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theses

This dissertation focuses on the gas phase properties and reactivity of two types of N-heterocyclic compounds: N-heterocyclic carbenes (NHCs) and nucleobase derivatives. Imidazole-2-ylidene and imidazolidin-2-ylidene are stabilized carbenes widely applied in organometallics and organocatalysis. The only structural difference between the two is the degree of unsaturation on their heterocyclic backbone. Imidazole-2-ylidene is unsaturated (denoted as unsatNHCs) while imidazolidin-2-ylidene is saturated (denoted as satNHC). Our studies focused on the proton affinities comparison between unsatNHCs and satNHCs. The results indicate that satNHCs are more basic than their unsaturated counterparts. They are both more basic than the first generation Grubbs catalyst ligand tricyclohexylphosphine. N-Heterocyclic carbenes (NHCs) catalyze Umpolung condensation reactions of carbonyl compounds, including the benzoin condensation and Stetter reaction. These types of reactions have not been examined in the gas phase. We explored the feasibility of examining these reactions in the absence of solvent. Charge-tagged thiazolylidene catalysts were used to track the reactions by mass spectrometry. We found that the addition of the NHC catalysts to a carbonyl compound to form the "Breslow intermediate" can only be accessed by introducing acylsilanes, which takes advantage of Brook rearrangement. The second step addition, with another aldehyde or a Michael acceptor, does not occur under our gas phase conditions. The differential reactivity between the condensed and gas phases was discussed. A light-responsive NHC was to have different electronic properties between its two isomers. We conducted a series of molecular orbital calculations to clarify the electronic structure difference between the two isomers. The DNA glycosylase MutY repairs the DNA damage by removing adenine from mismatched adenine:8-oxoganine base pair. To help understand the mechanism of MutY, gas phase proton affinities and acidities of four MutY substrates were measured. The measurement matches calculated values by our group. The tautomerization of protonated 6-methyl-1-deazaadenine was also discussed. It is hypothesized that nicotinamide adenine dinucleotide (NAD+) can initiate in vitro DNA transcription catalyzed by E.coli RNA polymerase (RNAP). To prove this hypothesis, a mixture of DNA template, E.coli RNAP, CTP and NAD+ were made, aiming to find the 5’-NAD+ modified RNA sequence NAD+pC. An LC-MS method was developed to analyze NAD+pC.

ETD_6793

Ph.D.

Includes bibliographical references

by Yuan Tian

doi:10.7282/T3Z89FDQ

ETD doctoral

The author owns the copyright to this work.