Electronic Asymmetry Research Articles

Distortions in trihapto-allyls induced by electronic asymmetry: A comparison of the structures of (η 5-C 5H 5)Mo(CO) 2(η 3-C 3H 5) and (η 5-C 5H 5)Mo(NO(I)(η 3-C 3H 5)

The electronic asymmetry induced by replacing two carbonyls by a nitrosyl and iodide ligand causes severe distortion in the allyl moiety. The allyl group in the nitrosyl complex is bound in a sigma-pi mode rather than the symmetrical mode found in the dicarbonyl. This change in ground state structure alters the exo—endo conformer interconversion mechanism from a rotation of the allyl in the dicarbonyl to a sigma-pi interconversion in the nitrosyl iodide.

NMR studies of low-spin ferric complexes of natural porphyrin derivatives. 1. Effect of peripheral substituents on the .pi. electronic asymmetry in biscyano complexes

NMR studies of low-spin ferric complexes of natural porphyrin derivatives. 1. Effect of peripheral substituents on the .pi. electronic asymmetry in biscyano complexes

Allowed β-transitions, weak magnetism and nuclear structure in light nuclei

The general formalism for allowed β-transitions is derived in the framework of the elementary particle as well as in the impulse approximation treatment. Explicit expressions for the shape factor, the asymmetry and anisotropy of electrons emitted from oriented nuclei, the β-γ (CP) correlation and the β-γ angular correlation are given. Emphasis is imputed to the question how model independently these quantities can be evaluated. This problem has been studied in detail for the β-transitions in the nuclei 12B 12N, 20F 20Na, 22Na and 24Na 24Al. The computations of the nuclear matrix elements are carried out for the A = 12 system in intermediate coupling and for the sd-shell nuclei in the SU(6)- SU(3) coupling scheme using different residual interactions. Comparison to experiments is made. All results can be explained with ordinary CVC predictions without invoking second class currents.

Asymmetry in inelastic electron tunneling peak intensities

Abstract Experiments show that for an organic material placed on an oxide one sees an asymmetry of inelastic electron tunneling peak intensity for bias voltages of opposite sign. When the barrier is composed only of the organic material with no deliberate oxidation such asymmetry disappears.

The theory of coincidence experiments on electron impact ionisation of inner atomic shells

A theoretical treatment is given of possible experiments on electron impact ionisation of inner atomic shells, in which an inelastically scattered electron is detected in coincidence with the decay products of the ion formed, namely with an X-ray photon or with an Auger electron. General expressions for the angular distribution and polarisation of the X-ray photons and Auger electrons are given in terms of the parameters describing the anisotropy of the ionic state, namely statistical tensors which depend on the electron scattering angle and are determined by the ionisation mechanism. The statistical tensors, the asymmetry and the polarisation of the X-rays and the asymmetry of the Auger electrons are calculated for ionisation of the 2p shell of Ar, the 3d shell of Kr and the 4d shell of Xe at different scattering angles of the fast electron.

First-order radiative corrections to asymmetry coefficients in neutron decay

Electromagnetic radiative corrections to the electron-neutrino, electron, and neutrino asymmetry coefficients in neutron $\ensuremath{\beta}$ decay are calculated. Strong-interaction effects are retained as suggested by Sirlin.

Inequivalent XPS binding energies in symmetrical delocalized mixed-valence complexes

It has previously been assumed that an ESCA measurement on a mixed-valence-e.g., M(II)-M(III) - compound which yields two peaks for an inner-shell M ionization at energies close to those measured for separate M(II) and M(III) ions provides direct evidence that the complex has an unsymmetrical (trapped-valence) ground state rather than one in which the electrons are symmetrically delocalized. This assumption is incorrect. A complex which has a symmetrical ground state will have two accessible unsymmetrical photoionized states owing to electron relaxation in the strong field of the core hole. For a range of values of binding energy differences and electron coupling parameters, the photoionized states will be very nearly localized and the peak separation for a complex with delocalized ground state will be close to that for isolated M(II) and M(III) ions. The appearance of two M binding energies is thus not in itself evidence for electronic ground-state asymmetry in a mixed-valence compound. A model is proposed from which quantitative predictions are made.

Contribution of strong interactions to the wings of hydrogen lines broadened by the charged particles in plasmas

The adiabatic theory applied in a reference system rotating with the perturbing field is used to describe the interaction between a hydrogen atom and a particle with charge Z pe . The time development operator T( t) obtained is exact for the no-quenching dipolar term to which the weak interactions are reducible. We have shown that this solution constitutes a good approximation for the treatment of the strong interactions which involve in addition the no-quenching quadrupolar term and the dipolar term connecting states with different principal quantum numbers. For the first well separated hydrogen lines ( n ⩽ 4) and the usual plasma spectroscopy temperatures ( T ≅ 10 4°K), it is found that the non-adiabatic effect does not exceed a few per cent. Within the framework of the one perturber approximation, the correlation function of the line wings is expressed by means of the phase shift and the intensity of the various components. These two parameters are time-dependent through the rotation angle φ ( t) and the instantaneous scalar distance R ( t) of the perturber with respect to the radiating atom. As an example, the detailed numerical calculation has been performed for the Lyman-α line. In addition to an increase of the broadening effect, we note the striking asymmetry effect due to the strong electron interactions. In the intermediate spectral region, the asymmetry favours the red wing and must be added to that coming from the ions. Farther into the line wings, where the central component no longer contributes, the electron asymmetry tends to change sign and to cancel the ion asymmetry partially. Comparison has been made of our theoretical results with the theoretical and experimental results given by other authors. Particularly satisfactory agreement has been obtained with the experimental data given by Elton and Griem for the Lyman-α red wing ( N = 3·6 × 10 17 cm -3, T = 2·04 × 10 4°K). The same is true with the experimental data of Boldt and Cooper ( N = 8·4 × 10 16 cm -3, T = 1·22 × 10 4°K) if the electron density is assumed to be lower.

Pyruvate Carboxylase from Chicken Liver: MAGNETIC RESONANCE STUDIES OF THE EFFECT OF SUBSTRATES AND INHIBITORS ON THE ENVIRONMENT OF THE BOUND MANAGANESE

Abstract Electron paramagnetic resonance spectra have been recorded for solutions of pyruvate carboxylase from chicken liver in the presence and absence of various ligands. The EPR spectra show that the intrinsic Mn(II) of the enzyme occupies a site of moderate electronic asymmetry. The symmetry of the coordination sphere of this Mn(II) is not influenced upon formation of complexes with substrates and inhibitors of the transcarboxylation partial reaction catalyzed by this enzyme. However, the electron spin relaxation time of the Mn(II), as reflected in the widths of the spectral lines, is very sensitive to the presence of substrates and inhibitors of the transcarboxylation partial reaction. Formation of enzyme-substrate or enzyme-inhibitor complexes causes a narrowing of individual lines in the spectrum, with oxalate and fluoropyruvate giving the greatest effect. Changes in the line widths of signals in the EPR spectrum of the bound Mn(II) correlate with changes in the nuclear spin relaxation time of solvent protons observed on formation of these complexes (Mildvan, A.S., Scrutton, M.C., and Utter, M.F. (1966) J. Biol. Chem. 241, 3488–3498). Both effects appear to relate to the degree of accessibility of bulk solvent to the vicinity of the bound Mn(II) with narrower EPR signals, and longer relaxation times for solvent protons, indicating decreased solvent accessibility to the Mn(II). Interaction of the biotinyl residues of pyruvate carboxylase with avidin causes broadening of the EPR spectra for the enzyme and its various complexes in accord with the prior observation of shortened solvent relaxation times in these complexes (Scrutton, M.C., and Mildvan, A.S. (1968) Biochemistry 7, 1490–1505). Thus, binding of avidin to pyruvate carboxylase appears to facilitate entry of bulk solvent to the vicinity of the Mn(II). Paramagnetic effects on the nuclear spin relaxation rates for the methyl protons of pyruvate have been measured at two frequencies. The data indicate that in the pyruvate carboxylase-pyruvate complex the methyl protons of this substrate are separated by 6 to 7 A from the bound Mn(II). The dissociation constant for the enzyme-pyruvate complex was estimated at 4 to 7 mm by equilibrium dialysis experiments, thus eliminating the possible presence of more tightly bound pyruvate molecules which would exchange slowly on the time scale of the nuclear magnetic resonance measurements. The EPR and NMR measurements lead to the conclusion that substrates and inhibitors of pyruvate carboxylase are bound near to the site of the Mn(II), but the data fail to support the previously suggested direct binding of these molecules to the Mn(II) (Mildvan, A.S., and Scrutton, M.C. (1967) Biochemistry 6, 2978–2994).

Contributions of second-class currents to hyperon decays

Recent measurements of the electron asymmetry of Σ−n beta-decay and that of eν correlation and asymmetries of Λp decay are analysed including pseudotensor andq2-dependent form factors. The result is compared with Wilkinson’s measurement of pseudotensor contributions in beta-decay of mirror nuclei, assuming someSU3 structure of a second-class current. Possible consequences of octet and decuplet representations of the second-class axial vector current are discussed.

Measurement of the electron asymmetry parameter in the decay of polarised Σ − hyperons

We wish to report on a measurement made at the Rutherford Laboratory of the electron asymmetry parameter in the decay Σ − → ne − ν using counters and wire spark chambers. Polarised Σ − were produced in the reaction π −p → Σ −K + at an incident momentum of 1.13 GeV/ c. The mean Σ − polarisation for detected events was P Σ − = −0.32 ± 0.11. The value obtained for the electron asymmetry parameter was α e =+0.39 −0.53 +1.9 based on 43 events. This yields a value for the ratio of axial vector to vector coupling constants for this decay of g A/ g V = −0.4 −1.5 +0.52. The Cabibbo prediction for this decay is +0.3. We use the sign convention that g A g V for neutron beta decay is −1.23.

Asymmetry in inelastic electron-polarized proton scattering

We have estimated the electron asymmetry induced by final electromagnetic interaction in inelastic scattering on a polarized target near the Δ(1236 MeV) resonance. The nucleon and the Δ-intermediate states only are considered. Unexpectedly, the nucleon contribution remains dominant for almost all energies. For incident energies larger than 5 GeV a maximum effect around 1% is found.

Up-Down Asymmetry in Inelastic Electron—Polarized-Proton Scattering

Up-Down Asymmetry in Inelastic Electron—Polarized-Proton Scattering

Conformation of cytochromes: IV. Conformational homology of functionally homologous cytochromes c

The conformational homology of functionally homologous cytochromes c from horse, beef, tuna, turkey, pigeon and moth has been investigated by comparison of the circular dichroism (CD) spectra of each preparation in both oxidation states of iron and in the wavelength region 600-185 mμ at pH 6.8. In the oxidized state all preparations exhibit similar dichroic features with only small variations in the relative magnitudes of various extrema, except for the aromatic circular dichroism curve for tuna cytochrome c. The preparations in the reduced state of iron also exhibit comparable dichroic spectra, both in the region of the Soret transition and the intrinsic absorption region. The CD patterns for the reduced cytochromes in the α-β absorption region, however, exhibit deviations suggestive of small but distinct differences in the electronic asymmetry of the prosthetic groups, especially of the porphyrin moiety, possibly because of differences in the electronically coupled chromophores. A gross conformational homology among various mammalian-type cytochromes c has, therefore, been suggested. The dichroic differences in the case of tuna cytochrome c have been imputed to be a reflection of an unusually asymmetric environment of the residue at position 33 of the polypeptide chain. The intrinsic CD curves above 200 mμ for all the preparations in both valence states of heme iron exhibit features characteristic of the presence of α-helical structures in the molecule. Below 200 mμ, however, the dichroic curves exhibit a single positive maximum at about 194 mμ and a definite minimum at 190 mμ. The former feature is usually associated with systems containing β-structure. The presence of a minimum at about 190 mμ, when taken in conjunction with the characterizing features for α-helical models (a large positive maximum at this wavelength), indicates the absence of α-helically organized structure in the molecule. An analysis of the conformation of the protein moiety in terms of proportions of reference model conformations (α-helix, β-structure and random coil) and based on the recently developed isodichroic method 24 confirms the low α-helical content of various cytochromes and further demonstrates the gross polypeptide conformational homology for various functionally homologous preparations.

East-west asymmetry and charge sign ratio of primary cosmic-ray electrons at 8.3 GV rigidity cut-off

East-west asymmetry and charge sign ratio of primary cosmic-ray electrons at 8.3 GV rigidity cut-off

The observation of 10–50 KeV solar flare X-rays by the OGO satellites and their correlation with solar radio and energetic particle emission

More than 70 cases have been observed of energetic solar flare X-ray bursts by large ionization chambers on the OGO satellites in space. The ionization chambers have an energy range between 10 and 50 KeV for X-rays and are also sensitive to solar protons and electrons. A study has been made of the X-ray microwave relationship, and it is found that the total energy released in the form of X-rays between 10 and 50 KeV is approximately proportional to the peak or total energy simultaneously released in the form of microwave emission. For a given burst the rise time, decay time and total duration are similar for the 10–50 KeV X-rays and the 3 to 10 cm radio emission. Roughly exponential decay phases are observed for both emissions with time constants between 1 and 10 min. All 3 or 10 cm radio bursts with peak intensity greater than 80 solar flux units are accompanied by an X-ray burst greater than 3 × 10−7 ergs cm−2 sec−1 peak intensity. The probability of detecting such X-ray events is low unless the radio spectrum extends into the centimetric range of wavelengths. The best correlation between cm-λ and energetic X-rays is observed for the first event in a flare. Subsequent structure and second bursts may not correspond even when the radio emission is rich in the microwave component. The mechanism for the energetic X-rays is shown to be bremsstrahlung probably of fast electrons on a cooler plasma. If the radio emission is assumed to be synchrotron radiation then a relationship is developed between density and magnetic field which meets the observed quantitative results. One finds, on the average, that 5 × 10−54 joules m−2 (CPS)−1 of microwave energy at the Earth are required per electron at the Sun to provide the radio emission for the various events.A strong correlation between interplanetary solar flare electrons observed by satellite and X-ray bursts is shown to exist. This correlation is weak for solar proton events. One may infer a strong propagation asymmetry for solar flare electrons along the spiral interplanetary magnetic field.

Measurement of the electron asymmetry in the leptonic decay of polarized Λ°

Measurement of the electron asymmetry in the leptonic decay of polarized Λ°

Observable Hyperfine Effects in Muon Capture by Complex Nuclei

The capture rates, $\ensuremath{\Lambda}_{\ifmmode\pm\else\textpm\fi{}}^{}{}_{}{}^{\mathrm{cap}}$, of the two hyperfine states ${F}_{\ifmmode\pm\else\textpm\fi{}}$ of the ($p\ensuremath{\mu}$) atom are, in general, expected to be different (spin dependence of muon capture). This difference depends quantitatively on the details of the interaction Hamiltonian, being maximum for an F-GT (i.e., $V\ensuremath{-}A$ type) interaction. An experimental comparison for the ($p\ensuremath{\mu}$) system appears at present difficult, but related spin-dependence effects will be exhibited by bound protons, i.e., complex nuclei. Observable hyperfine (hf) effects of this kind form the object of this paper; their theory is summarized in Sec. II. The character of such effects is dominated by the rate $R$ at which the upper hf state can be converted into the true ground state (through an $M1$ Auger process). Section III contains a detailed calculation of $R$ for all cases of practical interest, while a variety of possible experiments are discussed in Sec. IV. The considerations of this section show that ${\mathrm{F}}^{19}$ constitutes the ideal target, leading to the largest and most readily analyzable effects. We performed three experiments with this target, viz., measured (1) the time distribution of the neutral capture products, (2) the asymmetry of the decay electrons, and (3) the time distribution of the latter; these measurements are described and analyzed in Secs. V through VII. We conclude (Sec. VIII) on the basis of measurements (1) and (3) that the interaction is definitely of the F-GT (as opposed to F+GT) type, assuming that both F and GT interactions are present. Invoking independent observations on muon capture by complex nuclei, this assumption becomes redundant, and we may conclude that the universal Fermi interaction ("$V\ensuremath{-}xA$") is implied by our results. This conclusion is in agreement with recent results on muon capture in liquid hydrogen. The conversion rate observed in experiments (1) and (3) (6.1\ifmmode\pm\else\textpm\fi{}0.7 \ensuremath{\mu}${\mathrm{sec}}^{\ensuremath{-}1}$) agrees with our prediction ($R=5.8$ \ensuremath{\mu}${\mathrm{sec}}^{\ensuremath{-}1}$), which is qualitatively confirmed by experiment (2).

Annellation effects in the pyrene series and the classification of absorption spectra

The classification of absorption bands in the acene series (α, p, β-bands) was first based on the annellation effect and later on the polarization of the bands with regard to the molecular axes (L b,L a,B b,B a-bands). Both give the same result since annelation axes and molecular axes coincide. This is not so in the pyrene series. Annellation axes and molecular axes are different and it is shown that the classification of bands can be based only on the annellation effects. Moreover, the electronic asymmetry of the pyrene system is demonstrated by a striking asymmetric annellation effect. A number of higher annellated pyrenes have been synthesized: 1·-benzonaphtho-(2″·3″ :6·7)-pyrene, dinaphto-(2'·3 :1·2)-(2″·3″:6·7)-pyrene, 1·14,4·5-dibenzo-pentacene, 5·,15·16-dibenzohexacene, 6·7,16·17-dibenzoheptacene, 1·16,4·5-dibenzohexacene and 7·8,17·18-dibenzo-octacene.

Asymmetry in double Mott electron scattering for energies from 45 to 245 keV

The asymmetry of electron scattering in the energy region of 45 to 245 keV and for the angles θ 1 = θ 2 = 120° is measured using double Mott scattering on nuclei of gold.