Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 140, Issue 48, Pages 16855-16864Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b10923
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Funding
- Wellcome Trust [092506, 098335]
- University of York
- EPSRC [EP/R51181X/1]
- MRC [MR/M008991/1] Funding Source: UKRI
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Diazirines are important for photoaffinity labeling, and their photoisomerization is relatively well-known. This work shows how hyperpolarized NMR spectroscopy can be used to characterize an unstable diazo-compound formed via photoisomerization of a N-15(2)-labeled silyl-ether-substituted diazirine. This diazirine is prepared in a nuclear spin singlet state via catalytic transfer of spin order from para-hydrogen. The active hyperpolarization catalyst is characterized to provide insight into the mechanism. The photochemical isomerization of the diazirine into the diazo-analogue allows the NMR invisible nuclear singlet state of the parent compound to be probed. The identity of the diazo-species is confirmed by trapping with N-phenyl maleimide via a cycloaddition reaction to afford bicyclic pyrazolines that also show singlet state character. The presence of singlet states in the diazirine and the diazo-compound is validated by comparison of experimental nutation behavior with theoretical simulation. The magnetic state lifetime of the diazo-compound is determined as 12 +/- 1 s in CD3OD solution at room temperature, whereas its chemical lifetime is measured as 100 5 s by related hyperpolarized NMR studies. Indirect evidence for the generation of the photoproduct para-N-2 is presented.
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