Cluster Core Research Articles

Improved model of the Supernova Refsdal cluster MACS J1149.5+2223 thanks to VLT/MUSE

We present new \, observations of the Hubble Frontier Field (HFF) galaxy cluster MACS J1149.5+2223, lensing the well-known supernova ``Refsdal'' into multiple images, which has enabled the first cosmological applications with a strongly lensed supernova. Thanks to these data, targeting a northern region of the cluster and thus complementing our previous \, program on the cluster core, we have released a new catalog containing \, secure spectroscopic redshifts. We confirmed 22 cluster members, which had previously been only photometrically selected, and detected ten additional ones, resulting in a total of 308 secure members, of which 63<!PCT!> are spectroscopically confirmed. We further identified 17 new spectroscopic multiple images belonging to six different background sources. By exploiting these new and our previously published \, data, in combination with the deep HFF images, we developed an improved total mass model of MACS J1149.5+2223. This model includes 308 total mass components for the member galaxies and requires four additional mass profiles, one of which is associated with a cluster galaxy overdensity identified in the north, representing the dark matter mass distribution on larger scales. The values of the resulting 34 free parameters are optimized based on the observed positions of 106 multiple images from 34 different families, that cover an extended redshift range between 1.240 and 5.983. Our final model has a multiple image position root mean square value of which is in good agreement with other cluster lens models based on a similar number of multiple images. With this refined mass model, we have paved the way toward an improved strong-lensing analyses that will exploit the deep and high resolution observations with \, and \, on a pixel level in the region of the supernova Refsdal host. This will increase the number of observables by around two orders of magnitude, thus offering the opportunity to carry out more precise and accurate cosmographic measurements in the future.

X-ray-inferred kinematics of the core intracluster medium in Perseus-like clusters: Insights from the TNG-Cluster simulation

The intracluster medium (ICM) of galaxy clusters encodes the impact of the physical processes that shape these massive halos, including feedback from central supermassive black holes (SMBHs). In this study, we examine the gas thermodynamics, kinematics, and the effects of SMBH feedback on the core of Perseus-like galaxy clusters with a new simulation suite: TNG-Cluster. We first make a selection of simulated clusters similar to Perseus based on the total mass and inner ICM properties, such as their cool-core nature. We identify 30 Perseus-like systems among the 352 TNG-Cluster halos at z = 0. Many exhibit thermodynamical profiles and X-ray morphologies with disturbed features such as ripples, bubbles, and shock fronts that are qualitatively similar to X-ray observations of Perseus. To study observable gas motions, we generate XRISM mock X-ray observations and conduct a spectral analysis of the synthetic data. In agreement with existing Hitomi measurements, TNG-Cluster predicts subsonic gas turbulence in the central regions of Perseus-like clusters, with a typical line-of-sight velocity dispersion of 200 km s−1. This implies that turbulent pressure contributes < 10% to the dominant thermal pressure. In TNG-Cluster, such low (inferred) values of ICM velocity dispersion coexist with high-velocity outflows and bulk motions of relatively small amounts of super-virial hot gas, moving up to thousands of km s−1. However, detecting these outflows in observations may prove challenging due to their anisotropic nature and projection effects. Driven by SMBH feedback, such outflows are responsible for many morphological disturbances in the X-ray maps of cluster cores. They also increase both the inferred and intrinsic ICM velocity dispersion. This effect is somewhat stronger when velocity dispersion is measured from higher-energy lines.

JWST’s First Glimpse of a z > 2 Forming Cluster Reveals a Top-heavy Stellar Mass Function

Clusters and their progenitors (protoclusters) at z ∼ 2 − 4, the peak epoch of star formation, are ideal laboratories to study the formation process of both the clusters themselves and their member galaxies. However, a complete census of their member galaxies has been challenging due to observational difficulties. Here we present new JWST/NIRCam observations targeting the distant cluster CLJ1001 at z = 2.51 from the COSMOS-Web program, which, in combination with previous narrowband imaging targeting Hα emitters and deep millimeter surveys of CO emitters, provide a complete view of massive galaxy assembly in CLJ1001. In particular, JWST reveals a population of massive, extremely red cluster members in the long-wavelength bands that were invisible in previous Hubble Space Telescope (HST)/F160W imaging (HST-dark members). Based on this highly complete spectroscopic sample of member galaxies, we show that the spatial distribution of galaxies in CLJ1001 exhibits a strong central concentration, with the central galaxy density already resembling that of low-z clusters. Moreover, we reveal a “top-heavy” stellar mass function for the star-forming galaxies (SFGs), with an overabundance of massive SFGs piled up in the cluster core. These features strongly suggest that CLJ1001 is caught in a rapid transition, with many of its massive SFGs likely soon becoming quiescent. In the context of cluster formation, these findings suggest that the earliest clusters form from the inside out and top to bottom, with the massive galaxies in the core assembling first, followed by the less massive ones in the outskirts.

A “MeerKAT-meets-LOFAR” study of the complex multi-component (mini-)halo in the extreme sloshing cluster Abell 2142

Context. Clusters of galaxies are known to be turbulent environments, whether they are merging systems where turbulence is injected via the conversion of gravitational potential energy into the intracluster medium (ICM), or whether they are relaxed systems in which small-scale core sloshing is occurring within the potential well. In many such systems, diffuse radio sources associated with the ICM are found: radio haloes and mini-haloes. Aims. Abell 2142 is a rich cluster undergoing an extreme episode of core sloshing, which has given rise to four cold fronts and a complex multi-component radio halo. Recent work revealed that there are three primary components to the halo that spans a distance of up to around 2.4 Mpc. The underlying physics of particle acceleration on these scales is poorly explored, and requires high-quality multi-frequency data with which to perform precision spectral investigation. We aim to perform such an investigation. Methods. We used new deep MeerKAT L-band (1283 MHz) observations in conjunction with LOFAR HBA (143 MHz) data as well as X-ray data from XMM-Newton and Chandra to study the spectrum of the halo and the connection between the thermal and non-thermal components of the ICM. Results. We confirm the presence of the third halo component, detecting it for the first time at 1283 MHz and confirming its ultra-steep spectrum nature, as we recovered an integrated spectrum of αH3, total = −1.68 ± 0.10. All halo components follow power-law spectra with increasingly steep spectra moving towards the cluster outskirts. We profiled the halo in three directions, finding evidence of asymmetry and spectral steepening along an axis perpendicular to the main axis of the cluster. Our investigation of the thermal non-thermal connection shows sub-linear correlations that are steeper at 1283 MHz than 143 MHz, and we find evidence of different connections in different components of the halo. In particular, we find both a moderate anti-correlation (H1, the core) and positive correlation (H2, the ridge) between the radio spectral index and X-ray temperature. Conclusions. Our results are broadly consistent with an interpretation of turbulent (re-)acceleration following an historic minor cluster merger scenario in which we must invoke some inhomogeneities. However, the anti-correlation between the radio spectral index and X-ray temperature in the cluster core is more challenging to explain; the presence of three cold fronts and a generally lower temperature may provide the foundations of an explanation, but detailed modelling is required to study this further.

Sloshing cold fronts in galaxy cluster Abell 2566

This paper presents properties of the intracluster medium (ICM) in the environment of a cool core cluster Abell 2566 (redshift z= 0.08247) based on the analysis of 20 ks Chandra X-ray data. 2D imaging analysis of the Chandra data from this cluster revealed spiral structures in the morphology of X-ray emission from within the central 109 kpc formed due to gas sloshing. This analysis also witness sharp edges in the surface brightness distribution along the south-east and north-west of the X-ray peaks at 41.6 kpc and 77.4 kpc, respectively. Spectral analysis of 0.5 – 7 keV X-ray photons along these discontinuities exhibited sharp temperature jumps from 2.3 to 3.1 keV and 1.8 to 2.8 keV, respectively, with consistency in the pressure profiles, implying their association with cold fronts due to gas sloshing of the gas. Further confirmation for such an association was provided by the deprojected broken power-law density function fit to the surface brightness distribution along these wedge shaped sectorial regions. This study also witness an offset of 4.6′′(6.8 kpc) between the BCG and the X-ray peak, and interaction of the BCG with a sub-system in the central region, pointing towards the origin of the spiral structure due to a minor merger.

Ram pressure stripping in clusters: gravity can bind the ISM but not the CGM

ABSTRACT We explore the survival of a galaxy’s circumgalactic medium (CGM) as it experiences ram pressure stripping (RPS) moving through the intracluster medium (ICM). For a satellite galaxy, the CGM is often assumed to be entirely stripped/evaporated, an assumption that may not always be justified. We carry out 3D-hydrodynamic simulations of the interstellar and circumgalactic media (ISM + CGM) of a galaxy like JO201 moving through the ICM. The CGM can survive long at cluster outskirts ($\gtrsim 2 \rm \ Gyr$) but at smaller clustercentric distances, 90 per cent of the CGM mass is lost within ∼500 Myr. The gravitational restoring force on the CGM is mostly negligible and the CGM–ICM interaction is analogous to ‘cloud–wind interaction’. The CGM stripping time-scale does not depend on the ram pressure but on the CGM to ICM density contrast χ. Two distinct regimes emerge for CGM stripping: the χ > 1 regime, which is the well-known ‘cloud crushing’ problem, and the χ < 1 regime, which we refer to as the (relatively unexplored) ‘bubble drag’ problem. The first pericentric passage near the cluster core can rapidly – over a crossing time tdrag ∼ R/vrel – strip the CGM in the bubble drag regime. The ISM stripping criterion unlike the CGM criterion, still depends on the ram pressure $\rho _{\rm ICM} v_{\rm rel}^2$. The stripped tails of satellites contain contributions from both the disc and the CGM. The X-ray plume in M89 in the Virgo cluster and a lack of it in the nearby M90 might be attributed to their orbital histories. M90 has likely undergone stripping in the bubble drag regime due to a pericentric passage close to the cluster centre.

Gas-Phase Production of Hydroxylated Silicon Oxide Cluster Cations: Structure, Infrared Spectroscopy, and Astronomical Relevance.

The interaction of free cationic silicon oxide clusters, Si x O y + (x = 2-5, y ≥ x), with dilute water vapor, was investigated in a flow tube reactor. Product mass distributions indicate cluster size-dependent dissociative water adsorption. To probe the structure and vibrational spectra of the resulting Si x O y H2 + (x = 2-4) clusters, we employed infrared multiple photon dissociation spectroscopy and density functional theory calculations. The planar rhombic cluster core of the disilicon oxides (x = 2) appears to be retained upon dissociative adsorption of one H2O unit, whereas a significant structural transformation of the tri- and tetra-silicon oxides (x = 3 and 4) is induced, resulting in an increased coordination of the Si atoms and more 3D cluster structures. In an astronomical context, we discuss the potential relevance of Si x O y H z + clusters as seeds for dust nucleation and catalysts for carbon-based chemistry in diffuse or translucent interstellar clouds, where all the necessary conditions for producing these species are found. In the produced clusters, the frequency of the isolated silanol Si-OH stretching vibrational mode is considerably blue-shifted compared to that in hydroxylated bulk silica and small inorganic compounds. This mode has a characteristic frequency range between 1200 cm-1 (8.3 μm) and 1090 cm-1 (9.2 μm) and is associated with the anomalously small Si-OH bond lengths in these ionised species. In infrared observations such high frequency Si-O stretching modes are usually associated with a pure bulk silica component of silicate cosmic dust. The presence of Si x O y H2 + clusters in low silica astrophysical environments could thus potentially be detected via their signature Si-O band using the James Webb space telescope.

The case for hot-mode accretion in Abell 2029

ABSTRACT Radiative cooling and active galactic nucleus heating are thought to form a feedback loop that regulates the evolution of low-redshift cool-core galaxy clusters. Numerical simulations suggest that the formation of multiphase gas in the cluster core imposes a floor on the ratio of cooling time (tcool) to free-fall time (tff) at min(tcool/tff) ≈ 10. Observations of galaxy clusters show evidence for such a floor, and usually the cluster cores with min(tcool/tff) ≲ 30 contain abundant multiphase gas. However, there are important outliers. One of them is Abell 2029 (A2029), a massive galaxy cluster (M200 ≳ 1015 M⊙) with min(tcool/tff) ∼ 20, but little apparent multiphase gas. In this paper, we present high-resolution 3D hydrodynamic adaptive mesh refinement simulations of a cluster similar to A2029 and study how it evolves over a period of 1–2 Gyr. Those simulations suggest that A2029 self-regulates without producing multiphase gas because the mass of its central black hole (${\sim} 5 \times 10^{10} \, \mathrm{ M}_\odot$) is great enough for Bondi accretion of hot ambient gas to produce enough feedback energy to compensate for radiative cooling.

Traditional Village Morphological Characteristics and Driving Mechanism from a Rural Sustainability Perspective: Evidence from Jiangsu Province

(1) Background: The sustainable development of rural areas has become a critical factor in global economic and social transformation. As an essential part of China’s rural ecological and cultural system, traditional villages are now facing a crisis of yearly decline, and sustainable development has become a meaningful way to solve the problem. This study utilized morphological indicator analysis and the SDGs as an evaluation framework to reveal the correlation and driving factors between traditional villages’ spatial form and sustainability indicators. From the perspective of the spatial form, this approach has specific reference significance for improving the sustainability of traditional villages. (2) Methods: A framework for detecting the driving factors of rural sustainability based on four dimensions (morphology, environment, economy, and society) was constructed. A geographic information system (GIS) was used to analyze the geographic patterns and morphological indicator characteristics of traditional villages in Jiangsu Province, and GeoDetector was used to analyze the driving mechanisms of the spatial patterns of sustainability in traditional villages, providing the basis for spatial zoning and differentiated policy design for the construction, planning, and management of sustainable villages. (3) Results: ➀ The spatial patterns and morphological characteristics of traditional villages exhibit prominent geographical imbalances and significant cluster cores. ➁ The high-density and low-aspect-ratio rural form in the southern region (where rural industries are developed) promotes good economic sustainability in rural areas but also leads to poor environmental performance. The rural areas in the southwest and north (high-density forest areas) have medium density and a high aspect ratio, and the lack of agricultural space and external connections affects their social performance. The main focus is on poverty reduction and urban cooperation. The central and northern lakeside areas and the eastern coastal areas (important ecological protection areas) have low density and high aspect ratios, which have helped them to achieve excellent environmental performance but also led to contradictions in environmental, economic, and social performance. Maintaining low-density patterns, using clean energy, and protecting terrestrial and underwater biodiversity are essential to the sustainability of the rural environment. The agglomeration of spatial patterns promotes cooperation between rural and urban areas and improves industrial development, contributing to the sustainability of the rural economy. Improving social welfare and agricultural development contributes to the sustainability of rural societies. ➂ The impacts of various factors vary significantly; for example, Life below Water (SDG14), Climate Action (SDG13), and No Poverty (SDG1) are the most prominent, followed by Partnerships for the Goals (SDG17), Affordable and Clean Energy (SDG7), and Recent Work and Economic Growth (SDG8). (4) Conclusions: It is recommended that the government, with the driving mechanisms, divide the spatial management zoning of traditional villages in Jiangsu into three types of policy areas: environmental-oriented, economic-oriented, and social-oriented. Differentiated and targeted suggestions should be proposed to provide a critical decision-making basis for protecting and utilizing traditional villages in Jiangsu and similar provinces, as well as to help promote rural revitalization and sustainable rural construction in China.

Synthesis, characterization, crystal structures and biological activity of 4-chloro-2-(2-hydroxy-3-ethoxybenzylideneamino)phenol and complexes

Molecular nanoclusters comprising a heterometallic 3d-4f stoichiometry are an interesting class of compounds. In this paper, a chloro-containing Schiff base 4-chloro-2-(2-hydroxy-3-ethoxybenzylideneamino)phenol (H2L) was prepared by condensation reaction of 3-ethoxysalicylaldehyde with 2-amino-4-chlorophenol in methanol. The Schiff base is predisposed to chelate within a cluster core both 3d and 4f metal ions. Reaction of H2L with nickel salts afforded a tetranuclear NiII complex [Ni4L4(MeOH)4] (1), while with nickel salts and lanthanide(III) nitrate three tetranuclear NiII-LnIII complexes [Ni2Eu2L4(NO3)2(DMF)2] (2), [Ni2Er2L4(NO3)2(DMF)2] (3), [Ni2Tb2L4(CH3COO)2(DMF)2]·4DMF (4) were obtained. H2L and the complexes have been characterized by elemental analysis, IR, UV–Vis spectra. H2L has also been characterized by 1H and 13C NMR spectra. Molecular structures of the compounds have been determined by single crystal X-ray determination. In the complexes, the Schiff base ligands coordinate to the metal atoms via ether oxygen, imino nitrogen and two phenolate oxygen atoms. All the Ni atoms in the complexes are in octahedral coordination. The rare earth metal atoms are eight coordinated by the phenolate and ether oxygen of the Schiff base ligands, and anionic and solvent oxygen atoms, forming square antiprismatic coordination. The compounds were evaluated for their antibacterial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens, and antifungal activities on Candida albicans and Aspergillus niger, and gave interesting results.

Characterization of Post-COVID-19 Definitions and Clinical Coding Practices: Longitudinal Study.

Post-COVID-19 condition (colloquially known as "long COVID-19") characterized as postacute sequelae of SARS-CoV-2 has no universal clinical case definition. Recent efforts have focused on understanding long COVID-19 symptoms, and electronic health record (EHR) data provide a unique resource for understanding this condition. The introduction of the International Classification of Diseases, Tenth Revision (ICD-10) code U09.9 for "Post COVID-19 condition, unspecified" to identify patients with long COVID-19 has provided a method of evaluating this condition in EHRs; however, the accuracy of this code is unclear. This study aimed to characterize the utility and accuracy of the U09.9 code across 3 health care systems-the Veterans Health Administration, the Beth Israel Deaconess Medical Center, and the University of Pittsburgh Medical Center-against patients identified with long COVID-19 via a chart review by operationalizing the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) definitions. Patients who were COVID-19 positive with either a U07.1 ICD-10 code or positive polymerase chain reaction test within these health care systems were identified for chart review. Among this cohort, we sampled patients based on two approaches: (1) with a U09.9 code and (2) without a U09.9 code but with a new onset long COVID-19-related ICD-10 code, which allows us to assess the sensitivity of the U09.9 code. To operationalize the long COVID-19 definition based on health agency guidelines, symptoms were grouped into a "core" cluster of 11 commonly reported symptoms among patients with long COVID-19 and an extended cluster that captured all other symptoms by disease domain. Patients having ≥2 symptoms persisting for ≥60 days that were new onset after their COVID-19 infection, with ≥1 symptom in the core cluster, were labeled as having long COVID-19 per chart review. The code's performance was compared across 3 health care systems and across different time periods of the pandemic. Overall, 900 patient charts were reviewed across 3 health care systems. The prevalence of long COVID-19 among the cohort with the U09.9 ICD-10 code based on the operationalized WHO definition was between 23.2% and 62.4% across these health care systems. We also evaluated a less stringent version of the WHO definition and the CDC definition and observed an increase in the prevalence of long COVID-19 at all 3 health care systems. This is one of the first studies to evaluate the U09.9 code against a clinical case definition for long COVID-19, as well as the first to apply this definition to EHR data using a chart review approach on a nationwide cohort across multiple health care systems. This chart review approach can be implemented at other EHR systems to further evaluate the utility and performance of the U09.9 code.

Investigating Mass Segregation of the Binary Stars in the Open Cluster NGC 6819

We search for mass segregation in the intermediate-aged open cluster NGC 6819 within a carefully identified sample of probable cluster members. Using photometry from Gaia, Pan-STARRS, and the Two Micron All Sky Survey as inputs for a Bayesian statistics software suite, BASE-9, we identify a rich population of (photometric) binaries and derive posterior distributions for the cluster age, distance, metallicity, and reddening, as well as star-by-star photometric membership probabilities, masses, and mass ratios (for binaries). Within our entire sample, we identify 2632 cluster members and 777 binaries. We then select a main-sequence “primary sample” with 14.85 <G < 19.5, containing 1342 cluster members and 250 binaries with mass ratios q > 0.5, to investigate mass segregation. Within this primary sample, we find the binary radial distribution is significantly shifted toward the cluster center as compared to the single stars, resulting in a binary fraction that increases significantly toward the cluster core. Furthermore, we find that within the binary sample, more massive binaries have more centrally concentrated radial distributions than less massive binaries. The same is true for the single stars. We verify the expectation of mass segregation for this stellar sample in NGC 6819 through both relaxation time arguments and by investigating a sophisticated N-body model of the cluster. Importantly, this is the first study to investigate mass segregation of the binaries in the open cluster NGC 6819.

Population Health Management: A Bibliometric Analysis of Literature on Data Analytics and Public Health Interventions

Population health management (PHM) has emerged as a pivotal strategy in healthcare, aiming to address the health needs of communities while enhancing care quality and outcomes. Recent years have witnessed a surge in research at the intersection of data analytics and public health interventions within the realm of PHM. This paper presents a comprehensive bibliometric analysis of the literature on data analytics and public health interventions in the context of population health management. Through systematic data collection from reputable scholarly databases and rigorous analysis, this study aims to map out the trends, key contributors, and emerging themes shaping the discourse in this domain. The analysis encompasses publication trends, authorship patterns, citation metrics, and network visualizations to provide insights into the landscape of literature. Notable findings include a high citation rate per paper and author, indicative of scholarly interest and collaboration within the research community. Key themes identified include outcomes, interventions, population health improvement, determinants, and health disparities. Additionally, temporal analysis reveals a shift towards non-communicable diseases and the increasing role of data in patient care. The author collaboration network highlights a core cluster of researchers with extensive collaborative ties, alongside peripheral authors and topics representing specialized or nascent areas. The density visualization map identifies potential areas for future research, including health disparities, women's health issues, and geographic-specific studies.

Theoretical Spectroscopic Study of Normal Raman and Charge Transfer Surface-Enhanced Raman Scattering (SERS) Spectra of the Adsorbed l- and d-Cysteine on the Chiral Au34 and Ag4@Au30 Nanoclusters: Chirality Discrimination.

In this work, the discrimination of the enantiomers of cysteine (l- and d-CYS) using the chiral Au34 and Ag4@Au30 clusters was theoretically investigated in the gas phase and water. Two modes were considered for the interaction of each enantiomer with the clusters (via only its S atom or its S atom and NH2 group, simultaneously). The interaction energy (Eint) and adsorption energy (Ead) for the complexation of each enantiomer with the clusters for each interaction mode were calculated. Considering the calculated interaction energies, the interaction of d-CYS with Au34 is stronger than that of l-CYS with the same cluster. Also, it was observed that the substitution of the Au4 core of the Au34 cluster with the Ag4 cluster caused the increase of the interaction energy of l-CYS with the Ag4@Au30 cluster compared to the Au34 cluster, while the reverse trend was observed for d-CYS. Quantum theory of atoms in molecules (QTAIM) analysis was employed to calculate the interaction paths and their related bond critical points (BCPs) between the CYS enantiomers and the clusters to explain the difference between the interaction energy of the enantiomers with the clusters. The IR, normal Raman (NR), and surface-enhanced Raman scattering (SERS) spectra of the enantiomers interacting with the Au34 and Ag4@Au30 clusters were calculated, and the discrimination between l-CYS and d-CYS using the calculated spectra was explained. It was found that the discrimination of the enantiomers based on their interaction with the clusters is controlled by the charge transfer between the enantiomers and the clusters.

On the inefficiency of particle re-acceleration mechanisms in the cores of massive stellar clusters

ABSTRACT We consider scenarios for non-thermal particle acceleration and re-acceleration in the central cores of compact massive star clusters, aided by insights from high-resolution hydrodynamic simulations. We show that (i) particles are unlikely to interact with many shocks during their lifetimes in the core; (ii) colliding flows do not produce hard spectra; and (iii) turbulent re-acceleration in the core is suppressed. Inefficient re-acceleration mechanisms are not expected to produce hard components nor to increase the maximum energy within the cores of massive star clusters. Models in which the observed ultra-high-energy gamma rays originate in the core of massive stellar clusters are thus disfavoured.

Structural Chemistry of Titanium (IV) Oxo Clusters, Part 2: Clusters without Carboxylate or Phosphonate Ligands.

Homometallic titanium oxo clusters (TOC) are one of the most important groups of metal oxo clusters. In a previous article, TOC structures with carboxylato and phosphonato ligands were reviewed and categorized. This work is now extended to clusters with other ligands. Comparison of the different cluster types shows how the interplay between condensation of the titanium polyhedra by means of bridging oxygen atoms and the coordination characteristics of the ligands influences the cluster structures and allows working out basic construction principles of the cluster core.

Hydrophobic Clusters Regulate Surface Hydration Dynamics of Bacillus subtilis Lipase A.

The surface hydration diffusivity of Bacillus subtilis Lipase A (BSLA) has been characterized by low-field Overhauser dynamic nuclear polarization (ODNP) relaxometry using a series of spin-labeled constructs. Sites for spin-label incorporation were previously designed via an atomistic computational approach that screened for surface exposure, reflective of the surface hydration comparable to other proteins studied by this method, as well as minimal impact on protein function, dynamics, and structure of BSLA by excluding any surface site that participated in greater than 30% occupancy of a hydrogen bonding network within BSLA. Experimental ODNP relaxometry coupling factor results verify the overall surface hydration behavior for these BSLA spin-labeled sites similar to other globular proteins. Here, by plotting the ODNP parameters of relative diffusive water versus the relative bound water, we introduce an effective "phase-space" analysis, which provides a facile visual comparison of the ODNP parameters of various biomolecular systems studied to date. We find notable differences when comparing BSLA to other systems, as well as when comparing different clusters on the surface of BSLA. Specifically, we find a grouping of sites that correspond to the spin-label surface location within the two main hydrophobic core clusters of the branched aliphatic amino acids isoleucine, leucine, and valine cores observed in the BSLA crystal structure. The results imply that hydrophobic clustering may dictate local surface hydration properties, perhaps through modulation of protein conformations and samplings of the unfolded states, providing insights into how the dynamics of the hydration shell is coupled to protein motion and fluctuations.

Redox-Active Boron Clusters.

ConspectusIn this Account, we discuss our group's research over the past decade on a class of functionalized boron clusters with tunable chemical and physical properties, with an emphasis on accessing and controlling their redox behavior. These clusters can be thought of as three-dimensional aromatic systems that have distinct redox behavior and photophysical properties compared to their two-dimensional organic counterparts. Specifically, our lab has studied the highly tunable, multielectron redox behavior of B12(OR)12 clusters and applied these molecules in various settings. We first discuss the spectroscopic and electrochemical characterization of B12(OR)12 clusters in various oxidation states, followed by their use as catholytes and/or anolytes in redox flow batteries and chemical dopants in conjugated polymers. Additionally, the high oxidizing potential and visible light-absorbing nature of fluoroaryl-functionalized B12(OR)12 clusters have been leveraged by our group to generate weakly coordinating, photoexcitable species that can promote photooxidation chemistry.We have further translated these solution-phase studies of B12(OR)12 clusters to the solid state by using the precursor [B12(OH)12]2- cluster as a robust building block for hybrid metal oxide materials. Specifically, we have shown that the boron cluster can act as a thermally stable cross-linking material, which enhances electron transport between metal oxide nanoparticles. We applied this structural motif to create TiO2- and WO3-containing materials that showed promising properties as photocatalysts and electroactive materials for supercapacitors. Building on this concept, we later discovered that B12(OCH3)12, the smallest of the B12(OR)12 family, could retain its redox behavior in the solid state, a previously unseen phenomenon. We successfully harnessed this unique behavior for solid-state energy storage by implementing this boron cluster as a cathode-active material in a Li-ion prototype cell device. Recently, our group has also explored how to tune the redox properties of clusters other than B12(OR)12 species by synthesizing a library of vertex-differentiated clusters containing both B-OR and B-halogen groups. Due to the additive qualities of different functional groups on the cluster, these species allow access to a region of electrochemical potentials previously inaccessible by fully substituted closo-dodecaborate alkoxy-based derivatives.Lastly, we discuss our research into smaller-sized redox-active polyhedral boranes (B6- and B10-based cluster cores). Interestingly, these clusters show significantly less redox stability and reversibility than their dodecaborate-based counterparts. While exploring the functionalization of closo-hexaborate to create fully substituted derivates (i.e., [B6R6Hfac]-), we observed unique oxidative decomposition pathways for this cluster system. Consequently, we leveraged this oxidative instability to generate useful alkyl boronate esters via selective chemical oxidation. We further explored a closo-decaborate cluster as a platform to access electrophilic [B10H13]+ species capable of directly borylating arene compounds with unique regioselectivity. Upon chemical oxidation of the arylated decaborate clusters, we successfully synthesized various aryl boronate esters, establishing the generality of the oxidative cluster deconstruction concept.Overall, our work shows that boron clusters are an appealing class of redox-active molecules, and this fundamental and understudied property can be leveraged for constructing novel materials with tunable physical and electrochemical properties, as well as producing unique chemical reagents for small molecule synthesis.

Novel flexible aromatic Cu3 metal-organic π-cluster for electrocatalytic CO2 reduction reaction

Producing Cn products through electrocatalytic CO2 reduction reaction (CO2RR) is of great significance in addressing the global warming crisis. Organic-inorganic hybrid catalysts, characterized by precise and controllable active sites and metal-ligand synergistic interactions, can enhance the reaction activity and stability of Cu-based catalysts. Herein, based on density functional theory (DFT), a novel flexible aromatic Cu3 metal-organic π-cluster (Cu3-π cluster) was constructed, consisting of triple-atom active centers and pentalyne ligands. During the catalytic CO2RR process, the adsorption of H can promote the activation of CO2, this converts the competing hydrogen evolution reaction (HER) into promoting CO2RR. Enhanced aromaticity of its cluster core is credited with stabilizing the coadsorption of H and CO2 (H* + CO2*), consequently lowering the reaction free energy of the CO2 activation process. Research has shown that Cu3-π cluster have high catalytic activity for electrocatalytic CO2 generation of C2H4. Considering the solvation effect, the limit potential of this reaction is −0.60 V. Furthermore, the reaction free energies suggest that the Cu3-π cluster is more inclined to yield C2H4(g) products via COCO* coupling. Moreover, the high CO coverage at the triple-atom active centers not only makes it more challenging for this cluster to adsorb H, but also reduces the energy barrier of the COCO* coupling reaction.In the entire reaction pathway of C2H4(g), there exhibits dynamic self-adaptive behavior in the bond lengths and bond angles of the three Cu atoms in the cluster core, leading to fluctuations in aromaticity. The flexibility and aromaticity changes in this structure enable the Cu3-π cluster to better stabilize intermediates. This work provides theoretical guidance for the application of metal-organic π-clusters, accelerates the screening of catalysts for CO2RR, and provides powerful theoretical guidance for the structure-activity relationships between aromaticity and catalytic activity.

Regulation mechanism of the quorum sensing regulator AphA on the type Ⅵ secretion system VflT6SS2 in Vibrio fluvialis

Objective: To explore the regulation mechanism of the quorum sensing regulator AphA on the functional activity of type Ⅵ secretion system VflT6SS2 in Vibrio fluvialis. Methods: Western Blot analysis was used to detect the relative expression and secretion of VflT6SS2 signature component hemolysin-coregulated protein (Hcp) in wild type (WT), ΔaphA, and corresponding complementary strains. Quantitative reverse transcription PCR and luminescence activity assay of the promoter-lux fusion system was used to measure the mRNA expression levels and promoter activity of the VflT6SS2 core and accessory gene-cluster representative genes tssB2, hcp (tssD2) and vgrG (tssI2), and the quorum sensing regulator HapR in WT and ΔaphA strains. A point mutation experiment combined with a luminescence activity assay was used to verify the regulatory binding site of AphA in the tssD2b promoter region. Electrophoretic mobility shift assay (EMSA) was used to determine AphA binding to the hapR promoter. Results: The mRNA expression levels of tssB2, hcp(tssD2), vgrG (tssI2), and hapR as well as the protein expression and secretion levels of Hcp in ΔaphA strain, were significantly higher than those in the WT strain. The promoter activities of the VflT6SS2 core cluster, tssD2a, tssI2a, and hapR were higher in ΔaphA strain than in the WT strain, while the promoter activity of tssD2b showed the opposite trend. The promoter sequence analysis of tssD2a and tssD2b found significant differences in the region from -335 bp to -229 bp, and two potential AphA binding sites on tssD2b. The promoter activity of tssD2b decreased significantly after the point mutation of the two potential AphA binding sites. EMSA results showed that AphA binds directly to the promoter region of hapR. Conclusions: AphA indirectly inhibits the regulation of the VflT6SS2 core and accessory gene clusters at the promoter level by directly repressing the expression of hapR. AphA showed opposite regulation patterns for tssD2a and tssD2b, and AphA could positively regulate the expression of tssD2b by directly binding to the tssD2b promoter region (-335 bp to -229 bp).