Electron spin-echo envelope modulation spectroscopy

G.R. Eaton and S.S. Eaton, Electron-nuclear double resonance spectroscopy and electron spin echo envelope modulation spectroscopy, Comprehensive Coordination Chemistry II, Elsevier, Boston, 2004, 49. 

Morrissey, S. R., Horton, T. E., Grant, C. V., Hoogstraten, C. G., Britt, R. D., and DeRose, V. J. (1999). Mn2+-nitrogen interactions in RNA probed by electron spin-echo envelope modulation spectroscopy Application to the hammerhead ribozyme. 

To determine whether PLP was actually associated with the lysine radical, [4 - H]PLP was synthesized and exchanged into the enzyme, and the [4 - H]PLP-enzyme was used to prepare a sample of the putative product radical 3. The EPR spectrum of the sample containing [4 - H]PLP proved to be identical with that of a matched sample containing PLP. The two samples were submitted to electron spin echo envelope modulation spectroscopy (ESEEM). The ESEEM spectra revealed a signal corresponding to the Larmor frequency for deuterium in the sample containing [4 - H]PLP (Fig. 5) and no signal in the PLP sample. This meant that the deuterium in [4 - H]PLP must be... 

Britt, R. D., Sauer, K., Klein, M. P., Knaff, D. B., Kriauciunas, A., Yu, C. A., Yu, L., and Malkin, R., 1991, Electron spin echo envelope modulation spectroscopy supports the suggested coordination of two histidine ligands to the Rieske Fe-S centers of the cytochrome b6f complex of spinach and the cytochrome bcl complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides, and bovine heart mitochondria. Biochemistry 30 1892nl901. 

ESEEM spectroscopy is a time-domain (i.e. pulsed) analog of EPR see Electron Spin Echo Envelope Modulation Spectroscopy). In principle, ESEEM contains the same information as is found in EPR and ENDOR, although in practice ESEEM is much more sensitive to weakly coupled nuclei that are not easily detected by ENDOR. On the other hand, strongly coupled nuclei can be undetectable by ESEEM, thus the combination of both techniques is often useful. 

As an example of how to determine the electronic ground state of a low-spin iron(lll) compound, we present work on the ferric low-spin heme complex [TPPFe(NH2PzH)2]Cl, which has been shown to have a (dxy) (dxz, dj, ) electronic ground state. The field-dependent Mossbauer spectra of [TPP Fe(NH2PzH)2]Cl displayed in Fignre 12 are well reproduced by simulations, which yield 5 =0.25mms , AEq = ( )2.50imns, an asymmetry parameter rj = —3, and an anisotropic A tensor of" / nMn = (-47.6, 6.7, 18.3)T. The g values necessary for the 5" = 1 /2 spin Hamiltonian (g z = 2.39, gyy = 2.28, and gxx = L87) have been taken from a combined EPR and electron spin echo envelope modulation spectroscopy ESEEM analysis. 

CEMS = conversion electron Mossbauer spectroscopy DFT = density functional theory EFG = electric field gradient EPR = electron paramagnetic resonance ESEEM = electron spin echo envelope modulation spectroscopy GTO = Gaussian-type orbitals hTH = human tyrosine hydroxylase MIMOS = miniaturized mossbauer spectrometer NFS = nuclear forward scattering NMR = nuclear magnetic resonance RFQ = rapid freeze quench SAM = S -adenosyl-L-methionine SCC = self-consistent charge STOs = slater-type orbitals TMP = tetramesitylporphyrin XAS = X-ray absorption spectroscopy. 

S. A. Dikanov and Y. D. Tsvetkov, Electron Spin Echo Envelope Modulation Spectroscopy , CRC Press, Boca Raton, 1992. This book begins with the fundamental principles of ESEEM and develops the theory of the measurements with exquisite detail. 

ESEEM, Electron Spin Echo Envelope Modulation Spectroscopy... 

Thomann, H., M. Bernardo, D. Goldfarb, P.M.H. Kroneck, and V Ullrich (1995). Evidence for water binding to the Fe-center in cytochrome P450cam obtained by electron spin echo envelope modulation spectroscopy. J. Am. Chem. Soc. 117, 8243-8251. 

Zhang J, Carl PJ, Zimmermann H et al (2002) Investigation of the formation of MCM l by electron spin-echo envelope modulation spectroscopy. J Phys Chem B 106 5382-5389... 

Jeschke G, Rakhmatullin R, Schweiger A (1998) Sensitivity enhancement by matched microwave pulses in one- and two-dimensional electron spin echo envelope modulation spectroscopy. J Magn Reson 131(2) 261-271... 

Electron spin echo spectroscopy (ESE) monitors the spontaneous generation of microwave energy as a function of the timing of a specific excitation scheme, i.e. two or more short resonant microwave pulses. This is illustrated in Fig. 7. In a typical two-pulse excitation, the initial n/2 pulse places the spin system in a coherent state. Subsequently, the spin packets, each characterized by their own Larmor precession frequency m, start to dephase. A second rx-pulse at time r effectively reverses the time evolution of the spin packet magnetizations, i.e. the spin packets start to rephase, and an emission of microwave energy (the primary echo) occurs at time 2r. The echo ampHtude, as a fvmction of r, constitutes the ESE spectrum and relaxation processes lead to an irreversible loss of phase correlation. The characteristic time for the ampHtude decay is called the phase memory time T. This decay is often accompanied by a modulation of the echo amplitude, which is due to weak electron-nuclear hyperfine interactions. The analysis of the modulation frequencies and ampHtudes forms the basis of the electron spin echo envelope modulation spectroscopy (ESEEM). 

Complex 146 (entry 0-3 of Table 3) forms a free radical in THF solution and the electron paramagnetic resonance (EPR) spectrum shows a weak triplet signal with hyperflne splitting by coupling with the P ligands. The triplet disappears when Ag(0) precipitates. The presence of covalent radicals [Ag—CH(R)OH]"+, R = H, Me, in Ag(l)-containing molecular sieves loaded with MeOH or EtOH was detected by EPR and electron spin echo envelope modulation spectroscopies. ... 

Electron Paramagnetic Resonance Spectroscopy (S.S. Eaton, G.R. Eaton). Electron-Nuclear Double Resonance Spectroscopy and Electron Spin Echo Envelope Modulation Spectroscopy (S.S. Eaton, G.R. Eaton). 

The influence of the 2 -hydroxyl group conformation on the stability of A-form helices in RNA has been investigated and it was found that the 2 -hydroxyl group adopts a conformation in which it can favourably hydrogen bond to a water molecule in the nucleotide-base plane.The high affinity metal binding site in the hammerhead ribozyme has been determined using electron spin-echo envelope modulation spectroscopy. 

Reijerse E, Dikanov SA. 1991. Electron spin echo envelope modulation spectroscopy on orientationally disordered systems line shape singularities in 5 = A, / = A spin systems. J Chem Phys 95 836-845. 

Magliozzo RS, Peisach J. 1993. Evaluation of nitrogen nuclear h3q)erfine and quadru-pole coupling parameters for the proximal imidazole in myoglobin-azide, -cyanide and -mercaptoethanol complexes by electron spin echo envelope modulation. Spectroscopy 32(33) 8446-8456. 

Fukui K, Fujisawa Y, Ohya-Nishiguchi H, Kamada H, Sakurai H. 1999. In vivo coordination structural changes of a potent insulin-mimetic agent, bis(picolinato)oxovana-dium(IV), studied by electron spin echo envelope modulation spectroscopy. J Inorg Biochem 77 215-224. 

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