Isothermal titration calorimetric studies of surfactant interactions with negatively charged, ‘hairy’ latex nanoparticles

Isothermal titration calorimetry (ITC) measurements of the mixture of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) with negatively charged, hairy copolymer latices (poly-(2,3-epoxypropylmethacrylate-co-methacrylic acid) in different ratio) at high water excess indicate a monomer adsorption mechanism of CTAB by the polymer particles. The number of adsorbed CTAB molecules at saturation corresponds approximately to the number of negative elementary charges bound at the surface of the latices. The mixing enthalpy is the sum of demicellization and sorption enthalpies. At 25 °C for CTAB the demicellization enthalpy amounts to 10 kJ/mol, whereas the adsorption enthalpy varies from –7 kJ/mol (surface charge density of the latices =–0.37 C/m²) to +3 kJ/mol (=–0.085 C/m²). The hydrodynamic radius R_H of the latex particles upon titration of cationic detergent and salt (NaBr) decreases by about 2 nm until the onset of aggregation near the isoelectric point. Titration of nonionic or anionic detergents has much less influence on the hydrodynamic radius and produces no measurable adsorption heat. The results are consistent within a model of latex particles with extended negatively charged polymer chains interacting predominantly via Coulombic forces with detergents.     

Gd<Superscript>3+</Superscript> binding of carboxylated polyglycidyl methacrylate latices and their colloidal stability

The binding of Gd³⁺ to two carboxylated polyglycidyl methacrylate latices was investigated. The latices differed in size (60 and 140 nm for CL6 and CL3, respectively) and surface charge density. The Gd³⁺ concentration in aqueous suspension was determined using an arsenazo (III) assay. Using ¹⁵³Gd³⁺, the bound amount was determined directly. Because of the high binding affinity, ligand depletion became evident. The binding was pH dependent, investigated in buffer solutions not influencing the arsenazo (III) assay. Optimal binding occurs by formation of sodium salts of the carboxylic groups and replacement of Na⁺ and H⁺ by Gd³⁺. The dissociation constants of the particles were k _D ≈ 5 × 10⁻⁵ mol/L (CL3) and 10⁻⁴ mol/L (CL6), without cooperativity (Hill plot). Colloidal stability was investigated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Analysis of plasma protein adsorption onto polystyrene particles by two-dimensional electrophoresis: comparison of sample application and isoelectric focusing techniques

Two-dimensional electrophoresis (2-DE) was previously established for analysis of plasma protein adsorption patterns on particulate carriers for intravenous drug targeting. This study addresses a possible effect of polymeric particles on protein separation in the first dimension, e.g., hindrance of protein entry into the gel or interaction of particles with the gel matrix. Polystyrene beads of mean diameter 100, 200 and 1000 nm were used as model carriers. Two different separation techniques were performed in the first dimension of 2-DE to study possible interactions of the beads with the different gel matrices, i.e., carrier ampholytes (CA) and immobilized pH gradients (IPGs). Comparison of gels obtained from samples including the particles from samples separated from the polystyrene beads showed no noteworthy differences. Therefore, a negative effect of the particles can be excluded, and particle separation from the sample is not necessary. Another goal of this study was the transfer of analytical protocols for isoelectric focusing from CA to IPGs with regard to enhanced reproducibility, faster sample processing, and easier handling. Transfer from CA to IPGs was carried out successfully and showed improved resolution of basic proteins. In contrast to that, lower amounts of a few high molecular mass proteins were detected, especially when sample application cups were employed. A qualitative change in the obtained protein pattern was not observed. Increased entry of high molecular weight proteins was achieved by in-sample rehydration instead of using sample cups.     

Determination of hypericin and pseudohypericin from Hypericum perforatum in rat brain after oral administration

The popularity of St. John’s Wort (SJW) extracts for treating mild to moderate depression has increased over the last decades and great effort has been devoted to identify the active principle of SJW extract. Previous investigations suggest the contribution of at least three classes of compounds, the phloroglucinols, the quercetin flavonoids, and the phenanthroperylenequinones, to the clinical efficiency of SJW extracts. Up to now, a plausible molecular mechanism of action has been described only for the phloroglucinols. For the flavonoids and the phenanthroperylenequinones different targets were proposed on the basis of pharmacological studies. The vast majority of these targets are located in the CNS and therefore increasing interest in the question of the CNS availability of these substances arose. Recently, the ability of phloroglucinols and flavonoids to penetrate the blood brain barrier could be demonstrated. For the phenanthroperylenequinones an examination of CNS bioavailability is still missing. The aim of this work is to close this gap by developing and validating a HPLC method with electrochemical detection for the quantification of the phenanthroperylenequinones in brain tissue of rodents after oral application of SJW extract or pure hypericin. In our study, the phenanthroperylenequinone content in the CNS tissue was below the lower limit of detection of the analytical method and was thus lower than 16 pmol/g brain for hypericin and lower than 52 pmol/g brain for pseudohypericin after oral administration of 1600 mg/kg SJW extract or pure hypericin (5 mg/kg). Correspondence: Mario Wurglics, Institute of Pharmaceutical Chemistry, Johann Wolfgang Goethe University/ZAFES, 60438 Frankfurt am Main, Germany.     

Cationic flocculants carrying hydrophobic functionalities: applications for solid/liquid separation

The flocculation behaviors of three series of polycations with narrow molecular weight distributions carrying hydrophobic substituents on their backbones [poly(N-vinylbenzyl-N,N,N-trimethylammonium chloride), poly(N-vinylbenzyl-N,N-dimethyl-N-butylammonium chloride), and poly(N-vinylbenzylpyridinium chloride)] were investigated in dispersions of monodisperse polystyrene latexes and kaolin. Apparently, the charge density of the polycations decreases with increasing substituent hydrophobicity and increasing molecular weight of the polyelectrolytes. The necessary amount of flocculant for phase separation in dispersions with high substrate surface charge densities increases with increasing hydrophobicity of the polyelectrolyte. Nevertheless, the introduction of hydrophobic functionalities is beneficial, resulting in a substantial broadening of the range between the minimum and maximum amounts of flocculant necessary for efficient flocculation (flocculation window). An increase in ionic strength supports this effect. When the substrate has a low charge density, the hydrophobic interactions play a much more significant role in the flocculation process. Here, the minimum efficient doses remained the same for all three polyelectrolytes investigated, but the width of the flocculation window increased as the polycation hydrophobicity and the molecular weight increased. The necessary amount of flocculant increased with an increase in particle size at constant solid content of the dispersion, as well as with a decreasing number of particles at a constant particle size.     

CHANGES IN CHLOROPHYLL-PROTEIN COMPLEXES ASSOCIATED WITH JUNE YELLOWS OF STRAWBERRY*

Abstract— June yellows (J-y) of strawberry (Fragaria) is an inheritable condition for which no causal pathogen has been demonstrated. Spectroscopic analysis of intact leaf lamina was applied to strawberry leaves with J-y. The spectra were analyzed by fourth derivative technique. Differences were found between asymptomatic and affected leaves with respect to chlorophyll-protein complexes. Affected leaves show spectra consistent with loss of certain chlorophyll-a-proteins (Ca). Distinct types of effects are found. In one type Ca 684 decreases, in another Ca 693 is diminished. Studies of strawberry clone pedigree suggest that Ca 684 losses are observed in clones with Howard 17 parentage, and Ca 693 losses in clones with Aberdeen parentage. One clone with both Howard 17 and Aberdeen parentage had a spectra consistent with diminished Ca 684 and Ca 693. The simplest explanation of the data is that J-y results from several different types of genetic lesions on different Ca. Some viral infection effects on Ca spectra are also described.     

Analysis of lysergic acid amide in human serum and urine after ingestion of Argyreia nervosa seeds

The ergot alkaloid lysergic acid amide (LSA) is a secondary plant constituent in a number of plants, but it is mainly present in considerable amounts in Convolvulaceae, like Argyreia nervosa. Due to its close structural similarity to lysergic acid diethylamide, LSA is considered as psychedelic and therefore promoted as so-called “legal high” in various internet forums. During a human behavioral study with orally administered seeds of A. nervosa, blood and urine samples were obtained. The present study describes the validation of a sensitive and robust high performance liquid chromatography method with fluorescence detection, which was applied to the study samples. The limit of detection (LOD) and lower limit of quantification in human serum were 0.05 and 0.17 ng/mL, respectively, and in urine, the LOD was 0.15 ng/mL. Intra- and interday precision and accuracy were below 15 % relative standard deviation with a bias better than ±15 %. No conversion of LSA to its epimer iso-LSA was noted during analyses. The LSA concentrations in the authentic human serum samples were in the range of 0.66 to 3.15 ng/mL approximately 2 h after ingestion. In urine, LSA could be found 1–24 h after ingestion; after 48 h, no LSA could be detected. The LSA epimer iso-LSA was also detected in serum and urine in varying ratios. In conclusion, LSA serum levels in the low nanogram per milliliter range correlated with severe vegetative adverse effects (nausea, weakness, fatigue, tremor, blood pressure elevation) and a psychosis-like state, which led to study termination.