Spin Form Research Articles

On finite group actions on reductive groups and buildings

Let H be a connected reductive group over a non-archimedean local field k and let F ⊂ Autk(H) be a finite group of order not divisible by p, the residual characteristic of k. Let G = (H F )◦ be the identity component of the subgroup of H consisting of points fixed by F. The main theorem of this paper asserts that the Bruhat-Tits building B(G) of G can be identified with the set of F-fixed points of B(H). Several special cases of this theorem have been known previously. When E/k is a finite totally ramified Galois extension, H = ResE/k G, and F = Gal(E/k), the condition p #F is simply that E/k is tamely ramified. In this case, our main theorem is a well-known but unpublished theorem of G. Rousseau. Recently, one of us (G.P.) found a simple proof of this theorem [P]. When G is a classical group, realized in the standard way as the identity component of the group of fixed points of an involution φ of a general linear group H , Bruhat and Tits [BT4] have given a description of B(G) as a subset of B(H). In particular, it follows from their description that B(G) = B(H) when p = 2. Recently, this fact has been rediscovered by J. Kim and A. Moy [KM], and independently, a simple proof has been given by [GY]. Let H be the split form of Spin(8). Then one can choose an outer automorphism φ ∈ Aut(H) of order 3 such that G = H is of type G2. From a joint work [GY] by W.T. Gan and one of us (J.Y.), it is known that B(G) = B(H) is true for arbitrary p.

Electrochemically generated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii), tris(1,10-phenathroline)ruthenium(ii) and tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(ii) complexes

The electrochemically generated chemiluminescence (ECL) of the title complexes with four series of electroactive organic compounds Q in 0.1 M (C2H5)4NPF6 acetonitrile solutions has been studied using a triple-potential-step technique. The yields of the formation of the excited *RuL32+ ion produced by the electron transfer reaction of RuL3+ with aromatic amine or 2,3,7,8-tetramehoxythianthrene radical cations and by the reaction of RuL33+ with quinone or nitroaromatic radical anions as well as with N-methylpyridinium radicals have been determined. A reaction scheme describing generation of the excited *RuL32+ has been comparatively discussed with that for the quenching reactions with conclusion that spin conversion between two spin forms 3[RuL33+/+⋯Q−/+] and 1[RuL33+/+⋯Q−/+] of an activated complex play a crucial role in both electron transfer processes.

On the intersection forms of spin 4–manifolds bounded by spherical 3–manifolds

We determine the contributions of isolated singularities of spin V 4-manifolds to the index of the Dirac operator over them. From these data we derive certain constraints on the intersection forms of spin 4-manifolds bounded by spherical 3-manifolds, and also on the embeddings of the real projective planes into 4-manifolds.

Photoreducible high spin iron electron paramagnetic resonance signals in dark-adapted Photosystem II: are they oxidised non-haem iron formed from interaction of oxygen with PSII electron acceptors?

An electron paramagnetic resonance (EPR) signal near g=6 in Photosystem II (PSII) membranes has been assigned to a high spin form of cytochrome (Cyt) b 559 (R. Fiege, U. Schreiber, G. Renger, W. Lubitz, V.A. Shuvalov, FEBS Lett. 377 (1995) 325–329). Here we have further investigated the origin of this signal. A slow formation of the signal during storage in the dark is observed in oxygen-evolving PSII membranes, which correlate with the oxidation of Fe 2+ by plastosemiquinone or oxygen. Removal of oxygen inhibits formation of the high spin iron signal. The g=6 EPR signal is photoreduced at cryogenic temperatures and is restored slowly by subsequent dark storage at 77 K. The amplitude of the photoreduced signal increases as the pH is lowered, which shows that the origin is not the hydroxyl ligated Cyt b 559 species proposed previously. Different cryoprotectants also influence the amplitude and lineshape of the high spin iron signal in a manner suggesting that smaller cryoprotectants can penetrate the iron environment. A correlation between the high spin iron and g=1.6 EPR signal assigned to an interaction involving the semiquinones of Qa and Qb is shown. It is concluded that the appearance of the high spin iron signal in oxygen-evolving PSII membranes involves reduced PSII electron acceptors and oxygen and suggests that the signal is from the non-haem iron of PSII.

Spectroscopic studies on the active site of hydroperoxide lyase; the influence of detergents on its conformation

Expression of high quantities of alfalfa hydroperoxide lyase in Escherichia coli made it possible to study its active site and structure in more detail. Circular dichroism (CD) spectra showed that hydroperoxide lyase consists for about 75% of α-helices. Electron paramagnetic resonance (EPR) spectra confirmed its classification as a cytochrome P450 enzyme. The positive influence of detergents on the enzyme activity is paralleled by a spin state transition of the heme Fe(III) from low to high spin. EPR and CD spectra showed that detergents induce a subtle conformational change, which might result in improved substrate binding. Because hydroperoxide lyase is thought to be a membrane bound protein and detergents mimic a membrane environment, the more active, high spin form likely represents the in vivo conformation. Furthermore, the spin state appeared to be temperature-dependent, with the low spin state favored at low temperature. Point mutants of the highly conserved cysteine in domain D indicated that this residue might be involved in heme binding.

Experimental and Theoretical Reaction Cross Sections for the H + HCl System

The dynamics of the gas-phase reaction of H atoms with HCl has been studied experimentally employing the laser photolysis/vacuum-UV laser-induced fluorescence (LP/VUV-LIF) “pump-and-probe” technique and theoretically by means of quasiclassical trajectory (QCT) calculations performed on two versions of the new potential energy surface of Bian and Werner [Bian, W.; Werner, H.-J. J. Chem. Phys. 2000, 112, 220]. In the experimental studies translationally energetic H atoms with average collision energies of Ecol = 1.4 and 1.7 eV were generated by pulsed laser photolysis of H2S and HBr at 222 nm, respectively. Ground-state Cl(2P3/2) and spin−orbit excited Cl*(2P1/2) atoms produced in the reactive collision of the H atoms with room-temperature HCl were detected under single collision conditions by VUV-LIF. The measurements of the Cl* formation spin−orbit branching ratio φCl*(1.4 eV) = [Cl*]/[Cl + Cl*] = 0.07 ± 0.01 and φCl*(1.7 eV) = 0.19 ± 0.02 revealed the increasing importance of the nonadiabatic reaction channel H + HCl → H2 + Cl* with increasing collision energy. To allow for comparison with the QCT calculations, total absolute reaction cross sections for chlorine atom formation, σR(1.4 eV) = (0.35 ± 0.16) Å2 and σR(1.7 eV) = (0.13 ± 0.06) Å2, have been measured using a photolytic calibration method. In addition, further QCT calculations have been carried out for the H + DCl isotope reaction which can be compared with the results of previous reaction dynamics experiments of Barclay et al. [Barclay, V. J.; Collings, B. A.; Polanyi, J. C.; Wang, J. H. J. Phys. Chem. 1991, 95, 2921].

An FTIR study on the structure of the oxygen-evolving Mn-cluster of Photosystem II in different spin forms of the S(2) state.

The S(2) state of the oxygen-evolving Mn-cluster of Photosystem II (PS II) is known to have different forms that exhibit the g =2 multiline and g = 4.1 EPR signals. These two spin forms are interconvertible at > 200 K and the relative amplitudes of the two signals are dependent on the species of cryoprotectant and alcohol contained in the medium. Also, it was recently found that the mutiline form can be converted to the g = 4.1 form by absorption of near-infrared light by the Mn-cluster itself at around 150 K [Boussac et al. (1996) Biochemistry 35: 6984-6989]. We have used light-induced Fourier transform infrared (FTIR) difference spectroscopy to study the structural difference in these two S(2) forms. FTIR difference spectra for S(2)/S(1) as well as for S(2)Q(A) (-)/S(1)Q(A) measured at cryogenic temperatures using PS II membranes in the presence of various cryoprotectants, and monohydric alcohols did not show any specific differences except for intensities of amide I bands, which were larger when ethylene glycol or glycerol was present in addition to sucrose. This result was interpreted due to more flexible movement of the protein backbones upon S(2) formation with a higher cryoprotectant content. Light-induced difference spectra measured at 150 K using either blue light without near-infrared light or red plus near-infrared light also did not show any detectable difference. In addition, a different spectrum upon near-infrared illumination at 150 K of the PS II sample in which the S(2) state had been photogenerated at 200 K exhibited no meaningful signals. These results indicate that the two S(2) forms that give rise to the multiline and g = 4.1 signals have only minor differences, if any, in the structures of amino-acid ligands and polypeptide backbones. This conclusion suggests that conversion between the two spin states is caused by a spin-state transition in the Mn(III) ion rather than valence swapping within the Mn-cluster that would considerably affect the vibrations of ligands.

Amine conformational change and spin conversion induced by metal-assisted ligand oxidation: from the seven-coordinate iron(II)–TPAA complex to the two oxidized iron(II)–(py) 3tren isomers. Characterization, crystal structures, and density functional study

The tripodal heptadentate ligand TPAA (TPAA=tris[ N-(2-pyridylmethyl)-2-aminoethyl]amine) is found to undergo an iron(II)-assisted oxidative dehydrogenation with its three amine functions oxidized into three imine groups, giving the tripodal potentially heptadentate ligand (py) 3tren ((py) 3tren=tris[ N-(2-pyridylmethyl)-2-iminoethyl]amine). This oxidative process induces structural changes and spin conversion in the three identified iron(II) complexes, Fe–TPAA complex ( 1), Fe–py3tren complexes ( 2) and ( 3). X-ray crystallographic studies revealed differences in the coordination geometry of the bridging nitrogen atom and shifts in the coordination number from seven to six. Complex 1 is seven-coordinate and is characterized by a pyramidal environment of the tripodal centered nitrogen and a short N tripodalFe distance equal to 2.504 Å. Complex 3 is hexa-coordinate with a planar environment of the centered nitrogen located at 3.435 Å from iron(II) and therefore not bound to the iron. Complex 2 which is an isomeric form of complex 3 is found to be a structural intermediate between complexes 2 and 3 with a pseudo-coordination of six as shown by the N tripodalFe distance equal to 2.754 Å. Electronic changes were recognized from NMR studies in solution and EPR and SQUID measurements of susceptibilities in solid state. Complex 1 is high-spin with the S=2 state characterized by a g factor equal to 2.25. Complex 3 is low-spin but its isomer, the intermediate complex 2 exhibits a temperature-dependent spin conversion from the S=2 high-spin form at room temperature to a lower spin that we provisionally identify as a S=1 intermediate spin form. DFT Becke3LYP calculations were carried out on the two isomeric complexes 2 and 3. The planar complex was found to be 3.2 kcal mol −1 more stable than the pyramidal isomer, in agreement with the experiment.

First-Principles Study on the Multiplet Structures of CuO5Pyramid in Bi2Sr2CaCu2O8+δ

In this paper we investigate the multiplet structure of a single CuO 5 pyramid embedded in Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) for an insulating phase of δ=0 and a superconducting phase of δ=0 with T c = 85 K. In this study, we use the multi-configuration self-consistent field variational method with configuration interaction to calculate the lowest states of the Zhang-Rice spin-singlet ( 1 A 1 ) and Hund's coupling spin-triplet ( 3 B 1 ) as accurate as possible. In the case of δ=0 we find that the 1 A 1 state is the lowest. It is lower than the 3 B 1 state by 2.15 eV. On the other hand, in the case of δ=0.25 we find that the 1 A 1 and the 3 B 1 multiplets are very close in energy, and mixed easily by transfer interaction between clusters. In the case of δ=0.25, we show that a coherent state for a dopant hole is composed in such a way that the 1 A 1 and the 3 B 1 multiplets appear alternately when the localized spin form local antiferromagnetic ordering in a region of the spin-correlation length.

Functional Characterization of Chlamydomonas Mutants Defective in Cytochrome f Maturation

We have altered the N terminus of cytochrome f by site-directed mutagenesis of the chloroplast petA gene in Chlamydomonas reinhardtii. We have replaced the tyrosine residue, Tyr(32), located immediately downstream of the processing site Ala(29)-Gln(30)-Ala(31) by a proline. Tyr(32) is the N terminus of the mature protein and serves as the sixth axial ligand to the heme iron. This mutant, F32P, accumulated different forms of holocytochrome f and assembled them into the cytochrome b(6)f complex. The strain was able to grow phototrophically. Our results therefore contradict a previous report (Zhou, J., Fernandez-Velasco, J. G., and Malkin, R. (1996) J. Biol. Chem. 271, 1-8) that a mutation, considered to be identical to the mutation described here, prevented cytochrome b(6)f assembly. A comparative functional characterization of F32P with F29L-31L, a site-directed processing mutant in which we had replaced the processing site by a Leu(29)-Gln(30)-Leu(31) sequence (2), revealed that both mutants accumulate high spin cytochrome f, with an unusual orientation of the heme and low spin cytochrome f with an alpha-band peak at 552 nm. Both hemes have significantly lower redox potentials than wild type cytochrome f. We attribute the high spin form to uncleaved pre-holocytochrome f and the low spin form to misprocessed forms of cytochrome f that were cleaved at a position different from the regular Ala(29)-Gln-Ala(31) motif. In contrast to F29L-31L, F32P displayed a small population of functional cytochrome f, presumably cleaved at Ala(29), with characteristics close to those of wild type cytochrome f. The latter form would account for cytochrome b(6)f turnover and photosynthetic electron transfer that sustain phototrophic growth of F32P.

Formation of a molten-globule-like state of cytochrome c induced by high concentrations of glycerol

The effect of glycerol on the structure of cytochrome c was investigated by circular dichroism, absorbance and EPR spectroscopy. The results obtained show that an increasing concentration of the organic solvent (70–99.2%, v/v) in aqueous-polyalcohol mixtures converts native cytochrome c into a new, low spin form through a fully reversible, two-state transition. The glycerol-stabilized form (that we call here the G state) retains native-like amounts of α-helix structure while rigid tertiary structure and native Fe(III)-Met(80) axial bond are lost. Analysis of data suggests a molten globule character of the G state; support to this view is afforded by the striking similarities between the spectroscopic (and, thus, structural) properties of the G state with those of the acidic molten globule of the protein (A state).

Historical account of polarized neutrons in Grenoble

The history of polarized neutrons in Grenoble starts with reactor Melusine where a lifting counter diffractometer was constructed to measure spin densities and form factors. When the Institut Laue Langevin began to operate, the instruments of the first generation included only one multipurpose triple-axis spectrometer for polarization analysis, spin densities and form factor measurements. Soon the construction of the spin echo started and two other dedicated polarized neutron instruments were added: one for spin densities and one for diffuse scattering. Polarization analysis progressed from one-directional to three-directional and later was generalized to three-dimensional. The advance of polarizing devices such as monochromators, mirrors, supermirrors, and polarizing filters is also discussed.

Core-scattered combination orbits in theM=0Stark spectrum of helium

Scaled-energy spectroscopy is used to measure the $m=0$ Stark recurrence spectrum of the two spin forms of helium. This case is characterized by much stronger orbit-core interaction than the $m=1$ case studied previously. Viewed globally as a function of scaled energy $\ensuremath{\varepsilon}$ and scaled action $\ifmmode \hat{S}\else \^{S}\fi{}$ clusters of core-scattered recurrences are revealed, emphasizing their importance in the Stark spectrum. Data are interpreted using closed-orbit theory. Integrating recurrence peaks over scaled energy allows comparison between singlet and triplet core scattering, highlighting the link with $e+{\mathrm{He}}^{+}$ scattering.

Substrate Specificity of the Cytochrome P450 Enzymes CYP79A1 and CYP71E1 Involved in the Biosynthesis of the Cyanogenic Glucoside Dhurrin inSorghum bicolor(L.) Moench

The two multifunctional cytochrome P450 enzymes, CYP79A1 and CYP71E1, involved in the biosynthesis of the cyanogenic glucoside dhurrin inSorghum bicolor(L.) Moench have been characterized with respect to substrate specificity and cofactor requirements using reconstituted, recombinant enzymes and sorghum microsomes. CYP79A1 has a very high substrate specificity, tyrosine being the only substrate found. CYP71E1 has less stringent substrate requirements and metabolizes aromatic oximes efficiently, whereas aliphatic oximes are slowly metabolized. Neither CYP79A1 nor CYP71E1 catalyze the metabolism of a range of different herbicides. The reported resistance of sorghum to bentazon is therefore not linked to the presence of CYP79A1 or CYP71E1. NADPH is a much better cofactor than NADH although NADH does support the entire catalytic cycle of both P450 enzymes.KmandVmaxvalues for NADPH when supporting CYP71E1 activity are 0.013 mM and 111 nmol/mg protein/s. For NADH, the corresponding values are 0.3 mM and 42 nmol/mg protein/s. CYP79A1 is a fairly stable enzyme. In contrast, CYP71E1 is labile and prone to rapid denaturation at room temperature. CYP71E1 is isolated in the low spin form. CYP71E1 catalyzes an unusual dehydration reaction of an oxime to the corresponding nitrile which subsequently is C-hydroxylated. The oxime forms a peculiar reverse Type I spectrum, whereas the nitrile forms a Type I spectrum. Several compounds which do not serve as substrates formed Type I substrate binding spectra with the two P450 enzymes.

Characterization of a New Hemoprotein in the YeastSaccharomyces cerevisiae

The Saccharomyces cerevisiae gene YNL234w encodes a 426-amino acid-long protein that shares significant similarities with the globin family. Compared with known globins from unicellular organisms, the Ynl234wp polypeptide is characterized by an unusual structure. In this protein, a central putative heme-binding domain of about 140 amino acids is flanked by two sequences of about 160 and 120 amino acids, respectively, which share no similarity with known polypeptides. Northern analysis indicates that YNL234w transcription is very low in cells grown under normal aerobic conditions but is induced by oxygen-limited growth conditions and by other stress conditions such as glucose repression, heat shock, osmotic stress, and nitrogen starvation. However, the deletion of the gene had no detectable effect on yeast growth. The Ynl234wp polypeptide has been expressed in Escherichia coli, and the hemoprotein nature of the recombinant protein was demonstrated by heme staining after SDS/polyacrylamide gel electrophoresis and spectroscopic analysis. Our data indicate that purified recombinant Ynl234wp possesses a noncovalently bound heme molecule that is predominantly found in a low spin form.

純アルミニウム円管の揺動回転内フランジ成形法と成形限界

Although the possibility of orbital rotary forming of tube-end has been reported for an outward-flange having large value of flaring ratio, the possibility has not been illuminated previously for an inward-flange having large value of nosing ratio. In order to clarify the possibility of the inward-flanging, an orbital rotary forming process in which an inward-flanged shell is formed from a tube by means of rotary conical nosing and subsequent orbital rotary flanging has been proposed. Hard aluminum tubes are formed to inward-flanged shells, and the deformation behavior is examined. It is found that the inward-flange having large value of nosing ratio can be formed from a tube by means of the proposed process. The proposed method with a retainer ring which prevents buckling is found to be effective in improving the nosing limit. The inward-flanging limit of the proposed method is superior to those of conventional inward-flanging methods, such as spinning and press forming. Furthermore, the proposed method with a retainer ring seems to have a significant effect in making the flange thickness more uniform.

Electroluminescence Devices with CdS and CdS:Mn Nanoparticles and Polymer Blends

ABSTRACTWe have investigated the photophysical properties of surface capped CdS and CdS:Mn nanoparticles in the form of spin coated thin films of the pure nanoparticles and nanoparticle -polymer blends. The organic capping reagent was p-thiocresol. Electroluminescence (EL) devices were fabricated and characterized by their current/voltage characteristics and EL emission performance. This is to our knowledge the first report on Mn doped CdS nanoparticles applied in EL devices with a single layer device structure (ITO/CdS:Mn/Al). Photoluminescence (PL) and PL excitation measurements were performed on CdS:Mn nanoparticles in pyridine dispersion and on thin films. The PL excitation spectrum shows a narrow peak at 390nm. Excitation at this wavelength yields a broad PL spectrum spanning from about 450 to 700nm, which is dominated by a strong emission band at 585nm. This emission is attributed to transitions involving Mn levels in previous works. The EL emission peak is shifted to the red compared to the PL emission spectra. The characteristics and performance of these new types of EL devices will be presented and discussed.

The C331A Mutant of Neuronal Nitric-Oxide Synthase Is Defective in Arginine Binding

It has been proposed that Cys99 of human endothelial nitric oxide synthase (eNOS) is responsible for tetrahydrobiopterin (BH4) binding. To examine this possibility rigorously, we expressed rat neuronal NOS (nNOS) in Escherichia coli, with the homologous Cys331 to Ala mutation, and characterized structural and functional attributes of the purified, mutated enzyme. C331A-nNOS, as isolated, was catalytically incompetent. Upon prolonged incubation with L-arginine (L-Arg), not only BH4 binding but also catalytic activity could be restored. In contrast to wild-type nNOS (WT-nNOS), which exhibits an absorbance maximum at 407 nm that shifts immediately upon L-arginine addition to a high spin form, the C331A-nNOS mutant, as isolated, exhibited an absorbance maximum at 420 nm. C331A-nNOS, as isolated, did not bind detectable levels of either [3H]Nomega-nitro-L-arginine or [3H]BH4, but [3H]BH4 binding was reinstated after extended incubation with excess L-arginine. On the other hand, C331A-nNOS and WT-NOS were identical with regard to imidazole binding affinity, CaM binding affinity, and rates of cytochrome c and 2, 6-dichlorophenolindophenol reduction. EPR spectroscopy revealed conversion of low to high spin heme after extended incubation with high concentrations of L-arginine (0.1-10 mM). The estimated Kd for L-arginine binding to C331A-nNOS was two orders of magnitude greater than WT-nNOS (>100 microM versus 2-3 microM). Here we propose that Cys331 plays an important role in stabilizing L-arginine binding to nNOS. Our findings suggest that the primary dysfunction in the C331A mutant of nNOS, as isolated, is disruption of the BH4-substrate binding interactions as broadcast from this mutated cysteine residue. Prolonged incubation with L-arginine appears to cause remodeling of the mutant protein to a form similar to that of WT-nNOS, allowing for normalized BH4 binding and nitric oxide synthetic activity.

Heme speciation in alkaline ferric FixL and possible tyrosine involvement in the signal transduction pathway for regulation of nitrogen fixation.

The pH-dependent behavior of the ferric forms of two soluble truncations of Rhizobium meliloti FixL, FixL (heme and kinase domains, functional), and FixLN (heme domain) are examined by UV-visible, resonance Raman, and electron paramagnetic resonance spectroscopy. Global analysis of UV-visible data indicates that the pKa for hydroxide binding is slightly higher in FixL than in FixLN. Spectroscopic data show that high-spin and low-spin hydroxide adducts of FixLN and FixL exist in a thermal spin-state equilibrium with a significant fraction of the heme in the high spin form at room temperature. FixLN and FixL differ from myoglobin and hemoglobin in that their hemes are not fully ligated by hydroxide ion under strongly alkaline conditions. In addition to the binding of hydroxide ion, both FixLN and FixL undergo additional alkaline transitions that involve the deprotonation of tyrosine residues. FixLN contains four tyrosine residues. One has a pKa of 9.6, which is indistinguishable from that for hydroxide binding to the heme. The other three tyrosines have pKas greater than 11. At pH 11, the alkaline species react with cyanide to yield the familiar low-spin cyanide adduct. Upon reduction of the heme iron, the alkaline forms of the FixL deletion derivatives are converted to their deoxy forms. Resonance Raman spectra reveal that the Fe-His stretching vibrations of deoxyFixLN and deoxyFixL are not measurably shifted from those of their neutral counterparts. Treatment of the alkaline deoxyFixLs with O2 yields the respective oxy forms. Spectroscopic evidence indicates that the loss of activity at elevated pH cannot be attributed solely to generation of a low-spin heme hydroxide. Involvement of one or more tyrosines in signal transmission between the heme and kinase domains of FixL is proposed.

Magnetostatic volume waves in exchange-coupled ferrite films

The influence of exchange coupling of layers on the propagation of magnetostatic dipole volume waves in normally and tangentially magnetized two-layer epitaxial ferrite structures is investigated. It is shown that the indicated influence is manifested in the form of dynamic spin pinning effects on the interlayer boundary and formation of a common dipole-exchange wave spectrum for the entire structure. In this case, at the synchronism frequencies of the dipole and exchange waves the losses of the dipole waves grow and anomalous segments appear in the dispersion. In films magnetized in the “hard” direction relative to the axis of normal uniaxial surface anisotropy the magnetostatic dipole volume waves can interact resonantly with the surface spin waves supported by the boundaries with pinned spins.