Fossilized microorganisms preserved as fluid inclusions in epithermal veins, Vani Mn-Ba deposit, Milos Island, Greece

Fossilized microorganisms preserved as fluid inclusions are found in barite silica-Mn oxide veins in the marine rift basin-related Quaternary Mn-Ba deposit of Vani, Milos . Basin fill consists of 35-50 m thick sequence of glauconitic sediments sandwiched between volcaniclastic sandy tuffs, and, bedding-parallel barite Mn oxide( silica) horizons, pebble horizons, and massive gravel. Exhalative barite-rich deposits characteristic of sea-floor venting, such as white smoker(sulphate) structures in glauconitic sediments, feeder veins, bedding-conformable horizons, and extensive microbial mat- related structures in sandy tuffs, were recognized. The feeder veins host the microfossils and consist chiefly of banded barite and minor colloform quartz, Fe-oxyhydroxides, and hollandite-group minerals and MnO2 phases, and display epithermal textures characteristic of open-space precipitation. Curvilinear, branched filamentous microfossils with distinct segmentation of septa and a turgid appearance of knob-like outgrowths occur associated with spheroidal spore-like microfossils and small twisted microstructures. Both filamentous and spheroidal microstructures are filled with aqueous (liquid + vapour) and/or hydrocarbon phases. Oil and solid hydrocarbons in the fluid inclusions may represent decomposed biological material. Chitin was detected by the pigment Wheat Germ Agglutinin conjugated with Fluorescein Isothiocyanate (WGA-FITC) in some of the microfossils, indicating that they are fossilized fungi; a fungal interpretation is further supported by microfossil morphology. Smaller, often twisted filamentous microfossils with a simpler morphology in which chitin was not detected probably represent fossilized prokaryotes and, if so, prokaryotes and eukaryotes co-existed in the geothermal system of Vani. Fluid inclusion microthermometry shows that microfossils were trapped at temperatures of ~100°C in boiling water, probably evolved seawater. Preservation of microfossils occurred at shallow sub-marine conditions of <10 m depth. Our results show that fluid inclusions may contain valuable palaeobiological information and can be used both for establishing biogenicity but also for the reconstruction of the palaeoenvironment of fossilized microorganisms

Evidence of Mn-oxide biomineralization, Vani Mn deposit, Milos, Greece

We present evidence that precipitation of primary Mn-oxide minerals in the Vani volcanic hosted hybrid epithermal-VMS-type Mn-oxide and barite deposit was in part biogenically mediated. Manganese-oxides pseudomorphically replace small (1-5 mu m) spherical cell-like structures, and branching filamentous constructions (< 60 mu m long) probably representing manganese oxidizing bacteria. In addition, silicified consortia of spherical (5-10 mu m), filamentous, sheathed, septate and spiral (similar to 50-200 mu m) fossilized bacteria, proposed to represent photosynthetic thermophilic cyanobacteria, were found in quartz paragenetically related to the Mn ore. Fluid inclusions indicate formation temperatures around 100 degrees C. XRD and EMP analyses suggest X-ray-amorphous hollandite-group like Mn-oxide phases, and poorly crystalline todorokite and vernadite. These findings suggest a biological link between bacterial and mineralization processes

Density functional and ab initio study of the tautomeric forms of 3-acetyl tetronic and 3-acetyl tetramic acids

We propose all the accessible paths of interconversion between the tautomers of 3-acetyl tetronic and 3-acetyl tetramic acids by performing calculations with the density functional B3LYP method and the ab initio MP2 method. Our findings clarify at the atomic level the mechanisms of the equilibria between these tautomers, a topic so far only partially understood on the basis of studies by nuclear magnetic resonance (NMR) spectroscopy. We show that thermal effects via relative Gibbs free energies ΔG must be taken into account in order to reach good quantitative agreement with the available experimental information on the ratios of the most stable tautomers. The calculated 1H and 13C chemical shifts are in agreement with the experimental values from NMR spectroscopy. © 2003 Elsevier B.V. All rights reserved

Density functional and ab initio study of the tautomeric forms of 3-acetyl tetronic and 3-acetyl tetramic acids

We propose all the accessible paths of interconversion between the tautomers of 3-acetyl tetronic and 3-acetyl tetramic acids by performing calculations with the density functional B3LYP method and the ab initio MP2 method. Our findings clarify at the atomic level the mechanisms of the equilibria between these tautomers, a topic so far only partially understood on the basis of studies by nuclear magnetic resonance (NMR) spectroscopy. We show that thermal effects via relative Gibbs free energies ?G must be taken into account in order to reach good quantitative agreement with the available experimental information on the ratios of the most stable tautomers. The calculated 1H and 13C chemical shifts are in agreement with the experimental values from NMR spectroscopy

A novel access to 2-aminofuranones via cyclization of functionalized γ-hydroxy-α,β-butenoates derived from N-hydroxybenzotriazole esters of α-hydroxy acids

The reaction between the N-hydroxybenzotriazole esters of substituted glycolic acids and alkyl cyanoacetates or malononitrile leads to the synthesis of γ-hydroxy-functionalized butenoates which are cyclized under mild conditions to the corresponding 2-amino-3,5-disubstituted-4-furanones. That the products are optically active is confirmed by measurements of their optical rotations. On the other hand, replacement of N-hydroxybenzotriazole by N-hydroxysuccinimide might lead to by-products depending on the functionalized glycolic acid used