F. Guillermo Díaz Baños

Influence of ionic strength on the flexibility of alginate studied by size exclusion chromatography

SEC measurements of the [η]-M relationship for alginate from Macrocystis pyrifera and the wormlike model can be used to characterize flexibility through two independent treatments (Bohdaneckys equations and HYDFIT program), both providing the same results. Two different assumptions concerning mass per unit of length lead to different conclusions. First: persistence length decreases with ionic strength (the intrinsic component of the persistence length is 11.3 nm and the electrostatic component is 6 nm when ionic strength is 0.01). Second: persistence length is independent of ionic strength (12 nm). Either of these options shows that the wormlike model in itself is not sufficient to explain flexibility over the whole range of chain lengths for these polyelectrolytes. A plausible explanation could be the presence of a combination of short-range and long-range screening effects of the ions of the solutions. This would also explain some data found in the literature regarding alginate flexibility.

Aggregation behaviour of gold nanoparticles in presence of chitosan

Chitosan (CS) is a biocompatible polysaccharide with positive charge that is widely used as a coating agent for negatively charged nanoparticles. However, the types of structures that emerge by combining CS and nanoparticles as well as their behaviour are still poorly understood. In this work, we characterize the nanocomposites formed by gold nanoparticles (AuNPs) and CS and study the influence of CS in the expected aggregation process that should experience those nanoparticles under the favourable conditions of low pH and high ionic strength. Thus, at the working CS concentration, we observe the existence of CS structures that quickly trap the AuNPs and avoid the formation of nanoparticle aggregates in environmental conditions that, otherwise, would lead to such an aggregation.

Terminal carbohydrates abundance, immune related enzymes, bactericidal activity and physico-chemical parameters of the Senegalese sole (Solea senegalensis, Kaup) skin mucus

ABSTRACT Recently, interest in mucosal surfaces, more specifically fish skin and its secreted mucus, has greatly increased among immunologists. The abundance of terminal carbohydrates, several enzymes (proteases, lysozyme, peroxidase, alkaline phosphatase, esterases and ceruloplasmin), bactericidal activity against fish pathogenic and non‐pathogenic bacteria and several physico‐chemical parameters (protein concentration, pH, conductivity, redox potential, osmolarity, density and viscosity) in the skin mucus of Senegalese sole (Solea senegalensis, Kaup) have been evaluated. Present results evidence the abundance of N‐acetylneuraminic acid, mannose, glucose and N‐acetyl‐galactosamine in skin mucus. The levels of lysozyme, proteases, esterases and alkaline phosphatase were very similar (from 20 to 30 Units mg−1 protein). However, 93 Units mg−1 protein were detected of ceruloplasmin and only 4′88 Units mg−1 protein of peroxidase. Skin mucus of S. senegalensis showed high bactericidal activity against the tested pathogen bacteria but weak activity against non‐pathogenic bacteria. Finally, a clear relationship between mucus density and temperature was detected, while viscosity showed a direct shear‐ and temperature‐dependent behaviour. These results could be useful for better understanding the role of the skin mucus as a key component of the innate immune system, as well as, for elucidating possible relationships between biological and physico‐chemical parameters and disease susceptibility. HIGHLIGHTSN‐acetylneuraminic acid, mannose, glucose and N‐acetyl‐galactosamine are present in skin mucus of Solea senegalensis.Levels of ceruloplasmin and peroxidase were higher and lower, respectively, than the levels of the other studied enzymes.Skin mucus showed high bactericidal activity against the tested pathogen bacteria but weak activity against non‐pathogenic bacteria.Mucus density and temperature were related. Viscosity showed a direct shear‐ and temperature‐dependent behaviour.The results could be useful for elucidating possible relationships between biological and physico‐chemical parameters.

Enhanced Zn2+ ion-sensing behavior of a benzothiazole derivative on encapsulation by β-cyclodextrin

We report, in this paper, a benzothiazole derivative which shows selective binding of zinc ions among a pool of metal ions and the enhanced selectivity of the same metal ion by the derivative in its β-cyclodextrin bound form. The Zn2+ ion binding is studied using UV-visible absorption and fluorescence spectroscopy. The stoichiometry and binding mode of the benzothiazole derivative-β-cyclodextrin complex are determined using 1D and 2D NMR spectroscopic analysis. The cyclodextrin molecule slides over the benzothiazole derivative and resides above the aminomethyl group linking the benzothiazole and dihydroxyphenyl moieties. The site of binding of the Zn2+ ion with the compound remains the same both in the compounds free and cyclodextrin-complexed forms. Molecular modeling studies were also carried out in order to obtain more details about the cyclodextrin-compound and Zn2+-compound interactions, and their results are in close agreement with obtained experimental data.

Chitosan as stabilizing agent for negatively charged nanoparticles

Chitosan is a biocompatible polysaccharide with positive Z potential which can stabilize negative charged nanoparticles. Silk fibroin nanoparticles and citrate gold nanoparticles, both with negative Z potential, but they form aggregates at physiological ionic strength. In this work, we study the behavior of chitosan in solution when the ionic strength of the medium is increased and how the concentration of chitosan and the proportion of the two components (chitosan and AuNP or SFN) significantly affect the stability and size of the nanocomposites formed. In addition to experimental measurements, molecular modeling were used to gain insight into how chitosan interacts with silk fibroin monomers, and to identify the main energetic interactions involved in the process. The optimum values for obtaining the smallest and most homogeneous stable nanocomposites were obtained and two different ways of organization through which chitosan may exert its stabilizing effect were suggested.

Density and refractive index data of binary and ternary mixtures of imidazolium-based ionic liquids, n-hexane and organic compounds involved in the kinetic resolution of rac-2-pentanol

This data article is related to the subject of the research article “Extraction of Organic Compounds Involved in the Kinetic Resolution of rac-2-Pentanol from n-Hexane by Imidazolium-based Ionic Liquids: Liquid-Liquid Equilibrium” (Montalbán et al., 2018) [1]. It contains experimental data of density and refractive index of binary and ternary mixtures of imidazolium-based ionic liquids, n-hexane and organic compounds involved in the kinetic resolution of rac-2-pentanol (rac-2-pentanol, vinyl butyrate, rac-2-pentyl butyrate or butyric acid) measured at 303.15 K and 1 atm. These data are presented as calibration curves which help to determine the composition of the ionic liquid-rich phase knowing its density or refractive index.