Fig. 2.

Increase in NMR sensitivity achieved upon carrying out ¹H-detected ¹³C LC-photo-CIDNP with a cryogenic probe. All data were collected on 1 μM Trp on spectrometers equipped with cryogenic probes. The 1D ¹³C PREPRINT LC-photo-CIDNP spectra were acquired on a 600-MHz spectrometer in the presence of submicromolar amounts of oxygen-depleting enzymes and the fluorescein photosensitizer (Materials and Methods). Data were compared with corresponding 1D ¹³C PREPRINT experiments collected under dark (i.e., laser-off) conditions and with non–laser-enhanced 1D ¹H-¹³C CT-SE-HSQC or ¹H-¹³C CT-SOFAST-HMQC experiments acquired on a 900-MHz spectrometer. Vertical intensities were normalized to display approximately the same noise levels. (A) H^α spectral region. Data were collected with the same number of scans and had an identical total experiment time (excluding the dummy scans: 16 for ¹H-¹³C CT-SOFAST-HMQC and 2 for the other experiments). (B) H^α spectral region. Data collection and processing parameters were kept consistent in all experiments except that the non–photo-CIDNP experiments comprised a larger number of transients. (C) Aromatic spectral region. Data collection and processing were carried out as in A. (D) Aromatic spectral region. Data collection and processing were carried out as in B.