Push-pull Interaction Research Articles

Functional architecture of cerebral cortex during naturalistic movie watching.

Characterizing the functional organization of cerebral cortex is a fundamental step in understanding how different kinds of information are processed in the brain. However, it is still unclear how these areas are organized during naturalistic visual and auditory stimulation. Here, we used high-resolution functional MRI data from 176 human subjects to map the macro-architecture of the entire cerebral cortex based on responses to a 60-min audiovisual movie stimulus. A data-driven clustering approach revealed a map of 24 functional areas/networks, each explicitly linked to a specific aspect of sensory or cognitive processing. Novel features of this map included an extended scene-selective network in the lateral prefrontal cortex, separate clusters responsive to human-object and human-human interaction, and a push-pull interaction between three executive control (domain-general) networks and domain-specific regions of the visual, auditory, and language cortex. Our cortical parcellation provides a comprehensive and unified map of functionally defined areas in the human cerebral cortex.

Triplet carbenes with transition-metal substituents.

The extraordinary advances in carbene (R1-C-R2) chemistry have been fuelled by strategies to stabilize the electronic singlet state via π interactions. In contrast, the lack of similarly efficient approaches to obtain authentic triplet carbenes with appreciable lifetimes beyond cryogenic temperatures hampers their exploitation in synthesis and catalysis. Transition-metal substitution represents a potential strategy, but metallocarbenes (M-C-R) usually represent high-lying excited electronic configurations of the well-established carbyne complexes (M≡C-R). Here we report the synthesis and characterization of triplet metallocarbenes (M-C-SiMe3, M = PdII, PtII) that are persistent beyond cryogenic conditions, and their selective reactivity towards carbene C-H insertion and carbonylation. Bond analysis reveals significant stabilization by spin-polarized push-pull interactions along both π-bonding planes, which fundamentally differs from bonding in push-pull singlet carbenes. This bonding model, thus, expands key strategies for stabilizing the open-shell carbene electromers and closes a conceptual gap towards carbyne complexes.

Programming Tetrathiafulvalene-Based Covalent Organic Frameworks for Promoted Photoinduced Molecular Oxygen Activation.

Despite the pivotal role of molecular oxygen (O2) activation in artificial photosynthesis, the activation efficiency is often restricted by sluggish exciton dissociation and charge transfer kinetics within polymer photocatalysts. Herein, we propose two tetrathiafulvalene (TTF)-based imine-linked covalent organic frameworks (COFs) with tailored donor-acceptor (D-A) structures, TTF-PDI-COF and TTF-TFPP-COF, to promote O2 activation. Because of enhanced electron push-pull interactions that facilitated charge separation and transfer behavior, TTF-PDI-COF exhibited superior photocatalytic activity in electron-induced O2 activation reactions over TTF-TFPP-COF under visible light irradiation, including the photosynthesis of (E)-3-amino-2-thiocyano-α,β-unsaturated compounds and H2O2. These findings highlight the significant potential of the rational design of COFs with D-A configurations as suitable candidates for advanced photocatalytic applications.

Dynamic Imaging of Lipid Droplets in Cells and Tissues by Using Dioxaborine Barbiturate-Based Fluorogenic Probes.

Lipids are essential for various cellular functions, including energy storage, membrane flexibility, and signaling molecule production. Maintaining proper lipid levels is important to prevent health problems such as cancer, neurodegenerative disorders, cardiovascular diseases, obesity, and diabetes. Monitoring cellular lipid droplets (LDs) in real-time with high resolution can provide insights into LD-related pathways and diseases owing to the dynamic nature of LDs. Fluorescence-based imaging is widely used for tracking LDs in live cells and animal models. However, the current fluorophores have limitations such as poor photostability and high background staining. Herein, we developed a novel fluorogenic probe based on a push-pull interaction combined with aggregation-induced emission enhancement (AIEE) for dynamic imaging of LDs. Probe 1 exhibits favorable membrane permeability and spectroscopic characteristics, allowing specific imaging of cellular LDs and time-lapse imaging of LD accumulation. This probe can also be used to examine LDs in fruit fly tissues in various metabolic states, serving as a highly versatile and specific tool for dynamic LD imaging in cellular and tissue environments.

Grafting small organic molecules on donor-acceptor polymers to regulate electron push-pull interactions for efficient H2O2 production

Pyrene units are grafted on a D-A polymer by amidation to construct a D + -A structure and improve H2O2 production. Experimental results show that the H2O2 generation rate of this D + -A polymer (PTM-PY) is 2.94 mmol g−1 h−1, which is higher than the original D-A polymer (PTM) under the same conditions. Mechanistic studies reveal that the increased photocatalytic performance of PTM-PY is attributed to the enhanced light-harvesting capacity and electron push-pull interactions after grafting pyrene as a donor. Therefore, grafting the appropriate small organic molecules on the D-A polymer skeleton can improve their performance further, in addition to the routine methods of optimizing the donor/acceptor ratio and reaction conditions. This is the first report of small organic molecules grafted on a D-A polymer to construct a D + -A polymer for photocatalytic H2O2 generation.

Lewis Acid Mediated Alteration of Electron Density on a Copper Site via pπ-dπ Mixing Enhances the Electrochemical Nitrogen Reduction Reaction.

Strategic modulation of the electronic structure of the catalyst to foster the electrochemical nitrogen reduction reaction (eNRR) to the ammonia process significantly is still an area that needs to be explored. Herein, we report the incorporation of the Lewis acid into an electron-rich copper site regulating the electron density of the metal, which has been experimentally proved from the d-band center position to have a direct influence on the adsorption of N2 compared to the protons. The catalyst boron doped copper-cuprous oxide hybrid system (B-Cu/Cu2O) has shown promising Faradaic efficiency of 32% at -0.2 V vs reversible hydrogen electrode (RHE) compared to the pristine cuprous oxide (Cu2O(N)) system. The in situ Fourier transform infrared study confirms the presence of intermediates evolved during the electroreduction process. This study demonstrates the design of the active center with a specific push-pull interaction via the pπ-dπ bonding-antibonding approach and can shed light on the electrochemical activation and reduction of dinitrogen to produce ammonia.

Electrochemical oxygen activation driven by enamine-keto push-pull interactions in triazole-based covalent organic polymers.

We have developed two triazole-based covalent organic polymers (COPs) with donor-acceptor motifs. The keto-enriched COP demonstrated exceptional oxygen activation via electrochemical stimuli, driven by strong push-pull interactions. In situ studies and DFT calculations confirmed the critical role of enamine carbon positive charges in enhancing performance, setting new benchmarks in COP design.

2,3-Diphenylquinoxalin-6-yl based dyes: Synthesis and studies of photophysical, aggregation-induced emission enhancement and electrochemical properties

Herein, 2,3-diphenylquinoxalin-6-yl based derivatives were synthesized, characterized by various spectroscopic method and studied for photophysical, aggregation-induced emission enhancement (AIEE) and electrochemical properties. Existence of intramolecular charge transfer transition (ICT) at 372−379 nm in absorption spectra of molecules confer weak push-pull interaction within it. Broad range of emission from blue to orange with λem = 412−592 nm in dyes arose from different energy state emission viz., locally excited (LE), Twisted intramolecular charge transfer (TICT) and excimer emission. Switching in emission state of molecules from excimer to TICT emission were observed by changing the polarity of solvent due to stabilization of TICT in polar media. Dyes have good solid state emission and AIEE activity desirable for its solid/aggregate state application in OLED's. Good Stokes shift (2183−9703 cm−1), thermal stability and comparable HOMO (−5.65 to −6.02 eV) energy levels with reported hole transporting materials confer desirable role of molecules in various optoelectronic applications. Further, DFT calculation of dyes, designate comparable experimental and theoretical photophysical and electrochemical properties with respect to structure of dyes.

Side-Chain Molecular Engineering of Triazole-Based Donor-Acceptor Polymeric Photocatalysts with Strong Electron Push-Pull Interactions.

A new series of donor-acceptor (D-A)-type semiconductive polymers were generated by the integration of electron-deficient alkyl chain anchored triazole (TA) moieties and electron-rich pyrene units into the polymer skeleton. The polymer series demonstrated satisfactory light-harvesting ability and suitable band gaps. In the series, polymer P-TAME benefits from a minimized exciton binding energy, strongest D-A interaction, and favorable hydrophilicity, affording an outstanding photocatalytic H2 evolution rate of ca. 100 μmol h-1 (10 mg polymer, AQY420 nm =8.9 %) and H2 O2 production rate of ca. 190 μmol h-1 (20 mg polymer) under visible-light irradiation, which is superior to most currently reported polymers. All polymers in the series can mediate water oxidation reactions to evolve O2 . Thus, these TA-based polymers open up a new avenue toward tailor-made efficient photocatalysts with broad photocatalytic activities.

Metal/Support Interactions Regulate Substrate Binding in Fe/Co/Se Cluster Catalysts.

Here, we investigate the stereoelectronic requirements of a family of Fe/Co6Se8 molecular clusters to achieve a Goldilocks regime of substrate affinity for the catalytic coupling of tosyl azide and tert-butyl isocyanide. The reactivity of a catalytically competent iron-nitrenoid intermediate, observed in situ, is explored toward nitrene transfer and hydrogen-atom abstraction. The dual role of isocyanide, which, on the one hand, prevents catalyst degradation but, in large amounts, slows down reactivity, is exposed. The impact of distal changes (the number of neighboring active sites and the identity of supporting ligands) on the substrate affinity, electronic properties, and catalytic activity is investigated. Overall, the study reveals that the dynamic, push-pull interactions between the substrate (tBuNC), active site (Fe), and support (Co6Se8) create a regime where increased substrate activation occurs with facile dissociation.

A heptazine-based polymer photocatalyst with donor-acceptor configuration to promote exciton dissociation and charge separation

Polymeric carbon nitride (PCN) is an emerging class of polymer semiconductor photocatalysts, but bulk PCN typically suffers from low visible-light-harvesting ability, high activation energy, and rapid charge recombination. In this context, using the same core building block, a donor-acceptor (D-A) type heptazine-based polymer, namely BPCN, was proposed via Friedel-Crafts arylation reaction to tackle these issues. Comparatively, the affording BPCN features extended light absorption, reduced activation energy, and suppressed charge recombination, triggered by the electron push-pull interactions as a consequence of the D-A configuration. BPCN is elucidated to be an effective heterogeneous photocatalyst for aerobic organic transformations and a wide range of substrate scopes and reactions were realized. Besides, BPCN also showed an advantage in mediating the photocatalytic water oxidation reaction, achieving a nearly 10-fold oxygen evolution reaction (OER) rate over PCN. These findings demonstrate the great potential of the rational design of heptazine-based polymers with D-A configurations for artificial photosynthesis.

Divergent CO2 Activation by Tuning the Lewis Acid in Iron-Based Bimetallic Systems.

Bimetallic motifs mediate the selective activation and functionalization of CO2 in metalloenzymes and some recent synthetic systems. In this work, we build on the nascent concept of bimetallic frustrated Lewis pairs (FLPs) to investigate the activation and reduction of CO2 . Using the Fe0 fragment [(depe)2 Fe] (depe=1,2-bis(diethylphosphino)ethane) as base, we modify the nature of the partner Lewis acid to accomplish a divergent and highly chemoselective reactivity towards CO2 . [Au(PMe2 Ar)]+ irreversibly dissociates CO2 , Zn(C6 F5 )2 and B(C6 F5 )3 yield different CO2 adducts stabilized by push-pull interactions, while Al(C6 F5 )3 leads to a rare heterobimetallic C-O bond cleavage, and thus to contrasting reduced products after exposure to dihydrogen. Computational investigations provide a rationale for the divergent reactivity, while Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method substantiates the heterobimetallic bonding situation.

Mechanistic Insight into the Ni-Catalyzed Kumada Cross-Coupling: Alkylmagnesium Halide Promotes C-F Bond Activation and Electron-Deficient Metal Center Slows Down β-H Elimination.

The Ni-catalyzed Kumada-Tamao-Corriu (KTC) cross-coupling between aryl fluorides and alkyl Grignard reagents has been used to achieve a highly selective Csp2-Csp3 bond construction via the carbon-fluorine (C-F) bond activation. However, the detailed mechanism of this groundbreaking KTC reaction remains unclear. Herein, we perform a series of analyses by density functional theory (DFT) calculations in order to understand the reaction mechanisms for the selective activation of a highly inert C-F bond by Ni catalysts with bidentate phosphorus ligands. An alternative mechanism for Ni/Mg bimetallic cooperation C-F bond cleavage instead of a traditional oxidative addition was proposed. The push-pull interaction in the transition state provided by the Ni center and the Lewis acid of the Mg cation smoothly breaks the C-F bond, supported by the significantly decreased activation energy from 30.9 to 4.6 kcal mol-1 and principal interacting orbital analysis. Owing to the elevated lowest unoccupied molecular orbital energy level and the electron-deficient metal center caused by the bidentate phosphorus ligand, the β-H elimination could be impeded, increasing the selectivity of KTC cross-coupling. Our DFT results rationally explain the experimental observations, which will be helpful for further development of KTC cross-coupling.

Moving in Together?Synoikismosand Polis Formation at Sagalassos and in Southwest Anatolia

Topics such as polis formation and synoikismos have a rich background in classical studies, history, and archaeology. Such studies have mainly focused on the attestations of synoikismos events in literary sources and inscriptions. The archaeological side of such processes has not always been given equal weight. This paper presents a more encompassing view on patterns of synoikismos and polis formation by incorporating and assessing archaeological evidence in a model of push-pull interactions between local communities and the Hellenistic kingdoms in southwest Anatolia. This model will be applied on a case study of the origin of polis at Sagalassos and its relation with the nearby settlement at Düzen Tepe during its formative years in the Early to Middle Hellenistic period (3rd–2nd centuries b.c.). It will then situate this case in its wider context of settlement patterns and community formation in southwest Anatolia, focusing on the ancient regions of Pisidia, Lycia, and Pamphylia. The paper suggests that interactions between local communities and overarching central administrations offered suitable stimuli that resulted in local communities starting to participate in wider dynamics of economic and political importance. This ultimately resulted in observed patterns of polis formation and a potential synoikismos.

Quadrupolar Ultrafast Charge Transfer in Diaminoazobenzene-Bridged Perylenediimide Triads.

Strong push-pull interactions between electron donor, diaminoazobenzene (azo), and an electron acceptor, perylenediimide (PDI), entities in the newly synthesized A-D-A type triads (A=electron acceptor and D=electron donor) and the corresponding A-D dyads are shown to reveal wide-band absorption covering the entire visible spectrum. Electrochemical studies revealed the facile reduction of PDI and relatively easier oxidation of diaminoazobenzene in the dyads and triads. Charge transfer reversal using fluorescence-spectroelectrochemistry wherein the PDI fluorescence recovery upon one-electron oxidation, deterring the charge-transfer interactions, was possible to accomplish. The charge transfer state density difference and the frontier orbitals from the DFT calculations established the electron-deficient PDI to be an electron acceptor and diaminoazobenzene to be an electron donor resulting in energetically closely positioned PDIδ- -Azoδ+ -PDIδ- quadrupolar charge-transfer states in the case of triads and Azoδ+ -PDIδ- dipolar charge-transfer states in the case of dyads. Subsequent femtosecond transient absorption spectral studies unequivocally proved the occurrence of excited-state charge transfer in these dyads and triads in benzonitrile wherein the calculated forward charge transfer rate constants, kf , were limited to instrument response factor, meaning >1012 s-1 revealing the occurrence of ultrafast photo-events. The charge recombination rate constant, kr , was found to depend on the type of donor-acceptor conjugates, that is, it was possible to establish faster kr in the case of triads (∼1011 s-1 ) compared to dyads (∼1010 s-1 ). Modulating both ground and excited-state properties of PDI with the help of strong quadrupolar and dipolar charge transfer and witnessing ultrafast charge transfer events in the studied triads and dyads is borne out from the present study.

High-Performance Near-Infrared Aggregation-Induced Emission Luminogen with Mitophagy Regulating Capability for Multimodal Cancer Theranostics.

The construction of intelligent near-infrared (NIR) fluorophores for high specificity to cancer cells and application in multiple therapeutic modalities is crucial for precise cancer diagnostic and therapy. In this study, an aggregation-induced emission-active NIR fluorophore (TACQ) with mitophagy-modulating activity was synthesized and developed for mitochondrial targeting multimodal cancer theranostics. The strengthened push-pull interaction extended the emission of TACQ into the NIR-II region (>1000 nm). Further, the rotor structure and twisted molecular conformation enables nanoaggregates of TACQ to balance the radiative and nonradiative decays to simultaneously exhibit bright NIR emission, high photothermal conversion efficiency (55%), and efficient generation of reactive oxygen species. The lipocationic property of TACQ allows it to selectively accumulate in the mitochondria of cancer cells. TACQ can induce mitophagy and block mitophagic flux facilitating cancer cell apoptosis. Both in vitro and in vivo evaluations revealed that TACQ is an efficient theranostic agent for NIR fluorescence and photothermal imaging-guided synergistic chemo-photothermal and photodynamic therapy.

The unknown but knowable relationship between Presaccadic Accumulation of activity and Saccade initiation

The goal of this short review is to call attention to a yawning gap of knowledge that separates two processes essential for saccade production. On the one hand, knowledge about the saccade generation circuitry within the brainstem is detailed and precise - push-pull interactions between gaze-shifting and gaze-holding processes control the time of saccade initiation, which begins when omnipause neurons are inhibited and brainstem burst neurons are excited. On the other hand, knowledge about the cortical and subcortical premotor circuitry accomplishing saccade initiation has crystalized around the concept of stochastic accumulation - the accumulating activity of saccade neurons reaching a fixed value triggers a saccade. Here is the gap: we do not know how the reaching of a threshold by premotor neurons causes the critical pause and burst of brainstem neurons that initiates saccades. Why this problem matters and how it can be addressed will be discussed. Closing the gap would unify two rich but curiously disconnected empirical and theoretical domains.

Reassessing the Origin of Polis in Lycia and Southwest Anatolia

The polis was one of the most important community forms in antiquity. Its origins are situated in the Aegean during the eighth century BCE. At the same time, the concept has been applied on a far larger spatial and temporal context. This article will focus on what the emergence of polis communities beyond the Aegean heartland entailed. The aim is to move beyond a one-sided Hellenocentric approach. I will discuss the emergence and development of urban and political communities in southwestern Anatolia - focusing on Lycia, Pamphylia and Pisidia - through archaeological evidence from settlement patterns and material culture. I will study polis formation through the lens of push-pull interactions as drivers of community organization by means of a comparison between two models of change: peer polity interaction and the royal policy model. This article shows that the development of political and urban communities, subsumed under the moniker of polis formation, should be dissociated from Hellenization and the spread of Greek culture. Complex and multidimensional processes of community formation cannot be unilaterally reduced to Greek influences. The observed changes can be explained by the superposition of actors on multiple levels pursuing their aims and strategies within a locally and regionally embedded context.

Influence of rotational asymmetry on thermoacoustic instabilities in a can-annular lean-premixed combustor

Low-frequency combustion instabilities, and ultimately, engine-level dynamics in can-annular gas turbine combustion systems, are driven by acoustic interactions between adjacent combustors through an annular cross-talk section upstream of first stage turbine nozzles. This is an area of substantial technological challenges, because experimental and numerical complexities scale exponentially with the number of combustors, restricting most investigations to a single combustor or a coupled two-combustor configuration. We recently reported that in a can-annular combustion system consisting of four identical lean-premixed combustors pressure oscillations occur in many combinations of characteristic patterns and frequencies, including symmetric (push–push) and asymmetric (push–pull) interactions, when the system is subjected to rotationally symmetric operating conditions. The impact of rotational asymmetry on can-annular thermoacoustics is still a largely open subject; here we use the same experimental setup to perform multiple independent analyses of the effect of broken rotational symmetry on large-scale pattern formations and modal dynamics of multiple eigenmodes. We demonstrate that the presence of rotational asymmetry can lead to fundamentally different dynamic states, including pairwise push-pull modes, spinning azimuthal instabilities, superposition modes, and strong mode localization, which are totally absent under rotationally symmetric conditions. Of particular importance is the experimental observation of spinning azimuthal instabilities in the annular cross-talk section, which are acoustically separate from flame-dynamics-driven standing wave motion in the flame tube sections. This leads to the coexistence of traveling and standing waves in the can-annular system. In conjunction with FEM-based Helmholtz simulations, we determine the origin of the azimuthal modes to be the simultaneous excitation of two different pairwise push-pull interaction modes at the same frequency – a phenomenon known as degenerate eigenmodes.

Cross-talk-interaction-induced combustion instabilities in a can-annular lean-premixed combustor configuration

The prediction of self-excited combustion instabilities in a can-annular gas turbine combustion system is a significant challenge, mainly because the instabilities originate from the acoustic interactions between adjacent combustors via a cross-talk region upstream of the first stage turbine nozzles. Detailed characterization of these instabilities requires a thorough understanding of engine-level dynamics. Until now, a comprehensive experimental examination of such a can-annular configuration had not been conducted. Here we present new experiments using four lean fully-premixed swirl-stabilized combustors connected via a full-annular cross-talk section. We demonstrate that the global fluctuations at limit cycles are either in-phase interactions (push-push modes) or one of two different forms of out-of-phase interactions (push-pull modes), subject to uniform and non-uniform equivalence ratio combinations. Under certain symmetric conditions, the can-annular system undergoes in-phase synchronous modulations (Type I), giving rise to the formation of pressure antinodes at the inlets of the four combustors and in the cross-talk region. By contrast, out-of-phase interactions are sustained in the form of either an alternating pattern in four-coupled combustors (Type II) or a push-pull interaction in two opposite combustors only (Type III). The latter is dictated by strong out-of-phase fluctuations between two of the combustors and a pressure node-like condition – thermoacoustically decoupled from the global fluctuations – over the entire region of the other two combustors, experimentally demonstrating the existence of mode localization in can-annular thermoacoustic instabilities. We show that the mode clustering phenomenon is responsible for the excitation of closely-spaced multiple eigenmodes in the can-annular acoustic environment, and as a consequence the system can feature a mixed state with several distinct types of interaction patterns. By analyzing a large amount of experimental data acquired systematically for coupled two-combustor and four-can-annular configurations, we demonstrate that longitudinal-mode instabilities in a can-annular combustion system will preferentially emerge in the form of out-of-phase interactions.