Date of Award

6-2009

Document Type

Union College Only

Degree Name

Bachelor of Science

Department

Chemistry

Language

English

Keywords

catalyst, nmr, hydrogenation, para, phip

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is a quintessential non-destructive chemical analytical tool that can provide a wealth of information concerning chemical structure and properties. However, NMR spectroscopy is known for its low sensitivity and resulting weak signal strength. These shortcomings can be further exacerbated when working with biological systems, in the gas phase, or on a micro-volume scale. In this project, para-hydrogen induced polarization (PHIP) was employed to provide greatly enhanced NMR signals in single-scan 1H and 13C-NMR spectroscopy. Simple low-cost methods were developed to provide a continuous flow of para-enriched H2 gas that could be used in both PASADENA (Para-Hydrogen and Synthesis Allow for Dramatically Enhanced Nuclear Alignment) and ALTADENA (Adiabatic Longitudinal Transport After Disassociation Engenders Nuclear Alignment) -type para-hydrogenation experiments. Two principal unsaturated substrate/homogeneous hydrogenation catalyst combinations were employed for investigating PHIP, namely ethyl propiolate/[Rh(cod)(dppb)]BF4 and styrene/Rh[(PPh3)3]Cl. Despite modest reaction yields (≈8-10%), 1H-NMR signal enhancements of several orders of magnitude were observed in single-scan NMR spectroscopy. The 1H hyperpolarization in the para-hydrogenation product was transferred to 13C hyperpolarization via a simple field cycling method (diabatic demagnetization followed by adiabatic remagnetization). This was accomplished using a magnetic shield consisting of several concentric layers of μ-metal. This heteronuclear hyperpolarization transfer resulted in dramatically enhanced signals in single-scan 13C-NMR spectroscopy. With the aim of the possible application of these PHIP techniques to magnetic resonance imaging (MRI), preliminary experiments were conducted employing a polymer-bound Rh[(PPh3)3]Cl hydrogenation catalyst to the para-hydrogenation of styrene. Using such a heterogeneous catalyst would allow for simpler catalyst/sample separation techniques when using PHIP methods in biological systems. The polymer bound catalyst proved to be an effective hydrogenation catalyst, but attempts to observe PHIP using this catalyst are still ongoing.

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