We demonstrate sensitivity enhancement via recycling of proton magnetization in 2D Double Cross Polarization (Double CP) experiments performed on fully protonated and uniformly labeled (¹³C, ¹⁵N) samples at a magic angle spinning rate of 60 kHz. Unused proton magnetization is preserved during t₁ evolution either by locking it with CW irradiation or by employing rotor-synchronized pi pulses. A flip-back pulse together with a modified second CP block preserves unused proton magnetization resulting in enhanced sensitivity. We have achieved sensitivity enhancements of 15–20% and 25–28% in ¹H–¹³C and ¹H–¹⁵N 2D Double CP experiments respectively. At shorter recycle delays (∼0.25T₁), relative sensitivity enhancements of 40–45% and 55% were obtained in ¹H–¹³C and ¹H–¹⁵N 2D Double CP experiments respectively. An analysis of the sensitivity enhancements and theoretical estimation of lineshapes in indirect dimension in the presence of proton recycling is provided.

我们展示了通过对质子化且均一标记的（¹³ C，¹⁵ N）样品以60 kHz的幻角旋转速率进行的二维双交叉极化（Double CP）实验中质子磁化的回收，提高了灵敏度。通过使用CW辐射锁定或通过使用转子同步pi脉冲，可以在t ₁演化过程中保留未使用的质子磁化强度。反向脉冲与修改后的第二CP模块一起保留了未使用的质子磁化强度，从而提高了灵敏度。在¹ H– ¹³ C和¹ H– ^15中，我们的灵敏度提高了15–20％和25–28％分别进行N 2D Double CP实验。在较短的循环延迟（约0.25 T ₁）下，在¹ H– ¹³ C和¹ H– ¹⁵ N 2D Double CP实验中，相对灵敏度分别提高了40–45％和55％。提供了在质子再循环的情况下间接尺寸的线形灵敏度提高的分析和理论估计。