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4 Publications visible to you, out of a total of 4
Thermodynamic study on 8-hydroxyquinoline-2-carboxylic acid as a chelating agent for iron found in the gut of Noctuid larvae

Abstract (Expand)

The recognition of quinolinic carboxylic acids as natural chelants and the recent observation of a high production of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) in the gut of several Noctuid larvae … (e.g. Spodoptera littoralis) has inspired the study of the chelation properties of 8-HQA towards Fe2+ and Fe3+. Here, we report a detailed characterization of the thermodynamic solution behaviour of Fe2+/8-HQA and Fe3+/8-HQA systems as a function of the pH value. The acid–base properties of 8-HQA and its binding ability towards Fe2+ and Fe3+ have been investigated over a wide range of pH values (2.0 ≤ pH ≤ 11.0) by ISE-H+ (glass electrode) potentiometric titrations in KCl(aq) at I = 0.2 mol dm−3 and at T = 298.15 K. For both oxidation states, various FeLqHr species are formed, with q = 1, 2 (and 3), and −2 ≤ r ≤ 1. The presence of the main FeLqHr species was confirmed by HESI-HRMS. ESR measurements have also been performed to get some extra information on the Fe3+ coordination, indicating a distorted octahedral symmetry around the metal center. Quantum mechanical calculations have been carried out in order to characterize the structural features of selected metal complexes. The complexing ability of 8-HQA is generally much higher for Fe3+ than Fe2+. Nevertheless, the sequestering ability of 8-HQA towards these two oxidation states of this metal ion, obtained by the calculation of several pL0.5 values, resulted in it being highly dependent on the pH value: (i) at relatively low pH values, it is higher for Fe3+ (pL0.5 = 6.3 at pH = 3.0) than for Fe2+ (pL0.5 = 3.1 at pH = 3.0); (ii) it is almost the same at pH = 8.1 (Fe3+: pL0.5 = 8.3; Fe2+: pL0.5 = 8.1); (iii) it is higher for Fe2+ at high pH values (pL0.5 = 8.9 for Fe2+ and pL0.5 = 6.2 for Fe3+ at pH = 10.0). The determination of the stability constants of the Fe2+/8-HQA and Fe3+/8-HQA complexes was also complemented by data obtained by the ligand-competition approach, using EDTA as a competing ligand over a wide range of cation and ligand concentrations and ratios. This also allowed a more thorough investigation of both the Fe2+/EDTA and Fe3+/EDTA systems, providing an accurate stability constant dataset for the Fep(EDTA)qHr species under the above-mentioned experimental conditions, which are commonly used in biological studies.

Authors: Sofia Gama, Mariachiara Frontauria, Nico Ueberschaar, Giuseppe Brancato, Demetrio Milea, Silvio Sammartano, Winfried Plass

Date Published: 9th Apr 2018

Publication Type: Not specified

DeltaMS: a tool to track isotopologues in GC- and LC-MS data

Abstract (Expand)

Introduction: Stable isotopic labeling experiments are powerful tools to study metabolic pathways, to follow tracers and fluxes in biotic and abiotic transformations and to elucidate molecules involved …d in metal complexing. Objective: To introduce a software tool for the identification of isotopologues from mass spectrometry data. Methods: DeltaMS relies on XCMS peak detection and X13CMS isotopologue grouping and then analyses data for specific isotope ratios and the relative error of these ratios. It provides pipelines for recognition of isotope patterns in three experiment types commonly used in isotopic labeling studies: (1) Search for isotope signatures with a specific mass shift and intensity ratio in one sample set. (2) Analyze two sample sets for a specific mass shift and, optionally, the isotope ratio, whereby one sample set is isotope-labeled, and one is not. (3) Analyze isotope-guided perturbation experiments with a setup described in X13CMS. Results: To illustrate the versatility of DeltaMS, we analyze data sets from case-studies that commonly pose challenges in evaluation of natural isotopes or isotopic signatures in labeling experiment. In these examples, the untargeted detection of sulfur, bromine and artificial metal isotopic patterns is enabled by the automated search for specific isotopes or isotope signatures. Conclusion: DeltaMS provides a platform for the identification of (pre-defined) isotopologues in MS data from single samples or comparative metabolomics data sets.

Authors: Tim U. H. Baumeister, Nico Ueberschaar, Wolfgang Schmidt-Heck, J. Frieder Mohr, Michael Deicke, Thomas Wichard, Reinhard Guthke, Georg Pohnert

Date Published: 27th Feb 2018

Publication Type: Not specified

Sticking together: inter-species aggregation of bacteria isolated from iron snow is controlled by chemical signaling

Abstract (Expand)

Marine and lake snow is a continuous shower of mixed organic and inorganic aggregates falling from the upper water where primary production is substantial. These pelagic aggregates provide a niche for … microbes that can exploit these physical structures and resources for growth, thus are local hot spots for microbial activity. However, processes underlying their formation remain unknown. Here, we investigated the role of chemical signaling between two co-occurring bacteria that each make up more than 10% of the community in iron-rich lakes aggregates (iron snow). The filamentous iron-oxidizing Acidithrix strain showed increased rates of Fe(II) oxidation when incubated with cell-free supernatant of the heterotrophic iron-reducing Acidiphilium strain. Amendment of Acidithrix supernatant to motile cells of Acidiphilium triggered formation of cell aggregates displaying similar morphology to those of iron snow. Comparative metabolomics enabled the identification of the aggregation-inducing signal, 2-phenethylamine, which also induced faster growth of Acidiphilium. We propose a model that shows rapid iron snow formation, and ultimately energy transfer from the photic zone to deeper water layers, is controlled via a chemically mediated interplay.

Authors: J. F. Mori, N. Ueberschaar, S. Lu, R. E. Cooper, G. Pohnert, K. Kusel

Date Published: 1st Feb 2017

Publication Type: Not specified

A fast and direct liquid chromatography-mass spectrometry method to detect and quantify polyunsaturated aldehydes and polar oxylipins in diatoms

Abstract (Expand)

Polyunsaturated aldehydes (PUAs) are a group of microalgal metabolites that have attracted a lot of attention due to their biological activity. Determination of PUAs has become an important routine … procedure in plankton and biofilm investigations, especially those that deal with chemically mediated interactions. Here we introduce a fast and direct derivatization free method that allows quantifying PUAs in the nanomolar range, sufficient to undertake the analysis from cultures and field samples. The sample preparation requires one simple filtration step and the initiation of PUA formation by cell disruption. After centrifugation the samples are ready for measurement without any further handling. Within one chromatographic run this method additionally allows us to monitor the formation of the polar oxylipins arising from the cleavage of precursor fatty acids. The robust method is based on analyte separation and detection using ultra high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (UHPLC-APCI MS) and enables high throughput investigations by employing an analysis time of only 5 min. Our protocol thus provides an alternative and extension to existing PUA determinations based on gas chromatography-mass spectrometry (GC-MS) with shorter run times and without any chemical derivatization. It also enables researchers with widely available LC-MS analytical platforms to monitor PUAs. Additionally, non-volatile oxylipins such as ω-oxo-acids and related compounds can be elucidated and monitored.

Authors: Constanze Kuhlisch, Michael Deicke, Nico Ueberschaar, Thomas Wichard, Georg Pohnert

Date Published: 15th Oct 2016

Publication Type: Not specified

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