Two-Dimensional ESEEM Study of VO2+ Complexes with Imidazole and Histidine: Histidine Is a Polydentante Ligand

Abstract

The oxovanadium cation, V02+, has been successfully employed as a spin probe1 in electron-nuclear double resonance (ENDOR)2,3 and electron spin echo envelope modulation (ESEEM)3•4 studies of metalloprotein active sites. These techniques are often used to detect coordination by side chains of histidine residues.5•6 Interpretation usually relies on the ENDOR study by Mulks et al/ of oxovanadium complexes of imidazole or histidine. Unfortunately, the nitrogen ENDOR spectra were not completely analyzed, and the hyperfine coupling to the remote imidazole nitrogen has been questioned.8Here we demonstrate that the complex of V02+ with histidine has been misinterpreted and that the dominant ESEEM pattern is produced by the -amino group. Nevertheless, we show that

A CW-EPR and ESEEM spectroscopic study of the dithiadiazolyl radicals p-XC6F4CNSSN (X = CN, Br)

“…Correlation between the two "double quantum" (dq-dq) transitions frequently appears, provided that they are slightly affected by quadrupolar anisotropy. In the case of anisotropic shf interaction, ridges cor- responding to one "single quantum" (sq-sq) correlation have also been reported [16,21].…”

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

“…Similar values were also reported for coordination of ammonia to vanadyl sites of vanadium silicate-1 nanoparticles deposited in SBA-15 [75] and ZSM-5 zeolites [76] and are also comparable with values found for nitrogens equatorially bound to an oxo-vanadiumcation, VO 2? [77][78][79][80][81][82][83], characterized by a d 1 ground state with the unpaired electron in the d xy orbital.…”

Intensity of Cross-Peaks in Hyscore Spectra of S = 1/2, I = 1/2 Spin Systems

“…5 represent the four different powder cross-peak orientations which are typical in a 2D spectra (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). In Fig.…”

“…HYSCORE (hyperfine sublevel correlation) spectroscopy based on the four-pulse two-dimensional (2D) ESEEM experiment (1) finds increasing application in the study of complex paramagnetic centers where the unpaired electron interacts with a number of magnetically nonequivalent nuclei (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). The basic advantage of the HYSCORE technique is the creation of correlation cross-peaks in 2D spectra whose coordinates are nuclear frequencies (Ϯ ␣ , Ϯ ␤ ) from opposite electron spin manifolds (1,19).…”