Gloria Víllora

The effect of ionic liquid media on activity, selectivity and stability of Candida antarctica lipase B in transesterification reactions

Nineteen different 1,3-dialkylimidazolium-based ionic liquids (ILs) were used as reaction media for the synthesis of butyl butyrate by transesterification from vinyl butyrate and 1-butanol catalyzed by Candida antarctica lipase B (CaLB). The reaction was also carried out in hexane as a reference solvent. In all the water-immiscible ILs assayed, the enzymatic activity and selectivity were higher than that obtained in hexane. However, in water-miscible ILs, the activity was lower than in the reference solvent, although they showed >99.99% selectivity. Two solvent properties, hydrophobicity and nucleophilicity, were considered key parameters for analyzing the behavior of CaLB in ILs. In the case of ILs based on the same anion, the synthetic activity was gradually enhanced by increasing cation hydrophobicity. Furthermore, the activity of CaLB was greater in ILs containing anions of lower nucleophilicity. Stability studies indicate that CaLB exhibited greater stability in water-immiscible ILs than in water-miscible ILs.

Silk Fibroin Nanoparticles: Efficient Vehicles for the Natural Antioxidant Quercetin.

This article describes how silk fibroin nanoparticles (SFNs) are capable of adsorbing and releasing quercetin (Q) and how its integrity is highly preserved, as confirmed by antioxidant activity assays. Q loading onto SFNs was optimized in terms of the Q/SFN ratio (w/w), time of adsorption and solvent mixture. Quercetin-loaded silk fibroin nanoparticles (QSFNs) were characterized using the dynamic light scattering technique to measure the diameter (Z-Average) and Z-potential (ζ). Loaded particles were slightly bigger than the SFNs, while their ζ was less negative. The antioxidant activity against DPPH showed that the Q loaded in QSFNs not only retains the antioxidant activity but also has a synergistic scavenging activity due the intrinsic antioxidant activity of the SF. The drug loading content (DLC) and the encapsulation efficiency (EE) varied with the relation between Q and SFN in the loading solution. The sustained release of Q occurred throughout the experiment both in phosphate buffer saline (pH 7.4) and simulated intestinal fluid (pH 6.8). The results point to SFNs as promising candidates for Q loading, transport and gastrointestinal delivery with potential applications in nanomedicine, while retaining their nano-size and their antioxidant properties.

Thermal study of areneruthenium(II) derivatives

Abstract The TG and DTG study of areneruthenium(II) derivatives [Ru(arene)Cl 2 L ] (arene = benzene or p -cymene ( p -MeC 6 H 4 CHMe 2 ); L = aniline, diethylamine, dimethylsulfoxide, tetrahydrothiofene or dimethylsulfide) was carried out under a dynamic air atmosphere. The kinetics of the first step of thermal decomposition were evaluated from the dynamic weight loss data by means of Coats-Redfern, MacCallum-Tanner and Horowitz-Metzger methods. The D n and R n models were selected as the models best fitting the experimental TG curves. The values of activation energy, E , and frequency factor, A , of the thermal decomposition were calculated.

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.

(Liquid +Liquid) Equilibrium for Ternary Systems Containing of an Ionic Liquid, n-Hexane and an Organic Compound Involved in the Kinetic Resolution of rac-2-Pentanol

In this paper, (liquid +liquid) equilibrium (LLE) data for 12 ternary systems containing an ionic liquid + n-hexane +an organic compound involved in the racemic resolution of rac-2-pentanol (rac-2-pentanol, vinyl butyrate, rac-2-pentyl butyrate, or butyric acid) have been experimentally determined at 298.2 K and atmospheric pressure. The ionic liquids used were i. 1-ethyl-3-methylimidazolium ethylsulfate, [emim+] [EtSO4 −]; ii. 1-butyl-3–methylimidazolium tetrafluoroborate, [bmim+][BF4 −] and iii. 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [bmim+][NTf2 −]. The binodal curves and the tie line compositions of the conjugate solutions were obtained by means of refractive index (ionic liquid rich phase) and by gas cromatography (hexane rich phase) to determine their potential for selectively extracting organic compounds from an ionic liquid reaction mixture. The tie line data were correlated through the use of the Non-Random Two-Liquid (NRTL) model for statistical consistency, which provides excellent agreement with the experimental measurements. There are no literature data for the mixtures discussed in this paper.

Ecotoxicity assessment of dicationic versus monocationic ionic liquids as a more environmentally friendly alternative

One of the reasons why ionic liquids have received growing interest from researchers is their environmentally interesting characteristics, such as their negligible vapour pressure and their good chemical and thermal properties. In particular, dicationic ionic liquids whose thermal and electrochemical stability is higher than that of monocationic ionic liquids have begun to gain attention during recent years. In this work, monocationic and dicationic ionic liquids were synthesized, characterized and tested for their toxicity, which was assessed using the luminescent bacterium Vibrio fischeri. The results revealed that the toxicity of the ionic liquids mainly depends on the head groups and linkage chain length of their cationic structure. Introduction of a new cationic head decreased the EC50 (concentration which leads to 50% reduction in bioluminescence of the bacteria) of the ionic liquids. The results present a promising picture of dicationic ionic liquids as alternatives with lower environmental impact than their monocationic counterparts and underline the significance of designing particular structures for ionic liquids.

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.

Production of Curcumin-Loaded Silk Fibroin Nanoparticles for Cancer Therapy

Curcumin, extracted from the rhizome of Curcuma longa, has been widely used in medicine for centuries due to its anti-inflammatory, anti-cancer, anti-oxidant and anti-microbial effects. However, its bioavailability during treatments is poor because of its low solubility in water, slow dissolution rate and rapid intestinal metabolism. For these reasons, improving the therapeutic efficiency of curcumin using nanocarriers (e.g., biopolymer nanoparticles) has been a research focus, to foster delivery of the curcumin inside cells due to their small size and large surface area. Silk fibroin from the Bombyx mori silkworm is a biopolymer characterized by its biocompatibility, biodegradability, amphiphilic chemistry, and excellent mechanical properties in various material formats. These features make silk fibroin nanoparticles useful vehicles for delivering therapeutic drugs, such as curcumin. Curcumin-loaded silk fibroin nanoparticles were synthesized using two procedures (physical adsorption and coprecipitation) more scalable than methods previously described using ionic liquids. The results showed that nanoparticle formulations were 155 to 170 nm in diameter with a zeta potential of approximately −45 mV. The curcumin-loaded silk fibroin nanoparticles obtained by both processing methods were cytotoxic to carcinogenic cells, while not decreasing viability of healthy cells. In the case of tumor cells, curcumin-loaded silk fibroin nanoparticles presented higher efficacy in cytotoxicity against neuroblastoma cells than hepatocarcinoma cells. In conclusion, curcumin-loaded silk fibroin nanoparticles constitute a biodegradable and biocompatible delivery system with the potential to treat tumors by local, long-term sustained drug delivery.

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.