Hyperpolarizing DNA Nucleobases via NMR Signal Amplification by Reversible Exchange
2023
Bryce E. Kidd | Max E. Gemeinhardt | Jamil A. Mashni | Jonathan L. Gesiorski | Liana B. Bales | Miranda N. Limbach | Roman V. Shchepin | Kirill V. Kovtunov | Igor V. Koptyug | Eduard Y. Chekmenev | Boyd M. Goodson
The present work investigates the potential for enhancing the NMR signals of DNA nucleobases by parahydrogen-based hyperpolarization. Signal amplification by reversible exchange (SABRE) and SABRE in Shield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) of selected DNA nucleobases is demonstrated with the enhancement (&epsilon:) of 1H, 15N, and/or 13C spins in 3-methyladenine, cytosine, and 6-O-guanine. Solutions of the standard SABRE homogenous catalyst Ir(1,5-cyclooctadeine)(1,3-bis(2,4,6-trimethylphenyl)imidazolium)Cl (&ldquo:IrIMes&rdquo:) and a given nucleobase in deuterated ethanol/water solutions yielded low 1H &epsilon: values (&le:10), likely reflecting weak catalyst binding. However, we achieved natural-abundance enhancement of 15N signals for 3-methyladenine of ~3300 and ~1900 for the imidazole ring nitrogen atoms. 1H and 15N 3-methyladenine studies revealed that methylation of adenine affords preferential binding of the imidazole ring over the pyrimidine ring. Interestingly, signal enhancements (&epsilon:~240) of both 15N atoms for doubly labelled cytosine reveal the preferential binding of specific tautomer(s), thus giving insight into the matching of polarization-transfer and tautomerization time scales. 13C enhancements of up to nearly 50-fold were also obtained for this cytosine isotopomer. These efforts may enable the future investigation of processes underlying cellular function and/or dysfunction, including how DNA nucleobase tautomerization influences mismatching in base-pairing.
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