Pyridine Subunits Research Articles

Three Isomeric Tetraphenylethylene-pyridine Compounds: Synthesis, Crystal Structures, and Photophysical Properties.

Many aggregation-induced emission (AIE) molecules based on tetraphenylethylene (TPE) structure have been synthesized, but a clear understanding of the photophysical difference between different isomeric pyridyl-based tetraphenylethylene molecules remains elusive. Herein, we designed a series of isomeric tetraphenylethylene-pyridines (o-Py-TPE, m-Py-TPE, p-Py-TPE) to investigate the influence of the position of N atoms in the pyridine subunit on the photophysical property of the whole molecule by detailed DFT calculations and single crystal structures analysis. All compounds show typical AIE properties, and notably, the meta pyridyl isomer (m-Py-TPE) shows the highest solid photoluminescence quantum yield (PLQY) up to 64.56%. Further investigation and DFT calculations indicate that the center C=C bond dihedral angles of the TPE subunit in the solid state of these compounds, which are affected by C-H···π interaction, play a vital role in their emission and PLQY properties. This work provides underlying principles for the design of pyridyl-based TPE molecules with high photoluminescent performance in the future.

Bioinspired Total Synthesis of Pyritide A2 through Pyridine Ring Synthesis

AbstractPyritides belong to the ribosomally synthesized and post‐translationally modified peptide class of natural products that were recently genome‐predicted and are structurally defined by unique pyridine‐containing macrocycles. Inspired by their biosynthesis, proceeding through peptide modification and cycloaddition to form the heterocyclic core, we report the chemical synthesis of pyritide A2 involving pyridine ring synthesis from an amino acid precursor through aza‐Diels–Alder reaction. This strategy permitted the preparation of the decorated pyridine core with an appended amino acid residue in two steps from a commercially available arginine derivative and secured pyritide A2 in ten steps. Moreover, the synthetic logic enables efficient preparation of different pyridine subunits associated with pyritides, allowing rapid and convergent access to this new class of natural products and analogues thereof.

Adsorption-Induced Fluorescence of Pseudoisocyanine Monomers in Systems with Layered Silicates

Interaction of organic dyes with layered silicates can cause various changes in dye properties, such as metachromasia (color change), fluorescence quenching, resonance energy transfer, or even fluorescence enhancement. These phenomena are caused by the molecular aggregation or adsorption of dye molecules on silicate particles. The present work studied the photophysical properties of pseudoisocyanine (PIC) in colloidal dispersions of five samples of layered silicates (smectites) at variable PIC/smectite loadings. The silicates of variable composition and layer charge included one synthetic saponite, one synthetic hectorite, two synthetic Laponites, and one montmorillonite. Chemometric analysis of the absorption spectra revealed the formation of four spectral species: monomers and three types of molecular aggregates exhibiting light absorption in both H- and J-band regions. In addition, the samples of hybrid systems with silicates of lower layer charge under the condition of the lowest PIC/silicate ratio (0.01 mmol g–1) exhibited strong fluorescence surpassing that of J-aggregates. The luminescent species achieving quantum yields of about 50% were assigned to the adsorbed PIC monomers, a phenomenon that has never been observed for this dye. Theoretical calculations found that in water solution bending of the molecule supports nonradiative deactivation of the excited state of the free molecule. Adsorption of PIC molecules on the surface of silicate particles caused the change of the dihedral angle between pyridine subunits, which hinders the nonradiative deactivation channel and favors emission. Fluorescence from adsorbed monomers exhibited a maximum at ≈535 nm, which is at significantly lower wavelengths with respect to the J-aggregates emitting at ≈570 nm and thus cannot be related to dye aggregation as supported by the fact that this phenomenon occurs only at the lowest surface concentrations of the dye.

Cobalt Quaterpyridine Complexes for Highly Efficient Heterogeneous CO2 Reduction in Aqueous Media

AbstractLigands play a critical role in the electrocatalytic CO2 reduction reaction (CO2RR) based on heterogeneous molecular catalysts. Previous research on heterogeneous molecular electrocatalysis has mainly dealt with N4 ligands with pyrrole as subunits (porphyrin, phthalocyanine, etc.), while ligands constructed from pyridine subunits remain uncommon. The examples for comparing active configurations are few and far between. Herein, the development of new N4 cobalt complexes based on pyridine subunits is explored. After anchoring onto carbon nanotubes, they can exhibit CO2RR activity at a low overpotential of 140 mV, and high activity from ‐0.30 to ‐0.60 V versus reference hydrogen electrode with a selectivity of above 98%. Excellent performance at large current densities can also be observed in a flow cell. In situ attenuated total reflectance‐Fourier transform infrared spectroscopy proves that such electrocatalysts exhibit CO production at lower overpotential and moderate CO adsorption ability over a wide potential range. From density functional theory calculations, it is shown that a pyridine‐based cobalt complex on a carbon substrate can reduce the Gibbs free energy for reactions further than its counterpart pyrrole‐based ones. Further analysis proves that the semimetal behavior of optimized d‐orbitals may facilitate charge transfer and increase the activity. This provides a new insight for understanding catalytically active moieties in heterogeneous molecular catalysts with ligands constructed from pyridine subunits.

Asymmetric Sonogashira C(sp3)–C(sp) bond coupling enabled by a copper(i) complex of a new guanidine-hybrid ligand

A type of new chiral nitrogen-donor hybrid ligand bearing acyclic guanidine, amide, and pyridine subunits was rationalized for Cu(i)-catalyzed asymmetric Sonogashira C(sp3)–C(sp) cross-coupling.

Reductive Dimerization of Macrocycles Activated by BBr3.

A macrocyclic motif composed of carbazole and pyridine subunits linked by a carbonyl bridge (C=O) forms a skeleton with a peripheral reactivity that leads to a pinacol-like coupling activated by BBr3, eventually entrapping a substantially elongated C–C bond. Slightly modified conditions lead to the efficient transformation of the C=O unit to a CH2 linker that, after exposure to air, gives a dimeric molecule with multiple bonds between two macrocyclic units, as documented in spectroscopy and X-ray analysis.

A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors.

Three-dimensional (3D) triply interlocked catenanes are a family of chemical topologies that consist of two identical, mechanically interlocked coordination cage components with intriguingly complex structures. Although only a few successful constructions of 3D interlocked catenanes have been achieved to date via metal-mediated assembly, these complex structures have thus far only been targeted by metal-nitrogen/oxygen coordination techniques. Here, taking advantage of rational ligand design, we report the efficient construction of a series of 3D triply interlocked [2]catenanes of the formula [Ag3L2]2, wherein the metal ions exclusively form bonds to N-heterocyclic carbene (NHC) units, and their subsequent transmetalation to the corresponding [Au3L2]2 gold analogues. The formation and transmetalation reactions proceed under mild conditions and are generally applicable. A series of characterization techniques were applied to confirm the formation and structure of the desired 3D triply interlocked architectures: multinuclear NMR spectroscopy, ESI-MS, and single-crystal X-ray diffraction analysis. The solid-state structure of [Ag3(1a)2]2(PF6)6 unambiguously confirms the existence of a 3D catenane that consists of two identical, mechanically interlocked trinuclear hexacarbene cage components. The interlocking of two 3D cages into a [2]catenane is driven by the efficient π···π stacking of triazine-triazine stacks with cooperative interactions between imidazo[1,5-a]pyridine subunits. Notably, the triply interlocked organometallic cages exhibit good stability toward various organic solvents, concentrations, and temperatures, and no disassembly occurred in the presence of coronene or pyrene. The future construction of mechanically interlocked architectures using metal-carbene bonds rather than metal-nitrogen bonds may provide assemblies with interesting properties for as-yet-unimagined applications in fields such as sensors and molecular electrical conductors.

Design, synthesis, SAR and molecular docking of novel green niacin-triketone HPPD inhibitor

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is a very important target for the discovery of novel bleaching herbicides. In order to discover novel triketone green HPPD inhibitors with excellent herbicidal activity and crop selectivity, the natural product leptospermone was selected as the template compound, and niacin was employed as bioisostere to design and synthesize a series of novel substituted niacin-triketone derivatives. Some of the target compounds showed potent Arabidopsis thaliana HPPD (AtHPPD) inhibitory activity in vitro. Especially compound II-1 displayed the best herbicidal activity (IC50 = 0.262 μM, AtHPPD), and was safe for Zea mays at concentration of 300 g ai/ha. Molecular docking results indicated that the triketone moiety of compound II-1 could form a bidentate complex with Fe(II), and the pyridine subunit interacted with Phe430 and Phe360 via π−π packing. The present work indicated that 3-hydroxy-2-nicotinoylcyclohex-2-en-1-one could be a potential lead structure for developing novel green HPPD inhibitors.

Onydecalins, Fungal Polyketides with Anti- Histoplasma and Anti-TRP Activity.

We report an unusual 3-substituted pyridine polyketide, onydecalin A (1), which was obtained along with 2 as a major constituent from the fungus Aioliomyces pyridodomos (order: Onygenales) following a two-month fermentation. Feeding studies demonstrated that the pyridine subunit originates via an unprecedented biosynthetic process in comparison to other polyketide-linked pyridines or derivatives such as pyridones. The slow growth of the fungus led us to perform a one-year fermentation, leading to production of compounds 2-4 as the major constituents. These compounds showed modest but selective inhibition against a variety of transient receptor potential channels, as well as against the human pathogenic fungus Histoplasma capsulatum.

Design of Novel, Water Soluble and Highly Luminescent Europium Labels with Potential to Enhance Immunoassay Sensitivities.

To meet the continual demands of more-sensitive immunoassays, the synthesis of novel luminescent Eu(III) chelate labels having similar substituted 4-(phenylethynyl)pyridine chromophores in three different chelate structure classes are reported. Significantly enhanced luminescence intensities were obtained, evidently caused by the intra-ligand charge transfer (ILCT) mediated sensitization, but the alternative ligands triplet state process cannot be ruled out. Based on the present study, even quite small changes on the chelate structure, and, especially, on the substituents’ donor/acceptor strength on both ends of 4-(phenylethynyl)pyridine subunits have an unpredictable effect on the luminescence. The highest observed brightness was 16,400 M−1 cm−1 in solution and 69,500 M−1 cm−1 on dry surface, being 3.4 and 8.7 fold higher compared to the reference chelate. The new label chelates provide solutions for improved assay sensitivity up-to tenfold from the present concepts.

A computational study of substituent effects on the stability and geometry of carbazole‐pyridine complexes

AbstractHydrogen bonding between carbazole and pyridine is known to quench fluorescence emission of carbazole. Three carbazolopyridinophanes—compounds composed of carbazole and pyridine subunits such that an intramolecular hydrogen bond may exist between them—have been pursued as reversible fluorescent sensors that detect given analytes through fluorescence restoration. However, these sensors exhibit background fluorescence believed to be related to the proportion of non‐hydrogen‐bonded conformers present. In this computational investigation, the potential energy surfaces of various hydrogen‐bonded carbazole:pyridine complexes are investigated using density functional theory with the intent of explaining the observed background fluorescence for the carbazolopyridinophanes. The results indicate carbazolopyridinophane conformers most resembling the geometry of their corresponding free carbazole:pyridine complexes exhibit the least background fluorescence.

Group 12 Metal Complexes of an 18-Membered N2O2S2 Macrocycle Incorporating Two Pyridines: First Examples of an Infinite Mercury(I) Complex and a Dumbbell-Shaped Heteronuclear Complex with a Macrocyclic Ligand.

Homo- and heteronuclear group 12 metal (Zn2+, Cd2+, and Hg2+) complexes 1-6 containing a newly designed 18-membered N2O2S2 macrocycle incorporating two pyridine subunits (L) were prepared and structurally characterized. The individual complexes isolated exhibit unusual stoichiometries, geometries, oxidation states, and structural topologies and include an infinite mercurous complex and a heteronuclear dumbbell-shaped complex. Both the Zn(II) complex [Zn(L)][ZnBr4] (1) and the Cd(II) complex [Cd(L)Br2] (2) are mononuclear, with the metal ion located inside the macrocyclic cavity. The six-coordinated Zn(II) center in 1 adopts an octahedral geometry and is shielded from the anion and solvent by the strongly bound macrocycle. The Cd(II) center in 2 is seven-coordinate, being bound equatorially to two N donors, two O donors, and a S donor from the macrocycle and axially to two bromide ions on opposite sides of the macrocyclic plane, adopting a pentagonal-bipyramidal geometry. In the Hg(II) complexations, the configuration adopted by the macrocycle L shows a dependence of the nuclearity on the anion used. When mercury(II) bromide was used, the dinuclear complex [HgII2(L)Br4] (3) was obtained, while the reaction with mercury(II) nitrate afforded the unexpected Hg(I) complex {[HgI2(L)](NO3)2}n (4) with a one-dimensional polymeric structure. In heterometallic complexation experiments, one-pot reaction of L with a mixture of ZnBr2 and CdBr2·4H2O resulted in the stepwise isolation of two pure solubility-dependent Cd(II) complexes (2 and 5), including the half-dumbbell-type complex [Cd(L)(μ-Br)(CdBr3)] (5), while a mixture of CdBr2·4H2O and HgBr2 yielded the heterometallic bis(macrocycle) product [(CdL)2(μ-Hg2Br6)](Hg2Br6) (6). This is the first example of a heteronuclear dumbbell-shaped complex in which two terminal macrocyclic Cd(II) complexes are linked by a hexabromodimercury(II) cluster via Cd-Br-Hg bonds. The heterometallic dumbbell 6 can be considered as a good example of competition and collaboration between Cd(II) and Hg(II) ions because its formation is associated with the higher coordination affinity of Cd(II) toward the macrocycle and the formation of the (Hg2Br6)2- cluster, which links the two endocyclic Cd(II) complexes directly. Both NMR titration and comparative NMR data indicate a relatively higher coordination affinity of Cd(II) toward the macrocycle than occurs for Hg(II), in parallel to the situation observed in the solid state.

ChemInform Abstract: Strategies and Methods for the Synthesis of Pyridinocrownophanes (Microreview)

AbstractReview: [16 refs.

Strategies and methods for the synthesis of pyridinocrownophanes (microreview)

This review aims to highlight the most significant recent developments in the synthesis of pyridinofused azacrown ethers, which contain a minor azaheterocyclic moiety contributing its nitrogen atom to the macrocycle. This subfield of azacrown ethers draws constant attention of scientists over the last decades owing to their great theoretical and practical potential.1 Pyridinocrownophanes, azacrown ethers containing a pyridine subunit, are widely used as ligands for effective metal ion sequestration,2 as well as enantiomeric recognition.3 They are also excellent phase-transfer catalysts,1 membrane ion transporting vehicles,4 scaffolds for the design of organic sensors, nanosized on-off switches, and other molecular devices.5 Certain pyridinoazacrown compounds have been found to possess antibacterial6 and anticancer properties.7

Influence of Anion and Mole Ratio on the Coordination Behavior of an NO2S3-Macrocycle: The Formation of a Dumbbell-Shaped Macrocyclic Cadmium(II) Iodide Complex.

Anion and mole ratio dependent formations of cadmium(II) complexes with an NO2S3-macrocycle (L) incorporating a pyridine subunit are reported. When the cadmium(II) salts (1-10 equiv) with different halide ions (Br(-) or I(-)) were reacted with L, CdBr2 afforded a monomer complex, [Cd(L)Br]2[Cd2Br6]·CH2Cl2 (1), with three separated parts in the whole mole ratio range: two 1:1 stoichiometric complex cation parts and one Cd2Br6 cluster anion part. After separation of 1 by filtration, [Cd(L)Br]2[CdBr4]·CH2Cl2 (2) with similar composition was afforded, except the cluster was isolated from the filtrate. Unlike the CdBr2 complexation, CdI2 afforded the mole ratio dependent products (3-5). Below 2.5 equiv of CdI2, [Cd(L)I]2[CdI4]·CH2Cl2 (3) and [Cd(L)I]2[Cd2I6]·0.5CH2Cl2 (4) with different cadmium(II) iodide clusters were isolated as kinetic (3) and a thermodynamic (4) products. Notably, the use of 3 equiv or above amount of CdI2 gave a dumbbell-shaped complex, {[Cd(L)]2(μ-Cd4I12)} (5), in which two mononuclear macrocyclic complex units are linked by a (μ-Cd4I12)(4-) cluster. To monitor the mole ratio dependency as well as their reactivities, the systematic powder X-ray diffraction (PXRD) analysis has also been applied.

Boron complexes of cyclo[m]pyridine[n]pyrroles

Novel boron complexes were synthesized by reacting cyclo[[Formula: see text]]pyridine[[Formula: see text]]pyrroles ([Formula: see text] [Formula: see text] 6) with BF3. These complexes were characterized and studied by means of NMR, UV, and fluorescence spectroscopies, and X-ray crystallography. As compared to the non-boronated starting materials, the complexes of this study are more rigid and twisted, a feature that translates into a modulation of the optical features. Specifically, these boron complexes can be either strongly fluorescent or barely fluorescent, depending on the numbers of pyridine subunits contained within the macrocycle. The present approach could thus define an attractive and potentially generalizable means for modulating the inherent optical characteristics of expanded porphyrins.

Porphyrinoid Aromaticity Induced by the Interaction between Oxidized and Reduced Pyridine Subunits

Coupling of 3-hydroxypyridine-2,6-dicarbaldehyde with a tripyrrane-like precursor bearing a central pyridine ring afforded a new porphyrinoid with two pyridine-related subunits Spectroscopic and theoretical analyses demonstrate that the aromaticity of this porphyrinoid is fulfilled by the cooperative interaction between the two pyridinoid rings.

Complexation of some alkali and alkaline earth metal cations by macrocyclic compounds containing four pyridine subunits – a DFT study

Tetradentate pyridine-based macrocyclic compounds offer useful ligands capable of efficient and selective complexation of M = Li+, Na+, K+, Be2+, Mg2+and Ca2+.

A kinetic study of aqua ligand substitution in dinuclear Pt(II) complexes containing four non-coplanar pyridine ligands

Substitution reactions of the aqua ligands from azine-bridged dinuclear platinum(II) complexes of the type [{cis-Pt(py)2(OH2)} 2(μ-pzn)](ClO4)4 [pzn = pyrazine (Pt-PZN), 2,3-dimethylpyrazine (Pt-2,3PZN), 2,5-dimethylpyrazine (Pt-2,5PZN) or 2,6-dimethylpyrazine (Pt-2,6PZN)] by thiourea nucleophiles were investigated under pseudo first-order conditions as a function of concentration and temperature using the stopped-flow technique. The experimental results are discussed in reference to structures obtained by DFT calculations. The results are in good agreement with the pKa values of the complexes as well as DFT calculations. Compared to [{cis/trans-Pt(NH3)2(OH2)} 2(μ-pzn)](ClO4)4, the complexes in this series react faster by a factor of 10 or 23 respectively due to the presence of pyridine rings, which forces the geometry to allow π-back bonding to take place such that the electrons from the metal centres are accepted to the empty π*-orbitals of the pyridine subunits. The reactivity of the nucleophile is sterically dependent, with N,N,N′,N′-tetramethylthiourea reacting three times slower than thiourea. In all complexes and for both substitution steps, the mode of activation remains associative in nature. The presence of pyridine rings in [{cis-Pt(py)2(OH2)} 2(μ-pzn)](ClO4)4 where py = pyridine, pzn = pyrazine (Pt-PZN), 2,3-dimethylpyrazine (Pt-2,3PZN), 2,5-dimethylpyrazine (Pt-2,5PZN) and 2,6-dimethylpyrazine (Pt-2,6PZN) allows the substitution reactions by thiourea nucleophiles to proceed faster by a factor of 10 than [{cis-Pt(NH3)2(OH2)} 2(μ-pzn)](ClO4)4 through π-back bonding.

Synthesis and Characterization of New Organosoluble and Thermally Stable Poly(thioether-amide)s Bearing Pyridine Subunit in the Main Chain

We report the synthesis of new polyamides containing 2,6-bis(2-thio-2-(4-carboxyphenyl)-1-oxo)pyridine subunit, under microwave irradiation using Yamasaki phosphorylation method. The solubility, thermal behavior, and viscosity of polyamides were evaluated. The structures of polymers have been characterized using IR and 1H NMR spectroscopy. These polyamides showed good solubility, viscosity, high thermal stability, and glass transition temperatures. Their viscosities and glass transition temperatures are in the range of 0.63–0.88 and 223–295°C, respectively. Thermal stabilities for 10% weight loss (T10) are 137–173°C and for 50% weight loss (T50) are in the range of 483–523°C. The study of surface morphology showed particle and amorphous structures.