Stable water isotope patterns in a climate change hotspot: the isotope hydrology framework of Corsica (western Mediterranean)

The Mediterranean is regarded as a region of intense climate change. To better understand future climate change, this area has been the target of several palaeoclimate studies which also studied stable isotope proxies that are directly linked to the stable isotope composition of water, such as tree rings, tooth enamel or speleothems. For such work, it is also essential to establish an isotope hydrology framework of the region of interest. Surface waters from streams and lakes as well as groundwater from springs on the island of Corsica were sampled between 2003 and 2009 for their oxygen and hydrogen isotope compositions. Isotope values from lake waters were enriched in heavier isotopes and define a local evaporation line (LEL). On the other hand, stream and spring waters reflect the isotope composition of local precipitation in the catchment. The intersection of the LEL and the linear fit of the spring and stream waters reflect the mean isotope composition of the annual precipitation (δ_P) with values of?8.6(±0.2) ‰ for δ¹⁸O and?58(±2) ‰ for δ²H. This value is also a good indicator of the average isotope composition of the local groundwater in the island. Surface water samples reflect the altitude isotope effect with a value of?0.17(±0.02) ‰ per 100 m elevation for oxygen isotopes. At Vizzavona Pass in central Corsica, water samples from two catchments within a lateral distance of only a few hundred metres showed unexpected but systematic differences in their stable isotope composition. At this specific location, the direction of exposure seems to be an important factor. The differences were likely caused by isotopic enrichment during recharge in warm weather conditions in south-exposed valley flanks compared to the opposite, north-exposed valley flanks.     

Water oxidation catalysed by manganese compounds: from complexes to 'biomimetic rocks'

One of the most fundamental processes of the natural photosynthetic reaction sequence is the light-driven oxidation of water to molecular oxygen. In vivo, this reaction takes place in the large protein ensemble Photosystem II, where a μ-oxido-Mn(4)Ca- cluster, the oxygen-evolving-complex (OEC), has been identified as the catalytic site for the four-electron/four-proton redox reaction of water oxidation. This Perspective presents recent progress for three strategies which have been followed to prepare functional synthetic analogues of the OEC: (1) the synthesis of dinuclear manganese complexes designed to act as water-oxidation catalysts in homogeneous solution, (2) heterogeneous catalysts in the form of clay hybrids of such Mn(2)-complexes and (3) the preparation of manganese oxide particles of different compositions and morphologies. We discuss the key observations from the studies of such synthetic manganese systems in order to shed light upon the catalytic mechanism of natural water oxidation. Additionally, it is shown how research in this field has recently been motivated more and more by the prospect of finding efficient, robust and affordable catalysts for light-driven water oxidation, a key reaction of artificial photosynthesis. As manganese is an abundant and non-toxic element, manganese compounds are very promising candidates for the extraction of reduction equivalents from water. These electrons could consecutively be fed into the synthesis of "solar fuels" such as hydrogen or methanol.     

Direct fluorometric analysis of a newly synthesised fluorescein-labelled marker for glomerular filtration rate

There is an obvious and growing medical need for an accurate determination of kidney function in the diagnosis and management of renal diseases. The glomerular filtration rate (GFR) is the accepted gold standard measurement of kidney function. Several approaches to estimate the GFR are available, but most of them are inconvenient and, therefore, of limited acceptance. A new method of quantification with fluorescein-isothiocyanate (FITC) sinistrin (FS), a novel GFR marker, has been evaluated. The method is based on the fluorescence label of FS and can be performed with a standard fluorometer. To control the interference of protein with the fluorescence signal, a calibration function was developed. The accuracy of the fluorometric method established is comparable to the so-called gold standard of enzymatic determination of polyfructosan. Moreover, FS is easy to handle and requires low-cost instruments. Our results demonstrate the potential of the direct fluorometric analysis of the new FITC-labelled marker of being a precise, simple, rapid and cost-effective method for diagnosing disturbed kidney function and monitoring its treatment efficacy. The dramatic decrease in analytical effort will result in a significantly higher acceptability of GFR determination.     

Antimitotic rhizoxin derivatives from a cultured bacterial endosymbiont of the rice pathogenic fungus Rhizopus microsporus

The potent antimitotic polyketide macrolide rhizoxin, the causal agent of rice seedling blight, is not produced by the fungus Rhizopus microsporus, as has been believed for over two decades, but by endosymbiotic bacteria that reside within the fungal mycelium. Here we report the successful isolation and large-scale fermentation of the bacterial endosymbiont ("Burkholderia rhizoxina") in pure culture, which resulted in a significantly elevated (10x higher) production of antimitotics. In addition to several known rhizoxin derivatives, numerous novel natural and semisynthetic variants were isolated, and their structures were fully elucidated. Cell-based assays as well as tubulin binding experiments revealed that methylated seco-rhizoxin derivatives are 1000-10000 times more active than rhizoxin and thus rank among the most potent antiproliferative agents known to date. Furthermore, more stable didesepoxy rhizoxin analogues were obtained by efficiently inhibiting a putative P-450 monooxygenase involved in macrolide tailoring.     

Field desorption mass spectrometry of natural products—III: Corrinoid metal complexes derived from vitamin B12

Charged and uncharged metal complexes of secocorrin which are model compounds for the synthesis of biogenetically and pharmacologically interesting metal analogs of vitamin B₁₂, were investigated by field desorption mass spectrometry. The data contained in the spectra of these compounds permit an exact and reliable determination of the molecular weight. In addition structural information can be obtained based on typical fragmentation reactions. The support of the results received by high resolution and precise mass measurement was made by a direct analysis of the isotopic pattern of the corrinoid metal complexes. The first use of this combined method for field desorption mass spectrometry of a series of natural products of high molecular weight revealed that important indications can be obtained for the identification and characterisation of these compounds.     

Das Massenspktroskopische Fragmentierungsverhalten von Derivaten des Benzisothiazol-S-dioxids

The fragmentation behavior of derivatives of benzisothiazole-S-dioxide is discussed. A series of degradation processes typical for this class of compounds is observed whose relative importance, however, largely depends upon substituents present. Provided it is energetically favorable fragmentation of the substituents (frequently followed by expulsion of SO₂) prevails, otherwise degradation of the heteroaromatic ring is observed (sometimes with rearrangements involving the SO₂ group). No parallels between thermal and electron-impact induced rearrangements have been observed.