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The trivalent actinides are produced in the nuclear fuel cycle during power production and provide the largest long-term radiation dose in used nuclear fuel. It is ideal for these elements to be removed from used nuclear fuel for disposal and a necessity for fuel recycling. A key challenge to this is the similarity of chemical behavior of the trivalent actinides to the lanthanides that are also present as fission products in used fuel. Thus far, some of the most effective separations of actinides from lanthanides utilise chelating agents containing sulfur moieties such as dithiophosphinates that selectively bind to actinide ions because of a greater bond covalency relative to lanthanide ions. Typically, greater differences between actinide and lanthanide ions are observable the more ligands and chelators bonds have a covalent character. Here, a series of complexes of the trivalent actinides Np(III) through Cf(III) (excluding Bk(III)) with maleonitrile-1,2-dithiolate (mnt 2– ) are synthesized along with their lanthanide counterparts (La(III) – Nd(III), Sm(III) – Gd(III), Dy(III)), in order to characterize the nature of chemical bonds with these metal ions and a polarizable, non-innocent, sulfur-donor ligand. The metal-sulfur bonds in these complexes trend shorter than measured for lanthanides with equivalent ionic radii. However, particularly large deviations are observed in the neptunium and plutonium complexes in both structure and bonding, resulting in a nonlinear bond length trendline for the actinide series. Density Functional Theory (DFT) calculations with Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Order (NBO) analyses indicate that for the neptunium and plutonium complexes, the presence of increased 5 f -orbital participation, energy degeneracy of the metal and ligand orbitals, and the structure packing result in shortened M–S bonds. The stabilization of the energy of the 5 f -orbitals and the decrease in f -contribution to bonding orbitals in the later actinides results in structural properties more similar to the lanthanide complexes. Although the trivalent actinides are similar to the lanthanide series in terms of chemistry and bonding, their structures and properties can diverge significantly. Here, the authors report a series of complexes of the trivalent actinides Np(III) through Cf(III) along with their lanthanide counterparts using a polarizable non-innocent, sulfur-donor ligand.

Structural and electronic characterization of (Cp′ 3 Cm) 2 ( μ −4,4′−bpy) (Cp′ = trimethylsilylcyclopentadienyl, 4,4′−bpy = 4,4′−bipyridine) is reported and provides a rare example of curium−carbon bonding. Cp′ 3 Cm displays unexpectedly low energy emission that is quenched upon coordination by 4,4′−bipyridine. Electronic structure calculations on Cp′ 3 Cm and (Cp′ 3 Cm) 2 ( μ −4,4′−bpy) rule out significant differences in the emissive state, rendering 4,4′−bipyridine as the primary quenching agent. Comparisons of (Cp′ 3 Cm) 2 ( μ −4,4′−bpy) with its samarium and gadolinium analogues reveal atypical bonding patterns and electronic features that offer insights into bonding between carbon with f -block metal ions. Here we show the structural characterization of a curium−carbon bond, in addition to the unique electronic properties never before observed in a curium compound. Despite the distinct electronic properties of the wide variety Cm3+ compounds that have been prepared to date, no singlecrystal structural characterization of a complex containing a Cm−C bond has been reported. Here the authors report the synthesis of a Cm complex bearing trimethylsilylcyclopentadienyl and 4,4’-bipyridine ligands with a low energy emission and identify the 4,4’-bipyridine ligand as the primary quenching agent.

Variations in bonding between trivalent lanthanides and actinides is critical for reprocessing spent nuclear fuel. The ability to tune bonding and the coordination environment in these trivalent systems is a key factor in identifying a solution for separating lanthanides and actinides. Coordination of 4,4′−bipyridine (4,4′−bpy) and trimethylsilylcyclopentadienide (Cp′) to americium introduces unexpectedly ionic Am−N bonding character and unique spectroscopic properties. Here we report the structural characterization of (Cp′ 3 Am) 2 ( μ  − 4,4′−bpy) and its lanthanide analogue, (Cp′ 3 Nd) 2 ( μ  − 4,4′−bpy), by single-crystal X-ray diffraction. Spectroscopic techniques in both solid and solution phase are performed in conjunction with theoretical calculations to probe the effects the unique coordination environment has on the electronic structure. The coordination environment has a great impact on the electronic structure, bonding and properties of metal complexes. Here the authors report a dinuclear organometallic americium complex that displays unexpectedly ionic Am−N bonding, but enhanced covalency in the Am−C bonds compared to its neodymium analogue.

The actinides, from californium to nobelium (Z = 98–102), are known to have an accessible +2 oxidation state. Understanding the origin of this chemical behaviour requires characterizing CfII materials, but investigations are hampered by the fact that they have remained difficult to isolate. This partly arises from the intrinsic challenges of manipulating this unstable element, as well as a lack of suitable reductants that do not reduce CfIII to Cf°. Here we show that a CfII crown–ether complex, Cf(18-crown-6)I2, can be prepared using an Al/Hg amalgam as a reductant. Spectroscopic evidence shows that CfIII can be quantitatively reduced to CfII, and rapid radiolytic re-oxidation in solution yields co-crystallized mixtures of CfII and CfIII complexes without the Al/Hg amalgam. Quantum-chemical calculations show that the Cf‒ligand interactions are highly ionic and that 5f/6d mixing is absent, resulting in weak 5f→5f transitions and an absorption spectrum dominated by 5f→6d transitions.Californium is difficult to prepare in its divalent state. Now, crystals of a Cf(II) crown–ether complex have been synthesized by reduction of a Cf(III) precursor with an Al/Hg amalgam. They exhibit 5f→6d transitions in the visible region and near-infrared emission that are highly sensitive to changes in the coordination environment.

Curium is unique in the actinide series because its half-filled 5 f  7 shell has lower energy than other 5 f  n configurations, rendering it both redox-inactive and resistant to forming chemical bonds that engage the 5 f shell 1 – 3 . This is even more pronounced in gadolinium, curium’s lanthanide analogue, owing to the contraction of the 4 f orbitals with respect to the 5 f orbitals 4 . However, at high pressures metallic curium undergoes a transition from localized to itinerant 5 f electrons 5 . This transition is accompanied by a crystal structure dictated by the magnetic interactions between curium atoms 5 , 6 . Therefore, the question arises of whether the frontier metal orbitals in curium( iii )–ligand interactions can also be modified by applying pressure, and thus be induced to form metal–ligand bonds with a degree of covalency. Here we report experimental and computational evidence for changes in the relative roles of the 5 f /6 d orbitals in curium–sulfur bonds in [Cm(pydtc) 4 ] − (pydtc, pyrrolidinedithiocarbamate) at high pressures (up to 11 gigapascals). We compare these results to the spectra of [Nd(pydtc) 4 ] − and of a Cm( iii ) mellitate that possesses only curium–oxygen bonds. Compared with the changes observed in the [Cm(pydtc) 4 ] − spectra, we observe smaller changes in the f – f transitions in the [Nd(pydtc) 4 ] − absorption spectrum and in the f – f emission spectrum of the Cm( iii ) mellitate upon pressurization, which are related to the smaller perturbation of the nature of their bonds. These results reveal that the metal orbital contributions to the curium–sulfur bonds are considerably enhanced at high pressures and that the 5 f orbital involvement doubles between 0 and 11 gigapascal. Our work implies that covalency in actinides is complex even when dealing with the same ion, but it could guide the selection of ligands to study the effect of pressure on actinide compounds. Enhanced covalency is achieved for a curium complex with curium–sulfur bonds by subjecting the compound to high pressures, indicating that pressure can be used to tune covalency in actinide compounds.

The trivalent actinides are produced in the nuclear fuel cycle during power production and provide the largest long-term radiation dose in used nuclear fuel. It is ideal for these elements to be removed from used nuclear fuel for disposal and a necessity for fuel recycling. A key challenge to this is the similarity of chemical behavior of the trivalent actinides to the lanthanides that are also present as fission products in used fuel. Thus far, some of the most effective separations of actinides from lanthanides utilise chelating agents containing sulfur moieties such as dithiophosphinates that selectively bind to actinide ions because of a greater bond covalency relative to lanthanide ions. Typically, greater differences between actinide and lanthanide ions are observable the more ligands and chelators bonds have a covalent character. Here, a series of complexes of the trivalent actinides Np(III) through Cf(III) (excluding Bk(III)) with maleonitrile-1,2-dithiolate (mnt2–) are synthesized along with their lanthanide counterparts (La(III) – Nd(III), Sm(III) – Gd(III), Dy(III)), in order to characterize the nature of chemical bonds with these metal ions and a polarizable, non-innocent, sulfur-donor ligand. The metal-sulfur bonds in these complexes trend shorter than measured for lanthanides with equivalent ionic radii. However, particularly large deviations are observed in the neptunium and plutonium complexes in both structure and bonding, resulting in a nonlinear bond length trendline for the actinide series. Density Functional Theory (DFT) calculations with Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Order (NBO) analyses indicate that for the neptunium and plutonium complexes, the presence of increased 5f-orbital participation, energy degeneracy of the metal and ligand orbitals, and the structure packing result in shortened M–S bonds. The stabilization of the energy of the 5f-orbitals and the decrease in f-contribution to bonding orbitals in the later actinides results in structural properties more similar to the lanthanide complexes.

The actinide series is of great importance, possessing applications in clean energy, space travel, medicinal use, and even household smoke detectors. Despite everyday applications, our knowledge of the actinides is severely limited compared to the rest of the periodic table. Low available quantities of these elements, in addition to hazardous radiotoxicity, presents a unique set of challenges when studying them. Nuclear energy presents grand opportunities for clean energy and is a leading source adopted by many countries; however, difficulties in recycling and separating these elements from nuclear waste proves to be a pervasive task. Furthering the limited understanding of bonding and electronic properties characteristic of the actinide series will present new opportunities for recycling and waste separation techniques. Historically, f-electrons were thought to be chemically inert, only participating in electrostatic interactions and displaying heavily localized behavior. Actinides were thought to act like their lanthanide counterparts; however, this is now known to be false. Actinide−carbon bonding showed the first evidence of covalency in the actinide series, differentiating their bonding properties from the lanthanides. Furthermore, recent studies have demonstrated how the greater radial extension of the 5f orbitals beyond the 4f orbitals results in greater reactivity and a lower degree of localization of the 5f electrons. Chapter 1 will provide background information on the actinide series, as well as its historical importance and applications. Information regarding the importance of organometallic actinide chemistry, intervalence charge transfer, and challenges in working with these elements is discussed. Chapters 2 and 3 build a baseline for intervalence charge transfer studies within the actinide series, presenting a series of dinuclear systems with neptunium, plutonium, and various lanthanide analogues. These complexes allow for flexible redox studies and will be applied for the synthesis of mixed-valent systems displaying the delocalization of f-electrons, pushing the boundary on our understanding of these fundamental properties.Chapter 3 transitions from the localized properties of f-electrons to their unique bonding properties by introducing an organometallic synthetic precursor. Metal−carbon bonding is a nearly untouched field in transplutonium elements, which is surprising considering the reported differences in covalency between the actinide−carbon and lanthanide−carbon bonding, as well as the prevalence of americium and curium in nuclear waste. Chapters 5 demonstrates how the addition of azine bridging ligands to these organometallic systems allows for the tuning of covalency in actinide−nitrogen bonding, a common target in improving separations techniques. Chapter 6 presents the first reported structural characterization of a curium−carbon bond, opening doorways to a new field of actinide chemistry: organocurium chemistry. In addition to unexpected bonding differences between curium and its samarium analogue, organometallic curium demonstrates never before seen optical properties, including significantly redshifted emission in a putative Cp′3Cm, as well as the quenched photoluminescence of (Cp′3Cm)2(μ−4,4′−bpy). This work introduces actinide systems that serve as a baseline for intervalence charge transfer experiments and the delocalization of f-electrons, as well as a series of transplutonium complexes possessing actinide−carbon bonding, possessing bonding and electronic properties never before observed with these elements.

In this trial, high-risk nondiabetic relatives of patients with type 1 diabetes were randomly assigned to receive teplizumab (an anti-CD3 monoclonal antibody) or placebo and were followed for type 1 diabetes. Teplizumab delayed progression to clinical type 1 diabetes in high-risk participants.

In this randomized trial, the use of video laryngoscopy in critically ill patients undergoing intubation in the ED or ICU resulted in a higher incidence of successful intubation on the first attempt than direct laryngoscopy.

More than 90% of chondroblastomas contain a heterozygous mutation replacing lysine-36 with methionine-36 (K36M) in the histone H3 variant H3.3. Here we show that H3K36 methylation is reduced globally in human chondroblastomas and in chondrocytes harboring the same genetic mutation, due to inhibition of at least two H3K36 methyltransferases, MMSET and SETD2, by the H3.3K36M mutant proteins. Genes with altered expression as well as H3K36 di- and trimethylation in H3.3K36M cells are enriched in cancer pathways. In addition, H3.3K36M chondrocytes exhibit several hallmarks of cancer cells, including increased ability to form colonies, resistance to apoptosis, and defects in differentiation. Thus, H3.3K36M proteins reprogram the H3K36 methylation landscape and contribute to tumorigenesis, in part through altering the expression of cancer-associated genes.