Tin-DNA complexes investigated by nuclear inelastic scattering of synchrotron radiation

Nuclear inelastic scattering (NIS) of synchrotron radiation has been used to investigate the dynamics of tin ions chelated by DNA. Theoretical NIS spectra have been simulated with the help of density functional theory (DFT) calculations using 12 models for different binding sites of the tin ion in (CH3)Sn(DNAPhosphate)2. The simulated spectra are compared with the measured spectrum of the tin-DNA complex.

Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations.

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the m…

Structure and mixed spin state of the chloroiron(III) complex of 2,3,7,8,12,13,17,18-octaphenyl-5,10,15,20-tetraphenylporphyrin, Fe(dpp)Cl

Abstract The chloroiron(III) complex Fe(dpp)Cl (1) of the peripherally crowded 2,3,7,8,12,13,17,18-octaphenyl-5,10,15,20-tetraphenylporphyrin or dodecaphenylporphyrin (dpp), has been synthesized and characterized by X-ray crystallography, normal-coordinate structural decomposition analysis (NSD), EPR and Mossbauer spectroscopy and magnetic susceptibility measurements. The dpp ligand present in the crystal structure of this molecule is predominantly saddle-shaped. It is also ruffled and slightly domed according to an analysis of the out-of-plane distortions performed by using NSD. This saddle deformation is significantly smaller than those observed in the chloroiron(III) complexes of the β-p…

Basic Physical Concepts

Mossbauer spectroscopy is based on recoilless emission and resonant absorption of γ-radiation by atomic nuclei. The aim of this chapter is to familiarize the reader with the concepts of nuclear γ-resonance and the Mossbauer effect, before we describe the experiments and relevant electric and magnetic hyperfine interactions in Chaps. 3 and 4. We prefer doing this by collecting formulae without deriving them; comprehensive and instructive descriptions have already been given at length in a number of introductory books ([7–39] in Chap. 1). Readers who are primarily interested in understanding their Mossbauer spectra without too much physical ballast may skip this chapter at first reading and p…

The heterodinuclear iron(III) and copper(II) molecule Cu(salen)Fe(acac)2NO3 and its iron precursor Fe(acac)2NO3. Synthesis, magnetic susceptibility, EPR and Mössbauer investigations

Abstract The synthesis, EPR, magnetic and Mossbauer properties of two iron(III) complexes are reported. The heterodinuclear iron(III)-copper(II) complex Cu(salen)Fe(acac)2NO3 is obtained as an adduct from the reaction of the two mononuclear moieties, the Cu(salen) molecule and the mononuclear iron(III) molecule Fe(acac)2NO3 acting as a precursor of the dinuclear unit. The latter molecule itself has been prepared by ligand substitution from the tris-acetylacetonate Fe(acac)3. The dinuclear complex is characterized by comparing the properties of the mono- and the dinuclear complex. Fe(acac)2NO3 is identified from its typical IR spectrum with the main nitrate vibrations at 1380, 1250 and 1010 …

Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering

Nuclear inelastic scattering of synchrotron radiation has been used now since 10 years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a M\"ossbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations.

Some Special Applications

We have learned from the preceding chapters that the chemical and physical state of a Mossbauer atom in any kind of solid material can be characterized by way of the hyperfine interactions which manifest themselves in the Mossbauer spectrum by the isomer shift and, where relevant, electric quadrupole and/or magnetic dipole splitting of the resonance lines. On the basis of all the parameters obtainable from a Mossbauer spectrum, it is, in most cases, possible to identify unambiguously one or more chemical species of a given Mossbauer atom occurring in the same material.

Interpretation of Mössbauer Parameters of Iron Compounds

The task of this section is to show that for the interpretation of Mossbauer parameters — in the present case of electron densities, field gradients and magnetic hyperfine fields — bonding effects can play an important role, and free-ion or crystal field approaches may be a poor approximation.

Recombination studies of photodissociated MbCO by Mössbauer spectroscopy at low temperatures

Rebinding of carbonmonoxide to myoglobin after photodissociation has been studied by Mossbauer spectroscopy at 57.6 K and below for up to 9 days. The time dependence is reproduced by a set of exponentials representing a distribution of activation enthalpies. A shift to smaller values of these activation enthalpies and of the preexponential factor compared to optical studies at higher temperatures has been observed as well as pumping into long-living states.

Spin- and phase transition in the spin crossover complex [Fe(ptz)6](BF4)2 studied by nuclear inelastic scattering of synchrotron radiation and by DFT calculations

Abstract Nuclear inelastic scattering (NIS) spectra of [Fe(ptz) 6 ](BF 4 ) 2 (ptz = 1- n -propyl-tetrazole) have been measured for five phases differing in spin state and crystallographic structure. Different spectral patterns have been found for the low-spin and high-spin phases and are described in terms of normal coordinate analysis of the complex molecule. For both low-spin and high-spin phases the conversion from ordered to disordered phase results in splitting of the observed NIS bands. Packing becomes visible in the NIS spectra via coupling of the Fe–N stretching vibrations with those of the terminal n -propyl groups. The DFT-based normal coordinate analysis also reveals the characte…

The interaction of Fe(III), adriamycin and daunomycin with nucleotides and DNA and their effects on cell growth of fibroblasts (NIH-3T3)

The interactions of the iron complexes of the anthracycline antitumour drugs daunomycin (DN) and adriamycin (ADM) with the mononucleotide AMP, herring sperm DNA, plasmic pBR322 and immortalized 3T3 fibroblasts were studied. By means of Mössbauer spectroscopy it was demonstrated that DNA is a powerful ferric iron chelator as compared with AMP, which is not able to compete with DN or acetohydroxamic acid for ferric iron. The difference between AMP and DNA is postulated to be based on the chelate effect. The Mössbauer spectra of the ternary Fe-anthracycline-DNA systems differ from Fe-anthracycline binary complexes, indicating rearrangement reactions. Dialysis experiments clearly disclose the f…

Mathematical Evaluation of Mössbauer Spectra

As in many other spectroscopic methods, it is necessary in Mossbauer spectroscopy to determine the positions, intensities or areas of the absorption and emission lines as accurately as possible. In the case of poorly resolved or complex hyperfine spectra due to different chemical species or several lattice sites in the sample it is not possible to evaluate the Mossbauer spectra just by hand. In addition, often one is faced with the problem of taking into account cosine smearing effects (Sec. 4.2), thick absorbers associated with the calculation of the transmission integral (Sec. 3.5), magnetic or electric relaxation (Sec. 6.7), or delayed coincidence Mossbauer measurements (Sec. 3.5), which…

Nuclear Resonance Scattering Using Synchrotron Radiation (Mössbauer Spectroscopy in the Time Domain)

Conventional Mossbauer spectroscopy (MS) can be considered as “spectroscopy in the energy domain.” It has been widely used since its discovery in 1958 [1]. Nuclear resonant forward scattering (NFS) of synchrotron radiation has been successfully employed as a time-differential technique since 1991 [2]. Another related technique, nuclear inelastic scattering (NIS) of synchrotron radiation [3], can be regarded as an extension of conventional, energy-resolved MS (in the range 10−9 to 10−7 eV) to energies on the order of molecular vibrations (in the range 10−3 to 10−1 eV). So far only a few “Mossbauer” stations for NFS and NIS measurements have become available in synchrotron laboratories, i.e.,…

Molecular tunneling and pumping effects in low temperature MBCO recombination

Recombination of carbonmonoxide after photodissociation has been studied by Mossbauer spectroscopy at 4.2K and in the low temperature region, where tunneling effects play an important role in rebinding. We interpret the kinetic results in terms of a radiationless nonadiabatic multiphonon transition, which leads to a uniform description for all temperatures. Prolonged illumination at low temperature results in pumping into long-living states.

Exchange-coupled Fe-X-Fe model compounds for certain iron proteins

X-ray structure studies, Mossbauer experiments and magnetic susceptibility measurements were used in connection with molecular orbital calculations to monitor structurally induced changes of electronic and magnetic properties in exchangecoupled [Fe2S2 (SR)4]2- and [Fe2OCl6]2- anions.

The 5/2,3/2 Spin Admixture in the Chloroiron(III) Derivative of the Sterically Crowded 2,3,7,8,12,13,17,18-Octaethyl-5,10,15,20-tetraphenylporphyrin

Despite similar ring deformations in solution and in the solid state, the chloroiron(III) derivative of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin ([FeCl(oetpp)], shown schematically) prepared in this study exhibits only a very weak quantum-mechanical admixture of spin S=3/2 (only 4-10 %) with spin S=5/2. In contrast, for the variety of [FeCl(oetpp)] studied earlier by other researchers a 40 % contribution of the S=3/2 state was found.

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

Abstract The phenyliron derivative, [Fe(oetpp)C6H5)]SbCl6 (2) generated in dichloromethane by oxidation of the phenyliron(III) complex, Fe(III) (oetpp)C6H5 (1) of the 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin with 1 equiv. of phenoxathiinylium hexachloroantimonate, [C12H8OS]SbCl6, was studied by Mossbauer spectroscopy. This compound exhibits an isomer shift δ of 0.13 mm s−1 and a quadrupole splitting ΔEQ 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 con…

Mössbauer-Active Transition Metals Other than Iron

The previous chapters are exclusively devoted to the measurements and interpretation of 57Fe spectra of various iron-containing systems. Iron is, by far, the most extensively explored element in the field of chemistry compared with all other Mossbauer-active elements because the Mossbauer effect of 57Fe is very easy to observe and the spectra are, in general, well resolved and they reflect important information about bonding and structural properties. Besides iron, there are a good number of other transition metals suitable for Mossbauer spectroscopy which is, however, less extensively studied because of technical and/or spectral resolution problems. In recent years, many of these difficult…

Die 5/2,3/2-Spin-Beiträge im Chloroeisen(III)-Derivat des sterisch überfrachteten 2,3,7,8,12,13,17,18-Octaethyl-5,10,15,20-tetraphenylporphyrins