Coplanar Conformation Research Articles

Neo-N-confused Phlorins and Phlorinone: Rational Synthesis and Tunable Properties.

By the acid-catalyzed [2 + 2] condensation, an unprecedented neo-N-confused phlorin (neo-NCphlorin 1) was successfully synthesized. By treating 1 with N-chlorosuccinimide, the corresponding chloro-substituted neo-NCphlorin (1-Cl) was obtained. The oxidization of 1 with FeCl3 afforded the neo-N-confused phlorinone (neo-NCphlorinone 2), which bears a relatively coplanar conformation, different from the highly distorted ones observed for 1 and 1-Cl. Notably, 2 shows striking long-wavelength absorption beyond 1300 nm upon addition of TBAF.

Improving fiber alignment by increasing the planar conformation of isoindigo-based conjugated polymers

The weak interaction of the side-chain and the coplanar conformation in IID–TT were beneficial for the molecules forming parallel fibers.

Molecular Coplanarity and Self-Assembly Promoted by Intramolecular Hydrogen Bonds.

Active conformational control is realized in a conjugated system using intramolecular hydrogen bonds to achieve tailored molecular, supramolecular, and solid-state properties. The hydrogen bonding functionalities are fused to the backbone and precisely preorganized to enforce a fully coplanar conformation of the π-system, leading to short π-π stacking distances, controllable molecular self-assembly, and solid-state growth of one-dimensional nano-/microfibers. This investigation demonstrates the efficiency and significance of an intramolecular noncovalent approach in promoting conformational control and self-assembly of organic molecules.

Switching function of the diphenylacetylene molecule between carbon nanotubes & carbon chain: A DFT study

Using first-principles density functional theory and nonequilibrium Green’s function formalism, we investigate theoretically how the twist of torsional angle effect on the electronic transport properties of the diphenylacetylene (DPA) molecule bridged between a (5,5) capped carbon nanotubes (CCNTs) and linear carbon atomic chains. The tunneling current through the (5,5) capped CNT-DPA-linear carbon atomic chain system was found larger current when the torsional angle is 0° (coplanar conformation). BY increasing the torsional angle equal to 90° (perpendicular conformation), between two benzene rings, the current is strongly suppressed. These results suggest that the (5,5) capped CNT-DPA-linear carbon atomic chain system is a potential candidate for molecular switches. The physical origin of the switching behavior of the (5,5) capped CNT-DPA-linear carbon atomic chain system is systematically studied by analyses of transmission spectrum, energy gaps, the spatial distribution of frontier molecular orbital and current–voltage characteristics of the systems.

Iron-Catalyzed E-Selective Dehydrogenative Borylation of Vinylarenes with Pinacolborane

We report the dehydrogenative borylation of vinylarenes with pinacolborane (HBpin) catalyzed by an iron(0) complex “(PMe3)4Fe”. A variety of monosubstituted and disubstituted vinylarenes underwent this iron-catalyzed transformation, affording E-vinyl boronate esters (VBEs) selectively in high yields. In addition, we coupled this iron-catalyzed dehydrogenative borylation with further transformations of the resulting vinyl boronate esters and developed various one-pot procedures for the functionalization of the vinylic C–H bonds in vinylarenes. Mechanistic studies reveal that this Fe-catalyzed reaction proceeds through syn-insertion of vinylarenes into a Fe-boryl species followed by β-hydrogen elimination from a syn coplanar conformation of the borylalkyl iron intermediate.

Meso-Nitro- and meso-Aminosubporphyrinatoboron(III)s and meso-to-meso Azosubporphyrinatoboron(III)s.

meso-Nitrosubporphyrinatoboron(III) was synthesized by nitration of meso-free subporphyrin with AgNO2 /I2 . The subsequent reduction with a combination of NaBH4 and Pd/C gave meso-aminosubporphyrinatoboron(III). meso-Nitro- and meso-amino-groups significantly influenced the electronic properties of subporphyrin, which has been confirmed by NMR and UV/Vis spectra, electrochemical analysis, and DFT calculations. Oxidation of meso-aminosubporphyrinatoboron(III)s with PbO2 cleanly gave meso-to-meso azosubporphyrinatoboron(III)s that exhibited almost coplanar conformations and large electronic interaction through the azo-bridge.

Niclosamide is a Negative Allosteric Modulator of Group I Metabotropic Glutamate Receptors: Implications for Neuropathic Pain.

Novel therapeutics are greatly needed that target specific pathological receptors and pathways involved in Neuropathic Pain (NP). Extending our previous work published in this Journal on Group I metabotropic glutamate receptor (mGluR) modulators, we now investigate the therapeutic potential of niclosamide in modulating aberrant glutamate transmission in NP. Calcium mobilization assays and cross-receptor selectivity experiments are conducted to characterize the pharmacological activity of niclosamide. A focused series of niclosamide analogues is then prepared to elucidate key structural determinants that emerged from computational molecular modeling analysis on drug-receptor interactions. Finally, niclosamide and a carbamate derivative are studied to assess their efficacy in an NP-evoked mechanical hyperalgesia model in rats. Niclosamide is a low-nanomolar allosteric antagonist of Group I mGluRs with high selectivity for Group I over homologous Group III mGluRs. The phenolic hydroxyl group of niclosamide forms a crucial hydrogen bond with mGluR1/5. Its bioactive coplanar conformation is further stabilized by the nitro substituent on the B ring and an intramolecular bond. Mechanical hyperalgesia in NP rats is reversed by niclosamide through three different dosing routes. To our knowledge, this is the first report of the salicylanilide class of compounds as potential treatments for NP.

Hexa-peri-hexabenzocoronene and diketopyrrolopyrrole based D-A conjugated copolymers for organic field effect transistor and polymer solar cells

Hexa-peri-hexabenzocoronene (HBC) is a disc-shaped conjugated molecule with strong π-π stacking property, high intrinsic charge mobility and good self-assembly property. But for a long time, the organic photovoltaic (OPV) solar cells based on HBC small organic molecules demonstrated low power conversion efficiencies (PCEs). In this study, a series of polymers named as PHBCDPPC20, PHBCDPPC8, PHBCDPPF and PHBCDPPDT were designed and synthesized through copolymerization of HBC with bulky mesityl substituents and strong electron-withdrawing diketopyrrolopyrrole (DPP) with different alkyl side chains and various π-bridges. Introduction of DPP unit into the HBC derivatives broadened the absorption spectra and lowered the band gaps. Bulky mesityl substituents attached to periphery of HBC prevented polymers from self-aggregating into too large domain size in the blend films of photovoltaic devices. The different π-bridges have significant effect on the structure conformation of the polymers. The polymer PHBCDPPDT with bithiophene π-bridges demonstrated the broadest absorption for its extensive π-conjugation and more coplanar conformation compared with the thiophene π-bridge one. PHBCDPPC20, PHBCDPPC8, PHBCDPPF and PHBCDPPDT gave field-effect hole mobilities of 1.35 × 10−3, 2.31 × 10−4, 2.79 × 10−4 and 8.60 × 10−3 cm2 V−1 s−1, respectively. The solar cells based on these polymers displayed PCEs of 2.12%, 2.85%, 1.89% and 2.74%. To our knowledge, 2.85% is the highest PCE for the HBC-based photovoltaic materials till now.

Simple Bipolar Host Materials for High-Efficiency Blue, Green, and White Phosphorescence OLEDs.

3-(1H-Pyrazol-1-yl)pyridine is used as electron-transporting unit to construct bipolar host materials o-CzPyPz, m-CzPyPz, and p-CzPyPz for application in phosphorescent organic light-emitting diodes (PhOLEDs). By varying the ortho-, meta-, or para-linking mode between the n-type 3-(1H-pyrazol-1-yl)pyridine and the p-type carbazole on phenylene bridge, the optoelectronic parameters are tuned to large extent. The highly twisted o-CzPyPz has high triplet energy of 2.95 eV, while the isomer p-CzPyPz with more coplanar conformation has smaller triplet energy of 2.67 eV. The m-CzPyPz-hosted blue PhOLED exhibits a peak current efficiency of 49.1 cd A(-1) (corresponding to an external quantum efficiency of 24.5%) and low-efficiency roll-off, while the p-CzPyPz-hosted green PhOLEDs turns on at 2.8 V and exhibits high efficiencies of 91.8 cd A(-1) (96.1 lm W(-1) and 27.3%). Furthermore, two-emitting-layer white OLEDs are fabricated with m-CzPyPz or p-CzPyPz as common hosts for both blue and orange phosphors, which realize high efficiencies of 57.8 cd A(-1) (45.4 lm W(-1) and 23.6%) and 60.7 cd A(-1) (38.1 lm W(-1) and 23.1%). The optimization of host structure for good matching of host and dopant and finally for the ideal performance is discussed.

Molecular conformation and UV–visible absorption spectrum of emeraldine salt polyaniline as a hydrazine sensor

ABSTRACTA study on the molecular conformation and electronic properties of different degrees of polymerisation of emeraldine salt polyaniline (ES PANI) has been explored using ab-initio calculations in order to have an insight into the optoelectronic properties, such as band gap, molecular orbital distribution, and UV–visible absorption spectrum conductivity mechanism. The optimization was done with DFT and TD-DFT for calculated UV-visible spectrum using B3LYP/6–31 g(d,p) basis set. Systematic conformational search has been done to find the suitable monomer and dimer model of ES PANI. The monomer model tends to keep a coplanar conformation for π-π interaction where a dimer structure ES PANI has the twist angle between two central rings about 63 degrees. The UV-vis absorption spectrum has one peak in the visible range. A significant red-shift with more degree of polymerisation has the better prediction of experimental UV-visible spectrum.

Synthesis of chlorophyll-a derivatives methylated in the 3-vinyl group and their intrinsic site energy

Wittig reaction of methyl pyropheophorbide-d possessing the 3-formyl group gave readily methyl pyropheophorbides-a bearing a variety of 3-alkenyl groups as semi-synthetic models of chlorophyll-a. The 3-substituents rotated around the C3–C31 bond from the coplanar conformation with the chlorin π-system, moving the redmost visible absorption maxima to a shorter wavelength. The model experiments showed that natural chlorophyll-a carrying the 3-vinyl group would take a similar rotamer to control its intrinsic site energy.

Low Band Gap Coplanar Conjugated Molecules Featuring Dynamic Intramolecular Lewis Acid-Base Coordination.

Ladder-type conjugated molecules with a low band gap and low LUMO level were synthesized through an N-directed borylation reaction of pyrazine-derived donor-acceptor-donor precursors. The intramolecular boron-nitrogen coordination bonds played a key role in rendering the rigid and coplanar conformation of these molecules and their corresponding electronic structures. Experimental investigation and theoretical simulation revealed the dynamic nature of such coordination, which allowed for active manipulation of the optical properties of these molecules by using competing Lewis basic solvents.

Hydrogen Bonding in Bis(6-amino-1,3-dimethyluracil-5-yl)-methane Derivatives: Dynamic NMR and DFT Evaluation.

Three bis(6-amino-1,3-dimethyluracil-5-yl)-methane derivatives were studied experimentally by variable-temperature (1)H NMR in polar aprotic solutions (CD2Cl2, C5D5N, C2D2Cl4) and computationally by DFT. The unusual for diarylmethanes coplanar conformation of dimethyluracil rings of each molecule is held by a pair of unequal intramolecular N-H···O hydrogen bonds. We show the presence of two dynamic processes involving breakage/formation of these bonds. First, it is two independent NH2 group rotations, each coupled to nitrogen inversion. Second, it is uracil ring rotations (ring flips). The thermodynamic parameters (ΔH(‡), ΔS(‡), and ΔG(‡)) of both processes were estimated by the full line shape analysis of NMR signals and also by DFT calculations. We demonstrate that, though the ring flips exchange pairs of NH protons, the two processes are not coupled: during the ring flip NH2 groups do not rotate, and during the NH2 rotation the rings do not necessarily rotate. Unlike in many other diarylmethanes, the ring flips in the studied compounds are happening stepwise; i.e., the configuration when both rings are "in flight" at the same time is energetically unfavorable (small degree of "cog wheel effect"). The signs of the ΔS(‡) values indicate that the molecular flexibility increases during the NH2 rotations, but decreases during the ring flips.

Tricyclic Quinazoline Alkaloids Conjugated to Ferrocene: Synthesis, Structure, and Redox Behavior of Ferrocenylmethylene‐Substituted 7H‐Deoxyvasicinones

AbstractThe first organometallic derivatives of tricyclic quinazoline derivatives are prepared by condensation of the active C‐3 methylene group of 7H‐deoxyvasicinones with ferrocenecarbaldehyde. By following this route the conjugated parent alkaloid and derivatives with nitro, amino, as well as some alkanoylamino groups at C‐7 were attached at the ferrocene moiety, thereby significantly extending the π system. In addition, the parent compound was subjected to the reaction by treatment with ferrocene‐1,1′‐dicarbaldehyde, giving rise to the double condensation product, which is only the second case of a 1,1′‐disubstituted ferrocene derivative with two alkaloid substituents. A number of the compounds obtained were subjected to X‐ray crystallographic analyses. In all cases, the substituents adopt a coplanar conformation with the ferrocene cyclopentadienyl ligands. The influence of the substituents at C‐7 through the extended conjugated π system on the iron atom is reflected by results of cyclic voltammetric measurements as well as by DFT calculations.

Neutral bis(benzimidazole) Λ-shaped anion receptor

A neutral receptor, integrating a series of –N(H) and –C(H) donor groups organized in a Λ-shape motif was designed and prepared. This compound can form stable 1:1 complexes in acetonitrile solution with halides (F−, Cl−, Br−, and I−) and nitrate (NO3−) anions. The main binding site in the receptor is on the cleft and recognition occurs through a series of co-operative hydrogen bonding interactions including intramolecular hydrogen bonds which stabilizes the co-planar conformation of the host–guest complex. For halides, complex stability is determined by anion basicity, but for anions having other geometries, size and shape complementarity play a major role.

ChemInform Abstract: meso‐Free Corroles: Syntheses, Structures, Properties, and Chemical Reactivities.

5,10-Bis(pentafluorophenyl)corrole (5) and 5,15-bis(pentafluorophenyl)corrole (9) have been synthesized as meso-free corroles by rational synthetic routes. Both the structures of these corroles have been unambiguously revealed by X-ray diffraction analysis and their optical and electrochemical properties have been studied. Chlorination and oxidative dimerization of 5 and 9 have been explored, which revealed a marked different reactivity of the free meso-positions in 5 and 9. 10-Chlorinated corrole 11 was effectively prepared by the reaction of 9 with Palau‘chlor in the presence of 1 % pyridine whereas 5-chlorinated corrole 12 was obtained in a trace amount from similar chlorination of 5. 5,5′-Linked corrole dimer 13 was produced by reaction of 5 with AgNO2 in a good yield, whereas 10,10′-linked corrole dimer 14 was formed in a moderate yield by the reaction of 9 with [bis(trifluoroacetoxy)iodo]benzene. Observed large electronic interaction between the two corroles in 13 as compared with that in 14 has been ascribed mainly to conformational flexibility of the former, which allows more coplanar conformation.

Increasing the Stability of DNA:RNA Duplexes by Introducing Stacking Phenyl-Substituted Pyrazole, Furan, and Triazole Moieties in the Major Groove

Consecutive incorporations of our previously published thymidine analogue, 5-(1-phenyl-1H-1,2,3-triazol-4-yl)-2'-deoxyuridine monomer W in oligonucleotides, has demonstrated significant duplex-stabilizing properties due to its efficient staking properties in the major groove of DNA:RNA duplexes. The corresponding 2'-deoxycytidine analogue is not as well-accommodated in duplexes, however, due to its clear preference for the ring-flipped coplanar conformation. In our present work, we have used ab initio calculations to design two new building blocks, 5-(5-phenylfuran-2-yl)-2'-deoxycytidine monomer Y and 5-(1-phenyl-1H-pyrazol-3-yl)-2'-deoxycytidine monomer Z, that emulate the conformation of W. These monomers were synthesized by Suzuki-Miyaura couplings, and the pyrazole moiety was obtained in a cycloaddition from N-phenylsydnone. We show that the novel analogues Y and Z engage in efficient stacking either with themselves or with W due to a better overlap of the aromatic moieties. Importantly, we demonstrate that this translates into very thermally stable DNA:RNA duplexes, thus making Y and especially Z good candidates for improving the binding affinities of oligonucleotide-based therapeutics. Since we now have both efficiently stacking T and C analogues in hand, any purine rich stretch can be effectively targeted using these simple analogues. Notably, we show that the introduction of the aromatic rings in the major groove does not significantly change the helical geometry.

Investigation of photoreaction for 2-nitrobenzofuran and its 3-methyl derivative

Abstract Aromatic nitro compounds undergo various photoreactions such as photosubstitution, photoredox reactions, photodissociation, and photoinduced nitro–nitrite rearrangements. The reaction mechanisms for these photoreactions, especially nitro–nitrite rearrangement reactions have never been completely understood. It was originally assumed that the potential cause for a nitro–nitrite rearrangement originates from the twisted dihedral angle between the plane of the nitro group and the plane of the aromatic ring [O.L. Chapman et al., J. Am. Chem. Soc. 88 (1966) 5550–5554]. Although the majority of aromatic nitro compounds have coplanar conformation and undergo nitro–nitrite rearrangement, no studies clearly substantiate this theory. This study reports on the photochemical reactions of 2-nitrobenzofuran and the effects of 3-methyl substituent on the compound. The results show that a nitro–nitrite rearrangement selectively occurs in deaerated acetonitrile solution for the photoreactions of 2-nitrobenzofuran. Moreover, nitro–nitrite rearrangement might occur in the photoreaction of 3-methyl-2-nitrobenzofuran. The quantum yield of degradation for 3-methyl-2-nitrobenzofuran was higher than that for 2-nitrobenzofuran, indicating that the methyl substituent at the 3-position changes the photoreactivity of 2-nitrobenzofuran.

Addressing phototoxicity observed in a novel series of biaryl derivatives: Discovery of potent, selective and orally active phosphodiesterase 10A inhibitor ASP9436

We synthesized several biaryl derivatives as PDE10A inhibitors to prevent phototoxicity of 2-[4-({[1-methyl-4-(pyridin-4-yl)-1H-pyrazol-3-yl]oxy}methyl)phenyl]quinoline (1) and found that the energy difference between the energy-minimized conformation and the coplanar conformation of the biaryl moiety helped facilitate prediction of the phototoxic potential of biaryl compounds. Replacement of the quinoline ring of 1 with N-methyl benzimidazole increased this energy difference and prevented phototoxicity in the 3T3 NRU test. Further optimization identified 1-methyl-5-(1-methyl-3-{[4-(1-methyl-1H-benzimidazol-4-yl)phenoxy]methyl}-1H-pyrazol-4-yl)pyridin-2(1H)-one (38b). Compound 38b exhibited good selectivity against other PDEs, and oral administration of 38b improved visual-recognition memory deficit in mice at doses of 0.001 and 0.003mg/kg in the novel object recognition test. ASP9436 (sesquiphosphate of 38b) may therefore be used for the treatment of schizophrenia with a low risk of phototoxicity.

Meso-Free Corroles: Syntheses, Structures, Properties, and Chemical Reactivities.

5,10-Bis(pentafluorophenyl)corrole (5) and 5,15-bis(pentafluorophenyl)corrole (9) have been synthesized as meso-free corroles by rational synthetic routes. Both the structures of these corroles have been unambiguously revealed by X-ray diffraction analysis and their optical and electrochemical properties have been studied. Chlorination and oxidative dimerization of 5 and 9 have been explored, which revealed a marked different reactivity of the free meso-positions in 5 and 9. 10-Chlorinated corrole 11 was effectively prepared by the reaction of 9 with Palau'chlor in the presence of 1 % pyridine whereas 5-chlorinated corrole 12 was obtained in a trace amount from similar chlorination of 5. 5,5'-Linked corrole dimer 13 was produced by reaction of 5 with AgNO2 in a good yield, whereas 10,10'-linked corrole dimer 14 was formed in a moderate yield by the reaction of 9 with [bis(trifluoroacetoxy)iodo]benzene. Observed large electronic interaction between the two corroles in 13 as compared with that in 14 has been ascribed mainly to conformational flexibility of the former, which allows more coplanar conformation.