Gut-associated lymphoid tissue: a microbiota-driven hub of B cell immunity.

The diverse gut microbiota, which is associated with mucosal health and general wellbeing, maintains gut-associated lymphoid tissues (GALT) in a chronically activated state, including sustainment of germinal centers in a context of high antigenic load. This influences the rules for B cell engagement with antigen and the potential consequences. Recent data have highlighted differences between GALT and other lymphoid tissues. For example, GALT propagates IgA responses against glycans that show signs of having been generated in germinal centers. Other findings suggest that humans are among those species where GALT supports the diversification, propagation, and possibly selection of systemic B cells. Here, we review novel findings that identify GALT as distinctive, and able to support these processes.

A computationally-guided non-equilibrium synthesis approach to materials discovery in the SrO-Al2O3-SiO2 phase field.

Glass-crystallisation synthesis is coupled to probe structure prediction for the guided discovery of new metastable oxides in the SrO-Al2O3-SiO2 phase field, yielding a new ternary ribbon-silicate, Sr2Si3O8. In principle, this methodology can be applied to a wide range of oxide chemistries by selecting an appropriate non-equilibrium synthesis route.

Heritable diversity in the human antigen inexperienced B cell repertoire.

Human transitional B cells and naïve B cells are each variable beyond the widely discussed diversity in their B cell receptor repertoire, because whilst remaining within their subset definition, the phenotypes and transcriptomes of individual cells occur within a range of values. Cells can therefore have different functional biases. Here we have taken advantage of small clones of transitional and naïve B cells that exist within different tissue sites in pre-existing dataset to ask whether the transcriptomes of individual clone members are more similar to each other than to the transcriptomes of unrelated cells. We observe that cells that are clonally related are more similar to each other in terms of gene expression than they are to the remainder of cells in clones. This demonstrates that differences are shared between clone members and are therefore heritable. We suggest further that diversity in the transitional and naïve B cell populations has the potential to be propagated and thus sustained.

Psoriatic and rheumatoid arthritis joints differ in the composition of CD8+ tissue-resident memory T cell subsets.

CD69+CD103+ tissue-resident memory T (TRM) cells are important drivers of inflammation. To decipher their role in inflammatory arthritis, we apply single-cell, high-dimensional profiling to T cells from the joints of patients with psoriatic arthritis (PsA) or rheumatoid arthritis (RA). We identify three groups of synovial CD8+CD69+CD103+ TRM cells: cytotoxic and regulatory T (Treg)-like TRM cells are present in both PsA and RA, while CD161+CCR6+ type 17-like TRM cells with a pro-inflammatory cytokine profile (IL-17A+TNFα+IFNγ+) are specifically enriched in PsA. In contrast, only one population of CD4+CD69+CD103+ TRM cells is detected and at similarly low frequencies in both diseases. Type 17-like CD8+ TRM cells have a distinct transcriptomic signature and a polyclonal, but distinct, TCR repertoire. Type 17-like cells are also enriched in CD8+CD103- T cells in PsA compared with RA. These findings illustrate differences in the immunopathology of PsA and RA, with a particular enrichment for type 17 CD8+ T cells in the PsA joint.

Stabilization of the Trigonal Langasite Structure in Ca3Ga2-2xZnxGe4+xO14 (0 ≤ x ≤ 1) with Partial Ordering of Three Isoelectronic Cations Characterized by a Multitechnique Approach.

Crystallization of oxide glasses rich in Zn2+, Ga3+, and Ge4+ is of interest for the synthesis of new transparent ceramics. In this context, we report the identification and detailed structural characterization of a new solid solution Ca3Ga2-2xZnxGe4+xO14 (0 ≤ x ≤ 1). These compounds adopt the trigonal langasite structure type, offering three possible crystallographic sites for the coordination of isoelectronic Zn2+, Ga3+, and Ge4+. We used neutron diffraction to determine distributions of Ga3+/Ge4+ and Zn2+/Ge4+ in the simpler end members Ca3Ga2Ge4O14 and Ca3ZnGe5O14, while for the complex intermediate member Ca3GaZn0.5Ge4.5O14, we used an original approach combining quantitative 2D analysis of atomic-resolution STEM-EDS maps with neutron diffraction. This revealed that, across the solid solution, the tetrahedral D sites remain fully occupied by Ge4+, while Zn2+, Ga3+, and the remaining Ge4+ are shared between octahedral B- and tetrahedral C sites in proportions that depend upon their relative ionic radii. The adoption of the trigonal langasite structure by glass-crystallized Ca3ZnGe5O14, a compound that was previously observed only in a distorted monoclinic langasite polymorph, is attributed to substantial disorder between Zn2+ and Ge4+ over the B and C sites. The quantitative 2D refinement of atomic-resolution STEM-EDS maps is applicable to a wide range of materials where multiple cations with poor scattering contrast are distributed over different crystallographic sites in a crystal structure.

ChAdOx1 nCoV-19 vaccine elicits monoclonal antibodies with cross-neutralizing activity against SARS-CoV-2 viral variants.

Although the antibody response to COVID-19 vaccination has been studied extensively at the polyclonal level using immune sera, little has been reported on the antibody response at the monoclonal level. Here, we isolate a panel of 44 anti-SARS-CoV-2 monoclonal antibodies (mAbs) from an individual who received two doses of the ChAdOx1 nCoV-19 (AZD1222) vaccine at a 12-week interval. We show that, despite a relatively low serum neutralization titer, Spike-reactive IgG+ B cells are still detectable 9 months post-boost. Furthermore, mAbs with potent neutralizing activity against the current SARS-CoV-2 variants of concern (Alpha, Gamma, Beta, Delta, and Omicron) are present. The vaccine-elicited neutralizing mAbs form eight distinct competition groups and bind epitopes overlapping with neutralizing mAbs elicited following SARS-CoV-2 infection. AZD1222-elicited mAbs are more mutated than mAbs isolated from convalescent donors 1-2 months post-infection. These findings provide molecular insights into the AZD1222 vaccine-elicited antibody response.

Two subsets of human marginal zone B cells resolved by global analysis of lymphoid tissues and blood.

B cells generate antibodies that are essential for immune protection, but their subgroups are poorly defined. Here, we perform undirected deep profiling of B cells in matched human lymphoid tissues from deceased transplant organ donors and blood. In addition to identifying unanticipated features of tissue-based B cell differentiation, we resolve two subsets of marginal zone B (MZB) cells differing in cell surface and transcriptomic profiles, clonal relationships to other subsets, enrichment of genes in the NOTCH pathway, distribution bias within splenic marginal zone microenvironment, and immunoglobulin repertoire diversity and hypermutation frequency. Each subset is present in spleen, gut-associated lymphoid tissue, mesenteric lymph nodes, and blood. MZB cells and the lineage from which they are derived are depleted in lupus nephritis. Here, we show that this depletion is of only one MZB subset. The other remains unchanged as a proportion of total B cells compared with health. Thus, it is important to factor MZB cell heterogeneity into studies of human B cell responses and pathology.

A SIMPLI (Single-cell Identification from MultiPLexed Images) approach for spatially-resolved tissue phenotyping at single-cell resolution.

Multiplexed imaging technologies enable the study of biological tissues at single-cell resolution while preserving spatial information. Currently, high-dimension imaging data analysis is technology-specific and requires multiple tools, restricting analytical scalability and result reproducibility. Here we present SIMPLI (Single-cell Identification from MultiPLexed Images), a flexible and technology-agnostic software that unifies all steps of multiplexed imaging data analysis. After raw image processing, SIMPLI performs a spatially resolved, single-cell analysis of the tissue slide as well as cell-independent quantifications of marker expression to investigate features undetectable at the cell level. SIMPLI is highly customisable and can run on desktop computers as well as high-performance computing environments, enabling workflow parallelisation for large datasets. SIMPLI produces multiple tabular and graphical outputs at each step of the analysis. Its containerised implementation and minimum configuration requirements make SIMPLI a portable and reproducible solution for multiplexed imaging data analysis. Software is available at "SIMPLI [ https://github.com/ciccalab/SIMPLI ]".

Chemical Control of the Dimensionality of the Octahedral Network of Solar Absorbers from the CuI-AgI-BiI3 Phase Space by Synthesis of 3D CuAgBiI5.

A newly reported compound, CuAgBiI5, is synthesized as powder, crystals, and thin films. The structure consists of a 3D octahedral Ag+/Bi3+ network as in spinel, but occupancy of the tetrahedral interstitials by Cu+ differs from those in spinel. The 3D octahedral network of CuAgBiI5 allows us to identify a relationship between octahedral site occupancy (composition) and octahedral motif (structure) across the whole CuI-AgI-BiI3 phase field, giving the ability to chemically control structural dimensionality. To investigate composition-structure-property relationships, we compare the basic optoelectronic properties of CuAgBiI5 with those of Cu2AgBiI6 (which has a 2D octahedral network) and reveal a surprisingly low sensitivity to the dimensionality of the octahedral network. The absorption onset of CuAgBiI5 (2.02 eV) barely changes compared with that of Cu2AgBiI6 (2.06 eV) indicating no obvious signs of an increase in charge confinement. Such behavior contrasts with that for lead halide perovskites which show clear confinement effects upon lowering dimensionality of the octahedral network from 3D to 2D. Changes in photoluminescence spectra and lifetimes between the two compounds mostly derive from the difference in extrinsic defect densities rather than intrinsic effects. While both materials show good stability, bulk CuAgBiI5 powder samples are found to be more sensitive to degradation under solar irradiation compared to Cu2AgBiI6.

Emergence of A-Site Cation Order in the Small Rare-Earth Melilites SrREGa3O7 (RE = Dy-Lu, Y).

SrREGa3O7 melilite ceramics with large rare-earth elements (RE = La to Y) are famous materials especially known for their luminescence properties. Using an innovative approach, the full and congruent crystallization from glass process, SrREGa3O7 transparent polycrystalline ceramics with small rare earth elements (RE = Dy-Lu and Y) have been successfully synthesized and characterized. Interestingly, compared to the classic tetragonal (P4̅21m) melilite structure composed of mixed Sr/RE cationic sites, these compositions can crystallize in a 3 × 1 × 1 orthorhombic (P21212) superstructure. A detailed study of the superstructure, investigated using different techniques (synchrotron and neutron powder diffraction, STEM-HAADF imaging, and EDS mapping), highlights the existence of a Sr/RE cation ordering favored by a large Sr/RE size mismatch and a sufficiently small RE cation. An appropriate control of the synthesis conditions through glass crystallization enables the formation of the desired polymorphs, either ordered or disordered. The influence of this tailored cationic ordering/disordering on the RE luminescent spectroscopic properties have been investigated. A stronger structuration of the RE emission band is observed in the ordered ceramic compared to the disordered ceramic and the glass, whose band shapes are very similar, indicating that the RE environments in the glass and disordered ceramic are close.

Discovery of a Low Thermal Conductivity Oxide Guided by Probe Structure Prediction and Machine Learning.

We report the aperiodic titanate Ba10 Y6 Ti4 O27 with a room-temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low-thermal-conductivity oxides is metastable and located within a quaternary phase field that has been previously explored. Its isolation thus requires a precisely defined synthetic protocol. The necessary narrowing of the search space for experimental investigation was achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that would favour synthetically accessible new compositions, and assessment of their properties with machine-learning models.

Highly Absorbing Lead-Free Semiconductor Cu2AgBiI6 for Photovoltaic Applications from the Quaternary CuI-AgI-BiI3 Phase Space.

Since the emergence of lead halide perovskites for photovoltaic research, there has been mounting effort in the search for alternative compounds with improved or complementary physical, chemical, or optoelectronic properties. Here, we report the discovery of Cu2AgBiI6: a stable, inorganic, lead-free wide-band-gap semiconductor, well suited for use in lead-free tandem photovoltaics. We measure a very high absorption coefficient of 1.0 × 105 cm-1 near the absorption onset, several times that of CH3NH3PbI3. Solution-processed Cu2AgBiI6 thin films show a direct band gap of 2.06(1) eV, an exciton binding energy of 25 meV, a substantial charge-carrier mobility (1.7 cm2 V-1 s-1), a long photoluminescence lifetime (33 ns), and a relatively small Stokes shift between absorption and emission. Crucially, we solve the structure of the first quaternary compound in the phase space among CuI, AgI and BiI3. The structure includes both tetrahedral and octahedral species which are open to compositional tuning and chemical substitution to further enhance properties. Since the proposed double-perovskite Cs2AgBiI6 thin films have not been synthesized to date, Cu2AgBiI6 is a valuable example of a stable Ag+/Bi3+ octahedral motif in a close-packed iodide sublattice that is accessed via the enhanced chemical diversity of the quaternary phase space.

Sodium Site Exchange and Migration in a Polar Stuffed-Cristobalite Framework Structure.

The study of ionic dynamics in solids is essential to understanding and developing modern energy technologies. Here we study the ionic dynamics of orthorhombic Na2MgSiO4, an interesting case of a polar stuffed-cristobalite-type structure that contains two inequivalent Na sites within the channels of the magnesium silicate tetrahedral framework. Its preparation by a solid-state reaction method favors the presence of ∼2% of Na vacancies, converting it into a pure Na ionic conductor with an optimized ionic conductivity of ∼10-5 S cm-1 at 200 °C. The macroscopic migration has been characterized through impedance spectroscopy and molecular dynamics simulation, which proves the pure Na ionic character of the compound through hopping between Na1 and Na2 sites, forming three-dimensional migration zigzag-shaped paths. High-resolution solid-state 23Na magic-angle-spinning (MAS) NMR spectroscopy is employed to characterize the local structure and microscopic dynamics of Na-ion transport in Na2MgSiO4. Remarkably, variable-temperature 23Na MAS NMR and two-dimensional exchange spectroscopy evidence for the first time a Na site exchange phenomenon at room temperature, which further triggers Na ionic conduction at elevated temperatures.

Human marginal zone B cell development from early T2 progenitors.

B cells emerge from the bone marrow as transitional (TS) B cells that differentiate through T1, T2, and T3 stages to become naive B cells. We have identified a bifurcation of human B cell maturation from the T1 stage forming IgMhi and IgMlo developmental trajectories. IgMhi T2 cells have higher expression of α4ß7 integrin and lower expression of IL-4 receptor (IL4R) compared with the IgMlo branch and are selectively recruited into gut-associated lymphoid tissue. IgMhi T2 cells also share transcriptomic features with marginal zone B cells (MZBs). Lineage progression from T1 cells to MZBs via an IgMhi trajectory is identified by pseudotime analysis of scRNA-sequencing data. Reduced frequency of IgMhi gut-homing T2 cells is observed in severe SLE and is associated with reduction of MZBs and their putative IgMhi precursors. The collapse of the gut-associated MZB maturational axis in severe SLE affirms its existence in health.

Modelling the effects of environmental heterogeneity within the lung on the tuberculosis life-cycle.

Progress in shortening the duration of tuberculosis (TB) treatment is hampered by the lack of a predictive model that accurately reflects the diverse environment within the lung. This is important as TB has been shown to produce distinct localisations to different areas of the lung during different disease stages, with the environmental heterogeneity within the lung of factors such as air ventilation, blood perfusion and oxygen tension believed to contribute to the apical localisation witnessed during the post-primary form of the disease. Building upon our previous model of environmental lung heterogeneity, we present a networked metapopulation model that simulates TB across the whole lung, incorporating these notions of environmental heterogeneity across the whole TB life-cycle to show how different stages of the disease are influenced by different environmental and immunological factors. The alveolar tissue in the lung is divided into distinct patches, with each patch representing a portion of the total tissue and containing environmental attributes that reflect the internal conditions at that location. We include populations of bacteria and immune cells in various states, and events are included which determine how the members of the model interact with each other and the environment. By allowing some of these events to be dependent on environmental attributes, we create a set of heterogeneous dynamics, whereby the location of the tissue within the lung determines the disease pathological events that occur there. Our results show that the environmental heterogeneity within the lung is a plausible driving force behind the apical localisation during post-primary disease. After initial infection, bacterial levels will grow in the initial infection location at the base of the lung until an adaptive immune response is initiated. During this period, bacteria are able to disseminate and create new lesions throughout the lung. During the latent stage, the lesions that are situated towards the apex are the largest in size, and once a post-primary immune-suppressing event occurs, it is the uppermost lesions that reach the highest levels of bacterial proliferation. Our sensitivity analysis also shows that it is the differential in blood perfusion, causing reduced immune activity towards the apex, which has the biggest influence of disease outputs.

A CO2 -Tolerant Perovskite Oxide with High Oxide Ion and Electronic Conductivity.

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σo ) and electronic conductivity (σe ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σe but inadequate σo . It has been a long-standing challenge to develop MIECs with both high σo and stability under device operation conditions. For example, the well-known perovskite oxide Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF) exhibits exceptional σo and electrocatalytic activity. The reactivity of BSCF with CO2 , however, limits its use in practical applications. Here, the perovskite oxide Bi0.15 Sr0.85 Co0.8 Fe0.2 O3- δ (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σo among the highest for known MIECs, but also high CO2 tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO2 . The combination of high oxide transport properties and CO2 tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications.

Stabilization of O-O Bonds by d0 Cations in Li4+ xNi1- xWO6 (0 ≤ x ≤ 0.25) Rock Salt Oxides as the Origin of Large Voltage Hysteresis.

Multinary lithium oxides with the rock salt structure are of technological importance as cathode materials in rechargeable lithium ion batteries. Current state-of-the-art cathodes such as LiNi1/3Mn1/3Co1/3O2 rely on redox cycling of earth-abundant transition-metal cations to provide charge capacity. Recently, the possibility of using the oxide anion as a redox center in Li-rich rock salt oxides has been established as a new paradigm in the design of cathode materials with enhanced capacities (>200 mAh/g). To increase the lithium content and access electrons from oxygen-derived states, these materials typically require transition metals in high oxidation states, which can be easily achieved using d0 cations. However, Li-rich rock salt oxides with high valent d0 cations such as Nb5+ and Mo6+ show strikingly high voltage hysteresis between charge and discharge, the origin of which is uninvestigated. In this work, we study a series of Li-rich compounds, Li4+ xNi1- xWO6 (0 ≤ x ≤ 0.25) adopting two new and distinct cation-ordered variants of the rock salt structure. The Li4.15Ni0.85WO6 (x = 0.15) phase has a large reversible capacity of 200 mAh/g, without accessing the Ni3+/Ni4+ redox couple, implying that more than two-thirds of the capacity is due to anionic redox, with good cyclability. The presence of the 5d0 W6+ cation affords extensive (>2 V) voltage hysteresis associated with the anionic redox. We present experimental evidence for the formation of strongly stabilized localized O-O single bonds that explain the energy penalty required to reduce the material upon discharge. The high valent d0 cation associates localized anion-anion bonding with the anion redox capacity.

Layered CeSO and LiCeSO Oxide Chalcogenides Obtained via Topotactic Oxidative and Reductive Transformations.

The chemical accessibility of the CeIV oxidation state enables redox chemistry to be performed on the naturally coinage-metal-deficient phases CeM1- xSO (M = Cu, Ag). A metastable black compound with the PbFCl structure type (space group P4/ nmm: a = 3.8396(1) Å, c = 6.607(4) Å, V = 97.40(6) Å3) and a composition approaching CeSO is obtained by deintercalation of Ag from CeAg0.8SO. High-resolution transmission electron microscopy reveals the presence of large defect-free regions in CeSO, but stacking faults are also evident which can be incorporated into a quantitative model to account for the severe peak anisotropy evident in all the high-resolution X-ray and neutron diffractograms of bulk CeSO samples; these suggest that a few percent of residual Ag remains. A straw-colored compound with the filled PbFCl (i.e., ZrSiCuAs- or HfCuSi2-type) structure (space group P4/ nmm: a = 3.98171(1) Å, c = 8.70913(5) Å, V = 138.075(1) Å3) and a composition close to LiCeSO, but with small amounts of residual Ag, is obtained by direct reductive lithiation of CeAg0.8SO or by insertion of Li into CeSO using chemical or electrochemical means. Computation of the band structure of pure, stoichiometric CeSO predicts it to be a Ce4+ compound with the 4f-states lying approximately 1 eV above the sulfide-dominated valence band maximum. Accordingly, the effective magnetic moment per Ce ion measured in the CeSO samples is much reduced from the value found for the Ce3+-containing LiCeSO, and the residual paramagnetism corresponds to the Ce3+ ions remaining due to the presence of residual Ag, which presumably reflects the difficulty of stabilizing Ce4+ in the presence of sulfide (S2-). Comparison of the behavior of CeCu0.8SO with that of CeAg0.8SO reveals much slower reaction kinetics associated with the Cu1- xS layers, and this enables intermediate CeCu1- xLi xSO phases to be isolated.

Interstitial Oxide Ion Conductivity in the Langasite Structure: Carrier Trapping by Formation of (Ga,Ge)2O8 Units in La3Ga5-x Ge1+x O14+x/2 (0 < x ≤ 1.5).

Framework oxides with the capacity to host mobile interstitial oxide anions are of interest as electrolytes in intermediate temperature solid oxide fuel cells (SOFCs). High performance materials of this type are currently limited to the anisotropic oxyapatite and melilite structure types. The langasite structure is based on a corner-shared tetrahedral network similar to that in melilite but is three-dimensionally connected by additional octahedral sites that bridge the layers by corner sharing. Using low-temperature synthesis, we introduce interstitial oxide charge carriers into the La3Ga5-x Ge1+x O14+x/2 langasites, attaining a higher defect content than reported in the lower dimensional oxyapatite and melilite systems in La3Ga3.5Ge2.5O14.75 (x = 1.5). Neutron diffraction and multinuclear solid state 17O and 71Ga NMR, supported by DFT calculations, show that the excess oxygen is accommodated by the formation of a (Ge,Ga)2O8 structural unit, formed from a pair of edge-sharing five-coordinated Ga/Ge square-based pyramidal sites bridged by the interstitial oxide and a strongly displaced framework oxide. This leads to more substantial local deformations of the structure than observed in the interstitial-doped melilite, enabled by the octahedral site whose primary coordination environment is little changed by formation of the pair of square-based pyramids from the originally tetrahedral sites. AC impedance spectroscopy on spark plasma sintered pellets showed that, despite its higher interstitial oxide content, the ionic conductivity of the La3Ga5-x Ge1+x O14+x/2 langasite family is lower than that of the corresponding melilites La1+y Sr1-y Ga3O7+y/2. The cooperative structural relaxation that forms the interstitial-based (Ga,Ge)2O8 units stabilizes higher defect concentrations than the single-site GaO5 trigonal bipyramids found in melilite but effectively traps the charge carriers. This highlights the importance of controlling local structural relaxation in the design of new framework electrolytes and suggests that the propensity of a framework to form extended units around defects will influence its ability to generate high mobility interstitial carriers.

Reactivity of Solid Rubrene with Potassium: Competition between Intercalation and Molecular Decomposition.

We present the synthesis and characterization of the K+-intercalated rubrene (C42H28) phase, K2Rubrene (K2R), and identify the coexistence of amorphous and crystalline materials in samples where the crystalline component is phase-pure. We suggest this is characteristic of many intercalated alkali metal-polyaromatic hydrocarbon (PAH) systems, including those for which superconductivity has been claimed. The systematic investigation of K-rubrene solid-state reactions using both K and KH sources reveals a complex competition between K intercalation and the decomposition of rubrene, producing three K-intercalated compounds, namely, K2R, K(RR*), and K xR' (where R* and R' are rubrene decomposition derivatives C42H26 and C30H20, respectively). K2R is obtained as the major phase over a wide composition range and is accompanied by the formation of amorphous byproducts from the decomposition of rubrene. K(RR*) is synthesized as a single phase, and K xR' is obtained only as a secondary phase to the majority K2R phase. The crystal structure of K2R was determined using high-resolution powder X-ray diffraction, revealing that the structural rearrangement from pristine rubrene creates two large voids per rubrene within the molecular layers in which K+ is incorporated. K+ cations accommodated within the large voids interact strongly with the neighboring rubrene via η6, η3, and η2 binding modes to the tetracene cores and the phenyl groups. This contrasts with other intercalated PAHs, where only a single void per PAH is created and the intercalated K+ weakly interacts with the host. The decomposition products of rubrene are also examined using solution NMR, highlighting the role of the breaking of C-Cphenyl bonds. For the crystalline decomposition derivative products K(RR*) and K xR', a lack of definitive structural information with regard to R* and R' prevents the crystal structures from being determined. The study illustrates the complexity in accessing solvent-free alkali metal salts of reduced PAH of the type claimed to afford superconductivity.