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Authors = Marleen Häring

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12 pages, 2987 KiB  
Article
Effects of the Solvent Vapor Exposure on the Optical Properties and Photocatalytic Behavior of Cellulose Acetate/Perylene Free-Standing Films
by Gustavo Coderch, Alexander Cordoba, Oscar Ramírez, Sebastian Bonardd, Angel Leiva, Marleen Häring, David Díaz Díaz and Cesar Saldias
Polymers 2023, 15(13), 2787; https://doi.org/10.3390/polym15132787 - 23 Jun 2023
Cited by 1 | Viewed by 2082
Abstract
The search to deliver added value to industrialized biobased materials, such as cellulose derivatives, is a relevant aspect in the scientific, technological and innovation fields at present. To address these aspects, films of cellulose acetate (CA) and a perylene derivative (Pr) were fabricated [...] Read more.
The search to deliver added value to industrialized biobased materials, such as cellulose derivatives, is a relevant aspect in the scientific, technological and innovation fields at present. To address these aspects, films of cellulose acetate (CA) and a perylene derivative (Pr) were fabricated using a solution-casting method with two different compositions. Consequently, these samples were exposed to dimethylformamide (DMF) solvent vapors so that its influence on the optical, wettability, and topographical properties of the films could be examined. The results demonstrated that solvent vapor could induce the apparent total or partial preferential orientation/migration of Pr toward the polymer–air interface. In addition, photocatalytic activities of the non-exposed and DMF vapor-exposed films against the degradation of methylene blue (MB) in an aqueous medium using light-emitting diode visible light irradiation were comparatively investigated. Apparently, the observed improvement in the performance of these materials in the MB photodegradation process is closely linked to the treatment with solvent vapor. Results from this study have allowed us to propose the fabrication and use of the improved photoactivity “all-organic” materials for potential applications in dye photodegradation in aqueous media. Full article
(This article belongs to the Special Issue Photoactive Polymer Materials)
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21 pages, 10682 KiB  
Article
Urea Activation by an External Brønsted Acid: Breaking Self-Association and Tuning Catalytic Performance
by Isaac G. Sonsona, Eugenia Marqués-López, Marleen Häring, David Díaz Díaz and Raquel P. Herrera
Catalysts 2018, 8(8), 305; https://doi.org/10.3390/catal8080305 - 28 Jul 2018
Cited by 7 | Viewed by 6930
Abstract
In this work, we hypothesize that Brønsted acids can activate urea-based catalysts by diminishing its self-assembly tendency. As a proof of concept, we used the asymmetric Friedel–Crafts alkylation of indoles with nitroalkenes as a benchmark reaction. The resulting 3-substituted indole derivatives were obtained [...] Read more.
In this work, we hypothesize that Brønsted acids can activate urea-based catalysts by diminishing its self-assembly tendency. As a proof of concept, we used the asymmetric Friedel–Crafts alkylation of indoles with nitroalkenes as a benchmark reaction. The resulting 3-substituted indole derivatives were obtained with better results due to cooperative effects of the chiral urea and a Brønsted acid additive. Such synergy has been rationalized in terms of disassembly of the supramolecular catalyst aggregates, affording a more acidic and rigid catalytic complex. Full article
(This article belongs to the Special Issue Hydrogen Bonding Activation)
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16 pages, 2550 KiB  
Article
Synthesis, Characterization, and Self-Assembly of a Tetrathiafulvalene (TTF)–Triglycyl Derivative
by Sónia Pérez-Rentero, Ramon Eritja, Marleen Häring, César Saldías and David Díaz Díaz
Appl. Sci. 2018, 8(5), 671; https://doi.org/10.3390/app8050671 - 26 Apr 2018
Cited by 4 | Viewed by 4862
Abstract
In this work, we describe the synthesis, characterization, and self-assembly properties of a new tetrathiafulvalene (TTF)–triglycyl low-molecular-weight (LMW) gelator. Supramolecular organogels were obtained in various solvents via a heating–cooling cycle. Critical gelation concentrations (CGC) (range ≈ 5–50 g/L) and thermal gel-to-sol [...] Read more.
In this work, we describe the synthesis, characterization, and self-assembly properties of a new tetrathiafulvalene (TTF)–triglycyl low-molecular-weight (LMW) gelator. Supramolecular organogels were obtained in various solvents via a heating–cooling cycle. Critical gelation concentrations (CGC) (range ≈ 5–50 g/L) and thermal gel-to-sol transition temperatures (Tgel) (range ≈ 36–51 °C) were determined for each gel. Fourier transform infrared (FT-IR) spectroscopy suggested that the gelator is also aggregated in its solid state via a similar hydrogen-bonding pattern. The fibrillar microstructure and viscoelastic properties of selected gels were demonstrated by means of field-emission electron microscopy (FE-SEM) and rheological measurements. As expected, exposure of a model xerogel to I2 vapor caused the oxidation of the TTF unit as confirmed by UV-vis-NIR analysis. However, FT-IR spectroscopy showed that the oxidation was accompanied with concurrent alteration of the hydrogen-bonded network. Full article
(This article belongs to the Section Materials Science and Engineering)
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9 pages, 1434 KiB  
Article
Keratin Protein-Catalyzed Nitroaldol (Henry) Reaction and Comparison with Other Biopolymers
by Marleen Häring, Asja Pettignano, Françoise Quignard, Nathalie Tanchoux and David Díaz Díaz
Molecules 2016, 21(9), 1122; https://doi.org/10.3390/molecules21091122 - 25 Aug 2016
Cited by 13 | Viewed by 6410
Abstract
Here we describe a preliminary investigation on the ability of natural keratin to catalyze the nitroaldol (Henry) reaction between aldehydes and nitroalkanes. Both aromatic and heteroaromatic aldehydes bearing strong or moderate electron-withdrawing groups were converted into the corresponding β-nitroalcohol products in both DMSO [...] Read more.
Here we describe a preliminary investigation on the ability of natural keratin to catalyze the nitroaldol (Henry) reaction between aldehydes and nitroalkanes. Both aromatic and heteroaromatic aldehydes bearing strong or moderate electron-withdrawing groups were converted into the corresponding β-nitroalcohol products in both DMSO and in water in the presence of tetrabutylammonium bromide (TBAB) as a phase transfer catalyst. Negligible background reactions (i.e., negative control experiment in the absence of keratin protein) were observed in these solvent systems. Aromatic aldehydes bearing electron-donating groups and aliphatic aldehydes showed poor or no conversion, respectively. In general, the reactions in water/TBAB required twice the amount of time than in DMSO to achieve similar conversions. Moreover, comparison of the kinetics of the keratin-mediated nitroaldol (Henry) reaction with other biopolymers revealed slower rates for the former and the possibility of fine-tuning the kinetics by appropriate selection of the biopolymer and solvent. Full article
(This article belongs to the Special Issue Catalysis Applied to Biomass—Toward Sustainable Processes and Chemicals)
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27 pages, 7995 KiB  
Review
Magnetic Gel Composites for Hyperthermia Cancer Therapy
by Marleen Häring, Jana Schiller, Judith Mayr, Santiago Grijalvo, Ramon Eritja and David Díaz Díaz
Gels 2015, 1(2), 135-161; https://doi.org/10.3390/gels1020135 - 30 Sep 2015
Cited by 57 | Viewed by 16741
Abstract
Hyperthermia therapy is a medical treatment based on the exposition of body tissue to slightly higher temperatures than physiological (i.e., between 41 and 46 °C) to damage and kill cancer cells or to make them more susceptible to the effects of [...] Read more.
Hyperthermia therapy is a medical treatment based on the exposition of body tissue to slightly higher temperatures than physiological (i.e., between 41 and 46 °C) to damage and kill cancer cells or to make them more susceptible to the effects of radiation and anti-cancer drugs. Among several methods suitable for heating tumor areas, magnetic hyperthermia involves the introduction of magnetic micro/nanoparticles into the tumor tissue, followed by the application of an external magnetic field at fixed frequency and amplitude. A very interesting approach for magnetic hyperthermia is the use of biocompatible thermo-responsive magnetic gels made by the incorporation of the magnetic particles into cross-linked polymer gels. Mainly because of the hysteresis loss from the magnetic particles subjected to a magnetic field, the temperature of the system goes up and, once the temperature crosses the lower critical solution temperature, thermo-responsive gels undergo large volume changes and may deliver anti-cancer drug molecules that have been previously entrapped in their networks. This tutorial review describes the main properties and formulations of magnetic gel composites conceived for magnetic hyperthermia therapy. Full article
(This article belongs to the Special Issue Nanoparticle-Hydrogel Composites for Biomedical Applications)
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12 pages, 1375 KiB  
Article
DNA-Catalyzed Henry Reaction in Pure Water and the Striking Influence of Organic Buffer Systems
by Marleen Häring, Maria M. Pérez-Madrigal, Dennis Kühbeck, Asja Pettignano, Françoise Quignard and David Díaz Díaz
Molecules 2015, 20(3), 4136-4147; https://doi.org/10.3390/molecules20034136 - 4 Mar 2015
Cited by 10 | Viewed by 10473
Abstract
In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry) reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA). Both heteroaromatic [...] Read more.
In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry) reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA). Both heteroaromatic aldehydes (e.g., 2-pyridinecarboxaldehyde) and aromatic aldehydes bearing strong or moderate electron-withdrawing groups reacted satisfactorily with nitromethane obeying first order kinetics and affording the corresponding β-nitroalcohols in good yields within 24 h. In contrast, aliphatic aldehydes and aromatic aldehydes having electron-donating groups either did not react or were poorly converted. Moreover, we discovered that a number of metal-free organic buffers efficiently promote the Henry reaction when they were used as reaction media without adding external catalysts. This constitutes an important observation because the influence of organic buffers in chemical processes has been traditionally underestimated. Full article
(This article belongs to the Collection Recent Advances in Organocatalysis)
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