Proton driven spin diffusion (PDSD) experiments

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13C-13C correlation based on proton driven spin diffusion

This experiment is used to enable spin diffusion among low gamma nuclei (here carbon) under MAS making use of a densely coupled proton network, a common situation in the biological and organic samples.

First, transverse ¹³C magnetization is created using cross polarization (CP). After that, during t₁ the heteronulcear ¹H-¹³C coupling is removed using a high power decoupling scheme, such as SPINAL64. Then a 90^o pulse stores the carbon magnetisation along the z-axis. During t_mix spin diffusion occurs between the carbon atoms. At the same time the proton decoupler is switched off (Proton Driven Spin Diffusion PDSD) or is replaced by a weak recoupling field (DARR/RAD) which by broadening the carbon lines greatly facilitates the spin diffusion. Typical mixing times range from 1-1000ms. Finally the second 90^o pulse converts the carbon magnetisation back to the transverse plane and the FID is acquired under high power proton decoupling.