Asymmetric Doublets Research Articles

Experimental and DFT Study of Monensinate and Salinomycinate Complexes Containing {Fe3(µ3-O)}7+ Core.

Two trinuclear oxo-centred iron(III) coordination compounds of monensic and salinomycinic acids (HL) were synthesized and their spectral properties were studied using physicochemical/thermal methods (FT-IR, TG-DTA, TG-MS, EPR, Mössbauer spectroscopy, powder XRD) and elemental analysis. The data suggested the formation of [Fe3(µ3-O)L3(OH)4] and the probable complex structures were modelled using the DFT method. The computed spectral parameters of the optimized constructs were compared to the experimentally measured ones. In each complex, three metal centres were joined together at the axial position by a μ3-O unit to form a {Fe3O}7+ core. The antibiotics monoanions served as bidentate ligands through the carboxylate and hydroxyl groups located at the termini. The carboxylate moieties played a dual role bridging each two metal centres. Hydroxide anions secured the overall neutral character of the coordination species. Mössbauer spectra displayed asymmetric quadrupole doublets that were consistent with the existence of two types of high-spin iron(III) sites with different environments-two Fe[O5] and one Fe[O6] centres. The solid-state EPR studies confirmed the +3 oxidation state of iron with a total spin St = 5/2 per trinuclear cluster. The studied complexes are the first iron(III) coordination compounds of monensin and salinomycin reported so far.

Hyperfine interactions and some thermomagnetic properties of amorphous FeZr(Cr)NbBCu alloys

Abstract In this research, we studied the magnetic phase transition by Mössbauer spectroscopy and using vibrating sample magnetometer for amorphous Fe86-xZr7CrxNb2Cu1B4 (x = 0 or 6) alloys in the as-quenched state and after accumulative annealing in the temperature range 600-750 K. The Mössbauer investigations were carried out at room and nitrogen temperatures. The Mössbauer spectra of the investigated alloys at room temperature are characteristic of amorphous paramagnets and have a form of asymmetric doublets. However, at nitrogen temperature, the alloys behave like ferromagnetic amorphous materials. The two components are distinguished in the spectrum recorded at both room and nitrogen temperatures. The low field component in the distribution of hyperfine field induction shifts towards higher field with the annealing temperature. It is assumed that during annealing at higher temperature, due to diffusion processes, the grains of α-Fe are created in the area corresponding to this component. Both investigated alloys show the invar effect and the decrease of hyperfine field induction after annealing at 600 K for 10 min is observed. It is accompanied by the lowering of Curie temperature.

Independent positioning of magnetic nanomotors.

There is considerable interest in powering and maneuvering nanostructures remotely in fluidic media using noninvasive fuel-free methods, for which small homogeneous magnetic fields are ideally suited. Current strategies include helical propulsion of chiral nanostructures, cilia-like motion of flexible filaments, and surface assisted translation of asymmetric colloidal doublets and magnetic nanorods, in all of which the individual structures are moved in a particular direction that is completely tied to the characteristics of the driving fields. As we show in this paper, when we use appropriate magnetic field configurations and actuation time scales, it is possible to maneuver geometrically identical nanostructures in different directions, and subsequently position them at arbitrary locations with respect to each other. The method reported here requires proximity of the nanomotors to a solid surface, and could be useful in applications that require remote and independent control over individual components in microfluidic environments.

Possible Causes of Asymmetry in the Mössbauer Spectra of Brain Tissue

Iron present in the human brain plays important role in neurodegenerative diseases like Parkinson and Alzheimer diseases. Brain iron is mainly stored within globular protein called ferritin. Mossbauer spectra of brain tissue are asymmetric doublets at 300 K and 90 K. This asymmetry is slightly bigger in the case of samples taken from diseased subjects. Reason for this is still unknown. Few possible causes of aforesaid difference had been discussed. Nanometer-size of ferritin iron cores, pathological protein influence were taken into account. It was also discussed if experimentally available statistics is sufficient to obtain reliable asymmetry coefficient from Mossbauer spectra. Physical experiment were reproduced by means of computer simulations. Nevertheless, the reason for the asymmetry has not been completely elucidated yet.

Magnetic Enhancement of Phototaxing Catalytic Motors

We use the "stimulus-quench-fuse" (SQF) technique to fabricate micrometer-size colloidal heterodoublets. The doublets consist of silver and magnetic Dynabead microspheres, and the stimulus is a temporal lowering of the pH. The resulting asymmetric colloidal doublets behave as catalytic motors and show self-propulsion and phototaxis under ultraviolet (UV) light in the presence of hydrogen peroxide (H(2)O(2)), by the mechanism of diffusiophoresis. The magnetic heterodoublets show autonomous movement, in random directions, in the presence of H(2)O(2) and UV light, but if an external magnetic field is also present, they align themselves and show a directed motion forming exclusion regions around them. The assembly process described in this Article can be adapted to a wide variety of materials providing a simple, quick, inexpensive, reliable, and scalable approach for the development of synthetic motors capable of performing directed motion and forming exclusion zones and patterns.

Dimeric Fe (II, III) complex of quinoneoxime as functional model of PAP enzyme: Mössbauer, magneto-structural and DNA cleavage studies

Purple acid phosphatase, (PAP), is known to contain dinuclear Fe2 + 2, + 3 site with characteristic Fe + 3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe2 + 2, + 3 (o-NQCH3ox) (o-NSQCH3ox)2 (CAT) H2O]. Fe-2: [Fe + 3(o-NQCH3ox) (p-NQCH3ox)2]2 a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. 57Fe Mossbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. 57Fe Mossbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe + 3]A and [Fe + 2]B sites. The hyperfine interaction parameters are δ A = 0.152, (ΔE Q)A = 0.598 mm/s with overlapping doublet at δ B = 0.410 and (ΔE Q)B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe + 3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQCH3ox ligand surrounding Fe + 3(h.s.) state generates small field gradient indicated by quadrupole split ΔE Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe2 + 2, + 3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g 1 = 4.17 and g 2 = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe + 3(h.s.) configuration. SQUID data of \(\chi _m^{{\rm corr}} \mbox{.T}\) were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = −13.5 cm − 1 with an agreement factor of R = 1.89 × 10 − 5). The lower J value of antiferromagnetic exchange leads to Fe+3μ-(OH) Fe + 2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe + 3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = −12.4 cm − 1, g = 2.3 with R = 3.58 × 10 − 5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.

Asymmetric doublets in MAS NMR: coherent and incoherent mechanisms

It has been long noted that J-resolved doublets observed in solid-state MAS experiments are asymmetric. The asymmetry has been attributed to a coherent interference effect involving dipolar and CSA interactions. Recently, Bernd Reif and co-workers suggested that under fast MAS conditions the coherent portion of the effect is suppressed and it becomes possible to observe an incoherent mechanism reminiscent of TROSY. The researchers were able to observe the characteristic TROSY-type patterns in (15)N-(1)H(N) spectra of heavily deuterated protein samples (Chevlekov, Diehl, and Reif, previous article in this issue). In the present computer simulation study, we seek to obtain a unified picture of this phenomenon, including both coherent and incoherent aspects. The chosen model focuses on the (15)N-(1)H(N) pair from a polycrystalline sample subject to magic angle spinning. To mimic local dynamics, we assume that the corresponding peptide plane jumps between two orientations. The simulations demonstrate that this simple model reproduces both coherent and incoherent behavior, depending on the MAS speed and the time scale of local dynamics. Furthermore, semianalytical expressions can be derived for both coherent and incoherent (Redfield) limits. Of particular interest is the possibility to use solution-style Redfield results to probe internal protein motions, especially slower motions on the nanosecond time scale. Our simulations show that the differential relaxation measurement permits accurate determination of (15)N dipolar-CSA cross correlations already at moderately high MAS speed (ca 15 kHz).

Multivariate analysis in provenance studies: Cerrillos obsidians case, Peru

We present the preliminary results of a provenance study of obsidians samples from Cerrillos (ca. 800–100 b.c.) using Mossbauer Spectroscopy. The Cerrillos archaeological site, located in the Upper Ica Valley, Peru, is the only Paracas ceremonial center excavated so far. The archaeological data collected suggest the existence of a complex social and economic organization on the south coast of Peru. Provenance research of obsidian provides valuable information about the selection of lithic resources by our ancestors and eventually about the existence of communication routes and exchange networks. We characterized 18 obsidian artifacts samples by Mossbauer spectroscopy from Cerrillos. The spectra, recorded at room temperature using different velocities, are mainly composed of broad asymmetric doublets due to the superposition of at least two quadrupole doublets corresponding to Fe2+ in two different sites (species A and B), one weak Fe3+ doublet (specie C) and magnetic components associated to the presence of small particles of magnetite. Multivariate statistical analysis of the Mossbauer data (hyperfine parameters) allows to defined two main groups of obsidians, reflecting different geographical origins.

A trinuclear cluster containing the {Fe 3(μ 3-O)} 7+ core: Structural, magnetic and spectroscopic (IR, Mössbauer, EPR) studies

A ferric complex, [Fe 3O(O 2CPh) 6(EtOH) 2(N 3)] · 2.4EtOH ( 1 · 2.4EtOH) has been synthesized through the reaction of basic iron benzoate with NaN 3. It crystallizes in the C2/ c space group and it contains a planar {Fe 3(μ 3-O)} 7+ core typical of basic iron carboxylates. Mössbauer spectra above 80 K display asymmetric quadrupole-split doublets that are consistent with the existence of two iron sites with O 6 and O 5N environments in a 2:1 ratio, respectively. Below 80 K the linewidth increases and the asymmetry vanishes. Variable-temperature magnetic susceptibility studies reveal the interplay of antiferromagnetic interactions, which require a 2 J model for their interpretation (two equal J and one different J′ exchange constants). The fitting process yields two minima ( J = −26.4 cm −1, J′ = −40.0 cm −1 and J = −33.0 cm −1, J′ = −24.0 cm −1 for a H = −2 ΣJ ij S i S j spin Hamiltonian formalism), both of which lead to S = 1/2 ground states. Solid-state EPR measurements corroborate the existence of an S = 1/2 ground state, also indicating weak intermolecular interactions leading to broadened signals.

Magnetic properties and 57Fe Mössbauer spectroscopy of Mediterranean prehistoric obsidians for provenance studies

Samples from the Mediterranean source-islands: Gyali, Lipari, Melos, Palmarola, Pantelleria and Sardinia (Monte Arci) had their 57Fe Mössbauer spectra and magnetizations measured. The saturation magnetization ( M s) depends on the island of provenance and it reaches a maximum ∼0.3 emu/g for Palmarola obsidians, indicating a larger magnetic phase content. The coercive forces ( H c) range from 46 to 372 Oe for respectively samples from Pantelleria and Palmarola islands. Our analyses show that in a M r/ M s vs. H c/ H m plot the data points accumulate in areas that depend on obsidian provenance ( M r, remanent magnetization; H m, maximum applied field). The Mössbauer spectra are mainly composed of broad asymmetric doublets, which were fitted assuming two Fe 2+ and one Fe 3+ sites. In addition, the obsidians of Melos and Palmarola present a magnetic component attributed to magnetite and/or hematite. Binary diagrams comparing different Mössbauer hyperfine parameters for the Fe 3+ and Fe 2+ species gave indications of similarities and differences between obsidians of different origins. Since this kind of plot does not give an unambiguous characterization of samples from each island, a detailed analysis of the Mössbauer results is in progress using statistical method of clustering analysis as has been shown by Scorzelli et al. [Comptes Rendus Acad. Sci., Serie II, 332 (2001) 769] and Poupeau et al. [IAOS Bull. 28 (2001) 2] in previous studies.

Structure and Electronic Properties of [Ni(dsdm){Fe(CO)3}2], an Unusual, Triangular Nickel Diiron Compound

AbstractReaction of the low‐spin complex [Ni(dsdm)] with Fe2CO9 results in the unique trinuclear cluster [Ni(dsdm){Fe(CO)3}2]. NMR spectroscopy shows that the structure is diamagnetic, and, moreover, that the complex is stable in solution and C2‐symmetric. The X‐ray structure reveals short distances between the distorted octahedral nickel(II) ion and the two octahedral iron(0) centers. The observed diamagnetism is explained by the formation of a triangular metal core with three two‐electron two‐center bonds. The Mössbauer spectra, which are typical of iron(0), are composed of asymmetric quadrupole doublets as a result of the presence of two chemically similar, but crystallographically distinct, iron sites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Morphology of micron-sized polystyrene particles crosslinked with urethane acrylate

The morphology of micron-sized polystyrene particles crosslinked with a urethane acrylate crosslinker was studied with different concentrations of urethane acrylate and medium solvency by means of simple dispersion polymerization. The urethane acrylate employed as a crosslinker showed an excellent effect on maintaining the monodispersity of the polystyrene particles at a moderate crosslinker concentration (to about 5 wt%) in terms of the monomer-swellable surface of primary particles. By enhancing the medium solvency, the amount of urethane acrylate incorporated was increased, while the monodispersity of the final particles was maintained. It was believed that the increase in solvency on adding xylene to ethanol solution helped the diffusion of the styrene monomers into the primary particles. At high concentration of urethane acrylate, however, nonspherical particles, ellipsoidal or egg-like singlets and asymmetric doublets, were observed. The increased crosslinking density seemed to repel the styrene monomers during particle growth.

Mössbauer effect study of one-dimensional and two-dimensional quasicrystalline alloys in the AlPdFe system

Room temperature 57Fe Mössbauer effect measurements of the one-and two-dimensional quasicrystalline phases of Al 75Pd 15Fe 10 are reported. Both materials show Mössbauer spectra with asymmetric doublets which have been analyzed in terms of a distribution of quadrupole splittings, and in terms of a discrete expansion of quadrupole splittings. The one-dimensional material shows the following characteristics compared with the two-dimensional material; (1) a larger mean quadrupole splitting, (2) a more positive mean isomer shift and (3) a broader distribution of quadrupole splittings. These results indicate that the local Fe environments in the one-dimensional material are less isotropic than in the two-dimensional material and that this material is characterized by a higher concentration of open volume defects.

14N Population transfers in two-dimensional 13C 14N 1H triple-resonance magic-angle spinning nuclear magnetic resonance spectroscopy

A two-dimensional (2D) experiment has been used to show that 14N irradiation and magic-angle spinning (MAS) results in population transfers between the 14N Zeeman levels. This experiment was applied to a sample of N-acetyl- d,l-valine, a material where asymmetric doublets resulting from 13C 14N dipolar coupling are clearly resolved in the 13C spectrum at a field of 7 T for carbon atoms directly bonded to the nitrogen atom. The 13C transverse magnetization was allowed to evolve in the F1 and F2 dimensions, and the 14N spins were irradiated during the mixing period. Cross-peaks were observed in the 2D C spectrum between the two peaks of the CH asymmetric doublet. Since one peak of the doublet results primarily from coupling to the ¦0〉 state and the other peak from coupling to the ¦ − 1〉 and ¦ + 1〉 states, population changes between the 14N Zeeman levels have occurred during the mixing period. These population transfers are a consequence of the time dependence of the 14N quadrupole splitting Q under MAS conditions and 14N irradiation. Level anti-crossings of the 14N Zeeman levels occur at the zero-crossings of Q, and a continuous and slow change in Q will result in the transfer of 14N populations between the different Zeeman levels. If these passages are adiabatic, then the system returns to its original state after two zero-crossings. This is consistent with the experimental observation that the intensities of the cross-peaks for 14N irradiation are greater for half a rotor period than a full rotor period.

Direct evidence of free radical production after ischaemia and reperfusion and protective effect of desferrioxamine: ESR and vitamin E studies

After surgical renal revascularisation, warm renal ischaemia due to renal artery cross-clamping contributes to postoperative renal dysfunction. After reperfusion, free radicals are thought to be a significant cause of injury. Nevertheless, indisputable proof of free radical production is scarce, partly because of their transient nature. In this study, electron paramagnetic resonance and vitamin E levels were used to demonstrate the free radical production after renal ischaemia and reperfusion. Rabbit kidneys were submitted either to 15 or 60 minutes of ischaemia followed by reperfusion. A spin trap agent (alpha-phenyl-N-tert-butyl nitrone (PBN), 20mg/ml, 1 ml/min) was infused during reperfusion directly into the left renal artery via an aortic catheter before declamping. Blood samples were selectively drawn from the left renal vein for ESR analysis (Varian spectrometer E109) of lipidic residues extracted from blood samples. The vitamin E content of the left renal cortex was determined by HPLC procedure. The right renal cortex was used as a control for the vitamin E values. In the venous effluent, ESR analysis revealed the formation of a spectrum consisting of a triplet of asymmetric doublets. This signal resulted from the spin trapping by PBN of a mixture of both oxygen- and carbon- centred lipidic radicals. The amplitude of the signal which is proportional to the amount of free radicals was significantly higher after 60 minutes ischaemia than after 15 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Systematic Mössbauer study of YBa2Cu3−x Fe x Oδ and PrBa2Cu3−x Fe x Oδ as a function of temperature

We study the similitudes and differences between YBa2Cu3−xFexOδ and PrBa2Cu3−xFexOδ systems, using Mossbauer spectroscopy. Both systems, withz=0.04, were studied at several temperatures. The spectra of PrBa2Cu3−xFexOδ showed four asymmetric quadrupole doublets with apparently different line widths, which were fitted with four symmetric superimposed quadrupole doublets with the same line width, but assuming a small (∼4–6 kOe) residual magnetic field in the Fe sites, which are mainly the Cu(1) sites of the 1–2–3 structure. On the other hand, the PrBa2Cu3−xFexOδ spectra showed only three asymmetric quadrupole doublets which can be fitted with three superimposed symmetric doublets and a residual magnetic field. In this case, the Fe atoms also occupy the Cu(1) sites of the 1–2–3 structure. The temperature variations of the Mossbauer spectra and their parameters seem to indicate that, in the Pr-system, a structural change takes place between 12 K and 40 K.

Intensity asymmetry in the Mossbauer spectra of a layered cyanide

Results of 57Fe Mossbauer investigation in a layered cyanide Mg(Mg((CH2)6N4)2Fe(CN)6)2.nH2O for different stages of hydration are presented. Mossbauer spectra in the partially hydrated stages show an asymmetry in the intensity of the two absorption peaks of the quadrupolar doublet. The powder pattern has been analysed in terms of superposition of two asymmetric doublets arising from two inequivalent sites. An explanation for the asymmetry of the intensity in the doublet spectrum has been suggested in terms of the Goldanskii-Karyagin effect.

Solid-state NMR Studies of Functional Group Recognition in Channel Inclusion Compound Formation

Abstract Solid-state 13C CP-MAS NMR spectra of urea inclusion compounds of methyl undecanoate (MUDA) show a significant bias in the relative alignment of guest molecules in the channels. In these spectra, asymmetric doublets are observed for C11 and methoxy carbons, while bands from internal carbons, including the carbonyl carbon, are unsplit. Band doubling is caused by differences in nearest neighbors, as shown by comparison with spectra of symmetric analogs, such as dimethyl sebacate/urea. During crystal formation of MUDA/urea from methanol, head to tail alignment is favored over head to head (plus tail to tail) alignment by a factor of 1.27±0.06, as shown by simulation of C11 resonances for spectra taken with a wide variety of cross polarization contact times. Adsorption of the ester group onto the growing face of the inclusion compound crystal probably gives rise to the observed bias.

Uniform nonspherical latex particles as model interpenetrating polymer networks

AbstractPolystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerization of styrene–divinylbenzene mixtures in crosslinked monodisperse polystyrene particles. The resulting latexes comprised uniform nonspherical particles, e.g., ellipsodal and egg‐like singlets, symmetry and asymmetric doublets, and ice cream cone‐like and popcorn‐like multiplets. The nonspherical particles, which were formed by separation of the second‐stage monomer from the crosslinked seed network during swelling and polymerization, are excellent models for studying phase separation in IPN's. The degree of phase separation increased with increasing degree of crosslinking of the seed particles, monomer/polymer swelling ratio, polymerization temperature, and seed particle size, and with decreasing divinylbenzene concentration in the swelling monomer. The results were consistent with a thermodynamic analysis based on the elastic‐retractile force of the polymer network, the monomer/polymer mixing force, and interfacial tension force.

Models of cytochrome b: Mössbauer studies on bis-ligated complexes of (protoporphyrinato IX)iron(III) with histidine and its substituted derivatives

Mossbauer spectroscopic studies have been carried out on a series of complexes of the type [FeL(L′)2]+, where H2L = 3,7,12,17-tetramethyl-8,13-divinylporphyrin-2,18-dipropionic acid, L′= histidine, Nα-acetylhistidine, histamine, or pilocarpate. Measurements were made at various pH values in the range 7.5–12.0 in 20%(v/v) ethanol–water solution frozen at 80 K. When the pH is 8.0–8.5, the major species are low-spin bis complexes [δ= 0.25(2) mm s–1 and ΔEQ= 2.0–2.2 mm s–1]. These are rapidly converted into a molecular complex of histidine and [(FeL)2O] at high pH (10.1–12.0). The results for the bis(histidine) and related complexes show that histidine binds as a sterically hindered imidazole and that the iron–imidazole bonds are weak. The ΔEQ value of 2.14 mm s–1 and large linewidths (0.48–1.22 mm s–1) of the complexes indicate that the two imidazole planes in the bis(histidine) complex are non-parallel with a large angle between the planes. The observation of asymmetric quadrupole doublets and broad lines are typical of slow spin–lattice relaxation of iron similar to that observed for cytochrome C. The present Mossbauer spectroscopic results for the bis(histidine) complexes are similar to those found for low-spin iron(III)-cytochromes and cytochrome b5. Steric strain due to the histidine side-chains and electrostatic interactions between the charged groups and the porphyrin propionate carboxylates are found to influence the iron electronic structure and the imidazole plane orientations.