Synthesis, Characterization and Host-Guest Complexation Studies of Dendritic and Linear Pyridinium Derivatives

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Titel: Synthesis, Characterization and Host-Guest Complexation Studies of Dendritic and Linear Pyridinium Derivatives
Autor(en): Murugavel, Kathiresan
Erstgutachter: Prof. Dr. Lorenz Walder
Zweitgutachter: Prof. Heinz-Jürgen Steinhoff
Zusammenfassung: Convergent and divergent strategies for the synthesis of viologen dendrimers with 1,3,5-tri-methylene branching units are presented. The synthesis of 3,5-bis(hydroxymethyl) benzyl bromide was optimized. The analysis of the crystal structure of 1-[3,5-bis(hydroxymethyl)benzyl]-4-(pyridin-4-yl) pyridinium hexafluorophosphate together with PM3 calculations opens an avenue to judge the structure and conformation of benzylic viologen dendrimers. In order to study chemical trigger induced conformational changes, viologen dendrimers were spin-labeled via a divergent approach. 1-(2,4-dinitrophenyl)-4-(pyridin-4-yl)pyridinium hexafluorophosphate was used as the end group to yield an activated dendrimer of the respective generation. The corresponding dendrimers were spin-labeled by reacting the active functionality with 4-amino TEMPO. The products were characterized by ESR (spin-label efficiency) and conventional cyclic voltammetry. Dynamic ESR studies are planned. New trimethylene-dipyridinium dendrimers were synthesized via a divergent approach using 4-tert-butylbenzyl group as the peripheral group. These dendrimers are well soluble in DMF or DMSO as PF6 salts and they act as a host for anthraquinone-2,6-disulfonate (AQDS). They can be stoichiometrically titrated with AQDS as shown by 1H-NMR, DOSY and cyclic voltammetry. Upon loading them with AQDS, the dendrimers undergo first a contraction, they reach a minimum hydrodynamic radius for complete charge compensation and they re-open when overcharging takes place. The contraction is supported by MM+ calculations. Upon stepwise loading of G2 (42 positive charges) with AQDS (2 negative charges), the first 3 molar equivalents (6 neg. charges) occupy the innermost dendrimer shell (consisting of 6 pos. charges), the next 6 equivalents (12 neg. charges) occupy the middle shell (12 pos. charges) and the last 12 equivalents AQDS (24 neg. charges) occupy the outermost shell of the dendrimer (24 pos. charges), as supported by 1H-NMR titrations yielding the magic equivalent numbers of 3, 9=3+6, and 21=3+6+12. Such stepwise radial complexations again in DMSO were further demonstrated using other molecular guests (mono-, di- and trianionic) as well as with on purpose synthesized viologen dendrimers. α,ω-dibromoalkanes were bifunctionalized in two steps to yield alkyl phosphonates with pyridinium, trimethylenedipyridinium, bipyridinium or a sulfonate at their ω end. These compounds were used as surface modifiers to build biomimetic membranes on the pore walls of mesoporous TiO2. Host-guest interaction studies with on purpose synthesized viologen compounds have been performed in collaboration.
Schlagworte: Dendrimers; Host-Guest Complexation; DOSY; NMR titrations
Erscheinungsdatum: 20-Dez-2010
Enthalten in den Sammlungen:FB05 - E-Dissertationen

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