Compression of curium pyrrolidine-dithiocarbamate enhances covalency.

Curium is unique in the actinide series because its half-filled 5f 7 shell has lower energy than other 5f n configurations, rendering it both redox-inactive and resistant to forming chemical bonds that engage the 5f shell1-3. This is even more pronounced in gadolinium, curium's lanthanide analogue, owing to the contraction of the 4f orbitals with respect to the 5f orbitals4. However, at high pressures metallic curium undergoes a transition from localized to itinerant 5f electrons5. This transition is accompanied by a crystal structure dictated by the magnetic interactions between curium atoms5,6. 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 5f/6d 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 5f 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.

Conserved cell types with divergent features in human versus mouse cortex.

Elucidating the cellular architecture of the human cerebral cortex is central to understanding our cognitive abilities and susceptibility to disease. Here we used single-nucleus RNA-sequencing analysis to perform a comprehensive study of cell types in the middle temporal gyrus of human cortex. We identified a highly diverse set of excitatory and inhibitory neuron types that are mostly sparse, with excitatory types being less layer-restricted than expected. Comparison to similar mouse cortex single-cell RNA-sequencing datasets revealed a surprisingly well-conserved cellular architecture that enables matching of homologous types and predictions of properties of human cell types. Despite this general conservation, we also found extensive differences between homologous human and mouse cell types, including marked alterations in proportions, laminar distributions, gene expression and morphology. These species-specific features emphasize the importance of directly studying human brain.

Clinical immunogenicity outcomes from GENEr8-1, a phase 3 study of valoctocogene roxaparvovec, an AAV5-vectored gene therapy for hemophilia A.

Gene transfer therapies utilizing adeno-associated virus (AAV) vectors involve a complex drug design with multiple components that may impact immunogenicity. Valoctocogene roxaparvovec is an AAV serotype 5 (AAV5)-vectored gene therapy for the treatment of hemophilia A that encodes a B-domain-deleted human factor VIII (FVIII) protein controlled by a hepatocyte-selective promoter. Following previous results from the first-in-human phase 1/2 clinical trial, we assessed AAV5-capsid- and transgene-derived FVIII-specific immune responses with 2 years of follow-up data from GENEr8-1, a phase 3, single-arm, open-label study in 134 adult men with severe hemophilia A. No FVIII inhibitors were detected following administration of valoctocogene roxaparvovec. Immune responses were predominantly directed toward the AAV5 capsid, with all participants developing durable anti-AAV5 antibodies. Cellular immune responses specific for the AAV5 capsid were detected in most participants by interferon-γ enzyme-linked immunosorbent spot assay 2 weeks following dose administration and declined or reverted to negative over the first 52 weeks. These responses were weakly correlated with alanine aminotransferase elevations and showed no association with changes in FVIII activity. FVIII-specific cellular immune responses were less frequent and more sporadic compared with those specific for AAV5 and showed no association with safety or efficacy parameters.

Language impairments in seropositive and seronegative autoimmune encephalitis.

BACKGROUND AND OBJECTIVE: Autoimmune encephalitis (AE) is a rare neuroinflammatory disease affecting the central nervous system. To examine language functions in patients with different subsets of AE consisting of seropositive and seronegative groups. METHODS: Fifty-two patients were recruited from neurology departments in Melbourne, Australia, who met clinical criteria for possible AE. Language tests include the Naming Test from the Sydney Language Battery (SydBat), the semantic fluency trial from the Controlled Oral Word Association Test (COWAT), and the Vocabulary and Similarities subtests of the Weschler Abbreviated Scale of Intelligence-Second Edition. The results were standardised with normative data. RESULTS: The mean age of our cohort was 52.5 years old, with the average time from hospital admission to recruitment being 38.41 months. At an aggregate level, none of the mean language test z-scores were below normative data. At the patient level, impairment rates were 18.37% for COWAT (animals), 28.57% for SydBat (naming), 4.65% for Similarities, and 4.55% for Vocabulary. Chi-squared goodness of fit tests indicated that observed performances were significantly below expected performances for the SydBat (naming) test (p < 0.0001) and COWAT (animals) (p = 0.004). DISCUSSION: While, on average, language functions were within normal limits in patients with AE, but a subgroup exhibited lower performance in semantic fluency and visual confrontation naming, with impairment rates below expected norms. To advance understanding of language in chronic AE patients, exploring the impact of seizure burden, antiseizure medication use, and the relationship of language functions with other cognitive functions is crucial.

Atomic Level Interactions and Suprastructural Configuration of Plant Cell Wall Polymers in Dialkylimidazolium Ionic Liquids.

Ionic liquids (ILs) have been widely investigated for the pretreatment and deconstruction of lignocellulosic feedstocks. However, the modes of interaction between IL-anions and cations, and plant cell wall polymers, namely, cellulose, hemicellulose, and lignin, as well as the resulting ultrastructural changes are still unclear. In this study, we investigated the atomic level and suprastructural interactions of microcrystalline cellulose, birchwood xylan, and organosolv lignin with 1,3-dialkylimidazolium ILs having varying sizes of carboxylate anions. Analysis by 13C NMR spectroscopy indicated that cellulose and lignin exhibited stronger hydrogen bonding with acetate ions than with formate ions, as evidenced by greater chemical shift changes. Small-angle X-ray scattering analysis showed that while both cellulose and xylan adopted a single-stranded conformation in acetate-ILs, twice as many acetate ions were bound to one anhydroglucose unit than to an anhydroxylose unit. We also determined that a minimum of seven representative carbohydrate units must interact with an anion for that IL to effectively dissolve cellulose or xylan. Lignin is associated as groups of four polymer molecules in formate-ILs and dispersed as single molecules in acetate-ILs, which indicates that it is highly soluble in the latter. In summary, our study demonstrated that 1,3-dialkylimidazolium acetates displayed stronger binding interactions with cellulose and lignin, as compared to formates, and thus have superior potential to fractionate these polymers from lignocellulosic feedstocks.

Expanding Transuranium Organoactinide Chemistry: Synthesis and Characterization of (Cp'3M)2(µ-4,4'-bpy) (M = Ce, Np, Pu).

Dinuclear, organometallic, transuranium compounds, (Cp'3M)2(µ-4,4'-bpy) (Cp'- = trimethylsilylcyclopentadienide, 4,4'-bpy = 4,4'-bipyridine, M = Ce, Np, Pu), reported herein provide a rare opportunity to probe the nature of actinide-carbon bonding. Significant splitting of the f-f transitions results from the unusual coordination environment in these complexes and leads to electronic properties that are currently restricted to organoactinide systems. Structural and spectroscopic characterization in the solid state and in solution for (Cp'3M)2(µ-4,4'-bpy) (M = Np, Pu) are reported, and their structural metrics are compared to a cerium analogue.

Stabilization of Pu(IV) in PuBr4(OPCy3)2 and Comparisons with Structurally Similar ThX4(OPR3)2 (R = Cy, Ph) Molecules.

The pursuit of a trivalent plutonium halide phosphine oxide compound, e.g., "PuBr3(OPR)3," instead led to the isolation of the tetravalent trans-PuIVBr4(OPCy3)2, PuBr/Cy, compound by spontaneous oxidation of PuIII. The donating nature of phosphine oxides has allowed the isolation and characterization of PuBr/Cy by crystallographic, multinuclear NMR, solid state, and solution phase UV-vis-NIR spectroscopic techniques. The presence of a putative plutonyl(VI) complex formulated as "trans-PuVIO2Br2(OPCy3)2" was also observed spectroscopically and tentatively by single-crystal X-ray diffraction as a cocrystal of PuBr/Cy. A series of trans-ThX4(OPCy3)2 (X = Cl, ThCl/Cy; Br, ThBr/Cy; I, ThI/Cy) complexes were synthesized for comparison to PuBr/Cy. The triphenylphosphine oxide, OPPh3, complexes, trans-AnI4(OPPh3)2 (An = Th, ThI/Ph; U, UI/Ph), were also synthesized for comparison, completing the series trans-UX4(OPPh3)2 (X = Cl, Br, I), UX/Ph. To enable the synthesis of ThI/Cy and ThI/Ph, a new nonaqueous thorium iodide starting material, ThI4(Et2O)2, was synthesized. The syntheses of organic solvent soluble ThI4L2 (L = Et2O, OPCy3, and OPPh3) are the first examples of crystallographically characterized neutral thorium tetraiodide materials beyond binary ThI4. To show the viability of ThI4(Et2O)2 as a starting material for organothorium chemistry, (C5Me4H)3ThI was synthesized and crystallographically characterized.

Safety Findings of Dosing Gene Therapy Vectors in NHP With Pre-existing or Treatment-Emergent Anti-capsid Antibodies.

Replication-incompetent adeno-associated virus (AAV)-based vectors are nonpathogenic viral particles used to deliver therapeutic genes to treat multiple monogenic disorders. AAVs can elicit immune responses; thus, one challenge in AAV-based gene therapy is the presence of neutralizing antibodies against vector capsids that may prevent transduction of target cells or elicit adverse findings. We present safety findings from two 12-week studies in nonhuman primates (NHPs) with pre-existing or treatment-emergent antibodies. In the first study, NHPs with varying levels of naturally acquired anti-AAV5 antibodies were dosed with an AAV5-based vector encoding human factor VIII (hFVIII). In the second study, NHPs with no pre-existing anti-AAV antibodies were dosed with an AAV5-based vector carrying the beta subunit of choriogonadotropic hormone (bCG); this led to the induction of high-titer antibodies against the AAV5 capsid. Four weeks later, the same NHPs received an equivalent dose of an AAV5-based vector carrying human factor IX (hFIX). In both of these studies, the administration of vectors carrying hFVIII, bCG, and hFIX was well-tolerated in NHPs with no adverse clinical pathology or microscopic findings. These two studies demonstrate the safety of AAV-based vector administration in NHPs with either low-titer pre-existing anti-AAV5 antibodies or re-administration, even in the presence of high-titer antibodies.

Alternatives to Styrene- and Diisobutylene-Based Copolymers for Membrane Protein Solubilization via Nanodisc Formation.

Styrene-maleic acid copolymers (SMAs), and related amphiphilic copolymers, are promising tools for isolating and studying integral membrane proteins in a native-like state. However, they do not exhibit this ability universally, as several reports have found that SMAs and related amphiphilic copolymers show little to no efficiency when extracting specific membrane proteins. Recently, it was discovered that esterified SMAs could enhance the selective extraction of trimeric Photosystem I from the thylakoid membranes of thermophilic cyanobacteria; however, these polymers are susceptible to saponification that can result from harsh preparation or storage conditions. To address this concern, we herein describe the development of α-olefin-maleic acid copolymers (αMAs) that can extract trimeric PSI from cyanobacterial membranes with the highest extraction efficiencies observed when using any amphiphilic copolymers, including diisobutylene-co-maleic acid (DIBMA) and functionalized SMA samples. Furthermore, we will show that αMAs facilitate the formation of photosystem I-containing nanodiscs that retain an annulus of native lipids and a native-like activity. We also highlight how αMAs provide an agile, tailorable synthetic platform that enables fine-tuning hydrophobicity, controllable molar mass, and consistent monomer incorporation while overcoming shortcomings of prior amphiphilic copolymers.

Validation of an IFN-gamma ELISpot assay to measure cellular immune responses against viral antigens in non-human primates.

Adeno-Associated Virus (AAV)-based gene therapy vectors are in development for many inherited human disorders. In nonclinical studies, cellular immune responses mediated by cytotoxic T cells may target vector-transduced cells, which could impact safety and efficacy. Here, we describe the bioanalytical validation of an interferon-gamma (IFN-γ)-based Enzyme-Linked Immunospot (ELISpot) assay for measuring T cell responses against viral antigens in cynomolgus monkeys. Since ELISpots performed with antigen-derived peptides offer a universal assay format, method performance characteristics were validated using widely available peripheral blood mononuclear cells (PBMCs) responsive to cytomegalovirus peptides. The limit of detection and confirmatory cut point were established using statistical methods; precision, specificity, and linearity were confirmed. Monkey PBMCs from an AAV5 gene therapy study were then analyzed, using peptide pools spanning the vector capsid and transgene product. AAV5-specific T cell responses were detected only in 2 of 18 monkeys at Day 28, but not at Day 13 and 56 after vector administration, with no correlation to liver enzyme elevations or transgene expression levels. No transgene product-specific T cell responses occurred. In conclusion, while viral peptide-specific IFN-γ ELISpots can be successfully validated for monkey PBMCs, monitoring peripheral T cell responses in non-clinical AAV5 gene therapy studies was of limited value to interpret safety or efficacy.

Photoinduced Initiation of Olefin Polymerization: Enabling Spatial Control with Light.

Polyolefins constitute the majority of plastics produced worldwide. Despite the variety of precatalyst activation mechanisms known in the literature, the development of spatially controlled olefin polymerizations remains relatively unknown. If successful, control over the olefin polymerization process could provide unprecedented synthetic control and potentially broaden industrial applications. Herein, we demonstrate a simple olefin polymerization methodology termed photoinduced initiation of olefin polymerization (PIOP), wherein photoacid generators are used in conjunction with controlled irradiation to achieve precatalyst activation and olefin polymerization. These results demonstrate that PIOP can be used for solution-based polymerizations of ethylene and α-olefins and may be extended to heterogeneous polymerizations of gaseous ethylene and propylene, thereby achieving spatial control over the olefin polymerization process.

Effects of Esterified Styrene-Maleic Acid Copolymer Degradation on Integral Membrane Protein Extraction.

The detergent-free extraction of integral membrane proteins using styrene-maleic acid copolymers (SMAs) has shown promise as a potentially effective technique to isolate proteins in a more native-like conformation. As the field continues to develop, the protein selectivity and extraction efficiency of many analogues of traditional SMAs are being investigated. Recently, we discovered that the monoesterification of SMAs with alkoxy ethoxylate sidechains drastically affects the bioactivity of these copolymers in the extraction of photosystem I from the cyanobacterium Thermosynechococcus elongatus. However, subsequent investigations also revealed that the conditions under which these esterified SMA polymer analogues are prepared, purified, and stored can alter the structure of the alkoxy ethoxylate-functionalized SMA and perturb the protein extraction process. Herein, we demonstrate that the basic conditions required to solubilize SMA analogues may lead to deleterious saponification side reactions, cleaving the sidechains of an esterified SMA and dramatically decreasing its efficacy for protein extraction. We found that this process is highly dependent on temperature, with polymer samples being prepared and stored at lower temperatures exhibiting significantly fewer saponification side reactions. Furthermore, the effects of small-molecule impurities and exposure to light were also investigated, both of which are shown to have significant effects on the polymer structure and/or protein extraction process.

Psychometric deficits in autoimmune encephalitis: A retrospective study from the Australian Autoimmune Encephalitis Consortium.

BACKGROUND AND PURPOSE: Despite the rapid increase in research examining outcomes in autoimmune encephalitis (AE) patients, there are few cohort studies examining cognitive outcomes in this population. The current study aimed to characterise psychometric outcomes in this population, and explore variables that may predict psychometric outcomes. METHODS: This retrospective observational study collected psychometric data from 59 patients across six secondary and tertiary referral centres in metropolitan hospitals in Victoria, Australia between January 2008 and July 2019. Frequency and pattern analysis were employed to define and characterize psychometric outcomes. Univariable logistic regression was performed to examine predictors of intact and pathological psychometric outcomes. RESULTS: Deficits in psychometric markers of executive dysfunction were the most common finding in this cohort, followed by deficits on tasks sensitive to memory. A total of 54.2% of patients were classified as having psychometric impairments across at least two cognitive domains. Twenty-nine patterns were observed, suggesting outcomes in AE are complex. None of the demographic data, clinical features or auxiliary examination variables were predictors of psychometric outcome. CONCLUSIONS: Cognitive outcomes in AE are complex. Further detailed and standardized cognitive testing, in combination with magnetic resonance imaging volumetrics and serum/cerebrospinal fluid biomarkers, is required to provide rigorous assessments of disease outcomes.

Two Neptunium(III) Mellitate Coordination Polymers: Completing the Series Np-Cf of Trans-Uranic An(III) Mellitates.

Two neptunium(III) mellitates, 237Np2(mell)(H2O)9·1.5H2O (Np-1α) and 237Np2(mell)(H2O)8·2H2O (Np-1ß), have been synthesized from 237NpCl4(dme)2 by reduction with KC8 and subsequent reaction with an aqueous solution of mellitic acid (H6mell). Characterization by single-crystal X-ray crystallography and UV-vis-NIR spectroscopy confirms that the neptunium is in its +3 oxidation state and both polymorphs are isostructural to the previously reported plutonium mellitates. Of the two morphologies, Np-1α is indefinitely stable in air, while Np-1ß slowly oxidizes over several months. This is due to the change in the energy of the metal-ligand charge-transfer absorption exhibited by these compounds attributed to differing numbers of carboxylate bonds to Np(III), where in Np-1ß the energy is low enough to result in spontaneous oxidation.

Early Phase Clinical Immunogenicity of Valoctocogene Roxaparvovec, an AAV5-Mediated Gene Therapy for Hemophilia A.

Evaluation of immune responses to adeno-associated virus (AAV)-mediated gene therapies prior to and following dose administration plays a key role in determining therapeutic safety and efficacy. This report describes up to 3 years of immunogenicity data following administration of valoctocogene roxaparvovec (BMN 270), an AAV5-mediated gene therapy encoding human B domain-deleted FVIII (hFVIII-SQ) in a phase 1/2 clinical study of adult males with severe hemophilia A. Patients with pre-existing humoral immunity to AAV5 or with a history of FVIII inhibitors were excluded from the trial. Blood plasma and peripheral blood mononuclear cell (PBMC) samples were collected at regular intervals following dose administration for assessment of humoral and cellular immune responses to both the AAV5 vector and transgene-expressed hFVIII-SQ. The predominant immune response elicited by BMN 270 administration was largely limited to the development of antibodies against the AAV5 capsid that were cross-reactive with other common AAV serotypes. No FVIII inhibitor responses were observed within 3 years following dose administration. In a context of prophylactic or on-demand corticosteroid immunosuppression given after vector infusion, AAV5 and hFVIII-SQ peptide-specific cellular immune responses were intermittently detected by an interferon (IFN)-γ and tumor necrosis factor (TNF)-α FluoroSpot assay, but they were not clearly associated with detrimental safety events or changes in efficacy measures.

Mechanochemical Formation, Solution Rearrangements, and Catalytic Behavior of a Polymorphic Ca/K Allyl Complex.

Without solvents present, the often far-from-equilibrium environment in a mechanochemically driven synthesis can generate high-energy, non-stoichiometric products not observed from the same ratio of reagents used in solution. Ball milling 2 equiv. K[A'] (A'=[1,3-(SiMe3 )2 C3 H3 ]- ) with CaI2 yields a non-stoichiometric calciate, K[CaA'3 ], which initially forms a structure (1) likely containing a mixture of pi- and sigma-bound allyl ligands. Dissolved in arenes, the compound rearranges over the course of several days to a structure (2) with only η3 -bound allyl ligands, and that can be crystallized as a coordination polymer. If dissolved in alkanes, however, the rearrangement of 1 to 2 occurs within minutes. The structures of 1 and 2 have been modeled with DFT calculations, and 2 initiates the anionic polymerization of methyl methacrylate and isoprene; for the latter, under the mildest conditions yet reported for a heavy Group 2 species (one-atm pressure and room temperature).

Protein Extraction Efficiency and Selectivity of Esterified Styrene-Maleic Acid Copolymers in Thylakoid Membranes.

Amphiphilic styrene-maleic acid copolymers (SMAs) have been shown to effectively extract membrane proteins surrounded by an annulus of native membrane lipids via the formation of nanodiscs. Recent reports have shown that 2-butoxyethanol-functionalized SMA derivatives promote the extraction of membrane proteins from thylakoid membranes, whereas unfunctionalized SMA is essentially ineffective. However, it is unknown how the extent of functionalization and identity of sidechains impact protein solubilization and specificity. Herein, we show that the monoesterification of an SMA polymer with hydrophobic alkoxy ethoxylate sidechains leads to an increased solubilization efficiency (SE) of trimeric photosystem I (PSI) from the membranes of cyanobacterium Thermosynechococcus elongatus. The specific SMA polymer used in this study, PRO 10235, cannot encapsulate single PSI trimers from this cyanobacterium; however, as it is functionalized with alkoxy ethoxylates of increasing alkoxy chain length, a clear increase in the trimeric PSI SE is observed. Furthermore, an exponential increase in the SE is observed when >50% of the maleic acid repeat units are monoesterified with long alkoxy ethoxylates, suggesting that the PSI extraction mechanism is highly dependent on both the number and length of the attached side chains.

Virtual models of care for people with palliative care needs living in their own home: A systematic meta-review and narrative synthesis.

BACKGROUND: Access to palliative care in the community enables people to live in their preferred place of care, which is often home. Community palliative care services struggle to provide timely 24-h services to patients and family. This has resulted in calls for 'accessible and flexible' models of care that are 'responsive' to peoples' changing palliative care needs. Digital health technologies provide opportunities to meet these requirements 24-h a day. AIM: To identify digital health technologies that have been evaluated for supporting timely assessment and management of people living at home with palliative care needs and/or their carer(s), and the evidence-base for each. DESIGN: A systematic review of systematic reviews ('meta-review'). Systematic reviews evaluating evidence for virtual models of palliative or end-of-life care using one or more digital health technologies were included. Systematic reviews were evaluated using the Risk of Bias Tool for Systematic Reviews. A narrative approach was used to synthesise results. DATA SOURCES: Medline, Embase, Web of Science, CINAHL and Cochrane Database of systematic reviews were searched for English-language reviews published between 2015 and 2020. RESULTS: The search yielded 2266 articles, of which 12 systematic reviews met criteria. Sixteen reviews were included in total, after four reviews were found via handsearching. Other than scheduled telehealth, video-conferencing, or after-hours telephone support, little evidence was found for digital health technologies used to deliver virtual models of palliative care. CONCLUSIONS: There are opportunities to test new models of virtual care, beyond telehealth and/or video conferencing, such as 24-h command centres, and rapid response teams. SYSTEMATIC REVIEW REGISTRATION NUMBER: Prospero CRD42020200266.

Structural and Spectroscopic Investigation of Two Plutonium Mellitates.

The aqueous reaction of mellitic acid (H6mell) with 242PuBr3·nH2O forms two plutonium mellitates, 242Pu2(mell)(H2O)9·H2O (Pu-1α) and 242Pu2(mell)(H2O)8·2H2O (Pu-1ß). These compounds are compared to the isomorphous lanthanide mellitates with similar ionic radii via bond length analysis. Both plutonium compounds form three-dimensional metal-organic frameworks, with Pu-1α having two unique metal centers and Pu-1ß having one. All plutonium metal centers exhibit nine-coordinate geometries. Our results show metal-oxygen bond lengths for plutonium significantly shorter than those of the previously reported lanthanum and herein reported cerium analogues, consistent with the nine-coordinate ionic radii. Clear Laporte-forbidden 5f → 5f transitions are observed in the ultraviolet-visible-near-infrared spectra and are assigned to trivalent plutonium. However, there is a distinct color difference between the two plutonium compounds.

An η3 -Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex.

Milling two equivalents of K[1,3-(SiMe3 )2 C3 H3 ] (=K[A']) with MgX2 (X=Cl, Br) produces the allyl complex [K2 MgA'4 ] (1). Crystals grown from toluene are of the solvated species [((η6 -tol)K)2 MgA'4 ] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η1 ) allyl ligands. When recrystallized from hexanes, the unsolvated 1 forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C-C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η3 -allyl configuration on Mg is energetically preferred over the η1 - (σ-bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by 1, with activities that are comparable to K[A'] and greater than the homometallic magnesium complex [{MgA'2 }2 ].