Bridge Formation Research Articles

Nano eggshell based slurry as a direct pulp capping material: In vitro characterization and histopathological assessment in an experimental animal model.

Pulp vitality is essential for tooth integrity. Following pulp exposure, choosing a suitable pulp capping material is crucial to maintain pulp vitality. However, the reparative dentine bridge created by calcium hydroxide is generally porous and incomplete. To assess the in vitro and in vivo bioactivity of nano eggshell-based slurry (NES), using NES as direct pulp capping material, compared with calcium hydroxide (Ca(OH)2 ) in rabbit animal model. Nano eggshell powder (NE) was characterized for particle morphology, chemical composition, and ion release. In vitro bioactivity was tested by immersion in simulated body fluid (SBF) for 7 days. For histopathological evaluation, 36 adult New Zealand rabbits (72 pulp exposures) were divided into nine groups (n=8) according to the pulp capping material (NES, Ca(OH)2 and no capping as negative control group) and the animals were sacrificed after 7, 14 or 28 days. The pulps of the two lower central incisors were exposed then directly capped by Ca(OH)2 or NES, or left untreated. The cavities were then sealed with a glass ionomer cement. Teeth were collected for histopathological evaluation using optical microscope. Pulp haemorrhage, inflammation, fibrosis and calcific bridge formation were assessed. Results were statistically analyzed using ANOVA and Tukey's test. NE particles were spherical with 20 nm diameter and were composed mainly of calcite. Statistical analysis showed that there was significant increase in the release of all investigated ions between day 1 and 28, except for copper. NES group showed significantly higher release of all elements as compared to Ca(OH)2 . ESEM micrographs of NES incubated for 7 days in SBF showed the formation of HAp with Ca/P ratio (1.686). For histopathological evaluation, the difference between groups was statistically significant. At day 28, 75% of the pulps of Ca(OH)2 group showed mild calcific bridge in comparison with 100% moderate calcific bridge in NES group. The NES group showed significantly less inflammation at days 7 and 28, and higher fibrosis at day7 as compared with Ca(OH)2 . NES represents a promising novel direct pulp capping material with favourable pulp tissue response.

Structural Conformation and Activity of Spider-Derived Inhibitory Cystine Knot Peptide Pn3a Are Modulated by pH.

Numerous spider venom-derived gating modifier toxins exhibit conformational heterogeneity during purification by reversed-phase high-performance liquid chromatography (RP-HPLC). This conformational exchange is especially peculiar for peptides containing an inhibitor cystine knot motif, which confers excellent structural stability under conditions that are not conducive to disulfide shuffling. This phenomenon is often attributed to proline cis/trans isomerization but has also been observed in peptides that do not contain a proline residue. Pn3a is one such peptide forming two chromatographically distinguishable peaks that readily interconvert following the purification of either conformer. The nature of this exchange was previously uncharacterized due to the fast rate of conversion in solution, making isolation of the conformers impossible. In the present study, an N-terminal modification of Pn3a enabled the isolation of the individual conformers, allowing activity assays to be conducted on the individual conformers using electrophysiology. The conformers were analyzed separately by nuclear magnetic resonance spectroscopy (NMR) to study their structural differences. RP-HPLC and NMR were used to study the mechanism of exchange. The later-eluting conformer was the active conformer with a rigid structure that corresponds to the published structure of Pn3a, while NMR analysis revealed the earlier-eluting conformer to be inactive and disordered. The exchange was found to be pH-dependent, arising in acidic solutions, possibly due to reversible disruption and formation of intramolecular salt bridges. This study reveals the nature of non-proline conformational exchange observed in Pn3a and possibly other disulfide-rich peptides, highlighting that the structure and activity of some disulfide-stabilized peptides can be dramatically susceptible to disruption.

Outcome of Partial Pulpotomy in Immature Permanent Teeth with Symptomatic Irreversible Pulpitis: A Prospective Case Series Assessment

IntroductionThe aim of this prospective case series was to assess the clinical and radiographic outcome of partial pulpotomy in caries-exposed symptomatic, vital, immature, permanent molars. MethodsThirty-four immature molars with deep caries and symptoms of irreversible pulpitis were treated by partial pulpotomy and ProRoot MTA as a capping material. After complete caries removal, the inflamed part of the pulp was removed. Complete hemostasis was achieved using a sterile cotton pellet moist initially with sodium hypochlorite 1.5% and then with sterile saline. ProRoot MTA (Dentsply Sirona, Charlotte, NC) was placed as a capping material onto the remaining pulp tissue. The cavity was sealed using a light-curing resin-modified Ca(OH)2 cavity liner, and patients were referred to a pediatric dentist for permanent restoration. Descriptive statistics and cross tabulations were performed including variables examined before, during, and after the procedure. ResultsAll examined teeth presented a favorable clinical and radiographic outcome with normal periapical tissues, complete apical closure, and formation of a dentinal bridge beneath the capping material. Signs of partial pulp chamber calcification were only detected in 2 cases. Postoperatively, most patients did not report any pain (23/34, 67.7%), whereas the rest reported minor intensity pain (11/34, 32.3) and the use of analgesic or anti-inflammatory drugs only for 1 day (10/34, 29.4%). ConclusionsPartial pulpotomy seems to provide a universally successful outcome when managing symptomatic vital immature teeth with no signs of complications and completion of apical closure. It could be a viable treatment of choice in cases of caries-exposed vital immature teeth with symptoms of irreversible pulpitis.

Revisiting VH1 phosphatase at the time of monkeypox: back to the spotlight.

Vaccinia virus is a poxvirus that has been successfully leveraged to develop vaccines for smallpox, which is caused by the closely related Variola virus. Smallpox has been declared as 'eradicated' by the WHO in 1980; however, it still poses a potential bioterrorism threat. More recently, the spreading of monkeypox (MPox) in non-endemic countries has further highlighted the importance of continuing the exploration for druggable targets for poxvirus infections. The vaccinia H1 (VH1) phosphatase is the first reported dual specificity phosphatase (DUSP) able to hydrolyze both phosphotyrosine and phosphoserine/phosphotheonine residues. VH1 is a 20 kDa protein that forms a stable dimer and can dephosphorylate both viral and cellular substrates to regulate the viral replication cycle and host immune response. VH1 dimers adopt a domain swap mechanism with the first 20 amino acids of each monomer involved in dense electrostatic interaction and salt bridge formations while hydrophobic interactions between the N-terminal and C-terminal helices further stabilize the dimer. VH1 appears to be an ideal candidate for discovery of novel anti-poxvirus agents because it is highly conserved within the poxviridae family and is a virulence factor, yet it displays significant divergence in sequence and dimerization mechanism from its human closest ortholog vaccinia H1-related (VHR) phosphatase, encoded by the DUSP3 gene. As the dimeric quaternary structure of VH1 is essential for its phosphatase activity, strategies leading to disruption of the dimer structure might aid in VH1 inhibitor development.

Inflammatory Response and Odontogenic Differentiation of Inflamed Dental Pulp Treated with Different Pulp Capping Materials: An In Vivo Study.

Previous studies have evaluated the pulpal responses to calcium silicate cements (CSCs) on normal dental pulp, but investigations on the effects of CSCs on inflamed pulp are limited. This study aimed to test the inflammatory response and odontogenic differentiation of inflamed rat dental pulp after direct pulp capping with CSCs. Wistar rat molars pulps were exposed for 48 hours to induce inflammation and then capped with ProRoot MTA (Dentsply, Tulsa, OK, USA), Biodentine (Septodont, Saint-Maur-des-Fossés, France), RetroMTA (Bio MTA, Seoul, Korea) and Dycal (Dentsply Caulk, Milford, DE, USA). The degree of pulpal inflammation and hard tissue formation was evaluated by histological analysis. Immunofluorescence staining for interleukin (IL)-6, osteocalcin (OCN), and runt-related transcription factor 2 (RUNX2) was also performed. After 4 weeks, complete recovery from inflammation was evident in 22%, 37.5%, 10%, and none of the ProRoot MTA, Biodentine, RetroMTA and Dycal samples, respectively. Heavy hard tissue deposition as a continuous hard tissue bridge was observed in 77.8%, 75%, 70%, and 60% of the ProRoot MTA, Biodentine, RetroMTA, and Dycal samples, respectively. IL-6, OCN, and RUNX2 were detected in all materials, mainly adjacent to areas of inflammation and reparative dentine formation. At 1, 2, and 4 weeks, significant differences were not observed between the inflammation and hard tissue formation scores of the four material groups (P > .05). In this study, pulpal inflammation was still present in most specimens at 4 weeks after pulp capping and a significant number of samples showed incomplete and discontinuous dentine bridge formation. The results of this study suggest that initial inflammatory conditions of the pulp may risk the prognosis of teeth treated with CSCs.

DENND2B activates Rab35 at the intercellular bridge, regulating cytokinetic abscission and tetraploidy

Cytokinesis relies on membrane trafficking pathways regulated by Rabs and guanine nucleotide exchange factors (GEFs). During cytokinesis, the intercellular cytokinetic bridge (ICB) connecting daughter cells undergoes abscission, which requires actin depolymerization. Rab35 recruits MICAL1 to oxidize and depolymerize actin filaments. We show that DENND2B, a protein linked to cancer and congenital disorders, functions as a Rab35 GEF, recruiting and activating Rab35 at the ICB. DENND2B's N-terminal region also interacts with an active form of Rab35, suggesting that DENND2B is both a Rab35 GEF and effector. Knockdown of DENND2B delays abscission, leading to multinucleated cells and filamentous actin (F-actin) accumulation at the ICB, impairing recruitment of ESCRT-III at the abscission site. Additionally, F-actin accumulation triggers the formation of a chromatin bridge, activating the NoCut/abscission checkpoint, and DENND2B knockdown activates Aurora B kinase, a hallmark of checkpoint activation. Thus, our study identifies DENND2B as a crucial player in cytokinetic abscission.

Not the first leech: An unusual worm from the early Silurian of Wisconsin

AbstractAn unusual worm, previously interpreted as the earliest leech, is described from the early Silurian (Llandovery, Telychian) Brandon Bridge Formation Lagerstätte (Waukesha Biota) of Wisconsin (~437 Ma). Lacking preserved internal organs, it is up to ~16 cm long, 8.2 mm wide, with ~250 annulations and a circular structure at one end, interpreted here as the broken end of a molt. It is therefore referred to Cycloneuralia incertae sedis.

Histologic comparison of formocresol, platelet-rich fibrin, and hesperidin in pulpotomy: A randomized trial in dogs.

To histologically assess and compare formocresol (FC), platelet-rich fibrin (PRF), and hesperidin (HPN) as pulpotomy agents in dogs. Pulpotomy was attempted from the buccal surface (class V) of 48 teeth in three mongrel dogs (Canis Lupus). Cavities were randomly allocated for three groups (n = 16) according to the pulpotomy agent used; (group I: FC (control), group II: PRF, and group III: HPN). All cavities were then sealed with zinc oxide eugenol followed by resin-modified glass ionomer restoration. Two months later, dogs were euthanized; the specimens were obtained and prepared for histological assessment followed by statistical analysis. HPN specimens showed the best dentin bridge formation and the least inflammatory signs and pulp disorganization. Followed without statistically significant difference by PRF (P ≥ 0.05). Both of HPN and PRF, however, showed a significant difference statistically (P ≤ 0.05) to FC that showed no dentin bridging with more pronounced inflammation, necrosis, and pulp disorganization. For pulpotomy, HPN and PRF seemed histologically to be good substitutes for FC in the dog model.

DNA replication stress and mitotic catastrophe mediate sotorasib addiction in KRASG12C-mutant cancer

BackgroundSotorasib is the first KRASG12C inhibitor approved by the US Food and Drug Administration for treating KRASG12C-mutant non-small-cell lung cancer (NSCLC). Clinical trials on the therapeutic use of sotorasib for cancer have reported promising results. However, KRASG12C-mutant cancers can acquire resistance to sotorasib after treatment. We incidentally discovered that sotorasib-resistant (SR) cancer cells are addicted to this inhibitor. In this study, we investigated the mechanisms underlying sotorasib addiction.MethodsSotorasib-resistant cells were established using KRASG12C-mutant pancreatic cancer and NSCLC cell lines. Cell viability in the presence or absence of sotorasib and in combination with multiple inhibitors was assessed through proliferation assay and annexin V/propidium iodide (PI) flow cytometry assays. The mechanisms underlying drug addiction were elucidated through 5-bromo-2′-deoxyuridine (BrdU) incorporation assay, immunofluorescence staining, time-lapse microscopy, and comet assay. Furthermore, a subcutaneous xenograft model was used to demonstrate sotorasib addiction in vivo.ResultsIn the absence of sotorasib, the sotorasib-resistant cells underwent p21Waf1/Cip1-mediated cell cycle arrest and caspase-dependent apoptosis. Sotorasib withdrawal resulted in robust activation of mitogen-activated protein kinase (MAPK) pathway, inducing severe DNA damage and replication stress, which activated the DNA damage response (DDR) pathway. Persistent MAPK pathway hyperactivation with DDR exhaustion led to premature mitotic entry and aberrant mitosis, followed by micronucleus and nucleoplasmic bridge formation. Pharmacologic activation of the MAPK pathway with a type I BRAF inhibitor could further enhance the effects of sotorasib withdrawal on sotorasib-resistant cancer cells both in vitro and in vivo.ConclusionsWe elucidated the mechanisms underlying the sotorasib addiction of cancer cells. Sotorasib addiction appears to be mediated through MAPK pathway hyperactivity, DNA damage, replication stress, and mitotic catastrophe. Moreover, we devised a therapeutic strategy involving a type I BRAF inhibitor to strengthen the effects of sotorasib addiction; this strategy may provide clinical benefit for patients with cancer.

Evaluation of the pulp response following direct pulp capping with exogenous nitric oxide and Mineral Trioxide Aggregate (MTA) a histologic study

BackgroundRecently, vital pulp therapy is widely used all over the world. It aims to maintain the viability and function of the injured dental pulp tissue. Direct pulp capping is recognized as one of the most common used techniques in this approach. Aim of the studywe aimed to compare the histopathological response of the dental pulp following direct pulp capping using two different capping materials; the exogenous nitric oxide (NOC-18) and Mineral Trioxide Aggregate (MTA) in dogs’ teeth. Methods and materialsThe pulp of thirty-two premolars and canines from four dogs (eight teeth per each dog) the pulp was exposed and treated with either exogenous nitric oxide (NOC-18) and MTA (four teeth in each group). The treated teeth were extracted and prepared for histologic evaluation after one month and three months, respectively. The histologic study evaluated the formation of dentine bridge, the degree of pulpitis, calcification of the coronal pulp tissue and odontoblasts layer activity. We have the ethical approval to achieve this research from the scientific committee in Faculty of Dentistry, Damascus University. ResultsThe results showed that the active statue of odontoblasts layer in NOC-18 group was significantly more than in MTA group after a month of recall (P: 0.003). No significant difference was found between MTA and NOC-18 categories in the formation of dentine bridge after 3 months (P: 1.000). ConclusionExogenous nitric oxide (NOC-18) maybe has a positive impact on formation of calcified bridge and efficacy of odontoblasts layer on directly capped dog's teeth. Exogenous NO donors might offer alternative to current pulp capping agents in Vital Pulp Therapy in endodontic.

Water molecules jump through non-aligned disjoint nanochannels

The intricate design of nanochannels results in varying water transfer capabilities. The disjoint nanochannel provides a unique challenge to water molecules. However, the disjoint nanochannels are coaxial, in this study, we explore the transfer of water molecules through non-aligned disjoint nanochannels. Our findings reveal that the noncoaxial separation significantly influences water transfer properties in non-aligned disjoint nanochannels. Specifically, the formation of a water bridge is affected by the noncoaxial separation, and water molecules cannot jump through these non-aligned disjoint nanochannels when the noncoaxial separation reaches a critical point. Our results provide insights into the behavior of water in complex nanochannels.

Preferential Contamination in Electroadhesive Touchscreens: Mechanisms, Multiphysics Model, and Solutions

AbstractElectroadhesive surface haptic touchscreens can help augment user experiences by providing tactile effects. The electrode layout in current commercialized designs has separated electrodes for the sensing and actuating functions. During regular use, it is observed that fingerprint residue preferentially deposits on the actuating electrodes far more than the sensing electrodes, which makes the underlying electrode pattern apparent and is highly undesirable for touchscreen users. To address this issue, various physical phenomena (electrohydrodynamic deformation, capillary bridge stabilization, electrowetting, and electrophoretic deposition) are investigated to understand the mechanism. Through experimentation, multiphysics modeling, and surface characterization, it is found that the root cause can be attributed to two mechanisms occurring in the actuating regions: 1) electrohydrodynamic deformation of sebum droplets attached to the finger valleys leading to the formation of additional capillary bridges and residual droplets on the screen surface after their rupture, and 2) electric field‐induced stabilization of sebum capillary bridges existing between the finger ridges and the screen, leading to the coalescence and formation of larger‐sized droplets. The developed model can then be used to address the issue during the screen design process. An example of using the model to explore the impact of changes in screen oleophobicity is shown.

Impact of corticosteroid administration on the response of exposed dental pulp to capping with bioactive cements-experimental study on mongrel dogs

BackgroundCorticosteroids are commonly used as a treatment for a variety of pathological conditions, however, systemic corticosteroid administration has adverse effects including impaired immune response and wound healing. Such complications may affect pulp healing after direct pulp capping. The current study evaluated the influence of corticosteroids on the healing ability of exposed dogs’ dental pulps after direct pulp capping (DPC) with bioactive materials.MethodsTen healthy male dogs were assigned randomly into two groups, 5 dogs each: group I represent the control group which did not receive any medication, and group II was given corticosteroid for 45 days before DPC and till the dogs were euthanized (n = 75 teeth for each group). Following mechanical exposure, the pulps were randomly capped with either Ca(OH)2, MTA, or Biodentine. The pulpal tissues’ reaction to the capping materials was evaluated 65 days postoperatively according to the following parameters: calcific bridge formation, pulpal inflammation, pulp necrosis, and bacterial infiltration.ResultsThe corticosteroid-treated group revealed no significant difference compared to the control group concerning the pulp healing response (P > 0.05). Both Biodentine and MTA-treated specimens revealed significant differences with Ca(OH)2-treated specimens (P < 0.05) which displayed a superior positive effect of both MTA and Biodentine to Ca(OH)2 regarding all the parameters.ConclusionsDirect pulp capping technique whenever indicated in subjects treated with corticosteroid immunosuppressive drugs like prednisone performed well in aseptic conditions especially when capped with bioactive materials.

Study on the interfacial evolution and mechanical properties of Cu/SAC105/Cu solder joint modified by Si3N4 nanowires

In the present study, Si3N4 nanowires (NWs) with a mass fraction of 0.6 wt% were incorporated into Sn1.0Ag0.5Cu (SAC105) solder. Cu/SAC105/Cu and Cu/SAC105-Si3N4/Cu 3D structure joints were constructed by transient liquid-phase (TLP) bonding. To investigate the influence mechanism of Si3N4 NWs, the interfacial IMC evolution and mechanical properties of two solder joints were analyzed. It was found that the interfacial Cu3Sn IMC layer thickness of the joints containing Si3N4 NWs was thinner than that of the undoped ones at any given time. The growth of interfacial Cu6Sn5 IMC was inhibited, resulting in the retarded formation of interfacial IMC bridging and full-IMC joints. In addition, combined with the fracture morphology analysis, the brittle fracture behavior of the solder joints was suppressed, and the shear strength of the joints showed a significant improvement following the introduction of Si3N4 NWs. Moreover, Si3N4 NWs were found exposed on the fracture surface of Cu3Sn IMC layer, demonstrating that the doping of Si3N4 NWs shaped a joint similar to that of reinforced concrete structure, which facilitates the limitation of dislocations and crack expansion.

P-029 Centrifugation-free sperm separation device offers an efficient and standardized protocol to select high quality spermatozoa

Abstract Study question Can centrifugation-free sperm separation device be used to simplify and standardize the selection of high-quality spermatozoa? Summary answer Centrifugation-free CA0 sperm separation device minimizes inter- and intra-operator variability and yields spermatozoa with comparable fertilizing properties in a variety of semen conditions. What is known already Centrifugation-based sperm separation methods have been used in assisted reproductive technology (ART) for many decades. However, the conventional methods are criticized for harmful effects due to centrifugation. To overcome the disadvantage, more noninvasive technologies have been developed and attempted to improve the sperm separation process, e.g., the formation of capillary bridge to select motile spermatozoa, migration-sedimentation technique to sort out functional spermatozoa, microfluidic sorting chip to isolate healthy sperm. While these methods provide alternatives for noninvasive sperm separation, the limitations such as inconsistency of semen quality improvement and lack of standardized procedure remain to be resolved. Study design, size, duration A randomized controlled trial of 76 men who sought ART treatment (Lee Women’s Hospital, Taichung, Taiwan) from June to October 2022 was carried out. Seventy-six neat semen specimens were categorized into 27 normozoospermic specimens, and 49 non-normozoospermic samples (semen quality below any of the WHO 5th Edition lower reference values: concentration &amp;lt;15 million/mL, total motility &amp;lt;40%, or normal morphology &amp;lt;4%). Participants/materials, setting, methods Neat semen samples were separated for three replicates (replicate 1-3) using LensHooke® CA0 sperm separation device (Bonraybio, Taichung, Taiwan). Three operators (operators 1–3) performed CA0 procedures on each sample to test inter-technician variability. Interclass-correlation coefficient (ICC) between replicates as well as operators were evaluated. Pre-selection and post-selection semen quality were evaluated. The parameters included total motility, progressive motility, rapid progressive motility, morphology, DNA fragmentation index (DFI), and acrosome reaction rate (AR). Main results and the role of chance CA0 selects self-propelling spermatozoa within a microenvironment created by a microporous filter membrane. The procedure involves three pipetting steps: loading semen sample, adding sperm washing medium, and recovering the processed sample. Following the standard procedure, CA0 resulted in a low intra- and inter-operator variability and ICC values between replicates and different operators were all greater than 0.9, indicating an excellent reproducibility of CA0. In addition, significant higher levels of motility and normal morphology were observed in post-selection specimens either of normozoospermic or non-normozoospermic samples (pre-selection vs. post-selection, all p &amp;lt; 0.0001). In paired analysis of the advanced semen parameter, our study showed noteworthy results that CA0 significantly improved DFI from 18.2% to 2.6% for normozoospermic samples; such reduction was also found in non-normozoospermic sample processing, from 13.4% to 4.2% (both, p &amp;lt; 0.0001). The levels of AR were significantly reduced in normozoospermic samples (from 14.4% to 5.4%) and non-normozoospermic samples as well (from 12.8% to 5.0%) (both groups p &amp;lt; 0.0001). In conclusion, CA0 provides an efficient, noninvasive, standardized, and reproducible sperm separation model that CA0 diminishes the variations and ensures sperm quality. Limitations, reasons for caution The presented study was a pilot trial examining the sperm quality improvement. Follow-up analysis on IUI/IVF outcomes associated with the improvement in semen quality utilizing CA0 will be assessed in future studies. Wider implications of the findings CA0 provides multifaceted benefits covering consistent clinical outcomes, simplified and standardized procedure, user-friendliness, and cost reduction. We believe CA0 not only allows noninvasive sperm separation of clinically usable but also gives the possibility of standardization on sperm separation procedure. Trial registration number CS2-22039

A New Model for Charge Separation by Proton Transfer During Collision Between Ice Particles in Thunderstorms

AbstractField and laboratory observations strongly support the view that the development of electric fields in thunderstorms is caused by charge separation during rebounding collisions between ice crystals and graupels, followed by their gravitational separation. Although several plausible microphysical mechanisms have been proposed to explain the physics of charge separation, none have been found to be fully consistent with the experimental evidence, and a fresh approach is necessary. We propose a new mechanism for charge separation in ice‐ice collisions based on the fundamental molecular mechanism of charge transport in ice, involving the diffusion of H+ ions (excess protons or positive ionic defects) via a proton hopping relay along the hydrogen‐bond network of ice and the trapping and release of H+ ions from L‐orientational defects. The collision of two ice particles leads to the formation of a transient crystalline ice bridge at the contact point, which is spontaneously driven by the tendency for ice sintering, permitting rapid H+ diffusion between the two particles. Charge separation is achieved by the asymmetry in the concentrations of H+ ions or L‐orientational defects between the two ice surfaces. The proposed H+ transport mechanism successfully explains the direction and magnitude of charge transfer as well as its dependence on the relative growth rates of the two ice surfaces observed in laboratory studies. In addition, it offers a molecular‐level interpretation of the empirical rule that, during a collision, the faster‐growing ice surface is positively charged at the expense of negative charging of the slower‐growing or sublimating ice surface.

Single-Crystal to Single-Crystal Transformations: Stepwise CO2 Insertions into Bridging Hydrides of [(NHC)CuH]2 Complexes.

Mechanistic studies of substrate insertion into dimeric [(NHC)CuH]2 (NHC=N-heterocyclic carbene) complexes with two bridging hydrides have been shown to require dimer dissociation to generate transient, highly reactive (NHC)Cu-H monomers in solution. Using single-crystal to single-crystal (SC-SC) transformations, we discovered a new pathway of stepwise insertion of CO2 into [(NHC)CuH]2 without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH]2 (IPr*OMe=N,N'-bis(2,6-bis(diphenylmethyl)-4-methoxy-phenyl)imidazole-2-ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu]2 (μ-1,3-O2 CH)(μ-H). A second CO2 insertion produced a dicopper bis(formate), [(IPr*OMe)Cu]2 (μ-1,3-O2 CH)(μ-1,1-O2 CH), containing two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core cleanly ruptures to monomeric complexes when dissolved in a solvent.

Single‐Crystal to Single‐Crystal Transformations: Stepwise CO2 Insertions into Bridging Hydrides of [(NHC)CuH]2 Complexes

AbstractMechanistic studies of substrate insertion into dimeric [(NHC)CuH]2 (NHC=N‐heterocyclic carbene) complexes with two bridging hydrides have been shown to require dimer dissociation to generate transient, highly reactive (NHC)Cu−H monomers in solution. Using single‐crystal to single‐crystal (SC‐SC) transformations, we discovered a new pathway of stepwise insertion of CO2 into [(NHC)CuH]2 without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH]2 (IPr*OMe=N,N′‐bis(2,6‐bis(diphenylmethyl)‐4‐methoxy‐phenyl)imidazole‐2‐ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu]2(μ‐1,3‐O2CH)(μ‐H). A second CO2 insertion produced a dicopper bis(formate), [(IPr*OMe)Cu]2(μ‐1,3‐O2CH)(μ‐1,1‐O2CH), containing two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core cleanly ruptures to monomeric complexes when dissolved in a solvent.

Colloidal Deposition by Polymer-Surfactant Complexes with Dilution and Shear.

Deposition of silica microparticles on glass substrates was measured as a function of cationic polymer-anionic surfactant composition and shear rate. Particles were initially deposited in quiescent conditions in different polymer-surfactant compositions, which were chosen based on prior measurements of composition-dependent polymer-surfactant interactions and deposition behavior (up to 0.5 wt % polymer and 12 wt % surfactant). Programmed shear and dilution profiles in a flow cell together with optical microscopy observation were used to continuously track particle deposition, detachment, and redeposition. Knowledge of the shear-dependent torque on each particle provides information on adhesive torque mediated by polymer-surfactant complexes. Detachment of colloids initially deposited by depletion interactions occurs at low shear rates (∼100 s-1) due to lack of tangential forces or an adhesive torque. Further dilution produced redeposition of particles that resisted detachment (up to ∼2000 s-1) as the result of strong cationic polymer bridge formation, presumably due to preferential surfactant removal. Dilution from different initial compositions indicates a pathway dependence of polymer-surfactant de-complexation into shear-resistant cationic bridges. These findings demonstrate the ability to program deposition behavior via the informed design of initial polymer-surfactant compositions and shear profiles. The particle trajectory analysis developed in this work provides an assay to screen composition-dependent colloidal deposition in diverse materials and applications.

Pectin modifications promote haustoria development in the parasitic plant Phtheirospermum japonicum.

Parasitic plants are globally prevalent pathogens with important ecological functions but also potentially devastating agricultural consequences. Common to all parasites is the formation of the haustorium which requires parasite organ development and tissue invasion into the host. Both processes involve cell wall modifications. Here, we investigated a role for pectins during haustorium development in the facultative parasitic plant Phtheirospermum japonicum. Using transcriptomics data from infected Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), we identified genes for multiple P. japonicum pectin methylesterases (PMEs) and their inhibitors (PMEIs) whose expression was upregulated by haustoria formation. Changes in PME and PMEI expression were associated with tissue-specific modifications in pectin methylesterification. While de-methylesterified pectins were present in outer haustorial cells, highly methylesterified pectins were present in inner vascular tissues, including the xylem bridge that connects parasite to host. Specifically blocking xylem bridge formation in the haustoria inhibited several PME and PMEI genes from activating. Similarly, inhibiting PME activity using chemicals or by overexpressing PMEI genes delayed haustoria development. Our results suggest a dynamic and tissue-specific regulation of pectin contributes to haustoria initiation and to the establishment of xylem connections between parasite and host.