Lymphomatosis cerebri (LC) is a rare variant of primary central nervous system lymphoma (PCNSL). Clinically, the disease typically presents with a rapidly progressive dementia and unsteadiness of gait. Its presentation on cerebral MRI, which is characterised by diffuse leukoencephalopathy without contrast enhancement, often causes diagnostic confusion1 with suspected diagnoses ranging from Binswanger's disease to leukoencephalopathy or encephalomyelitis. Here we report a patient with subacute dementia and diffuse bilateral white matter changes in the cerebral hemispheres and additional involvement of the brainstem, basal ganglia and thalamus on MRI. Initially, she was considered to suffer from an autoimmune encephalitis, transiently responded to immunosuppression but then developed multiple solid appearing cerebral lymphomas.

Objective: Peripheral neuropathy with optic atrophy is a clinically and genetically heterogeneous group of disorders classified as hereditary motor and sensory neuropathy (HMSN) Type VI. We report on a case which shows not only peripheral but also central myelinisation defects.

The linear trinuclear iron complex Fe3 (SPh)6 (CO)6 with bridging benzenethiolate ligands is the subject of temperature-and field-dependent Mössbauer studies and of temperature-dependent magnetic susceptibility studies. The results reveal the two terminal iron atoms to be diamagnetic Fe(II) and the central iron atom to be high-spin Fe(II). The latter exhibits an enhanced effective magnetic moment compared to the (S = 2) spin-only value of 4.9 μB, and its magnetic Mössbauer pattern is dominated by a positive (!) internal field. Complementary to the experimental studies also theoretical studies are performed. Local density molecular orbital and ligand-field calculations yield an orbitally degenerate ground state that accounts for the unusual electronic and spectroscopic properties. With these results inconsistencies in previously reported spectroscopic studies of Fe3 (SPh)6 (CO)6 are resolved.

The magnetic properties of the Fe(II)‐binding sites in Fe(II)7‐metallothionein (MT) have been studied using Mössbauer spectroscopy and magnetic‐susceptibility measurements. In agreement with our previous results, simulation of the Mössbauer spectra showed the presence of paramagnetic and diamagnetic subspectra in the ratio 3:4. By comparison with Mössbauer spectra of the inorganic adamantane‐like (Et4N)2[Fe4(SEt)10] model compound, the diamagnetic component in Fe(II)7‐MT has been assigned to a four‐metal cluster in which there is antiferromagnetic coupling between the high‐spin Fe(II) ions. It is suggested that the organization of this cluster is similar to that determined in the three‐dimensional structure of the protein, containing diamagnetic Zn(II) and/or Cd(II) ions. From magnetic‐susceptibility studies, an average magnetic moment of approximately 8.5 μB was obtained for the three remaining bound Fe(II) ions, responsible for the paramagnetic component observed in the Mössbauer studies. This value is slightly lower than that for three completely uncoupled Fe(II) ions, suggesting the existence of a three‐metal cluster within which there is weak exchange coupling between adjacent Fe(II) ions. The spin‐Hamiltonian formalism including, besides zero‐field and Zeeman interaction, also exchange interaction among the three Fe(II) ions in the three‐metal cluster, H = ‐J12 (S1·S2)‐J23 (S2·S3‐J13 (S1·S3), was applied to simulate both magnetic‐Mössbauer and magnetic‐susceptibility data. Reasonable fits were achieved only with values |J12|=|J23|=|J13|=|J| < 1 cm−1. Such a situation could not be reconciled with the chair‐like geometry of the [M3(CysS)9]3‐ cluster determined with paramagnetic metal ions, where significantly stronger coupling would be anticipated (|J|= 50–70 cm−1). However, modest exchange‐coupling properties have been reported for a number of crystallographically characterized trinuclear [Fe3(SR)3X6]3‐ clusters (X = Cl, Br; R = Phe, p‐tolyl, 2,6‐Me2C6H3) distinguished by the preferential formation of a planar Fe3(μ2‐SR)3 ring [Whitener, M. A., Bashkin, J. A., Hagen, K. S., Girerd, J.‐J., Gamp, E. Edelstein, N. & Holm, R. H. (1986) J. Amer. Chem. Soc. 108, 5607–5620]. It is therefore more likely that a pseudo‐planar geometry rather than a chair‐like geometry is present in the Fe3 cluster of Fe(II)7‐MT. This would represent the first example of structural differences on binding divalent metal ions to this protein.

We have performed Mössbauer studies on deoxy-myoglobin in applied fields of 1, 2 and 6.2 T in the temperature range from 1.5 to 200 K. The spectra could be interpreted in the framework of the spin-Hamiltonian formalism with the inclusion of spin-lattice relaxation. A fractal dimension of 1.6 was found.

Iron(II)-substituted yeast metallothionein has been studied with Mössbauer spectroscopy. The iron in the protein is in the high-spin ferrous state. A maximum metal content of four iron(II)/molecule has been determined, with the four metal ions forming a diamagnetic cluster due to the antiferromagnetic exchange interaction between Fe2+ via bridging thiolates. In the case where the iron titration gives a value of less than four iron(II)/apoprotein, the metal ions are magnetically noninteracting, with each individual iron(II) behaving like iron(II) in reduced rubredoxin.

Exchange interactions and charge transfer in the Fe2+Fe3+ of the mixed valence [Fe2S2 (dimethylmethanebisbenzimidazolate)2]3- trianion have been studied by analysis of Mossbauer spectra in the temperature range of 1.5-180 K and in applied fields of 10 mT, 0.35 T, and 6.2 T. The low-temperature spectra reveal a ground state with total spin S(t) = 1/2 and hyperfine parameters intermediate between values for a Fe2+Fe3+ localized mixed-valence pair and a fully delocalized system where the two iron atoms are equivalent. A consistent set of hyperfine parameters has been derived by fitting the spectra with a stochastic relaxation model taking into account spin relaxation in the S(t) = 1/2 state and electron hopping between the iron ions. An interpretation of the values of the hyperfine parameters has been given by solving a spin Hamiltonian, which includes antiferromagnetic and double exchange in an asymmetric Fe2+Fe3+ pair and which allows partial electron delocalization. Using the value a2 = 0.8 for the delocalization coefficient and an estimate of DELTA = 105 cm-1 for the difference between the S(t) = 1/2 and the first excited S(t) = 3/2 state we have derived limits for the exchange-coupling constant J, the double-exchange parameter B, and the energy difference E(A) - E(B) arising from the two possible configurations Fe(A)2+Fe(B)3+ and Fe(A)3+Fe(B)2+, i.e., 70 cm-1 less than or similar to J less than or similar to 300 cm-1, 0 < Absolute value of B less than or similar to 395 cm-1, and 0 < \E(A) - E(B)\ less than or similar to 590 cm-1.

Oxoferrylporphyrin cation radical complexes were generated using the prophyrin dianions: tetrakis 2,6-dichlorophenyl (TDCPP) and tetrakis 2,4,6-trimethoxyphenyl (TTMPP). Spin coupling between ferryl iron (S=1) and porphyrin radical S′=1/2), ligand field interaction and hyperfine parameters of iron were studied by Mössbauer and EPR measurements and corresponding spin Hamiltonian analyses. Samples of [FeIV=0 TDCPP], which had to be prepared in CH2Cl2, were “vacuum dried” in order to obtain Mössbauer spectra.

The ferrous and ferric form of a ("picket-fence" porphyrinato)(acetato)iron complex, [Fe(II/III)(CH3CO2)(TPpivP)]-,0, were synthesized and characterized by UV-visible, H-1 NMR, EPR, and Mossbauer spectroscopy. The structure of the ferrous complex was determined by X-ray diffraction. Crystal data at -100-degrees-C: [Fe(II)(CH3CO2)(TPpivP)][Na subset-of C222].C6H5Cl(C90H108N10O12NaClFe); monoclinic; a = 18.040 (5), b = 21.521 (5), c = 22.605 (5) angstrom; beta = 100.37 (5)-degrees; Z = 4, D(calc) = 1.259 g cm3; space group P2(1)/n. The five-coordinate iron atom is bonded to four porphyrinato nitrogens [Fe-N(p)] = 2.107 (14) angstrom and to an oxygen atom of the acetate ion (Fe-O(acetate) = 2.034 (3) angstrom), placed inside the molecular cavity of the picket-fence porphyrin. Mossbauer spectra were recorded in the two oxidation states of thc complex at temperatures varying from 1.5 to 200 K in fields of 0-6.21 T. The ferrous complex has a large quadrupole splitting, DELTA-E(Q) = 4.25 mm s-1, nearly independent of temperature. In the ferric species, the quadrupole splitting, DELTA-E(Q) = 1.1 mm s-1, is as normally found in ferric high-spin iron porphyrins. The spin-Hamiltonian analysis of the spectra yields the zero-field parameters D = -0.9 cm-1 and E/D = 0.33 and the magnetic hyperfine parameters A(x,y) = -17 T and A(z) = -13.3 T in the ferrous complex (spin S = 2) and D = 7.5 cm-1, E/D almost-equal-to 0 and A(x,y,z) = -20 T in the ferric species (S = 5/2). The values of the zero-field parameters of the ferric species are confirmed by EPR analysis; the g values are g(x) = 1.960, g(y) = 2.017, and g(z) = 2.00. The zero-field splittings and effective g values in the ferric complex are interpreted in terms of a crystal-field model. Theoretical estimates of the quadrupole splitting and zero-field parameters in the ferrous complex are given on the basis of molecular-orbital calculations. The relation between the zero-field tensor (D) and electronic and X-ray structure in the ferrous species is discussed.

Magnetic properties of frozen solutions of highly oxidized iron porphyrin complexes were investigated by EPR and Mössbauer spectroscopy. The Mössbauer spectra, recorded at low temperatures in various magnetic fields, were analyzed on the basis of spin Hamiltonian simulations. Spin coupling between ferryl iron (FeIV) and porphyrin cation radical was taken into account explicitly. Hyperfine and spin-coupling parameters are given for several complexes, together with zero-field parameters. One of the complexes exhibits weak spin coupling, it is the first model system exhibiting properties comparable to those of the oxoferryl cation radical enzyme Horse Radish Peroxidase I.

In this paper, we briefly summarize the main conclusions of the Mössbauer analysis of [L2Fe2(μ-OH)3] (ClO4)2·2CH3OH·2H2O with L=N,N',N"-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which possesses a central exchange-coupled delocalized-valence Fe(II/III) unit. The complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. The magnetic Mössbauer spectra imply a system spinSt=9/2 for the dimer in its ground state. The values for hyperfine and spin-Hamiltonian parameters, obtained from simulations of the Mössbauer spectra, are δ=0.74 mms−1, ΔEQ=−2.14 mms−1,A⊥=−10.6 T,A∥=−13.5 T andD=1.8 cm−1. The system spinSt=9/2 is interpreted to be a consequence of double-exchange coupling.

In this paper we present the characterization by UV-VIS, Mössbauer, and EPR spectroscopy of [L2Fe2(μ-OH)3](ClO4)2⋅2CH3OH⋅2H2O, with L=N,N′,N″-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which is shown to possess a central exchange-coupled delocalized-valence Fe(II/III) pair. Complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. Mössbauer, EPR, and magnetic susceptibility data imply a system spin St =9/2 for the ground state. This finding is explained as being a consequence of the double-exchange interaction which is generated by the delocalized electron. Experimental values obtained from UV-VIS, Mössbauer, and EPR spectroscopy are for the double-exchange parameter B=1300 cm−1, the g factors gx,y =2.04 and gz =2.3, the parameters for zero-field splitting D=4 cm−1 and E≊0 cm−1, and for the hyperfine parameters ΔEQ =−2.14 mm s−1, Ax,y =−21.2 T, Az =−27 T, and δ=0.74 mm s−1. From our temperature-dependent studies we assign to the first excited state a spin-octet with an excitation energy Δ>175 cm−1. From this value a lower bound of −235 cm−1 has been deduced for the exchange-coupling constant J. In the framework of a simplified description of the iron atoms by unperturbed 3d orbitals, the values of the A tensor components as well as the quadrupole splitting ΔEQ can be interpreted in a consistent manner by assuming the excess electron being delocalized over two dσ orbitals centered at the two iron sites of the dimer and directed along the iron–iron axis as the z direction.

Oxoferrylporphyrin cation radical complexes were generated by m-chloroperoxybenzoic acid oxidation of the chloro and trifluoromethanesulfonato complexes of tetramesitylporphyrinatoiron(III) [(TMP)Fe] and the trifluoromethanesulfonato complex of tetra(2,6-dichlorophenyl)porphyrinatoiron(III) [TPP(2,6-Cl)Fe]. Coupling between ferryl iron (S = 1) and porphyrin radical (S' = 1/2) spin systems was investigated by Mössbauer and EPR spectroscopy. The oxoferrylporphyrin cation radical systems generated from the TMP complexes show strong ferromagnetic coupling. Analysis of the magnetic Mössbauer spectra, using a spin Hamiltonian explicitly including a coupling tensor J, suggests an exchange-coupling constant J greater than 80 cm-1. The EPR spectra show non-zero rhombicity, the origin of which is discussed in terms of contributions from the usual zero-field effects of iron and from iron-radical spin-dipolar interaction. A consistent estimate of zero-field splitting parameter D approximately + 6 cm-1 was obtained by EPR and Mössbauer measurements. EPR and Mössbauer parameters are shown to be slightly dependent on solvent, but not on the axial ligand in the starting (TMP)Fe complex. In contrast to the TMP complex, the oxoferrylporphyrin cation radical system generated from [TPP(2,6-Cl)FeOSO2CF3] exhibits Mössbauer and EPR spectra consistent with weak iron-porphyrin radical coupling of magnitude of J approximately 1 cm-1.

The catalytic Zn(II) ion of horse liver alcohol dehydrogenase (EE isozyme) was replaced by Fe(II), providing a novel iron protein with the unusual coordination of Fe(II) to two cysteines residues, one histine residue and water. The electronic structure of iron in this system was characterized by Mössbauer spectroscopy at various temperatures as well as applied magnetic fields and analysed in terms of the spin Hamiltonian formalism. The novelty we found is an unusually weak spin coupling (|J| < 0.1 cm−1) of a paramagnet (S= 1) with iron (S= 2). From EPR and biochemical studies we conclude that the corresponding chemical species is triplet oxygen (O2). The quantitative determination of the coupling energy was possible utilizing the competition between Zeemann interaction and spin coupling at weak magnetic fields and low temperature. Oxidation experiments followed by Mössbauer spectroscopy showed that the spin‐coupled system is an outer‐sphere Fe(II) · (O2)aq complex occurring as an intermediate during a Fe(II)‐catalyzed dioxygen activation. We observed two additional Fe(II) species after treatment with O2 and dithionite. The spin Hamiltonian parameters of iron in the coupled system are presented. The results are compared with those of iron in other non‐heme iron proteins.

The reaction of Fe(CIO4)2·6H2O with N,N′,N,″-trimethyl-1,4,7-triazacyclononane (L) in methanol affords, in the presence of a small amount of oxygen, the deep blue binuclear complex [L2Fe2(µ-OH)3](CIO4)2·2MeOH·2H2O which was characterized by EXAFS, e.s.r., u.v.-visible and Mössbauer spectroscopy to be a mixed valence iron (II/III) species of class III with an Stot= 9/2 ground state.