Asymmetric Doublet Research Articles

High resolution solid state 13C NMR spectra of carbons bonded to nitrogen in a sample spinning at the magic angle

High resolution solid state 13C NMR spectra of amino acids and nitrile compounds have been obtained by a combination of cross-polarization, dipolar decoupling, and magic angle spinning techniques (CP–MAS). The resonances of Cα and cyano carbons in the observed 13C spectra show asymmetric doublet patterns. This problem has been treated by using the adiabatic approximation since the 14N quadrupole interaction is much larger than the spinning frequency. Theoretical spectra have been simulated for these carbons and they show very good agreement with experimental observations.

Chemical shielding tensor and 13C–14N dipolar splitting in single crystals of L-alanine

Chemical shielding tensors have been determined for three chemically distinct carbons in a single crystal of L-alanine using proton-enhanced 13C NMR. The results indicate that the most shielded direction is perpendicular to the sp2 plane for the carboxyl carbon and the C3 axis for the methyl carbon. 13C–14N dipolar splittings have been observed for the Ca carbon, causing further complication in spectral analysis. Since the 14N quadrupole coupling constant is of comparable order with the 14N Zeeman interaction, 14N quadrupole interaction is effective in the 13C–14N dipolar splittings. The 14N quadrupole effect is observed and demonstrated by calculation and the sign of the quadrupole coupling constant e2Qq has been determined to be positive. The chemical shielding tensor for the Ca carbon is determined by considering the 13C–14N dipolar interaction and the 14N quadrupole interaction. It is shown that the 14N quadrupole interaction causes the asymmetric doublet pattern in the 13C NMR signal for the Ca carbon in magic angle spinning (MAS) experiments.

Mössbauer studies on some glasses and crystals in the Na 2OFe 2O 3SiO 2 system

Mössbauer absorption measurements have been made at room temperature on 57Fe in iron sodium silicate glasses containing 3–15 mol% Fe 2O 3 and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s −1, while those of Na 2O · Fe 2O 3 · 4 SiO 2 and 5 Na 2O · Fe 2O 3 · 8 SiO 2 crystals showed much smaller quadrupole splitting, 0.28 mm s −1 and 0.10 mm s −1, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi 2O 6 and MFeSi 3O 8 crystals, the quadrupole splitting became wider and approached to 0.73 mm s −1. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.

Homopolar grafting in Blepharisma japonicum

AbstractResults of homoplastic grafting in Blepharisma japonicum v. intermedium are described. The parabiotic homopolar fusion complex of two cells either simply splits into two singlets, or undergoes cell division. In the latter case the division results either in two doublets or in two singlets (proters) and a doublet (opisthe). If one or two of the systems of feeding organelles are removed after parabiotic homopolar fusion of two cells, the fusion complex does not split, but undergoes division. If an almost complete set of feeding organelles is lacking, the division of the graft complex usually results either in a singlet proter and a doublet opisthe or in two doublets. If two complete sets of feeding organelles have been excised from the graft complex, division occurs after the regeneration of the missing organelles, most frequently resulting in two doublets. The same operation on the graft complex with two primordium sites placed very close to each other may result in the regeneration of one normal and one reversed peristome, the latter being to the right of the former. The doublet biotypes derived from the graft complexes with or without further experimental changes usually reproduced true to type. The asymmetric doublet with two peristomes less than 180° apart tends to resorb the left peristome, that is, one with a larger left‐hand somatic area than the other. The asymmetric doublet may also form a third peristome on the right side of the original left peristome. The third peristome is usually of reversed asymmetry. That the appearance of the third primordium site might be due to the presence of the original line of fusion of two components of the doublet, and that the tendency of the original primordium sites to reestablish themselves might give rise to the third one, when the original ones fail to be kept away from one another, are discussed.

Goldanskii-Karyagin effect in FePS3

Mossbauer studies have been performed on FePS3 in powder form between 125 K and 450 K. The Mossbauer spectrum consists of an asymmetric doublet, ratio∼0.93 at room temperature. The asymmetry is attributed to the Goldanskii-Karyagin effect and the lattice anisotropy is found to be ∼1.4, with the largest vibrations parallel to thec⋆ axis of the monoclinic unit cell. The Debye temperature is ∼200 K.

Mössbauer studies in the colloid system β-FeOOH–β-Fe2O3: structures and dehydration mechanism

The Mossbauer spectrum of the recently reported β-iron(III) oxide has been measured and that of β-iron(III) oxide hydroxide re-investigated. The Neel temperature of β-iron(III) oxide lies between 300 and 380 K and the average magnetic field at 4.2 K is 49.5 tesla. Magnetic relaxation effects are observed. The spectrum above the Neel temperature is a broad asymmetric doublet, consisting of peaks having a continuous distribution of velocities, with the most probable quadrupole splitting occurring at 1.0 mm s–1, and the most probable isomer shift, extrapolated to 295 K, occurring at 0.31 mm s–1. While the distribution is within the known range of parameters of 6 or 5 co-ordinated Fe3+ in oxides, a proportion of tetrahedral Fe3+, with a lower isomer shift, could also exist within the broad spectral envelope, and a possible concentration range of from 0 to 40 % was estimated.The spectrum of β-iron(III) oxide hydroxide is consistent with octahedral Fe3+. The high proportion of ions on the internal surfaces of the tubular structure results in a non-stoichiometric surface anion excess, and the conventional formula β-FeOOH has been reformulated as β-FeOx(OH)3–2x, where x≈ 0.9.Four models of the anion vacancy distribution in β-iron(III) oxide are considered within the framework of the tubular structure retained during dehydration, and a defect structure is proposed which is consistent with the Mossbauer, X-ray, magnetic and B.E.T. data: all the internal Fe3+ ions are 5 co-ordinated whilst the surface Fe3+ ions are tetrahedrally co-ordinated.

The Mechanism of Action of Ethanolamine Ammonia-Lyase, a B12-dependent Enzyme: THE PARTICIPATION OF PARAMAGNETIC SPECIES IN THE CATALYTIC DEAMINATION OF 2-AMINOPROPANOL

Abstract Ethanolamine ammonia-lyase catalyzed the adenosylcobalamin-dependent deamination of 2-aminopropanol as well as that of ethanolamine. When the enzyme-coenzyme complex was frozen in liquid nitrogen while it was acting on 2-aminopropanol, a large, well defined EPR spectrum was demonstrated. The spectrum consisted of two components: a broad signal at g = 2.34, and an asymmetrical doublet with g values of 2.04 and 1.99. The over-all signal corresponded to about 1.3 spins per active site, the electron density being approximately equally divided between the species producing the g = 2.34 component and the one represented by the asymmetrical doublet. The configuration of the signal was the same regardless of whether the incubation was conducted aerobically or anaerobically. Both components of the signal were saturated by increasing power, the doublet being the more easily saturated component. EPR spectroscopy at two different microwave frequencies (X band and K band) showed that the doublet represented a single paramagnetic species whose signal was split by an interaction with another paramagnetic species in its vicinity. By its location, configuration, and the characteristics of the superimposed hyperfine structure, the g = 2.34 signal was assigned to the unpaired electron of cob(II)alamin. Experiments with isotopically labeled propanolamine permitted the doublet signal to be assigned to the 2-aminopropanol-1-yl radical. The major splitting of the doublet signal was attributed to a dipole-dipole interaction between the 2-amino-propanol-1-yl radical and the unpaired electron on cob(II)-alamin; assuming this explanation to be correct, the distance between the two spins was calculated to be ∼6 A. Rapid mixing, quick freeze experiments showed that the appearance of the paramagnetic species was a first order process with a rate constant of 7 s-1. Since the turnover number for propanolamine is 1 to 2 s-1, the process by which the paramagnetic species are generated is kinetically competent with respect to over-all catalysis. Once formed, the species disappeared with a half-time of about 1 to 2 min. Their disappearance is probably associated with the irreversible destruction of adenosylcobalamin by a side reaction not directly relevant to the catalytic mechanism. These results have been interpreted in terms of a mechanism whereby the early hydrogen transfer steps in the adenosylcobalamin-dependent rearrangement of propanolamine are as follows: [see PDF for equation]

Electron Spin Resonance of the Iron-containing Protein B2 from Ribonucleotide Reductase

Abstract Protein B2 is an iron-containing subunit of ribonucleotide reductase. Its light absorption spectrum has similarities to that of oxyhemerythrin, but in addition shows a sharp peak at 410 nm. The electron spin resonance (ESR) spectrum recorded from 14–293 °K shows a slightly asymmetric doublet centered at g = 2.0047. Even though the integrated ESR absorption corresponded at the most to a spin concentration of only 30% of the total iron content, different lines of evidence strongly link the presence of the ESR signal (and the peak at 410 nm) to the enzymatic activity of protein B2. Several characteristics of the signal would suggest that it is due to a free radical. It is, however, dependent on the presence of iron in protein B2. A mononuclear or dinuclear iron complex is considered less likely as an explanation of the data.