Aromatic Subunits Research Articles

Glycerol as Reaction Medium for Sonogashira Couplings: A Green Approach for the Synthesis of New Triarylamine-Based Materials with Potential Application in Optoelectronics.

This study focuses on the design, eco-friendly synthesis, and characterization of several novel three-legged triphenylamine derivatives. By performing Sonogashira couplings of functionalized aryl iodides with tris(4-ethynylphenyl)amine in glycerol, a readily available bio-derived solvent, we achieved the synthesis of target products in short times and high yields, up to 94 %, with consistently lower E-factors and reduced costs compared to standard conditions using toluene as the reaction medium. The target molecules possess a D-(π-A)₃ or D-(π-D)₃ structure, where an electron-donating core connects to three electron-donating (D) or electron-accepting (A) peripheral aromatic subunits through an acetylene spacer. Their main optical and electronic properties have been determined experimentally and by DFT simulations and suggest a possible implementation in energy conversion technologies such as luminescent solar concentrators (LSCs) and perovskite solar cells (PSCs).

Catabolism of β-5 linked aromatics by Novosphingobium aromaticivorans.

In the transition to a circular bioeconomy, the plant polymer lignin holds promise as a renewable source of industrially important aromatic chemicals. However, since lignin contains aromatic subunits joined by various chemical linkages, producing single chemical products from this polymer can be challenging. One strategy to overcome this challenge is using microbes to funnel a mixture of lignin-derived aromatics into target chemical products. This approach requires strategies to cleave the major inter-unit linkages of lignin to release monomers for funneling into valuable products. In this study, we report newly discovered aspects of a pathway by which the Novosphingobium aromaticivorans DSM12444 catabolizes aromatics joined by the second most common inter-unit linkage in lignin, the β-5 linkage. This work advances our knowledge of aromatic catabolic pathways, laying the groundwork for future metabolic engineering of this and other microbes for optimized conversion of lignin into products.

A theoretical study on application of BN/CC isosterism to modify topology of coronene aromaticity and HOMO–LUMO energy gaps

A gradual replacement of peripheral CC bonds of coronene with BN ones can isolate aromatic carbocyclic subunits that dominate frontier orbital shapes and energies, thus enabling their modulation.

Coordination Chemistry of Open-Ring Hemiporphyrazines

Hemiporphyrazines, phthalocyanine analogues consisting of two isoindoline subunits and two pyridine or other aromatic subunits, have attracted considerable interest not only from the viewpoint of their fundamental properties but also in materials science. Since the first report on hemiporphyrazine about 70 years ago, various types of hemiporphyrazines have been synthesized to date. However, when comparing the rich chemistry of porphyrins and other porphyrinoids, the structural diversity of hemiporphyrazines and azaporphyrinoids is still limited. In particular, much less attention has been paid for acyclic hemiporphyrazines, which is in sharp contrast to many reports on acyclic porphyrinoids. Herein we report synthesis of open-ring hemiporphyrazines and their coordination chemistry. Helical metal complexes (1M ) and dinuclear metal complexes ((2M)2 ) were obtained depending on the terminal subunit of the open-hemiporphyrazine ligands. The effects of the central metal ion on molecular and electronic structures will be discussed in the presentation. Figure 1

P-Azaquinodimethane: A Versatile Quinoidal Moiety for Functional Materials Discovery.

ConspectusThe past 50 years of discovery in organic electronics have been driven in large part by the donor-acceptor design principle, wherein electron-rich and electron-poor units are assembled in conjugation with each other to produce small band gap materials. While the utility of this design strategy is undoubtable, it has been largely exhausted as a frontier of new avenues to produce and tune novel functional materials to meet the needs of the ever-increasing world of organic electronics applications. Its sister strategy of joining quinoidal and aromatic groups in conjugation has, by comparison, received much less attention, to a great extent due to the categorically poor stability of quinoidal conjugated motifs.In 2017 though, the p-azaquinodimethane (AQM) motif was first unveiled, which showed a remarkable level of stability despite being a close structural analogue to p-quinodimethane, a notably reactive compound. In contrast, dialkoxy AQM small molecules and polymers are stable even under harsh conditions and could thus be incorporated into conjugated polymers. When polymerized with aromatic subunits, these AQM-based polymers show notably reduced band gaps that follow reversed structure-property trends to some of their donor-acceptor polymer counterparts and yield organic field-effect transistor (OFET) hole mobilities above 5 cm2 V-1 s-1. Additionally, in an ongoing study, these AQM-based compounds are also showing promise as singlet fission (SF) active materials due to their mild diradicaloid character.An expanded world of AQMs was accessed through their ditriflate derivatives, which were first used to produce ionic AQMs (iAQMs) sporting two directly attached cationic groups that significantly affect the AQM motif's electronics, producing strongly electron-withdrawing quinoidal building blocks. Conjugated polyelectrolytes (CPEs) created with these iAQM building blocks exhibit optical band gaps stretching into the near-infrared I (NIR-I) region and showed exemplary behavior as photothermal therapy agents.In contrast to these stable AQM examples, the synthetic exploration of AQMs also produced examples of more typical diradicaloid reactivity but in forms that were controllable and produced intriguing and high-value products. With certain substitution patterns, AQMs were found to dimerize to form highly substituted [2.2]paracyclophanes in distinctly more appreciable yields than typical cyclophane formation reactions. Certain AQM ditriflates, when crystallized, undergo light-induced topochemical polymerization to form ultrahigh molecular weight (>106 Da) polymers that showed excellent performances as dielectric energy storage materials. These same AQM ditriflates could be used to produce the strongly electron-donating redox-active pentacyclic structure: pyrazino[2,3-b:5,6-b']diindolizine (PDIz). The PDIz motif allowed for the synthesis of exceedingly small band gap (0.7 eV) polymers with absorbances reaching all the way into the NIR-II region that were also found to produce strong photothermal effects. Both as stable quinoidal building blocks and through their controllable diradicaloid reactivity, AQMs have already proven to be versatile and effective as functional organic electronics materials.

Comparison of Antiaromatic Properties in a Series of Structurally Isomeric Naphthothiophene-fused s-Indacenes.

Fusion of aromatic subunits to stabilize an antiaromatic core allows the isolation and study of otherwise unstable paratropic systems. A complete study of a series of six naphthothiophene-fused s-indacene isomers is herein described. Additionally, the structural modifications resulted in increased π-π overlap in the solid state, which was further explored through changing the sterically blocking mesityl group to (triisopropylsilyl)ethynyl in three derivatives. The computed antiaromaticity of the six isomers is compared to the observed physical properties, such as NMR chemical shift, UV-vis, and CV data. We find that the calculations predict the most antiaromatic isomer and give a general estimation of the relative degree of paratropicity for the remaining isomers, when compared to the experimental results.

Tuning the Effect of Chitosan on the Electrochemical Responsiveness of Lignin Nanoparticles.

Chitosan and lignin mixed nanoparticles were prepared by layer-by-layer and nanoprecipitation methodologies as responsive platforms for sustainable biosensors. The novel nanoparticles showed effective chemophysical and electrochemical properties dependent on the preparation methodology, molecular weight of chitosan, and type of lignin. HOMO-LUMO energy gap calculations suggested the presence of structure-activity relationships between the electrochemical responsiveness and the order and orientation of lignin aromatic subunits and chitosan chains in the nanodevices.

Unraveling the Chemistry of High Valent Arylcopper Compounds and Their Roles in Copper-Catalyzed Arene C-H Bond Transformations Using Synthetic Macrocycles.

Recent decades have witnessed a resurgence of the study of copper-catalyzed organic reactions. As the surrogate of noble metal catalysts, copper salts have been shown to exhibit remarkable versatility in activating various C-H bonds enabling the construction of diverse carbon-carbon and carbon-heteroatom bonds. Advantageously, copper salts are also naturally abundant, inexpensive, and less toxic in comparison to precious metals. Despite significant developments in synthesis, the mechanism of copper catalysis remains elusive. Hypothetical pathways such as the two-electron Cu(III)/Cu(I) and Cu(II)/Cu(0) catalytic cycles and the one-electron Cu(II)/Cu(I) catalytic cycle have been invoked to diagram C-H bond transformations because of the formidable challenges to isolate and characterize transient high valent organocopper intermediates. In fact, organocopper chemistry has been dominated for a long time by the acknowledged nucleophilic organocopper(I) compounds. Since the beginning of the new millennium, we have been systematically studying the supramolecular chemistry of heteracalix[n]aromatics. Owing to the ease of their synthesis and selective functionalizations, self-tunable conformation and cavity structures resulting from the interplay of heteroatoms with aromatic subunits, and outstanding properties in molecular recognition and self-assembly, heteracalix[n]aromatics have become a class of privileged synthetic macrocyclic hosts. Our journey to the chemistry of high valent organocopper compounds started with a serendipitous discovery of the facile formation of a stable organocopper compound, which contains astonishingly a Ph-Cu(III) σ-bond under very mild aerobic conditions. When we examined routinely the effect of the macrocyclic structures on noncovalent complexation properties, titration of tetraazacalix[1]arene[3]pyridine with Cu(ClO4)2·6H2O resulted in the precipitation of dark-purple crystals of phenylcopper(III) diperchlorate. Our curiosity about the transformation of an arene C-H bond into an Ar-Cu(III) bond prompted us to conduct an in-depth investigation of the reaction of macrocyclic arenes with copper(II) salts, leading to the isolation of arylcopper(II) compounds which are unprecedented and the missing link in organocopper chemistry. With structurally well-defined organometallics in hand, we have explored extensively the reactivities of both arylcopper(II) and arylcopper(III) compounds, demonstrating their versatility and uniqueness in chemical synthesis. Novel and fascinating arene C-H transformations under copper catalysis have been developed. Using acquired high valent arylcopper compounds as molecular probes, and employing the functionalizations of tetraazacalix[1]arene[3]pyridines as model reactions, we have revealed the diverse mechanisms of copper-promoted arene C-H bond reactions. Elusive reaction pathways of some copper-catalyzed C-X bond activations have also been unraveled. In the meantime, we have also witnessed pleasingly the rapid development of field with the advent of new high valent organocopper compounds. Without any doubt, studies of the synthesis, reactivity, and catalysis of high valent organocopper compounds have been reshaping the field of organocopper chemistry. This Account summarizes our endeavors to explore the chemistry of structurally well-defined arylcopper(II) and arylcopper(III) compounds and the mechanisms of copper-catalyzed arene C-H and C-X bond transformations. We hope this Account will inspire chemists to study thoroughly the fundamentals and the cutting-edge catalysis of high valent organocopper compounds advancing and redefining the discipline of organocopper chemistry.

Supramolecular Organic Frameworks: Exploring Water-Soluble, Regular Nanopores for Biomedical Applications.

In past decades, regular porous architectures have received a great amount of attention because of their versatile functions and applications derived from their efficient adsorption of various guests. However, most reported porous architectures exist only in the solid state. Therefore, their applications as biomaterials may face several challenges, such as phase separation, slow degradation, and long-term accumulation in the body. This Account summarizes our efforts with respect to the development and biomedical applications of water-soluble 3D diamondoid supramolecular organic frameworks (dSOFs), a family of supramolecular polymers that possess intrinsic regular nanoscale porosity.dSOFs have been constructed from tetratopic components and cucurbit[8]uril (CB[8]) through hydrophobically driven encapsulation by CB[8] for intermolecular dimers formed by peripheral aromatic subunits of the tetratopic components in water. All dSOFs exhibit porosity regularity or periodicity in aqueous solution, which is confirmed by solution-phase synchrotron SAXS and XRD experiments. Dynamic light scattering (DLS) reveals that their sizes range from 50 to 150 nm, depending on the concentrations of the components. As nonequilibrium supramolecular architectures, dSOFs can maintain their nanoscale sizes at micromolar concentrations for dozens of hours. Their diamondoid pores have aperture sizes ranging from 2.1 to 3.6 nm, whereas their water solubility and porosity regularity allow them to rapidly include discrete guests driven by ion-pair electrostatic attraction, hydrophobicity, or a combination of the two interactions. The guests may be small molecule or large macromolecular drugs, photodynamic agents (PDAs), or DNA.The rapid inclusion of bioactive guests into dSOFs has led to two important biofunctions. The first is to function as antidotes through including residual drugs. For heparins, the inclusion results in full neutralization of their anticoagulant activity. For clinically used porphyrin PDAs, the inclusion can alleviate their long-term posttreatment phototoxicity but does not reduce their photodynamic efficacy. The second is to function as in situ loading carriers for the intracellular delivery of antitumor drugs or DNA. Their nanoscale sizes bring out their ability to overcome the multidrug resistance of tumor cells, which leads to a remarkable enhancement of the bioactivity of the included drugs. By conjugating aldoxorubicin to tetrahedral components, albumin-mimicking prodrugs have also been constructed, which conspicuously improves the efficacy of aldoxorubicin toward multi-drug-resistant tumors through the delivery of the frameworks. As new supramolecular drugs and carriers, dSOFs are generally biocompatible. Thus, further efforts might lead to medical benefits in the future.

Facile Preparation of a Thienoisoindigo-Based Nanoscale Covalent Organic Framework with Robust Photothermal Activity for Cancer Therapy.

The covalent organic frameworks (COFs) so far are usually built with small aromatic subunits, which makes their absorption spectra mainly located in the high-energy part of the visible region. In this work, we have developed a COF with a low band gap by integrating electron-deficient thienoisoindigo and electron-rich triphenylamine. The intramolecular charge-transfer effect combining the extended length of the π-conjugated backbone of COF endow it with broad absorption even to the second near-infrared region. After optimizing the solvent, a uniform size and colloidal stable COF is obtained. Benefiting from the coplanar structure of the monomer, this COF achieves a considerable photothermal conversion efficiency (PCE) of 48.2%. With these advantages, it displays convincing cancer cell killing effect upon laser irradiation in vitro or in vivo. This work provides a simple and practical method to acquire promising a COF-based phototherapy reagent that is applied in biomedicine field.

Revival of Hückel Aromatic (Poly)benzenoid Subunits in Triplet State Polycyclic Aromatic Hydrocarbons by Silicon Substitution.

By employing density functional theory (DFT) calculations we show that mono- and disilicon substitution in polycyclic aromatic hydrocarbons, having two to four benzene units, quenches their triplet state antiaromaticity by creating Hückel aromatic (poly)benzenoid subunit(s) and weakly antiaromatic, or almost nonaromatic silacycle. Therefore, such systems are predicted to be globally aromatic in both the ground state and the first excited triplet state. Putting the silicon atom(s) into various positions of a hydrocarbon provides an opportunity to tune the singlet-triplet energy gaps. They depend on the global aromaticity degree which, in turn, depends on the type of aromatic carbocyclic subunit(s) and the extent of their aromaticity. On the basis of the set of studied compounds, some preliminary rules on how to regulate the extent of global, semiglobal and local aromaticity are proposed. The results of this work extend the importance of Hückel aromaticity concept to excited triplet states which are usually characterized by the Baird type of (anti)aromaticity.

Geometries, molecular Rayleigh scattering, Raman and infrared frequencies of polycyclic aromatic hydrocarbons and subunits of graphite studied by DFT methods

A computational investigation of geometric parameters, infrared (IR) and Raman frequencies as well as molecular Rayleigh scattering of polycyclic aromatic hydrocarbons (PAHs), used as models for subunits of larger graphitic materials.

Fused BODIPY: Synthesis of diketobenzofuran derivatives towards DiBenzoFuranBODIPYs

Two series of diketobenzofurans (5-acetylbenzofurans substituted by an aroyl group in 4 or 6 positions) have been prepared. The synthetic approach developed here makes it possible to vary the nature of the aromatic subunits (ethylthiophene, anisol, N,N-dimethylaniline) and substituents (butyl, 2-methoxyethoxyethyl, N,N-dibutylaminophenyl) on the furan fractions. The self-condensation of these diketones followed by boron complexation allows us to obtain dibenzofuranBODIPYs. The synthesis strategy used is the same as for the dibenzoBODIPYs. Their linear or banana architectures are due to the structures of the precursor diketones and the spectral properties of the BODIPYs are also modulated by the nature of the substituents. Their optical properties have shown a high quantum efficiency associated with a notorious hyperchromic shift leading to fluorophore with improved brightness in the near infrared region.

Extended porphyrinoid chromophores: heteroporphyrins fused to phenanthrene and acenaphthylene

Fusion of aromatic subunits onto porphyrin chromophores produces variable results and in some cases only minor bathochromic shifts are observed. In order to extend these observations, a series of oxa-, thia- and selenaporphyrins with fused acenaphthylene or phenanthrene units have been synthesized. Phenanthro[5,6-b]porphyrins were previously prepared via conventional ‘2 + 2’ MacDonald condensations, but a more versatile ‘3 + 1’ synthesis is now reported. Phenanthrotripyrranes reacted with a pyrrole dialdehyde in the presence of trifluoroacetic acid, followed by an oxidation step, to give phenanthroporphyrins. However, this chemistry initially gave products that were contaminated with isomeric impurities. Fortunately, good yields of isomerically pure phenanthroporphyrins were obtained when the reactions were carried out under relatively concentrated conditions, and a diphenanthroporphyrin was also obtained using this strategy. An alternative ‘3 + 1’ synthesis was performed where a phenanthropyrrole dialdehyde was condensed with a tripyrrane and this also afforded a phenanthroporphyrin in good yields. Furan, thiophene and selenophene dialdehydes similarly reacted with phenanthro- and acenaphthotripyrranes to give a series of heteroporphyrins with fused phenanthrene and acenaphthylene rings. All of these porphyrinoids retained highly diatropic characteristics. As is the case for tetrapyrrolic porphyrins, the presence of a fused acenaphthylene unit leads to highly modified UV–vis spectra with multiple Soret bands and relatively strong Q bands above 650 nm. However, the longest wavelength absorptions for the acenaphthylene series were only red shifted by 12–15 nm compared to the phenanthrene-fused heteroporphyrin series, which is a somewhat reduced effect compared to previously reported phenanthroporphyrins and acenaphthoporphyrins. Nevertheless, the combined effects of core modification and acenaphthylene ring fusion affords potentially valuable strongly red shifted absorption bands between 677 and 684 nm.

Chemically Modified Lignin: Correlation between Structure and Biodegradability

Lignin is the most abundant heteropolymer based on aromatic subunits in nature. Large quantities of lignin are annually produced from pulping processes and biorefinery industries. Its unclearly defined structure and difficult biodegradation mainly limit its utilization. This work focused on the effect of hydroxylation of lignin on its microbial degradation. Butyloxy carbonyl-modified lignin, and hydroxylated-lignin were synthesized with di-tert-butyl dicarbonate and hydrogen peroxide, respectively, using lignin as raw material. The degradation of the modifiedlignins both by P. chrysosporium and B. subtilis were analyzed using UV-vis spectroscopy. Results revealed that the lignin degradation velocity raises with the increase hydroxylation level of lignin. Moreover, FTIR and 1H NMR analysis of the biodegradation products of lignin further indicated that higher content of hydroxyl groups in lignin facilitated the demethylation combined with the aromatic ring cracking in the presence of fungus and bacteria.

Biology and biotechnology of microbial pilus nanowires.

Type IV pili (T4P) are bacterial appendages used for cell adhesion and surface motility. In metal-reducing bacteria in the genus Geobacter, they have the unique property of being conductive and essential to wire cells to extracellular electron acceptors and other cells within biofilms. Theseelectroactivebacteria use a conserved pathway for biological assembly and disassembly of a short and aromatic dense peptide subunit (pilin). The polymerization of thepilins clusters aromatic residues optimally for charge transport and exposes ligands for metal immobilization and reduction. The simple design yet unique functionalities of conductive T4P afford opportunities for the scaled-up production of recombinant pilins and their in vitro assembly into electronic biomaterials of biotechnological interest. This review summarizes current knowledge of conductive T4P biogenesis and functions critical to actualize applications in bioelectronics, bioremediation, and nanotechnology.

Sequential fractionation of sugarcane bagasse using liquid hot water and formic acid-catalyzed glycerol-based organosolv with solvent recycling

A fractionation scheme for lignocellulosic biomass where major constituent biopolymers are recovered in applicable forms is essential for integrated biorefinery. In this study, a sequential two-step fractionation of sugarcane bagasse using liquid hot water followed an organic acid-catalyzed aqueous glycerol-based organosolv process was developed. Under optimal conditions, 66.1% of the hemicellulose was recovered as saccharides by the acid-catalyzed hydrothermal step. Formic acid was superior to H2SO4 and HNO3 as a catalyst for the subsequent organosolv step using aqueous glycerol in terms of delignification efficiency and selectivity, resulting in a maximum of 78.3% lignin recovery after acetone extraction with > 90% purity and better conservation of aromatic subunit structure according to 2D-NMR. The majority of cellulose (86.4%) was retained as a solid with high purity (74.8%) and enzymatic digestibility, resulting in 78.2% glucose recovery. The formic acid-aqueous glycerol-spent liquor could be recycled for at least four consecutive batches with no significant decrease in product yield or selectivity. The work represents an efficient sequential process for fractionation of lignocellulose-derived components which allowed solvent recycling and recovery of high-purity lignin with conserved subunit structure. The separated product streams are suitable for valorization in biorefinery. Graphical abstract

Nitrogen and Oxygen Co‐doped Hierarchical Porous Carbon: Electrode Materials for High‐Energy Density and Flexible Solid‐State Supercapacitors

AbstractNitrogen and oxygen co‐doped hierarchically porous carbons (NO−HPCs) with robust tailored pore structures were fabricated through a soft chemistry synthetic strategy involving the use of F127 and the Friedel‐Crafts alkylation reaction, referred to as NO−HPC−FH. The obtained carbon of NO−HPC−FH has rich nitrogen and oxygen contents, high surface area (up to 1715 m2/g), wider range pore‐size distribution, and high pore volume (up to 2.8 cm3/g). Herein, NO−HPC−FH exhibits a high specific capacitance of 382 F/g at 0.5 A/g and an excellent cycling stability after 15 000 cycles at 20 A/g (capacitance retention is nearly 100 %), in which the contribution of the pseudocapacitance to the total specific capacitance was found to reach about 78 %. In particular, an all‐solid‐state flexible supercapacitor was fabricated, which also exhibited a high energy density of 33.4 Wh/kg at the power output of 879.9 W/kg, and a high cycling stability and flexibility. Therefore, this synthetic protocol using soft templates provides an alternative strategy to synthesize heteroatom‐doped HPCs based on “knitted” aromatic subunits and, thus, has promising potential for application in supercapacitive materials.

Effects of Fenton oxidation on structural changes of lignin from steam-exploded poplar

Pretreatment of steam-exploded poplar by Fenton oxidation was used to effectively biodegrade lignin. The structure of lignin samples (LS from steam-exploded poplar and LSF from samples further treated by Fenton oxidation) obtained by enzymatic hydrolysis during pretreatment were characterized and compared. The results showed that the demethoxy reaction occurred in the process of Fenton oxidation. GPC results indicated that the weight average molecular weight (Mw) of LSF did not change significantly, indicating that that there was no significant condensation during Fenton oxidation pretreatment. Heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR) results suggested that the proportion of the three-unit basic structural units of poplar (H, G, and S) were significantly changed during Fenton oxidation process, and more lignin S units were removed than lignin G units. The content of β-O-4 linkages was lower in LSF (74.0%, as a fraction of β-O-4 + β-5 + β-β) than in LS (78.2%), which indicated that β-O-4 linkages were destroyed to a certain extent during Fenton oxidation process, and the content of total lignin interunit linkages including β-O-4, β−β, and β-5 linkages over total lignin aromatic subunits (Ar%) in LSF was higher, reaching 49.9%.

Transcriptional and Post-transcriptional Regulation of Lignin Biosynthesis Pathway Genes in Populus

Lignin is a heterogeneous polymer of aromatic subunits derived from phenylalanine. It is polymerized in intimate proximity to the polysaccharide components in plant cell walls and provides additional rigidity and compressive strength for plants. Understanding the regulatory mechanisms of lignin biosynthesis is important for genetic modification of the plant cell wall for agricultural and industrial applications. Over the past 10 years the transcriptional regulatory model of lignin biosynthesis has been established in plants. However, the role of post-transcriptional regulation is still largely unknown. Increasing evidence suggests that lignin biosynthesis pathway genes are also regulated by alternative splicing, microRNA, and long non-coding RNA. In this review, we briefly summarize recent progress on the transcriptional regulation, then we focus on reviewing progress on the post-transcriptional regulation of lignin biosynthesis pathway genes in the woody model plant Populus.