The purpose of this work was to apply multinuclear and multidimensional nuclear magnetic resonance (NMR) spectroscopy techniques to determine the characteristics of the structure and intermolecular interactions of dendrimers supramolecular assemblies, polyalkylsilane oligomer and Nafion® fluoropolymer.
In the one of the studies, a mixture of alkylpolysilane oligomers was characterized by one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy. The oligomeric products were observed to have chains of up to 5-6 silicons. Complete unambiguous resonance assignments were obtained with the help of 1D 1H, 13C, 29Si and 2D 1H{29Si}gHSQC/gHSQC-TOCSY/gHMBC experiments. Finally, the discovery of the quarternary Si atoms by using HMBC technique provides evidence for branching in the structures.
In a separate study, multidimensional NMR spectroscopy was used to analyze the supramolecular chemistry of poly(propylene imine) dendrimers that have urea-adamantane as end groups with numerous acidic guest molecules. Data about the close proximity of the host and guest molecules was determined by two-dimensional (2D) nuclear Overhauser enhancement spectroscopy (NOESY). These interactions support a specific binding model for the formation of a stable host-guest complex. Diffusion studies concerning a ratio of host and guest molecule helped to support the data collected.
Finally, the Nafion® fluoropolymer, used for proton exchange membranes, was investigated using regional or band selective excitation to perform selective nD NMR experiments. The microstructure of the Nafion® prepolymer with the sulfonyl fluoride functional group was characterized by homonuclear band-selective 19F-19F COSY. When compared with signals in a standard COSY spectrum, the cross-peaks in the selective homonuclear 19F-19F COSY give more intense and cleaner signals. To further simplify the complex cross-peak patterns, a q3 and Gaussian 180° inversion pulse was introduced to remove fluorine homonuclear coupling during the t1 evolution time.