A. X. Trautwein

A structural and magnetochemical study of some copper(II) complexes containing the ligands 1,4,7-triazacyclononane-N-acetate (L1) and N-(2-hydroxybenzyl)-1,4,7-triazacyclononane (HL2)

The tetradentate macrocyclic ligands 1,4,7-triazacyclononane-N-acetate (L1) and N-(2-hydroxybenzyl)-1,4,7-triazacyclononane (HL2) react in methanol with CuCl2 or Cu(ClO4)2·6H2O in the absence or presence of LiOH·H2O with formation of the following complexes containing square based pyramidal Cu(II)ions: [L1CuCl] (1), [L1CuCl]LiCl·2H2O (2), [L1Cu](ClO4) (3) and [L22Cu2](ClO4)2 (4). Complexes 2 and 4 have been characterized by single crystal X-ray crystallography; the structure of 3 has been reported previously [3]. Crystal data: 2, space group P21/c, a = 11.674(4), b = 7.543(2), c = 17.560(5) A, β = 106.59(8)°, V = 1481.9(7) A3 Z = 4, Dcalc = 1.63 g cm−3, R = 0.044 based on 2499 reflections; 4, space group Pbca, a = 17.742(4), b = 10.335(2), c = 17.742(4) A, V = 3253(1) A3, Dcalc = 1.62, Z = 4, R = 0.048 based on 2147 reflections. From temperature dependent magnetic susceptibility measurements (2–293 K) weak intermolecular antiferromagnetic exchange coupling has been established for 1 and 2, whereas for the helical chain structure 3 weak ferromagnetic exchange coupling has been observed. In dinuclear 4 strong antiferromagnetic intramolecular coupling leads to an S = 0 ground state.

Mössbauer investigations of the hexachlorantimonate salt of the phenyliron 2,3,7,8,l2,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrinate, [Fe(oetpp)Ph]SbCl6 and X-ray structure of the phenyliron(III) precursor Fe(III)(oetpp)Ph

The phenyliron derivative, [Fe(oetpp)C 6 H 5 )]SbCl 6 ( 2 ) generated in dichloromethane by oxidation of the phenyliron(III) complex, Fe(III) (oetpp)C 6 H 5 ( 1 ) of the 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin with 1 equiv. of phenoxathiinylium hexachloroantimonate, [C 12 H 8 OS]SbCl 6 , was studied by Mossbauer spectroscopy. This compound exhibits an isomer shift δ of 0.13 mm s −1 and a quadrupole splitting Δ E Q of 3.23 mm s −1 . The measured magnetic hyperfine pattern obtained in the temperature range 4.2–40 K in a field of 3.5 and 7 T, applied perpendicular to the γ-beam, has been consistently analyzed in the spin Hamiltonian approximation assuming an iron(IV) S =1 electronic configuration. This result indicates that oxidation of the ferric precursor 1 causes oxidation of the metal and not from the macrocycle. This finding corresponds to that of the corrole complex Fe(me 2 et 6 c)C 6 H 5 (me 2 et 6 c=trianion of 7,13-dimethyl-2,3,8,l2,l7,l8-hexaethylcorrole) which recently was also characterized as an iron(IV) S =1 derivative. The molecular structure of the five-coordinate, low-spin, ferric starting derivative, Fe(oetpp)C 6 H 5 ( 1 ) is reported. A comparison of the porphyrin ring conformations in the phenyliron(III) species, Fe(tpp)C 6 H 5 ( 3 ) and Fe(oetpp)C 6 H 5 ( 1 ) indicates that the more favorable oxidation potential of the oetpp complex 1 relative to that of the non-peripherally crowded tpp ring derivative 3 is related to the non-planar distortion of the oetpp ring, distortion which is, due to the steric crowding, maintained in solution.

Mössbauer and EXAFS studies of bacterioferritin fromStreptomyces olivaceus

Mössbauer spectra of bacterioferritin fromStreptomyces olivaceus in zero field show essentially a transition from a quadrupole doublet to a six-line pattern at a temperature around 7–8 K and a distribution of hyperfine fields from 40 to 50 T. The EXAFS data reveal 3–4 phosphorus atoms in the second coordination shell. These features are found to be typical for various bacterioferritins.

Rapid spin-state interconversion in the Bis-complex of tris-(1-pyrazolyl) methane with Fe(II) studied by Mössbauer spectroscopy

Dynamic spin equilibrium is observed in a complex of the [Fe(II)-N6] type above room temperature. The Mössbauer lineshapes as function of temperature can be understood by means of the random-frequency-modulation model. Taking into accout the different Lamb-Mössbauer factors of the low- and high-spin state yields true populations of the two spin states. The transition rates follow rather well an Arrhenius law. With appropriate assumptions an activation energy ΔELH=18(1) kJmol−1 is deduced.

Mössbauer studies of spin-lattice relaxation in deoxy-myoglobin

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.

Siderophores as iron storage compounds in the yeastsRhodotorula minuta andUstilago sphaerogena detected by in vivo Mössbauer spectroscopy

In the yeastsRhodotorula minuta andUstilago sphaerogena siderophores represent the main intracellular iron pool. We suggest a ferritin substituting function of these siderophores in addition to their role as iron transport agents. InRhodotorula transport and storage siderophore is the same compound whereas in Ustilago the iron-storage siderophore is ferrichrome. Besides siderophores, merely two iron metabolites can be observed. Other iron-requiring compounds are at least one order of magnitude less abundant in these yeasts. The ferrous metabolite has been detected in many other microbial systems and seems to be of general occurence and importance.

How a blood sucking insect gets its meal: The ferriheme proteins Nitrophorin 2 and 4 studied by Mössbauer Spectroscopy

Nitrophorins are ferriheme proteins contained in the salivary glands of the blood-sucking insect Rhodnius prolixus, also known as the kissing bug. The heme iron binds nitric oxide (NO). These proteins liberate NO after injection into the victim’s tissues; NO can diffuse to the capillaries to dilate them and bring more blood to the site of the bite. The open binding-site at the iron is used by the protein to bind histamine, which has been produced by the victim as a response to the injury. Nitrophorin 2 and 4 (NP2, NP4) in the NO- and histamine-ligated form have been studied by low temperature Mossbauer spectroscopy in magnetic fields up to 7T. At 4.2 K the NO complex of NP2 exhibits δ = 0.00 mm/s and ΔEQ = 1.84 mm/s. High-field measurements indicate that the Fe-NO adduct is diamagnetic, which is also the case for the Fe-NO adduct of NP4. The histamine-ligated forni of NP2, on the other hand, shows a broad magnetic pattern at 4.2 K in applied fields from 10 mT up to 7T, characteristic for a ferric low-spin heme-iron, which is consistent with a recent EPR investigation performed on a Nitrophorin 1-histamine complex [2].

Mössbauer spectroscopy in the time domain applied to the study of single‐crystalline guanidinium nitroprusside

Guanidinium nitroprusside GNP, (CN3H6)2[Fe(CN)5NO] has been investigated in single‐crystalline form by nuclear resonant forward scattering (NFS) using synchrotron radiation (Mössbauer spectroscopy in the time domain). This method provides a direct measure of effective absorber thickness and therefore also of the Lamb–Mössbauer factor fLM. GNP has the advantage that all [Fe(CN5)NO]2- anions are practically aligned within the crystal. For the two different crystal orientations, with the crystallographic a- and c-direction parallel to the synchrotron beam, respectively, we have obtained fLM(a)= 0.122(10) and fLM(c)= 0.206(10), i.e., GNP exhibits significant anisotropic vibrational behavior. The quantum beat pattern of the NFS spectra obtained for the two different crystal orientations is discussed on the basis of radiation characteristics of the polarized synchrotron beam and the multipole transitions of oriented 57Fe nuclei.

Mössbauer studies of the vibrational anisotropy and of light-induced metastable states in single-crystalline guanidinium nitroprusside

Mössbauer studies in the energy and time domain were performed on single crystals of guanidinium nitroprusside with different orientations of their crystallographic a-, b- and c-axes with respect to the incident radiation. A remarkable anisotropy of the Lamb-Mössbauer factor is observed. Metastable states of the nitroprusside anion were populated by means of incoherent irradiation from light-emitting diodes. Calculated hyperfine parameters for the ground state and for the excited states have been retrieved from density functional calculations.

The association between the antineoplastic drug daunomycin and iron. evidence for polynuclear aggregates

In contrast to literature data, at millimolar iron and daunomycin (DN) concentrations no solitary Fe(DN)3 complexes are formed in appreciable amounts. The Mössbauer spectroscopic analysis revealed severe dependencies on temperature and on the metal ligand ratio. Two species can be discerned: exchange-coupled polynuclear aggregates, which are magnetically highly anisotropic and another superparamagnetic system, exhibiting much less magnetic anisotropy. The cooperative phenomena observed are attributed to stacking effects of daunomycin.