Population Of Spin States Research Articles

Nuclear Data Sheets for A=244

Available information pertaining to the nuclear structure of ground and excited states for all known nuclei with mass numbers A=244 have been compiled and evaluated. The adopted level and decay schemes, as well as the detailed nuclear properties and configuration assignments based on experimental data are presented for these nuclides. When there are insufficient data, expected values from systematics of nuclear properties and/or theoretical calculations are quoted. Unexpected or discrepant experimental results are also noted. Information provided in 244U is tentative as it is from the possible production in the study of 1960Di03 of debris of the first large-scale thermonuclear test (Ivy Mike) of November 1, 1952 in the Pacific Ocean. No new experimental data are available for 244Np with the information for g.s Jπ considered tentative. Experimental work is needed for 244Np as theoretical work and systematics along with the Gallagher-Moszkowski rules that suggest either Jπ=2+ or 7−. Jπ = (7−) g.s has been considered by the evaluator due to population of high spin states in the beta decay study. In 244Pu, a new K isomer was identified and in addition rotational bands built on the isomer have been observed via the deep inelastic excitation. However, there has been no new measurements since the last evaluation to determine the ratio of the energy levels of the first 4+ state to the first 2+ state (E4+/E2+) in 244Pu that showed a discrepancy from a typical value of 3.333. In the current evaluation, the evaluator has considered the 110γ measured in the 244Np β-decay questionable. Further research into the determination of the gammas depopulating these levels is necessary. In 244Am, specifically the (d,p) transfer reaction and in the (n, γ) secondary γ's, there are a large number of gammas that are unplaced. Since its last measurement in 1966, the electron capture dataset has been updated with a tentative partial level scheme for 244Cm which also provided a new half-life measurement for 244Bk. In 244Fm, a fusion evaporation experiment measured the half-life and provided upper limits for the SF, α decay, and ε branching. A summary and compilation of the discovery of various isotopes in this mass region is given in 2013Fr02 (244Np, 244Pu, 244Am, 244Cm, 244Bk, and 244Cf), 2011Me01 (244Es), and 2013Th02 (244Fm). This work supersedes the 2003 evaluation by Y.A. Akovali (2003Ak04).

Coulomb Correlations Intertwined with Spin and Orbital Excitations in LaCoO3

We carried out temperature-dependent (20-550K) measurements of resonant inelastic x-ray scattering on LaCoO_{3} to investigate the evolution of its electronic structure across the spin-state crossover. In combination with charge-transfer multiplet calculations, we accurately quantified the renomalized crystal-field excitation energies and spin-state populations. We show that the screening of the effective on-site Coulomb interaction of 3d electrons is orbital selective and coupled to the spin-state crossover in LaCoO_{3}. The results establish that the gradual spin-state crossover is associated with a relative change of Coulomb energy versus bandwidth, leading to a Mott-type insulator-to-metal transition.

Correlated oxygen displacements and phonon mode changes in LaCoO3 single crystal

X-ray diffraction and inelastic X-ray scattering studies have been performed across the spin (~100K) and semiconductor-metal (~500K) transitions in LaCoO3 single crystals. The quadratic increase with temperature of the oxygen displacement parameters parallel and perpendicular to the Co-O bond has been correlated with softening of the TO2 and hardening of the TO1 phonon branches along the [0 ξ ξ] high symmetry direction. The latter effect can be associated with the weakening of the Co-O bond strength derived from the increase of Co-O bond length and angle as expected upon increasing the high spin state population of the system with temperature.

Active Site Structures of CYP11A1 in the Presence of Its Physiological Substrates and Alterations upon Binding of Adrenodoxin.

The rate-limiting step in the steroid synthesis pathway is catalyzed by CYP11A1 through three sequential reactions. The first two steps involve hydroxylations at positions 22 and 20, generating 20(R),22(R)-dihydroxycholesterol (20R,22R-DiOHCH), with the third stage leading to a C20-C22 bond cleavage, forming pregnenolone. This work provides detailed information about the active site structure of CYP11A1 in the resting state and substrate-bound ferric forms as well as the CO-ligated adducts. In addition, high-quality resonance Raman spectra are reported for the dioxygen complexes, providing new insight into the status of Fe-O-O fragments encountered during the enzymatic cycle. Results show that the three natural substrates of CYP11A1 have quite different effects on the active site structure, including variations of spin state populations, reorientations of heme peripheral groups, and, most importantly, substrate-mediated distortions of Fe-CO and Fe-O2 fragments, as revealed by telltale shifts of the observed vibrational modes. Specifically, the vibrational mode patterns observed for the Fe-O-O fragments with the first and third substrates are consistent with H-bonding interactions with the terminal oxygen, a structural feature that tends to promote O-O bond cleavage to form the Compound I intermediate. Furthermore, such spectral data are acquired for complexes with the natural redox partner, adrenodoxin (Adx), revealing protein-protein-induced active site structural perturbations. While this work shows that Adx has an only weak effect on ferric and ferrous CO states, it has a relatively stronger impact on the Fe-O-O fragments of the functionally relevant oxy complexes.

Spin-State-Controlled Photodissociation of Iron(III) Azide to an Iron(V) Nitride Complex.

The generation of iron(V) nitride complexes, which are targets of biomimetic chemistry, is reported. Temperature-dependent ion spectroscopy shows that this reaction is governed by the spin-state population of their iron(III) azide precursors and can be tuned by temperature. The complex [(MePy2 TACN)Fe(N3 )]2+ (MePy2 TACN=N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) exists as a mixture of sextet and doublet spin states at 300 K, whereas only the doublet state is populated at 3 K. Photofragmentation of the sextet state complex leads to the reduction of the iron center. The doublet state complex photodissociates to the desired iron(V) nitride complex. To generalize these findings, we show results for complexes with cyclam-based ligands.

Magnetism and the spin state in cubic perovskite CaCoO3 synthesized under high pressure

Cubic $\mathrm{SrCo}{\mathrm{O}}_{3}$ with an intermediate spin state can only be stabilized by high pressure and high temperature (HPHT) treatment. It is metallic and ferromagnetic with the highest Curie temperature of the transition-metal perovskites. The chemical substitution by Ca on Sr sites would normally lower crystal symmetry from cubic to orthorhombic as seen in the perovskite family of $\mathrm{Ca}M{\mathrm{O}}_{3}$ ($M={M}^{4+}$ of transition metals, $\mathrm{G}{\mathrm{e}}^{4+}, \mathrm{S}{\mathrm{n}}^{4+}$, and $\mathrm{Z}{\mathrm{r}}^{4+}$) at room temperature. This structural change narrows the bandwidth, so as to further enhance the Curie temperature as the crossover to the localized electronic state is approached. We report a successful synthesis of the perovskite $\mathrm{CaCo}{\mathrm{O}}_{3}$ with a HPHT treatment. Surprisingly, $\mathrm{CaCo}{\mathrm{O}}_{3}$ crystallizes in a simple cubic structure that remains stable down to 20 K, the lowest temperature in the structural study. The new perovskite has been thoroughly characterized by a suite of measurements including transport, magnetization, specific heat, thermal conductivity, and thermoelectric power. Metallic $\mathrm{CaCo}{\mathrm{O}}_{3}$ undergoes two successive magnetic transitions at 86 K and 54 K as temperature decreases. The magnetization at 5 K is compatible with the intermediate spin state ${t}^{4}{e}^{1}$ of $\mathrm{C}{\mathrm{o}}^{4+}$ at the octahedral site. The thermal expansion of the Co-O bond length indicates that the population of high spin state ${t}^{3}{e}^{2}$ increases for $Tg100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The shortest Co-O bond length in cubic $\mathrm{CaCo}{\mathrm{O}}_{3}$ is responsible for delocalizing electrons in the ${\ensuremath{\pi}}^{*}$-band and itinerant-electron ferromagnetism at $Tl54\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. A comprehensive comparison between $\mathrm{SrCo}{\mathrm{O}}_{3}$ and $\mathrm{CaCo}{\mathrm{O}}_{3}$ and the justification of their physical properties by first-principles calculation have also been made in this report. Partially filled ${\ensuremath{\pi}}^{*}$ and ${\ensuremath{\sigma}}^{*}$ bands would make $\mathrm{CaCo}{\mathrm{O}}_{3}$ suitable to study the Hund's coupling effect in a metal.

New Possibilities for Magnetic Control of Chemical and Biochemical Reactions.

Chemistry is controlled by Coulomb energy; magnetic energy is lower by many orders of magnitude and may be confidently ignored in the energy balance of chemical reactions. The situation becomes less clear, however, when reaction rates are considered. In this case, magnetic perturbations of nearly degenerate energy surface crossings may produce observable, and sometimes even dramatic, effects on reactions rates, product yields, and spectroscopic transitions. A case in point that has been studied for nearly five decades is electron spin-selective chemistry via the intermediacy of radical pairs. Magnetic fields, external (permanent or oscillating) and the internal magnetic fields of magnetic nuclei, have been shown to overcome electron spin selection rules for pairs of reactive paramagnetic intermediates, catalyzing or inhibiting chemical reaction pathways. The accelerating effects of magnetic stimulation may therefore be considered to be magnetic catalysis. This type of catalysis is most commonly observed for reactions of a relatively long-lived radical pair containing two weakly interacting electron spins formed by dissociation of molecules or by electron transfer. The pair may exist in singlet (total electron spin is zero) or triplet (total spin is unity) spin states. In virtually all cases, only the singlet state yields stable reaction products. Magnetic interactions with nuclear spins or applied fields may therefore affect the reactivity of radical pairs by changing the angular momentum of the pairs. Magnetic catalysis, first detected via its effect on spin state populations in nuclear and electron spin resonance, has been shown to function in a great variety of well-characterized reactions of organic free radicals. Considerably less well studied are examples suggesting that the basic mechanism may also explain magnetic effects that stimulate ATP synthesis, eliminating ATP deficiency in cardiac diseases, control cell proliferation, killing cancer cells, and control transcranial magnetic stimulation against cognitive deceases. Magnetic control has also been observed for some processes of importance in materials science and earth and environmental science and may play a role in animal navigation. In this Account, the radical pair mechanism is applied as a consistent explanation for several intriguing new magnetic phenomena. Specific examples include acceleration of solid state reactions of silicon by the magnetic isotope 29Si, enrichment of 17O during thermal decomposition of metal carbonates and magnetic effects on crystal plasticity. In each of these cases, the results are consistent with an initial one-electron transfer to generate a radical pair. Similar processes can account for mass-independent fractionation of isotopes of mercury, sulfur, germanium, tin, iron, and uranium in both naturally occurring samples and laboratory experiments. In the area of biochemistry, catalysis by magnetic isotopes has now been reported in several reactions of DNA and high energy phosphate. Possible medical applications of these observations are pointed out.

Coherent evolution of singlet spin states in PHOTO-PHIP and M2S experiments.

A consistent theoretical description of the spin dynamics underlying photo-PHIP (para-hydrogen induced polarization) experiments is given and validated experimentally: spectra from zero-quantum coherence (ZQC) "in-phase" and "out-of-phase" were obtained and evolution of ZQCs and the population of singlet spin state was tracked and modeled. Data from recent literature [O. Torres et al., J. Am. Chem. Soc., 2014] are reinterpreted. Advantages of using M2S sequences such as APSOC for detecting photo-PHIP are demonstrated. A sequence for 2D ZQ spectroscopy based on APSOC is proposed and the fundamental principles of ZQ spectroscopy are formulated. This investigation opens a new way to obtain information on the sign of J-couplings using ZQ spectroscopy. The proposed method is also useful to track the redistribution of the singlet spin population in various PHIP related experiments, which is essential for efficient polarization transfer to target nuclei.

PH-Dependent spin state population and 19F NMR chemical shift via remote ligand protonation in an iron(ii) complex.

An FeII complex that features a pH-dependent spin state population, by virtue of a variable ligand protonation state, is described. This behavior leads to a highly pH-dependent 19F NMR chemical shift with a sensitivity of 13.9(5) ppm per pH unit at 37 °C, thereby demonstrating the potential utility of the complex as a 19F chemical shift-based pH sensor.

An EPR Study of Small Magnetic Nanoparticles

Abstract Magnetic nanoparticles (MNPs) of spinel type iron oxide (of approximately 4 nm) mineralized inside the internal cavity of a mini ferritin-type protein have been investigated by means of electron magnetic resonance (EMR) spectroscopy. EMR measurements have been recorded at different temperatures in perpendicular and parallel configurations. The spectra have been interpreted using an approach based on the giant spin model. We confirm the quantum behavior of the MNPs, moreover, the thermal evolution of the spin system in terms of population of excited spin states is showed.

Synthesis of 4-Hydroxy-2,6-di(pyrazol-1-yl)pyridine, and the Spin State Behaviour of Its Iron(II) Complex Salts

Treatment of 4-hydroxy-2,6-dibromopyridine with four equivalent of deprotonated pyrazole in hot diglyme affords 4-hydroxy-2,6-di(pyrazol-1-yl)pyridine (L) in low yield. The three complex salts [FeL2]X2 (X− = BF4−, 1; X− = ClO4−, 2; X− = PF6−, 3) have been prepared, and crystallographically characterised as their methanol solvates. The solvate structures contain complexes that are fully high-spin (1 and 3), or in a mixed high:low spin state population at 150 K (2). Bulk samples of 1 and 2 obtained from methanol/diethyl ether contain a second, minor crystal phase that exhibits an abrupt spin-transition near 200 K. Recrystallisation of 1 and 2 from nitromethane/diethyl ether affords powder samples that are highly enriched in this spin-transition phase.

The origin of the antiferromagnetic behaviour of the charge-transfer compound (HMTTF)[Ni(mnt)2

The charge-transfer (HMTTF)[Ni(mnt)2] material (1) was the first mixed-stack compound reported to present ferromagnetic (FM) interactions between the donor (D) and acceptor (A) units within each mixed-stack. Despite the presence of a dominant FM interaction, its magnetic susceptibility curve, χ(T), corresponded to that of an antiferromagnetic (AFM) compound at low temperatures, a fact that was tentatively explained in terms of a FM-to-AFM magnetic transition. In this work, the First-Principles Bottom-Up procedure has been applied to rationalize the magnetic properties of 1. The results presented herein indicate the presence of up to five sizeable JAB magnetic exchange interactions (26.0, -1.7, 1.9, 0.1, and -99.3 cm(-1)) that create a complex 2D magnetic network. This magnetic topology not only produces a calculated χ(T) curve that is in excellent agreement with the experimental measurements, but also allows us to understand the magnetic behaviour of 1, in the full range of temperatures, solely in terms of the different Boltzmann population of diamagnetic and paramagnetic spin states as the temperature changes. Our data thus provide a plausible explanation for the AFM behaviour of 1 at low temperatures that does not involve a phase transition.

Reducing collective quantum state rotation errors with reversible dephasing

We demonstrate that reversible dephasing via inhomogeneous broadening can greatly reduce collective quantum state rotation errors, and observe the suppression of rotation errors by more than 21 dB in the context of collective population measurements of the spin states of an ensemble of 2.1×105 laser cooled and trapped 87Rb atoms. The large reduction in rotation noise enables direct resolution of spin state populations 13(1) dB below the fundamental quantum projection noise limit. Further, the spin state measurement projects the system into an entangled state with 9.5(5) dB of directly observed spectroscopic enhancement (squeezing) relative to the standard quantum limit, whereas no enhancement would have been obtained without the suppression of rotation errors.

Using resonance Raman cross-section data to estimate the spin-state populations of cytochromes P450

The cytochromes P450 (CYPs) are heme proteins responsible for the oxidation of xenobiotics and pharmaceuticals and the biosynthesis of essential steroid products. In all cases, substrate binding initiates the enzymatic cycle, converting ferric low spin (LS) to high-spin (HS), with the efficiency of the conversion varying widely for different substrates, so documentation of this conversion for a given substrate is an important objective. Resonance Raman (rR) spectroscopy can effectively yield distinctive frequencies for the ν3 "spin state marker" bands. Here, employing a reference cytochrome P450 (CYP101), the intensities of the ν3 modes (ILS) and (IHS) relative to an internal standard (sodium sulfate) yield relative populations for the two spin states; i.e., a value of 1.24 was determined for the ratio of the relative cross sections for the ν3 modes. Use of this value was then shown to permit a reliable calculation of relative populations of the two spin states from rR spectra of several other Cytochromes P450. The importance of this work is that, using this information, it is now possible to conveniently document by rR the spin state population without conducting separate experiments requiring different analytical methods, instrumentation and additional sample.

Elastic and anelastic anomalies due to spin-state transitions in orthorhombic perovskite from isoelectronic behavior of Co3+ and Fe2+

Elastic and anelastic anomalies associated with spin-state transitions of Co3+ in NdCoO3 and GdCoO3 perovskites with the Pnma structure have been investigated using resonant ultrasound spectroscopy (RUS) at high frequencies (0.1–1.5 MHz) and dynamic mechanical analysis (DMA) at low frequencies (0.1–50 Hz). Analysis of spontaneous strains related to octahedral tilting transitions and calculated using lattice parameter data from the literature show that the sequence of changing spin states with increasing temperature, low spin → low spin + high-spin → intermediate spin, is accompanied by significant variations in shear strain due to changes in ionic radius of the Co3+ ions. This implies significant spin state/strain coupling, which, in turn, leads to renormalization of the shear modulus. In NdCoO3 the shear strains are small, so the coupling is weak and the shear modulus increases with falling temperature in a manner that scales semi-quantitatively with an empirical spin order parameter. In GdCoO3 the shear strains are much greater and softening of the shear modulus by up to ~35% in the low-spin + high-spin field arises through the influence of both the spin state/strain coupling and the order parameter susceptibility. Enhanced acoustic dissipation is also observed in the low-spin + high-spin field and is tentatively attributed to mobility of transformation twin walls, which are likely to have structures modified by changes in local Co3+ spin-state populations. Co3+ is isoelectronic with Fe2+ and, although the spin-state transitions observed in cobaltate and silicate perovskites are not the same, the large shear strains associated with octahedral tilting in (Mg,Fe)SiO3 at high pressures suggest that the effects of a high-spin → intermediate-spin transition of Fe2+ would be closely analogous to those shown by GdCoO3. A spin-state transition of Fe3+ in silicate perovskite would have a similar influence, due to the change in radius and its influence on octahedral tilting via the Goldschmidt tolerance factor.

Ultrafast time resolved x-ray diffraction, extended x-ray absorption fine structure and x-ray absorption near edge structure

Ultrafast time resolved x-ray absorption and x-ray diffraction have made it possible to measure, in real time, transient phenomena structures and processes induced by optical femtosecond pulses. To illustrate the power of these experimental methods, we present several representative examples from the literature. (I) Time resolved measurements of photon/electron coupling, electron/phonon interaction, pressure wave formation, melting and recrystallization by means of time resolved x-ray diffraction. (II) Ultrafast x-ray absorption, EXAFS, for the direct measurement of the structures and their kinetics, evolved during electron transfer within molecules in liquid phase. (III) XANES experiments that measure directly pathway for the population of high spin states and the study of the operating mechanism of dye activated TiO2 solar cell devices. The construction and use of novel polycapillary x-ray lenses that focus and collimate hard x-rays efficiently are described.

Neutron bound beta-decay: BOB

An experiment to observe the bound beta-decay (BOB) of the free neutron into a hydrogen atom and an electron anti-neutrino is described. The hyperfine spin state population of the monoenergetic hydrogen atom yields the neutrino left-handedness or possible right-handed admixture as well as possible small scalar and tensor contributions to the weak force. The BOB H(2s) hyperfine states can be separated with a Lamb-Shift Spin Filter. These monoenergetic H(2s) atoms are ionised into H− by charge exchanging within an argon cell. These ions are then separated using an adaptation of a MAC-E Filter. A first experiment is proposed at the FRMII high thermal-neutron flux beam reactor SR6 through-going beam tube, where we will seek to observe this rare neutron decay-mode for the first time and determine the branching ratio. After successful completion, the hyperfine spin state population will be determined, possibly at the ILL high-flux beam reactor through-going beam tube H6–H7, where the thermal neutron flux is a factor of four larger.

An iron(ii) complex exhibiting five anhydrous phases, two of which interconvert by spin-crossover with wide hysteresis

[FeL2][BF4]2·2H2O (L = 2,6-di{5-methylpyrazol-3-yl}pyridine) adopts a 1 : 1 high : low spin state population, and can be converted into different high-spin anhydrous phases by recrystallisation (phase 1AA) or by thermal dehydration (phase 1BB). Upon cooling in vacuo, the latter undergoes a thermal spin-state transition centred near T1/2 = 205 K. The transition has a thermal hysteresis width of 65 K in freshly prepared samples, although this gradually narrows to 37 K on repeated scanning. X-Ray powder diffraction measurements performed in vacuo show that 1BB, initially formed at 375 K, exhibits two consecutive crystallographic phase changes near 300 and 270 K, before undergoing a third phase change concomitant with its spin-state transition. None of these new phases is isostructural with 1AA, which itself undergoes a thermal spin-crossover on cooling without a change in crystal symmetry.

Effect of periodically time-dependent magnetic fields on a population of spin states of radical pairs

The time dependences for a population of radical pair spin states and the amplitudes of the transitions between them are calculated for magnetic fields of complex configuration. The abovementioned values are derived directly from the solution to the Liouville equation for the components of a spin density matrix for a radical pair. The oscillating mechanism of the relaxation of partial populations of spin levels upon the monotonous reduction of the full population was established in the course of our calculations.

Identification of a New Charge-Transfer Transition through the Partial Unfolding of Cytochrome C under Mild Acidic Conditions

Cytochrome c, a model protein, has been isolated from a wide variety of prokaryotic and eukaryotic sources. It is commonly believed that proteins behave identically if it is extracted from the same source. This investigation illustrates the unexpected conformational change on the exposure of oxidized equine heart cytochrome c to TCA, as opposed to the preparation from acetic acid, both obtained from Sigma-Aldrich and dissolved at a concentration of 0.5 mM in 1.0 mM monobasic phosphate buffer. Without further purification an earlier unfolding event was obtained with the TCA exposed protein (pH 7.0, Temp. 338K). To unravel this enigma a variety of purification methods were employed utilizing partial unfolding-refolding protocols. The complete oxidation of cytochrome c was achieved by adjusting the pH of the sample to 11.5, neutralizing the positive patches on the protein surface. After complete oxidization, the protein was passed over a Sephadex G10 column. Subsequently, the pH of the solution was adjusted back to 8.0, which was the starting point of a titration which covered the region between 8.0 and 4.0. Surprisingly we observed a weak absorption band at 625nm, which increased with decreasing pH, reflecting the protonation of a titratable group (pK=5.2). This value strongly indicates a H33 as the involved residue. Normally, this band is indicative of the population of a ferric high spin state of the heme iron. However, in our case the 695nm band, which is an indicator of the intactness of the Fe(III)-M80 bond, remained present without any loss of intensity. Our observation suggest the stabilization of an excited charge transfer state, possibly resulting from an A2u->dπ transition by the positive charge on H33 in a heme cavity modified by the initially present TCA.