA to a level normally found between species or even genera (maximal within population nucleotide divergence reached 0.16 ± 0.018), shared the same 28S rRNA gene sequence. Only populations from hydrographically isolated karst water systems in the northwestern Dinaric Karst had distinct 28S sequences. Here isolation seemed to be strong enough to prevent homogenization of the rRNA gene family, whereas across the rest of Europe genetic contact was sufficient for concerted evolution to act.

The ecology of anchihaline caves

The dark, mostly brackish, aquatic habitats along the coasts are inhabited by a number of phylogenetically and/or biogeographically interesting animal taxa, whose ecology is poorly known. We are especially ignorant about the nature of the deoxygenated strata that occur in most of these habitats. Are these strata anoxic or only dysoxic? And how are their inhabitants adapted to low oxygen tensions?

Eocene habitat shift from saline to freshwater promoted Tethyan amphipod diversification

Current theory predicts that a shift to a new habitat would increase the rate of diversification, while as lineages evolve into multiple species, intensified competition would decrease the rate of diversification. We used Holarctic amphipods of the genus Gammarus to test this hypothesis. We sequenced four genes (5,088 bp) for 289 samples representing 115 Gammarus species. A phylogenetic analysis showed that Gammarus originated from the Tethyan region with a saline ancestry in the Paleocene, and later colonized the freshwater habitat in the Middle Eocene. Ancestral range reconstruction and diversification mode analysis combined with paleogeological and paleoclimatic evidence suggested that the habitat shift from saline to freshwater led to an increased diversification rate. The saline lineage of Gammarus dispersed to both sides of the Atlantic at 55 million years ago (Ma), because of the few barriers between the Tethys and the Atlantic, and diversified throughout its evolutionary history with a constant diversification rate [0.04 species per million years (sp/My)]. The freshwater Gammarus, however, underwent a rapid diversification phase (0.11 sp/My) until the Middle Miocene, and lineages successively diversified across Eurasia via vicariance process likely driven by changes of the Tethys and landmass. In particular, the freshwater Gammarus lacustris and Gammarus balcanicus lineages had a relatively high diversification shift, corresponding to the regression of the Paratethys Sea and the continentalization of Eurasian lands during the Miocene period. Subsequently (14 Ma), the diversification rate of the freshwater Gammarus decreased to 0.05 and again to 0.01 sp/My. The genus Gammarus provides an excellent aquatic case supporting the hypothesis that ecological opportunities promote diversification.

Global diversity of leeches (Hirudinea) in freshwater

Leeches (Hirudinea) constitute a relatively small monophyletic group of highly specialized annelids, but may play important roles as invertebrate predators in freshwater, while others are infamous for their ectoparasitic bloodsucking. About 15% of the 680 described species are marine and slightly less have switched to terrestrial life; the rest are freshwater, divided among 91 genera. They are globally distributed on all continents except Antarctica, reaching the highest diversity in the Holarctic region with one-half of all continental species. Known areas of local endemism are the ancient Siberian lake Bajkal and lake Ohrid (about 10 species each) on the Balkan Peninsula, which is an endemicity area in itself. A small number of sanguivorous species known as “medicinal leeches” have played an important role in traditional and modern medicine, most noticeably four Hirudo spp. from the Western Palearctic.

Phylogeography of subterranean and surface populations of water lice Asellus aquaticus (Crustacea: Isopoda).

The water louse Asellus aquaticus is a widespread, euryoecious species, mostly uniform throughout its range. However, six subspecies are known from the Dinaric karst in the northwestern Balkans. They include some specialized subterranean populations. The pattern of genetic variation among subterranean and surface populations in this hydrographically highly fragmented karst region was investigated using a 653 bp fragment of the mitochondrial gene (COI). Sequencing of 168 individuals from 25 localities revealed 72 haplotypes. amova and methods of phylogenetic reconstruction all uncovered hydrographic structuring of genetic variation of the populations. Nested clade analysis pointed out several fragmentation events, along with some range expansions within hydrographical systems. By superimposing the subterranean mode of life on the phylogeographical pattern, three independent cave colonizations could be inferred within a distance of < 100 km. Caves were invaded after the ancestral surface populations became isolated through vicariant fragmentation. A possible scenario of hydrographic history of the region was constructed combining the molecular data with palaeogeographical information.

HIGH BIODIVERSITY IN HYPOGEAN WATERS AND ITS ENDANGERMENT – THE SITUATION IN SLOVENIA, THE DINARIC KARST, AND EUROPE

Of approximately 12,600 aquatic animal species, registered in 1978 in Europe, more than 200 were facultative cave dwellers, approximately 1,000 species (in 1998 already 2,000 taxa) or 8%, were specialized stygobionts. More than half are Crustacea. The relatively high number of crustacean hypogean species is rendered possible mainly by (1) the absence of their insect competitors as well as (2) spatial partition due to the small distribution areas of most stygobionts. Slovenia, with approximately 200 taxa in its 20,000 km2, has the highest density, and the Dinaric area with nearly 400 taxa in its only 153,400 km2 has the highest absolute number of stygobiont taxa known in the world. The situation is similar for terrestrial cave faunas. The crustacean diversity is mostly a result of ecological and morphological diversification within a few genera (e.g., Niphargus, Proasellus, Monolistra). However, higher taxa (families, orders) are well represented. Besides some non-specialized newcomers to hypogean habitats, some ubiquitous species (e.g., Asellus aquaticus, Synurella ambulans) possess a number of isolated hypogean populations that are troglomorphic to varying degrees. Hypogean species are endangered by urbanization and other uses of the sensitive karst landscape. Although a slight organic pollution of the energy poor cave waters is favourable to their inhabitants, it may enable invaders from the surface to outcompete troglomorphic specialists in sinking rivers. Conservation of cave species is very demanding, since it requires protection of the whole drainage areas on the surface. Von ungefahr 12.600 im Jahre 1978 registrierten aquatischen Tierarten in Europa, waren mindestens 200 fakultative Hohlenbewohner und etwa 1.000 Arten (1998 schon 2.000 Taxa), also 8%, waren spezialisierte Stygobionten. Mehr als die Halfte davon sind Krebsarten (Crustacea). Zwei Hauptfaktoren ermoglichen vermutlich die relativ hohe Zahl der unterirdischen Krebsarten: (1) die Abwesenheit der kompetierenden Insekten und (2) eine kleinraumliche Einteilung der Verbreitungsareale (wass eine allgemeine Folge des hohen Endemismus der Stygobionten Arten, nicht nur der Krebse, ist). Slovenien hat mit etwa 200 Stygobionten Taxa auf einer Flache von 20.000 km2 die hochste bekannte Arten-Dichte und das Dinarische Gebiet hat mit fast 400 Taxa auf einer Flache von 153.400 km2 die artenreichste Stygofauna der Welt. Diese Verhaltnisse sind auch bei den terrestrischen Hohlenfaunen ahnlich. Der Artenreichtum der Crustacea ist vor allem eine Folge der okologischen und morphologischen Differenzierung innerhalb einiger Gattungen (z.B. Niphargus, Proasellus, Monolistra). Weiterhin sind aber auch hohere Taxa (Familien, Ordnungen) zahlreich vertreten. Nebst einiger nicht spezialisierten (Neu-)Einwanderer in unterirdische Habitate gibt es auch isolierte Populationen einiger ubiquistischen Arten (z.B. Asellus aquaticus, Synurella ambulans), die schon teilweise troglomorph sind. Unterirdische Arten sind bedroht durch Urbanisierung und andere Nutzungsformen der empfindlichen Karst-Landschaft. Obwohl eine leichte organische Verunreinigung der nahrstoffarmen Hohlengewasser fur ihre Einwohner gunstig ist, erleichtert sie in Sickerflussen das eindringen epigaischer Arten, die troglomorphe Spezialisten verdrangen konnen. Der Schutz von Hohlenarten ist ein anspruchsvolles Vorhaben, dass den Schutz ganzer Gewassersysteme an der Oberflache erfordert.

Study of macroaggregate composition using FT-IR and 1H-NMR spectroscopy

Abstract Mucous macroaggregates, recently observed in the northern Adriatic in summer of 1997 and late spring of 2000, are primarily the product of phytoplankton (diatom) exudates during favourable environmental conditions in late spring, and can be viewed as macrogels. The FT-IR and 1H-NMR spectra of macroaggregate samples from the northern Adriatic, collected in different formation stages in July 1997, August 1997, September 1997 and June 2000, as well as of cultured diatom Skeletonema costatum, showed that they are similar and composed of aliphatic components and polysaccharides bonded through carboxylic and amide groups, and organosilicon compounds. The stability of macrogels of macroaggregates is, according to FT-IR and X-ray analyses, most probably enhanced by interactions with entrapped particles of calcite, quartz and clay minerals. These organic-mineral associations seem to be important for mucous phenomena. According to 1H-NMR spectra, the temporal differences in macroaggregate composition show a relative increasing percentage of organosilicon compounds and aliphatic components bonded to carbohydrates through ester and amide groups, and an increasing ratio between aliphatic structures and carbohydrates. This indicates that aliphatic chains bonded to Si and carbohydrates may contribute to the persistence and stability of macroaggregates in the summer stratified waters in the northern Adriatic, while the temporal decrease of carbohydrate content is most probably due to microbial and photochemical degradation of algal reserve polysaccharides.