Iron components in PS II particles of spinach by Mössbauer spectroscopy

Mössbauer spectrum measured for the iron components of photosystem II (PS II) particles of spinach is a superposition of 4 doublets. Quadrupole splitting and chemical shifting of doublets I–IV are characteristics of proteins with oxidized cytochrome b-559, reduced cytochrome b-559, Fe³⁺-Q complex and Fe²⁺ -Q complex respectively. After the PS II particles are treated with La³⁺, two doublets of Fe²⁺ disappear and Fe²⁺ is converted into Fe³⁺, indicating that the reduced cytochrome b-559 has been converted into the oxidized cytochrome b-559, and Fe²⁺ -Q complex into Fe³⁺ -Q complex. The Mössbauer spectrum of PS II particles treated with La³⁺ and Ca²⁺ shows that Ca²⁺ can weaken the inhibitory effect of La³⁺ in part, and a portion of the reduced cytochrome b-559 and Fe-Q complex still exist.     

The fractionation of iron-phosphorus compounds in sediments studied by Mössbauer spectroscopy

Iron compounds of phosphorus form a large part of the phosphorus bound in sediments. Mössbauer spectroscopy is a technique that enables us to study, directly, chemical forms of iron in solid samples. Mössbauer spectroscopy allowed us to check, directly, the selectivity of the extraction scheme for soil phosphorus proposed by Chang &; Jackson (1957), but only as far as the iron compounds are concerned. It appears that selectivity of the extraction method leaves much to be desired.

     

Structure,bonding and lattice dynamics of tri- and tetraphenyltin derivatives as studied by Mössbauer and multinuclear NMR spectroscopy

The structure and bonding properties of a number of closely related tetraphenyltin- and triphenyltin chloride compounds have been studied by the ¹¹⁹Sn Mössbauer effect and multinuclear NMR spectroscopy. The comparison of liquid and solid state ¹³C and ¹¹⁹Sn NMR spectra and of glassy solution matrix and neat solid state Mössbauer spectra provides information about the extent of intermolecular association effects in these compounds. The results indicate that all materials with the exception of (p-CF₃Ph)₃SnCl are adequately described as monomeric solids with tetrahedral geometry around the metal atom. For the latter compound spectroscopic evidence for the presence of a five-coordinated tin species is presented.     

The photocycle and the structure of iron containing bacteriorhodopsin —a kinetic and Mössbauer spectroscopy investigation

Bacteriorhodopsin (bR), converted by deionization to the blue form was reconstituted to the active purple membrane by the addition of Fe²⁺ or Fe³⁺ ions. ⁵⁷Fe Mossbauer spectra of these samples were measured at different pH values (pH 3.9, pH 5.0 and pH 7.0) and at temperatures ranging from 4 K to 300 K. The hyperfine parameters reveal two iron environments with oxygen atoms in the neighbourhood of iron. Iron type 1 is in the 3⁺ high spin state. It is bound to acid side chains of the protein and/or the phosphate groups of the lipids. Iron type 2 is in the 2⁺ high spin state and is linked to carboxy groups of the protein in a rather unspecific way. Dynamics as measured by Mossbauer spectroscopy show that the purple membrane becomes flexible only above 220 K. At the interface between membrane and bulk water the mobility is comparable to that of proteins with hydrophilic surfaces. The photocycle of Fe ³⁺-bR is slowed down compared to native bR. 3–5 Fe³⁺/bR are sufficient to inhibit the photocycle turnover by one order of magnitude. This specific effect is also found with Cr³⁺, though it is less pronounced. Mössbauer spectra of Fe³⁺-bR at 4 K reveal that iron nuclei are spin-coupled, indicating their close spatial proximity. It is proposed that iron trinuclear clusters interact with the proton uptake site of bR. Offprint requests to: M. Engelhard     

Synthesis and reactivity of perchlorate bis(tetrahydrothiophen)gold(I). 197Au Mössbauer spectra of three-coordinate gold(I) complexes

The displacement of tetrahydrothiophen (tht) in [Au(tht)₂]ClO₄ by neutral ligands gives bi-, tri- or tetra-coordinated complexes of the type [Au- (py)₂]ClO₄, [(tht)AuPPh₂NHPPh₂Au(tht)] (ClO₄)₂, [LAu(LL)]ClO₄ (L=tht, PPh₃; LL=bipy, phen) or [AuL₄]ClO₄ (L=PPh₃, AsPh₃ or SbPh₃). The reaction between [Au(tht)₂]ClO₄ and (Bu₄N)[AuR₂] (R=C₆F₅, C₆Cl₅, C₆F₃H₂) yields RAu(tht). The ¹⁹⁷Au Mössbauer spectrum of [LAu(LL)]ClO₄ establishes it as a tri-coordinated species, albeit with an asymmetrically linked bidentate ligand.     

Low temperature photodissociation studies of ferrous hemoglobin and myoglobin complexes by Mössbauer spectroscopy

⁵⁷Fe-enriched complexes of hemoglobin and myoglobin with CO and O₂ were photodissociated at 4.2°K, and the resulting spectra were compared with those of the deoxy forms. Differences in both quadrupole splitting and isomer shift were noted for each protein, the photoproducts having smaller isomer shift and larger quadrupole splitting than the deoxy forms. The photoproducts of HbCO and HbCO₂ had narrow absorption lines, indicating a well-defined iron environment. The corresponding myoglobin species had broader absorption lines, as did both deoxy forms. The weak absorption lines of photodissociated NO complexes appeared to be wide, possibly indicating magnetic interaction with the unpaired electron of the nearby NO.     

Iron coordination geometry in full-length, truncated, and dehydrated forms of human tyrosine hydroxylase studied by Mössbauer and X-ray absorption spectroscopy

Full-length human tyrosine hydroxylase 1 (hTH1) and a truncated enzyme lacking the 150 N-terminal amino acids were expressed in Escherichia coli and purified either with or without (6×histidine) N-terminal tags. After reconstitution with ⁵⁷Fe(II), the Mössbauer and X-ray absorption spectra of the enzymes were compared before and after dehydration by lyophilization. Before dehydration, >90% of the iron in hTH1 had Mössbauer parameters typical for high-spin Fe(II) in a six-coordinate environment [isomer shift δ(1.8–77?K)=1.26–1.24?mm s^–1 and quadrupole splitting ΔE _Q=2.68?mm s^–1]. After dehydration, the Mössbauer spectrum changed and 63% of the area could be attributed to five-coordinate high-spin Fe(II) (δ=1.07?mm s^–1 and ΔE _Q=2.89?mm s^–1 at 77?K), whereas 28% of the iron remained as six-coordinate high-spin Fe(II) (δ=1.24?mm s^–1 and ΔE _Q=2.87?mm s^–1 at 77?K). Similar changes upon dehydration were observed for truncated TH either with or without the histidine tag. After rehydration of hTH1 the spectroscopic changes were completely reversed. The X-ray absorption spectra of hTH1 in solution and in lyophilized form, and for the truncated protein in solution, corroborate the findings derived from the Mössbauer spectra. The pre-edge peak intensity of the protein in solution indicates six-coordination of the iron, while that of the dehydrated protein is typical for a five-coordinate iron center. Thus, the active-site iron can exist in different coordination states, which can be interconverted depending on the hydration state of the protein, indicating the presence or absence of a water molecule as a coordinating ligand to the iron. The present study explains the difference in iron coordination determined by X-ray crystallography, which has shown a five-coordinate iron center in rat TH, and by our recent spectroscopic study of human TH in solution, which showed a six-coordinated iron center.     

Structure and bonding of gold(I) and gold(III) nucleosides studied by 197Au Mössbauer spectroscopy

¹⁹⁷Au Mössbauer spectra of the series of complexes of gold(I), Au(nucl)₂Cl and gold(III), Au(nucl)Cl₃, Au(nucl - H⁺)Cl₂ and Au(nucl)₂Cl₃ were measured at 4.2 K, (nucl = nucleoside, e.g. guanosine(guo), inosine(ino), triacetylguanosine-(trguo) and triacetylinosine(trino)). It is concluded from the spectra that the gold(I) nucleosides have linear ClAuN coordination, with one coordinated nucleoside molecule per gold(I) ion, bound via the N(7) atom. The σ-donor strength of the guo ligand is somewhat higher than that of the ino ligand. The complexes Au(ino)Cl₃ and Au(guo)Cl₃, in the series Au(nucl)Cl₃, have significantly higher IS and QS values than the corresponding complexes with the triacetylnucleosides, Au(trino)Cl₃ and Au(trguo)Cl₃. This may be explained by a weak O(6)-interaction with gold(III), in a nearly trigonal bipyramidal configuration in the former case and by the presence of the strongly electron withdrawing acetyl groups in the latter, which reduces the donor strength of their N(7) atoms. The complexes of the Au(nucl - H⁺)Cl₂ series all appear to have a polymeric structure. The gold(III) ion is bound to the N(7) atom and the O(6) or the N(1) atom of the nucleosides. Finally, the Mössbauer spectra of the series Au(nucl)₂)Cl₃ can only be explained by assuming approximately octahedral AuN₂Cl₄ structures, with bridging chlorine atoms.     

Mössbauer spectrum and magnetic behavior of the iron(II)-saccharinate complex

The room temperature ⁵⁷Fe-Mössbauer spectrum and magnetic susceptibility measurements, in a wide temperature range, demonstrate that the iron-tetraaquabis(saccharinate) complex contains Fe(II) as a high spin species in an octahedral environment. The isostructural Ni(II) complex, measured for comparative purposes, shows a similar magnetic behavior.     

Solution studies on tetra(p-carboxyphenyl)porphyrin iron(II) using Mössbauer spectroscopy and electronic absorption spectroscopies

Mössbauer (78 K) and electronic absorption spectra (298 K) of tetra(p-carboxyphenyl)porphyrin iron(II) solutions are reported and discussed. Evidence for only two iron(II) complexes, the first an intermediate spin and the second a high spin complex, is found in the Mössbauer spectra. Electronic absorption spectra show a low spin complex is present at very low concentrations. It is observed from these results that the carboxy groups on the phenyl rings of this porphyrin greatly influence the chemistry. From the difference in the quadrupole splitting for the intermediate spin complex compared to that found in the tetra(p-sulphophenyl)porphyrin iron(II) system, the substituent on the phenyl ring clearly changes the electron density on the pyrrole nitrogen atoms.     

Study of a low-selenium environment in China by INAA and Mössbauer spectrometry

Biological Trace Element Research - The neutron activation analysis, γ coincidence spectroscopy, nondispersive hydrogen flame atomic fluorescence spectroscopy, and Mössbauer spectrometry...     

Piezochromic and thermochromic behaviour of ternary diimine–cyanide–Iron(II) and –Iron(III) complexes

Solvent, pressure, and temperature effects on charge-transfer spectra of several iron(II)– and iron(III)–diimine–cyanide complexes are described. The effects for MLCT and LMCT bands are in opposite direction; the solvatochromic, piezochromic, and thermochromic behaviour of the iron(II) complexes parallels that of molybdenum(0)–carbonyl–diimine complexes.     

Dicyanamido-metal(II) complexes. Part 4: Synthesis, structure and magnetic characterization of polynuclear Cu(II) and Ni(II) complexes bridged by μ-1,5-dicyanamide

The one pot aqueous reaction of M(ClO₄)₂ (M = Cu²⁺ or Ni²⁺) with N-methylbis[2-(2-pyridylethyl)]amine (MeDEPA) and N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethylenediamine (bpmen) and 1,4,7,10-tetraazacyclododecane (cyclen) in presence of sodium dicyanamide (Nadca) yielded dicyanamido-bridged polynuclear complex {[Cu(MeDEPA)(μ-1,5-dca)]ClO₄}_n (1), and two dinuclear complexes [Cu₂(bpmen)₂(μ-1,5-dca)]₂(ClO₄)₅dca (2) and [Ni(cyclen)(μ-1,5-dca)]₂(ClO₄)₂ (3). These complexes were characterized by IR and UV-Vis spectroscopy. Room temperature single-crystal X-ray studies have confirmed that the Cu(II) centers in 1 and 2 adopt geometries that are more close to trigonal bipyramidal (TBP) in 1 and close to square pyramidal (SP) in 2, whereas in 3, the Ni(II) centers are located in octahedral environment with doubly bridged μ-1,5-dca bonding mode. The intermolecular M···M distances in these complexes are in the range of 7.3-8.6 Å. Variable temperature magnetic susceptibility studies have confirmed that the dca-bridges mediate very weak antiferromagnetic interaction between the M(II) centers with J values of −0.35, −0.18 and −0.43 cm⁻¹ for 1, 2 and 3, respectively. The results are compared and discussed in the light of other related bridged μ-1,5-dca Cu(II) and Ni(II) complexes.     

Heterodinuclear Cu(II)Zn(II) complexes: F NMR as a versatile tool to control the synthesis

The dinucleating ligands 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (H-BPMP) and 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-fluorophenol (H-BPFP) were used to synthesize heterodinuclear (μ-phenoxo)(μ-hydroxo) Cu(II)Zn(II) complexes. The labeled ligand with a fluorine atom allows the use of ¹⁹F NMR spectroscopy, which turned to be a rapid and powerful tool to tune the synthesis of the heterodinuclear paramagnetic complex [CuZnBPFP(μOH)](ClO₄)₂ and avoid mixing of complexes with statistical distribution. When applied to the non-fluorinated ligand, this experimental procedure leads to prepare and isolate easily the complex [CuZnBPMP(μOH)](ClO₄)₂. The X-ray structure is described.     

A Mössbauer study of gold(I) and gold(III) dithiolate complexes related to anti-arthritic drugs

The sensitivity of the ¹⁹⁷Au Mössbauer isomer shift and quadrupole splitting to gold oxidation state has enabled characterization of new stable, water—soluble Au(I) and Au(III) complexes of dimercaptosuccinic acid. The Au(I) complex exhibits a curious asymmetric line—broadening effect. Comparisons are also made with dimercaptopropanol and dithiocarbamate complexes. Relationships to existing and potential gold drugs are discussed.     

125Te Mössbauer spectra of the intercalation compound (Te2)2(I2)

The quadrupole split asymmetric ¹²⁵Te Mössbauer spectrum recorded from the compound (Te₂)₂(I₂), in which monomolecular planar layers of iodine molecules are intercalated between layers of tellurium, is a reflection of the distorted environment of tellurium atoms in a two-dimensional layered compound in which the elongated flat crystals are preferentially orientated. The differences between the Mössbauer parameters recorded from (Te₂)₂(I₂) and those recorded from elemental tellurium and the tellurium(0) species in the compound Te₃Cl₂ are associated with small differences between the environments of tellurium in the three compounds. The Mössbauer spectra recorded from (Te₂)₂(I₂) are consistent with a recently proposed model on which the electronic band structure of (Te₂)₂(I₂) has been derived.     

Structural,infrared and Mössbauer studies of octahedral cis-dichlorobis(diketonate)tin(IV) complexes having anti-tumour activity

Two complexes, SnCl₂(bzac)₂ [Hbzac = benzoylacetone] and SnCl₂(bzbz)₂ [Hbzbz = dibenzoylmethane], have been prepared and characterised by analytical, infrared and Mössbauer studies. In addition, the X-ray crystal structure of SnCl₂(bzbz)₂ has been determined. The crystals are orthorhombic, space group Pbca with cell parameters a=18.767(9), b=17.611(8), c=16.563(8) Å. A total of 2116 reflections with I/σ(I)⩾3 gave R=3.0%. The tin is coordinated to two cis-chlorine and four oxygen atoms from the dibenzoylmethanato ligands in an approximately octahedral arrangement. The bond distances in the tin coordination sphere are SnCl 2.335(2) and 2.344(2) Å and SnO 2.062(4), 2.074(4), 2.063(4) and 2.063(4) Å and the ClSnCl angle is 95.1(1)°. The results of anti-tumour tests on these complexes are given and attempts are made to correlate the anti-tumour activity of SnCl₂(bzbz)₂ with its structure.     

Non-equilibrium state of a monomeric insect haemoglobin induced by γ-irradiation and detected by Mössbauer spectroscopy

The met-aquo form of the monomeric insect haemoglobin CTT III has been investigated by Mössbauer spectroscopy before and after reduction with thermolyzed electrons at low temperature. The native met haemoglobin dissolved in water and water/glycerol mixtures, respectively, exhibits in the range of pH 5.8 to 9.0 high-spin iron(III). The electronic state of the haemoglobin is not affected by the solvent conditions. In water/glycerol γ-irradiation at 77 K results in the reduction of the haem iron by thermolyzed electrons. Due to this process, the hexacoordinated high-spin iron(III) is transformed into a hexacoordinated low-spin iron(II). This latter complex is a transition state which changes into the high-spin iron(II) state of the deoxyhaemoglobin when increasing the temperature. Thus, a kinetically stabilized non-equilibrium state of the haemoglobin exists at low temperature which relaxes with increasing temperature and finally reaches the equilibrium state to form deoxyhaemoglobin. This transition occurs at T > 190 K and corresponds with drastic changes in the temperature dependence of the Lamb-Mössbauer factor. Both effects indicate an alteration of the intramolecular flexibility of the haemoglobin.