Protein Disorder in Plant Stress Adaptation: From Late Embryogenesis Abundant to Other Intrinsically Disordered Proteins.

Global climate change has caused severe abiotic and biotic stresses, affecting plant growth and food security. The mechanical understanding of plant stress responses is critical for achieving sustainable agriculture. Intrinsically disordered proteins (IDPs) are a group of proteins without unique three-dimensional structures. The environmental sensitivity and structural flexibility of IDPs contribute to the growth and developmental plasticity for sessile plants to deal with environmental challenges. This article discusses the roles of various disordered proteins in plant stress tolerance and resistance, describes the current mechanistic insights into unstructured proteins such as the disorder-to-order transition for adopting secondary structures to interact with specific partners (i.e., cellular membranes, membrane proteins, metal ions, and DNA), and elucidates the roles of liquid-liquid phase separation driven by protein disorder in stress responses. By comparing IDP studies in animal systems, this article provides conceptual principles of plant protein disorder in stress adaptation, reveals the current research gaps, and advises on the future research direction. The highlighting of relevant unanswered questions in plant protein disorder research aims to encourage more studies on these emerging topics to understand the mechanisms of action behind their stress resistance phenotypes.

Incorporating economic constraints for optimal control of immunizing infections.

It is well-known that the interruption of transmission of a disease can be achieved, provided the vaccinated population reaches a threshold depending on, among others, the efficacy of vaccines. The purpose of this paper is to address the optimal vaccination strategy by imposing the economic constraints. In particular, an S--(I,V)--S model used to describe the spreading of the disease in a well-mixed population and a cost function consisting of vaccination and infection costs are proposed. The well-definedness of the above-described modeling is provided. We were then able to provide an optimal strategy to minimize the cost for all parameters. In particular, the optimal vaccination level to minimize the cost can be completely characterized for all parameters. For instance, the optimal vaccination level can be classified by the magnitude of the failure rate of the vaccine with other parameters being given. Under these circumstances, the optimal strategy to minimize the cost is roughly to eliminate the disease locally (respectively, choose an economic optimum resulting in not to wipe out the disease completely or take no vaccination for anyone) provided the vaccine failure rate is relatively small (respectively, intermediate or large). Numerical simulations to illustrate our main results are also provided. Moreover, the data collected at the height of the Covid-19 pandemic in Taiwan are also numerically simulated to provide the corresponding optimal vaccination strategy.

An Intrinsically Disordered Protein Interacts with the Cytoskeleton for Adaptive Root Growth under Stress.

Intrinsically disordered proteins function as flexible stress modulators in vivo through largely unknown mechanisms. Here, we elucidated the mechanistic role of an intrinsically disordered protein, REPETITIVE PRO-RICH PROTEIN (RePRP), in regulating rice (Oryza sativa) root growth under water deficit. With nearly 40% Pro, RePRP is induced by water deficit and abscisic acid (ABA) in the root elongation zone. RePRP is sufficient and necessary for repression of root development by water deficit or ABA. We showed that RePRP interacts with the highly ordered cytoskeleton components actin and tubulin both in vivo and in vitro. Binding of RePRP reduces the abundance of actin filaments, thus diminishing noncellulosic polysaccharide transport to the cell wall and increasing the enzyme activity of Suc synthase. RePRP also reorients the microtubule network, which leads to disordered cellulose microfibril organization in the cell wall. The cell wall modification suppresses root cell elongation, thereby generating short roots, whereas increased Suc synthase activity triggers starch accumulation in "heavy" roots. Intrinsically disordered proteins control cell elongation and carbon reserves via an order-by-disorder mechanism, regulating the highly ordered cytoskeleton for development of "short-but-heavy" roots as an adaptive response to water deficit in rice.

Rice Big Grain 1 promotes cell division to enhance organ development, stress tolerance and grain yield.

Grain/seed yield and plant stress tolerance are two major traits that determine the yield potential of many crops. In cereals, grain size is one of the key factors affecting grain yield. Here, we identify and characterize a newly discovered gene Rice Big Grain 1 (RBG1) that regulates grain and organ development, as well as abiotic stress tolerance. Ectopic expression of RBG1 leads to significant increases in the size of not only grains but also other major organs such as roots, shoots and panicles. Increased grain size is primarily due to elevated cell numbers rather than cell enlargement. RBG1 is preferentially expressed in meristematic and proliferating tissues. Ectopic expression of RBG1 promotes cell division, and RBG1 co-localizes with microtubules known to be involved in cell division, which may account for the increase in organ size. Ectopic expression of RBG1 also increases auxin accumulation and sensitivity, which facilitates root development, particularly crown roots. Moreover, overexpression of RBG1 up-regulated a large number of heat-shock proteins, leading to enhanced tolerance to heat, osmotic and salt stresses, as well as rapid recovery from water-deficit stress. Ectopic expression of RBG1 regulated by a specific constitutive promoter, GOS2, enhanced harvest index and grain yield in rice. Taken together, we have discovered that RBG1 regulates two distinct and important traits in rice, namely grain yield and stress tolerance, via its effects on cell division, auxin and stress protein induction.

Unveiling the role of microRNA-7 in linking TGF-ß-Smad-mediated epithelial-mesenchymal transition with negative regulation of trophoblast invasion.

Several pregnancy complications result from abnormal trophoblast invasion. The dichotomous effect of TGF-ß on epithelial-mesenchymal transition (EMT) between trophoblast invasion and cancer progression remains unknown and a critical concern. We attenuated the expression of TGF-ß type 1 receptor (coding by TGFBR1) with RNA interference in trophoblastic cells and significantly enhanced the trophoblastic invasion. Analysis of microRNA profiles in trophoblasts indicated microRNA-7 as a key molecule linking TGF-ß with the negative regulation of trophoblast invasion. We then attenuated TGFBR1 and miR-7 transcription by transducing either short hairpin RNA targeting TGFBR1 or anti-miR-7-locked nucleonic acid, and we observed an up-regulation of EMT-related transcription factors (TFs) and their downstream effectors, causing a mesenchymal transition of trophoblasts. Conversely, overexpression of TGFBR1 or miR-7 led to the epithelial transition of trophoblasts. Our results showed that TGF-ß-induced miR-7 expression negatively modulated the TGF-ß-SMAD family member 2-mediated EMT pathway via targeting EMT-related TFs and down-regulating their mesenchymal markers. These findings possibly explain, at least in part, why TGF-ß exerts an opposite effect on EMT during trophoblast invasion and cancer progression.-Shih, J.-C., Lin, H.-H., Hsiao, A.-C., Su, Y.-T., Tsai, S., Chien, C.-L., Kung, H.-N. Unveiling the role of microRNA-7 in linking TGF-ß-Smad-mediated epithelial-mesenchymal transition with negative regulation of trophoblast invasion.

Arabidopsis ACYL-COA-BINDING PROTEIN1 interacts with STEROL C4-METHYL OXIDASE1-2 to modulate gene expression of homeodomain-leucine zipper IV transcription factors.

Fatty acids (FAs) and sterols constitute building blocks of eukaryotic membranes and lipid signals. Co-regulation of FA and sterol synthesis is mediated by sterol regulatory element-binding proteins in animals but remains elusive in plants. We reported recently that Arabidopsis ACYL-COA-BINDING PROTEIN1 (ACBP1) modulates sterol synthesis via protein-protein interaction with STEROL C4-METHYL OXIDASE1-1 (SMO1-1). Herein, ACBP1 was demonstrated to co-express and interact with SMO1-2 by yeast two-hybrid, co-localization, pull-down, co-immunoprecipitation and ß-glucuronidase assays. SMO1-2 silenced in acbp1 was used in phenotyping, GC-MS and expression profiling. ACBP1 co-expressed with SMO1-2 in embryo sacs, pollen and trichomes, corroborating with cooperative tissue-specific functions unseen with SMO1-1. SMO1-2 silencing in acbp1 impaired seed development, male and female gamete transmission, and pollen function. Genes encoding homeodomain-leucine zipper IV transcription factors (HDG5, HDG10, HDG11 and GLABRA2), which potentially bind phospholipids/sterols, were transcribed aberrantly. GLABRA2 targets (MYB23, MUM4 and PLDα1) were misregulated, causing glabra2-resembling trichome, seed coat mucilage and oil-accumulating phenotypes. Together with altered sterol and FA compositions upon ACBP1 mutation and/or SMO1-2 silencing, ACBP1-SMO1 interaction appears to mediate homeostatic co-regulation of FAs and sterols, which serve as lipid modulators for gene expression of homeodomain-leucine zipper IV transcription factors.

Acyl-CoA-Binding Protein ACBP1 Modulates Sterol Synthesis during Embryogenesis.

Fatty acids (FAs) and sterols are primary metabolites that exert interrelated functions as structural and signaling lipids. Despite their common syntheses from acetyl-coenzyme A, homeostatic cross talk remains enigmatic. Six Arabidopsis (Arabidopsis thaliana) acyl-coenzyme A-binding proteins (ACBPs) are involved in FA metabolism. ACBP1 interacts with PHOSPHOLIPASE Dα1 and regulates phospholipid composition. Here, its specific role in the negative modulation of sterol synthesis during embryogenesis is reported. ACBP1, likely in a liganded state, interacts with STEROL C4-METHYL OXIDASE1-1 (SMO1-1), a rate-limiting enzyme in the sterol pathway. Proembryo abortion in the double mutant indicated that the ACBP1-SMO1-1 interaction is synthetic lethal, corroborating with their strong promoter activities in developing ovules. Gas chromatography-mass spectrometry revealed quantitative and compositional changes in FAs and sterols upon overexpression or mutation of ACBP1 and/or SMO1-1 Aberrant levels of these metabolites may account for the downstream defect in lipid signaling. GLABRA2 (GL2), encoding a phospholipid/sterol-binding homeodomain transcription factor, was up-regulated in developing seeds of acbp1, smo1-1, and ACBP1+/-smo1-1 in comparison with the wild type. Consistent with the corresponding transcriptional alteration of GL2 targets, high-oil, low-mucilage phenotypes of gl2 were phenocopied in ACBP1+/-smo1-1 Thus, ACBP1 appears to modulate the metabolism of two important lipid classes (FAs and sterols) influencing cellular signaling.

Ectopic Expression of WINDING 1 Leads to Asymmetrical Distribution of Auxin and a Spiral Phenotype in Rice.

Ectopic expression of the rice WINDING 1 (WIN1) gene leads to a spiral phenotype only in shoots but not in roots. Rice WIN1 belongs to a specific class of proteins in cereal plants containing a Bric-a-Brac/Tramtrack/Broad (BTB) complex, a non-phototropic hypocotyl 3 (NPH3) domain and a coiled-coil motif. The WIN1 protein is predominantly localized to the plasma membrane, but is also co-localized to plasmodesmata, where it exhibits a punctate pattern. It is observed that WIN1 is normally expressed in roots and the shoot-root junction, but not in the rest of shoots. In roots, WIN1 is largely localized to the apical and basal sides of cells. However, upon ectopic expression, WIN1 appears on the longitudinal sides of leaf sheath cells, correlated with the appearance of a spiral phenotype in shoots. Despite the spiral phenotype, WIN1-overexpressing plants exhibit a normal phototropic response. Although treatments with exogenous auxins or a polar auxin transport inhibitor do not alter the spiral phenotype, the excurvature side has a higher auxin concentration than the incurvature side. Furthermore, actin filaments are more prominent in the excurvature side than in the incurvature side, which correlates with cell size differences between these two sides. Interestingly, ectopic expression of WIN1 does not cause either unequal auxin distribution or actin filament differences in roots, so a spiral phenotype is not observed in roots. The action of WIN1 appears to be different from that of other proteins causing a spiral phenotype, and it is likely that WIN1 is involved in 1-N-naphthylphthalamic acid-insensitive plasmodesmata-mediated auxin transport.

The Arabidopsis cytosolic Acyl-CoA-binding proteins play combinatory roles in pollen development.

In Arabidopsis, six acyl-CoA-binding proteins (ACBPs) have been identified and they have been demonstrated to function in plant stress responses and development. Three of these AtACBPs (AtACBP4-AtACBP6) are cytosolic proteins and all are expressed in floral organs as well as in other tissues. The roles of cytosolic AtACBPs in floral development were addressed in this study. To this end, a T-DNA insertional knockout mutant of acbp5 was characterized before use in crosses with the already available acbp4 and acbp6 T-DNA knockout mutants to examine their independent and combinatory functions in floral development. The single-gene knockout mutations did not cause any significant phenotypic changes, while phenotypic deficiencies affecting siliques and pollen were observed in the double mutants (acbp4acbp6 and acbp5acbp6) and the acbp4acbp5acbp6 triple mutant. Vacuole accumulation in the acbp4acbp6, acbp5acbp6 and acbp4acbp5acbp6 pollen was the most severe abnormality occurring in the double and triple mutants. Furthermore, scanning electron microscopy and transmission electron microscopy revealed exine and oil body defects in the acbp4acbp5acbp6 mutant, which also displayed reduced ability in in vitro pollen germination. Transgenic Arabidopsis expressing ß-glucuronidase (GUS) driven from the various AtACBP promoters indicated that AtACBP6pro::GUS expression overlapped with AtACBP4pro::GUS expression in pollen grains and with AtACBP5pro::GUS expression in the microspores and tapetal cells. Taken together, these results suggest that the three cytosolic AtACBPs play combinatory roles in acyl-lipid metabolism during pollen development.

Enterovirus 71 infection caused neuronal cell death and cytokine expression in cultured rat neural cells.

Fatal enterovirus type-71 (EV71) cases are associated with central nervous system infection characterized by inflammatory cell infiltration and activation, cytokine overproduction, and neuronal cell death. Although EV71 antigen has been detected in neurons and glia, the molecular mechanisms underlying EV71-associated neuroinflammation and neuronal cell death are not fully understood. Using cultured rodent neural cell models, we found that EV71 infection preferentially caused cell death in neurons but not brain-resident immune cells astrocytes and microglia. Neurons, astrocytes, and microglia responded to EV71 infection by releasing distinct profiles of cytokines, including nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß, regulated on activation normal T cell expressed and secreted (RANTES), and glutamate. EV71 infection-induced neuronal cell death correlated well with the elevated production of NO, TNF-α, IL-1ß, and glutamate as well as activation of microglia. Exogenous addition studies further demonstrated the neurotoxic potential of NO, TNF-α, IL-1ß, and glutamate. EV71 infection-induced cytokine expression was accompanied by activation of protein tyrosine phosphorylation, mitogen-activated protein kinases (MAPKs), and NF-κB. Intriguingly, EV71 susceptibility was accompanied by infection-elevated neuronal human scavenger receptor class B member 2 expression in cultured neural cells with age-dependent manner. Biochemical and pharmacological studies revealed that after EV71 infection, microglia and accompanied cytokines play an active role in triggering bystander damage to neurons involving the tyrosine kinase/MAPKs/NF-κB signaling cascade. These data suggest that bystander damage caused by activated glia particularly the microglia could be an alternative mechanism of EV71-associated neuronal cell death. However, its clinical importance and implication require further investigation.

Subcellular localization of rice acyl-CoA-binding proteins (ACBPs) indicates that OsACBP6::GFP is targeted to the peroxisomes.

Acyl-CoA-binding proteins (ACBPs) show conservation at the acyl-CoA-binding (ACB) domain which facilitates binding to acyl-CoA esters. In Arabidopsis thaliana, six ACBPs participate in development and stress responses. Rice (Oryza sativa) also contains six genes encoding ACBPs. We investigated differences in subcellular localization between monocot rice and eudicot A. thaliana ACBPs. The subcellular localization of the six OsACBPs was achieved via transient expression of green fluorescence protein (GFP) fusions in tobacco (Nicotiana tabacum) epidermal cells, and stable transformation of A. thaliana. As plant ACBPs had not been reported in the peroxisomes, OsACBP6::GFP localization was confirmed by transient expression in rice sheath cells. The function of OsACBP6 was investigated by overexpressing 35S::OsACBP6 in the peroxisomal abc transporter1 (pxa1) mutant defective in peroxisomal fatty acid ß-oxidation. As predicted, OsACBP1::GFP and OsACBP2::GFP were localized to the cytosol, and OsACBP4::GFP and OsACBP5::GFP to the endoplasmic reticulum (ER). However, OsACBP3::GFP displayed subcellular multi-localization while OsACBP6::GFP was localized to the peroxisomes. 35S::OsACBP6-OE/pxa1 lines showed recovery in indole-3-butyric acid (IBA) peroxisomal ß-oxidation, wound-induced VEGETATIVE STORAGE PROTEIN1 (VSP1) expression and jasmonic acid (JA) accumulation. These findings indicate a role for OsACBP6 in peroxisomal ß-oxidation, and suggest that rice ACBPs are involved in lipid degradation in addition to lipid biosynthesis.

Acupuncture for Combat-Related Posttraumatic Stress Disorder: A Randomized Clinical Trial.

Importance: Current interventions for posttraumatic stress disorder (PTSD) are efficacious, yet effectiveness may be limited by adverse effects and high withdrawal rates. Acupuncture is an emerging intervention with positive preliminary data for PTSD. Objective: To compare verum acupuncture with sham acupuncture (minimal needling) on clinical and physiological outcomes. Design, Setting, and Participants: This was a 2-arm, parallel-group, prospective blinded randomized clinical trial hypothesizing superiority of verum to sham acupuncture. The study was conducted at a single outpatient-based site, the Tibor Rubin VA Medical Center in Long Beach, California, with recruitment from April 2018 to May 2022, followed by a 15-week treatment period. Following exclusion for characteristics that are known PTSD treatment confounds, might affect biological assessment, indicate past nonadherence or treatment resistance, or indicate risk of harm, 93 treatment-seeking combat veterans with PTSD aged 18 to 55 years were allocated to group by adaptive randomization and 71 participants completed the intervention protocols. Interventions: Verum and sham were provided as 1-hour sessions, twice weekly, and participants were given 15 weeks to complete up to 24 sessions. Main Outcomes and Measures: The primary outcome was pretreatment to posttreatment change in PTSD symptom severity on the Clinician-Administered PTSD Scale-5 (CAPS-5). The secondary outcome was pretreatment to posttreatment change in fear-conditioned extinction, assessed by fear-potentiated startle response. Outcomes were assessed at pretreatment, midtreatment, and posttreatment. General linear models comparing within- and between-group were analyzed in both intention-to-treat (ITT) and treatment-completed models. Results: A total of 85 male and 8 female veterans (mean [SD] age, 39.2 [8.5] years) were randomized. There was a large treatment effect of verum (Cohen d, 1.17), a moderate effect of sham (d, 0.67), and a moderate between-group effect favoring verum (mean [SD] Δ, 7.1 [11.8]; t90 = 2.87, d, 0.63; P = .005) in the intention-to-treat analysis. The effect pattern was similar in the treatment-completed analysis: verum d, 1.53; sham d, 0.86; between-group mean (SD) Δ, 7.4 (11.7); t69 = 2.64; d, 0.63; P = .01). There was a significant pretreatment to posttreatment reduction of fear-potentiated startle during extinction (ie, better fear extinction) in the verum but not the sham group and a significant correlation (r = 0.31) between symptom reduction and fear extinction. Withdrawal rates were low. Conclusions and Relevance: The acupuncture intervention used in this study was clinically efficacious and favorably affected the psychobiology of PTSD in combat veterans. These data build on extant literature and suggest that clinical implementation of acupuncture for PTSD, along with further research about comparative efficacy, durability, and mechanisms of effects, is warranted. Trial Registration: ClinicalTrials.gov Identifier: NCT02869646.

Hypoxia-induced long non-coding RNA HIF1A­AS2 regulates stability of MHC class I protein in head and neck cancer.

Intratumoral hypoxia not only promotes angiogenesis and invasiveness of cancer cells, but also creates an immunosuppressive microenvironment that facilitates tumor progression. However, the mechanisms by which hypoxic tumor cells disseminate immunosuppressive signals remain unclear. In this study, we demonstrate that a hypoxia-induced long non-coding RNA (lncRNA) HIF1A Antisense RNA 2 (HIF1A-AS2) is upregulated in both hypoxic tumor cells and hypoxic tumor-derived exosomes (TEXs) in head and neck squamous cell carcinoma (HNSCC). Hypoxia-inducible factor 1 alpha 1 (HIF-1α) was found to directly bind to the regulatory region of HIF1A-AS2 to enhance its expression. HIF1A-AS2 reduced the protein stability of major histocompatibility complex class I (MHC-I) by promoting the interaction between the autophagy cargo receptor Neighbor of BRCA1 gene 1 protein (NBR1) and MHC-I, thereby increasing the autophagic degradation of MHC-I. In HNSCC samples, the expression of HIF1A-AS2 was found to correlate with hypoxic signatures and advanced clinical stages. Patients with high HIF-1α and low HLA-ABC expression showed reduced infiltration of CD8+ T cells. These findings define a mechanism of hypoxia-mediated immune evasion in HNSCC through downregulation of antigen-presenting machinery via intracellular or externalized hypoxia-induced lncRNA.

Microtubule Regulation in Plants: From Morphological Development to Stress Adaptation.

Microtubules (MTs) are essential elements of the eukaryotic cytoskeleton and are critical for various cell functions. During cell division, plant MTs form highly ordered structures, and cortical MTs guide the cell wall cellulose patterns and thus control cell size and shape. Both are important for morphological development and for adjusting plant growth and plasticity under environmental challenges for stress adaptation. Various MT regulators control the dynamics and organization of MTs in diverse cellular processes and response to developmental and environmental cues. This article summarizes the recent progress in plant MT studies from morphological development to stress responses, discusses the latest techniques applied, and encourages more research into plant MT regulation.

NKG2A and circulating extracellular vesicles are key regulators of natural killer cell activity in prostate cancer after prostatectomy.

Extracellular vesicles (EVs) are an important regulatory factor for natural killer cell activity (NKA) in the tumor microenvironment. The relationship between circulating EVs in the peripheral blood and natural killer (NK) cells in prostate cancer (PCa) is unclear. This study aimed at investigating the key regulators in the interaction between circulating EVs and NK cells in PCa patients before and after tumor removal. NK-cell characteristics were prospectively assessed in 79 patients treated with robot-assisted laparoscopic radical prostatectomy preoperatively and postoperatively. Compared with healthy donors, the existence of prostate tumors increased the number of circulating EVs and altered ligand expression of EVs. Circulating EVs extracted from cancer patients significantly decreased NKA of NK cells compared with those extracted from healthy donors. Upon treatment with an inhibiting antibody or small interfering RNA, natural killer cell protein group 2A (NKG2A) was identified as the main NKA regulator in cancer patients for accepting the signal from circulating EVs. After surgery, NKA was increased and NKG2A expression on NK cells was significantly reduced. The expression of ligands for natural killer cell protein group 2D (NKG2D) on EVs and the level of circulation EVs both significantly increased. With the decrease in NKG2A levels on NK cells and the increase in total NKG2D ligands on circulating EVs, which was increased postoperatively, both NKG2A on NK cells and NKG2D ligands on circulating exosomes are main regulators of NKA restoration after prostatectomy.

Dye molecular structure device open-circuit voltage correlation in Ru(II) sensitizers with heteroleptic tridentate chelates for dye-sensitized solar cells.

Dicarboxyterpyridine chelates with π-conjugated pendant groups attached at the 5- or 6-position of the terminal pyridyl unit were synthesized. Together with 2,6-bis(5-pyrazolyl)pyridine, these were used successfully to prepare a series of novel heteroleptic, bis-tridentate Ru(II) sensitizers, denoted as TF-11-14. These dyes show excellent performance in dye-sensitized solar cells (DSCs) under AM1.5G simulated sunlight at a light intensity of 100 mW cm(-2) in comparison with a reference device containing [Ru(Htctpy)(NCS)(3)][TBA](3) (N749), where H(3)tctpy and TBA are 4,4',4"-tricarboxy-2,2':6',2"-terpyridine and tetra-n-butylammonium cation, respectively. In particular, the sensitizer TF-12 gave a short-circuit photocurrent of 19.0 mA cm(-2), an open-circuit voltage (V(OC)) of 0.71 V, and a fill factor of 0.68, affording an overall conversion efficiency of 9.21%. The increased conjugation conferred to the TF dyes by the addition of the π-conjugated pendant groups increases both their light-harvesting and photovoltaic energy conversion capability in comparison with N749. Detailed recombination processes in these devices were probed by various spectroscopic and dynamics measurements, and a clear correlation between the device V(OC) and the cell electron lifetime was established. In agreement with several other recent studies, the results demonstrate that high efficiencies can also be achieved with Ru(II) sensitizers that do not contain thiocyanate ancillaries. This bis-tridentate, dual-carboxy anchor configuration thus serves as a prototype for future omnibearing design of highly efficient Ru(II) sensitizers suited for use in DSCs.

Cationic iridium complexes with intramolecular π-π interaction and enhanced steric hindrance for solid-state light-emitting electrochemical cells.

Cationic iridium complexes incorporated 4,5-diaza-9,9'-spirobifluorene as N(∧)N ancillary ligands, in which one (2) or two (3) phenyl groups were introduced onto 4,5-diazafluorene to afford intraligand π-π interactions. The X-ray crystal structures of complexes 2 and 3 show that the pendant phenyl ring forms strong intramolecular face-to-face π-stacking with the difluorophenyl ring of the cyclometalated ligand with distances of 3.38 Å for complex 2 and 3.40 and 3.46 Å for complex 3. This π-π stacking interaction minimizes the expansion of the metal-ligand bonds in the excited state, resulting in a longer device lifetime in the light-emitting electrochemical cell (LEC) devices.

Stepwise formation of iridium(III) complexes with monocyclometalating and dicyclometalating phosphorus chelates.

With the motivation of assembling cyclometalated complexes without nitrogen-containing heterocycle, we report here the design and systematic synthesis of a class of Ir(III) metal complexes functionalized with facially coordinated phosphite (or phosphonite) dicyclometalate tripod, together with a variety of phosphine, chelating diphosphine, or even monocyclometalate phosphite ancillaries. Thus, treatment of [IrCl(3)(tht)(3)] with stoichiometric amount of triphenylphosphite (or diphenyl phenylphosphonite), two equiv of PPh(3), and in presence of NaOAc as cyclometalation promoter, gives formation of respective tripodal dicyclometalating complexes [Ir(tpit)(PPh(3))(2)Cl] (2a), [Ir(dppit)(PPh(3))(2)Cl] (2b), and [Ir(dppit)(PMe(2)Ph)(2)Cl] (2c) in high yields, where tpitH(2) = triphenylphosphite and dppitH(2) = diphenyl phenylphosphonite. The reaction sequence that afforded these complexes is established. Of particular interest is isolation of an intermediate [Ir(tpitH)(PPh(3))(2)Cl(2)] (1a) with monocyclometalated phosphite, together with the formation of [Ir(tpit)(tpitH)(PPh(3))] (3a) with all tripodal, bidentate, and monodentate phosphorus donors coexisting on the coordination sphere, upon treatment of 2a with a second equiv of triphenylphosphite. Spectroscopic studies were performed to explore the photophysical properties. For all titled Ir(III) complexes, virtually no emission can be observed in either solution at room temperature or 77 K CH(2)Cl(2) matrix. Time-dependent DFT calculation indicates that the lowest energy triplet manifold involves substantial amount of metal centered (3)MC dd contribution. Due to its repulsive potential energy surface (PES) that touches the PES of ground state, the (3)MC dd state executes predominant nonradiative deactivation process.

Studies of excited-state properties of multibranched triarylamine end-capped triazines.

Electron donor-acceptor types of multibranched triarylamine end-capped triazines have been systematically investigated by steady-state electronic spectroscopy, electrochemistry, femtosecond fluorescence anisotropy and solvent relaxation dynamics. The results, together with computational approach, have gained in-depth insight into their excited-state properties, especially the interactions between branches. Among different branched triarylamines of one, two and three arms, the interbranch interaction between each arm is weak, as evidenced by their nearly identical absorption spectral profile and frontier orbitals analyses. Upon S(0) → S(1) excitation, the electronic delocalization in the three-branched triarylamine end-capped triazine is resolved to be 680 ± 130 fs, followed by a slow (28 ± 3 ps) electronic localization into one branch and consequently a rotational depolarization of 2.0 ± 0.1 ns. Similar delocalization dynamics was resolved for the two-branched triarylamine end-capped triazine (electronic delocalization, 500 ± 90 fs; twisting localization, 21 ± 5 ps; rotational depolarization, 700 ± 30 ps). The comparable electron delocalization and solvent relaxation time scale may set up a new paradigm to investigate their specific correlation in the early time domain.

The empirical correlation between hydrogen bonding strength and excited-state intramolecular proton transfer in 2-pyridyl pyrazoles.

A series of 2-pyridyl pyrazoles 1a and 1-5 with various functional groups attached to either pyrazole or pyridyl moieties have been strategically designed and synthesized in an aim to probe the hydrogen bonding strength in the ground state versus dynamics of excited-state intramolecular proton transfer (ESIPT) reaction. The title compounds all possess a five-membered-ring (pyrazole)N-H···N(pyridine) intramolecular hydrogen bond, in which both the N-H bond and the electron density distribution of the pyridyl nitrogen lone-pair electrons are rather directional, so that the hydrogen bonding strength is relatively weak, which is sensitive to the perturbation of subtle chemical substitution and consequently reflected from the associated ESIPT dynamics. Various approaches such as (1)H NMR (N-H proton) to probe the hydrogen bonding strength and absorption titration to assess the acidity-basicity property were made for all the title analogues. The results, together with supplementary support provided by a computational approach, affirm that the increase of acidity (basicity) on the hydrogen bonding donor (acceptor) sites leads to an increase of hydrogen-bonding strength among the title 2-pyridyl pyrazoles. Luminescence results and the associated ESIPT dynamics further reveal an empirical correlation in that the increase of the hydrogen bonding strength leads to an increase of the rate of ESIPT for the title 2-pyridyl pyrazoles, demonstrating an interesting relationship among N-H acidity, hydrogen bonding strength, and the associated ESIPT rate.