Niclas Johansson

Increase in the production of allelopathic substances by Prymnesium parvum cells grown under N- or P- deficient conditions

Increase in the production of allelopathic substances by Prymnesium parvum cells grown under N- or P- deficient conditions

Influence of different nutrient conditions on cell density, chemical composition and toxicity of Prymnesium parvum (Haptophyta) in semi-continuous cultures

Abstract The influence of various nitrogen (N) and phosphorus (P) levels on the cell density, chemical composition and toxicity of the marine haptophyte Prymnesium parvum were studied. A non-axenic strain of P. parvum was grown in semi-continuous cultures under either N- or P-limited conditions or nutrient-sufficient conditions (N:P=1:1, 160:1 and 16:1, respectively). Cell toxicity was measured on two occasions at steady state using a haemolytic test. Haemolytic activity was determined as saponin nano-equivalents (SnE) and HE 50 (50% haemolysis). Haemolytic activity was demonstrated in all treatments. However, haemolytic activity was significantly higher in P. parvum cells grown under N- or P-limited conditions (287.7±14.0 and 256.8±38.1 SnE cell −1 , respectively) compared to cells grown under non-limiting conditions (42.4±3.3 SnE cell −1 ). Our results document, for the first time, enhanced haemolytic activity in P. Parvum cells irrespective of which nutrient (N or P) was limiting growth. Our results suggest that the toxicity of P. parvum is related to cellular physiological stress, due to nutrient limitation rather than to the direct involvement of either N or P in toxin synthesis.

The new ambient-pressure X-ray photoelectron spectroscopy instrument at MAX-lab

The new instrument for ambient-pressure X-ray photoelectron spectroscopy at the Swedish synchrotron radiation facility MAX IV Laboratory is presented. The instrument is based on the use of a retractable and exchangeable high-pressure cell, which implies that ultrahigh-vacuum conditions are retained in the analysis chamber and that dual ambient pressure and ultrahigh-vacuum use is possible.

Covalent immobilization of molecularly imprinted polymer nanoparticles using an epoxy silane.

Molecularly imprinted polymers (MIPs) can be used as antibody mimics to develop robust chemical sensors. One challenging problem in using MIPs for sensor development is the lack of reliable conjugation chemistry that allows MIPs to be fixed on transducer surface. In this work, we study the use of epoxy silane to immobilize MIP nanoparticles on model transducer surfaces without impairing the function of the immobilized nanoparticles. The MIP nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model transducer surface is functionalized with a self-assembled monolayer of epoxy silane, which reacts with the core-shell MIP particles to enable straightforward immobilization. The whole process is characterized by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show that the MIP particles are immobilized uniformly on surface. The photoelectron spectroscopy results further confirm the action of each functionalization step. The molecular selectivity of the MIP-functionalized surface is verified by radioligand binding analysis. The particle immobilization approach described here has a general applicability for constructing selective chemical sensors in different formats.

Oxidation of Ultrathin FeO(111) Grown on Pt(111): Spectroscopic Evidence for Hydroxylation

Using high resolution and ambient pressure X-ray photoelectron spectroscopy we show that the catalytically active FeO

Adsorption of CO on the Fe3O4(001) Surface

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Iron phthalocyanine on Cu(111): Coverage-dependent assembly and symmetry breaking, temperature-induced homocoupling, and modification of the adsorbate-surface interaction by annealing

2 trilayer films grown on Pt(111) are very active for water dissociation, in contrast to inert FeO(111) bilayer films. The FeO