Dpp Ligand Research Articles

Overexpressed Gliotactin activates BMP signaling through interfering with the Tkv-Dad association.

Epithelial junctions ensure cell-cell adhesion and establish permeability barriers between cells. At the corners of epithelia, the tricellular junction (TCJ) is formed by three adjacent epithelial cells and generates a functional barrier. In Drosophila, a key TCJ protein is Gliotactin (Gli) where loss of Gli disrupts barrier formation and function. Conversely, overexpressed Gli spreads away from the TCJ and triggers apoptosis, delamination, and cell migration. Thus, Gli protein levels are tightly regulated and by two mechanisms, at the protein levels by tyrosine phosphorylation and endocytosis and at the mRNA level through microRNA-184. Regulation of Gli mRNA is mediated through a Gli-BMP-miR184 feedback loop. Excessive Gli triggers BMP signaling pathway through the activation of Tkv type-I BMP receptor and Mad. Elevated level of pMad induces micrRNA-184 expression which in turn targets the Gli 3'UTR and mRNA degradation. Gli activation of Tkv is not through its ligand Dpp but rather through the inhibition of Dad, an inhibitory-Smad. Here, we show that ectopic expression of Gli interferes with Tkv-Dad association by sequestering Dad away from Tkv. The reduced inhibitory effect of Dad on Tkv results in the increased Tkv-pMad signaling activity, and this effect is continuous through larval and pupal wing formation.

A new Cd-coordination polymer based on 1,3-di(4-pyridyl)propane: synthesis, crystal structure, thermogravimetric analysis, and photoluminescent properties

Hydrothermal reaction of cadmium iodide (CdI2) and 1,3-di(4-pyridyl)propane (dpp) results in the formation of the 2-D coordination polymer [Cd2(µ-ddp)4I4]n (1) where the Cd(II) ions assume octahedral I2N4 geometries. The dpp ligands adopt anti-anti (TT) and gauche-gauche′ (GG′) conformations. Thermogravimetric analysis reveals that 1 decomposes in two steps comprising dissociation of one dpp ligand followed by complete decomposition of the framework corresponding to the remaining three dpp ligands and iodides. Polymer 1 is luminescent at 386 nm.

A novel mixed ligand Zn-coordination polymer: Synthesis, crystal structure, thermogravimetric analysis and photoluminescent properties

A novel mixed ligand based coordination network of Zn, having formula [Zn8(Or)8(dpp)4(H2O)8]n (1), have been engineered and synthesized at room temperature by self-assembly of potassium orotate (OrK) and 1,3 di(4-pyridyl)propane (dpp) with metal salt, Zn(OAc)2·2H2O Single crystal X-ray structural analysis reveals that coordination sphere around Zn(II) ions, in Or-Zn-dpp moiety, having different atomic arrangement with distorted square pyramidal geometry. The syn-anti μ2η1:η1 bridging carboxylate and pyridyl moieties extended the Or-Zn-dpp skeleton into 2D coordination network showing square grid sheet. The emission spectrum of Zn-complex was recorded with 290 nm excitation wavelength which reflects that 1 has strong luminescence with peak maximum of 380 nm (3.2627 eV) and is a result of the n–π* and π–π* transitions of H3Or and dpp ligand. Thermogravimetric analysis shows that when the coordinated water molecule completely comes out from the complex around 320 °C, the dehydrated forms steadily starts to degrade, and the complete decomposition is observed above 350 °C.

Detection of the site protected 7-coordinate RuV = O species and its chemical reactivity to enable catalytic water oxidation

Artificial photosynthesis could promise cheap and abundant energy but requires the discovery of new water oxidation catalysts. A RuV = O 7-coordinate intermediate is implicated in the reactivity of the fastest water oxidation catalysts. Previously we reported in situ characterization of the 7-coordinate [RuV = O(L)2(bda)]+ stabilized on the electrode. Here we use ligand protection to stabilize [RuV = O(pic)2(dpp)]3+. We report the transformation of [RuII(pic)2(dpp)]2+ (dpp = 2,9-di-(pyrid-2′-yl)-1,10-phenanthroline, pic = 4-picoline) water oxidation catalyst using a combination of electron paramagnetic resonance (EPR), X-ray diffraction, resonance Raman (RR) and density functional theory (DFT). We observe the generation of [RuV = O(pic)2(dpp)]3+ and its chemical reactivity in solution. Lag phase in the oxygen evolution by [RuII(pic)2(dpp)]2+ is due to catalyst activation via an oxygen atom transfer from [RuV = O(pic)2(dpp)]3+ to the polypyridine dpp ligand and formation of [RuIII(pic)2(dpp-NO,NO)]3+. Detailed information regarding catalyst activation during the reaction will enable the design of more active and stable catalysts.

QM/MM nonadiabatic dynamics simulation on ultrafast excited-state relaxation in osmium(II) compounds in solution

Photoinduced excited-state relaxation dynamics of organometallic compounds, due to their potential applications in solar cells, organic light-emitting diodes, photocatalysis, etc., have been recently explored by a wealth of ultrafast experimental techniques. However, the corresponding nonadiabatic dynamics simulations are rarely reported. In this work, the early-time excited-state relaxation dynamics of two Os(II) compounds i.e. Os(bpy)3 and Os(bpy)2(dpp) (Os1 and Os2) have been investigated by our recently implemented TD-DFT based generalized surface-hopping dynamics simulation method in combination with the quantum mechanics/molecular mechanics (QM/MM) approach. The metal-to-ligand charge transfer (MLCT) excited singlet states from the Os atom to the bpy and dpp ligands are first populated in the Franck-Condon region. These initially populated excited singlet states will be converted through a series of ultrafast internal conversion and intersystem crossing processes to the lowest triplet state as a result of significant nonadiabatic and spin-orbit couplings among singlet and triplet electronic excited states. The intersystem crossing rates are estimated to be 72 and 53 fs for Os1 and Os2, respectively, which are consistent with experimental measured 100 fs and less than 50 fs. The time-dependent transition density analysis reveals that the MLCT excited states are dominant in the entire relaxation dynamics for either Os1 or Os2; however, the MLCT character changes in these processes. In Os1, the initially populated MLCT state is mainly from the Os atom to one bpy ligand, which is changed to the other two MLCT states. In Os2, the MLCT state that is mainly from the Os atom to the two bpy ligands is converted to the MLCT state from the Os to the dpp ligand. Finally, we have found that inter-ligand electron transfer plays a major role in the excited-state relaxation dynamics of Os1 and Os2; while, the hole transfer is minor. Our results also show that the ligand properties have significant influence on the excited-state relaxation dynamics of organometallic compounds. The insights gained in the present study provide atomistic insights for early-time excited-state relaxation dynamics of Osmium(II) compounds.

Drosophila ML-DmD17-c3 cells respond robustly to Dpp and exhibit complex transcriptional feedback on BMP signaling components

BackgroundBMP signaling is involved in myriad metazoan developmental processes, and study of this pathway in Drosophila has contributed greatly to our understanding of its molecular and genetic mechanisms. These studies have benefited not only from Drosophila’s advanced genetic tools, but from complimentary in vitro culture systems. However, the commonly-used S2 cell line is not intrinsically sensitive to the major BMP ligand Dpp and must therefore be augmented with exogenous pathway components for most experiments.ResultsHerein we identify and characterize the responses of Drosophila ML-DmD17-c3 cells, which are sensitive to Dpp stimulation and exhibit characteristic regulation of BMP target genes including Dad and brk. Dpp signaling in ML-DmD17-c3 cells is primarily mediated by the receptors Put and Tkv, with additional contributions from Wit and Sax. Furthermore, we report complex regulatory feedback on core pathway genes in this system.ConclusionsNative ML-DmD17-c3 cells exhibit robust transcriptional responses to BMP pathway induction. We propose that ML-DmD17-c3 cells are well-suited for future BMP pathway analyses.

Versatility of copper(II) coordination compounds with 2,3-bis(2-pyridyl)pyrazine mediated by temperature, solvents and anions choice

Tuning reaction temperatures as well as the variation in starting copper salts and solvents led to the formation of a new series of Cu(II) coordination compounds with 2,3-bis(2-pyridyl)pyrazine (dpp): a mononuclear [Cu(acac)(dpp)(NO3)] (1) complex, two dinuclear [Cu2(acac)2(dpp)(NO3)(H2O)]NO3 (2) and [Cu2(Hdpp)2(ox)(Cl)2(H2O)2]Cl2·6(H2O) (4) complexes, and four coordination polymers {[Cu4(dpp)2(ox)(Cl)6]}n (3), {[Cu4(dpp)2(ox)(NO3)6(H2O)2]∙1.2(H2O)}n (5), {[Cu(dpp)(NO3)](NO3)·(H2O)}n (6) and {[Cu(dpp)(SO4)(H2O)2]}n (7), where acac− = acetylacetonate, ox2− = oxalate. Remarkably, the treatment of Cu(II) chloride dihydrate with dpp in methanol solution led to an unusual in situ condensation of dpp with acac− to produce [Cu2(acdpp)2(Cl)4]·2(MeOH) (8). The structure of 1 consists of neutral, mononuclear [Cu(acac)(dpp)(NO3)] units with acac− and dpp acting as bidentate ligands. In 2, the dpp ligand coordinates in a bis-chelating mode to two Cu(II) ions and bridges them into a dimeric entity, whereas an oxalate linker joins [Cu(Hdpp)(Cl)2(H2O)]+ units into a dimer in 4. Compounds 3, 5, 6 and 7 are 1D chain coordination polymers, which incorporate two symmetry independent metal centers and different bridging ligands: Hdpp+ as a protonated cationic or dpp as a neutral chelating ligand and oxalate, Cl− anions or sulfate di-anions as bridging ligands. Magnetic studies were performed on samples 1 and 2, and the analysis reveals a very weak magnetic exchange coupling mediated via the dpp ligand.

Tuning spin transitions of iron(II)-dpp systems

Chemical modifications of the yet reported iron(II) compound [Fe(dpp)2(NCS)2]⋅Py (dpp = dipyrido[3,2a:2’3’c]phenazine, Py = pyridine) which shows abrupt spin crossover below room temperature with large hysteresis have been made. The purpose was to stabilize different spin states at room temperature as well as to adjust the spin crossover in temperature and hysteresis width. We modified the bidentate ligand dpp by substituting hydrogens at the phenazine by different functional groups. In addition, we substituted the thiocyanate monodentate ligands by NCSe−. The spin states of these compounds have been investigated by Mossbauer spectroscopy at two temperatures and temperature depending IR spectroscopy. These methods indicating that the chemical modifications are influencing the observed spin configuration of the complexes alongside the spin crossover behavior which changed to gradual and incomplete transitions. These promising results offer interesting possibilities for chemical adjustments of the shown spin crossover systems.

Wnt6 maintains anterior escort cells as an integral component of the germline stem cell niche.

ABSTRACTStem cells reside in a niche, a local environment whose cellular and molecular complexity is still being elucidated. In Drosophila ovaries, germline stem cells depend on cap cells for self-renewing signals and physical attachment. Germline stem cells also contact the anterior escort cells, and here we report that anterior escort cells are absolutely required for germline stem cell maintenance. When escort cells die from impaired Wnt signaling or hid expression, the loss of anterior escort cells causes loss of germline stem cells. Anterior escort cells function as an integral niche component by promoting DE-cadherin anchorage and by transiently expressing the Dpp ligand to promote full-strength BMP signaling in germline stem cells. Anterior escort cells are maintained by Wnt6 ligands produced by cap cells; without Wnt6 signaling, anterior escort cells die leaving vacancies in the niche, leading to loss of germline stem cells. Our data identify anterior escort cells as constituents of the germline stem cell niche, maintained by a cap cell-produced Wnt6 survival signal.

Redox, spectroscopic, photo-induced ligand exchange, and DNA interaction studies of a new Ru(II)Pt(II) bimetallic complex

A new bimetallic complex, [Ru(biq)2(dpp)PtCl2](PF6)2 (where biq = 2,2′-biquinoline and dpp = 2,3-bis(2-pyridyl)pyrazine), containing a cis-PtCl2 moiety coupled to a sterically strained Ru(II)-based chromophore was designed, synthesized, and investigated with respect to its spectroscopic, redox, photo-induced ligand exchange, and DNA-interaction properties. The electrochemistry of the designed complex was found to be consistent with the bridging coordination of the dpp ligand and formation of the bimetallic complex. The complex displays intense ligand-based π → π* transitions in the UV region and metal-to-ligand charge-transfer transitions (MLCT) in the visible region. The loss of bridging coordination of the dpp ligand and formation of complexes, [Ru(biq)2(CH3CN)2]2+ and [Pt(dpp)(CH3CN)2]2+ was observed when an acetonitrile solution of the metal complex was irradiated with visible light (λirr ≥ 550 nm). The designed complex displays covalent binding with DNA in dark through the cis-PtCl2 moiety, as confirmed by agarose gel electrophoresis. Upon photoirradiation, the complex dissociates into two DNA-binding moieties and displays covalent binding through: (i) a cis-PtL2 subunit of [Ptdpp(L)2]2+ and (ii) open coordination sites of the ruthenium of [Ru(biq)2(L)2]2+ (L = solvent). The designed complex represents the first Ru(II)Pt(II) complex that undergoes photo-induced ligand exchange and displays multifunctional interactions with DNA upon photoirradiation.

Basement Membrane Manipulation in Drosophila Wing Discs Affects Dpp Retention but Not Growth Mechanoregulation

Basement membranes (BMs) are extracellular matrix polymers basally underlying epithelia, where they regulate cell signaling and tissue mechanics. Constriction by the BM shapes Drosophila wing discs, a well-characterized model of tissue growth. Recently, the hypothesis that mechanical factors govern wing growth has received much attention, but it has not been definitively tested. In this study, we manipulated BM composition to cause dramatic changes in tissue tension. We found that increased tissue compression when perlecan was knocked down did not affect adult wing size. BM elimination, decreasing compression, reduced wing size but did not visibly affect Hippo signaling, widely postulated to mediate growth mechanoregulation. BM elimination, in contrast, attenuated signaling by bone morphogenetic protein/transforming growth factor β ligand Dpp, which was not efficiently retained within the tissue and escaped to the body cavity. Our results challenge mechanoregulation of wing growth, while uncovering a function of BMs in preserving a growth-promoting tissue environment.

Syntheses and characterization of three diphenyl phosphate based Cu(II) complexes and the effect of non-covalent interactions on their supramolecular framework

Assembly of diphenylphosphate (dpp) with Cu(II) salts in combination with the different N-donor linkers, e.g., pentamethyldiethylenetriamine (pmdeta), bis-(3-aminopropyl)amine (bapa) and 4-Picolene (4-pic), yielded three new metal-organic coordination complexes, namely {[Cu(dpp)(pmdeta)] ⋅ClO4.H2O}2 (1), {[{[Cu(dpp)(bapa)H2O] ⋅ClO4} (2) and [Cu(dpp)2(4-pic)2]2 (3) by stirring the constituent reactants at room temperature. Complexes 1–3 were characterized by single crystal X-ray diffraction analysis and were further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD) studies. Compound 1 exhibits a dimeric Cu(II) complex which forms a 1D supramolecular chain along the crystallographic c-axis by means of intermolecular π…π interactions. Compounds 2 and 3 form a monomeric and dimeric complex of Cu(II) respectively, which are further extended into a supramolecular 2D structure via C-H.. π interactions for 2 and a 3D structure for 3 with the help of both intermolecular C-H.. π and π…π interactions for 3. In addition, the solid state UV-Vis spectra of compounds 1-3 and free dpp ligand have been investigated at room temperature. Three Cu(II) complexes based on diphenylphosphate (dpp) and different N-donor linkers, e.g., pentamethyldiethylenetriamine (pmdeta), bis-(3-aminopropyl)amine (bapa) and 4-Picolene (4-pic) were successfully synthesized and characterized. These complexes show fascinating supramolecular 1D, 2D and 3D structures by means of intermolecular π…π and C-H…π interactions additively or individually.

DNA interaction studies and photoinduced ligand exchange kinetics of a sterically strained ruthenium(II) complex

Sterically strained ruthenium polypyridyl complexes represent an emerging class of bioactive molecules, capable of photoinduced ligand exchange and covalent binding with DNA, in a manner similar to cisplatin. A sterically strained complex, [Ru(biq)2(dpp)](PF6)2, where biq=2,2′-biquinoline, dpp=2,3-bis(2-pyridyl)pyrazine, was synthesized, and investigated with respect to its photoinduced ligand exchange and DNA interaction properties. Although synthesis and redox properties of the complex, [Ru(biq)2(dpp)](PF6)2, have been reported, the photoinduced ligand exchange properties and DNA binding properties have not yet been reported. Photoinduced dissociation of the dpp ligand was observed upon irradiation of water or acetonitrile solutions of the metal complex with visible light (λirr⩾550nm) to generate [Ru(biq)2(H2O)2](PF6)2 and [Ru(biq)2(CH3CN)2](PF6)2 complexes, respectively. The half-lives of photoactivated exchange of the dpp ligand with water and acetonitrile were found to be 14min and 6min, respectively. The dissociation of the dpp ligand upon irradiation with light was confirmed by mass spectrometry. The synthesized complex displays covalent binding with DNA upon irradiation with visible light, confirmed by slowing down of the rate of DNA migration in agarose gel electrophoresis. No effect on the rate of migration of DNA was observed when incubated with metal complex in dark. The spectroscopic, photoinduced ligand exchange kinetics and DNA interaction properties are presented.

Formation of heterocaryotic and homonuclear bridged–dimeric complexes on surface

Abstract The formation of coordinated dimeric complexes bridged by axial ligands on surface is observed with the help of a 1,3,5-tris(10-carboxydecyloxy)benzene (TCDB) template through scanning tunneling microscopy (STM). STM images of molecular adlayers of zinc tetraphenylporphyrin (ZnTPP), zinc phthalocyanine (ZnPc), and their mixture are reported. ZnTPP and ZnPc can spontaneously form highly an ordered structure with a 1:1 molar ratio, which is different from that of individual ZnPc. The coordinated bimolecular complexes bridged with axial ligands, simply as ZnPc–DPP–ZnTPP and ZnPc–DPE–ZnPc, are presented and the corresponding surface structures are compared. ZnPc and ZnTPP can be connected by an axial ligand DPP and formed assembled structures out of surface. Two types of arrays with entirely new structure are obtained for the ZnPc–DPE–ZnPc complex. These bridged hybrid complexes provide an example of design of self-organized crystals on the basis of coordination through non-covalent interactions.

Electrocatalytic H2 Evolution by Supramolecular Ru(II)-Rh(III)-Ru(II) Complexes: Importance of Ligands as Electron Reservoirs and Speciation upon Reduction.

The supramolecular water reduction photocatalysts [{(Ph2phen)2Ru(dpp)}2RhX2](PF6)5 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline, dpp =2,3-bis(2-pyridyl)pyrazine X = Cl, Br) are efficient electrocatalysts for the reduction of CF3SO3H, CF3CO2H, and CH3CO2H to H2 in DMF or DMF/H2O mixtures. The onset of catalytic current occurs at -0.82 V versus Ag/AgCl for CF3SO3H, -0.90 V for CF3CO2H, and -1.1 V for CH3CO2H with overpotentials of 0.61, 0.45, and 0.10 V, respectively. In each case, catalysis is triggered by the first dpp ligand reduction implicating the dpp as an electron reservoir in catalysis. A new species with Epc ∼ -0.75 V was observed in the presence of stoichiometric amounts of strong acid, and its identity is proposed as the Rh(H)(III/II) redox couple. H2 was produced in 72-85% Faradaic yields and 95-116 turnovers after 2 h and 435 turnovers after 10 h of bulk electrolysis. The identities of Rh(I) species upon reduction have been studied. In contrast to the expected dissociation of halides in the Rh(I) state, the halide loss depends on solvent and water content. In dry CH3CN, in which Cl(-) is poorly solvated, a [Ru] complex dissociates and [(Ph2phen)2Ru(dpp)Rh(I)Cl2](+) and [(Ph2phen)2Ru(dpp)](2+) are formed. In contrast, for X = Br(-), the major product of reduction is the intact trimetallic Rh(I) complex [{(Ph2phen)2Ru(dpp)}2Rh(I)](5+). Chloride loss in CH3CN is facilitated by addition of 3 M H2O. In DMF, the reduced species is [{(Ph2phen)2Ru(dpp)}2Rh(I)](5+) regardless of X = Cl(-) or Br(-).

Nanotubes mediate niche-stem-cell signalling in the Drosophila testis.

Stem cell niches provide resident stem cells with signals that specify their identity. Niche signals act over a short-range such that only stem cells but not their differentiating progeny receive the self-renewing signals1. However, the cellular mechanisms that limit niche signaling to stem cells remain poorly understood. Here we show that the Drosophila male germline stem cells (GSCs) form previously unrecognized structures, microtubule-based (MT)-nanotubes, which extend into the hub, a major niche component. MT-nanotubes are observed specifically within GSC populations, and require IFT (intraflagellar transport) proteins for their formation. The BMP receptor Tkv localizes to MT-nanotubes. Perturbation of MT-nanotubes compromises activation of Dpp signaling within GSCs, leading to GSC loss. Moreover, Dpp ligand and Tkv receptor interaction is necessary and sufficient for MT-nanotube formation. We propose that MT-nanotubes provide a novel mechanism for selective receptor-ligand interaction, contributing to the short-range nature of niche-stem cell signaling.

Nonchromophoric halide ligand variation in polyazine-bridged Ru(II),Rh(III) bimetallic supramolecules offering new insight into photocatalytic hydrogen production from water.

The new bimetallic complex [(Ph2phen)2Ru(dpp)RhBr2(Ph2phen)](PF6)3 (1) (Ph2phen = 4,7-diphenyl-1,10-phenanthroline; dpp = 2,3-bis(2-pyridyl)pyrazine) was synthesized and characterized to compare with the Cl(-) analogue [(Ph2phen)2Ru(dpp)RhCl2(Ph2phen)](PF6)3 (2) in an effort to better understand the role of halide coordination at the Rh metal center in solar H2 production schemes. Electrochemical properties of complex 1 display a reversible Ru(II/III) oxidation, and cathodic scans indicate multiple electrochemical mechanisms exist to reduce Rh(III) by two electrons to Rh(I) followed by a quasi-reversible dpp(0/-) ligand reduction. The weaker σ-donating ability of Br(-) vs Cl(-) impacts the cathodic electrochemistry and provides insight into photocatalytic function by these bimetallic supramolecules. Complexes 1 and 2 exhibit identical light-absorbing properties with UV absorption dominated by intraligand (IL) π → π* transitions and visible absorption by metal-to-ligand charge transfer (MLCT) transitions to include a lowest energy Ru(dπ) → dpp(π*) (1)MLCT transition (λ(abs) = 514 nm; ε = 16 000 M(-1) cm(-1)). The relatively short-lived, weakly emissive Ru(dπ) → dpp(π*) (3)MLCT excited state (τ = 46 ns) for both bimetallic complexes is attributed to intramolecular electron transfer from the (3)MLCT excited state to populate a low-energy Ru(dπ) → Rh(dσ*) triplet metal-to-metal charge transfer ((3)MMCT) excited state that allows photoinitiated electron collection. Complex 1 outperforms the related Cl(-) bimetallic analogue 2 as a H2 photocatalyst despite identical light-absorbing and excited-state properties. Additional H2 experiments with added halide suggest ion pairing plays a role in catalyst deactivation and provides new insight into observed differences in H2 production upon halide variation in Ru(II),Rh(III) supramolecular architectures.

Co(III) complexes of tetradentate X3L type ligands: Synthesis, electronic structure, and reactivity

Co(III) complexes of DPP (DPP=(Z)-2-(2-((5-(2-hydroxyphenyl)-1H-pyrrol-2-yl)(phenyl)methylene)-2H-pyrrol-5-yl)phenol) and two fluorinated DPP variants are prepared, structurally characterized, and their reactivity explored in the catalytic ring-opening of 1,2-epoxyhexane with alcohols. While the related Co(III) salen and porphyrin complexes are highly active for this catalytic transformation, the Co(III) DPP complexes are shown to be catalytically inert under the conditions studied. Computational characterization of the electronic structure of all the complexes shows that the Co(III) complexes ligated by the DPP ligands (tetradentate X3L type) do not have sufficient Lewis acidity to activate the epoxide, whereas the Co(III) porphyrin and salen (tetradentate X2L2 type) incorporate a counter-ion that draws electron density away from the metal center, creating a more Lewis acidic Co species that is catalytically active for alcohol ring-opening of epoxides. The work thus gives insight into the requirements for effective Lewis acidic epoxide ring-opening catalysts based on cobalt.

Monometallic europium, terbium, and neodymium complexes formed from the bridging ligand 2,3-bis(2-pyridyl)pyrazine: Crystal structure and temperature dependent luminescent properties

Lanthanide complexes of the form Ln(tdh)3dpp (where Ln=Nd(III), Eu(III) or Tb(III); tdh=1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione and dpp=2,3-bis(2-pyridyl)pyrazine) have been structurally characterized. X-ray quality crystals were grown by the slow evaporation of concentrated solutions of the complexes. Each metal is 8-coordinate with 6 oxygens from the tdh ligand, 1-pyridyl nitrogen, and 1-pyrazine nitrogen from the dpp ligand. Luminescent studies show that the Nd complex undergoes non-radiative relaxation through solvent vibrational deactivation. In contrast, the Eu and Tb complexes emit in the visible region of the spectrum when solutions of the complex are excited at 388nm associated with the π–π∗ transition of the tdh ligand. Emission lines corresponding to transitions from the 5D0 and 5D4 state to the 7FJ manifold of the Eu(III) and Tb(III), respectively, are observed. The intensity of these emissions decreases as temperature is increased.

Dpp/Gbb signaling is required for normal intestinal regeneration during infection

Maintaining tissue homeostasis is a critical process during infection and inflammation. Tissues with a high intrinsic turnover, such as the intestinal epithelium, must launch a rapid response to infections while simultaneously coordinating cell proliferation and differentiation decisions. In this study, we searched for genes required for regeneration of the Drosophila intestine, and thereby affecting overall organism survival after infection with pathogenic bacteria. We found that Dpp/Gbb (BMP) signaling is essential for normal midgut regeneration, and that infection induces the BMP signaling ligands Dpp and Gbb. We demonstrate that Dpp is induced in visceral muscle and required for signaling activation. Subsequently, Gbb is induced in enterocytes after oral infection. Loss-of Dpp signaling in ISCs and transient committed progenitors called enteroblasts (EBs), or in EBs alone, led to a blockage in EC differentiation or maturation. Furthermore, our data show that down-regulation of Dpp signaling in the precursor cells including EBs also resulted in an increased number of abnormally small Pdm1-positive cells, suggesting a role of Dpp/Gbb signaling in EC growth. In addition, we show that Dpp/Gbb signaling acted downstream or in parallel to the Notch pathway to promote EC differentiation and growth. Our results suggest that Dpp/BMP signaling plays an important role in EBs to maintain tissue integrity and homeostasis during pathogenic infections.