Preparative liquid chromatography with analytical separation quality : Internal injection/displacement reversed-phase high-performance liquid chromatography

A method for the enrichment and separation of compounds, called interval injection/displacement reversed-phase high-performance liquid chromatography (HPLC), was applied to several analytical and preparative separations. In principle, the surface of a reversed-phase stationary phase, equilibrated with a weak mobile phase, is “coated” with compounds by stepwise injection of small samples. Distinct time intervals between injections allow the stationary phase to re-equilibrate. In this way, sample enrichment can be achieved in ranges comparable to those in overload elution or displacement HPLC. Sample fractionation proceeds in a similar manner to conventional displacement modes. Also under full mass load conditions, a quality of separation similar to that in analytical elution HPLC is achieved. The results obtained indicate that a very large number of samples can be applied to conventionally sized columns without overload problems, the full mass capacity of a column can be utilized and the method is useful for enriching and separating compounds with a wide range of polarities. Interval injection/displacement reversed-phase HPLC was successfully applied to complex mixtures of natural products and enzyme assay mixtures. Further, this technique is likely to be useful for the analysis of trace compounds and quality control of chemicals. The experiments reported were performed on highly unstable natural products (thiophenic and benzofuran compounds) from Tagetes plants

Polymerization of resorcinol by an cryptophycean exoenzyme.

In aqueous solutions exposed to sunlight, resorcinol, a m-dihydroxyphenol, does not undergo autoxidation as compared to catechol, an o-dihydroxyphenol. However, water taken from a lake (Schöhsee, Plön) caused a disappearance of resorcinol and enhanced catechol conversion. A screening involving species of various algae groups showed that resorcinol was being converted specifically by members of the Cryptophyceae family. The algae could be separated by ultrafiltration from the culture medium with full viability; the activity was found in the medium and could be characterized by protein precipitation and denaturation as a Cryptomonad exoenzyme with a M.W. congruent to 10⁵. The conversion rates of resorcinol increased exponentially during successive additions of substrate, pointing to a reaction on which the product functions as an increasing matrix for the addition of next substrate molecules. After seven resorcinol pulses of about 30 nmol/ml resorcinol to the same enzyme source, irregularly-shaped, water-insoluble crystals appeared as reaction products. The algae themselves, however, were severely affected after the third resorcinol application and did not survive subsequent addition. In the freshwater research, this result represents the complete sequence of an allelopathic interaction between resorcinol exuding aquatic macrophytes and surrounding microphytes; it may also contribute to the solution of open questions about the origin and turnover of phenolic DOM in aqueous systems. In environmental terms, it questions the role of industrial wastewater inputs, and on one hand the toxicity of resorcinol and on the other hand, the detoxification capability of natural waters. Lastly, it should be considered that this kind of enzymatic monophenol condensation could also participate in the synthesis of various polyphenolic compounds of higher terrestrial plants

Polymerization of resorcinol by an cryptophycean exoenzyme.

In aqueous solutions exposed to sunlight, resorcinol, a m-dihydroxyphenol, does not undergo autoxidation as compared to catechol, an o-dihydroxyphenol. However, water taken from a lake (Schöhsee, Plön) caused a disappearance of resorcinol and enhanced catechol conversion. A screening involving species of various algae groups showed that resorcinol was being converted specifically by members of the Cryptophyceae family. The algae could be separated by ultrafiltration from the culture medium with full viability; the activity was found in the medium and could be characterized by protein precipitation and denaturation as a Cryptomonad exoenzyme with a M.W. congruent to 10⁵. The conversion rates of resorcinol increased exponentially during successive additions of substrate, pointing to a reaction on which the product functions as an increasing matrix for the addition of next substrate molecules. After seven resorcinol pulses of about 30 nmol/ml resorcinol to the same enzyme source, irregularly-shaped, water-insoluble crystals appeared as reaction products. The algae themselves, however, were severely affected after the third resorcinol application and did not survive subsequent addition. In the freshwater research, this result represents the complete sequence of an allelopathic interaction between resorcinol exuding aquatic macrophytes and surrounding microphytes; it may also contribute to the solution of open questions about the origin and turnover of phenolic DOM in aqueous systems. In environmental terms, it questions the role of industrial wastewater inputs, and on one hand the toxicity of resorcinol and on the other hand, the detoxification capability of natural waters. Lastly, it should be considered that this kind of enzymatic monophenol condensation could also participate in the synthesis of various polyphenolic compounds of higher terrestrial plants

Exudation of UV-light absorbing natural products by seedlings Nuphar lutea

Seedlings of Nuphar lutea (L.) Sm. were raised from seeds and cultivated in a synthetic sterile nutrient solution under physiologically controlled and undisturbed conditions. The extracellular release of carbon compounds from the plants into the surrounding medium was examined by direct carbon estimation, by various specific chemical assays and by HPLC analysis. Direct carbon estimation was not sensitive enough to obtain reliable values; five of six specific chemical assays also failed. Only the Folin-Denis assay indicated there was a production of phenolic compounds, which followed a linear course that took up to six days of incubation. The phenolic compounds ranged between 0.2 and 1.3 µg/h g dry weight. Rp-HPLC with UV detection yielded a major fraction containing at least five highly polar compounds (not retainable on reversed phase), and a minor fraction of at least eight less polar (rp-retainable) compounds. Exudation followed a linear course for some days up to a distinct level of saturation in the surrounding medium. Cultures incubated in light or absolute darkness exhibit the same production rates; however, lower temperatures caused significant reduction in the production rate and on the pattern of exuded compounds as well. After withdrawing the exuded compounds by rinsing the cultures, a new production can be repeatedly induced many times until the potential of the system is seemingly exhausted. Nuphar seedlings procedures are introduced as a new macrophyte system suitable for studying the mechanism of extracellular secretion among aquatic macrophytes

Polyphenols with algicidal activity in the submerged macrophyte Myriophyllum spicatum L.

The role of phenols as defence mechanisms in various terrestrial plants is well studied. However, in aquatic environments, they are probably involved also in the chemical interactions between species. A periodic shift from dominance by submerged macrophytes to dominance by phytoplankton and vice versa without apparent change in the external nutrient loading is sometimes observed in shallow eutrophic lakes. Due to the fact that nutrient levels are not usually limiting to phytoplankton growth, the release of allelochemicals by macrophytes is suspected to be responsible for poor algal growth. Myriophyllum spicatum is known to produce several phenolic compounds. Aqueous methanolic extracts of fresh or lyophilized as well as axenic or non-axenic M. spicatum plant material exhibited strong algicidal activity against cyanobacteria. Chlorophytes and diatoms are also affected, but to a lesser extent. Bioassay directed fractionation of the extract lead to the isolation of two strong algicidal compounds. These compounds are constitutively present in the plant and were characterized as galloyl glycosides (500-1000 dalton). To test the ecological importance of these substances, the culture water was screened for exudated phenolic compounds. At least 5-10 different polyphenols could be detected. An algicidal galloyl ester and several derivatives of ellagic acid were among them. The possible release mechanisms and the mode of action of these polyphenols as defence compounds are discussed

Etude de l' inclusion d' ions métalliques dans les cristaux de molybdate de zirconium et son impact sur les cinétiques de formation

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Response: Commentary: Using Virtual Reality to Assess Ethical Decisions in Road Traffic Scenarios: Applicability of Value-of-Life-Based Models and Influences of Time Pressure

In the paper discussed (Sütfeld et al., 2017), we examined the feasibility of using virtual reality (VR) as an assessment method for models of human moral behavior in road traffic scenarios. Furthermore, this experimental approach allowed us to analyze the applicability of logistic regression-based value-of-life models for modeling human behavior. We consider this study to be a contribution to the discussion about ethical decision-making systems in autonomous vehicles (AVs)