Dimeric Fe (II, III) complex of quinoneoxime as functional model of PAP enzyme: Mössbauer, magneto-structural and DNA cleavage studies

Purple acid phosphatase, (PAP), is known to contain dinuclear Fe₂ ^?+?2,?+?3 site with characteristic Fe^?+?3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe₂ ^?+?2,?+?3 (o-NQ_CH3ox) (o-NSQ_CH3ox)₂ (CAT) H₂O]. Fe-2: [Fe^?+?3(o-NQ_CH3ox) (p-NQ_CH3ox)₂]₂ a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. ⁵⁷Fe Mössbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. ⁵⁷Fe Mössbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe^?+?3]_A and [Fe^?+?2]_B sites. The hyperfine interaction parameters are δ _A = 0.152, (ΔE _Q)_A = 0.598 mm/s with overlapping doublet at δ _B = 0.410 and (ΔE _Q)_B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe^?+?3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQ_CH3ox ligand surrounding Fe^?+?3(h.s.) state generates small field gradient indicated by quadrupole split ΔE _Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe₂ ^?+?2,?+?3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g ₁ = 4.17 and g ₂ = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe^?+?3(h.s.) configuration. SQUID data of $\chi _m^{{\rm corr}} \mbox{.T}$ were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = ?13.5 cm^???1 with an agreement factor of R = 1.89 × 10^???5). The lower J value of antiferromagnetic exchange leads to Fe⁺³μ-(OH) Fe^?+?2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe^?+?3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = ?12.4 cm^???1, g = 2.3 with R = 3.58 × 10^???5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.     

Nuclear-structure corrections to the energy spectra of ordinary and muonic deuterium

One-loop nuclear-structure-induced corrections of order (Zα)⁵ to the Lamb shift and to the hyperfine structure of deuterium are calculated. The contribution of deuteron-structure effects to the (ep)-(ed) and (μp)-(μd) isotopic shifts for the 1S–2S splitting is obtained with the aid of modern experimental data on the electromagnetic form factors for the deuteron. A comparison with the analogous contributions to the Lamb shift for ordinary and muonic hydrogen shows that the relative contribution of corrections associated with the nuclear structure increases as we go over from the hydrogen to the deuterium atom owing to the growth of the nuclear size.     

The size of the proton

The root-mean-square (rms) charge radius r _p of the proton has so far been known only with a surprisingly low precision of about 1% from both electron scattering and precision spectroscopy of hydrogen. We have recently determined r _p by means of laser spectroscopy of the Lamb shift in the exotic “muonic hydrogen” atom. Here, the muon, which is the 200 times heavier cousin of the electron, orbits the proton with a 200 times smaller Bohr radius. This enhances the sensitivity to the proton’s finite size tremendously. Our new value r _p?=?0.84184 (67) fm is ten times more precise than the generally accepted CODATA-value, but it differs by 5 standard deviations from it. A lively discussion about possible solutions to the “proton size puzzle” has started. Our measurement, together with precise measurements of the 1S–2S transition in regular hydrogen and deuterium, also yields improved values of the Rydberg constant, R _?∞??=?10,973,731.568160 (16) m^???1.     

Maximal acceleration corrections to the Lamb shift of hydrogen,deuterium and He+

The maximal acceleration corrections to the Lamb shift of one-electron atoms are calculated in a nonrelativistic approximation. They are compatible with experimental results, are in particularly good agreement with the 2S2P Lamb shift in hydrogen and reduce by ∼ 50% the experiment-theory discrepancy for the 2S2P shift in He⁺.     

Theory of the lamb shift in muonic deuterium

We present new calculation of the Lamb shift (2P _1/2 ? 2S _1/2), fine splitting of the 2P state and hyperfine splitting of the 2S state in muonic deuterium (µd) using the quasipotential method in quantum electrodynamics. The vacuum polarization, nuclear structure, and recoil effects are calculated with the account of contributions of orders α ³, α ⁴, α ⁵, and α ⁶. The obtained numerical value of the Lamb shift 202.4139 meV can be considered as a reliable estimate for the comparison with forthcoming experimental data.     

First exclusive measurements of the K − pp state populated in the pp → K + Λp reaction at 2.85 GeV

We have analyzed data of the DISTO experiment on the exclusive pp → K ^?+? Λp process at T _p ?=?2.85 GeV to search for a K ^??? pp  (?≡?X) nuclear bound state to be formed in the pp → K ^?+??+?X reaction. The deviation spectra of the K ^?+? missing-mass ΔM (K ^?+?) and Λp invariant-mass M(Λp) with selection of large-angle proton emission revealed a structure with M _X ?=?2265 ±2 MeV/c ² and Γ _X ?=?118 ±8 MeV.     

Electrical conductivity, DSC, XRD, and 7Li NMR studies of rotator crystals n-C21H43COOLi x K(1 − x) (0.33 ≤ x ≤ 0.50), n-C m H(2m + 1)COOLi, and n-C m H(2m + 1)COOK (m = 13, 15, 17, 19, and 21)

Differential scanning calorimetry (DSC) thermograms, X-ray diffraction (XRD) analysis, electrical conductivity (σ), and ⁷Li NMR spectroscopy characterization of n-C _m H_(2m?+?1)COOM solids (M = Li, Na, K; m?=?13, 15, 17, 19, 21) and mixed crystals n-C₂₁H₄₃COOLi _x K_(1???x) (0.25?≤?x?≤?0.75) was performed as a function of temperature. DSC thermograms of n-C _m H_(2m?+?1)COOM revealed several solid-solid phase transitions with large entropy changes. Electrical conductivity studies established that n-C _m H_(2m?+?1)COOLi crystals are poor electrical conductors. In contrast, n-C _m H_(2m?+?1)COOK salts were found to have σ values of 10^???7–10^???8 S·cm^???1. Since the crystal structures and phase-transition temperatures of both n-C _m H_(2m?+?1)COOLi and n-C _m H_(2m?+?1)COOK crystals were similar, they were able to form mixed crystals with the structure n-C _x H_(2m?+?1)COOLi _x K_(1???x). DSC thermograms of the mixed crystals showed a small entropy change at the melting point (ΔS _mp?<?13 J K^???1 mol^???1), in addition, large ΔS values at the solid-solid phase transition temperature. The σ values obtained for mixed crystals were roughly one order of magnitude greater than those determined for n-C₂₁H₄₃COOK crystals. ⁷Li NMR spectra of the mixed crystals recorded at various temperatures suggested that the self-diffusion of Li^?+? ions was excited in the highest-temperature solid phase. Based on these results, we have classified these mixed crystals as rotator crystals.     

Helium irradiation-induced defects in deformed 316L stainless steel

Well-annealed 316L stainless steel was first cold rolled to 10% and 20% reductions in thickness and then irradiated by 50 keV He⁺ to a dose of 1 × 10²⁰ He⁺/m² at room temperature. Thermal desorption spectroscopy was used to investigate the helium desorption behaviour at different helium trapping states. The results showed that high-density dislocations had stronger inhibitory effect for helium desorption at temperatures from 800 to 1200 K. Positron annihilation Doppler broadening spectroscopy measurements were used to investigate the distribution of helium irradiation-induced defects. The S–E and ΔS–E plots clearly demonstrated that the helium irradiation-induced defects were trapped and restricted in motion by dislocations. The interaction between dislocations and helium irradiation-induced defects in deformed 316L stainless steel was investigated.     

Spins,moments and charge radii in the isotopic series181Hg-191Hg

The hyperfine structure splitting and the isotope shift in the (6 s^{2 1}S₀ - 6s 6p³P₁,λ=2,537 Å) line of very neutron deficient Hg isotopes were determined by the β radiation detected optical pumping method (β-RADOP). In addition, nuclear magnetic resonance was observed in the atomic ground state. The results are Mean-square nuclear charge radii are calculated. Interpreting the sudden change of nuclear radius between¹⁸⁷Hg and¹⁸⁵Hg δ〈r²〉^187,185=0.42(5)fm² as oblate-prolate shape transition, one obtains δ〈β²〉 =0.054(5).     

Searches for Lorentz violation in 3He/129Xe clock comparison experiments

We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized ³He or ¹²⁹Xe samples with a SQUID as magnetic flux detector. Characteristic spin precession times $T_2^\ast$ of up to 115 h were measured in low magnetic fields (about 1 μT) and in the regime of motional narrowing. With the detection of the free precession of co-located ³He/¹²⁹Xe nuclear spins (clock comparison), the device can be used as ultra-sensitive probe for non-magnetic spin interactions, since the magnetic dipole interaction (Zeeman-term) drops out in the weighted frequency difference, i.e., Δω?=?ω _He ???γ _He /γ _Xe ·ω _Xe . We report on searches for Lorentz violating signatures by monitoring the Larmor frequencies of co-located ³He/¹²⁹Xe spin samples as the laboratory reference frame rotates with respect to distant stars (sidereal modulation).     

KAIUM at DAΦNE?

The possibility of producing and detecting at DAΦNE a new hydrogen isotope formed by a (K ^?+? e ^???) bound system (Kaium) is addressed, considering a dedicated, and relatively simple experiment of short duration. If Kaium will be detected, it could in perspective pave the way for a series of highly sophisticated experiments focused on the precision measurement of several observables, as the K ^?+????K ^??? mass difference, strictly related to CPT invariance.     

Phase transition and proton exchange in 1,3-diazinium hydrogen chloranilate monohydrate

In the hydrate crystal of 1:1 salt with 1,3-diazine and chloranilic acid (H₂ca), (1,3-diazineH)·H₂O·Hca, an unique hydrogen-bonded molecular aggregate is formed. There exists proton disorder in the N–H...O hydrogen bond between 1,3-diazinium ion and water (H₂O) of crystallization. In order to reveal dynamic aspect of this disorder, ³⁵Cl NQR measurements were conducted. Two resonance lines observed at 35.973 and 35.449 MHz at 321 K split into four lines below T _c?=?198 K clearly showing occurrence of a solid–solid phase transition; 36.565, 36.357, 36.011, 35.974 MHz at 77 K. Temperature dependence of spin-lattice relaxation time T ₁ in high-temperature phase was observed to obey an Arrhenius-type relation with the activation energy of 8.5 kJ mol^???1. This result leads to the conclusion that proton exchange in the N–H...O hydrogen bond takes place in the high-temperature phase. Specific heat measurements by DSC resulted in the transition entropy ΔS?=?1.3 J K^???1 per 1 mole [(1,3-diazineH)·H₂O·Hca]₂ which is far less than 2R ln2 = 11.5 J K^???1 mol^???1. It is expected that proton exchange in the two hydrogen bonds within the aggregate does not occur independently but concertedly with strong correlation in the high-temperature phase.     

Isotope shift of182Hg and an update of nuclear moments and charge radii in the isotope range181Hg-206Hg

The technique of collinear fast-beam laser spectroscopy has been used to measure the isotope shifts of the even-even isotopes of Hg (Z=80) in the mass range 182≤A≤198 at the on-line mass separator ISOLDE at CERN. The atomic transition studied (6s 6p ³ P ₂- 6s7s ³ S ₁,λ=546.1 nm) starts from a metastable state, which is populated in a quasi resonant charge transfer process. The resulting changes in nuclear mean square charge radii show clearly that¹⁸²Hg follows the trend of the heavier, even, weakly oblate isotopes. Correspondingly the huge odd-even shape staggering in the light Hg isotopes continues and the nuclear shape staggering and shape coexistence persists down to the last isotope investigated,¹⁸¹Hg. An update of isotope shift and hyperfine structure data for^181–206Hg is given, with a revised evaluation of the differences in nuclear mean square charge radii and of spectroscopic quadrupole moments.     

2-D electron spin transient nutation spectroscopy of Lanthanoid ion Eu2+(8S7/2) in a CaF2 single crystal on the basis of FT-pulsed electron spin resonance spectroscopy: Transition moment spectroscopy

This work demonstrates the usefulness of pulsed electron spin resonance (ESR)-based two-dimensional electron spin transient nutation (2-D ESN) spectroscopy for complete assignments of complicated fine-structure hyperfine ESR spectra including hyperfine forbidden transitions from electronic and nuclear high-spin systems. The 2-D ESN spectroscopy is termed transition moment spectroscopy as spectra are acquired as a function of transition moment instead of transition energy used in conventional spectroscopy. We have applied the novel spectroscopic technique to Eu²⁺ ion (S=7/2,I=5/2), which has two isotopes (¹⁵¹Eu [47.9%] and¹⁵³Eu [52.1%]), in a CaF₂ single crystal as a model system. We have completely identified the complicated fine-structure hyperfine ESR spectra by invoking the spectral simulation of the 2-D ESN spectra on the basis of transition moment analyses. The analyses are based on exact numerical calculations of the transition moments as well as a perturbation-based analytical approach combined with reduced rotation matrices for the nuclear part of the transition moment. This is the first example of the spectral simulation for 2-D ESN spectra including the hyperfine allowed and forbidden transitions in high-spin systems. In addition, we have made simulation of the fine-structure forbidden transitions, which reproduces the angular variations of the observed spectra at liquid helium temperatures.     

Search for kaonic nuclear state, K − pp, in the p + p → X + K + reaction with FOPI

We search for the most fundamental kaonic nuclear state, K ^??? pp by employing the reaction p?+?p→K ^?+??+?X at 3.0 GeV incident beam energy. The experiment makes use of the SIS-18 synchrotron and the ~4π acceptance FOPI apparatus in the cave-B at the GSI, Darmstadt, Germany and aims to collect full kinematics information of the reaction. We look for a signature of the X (?≡?K ^??? pp) in both missing mass spectrum by measuring K ^?+?, and invariant mass spectrum by measuring decay particles; X?→?Λ?+?p. The experiment is planned to take place in 2009.     

Cluster Model Analysis of Pion Elastic and Inelastic Scattering from 12C

Angular distributions of differential cross sections for the ¹²C(π ^±, π ^±)¹²C and ¹²C(π ^±, π ^±)¹²C^* reactions at pion kinetic energy ranging from 50 to 260 MeV have been analyzed with the 3α-particle model of ¹²C. The model provides good fits to a wide range of data. Differential cross sections for inelastic transitions to the (2^?+?; 4.44 MeV) and (3^???; 9.64 MeV) states in ¹²C are computed and the deformation lengths δ ₂ and δ ₃ are extracted. It is found that the extracted deformation lengths are sensitive to the nuclear model used and similar to the corresponding values found with other probes and nuclear models.     

Electrical conductivity and local structure of lithium tin iron vanadate glass

A relationship between electrical conductivity (σ) and local structure of 15Li₂O·10Fe₂O₃·xSnO₂·(70–x)V₂O₅·5P₂O₅ glass (x = 0–20 mol%), abbreviated as xLFSVP glass, was investigated by ⁵⁷Fe- and ¹¹⁹Sn-Mössbauer spectroscopies, differential thermal analysis (DTA) and dc-four probe method. A small increase in quadrupole splitting (Δ) for Fe^III was observed from 0.70 to 0.74_{± 0.02} mm s^???1 with an increase of “x”, whereas isomer shift (Δ) values of 0.40_±0.01 mm s^???1 were independent of “x”. This result suggests that local distortion of Fe^IIIO₄ tetrahedra was slightly increased in SnO₂-containing vanadate glasses, which was reflected as an increase in glass transition temperature (T_g) from 266 to 285_±5 °C. A slope of 675 K / (mm s^???1) obtained in ‘T_g vs. Δ plot’ proved that Fe^III occupied the site of network former (NWF). An isothermal annealing of 10LFSVP glass at 500 °C for 100 min resulted in a marked decrease of Δ from 0.72 to 0.56_±0.02 mm s^???1, indicating that local distortion of FeO₄ tetrahedra was reduced by the structural relaxation of 3D-network. In contrast, identical δ and Δ values of 0.07_±0.01 and 0.53_±0.02 mms^???1, respectively, were observed in ¹¹⁹Sn-Mössbauer spectra of 10LFSVP glass before and after the annealing. These results indicate that Sn^IVO₆ octahedra are loosely bound in the glass matrix as a network modifier (NWM). A marked increase in σ from 7.4 × 10^???7 to 9.1 × 10^???3 S cm^???1 was observed in 20LFSVP glass after the isothermal annealing, indicating that structural relaxation of 3D-network evidently causes a marked increase in σ.     

Nuclear moments and charge radii of107–111in determined by laser spectroscopy

Collinear fast beam laser spectroscopy has been used to measure the hyperfine structure and isotope shift in the atomic 5s ² 5p ² P _3/2-5s ² 6s ² S _1/2 transition (λ=451 nm) of^107–111In. Secondary beams of neutron deficient indium isotopes were prepared at the GSI on-line mass separator following fusion evaporation reactions. Magnetic dipole moments and electric quadrupole moments have been determined. The isotope shifts are discussed in terms of the change of the mean square nuclear charge radii and compared with the droplet model predictions and the deformation values calculated from the quadrupole moments.     

Nuclear Polarization Effects in Muonic Atoms

We illustrate how nuclear polarization corrections in muonic atoms can be formally connected to inelastic response functions of a nucleus. We first discuss the point-nucleon approximation and then include finite-nucleon-size corrections. As an example, we compare our ab-initio calculation of the third Zemach moment in μ ⁴He⁺ to previous phenomenological results.     

Nuclear matter sizes and isoscalar octupole transition rates of204,206,208Pb from 104 MeV α-particle scattering

Differential cross sections for elastic and inelastic scattering of 104 MeVα-particles from^204,206,208Pb were measured with high angular accuracy. The experimental results were analysed on the basis of a semimicroscopic folding model in order to determine the matter distributions at the nuclear surface and the transition densities. Using phenomenological parametrizations of the densities the analyses of elastic scattering yield rms radii of 〈r ²〉^1/2=5.55±0.06 (²⁰⁴Pb), 5.57±0.06 (²⁰⁶Pb), 5.63±0.05 (²⁰⁸Pb) fm. Various sensitivities affecting the results were studied. From the inelastic cross sections for the 3 ₁ ^? -states octupole transition probabilities and transition radii were derived by using different methods proposed in literature.