Structure, Disorder, and Molecular Dynamics in Zn(d,l-histidine)₂:  EPR of Copper Ion Dopants, X-ray Diffraction, and Calorimetric Studies

Abstract

We report EPR, X-ray crystallographic, and calorimetric measurements in copper-doped and pure Zn(II) bis(D,L-histidino)pentahydrate (C 12 H 26 N 6 O 9 Zn), to be called Zn(D,L-histidine) 2 . EPR data in copper-doped single crystals were obtained at 9.8 GHz as a function of the orientation of the magnetic field B at 298 and 80 K, and as a function of temperature (T) for fixed orientations of B. Powder samples were studied at 9.8 and 35 GHz. Steep changes of the EPR spectra with temperature occur around T c ) 268 K. Above T c we observe spectra arising from a single copper with rhombic g and copper hyperfine A tensors. The resonances display a strong dependence of the line width with the hyperfine component. Below T c the spectra can be assigned to two different copper ions displaying axial symmetry and related by a C 2 rotation. As T increases approaching T c , they collapse into the high-temperature spectrum. A peak in the differential specific heat of pure Zn(D,L-histidine) 2 between 235 and 270 K indicates a transition intrinsic to the host material. Full X-ray structural studies were performed at 293 and at 150 K, above and below T c . At 293 K our results are similar to those reported before. The low-temperature data show disorder in the water molecules. We interpret the experimental results with a model where the copper atoms hop randomly between different states. This dynamics is related to the fluctuating disorder in the lattice and produces steep changes on the EPR spectra of copper ion dopants. The role of dynamic Jahn-Teller distortions is discussed. A bonding scheme for the copper ions in Zn(D,L-histidine) 2 is proposed, and it is compared with that encountered in type 1 blue copper proteins.

Electron Paramagnetic Resonance Spectroscopic Study of Copper Hopping in Doped Bis(l-histidinato)cadmium Dihydrate

“…The room temperature g and copper hyperfine tensors listed in Table 3A are unusual for d x 2 -y 2 copper model complexes 16 . They are more comparable with the room temperature tensors reported in Cu 2+ -doped Zn 2+ -(D,L-histidine) 2 pentahydrate 9 and in copper-doped tutton salt crystals undergoing dynamic Jahn-Teller distortions 17,18 .…”

“…The basic theoretical approach follows that described by Dalosto et al 9 The important concepts are the following. The temperature variation observations were interpreted using a dynamic model based upon Anderson’s theory of motional narrowing of spectral lines 1 The application of this theory provides important information on the molecular motions, specifically the rates and energy barrier between interacting states.…”

“…1,9 This happens when the transition rate p jk becomes comparable to the resonant frequency difference between the exchanging lines. Figure 10 displays a simulated EPR pattern in the presence of dynamic averaging based upon a 2-state model.…”

Magnetic and structural properties of two open-frameworks Nd(III) adipates

“…It is worthwhile to mention that AC magnetic susceptibility data obtained from partially rehydrated samples of 3 have shown a correlation between the increase of water content and the amplification of the susceptibility value [24]. This can be assigned to different causes, such as changes in CF parameters, modifications of inter-chain interactions and hydrogen bonding, as found by Price et al [29] in some Mn(III) complexes, or contribution of vibronic interactions induced by waters as those observed by Dalosto et al [30] in copper-doped bis(D,Lhistidino)pentahydrate (C 12 H 26 N 6 O 9 Zn).…”

Synthesis of Zn compounds derived from 1H-benzimidazol-2-ylmethanamine

“…[1][2][3][4][5] For example, in the active site of zinc-metalloenzymes there is present a Zn(II) ion coordinated principally to histidine, cysteine, aspartic acid, or H 2 O. 4,[6][7][8] The interaction of Zn(II) ion with the environment of the Polyligand derived from imidazole and benzimidazole are used as working models to understanding the role of the Zn(II) ions in biological systems because they can mimic the histidine side chain. 4,[7][8][9] In our ongoing research on benzimidazole derivatives we are interested in the coordinating acid and behavior of 1H-benzimidazol-2-ylmethanamine (HL) 1.…”