Nuclea r magneti c resonanc e spectroscop y is on e of the few
technique s tha t permit s direc t observatio n of proton s situate d
in hydroge n bonds . Thi s possibilit y ha d bee n realize d ver y
earl y in the applicatio n o f NM R to structura l studie s o f alco -
hol s (Liddel and Ramsey , 1951) . Sinc e the n numerou s studie s
hav e bee n carrie d ou t o n smal l molecule s fro m whic h it becam e
clea r tha t hydroge n bondin g result s in downfiel d shift s o f th e
resonance s of proton s involve d in hydroge n bonds . Kearn s et
A L . (1971) wer e th e firs t to observ e hydrogen-bonde d proto n
resonance s in nuclei c acids . Thes e investigator s studie d the
N M R spectr a of transfe r RNA s and found tha t the rin g Ν proton s
of uridin e and guanine , whe n involve d in hydroge n bonding , giv e
rise to resonance s shifted far downfiel d to abou t 14 pp m fro m
t he methy l resonanc e of th e referenc e 2,2-dimethyl-4-silapen -
tane-l-sulfonat e (DSS) . Thes e finding s provide d the experi -
mentalist s wit h "a window " throug h whic h importan t junction s in
suc h biologica l macromolecule s coul d be observe d and therefor e
triggere d a numbe r of experiment s in whic h the structur e and
stabilit y of nuclei c acid s wer e studied . Thi s chapte r is pri -
maril y concerne d wit h the exchang e behavio r o f the hydrogen -
bonde d proton s an d its influenc e o n thei r NM R spectra . Suc h
studie s are importan t for two reasons . Firs t a goo d under -
standin g of the exchang e phenomen a of proton s in hydroge n bond s
is require d in orde r to b e abl e to deriv e structura l informa -
tion from the hydrogen-bonde d proto n resonanc e spectra . Fo r
instance , in so-calle d meltin g experiment s in whic h the disap -
pearanc e of hydrogen-bonde d resonance s is studie d a s a functio n