The presence or absence of imino proton resonances, or of coupling between 15 N atoms across a hydrogen bond, indicates the presence or absence of basepairing.
2.
With off-resonance decoupling, the noise decoupler irradiates the sample at 1000-2000 Hz upfield or 2000-3000 Hz downfield of the proton resonance frequency.
3.
Smaller permanent magnet systems were developed in the 1960s-70s at proton resonance frequencies at 60 and 90 MHz and were widely used for chemical analysis using continuous wave methods.
4.
Steric repulsion is also largely responsible for the stabilizing of colloids by coating the surface with a polymer, and can also cause bond length shortening, steric deshielding of proton resonance and compressional frequency enhancement in the IR spectrum.
5.
In 1977 Bodenhausen and Freeman showed how it was possible by observing a heteronucleus ( an atomic nucleus other than a proton ) spectrum to get a indirect detection of the proton resonance frequencies, and the correlations of chemical shifts between protons and heteronuclei.
6.
Early nucleic acid NMR studies were performed as early as 1971, and focused on using imino proton resonances to probe base pairing interactions, such as in tRNA . With the advent of oligonucleotide synthesis, the first NMR spectrum of double-helical DNA was published in 1982, and methods for sequential assignment of the resonances were published the following year.
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