Carboxylic Units Research Articles

Sustainable waste-treating-waste strategy: Catalytic recycling of polyethylene terephthalate over reconstructed waste catalysts

Polyethylene terephthalate (PET) is the most widely used polyester plastic, but difficulties associated with PET recycling have led to significant environmental issues. The recycling of PET waste into building monomers and valuable chemicals has attracted increasing attention. Herein, we propose a sustainable circular strategy for efficiently hydrogenolytic depolymerizing the waste PET by using reconstructed spent catalysts from the heavy oil slurry-phase hydrocracking. Two types of molybdenum sulphide/activated petroleum-based carbon compounds, a-MoSx/APC and MoS2/APC, were constructed using waste refining catalyst through the activation and annealing methods, which were used as catalysts for the hydrogenolytic depolymerisation of waste PET. Experimental results revealed that the different active components in the two reconstructed catalysts, molybdenum sulphide clusters, and few-layered molybdenum disulfide, show different activity and selectivity for the catalytic depolymerisation of PET. After the β-scission process of PET, the formed intermediate vinyl-terminated carboxylate units are converted to monoethyl terephthalate (MET) through a CC insertion pathway catalyzed by MoV, while to terephthalic acid (TPA) through a hydrogenolysis pathway catalyzed by MoIV. Therefore, MoS2/APC converts PET to TPA with a yield of 83 % within 24 hours at 270 °C under 1 atmosphere of H2 and solvent-free conditions, without generating any MET products. Moreover, this process is effective for both commercial and waste PET, and the catalyst could be reused for at least ten runs with stable activity. The sustainable waste-treating-waste strategy highlights a potential approach to the circular economy.

Regulating the Topologies and Photoresponsive Properties of Lanthanum-Organic Frameworks.

Metal-organic frameworks (MOFs) show potential application in many domains, in which photochromic MOFs (PMOFs) have received enormous attention. Researchers mainly utilize photoactive ligands to build PMOFs. Recently, the mixed electron donating and accepting ligands strategies have also been used to construct PMOFs driven by the electron transfer between nonphotochromic moieties. However, the potential interligand competition inhibits the formation of PMOFs. Therefore, the exploration of single-ligand-guided assembly is conductive for building PMOFs. Considering the existing electron accepting and donating role of pyridyl and carboxyl, the pyridinecarboxyate derived from the fusion of pyridyl and carboxyl units may serve as single ligand to yield PMOFs (Figure 1d). In this work, the coordination assembly of bipyridinedicarboxylate (2,2'-bipyridine-4,4'-dicarboxylic acid, H2bpdc; 1,10-phenanthroline-2,9-dicarboxylic acid, H2pda) and LaCl3 generate two PMOFs, [La(bpdc)(H2O)Cl] (1) and [La(pda)(H2O)2Cl]⋅2H2O (2). Both complexes feature dinuclear lanthanum as building blocks with differences in the connecting number of likers, in which 1 has (4,8)-connected topology and 2 exhibits sql topology. Their structural differences result in the diversities of photoresponsive functionalities. Compared with reported PMOFs built from photoactive ligands and mixed ligands, this study provides new available categories of single ligand for generating PMOFs and tuning the structure and photoresponsive properties via ligand substitution and external photostimulus.

Efficient removal of sulfamethazine and sulphanilamide using modified amberlite with metal organic framework based copper and cobalt

The presence of antimicrobial sulfa chemicals in water is becoming a more serious problem and action must be taken to create an effective decontamination process for wastewater treatment. In this way, current thinking has focused on removing sulfa drugs as broad-spectrum antimicrobials from water by metal organic framework ((Cu&Co)-benzenetricarboxylate, M−BTC) bound within the amberlite polymer. Here, M(Cu&Co)-BTC is synthesized and incorporated within amberlite polymer in a single step. Moreover, the adsorptive capacities of the various sulfa drugs (sulfamethazine and sulphanilamide) were investigated using M−BTC@amberlite compounds for the first time. The adsorption efficiency of the sulfa drugs was monitored (higher performance for sulfamethazine rather than sulfanilamide), and the adsorption uptake was reached 99 % within about 60 min. The adsorption isotherms were best fitted using the Langmuir and pseudo-second-order model, individually. The greatest potencies for Cu-BTC@amberlite and Co-BTC@amberlite were 205 and 306 mg/g for sulfamethazine and 326 and 488 mg/g for sulfanilamide, separately. By incorporating Co-BTC within amberlite, the absorption capacity of sulfamethazine and sulfanilamide was extended by 1.72 and 1.83 times, respectively, while incorporation of Cu-BTC within amberlite, the adsorption capacity of sulfamethazine and sulfanilamide was extended by 2.56 and 2.73 times, respectively. The attached MOFs with polymer showed very high reusability and their efficacy in uptake of sulfamethazine and sulfanilamide diminished by 14.8–15.9 % and 11.3–12.7 %, separately, after five sequential adsorption cycles. Hence, in agreement with the adsorption result, a conceivable tool is proposed. The sulfa drug adsorption performed on a range of BTC-MOFs with diverse physicochemical properties and point-by-point characterization confirmed that the highest adsorption capacity of MOFs is achieved through bi-bi interaction; H-bonding between NH sites of sulfa drug particles and O sites of carboxyl units within MOFs. In scale-up, M−BTC@amberlite has demonstrated remarkable reusability, which is enticing for potential applications in the adsorption of sulfa drugs from wastewater.

Red-emission, photobiological properties and antimicrobial photodynamic assays using mono-substituted corroles contain carboxylic acid and ester units

The mono-substituted corrole derivatives COOH-Cor and COOMe-Cor were obtained by Gryko methodology and characterized by microanaysis. In addition, we investigated experimental photophysical properties (absorption, emission by steady-state and time-resolved fluorescence) in some solvents and TDDFT calculations. Photobiological parameters such as aggregation, photostability and reactive oxygen species generation (ROS) was conducted. In addition, we also evaluated the preliminary antimicrobial photodynamic assays (aPDT) between studied corroles and bacteria strains, by white-light conditions.

Suzuki-Miyaura, Sonogashira cross-coupling and CuACC reactions suite for the access to a large macrocycle with m,m’-terphenyl motif

The access to a large semirigid macrocycle exhibiting two m,m’-terphenyl units was carried out by a suite of Suzuki-Miyaura, Sonogashira cross-coupling and CuAAC (“click”) reactions. The target macrocycle exhibits two triazole and two ester protected carboxyl units of great use for the development of further applications.

Lithium and sodium 3-(3,4-di-hydroxy-phen-yl)propenoate hydrate.

Treatment of 3-(3,4-di-hydroxy-phen-yl)propenoic acid (caffeic acid or 3,4-di-hydroxy-cinnamic acid) with the alkali hydroxides MOH (M = Li, Na) in aqueous solution led to the formation of poly[aqua-[μ-3-(3,4-di-hydroxy-phen-yl)propenoato]lithium], [Li(C9H7O4)(H2O)]n, 1, and poly[aqua-[μ-3-(3,4-di-hydroxy-phen-yl)propenoato]sodium], [Na(C9H7O4)(H2O)]n, 2. The crystal structure of 1 consists of a lithium cation that is coordinated nearly tetra-hedrally by three carboxyl-ate oxygen atoms and a water mol-ecule. The carboxyl-ate groups adopt a μ3-κ3 O:O':O' coordination mode that leads to a chain-like catenation of Li cations and carboxyl-ate units parallel to the b axis. Moreover, the lithium carboxyl-ate chains are connected by hydrogen bonds between water mol-ecules attached to lithium and catechol OH groups. The crystal structure of 2 shows a sevenfold coordination of the sodium cation by one water mol-ecule, two monodentately binding carboxyl-ate groups and four oxygen atoms from two catechol groups. The coordination polyhedra are linked by face- and edge-sharing into chains extending parallel to the b axis. The chains are inter-linked by the bridging 3-(3,4-di-hydroxy-phen-yl)propenoate units and by inter-molecular hydrogen bonds to form the tri-periodic network.

Pseudodiproline (Pro-Cyp) Oligomers Fold into Helical Polyproline Type secondary structures.

The synthesis and conformational properties of oligo-proline mimetics composed of dimeric and tetrameric Pro-Cyp constructs linked by a hydroxymethylene unit are reported. Oligomers were studied both in the solid state and in solution, unveiling right-handed helical conformation depending on the configuration of the vicinally substituted trans-cyclopentane carboxylic acid unit (Cyp). Unlike polyproline oligomers, the alternating synthetic Pro-Cyp counterparts are not stabilized by n-π* interactions but rely instead on the steric demands of the extended backbone conformation within the hydroxymethylene-linked Pro-Cyp repeating units.

Color‐Tunable Luminescence of Eu‐Doped LaF3 Particles Sensitized by d–f Energy Transfer from a Two‐Photon Absorbing Ir(III) Complex

AbstractThe surface of Eu0.3La0.7F3 submicron particles is functionalized with a blue‐emitting Ir(III) complex (1) specifically designed to coordinate lanthanide(III) ions efficiently through a carboxylic unit. In this Eu0.3La0.7F3@1 composite, the Ir(III) complexes are randomly coordinated to either superficial La(III) ions or Eu(III) ions (Ir‐Lasurface and Ir‐Eusurface pairs, respectively) and its color emission, a balance between blue (Ir‐based) and red (Eu‐based) light, can be tuned as a function of the excitation wavelength. Irradiation at the maximum of the excitation band in 1 promotes blue emission from Ir‐Lasurface pairs and red emission from Eusurface ions sensitized by Ir → Eusurface energy transfer (EnT). At λexc = 396 nm (maximum of the Eu(III) 5L6 ← 7F0 absorption band) the red emission from inner Eu(III) ions becomes dominant. Excitation of 1 can also be achieved by two photon‐absorption (TPA) since this complex has a moderate cross‐section of σ2 = 9.4 ± 1.0 GM at 780 nm (σ2 = 5.8 ± 0.6 GM at 800 nm). Phosphorescence lifetime imaging (PLIM) allows the emission of individual particles to be visualized and the Ir‐, Eusurface‐, and Eucore‐based emissions can be distinguished due to the significant differences in their respective emission lifetimes.

Carboxy-substituted D-π-A arylated chalcones: Synthesis, photophysical properties and preliminary evaluation as photosensitizers for DSSCs

Chalcones are versatile molecules with potential use in various fields and technologies. The judicious choice of chalcones’ building blocks allows the design of compounds with different properties and applications. In the present work, four highly conjugated carboxy-substituted chalcones with D-π-A architecture were synthesized aiming their evaluation as photosensitizers for dye-sensitized solar cells (DSSCs). In their architecture, electron-rich aldehydes were used as precursors of the donor units, and carboxylate or cyanoacrylate acceptor units were bonded to the acetophenone portion. The compounds presented intense UV–vis absorptions (ε in the order of 104 mol L−1 cm−1) centered between 322 and 429 nm, and blue to yellow fluorescence, with quantum yields ranging from less than 0.01 to 0.35. These chalcones were evaluated as photosensitizers for DSSCs, displaying short-circuit current density (ISC) ranging from 0.18 to 0.36 mA cm−2, open circuit voltage (Voc) from 0.52 to 0.56 V, fill factor (FF) between 54 and 67%, and power conversion efficiency from 0.05 to 0.13%. The two best performances were obtained with photosensitizers 6a and 7b which display the pairs dimethylaminophenyl/carboxylate and vanillin/cyanoacrylate as the donor and acceptor/anchoring units, respectively.

Experimental synthesis and characterization of PVA‐fumaric acid cross‐linked biodegradable films: Implications as a sustainable matrix for composites

AbstractPolyvinyl alcohol (PVA) is a widely used polymer that is biocompatible, nontoxic, and water‐soluble due to the presence of hydroxyl groups in its domain. This study aims to investigate the effects of fumaric acid (FA) cross‐linking and thermal cross‐linking (TC) on the PVA's mechanical and thermal properties. When the FA is mixed with PVA, it was found in the chemical reaction that the OH groups of PVA are condensing with the carboxylic acid units of FA to yield new ester linkages and water as a by‐product, which further results in the reduction of the water absorption capacity. Quantitatively, the addition of 8 (wt. /wt. %) FA resulted in a minimum of 65% water absorption rate, as compared with 117% for pure PVA. The mechanical and thermal properties of PVA also enhanced with the addition of 2% to 8% FA by weight. For the TC case, the % increase in ultimate tensile strength was 30.9% and 42.5% with and without TC, respectively. As the wt. % of FA increased from 2 to 10%, the % elongation value decreased for both with and without TC films relative to pure PVA. The thermogravimetric analysis revealed the change in degradation temperature of FA‐PVA blended film in comparison with pure PVA. Dynamic mechanical analysis was utilized to analyze the viscoelastic nature and temperature variation at the glass transition temperature. The current fabricated film is a potential candidate for the food packaging films application; moreover, the results reported in this investigation will accelerate the industrial applications of biodegradable PVA.Highlights Increasing the weight percentage of fumaric acid leads to an enhancement in mechanical and thermal properties of the film. Esterification is the usual reaction between fumaric acid and polyvinyl alcohol (PVA), in which ester linkages are formed when the carboxyl groups (‐COOH) of fumaric acid and the hydroxyl groups (‐OH) of PVA combine. Water absorption characteristics of the film reduces as the wt. % of fumaric acid increases. Thermal cross‐linking of the film leads to further improvements in mechanical and thermal properties. The overall effect of increasing the wt. % of fumaric acid is negative on the glass transition temperature of the film. The developed film is a potential candidate for the food packaging films application.

The impact of carboxylic acid anchoring groups on the optoelectronic and nonlinear optical properties of Ru complex dyes: A computational approach

In this study, density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were used to analyze the effects of varying the number and positions of carboxylic acid anchoring groups attached to the bpy ligand of the [Ru(bpy)2(NCS)2] complex. Also the geometric structures, absorption geometry, electronic structures, optical properties, photovoltaic parameters, and nonlinear optical (NLO) properties of the designed [Ru(bpy)2(NCS)2] derivatives were investigated and compared with each other. The results indicate that the optoelectronic properties of these ruthenium (II) complexes are influenced by the number and positioning of carboxylic acid groups on the bipyridine moiety. Calculated values of ΔGinject and ΔGreg for the studied Ru(II) complexes suggest that the energy level alignment with the semiconductor and electrolyte satisfies the criteria. Furthermore, it was observed that the number and position of the anchoring carboxylic acid units is an effective approach to improve their NLO response. Overall, the structural modifications by the anchoring carboxylic acid groups on the bpy ligand of [Ru(bpy)2(NCS)2] complexes seem to fine-tune their DSSC performance and NLO response characteristics.

Covalent Organic Frameworks: Reversible 3D Coalesce via Interlocked Skeleton-Pore Actions and Impacts on π Electronic Structures.

Covalent organic frameworks (COFs) create extended two-dimensional (2D) skeletons and aligned one-dimensional (1D) channels, constituting a class of novel π architectures with predesignable structural ordering. A distinct feature is that stacks of π building units in skeletons shape the pore walls, onto which a diversity of different units can be assembled to form various pore interfaces, opening a great potential to trigger a strong structural correlation between the skeleton and the pore. However, such a possibility has not yet been explored. Herein, we report reversible three-dimensional (3D) coalescence and interlocked actions between the skeleton and pore in COFs by controlling hydrogen-bonding networks in the pores. Introducing carboxylic acid units to the pore walls develops COFs that can confine water molecular networks, which are locked by the surface carboxylic acid units on the pore walls via multipoint, multichain, and multidirectional hydrogen-bonding interactions. As a result, the skeleton undergoes an interlocked action with pores to shrink over the x-y plane and to stack closer along the z direction upon water uptake. Remarkably, this interlocked action between the skeleton and pore is reversibly driven by water adsorption and desorption and triggers profound effects on π electronic structures and functions, including band gap, light absorption, and emission.

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part C: The Domino Diarylation and Annelation Reactions

AbstractThe efficiency of the formation of C−C bonds under palladium catalysis often depends on the nature of the carboxylate ligand and carboxylic acids or alkali metal carboxylates additives. This review which is Part C of a trilogy devoted to the topic, highlights the influence of the carboxylate units on domino diarylation and annelation reactions. The plausible reaction mechanisms are presented with, as far as possible, personal comments.

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part A: the C(sp2)−C(sp2), C(sp2)−C(sp3) and C(sp3)−C(sp3) Bonds

AbstractA variety of Pd‐catalyzed reactions are carried out with palladium carboxylates in the presence of carboxylic acids and/or alkali metal carboxylates. This review is Part A of three reviews highlighting the dependence of the efficiency of the formation of the different C−C bonds on the nature of the carboxylate unit. Part A concerns inter‐ and intramolecular reactions leading to the formation of a C(sp2)−C(sp2), C(sp2)−C(sp3) or C(sp3)−C(sp3) bond. The variety of procedures and additives is presented as well as the reaction mechanisms with, as far as possible, personal comments.

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part B: The Hydro(hetero)arylation, Hydroalkenylation and Hydroalkylation Reactions

AbstractThe efficiency of the formation of C−C bonds under palladium catalysis often depends on the nature of the carboxylate ligand and carboxylic acids or alkali metal carboxylates additives. This review which is Part B of a trilogy devoted to the topic, highlights the influence of the carboxylate unit on the hydro(hetero)arylation, hydroalkenylation and hydroalkylation reactions. The plausible reaction mechanisms are presented with, as far as possible, personal comments.

2D-3D supramolecular assemblies containing 2-amino-4,6-dimethoxypyrimidine and carboxylic acids: Preparation, crystallographic characterization, and Hirshfeld surface analysis

Eight crystals (1–8) derived from various substituted carboxylic acids of 2-pyrazinecarboxylic acid, 3,4-methylenedioxybenzoic acid, 4‑hydroxy-3-nitrobenzoic acid, 4‑chloro-2-nitrobenzoic acid, mandelic acid, 4-nitrophenylacetic acid, 3,4,5-trimethoxycinnamic acid, and itaconic acid and 2-amino-4,6-dimethoxypyrimidine (admpm) were prepared and identified, and further characterized thoroughly with single crystal X-ray diffraction (SCXRD), and elemental analysis techniques. The melting points were also measured. Significant non-covalent interactions were calculated by means of the Hirshfeld surface analysis. Among the eight crystals, proton transfer from the carboxylic acid to ring N of the pyrimidine has occurred only at 1, while the remaining ones 2–8 were co-crystals. It is obvious that the R22(8) ring motif occurs in all cases when a carboxyl unit interacts with a pyrimidine base. The present work surely indicates that there are two main associate modes between the 2-amino-4,6-dimethoxypyrimidine and the carboxylic acids, which regularly occur, linear heterotetramer (LHT), and cyclic heterotetramer (CHT). Here, LHT is dominant as it occurs in 5/8 frequency (at 3–4 and 6–8), CHT in 2/8 (at 1–2), with the remaining one structure (5) forming a heterodimer. The heterotrimer (HT) was not established in this test. Thus LHT is more stable than CHT and other synthons.

Proton conductive properties of one water-stable nickel(II) supramolecule bearing tri-pyridyl and tri-carboxylate ligand

The construction of highly stable complexes using azacyclic carboxylate ligands is an important way to obtain crystalline proton-conducting materials with high performance. In this paper, one three-dimensional supramolecule, [Ni(H2ttp)2]⋅3H2O (1) [H3ttp = 4-(2,4,6-tricarboxyphenyl)-2,2′,6,2′′-terpyridine] has been prepared according to literature approach with slight modification. Firstly, its molecular structure was determined by powder X-ray diffraction, infrared spectroscopy, and elemental analysis, followed by a thermogravimetric determination to confirm its thermal and water stability. The N2 and water H2O adsorption abilities were also measured. Electrochemical experiments have shown 1 to be a typical temperature and humidity-dependent proton conductor with an optimum proton conductivity of 4.00 × 10−4 S/cm (98% RH/100 °C). A large number of uncoordinated carboxylate units and crystalline water molecules, as well as the H-bonding networks inside the framework, provide effective channels for proton transportation. The proton-conductive mechanism was further postulated following the calculated value of activation energy.

Mechanistic Studies of Iron-PyBOX-Catalyzed Olefin Amino-Oxygenation with Functionalized Hydroxylamines.

Iron-catalyzed amino-oxygenation of olefins often uses discrete ligands to increase reactivity and broaden substrate scope. This work is focused on examining ligand effects on reactivity and in situ iron speciation in a system which utilizes a bisoxazoline ligand. Freeze-trapped 57Fe Mössbauer and EPR spectroscopies as well as SC-XRD experiments were utilized to isolate and identify the species formed during the catalytic reaction of amino-oxygenation of olefins with functionalized hydroxylamines, as well as in the precatalytic mixture of iron salt and ligand. Experiments revealed significant influence of ligand and solvent on the speciation in the precatalytic mixture which led to the formation of different species which had significant influence on the reactivity. In situ experiments showed no evidence for the formation of an Fe(IV)-nitrene intermediate, and the isolation of a reactive intermediate was unsuccessful, suggesting that the use of the PyBOX ligand led to the formation of more reactive intermediates than observed in the previously studied system, preventing direct detection of intermediate species. However, isolation of the seven coordinate Fe(III) species with three carboxylate units of the hydroxylamine and spin-trap EPR experiments suggest formation of a species with unpaired electron density on the hydroxylamine nitrogen, which is in accordance with formation of a potential iron iminyl radical species, as recently proposed in literature. An observed increase in yield when substrates devoid of C-H bonds as well as isolation of a ring-closed dead-end species with substrates containing these bonds suggests the identity of the functionalized hydroxylamine can dictate the reactivity observed in these reactions.

Modification of polyacrylonitrile (PAN) membrane with anchored long and short anionic chains for highly effective anti-fouling performance in oil/water separation

Conventional polymeric membranes are usually prone to fouling by oily substances and therefore are greatly hindered in their applications for oil/water separation. In this study, we carried out a new strategy of modifying PAN membrane for highly effective anti-oil fouling performance. The modified membrane surface was anchored with negatively charged long and short chains, where the long chains could reject oil droplets at far away from the membrane surface while the short chains near the membrane surface could increase its hydrophilicity and thus enhance the permeate flux during the filtration of oil emulsion. The negatively charged long chains were constructed with sulfonate-terminated units and the short chains with carboxylate units. The prepared PAN membranes were tested to show both superhydrophilic and underwater superoleophobic surface properties, and displayed very high resistance to the adhesion of various types of oils. In the membrane separation experiments with 1000 mg‧L-1 surfactant-stabilized oil-in-water emulsion, the developed PAN membrane exhibited an initial water flux of 115.4 L·m−2·h−1, and less than 16% of flux decay but higher than 97% in flux recovery after 3 filtration cycles (45 min each). Furthermore, in a challenging test, the membrane also showed excellent recovery in its performance after being fouled by a heavy fuel oil but cleaned simply by the action of soaking it into water. Therefore, the current study appeared to provide a new and effective alternative in the modification of conventional PAN membrane to enhance or expand its anti-oil fouling performance, especially for oil recovery or oil removal in oily wastewater treatment.

A polymeric hydrogel electrocatalyst for direct water oxidation

Metal-free electrocatalysts represent a main branch of active materials for oxygen evolution reaction (OER), but they excessively rely on functionalized conjugated carbon materials, which substantially restricts the screening of potential efficient carbonaceous electrocatalysts. Herein, we demonstrate that a mesostructured polyacrylate hydrogel can afford an unexpected and exceptional OER activity – on par with that of benchmark IrO2 catalyst in alkaline electrolyte, together with a high durability and good adaptability in various pH environments. Combined theoretical and electrokinetic studies reveal that the positively charged carbon atoms within the carboxylate units are intrinsically active toward OER, and spectroscopic operando characterizations also identify the fingerprint superoxide intermediate generated on the polymeric hydrogel backbone. This work expands the scope of metal-free materials for OER by providing a new class of polymeric hydrogel electrocatalysts with huge extension potentials.