Herein we report the direct observation of C-H bond activation at an isolated mononuclear Pd(iii) center. The oxidation of the Pd(ii) complex (
N4)Pd
(neophyl)Cl (neophyl = -CH
C(CH
)
Ph;
N4 =
,
...'-dimethyl-2,11-diaza3.3(2,6)pyridinophane) using the mild oxidant ferrocenium hexafluorophosphate (FcPF
) yields the stable Pd(iii) complex (
N4)Pd
(neophyl)ClPF
. Upon the addition of an acetate source, (
N4)Pd
(neophyl)ClPF
undergoes Csp
-H bond activation to yield the cyclometalated product (
N4)Pd
(cycloneophyl)PF
. This metalacycle can be independently prepared, allowing for a complete characterization of both the starting and final Pd(iii) complexes. The C-H activation step can be monitored directly by EPR and UV-Vis spectroscopies, and kinetic isotope effect (KIE) studies suggest that either a pre-association step such as an agostic interaction may be rate limiting, or that the C-H activation is partially rate-limiting in conjunction with ligand rearrangement. Density functional theory calculations support that the reaction proceeds through a κ
ligand coordination and that the flexible ligand structure is important for this transformation. Overall, this study represents the first example of discrete C-H bond activation occurring at a Pd(iii) center through a concerted metalation-deprotonation mechanism, akin to that observed for Pd(ii) and Pd(iv) centers.
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Abstract
The formation and differentiation of the crust of Mars in the first tens of millions of years after its accretion can only be deciphered from incredibly limited records. The martian breccia ...NWA 7034 and its paired stones is one of them. This meteorite contains the oldest martian igneous material ever dated: ~4.5 Ga old. However, its source and geological context have so far remained unknown. Here, we show that the meteorite was ejected 5–10 Ma ago from the north-east of the Terra Cimmeria—Sirenum province, in the southern hemisphere of Mars. More specifically, the breccia belongs to the ejecta deposits of the Khujirt crater formed 1.5 Ga ago, and it was ejected as a result of the formation of the Karratha crater 5–10 Ma ago. Our findings demonstrate that the Terra Cimmeria—Sirenum province is a relic of the differentiated primordial martian crust, formed shortly after the accretion of the planet, and that it constitutes a unique record of early crustal processes. This province is an ideal landing site for future missions aiming to unravel the first tens of millions of years of the history of Mars and, by extension, of all terrestrial planets, including the Earth.
Aims.
The Rosetta mission provided us with detailed data of the surface of the nucleus of comet 67P/Churyumov-Gerasimenko. In order to better understand the physical processes associated with the ...comet activity and the surface evolution of its nucleus, we performed a detailed comparative morphometrical analysis of two depressions located in the Ash region.
Methods.
To detect morphological temporal changes, we compared pre- and post-perihelion high-resolution (pixel scale of 0.07–1.75 m) OSIRIS images of the two depressions. We quantified the changes using the dynamic heights and the gravitational slopes calculated from the digital terrain model of the studied area. In particular, we measured seven geometric parameters associated with the two depressions (length, three width values, height, area, and volume) using the ArcGIS software before and after perihelion.
Results.
Our comparative morphometrical analysis allowed us to detect and quantify the temporal changes that occurred in two depressions of the Ash region during the last perihelion passage. We find that the two depressions grew by several meters. The area of the smallest depression (structure I) increased by 90 ± 20%, with two preferential growths: one close to the cliff associated with the apparition of new boulders at its foot, and a second one on the opposite side of the cliff. The largest depression (structure II) grew in all directions, increasing in area by 20 ± 5%, and no new deposits have been detected. We interpreted these two depression changes as being driven by the sublimation of ices, which explains their global growth and which can also trigger landslides. The deposits associated with depression II reveal a stair-like topography, indicating that they have accumulated during several successive landslides from different perihelion passages. Overall, these observations bring additional evidence of complex active processes and reshaping events occurring on short timescales (months to years), such as depression growth and landslides, and on longer timescales (decades to millenniums), such as cliff retreat.
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The characterization of acoustic sources typically involves the retro-propagation of the acoustic field measured with a microphone array to a mesh of the surface of interest, which amounts to solve ...an inverse problem. Such an inverse problem is built on the basis of a forward model prone to uncertainties arising from mismatches with the physics of the experiment. Assessing the effects of these unavoidable uncertainties on the resolution of the inverse problem represents a challenge. The present paper introduces a practical solution to measure these effects by conducting a sensitivity analysis. The latter provides a mean to identify and rank the main sources of uncertainty through the estimation of sensitivity indices. Two inverse methods are investigated through the sensitivity analysis: conventional Beamforming and Bayesian focusing. The propagation of uncertainties is carried on numerically. The consistency between the real experiment and its numerical simulation is assessed by means of a small batch of measurements performed in a semi-anechoic chamber.
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Context. Asteroid modeling efforts in the last decade resulted in a comprehensive dataset of almost 400 convex shape models and their rotation states. These efforts already provided deep insight into ...physical properties of main-belt asteroids or large collisional families. Going into finer detail (e.g., smaller collisional families, asteroids with sizes ≲20 km) requires knowledge of physical parameters of more objects. Aims. We aim to increase the number of asteroid shape models and rotation states. Such results provide important input for further studies, such as analysis of asteroid physical properties in different populations, including smaller collisional families, thermophysical modeling, and scaling shape models by disk-resolved images, or stellar occultation data. This provides bulk density estimates in combination with known masses, but also constrains theoretical collisional and evolutional models of the solar system. Methods. We use all available disk-integrated optical data (i.e., classical dense-in-time photometry obtained from public databases and through a large collaboration network as well as sparse-in-time individual measurements from a few sky surveys) as input for the convex inversion method, and derive 3D shape models of asteroids together with their rotation periods and orientations of rotation axes. The key ingredient is the support of more that 100 observers who submit their optical data to publicly available databases. Results. We present updated shape models for 36 asteroids, for which mass estimates are currently available in the literature, or for which masses will most likely be determined from their gravitational influence on smaller bodies whose orbital deflections will be observed by the ESA Gaia astrometric mission. Moreover, we also present new shape model determinations for 250 asteroids, including 13 Hungarias and three near-Earth asteroids. The shape model revisions and determinations were enabled by using additional optical data from recent apparitions for shape optimization.
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Context. Determining the source regions of meteorites is one of the major goals of current research in planetary science. Whereas asteroid observations are currently unable to pinpoint the source ...regions of most meteorite classes, observations of meteors with camera networks and the subsequent recovery of the meteorite may help make progress on this question. The main caveat of such an approach, however, is that the recovery rate of meteorite falls is low (<20%), implying that the meteoritic analogues of at least 80% of the observed falls remain unknown. Aims. Spectroscopic observations of incoming bolides may have the potential to mitigate this problem by classifying the incoming meteoritic material. Methods. To probe the use of spectroscopy to determine the meteoritic analogues of incoming bolides, we collected emission spectra in the visible range (320–880 nm) of five meteorite types (H, L, LL, CM, and eucrite) acquired in atmospheric entry-like conditions in a plasma wind tunnel at the Institute of Space Systems (IRS) at the University of Stuttgart (Germany). A detailed spectral analysis including a systematic line identification and mass ratio determinations (Mg/Fe, Na/Fe) was subsequently performed on all spectra. Results. It appears that spectroscopy, via a simple line identification, allows us to distinguish the three main meteorite classes (chondrites, achondrites and irons) but it does not have the potential to distinguish for example an H chondrite from a CM chondrite. Conclusions. The source location within the main belt of the different meteorite classes (H, L, LL, CM, CI, etc.) should continue to be investigated via fireball observation networks. Spectroscopy of incoming bolides only marginally helps precisely classify the incoming material (iron meteorites only). To reach a statistically significant sample of recovered meteorites along with accurate orbits (>100) within a reasonable time frame (10–20 years), the optimal solution may be the spatial extension of existing fireball observation networks.
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Cysteine plays an essential role in maintaining cellular redox homeostasis and perturbations in cysteine concentration are associated with cardiovascular disease, liver disease, and cancer. 19F MRI ...is a promising modality for detecting cysteine in biology due to its high tissue penetration and negligible biological background signal. Herein we report fluorinated macrocyclic copper complexes that display a 19F NMR/MRI turn-on response following reduction of the Cu(ii) complexes by cysteine. The reactivity with cysteine was studied by monitoring the appearance of a robust diamagnetic 19F signal following addition of cysteine in conjunction with UV-vis and EPR spectroscopies. Importantly, complexes with –CH2CF3 tags display good water solubility. Studies with this complex in HeLa cells demonstrate the applicability of these probes to detect cysteine in complex biological environments.
We publish a set of 16 light curves of mutual events inside the synchronous system of the Jupiter Trojan (617) Patroclus. Patroclus is th only binary system of the six target asteroids of the ...forthcoming NASA Discovery-class mission Lucy. Determining the physical parameters of the system is therefore of primary importance in helping to plan the flyby mission.
Light curves were acquired during two follow-up campaigns of 6 months each between January–June 2007 and July–December 2012. Eight small eclipse events of amplitude of 0.2–0.3 mag were recorded in 2007. On the other hand, in 2012, the amplitudes of the phenomena were much deeper, between 0.6 and 0.8 mag, due to a nearly edge-on configuration of the system.
We refined the sidereal period to 102.78624 ± 0.00015h = 4.282760 ± 0.000005days. The J2000 ecliptic coordinates of the pole of the system were found to be λ = 235.3 ± 1.2° andβ = − 62.4 ± 0.2°. The volume ratio was determined equal to q = 0.69 ± 0.08. By using a model of inhomogeneous Roche ellipsoids in hydrostatic equilibrium, we derived a bulk density of 0.81 ± 0.16g/cm3 and a surface grain density of 2.69 ± 0.36g/cm3 in agreement with spectroscopic observations of this P-type asteroid.
As a validation, our solution was applied to revisit recent results obtained from observations of another type: AO astrometry and stellar occultation. Our model is thus perfectly able to account for these observations after fitting the mutual separation to the value of 695 ± 10km. Consequently, the area-equivalent diameter of the system as a whole is derived DΑ = 168.8 ± 2.6km.
•The paper presents the results obtained by the two first photometric observation campaigns of mutualevents within the binary system of the asteroid (617) Patroclus.•The implementation of a complete model based on the assumption of a system in hydrostatic equilibrium allowed to determine all the physical and dynamical parameters of the system.•The general solution found was then applied to previous observations made in adaptive optics and during a stellar occultation.
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Context.
In meteor physics, the luminous efficiency
τ
is used to convert the meteor’s magnitude to the corresponding meteoroid’s mass. However, a lack of sufficiently accurate verification methods or ...adequate laboratory tests mean that discussions around this parameter are a subject of controversy.
Aims.
In this work, we aim to use meteor data obtained by the Fireball Recovery and InterPlanetary Observation to calculate the luminous efficiencies of the recorded meteors. We also show the limitations of the methods presented herein.
Methods.
Deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. These can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. Fragmentation of the meteoroids is not considered within this model. Good measurements of the meteor deceleration are required.
Results.
We find
τ
-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10
−6
–100 kg. The derived
τ
-values have a median of
τ
median
= 2.17%. Most of them are of the order of 0.1–10%. We present how our values are obtained, compare them with data reported in the literature, and discuss several methods. A dependence of
τ
on the pre-atmospheric velocity of the meteor,
v
e
, is noticeable with a relation of τ = 0.0023⋅
v
e
2.3
. Furthermore, a dependence of
τ
on the initial meteoroid mass,
M
e
, is found with negative linear behaviour in log–log space: τ = 0.48⋅
M
e
−0.47
.
Conclusions.
The higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, the negative dependence of
τ
on
M
e
implies that the radiation of smaller meteoroids is more efficient. The results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency.
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