![[img]](https://epub.uni-regensburg.de/style/images/fileicons/application_pdf.png) | License: Creative Commons Attribution 4.0 PDF - Accepted Version (3MB) |
- URN to cite this document:
- urn:nbn:de:bvb:355-epub-376794
- DOI to cite this document:
- 10.5283/epub.37679
| Item type: | Thesis of the University of Regensburg (PhD) |
|---|---|
| Date: | 1 August 2019 |
| Referee: | Prof. Dr. Richard Buchner and Prof. Dr. Edgar F. Vargas and Prof. Dr. Dominik Horinek and Prof. Dr. Wolfram Baumann and Prof. Carmen Maria Romero |
| Date of exam: | 3 August 2018 |
| Institutions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) > PD Dr. Richard Buchner |
| Keywords: | Solvation, ionic resorcin[4]arenes, dielectric relaxation spectroscopy, partial molar volumes, isentropic compressibilities, electric molar conductivities, water, DMSO, isothermal titration calorimetry, supramolecular chemistry |
| Dewey Decimal Classification: | 500 Science > 540 Chemistry & allied sciences |
| Status: | Published |
| Refereed: | Yes, this version has been refereed |
| Created at the University of Regensburg: | Yes |
| Item ID: | 37679 |
Abstract (English)
Resorcin[4]arenes are a type of supramolecular receptor, with a bowl resembling structure that posses a synthetic versatility and supramolecular capabilities of value for the development of chemical technologies. Currently, its use in solution is limited to non-polar media where intermolecular reversible interactions are easily handled, but when they are transferred to polar media they exhibit a ...
Abstract (English)
Resorcin[4]arenes are a type of supramolecular receptor, with a bowl resembling structure that posses a synthetic versatility and supramolecular capabilities of value for the development of chemical technologies. Currently, its use in solution is limited to non-polar media where intermolecular reversible interactions are easily handled, but when they are transferred to polar media they exhibit a limited performance. An example of this situation is the attempt to encapsulate guest species in dimethyl sulphoxide (DMSO) using two ionic c-methylresorcin[4]arenes with opposite charges in the upper rim, one functionalized with dialkylaminomethylated hydrochloride residues (-CH2(CH3)2NHCl,TAM(HCl)4) and another with sodium ethylsulphonate groups (-CH2SO3Na, Na4TES), to form a capsule resemble structure mediated by ionic interactions. Unfortunately, the study indicates that despite the formation of the capsule ensemble, it was not possible the further inclusion of a guest molecule. Nonetheless, studies of supramolecular systems in nature, indicate that in water solvation plays an important role. Thus, since many applications of supramolecular receptors takes place in polar media, assessment of the solvation effect is of
interest. Unfortunately, these studies are scarce since the main focus has been in the understanding of structural features of receptors on their supramolecular properties. In order to contribute to the understanding of solvation and supramolecular behavior, in this work the assessment of solvation effects were studied on the formation of the capsule resembling structure formed by the two ionic c-methylresorcin[4]arenes, Na4TES and TAM (HCl)4. It was done by elucidating first the solvation process of each ionic resorcin[4]arene in water and DMSO, and, second, by studying the interaction between ionic c-methylresorcin[4]arenes in
solution. For this purpose, different techniques were used.
In the first part, the results from the studies using Dielectric Relaxation Spectroscopy are presented. They showed that solutions in water and DMSO of the ionic c-methylresorcin[4]arenes at 298.15 K illustrate two important scenarios for the Na4TES and TAM (HCl)4 behavior in solution. First, each resorcin[4]arene affected differently the dynamics of water molecules. In TAM (HCl)4 solutions, both moderate retardation and complete immobilization of water molecules are present, while for solutions of Na4TES only showed the latter. This pattern suggests that Na4TES solvation is driven mostly by hydrophilicity while for TAM H4+ hydrophobicity is also present. Solutions in DMSO also suggested that both mechanisms are present but in a lesser extent. The second important result is that it was found evidence of ion association with rather large values for polar media. In the case of Na4TES solutions, the medium did not show to much influence on the ion association strength, while for TAM (HCl)4 solutions showed a signi�cant contribution. Determination of apparent molar volumes and isentropic compressibilities as a function of temperature allowed to asses the temperature effect on the solvation. This was done by analysis of derived standard ionic molar volumes, their contributions, apparent molar isentropic compressibilities at in�ffinitete dilution and solvation numbers. The changes presented by these quantities suggest that in water the solute-solvent interactions are sensitive to the change of temperature and to the solute structural features. A similar analysis for the quantities in DMSO shown that no signi�cant effect of temperature or structure was observed, suggesting that in DMSO solute-solvent interactions are not the main driving force behind solvation.
Measurement of the electrical molar conductivity as a function of temperature, allowed to further study the strength of ion association between the c-methylresorcin[4]arene and their counter ion as well as ion-solvent interactions. Ion association constants showed that this process is temperature independent, but mainly influenced by the medium. Analysis of the thermodynamic properties of ion association showed that the process is entropically driven. On the other hand, analysis of limiting ionic conductivities indicated that ionic c-methylresorcin[4]arenes moves with a loose solvation shell, and such mobility is larger in water than in DMSO, but with an important temperature effect in DMSO.
Formation of the capsule between ionic c-methylresorcin[4]arenes in mixtures of water and DMSO at 298.15 K was studied using isothermal titration calorimetry. The results suggested that the capsule formation is not prevented by ion-association since the association constants for the capsule formation are larger. Additionally, it was observed that the association constant increased with increasing polarity of the solvent mixture, despite being the association mediated by ionic interactions. However, it was also found that the capsule is only soluble in mixtures with a DMSO mass fraction larger than 0.5, indicating that preferential solvation also might play a role. These results indicate that a solvophobic effect is the main driving force behind the association and it can be tuned by changing the solvent composition, which in turn changes the extent of the hydrogen bonding network which promotes the association. Lastly, attempts to encapsulate guest molecules were unsuccessful, most likely due to the differences in solvation between the counterparts of the capsule and the guest.
Finally, it can be said that the capsule formation between the two ionic c-methylresorcin[4]arenes is promoted mainly by the solvent and complemented by the ionic interactions. Thus, in order to encapsulate guest molecules in polar media, with ionic resorcin[4]arenes the process should consider features that take advantage of the solvophobic effect, which include, for example, a medium which promotes association, but no precipitation, and structural similarities within receptors and guest molecule to avoid differences in solvation.
Translation of the abstract (Spanish)
Los resorcin[4]arenos son un tipo de receptores con versatilidad sintética y una estructura que permite propiedades supramoleculares de valor para el desarrollo de nuevas tecnologías. Actualmente, su uso en solución es limitado a medios no polares donde las interacciones reversibles son fáciles de controlar; sin embargo, al transferirse a medios polares su desempeño es mucho menor a causa de la ...
Translation of the abstract (Spanish)
Los resorcin[4]arenos son un tipo de receptores con versatilidad sintética y una estructura que permite propiedades supramoleculares de valor para el desarrollo de nuevas tecnologías. Actualmente, su uso en solución es limitado a medios no polares donde las interacciones reversibles son fáciles de controlar; sin embargo, al transferirse a medios polares su desempeño es mucho menor a causa de la solvatación, un proceso que compite contra la formación de las estructuras supramoleculares. Como ejemplo de esto es el uso de resorcin[4]arenos iónicos con cargas opuestas, que aunque se asocian el ensamble resultante es solo soluble en DMSO y no muestra posibilidades de encapsulamiento. Con el fin de entender el rol de la solvatación y como se puede utilizar para controlar la formación de estructuras supramoleculares, esta tesis estudia la solvatación en agua y DMSO de dos resorcin[4]arenos iónicos de carga opuesta, uno aminometilado en la parte superior, TAM(HCl)4 (-CH2(CH3)2NHCl) y otro sulfonado, Na4TES (-CH2SO3Na). Los estudios se llevaron a cabo en agua y DMSO usando diferentes técnicas.
Inicialmente, los espectros de relajación dieléctrica a 298.15 K indican que los resorcin[4]arenos muestra asociación iónica, con sus contra iones, y patrones diferentes de solvatación a pesar de su similitud estructural. En agua, el resorcin[4]areno cargado positivamente en la parte superior, TAM(HCl)4, muestra solvatación solvofóbica y solvofílica mientras que el cargado negativamente, Na4TES, solamente la última. En DMSO se ve menor solvatación y una reducción significativa de la solubilidad del TAM(HCl)4.
Determinación de propiedades termodinámicas a partir de la densidad y velocidad del sonido de las soluciones permitió profundizar el estudio de la solvatación en función de la temperatura. A partir de las densidades, se determinó el volumen molar estándar iónico de cada resorcin[4]areno en agua y DMSO. El análisis de esta cantidad en función de la temperatura mostró que en agua la solvatación es más sensible a la temperatura en comparación con DMSO, donde la el efecto es muy similar. Estimación de la contribución por interacciones en solución señala que el ion TES4- tiene una contribución mayor que el TAMH4+ a pesar de que este último tiene un mayor volumen. Por otro lado, a partir de la velocidad del sonido se determinó la compresibilidad isotrópica molar parcial de la solución, corroborando que hay mayor interacción en agua y que un aumento de la temperatura debilita las interacciones en este solvente. En DMSO, el efecto de la temperatura es mucho menor y se observó una menor interacción. La determinación de números de solvatación mostró que en las soluciones de Na4TES a todas las temperaturas tienen una mayor solvatación que en las soluciones de TAM(HCl)4 y que un aumento en la temperatura disminuye la solvatación.
La determinación de la conductividad electrolítica molar permitió determinar la contribución iónica y constantes de asociación. La primera permitió calcular el radio de Stokes el cual en agua es bastante menor, sugiriendo que la esfera de solvatación no está fuertemente unida, mientras en DMSO el radio de Stokes es muy cercano al de van der Waals mostrando que no hay una fuerte interacción con el solvente. Análisis de las constates de asociación mostraron que hay mayor asociación en DMSO que en Agua, pero esta no es controlada únicamente por la permeabilidad eléctrica del medio, sino que también por la solvatación del contraion.
Finalmente, interacciones de entre TES4- y TAMH4+ en mezclas de DMSO-Agua mostraron que la interacción es mayor a medida que aumenta la cantidad de agua. Este resultado indica que la asociación es controlada por un efecto solvofóbico y la interacción electroestática sirve principalmente para controlar la orientación. Adicionalmente al analizar la magnitud de las constantes, se corrobora que la asociación iónica entre el resorcin[4]areno y su contra ion no limitan la formación del asociado. Adicionalmente, el estudio en presencia de iones muestra que la colina evita la formación del asociado iónico mientras que el Cd2+ compite.
En conclusión esta tesis describe como la solvatación hidrofóbica es la fuerza directriz en la formación de asociados iónicos de resorcin[4]arenos. Esto sugiere que para poder encapsular se debe considerar especies que se favorezcan también de este fenómeno, y escoger medios que promuevan esta asociación como por ejemplo solventes próticos con redes de puentes de hidrógeno.
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