Breakdown of Boltzmann-type models for the alignment of self-propelled rods.

Studies in the collective motility of organisms use a range of analytical approaches to formulate continuous kinetic models of collective dynamics from rules or equations describing agent interactions. However, the derivation of these kinetic models often relies on Boltzmann's "molecular chaos" hypothesis, which assumes that correlations between individuals are short-lived. While this assumption is often the simplest way to derive tractable models, it is often not valid in practice due to the high levels of cooperation and self-organization present in biological systems. In this work, we illustrated this point by considering a general Boltzmann-type kinetic model for the alignment of self-propelled rods where rod reorientation occurs upon binary collisions. We examine the accuracy of the kinetic model by comparing numerical solutions of the continuous equations to an agent-based model that implements the underlying rules governing microscopic alignment. Even for the simplest case considered, our comparison demonstrates that the kinetic model fails to replicate the discrete dynamics due to the formation of rod clusters that violate statistical independence. Additionally, we show that introducing noise to limit cluster formation helps improve the agreement between the analytical model and agent simulations but does not restore the agreement completely. These results highlight the need to both develop and disseminate improved moment-closure methods for modeling biological and active matter systems.

Cluster Formation of Self-Assembled Triarylbismuthanes and Charge Transport Characterizations of Gold-Triarylbismuthane-Gold Junctions.

Organometallic molecules are promising for molecular electronic devices due to their potential to improve electrical conductance through access to complex orbital covalency that is not available to light-element organic molecules. However, studies of the formation of organometallic monolayers and their charge transport properties are scarce. Here, we report the cluster formation and charge transport properties of gold-triarylbismuthane-gold molecular junctions. We found that triarylbismuthane molecules with -CN anchoring groups form clusters during the creation of self-assembled submonolayers. This clustering is attributed to strong interactions between the bismuth (Bi) center and the nitrogen atom in the -CN group of adjacent molecules. Examination of the influence of -NH2 and -CN anchoring groups on junction conductance revealed that, despite a stronger binding energy between the -NH2 group and gold, the conductance per molecular unit (i.e., molecule for the -NH2 group and cluster for the -CN group) is higher with the -CN anchoring group. Further analysis showed that an increase in the number of -CN groups from one to three within the junctions leads to a decrease in conductance while increasing the size of the cluster. This demonstrates the significant effects of different anchoring groups and the impact of varying the number of -CN groups on both the charge transport and cluster formation. This study highlights the importance of selecting the appropriate anchoring group in the design of molecular junctions. Additionally, controlling the size and formation of clusters can be a strategic approach to engineering charge transport in molecular junctions.

Highly Active Oxidation Catalysts through Confining Pd Clusters on CeO2 Nano-Islands.

CeO2-supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO2-Al2O3 support. The preferential location of Pd on CeO2 islands leads to a high local surface noble metal concentration and promotes the in situ formation of small Pd clusters at a rather low noble metal loading (0.5 wt %), which are shown to be the active species for CO conversion at low temperatures. As elucidated by complementary in situ/operando techniques, the spatial separation of CeO2 islands on Al2O3 confines the mobility of Pd, preventing the full redispersion or the formation of larger noble metal particles and maintaining a high CO oxidation activity at low temperatures. In a broader perspective, this approach to more efficiently use the noble metal can be transferred to further systems and reactions in heterogeneous catalysis.

Cholesterol suppresses spontaneous activation of EGFR-mediated signal transduction.

Epidermal growth factor receptor (EGFR)-mediated signal transduction controls cell growth and proliferation. The signaling pathway is regulated so that it is activated only by external EGF stimuli, but the mechanisms that prevent EGF-independent spontaneous activation of EGFR-mediated signaling are unknown. Here we report cholesterol depletion activates EGFR-mediated signaling without EGF. We applied automated single-molecule imaging to EGFR and characterized the lateral diffusion and cluster formation on cholesterol-depleted and cholesterol-supplemented membranes. In cells in which cholesterol was depleted by methyl-ß-cyclodextrin (MßCD) treatment, EGFR exhibited a reduction in lateral diffusion, an acceleration of cluster formation, and autophosphorylation without EGF. Concurrently, extracellular signal-regulated kinase (ERK), which is regulated by EGFR-mediated signaling, exhibited phosphorylation and nuclear translocation without EGF. These cholesterol depletion-induced changes were similar, albeit less efficient, to those that occurred with EGF stimulation in normal cells without MßCD, indicating the spontaneous activation of EGFR signaling. The exogenous supplementation of cholesterol suppressed the MßCD-induced spontaneous activation of EGFR and ERK nuclear translocation. Single-molecule imaging of EGFR in a large number of cells revealed cell-to-cell heterogeneity, with a sub-population showing a high ability for spontaneous activation. These results provide evidence that EGFR-mediated signaling is properly regulated by cholesterol metabolism to prevent uncontrolled spontaneous activation.

Au30(PiPr2nBu)12Cl6-An Open Cluster Provides Insight into the Influence of the Sterical Demand of the Phosphine Ligand in the Formation of Metalloid Gold Clusters.

Phosphine-stabilized gold clusters are an important subgroup of metalloid gold cluster compounds and are important model compounds for nanoparticles. Although there are numerous gold clusters with different phosphine ligands, the effect of phosphine on cluster formation and structure remains unclear. While the linear alkyl-substituted phosphine gold chlorides result in a Au32 cluster, the bulky tBu3P leads to a Au20 cluster. The reduction of (iPr2nBuP)AuCl, with the steric demand of the phosphine ligand between the mentioned phosphines, results in the successful synthesis and crystallization of a new metalloid gold cluster, Au30(PiPr2nBu)12Cl6. Its structure is similar to the Au32 cluster but with two missing AuCl units. The UV/Vis studies and quantum chemical calculations show the similarities between the two clusters and the influence of the phosphine ligand in the synthesis of metalloid gold clusters.

Reversible Structural Evolution of Metal-Nitrogen-Doped Carbon Catalysts During CO2 Electroreduction: An Operando X-ray Absorption Spectroscopy Study.

Electrochemical CO2 reduction (CO2 RR) is a rising technology, aiming to reduce the energy sector dependence on fossil fuels and to produce carbon-neutral raw materials. Metal-nitrogen-doped carbons (M-N-C) are emerging, cost-effective catalysts for this reaction; however, their long-term stability is a major issue. To overcome this, understanding their structural evolution is crucial, requiring systematic in-depth operando studies. Here a series of M-N-C catalysts (M = Fe, Sn, Cu, Co, Ni, Zn) is investigated using operando X-ray absorption spectroscopy. It is found that the Fe-N-C and Sn-N-C are prone to oxide clusters formation even before CO2 RR. In contrast, the respective metal cations are singly dispersed in the as-prepared Cu-N-C, Co-N-C, Ni-N-C, and (Zn)-N-C. During CO2 RR, metallic clusters/nanoparticles reversibly formed in all catalysts, except for the Ni-N-C. This phenomenon, previously observed only in Cu-N-C, thus is ubiquitous in M-N-C catalysts. The competition between M-O and M-N interactions is an important factor determining the mobility of metal species in M-N-C. Specifically, the strong interaction between the Ni centers and the N-functional groups of the carbon support results in higher stability of the Ni single-sites, leading to the excellent performance of Ni-N-C in the CO2 to CO conversion, in comparison to other transition metals.

Maternally inherited siRNAs initiate piRNA cluster formation.

PIWI-interacting RNAs (piRNAs) guide transposable element repression in animal germ lines. In Drosophila, piRNAs are produced from heterochromatic loci, called piRNA clusters, which act as information repositories about genome invaders. piRNA generation by dual-strand clusters depends on the chromatin-bound Rhino-Deadlock-Cutoff (RDC) complex, which is deposited on clusters guided by piRNAs, forming a positive feedback loop in which piRNAs promote their own biogenesis. However, how piRNA clusters are formed before cognate piRNAs are present remains unknown. Here, we report spontaneous de novo piRNA cluster formation from repetitive transgenic sequences. Cluster formation occurs over several generations and requires continuous trans-generational maternal transmission of small RNAs. We discovered that maternally supplied small interfering RNAs (siRNAs) trigger de novo cluster activation in progeny. In contrast, siRNAs are dispensable for cluster function after its establishment. These results reveal an unexpected interplay between the siRNA and piRNA pathways and suggest a mechanism for de novo piRNA cluster formation triggered by siRNAs.

Role of site-site interaction on the phase equilibria of multiple-site associating fluids in a functionalized slit pore.

Vapor-liquid phase equilibria for multiple sites associating fluids with different associating strengths are investigated in a slit pore using grand-canonical transition matrix Monte Carlo method. The increase of critical temperature from two-site to four-site associating fluids at constant site strength is quite significant as compared to that of the one-site to two-site associating fluids, which is more pronounced at higher associating strength (ϵ* = 6). Monomer fraction and cluster size distribution are used to investigate the association of fluid particles in coexistence phases. The monomer fraction for both phases decreases with increased associating sites on the fluid particles due to more site-site interaction with neighboring fluid particles and forming a larger cluster. Therefore, the number of associating sites and their distribution play a vital role in the association of fluid particles. Moreover, the saturation chemical potential changes with the arrangement of the sites. For two-site associating fluids, we observe early vapor-liquid transition when the sites are oppositely placed, and when the sites are placed at 90°, the vapor-liquid transition is observed at the higher chemical potential. Moreover, four-site associating fluids with a square arrangement show early vapor-liquid phase transition, mainly because these arrangements of sites effectively interact with surface sites and the molecules in the next layer.

Modeling the effect of acquired resistance on cancer therapy outcomes.

Adaptive therapy (AT) is an evolution-based treatment strategy that exploits cell-cell competition. Acquired resistance can change the competitive nature of cancer cells in a tumor, impacting AT outcomes. We aimed to determine if adaptive therapy can still be effective with cell's acquiring resistance. We developed an agent-based model for spatial tumor growth considering three different types of acquired resistance: random genetic mutations during cell division, drug-induced reversible (plastic) phenotypic changes, and drug-induced irreversible phenotypic changes. These three resistance mechanisms lead to different spatial distributions of resistant cells. To quantify the spatial distribution, we propose an extension of Ripley's K-function, Sampled Ripley's K-function (SRKF), which calculates the non-randomness of the resistance distribution over the tumor domain. Our model predicts that the emergent spatial distribution of resistance can determine the time to progression under both adaptive and continuous therapy (CT). Notably, a high rate of random genetic mutations leads to quicker progression under AT than CT due to the emergence of many small clumps of resistant cells. Drug-induced phenotypic changes accelerate tumor progression irrespective of the treatment strategy. Low-rate switching to a sensitive state reduces the benefits of AT compared to CT. Furthermore, we also demonstrated that drug-induced resistance necessitates aggressive treatment under CT, regardless of the presence of cancer-associated fibroblasts. However, there is an optimal dose that can most effectively delay tumor relapse under AT by suppressing resistance. In conclusion, this study demonstrates that diverse resistance mechanisms can shape the distribution of resistance and thus determine the efficacy of adaptive therapy.

Intracellular mechanics and TBX3 expression jointly dictate the spreading mode of melanoma cells in 3D environments.

Cell stiffness and T-box transcription factor 3 (TBX3) expression have been identified as biomarkers of melanoma metastasis in 2D environments. This study aimed to determine how mechanical and biochemical properties of melanoma cells change during cluster formation in 3D environments. Vertical growth phase (VGP) and metastatic (MET) melanoma cells were embedded in 3D collagen matrices of 2 and 4 mg/ml collagen concentrations, representing low and high matrix stiffness. Mitochondrial fluctuation, intracellular stiffness, and TBX3 expression were quantified before and during cluster formation. In isolated cells, mitochondrial fluctuation decreased and intracellular stiffness increased with increase in disease stage from VGP to MET and increased matrix stiffness. TBX3 was highly expressed in soft matrices but diminished in stiff matrices for VGP and MET cells. Cluster formation of VGP cells was excessive in soft matrices but limited in stiff matrices, whereas for MET cells it was limited in soft and stiff matrices. In soft matrices, VGP cells did not change the intracellular properties, whereas MET cells exhibited increased mitochondrial fluctuation and decreased TBX3 expression. In stiff matrices, mitochondrial fluctuation and TBX3 expression increased in VGP and MET, and intracellular stiffness increased in VGP but decreased in MET cells. The findings suggest that soft extracellular environments are more favourable for tumour growth, and high TBX3 levels mediate collective cell migration and tumour growth in the earlier VGP disease stage but play a lesser role in the later metastatic stage of melanoma.

Unravelling the orientation of the inositol-biphosphate ring and its dependence on phosphatidylinositol 4,5-bisphosphate cluster formation in model membranes.

HYPOTHESIS: Inositol phospholipids are well known to form clusters in the cytoplasmic leaflet of the plasma membrane that are responsible for the interaction and recruitment of proteins involved in key biological processes like endocytosis, ion channel activation and secondary messenger production. Although their phosphorylated inositol ring headgroup plays an important role in protein binding, its orientation with respect to the plane of the membrane and its lateral packing density has not been previously described experimentally. EXPERIMENTS: Here, we study phosphatidylinositol 4,5-bisphosphate (PIP2) planar model membranes in the form of Langmuir monolayers by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry to elucidate the relation between lateral (in-plane) and perpendicular (out-of-plane) molecular organization of PIP2. FINDINGS: Different surface areas were explored through monolayer compression, allowing us to correlate the formation of transient PIP2 clusters with the change in orientation of the inositol-biphosphate headgroup, which was experimentally determined by neutron reflectometry.

Between Elemental Match and Mismatch: From K12 Ge3.5 Sb6 to Salts of (Ge2 Sb2 )2- , (Ge4 Sb12 )4- , and (Ge4 Sb14 )4.

The solid mixture "K2 GeSb" was shown to comprise single-crystalline K12 Ge3.5 Sb6 (1), a double salt of K5 [GeSb3 ] with carbonate-like [GeSb3 ]5- anions, and the metallic Zintl phase K2 Ge1.5 . Extraction of 1 with ethane-1,2-diamine in the presence of crypt-222 afforded [K(crypt-222)]+ salts of several novel binary Zintl anions: (Ge2 Sb2 )2- (in 2), (Ge4 Sb12 )4- (in 3), and in the presence of [AuMePPh3 ] also (Ge4 Sb14 )4- (in 4). The anion in 2 represents a predicted, yet heretofore missing pseudo-tetrahedral anion. 4 comprises a cluster analogous to (Ge4 Bi14 )4- and (Ga2 Bi16 )4- , and thus one of the most Sb-rich binary p-block anions. The unprecedented cluster topology in 3 can be viewed as a defect-version of the one in 4 upon following a "dead end" of cluster growth. The findings indicate that Ge and Sb atoms are at the border of a well-matching and a mismatch elemental combination. We discuss the syntheses, the geometric structures, and the electronic structures of the new compounds.

Nonisothermal nucleation in the gas phase is driven by cool subcritical clusters.

Nucleation of clusters from the gas phase is a widely encountered phenomenon, yet rather little is understood about the underlying out-of-equilibrium dynamics of this process. The classical view of nucleation assumes isothermal conditions where the nucleating clusters are in thermal equilibrium with their surroundings. However, in all first-order phase transitions, latent heat is released, potentially heating the clusters and suppressing the nucleation. The question of how the released energy affects cluster temperatures during nucleation as well as the growth rate remains controversial. To investigate the nonisothermal dynamics and energetics of homogeneous nucleation, we have performed molecular dynamics simulations of a supersaturated vapor in the presence of thermalizing carrier gas. The results obtained from these simulations are compared against kinetic modeling of isothermal nucleation and classical nonisothermal theory. For the studied systems, we find that nucleation rates are suppressed by two orders of magnitude at most, despite substantial release of latent heat. Our analyses further reveal that while the temperatures of the entire cluster size populations are elevated, the temperatures of the specific clusters driving the nucleation flux evolve from cold to hot when growing from subcritical to supercritical sizes and resolve the apparent contradictions regarding cluster temperatures. Our findings provide unprecedented insight into realistic nucleation events and allow us to directly assess earlier theoretical considerations of nonisothermal nucleation.

Cluster Formation for Analyses of Glaucomatous Visual Field Defects in Central 10-2 Visual Field in Normal Tension Glaucoma Eyes.

Purpose: To develop a cluster system to analyze the retinal sensitivity loss of 68 test points in the central 10 degrees of standard automated perimetry (SAP) in eyes with normal tension glaucoma (NTG). Patients and Methods: Patients with NTG who met the following criteria were included: visual acuity ≥0.7, SAP-derived mean deviation ≥-15 dB, and pattern deviation probability plots with at least one point with a probability of <0.5% and/or two or more contiguous points with a probability of <1% that did not cross the horizontal meridian in the central 12 points of the 24-2 test points. SAP with the Swedish Interactive Threshold Algorithm Standard (SITA-S) 10-2 program (10-2) was performed within 6 months of the SITA-S 24-2. The averaged total deviation (TD) for each of the 68 test points in the 10-2 was calculated. Hierarchical cluster analyses were performed based on the deviation of the TDs of the test points, and a dendrogram was created. The number of clusters was determined following the Sturges' rule. Results: One hundred and twenty-six eyes of 126 patients (61.9±11.4 years) were studied. Hierarchical cluster analysis of the TD values statistically obtained a dendrogram that divided the 68 test points into 7 clusters. Of these 7 clusters, 21 points belonging to the clusters in the papillomacular region included cluster 5. Cluster 5 was distributed above and below the horizontal meridian, which does not agree with the course of the retinal nerve fiber layer (RNFL). Conclusion: The hierarchical cluster analysis of the TD values stratified the 68 test points of the 10-2 into seven clusters. Considering the course of the RNFL, cluster 5 was divided into clusters of 5a and 5b, and consequently eight clusters were considered to be appropriate for detecting glaucomatous visual field defects in the central 10 degrees in NTG eyes.

Thermodynamics, static properties and transport behaviour of fluids with competing interactions.

Competing interaction fluids have become ideal model systems to study a large number of phenomena, for example, the formation of intermediate range order structures, condensed phases not seen in fluids driven by purely attractive or repulsive forces, the onset of particle aggregation under in- and out-of-equilibrium conditions, which results in the birth of reversible and irreversible aggregates or clusters whose topology and morphology depend additionally on the thermodynamic constrictions, and a particle dynamics that has a strong influence on the transport behaviour and rheological properties of the fluid. In this contribution, we study a system of particles interacting through a potential composed by a continuous succession of a short-ranged square-well (SW), an intermediate-ranged square-shoulder and a long-ranged SW. This potential model is chosen to systematically analyse the contribution of every component of the interaction potential on the phase behaviour, the microstructure, the morphology of the resulting aggregates and the transport phenomena of fluids described by competing interactions. Our results indicate that the inclusion of a barrier and a second well leads to new and interesting effects, which in addition result in variations of the physical properties associated to the competition among interactions.

A novel nonlocal partial differential equation model of endothelial progenitor cell cluster formation during the early stages of vasculogenesis.

The formation of new vascular networks is essential for tissue development and regeneration, in addition to playing a key role in pathological settings such as ischemia and tumour development. Experimental findings in the past two decades have led to the identification of a new mechanism of neovascularisation, known as cluster-based vasculogenesis, during which endothelial progenitor cells (EPCs) mobilised from the bone marrow are capable of bridging distant vascular beds in a variety of hypoxic settings in vivo. This process is characterised by the formation of EPC clusters during its early stages and, while much progress has been made in identifying various mechanisms underlying cluster formation, we are still far from a comprehensive description of such spatio-temporal dynamics. In order to achieve this, we propose a novel mathematical model of the early stages of cluster-based vasculogenesis, comprising of a system of nonlocal partial differential equations including key mechanisms such as endogenous chemotaxis, matrix degradation, cell proliferation and cell-to-cell adhesion. We conduct a linear stability analysis on the system and solve the equations numerically. We then conduct a parametric analysis of the numerical solutions of the one-dimensional problem to investigate the role of underlying dynamics on the speed of cluster formation and the size of clusters, measured via appropriate metrics for the cluster width and compactness. We verify the key results of the parametric analysis with simulations of the two-dimensional problem. Our results, which qualitatively compare with data from in vitro experiments, elucidate the complementary role played by endogenous chemotaxis and matrix degradation in the formation of clusters, suggesting chemotaxis is responsible for the cluster topology while matrix degradation is responsible for the speed of cluster formation. Our results also indicate that the nonlocal cell-to-cell adhesion term in our model, even though it initially causes cells to aggregate, is not sufficient to ensure clusters are stable over long time periods. Consequently, new modelling strategies for cell-to-cell adhesion are required to stabilise in silico clusters. We end the paper with a thorough discussion of promising, fruitful future modelling and experimental research perspectives.

Simulation of Cluster Dynamics of Proton-Bound Water Clusters in a High Kinetic Energy Ion-Mobility Spectrometer.

Ions are separated in ion mobility spectrometry (IMS) by their characteristic motion through a gas-filled drift tube with a static electric field present. Chemical dynamics, such as clustering and declustering of chemically reactive systems, and physical parameters, as, for example, the electric field strength or background gas temperature, impact on the observed ion mobility. In high kinetic energy IMS (HiKE-IMS), the reduced electric field strength is up to 120 Td in both the reaction region and drift region of the instrument. The ion generation in a corona discharge driven chemical ionization source leads generally to formation of proton-bound water clusters. However, the reduced electric field strength and therefore the effective ion temperature has a significant influence on the chemical equilibria of this reaction system. In order to characterize the effects occurring in IMS systems in general, numerical simulations can support and potentially explain experimental observations. The comparison of the simulation of a well characterized chemical reaction system (i.e., the proton-bound water cluster system) with experimental results allows us to validate the numerical model applied in this work. Numerical simulations of the proton-bound water cluster system were performed with the custom particle-based ion dynamics simulation framework (IDSimF). The ion-transport calculation in the model is based on a Verlet integration of the equations of motion and uses a customized Barnes-Hut method to calculate space charge interactions. The chemical kinetics is modeled stochastically with a Monte Carlo method. The experimental and simulated drift spectra are in good qualitative and quantitative agreement, and experimentally observed individual transitions of cluster ions are clearly reproduced and identified by the numerical model.

Quality Verification with a Cluster-Controlled Manufacturing System to Generate Monocyte-Derived Dendritic Cells.

Dendritic cell (DC) vaccines for cancer immunotherapy have been actively developed to improve clinical efficacy. In our previous report, monocyte-derived DCs induced by interleukin (IL)-4 with a low-adherence dish (low-adherent IL-4-DCs: la-IL-4-DCs) improved the yield and viability, as well as relatively prolonged survival in vitro, compared to IL-4-DCs developed using an adherent culture protocol. However, la-IL-4-DCs exhibit remarkable cluster formation and display heterogeneous immature phenotypes. Therefore, cluster formation in la-IL-4-DCs needs to be optimized for the clinical development of DC vaccines. In this study, we examined the effects of cluster control in the generation of mature IL-4-DCs, using cell culture vessels and measuring spheroid formation, survival, cytokine secretion, and gene expression of IL-4-DCs. Mature IL-4-DCs in cell culture vessels (cluster-controlled IL-4-DCs: cc-IL-4-DCs) displayed increased levels of CD80, CD86, and CD40 compared with that of la-IL-4-DCs. cc-IL-4-DCs induced antigen-specific cytotoxic T lymphocytes (CTLs) with a human leukocyte antigen (HLA)-restricted melanoma antigen recognized by T cells 1 (MART-1) peptide. Additionally, cc-IL-4-DCs produced higher levels of IFN-γ, possessing the CTL induction. Furthermore, DNA microarrays revealed the upregulation of BCL2A1, a pro-survival gene. According to these findings, the cc-IL-4-DCs are useful for generating homogeneous and functional IL-4-DCs that would be expected to promote long-lasting effects in DC vaccines.

Reciprocal Fitness Feedbacks Promote the Evolution of Mutualistic Cooperation.

Mutually beneficial interactions are ubiquitous in nature and have played a pivotal role for the evolution of life on earth. However, the factors facilitating their emergence remain poorly understood. Here, we address this issue both experimentally and by mathematical modeling using cocultures of auxotrophic strains of Escherichia coli, whose growth depends on a reciprocal exchange of amino acids. Coevolving auxotrophic pairs in a spatially heterogeneous environment for less than 150 generations transformed the initial interaction that was merely based on an exchange of metabolic byproducts into a costly metabolic cooperation, in which both partners increased the amounts of metabolites they produced to benefit their corresponding partner. The observed changes were afforded by the formation of multicellular clusters, within which increased cooperative investments were favored by positive fitness feedbacks among interacting genotypes. Under these conditions, non-cooperative individuals were less fit than cooperative mutants. Together, our results highlight the ease with which mutualistic cooperation can evolve, suggesting similar mechanisms likely operate in natural communities. VIDEO ABSTRACT.

Fluorescent linear polyurea based on toluene diisocyanate: Easy preparation, broad emission and potential applications.

In contrast to conventional fluorescent polymers featured by large conjugation structures, a new class of fluorescent polymers without above conjugations are gaining constant interest owing to their significant academic importance and promising applications in diverse fields. These unconventional fluorescent polymers are in general composed of heteroatoms (e.g. N, O, P, and S) under different forms. Here we report our recent study on polyurea, prepared by a very simple one step precipitation polymerization of toluene diisocyanate in a binary solvent of water-acetone. This polyurea, basically consisting of phenyl ring and urea group, shows fluorescent emission in a broad concentration range, from very low (10-5 mg/mL) to its solubility limit (50 mg/mL), and in a wide range of emission wavelength from UV to visible regions of up to 500 nm under varied excitation wavelength. The emission behaviors were fully studied under different concentrations and excitations. It was concluded that the emission in UV region was intrinsic due to the conjugation between the phenyl and the adjacent urea unit; while the emission in visible region, strongly excitation dependent, was caused by the cluster formation of the molecular chains, in accordance with the cluster-triggered-emission (CTE) mechanism. The formation of the cluster was tested through dynamic light scattering, FTIR and UV absorbance. Tested in presence of different metal ions, Fe3+ demonstrated a quenching effect with high selectivity. Based on this study, different paper-based sensors were designed to detect Fe3+, H2O2 in bioanalysis and for data encryption. This work provides a simple way to prepare a polyurea, a novel type of unconventional fluorescent polymer, with high emission performance distinct from its known analogues.