Question

For proton NMR spectrum, what effect does PO4 have and why? Why is this important?

Example, examine the proton NMR spectrum of dpG, dpC, and dpA. How will presence of phosphate (PO4) alter the NMR spectrum? What useful information does this provide?

dpG - deoxyguanosine phosphate dpC - deoxycytidine phosphate dpA - deoxyadenosine phosphate

Answer 1

Outline for the effect of PO₄ in the ¹H NMR spectrum: The proton couples with 31P nucleus and gives a signal having a multiplicity of 2nI + 1, where n = no. of ³¹P nuclei, I = its nuclear spin quantum no. = 1/2.

Now, consider all the cases of dpG, dpC and dpA: The corresponding structures are shown below.

In all the three cases, the CH₂ protons, which are shown in the bold-manner in the above drawings, will couple(³J) with the proton on the adjacent to give a doublet, in which each peak splits into another doublet by coupling (³J) with phosphorus.