Martin Luther University of Halle-Wittenberg

About: Martin Luther University of Halle-Wittenberg is a education organization based out in Halle, Germany. It is known for research contribution in the topics: Population & Liquid crystal. The organization has 20232 authors who have published 38773 publications receiving 965004 citations. The organization is also known as: MLU & University of Wittenberg.

Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline Phases

Abstract: A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3 a-f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by (1)H NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The pi-pi aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted pi-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3x10(4) and 30 M(-1). The photoluminescence spectra of the dimers of PBIs 3 a-f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective pi-pi stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the pi systems on their pi-pi stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3 a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H-type into strongly fluorescent J-type packing of the dyes.

Meta-analysis of multidecadal biodiversity trends in Europe

Abstract: Local biodiversity trends over time are likely to be decoupled from global trends, as local processes may compensate or counteract global change. We analyze 161 long-term biological time series (15–91 years) collected across Europe, using a comprehensive dataset comprising ~6,200 marine, freshwater and terrestrial taxa. We test whether (i) local long-term biodiversity trends are consistent among biogeoregions, realms and taxonomic groups, and (ii) changes in biodiversity correlate with regional climate and local conditions. Our results reveal that local trends of abundance, richness and diversity differ among biogeoregions, realms and taxonomic groups, demonstrating that biodiversity changes at local scale are often complex and cannot be easily generalized. However, we find increases in richness and abundance with increasing temperature and naturalness as well as a clear spatial pattern in changes in community composition (i.e. temporal taxonomic turnover) in most biogeoregions of Northern and Eastern Europe.

Contribution of dissolved organic matter to carbon storage in forest mineral soils

Abstract: Dissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant-derived carbohydrates seem easily degradable. Carbohydrates and N-rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co-)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from 90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co-)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM-derived soil C ranges from 20 to 55 Mg ha–1 in the mineral soil, which represents 19%–50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co-)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM-derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co-)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co-)precipitation with Al and Fe to DOM retention.