Pendant Carboxyl Research Articles

Lewis basicity generated by localised charge imbalance in noble metal nanoparticle-embedded defective metal\u2013organic frameworks

Interactions between metal nanoparticles (NPs) and metal–organic frameworks (MOFs) in their composite forms have proven to exhibit beneficial properties, such as enhanced catalytic performance through synergistic effects. Herein, we show that Lewis basic sites can be created within an anionic defective MOF by engineering the electronic state of the pendant carboxylate groups situated at the defect sites. This is achieved from the concerted interactions between the pendant carboxylate groups, embedded Pd NPs and charge-balancing cations (Mn+ = Ce3+, Co2+, Ni2+, Cu2+, Mg2+, Li+, Na+ or K+). This work is the first example of generating a new collective property, i.e. Lewis basicity, in metal-carboxylate MOFs. Importantly, the choice of Mn+, used during cation exchange, acts as a convenient parameter to tune the Lewis basicity of the MOF-based nanocomposites. It also provides a facile way to incorporate active metal sites and basic sites within carboxylate-based MOFs to engineer multifunctional nanocatalysts.

Hybrid inorganic (nonporous silica)/organic (alginate) core-shell platform for targeting a cisplatin-based Pt(IV) anticancer prodrug

Nonporous silica nanoparticles with an external shell containing the 3‑aminopropyl arm (SiNP) were further decorated with alginic acid (SiNP-ALG) as a potential biocompatible delivery system for Pt antitumor agents. Such particles were coupled with the prodrug (OC‑6‑44)‑acetato(β‑alaninato)diamminedichloridoplatinum(IV), 1, through the formation of amide bonds between the pendant carboxylate groups on SiNP-ALG and the free amino group of the complex. Cytosol extracted from tumor cells was able to quickly and efficiently reduce the Pt(IV) prodrug, and produces the active metabolite cisplatin. SiNP-ALG-Pt conjugate was more active than both cisplatin and 1, due to its more efficient cell uptake, whereas the SiNP-ALG unplatinated nanoparticles were deprived of any nonspecific toxicity.

Comparing Morphological Evolution during Tensile Deformation of Two Precise Polyethylenes via 2D Fitting of in Situ X-ray Scattering

Some types of precise polyethylenes, or linear polyethylenes containing precisely periodic functional groups, exhibit significant strain hardening under tensile deformation. Here we perform in situ X-ray scattering during tensile deformation of two precise polyethylenes: one with pendant carboxylic acid groups every 21st carbon (p21AA) and another with pendant imidazolium bromide groups every 15th carbon (p15ImBr). p21AA exhibits significant strain hardening and its layered structure orients with the layer normal along the tensile axis, while p15ImBr does not exhibit strain hardening and its layer normal orients perpendicular to the tensile axis. Quantitative evaluation of the 2D fiber patterns shows that p21AA undergoes a morphological transition, from a semicrystalline structure to a nanofibrillar structure, while the morphology of p15ImBr reorients and the chain folding structure is preserved. This suggests that fibrillization plays an important role in the strain hardening mechanism.

Optimization and Characterization of Wheat Bran Modified by Citric Acid Using a Dry Reaction Method for Enhancement of Methylene Blue Adsorption

Abstract Wheat bran is modified thermochemically through reaction with citric acid, as carboxyl groups bearing agent, according to a dry condition method at the elevated temperature. In this study, the main objectives are optimization the factors affecting on the pendant carboxylic acid groups of wheat bran–citrate, including concentration of citric acid solution (0–1.8 M), volume of citric acid solution (5.4–16.2 g), curing temperature (0–170 °C), curing time (0–90 min.), mixing method (solution mixing vs kneading) of reactants, and the catalyst effect (0–5, sodium phosphate dibasic dodecahydrate/citric acid molar ratio). The amount of pendant carboxylic acid groups is determined by simple acid-base titration. The obtained methylene blue adsorption data is well matched with the amount of pendant carboxylic acid groups in wheat bran–citrate and this amount increase with an increase in pendant carboxylic acid groups.

Metal ions crosslinked poly (arylene ether nitrile) adsorbent for removal of rhodamine B

A novel water soluble poly (Arlene ether nitrile) (PEN) containing pendent carboxyl and sulfonic acid groups was synthesized, which displayed high reactivity to different metal ions and Rhodamine B (ChB). After a crosslinking with certain metal ions, the PEN produced obvious precipitate in aqueous solution. Moreover, the precipitate was capable to adsorb ChB and the effect of operational parameters (contact time, dye concentration, temperature and pH) on RhB removal was studied. Results showed the adsorption capacity at 25 ° C could reach up to 112.5 mg/g.

Crosslinking effect in nanocrystalline cellulose reinforced sulfonated poly(aryl ether ketone) proton exchange membranes

Two novel series of poly(aryl ether ketone)s (PAEK) bearing pendant carboxylic acid groups have been synthesized, and subsequently sulfonated to obtain sulfonated poly(aryl ether ketone)s with carboxylic acid groups (SPAEK-COOH-x). The expected structures of the sulfonated copolymers were confirmed by FTIR. Modified nanocrystalline cellulose (NCC) was prepared and introduced into the SPAEK-COOH-x as the “performance-enhancing” filler and crosslinking agent. The nanocomposite proton exchange membranes were prepared via a solution-casting procedure. The composite membranes containing NCC presented the higher proton conductivity and better mechanical properties. After further crosslinking, the covalent crosslinked composite membranes showed even better mechanical properties while the proton conductivity and thermal stability were maintained. The hydrophilic/hydrophobic domains were observed from the TEM morphology investigation of COOH-10/NCC-y and C/COOH-10/NCC-y membranes. A balance of mechanical stabilities, proton conductivity, and thermal property could be designed by the incorporation of NCC and the crosslinking between NCC and SPAEK-COOH-10 to meet the requirements for the applications in the fuel cells.

Proton-Coupled Electron Transfer Enhances the Electrocatalytic Reduction of Nitrite to NO in a Bioinspired Copper Complex

The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (among others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled electron transfer during nitrite reduction when such synthetic complexes are used. Herein, we describe the synthesis and characterization of two previously unreported Cu complexes (3 and 4) for the electrocatalytic reduction of nitrite to NO, in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed. Complex 4 bears a pendant carboxylate group in close proximity to the copper center, whi...

Nanoencapsulation of Novel Inhibitors of PNKP for Selective Sensitization to Ionizing Radiation and Irinotecan and Induction of Synthetic Lethality

There is increasing interest in developing and applying DNA repair inhibitors in cancer treatment to augment the efficacy of radiation and conventional genotoxic chemotherapy. However, targeting the inhibitor is required to avoid reducing the repair capacity of normal tissue. The aim of this study was to develop nanodelivery systems for the encapsulation of novel imidopiperidine-based inhibitors of the DNA 3'-phosphatase activity of polynucleotide kinase/phosphatase (PNKP), a DNA repair enzyme that plays a critical role in rejoining DNA single- and double-strand breaks. For this purpose, newly identified hit compounds with potent PNKP inhibitory activity, imidopiperidines A12B4C50 and A83B4C63 were encapsulated in polymeric micelles of different poly(ethylene oxide)- b-poly(ε-caprolactone) (PEO- b-PCL)-based structures. Our results showed efficient loading of A12B4C50 and A83B4C63 in PEO- b-PCLs with pendent carboxyl and benzyl carboxylate groups, respectively, and relatively slow release over 24 h. Both free and encapsulated inhibitors were able to sensitize HCT116 cells to radiation and the topoisomerase I poison, irinotecan. In addition, the encapsulated inhibitors were capable of inducing synthetic lethalilty in phosphatase and tensin homologue (PTEN)-deficient cells. We also established the validity of the peptide GE11 as a suitable ligand for active targeted delivery of nanoencapsulated drugs to colorectal cancer cells overexpressing epidermal growth factor receptor (EGFR). Our results show the potential of nanoencapsulated inhibitors of PNKP as either mono or combined therapeutic agents for colorectal cancer.

Reversible pH-Responsive Behavior of Ruthenium(II) Arene Complexes with Tethered Carboxylate.

Five complexes of formula [Ru(η6-C6H5CH2COOH)(XY)Cl]Cl/Na (XY = ethylenediamine (1), o-phenylenediamine (2), phenanthroline (3), and oxalato (4)) and [Ru(η6:κ1-C6H5CH2COO)(tmen)]Cl (tmen = N, N, N', N'-tetramethylethylenediamine, 5C) have been synthesized and fully characterized. Five new X-ray crystal structures ([Ru(η6-C6H5CH2COOH)(μ-Cl)Cl]2, 1, 3, 4, and 5C·PF6) have been determined, which are the first examples of ruthenium(II) structures with phenylacetic acid as arene ligand. Furthermore, 5C·PF6 is the first example of a five-membered tether ring with a Ru(η6:κ1-arene:O) bond. The tether ring in these complexes opens in acidic pH (<5) and closes reversibly in aqueous solution. The chlorido open-form undergoes aquation, and the aqua adduct can be observed (prior to ring closure) by NMR. The speciation has an attractive complexity in the pH range 0-12, showing interconversion of the three species (chlorido, aqua, and closed tether), dependent on the proton concentration and the nature of the XY chelating ligand. The closed tether version of 3, complex 3C, with σ-donor/π-acceptor phenanthroline as chelating ligand, opens up more readily (pH 4), while the tether ring in complex 5C hardly opens even at pH as low as 1. We have determined the p Ka of the pendant carboxylic group and that of the aqua adduct (ca. 3 and ca. 7, respectively), which can be finely tuned by the appropriate choice of XY. Complexes 1 and 2, which predominate in their inactive (closed-tether) form in intracellular conditions, show some cytotoxic activity (IC50 130 and 117 μM, respectively) in A2780 ovarian cancer cells. Complex 1 catalyzes the reduction through transfer hydrogenation of pyruvate to lactate and NAD+ to NADH in the presence of formate as H-source. Co-incubation with sodium formate decreases the IC50 value of 1 in A2780 cancer cells significantly.

Synthesis of hydroxyl-terminated polybutadiene bearing pendant carboxyl groups by combination of anionic polymerization and blue light photocatalytic thiol-ene reaction and its pH-triggered self-assemble behavior

Polybutadiene with the simultaneous presence of hydroxyl end-groups and pendant carboxyl side groups was successfully synthesized by combination of living anionic polymerization and blue light photocatalytic thiol-ene “click” reaction. Firstly, hydroxyl-terminated polybutadiene (HTPB) with high content of 1,4-butadiene unit was synthesized by living anionic polymerization using hydroxy-protected initiator, and followed by de-protection. Then, double bonds in backbone of HTPB were modified into pendant carboxyl side groups by blue light photocatalytic thiol-ene “click” reaction using Ru(bpy)3Cl2 and p-toluidine as photoredox catalysts. The blue light photocatalytic thiol-ene reaction exhibit high-efficiency, and all the unsaturated bonds were modified after reacting for 5 h, in spite of that in-chain double bonds in 1,4-butadiene units are much less reactive than vinyl groups in 1,2-butadiene units. When all the double bonds were modified, the structure of resulting polymer can be deemed as carboxyl functionalized hydroxyl-terminated polyethylene. Furthermore, the solution properties of resulting polymer have been investigated by various technologies. The results showed carboxyl functionalized hydroxyl-terminated polyethylene experience a dissolution-assembly-aggregation transition process with pH value of solution decreased from 12.0 to 2.0. The mechanism of this pH-triggered phase transition behavior was supposed to depend on the ionization of carboxyl side groups at varying pH values.

Fe3+ mediated self-assembling of polyarylene ether nitrile block copolymer into cationic dye adsorptive sub-micrometer spheres

Polymeric adsorbents normally need to be chemically crosslinked to be effective in aggressive scenarios, which thus triggers the non-recyclable concern of crosslinked plastics. In this study, we firstly synthesized a novel thermoplastic polyarylene ether nitrile (PEN) block copolymer containing pendant carboxyl and sulfonate groups, which were employed to prepare the sub-micrometer PEN spheres with rough surface and porous morphology via a Fe3+ mediated emulsion self-assembling protocol. Furthermore, the obtained PEN microspheres (MS) demonstrated a maximum adsorption capacity of 738 mg/g towards methylene blue (MB), and more than 90% of MB can be removed at 90 °C for 5 min.

Synthesis and Metal‐Complexation Ability of Cross‐Linking Materials Containing Noria‐Templated Cavities with Pendant Carboxylic Acid Groups

AbstractWe synthesized noria‐containing cross‐linking materials, Cross(Noria‐MA‐co‐DM[n]m), by radical polymerization of a noria derivative with pendant methacryloyl groups (noria‐MA) and α, ω‐alkanedimethacrylamides (DM[n], n=3, 6, 12) at feed ratios of noria‐MA/DM[n]=1/2.4, 1/12, and 1/24 (m=2.4, 12. and 24). Alkaline hydrolysis reaction of Cross(Noria‐MA‐co‐DM[n]m) removed the noria moieties to give corresponding cross‐linking materials, Cross‐COOH‐DM[n]m, containing noria‐templated fixed cavities with pendant carboxylic acid groups. Among the noria‐containing cross‐linking materials, Cross(Noria‐MA‐co‐DM[6]24) showed the greatest extent of removal of noria upon hydrolysis. Nitrogen and carbon dioxide absorption studies indicated that Cross(Noria‐MA‐co‐DM[6]24) contains fixed cavities, whereas Cross‐COOH‐DM[6]24 does not in the solid (unswollen) state. Examination of the inclusion‐complex‐forming ability of the synthesized cross‐linking materials using aqueous solutions of metal ions revealed that Cross‐COOH‐DM[6]24 has the greatest absorption capacity. These results indicate that Cross‐COOH‐DM[6]24 indeed contains noria‐templated cavities that can accommodate metal ions in aqueous solution.

A new copper(II) supramolecular coordination polymer and a dinuclear compound with multifunctional 2-amino-5-sulfobenzoic acid and flexible N-donor ligands: synthesis, structure and characterization.

Multifunctional 2-amino-5-sulfobenzoic acid (H2afsb) can exhibit a variety of roles during the construction of supramolecular coordination polymers. The pendant carboxylic acid, sulfonic acid and amino groups could not only play a role in directing bonding but could also have the potential to act as hydrogen-bond donors and acceptors, resulting in extended high-dimensional supramolecular networks. Two new CuII coordination compounds, namely catena-poly[[[diaquacopper(II)]-μ-1,6-bis(1H-1,2,4-triazol-1-yl)hexane-κ2N4:N4'] bis(3-amino-4-carboxybenzenesulfonate) dihydrate], {[Cu(C10H16N6)2(H2O)2](C7H6NO5S)2·2H2O}n or {[Cu(bth)2(H2O)2](Hafsb)2·2H2O}n, (1), and bis(μ-2-amino-5-sulfonatobenzoato-κ2O1:O1')bis{μ-1,2-bis[(1H-imidazol-1-yl)methyl]benzene-κ2N3:N3'}bis[aquacopper(II)] trihydrate, [Cu2(C7H5NO5S)2(C14H14N4)2(H2O)2]·3H2O or [Cu2(afsb)2(obix)2(H2O)2]·3H2O, (2), have been obtained through the assembly between H2afsb and the CuII ion in the presence of the flexible N-donor ligands 1,6-bis(1H-1,2,4-triazol-1-yl)hexane (bth) and 1,2-bis[(1H-1,2,4-triazol-1-yl)methyl]benzene (obix), respectively. Compound (1) consists of a cationic coordination polymeric chain and 3-amino-4-carboxybenzenesulfonate (Hafsb-) anions. Compound (2) exhibits an asymmetric dinuclear structure. There are hydrogen-bonded networks within the lattices of (1) and (2). Interestingly, both (1) and (2) exhibit reversible dehydration-rehydration behaviour.

Crosslinked poly(ether ether ketone): cost-effective proton exchange membranes for fuel cell application

Sulphonated poly(ether ether ketone) copolymers bearing pendant carboxylic acid (SPEEK-C) have been synthesized via nucleophilic condensation reaction of 4,4\(^\prime \)-difluorobenzophenone, sulphonated 4,4\(^\prime \)-difluorobenzophenone and 3,5-dihydroxy benzoic acid. The structure of the sulphonated copolymer was identified from FT-IR and \(^{1}\)H-NMR spectrum. The pendant carboxylic groups of SPEEK-C were further crosslinked with poly(vinyl alcohol) (PVA) to fabricate the crosslinked (SPEEK/PVA) membranes. The performance of the membranes was evaluated in terms of water uptake, proton conductivity and oxidative stability. The thermal stabilities of the membranes were determined by thermogravimetric analysis and differential scanning calorimetry techniques, whereas the morphological analysis was performed by atomic force microscopy.

Non‐catalytic, solvent‐free synthesis of poly(tartronic‐co‐glycolic acid) as a versatile coating for different surfaces

AbstractThe synthesis of poly(tartronic‐co‐glycolic acid) from tartronic acid is achieved by a simple thermal polycondensation method. This novel polyester was characterized by NMR and Fourier transform infrared spectroscopy as well as by high‐resolution electrospray ionization mass spectrometry. It contains pendent carboxyl groups at the tartronic acid units which therefore render it a more hydrophilic and more versatile analogue of poly(glycolic acid) combining the known biodegradability with the functionality of the pendent carboxyl groups. Thus, it is of interest for application in the synthesis of drug‐carrying biodegradable matrices. The copolymer was further used for coating different surfaces of magnetic nanoparticles such as magnetite, silica, titanium dioxide and exploited as a platform for further functionalization. © 2017 Society of Chemical Industry

Multifunctional PEG-carboxylate copolymer coated superparamagnetic iron oxide nanoparticles for biomedical application

Biocompatible magnetite nanoparticles (MNPs) were prepared by post-coating the magnetic nanocores with a synthetic polymer designed specifically to shield the particles from non-specific interaction with cells. Poly(ethylene glycol) methyl ether methacrylate (PEGMA) macromonomers and acrylic acid (AA) small molecular monomers were chemically coupled by quasi-living atom transfer radical polymerization (ATRP) to a comb-like copolymer, P(PEGMA-co-AA) designated here as P(PEGMA-AA). The polymer contains pendant carboxylate moieties near the backbone and PEG side chains. It is able to bind spontaneously to MNPs; stabilize the particles electrostatically via the carboxylate moieties and sterically via the PEG moieties; provide high protein repellency via the structured PEG layer; and anchor bioactive proteins via peptide bond formation with the free carboxylate groups. The presence of the P(PEGMA-AA) coating was verified in XPS experiments. The electrosteric (i.e., combined electrostatic and steric) stabilization is efficient down to pH 4 (at 10 mM ionic strength). Static magnetization and AC susceptibility measurements showed that the P(PEGMA-AA)@MNPs are superparamagnetic with a saturation magnetization value of 55 emu/g and that both single core nanoparticles and multicore structures are present in the samples. The multicore components make our product well suited for magnetic hyperthermia applications (SAR values up to 17.44 W/g). In vitro biocompatibility, cell internalization, and magnetic hyperthermia studies demonstrate the excellent theranostic potential of our product.

Biocompatible poly(ether-ether-ketone)/Ag-zeolite L composite films with antimicrobial properties

Aromatic poly(ether-ether-ketone)s (PEEKs) have received much attention to be used in biomedical field, due to their good physicochemical properties, processability and biocompatibility. Metal-exchanged zeolites have demonstrated to be good biomaterials in various applications, because of their low-toxicity, functional groups for grafting and high dispersibility. In this study, new materials based on silver-containing zeolite L (Ag-ZL) and a PEEK containing phthalide units and pendant carboxylic groups were prepared. The films were characterized by FTIR spectroscopy, scanning electron microscopy and humidity absorption measurements. Their antimicrobial activity and cytotoxicity were investigated. The films having 12% Ag-ZL showed antimicrobial activity against Gram positive bacteria (Staphylococcus aureus 25923 ATCC and Staphylococcus aureus MRSA 43300 ATCC) and Gram negative bacteria (Escherichia coli 25922 ATCC) while those having 2% Ag-ZL were active only towards Gram positive bacteria. All the samples exhibited reduced cytotoxicity being thus potential candidates for biomedical applications.

Design of the phthalonitrile‐based composite laminates by improving the interfacial compatibility and their enhanced properties

ABSTRACTPhthalonitrile containing benzoxazine (BA‐ph) and cyanate ester (CE) were chosen as the thermosetting matrix and the glass fiber (GF) reinforced laminates formed at low temperature were designed. The polyarylene ether nitriles containing pendent carboxyl groups (CPEN) was selected to modify the interfacial interaction between the resin matrix and GFs. Two methods of introducing CPEN were compared and the effects of CPEN on curing behaviors and properties of the composites were investigated. Results showed that with the CPEN, exothermic peaks shifted to lower temperature and curing temperatures of BA‐ph/CE decreased slightly. The mechanical and thermal properties of GF‐reinforced composites were discussed and the results indicated that the composites of modified GFs with CPEN exhibited outstanding mechanical properties, higher glass transition temperature (Tg &gt; 290 °C) than that of composites composed of CPEN mixed with BA‐ph/CE. Moreover, GF‐reinforced composites showed stable dielectric constants (3.8–4.5) and low dielectric loss (0.005–0.01), which were independent of the frequency. In sum, the various methods of the introduction of CPEN in the GF‐reinforced composites may provide a new route to prepare improved composites, meanwhile, composites with outstanding processability and excellent mechanical and thermal properties are expected to be widely applied in the fields of high‐performance structural materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45881.

Protonation of carboxyl groups in EuDOTA-tetraamide complexes results in catalytic prototropic exchange and quenching of the CEST signal.

The CEST properties of EuDOTA-tetraamide complexes bearing pendant carboxylate and carboxyl ethyl esters were measured as a function of pH. The CEST signal from the Eu3+-bound water molecule decreased in intensity between pH 8.5 and 4.5 while the proton exchange rates (kex) increased over this same pH range. In comparison, the CEST signal in the corresponding carboxyl ester derivatives was nearly constant. Both observations are consistent with stepwise protonation of the four carboxylic acid groups over this same pH range. This indicates that negative charges on the carboxyl groups above pH 6 facilitate the formation of a strong hydrogen-bonding network in the coordination second sphere above the single Eu3+-bound water molecule, thereby decreasing prototropic exchange of protons on the bound water molecule with bulk water protons. The percentage of square antiprismatic versus twisted square antiprism coordination isomers also decreased as the appended carboxylic acid groups were positioned further away from the amide. The net effect of lowering the pH was an overall increase in kex and a quenching of the CEST signal.This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.

Thermally stable helical poly(4-carboxyphenyl isocyanide) with a helicity memory assisted by metal coordination

A versatile method for stabilizing an excess-handed helical polyisocyanide induced and memorized in the polymer backbone has been developed using divalent and trivalent metal ions that can coordinate to the pendant carboxylate residues in the polyisocyanide, thereby forming a noncovalently cross-linked network through intra- and/or intermolecular coordination. Among the metal ions investigated, the lanthanide ions were proved to be the most efficient and remarkably improved the thermal stability of the helical polyisocyanide in solution as well as in a gel.