Electron spin resonance spectroscopy, iron

Jezowska-Trezebiatowska, B., and Jezierski, A. (1973). Electron spin resonance spectroscopy of iron nitrosyl complexes with organic ligands. J. Mol. Struct. 19, 635-640. 

The electron-transport chain contains a number of iron-sulfur proteins (also known as nonheme iron proteins). The iron atoms are bound to the proteins via cysteine —S— groups and sulfide ions one such 4-Fe cluster is shown in Fig. 14-1. These proteins mediate electron transport by direct electron transfer changes in oxidation state of the iron in iron-sulfur proteins can be monitored by electron spin resonance spectroscopy (ESR). 

The relevant biological questions are how the iron is converted from mineral to protein and once in the protein what is the specialized role played by the iron in the function of that protein In this chapter we concern ourselves with the means by which iron is obtained and secured for the living organism through the iron storage and transport proteins, and in particular how Mossbauer effect and electron spin resonance spectroscopy can help to understand the electronic and molecular structure of these proteins. 

Symons MCR, Petersen RL (1978) Electron capture at the iron-oxygen center in single erystals of oxymyoglobin studied by electron spin resonance spectroscopy. Biochim Biophys Acta 535 241 246... 

Electron spin resonance spectroscopy, or ESR, has been useful in the elucidation of structure and function of the iron proteins and when used in conjunction with other techniques has provided information on the electronic state of the iron, its ligand binding, and change of oxidation state (Peisach et al, 1968). ESR measurements have proven to be particularly useful in dealing with systems containing a mixture of iron protein species. It is the intention of the present review to describe some of the more recent developments in the application of ESR spectroscopy in establishing the structure and function relationships of the iron proteins. 

Porphyrin is a multi-detectable molecule, that is, a number of its properties are detectable by many physical methods. Not only the most popular nuclear magnetic resonance and light absorption and emission spectroscopic methods, but also the electron spin resonance method for paramagnetic metallopor-phyrins and Mossbauer spectroscopy for iron and tin porphyrins are frequently used to estimate the electronic structure of porphyrins. By using these multi-detectable properties of the porphyrins of CPOs, a novel physical phenomenon is expected to be found. In particular, the topology of the cyclic shape is an ideal one-dimensional state of the materials used in quantum physics [ 16]. The concept of aromaticity found in fuUerenes, spherical aromaticity, will be revised using TT-conjugated CPOs [17]. 

Cammack, R., Patil, D. S. and Eernandez, V. M. (1985) Electron-spin-resonance/electron-para-magnetic-resonance spectroscopy of iron-sulfur enzymes. Biochem. Soc. Trans., 13, 572-8. 

Other spectroscopic techniques used to characterize iron oxides are photoelectron (PS), X-ray absorption (XAS), nuclear magnetic resonance (NMR) (Broz et ah, 1987), Auger (AES) (Seo et ah, 1975 Kamrath et ah, 1990 Seioghe et ah 1999), electron loss (EELS)), secondary ion mass (SIMS) and electron spin resonance (ESR) spectroscopy (Gehring et ah, 1990, Gehring Hofmeister, 1994) (see Tab. 7.8). Most of these tech-... 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

Senesi et al. (1977), using the methods of electron spin resonance and Mossbauer spectroscopy in conjunction with chemical methods, established that at least two and possibly three forms of binding of Fe occur in humic materials. Ferric iron is firmly bound and protected in tetrahedral or octahedral coordination this form of binding of iron is resistant to chemical complexing and reduction. Fe adsorbed on the outer surfaces of humic materials is less firmly bound. The iron-fulvic acid complexes studied contain from 5.5 to 50.1% Fe, but a large part of the iron is bound to the surficial octahedral position. 

A number of transition metal nuclei can be studied by Mossbauer techniques (e.g., Fe, Ni, Ru, W, Os, Ir, and Pt). Of these, only Ir, Ru, and Fe have been used to study nitrosyl bonding. The most detailed studies have been on the well-known iron complexes [Fe(CN)5(NO)] - (87. 89) and [Fe(NO)(dtc)z] (88-90) (dtc is N,N-dialkyldithiocarbamato). In the latter, high-spin/low-spin equilibria can be followed by Fe Mossbauer spectroscopy, and the Mossbauer parameters agree well with data from electron spin resonance (ESR) spectroscopy in determining the ground states of these complexes. 

The third principal application of the electron spin resonance technique is to the study of paramagnetic transition metal ions in biochemical systems. Most examples are complexes of copper, iron, manganese, chromium, cobalt and molybdenum. Other metals such as titanium, vanadium and nickel are sometimes employed as structural probes. Only four of these ions, Cu ", Mn, Gd " and VO ", are seen in ESR spectroscopy at room temperature under virtually all conditions. Therefore, they are of special importance. 

Iron-containing mesoporous materials have been widely studied due to the unique catalytic performance of selective reduction, hydrocarbon oxidation, and acylation and alkylation reactions (Vinu et al. 2007). Thus, Tanglumlert et al. (2008) were interested in the room temperature synthesis of Fe-SBA-1 using FeCl3 via the sol-gel process. The results illustrated that up to 6 wt% Fe could be contained in the SBA-1 framework without destroying the mesopore order. Nevertheless, extraframework FeOg clusters were also found, as suggested by electron spin resonance (ESR) spectroscopy. The BET surface area was 1062 m /g, with a pore diameter around 2.1 nm. 

Recently, iron(V) nitride complex [PhB( Bulm)3Fe =N]BArF24 (PhB( Bulm)3 = phenyltris(3-tert-butylimidazol-2-ylidene)borato BArp24 = B(3,5-(CF3)2QH3)4 ) has been prepared [100]. This complex has a four-coordinate iron ion with a terminal nitride ligand. The characterization of the complex by Mossbauer and electron paramagnetic resonance spectroscopy demonstrated d iron(V) metal center in a low-spin (S= 1/2) electron configuration. The decomposition of the complex by water at low temperature formed ammonia and iron(ll) species. 

Cross-conjugated dihydroacepentalene complexes 156 (NR2 = NEt2, piperidino, 3,5-dimethylpiperidino, morpholino) and 159 were prepared by de Meijere and Butenschon [179, 180] by treatment of the ligands with either Fe2(CO)9 or CpCo(H2CCH2)2 in yields up to 70%. When complex 156 was reduced with sodium, the persistent radical anion was detected with spin density on the iron atom as indicated by electron spin resonance (ESR) spectroscopy. Further reduction with sodium afforded the ferrate(-2) 158, which is diamagnetic and could be characterized by NMR investigations (Scheme 10.56). 

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