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Quantifying hydrogen-bonding strength: The measurement of 2hJNN couplings in self-assembled guanosines by solid-state 15N spin-echo MAS NMR

Research output: Contribution to journalJournal article

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  • Tran N. Pham
  • John M. Griffin
  • Stefano Masiero
  • Stefano Lena
  • Giovanni Gottarelli
  • Paul Hodgkinson
  • Claudiu Fillip
  • Steven P. Brown
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<mark>Journal publication date</mark>14/07/2007
<mark>Journal</mark>Physical Chemistry Chemical Physics
Issue number26
Volume9
Number of pages8
Pages (from-to)3416-3423
StatePublished
Early online date25/04/07
Original languageEnglish

Abstract

2hJNN hydrogen-bond mediated J couplings are measured in the solid state for two synthetic deoxyguanosine derivatives by 15N MAS NMR spin-echo experiments. The use of rotor-synchronised Hahn-echo pulse train (RS-HEPT) 1H decoupling, with a duty cycle of 6%, allows spin-echo durations out to 200 ms, hence enabling the accurate determination of J couplings as small as 3.8 Hz. A single-crystal X-ray diffraction structure exists for the shorter alkyl chain derivative dG(C3)2: the observation of significantly different 2hJNN couplings, 6.2 ± 0.4 and 7.4 ± 0.4 Hz, for the two resolved N7 resonances is to be expected given the NH…N hydrogen-bonding distances of 2.91 and 2.83 Å for the two distinct molecules in the asymmetric unit cell. For the longer alkyl chain derivative, dG(C10)2, for which there is no single-crystal diffraction structure, a 15N refocused INADEQUATE spectrum (Pham et al., J. Am. Chem. Soc., 2005, 127, 16018-16019) has demonstrated the presence of N2-H…N7 intermolecular hydrogen-bonds indicative of a quartet-like structure. The 2hJNN hydrogen-bond mediated J coupling of 5.9 ± 0.2 Hz is at the lower end of the range (5.9-8.2 Hz) of 2hJNN couplings determined from solution-state NMR of guanosine quartets in quadruplex DNA. A full discussion of the determination of error bars on the fitted parameters is given; specifically, error bars determined by a non-linear fitting (using the covariance matrix) or in a Monte-Carlo fashion are found to give effectively identical results.