Chromatographic purification of chromium (Cr), which is required for high-precision isotope analysis, is complicated by the presence of multiple Cr-species with different effective charges in the ...acid digested sample aliquots. The differing ion exchange selectivity and sluggish reaction rates of these species can result in incomplete Cr recovery during chromatographic purification. Because of large mass-dependent inter-species isotope fractionation, incomplete recovery can affect the accuracy of high-precision Cr isotope analysis. Here, we demonstrate widely differing cation distribution coefficients of Cr(III)-species (Cr3+, CrCl2+ and CrCl2+) with equilibrium mass-dependent isotope fractionation spanning a range of ∼1‰/amu and consistent with theory. The heaviest isotopes partition into Cr3+, intermediates in CrCl2+ and the lightest in CrCl2+/CrCl3°. Thus, for a typical reported loss of ∼25% Cr (in the form of Cr3+) through chromatographic purification, this translates into 185ppm/amu offset in the stable Cr isotope ratio of the residual sample. Depending on the validity of the mass-bias correction during isotope analysis, this further results in artificial mass-independent effects in the mass-bias corrected 53Cr/52Cr (μ53Cr* of 5.2ppm) and 54Cr/52Cr (μ54Cr* of 13.5ppm) components used to infer chronometric and nucleosynthetic information in meteorites. To mitigate these fractionation effects, we developed strategic chemical sample pre-treatment procedures that ensure high and reproducible Cr recovery. This is achieved either through 1) effective promotion of Cr3+ by >5 days exposure to HNO3H2O2 solutions at room temperature, resulting in >∼98% Cr recovery for most types of sample matrices tested using a cationic chromatographic retention strategy, or 2) formation of Cr(III)-Cl complexes through exposure to concentrated HCl at high temperature (>120°C) for several hours, resulting in >97.5% Cr recovery using a chromatographic elution strategy that takes advantage of the slow reaction kinetics of de-chlorination of Cr in dilute HCl at room temperature. These procedures significantly improve cation chromatographic purification of Cr over previous methods and allow for high-purity Cr isotope analysis with a total recovery of >95%.
The decay of radioactive 26Al to 26Mg (half-life of 730,000years) is postulated to have been the main energy source promoting asteroidal melting and differentiation in the nascent solar system. ...High-resolution chronological information provided by the 26Al–26Mg decay system is, therefore, intrinsically linked to the thermal evolution of early-formed planetesimals. In this paper, we explore the timing and style of asteroidal differentiation by combining high-precision Mg isotope measurements of meteorites with thermal evolution models for planetesimals. In detail, we report Mg isotope data for a suite of olivine-rich Al/Mg∼0 achondritic meteorites, as well as a few chondrites. Main Group, pyroxene and the Zinder pallasites as well as the lodranite all record deficits in the mass-independent component of μ26Mg (μ26Mg∗) relative to chondrites and Earth. This isotope signal is expected for the retarded ingrowth of radiogenic 26Mg∗ in olivine-rich residues produced through partial silicate melting during 26Al decay and consistent with their marginally heavy Mg isotope composition relative to ordinary chondrites, which may reflect the early extraction of isotopically light partial melts from the source rock. We propose that their parent planetesimals started forming within ∼250,000years of solar system formation from a hot (>∼500K) inner protoplanetary disk region characterized by a reduced initial (26Al/27Al)0 abundance (∼1–2×10−5) relative to the (26Al/27Al)0 value in CAIs of 5.25×10−5. This effectively reduced the total heat production and allowed for the preservation of solid residues produced through progressive silicate melting with depth within the planetesimals. These ‘non-carbonaceous’ planetesimals acquired their mass throughout an extended period (>3Myr) of continuous accretion, thereby generating onion-shell structures of incompletely differentiated zones, consisting of olivine-rich residues, overlaid by metachondrites and undifferentiated chondritic crusts. In contrast, individual olivine crystals from Eagle Station pallasites record variable μ26Mg∗ excesses, suggesting that these crystals captured the 26Mg∗ evolution of a magmatic reservoir controlled by fractional crystallization processes during the lifespan of 26Al. Similar to previous suggestions based on isotopic evidence, we suggest that Eagle Station pallasites formed from precursor material similar in composition to carbonaceous chondrites from a cool outer protoplanetary disk region characterized by (26Al/27Al)0⩾2.7×10−5. Protracted planetesimal accretion timescales at large orbital distances, with onset of accretion 0.3–1Myr post-CAIs, may have resulted in significant radiative heat loss and thus efficient early interior cooling of slowly accreting ‘carbonaceous’ planetesimals.
Group IVA iron and siliate-iron meteorites record a large range of cooling rates attributed to an impact-related disruption of a molten and differentiated ca. 1000 km diameter planetary embryo of ...chondritic composition before re-accretion of mainly the metallic core with minor silicates. To better understand the timing of primary accretion, disruption, re-accretion and cooling of the Group IVA parent body, we have determined Pb-Pb and Al-Mg ages for the Group IVA silicate-iron Steinbach meteorite. A Pb-Pb age based on multiple fractions of late-phase, slowly-cooled orthopyroxene from Steinbach yields an absolute age of 4565.47 ± 0.30 Ma corresponding to a relative age of 1.83 ± 0.34 Myr after formation of calcium-aluminium-rich inclusions (CAIs). This is the oldest U-corrected Pb-Pb absolute age for a differentiated meteorite. We use the deficit Al-Mg dating method on one whole rock sample and two mineral separates to produce a model age of 1.3−0.3+0.5 Myr after CAI formation corresponding to the depletion age of Al relative to Mg in the source material for Steinbach. Assuming this fractionation event occurred in the pre-impact parent body, this provides a maximum time after CAI formation for the disruption of the original Group IVA parent body. Together, these ages require that the original parent body accreted very early and differentiated prior to the impact-related break up, re-accretion and cooling between 1.3−0.3+0.5 Myr and 1.83 ± 0.34 Myr after CAI formation. These ages are fully consistent with a growing body of evidence from meteorites and astronomical observation supporting the early and efficient growth of planetary embryos and with numerical models of pebble accretion that predict rapid growth of embryos in the presence of chondrules. This time frame for the efficient formation of planetary embryos by chondrule accretion is inconsistent with a proposed ∼1.5 Myr delay in chondrule formation, a contradiction that is resolved by a non-canonical abundance of 26Al in the inner Solar System during at least the first million years of the protoplanetary disk.
•We report a Pb-Pb age of 4565.47 ± 0.30 Ma for the Group IVA meteorite Steinbach.•This age represents the oldest absolute age for an achondrite to date.•We report a model 26Al-26Mg age of 1.3−0.3+0.5 Myr for Al/Mg fractionation.•These ages require extremely rapid formation of this meteorite's parent embryo.•Supports early chondrule formation if pebble accretion is an important mechanism.
The molecular structuring of complex architectures and the enclosure of space are essential requirements for technical and living systems. Self‐assembly of supramolecular structures with desired ...shape, size, and stability remains challenging since it requires precise regulation of physicochemical and conformational properties of the components. Here a general platform for controlled self‐assembly of tailored amphiphilic elastin‐like proteins into desired supramolecular protein assemblies ranging from spherical coacervates over molecularly defined twisted fibers to stable unilamellar vesicles is introduced. The described assembly protocols efficiently yield protein membrane–based compartments (PMBC) with adjustable size, stability, and net surface charge. PMBCs demonstrate membrane fusion and phase separation behavior and are able to encapsulate structurally and chemically diverse cargo molecules ranging from small molecules to naturally folded proteins. The ability to engineer tailored supramolecular architectures with defined fusion behavior, tunable properties, and encapsulated cargo paves the road for novel drug delivery systems, the design of artificial cells, and confined catalytic nanofactories.
A platform of environmentally controlled architectures ranging from twisted fibers to stable vesicles is demonstrated. Supramolecular architectures are designed via a library of amphiphilic elastin‐like proteins (ELPs). Tailored ELPs, responsive to environmental parameters enable the assembly of complex materials with tunable properties. The described assembly protocols yield Protein Membrane‐Based Compartments enabling the encapsulation of delicate cargo.
We present a U-corrected Pb–Pb age of 4566.19 ± 0.20 Ma (1.11 ± 0.26 Myr after t _0 ) for the moderately volatile element rich, andesitic meteorite Erg Chech 002 (EC002). Our Al–Mg isochron defines a ...^26 Al/ ^27 Al initial ratio of (8.65 ± 0.09) × 10 ^−6 that corresponds to a ^26 Al/ ^27 Al ratio of ${2.48}_{-0.56}^{+0.67}$ × 10 ^−5 for the parent body precursor at the time of solar system formation. Whereas the published bulk chemistry and our high-precision Ca isotope measurement correspond to those for inner solar system materials, the ^26 Al/ ^27 Al ratio overlaps that for outer solar system CI chondrites. This indicates that the carriers and/or processes responsible for the nucleosynthetic isotope compositions for inner and outer disk materials are different than those controlling the heterogeneous distribution of ^26 Al. A low μ ^26 Mg* initial value of −6.1 ± 1.7 ppm infers a source region with a subchondritic Al/Mg ratio until 1.1 Myr after t _0 such that melt generation must have immediately preceded its crystallization. With ^26 Al as the main heating source, a modeled temperature–time path for a 100 km radius parent body with our inferred ^26 Al abundance suggests that accretion must have occurred before 0.5 Myr after t _0 to reach melting temperatures at appropriate depths within 1.1 Myr. This requires that the parent body formed very early within the protoplanetary disk, consistent with predictions of rapid formation of planetesimals by streaming instabilities within high-density dust filaments during the earliest phase of the protoplanetary disk. Finally, an absence of initial Pb in this otherwise moderately volatile-rich achondrite implies Pb was effectively sequestered to the Fe–Ni core.
The complexity of macrophage (MΦ) plasticity and polarization states, which include classically activated pro-inflammatory (M1) and alternatively activated anti-inflammatory (M2) MΦ phenotypes, is ...becoming increasingly appreciated. Within the M2 MΦ polarization state, M2a, M2b, M2c, and M2d MΦ subcategories have been defined based on their expression of specific cell surface receptors, secreted cytokines, and specialized immune effector functions. The importance of immunometabolic networks in mediating the function and regulation of MΦ immune responses is also being increasingly recognized, although the exact mechanisms and extent of metabolic modulation of MΦ subtype phenotypes and functions remain incompletely understood. In this study, proton (
H) nuclear magnetic resonance (NMR) metabolomics was employed to determine the polar metabolomes of M2 MΦ subtypes and to investigate the relationship between aqueous metabolite profiles and M2 MΦ functional phenotypes. Results from this study demonstrate that M2a MΦs are most distinct from M2b, M2c, and M2d MΦ subtypes, and that M2b MΦs display several metabolic traits associated with an M1-like MΦ phenotype. The significance of metabolome differences for metabolites implicated in glycolysis, the tricarboxylic acid (TCA) cycle, phospholipid metabolism, and creatine-phosphocreatine cycling is discussed. Altogether, this study provides biochemical insights into the role of metabolism in mediating the specialized effector functions of distinct M2 MΦ subtypes and supports the concept of a continuum of macrophage activation states rather than two well-separated and functionally distinct M1/M2 MΦ classes, as originally proposed within a classical M1/M2 MΦ framework.
Nanoscale biological materials formed by the assembly of defined block-domain proteins control the formation of cellular compartments such as organelles. Here, we introduce an approach to ...intentionally 'program' the de novo synthesis and self-assembly of genetically encoded amphiphilic proteins to form cellular compartments, or organelles, in Escherichia coli. These proteins serve as building blocks for the formation of artificial compartments in vivo in a similar way to lipid-based organelles. We investigated the formation of these organelles using epifluorescence microscopy, total internal reflection fluorescence microscopy and transmission electron microscopy. The in vivo modification of these protein-based de novo organelles, by means of site-specific incorporation of unnatural amino acids, allows the introduction of artificial chemical functionalities. Co-localization of membrane proteins results in the formation of functionalized artificial organelles combining artificial and natural cellular function. Adding these protein structures to the cellular machinery may have consequences in nanobiotechnology, synthetic biology and materials science, including the constitution of artificial cells and bio-based metamaterials.
An exaggerated exercise pressor reflex (EPR) is associated with excessive sympatho-excitation and exercise intolerance in the chronic heart failure (CHF) state. We hypothesized that brain-derived ...neurotrophic factor (BDNF) causes the exaggerated EPR via sensitizing muscle mechanosensitive afferents in CHF. Increased BDNF expression was observed in lumbar dorsal root ganglia (DRGs) from CHF rats compared to sham rats. Immunofluorescence data showed a greater increase in the number of BDNF-positive neurons in medium and large-sized DRG subpopulations from CHF rats. Patch clamp data showed that incubation with BDNF for 4⁻6 h, significantly decreased the current threshold-inducing action potential (AP), threshold potential and the number of APs during current injection in Dil-labeled isolectin B4 (IB4)-negative medium-sized DRG neurons (mainly mechano-sensitive) from sham rats. Compared to sham rats, CHF rats exhibited an increased number of APs during current injection in the same DRG subpopulation, which was significantly attenuated by 4-h incubation with anti-BDNF. Finally, chronic epidural delivery of anti-BDNF attenuated the exaggerated pressor response to either static contraction or passive stretch in CHF rats whereas this intervention had no effect on the pressor response to hindlimb arterial injection of capsaicin. These data suggest that increased BDNF in lumbar DRGs contributes to the exaggerated EPR in CHF.
It's not natural: The nonnatural amino acid phenylselenocysteine has been genetically incorporated into proteins in E. coli in response to the amber nonsense codon TAG. Oxidative elimination followed ...by Michael addition led to incorporation of (S)‐hexadecyl‐ and (S)‐mannosylcysteine into green fluorescent protein. This approach provides a useful method to modify protein side chains and backbone structures.
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