Broad Doublet Research Articles

Temperature-dependent crystallographic studies on ferric spin-crossover complexes with different spin-interconversion rates

Crystallographic studies of [Fe(acpa)*]X (Hacpa = N-( I-acetyl-2-propylidene)(2-pyridylmethyl)amine; X = BPh4 (tetraphenylborate) and PF6 (hexafluorophosphate)) have been done at several temperatures (120,202,247, and 31 1 K for the BPh4salt and 120, 205, and 290 K for the PF6salt). Temperature dependences of the magnetic susceptibilities show that both compounds undergo gradual spin transitions between high-spin (6AI,) and low-spin (*T2 ) states, and 85.2% at 320 K and 97.8% at 290 K of the spin transitions to the high-spin state are observed for the BPh4and thebFC salts, respectively. s7Fe Mbsbauer spectra at 78 and 310 K for both compounds consist of a single quadrupole doublet corresponding to the lowand high-spin states. Within the spin transition temperature range, Mbsbauer spectra of the PF6salt consist of a superpasition of the highand low-spin species, while the BPh4salt shows only one broad quadrupole doublet with isomer shift and quadrupole splitting parameters in proportion to the fraction of the highor low-spin species. The Miissbauer spectra imply a rapid spin interconversion rate for the BPhL salt compared with the reciprocal of the Mbsbauer lifetime s) and also indicate that the BPh4salt interconverts its spin state faster than the PFC salt. The BPh4and PFC salts crystallize in triclinic and monoclinic space groups, respectively, and show no drastic structural change such as order-disorder transformations when the temperature is varied. Crystallographic studies at different temperatures, however, reveal remarkable changes of coordination bond lengths going along with the spin-state interconversion (AFe-0, = 0.026 A, AFtN(pyridine),, = 0.130 A, and AFe-N(imine), = 0.1 12 A for the BPh4-salt and A F t O = 0.051 A, AFe-N(pyridine) = 0.168 A, and AFe-N(imine) = 0.143 A for the PFc salt). The smaller bond length changes for the BPh4salt are responsible for a smaller activation energy, AEa, between the highand low-spin states, hence the faster spin interconversion rate for the BPhC salt than for the PF6salt. Crystal data: X = BPh4-, 120 K, triclinic, P i , Z = 2, a = 12.784 (3) A. b = 13.290 (4) A, c = 11.776 (4) A, a = 93.35 (3)O, j3 = 102.29 (2), y = 98.37 (2)O, refinement to R = 0.038 and R, = 0.047; X = BPh4-, 202 K, triclinic, Pi, Z = 2, a = 12.868 (4) A, b = 13.383 (3) A, c = 11.820 (4) A, a = 93.38 (2)O, 6 = 102.37 (2)O, y = 98.17 (2)O, refinement to R = 0.033 and R, = 0.039; X = BPh4-, 247 K triclinic, Pi, Z = 2, u = 12.918 (3) A, b = 13.458 (2) A, c = 11.800 (3) A, a = 92.23 (I)', j3 = 102.25 (2)O, y = 98.30 ( 2 ) O , refinement to R = 0.036 and R, = 0.040;X=BPh[,311 K,tr ic l inic ,Pi ,Z=2,a= 12.982(3)A,b= 13.592(2)A,c=11.791(3)A,a=92.87(1)0,~=101.77 (2)O, y = 98.74 (I) ' , refinement to R = 0.042 and R, = 0.044; X = PFC, 120 K, monoclinic, P2/a , Z = 2, a = 13.626 (2) A, b = 9.847 ( 1 ) A, c = 10.169 1) A, j3 = 111.93 (I)O, refinement to R = 0.045 and R, = 0.049; X = PFc, 205 K, monoclinic,

Protonation of 1,8-bis(dimethylamino)naphthalene by N–H proton donors in acetonitrile

FTIR studies were carried out on a number of systems composed of 1,8-bis(dimethylamino)naphthalene (DMAN) and various N–H proton donors in acetonitrile. The degree of protonation was estimated based on the intensity of the Bohlmann bands. As in the case of systems containing OH acids homoconjugated anions play an important role in ionic equilibria. In the case of moderately strong proton donors the species present in solution are protonated DMAN, free DMAN, NHN– homoconjugated anions and more complicated self-solvated species. The homoconjugated NHN– anions are characterized by a broad doublet with submaxima at ca. 1950 and 2500 cm–1.

Electron–nuclear double resonance of long-lived radicals in aged X- and Y-type zeolite catalysts

During the conversion of 2-methylfuran to 2-methylthiophen on MNaX and MNaY zeolite catalysts (M = Li, Na, K, Rb, Cs), stable radicals are formed. We investigated these by ENDOR spectroscopy. 1H and 23Na ENDOR were observed with any aged catalyst. 7Li and 133Cs ENDOR were also observed, respectively, in lithium- and caesium-substituted zeolites. The 1H ENDOR consists of the superposition of a broad doublet and a narrow single line. 7Li and 23Na ENDOR are single Lorentzian lines centred about the respective free nucleus frequency. In contrast, 133Cs ENDOR is a well resolved doublet. An accurate lineshape analysis was carried out based on models available in the literature. It was found that the observed proton splittings must be ascribed to an isotropic hyperfine interaction. A correlation was found between the experimental proton coupling constant and the calculated lattice oxygen charge. The paramagnetic centre can reasonably be pictured as an AlO˙4 site. The caesium cation showed markedly different behaviour with respect to the lighter alkali-metal cations.

ChemInform Abstract: A New System Exhibiting a High Barrier to Rotation About the P‐N Bond. Syntheses and Spectral Studies of 1,3,2‐Diazaphosphetidin‐4‐one Derivatives.

AbstractThe 1H HMR signals of the title compounds (III) (9 examples) at ambient temp. display a broad doublet which eventually coalesces before becoming sharp upon warming, and the 13C NMR spectra show that the α‐ and β‐carbons of the dialkylamino group are non‐equivalent.

Rates of transformations in the ferrosilicon system

Mossbauer spectroscopy has been used to determine the time-temperature-transformation diagram (TTT) for the eutectoid transformation in the silicon rich part of the Fe−Si binary system. Studies of TTT-diagram of samples consisting of 55 and 75 weight percent Si respectively have been carried out in nominally pure samples as well as commercial ones. Under equilibrium conditions these represent two phases, the zeta-alpha phase and the zeta-beta phase. The former is a high temperature, phase whereas the latter is stable below about 967°C. The eutectoid transformation from alpha into beta phase involves changes in crystal structure and a complete change in the vacancy distribution characterizing the alpha phase. Mossbauer spectra of samples involved were fitted, according to former results, with two well defined doublets characterizing the beta phase and two broad line doublets attributed to the more complicated alpha phase. The paper proposes a model explaining the relationship between thermal history and material strength in the system.

A NEW SYSTEM EXHIBITING A HIGH BARRIER TO ROTATION ABOUT THE P—N BOND. SYNTHESES AND SPECTRAL STUDIES OF 1,3,2-DIAZAPHOSPHETIDIN-4-ONE DERIVATIVES

Abstract 1,3,2-Diazaphosphetidin-4-one derivatives were synthesized. Their 1H NMR signals at ambient temperature displaed a broad doublet which eventually coalesced before becoming sharp upon warming, and the 13C NMR spectra also showed that the α-and β-carbons of the dialkylamino group were non-equivalent. The phenomena were ascribed to restricted rotation about the exocyclic P—N bond.

ESR Study of the Thymine Anion Radical in a Single Crystal of Thymine Monohydrate

ESR spectroscopy was used to study free radicals in an irradiated single crystal of thymine monohydrate at 77 K. At low microwave power (20 microW), a broad doublet is found to be super-imposed on the well known resonance patterns of the 5-yl and 7-yl radicals. The doublet spectrum has been analysed as a difference spectrum. Its spectroscopic properties and the observed transformation into the 5-yl, H-addition radical on warming the crystal are consistent with its anion nature, T(-).

Redox Intermediates of Desulfovibrio gigas [NiFe] Hydrogenase Generated Under Hydrogen: MÖssbauer and epr characterization of the metal centers

The hydrogenase (EC 1.2.2.1) of Desulfovibrio gigas is a complex enzyme containing one nickel center, one [3Fe-4S] and two [4Fe-4S] clusters. Redox intermediates of this enzyme were generated under hydrogen (the natural substrate) using a redox-titration technique and were studied by EPR and Mossbauer spectroscopy. In the oxidized states, the two [4Fe-4S]2+ clusters exhibit a broad quadrupole doublet with parameters (apparent delta EQ = 1.10 mm/s and delta = 0.35 mm/s) typical for this type of cluster. Upon reduction, the two [4Fe-4S]1+ clusters are spectroscopically distinguishable, allowing the determination of their midpoint redox potentials. The cluster with higher midpoint potential (-290 +/- 20 mV) was labeled Fe-S center I and the other with lower potential (-340 +/- 20 mV), Fe-S center II. Both reduced clusters show atypical magnetic hyperfine coupling constants, suggesting structural differences from the clusters of bacterial ferredoxins. Also, an unusually broad EPR signal, labeled Fe-S signal B', extending from approximately 150 to approximately 450 mT was observed concomitantly with the reduction of the [4Fe-4S] clusters. The following two EPR signals observed at the weak-field region were tentatively attributed to the reduced [3Fe-4S] cluster: (i) a signal with crossover point at g approximately 12, labeled the g = 12 signal, and (ii) a broad signal at the very weak-field region (approximately 3 mT), labeled the Fe-S signal B. The midpoint redox potential associated with the appearance of the g = 12 signal was determined to be -70 +/- 10 mV. At potentials below -250 mV, the g = 12 signal began to decrease in intensity, and simultaneously, the Fe-S signal B appeared. The transformation of the g = 12 signal into the Fe-S signal B was found to parallel the reduction of the two [4Fe-4S] clusters indicating that the [3Fe-4S]o cluster is sensitive to the redox state of the [4Fe-4S] clusters. Detailed redox profiles for the previously reported Ni-signal C and the g = 2.21 signal were obtained in this study, and evidence was found to indicate that these two signals represent two different oxidation states of the enzyme. Finally, the mechanistic implications of our results are discussed.

Mössbauer study of (Fe 2O 3) x(Al 2O 3) y(SiO) 1-x-y system with spinel-type structure

The oxide system, (Fe 2O 3) x(Al 2O 3) y(SiO) 1-x-y (x=33.3−50.0; y=20.0−40.0) with spinel type structure has been prepared, and its crystallographic and magnetic properties has been investigated with X-ray and Mössbauer effect methods. The crystal structure of the system is found to be a cubic spinel type. The lattice parameters increase with increasing Fe 2O 3 concentration, while the influence of Al 2O 3 substitution for SiO is small. The Mössbauer spectra which show broad quadrupole doublets at x=33.3, 43.7 and y=33.3, 21.8 change into the complex Zeeman patterns when x=50.0 and y=20.0, 30.0 and 40.0. Also the partly existing ferrous states of iron ions change into the ferric states. In the Zeeman sextets, the magnetic hyperfine fields and Néel temperature increase as the Al 2O 3 content increases. These variations can be explained on the basis of increasing A-B superexchange interaction.

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B+ and C+ implantation (50 kV, 1×1018 ions cm−2) were analyzed by CEMS. The CEM spectrum of B+ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe2B by annealing at 500°C.

Synthesis and spectroscopic studies of Fe 3+ substituted ZSM-5 zeolite

A method is described for the preparation of Fe 3+-zeolites of the ZSM-5 type, where Fe 3+ is incorporated in the zeolite lattice. Samples with overall Si Fe ratios of 10 and 65 have been synthesized and characterized by 57Fe Mössbauer Spectroscopy, e.p.r. and 29Si MAS n.m.r. This paper deals mainly with the interpretation of our Mössbauer results. All samples have room temperature Mössbauer spectra, consisting of broad quadrupole split doublets. By lowering the temperature and applying external magnetic fields at least two spectral components can be recognized and assigned: 1. (1) Fe 3+ ions incorporated in tetrahedric sites in the zeolite framework, causing slow electronic relaxation phenomena in the spectra. 2. (2) Fe(III) oxides, precipitated as small particles on the zeolite surface, exhibiting superparamagnetic relaxation. Mössbauer spectra are presented of some samples after dehydration. This causes an increase of the average quadrupole interaction, indicating an increase of the asymmetry of the charge distribution around the iron nucleus. Dehydration at temperatures less than 250°C is reversible.

Hyperfine interactions in the mixed ligand complexes of phenolic compounds with iron phthalimide

Six new mixed ligand complexes of iron phthalimide with gallic acid, pyridoxine, sulphosalicylic acid, salicylaldehyde, anisaldehyde, and naphthaldehyde have been prepared and characterised on the basis of conductance, magnetic susceptibility, IR, electronic and Mossbauer spectroscopic studies. The room temperature Mossbauer spectra exhibit a broad and asymmetric doublet which persists down to 50 K. The I. S. and Q. S. values indicate iron to be in +3 and high spin state. The magnetic moment values (∼5.0 BM at 300 K decreasing to ∼ 3.0 BM at 77 K) do not show any magnetic transition.

A model for the 2H nuclear magnetic resonance lineshape of crosslinked elastic polymers

The theory of the 2H nuclear magnetic resonance (n.m.r.) lineshape of elastic polymer networks is developed on the basis of existing concepts of quadrupole effects in n.m.r. Averaging of the quadrupole interaction Hamiltonian is carried out with the help of the freely jointed chain model. The ends of the model chain are assumed to be fixed in space. It is found that a broad doublet should be expected for a regular network. The doublet splitting is proportional to the degree of crosslinking. The peculiar lineshape is shown to be expected for an irregular network. Irregularities such as distribution of chain lengths through the sample and presence of macromolecular loose ends are considered. The results of theoretical evaluations with the irregularity of the network taken into account are consistent with the experimental data.

Partial purification and characterization of dipeptidyl peptidase II (DPP II) from guinea pig testes

AbstractDepeptidyl peptidase (DPP II) was partially purified from guinea pig testes by (NH4)2SO4 precipitation, Con A‐Sepharose 4B chromatography, and Sephadex G‐200 chromatography to a specific activity of 27.4 μmol Ala3 hydrolyzed min−1 mg−1 protein. Chromatography on a calibrated G‐200 column yielded a molecular weight of 135,000 daltons for the enzyme. Sodium dodecyl sulfate polyacrylamide electrophoresis showed an enrichment of a broad doublet at 64–66,000 daltons. The enzyme had optimal activity toward hydrolysis of L‐alanyl‐alanyl‐alanine at pH 4.5 and showed sensitivity to cations of increasing size with Tris producing the most inhibition of those tested. The enzyme was moderately inhibited by serine proteinase inhibitors. Thin‐layer chromatography revealed the dipeptidase nature of the enzyme's activity on tripeptides and dipeptidyl arylamides. A doublet of activity occurred when nitrocellulose electroblots of nondenaturing gel electrophoresis of the (NH4)2SO4 fraction were reacted with the specific DPP II substrate, lysyl‐alanyl‐4‐methoxy‐2‐napthylamide. Analytical isoelectric focusing of the G‐200 fraction followed by fluorescent enzyme activity detection that used cellulose triacetate overlay membranes impregnated with the specific DPP II substrate, lysyl‐alanyl‐7‐amino‐4‐trifluoromethylcou‐marin, revealed multiple isoforms focusing at pI = 4.8–5.6. Two prominent bands focused at pI = 4.9 and pI = 5.1. The properties of guinea pig testicular DPP II are compared and contrasted with similar dipeptidyl peptidases from other sources.

The structure and stability of sulfated alumina and titania

The oxidation of H 2S or SO 2 in excess O 2 over Al 2O 3 or TiO 2 (anatase) yields, for either catalyst under anhydrous conditions, an infrared spectrum which is characterized by an intense sharp band near 1380 cm −1 and a broad band or doublet near 1040 cm −1. The same spectrum arises from the impregnation of Al 2O 3 with either (NH 4) 2SO 4 or Al 2(SO 4) 3 · 18H 2O or of TiO 2 with (NH 4) 2SO 4 or TiOSO 4 and heating the dried mixture at 450 °C under vacuum. The sulfated surface does not exchange with 18O 2 but does with H 2 18O and only one new shifted high-wavenumber band is produced for partial or complete oxygen-18 exchange. The infrared spectrum changes in the presence of H 2O at 20 °C and resembles that of a more traditional bidentate type sulfate species and we postulate that, in the absence of OH groups or water the sulfate has a structure resembling ( M 3 O 3) S O [ M = Al or Ti], whereas in the presence of H 2O or excess surface OH groups this is converted to ▪ type groups, thus accounting for the increased Brønsted acidity. Finally, the sulfated Al 2O 3 surface is more thermally stable and more resistant to reduction in H 2 than is the TiO 2 surface and the ramifications are discussed in terms of the use of these oxides for SO x transfer catalysts or in air pollution abatement.

Influence of elastic scattering from neutral impurities on the exciton-polariton photoluminescence lineshape in GaAs

The low temperature photoluminescence spectral lineshape of the free exciton in undoped bulk GaAs, a broad weak doublet whose shape is commonly assumed a consequence of intrinsic processes, is experimentally demonstrated to be of extrinsic origin. In particular, the doublet shape is associated with the presence of residual donor impurities. A model, based on elastic scattering from neutral impurities and incorporating the polariton nature of the exciton, was developed. The excellent agreement between the model calculations and the experimental spectra demonstrates the importance of scattering processes on exciton-polariton transport. This model is applicable to any material with a dipole active exciton and may account for the structure observed in the lineshapes of free excitons in other compound semiconductors which have previously been attributed to other mechanisms.

On the magnetic ordering in the insulating spinel Ga 0.8Fe 0.2NiCrO 4 with the A sublattice diluted to below the percolation threshold

The results of a.c. susceptibility, d.c. magnetization and Mössbauer measurements on the insulating spinel system Ga 0.8Fe 0.2NiCrO 4 are reported. This system has the A sublattice diluted to below the percolation threshold and hence cannot retain any long-range ferrimagnetic order. The a.c. susceptibility shows a peak at T f ≈ 50K. For T#62; 1.5T f the magnetization is highly non-linear and tend to saturate above H #62; 2kOe. The Mössbauer spectra show broad doublets at 77 and 300 K. These observations lead to the picture of gradually evolving spin clusters ferrimagnetically coupled within, as the temperature is lowered, till the intercluster interaction brings about a cluster spin-glass ordering with randomly frozen cluster moments at T f. The absence of the Zeeman splitting in the Fe 57 Mössbauer spectra could be understood in terms of the dynamical effects arising from the thermal excitation of spin clusters.

Identification of an additional class of C3-binding membrane proteins of human peripheral blood leukocytes and cell lines.

Proteins binding the third component of complement (C3) were isolated by affinity chromatography from surface-labeled solubilized membranes of human peripheral blood cells and cell lines. The isolated molecules were subjected to NaDodSO4/PAGE, and autoradiographs of these gels indicated that C3-binding proteins could be divided into three groups based on Mr: (i) gp200, an approximately 200,000 Mr molecule previously identified as the C3b/C4b receptor or CR1; (ii) gp140, an approximately 140,000 Mr molecule previously identified as the C3d receptor or CR2; and (iii) gp45-70, a heretofore unrecognized group of 45,000-70,000 Mr C3-binding molecules. The cell distribution, Mr, antigenic cross-reactivity, and specificity of gp45-70 were examined. Erythrocytes have no detectable gp45-70, but all leukocyte populations examined possess this group of molecules. On neutrophils and mononuclear phagocytes, CR1 is the predominant C3-binding glycoprotein, but gp45-70 is present on both cell populations and on macrophage and neutrophil cell lines. B plus null cells, chronic lymphocytic leukemia cells, and an Epstein-Barr virus-transformed B-cell line possess CR1, CR2, and gp45-70. On T cells and T-cell lines gp45-70 is the predominant or, in some cases, the only C3-binding protein isolated. gp45-70 is structurally characterized as a broad band or doublet with a mean Mr that is slightly different for each cell population. gp45-70 binds iC3, C3b, and C4b, but not C3d, indicating that the binding region is probably within the C3c portion of C3b. A polyclonal antibody to CR1 and monoclonal antibodies to CR1 and CR2 do not immunoprecipitate gp45-70. While gp45-70 has not been previously characterized on human cells, a C3b-binding glycoprotein of similar Mr is present on rabbit alveolar macrophages. We conclude that gp45-70 is an additional group of membrane proteins present on human leukocytes that possess ligand-binding activity for C3b.

Analysis of black layers on steel using conversion electron M�ssbauer spectrometry

Iron and steel were treated in alkaline solutions at boiling point, and the black layers produced on their surfaces were analysed using conversion electron Mossbauer spectrometry (CEMS). The CEM spectra, measured at room temperature, consisted of distorted magnetically split peaks or broad doublet peaks due to ferrimagnetic and superparamagnetic magnetite, respectively. The refined and black surface of steel consisted of fine particles of magnetite with many cations' vacancies at the octahedral structure (B site).

Chelation of ferrous sulphate solutions by pyridoxal isonicotinoyl hydrazone

In an attempt to improve upon desferrioxamine B (‘desferal’, DF) as an agent for the treatment of iron overload, the non-toxic and inexpensive pyridoxal isonicotinoyl hydrazone (PINH) emerged as an effective iron mobilizer which compares with DF when given parenterally or orally to mice. PINH was noted for its enhanced affinity for ferrous ions, functioning as a tridentate ligand, in which the phenolic group, the double-bonded nitrogen, and the oxygen atom of the carbonyl group were observed to participate in metal binding. At around pH 7.0 a dark brown iron-complex was crystallized out from aqueous solution and analyzed as a (PINH) 2Fe·2H 2O compound. To ascertain the oxidation and the spin states of iron chelated by PINH, the latter was subjected to a Mössbauer spectroscopic study in the polycrystalline state. It exhibited a broad doublet at 88 K with δ 0.51 mm/s, quadrupole splitting, Δϵ 0.63 mm/s, and at 300 K, δ = 0.41 mm/s and Δϵ = 0.57 mm/s, suggesting a μ-oxo complex, with non-equivalent locations for the two iron atoms. These correspond to the presence of high-spin tri-valent iron in the complex. We could not however, exclude at this stage the possibility of the presence of low-spin di-valent iron atoms. The spatial structure of the complex and its resemblance to the air-sensitive iron-porphyrin complexes will be discussed.