Isomeric Level Research Articles

Development and Characterization of a Tunable Metal-Organic Framework (MOF) for the Synthesis of a Rare Sugar D-Tagatose.

D-tagatose is a valuable rare sugar with potential health benefits such as antiobesity, low-calorie, prebiotic, and anticancer. However, its production is mainly depending on chemical or enzymatic catalysis. Herein, a cobalt-based metal-organic framework (MOF) was developed at room temperature in an aqueous system using a self-assembly method. The L-arabinose isomerase (L-AI) was immobilized into this unique MOF by an in situ encapsulation process. The morphology and structural aspects of the MOF preparations were characterized by different analytical techniques such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FT-IR), and X-Ray diffraction (XRD). Moreover, thermogravimetric analysis (TGA) suggested the high thermal stability of the L-AI@MOF. Significantly, the immobilized catalyst exhibited enhanced catalytic efficiency (kcat/Km) of 3.22mM-1s-1 and improved turnover number (kcat) of 57.32s-1. The L-AI@MOF efficiently catalyzes the synthesis of D-tagatose from D-galactose up to the equilibrium level (~ 50%) of isomerization in heterogeneous catalysis. Interestingly, L-AI@MOF was found stable and reusable for more than five cycles without the requirement of additional metal ions during catalysis. Thus, L-AI stabilized in the MOF system demonstrated a higher catalytic activity and potential guidance for the sustainable synthesis of rare sugar D-tagatose.

Aza-Prilezhaev Aziridination-Enabled Multidimensional Analysis of Isomeric Lipids via High-Resolution U-Shaped Mobility Analyzer-Mass Spectrometry.

Unsaturated lipids constitute a significant portion of the lipidome, serving as players of multifaceted functions involving cellular signaling, membrane structure, and bioenergetics. While derivatization-assisted liquid chromatography tandem mass spectrometry (LC-MS/MS) remains the gold standard technique in lipidome, it mainly faces challenges in efficiently labeling the carbon-carbon double bond (C═C) and differentiating isomeric lipids in full dimension. This presents a need for new orthogonal methodologies. Herein, a metal- and additive-free aza-Prilezhaev aziridination (APA)-enabled ion mobility mass spectrometric method is developed for probing multiple levels of unsaturated lipid isomerization with high sensitivity. Both unsaturated polar and nonpolar lipids can be efficiently labeled in the form of N-H aziridine without significant side reactions. The signal intensity can be increased by up to 3 orders of magnitude, achieving the nM detection limit. Abundant site-specific fragmentation ions indicate C═C location and sn-position in MS/MS spectra. Better yet, a stable monoaziridination product is dominant, simplifying the spectrum for lipids with multiple double bonds. Coupled with a U-shaped mobility analyzer, identification of geometric isomers and separation of different lipid classes can be achieved. Additionally, a unique pseudo MS3 mode with UMA-QTOF MS boosts the sensitivity for generating diagnostic fragments. Overall, the current method provides a comprehensive solution for deep-profiling lipidomics, which is valuable for lipid marker discovery in disease monitoring and diagnosis.

Stable-Isotope N-Me Aziridination Enables Accurate Quantitative C═C Isomeric Lipidomics.

Accurate lipid quantification is essential to revealing their roles in physiological and pathological processes. However, difficulties in the structural resolution of lipid isomers hinder their further accurate quantification. To address this challenge, we developed a novel stable-isotope N-Me aziridination strategy that enables simultaneous qualification and quantification of unsaturated lipid isomers. The one-step introduction of the 1-methylaziridine structure not only serves as an activating group for the C═C bond to facilitate positional identification but also as an isotopic inserter to achieve accurate relative quantification. The high performance of this reaction for the identification of unsaturated lipids was verified by large-scale resolution of the C═C positions of 468 lipids in serum. More importantly, by using this bifunctional duplex labeling method, various unsaturated lipids such as fatty acids, phospholipids, glycerides, and cholesterol ester were accurately and individually quantified at the C═C bond isomeric level during the mouse brain ischemia. This study provides a new approach to quantitative structural lipidomics.

Optical control of the β2-adrenergic receptor with opto-prop-2: A cis-active azobenzene analog of propranolol

SummaryIn this study, we synthesized and evaluated new photoswitchable ligands for the beta-adrenergic receptors β1-AR and β2-AR, applying an azologization strategy to the first-generation beta-blocker propranolol. The resulting compounds (Opto-prop-1, -2, -3) have good photochemical properties with high levels of light-induced trans-cis isomerization (>94%) and good thermal stability (t1/2 > 10 days) of the resulting cis-isomer in an aqueous buffer. Upon illumination with 360-nm light to PSScis, large differences in binding affinities were observed for photoswitchable compounds at β1-AR as well as β2-AR. Notably, Opto-prop-2 (VUF17062) showed one of the largest optical shifts in binding affinities at the β2-AR (587-fold, cis-active), as recorded so far for photoswitches of G protein-coupled receptors. We finally show the broad utility of Opto-prop-2 as a light-dependent competitive antagonist of the β2-AR as shown with a conformational β2-AR sensor, by the recruitment of downstream effector proteins and functional modulation of isolated adult rat cardiomyocytes.

Thermal Neutron Detection in Mixed Neutron-Gamma Fields With Common NaI(Tl) Detectors

NaI(Tl) scintillators can detect thermal neutrons with surprising efficiency, even in the presence of ambient gamma radiation. This is due to a peculiarity of the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">128</sup> I level scheme. Deexcitation cascades following neutron captures in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">127</sup> I, a main constituent of NaI with quite large neutron capture cross section, unexpectedly often involve the 167.4 keV state of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">128</sup> I with 175 ns half-life, which feeds another isomeric level at 137.9 keV having a half-life of 845 ns. The 29.5 keV transition between both levels, as well as the subsequent deexcitation sequence to ground state comprising 137.9 keV sum energy, are almost certainly absorbed in the crystal. Signals including three scintillation pulses within few microseconds, the first one caused by a prompt part of the cascade, the second and third one disclosing 30 and 138 keV energy depositions and characteristic delays, are clearly related to such neutron captures. Double-pulse sequences comprising only the primary pulse and a delayed 138 keV signal are also distinctive but more prone to load-dependent background by random pulse pileups. This article demonstrates neutron detection with a Ø2” <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times2$ </tex-math></inline-formula> ” NaI(Tl) scintillation detector by finding and analyzing such double- and triple-pulse sequences in digitized detector signals. It quantifies effect and background rates as a function of the detector load ranging up to 30 kcps. Complementary measurements with a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li codoped Ø2” <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times2$ </tex-math></inline-formula> ” NaI(Tl) (NaIL) scintillator allow relating the neutron detection yield by delayed-coincidence counting to the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li capture rate in the same crystal and thus to evaluate prospects and limits of this technique.

High precision measurement of the half-life of the 391.6 keV metastable level in Pu239

Materials selection for rare event physics requires high performance detectors and customized analyses. In this context a novel $\beta$-$\gamma$ detection system, comprised of a liquid scintillator in coincidence with a HPGe, was developed with the main purpose of studying ultra trace contamination of uranium, thorium and potassium in liquid samples. In the search for $^{238}\textrm{U}$ contaminations through neutron activation analysis, since the activation product $^{239}\textrm{Np}$ decays to a relatively long-lived isomeric state of $^{239}\textrm{Pu}$, it is possible to perform a time selection of these events obtaining a strong background suppression. Investigating the time distribution of the coincidences between the $\beta^-$ decay of $^{239}\textrm{Np}$ and the delayed events following the de-excitation of the $^{239}\textrm{Pu}$ isomeric level at 391.6 keV, a precision measurement of the half-life of this level was conducted. The half-life of the 391.6 keV $^{239}\textrm{Pu}$ level resulted $190.2 \pm 0.2$ ns, thus increasing the precision by about a factor of 20 over previous measurements.

Features of coherent excitation of [formula omitted]Th

The paper studies the effects that arise at the coherent excitation of the anomalously low-lying isomeric level 3/2+(8.19±0.12 eV) in the 229Th nucleus driven by laser radiation in wide band gap dielectrics. It is shown that in such an excitation a) the appearance of additional decay channels with a width Γ of the 229mTh isomer due to electron states in the band gap leads to an effective “freezing” of the system in the ground state (the repopulation process at relatively small Γ and the Zeno effect at large Γ), making the process of nuclear excitation practically impossible, b) the probability of the α decay of a coherent superposition of the ground and isomeric states becomes equal to the half-sum of the α widths of both levels and is increased by about a factor of two in comparison with the probability of the α decay of 229Th, c) the intensity of the main α lines oscillates with the Rabi frequency and the total α spectrum shifts towards higher energies for long time measurements, d) the inverse population of nuclear levels required for the Thorium γ ray laser is achieved relatively quickly within the π pulse duration, e) the observation of the Zeno effect according to the Cook's scheme is possible for the system of three lower levels of the 229Th nucleus.

Unsaturated lipid isomeric imaging based on the Paternò–Büchi reaction in the solid phase in ambient conditions

In recent years, the development of unsaturated lipid isomeric imaging based on the Paternò–Büchi (PB) reaction has improved significantly. However, research on this imaging method in ambient conditions needs to expand. In this paper, a method of PB reaction in the solid phase in ambient conditions is developed, which is combined with air-flow-assisted desorption electrospray ionisation mass spectrometry (AFADESI-MS) to achieve in situ imaging of lipids at an isomeric level. Experiments showed that the efficiency of the PB reaction was much higher when spraying the reagent solution than when sprinkling the reactant powder directly, and it was not lower than that in the liquid phase. This method can simplify the reaction conditions in the imaging process and can be applied to tissue section samples with only 10 min of pre-processing. The study successfully demonstrated the spatial distribution of unsaturated lipid isomers, and the isomeric ratio corresponded to the lesion areas in mouse brain cancer tissues. Due to its simple operation and performance in ambient conditions, this method may be useful for future studies on lipid isomers in tissues.

Exploiting Isospin Symmetry to Study the Role of Isomers in Stellar Environments.

Proton capture on the excited isomeric state of ^{26}Al strongly influences the abundance of ^{26}Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic ^{26}Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical ^{26m}Al(p,γ)^{27}Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of ^{26}Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of ^{26}Al.

Rapid Imaging of Unsaturated Lipids at an Isomeric Level Achieved by Controllable Oxidation.

Lipid imaging plays an important role in the research of some diseases, such as cancers. Unsaturated lipids are often present as isomers that can have different functions; however, traditional tandem mass spectrometry imaging (MSI) cannot differentiate between different isomers, which presents difficulties for the pathological study of lipids. Herein, we propose a method for the MSI of the C═C double-bond isomers of unsaturated lipids based on oxidative reactions coupled with air flow-assisted desorption electrospray ionization, which can conveniently achieve rapid MSI of unsaturated lipids at an isomeric level. Using this method, tissue sections can be scanned directly with MSI after only 10 min of accelerated oxidation. This method was used for the imaging of mouse lung cancer tissues, revealing a distributional difference in the unsaturated lipid isomers of normal and pathological regions. Through the MSI of unsaturated lipids at an isomeric level in tissues infected with cancer cells, the regions where the isomers were enriched were exhibited, indicating that these regions were the most concentrated regions of cancer cells. This method provides a convenient platform for studying the functional effects of the isomers of unsaturated lipids in pathological tissues.

Metastable States of ^{92,94}Se: Identification of an Oblate K Isomer of ^{94}Se and the Ground-State Shape Transition between N=58 and 60.

Here we present new information on the shape evolution of the very neutron-rich ^{92,94}Se nuclei from an isomer-decay spectroscopy experiment at the Radioactive Isotope Beam Factory at RIKEN. High-resolution germanium detectors were used to identify delayed γ rays emitted following the decay of their isomers. New transitions are reported extending the previously known level schemes. The isomeric levels are interpreted as originating from high-K quasineutron states with an oblate deformation of β∼0.25, with the high-K state in ^{94}Se being metastable and K hindered. Following this, ^{94}Se is the lowest-mass neutron-rich nucleus known to date with such a substantial K hindrance. Furthermore, it is the first observation of an oblate K isomer in a deformed nucleus. This opens up the possibility for a new region of K isomers at low Z and at oblate deformation, involving the same neutron orbitals as the prolate orbitals within the classic Z∼72 deformed hafnium region. From an interpretation of the level scheme guided by theoretical calculations, an oblate deformation is also suggested for the ^{94}Se_{60} ground-state band.

Activation Level and Probabilities of Electromagnetic γ-transitions in the Reaction 77Se(γ,γ’)77mSe

The dependence of the absolute yield from energies for reaction (γ,γ’)m on the nucleus 77Se was approximated by fit dependences (lines). Due to the visually detected fracture of the reaction yield, the energy interval 5.75-8.0 MeV is conventionally divided into two parts. For the transition step as one experimental point, the left part was approximated to 6.6 MeV, and the right part - from 6.26 MeV. There approximations were eight for both intervals. Given the features of the calculation and the minimum values for χ2, the "best" two fits are approximation dependences in the neighborhood of the intersection point x0 for the left and right arrays of energies. The energy for the activation level (the intersection point for these functions) is Ea≈6.35 MeV. The scheme of electromagnetic γ- transitions for nucleus 77Se are constructed and analyzed. Possible transitions to the isomeric level from higher levels are indicated. Weiskopf model was used to estimate the values of the reduced probabilities of electric EJ- and magnetic MJ- transitions, the probabilities of transitions per unit time and half-life. The theoretical values of the half-lives T1/2 are compared with the experimental data. Prospects for further use of the obtained results for topical problems of nuclear physics are discussed.

α -decay properties of Fr200,202

Background: The neutron-deficient lead region provides a range of nuclear phenomena, including isomerism at low energies. This phenomenon can be studied by α decay because the degree of hindrance of α decay provides information on the change in nuclear structure of connected states. Purpose: The aim of this work was to investigate the α-decay properties of $^{200,202}$FR and daughter products. Method: Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Surface ionization and mass-separation techniques were employed to provide a pure radioactive ion beam at a radiation-detection setup. Results: Due to the very high statistics and the high beam purity, improved decay data for $^{202}$FR and its daughters were obtained. In particular, this data set allowed us to identify many fine-structure α lines with a relative reduced α-decay width up to five orders of magnitude lower as the strongest ground-to-ground state or isomeric-to-isomeric state α-decay transition. In addition, several half-life values were extracted with similar or better precision as compared with the literature. Conclusions: The observation of crossover transitions positioned the isomeric high-spin level of $^{198}$At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of $^{198}$At and 52(3) ms for the ground-state decay of $^{200}$FR. Furthermore, α-decay schemes for Fr202 and its daughter $^{198}$At could be constructed.

Glycoqueuing: Isomer-Specific Quantification for Sialylation-Focused Glycomics.

Changes of α-2,3-/α-2,6-linked sialic acids (SAs) in sialylglycans have been found to be closely related with some diseases. However, accurate quantification of sialylglycans at the isomeric level remains challenging due to their instability, structural complexity, and low mass spectrometry (MS) detection sensitivity. Herein, we propose an analytical strategy named "glycoqueuing", which allows sequential chromatographic elution and high-sensitivity MS quantification of various sialylglycan isomers based on isotopic labeling followed by analysis via online reversed-phase high performance liquid chromatography coupling with MS (RP-HPLC-MS). The new method was validated by detailed structural identification and quantification of fetal bovine serum (FBS) N-linked sialylglycan isomers, during which many branching isomers were successfully differentiated, and 28 sialylglycan compositions with Neu5Gc residues were analyzed. The method was successfully applied to isomer-specific, quantitative comparison of sialylated N-glycans between bovine and rabbit immunoglobulin G (IgG) and the search for serum sialylated N-glycan biomarker candidates of hepatocellular carcinoma, during which a 55% increase of α-2,6-sialylated fucosylated N-glycans was revealed, demonstrating the great applicability and potential clinical usage of the method.

Alpha-gamma decay studies of 258Db and its (grand)daughter nuclei 254Lr and 250Md

The superheavy isotope 258Db was produced in the 209Bi(50Ti, 1n)258Db reaction at GSI, Germany. A detailed $ \alpha$-spectroscopy study of this isotope and its $ \alpha$-decay daughter products was performed. Two long-lived $ \alpha$-decaying states in 258Db are observed. A spin-parity of $ 0^{-}$ is tentatively assigned to the ground state for which a half-life of $ 2.17 \pm 0.36$ s is determined. Spins and parities of either $ 5^{+}$ or $ 10^{-}$ are proposed for the isomeric state found at an excitation energy of 51 keV with a half-life of $ 4.41 \pm 0.21$ s. The $ \alpha$ -decay daughter isotope 254Lr displays a similar behavior. A half-life of $ 11.9 \pm 0.9$ s is determined for the 254Lr ground state which is tentatively assigned a spin-parity of $ 4^{+}$. The isomeric level of this isotope placed at 108 keV with a half-life of $ 20.3 \pm 4.2$ s is tentatively assigned a spin-parity of $ 1^{-}$. Two long-lived $ \alpha$-decaying states are observed in the granddaughter isotope 250Md . The ground state has a half-life of $ 59.5 \pm 9.1$ s. A half-life of $ 42.4 \pm 4.5$ s is measured for the isomeric state positioned at an excitation energy of 123 keV. Partial, tentative level schemes for 254Lr, 250Md and 246Es are proposed based on the $ \alpha$-$ \gamma$ coincidences.

Experimental investigation and nuclear model calculations for proton induced reactions on indium around thresholds

Proton reactions with natural indium were found to give biased reaction cross section due to self-induced accompanying neutron-induced reactions in the target. We gave state-of-art and provided original experimental measurement for combined proton- and proton-induced-neutron reactions on indium isotopes. Low-energy protons incident on targets of stacked metallic indium foils were used to investigate the cross section and reaction yield around threshold. Two equivalent targets were designed to compensate the effect of neutron fluctuation in the sample and to swap the energy range below 14 MeV. The presence of significant neutron had been probed through the variation of reaction rate for formation of 116mIn fluence through-out the target foils; 116mIn yield was dependent on the stack arrangement. The interplay between the proton reactions on target isotopes through the 113In(p,n) 113m+gSn, 113In(p,p′) 113mIn, 115In(p,p′) 115mIn, 115In(p,np)114mIn, and 113In(p,3H) 111mIn routes from one side and the reactions of proton-induced-neutrons from the other side alters the experimental results and strengthen the formation of 113m+gSn and 114mIn on the expense of exhausting other reaction products. We stated the experimental values for the apparent reaction cross sections of these reactions in addition to the reaction cross section of short-lived isomeric level of 113mSn (T=121284 s) through the decay gamma-line at 77.38 keV. Nuclear model calculations were performed for all the related reactions and used to adopt our hypothesized values concerning the combined proton- and proton-induced-neutron reaction cross sections. Two resonance states for the reaction 113In(p,3H) 111mIn were identified at 11.51 MeV (Γt=0.961 MeV) and 14.12 MeV (Γt=0.194 MeV).

Factors influencing the ecological and human health risks of DDTs in soils and air at the isomeric and enantiomeric levels.

Even though the application of dichlorodiphenyltrichloroethanes (DDTs) has been restricted for over 30 years, their ubiquitous existence still poses profound adverse impacts on ecosystem and human health. In this study, simultaneous soil and air sampling campaigns at different functional areas were conducted in warm and cold seasons. Based on the residue levels and enantiomeric signatures of DDT and its metabolites in soils and air, the parameters influencing ecological and human health risks were explored. ΣDDT concentrations in soils correlated positively with organic matter (OM) and negatively with pH, whereas atmospheric DDT levels were primarily facilitated by increased temperature. High temperature and low soil pH were also favorable for the transformation of DDT into its metabolites. The inhabitants living in agricultural regions or in areas with higher soil OM or pH < 7 were exposed to higher existing and potential health risks of soil DDTs. In addition, at lower temperatures, the existing and potential carcinogenic risks of DDTs from soil exposure were higher, whereas risks from air inhalation were lower. Health risks would be increased when considering the enantioselective toxicity of o,p'-DDT and o,p'-DDD. The results from this study could provide baseline support for risk control and avoidance of DDTs.

Oxidation of squalene by singlet oxygen and free radicals results in different compositions of squalene monohydroperoxide isomers

Oxidation of squalene (SQ) causes a decline in the nutritional value of SQ in foods, as well as an accumulation of SQ oxidation products in skin lipids which lead to adverse skin conditions. However, mechanistic insights as to how SQ is oxidized by different oxidation mechanisms have been limited, and thus effective measures towards the prevention of SQ oxidation have not been identified. In this study, we oxidized SQ by either singlet oxygen oxidation or free radical oxidation, and monitored the formation of the six SQ monohydroperoxide (SQOOH) isomers, the primary oxidation products of SQ, at the isomeric level. While singlet oxygen oxidation of SQ resulted in the formation of similar amounts of the six SQOOH isomers, free radical oxidation of SQ mainly formed two types of isomers, 2-OOH-SQ and 3-OOH-SQ. The addition of β-carotene during singlet oxygen oxidation, and the addition of α-tocopherol during free radical oxidation lead to a dose-dependent decrease in the formation of SQOOH isomers. Such results suggest that the analysis of SQOOH at the isomeric level allows for the determination of the cause of SQ oxidation in various samples, and provides a foothold for future studies concerning the prevention of SQ oxidation.

Surface physicochemical properties and decay of the low-lying isomer in the 229Th nucleus

The effect of the 229Th nucleus proximity to the CsI surface on the decay probability of its anomalously low lying isomeric level is studied. Results of experimental and theoretical studies show that the CsI surface does not produce chemical bonding with Th and does not noticeably change its valence shells. Hence, it is an optimal substrate for measuring the probability of the 229Th isomer state decay via internal electron conversion. The half-life of the 229Thm isomer in the thorium atom is calculated for neutral chemical environment.

Decay Rate of the Nuclear Isomer ^{229}Th(3/2^{+},7.8 eV) in a Dielectric Sphere, Thin Film, and Metal Cavity.

The main decay channels of the anomalous low-energy 3/2^{+}(7.8±0.5 eV) isomeric level of the ^{229}Th nucleus, namely the γ emission and internal conversion, inside a dielectric sphere, dielectric thin film, and conducting spherical microcavity are investigated theoretically, taking into account the effect of media interfaces. It is shown that (1)the γ decay rate of the nuclear isomer inside a dielectric thin film and dielectric microsphere placed in a vacuum or in a metal cavity can decrease (increase) in dozen of times, (2)the γ activity of the distributed source as a function of time can be nonexponential, and (3)the metal cavity, whose size is of the order of the radiation wavelength, does not affect the probability of the internal conversion in ^{229}Th, because the virtual photon attenuates at much shorter distances and the reflected wave is very weak.