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Detection of fibrinogen monolayers on mica by the colloid enhancement

Nattich-Rak M., Adamczyk Z., Wasilewska M., Radziszewska M.

Environmental Biotechnology

2011

Vol. 7, No. 1

1-11

Physicochemical properties of bovine plasma fibrinogen (Fb) in electrolyte solutions were characterised, comprising the diffusion coefficient (hydrodynamic radius), electrophoretic mobility (zeta potential) and the isoelectric point, found to be at pH=5.8. Similar electrokinetic measurements were performed for the mica substrate using the streaming potential cell. The kinetics of Fb adsorption on mica under diffusion-controlled transport was also studied. The surface concentration of Fb on mica was determined directly by AFM counting. By adjusting the time of adsorption, and bulk Fb concentration, monolayers of desired coverage were produced. It was confirmed that Fb adsorbed irreversibly on mica both at pH=3.5 and pH=7.4 (physiological value). It was postulated that in the latter case, where both the substrate and fibrinogen molecules were negatively charged, adsorption was due to heterogeneous charge distribution over the protein molecule. In order to check this hypothesis, monolayers of Fb on mica were studied using the colloid enhancement (CE) method, in which negatively and positively charged latex particles were used. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH=3.5 and 7.4, respectively. This allowed one to determine limits of applicability of the classical DLVO theory and confirm a heterogeneous charge distribution over the Fb molecule. It was also concluded that the CE method can be used for a sensitive determination of the Fb bulk concentration for the range inaccessible for other methods, i.e., for 0.1ppm and below. Another effect of vital significance confirmed in this work was that for some range of fibrinogen coverage both the negative and positive latexes efficiently adsorbed. This indicates the formation of superadsorbing surfaces having potential significance for various filtration processes.

Adsorpcja fenoli na węglu aktywnym

Dąbrowski A., Podkościelny P., Hubicki Z., Barczak M., Robens E.

Wiadomości Chemiczne

2005

[Z] 59, 7-8

639--694

Adsorption of phenolic compounds on activated carbons is considered based on survey of abundant literature on it. Phenols belong to a group of common environmental contaminants. Since they are highly toxic and, in general, not amenable to biological degradation, methods of treatment are continuously being modified and developed. Adsorption by activated carbons is the best and most frequently used method to remove phenols from waters. Numerous factors are known to have important influence on this phenomenon: type of carbon, carbon surface functionalities, pH value of the coexisting bulk liquid phase, oxygen availability, etc. In this review, we have tried to discuss the significance of the above-mentioned factors. The first chapter of the review deals with characterization of the activated carbon from the point of view of application for phenols uptake. The selection of precursors of activated carbon as well as generation of porosity and surface chemical composition are taken into account. Adsorption of phenolic compounds has been described critically, showing the development of investigations on the subject and presenting some of the most important results. A special attention is paid to the effect of surface functionalities and pH of solution. These two factors are considered together, because owing to the amphoteric character of a carbon surface its surface properties may be influenced by the pH value of the coexisting liquid bulk phase. The fundamental mechanisms of phenol adsorption have been emphasized i.e. "π-π interactions" and ,.donor-acceptor complex formation", taking into account the influence of the so-called "solvent effect". Energetic heterogeneity of activated carbons is presented on the basis of adsorption energy distribution functions, calculated by using algorithm based on a regularization method. Analysis of these functions provides significant comparative information about their heterogeneity. Problems associated with irreversible adsorption from aqueous solutions of phenols and their surface polymerization are reported in vast paragraph. We concluded that the presence of molecular oxygen and its amount has a significant influence on the adsorption capacity of activated carbon for phenol and its derivatives. Oxidative coupling in the presence of molecular oxygen causes irreversible adsorption (chemisorption). Effects of different substituents of phenols are considered too. Bigger size and/or larger number of groups of an adsorbate lead to a higher heterogeneity for the same surface. It has been stressed that, neither of the substituent groups was involved directly in the interaction with the carbon surface, but they contribute to the electron-acceptor characteristics of the aromatic ring of the solute. The cheap precursors of activated carbons from the waste materials are also described in our review. Finally, some remarks dealing with application of novel adsorbents for phenols adsorption, such as activated carbon fibers are discussed.