Mellitic Acid Research Articles

Rationally Designed Semiconducting 2D Surface-Confined Metal-Organic Network.

Two-dimensional (2D) surface-confined metal-organic networks (SMONs) are metal-doped self-assembled monolayers of molecules on solid surfaces. We report the formation of uniform large-area solution-processed semiconducting SMONs of Pd and Zn with mellitic acid (MA) on a highly oriented pyrolytic graphite (HOPG) surface under ambient conditions. The microscopic structure is determined using scanning tunneling microscopy (STM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Using tunneling spectroscopy, we observed a reduction in the band gap of ≈900 and ≈300 meV for MA-Pd and MA-Zn SMONs, respectively, compared to the pure MA assembly. Concomitant density functional theory (DFT) calculations reveal that the coordination geometry and microscopic arrangement give rise to the observed reduction in the band gap. The dispersion of the frontier bands and their delocalization due to strong electronic coupling (between MA and metal) suggest that the MA-Pd SMON could potentially be a 2D electronic material.

Mellitic acid production by ruthenium ion-catalyzed oxidation of cokes

Cokes are rich in highly condensed aromatic rings, however, the current applications of cokes mainly focus on the thermal energy or carbon-rich structures, and the aromatic ring structures in cokes are underutilized, which are usually employed as feedstock to fabricate valuable fine chemicals and synthesized with complex steps. The pyrolysis temperatures have great impact on the structures of resulting cokes. It is necessary to learn about the structural features of cokes produced from different pyrolysis conditions to explore the optimal reaction conditions. This study reported an eco-friendly and efficient method, ruthenium ion-catalyzed oxidation, to utilize Guizhou cokes produced from different pyrolysis temperatures for green and value-added chemical production. The results indicate that arenecarboxylic acids account for more than 90% of all the oxidation products, in which mellitic acid could be up to more than 70%. Compared with previous studies, this is the highest mellitic acid yield achieved in the oxidation products of fossil resources, indicating that cokes show good performance for the clean production of mellitic acid. The ruthenium ion-catalyzed oxidation product distribution demonstrates that 1,200 °C is a turning point during coking of Guizhou coals and the structure and reactivity of Guizhou coke1,200 deviate from the expected variation tendency, which is related to the inverse influence of pyrolysis temperatures on condensation degree and ash property of cokes. Effect of pyrolysis temperatures on aromatic structures and reactivity of Guizhou cokes was also discussed further.

Thermal treatment of Shengli lignite and subsequent oxidation

Shengli lignite (SL) was thermally treated at 150 °C–650 °C. SL and each residue (RTT) from the thermal treatment (TT) were oxidized using aqueous hydrogen peroxide (AHPO)/acetic acid (AA) to afford a soluble portion (SP). SL and each RTT were characterized with a X-ray diffractometer and Fourier transform infrared spectrometer, and 11 typical benzenepolycarboxylic acids (BPCAsI) in the SPs were analyzed with a high-performance liquid chromatograph. The results show that the condensation degree (CDARs) of aromatic rings (ARs) in each RTT is higher than that of SL and increases with raising the TT temperature, while the oxidation of a RTT resulting from lower-temperature TT produces BPCAsI, especially mellitic acid, in higher yields. HOO· produced in AHPO/AA could play an crucial role in oxidizing AR-containing macromolecular species in SL and each RTT to BPCAsI.

Structural and Spectroscopic Investigation of Two Plutonium Mellitates.

The aqueous reaction of mellitic acid (H6mell) with 242PuBr3·nH2O forms two plutonium mellitates, 242Pu2(mell)(H2O)9·H2O (Pu-1α) and 242Pu2(mell)(H2O)8·2H2O (Pu-1β). These compounds are compared to the isomorphous lanthanide mellitates with similar ionic radii via bond length analysis. Both plutonium compounds form three-dimensional metal-organic frameworks, with Pu-1α having two unique metal centers and Pu-1β having one. All plutonium metal centers exhibit nine-coordinate geometries. Our results show metal-oxygen bond lengths for plutonium significantly shorter than those of the previously reported lanthanum and herein reported cerium analogues, consistent with the nine-coordinate ionic radii. Clear Laporte-forbidden 5f → 5f transitions are observed in the ultraviolet-visible-near-infrared spectra and are assigned to trivalent plutonium. However, there is a distinct color difference between the two plutonium compounds.

Black carbon as a significant component of aromatic carbon in surface soils and its importance is enhanced in volcanic ash soil profiles

Black carbon (BC) constitutes a refractory carbon (C) pool in soil and other environments. Estimating the amount and dynamics of BC in soil is important in terms of the global C cycle. The goal of this study was to characterize the contribution of BC to total and aromatic C in a variety of soils using the benzene polycarboxylic acid (BPCA) method and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Thirteen A-/Ap (plowed layer)-horizon soils that belong to widely distributed soil series (Humic Andosols, Dystric Cambisols, Gleyic Cambisols, Eutric Fluvisols, and Dystric Planosols) under typical land uses (forest, grassland, upland field, and paddy field) in Japan and two Andosol profiles were analyzed. Three humic acid samples including the green fraction, which contains 4,9-dihydroxyperylene-3,10-quinone (DHPQ) as a chromophore and has mycorrhiza as a possible source (referred to as Pg), were also subjected to the BPCA procedure. The BC content in the 13 A-/Ap-horizon soils was 0.3–53 gC kg−1 or 5.7–48% of the total soil C (BC%). The BC content correlated positively with the total C content and with aromatic C content, while the relationship between BC% and soil order or land use was not clear. An analysis of Pg suggested the potential contribution of DHPQ to the yield of benzenehexacarboxylic acid in the BPCA method. The variations in BC content and C composition of two Andosol profiles indicated a greater stability of BC than the other types of C, including monocyclic aromatic C. The contribution of BC to aromatic C in their lower layers was estimated to be ca. 55–70% based on a regression equation when assuming that 70–90% of the BC was aromatic C.

Synthesis of a Redox-active Metal–Organic Framework MIL-116(Fe) and Its Lithium Ion Battery Cathode Properties

A metal–organic framework of iron (III) and mellitic acid was synthesized. The crystal structure of the MOF determined by single crystal X-ray analysis was isostructural to MIL-116. It was applied ...

The Rel stringent factor from Thermus thermophilus: crystallization and X-ray analysis.

The stringent response, controlled by (p)ppGpp, enables bacteria to trigger a strong phenotypic resetting that is crucial to cope with adverse environmental changes and is required for stress survival and virulence. In the bacterial cell, (p)ppGpp levels are regulated by the concerted opposing activities of RSH (RelA/SpoT homologue) enzymes that can transfer a pyrophosphate group of ATP to the 3' position of GDP (or GTP) or remove the 3' pyrophosphate moiety from (p)ppGpp. Bifunctional Rel enzymes are notoriously difficult to crystallize owing to poor stability and a propensity for aggregation, usually leading to a loss of biological activity after purification. Here, the production, biochemical analysis and crystallization of the bifunctional catalytic region of the Rel stringent factor from Thermus thermophilus (RelTtNTD) in the resting state and bound to nucleotides are described. RelTt and RelTtNTD are monomers in solution that are stabilized by the binding of Mn2+ and mellitic acid. RelTtNTD crystallizes in space group P4122, with unit-cell parameters a = b = 88.4, c = 182.7 Å, at 4°C and in space group P41212, with unit-cell parameters a = b = 105.7, c = 241.4 Å, at 20°C.

Concurrent Modulation of Competitive Mechanisms to Design Stimuli‐Responsive Ln‐MOFs: A Light‐Operated Dual‐Mode Assay for Oxidative DNA Damage

AbstractThe identification of biomolecules for disease diagnosis requires facile analytical technologies with high precision and reliability. Several signal transduction pathways have inspired the development of various bioanalytical systems. However, most systems are greatly limited by a single‐mechanism/mode assay, which easily results in false‐positive/negative results. Herein, a multiple‐mechanism‐driven optical biosensor for 8‐oxo‐2′‐deoxyguanosine (8‐oxo‐dG), an early pathological signature of DNA lesions and various diseases, is designed by assembling adenine as a recognition element, mellitic acid as energy donors and Eu3+ as signal reporters into one metal‐organic framework (MOF) system. Significantly, by regulating the delicate competition between the different mechanisms, the fabricated single platform (Eu‐ade‐MOF) concurrently provides two switchable approaches for rapid qualitative (30 s and 4 min) and quantitive (ppb level) recognition of 8‐oxo‐dG in both complex artificial and real human urine environments. Compared with those single‐mechanism/mode‐driven detections, this light‐operated dual‐mode analysis system can inherently boost the analysis reliability and largely minimize the chances of false negatives/positives for a non‐invasive diagnosis of DNA damage and related diseases. This work represents the first effort in designing a luminescent sensor coupling multiple mechanisms in a single interface to determine DNA damage degree and provides a new approach for developing multimode analysis platforms for human health monitoring.

PH-Responsive Pillar[6]arene-based Water-Soluble Supramolecular Hexagonal Boxes.

We describe the preparation of the first water-soluble pH-responsive supramolecular hexagonal boxes (SHBs) based on multiple charge-assisted hydrogen bonds between peramino-pillar[6]arenes 2 with the molecular "lid" mellitic acid (1 a). The interaction between 2 and 1 a, as well as the other "lids" pyromellitic and trimesic acids (1 b and 1 c, respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2, that is, 3, with bis-sulfonate 4 a or 4 b, immediately led to guest escape along with the formation of closed 1 a2 2 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH-responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications.

PH‐Responsive Pillar[6]arene‐based Water‐Soluble Supramolecular Hexagonal Boxes

AbstractWe describe the preparation of the first water‐soluble pH‐responsive supramolecular hexagonal boxes (SHBs) based on multiple charge‐assisted hydrogen bonds between peramino‐pillar[6]arenes 2 with the molecular “lid” mellitic acid (1 a). The interaction between 2 and 1 a, as well as the other “lids” pyromellitic and trimesic acids (1 b and 1 c, respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2, that is, 3, with bis‐sulfonate 4 a or 4 b, immediately led to guest escape along with the formation of closed 1 a22 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH‐responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications.

Formation of benzene polycarboxylic acids using alkali‑oxygen oxidation of coal-tar pitch pre-treated by extraction and air-blowing

Benzene polycarboxylic acids (BPCAs) could be produced from oxidation of a coal-tar pitch (CTP) by oxygen in NaOH solution. In this work, CTP was extracted by methanol and subsequently air-blown prior to oxidation by oxygen at 260 °C for 1 h, during which the amount and condensed degree of aromatic portion obviously increased, while the oxygen-containing groups were successfully introduced into CTP. The pre-treatment of CTP not only increased the yield of BPCAs in the resulting oxidation products, but also improved the distribution of BPCAs, especially selectively increasing the content of mellitic acid and benzenepentacarboxylic acid in the BPCAs. This investigation provides a promising approach for obtaining BPCAs especially high value-added mellitic acid and benzenepentacarboxylic acid using inexpensive and underutilized CTP.

Hydrothermal Synthesis of Composition- and Morphology-Tunable Polyimide-Based Microparticles.

Polyimide is one of the most important high-performance polymers, which is widely used due to its excellent mechanical performance and thermal stability. Unlike the conventional synthetic approach, hydrothermal polymerization enables the synthesis of polyimides without any toxic solvent and catalyst. Herein, we report the synthesis of polyimide-based microparticles (PIMs) through one-pot hydrothermal polymerization using precursors of mellitic acid (MA) and three isomers of phenylenediamine (PDA) (o-, m-, and p-PDA). Interestingly, the chemical composition of PIMs was highly tunable with the choice of the PDA isomers, leading to considerable morphological differences between PIMs. The molecular dynamics simulation and density functional theory calculation of the polymeric segment of the respective PIMs suggested that the relative ratio of amide to imide influenced the rotational freedom of the polymeric chains and number of hydrogen bonds, resulting in the well-defined structures of respective PIMs. Considering the highly tunable nature of PIMs coupled with the facile synthetic protocol, we anticipate prospective potentials of PIMs in materials, energy, and composite applications.

Selective production and characterization of aromatic carboxylic acids from Xianfeng lignite-derived residue by mild oxidation in aqueous H2O2 solution

Lignites show great potential as feedstock for the production of valuable carboxylic acids by mild oxidation. In this study, valuable aromatic polycarboxylic acids were produced from Xianfeng lignite-derived residue (XLDR) through mild oxidation in green aqueous H2O2 solution. The results show that XLDR oxidation can produce benzene carboxylic acids (BCAs) and polycyclic aromatic carboxylic acids (PCACAs) in high selectivity. The BCAs are dominated by mellitic acid and benzenepentacarboxylic acid with 55.5% and 13.3% in the total yield of all group components based on the analysis with gas chromatography/mass spectrometer. Moreover, three series of PCACAs with an aliphatic ring were identified by direct analysis in a real-time ionization source coupled to a time-of-flight mass spectrometer. The BCAs and PCACAs could be generated from different kinds of aromatic structures via oxidation by OH produced from H2O2.

Effects of Organic Compounds on Dissolution of the Phosphate Minerals Chlorapatite, Whitlockite, Merrillite, and Fluorapatite: Implications for Interpreting Past Signatures of Organic Compounds in Rocks, Soils and Sediments.

Phosphate is an essential nutrient for life on Earth, present in adenosine triphosphate (ATP), deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and phospholipid membranes. Phosphorus does not have a significant volatile phase, and its release from minerals is therefore critical to its bioavailability. Organic ligands can enhance phosphate release from minerals relative to release in inorganic solutions, and phosphorus depletion in paleosols has consequently been used as a signature of the presence of ligands secreted by terrestrial organisms on early Earth. We performed batch dissolution experiments of the Mars-relevant phosphate minerals merrillite, whitlockite, chlorapatite, and fluorapatite in solutions containing organic compounds relevant to Mars. We also analyzed these phosphate minerals using the ChemCam laboratory instrument at Los Alamos, providing spectra of end-member phosphate phases that are likely present on the surface of Mars. Phosphate release rates from chlorapatite, whitlockite, and merrillite were enhanced by mellitic, oxalic, succinic, and acetic acids relative to inorganic controls by as much as >35 × . The effects of the organic compounds could be explained by the denticity of the ligand, the strength of the complex formed with calcium, and the solution saturation state. Merrillite, whitlockite, and chlorapatite dissolution rates were more strongly enhanced by acetic and succinic acids relative to inorganic controls (as much as >10 ×) than were fluorapatite dissolution rates (≲2 ×). These results suggest that depletion of phosphate in soils, rocks or sediments on Mars could be a sensitive indicator of the presence of organic compounds.

Production of benzenepolycarboxylic acids by oxidation of pre-pyrolyzed Shengli lignite

ABSTRACTLignite oxidation would produce benzene polycarboxylic acids (BPCAs), however, the coexisting aliphatic acids in the resulting oxidation products seriously affect the separation of BPCAs. In the study, Shengli lignite was pre-pyrolyzed at different temperatures from 250°C to 550°C, and then the obtained pyrolyzed residues were subjected to oxidation under the same condition. Oxidation reactivity of pyrolyzed residues decreased with increasing pyrolysis temperature. However, compared with Shengli lignite, its pyrolyzed residues at proper temperatures (250°C and 350°C) generated more BPCAs, especially mellitic acid with more yield and relative content. By XRD analyses of the pyrolyzed residues, more condensed aromatic structures would result in decreasing oxidation reaction activity of the pyrolyzed residues, while more amounts of aromatic species and larger aromatic unit would contribute to the increase of BPCAs and mellitic acid, respectively.

Solid-state supramolecular structure formed between the 1-(diaminomethylene)thiourea and mellitic acid

The single crystals of hexakis(1-(diaminomethylene)thiouron-1-ium) benzene-1,2,3,4,5,6-hexacarboxylate (mellitate(6-)) tetrahydrate suitable for the X-ray analysis were grown using a solution growth technique at room temperature. The compound crystallises in centrosymmetric space group of the triclinic system. The conformation of six crystallographically independent 1-(diaminomethylene)thiouron-1-ium cations is not strictly planar, but twisted. Both planar arms of the cations are oppositely rotated by 6.1(1) ÷ 20.9(1)o around the CN bonds involving the central N atom. All of the carboxylate groups of mellitate(6-) anion are inclined to the plane of aromatic six-membered carbon ring by 43.0(1) ÷ 72.0(1)o. Oppositely charged components i.e. 1-(diaminomethylene)thiouron-1-ium cations and mellitate(6-) anion interact each other via NH⋯O hydrogen bonds forming hexakis(1-(diaminomethylene)thiouron-1-ium) mellitate units that further interact with the water molecules forming hexakis(1-(diaminomethylene)thiouron-1-ium) mellitate tetrahydrate supramolecular architecture. Hirshfeld surface and the analysis of 2D fingerprint plots are used for illustrate both qualitatively and quantitatively interactions between the units governing the supramolecular assemblies. The compound was also characterised by vibrational spectroscopy. The vibrational assignment have been supported by the isotopic frequency shift.

Mellitate: A multivalent anion with extreme charge density causes rapid aggregation and misfolding of wild type lysozyme at neutral pH.

Due to its symmetric structure and abundance of carboxyl groups, mellitic acid (MA–benzenehexacarboxylic acid) has an uncommon capacity to form highly ordered molecular networks. Dissolved in water, MA dissociates to yield various mellitate anions with pronounced tendencies to form complexes with cations including protonated amines. Deprotonation of MA at physiological pH produces anions with high charge densities (MA5- and MA6-) whose influence on co-dissolved proteins has not been thoroughly studied. As electrostatic attraction between highly symmetric MA6- anions and positively charged low-symmetry globular proteins could lead to interesting self-assembly patterns we have chosen hen egg white lysozyme (HEWL), a basic stably folded globular protein as a cationic partner for mellitate anions to form such hypothetical nanostructures. Indeed, mixing of neutral HEWL and MA solutions does result in precipitation of electrostatic complexes with the stoichiometry dependent on pH. We have studied the self-assembly of HEWL-MA structures using vibrational spectroscopy (infrared absorption and Raman scattering), circular dichroism (CD), atomic force microscopy (AFM). Possible HEWL-MA6- molecular docking scenarios were analyzed using computational tools. Our results indicate that even at equimolar ratios (in respect to HEWL), MA5- and MA6- anions are capable of inducing misfolding and aggregation of the protein upon mild heating which results in non-native intermolecular beta-sheet appearing in the amide I’ region of the corresponding infrared spectra. The association process leads to aggregates with compacted morphologies entrapping mellitate anions. The capacity of extremely diluted mellitate anions (i.e. at sub-millimolar concentration range) to trigger aggregation of proteins is discussed in the context of mechanisms of misfolding.

Online quantification and compound‐specific stable isotopic analysis of black carbon in environmental matrices via liquid chromatography‐isotope ratio mass spectrometry

AbstractBlack carbon (BC) is derived from the burning of biomass, a considerable portion of organic matter across terrestrial and marine ecosystems, and a major contributor to global carbon cycles. The benzenepolycarboxylic acid method, which converts condensed aromatic BC structures to molecular markers (BPCAs), has been widely adopted for environmental BC assessments. We present a novel analytical method for the online separation, quantification, and determination of compound‐specific stable carbon isotopes of individual BPCAs via high performance liquid chromatography‐stable carbon isotope ratio mass spectrometry (HPLC‐C‐IRMS). To assess δ13C values of environmental BC, the HPLC‐C‐IRMS method was applied to a variety of samples (soil, char, aerosol, and dissolved organic matter). The method reliably measured amounts and δ13C values of benzenepentacarboxylic acid (B5CA) and mellitic acid (B6CA) over a range of 8.3–130 μmol‐C of organic matter oxidized. BPCA‐specific δ13C values deviated from bulk OC δ13C values for different sample types. However, the stable carbon isotopic composition of B5CA and B6CA was found to be generally correlated with that of bulk organic carbon. The stable isotopic compositions of environmental samples covered a wide dynamic range, indicating BC‐specific δ13C values will be useful for tracking BC sources and processing. For instance, the BPCAs derived from marine dissolved organic matter (DOM) were enriched in 13C relative to BPCAs from riverine DOM, suggesting rivers are not the only source of dissolved black carbon to the oceans.

High-κ Samarium-Based Metal-Organic Framework for Gate Dielectric Applications.

The self-assembly of a samarium-based metal-organic framework [Sm2(bhc)(H2O)6]n (1) in good yield was achieved by reacting Sm(NO3)3·6H2O with benzenehexacarboxylic acid (bhc) in a mixture of H2O-EtOH under hydrothermal conditions. A structural analysis showed that compound 1 crystallized in a space group of Pnmn and adopted a 3D structure with (4,8) connected nets. Temperature dependent dielectric measurements showed that compound 1 behaves as a high dielectric material with a high dielectric constant (κ = 45.1) at 5 kHz and 310 K, which is comparable to the values for some of the most commonly available dielectric inorganic metal oxides such as Sm2O3, Ta2O5, HfO2, and ZrO2. In addition, electrical measurements of 1 revealed an electrical conductivity of about 2.15 × 10-7 S/cm at a frequency of 5 kHz with a low leakage current (Ileakage = 8.13 × 10-12 Amm-2). Dielectric investigations of the Sm-based MOF provide an effective path for the development of high dielectric materials in the future.

The generation of benzene carboxylic acids from lignite and the change in structural characteristics of the lignite during oxidation

Production of carboxylic acids (including 12 types of benzene carboxylic acids (BCAs) and small-molecule fatty acids) from lignite via oxidation has been widely studied, but few studies addressed the relationship between distribution of BCAs and structure of lignite. This work studies alkali-oxygen oxidation of Xiaolongtan lignite and distributions of BCAs with 13C NMR as well as the relationship between the distributions of BCAs and the lignite structures. The results indicate that the dominant aromatic structures in the lignite are naphthalene and benzene with a mole ratio of around 3, and an alkyl-substituted degree of aromatic rings of 0.359. These structure characters determine that the yields of benzene tricarboxylic acids, benzene tetracarboxylic acids, benzene pentacarboxylic acid and mellitic acid are more than those of other BCAs. In the oxidation process, the organic matter of lignite is first converted to humic acids (HAs), then to water soluble acids, and last to carboxylic acids. The last conversion step is the rate-controlling step. Analyses of the residues and HAs indicate that C–O bond of lignite is easily cleaved. The aromatic structures (except condensed aromatic rings) are easily depolymerized from lignite, but the condensed aromatic rings and long alkyl chains are difficult to be oxidized. With an increase in oxidation time, in the residues, the contents of aromatic structures decrease, but the contents of condensed aromatic rings and long alkyl chains both increase. While in HAs, the contents of condensed aromatic rings increase, but the average methylene chain length (Cn) decreases.