Doublet Signal Research Articles

Competition between electron-phonon interaction and electron-correlation in Ni-Pd mixed-metal MX chain compounds

The IR, XPS and resonance Raman spectra of a series of Ni-Pd mixed-metal MX-chain compounds, Ni 1−xPd x(chxn) 2Br 3 have been measured in order to investigate the competition between the electron-correlation in Ni III and the electron-phonon interaction in Pd II–Pd IV states. The splitting of doublet signals of the Pd II–Pd IV in IR spectra and the integrated intensity of the Pd IV-Br stretching in Raman spectra decrease with decrease of Pd components. These results suggest that the Pd II–Pd IV mixed-valence states are effectively influenced by Ni III states, approaching toward the Pd III states.

Improved proton spectroscopic U-FLARE imaging for the detection of coupled resonances in the rat brain in vivo

Modifications of the pulse sequence for spectroscopic U-FLARE imaging are discussed to detect not only the predominant singlet signals of N-acetylaspartate, total creatine, and choline containing compounds or the doublet signal of lactate, but also the coupled resonances of glutamate, glutamine, taurine and myo-inositol. Effective homonuclear decoupling is achieved by use of constant time chemical shift encoding. A maximum signal-to-noise ratio (SNR) can be obtained for a certain coupled resonance of interest by optimizing the evolution period t c of the J modulated spin echo. Good reproducibility and a high SNR were achieved by combining several methods for water suppression and by using the displaced variant of U-FLARE. Measurements of a 3 mm slice of the rat brain were performed in vivo within 4 min, giving a nominal voxel size of 1.5 × 1.5 × 3.0 mm 3 or 1.5 × 0.75 × 3.0 mm 3. Thus, optimized spectroscopic U-FLARE is a powerful tool for proton spectroscopic imaging with high spectral, spatial and temporal resolution.

1PB051 Ca^<2+>-除去配向PS IIのESRの磁気的異方性

1PB051 Ca^<2+>-除去配向PS IIのESRの磁気的異方性

Identification of radicals from hyaluronan (hyaluronic acid) and cross-linked derivatives using electron paramagnetic resonance spectroscopy

The reaction of hydroxyl radicals generated using a Ti(III)–H 2O 2 redox couple with hyaluronan and cross-linked derivatives (hylan) has been studied using a rapid-flow electron paramagnetic resonance spectroscopy (EPR) system. Radicals were detected as a result of hydrogen atom abstraction from the carbohydrate at pH 3.6; these gave rise to both relatively broad and sharp isotropic features. The broad signals are assigned to high-molecular-weight hyaluronan-derived radicals, whereas the isotropic features are due to rapidly tumbling radicals present either at the ends of the polymer or on low-molecular-weight fragments. These isotropic signals have been interpreted in terms of the presence of two major radicals; one of these gives rise to a doublet signal ( a H 1.36 mT, g 2.0049), the other a doublet of doublets ( a α-H 1.86 mT, a β-H 0.81 mT, g 2.0035). The former signal has parameters identical to those observed for the radical generated as a result of hydrogen abstraction from the C 5 position of the model compound glucuronic acid, and is therefore assigned to this species on the polymer. The second signal, which has parameters characteristic of a radical with both α-H and β-H splittings, is believed to be generated as a result of hydrogen abstraction from C 6 on the N-acetyl- d-glucosamine monomer. Less intense signals were observed with the cross-linked material hylan, in accord with previous data which show that this material is less readily degraded than the linear polymer. These EPR data fully support the chain scission processes previously proposed for aqueous hyaluronan and hylan systems, where each hydroxyl radical results in a single chain scission.

Interaction between sodium ascorbate and dopamine

The interaction between sodium ascorbate and dopamine was investigated by three different parameters: radical intensity, prooxidant action, and cytotoxicity induction. Sodium ascorbate and dopamine produced the doublet and quartet ESR signals under alkaline conditions (pH 8.0–9.5), respectively. Addition of increasing concentrations of sodium ascorbate completely scavenged the dopamine radical and replaced the latter with its own radical. Similarly, dopamine slightly, but significantly reduced the radical intensity of sodium ascorbate. These two compounds stimulated the methionine oxidation and hydrogen peroxide generation in culture medium, but in combination, their stimulation activities were weakened. Both of these two compounds dose-dependently reduced the viable cell number of human oral squamous carcinoma HSC-4 cells, and their cytotoxic activity was significantly reduced by catalase. When these two compounds were mixed together before adding to HSC-4 cells, both of their cytotoxic activities were diminished. The present study demonstrates the interaction between sodium ascorbate and dopamine, which might modify their biological activities and generation of nerve disorders such as Parkinson’s disease.

Electron spin resonance study of the homopolymerization of aromatic bismaleimides

Maleimide homopolymerization can be initiated by the maleimide monomer without the need for added initiator. This self-initiation is believed to occur through a donor–acceptor complex formed between maleimide groups. An in-situ electron spin resonance (e.s.r.) spectroscopic technique was used to study the free-radical homopolymerization of 1,1′-(methylenedi-4,1-phenylene)bismaleimide (MDP-BMI) over a range of temperatures. Total radical concentrations were measured as a function of time at polymerization temperatures from 180 to 230°C. By analysis of the e.s.r. spectra from different maleimide monomers, MDP-BMI, N-phenylmaleimide (NPM) and 1,1′-[methylenebis-(2,6-diethyl-4,1-phenylene)] bismaleimide (MDEP-BMI), with and without free-radical initiators, it was possible to identify the e.s.r. signals due to various radical species. Unreactive diphenylmethylene radicals were observed on the polymer chains formed from MDP-BMI. Additional spectral features are present that include the signal due to the propagating radical. Maleimides containing free-radical initiator also exhibited a broad doublet signal assigned to a vinyl radical formed by hydrogen abstraction from the maleimide double bond. From comparison of the spectra of NPM and MDEP-BMI monomers, both with and without free-radical initiators, it was shown that the maleimide propagating radical gives an unusually narrow, singlet e.s.r. peak quite different from the four-line signal previously reported. © Elsevier Science Ltd.

Visualization of a self-incompatibility gene in Brassica campestris L. by multicolor FISH

The physical localization of the S-glycoprotein (SLG) locus in the chromosome of Brassica campestris L. ‘pekinensis’ cv ‘Kukai’ was visualized by multi-color fluorescent in situ hybridization (McFISH). ‘Kukai’, which is an F1 hybrid between two parental lines, T-17 and T-18, has two SLG genes from both T-17 and T-18. In this study, a 1.3-kb DNA fragment was amplified from the genomic DNA of T-17 by PCR using a set of primers specific to the class-I SLG. From the genomic DNA of T-18, no DNA fragment was amplified using these primers. In the genomic Southern hybridization, a cloned PCR product hybridized with the genomic DNA of T-17 or F1 but not with that of T-18. The PCR product had a sequence homology of approximately, 85% to another class-I SLG gene, SLG-9. Therefore, the PCR product from T-17 was named SLG-17, as it is thought to be a member of the class-I SLG. Using SLG-17 as the probe, FISH was carried out to visualize the position of the SLG locus. McFISH was also carried out simultaneously using the SLG-17 and SLG-9 genes as probes. The SLG-17 gene was detected as a doublet signal at the interstitial region close to the end of a small chromosome, with the signal site being identical to that of SLG-9. Therefore, it is concluded that the SLG-17 gene is localized at the interstitial region close to the end of the chromosome derived from T-17 in Brassica campestris L. ‘pekinensis’ cv ‘Kukai’.

Replication timing of the various FMR1 alleles detected by FISH: inferences regarding their transcriptional status.

Following the application of two-color fluorescence in-situ hybridization (FISH) to human interphase cells, we examined the replication timing of the fragile-X locus relative to the non-transcribed late replicating alpha-satellite region of chromosome-X, a built-in intracellular reference locus. In this assay, an unreplicated locus is identified by a single hybridization signal (singlet; S), whereas a replicated locus is identified by a duplicated signal (doublet; D). Hence, following simultaneous hybridization with the FMR1 and alpha-satellite probes, male cells with one singlet and one doublet signal per cell (SD cells) indicate S-phase cells where only one of the two loci has replicated. The studied cell samples (lymphocytes and amniocytes) were derived from normal males, fragile-X male patients, and premutation male carriers. Three distinct populations of SD cells were identified among the various samples. The first population had a high frequency of cells showing a doublet FMR1; this pattern, indicating early replication of FMR1, characterized the SD cell population of normal males. The second population had a high frequency of cells showing a singlet FMR1; this pattern, indicating very late replication of FMR1, characterized the SD population of fragile-X patients. The third population had about one half of the cells showing a singlet FMR1 and the other half with a doublet FMR1, indicating somatic variation in the replication timing of FMR1; this pattern was seen in the SD cell population of premutation carriers. The replication status of the FMR1 locus in the cells of patients was altered from late to early in the presence of 5-azadeoxycytidine, an activator of various silent genes. Based on the vast amount of information showing that expressed loci replicate early, whereas unexpressed loci replicate late, we inferred from the replication status of the FMR1 locus that: (1) the normal FMR1 allele is transcriptionally active in lymphocytes and amniocytes; (2) the fully mutated FMR1 allele is transcriptionally silent; (3) the transcriptional activity of the premutated allele is somewhat disturbed; (4) 5-azadeoxycytidine activates the fully mutated FMR1 allele.

Carbon-Carbon and Carbon-Nitrogen Spin-Spin Coupling in NMR Spectroscopy: Simple Examples Based on Isotope-Labeled Glycines

The phenomena of carbon-carbon and carbon-nitrogen spin-spin coupling, not visible in 13C and 15N NMR spectra recorded at natural abundance, are demonstrated using routine conditions primarily in a series of 13C/15N-labeled t-butoxycarbonyl- glycine isotopomers. Doublet and doublet of doublet signals, originating from one and two bond homo- and/or heteronuclear spin-spin coupling, are thereby obtained. Furthermore, from all these NMR spectra the presence of each isotopomer in two con formations is clearly demonstrated. Such compounds are in principle easy to make, but preparative work especially involving the 13C nucleus is costly, for which reason two other more affordable alternatives are also presented, based only on 15N labeling, in which cases 13C nuclei directly attached to 15N give rise to doublet signals. These two preparations can conveniently be performed on a small scale. The first one involves the synthesis of a 15N-labeled imidodicarbonate, whereas the second demonstrates its efficient alkylation under simple phase-transfer catalysis conditions.

Conformational Studies by Dynamic NMR. 62.1 Stereomutations of Rotamers and of Conformational Enantiomers in 1,2-Diacylbenzenes

A number of 1,2-diacylbenzenes have been investigated by dynamic NMR spectroscopy. The 1,2-formyl derivative 1 was found to exist (at −162 °C) in the nearly coplanar ZE and EE conformations (70% and 30%, respectively) that interconvert with a free energy of activation of 4.9 kcal mol-1. On the contrary, the more hindered 1,2-diisobutanoylbenzene (4) adopts a twisted conformation (as indicated by the 13C spectrum at −157 °C) which, in principle, might correspond either to a meso or to a racemic stereolabile structure. Only the racemic conformer is, however, believed to be populated, and the interconversion barrier between the RR and SS conformational enantiomers has been determined (5.6 kcal mol-1). Although the 1,2-diacetyl- and 1,2-dipropanoylbenzenes did not exhibit dynamic NMR effects in solution, they were assigned a twisted (racemic) conformation on the basis of the corresponding solid state 13C CP-MAS spectra, in that they display a 1:1 doublet signal for each pair of enantiotopic carbons. All these conclusions agree with the predictions of molecular mechanics calculations.

Analysis of replication timing of ribosomal RNA genes by fluorescence in situ hybridization.

Fluorescence in situ hybridization has been used to study the replication timing of various repeat DNA families in the short arms of human acrocentric chromosomes. In interphase nuclei, unreplicated DNA segments show singlet hybridization signals whereas replicated loci have doublet signals. The distribution of these two patterns in unsynchronized cell cultures revealed that the rRNA gene clusters replicate earlier than the closely juxtaposed alpha- and beta-satellite DNA sequences. Within the rDNA repeat unit, replication of the intergenic spacer appears to precede that of the transcribed rDNA.

Donor function of phosphate ions in photosystem 2

Evidence was obtained for the interaction between the photosystem 2 (PS2) reaction centre (RC) chlorophyll (Chl) P680 and inorganic phosphate, Pi. The light-induced endogenous basal electron transport to ferricyanide in PS2 depended on endogenous Pi. The electron transport in phosphate deficient was absent, and could be resumed upon the addition of exogenous Pi or of the exogenous electron donor, diphenylcarbazide. Some chloroplast Chl molecules were apparently bound with Pi to a complex via the magnesium atom that was detected by the increase in absorbance in the Chl a absorption maximum at 435 nm observed after the consumption of endogenous Pi in the photophosphorylation reactions. The electron paramagnetic resonance (EPR) Signal I, found in the spectra at 77 K after irradiation of frozen samples in poor in endogenous Pi, was the sum of P700+ and P680+ signals. The P680+ signal disappeared after addition of Pi, diphenylcarbazide or to the before freezing. In addition, the EPR doublet signal of the phosphate anion radicals was recorded at 77 K after irradiation in the ethanol solutions of Chl a containing potassium phosphate. The same doublet signal was discovered in the difference EPR spectrum chloroplasts minus with diuron at 77 K after irradation. The results are a possible evidence of the participation of phosphate ions in the primary light reactions of PS2.

An electron paramagnetic resonance study on the mechanism-based inactivation of adenosylcobalamin-dependent diol dehydrase by glycerol and other substrates

Adenosylcobalamin-dependent diol dehydrase undergoes mechanism-based inactivation by glycerol or other substrates during catalysis. X-band electron paramagnetic resonance spectra of holoenzyme were measured at −130°C after reaction with such substrates. After short time of incubation, broad signals assigned to low-spin Co(II) of cob(II)alamin and doublet signals assigned to an organic radical intermediate derived from each substrate were observed with 1,2-propanediol, 1,2-ethanediol, glycerol and meso-2,3-butanediol with the magnitude of their exchange interaction ( J-value) decreasing in this order. A substrate with the smaller magnitude of exchange interaction between low-spin Co(II) and an organic radical intermediate seems to be an efficient mechanism-based inactivator. Since the magnitude of exchange interaction decreases with the distance between radical species in a radical pair, these results suggest that a stabilizing effect of holoenzyme on radical intermediates during reactions decreases with the distance between Co(II) and a radical.

An ESR study of defects in irradiated hydroxyapatite

Radiation-induced defects in synthetic hydroxyapatite (HAp) of six different origins have been investigated by electron spin resonance (ESR), X-ray diffraction (XRD), Raman scattering and IR measurements. The orthorhombic CO 2 − radicals were detected in almost of all the samples examined, but the isotropic CO 2 − was produced only in water-containing HAp with low crystallinity. The doublet signal due to H 0 was clearly detected in HAp with extreme calcium deficiency as compared to the stoichiometry. The results of ESR and FTIR suggest that water molecules in low crystalline HAp are not on the surface but embedded in the HAp crystalline lattice.

Electron spin resonance studies in β-FeSi2 crystals

The electron spin resonance studies have been carried out in the temperature range 130–300 K on semiconducting β-FeSi2 single crystals grown by a chemical vapor transport technique. Two anisotropic doublets with apparent g factors in the range 2.025–2.05 and 1.98–2.03, as well as one complex signal having an isotropic g factor of 2.0195 and exhibiting a five-line hyperfine structure, have been detected. The doublet signals are believed to arise from spin triplet (S=1) states of, presumably, substitutional Ni2+ transition ions, whereas the signal exhibiting the hyperfine structure has been attributed to the spin of a hole, captured by silicon vacancy and interacting with nuclear spins of four iron atoms in the first shell surrounding of the silicon vacancy.

Selectively reductive cleavage of the protected taxol side chain with sodium borohydride

（27%）still had the acetyl group at 20-C and the signal for the 10-C proton at 6.61 ppm（s）was shifted to 6.31 ppm（d, J=3.79 Hz）. A new doublet signal at 3.62 ppm(d, J=3.80

Structural studies on an iron(III) complex containing (Z)-2-(2-aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide, a model compound for a cephalosporin antibiotic Cefdinir

(Z)-2-(2-Aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide (HL) has been employed as a model compound for a cephalosporin antibiotic, Cefdinir. A trinuclear iron(III) complex [Fe3L6]Cl[OH]21 has been obtained from a methanol solution containing HL and FeCl3 and its structure determined by X-ray crystallography: monoclinic, space group P21/n, a= 15.559(1), b= 19.295(2), c= 10.963(1)Å, β= 101.29(1)°, Z= 2. The molecular structure contains a linear Fe(1)–Fe(2)–Fe(1′) arrangement, the central atom Fe(2) being an inversion centre. Atom Fe(1) is co-ordinated to three molecules of L through the thiazole and oximate nitrogen atoms to form Fe(1)L3, and Fe(2) to six oximate oxygen atoms of the two Fe(1)L3 units. The two Fe(1)L3 units are bridged by the central iron atom Fe(2). The Mössbauer spectrum of 1 gave an apparent doublet signal consisting of two doublets, A and B, assigned to Fe(1) and Fe(2), respectively. The isomer shifts δ of these doublets are the same (0.26 mm s–1), and are typical for high-spin iron(III). In addition, the reflectance spectrum did not show any intervalence bands. These spectral data indicate that the three iron atoms are high-spin iron(III). The compound co-ordinates to iron(III)via the thiazole ring nitrogen atom and the oximate nitrogen atom (2N mode) in methanol which is different from that in water, where L prefers to co-ordinate to an iron(III) through the oximate oxygen atom and the amide oxygen atom (2O mode).

Reference Deconvolution Using Multiplet Reference Signals

Reference deconvolution [G. A. Morris,J. Magn. Reson.80,547 (1988)], in which the experimental lineshape of a reference signal is used to deconvolve a spectrum in order to correct instrumental errors, normally requires a well-resolved singlet as the reference signal. The presence of zeroes in the time-domain signal of a multiplet makes it unsuitable for use in the normal reference deconvolution algorithm, since the zeroes would give rise to discontinuities in the correction function. The problem may be circumvented if the algorithm is adapted to include interpolation over the gaps in the correction function caused by the zeroes. Practical details of the interpolation and of the choice of reference signal are discussed, and experimental results are shown for spectra deconvolved using a doublet signal as reference.

Pulsed electron paramagnetic resonance studies of the lysine 2,3-aminomutase substrate radical: Evidence for participation of pyridoxal 5'-phosphate in a radical rearrangement

The role of pyridoxal 5'-phosphate (PLP) in the radical-mediated amino group migration catalyzed by lysine 2,3-aminomutase from Clostridia SB4 has been investigated by electron spin echo envelope modulation (ESEEM) spectroscopy. This pulsed electron paramagnetic resonance (EPR) method was used to estimate the distance between the unpaired electron in the alpha-radical of beta-lysine, a steady-state intermediate in the reaction, and deuterium at the C4' position of the cofactor, PLP. [4'-2H]PLP was synthesized and exchanged into the enzyme. The steady-state radical was generated in the labeled samples and in samples with unlabeled PLP by addition of L-lysine.H2SO4 to activated enzyme. ESEEM spectra of the samples prepared with [4'-2H]PLP exhibited distinctive low-frequency modulations that were not present in spectra of matched samples with unlabeled PLP. Fourier transformation of the modulations yielded a prominent doublet signal centered about the Larmor frequency of deuterium. The magnitude of the doublet splitting of the 2H ESEEM signal exhibited angle selection across the CW EPR powder pattern. The observed angle selection, as well as simulation of the time domain spectra, indicated that the doublet splitting was due to the combined effects of the 2H hyperfine and nuclear quadrupole interactions. The influences of the quadrupole interaction and of isotropic and dipolar hyperfine interactions were explored by simulations of the ESEEM spectra. The analysis indicates a distance of < 3.5 A between the 2H at C4' of PLP and the radical center at C alpha lysine. The data are most compatible with an aldimine linkage between PLP and the beta-nitrogen of beta-lysine.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct detection of ascorbyl radical in experimental brain injury: microdialysis and an electron spin resonance spectroscopic study.

To examine the role played by free radicals in brain injury, we performed experiments to detect radicals in the frontal cortex of rats, using electron spin resonance (ESR) and microdialysis. A dialysis probe was inserted into the frontal cortex, and spin adducts in perfusates were immediately detected by ESR. We obtained a relatively stable doublet signal, with parameters of g = 2.0057 and aH = 0.17 mT. This signal corresponded with that of the ascorbyl radical. Ascorbyl radical in the perfusate collected from the frontal cortex was augmented by microinjection of H2O2 and FeCl2 adjacent to the dialysis probe. When the rats were challenged with cold-induced brain injury, ascorbyl radical and lactate dehydrogenase (LDH) level in the perfusate increased significantly. Pretreatment with superoxide dismutase and catalase attenuated the increase in ascorbyl radical and LDH level induced by the cold injury. Infusion of FeCl2 dissolved in perfusate caused a pronounced increase in ascorbyl radical and LDH level after the cold injury. We conclude that the direct detection of free radical formation further supports the hypothesis that free radicals play an important role in traumatic brain injury. Our findings also indicate that combined microdialysis with ESR spectroscopy is a useful in vivo method for monitoring free radical production in the brain.