An ESEEM investigation of single crystals and powders of copper-dopedl-histidine hydrochloride monohydrate

Abstract

In this paper we present an investigation of the remote nitrogen of imidazole in copper-doped I-histidine hydrochloride monohydrate, which is a model system for a wide range of biologically important copper-imidazole complexes. Since these systems are mostly not available in a crystalline form it is interesting to investigate to what extent information that can be obtained from these disordered systems using ESEEM techniques is reliable. From single crystal ESEEM and HYSCORE experiments we have determined the hyperfine and quadrupole coupling tensors of the remote nitrogen in this model system. Additionally, we determined information on these tensors from powdered material, independent of the single crystal results, using orientation selective multifrequency and two-dimensional experiments. The availability of the coupling tensors from the single crystal investigation allowed an assessment of the applicability of the employed powder techniques to this important class of systems. The two-dimensional stimulated echo experiment was found to be a very useful spectroscopic tool for the study of these systems when combined with simulations.

Inhomogeneous Line-Broadening Effects in1H Two-Dimensional Four-Pulse ESEEM Spectra of Betaine Phosphite Single Crystals

“…plexes (2,5) of hyperfine parameters was observed for the hyperfine parameters of proton H13 in the ordered ferroelectric phase. The signals of proton H12 show no hyperfine parameter distribution effects either in the antiferrodistortive or in the ferroelectric phase.…”

“…For inhomogeneously broadened peaks, the frewidth. Very comparable lineshapes of cross peaks were discussed in quite disordered systems (2,5), where, in fact, quencies with respect to v t vary over the cross peaks (v t , v 1 ) in the 2D experiment in a very characteristic manner the quantity U is distributed (x Å U). The correlations be-and very special peak shapes arise as shown in Fig.…”

“…As discussed in Refs. (5,13), the phase In the following, we restrict our considerations to S Å 1 2 , modulation due to the dependence of the cosine terms in I Å 1 2 spin systems. The theoretical expression for the modu-Eq.…”

Two-Dimensional ENDOR-ESEEM Correlation Spectroscopy

“…CuCl 2 (0.5% mol) was added to an aqueous solution of 98% L-histidine HCl ⅐ H 2 O (18). Slow evaporation at room temperature over a period of a few days generated large crystals.…”

“…The detection of spectral correlations and the enhanced resolution due to the spread of the spectra into a second dimension facilitates considerably signal assignments. An example is the 2D hyperfine sublevel correlation (HYSCORE) experiment, which has revolutionized the field of ESEEM spectroscopy (10,18). In this experiment correlations between nuclear frequencies belonging to the same paramagnetic center and different M S manifolds are obtained.…”