Characterization of Reverse Micelles Formulated with the Ionic-Liquid-like Surfactant Bmim-AOT and Comparison with the Traditional Na-AOT: Dynamic Light Scattering, 1H NMR Spectroscopy, and Hydrolysis Reaction of Carbonate as a Probe.

The present study investigated how the presence of butylmethylimidazolium cation (bmim+) alters the interfacial properties of reverse micelles (RMs) created with the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT), in comparison to sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) RMs, employing dynamic light scattering (DLS) and 1H NMR techniques. Moreover, through the hydrolysis reaction of bis(4-nitrophenyl)carbonate inside both RMs as reaction probe, interfacial properties changes were explored in more detail. The kinetic solvent isotope effect was also analyzed. Micellar systems were formed using n-heptane as external nonpolar solvent and water as the polar component. According to the DLS studies, water is encapsulated inside the organized media; however, a different tendency is observed depending on the cationic component of the surfactant. For Na-AOT system, the results suggest that the micellar shapes are probably spherical, while in the case of bmim-AOT, a transition from ellipsoidal to spherical micelles could be occurring when water is added. 1H NMR data show that water is structured differently when Na+ cation is replaced by bmim+; in bmim-AOT RMs, the interaction of water with the surfactant is weaker and the water hydrogen-bonding network is less disturbed than in Na-AOT RMs. Kinetic studies reveal that the hydrolysis reaction in bmim-AOT RMs was much more favorable in comparison to Na-AOT RMs. In addition, when water content decreases in bmim-AOT RMs, the hydrolysis reaction rate increases and the solvent isotope effect remains constant, while for Na-AOT solutions, both the reaction rate and the solvent isotope effect decrease. Our results indicate that bmim+ cation would be located in the surfactant layer in such a way the negative charge density in the interface is less than that in Na-AOT RMs, and the reaction is more favorable. Additionally, as 1H NMR studies reveal, the interfacial water molecules would be more available in bmim-AOT RMs to participate in the nucleophilic attack. Therefore, the present study evidences how the replacement of Na+ counterion by bmim+ alters the composition of the interface of AOT RMs.

Binding of Flavylium Ions to Sulfonatocalix[4]arene and Implication in the Photorelease of Biologically Relevant Guests in Water.

The formation of host-guest complexes between seven flavylium cations and water-soluble p-sulfonatocalix[4]arene (SC4) was investigated by UV/vis absorption, fluorescence, and NMR spectroscopies. The results show the cationic guests form complexes with affinities in the submillimolar range. A representative chalcone/flavylium photoswitch was investigated in more detail regarding its pH- and light-triggered interconversion between the two forms. The dramatic affinity differentiation of the SC4 binding of the two switchable species (40 M-1 for the trans-chalcone versus 3.5 × 104 M-1 for the flavylium cation) enables the pH-gated photocontrol of the complexation process. These responsive properties were explored to demonstrate the competitive and selective release of biologically relevant guests from their supramolecular complexes with p-sulfonatocalix[4]arene (SC4), following the principle of AND logic. The guest release can be reverted by the thermally activated reaction of the flavylium ion back to the trans-chalcone.

Novel Supramolecular Nanoparticles Derived from Cucurbit[7]uril and Zwitterionic Surfactants.

Binding constants, log K ≈ 6.6 M-1, and NMR characterization of the complexes formed by sulfobetaines and cucurbit[7]uril (CB7) support the electrostatic interaction as the major driving force. This very strong binding motif is cross-linked by additional CB7 molecules, resulting in the formation of supramolecular nanoparticles (SNPs) with an average diameter of 172 nm and a negative surface potential. The time course evolution of the particle size and the surface potential suggests the very fast formation of an amorphous aggregate that absorbs an additional amount of sulfobetaine. These aggregates afford very stable (more than 2 weeks) nanoparticles in an aqueous dispersion. The reversibility of the sulfobetaine/CB7 host/guest complexes allows SNP disaggregation by adding a competitive guest as shown by treatment with tetraethylammonium chloride. The addition of this competitive cation triggers a SNP-to-micelle transition. The potential application of these nanoparticles as drug delivery vehicles was investigated by using carboxyfluorescein. These experiments revealed that upon externally induced disruption of the SNPs (by tetraethylammonium chloride) the fluorescent dye was trapped in micellar aggregates that can be further disrupted by cyclodextrin addition.

A journey from calix[4]arene to calix[6] and calix[8]arene reveals more than a matter of size. Receptor concentration affects the stability and stoichiometric nature of the complexes.

The formation of inclusion complexes between lucigenin (N,N'-dimethyl-9,9'-biacridinium dinitrate) and p-sulfonatocalix[n]arenes (SCn; n = 6, 8) was investigated by fluorescence and NMR spectroscopy. Both SC6 and SC8 were found to form 1 : 1 and 1 : 2 host-guest complexes with lucigenin showing up to 109 M-1 binding affinities. Strong quenching of the lucigenin fluorescence upon complexation was observed. Fluorescence regeneration after competitive binding with other potential guests present in solution was used as an indicator displacement assay to characterize the binding mechanism and affinity of alkaline metal ions (Li+, Na+, K+ and Cs+) with SC6 and SC8. The results demonstrate the formation of 1 : 1 and 1 : 2 calixarene : metal complexes with association constants on the order of 103 M-1 and heteroternary calixarene : lucigenin : metal complexes that predominate at metal cation concentrations above the millimolar range. Owing to the ubiquitous presence of metal cations in SCn solutions as counterions (typically Na+), the detailed description of the complexation of these species is crucial to understand and quantify the host-guest binding properties of these receptors. This work demonstrates that both the thermodynamic stability and the stoichiometric nature of the complexes is dependent on the metal ion concentration and, consequently, on the calixarene concentration.

[Instrument validation that measures disruptive education on clinical training]. / Validación de instrumento que mide la educación disruptiva en la formación clínica.

Background: During the contingency derived from the COVID-19 pandemic, there were no instruments assessing the aspects of clinical training, which is why it is necessary to have a questionnaire that let us know the opinion of medical students about the disruptive education. Objective: To validate a questionnaire designed to know the opinion of medical students about disruptive education in their clinical training. Material and methods: Validation cross-sectional study which was developed in three phases: 1) Elaboration of the questionnaire aimed at undergraduate medical students who include clinical science subjects in their curricular program; 2) validation of content by Aiken's V test with 7 expert judges and reliability estimation with Cronbach's alpha coefficient in a pre-sample test with 48 students; 3) analysis of the information through descriptive statistics, where the following results were observed: Aiken's V index of V = 0.816; Cronbach's alpha coefficient = 0.966. A total of 54 items were incorporated in the questionnaire after the pre-sampling test. Conclusions: We can rely on a valid and reliable instrument that objectively measures disruptive education in the clinical training of medical students.

Introducción: durante la contigencia sanitaria derivada de la pandemia por COVID-19, no hubo instrumentos que valoraran los aspectos de la formación clínica, por lo que es necesario contar con un cuestionario para conocer la opinión de los estudiantes de medicina sobre la educación disruptiva. Objetivo: validar un cuestionario diseñado para conocer la opinión de los estudiantes de medicina acerca de la educación disruptiva en su formación clinica. Material y métodos: estudio de validación con corte transversal que se desarrolló en tres fases: 1) elaboración del cuestionario dirigido a estudiantes de medicina de pregrado que tomaran materias de ciencias clínicas en su programa curricular; 2) validación de contenido mediante prueba V de Aiken con 7 jueces expertos y estimación de confiabilidad con coeficiente alfa de Cronbach en prueba premuestreo con 48 estudiantes; 3) análisis de la información por medio de estadística descriptiva, donde se observaron los siguientes resultados: índice V de Aiken de V = 0.816; coeficiente alfa de Cronbach = 0.966. El cuestionario quedó integrado con un total de 55 ítems posterior a la prueba premuestreo. Conclusiones: se cuenta con un instrumento válido y confiable para medir objetivamente la educación disruptiva en la formación clínica de estudiantes de medicina.