Ligand endor study of Cu(II)-doped l-histidine deuterochloride monodeuterohydrate single crystals at 4.2 K

Two-Dimensional Pulsed TRIPLE at 95 GHz

“…Since all lines that belong to one center exhibit correlations within this range it is concluded that they originate from hyperfine couplings with the same signs, in agreement with Ref. (30). The absolute sign of the strongly coupled 14 N/ 35 Cl hyperfine constants has been reported to be positive (30) Based on the recent development of high frequency ENDOR which is highly sensitive to size limited samples, it is expected that more single crystal studies on proteins and other size limited crystals will become plausible and the 2D TRIPLE experiment will be very useful for spectral editing and assignment.…”

“…(30). The absolute sign of the strongly coupled 14 N/ 35 Cl hyperfine constants has been reported to be positive (30) Based on the recent development of high frequency ENDOR which is highly sensitive to size limited samples, it is expected that more single crystal studies on proteins and other size limited crystals will become plausible and the 2D TRIPLE experiment will be very useful for spectral editing and assignment. In principle, the 2D TRIPLE experiment should be very useful also for orientationally disordered systems, provided that the number of coupled nuclei is relatively small.…”

“…The EPR spectrum of a single crystal of Cu-His should exhibits two quartets, corresponding to the two crystallographic sites (30). The FS-ED EPR spectrum of the Cu-His crystal we used, placed at an arbitrary orientation with respect to the magnetic field, is presented in Fig.…”

“…The space group of the crystal is P2 1 2 1 2 1 and two Cu 2ϩ ions, located in two different, symmetry related, crystallographic sites contribute to the EPR and ENDOR spectra (29). This system has been a subject of many investigations and the hyperfine and quadrupole tensors of the coupled nuclei have been determined (29,30). The Cu 2ϩ ions are coordinated by two histidine molecules through their amino and imidazole nitrogens, respectively.…”

A W-Band Pulsed ENDOR Spectrometer: Setup and Application to Transition Metal Centers

“…For example, in the X-band ENDOR spectrum of a Cu(II) doped L-histidine hydrochloride (Cu-His) single crystal, some of the 1 H peaks appear in the region of the 14 N signals (25), while in the W-band spectrum they are very well separated, as shown in Fig. 6.…”