Genome evolution of the ancient hexaploid Platanus × acerifolia (London planetree).

Whole-genome duplication (WGD; i.e., polyploidy) and chromosomal rearrangement (i.e., genome shuffling) significantly influence genome structure and organization. Many polyploids show extensive genome shuffling relative to their pre-WGD ancestors. No reference genome is currently available for Platanaceae (Proteales), one of the sister groups to the core eudicots. Moreover, Platanus × acerifolia (London planetree; Platanaceae) is a widely used street tree. Given the pivotal phylogenetic position of Platanus and its 2-y flowering transition, understanding its flowering-time regulatory mechanism has significant evolutionary implications; however, the impact of Platanus genome evolution on flowering-time genes remains unknown. Here, we assembled a high-quality, chromosome-level reference genome for P. × acerifolia using a phylogeny-based subgenome phasing method. Comparative genomic analyses revealed that P. × acerifolia (2n = 42) is an ancient hexaploid with three subgenomes resulting from two sequential WGD events; Platanus does not seem to share any WGD with other Proteales or with core eudicots. Each P. × acerifolia subgenome is highly similar in structure and content to the reconstructed pre-WGD ancestral eudicot genome without chromosomal rearrangements. The P. × acerifolia genome exhibits karyotypic stasis and gene sub-/neo-functionalization and lacks subgenome dominance. The copy number of flowering-time genes in P. × acerifolia has undergone an expansion compared to other noncore eudicots, mainly via the WGD events. Sub-/neo-functionalization of duplicated genes provided the genetic basis underlying the unique flowering-time regulation in P. × acerifolia. The P. × acerifolia reference genome will greatly expand understanding of the evolution of genome organization, genetic diversity, and flowering-time regulation in angiosperms.

Effect of In utero Exposure to Air Pollution on Adulthood Hospitalizations.

Empirical analyses have demonstrated that individuals exposed to severe air pollution in utero have worse health outcomes during childhood. However, there is little evidence on the long-term health impacts of air pollution exposure. The objective of this paper is to estimate the effect of in utero exposure to the Great London Smog of 1952 (GLS) on five health outcomes identified through a scoping review to be those most likely affected: respiratory, circulatory, neoplasms, mental health, and nervous system conditions. We use the GLS, an extreme air pollution event in December 1952, as a quasi-natural experiment to estimate the effect of exposure to air pollution in utero on adulthood health. Data from the UK Biobank is analysed for a cohort of participants born from December 1952 to July 1956. Differences in health outcomes between adults exposed and not exposed to the GLS due to their birth dates, born inside and outside London, were explored. Our primary focus is hospitalization events between 1997 and 2020 (corresponding to ages 40 to 69), as recorded in linked administrative data from the National Health Service (NHS). Specifically, the five primary outcomes are binary variables indicating that the individual had at least one hospitalization where the main cause of hospitalization is related to respiratory, circulatory, neoplasms, mental health, or nervous system conditions. The analytical sample comprised 36,281 individuals. A positive effect on adulthood hospitalizations due to respiratory conditions was observed. If exposed to the GLS in utero, the probability of at least one respiratory health-related hospitalization between 1997 and 2020 increased by 2.58 percentage points (95% CI 0.08, 4.30, p = 0.03), a 23% increase relative to the sample mean. Small effects were found for all other outcomes, suggesting that these conditions were not affected by the GLS. We do not find heterogeneous effects by sex or childhood socioeconomic status. This study found that a 5-day pollution exposure event while in utero significantly increased respiratory-related hospitalizations at ages 40 to 69 but had no impact on hospitalizations due to circulatory, neoplasms, mental health, and nervous system conditions.

Ethnic inequalities during clinical placement: A qualitative study of student nurses' experiences within the London National Health Service.

AIM: To understand how student nurse experiences on clinical placement, within National Health Service (NHS) hospitals, differ for ethnic minority and White British groups. DESIGN: A qualitative thematic analysis with an inductive approach. METHODS: Data from semi-structured interviews with 21 London (United Kingdom) hospital-based student nurses were examined using thematic analysis. Participants were interviewed as part of the Tackling Inequalities and Discrimination Experiences in Health Services (TIDES) study and asked about their experiences during clinical placement. RESULTS: Five main themes were identified: (1) Role of mentors, (2) Discrimination and unfair treatment, (3) Speaking up/out, (4) Career progression, and (5) Consequences of adverse experiences. All themes were linked, with the social dynamics and workplace environment (referred to as "ward culture") providing a context that normalizes mistreatment experienced by nursing students. Students from ethnic minority backgrounds reported racism as well as cultural and/or religious microaggressions. While being valued for their race and ethnicity, White British students also experienced discrimination and inequity due to their age, sex, gender, and sexual orientation. Students from both White British and ethnic minority groups acknowledged that being treated badly was a barrier to career progression. Ethnic minority students also noted the lack of diverse representation within senior nursing positions discouraged career progression within the UK NHS. CONCLUSION: These initial experiences of inequality and discrimination are liable to shape a student's perspective of their profession and ability to progress within nursing. The NHS is responsible for ensuring that student nurses' developmental opportunities are equal, irrespective of ethnicity. IMPACT: Ward culture is perpetuated by others who normalize mistreatment and concurrently disadvantage ethnic minority students, making them feel unvalued. This in turn impacts both staff retention and career progression within the NHS. Training assessors should be aware of the existing culture of discrimination within clinical placements and work to eradicate it.

Thermal Surface Properties, London Dispersive and Polar Surface Energy of Graphene and Carbon Materials Using Inverse Gas Chromatography at Infinite Dilution.

The thermal surface properties of graphenes and carbon materials are of crucial importance in the chemistry of materials, chemical engineering, and many industrial processes. BACKGROUND: The determination of these surface properties is carried out using inverse gas chromatography at infinite dilution, which leads to the retention volume of organic solvents adsorbed on solid surfaces. This experimental and fundamental parameter actually reflects the surface thermodynamic interactions between injected probes and solid substrates. METHODS: The London dispersion equation and the Hamieh thermal model are used to quantify the London dispersive and polar surface energy of graphenes and carbon fibers as well their Lewis acid-base constants by introducing the coupling amphoteric constant of materials. RESULTS: The London dispersive and polar acid-base surface energies, the free energy of adsorption, the polar enthalpy and entropy, and the Lewis acid-base constants of graphenes and carbon materials are determined. CONCLUSIONS: It is shown that graphene exhibited the highest values of London dispersive surface energy, polar surface energy, and Lewis acid-base constants. The highest characteristics of graphene justify its great potentiality and uses in many industrial applications.

Temperature Dependence of the Polar and Lewis Acid-Base Properties of Poly Methyl Methacrylate Adsorbed on Silica via Inverse Gas Chromatography.

The adsorption of polymers on solid surfaces is common in many industrial applications, such as coatings, paints, catalysis, colloids, and adhesion processes. The properties of absorbed polymers commonly vary with temperature. In this paper, inverse gas chromatography at infinite dilution was used to determine the physicochemical characterization of PMMA adsorbed on silica. A new method based on the London dispersion equation was applied with a new parameter associating the deformation polarizability with the harmonic mean of the ionization energies of the solvent. More accurate values of the dispersive and polar interaction energies of the various organic solvents adsorbed on PMMA in bulk phase and PMMA/silica at different recovery fractions were obtained, as well as the Lewis acid-base parameters and the transition temperatures of the different composites. It was found that the temperature and the recovery fraction have important effects on the various physicochemical and thermodynamic properties. The variations in all the interaction parameters showed the presence of three transition temperatures for the different PMMA composites adsorbed on silica with various coverage rates, with a shift in these temperatures for a recovery fraction of 31%. An important variation in the polar enthalpy and entropy of adsorption, the Lewis acid-base parameters and the intermolecular separation distance was highlighted as a function of the temperature and the recovery fraction of PMMA on silica.

Self-Association and Microhydration of Phenol: Identification of Large-Amplitude Hydrogen Bond Librational Modes.

The self-association mechanisms of phenol have represented long-standing challenges to quantum chemical methodologies owing to the competition between strongly directional intermolecular hydrogen bonding, weaker non-directional London dispersion forces and C-H⋯π interactions between the aromatic rings. The present work explores these subtle self-association mechanisms of relevance for biological molecular recognition processes via spectroscopic observations of large-amplitude hydrogen bond librational modes of phenol cluster molecules embedded in inert neon "quantum" matrices complemented by domain-based local pair natural orbital-coupled cluster DLPNO-CCSD(T) theory. The spectral signatures confirm a primarily intermolecular O-H⋯H hydrogen-bonded structure of the phenol dimer strengthened further by cooperative contributions from inter-ring London dispersion forces as supported by DLPNO-based local energy decomposition (LED) predictions. In the same way, the hydrogen bond librational bands observed for the trimeric cluster molecule confirm a pseudo-C3 symmetric cyclic cooperative hydrogen-bonded barrel-like potential energy minimum structure. This structure is vastly different from the sterically favored "chair" conformations observed for aliphatic alcohol cluster molecules of the same size owing to the additional stabilizing London dispersion forces and C-H⋯π interactions between the aromatic rings. The hydrogen bond librational transition observed for the phenol monohydrate finally confirms that phenol acts as a hydrogen bond donor to water in contrast to the hydrogen bond acceptor role observed for aliphatic alcohols.

New Progress on London Dispersive Energy, Polar Surface Interactions, and Lewis's Acid-Base Properties of Solid Surfaces.

The determination of the polar surface free energy, polar properties, and Lewis's acid base of solid materials is of capital importance in many industrial processes, such as adhesion, coatings, two-dimensional films, and adsorption phenomena. (1) Background: The physicochemical properties of many solid particles were characterized during the last forty years by using the retention time of injected well-known molecules into chromatographic columns containing the solid substrates to be characterized. The obtained net retention time of the solvents adsorbed on the solid, allowing the determination of the net retention volume directly correlated to the specific surface variables, dispersive, polar, and acid-base properties. (2) Methods: Many chromatographic methods were used to quantify the values of the different specific surface variables of the solids. However, one found a large deviation between the different results. In this paper, one proposed a new method based on the London dispersion equation that allowed the quantification of the polar free energy of adsorption, as well as the Lewis's acid-base constants of many solid surfaces. (3) Results: The newly applied method allowed us to obtain the polar enthalpy and entropy of adsorption of polar model organic molecules on several solid substrates, such as silica, alumina, MgO, ZnO, Zn, TiO2, and carbon fibers. (4) Conclusions: our new method based on the separation between the dispersive and polar free surface energy allowed us to better characterize the solid materials.

The Nature and Purpose of Public Dissections in Early Modern London.

Modern scholarship on the early modern European anatomy theater has long argued that public dissections were theatrical, carnivalesque affairs characterized by viewers' fascination with the material exposure of the dissected body. This essay builds from the recent work on early modern public dissections to argue against such monolithic presentations of the early modern anatomy. To this end, the essay examines three principal source materials connected with public dissections in early modern London to more specifically argue that public dissections in sixteenth- and seventeenth-century London were solemn events focused on promoting the status of London's barber-surgeons' guild, the Royal College of Physicians, and the education and knowledge of their respective members. In this regard, the essay further suggests that there was no single, dominant perception of dissection and anatomy at the time, but that dissection was utilized as a tool for different individual, occupational, and institutional purposes.

Are Redox-Active Centers Bridged by Saturated Flexible Linkers Systematically Electrochemically Independent?

The extent to which electrophores covalently bridged by a saturated linker are electrochemically independent was investigated considering the charge/spin duality of the electron and functionality of the electrophore as a spin carrier upon reduction. By combining computational modeling with electrochemical experiments, we investigated the mechanism by which tethered electrophores react together within 4,4'-oligo[n]methylene-bipyridinium assemblies (with n=2 to 5). We show that native dicationic electrophores (redox state Z=+2) are folded prior to electron injection into the system, allowing the emergence of supra-molecular orbitals (supra-MOs) likely to support the process of the reductive σ bond formation giving cyclomers. Indeed, for Z=+2, London Dispersion (LD) forces contribute to flatten the potential energy surface such that all-trans and folded conformers are approximately isoenergetic. Then, upon one-electron injection, for radical cations (Z=+1), LD forces significantly stabilize the folded conformers, except for the ethylene derivative deprived of supra-MOs. For radical cations equipped with supra-MOs, the unpaired electron is delocalized over both heterocycles through space. Cyclomer completion (Z=0) upon the second electron transfer occurs according to the inversion of redox potentials. This mechanism explains why intramolecular reactivity is favored and why pyridinium electrophores are not independent.

Computational study of ground-state properties of µ2 -bridged group 14 porphyrinic sandwich complexes.

The structural properties of µ2 -bridged porphyrinic double-decker complexes are investigated and the influence of various ligands, metals, substituents, and bridging atoms on the dominant structural motif is elucidated. A variety of quantum chemical methods including semiempirical (SQM) methods and density functional theory (DFT) is assessed for the calculation of ecliptic and staggered conformational energies. Local coupled cluster (DLPNO-CCSD(T1)) data are generated for reference. The r2 SCAN-3c composite scheme as well as the B2PLYP-D4/def2-QZVPP approach are identified as reliable methods. Energy decomposition analyses (EDA) and localized molecular orbital analyses (LMO) are used to investigate the bonding situation and the nature of the inter-ligand interaction energy underlining the crucial role of attractive London dispersion interactions. Targeted modification of the bridging atom, e.g., by replacing O2- by S2- is shown to drastically change the major structural features of the investigated complexes. Further, the influence of different substituents of varying size at the phthalocyanine ligand regarding the dominant conformation is described.

London Dispersion Effects on the Stability of Heavy Tetrel Molecules.

London dispersion (LD) interactions, which stem from long-range electron correlations arising from instantaneously induced dipoles can occur between neighboring atoms or molecules, for example, between H atoms within ligand C-H groups. These interactions are currently of interest as a new method of stabilizing long bonds and species with unusual oxidation states. They can also limit reactivity by installing LD enhanced groups into organic frameworks or ligand substituents. Here, we address the most recent advances in the design of LD enhanced ligands, the sterically counterintuitive structures that can be generated and the consequences that these interactions can have on the structures and reactivity of sterically crowded heavy group 14 species.

Parallel and identical test-retest reliability of the Tower of London test - Freiburg version.

OBJECTIVES: The Tower of London - Freiburg version (TOL-F) was developed in three parallel-test versions (A, B, and C) that only differ in their physical appearance by interchanged ball colors, but not in their cognitive demands. We addressed the question whether the test-retest reliability of an identical problem set differs from the parallel test-retest reliability of a structurally identical problem set with a marginally different physical appearance. METHODS: Reliabilities were assessed in two samples of young adults over a 1-week interval: In the parallel test-retest sample (n = 93; 49 female), half of the participants accomplished version A at the first session and version B at the second session, while the other half started with version B in the first session and continued with A in the second session. In the identical test-retest sample (n = 86; 48 female), half of the participants performed on version A in both the first and the second session, while the other half went through the same procedure with version B. RESULTS: For overall planning accuracy, intraclass correlation coefficients for absolute agreement were r = .501 for the parallel test-retest and r = .605 for the identical test-retest sample, with Pearson correlations of r = .559 and r = .708 respectively. Greatest lower bound estimates of reliability were adequate to high in the two samples (ranging between .765 and .854) confirming previous studies. CONCLUSIONS: Although the TOL-F revealed only moderate intraclass correlations for absolute agreement, it showed some of the highest psychometric indices compared to repeated assessments with other TOL tests.

Functional characterization of three TERMINAL FLOWER 1-like genes from Platanus acerifolia.

KEY MESSAGE: TFL1-like genes of the basal eudicot Platanus acerifolia have conserved roles in maintaining vegetative growth and inhibiting flowering, but may act through distinct regulatory mechanism. Three TERMINAL FLOWER 1 (TFL1)-like genes were isolated and characterized from London plane tree (Platanus acerifolia). All genes have conserved genomic organization and characteristic of the phosphatidylethanolamine-binding protein (PEBP) family. Sequence alignment and phylogenetic analysis indicated that two genes belong to the TFL1 clade, designated as PlacTFL1a and PlacTFL1b, while another one was grouped in the BFT clade, named as PlacBFT. qRT-PCR analysis showed that all three genes primarily expressed in vegetative phase, but the expression of PlacTFL1a was much higher and wider than that of PlacTFL1b, with the latter only detected at relatively low expression levels in apical and lateral buds in April. PlacBFT was mainly expressed in young stems of adult trees followed by juvenile tissues. Ectopic expression of any TFL1-like gene in Arabidopsis showed phenotypes of delayed or repressed flowering. Furthermore, overexpression of PlacTFL1a gene in petunia also resulted in extremely delayed flowering. In non-flowering 35:PlacTFL1a transgenic petunia plants, the FT-like gene (PhFT) gene was significantly upregulated and AP1 homologues PFG, FBP26 and FBP29 were significantly down-regulated in leaves. Yeast two-hybrid analysis indicated that only weak interactions were detected between PlacTFL1a and PlacFDL, and PlacTFL1a showed no interaction with PhFDL1/2. These results indicated that the TFL1-like genes of Platanus have conserved roles in repressing flowering, but probably via a distinct regulatory mechanism.

Tackling barriers to COVID-19 vaccine uptake in London: a mixed-methods evaluation.

BACKGROUND: In response to the COVID-19 pandemic, the first vaccine was administered in December 2020 in England. However, vaccination uptake has historically been lower in London than in other English regions. METHODS: Mixed-methods: This comprised an analysis of cumulative percentage uptake across London between 8 December 2020 and 6 June 2021 by vaccine priority cohorts and ethnicity. We also undertook thematic analyses of uptake barriers, interventions to tackle these and key learning from a qualitative survey of 27 London local authority representatives, vaccine plans from London's five Integrated Care Systems and interviews with 38 London system representatives. RESULTS: Vaccine uptake was lower in Black ethnic (57-65% uptake) compared with the White British group (90% uptake). Trust was a critical issue, including mistrust in the vaccine itself and in authorities administering or promoting it. The balance between putative costs and benefits of vaccination created uptake barriers for zero-hour and shift workers. Intensive, targeted and 'hyper-local' initiatives, which sustained community relationships and were not constrained by administrative boundaries, helped tackle these barriers. CONCLUSIONS: The success of the national vaccination programme depended on conceding local autonomy, investing in responsive and long-term partnerships to engender trust through in-depth understanding of communities' beliefs.

Acceleration of plague outbreaks in the second pandemic.

Historical records reveal the temporal patterns of a sequence of plague epidemics in London, United Kingdom, from the 14th to 17th centuries. Analysis of these records shows that later epidemics spread significantly faster ("accelerated"). Between the Black Death of 1348 and the later epidemics that culminated with the Great Plague of 1665, we estimate that the epidemic growth rate increased fourfold. Currently available data do not provide enough information to infer the mode of plague transmission in any given epidemic; nevertheless, order-of-magnitude estimates of epidemic parameters suggest that the observed slow growth rates in the 14th century are inconsistent with direct (pneumonic) transmission. We discuss the potential roles of demographic and ecological factors, such as climate change or human or rat population density, in driving the observed acceleration.

African migrant women acquisition of clay for ingestion during pregnancy in London: a call for action.

OBJECTIVES: This study aimed to explore how African migrant women go about acquiring clay for ingestion during pregnancy in London against a backdrop of restrictions and warnings by the Food Standard Agency and Public Health England due to the potential health risks to expectant mothers and their unborn babies. STUDY DESIGN: This was a qualitative study using an interpretative phenomenological approach. METHODS: Individual in-depth interviews and a focus group discussion were used for data collection. Data collection took place between May and August 2020. RESULTS: Participants acquired clay from African shops and markets in London, countries of origin and online/social media platforms. Due to official restrictions and warnings, transactions were conducted under the counter based on trust between sellers and the women underpinned by shared community identities. However, clay was acquired, social networks emerged as crucial facilitators. The current top-down approach, which is also lacking a regulatory policy framework, has pushed clay transactions underground, thereby leaving pregnant women potentially ingesting toxic clay with little chances of dictation by authorities. CONCLUSION: We call on the UK Health Security Agency (UKHSA) and public health practitioners to collaborate with communities to design multilevel/multisectoral interventions as well as the Food Standards Agency (FSA) to consider an appropriate regulatory policy framework.

Algorithms for the adaptive assessment of procedural knowledge and skills.

Procedural knowledge space theory (PKST) was recently proposed by Stefanutti (British Journal of Mathematical and Statistical Psychology, 72(2) 185-218, 2019) for the assessment of human problem-solving skills. In PKST, the problem space formally represents how a family of problems can be solved and the knowledge space represents the skills required for solving those problems. The Markov solution process model (MSPM) by Stefanutti et al. (Journal of Mathematical Psychology, 103, 102552, 2021) provides a probabilistic framework for modeling the solution process of a task, via PKST. In this article, three adaptive procedures for the assessment of problem-solving skills are proposed that are based on the MSPM. Beside execution correctness, they also consider the sequence of moves observed in the solution of a problem with the aim of increasing efficiency and accuracy of assessments. The three procedures differ from one another in the assumption underlying the solution process, named pre-planning, interim-planning, and mixed-planning. In two simulation studies, the three adaptive procedures have been compared to one another and to the continuous Markov procedure (CMP) by Doignon and Falmagne (1988a). The last one accounts for dichotomous correct/wrong answers only. Results show that all the MSP-based adaptive procedures outperform the CMP in both accuracy and efficiency. These results have been obtained in the framework of the Tower of London test but the procedures can also be applied to all psychological and neuropsychological tests that have a problem space. Thus, the adaptive procedures presented in this paper pave the way to the adaptive assessment in the area of neuropsychological tests.

Royal London Space Planning as a learning tool for postgraduate Orthodontic students. A mixed methods study.

OBJECTIVE: To assess the effectiveness of the Royal London Space Planning (RLSP) as a learning tool among postgraduate orthodontic students as well as investigate students' attitudes to its use. The RLSP tool is a structured method of orthodontic case assessment and treatment planning. DESIGN: A prospective cohort study of first year postgraduate orthodontic students who attended teaching of the RLSP. SETTING: Postgraduate teaching institute. PARTICIPANTS: First year postgraduate orthodontic students. METHODS: The outcome measured was the accuracy in assessment and planning of a standardised orthodontic simulated case before and after teaching. Qualitative assessment was conducted through focus group and a semi-structured format after the teaching. RESULTS: Nineteen students were included in the study. There was an overall improvement in assessment and planning of 20% after the teaching intervention (P < 0.05). Assessment improved by 34% in comparison to treatment planning, which improved by 17% (P < 0.05). The impact of the RLSP was most noticeable on the assessment of crowding in the lower arch which improved by 37% after teaching (P < 0.05). Students felt using the RLSP tool made them more confident and was advantageous to use in training; most felt they would not use the tool after qualification. CONCLUSION: The RLSP tool is an effective method of teaching assessment and treatment planning to postgraduate orthodontic students. The effect of the RLSP is greater at assessments and less significant for treatment planning. The participant students felt the RLSP improved their confidence in assessment and treatment planning.

Paradoxes of social mobility in London.

We analyse social mobility in London and seek to address two paradoxes. Among people living in London, relative mobility, or social fluidity, appears to be remarkably low when compared with other regions of Great Britain. But social fluidity among people who were brought up in London is similar to that of people brought up elsewhere in Britain. This is our first paradox. Furthermore, it is widely held that social fluidity is higher among people with higher levels of education, yet, the proportion of people with a University degree is much higher among people living in London than in any other region: how is this compatible with its relatively low social fluidity? This is our second paradox. We address these puzzles and find that they are largely explained by patterns of migration into and out of London by two groups that have received little attention hitherto in studies of mobility in the capital: International migrants and people who were brought up in London but who no longer live there.

London Dispersion Effects in a Distannene/Tristannane Equilibrium: Energies of their Interconversion and the Suppression of the Monomeric Stannylene Intermediate.

Reaction of {LiC6 H2 -2,4,6-Cyp3 ⋅Et2 O}2 (Cyp=cyclopentyl) (1) of the new dispersion energy donor (DED) ligand, 2,4,6-triscyclopentylphenyl with SnCl2 afforded a mixture of the distannene {Sn(C6 H2 -2,4,6-Cyp3 )2 }2 (2), and the cyclotristannane {Sn(C6 H2 -2,4,6-Cyp3 )2 }3 (3). 2 is favored in solution at higher temperature (345 K or above) whereas 3 is preferred near 298 K. Van't Hoff analysis revealed the 3 to 2 conversion has a ΔH=33.36 kcal mol-1 and ΔS=0.102 kcal mol-1 K-1 , which gives a ΔG300 K =+2.86 kcal mol-1 , showing that the conversion of 3 to 2 is an endergonic process. Computational studies show that DED stabilization in 3 is -28.5 kcal mol-1 per {Sn(C6 H2 -2,4,6-Cyp3 )2 unit, which exceeds the DED energy in 2 of -16.3 kcal mol-1 per unit. The data clearly show that dispersion interactions are the main arbiter of the 3 to 2 equilibrium. Both 2 and 3 possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results).