Nuestros investigadores

Publicaciones científicas más recientes (desde 2010)

Autores: Monreal-Perez, P.; Isasi, José Ramón, (Autor de correspondencia); Gonzalez-Benito, J.; et al.
Revista: NANOMATERIALS
ISSN 2079-4991  Vol. 8  Nº 9  2018  págs. 642
The modification of the surface of titanium dioxide nanoparticles (TiO2 NPs) by the incorporation of cyclodextrins (CDs), cyclic oligosaccharides with a hydrophobic cavity, can largely improve the functionality of TiO2 by lodging molecules of interest in the CD to act directly on the surface of the nanoparticles or for further release. With this aim, we have synthesized beta CD-modified nanoparticles (beta CDTiO2 NPs) by a two-step reaction that involves the incorporation of a spacer and then the linking of the macrocycle, and characterized them by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The capacity of the functionalized structures to trap model compounds (Rhodamine and 1-naphthol) has been compared to that of bare TiO2 NPs by fluorescence and Ultraviolet-visible (UV-visible) spectroscopy. The presence of the CDs on the surface of the TiO2 avoids the photo-degradation of the guest, which is of interest in order to combine the photocatalytic activity of TiO2, one of its most interesting features for practical purposes, with the delivery of compounds susceptible of being photo-degraded. The beta CDTiO2 NPs have been dispersed in polymeric matrices of frequently used polymers, polyethylene (LDPE) and polyethylene oxide (PEO), by cryogenic high energy ball milling to produce nanocomposites in the form of films. The surface modification of the nanoparticles favors the homogenization of the filler in the matrix, while the nanoparticles, either in bare or functionalized form, do not seem to alter the crystallization properties of the polymer at least up to a 5% (w/w) load of filler.
Autores: Serres-Gomez, M.; González-Gaitano, Gustavo; Kaldybekov, D. B. ; et al.
Revista: LANGMUIR
ISSN 0743-7463  Vol. 34  Nº 36  2018  págs. 10591 - 10602
Polypseudorotaxanes are polymer chains threaded by molecular rings that are free to unthread; these "pearl-necklace" can self-assemble further, leading to higher-order supramolecular structures with interesting functionalities. In this work, the complexation between alpha-cyclodextrin (alpha-CD), a cyclic oligosaccharide of glucopyranose units, and poly(ethylene glycol) (PEG) grafted to silica nanoparticles was studied. The threading of alpha-CD onto the polymeric chains leads to their aggregation into bundles, followed by either the precipitation of the inclusion complex or the formation of a gel phase, in which silica nanoparticles are incorporated. The kinetics of threading, followed by turbidimetry, revealed a dependence of the rate of complexation on the following parameters: the concentration of alpha-CD, temperature, PEG length (750, 4000, and 5000 g mol(-1)), whether the polymer is grafted or free in solution, and the density of grafting. Complexation is slower, and temperature has a higher impact on PEG grafted on silica nanoparticles compared to PEG free in solution. Thermodynamic parameters extracted from the transition-state theory showed that inclusion complex formation is favored with grafted PEG compared to free PEG and establishes a ratio of complexation of five to six ethylene oxide units per cyclodextrin. The complexation yields, determined by gravimetry, revealed that much higher yields are obtained with longer chains and higher grafting density.
Autores: García-Padial, Marcos; Martínez-Oharriz, M.C.; Isasi, José Ramón; et al.
Revista: JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
ISSN 0021-8561  Vol. 65  Nº 24  2017  págs. 4905 - 4910
The sorption and release of tyrosol and caffeic acid, two biophenolic antioxidants with known health benefits, in different insoluble cyclodextrin polymers have been studied. Cyclodextrin polymers were synthesized by cross-linking, beta-cyclodextrin or 50:50 w/w nominal mixtures of alpha- and beta-cyclodextrins using either epichlorohydrin (EP) or toluene-2,4-diisocyanate (TDI) as cross-linking agents. An analogous sucrose polymer was prepared using EP as cross-linking reagent. Freundlich isotherms and isosteric heats of sorption for tyrosol and caffeic acid in the insoluble beta-cyclodextrin polymer cross-linked with epichlorohydrin at 50 degrees C were obtained and discussed. Finally, the release of tyrosol and caffeic acid has been studied from loaded polymer disks, the microstructures of which were characterized by mercury intrusion porosimetry. Caffeic acid shows greater affinity than tyrosol for the polymeric matrices as it presents a higher sorption and a lower and slower release. However, tyrosol has a higher isosteric heat of sorption for low coverages.
Autores: González-Gaitano, Gustavo; Isasi, José Ramón; Vélaz, I.; et al.
Revista: CURRENT PHARMACEUTICAL DESIGN
ISSN 1381-6128  Vol. 23  Nº 3  2017  págs. 411 - 432
The pharmaceutical applications of cyclodextrins (CDs), cyclic oligosaccharides capable of including hydrophobic molecules inside their cavities, have been known for decades. Besides the solubilising and encapsulating abilities of natural and modified CDs due to the formation of inclusion complexes, there is an increasing interest in organized macrostructures based on CDs as potential drug delivery devices and gene carrier systems. The present review discusses first the case of drug carriers based on monomeric modified CDs (amphiphilic and CD core-star polymers), in which self-assembly plays a major role. Polyrotaxanes, i.e., CDs threaded onto a polymer chain, are then reviewed in relation to their pharmaceutical applications. Finally, covalently linked CDs, either by grafting or crosslinking, are analyzed, including more complex structures formed by assembling CD-containing networks or chains. We have tried along this review to cover the most recent developments on these structures for drug delivery in a "beyond the cyclodextrin" approach. The review will be helpful, both for readers who want to be introduced into the world of these remarkable structures, or for specialists who are doing research in this field.
Autores: Vélaz, I.; Isasi, José Ramón, (Autor de correspondencia)
Revista: JOURNAL OF INCLUSION PHENOMENA AND MACROCYCLIC CHEMISTRY
ISSN 1388-3127  Vol. 86  Nº 3 - 4   2016  págs. 283 - 289
Cyclodextrin (CD) hydrogels were synthesized by a crosslinking reaction with the same cyclodextrin/epichlorohydrin mole ratio (1/11) using alphaCD, ßCD, gammaCD, and 50:50 mixtures of alpha/ßCD and ß/gammaCD. In order to investigate the sorption capacity of these hydrogels to different solutes, five model molecules have been selected: phenol, 3-nitrophenol, 4-nitrophenol, 1-naphthol, and the antiinflamatory drug diflunisal. The amounts sorbed have been related to the different affinities of the solutes. 1-naphthol shows the highest affinity for these polymers, especially in the case of sorbents containing ßCD. The sorption is considerably poorer for phenol than for its nitro derivatives. The two structural isomers 3- and 4-nitrophenol show significant differences in their affinities towards alphaCD, ßCD and alpha/ßCD. Finally, in the case of diflunisal, a bulkier model molecule, remarkable differences were found on the sorption behaviour by polymers whose cyclodextrins have a similar affinity for this solute (ßCD, gammaCD, and ß/gammaCD).
Autores: Martínez-Oharriz, M.C.; Vélaz, I.; et al.
Revista: JOURNAL OF PHARMACEUTICAL SCIENCES
ISSN 0022-3549  Vol. 103  Nº 1  2014  págs. 197 - 206
Gels obtained by complexation of octablock star polyethylene oxide/polypropylene oxide copolymers ( Tetronic 90 R4) with alpha-cyclodextrin (alpha- CD) were evaluated as matrices for drug release. Both molecules are biocompatible so they can be potentially applied to drug delivery systems. Two different types of matrices of Tetronic 90 R4 and alpha-CD were evaluated: gels and tablets. These gels are capable to gelifying in situ and show sustained erosion kinetics in aqueous media. Tablets were prepared by freeze-drying and comprising the gels. Using these two different matrices, the release of two model molecules, L-tryptophan ( Trp), and a protein, bovine serum albumin ( BSA), was evaluated. The release profiles of these molecules from gels and tablets prove that they are suitable for sustained delivery. Mathematical models were applied to the release curves from tablets to elucidate the drug delivery mechanism. Good correlations were found for the fittings of the release curves to different equations. The results point that the release of Trp from different tablets is always governed by Fickian diffusion, whereas the release of BSA is governed by a combination of diffusion and tablet erosion.
Autores: Estévez, C. A.; Isasi, José Ramón; et al.
Revista: BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY
ISSN 1860-5397  Vol. 10  2014  págs.  3127 - 3135
All mammals lose their ability to produce lactase (ß-galactosidase), the enzyme that cleaves lactose into galactose and glucose, after weaning. The prevalence of lactase deficiency (LD) spans from 2 to 15% among northern Europeans, to nearly 100% among Asians. Following lactose consumption, people with LD often experience gastrointestinal symptoms such as abdominal pain, bowel distension, cramps and flatulence, or even systemic problems such as headache, loss of concentration and muscle pain. These symptoms vary depending on the amount of lactose ingested, type of food and degree of intolerance. Although those affected can avoid the uptake of dairy products, in doing so, they lose a readily available source of calcium and protein. In this work, gels obtained by complexation of Tetronic 90R4 with ¿-cyclodextrin loaded with ß-galactosidase are proposed as a way to administer the enzyme immediately before or with the lactose-containing meal. Both molecules are biocompatible, can form gels in situ, and show sustained erosion kinetics in aqueous media. The complex was characterized by FTIR that evidenced an inclusion complex between the polyethylene oxide block and ¿-cyclodextrin. The release profiles of ß-galactosidase from two different matrices (gels and tablets) of the in situ hydrogels have been obtained. The influence of the percentage of Tetronic in media of different pH was evaluated. No differences were observed regarding the release rate from the gel matrices at pH 6 (t50 = 105 min). However, in the case of the tablets, the kinetics were faster and they released a greater amount of 90R4 (25%, t50 = 40¿50 min). Also, the amount of enzyme released was higher for mixtures with 25% Tetronic. Using suitable mathematical models, the corresponding kinetic parameters have been calculated. In all cases, the release data fit quite well to the Peppas¿Sahlin model equation, indicating that the release of ß-galactosidase is governed by a combination of diffusion and erosion processes. It has been observed that the diffusion mechanism prevails over erosion during the first 50 minutes, followed by continued release of the enzyme due to the disintegration of the matrix.
Autores: Isasi, José Ramón;
Revista: CARBOHYDRATE POLYMERS
ISSN 0144-8617  Vol. 102  2014  págs. 674 - 681
Different types of gels were prepared by combining poloxamines (Tetronic), i.e. poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) octablock star copolymers, and cyclodextrins (CD). Two different poloxamines with the same molecular weight (ca. 7000) but different molecular architectures were used. For each of their four diblock arms, direct Tetronic 904 presents PEO outer blocks while in reverse Tetronic 90R4 the hydrophilic PEO blocks are the inner ones. These gels were prepared by combining ¿-CD and poloxamine aqueous solutions. The physicochemical properties of these systems depend on several factors such as the structure of the block copolymers and the Tetronic/¿-CD ratio. These gels were characterized using differential scanning calorimetry (DSC), viscometry and X-ray diffraction measurements. The 90R4 gels present a consistency that makes them suitable for sustained drug delivery. The resulting gels were easily eroded: these complexes were dismantled when placed in a large amount of water, so controlled release of entrapped large molecules such as proteins (Bovine Serum Albumin, BSA) is feasible and can be tuned by varying the copolymer/CD ratio.
Autores: Sirera, R; Álvarez, J.I.; Duran, A.; et al.
Revista: REVISTA INTERNACIONAL DE EDUCACIÓN Y APRENDIZAJE
ISSN 2255-453X  Vol. 2  Nº 1  2014  págs. 83 - 92
Los medios audiovisuales son herramientas adecuadas hoy en día para ilustrar el desarrollo de las clases magistrales impartidas por el profesor universitario. El alumno se desenvuelve con soltura en estos soportes, y la utilización de estos medios es un óptimo complemento para una buena comprensión del tema. Particularizando esta acción en estudios experimentales, como la Química, las ventajas que aporta el empleo de estos materiales son claras, tanto en el entendimiento de los temas como en el propio acercamiento del alumno a aspectos más prácticos y relacionados con el ejercicio profesional al que se dedicarán cuando finalicen los estudios. El presente trabajo evalúa los resultados de aplicar las nuevas tecnologías en la enseñanza de la Química a estudiantes de la Universidad de Navarra. Se pretende identificar elementos propios del ejercicio profesional del químico y relacionar los contenidos teórico-prácticos de las asignaturas con el mismo, consiguiendo además con ello un mejor conocimiento de la materia objeto de estudio. La percepción de los alumnos ha sido ciertamente positiva en términos de un incremento de interés por las materias implicadas y de una mejora en la comprensión de las mismas.
Autores: García-Padial, Marcos; Martínez-Oharriz, M.C.; Isasi, José Ramón; et al.
Revista: JOURNAL OF INCLUSION PHENOMENA AND MACROCYCLIC CHEMISTRY
ISSN 1388-3127  Vol. 75  Nº 3-4  2013  págs. 241 - 246
Tyrosol (TY), 4-(2-hydroxyethyl)phenol, is an olive oil biophenol with antioxidant activity and positive effects on human health. This study has investigated the interactions of TY with cyclodextrins (CD) and a CD polymer. Complexation of TY with beta-CD, hydroxypropyl-beta-CD (HP-beta-CD), and methyl-beta-CD (Me-beta-CD) has been evaluated both in aqueous solution and in the solid state. The techniques employed in solution to determine the apparent stability constants of the respective complexes were fluorescence and UV-visible spectroscopies. Complexation with beta-CD and its derivatives involved an increase of both the UV absorbance and the intrinsic fluorescence of TY; a bathochromic shift of the UV spectrum was detected as well. The apparent stability constants obtained with native beta-CD, Me-beta-CD and HP-beta-CD presented similar values. Complexes in the solid state were obtained by coevaporation and kneading. They were characterised by X-ray diffraction analysis and differential thermal analysis. The interaction of TY with beta-CD led to a crystalline complex; the same diffraction pattern was obtained by coevaporation and kneading. The complexes obtained with methyl- and HP-beta-CD were amorphous irrespective of the preparation method. In addition, the retention of TY in an insoluble polymer of CD crosslinked with epichlorohydrin has been quantified. In approximately 20 min, 1 mg of TY per gram of polymer was retained.
Autores: Isasi, José Ramón; Vélaz, I.;
Revista: EUROPEAN POLYMER JOURNAL
ISSN 0014-3057  Vol. 49  Nº 12  2013  págs. 3912 - 3920
Hydrogel networks of ¿, ß or ¿-cyclodextrin (CD) and mixtures of ¿/ß or ß/¿ CDs have been obtained using epichlorohydrin (EP) as a crosslinking agent. Discs of the resulting polymers were evaluated as drug carriers for controlled release using the antiinflammatory naproxen (NAP) as a model drug. ßCD polymer (ßCDP) has shown the highest amount of drug loaded and the lowest one corresponds to the polymer containing ¿CD, in agreement with the affinities of NAP for the corresponding cyclodextrins. In addition, in vitro drug release kinetics assays from the loaded discs have been carried out. The different release profiles at simulated physiological conditions of pH and temperature have been correctly defined, identifying in each case the release mechanisms. Using suitable mathematical models, the apparent diffusional coefficients and the corresponding kinetic parameters have been calculated. It can be inferred that a simple Fickian diffusion mechanism occurs, except for the mixed polymers at pH 1.2 (anomalous transport) and in the case ¿CDP at pH 7.0 (burst phenomenon). Furthermore, the diffusion and relaxation contributions have been determined for the mixed polymers in order to achieve progress in the design of new polymer matrices according to the structure of the selected drugs.
Autores: Isasi, José Ramón;
Revista: LANGMUIR
ISSN 0743-7463  Vol. 29  Nº 4  2013  págs. 1045-1053
The phase behavior of two types of poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) copolymers in aqueous solutions was studied by light scattering, viscometry, and infrared spectroscopy. Both the reverse poloxamer (Pluronic 10R5) and the star type poloxamine (Tetronic 90R4) have practically the same PEO/PPO ratio with their hydrophobic blocks (PPO) located in the outer part. The temperature-composition phase diagrams show that both 10R5 and 90R4 tend to form aggregates in water. Up to four different phases can be detected in the case of Tetronic 90R4 for each temperature: unimers, random networks, micellar networks, and macrophase separation. Viscometric and infrared measurements complemented the results obtained by light scattering and visual inspection.
Autores: Isasi, José Ramón; Vélaz, I.;
Revista: Carbohydrate Polymers
ISSN 0144-8617  Vol. 87  Nº 3  2012  págs. 2024 - 2030
Autores: Isasi, José Ramón;
Revista: LANGMUIR
ISSN 0743-7463  Vol. 28  Nº 34  2012  págs. 12457 - 12462
A series of supramolecular aggregates were prepared using a poly(propylene oxide) poly(ethylene oxide) poly(propylene oxide) (PPO-PEO-PPO) block copolymer and beta- or alpha-cyclodextrins (CD). The combination of beta-CD and the copolymer yields inclusion complexes (IC) with polypseudorotaxane structures. These are formed by complexation of the PPO blocks with beta-CD molecules producing a powder precipitate with a certain crystallinity degree that can be evaluated by X-ray diffraction (XRD). In contrast, when combining alpha-CD with the block copolymer, the observed effect is an increase in the viscosity of the mixtures, yielding fluid gels. Two cooperative effects come into play: the complexation of PEO blocks with alpha-CD and the hydrophobic interactions between PPO blocks in aqueous media. These two combined interactions lead to the formation of a macromoleculaf network. The resulting fluid gels were characterized using different techniques such as differential scanning calorimetry (DSC), viscometry, and XRD measurements.
Autores: Isasi, José Ramón; Peñas, Francisco Javier;
Revista: JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY
ISSN 0268-2575  Vol. 87  Nº 3  2012  págs. 402 - 409
BACKGROUND: Because of the lower fluidization energy required and the protection against shock loading and starvation due to their sorption capacity, light adsorbents such as hydrogels could be used as biofilm carrier media in fluidized bed bioreactors for wastewater processing. This work explores the feasibility of a cyclodextrin hydrogel as biomass support to degrade phenol under extremely low-nitrogen availability and under nitrogen amendments. RESULTS: Phenol removal capacity was low (mean 0.589 kg m(-3) day(-1)) under extreme nitrogen-limited conditions (mean C : N ratio 3830). A pulsed nitrogen amendment increased the elimination capacity (up to 1.97 kg m(-3) day-1) controlling the biofilm thickness. An 8-h nitrogen pulse had a highly efficient long-term effect removing 93.5 mg-C mg(-1)-N in 300 h. The continuous nitrogen amendment enhanced the elimination capacity (up to 5.84 kg m(-3) day-1) although rapidly increasing the biomass growth. The inhibiting phenol concentration was smaller during the nitrogen-limited period (below 100 mg L-1) than in the nitrogen-amendment periods (140 mg L-1). Low liquid velocities were needed to fluidize the bioparticles (less than 3.1 mm s(-1)) during the entire experimentation. CONCLUSION: This work shows that a fluidized-bed bioreactor with mixed culture on cyclodextrin-based particles can be operated for long periods at extreme nitrogen limitation, and that a limited nitrogen supply with periodic pulsed amendments would be adequate for controlling the biofilm thickness.
Autores: Zornoza, Arantza; Isasi, José Ramón; et al.
Revista: Journal of Inclusion Phenomena and Macrocyclic Chemistry
ISSN 1388-3127  Vol. 69  Nº 3-4  2011  págs. 469 - 474
Autores: Maddens, T.; Vélaz, I.; et al.
Revista: Journal of Inclusion Phenomena and Macrocyclic Chemistry
ISSN 1388-3127  Vol. 70  Nº 3-4  2011  págs. 415 - 419
Autores: Centelles, Miguel Nöel; Isasi, José Ramón; et al.
Revista: Journal of Microencapsulation
ISSN 0265-2048  Vol. 27  Nº 5  2010  págs. 460 - 469
A commercially available chitosan with a degree of deacetylation (DD) of 85% and a molecular weight (Mw) of 400 kDa was modified by acetylation with acetic anhydride to obtain a chitosan with a DD of 75%. Both polysaccharides were used to prepare DNA-chitosan nanoparticles by charge interactions with pDNA (coacervation process). Both resulting nanoparticles showed an almost total DNA loading efficiency (96%) and displayed similar physico-chemical properties with a size of similar to 200 nm and a zeta potential close to +20 mV. In order to study the effect of the DD on the properties of DNA-chitosan nanoparticles as gene delivery systems, the hydrodynamics-based procedure was used. The transgene expression was observed using either the green fluorescent protein (GFP) or the luciferase (Luc) as reporter genes. After the hydrodynamic injection, the DNA-chitosan nanoparticles were accumulated in the liver, where the transgene expression was mostly localized. Interestingly, the decrease of the DD affected the transgene expression, improving the initial burst effect and accelerating the DNA release. Both combined effects led to an increase in the transgene expression levels. In addition, the emitted bioluminescence could be detected over 105 days for all the formulations injected. The calculation of the kinetic parameters (C(max), AUC, Ke, t(1/2) Ke and MET) gave some interesting information regarding the abilities to control the DNA release of the two DNA-chitosan formulations tested and allowed narrower comparisons.
Autores: Peñas, Francisco Javier; Isasi, José Ramón;
Libro:  Handbook of hydrogels: properties, preparation & applications
2010  págs. 341 - 364
Autores: Peñas, Francisco Javier; Isasi, José Ramón;
Libro:  Advances in Chemical Engineering
2010  págs. 175 - 186