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Ethyl 5-cyano-1,6-dihydro-2-methyl-4-(2'-thienyl)-6-thioxonicotinate ( A ) was synthesized and reacted with ethyl chloroacetate in the presence of sodium acetate or sodium carbonate to give ethyl 5-cyano-6-((2-ethoxy-2-oxoethyl)thio)-2-methyl-4-(2'-thienyl)nicotinate ( 1a ) or its isomeric thieno[2,3- b ]pyridine 2a . 3-Aminothieno[2,3- b ]pyridine-2-carboxamide 2b was also synthesized by the reaction of A with 2-chloroacetamide. The reaction of 1a with hydrazine hydrate in boiling ethanol gave acethydrazide 3 . Heating ester 1a with hydrazine hydrate under neat conditions afforded 3-amino-1 H -pyrazolo[3,4- b ]pyridine 10 . Compounds 2b , 3, and 10 were used as precursors for synthesizing other new thieno[2,3- b ]pyridines and pyrazolo[3,4- b ]pyridines containing mainly the ethyl nicotinate scaffold. Structures of all new compounds were confirmed by elemental and spectral analyses. Most of the obtained compounds were evaluated for their insecticidal activity toward the nymphs and adults of Aphis gossypii (Glover,1887). Some compounds such as 4 , 9b, and 9c showed promising results. The effect of some sublethal concentrations, less than LC 50 , of compounds 4 , 9b, and 9c on the examined Aphis was subjected to a further study. The results demonstrated that exposure of A. gossypii nymphs to sublethal concentrations of compounds 4 , 9b, and 9c had noticeable effects on their biological parameters, i.e., nymphal instar duration, generation time, and adult longevity. The highest concentration C1 of all three compounds increased the nymphal instar duration and generation time and decreased adult longevity and vice versa.

Herein, we report a heterogeneous intermetallic nickel silicide catalyst prepared by the impregnation of nickel acetate/1,10-phenanthroline on fumed silica and subsequent pyrolysis. The optimal catalyst exhibits good activity and selectivity for the hydrogenation of N-heterocycles including pyridines and quinolines under comparably mild conditions using water as the solvent. To our knowledge, it is the first reported efficient nickel-based heterogeneous catalyst for catalytic pyridine hydrogenation. [ABSTRACT FROM AUTHOR]

Protonation, hydration, and cluster formation of ammonia, formaldehyde, formic acid, acetone, butanone, 2-ocatanone, 2-nonanone, acetophenone, ethanol, pyridine, and its derivatives were studied by IMS-TOFMS technique equipped with a corona discharge ion source. It was found that tendency of the protonated molecules, MH+, to participate in hydration or cluster formation depends on the basicity of M. The molecules with higher basicity were hydrated less than those with lower basicity. The mass spectra of the low basic molecules such as formaldehyde exhibited larger clusters of MnH+(H2O)n, while for compounds with high basicity such as pyridine, only MH+ and MH+M peaks were observed. The results of DFT calculations show that enthalpies of hydrations and cluster formation decrease as basicities of the molecules increases. Using comparison of mass spectra of formic acid, formaldehyde, and ethanol, effect of structure on the cluster formation was also investigated. Formation of symmetric (MH+M) and asymmetric proton-bound dimers (MH+N) was studied by ion mobility and mass spectrometry techniques. Both theoretical and experimental results show that asymmetric dimers are formed more easily between molecules (M and N) with comparable basicity. As the basicity difference between M and N increases, the enthalpy of MH+N formation decreases. [ABSTRACT FROM AUTHOR]

A novel asymmetric 6-endo aminoacetoxylation of unactivated alkenes by palladium catalysis, which yields chiral β-acetoxylated piperidines with excellent chemo-, regio- and enantioselectivities under very mild reaction conditions, has been established herein by employing a new designed pyridine-oxazoline (Pyox) ligand. Importantly, introducing a sterically bulky group into the C-6 position of Pyox is crucial to enhance the reactivity of the aminoacetoxylation of alkenes. [ABSTRACT FROM AUTHOR]

The multicomponent synthesis of a mini-library of histone deacetylase inhibitors with imidazo[1,2-a]pyridine-based cap groups is presented. The biological evaluation led to the discovery of the hit compound MAIP-032 as a selective HDAC6 inhibitor with promising anticancer activity. The X-ray structure of catalytic domain 2 from Danio rerio HDAC6 complexed with MAIP-032 revealed a monodentate zinc-binding mode. [ABSTRACT FROM AUTHOR]

The first intermolecular ring-expansion cascade of azirines with alkynes for the synthesis of pyridines, enabled by a copper/triethylamine catalytic system via simultaneous generation and utilization of yne-enamine and skipped-yne-imine intermediates, is reported. Experimental as well as computational mechanistic studies revealed that the role of triethylamine is crucial in deciding the reaction pathway toward the pyridine products. This process offers a novel, one-step, direct, and practical strategy for the rapid construction of highly substituted pyridines under exceedingly mild conditions, and an installed alkyne functionality. [ABSTRACT FROM AUTHOR]

A trace amount of acetylene (C2H2, 1%) removal from ethylene/acetylene mixture is crucial for the production of polymer-grade ethylene (C2H4), which is a highly challenging task and currently is mainly realized via highly energy-intensive technologies. Herein, we first report the highly efficient trapping of C2H2 from C2H2/C2H4 mixtures using two hexafluorogermanate (GeF62-, GeFSIX) anion-functionalized hybrid ultramicroporous materials, GeFSIX-2-Cu-i and GeFSIX-14-Cu-i (also termed ZU-32 and ZU-33), as novel adsorbents. These GeFSIX materials exhibit high thermal stability and tunable pore structures and have a high density of electronegative GeF62- anions decorated on the pore surface. ZU-32 with an aperture size of 4.5 Å exhibits preferential binding ability for C2H2 molecules and thus offers an excellent separation selectivity of 67 for the C2H2/C2H4 (1/99) mixture. ZU-33 with 4,4-azopyridine (azpy, 9.0 Å) as an organic linker exhibits a contracted pore window size with pyridine ring tilting of ca. 30°, which could efficiently block C2H4 molecules but still permit C2H2 molecules trapping into the pore channels. The strong hydrogen-bonding interactions between GeF62- and C2H2 and cooperative van der Waals (vdW) interactions between organic linkers and C2H2 enable ZU-33 to exhibit a record high C2H2 volumetric uptake of 61.5 cm3 cm-3 at 0.01 bar and 298 K with separation selectivity over 1100 for C2H2/C2H4 (1/99) mixture. The actual separation performances of GeFSIX materials are evaluated by conducting experimental breakthrough tests. A total of 99.9999% C2H4 can be obtained from a C2H2/C2H4 (1/99) mixture by one-step column adsorption using GeFSIX materials as adsorbents with a C2H4 productivity up to 1662.1 mL g-1. The binding sites of GeFSIX materials for C2H2 molecules were investigated by first-principles density functional theory (DFT) calculations. This work not only indicates that GeFSIX materials are lead candidates for the separation of C2H2/C2H4 mixture but also are attractive adsorbents for the separation of other gas mixtures containing acidic or polar gaseous components. [ABSTRACT FROM AUTHOR]

Insight into the molecular interactions of homotactic and heterotactic association of caffeine and pyridine in aqueous solution is given on the basis of both experimental and simulation studies. Caffeine is about 5 times more soluble in a 3 m aqueous pyridine solution than it is in pure water (an increase from ~0.1 m to 0.5 m). At this elevated concentration the system becomes suitable for neutron scattering study. Caffeine-pyridine interactions were studied by neutron scattering and molecular dynamics simulations, allowing a detailed characterization of the spatial and orientational structure of the solution. It was found that while pyridine-caffeine interactions are not as strong as caffeine-caffeine interactions, the pyridine-caffeine interactions still significantly disrupted caffeine-caffeine stacking. The alteration of the caffeine-caffeine stacking, occasioned by the presence of pyridine molecules in solution and the consequent formation of heterotactic interactions, leads to the experimentally detected increase in caffeine solubility. [ABSTRACT FROM AUTHOR]

Organoruthenium compounds have been widely investigated for their anticancer activity. Here we use one of the classic ligand classes found in organometallics, i.e., N-heterocyclic carbenes (NHC), and coordinate them to the Ru(η6-p-cymene) scaffold as N,C-bidentate ligands substituted with a pyridyl moiety. Introduction of different substituents gave compounds with a wide variety of properties. We investigated their stability in solution and in the presence of biomolecules, in vitro anticancer activity, and cellular uptake to rationalize their biological properties in dependence on the structure. A clear effect of their structure on the stability in water and DMSO was found for some derivatives, which was reflected in the reactivity to biomolecules that was determined with selected representatives of the compound classes. The antiproliferative activity of the compounds was widely dependent on the lipophilicity of the N,C-bidentate ligand, but as cellular accumulation studies revealed, lipophilicity does not provide the full picture and additional effects must be responsible for the anticancer activity. [ABSTRACT FROM AUTHOR]

In this work, we report a new class of blue-emitting cyclometalated iridium complexes supported by acyclic diaminocarbene (ADC) ancillary ligands. These neutral, tris-chelated complexes are not obtainable via traditional synthesis routes and instead are generated through metal-mediated nucleophilic addition to a metal-bound isocyanide, which is followed by orthometalation of the ADC under mild conditions. Importantly, four of the variants exhibit efficient phosphorescence when immobilized in PMMA matrix, achieving quantum yields of 79% for blue emitters with a 2-(2,4-difluorophenyl)pyridine (F2ppy) C^N ligand and 30-37% for orange emitters with a 2-phenylbenzothiazole (bt) C^N ligand. Electrochemical studies demonstrate significantly higher-lying HOMO levels in the ADC complexes relative to the NHC analogues, a phenomenon that results in enhanced charge-transfer character in the excited states of the ADC complexes. This study demonstrates that ADC ancillary ligands not only give rise to new structures for Ir(III)-based phosphorescent emitters but also are promising targets for use in light-emitting devices and other thin-film optical applications. [ABSTRACT FROM AUTHOR]

A regioselective functionalization of the pyrazolo[1,5-a]pyridine scaffold using Mg- and Zn-TMP bases (TMP = 2,2,6,6-tetramethylpiperidyl) in the presence or absence of BF3·OEt2 is described. Also, various functionalized pyrazolo[1,5-a]pyridines bearing an ester function (and an NHBoc or ethyl group) are magnesiated and functionalized, leading to polysubstituted heterocycles. Additionally, a sulfoxide directed ortho-metalation, followed by the transition-metal-free amination of a pyrazolo[1,5-a]pyridine sulfoxide, using a magnesium amide, is reported. [ABSTRACT FROM AUTHOR]

The reaction of o-aminoacetophenones and arylboronic acids catalyzed by copper(II) salts in the presence of pyridine under an O2 atmosphere provides a general and efficient one-pot preparation of biologically interesting acridones. This relay reaction comprises an intermolecular Suzuki cross-coupling, intramolecular oxidative C(sp³)-H amination, and C(sp²)-H activation with simultaneous rearrangement of the generated isatin intermediates. This strategy tolerates both electron-donating and -withdrawing functionalities to afford various acridones in good to excellent yields. [ABSTRACT FROM AUTHOR]

Palmitoylation, a type of fatty acylation, has vital roles in many biological processes. For ultradeep identification of protein palmitoylation, an enrichment approach based on a novel magnetic microsphere modified with 2,2′-dithiodipyridine (Fe3O4/SiO2-SSPy microsphere) is presented in this study. The Fe3O4/SiO2-SSPy microspheres were synthesized by directly coating thiol-containing silane coupling agent onto the magnetic supraparticles in aqueous solution at room temperature. Due to the intrinsic magnetic properties, high surface-to-volume ratios, and abundant reactive functional groups on the surface, these microspheres enabled direct capture of palmitoylated targets and convenient isolation, contributing to remarkable enrichment selectivity (purifying palmitoylated peptides from mixtures with nonpalmitoylated peptides even at a 1:500 molar ratio) and sensitivity (the detection limit was at femtomole level), thus enabling a global annotation of protein palmitoylation for complex biological samples. We successfully identified 1304 putative palmitoylated proteins from mouse brain tissues by using this method, which is the largest mouse palmitoylome data set to date. Except for those known members, many new proteins and pathways were also found to be regulated by palmitoylation. [ABSTRACT FROM AUTHOR]

A straightforward process to aminate pyridines and diazines is presented by reacting phosphonium salt derivatives with sodium azide. The iminophosphorane products are versatile precursors to several nitrogen-containing functional groups, and the process can be applied to building block heterocycles, to drug-like fragments, and for late-stage functionalization of complex pharmaceuticals. Appealing features of this strategy include using C-H bonds as precursors, precise regioselectivity, and a distinct scope from other amination methods, particularly those relying on halogenated azaarenes. [ABSTRACT FROM AUTHOR]

An electrochemical method was developed for the redox switchable polymerization of lactide and cyclohexene oxide. Using a lithium reversible sacrificial electrode and a high surface area carbon working electrode, efficient transformation between formally iron- (II) and iron(III) oxidation states of a bis(imino)pyridine iron alkoxide complex was possible, which led to the ability to activate the complex for ring opening polymerization reactions. In addition to serving as a redox trigger, an electrochemical toggle switch was developed in which the chemoselectivity for lactide and epoxide polymerization was altered in situ. These findings led to the synthesis of poly(lactic acid-b-cyclohexene oxide) block copolymers in which the sequence of monomers incorporated is controlled by the electrical potential applied. [ABSTRACT FROM AUTHOR]

This article describes the development of a second-generation catalyst system for the transannular C-H functionalization of alicyclic amines. Pyridine- and quinoline-carboxylate ligands are shown to be highly effective for increasing the reaction rate, yield, and scope of Pd-catalyzed transannular C-H arylation reactions of azabicyclo[3.1.0]-hexane, azabicyclo[3.1.1]heptane, azabicyclo[3.2.1]octane, and piperidine derivatives. Mechanistic studies reveal that the pyridine/quinoline-carboxylates play a role in impeding both reversible and irreversible catalyst decomposition pathways. These ligands enable the first reported examples of the transannular C-H arylation of the ubiquitous tropane, 7-azanorbornane, and homotropane cores. Finally, the pyridine/quinoline-carboxylates are shown to promote both transannular C-H arylation and transannular C-H dehydrogenation on a homotropane substrate. [ABSTRACT FROM AUTHOR]

Substantial attention has been given to modern organocopper chemistry in recent years since copper salts are naturally abundant, cheap, and less toxic in comparison to precious metals. Copper salts also exhibit versatility in catalyzing and mediating carbon-carbon and carbon-heteroatom bond forming reactions. Despite the wide applications of copper salts in catalysis, reaction mechanisms have remained elusive. Using azacalix[1]arene[3]pyridine, an arene-embedded macrocycle, and its isolated and structurally well-defined ArCu(II) and ArCu(III) compounds as molecular tools, we now report an in-depth experimental and computational study on the mechanism of a Cu(II)-catalyzed oxidative cross-coupling reaction between arenes and boronic acids with air as the oxidant. Stoichiometric reaction of organocopper compounds with p-tolylboronic acid validated arylcopper(II) rather than arylcopper(III) as a reactive organometallic intermediate. XPS, EPR, ¹H NMR, HRMS, and UV-vis spectroscopic evidence along with the isolation and quantification of all products and copper speciation, combined with computational analysis of the electronic structure and energetics of the transient intermediates, suggested a reaction sequence involving electrophilic metalation of arene by Cu(II), transmetalation of arylboronate to ArCu(II), the redox reaction between the resulting ArCu(II)Ar' and ArCu(II) to form respectively ArCu(III)Ar' and ArCu(I), and finally reductive elimination of ArCu(III)Ar'. Under aerobic catalytic conditions, all Cu(I) ions released from reductive elimination of ArCu(III)Ar' and from protolysis of ArCu(I) were oxidized by oxygen to regenerate Cu(II) species that enters into the next catalytic cycle. The unraveled reactivity of arylcopper(II) compounds and the catalytic cycle would enrich our knowledge of modern organocopper chemistry and provide useful information in the design of copper-catalyzed reactions. [ABSTRACT FROM AUTHOR]

A palladium(II)-catalyzed asymmetric 1,2-diamination of 1,3-dienes with readily available dialkylureas was established by using a chiral pyridine-oxazoline ligand. The diamination reaction exclusively occurs at the terminal C-C double bond of the 1,3-dienes to give 4-vinylimidazolidin-2-ones in high yields and with excellent levels of enantioselectivity (up to 99% yield, 97% ee). The reaction could feasibly be applied for gram-scale synthesis with a 1:1 ratio of the diene and the urea. [ABSTRACT FROM AUTHOR]

A novel approach for the synthesis of indolizines from 2-(pyridin-2-yl)acetates, ynals, and alcohols or thiols has been developed. This MCR (multicomponent reaction) that proceeds under the solvent- and metal-free conditions has provided a straightforward path to construct indolizines. Furthermore, this reaction demonstrates other attractive features such as widely available starting materials, mild conditions, good functional group tolerance, and high efficiency. [ABSTRACT FROM AUTHOR]

We show that a chiral copper hydride (CuH) complex catalyzes C-C bond-forming dearomatization of pyridines and pyridazines at room temperature. The catalytic reaction operates directly on free heterocycles and generates the nucleophiles in situ, eliminating the need for stoichiometric preactivation of either reaction partner; further, it is one of very few methods available for the enantioselective 1,4-dearomatization of heteroarenes. Combining the dearomatization with facile derivatization steps enables one-pot syntheses of enantioenriched pyridines and piperidines. [ABSTRACT FROM AUTHOR]

Carbon nanothreads are a new one-dimensional sp³ carbon nanomaterial. They assemble into hexagonal crystals in a room temperature, nontopochemical solid-state reaction induced by slow compression of benzene to 23 GPa. Here we show that pyridine also reacts under compression to form a well-ordered sp³ product: C5NH5 carbon nitride nanothreads. Solid pyridine has a different crystal structure from solid benzene, so the nontopochemical formation of low-dimensional crystalline solids by slow compression of small aromatics may be a general phenomenon that enables chemical design of properties. The nitrogen in the carbon nitride nanothreads may improve processability, alters photoluminescence, and is predicted to reduce the bandgap. [ABSTRACT FROM AUTHOR]

Four coordination polymers, [CuII(L)H2O]•2DMF (1), [CuICuII2L2(H2O)(pyridine)2]•(NO3)•4DMF•3H2O (2), [CuICuII2L2(pyridine)3]•(NO3)•DMF•4H2O (3), and [CuII2L(μ-O)(DMF)]•4DMF•5H2O (4), have been synthesized under solvothermal conditions using a single methylene-bispyrazole based carboxylic acid ligand, L, and Cu(NO3)2. All the compounds were comprised of copper paddle wheel secondary building units (SBUs). The structural differences in 1-4 arise due to different compositions of the solvent system as well as pH of the medium. Compound 1 exhibited a one-dimensional (1D) double chain structure with a porous three-dimensional (3D) supramolecular network, while 2 and 3 represent mixed Cu(II)/Cu(I) based porous frameworks. MOFs 2 and 3 were obtained by systematic binding of pyridine molecules on the axial positions of Cu paddle-wheel SBU, having a rare topology, sur; bbf-3,4-Cccm and a new topology, respectively. MOF 4 is a 3D porous network containing a Cu2(μ-O)2 moiety and exhibits a 3,4,4-c net. It contains open channels with 46.9% void volume. Gas sorption studies of 4showed the microporous nature of the framework with 66 mL g-1 of CO2 uptake at 273 K and 31 mL g-1 at 298 K with a high Qst value of 30.7 kJ mol-1 at zero loading. [ABSTRACT FROM AUTHOR]

The ground and excited state photophysical properties of a series of fac-[Re(L)(CO)3(α-diimine)]n+ complexes, where L = Br-, Cl-, 4-dimethylaminopyridine (dmap) and pyridine (py) have been extensively studied utilizing numerous electronic and vibrational spectroscopic techniques in conjunction with a suite of quantum chemical methods. The α-diimine ligand consists of 1,10-phenanthroline with the highly electron donating triphenylamine (TPA) appended in the 5 position. This gives rise to intraligand charge transfer (ILCT) states lying lower in energy than the conventional metal-to-ligand charge transfer (MLCT) state, the energies of which are red and blue-shifted, respectively, as the ancillary ligand, L becomes more electron withdrawing. The emitting state is ³ILCT in nature for all complexes studied, characterized through transient absorption and emission, transient resonance Raman (TR²), time-resolved infrared (TRIR) spectroscopy and TDDFT calculations. Systematic modulation of the ancillary ligand causes unanticipated variation in the ³ILCT lifetime by 2 orders of magnitude, ranging from 6.0 µs for L = Br- to 27 ns for L = py, without altering the nature of the excited state formed or the relative order of the other CT states present. Temperature dependent lifetime measurements and quantum chemical calculations provide no clear indication of close lying deactivating states, MO switching, contributions from a halide-to-ligand charge transfer (XLCT) state or dramatic changes in spin-orbit coupling. It appears that the influence of the ancillary ligand on the excited state lifetime could be explained in terms of energy gap law, in which there is a correlation between ln(knr) and Eem with a slope of -21.4 eV-1 for the ³ILCT emission. [ABSTRACT FROM AUTHOR]

We explored the elementary reaction of atomic carbon (C; 3Pj) with pyridine (C5H5; X1A1) at a collision energy of 34 ± 4 kJ mol-1 utilizing the crossed molecular beams technique. Forward-convolution fitting of the data was combined with high-level electronic structure calculations and statistical (RRKM) calculations on the triplet C6H5N potential energy surface (PES). These investigations reveal that the reaction dynamics are indirect and dominated by large range reactive impact parameters leading via barrier-less addition to the nitrogen atom and to two chemically nonequivalent "aromatic" carbon-carbon bonds forming three distinct collision complexes. At least two reaction pathways through atomic hydrogen loss were identified on the triplet surface. These channels involve multiple isomerization steps of the initial collision complexes via ring-opening and ring expansion forming an acyclic 1-ethynyl-3-isocyanoallyl radical (P1; 2A") and a hitherto unreported seven-membered 1-aza-2-dehydrocyclohepta-2,4,6-trien-4-yl radical isomer (P3; 2A), respectively. For RRKM calculations at zero collision energy, representing conditions in cold molecular clouds, the ring expansion product P3 is formed nearly exclusively for the atomic hydrogen loss channel, but based on these computations, the molecular fragmentation channel forming acetylene (C2H2) plus 3-cyano-2-propen-1-ylidene (P6; 3A") accounts for nearly all of the degradation products of the reaction of atomic carbon with pyridine, proposing a destruction pathway of interstellar pyridine, which may account for the absence in the detection of pyridine in the interstellar medium. These results are also discussed in light of the isoelectronic carbon-benzene (C6H6; X1A1) system with important implications to the rapid degradation of nitrogen-bearing polycyclic aromatic hydrocarbons (NPAHs) in the interstellar medium compared to mass growth processes of PAH counterparts through ring expansion. [ABSTRACT FROM AUTHOR]

Oriented external electric fields (OEEFs) are potent effectors of chemical change and control. We show that the Menshutkin reaction, between substituted pyridines and methyl iodide, can be catalyzed/inhibited at will, by just flipping the orientation of the EEF (FZ) along the "reaction axis" (Z), N---C--- I. A theoretical analysis shows that catalysis/inhibition obey the Bell-Evans-Polanyi principle. Significant catalysis is predicted also for EEFs oriented off the reaction axis. Hence, the observation of catalysis can be scaled up and may not require orienting the reactants vis-à-vis the field. It is further predicted that EEFs can also catalyze the frontside nucleophilic displacement reaction, thus violating the Walden-inversion paradigm. Finally, we considered the impact of gold-thiolate linkers, used experimentally to deliver the EEF stimuli, on the Menshutkin reaction. A few linkers were tested and proved not to be innocent. In the presence of FZ, the linkers participate in the electronic reorganization of the molecular system. In so doing, these linkers induce local electric fields, which map the effects of the EEF and induce catalysis/inhibition at will, as in the pristine reaction. However, as the EEF becomes more negative than -0.1 V/Å, an excited charge transfer state (CTS), which involves one-electron transfer from the 5p lone pair of iodine to an antibonding orbital of the gold cluster, crosses below the closed-shell state of the Menshutkin reaction and causes a mechanistic crossover. This CTS catalyzes nucleophilic displacement of iodine radical from the CH3I*+ radical cation. The above predictions and others discussed in the text are testable. [ABSTRACT FROM AUTHOR]

We demonstrate pyridine hydroboration catalyzed by a diazaphospholene hydride precatalyst. Pyridines bearing electron-withdrawing groups in the 3-position are hydroborated efficiently. This system features low catalyst loadings, fast reaction times at ambient temperature, and tolerance of other reducible functionality. Off-cycle products of pyridine hydrophosphination were also obtained in one case from a stoichiometric reaction and structurally characterized. [ABSTRACT FROM AUTHOR]

The inclusion of solvent effects in the calculation of excited states is vital to obtain reliable absorption spectra and density of states of solvated chromophores. Here we analyze the performance of three classical approaches to describe aqueous solvent in the calculation of the absorption spectra and density of states of pyridine, tropone, and tropothione. Specifically, we compare the results obtained from quantum mechanics/polarizable continuum model (QM/PCM) versus quantum mechanics/molecular mechanics (QM/MM) in its electrostatic-embedding (QM/MMee) and polarizable-embedding (QM/MMpol) fashions, against full-QM computations, in which the solvent is described at the same level of theory as the chromophore. We show that QM/PCM provides very accurate results describing the excitation energies of ππ* and nπ* transitions, the last ones dominated by strong hydrogen-bonding effects, for the three chromophores. The QM/MMee approach also performs very well for both types of electronic transitions, although the description of the ππ* ones is slightly worse than that obtained from QM/PCM. The QM/MMpol approach performs as well as QM/PCM for describing the energy of ππ* states, but it is not able to provide a satisfactory description of hydrogen-bonding effects on the nπ* states of pyridine and tropone. The relative intensity of the absorption bands is better accounted for by the explicit-solvent models than by the continuum-solvent approach. [ABSTRACT FROM AUTHOR]

This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis(4-phenyl-2-oxazolinyl)pyridine [(R)- or (S)-Ph-Pybox] are successfully directed to the fabrication of a D2-symmetrical alternating circular helicate with the general formula [(R)- or (S)- Ph-Pybox]4(LnIII)4(BTP)6. The lanthanide(III) LnIII assemblies (LnIII4-RRRR and LnIII4-SSSS) have a nanometer-size squarelike grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate LnIII 2L2 units, where both show (M)-helicity for LnIII 4-RRRR and (P)-helicity for LnIII 4-SSSS, where π-π stacking interaction is present between the side arm of (R)-Ph-Pybox (Ph1) and the adjacent BTP ligand around the EuIII metal center (dππ = 3.636 Å: the diketonate plane···Ph1 distance). The newly obtained circular lanthanide(III) helicate exists as single and homochiral diastereomers in solution (LnIII 4-RRRR and LnIII 4-SSSS), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (i.e., LnIII 4-RRRR/LnIII 4-SSSS). [ABSTRACT FROM AUTHOR]

Pseudo-octahedral complexes built on chelating ligands offer valuable isomeric properties such as the formation of fac vs mer isomers, and Λ vs Δ enantiomers. This article discusses factors guiding the fac vs mer selection of complexes built from the triazolyl-pyridine platform bearing a benzyl substituent, in conjunction with labile metal ions such as zinc(II), iron(II), and nickel(II). Critical parameters that are explored include the geometrical flexibility of the individual metal ion, and the nature of the counteranion. In essence, it was observed that ions which can withstand significant distortions in their first coordination sphere, such as zinc(II), generally prefer forming the mer isomer irrespective of the counteranion, whereas ions with more restricted geometry, such as iron(II), are directed either to a fac arrangement by small, tetrahedral anions such as tetrafluoroborate or perchlorate or to a mer organization by counteranions of lower symmetry, such as triflate. The molecular interactions operating the selection are discussed. Interestingly, such iron(II) complexes are prime candidates for spin crossover behavior; hence, understanding their isomeric selection may assist in guiding the design of solid-state magnetic materials. [ABSTRACT FROM AUTHOR]

Herein, 2-vinylpyridines as a new type of electron-poor system for the asymmetric cross Rauhut-Currier reaction are reported. 2-Vinylpyridines are chemo- and enantioselectively activated by a newly designed chiral phosphine catalyst. The new reaction provides a powerful synthetic tool for accessing structurally diverse, highly valued chiral pyridine building blocks in good yields and with high enantioselectivities. Preliminary mechanistic studies reveal that two NH protons in the catalyst are critical for the synergistic activation of the substrates and governing the stereoselectivity of this reaction. [ABSTRACT FROM AUTHOR]

Ruthenium(II) hydride complexes bearing a pyrazolyl-(2-indol-1-yl)-pyridine ligand were synthesized and structurally characterized by NMR analysis and X-ray single crystal crystallographic determinations. These complexes efficiently catalyzed acceptorless dehydrogenation of N-heterocycles and secondary alcohols, respectively, exhibiting highly catalytic activity with a broad substrate scope. The present work has established a strategy to construct highly active transition metal complex catalysts and provides an atom-economical and environmentally benign protocol for the synthesis of aromatic N-heterocyclic compounds and ketones. [ABSTRACT FROM AUTHOR]

Nicotinamide N-methyltransferase (NNMT) catalyzes the N-methylation of pyridine-containing compounds using the cofactor S-5'-adenosyl-l-methionine (SAM) as the methyl group donor. Through the regulation of the levels of its substrates, cofactor, and products, NNMT plays an important role in physiology and pathophysiology. Overexpression of NNMT has been implicated in various human diseases. Potent and selective small-molecule NNMT inhibitors are valuable chemical tools for testing biological and therapeutic hypotheses. However, very few NNMT inhibitors have been reported. Here, we describe the discovery of a bisubstrate NNMT inhibitor MS2734 (6) and characterization of this inhibitor in biochemical, biophysical, kinetic, and structural studies. Importantly, we obtained the first crystal structure of human NNMT in complex with a small-molecule inhibitor. The structure of the NNMT-6 complex has unambiguously demonstrated that 6 occupied both substrate and cofactor binding sites. The findings paved the way for developing more potent and selective NNMT inhibitors in the future. [ABSTRACT FROM AUTHOR]

Metallo-supramolecular engineering on surfaces provides a powerful strategy toward low-dimensional coordination architectures with prospects for several application fields. To date, most efforts have relied on transition metal centers, and only recently did we pioneer lanthanide-directed assembly. Coordination spheres and motifs with rare-earth elements generally display distinct properties and structural features. The size of the cations and shielding role of the 4f orbitals induces high coordination numbers, frequently entailing flexible coordination geometries. Following Pearson's hard and soft acid-base theory, lanthanide cations are hard Lewis acids and thus feature strong affinity for nitrile, terpyridine, and carboxylate donor moieties. The prevailing oxidation state is +3, although in certain compounds stable +2 or +4 cations occur. The chemistry of rare-earth elements is currently receiving widespread attention, as they are key ingredients for established and emerging 21st century science and technology with relevance for energy conversion, sensing, catalysis, magnetism, photonics, telecommunications, superconductivity, biomedicine, and quantum engineering. In this Account, we review recent advances toward the design of interfacial supramolecular nanoarchitectures incorporating lanthanide centers. We apply controlled ultrahigh vacuum conditions whereby atomistically clean substrates are prepared and exposed to ultrapure atomic and molecular beams of the chosen sublimable constituents. We focus on direct molecular-level investigations and in situ assembly operative close to equilibrium conditions. Our scanning probe microscopy techniques provide atomistic insights regarding the formation, stability, and manipulability of metal-organic compounds and networks. In order to gain deeper insights into the experimental findings, complementary computational analysis of bond characteristics, electronic properties, and coordination motifs has been performed for several case studies. Exemplary elements under consideration include cerium, gadolinium, dysprosium, and europium. By the use of ditopic molecular linkers equipped with carbonitrile moieties, adaptive coordination spheres are unveiled, yielding vertices with two- to sixfold symmetry. The respective coordination nodes underlie the expression of complex networks, such as semiregular Archimedean tessellations for cerium- or gadolinium-directed assemblies and random-tiling quasicrystalline characteristics for europium. Tunability via constituent stoichiometry regulation is revealed for bimolecular arrangements embedding europium centers, simultaneously connecting to carbonitrile and terypyridine ligands. Ditopic carboxylate linkers yield robust reticular networks based on a lateral coordination number of 8 for either gadolinium or dysprosium complexation, featuring a prevalent ionic nature of the coordination bond. Orthogonal insertion protocols give rise to d-f reticular architectures exploiting macrocyclic tetradentate cobalt complexation and peripheral carbonitrile-gadolinium coordination, respectively. Furthermore, lanthanides may afford metalation of adsorbed free-base tetrapyrrole species and can be engaged for interfacial synthesis of sandwich compounds, thus providing prospects for columnar design of coordination architectures. Finally, direct manipulation experiments achieved lateral displacement of single supramolecules and molecular rotation of sandwich or other molecular units. These findings evidence prospects for advancing molecular machinery components. The presented accomplishements herald further advancements in metallo-supramolecular design on surfaces, with versatile nanosystems and architectures emanating from the flexible coordination spheres. The embedding and systematic rationalization of lanthanide centers in tailored interfacial environments are keys to establishing relations between structure and physicochemical characteristics toward the generation of novel functionalities with technological significance. [ABSTRACT FROM AUTHOR]

Methods to incorporate deuterium and tritium atoms into organic molecules are valuable for medicinal chemistry. The prevalence of pyridines and diazines in pharmaceuticals means that new ways to label these heterocycles will present opportunities in drug design and facilitate absorption, distribution, metabolism, and excretion (ADME) studies. A broadly applicable protocol is presented wherein pyridines, diazines, and pharmaceuticals are converted into heterocyclic phosphonium salts and then isotopically labeled. The isotopes are incorporated in high yields and, in general, with exclusive regioselectivity. [ABSTRACT FROM AUTHOR]

One of the principal aims of single-molecule electronics is to create practical devices out of individual molecules. Such devices are expected to play a particularly important role as novel sensors thanks to their response to wide ranging external stimuli. Here we show that the conductance of a molecular junction can depend on two independent stimuli simultaneously. Using a scanning tunnelling microscope break-junction technique (STM-BJ), we found that the conductance of 4,4'-vinylenedipyridine (44VDP) molecular junctions with Ni contacts depends on both the electrochemically applied gate voltage and the pH of the environment. Hence, not only can the Ni|44VDP|Ni junction function as a pH-sensitive switch, but the value of the pH at which switching takes place can be tuned electrically. Furthermore, through the simultaneous control of pH and potential the STM-BJ technique delivers unique insight into the acid-base reaction, including the observation of discrete proton transfers to and from a single molecule. [ABSTRACT FROM AUTHOR]

Five distinct α,α′-bis(arylimino)-2,3:5,6-bis(hexamethylene)pyridine-cobalt(II) chloride complexes, [2,3:5,6-{C5H10C(NAr)}2C5HN]CoCl2 (Ar = 2,6-Me2C6H3, Co1; 2,6-Et2C6H3, Co2; 2,6-i-Pr2C6H3, Co3; 2,4,6-Me3C6H2, Co4; 2,6-Et2-4-MeC6H2, Co5), have been synthesized by one-pot template reaction of α,α′-dioxo-2,3:5,6-bis(hexamethylene)pyridine with the corresponding aniline and cobalt(II) chloride in acetic acid. The molecular structures of Co2 and Co3 reveal distorted square pyramidal geometries with two conformationally flexible eight-membered rings, a feature of the ligand manifold. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all five complexes displayed high catalytic activities for ethylene polymerization (up to 3.62 × 106 g PE mol-1 (Co) h-1) generating strictly linear polyethylenes with the activity decreasing in the orders: Co4 > Co5 > Co1 > Co2 > Co3 (MAO) and Co1 > Co4 > Co2 > Co5 > Co3 (MMAO). Moreover, the nature of the aluminoxane cocatalyst employed had a marked effect on the molecular weight and distribution (Mw/Mn) of the polymeric material obtained. For example using MAO, high molecular weight polyethylene (Mw ≈ 105 g mol-1) with a narrow monomodal molecular weight distribution (2.1-3.6) was a characteristic, while using MMAO, the polyethylene was of lower molecular weight (Mw ≈ 104 g mol-1) and exhibited a mono- to bimodal distribution (10.1-23.8) depending on the ratio of MMAO employed, temperature, and run time. [ABSTRACT FROM AUTHOR]

We report here the tridentate, P-stereogenic, C2-symmetric PNP pincer ligand (SP,SP)-2,6-bis((cyclohexyl(methyl)phosphanyl)methyl)pyridine (1a) and its iron(II) complexes [FeBr2(CO)(1a)] (2a), [FeHBr(CO)(1a)] (3a), and [FeH2(CO)(1a)] (4a). In the presence of base, bromocarbonylhydride 3a catalyzes the hydrogenation of acetophenone to (S)-1-phenylethanol with 48% ee. The transition states of the enantiodetermining transfer of hydride from 3a to the carbonyl group of acetophenone were studied by density functional theory (DFT) with a full conformational analysis of the PNP ligand for the three different mechanistic models recently proposed for a related achiral catalyst. The DFT calculations show that the outer-sphere monohydride mechanism originally proposed by Milstein reproduces the experimentally observed sense of induction (S) and enantioselectivity, whereas the dihydride and inner-sphere pathways predict the formation of the R enantiomer. [ABSTRACT FROM AUTHOR]

A well-defined homogeneous silver precatalyst can be utilized for the direct C–H functionalization of a wide range of aromatic nitrogen heterocycles with cyclopropanols under acid-free conditions. This reaction can be conducted on gram-scale and with low catalyst loadings (as low as 1%), which is rare for silver-catalyzed Minisci-type reactions. Moreover, reactivity trends, as well as steric and calculated electronic properties of the heterocycles, strongly suggest that silver–heterocycle complexes formed in situ behave as redox active catalysts and as Lewis acid activators of the heterocycle and that the electronic nature of the heterocyclic substrates tunes the reactivity of the resulting complexes. [ABSTRACT FROM AUTHOR]

One hexanuclear Cu(I) cluster of 4,6-dimethylpyrimidine-2-thiolate efficiently catalyzes the dehydrogenative cross-coupling of secondary and primary alcohols to α-alkylated ketones with high selectivity. This transformation proceeds through a one-pot sequence of dehydrogenation of alcohols, condensation of aldehydes and ketones, hydrogenation of the resulting α,β-unsaturated ketones, and dehydrogenation of the α-alkylated alcohols to generate α-alkylated ketones. This catalytic system also displays high activity for the annulation reaction of secondary alcohols with γ-amino- and 2-aminobenzyl alcohols to yield pyridines and quinolines, respectively. [ABSTRACT FROM AUTHOR]

A new class of water-soluble double complex salts (DCSs), [Pt{bzimpy(TEG)[sub 2]}Cl][Pt{bzimpy(PrSO[sub 3])[sub 2]}- Cl] and its alkylplatinum(II) bzimpy derivatives (bzimpy = 2,6-bis(benzimidazol-2'-yl)pyridine, has been demonstrated to exhibit strong aggregation in water through Pt-Pt and π-π stacking interactions to give a variety of distinctive nanostruc-tures based on the formation of one-dimensional (1D) infinite chains. The self-association process can be systemically controlled by varying the solvent composition and temperature and has been studied by 1H NMR, 2D NOESY NMR, mass spectrometry, electron and confocal fluorescence microscopy, UV-vis absorption, and emission spectroscopy. [ABSTRACT FROM AUTHOR]

N-Heterocyclic phosphenium triflates (NHP-OTf) 1 serve as efficient catalysts for the regio- and chemoselective hydroboration of pyridines under ambient condition with good functional group tolerance. Mechanistic studies indicate that a boronium salt, [(Py)2·Bpin]OTf 4, is generated concomitant with NHP-H 5 via hydride abstraction from HBpin by 1 in the initial reaction step. Hydride reduction of the activated pyridine in [(Py)2·Bpin]OTf 4 by NHP-H 5 affords the 1,4-hydroboration product selectively. Thus, the phosphenium species act as a hydrogen transfer reagent in the catalytic cycle. [ABSTRACT FROM AUTHOR]

An effective pyridine based U-shaped template has been developed to enable a diverse range of meta-C-H functionalizations of phenylacetic acid scaffolds. This new template has extended the reaction scope to cross-coupling with ArBF3K as well as iodination using 1,3-diiodo-5,5-dimethylhydantoin as the iodination reagent. [ABSTRACT FROM AUTHOR]