Aromatic Building Blocks Research Articles

Characterization and Physicochemical Properties of Condensed Tannins from Acacia catechu.

Condensed tannins from Acacia catechu were carefully studied to determine their chemical structure and physicochemical properties. The combined use of MALDI-TOF-MS and (13)C NMR revealed that catechin and epicatechin are the predominant monomers. Most of the compounds were dimers, as confirmed by size exclusion chromatography measurements. To evaluate their potential as aromatic building block in polymer synthesis, special care was given to the characterization and quantification of the different OH groups. A detailed (31)P NMR analysis showed the predominance of catechin, with a catechin/epicatechin ratio of 4.2:1. Two distinct (1)H NMR measurements confirmed the quantification. The thermal properties were also determined: the tannins showed a high temperature of degradation (ca. 190 °C) and a high glass transition temperature (ca. 140 °C), allowing for thermal processing or chemical reactions at relatively high temperature. A. catechu tannins thus present interesting features to be used as aromatic building blocks in polymer materials.

Development and substrate specificity screening of an in vivo biosensor for the detection of biomass derived aromatic chemical building blocks.

Measuring substrate and/or product concentration can create a major bottleneck for synthetic and biosynthetic processes. Here we report the development and substrate screening of a whole cell biosensor to detect biomass-derived aromatic chemical building blocks, supporting the use of sustainable feedstocks in the bulk and fine chemical industries.

Ferrocene-containing poly(fluorenylethynylene)s for nonvolatile resistive memory devices

The memory behaviours of the prepared ferrocene-containing poly(fluorenylethynylene)s (PFcFE) can be easily tuned by changing the chemical structures of the embedded aromatic building blocks.

Lignin Refinery: Towards the Preparation of Renewable Aromatic Building Blocks

AbstractWith its wide availability and its low cost, lignocellulosic biomass represents a very convenient and sustainable alternative to fossil fuels for the preparation of energy, materials, and chemical building blocks. While processes for cellulose and hemicellulose conversion into valuable products are already advanced, adding value to lignin is still a challenge, due to its complex structure and its relatively high stability towards a variety of chemical transformations. The pathway for the valorization of lignin from biomass often includes an initial extraction step, which in some cases can affect the native structure of the lignin backbone. At this stage, a further catalytic depolymerization step can follow, leading to the production of bio‐based small aromatic building blocks. In this review we describe the most important lignin extraction methods applied in industry (Kraft, Sulfite and Soda processes) as well as more recent processes based on so‐called organosolv and ionosolv protocols. In addition, the most important approaches for the heterogeneous catalytic depolymerization of lignin are critically discussed.

Electronic and Morphological Studies of Conjugated Polymers Incorporating a Disk-Shaped Polycyclic Aromatic Hydrocarbon Unit.

As more research findings have shown the correlation between ordering in organic semiconductor thin films and device performance, it is becoming more essential to exercise control of the ordering through structural tuning. Many recent studies have focused on the influence of side chain engineering on polymer packing orientation in thin films. However, the impact of the size and conformation of aromatic surfaces on thin film ordering has not been investigated in great detail. Here we introduce a disk-shaped polycyclic aromatic hydrocarbon building block with a large π surface, namely, thienoazacoronenes (TACs), as a donor monomer for conjugated polymers. A series of medium bandgap conjugated polymers have been synthesized by copolymerizing TAC with electron donating monomers of varying size. The incorporation of the TAC unit in such semiconducting polymers allows a systematic investigation, both experimentally and theoretically, of the relationships between polymer conformation, electronic structure, thin film morphology, and charge transport properties. Field effect transistors based on these polymers have shown good hole mobilities and photoresponses, proving that TAC is a promising building block for high performance optoelectronic materials.

Knitting hypercrosslinked conjugated microporous polymers with external crosslinker

A new series of hypercrosslinked polymers were efficiently synthesized by knitting rigid aromatic building blocks using a novel external crosslinker (1,4-dimethoxybenzene, DMB) which result in a conjugated microporous structure. This knitting hypercrosslinked conjugated microporous polymers (HCCMPs) are predominantly microporous and exhibit high surface area of up to 800 m2 g−1, which also show comparable gas uptake properties reaching 1.14 wt. % H2 adsorption at 1.13 bar/77 K, and 12.72 wt. % CO2 adsorption at 1.13 bar/273 K, respectively. The extended π-conjugated structure and the three-dimensional network of π–π stacked aryl rings enable these HCCMPs good luminescence properties and high electrical conductivity.

Dialkoxynaphthalene as an electron-rich unit for high-performance polymer solar cells with large open circuit voltages

Dialkoxynaphthalene is a simple aromatic building block, which can be synthesized easily in a large scale. In this work, two dialkoxynaphthalene derivatives were copolymerized with electron-withdrawing benzothiadiazole (BT) derivatives to afford three donor-acceptor copolymers, PNDTBT, PNT2FTBT and PN2FTBT. The three copolymers have diverse bandgaps ranged from 1.73 to 1.86 eV, and deep HOMO energy levels up to −5.61 eV. Thermogravimetric analysis and electrochemical measurements show that these copolymers have good thermal and environment stability. The hole mobilities of these copolymers were investigated using the space charge limited current (SCLC) method as well as the organic field effect transistor (OFET) method. Polymer solar cells based on PNDTBT exhibit the best photovoltaic performance with a power conversion efficiency of 6.24% and a Voc of 0.94 V, much better than those of previously reported copolymers based on dialkoxynaphthalene.

ChemInform Abstract: Heterogeneous Foldamers from Aliphatic—Aromatic Amino Acid Building Blocks: Current Trends and Future Prospects

AbstractReview: 105 refs.

Catalytic Hydrogenolysis of Aryl Ethers: A Key Step in Lignin Valorization to Valuable Chemicals

Lignin is a robust biomacromolecule (or a polymer) that gives structural integrity to plants and constitutes 25–35% of the woody biomass. Lignin is inedible, barely used, and contains mostly aromatic building blocks. Because of these features, lignin is considered an important renewable feedstock for the production of fine chemicals (or fuels) and the only significant feedstock providing aromatic compounds. The C–O bonds of aryl ethers are the most abundant linkages in the framework of lignin. In this Perspective, the state-of-the-art of selective hydrogenolysis (HGL) of C–O bonds of aryl ethers is discussed. Particularly, progress made recently and ethers relevant to lignin valorization are reviewed.

Heterogeneous Foldamers from Aliphatic–Aromatic Amino Acid Building Blocks: Current Trends and Future Prospects

AbstractChemists' constant pursuit of understanding of the underlying principles of nature's most intricate phenomenon such as protein folding has led to the development of the field of “foldamers”. The emergence of diverse classes of unnatural amino acid building blocks has unleashed countless opportunities to design, develop and explore the structural and functional aspects of synthetic peptides. One current trend in foldamer chemistry is the heterofoldamer approach, which involves systematic stoichiometric variation of various natural/unnatural amino acid residues, leading to conformational ordering with intriguing structural architectures. In this regard, the incorporation of aromatic amino acids provides efficient structural rigidification and tunability to the molecular scaffolds, which can exhibit a range of secondary structural features. Recent times have witnessed an upsurge of foldamers featuring aliphatic‐aromatic residues with diverse structural propensities. This review is an effort to cover this rapidly developing field of foldamer science and also to envisage its future perspectives.

Microbial production of the aromatic building‐blocks (S)‐styrene oxide and (R)‐1,2‐phenylethanediol from renewable resources

(S)-Styrene oxide and (R)-1,2-phenylethanediol are chiral aromatic molecular building blocks used commonly as precursors to pharmaceuticals and other specialty chemicals. Two pathways have been engineered in Escherichia coli for their individual biosynthesis directly from glucose. The novel pathways each constitute extensions of the previously engineered styrene pathway, developed by co-expressing either styrene monooxygenase (SMO) or styrene dioxygenase (SDO) to convert styrene to (S)-styrene oxide and (R)-1,2-phenylethanediol, respectively. StyAB from Pseudomonas putida S12 was determined to be the most effective SMO. SDO activity was achieved using NahAaAbAcAd of Pseudomonas sp. NCIB 9816-4, a naphthalene dioxygenase with known broad substrate specificity. Production of phenylalanine, the precursor to both pathways, was systematically enhanced through a number of mutations, most notably via deletion of tyrA and over-expression of tktA. As a result, (R)-1,2-phenylethanediol reached titers as high as 1.23 g/L, and at 1.32 g/L (S)-styrene oxide titers already approach their toxicity limit. As with other aromatics, product toxicity was strongly correlated with a model of membrane accumulation and disruption. This study additionally demonstrates that greater flux through the styrene pathway can be achieved if its toxicity is addressed, as achieved in this case by reacting styrene to less toxic products.

Peptide-based hydrogel nanoparticles as effective drug delivery agents

Peptide-based hydrogel nanoparticles represent a promising alternative to current drug delivery approaches. We have previously demonstrated that the Fmoc-FF aromatic dipeptide building block can self-assemble in aqueous solutions to form nano-scaled ordered hydrogels of remarkable mechanical rigidity. Here, we present a scalable process for the assembly of this peptide into hydrogel nanoparticles (HNPs) aimed to be utilized as potential drug delivery carriers. Fmoc-FF based HNPs were formulated via modified inverse-emulsion method using vitamin E-TPGS as an emulsion stabilizer and high speed homogenization. The formed HNPs exhibited two distinguishable populations with an average size of 21.5±1.3 and 225.9±0.8nm. Gold nanoparticles were encapsulated within the hydrogel nanoparticles as contrast agents to monitor the formation of the assemblies and their ultrastructural properties. Next, we demonstrated a robust experimental procedure developed and optimized for the formulation, purification, storage and handling procedures of HNPs. Encapsulation of doxorubicin (Dox) and 5-flourouracil (5-Fu) within the HNPs matrix showed release kinetics of the drugs depending on their chemical structure, molecular weight and hydrophobicity. The results clearly indicate that Fmoc-FF based hydrogel nanoparticles have the potential to be used as encapsulation and delivery system of various drugs and bioactive molecules.

4-[18F]Fluoro-N-methyl-N-(propyl-2-yn-1-yl)benzenesulfonamide ([18F]F-SA): a versatile building block for labeling of peptides, proteins and oligonucleotides with fluorine-18 via Cu(I)-mediated click chemistry

Cu(I)-mediated [3+2]cycloaddition between azides and alkynes has evolved into a valuable bioconjugation tool in radiopharmaceutical chemistry. We have developed a simple, convenient and reliable radiosynthesis of 4-[18F]fluoro-N-methyl-N-(propyl-2-yn-1-yl)benzenesulfonamide ([18F]F-SA) as a novel aromatic sulfonamide-based click chemistry building block. [18F]F-SA could be prepared in a remotely controlled synthesis unit in 32 ± 5% decay-corrected radiochemical yield in a total synthesis time of 80 min. The determined lipophilicity of [18F]F-SA (logP = 1.7) allows handling of the radiotracer in aqueous solutions. The versatility of [18F]F-SA as click chemistry building block was demonstrated by the labeling of a model peptide (phosphopeptide), protein (HSA), and oligonucleotide (L-RNA). The obtained radiochemical yields were 77% (phosphopeptide), 55-60% (HSA), and 25% (L-RNA), respectively. Despite the recent emergence of a multitude of highly innovative novel bioconjugation methods for 18F labeling of biopolymers, Cu(I)-mediated click chemistry with [18F]F-SA represents a reliable, robust and efficient radiolabeling technique for peptides, proteins, and oligonucleotides with the short-lived positron emitter 18F.

ChemInform Abstract: Efficient and Eco‐Friendly Synthesis of Iodinated Aromatic Building Blocks Promoted by Iodine and Hydrogen Peroxide in Water: A Mechanistic Investigation by Mass Spectrometry.

AbstractThe reaction of aromatic compounds with molecular iodine in the presence of aqueous hydrogen peroxide gives mono‐, di‐ and triiodinated arenes and hetarenes under the same conditions.

A Novel Approach to the Pyridoacridine Ring System: Synthesis of the Topoisomerase Inhibitor 13‐Deazaascididemin

A novel approach to the pyridoacridine ring system of the ascididemin-type marine alkaloids is presented. This approach allows for the introduction of the ring A of the alkaloids by using a simple aromatic aldehyde building block. The viability of this approach is demonstrated with the synthesis of AK37, a bioactive deaza analogue of the alkaloid ascididemin. Starting from 3-cyano-4-methylquinoline, a sequence of regioselective homolytic benzoylation, annulation of a bromopyridine ring, and radical cyclization leads to the pentacyclic ring system.

Synthesis and binding properties of guanidinium biscarboxylates

The ammonium ion binding site of the enzyme glutaminase HisF inspired us to design guanidinium biscarboxylates as potential self-organized ionophores in molecular recognition. The syntheses of the title compounds based on aliphatic and aromatic building blocks, along with a general method for the preparation of δ-aminoethoxyacetic acids, are presented in this work. Investigation of the binding properties of the title compounds in dimethyl sulfoxide (DMSO) and methanol solution revealed no ammonium ion affinity, but interaction of the guanidinium moiety with acetate ions.

A new aluminium-based microporous metal–organic framework: Al(BTB) (BTB = 1,3,5-benzenetrisbenzoate)

The system Al3+/H3BTB/DMF/additive was systematically investigated using high-throughput methods and the new, microporous MOF [Al(BTB)] (BTB=1,3,5-benzenetrisbenzoate), named CAU-4 (CAU=Christian-Albrechts-University), was discovered. The synthesis was optimized changing chemical and process parameters and the final synthesis procedure was scaled up to the gram scale. CAU-4 is thermally stable up to 400°C in air and exhibits a BET-surface area of 1520m2/g and a micropore volume of 0.61cm3/g. A structure model was developed using a computationally assisted structure determination that was further validated by a good agreement with the experimental X-ray diffraction patterns and the geometrical features. The framework structure consists of isolated [AlO6]-octahedra which are bridged by carboxylate groups of the BTB-linker to form chains. These chains are connected by the tritopic aromatic building blocks, to form one-dimensional hexagonal channels with a diameter of ca. 9.6Å.

A New Strategy to Microporous Polymers: Knitting Rigid Aromatic Building Blocks by External Cross-Linker

A series of microporous polymers has been obtained via a low-cost versatile strategy, which involves “knitting” rigid aromatic building blocks, such as benzene, biphenyl, 1,3,5-triphenylbenzene, methylbenzene, chlorobenzene, and phenol using an external cross-linker. These materials are predominantly microporous and exhibit high surface areas. Moreover, different building blocks can generate materials with different pore structures, functional groups and application properties, which are significant for materials design.

Synthesis, Crystal Structure, and Luminescent Properties of One New Binary Cocrystal Achieved from Aromatic Dicarboxylic Acid and Imine-based Dipyridyl Building Block

A new binary cocrystal [C 26 H 20 N 6 ][C 14 H 10 O 4 S 2 ]1 has been synthesized and characterized by IR, elemental analysis, TG technique and X-ray crystallography with N′,N′-bis[1-(pyridin-4-yl)methylidene]benzil dihydrazone and 2,2-dithiosalicylic acid. Analysis of the crystal packing of 1 suggests that there are classical intermolecular O−H···N hydrogen bonds between acid and base components and obvious six types of C−H···π interactions involving aromatic rings of adjacent molecules in the crystal packing. The luminescent properties of the compound 1 were investigated.

Can pyrolysis-GC/MS be used to estimate the degree of thermal alteration of black carbon?

Very little is known about the macromolecular properties of biomass combustion residues referred to as black carbon (BC). Pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) was performed on: (i) peat from Spain at 400–1200 °C to investigate the effect of charring on pyrolysis fingerprint and (ii) natural charcoal from Laos in order to link molecular information to published chemical and reactivity parameters. Confirming earlier Py-GC/MS studies, the BC in the artificially charred peat and the natural charcoal produced predominantly benzene, toluene, C 2-benzenes, PAHs and benzonitriles. Furthermore, some charcoal samples produced significant amounts of phenols, methoxyphenols, carbohydrate markers, n-alkanes and n-alkenes upon pyrolysis, reflecting non-charred and weakly charred biomass. A series of pyrolysis product ratios related to the degree of dealkylation of the pyrolysis products (benzene/toluene, naphthalene/C 1-naphthalenes, C 1-naphthalenes/C 2-naphthalenes, benzofuran/C 1-benzofurans and benzonitrile/C 1-benzonitrile) increased with increasing artificial charring (peat) and, for the natural charcoal, these ratios were in accordance with established chemical and reactivity parameters related to charring intensity from other methods: proportion of aromatic C obtained from solid state 13C nuclear magnetic resonance spectroscopy (NMR), the proportion of charred material as estimated from NMR in conjunction with a molecular mixing model (NMR–MMM) and the resistance to acid dichromate oxidation. The alkyl side chains of aromatic pyrolysis products are probably inherited from short chain aliphatic C chains that cross link the predominantly aromatic building blocks of BC, and these linkages seem to disappear with increasing charring intensity. Thus, the degree of thermal alteration of BC can be discerned from the pyrolysis fragmentation pattern.