Cross-hydrogen bond ^3hJ_CO,N coupling constants ( 99JACS1601, 99JACS2949, 99JB181, 99JACS6275, 99JACS8661, 00JMR387-143, 00JACS12835, and 01JB221-21), ranging from -0.25 Hz to -0.9 Hz, can be measured from backbone hydrogen bonds having a R_NO bond length less than 3.3 armstrongs.

The size of these constants anti-correlate with the hydrogen bond length. Thus, larger ^3hJ_CO,N values are observed for beta sheet conformations when comparing with alpha helical regions. Absolute values are measured from a J-quantitative long-range 2D H(N)CO or 3D HNCO-TROSY experiments whereas the sign of these couplings are obtained from a related ZQ/DQ methodology.

A correlation between ^3hJ_CO,N and ¹J_CO,N has been proposed ( 01JACS4099). A more complete study on the structural dependencies of these couplings has appeared (02JACS4158) and its application to quantify H/D isotope effects has been also published (04JB309-29)

The effect of presure (00JB207-18) and temperature (02JMB739) on these couplings has been reported.

The following equations have been proposed to correlate the ^3hJ_CO,N coupling constant value and the hydrogen bond length, R_NO:

R_NO = 2.75 -0.25ln(^3hJ_CO,N)+-0.06
^3hJ_CO,N=-59000exp(-4R_NO)+-0.09
Backbone amide to side-chain carboxyl hydrogen bonds have been also detected, and the measured values tend to be smaller than expected. Modified HNCO experiments have been proposed to detect such couplings without resorting to perdeuteration ( 00JB55-17 and 00JB79-17 ). Also side chain-side chain hydrogen bonds have been reported ( 00JB305)