Pendant Carboxylic Acid Groups Research Articles

Enhanced both water flux and salt rejection of reverse osmosis membrane through combining isophthaloyl dichloride with biphenyl tetraacyl chloride as organic phase monomer for seawater desalination

The mixed organic monomers of isophthaloyl dichloride (IPC) and 3,3′,5,5′-biphenyl tetraacyl chloride (BTEC) were used to prepare polyamide thin film composite (PA TFC) membranes for seawater desalination. IPC and BTEC act as a linear monomer and a cross-linking agent, respectively. As a result, the ratio of linear portion to cross-linking portion of polyamide film can be controlled by adjusting the fraction of monomer. It was found that the chemical composition, chain segment relaxation property, and the surface morphology of polyamide films changed significantly with the ratio of IPC to BTEC increasing. The rougher surface is formed while less pendant carboxylic acid groups present at higher IPC concentrations or lower BTEC concentrations. As the fraction of IPC increases, the length of linear segment between two cross linking point is increased, hence the enlarged polyamide network pore is formed. When IPC weight percentage increases from 0% to 70%, the water flux of the TFC membrane increases from 30 to 43.7L/m2h and the salt rejection increases from 99.3% to 99.7% at 5.5MPa, 32800ppm NaCl, 25±3°C testing condition. We demonstrated that both water flux and salt rejection of the polyamide membrane can be improved by the control of ratio of IPC to BTEC.

Functionalization of emissive conjugated polymer nanoparticles by coprecipitation: consequences for particle photophysics and colloidal properties

The functionalization of polyfluorene (PFO) nanoparticles by coprecipitation of the conjugated polymer with an amphiphilic comb polymer, consisting of a hydrophobic polystyrene backbone with hydrophilic, carboxylic acid-terminated polyethylene oxide side-chains (PS-PEG-COOH), is investigated. The comb polymer affects the properties of the formed hybrid nanoparticles. Non-functionalized particles are typically larger (28 nm) than functionalized ones (20 nm); peak molar extinction coefficients are found to differ in a similar trend. Zeta potentials are negative, consistent with negative surface charge on PFO particles due to chemical defect formation, with additional charge on functionalized particles due to the pendant carboxylic acid groups. Emission quantum yields of functionalized particles are typically larger, consistent with lower efficiency of energy transfer to quenchers in smaller particles and weaker PFO interchain interactions due to chain dilution. The trend in per-particle fluorescence brightness values, as confirmed by single particle fluorescence imaging, reflects the nanoparticle extinction coefficients. Photostability studies on aqueous dispersions of hybrid particles indicate mild photobrightening under continuous illumination while PFO particles exhibit slow exponential emission decay. Functionalized particles are also resistant to aggregation during exposure to adenocarcinoma cells. Generally, the hybrid particles exhibit more favorable time-, pH- and medium-dependent stabilities, likely due to steric and electrostatic stabilization by PEG-carboxylic acid functionalities. Overall, the functionalized particles exhibit attractive properties: Reasonably small size, tight size distribution, high absorption cross section, radiative rate and emission quantum yield, excellent brightness and photostability, and good colloidal stability.

PEG–PLGA copolymers bearing carboxylated side chains: Novel hydrogels with enhanced crosslinking via ionic interactions

ABSTRACTNovel water‐soluble amphiphilic block copolymers with pendant carboxylic acid groups are synthesized and used for the preparation of ionically crosslinked hydrogels. d,l‐Lactide (DLLA) and l−3‐(2‐benzyloxycarbonyl)ethyl‐1,4‐dioxane‐2,5‐dione (BED) are copolymerized at different ratios via organo‐catalyzed ring‐opening polymerization using a hydroxyl‐terminated poly(ethylene glycol) (PEG–OH) macroinitiator. Dynamic light‐scattering experiments show that, at low concentrations, aqueous solutions of these PEG‐P(BED‐DLLA) copolymers form micelles and aggregates. At higher concentrations, thermo‐sensitive gels are obtained, exhibiting a reversible gel‐to‐sol transition upon a temperature increase. Ionic interactions between the COOH groups and metal ions (Cu2+ or Ca2+) are shown to significantly shift the gel–sol transition to higher temperatures. Thus, the introduction of COOH groups significantly enhances the water solubility of the amphiphilic PEG–polyester copolymer and allows additional crosslinking interactions to form functionalized hydrogels with improved physical properties, making this new class of hydrogels interesting for various applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1222–1227

Covalent drug immobilization in poly(ester amide) nanoparticles for controlled release

AbstractThe use of polymeric nanoparticles to encapsulate and deliver drug molecules is a promising approach for improving drug properties such as water dispersibility, pharmacokinetics, and selectivity for the in vivo target. Described here is the development of poly(ester amide) (PEA) nanoparticles prepared from PEAs with pendant functional groups that allow for covalent conjugation of the drugs in order to mitigate the undesirable burst release of drug, commonly observed for nanoparticle‐based drug delivery systems. Parameters including the surfactant and PEA concentration in an emulsification‐evaporation procedure were studied in order to determine conditions for preparing particles with diameters < 200 nm. A hydroxyl‐functionalized rhodamine derivative, as a model drug, was then conjugated to a PEA having pendant carboxylic acid groups to afford a PEA‐rhodamine conjugate with the dye covalently attached by ester linkages. The emulsification‐evaporation procedure was used to prepare nanoparticles from this conjugate and these particles were found to release the dye much more slowly and without a burst effect, in comparison with analogous nanoparticles having the rhodamine physically encapsulated. The same approach was applied to the anti‐cancer drug floxuridine and the resulting nanoparticles also afforded sustained drug release. This work suggests the promise of PEAs with pendant functional groups for providing nanoparticle‐based drug delivery vehicles with slow and sustained drug release.

Preparation and Characterization of Succinyl‐Chitosan Nanoparticles for Drug Delivery

SummarySuccinyl‐Chitosan (SCS), a water soluble CS derivative, exhibits biocompatibility, low toxicity and long‐term retention in the body. SCS offers unique characteristics as polymer for obtaining drug delivery nanosystems, due to its many reactive amino, hydroxyl, and carboxylic acid pendant groups. Chemical modifications of SCS with antibodies and other active species are easily achieved through bonding with these groups, allowing targeting and detection. In this work, SCS was obtained by amidation of primary amine groups of CS with succinic anhydride. The succinylation degree, determined by 1H‐NMR, was 28%. Evaluation by zeta potential measurements of SCS showed a pH‐dependent charge profile, which can be conveniently exploited to prepare pH‐sensitive nanoparticles. Colloidal stable SCS/CS and SCS nanoparticles, useful in drug delivery, were prepared by ionic crosslinking from mixtures of CS and SCS in different weight percentages. Nanoparticles with sizes between 140–250 nm (after purification process) are obtained, which through further surface functionalization are suitable for application in drug delivery. The colloidal stability of the particles in water was studied by particle size measurements during 30 days and aggregation or formation of larger particles was not observed.

High surface area porous carbon for ultracapacitor application by pyrolysis of polystyrene containing pendant carboxylic acid groups prepared via click chemistry

Strategic designing and synthesis of polystyrene derivative is performed via click chemistry to achieve micro/meso-porous conducting carbon with high surface area (1860m2g−1) by controlled pyrolysis. The design is done with the objective to get graphene-like framework (by polystyrene backbone), nitrogen doping (by triazole ring) and high porosity (salt of carboxylic acid). Potassium hydroxide is reacted with the carboxylic acid groups of the polymer to achieve uniform in situ molecular activation. The obtained hierarchically porous carbon is characterized and studied for the electric double layer capacitor in organic electrolyte as well as lithium ion hybrid electrochemical capacitor (Li-HEC) performance. A specific capacitance of 137.8Fg−1 is obtained for the applied current density of 0.5Ag−1 using tetraethyl ammonium tetrafluoroborate in propylene carbonate as an electrolyte, in the potential range of 0–2.7V. The Li-HEC cell is found to deliver the maximum energy and power densities of 61Whkg−1 and 10,015Wkg−1, respectively, with ∼70% capacitance retention after 2000 charge–discharge cycles at the current density of 2Ag−1.

Regio- and Diastereoselective Synthesis of Highly Substituted, Oxygenated Piperidines from Tetrahydropyridines.

Diastereoselective epoxidation and regioselective ring-opening methods were developed for the synthesis of densely substituted, oxygenated piperidines from two classes of tetrahydropyridines with distinct stereochemical displays of functionalities. A new and practical in situ prepared epoxidation reagent was developed for the diastereoselective epoxidation of one class of sterically hindered tetrahydropyridines. The novel bifunctional epoxidation reagent, 2-carboperoxy-3,4,5,6-tetrafluorobenzoic acid, was designed to incorporate highly reactive percarboxy acid and pendant carboxylic acid groups, which through hydrogen bonding to the amino group successfully overrode steric effects and directed epoxidation to occur at the more hindered face of the tetrahydropyridine. Nucleophilic ring-opening of the epoxides with water, alcohols, and HF proceeded with high regioselectivity, affording piperidinol products with adjacent tetrasubstituted carbons.

Synthesis and investigation of novel spiro-isoxazolines as anti-cancer agents

A series of structurally diverse 4-bromo spiro-isoxazolines possessing a variety of aromatic and aliphatic substituents at the 3 position, were synthesized through a 1,3-dipolar cycloaddition followed by intramolecular cyclization of a pendant hydroxyl or carboxylic acid group. The biochemical antiproliferative activity was evaluated in vitro by using two breast cancer cell lines (MCF-7 and MDA-MB-231) and two prostate cancer cell lines (PC-3 and DU-145) using the MTT viability assay, and the IC50 values were obtained. Spiro-isoxazoline derivatives bearing a p-chloro or an o-dichloro aromatic substituent at the 3-position of the isoxazoline showed considerable antitumor activities in all four cell lines with IC50 values ranging from 43μM to 56μM.

Synthesis, characterization and dielectric properties of sulfonated poly(1,3,4-oxadiazole-ether) sulfone copolymer with functional pendant carboxylic acid groups

This work reports the synthesis and electrical characterization of sulfonated copolymer with flexible carboxylic acid pendants with 1,3,4-oxadiazole unit in the main polymer structure contrived successfully via nucleophilic displacement polycondensation among 2,5-Bis(4-fluorophenyl)-1,3,4-oxadiazole (BFPOx), 4,4′-Bis(4-hydroxyphenyl) valeric acid (BPV) and Disodium-3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (S-DCDPS). The molecular structural characterization of the copolymer was achieved by NMR spectroscopic studies, TGA was performed to verify the thermal stability, dielectric studies were executed by compressing the copolymer sample in to tablets and results were discussed.

Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands.

A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(ĈN)] (ĈN is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center.

The influence of pressure on the structure of a 2D uranium(VI) carboxyphosphonoate compound

We report the first quantitative analysis of the structural evolution of a uranyl bearing coordination polymer in response to pressure. The material that is central to this study, (UO2)(O3PCH2CO2H) (1), is constructed from rigid 2D inorganic layers comprising edge sharing UO7 pentagonal bipyramids cross-linked by [PO3(COOH)]2− anions. Strong hydrogen bonding interactions exist between the pendent carboxylic acid groups on adjacent layers. Under pressure, 1 exhibits compressional behaviour primarily in the direction perpendicular to the inorganic layers, which is aided by a reduction in the interlayer distance and shifting of the layers with respect to each other. The bulk modulus for the 2D compound 1 is unexpectedly high [18.1(1)GPa] and is within the range reported for 3D CPs assembled from ZnII cations and inflexible imidazolate anions, and is at the lower end of the range of moduli observed for aluminosilicate zeolites (19–59GPa).

Biomimetic l-aspartic acid-derived functional poly(ester amide)s for vascular tissue engineering

Functionalization of polymeric biomaterials permits the conjugation of cell signaling molecules capable of directing cell function. In this study, l-phenylalanine and l-aspartic acid were used to synthesize poly(ester amide)s (PEAs) with pendant carboxylic acid groups through an interfacial polycondensation approach. Human coronary artery smooth muscle cell (HCASMC) attachment, spreading and proliferation was observed on all PEA films. Vinculin expression at the cell periphery suggested that HCASMCs formed focal adhesions on the functional PEAs, while the absence of smooth muscle α-actin (SMαA) expression implied the cells adopted a proliferative phenotype. The PEAs were also electrospun to yield nanoscale three-dimensional (3-D) scaffolds with average fiber diameters ranging from 130 to 294nm. Immunoblotting studies suggested a potential increase in SMαA and calponin expression from HCASMCs cultured on 3-D fibrous scaffolds when compared to 2-D films. X-ray photoelectron spectroscopy and immunofluorescence demonstrated the conjugation of transforming growth factor-β1 to the surface of the functional PEA through the pendant carboxylic acid groups. Taken together, this study demonstrates that PEAs containing aspartic acid are viable biomaterials for further investigation in vascular tissue engineering.

Assembling chiral salan–copper(II) complexes into a 2D-network with carboxylic acid functionalization

In this work, we aim to assemble a polymeric copper(II) network by ligand modifications with carboxylic acid functional groups. A chiral, reduced salen ligand, salan R,R-H21 with pendant ester functionalities has been synthesized. Its copper(II) complex, [Cu(R,R-1)], has been isolated, and its crystal structure determined by X-ray crystallography. Hydrolysing the ester groups of R,R-H21 to carboxylic acids yields R,R-H42 as the hydrochloride salt R,R-H42·2HCl. Treatment of R,R-H42·2HCl with copper(II) acetate in the presence of triethylamine yields the complex [Cu(R,R-H22)]n and X-ray structural analysis reveals that this consists of a 2D polymeric network. Each copper(II) center is bound within the near square-planar N2O2 donor set of the Schiff base ligand [R,R-H22]2− and pendant carboxylic acid groups of adjacent units coordinate through the CO2H carbonyl units in the axial sites of the copper ion to complete an axially distorted octahedral coordination environment. The sheets are stacked via interdigitation of the cyclohexyl domains, giving an overall porous assembly containing carboxylic acid functionalities. This has proven to be an effective strategy for adding the dimensionality of metal–organic complexes by carboxylic acid functionalization of ligands.

The effects of molecular structure on sol-to-gel transition of biodegradable poly(depsipeptide-co-lactide)-g-PEG copolymers

We report on the effects of number and length of PEG chains in poly(depsipeptide-co-dl-lactide)-g-poly(ethylene glycol) (P(DG-dl-LA)-g-PEG) copolymers on their sol-to-gel transition behavior. The graft-type copolymer is suitable for the systematic study of the effects of molecular structure and hydrophilic/hydrophobic balance on its sol-to-gel transition. We prepared various P(DG-dl-LA)-g-PEG copolymers through coupling reactions between the pendant carboxylic acid groups of P(GD-dl-LA) and the end hydroxyl group of MeO-PEG having various molecular weights. Temperature-responsive sol-to-gel transition of the obtained copolymer solution in phosphate-buffered solution (pH 7.4, ionic strength = 0.14) was investigated by the test tube inverting method and rheological measurements. P(GD-dl-LA)-g-PEG copolymer prepared from higher molecular weight PEG showed higher sol-to-gel transition temperatures compared with the copolymers prepared from lower molecular weight PEG, although these copolymers have similar weight content of PEG (23–24 wt.%). Similar trends were observed for groups of copolymers whose PEG contents were 27 or 30 wt.%. These results are informative for providing strategies on rational design of thermo-gelling polymers.

Poly(ethylene oxide)‐graft‐methotrexate Macromolecular Drugs Conjugating via Aminopteridine Ring Exhibit Potent Anticancer Activity

AbstractWater soluble poly(ethylene oxide)‐graft‐methotrexate (PEO‐g‐MTX) conjugates with a robust amide linkage via the amine or carboxylic acid groups of MTX were designed, prepared and investigated for in vitro anti‐tumor effects. MTX was conjugated to multi‐functional PEO containing multiple pendant carboxylic acid (PEO‐g‐COOH) or amine groups (PEO‐g‐NH2) via the carbodiimide chemistry, which afforded PEO‐g‐MTX conjugates with an amide bond to the aminopteridine ring or carboxylic acid groups of MTX (denoted as PEO‐g‐MTX(COOH) and PEO‐g‐MTX(NH2), respectively). Dynamic light scattering (DLS) revealed that all PEO‐g‐MTX conjugates, with MTX contents varying from 4.8 to 19.6 wt%, existed as unimers in phosphate buffer (PB, pH 7.4, 20 mmol·L−1). Interestingly, MTT assays showed that PEO‐g‐MTX(COOH) exhibited potent anti‐tumor activity in HeLa, A549, KB and NIH3T3 cells with cytotoxicity profiles comparable to that of free MTX. In contrast, PEO‐g‐MTX(NH2) revealed diminishing cytostatic effect with IC50 (half maximal inhibitory concentration) ten to hundred times higher than that of PEO‐g‐MTX(COOH). Moreover, PEO‐g‐MTX(COOH) conjugates allowed facile conjugation with targeting ligands. Notably, folate‐decorated PEO‐g‐MTX(COOH) macromolecular drugs showed apparent targetability to folate receptor‐overexpressing KB cells with an IC50 over 12‐fold lower than non‐targeting PEO‐g‐MTX(COOH) control and about 2‐fold lower than free MTX under otherwise the same conditions.

Synthesis and radiopharmacological evaluation of 64Cu-labeled bombesin analogs featuring a bis(2-pyridylmethyl)-1,4,7-triazacyclononane chelator

The bifunctional chelating agent 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid, DMPTACN-COOH, has been found to bind strongly to copper(II), resulting in a radiocopper(II)-ligand complex that exhibits high in vivo stability. The pendant carboxylic acid group enables this derivative to be conjugated to the N-terminal amino acid residues of peptides. Exploiting this, two stabilized bombesin (BBN) derivatives, βAla-βAla-[Cha13,Nle14]BBN(7–14) and βhomo-Glu-βAla-βAla-[Cha13,Nle14]BBN(7–14) have been coupled to DMPTACN-COOH and radiolabeled with the positron emitter copper-64 (64Cu-1 and 64Cu-3). The in vitro binding characteristics of the [64Cu]Cu-labeled bombesin conjugates in gastrin-releasing peptide receptor (GRPR) over-expressing prostate cancer (PC-3) cells have been evaluated. Biodistribution studies performed in Wistar rats indicate a specific uptake in the GRPR-rich pancreas and rapid renal elimination for both 64Cu-1 and 64Cu-3. Small animal PET imaging studies performed in NMRI nu/nu mice bearing the human prostate tumor PC-3 demonstrated a very high degree of tumor accumulation for 64Cu-1 and 64Cu-3. Incorporation of a single additional glutamic acid residue within the spacer between bombesin and the radiolabeled complex (64Cu-3) leads to a higher tumor-to-muscle uptake ratio (amounting to >30 at 100 min post injection) compared to 64Cu-1.

Acid pH-activated glycol chitosan/fullerene nanogels for efficient tumor therapy

Glycol chitosan (GC) grafted with 2,3-dimethylmaleic acid (DMA) and fullerene (C60) conjugates (GC-g-DMA-g-C60) were developed for use in a photosensitizer prodrug. GC-g-DMA-g-C60 was prepared via the simple two-step chemical grafting reactions of (i) DMA to free amine groups of GC and (ii) hydroxyl groups of GC-g-DMA to ππ carbon bonds of C60. This conjugate was self-assembled to form polysaccharidic nanogels consisting of a hydrophilic block (GC and DMA) and a hydrophobic block (C60). Here, GC-g-DMA-g-C60 nanogels also formed multi-nanogel aggregates due to the electrostatic interaction between the pendant carboxylic acid group (due to the DMA) and residual free amine group of GC at pH 7.4. Interestingly, the nanogel aggregates can be disintegrated at pH 5.0 due to the reduction of electrostatic interaction resulting from the cleavage of the DMA blocks at pH 5.0. Upon 670nm light illumination, photo-responsive properties of the nanogel aggregates allowed different singlet oxygen generation according to the pH condition: the reduced singlet oxygen generation (due to increased photo-interference effect between C60 molecules close-packed in nanogel aggregates) at pH 7.4, but the elevated singlet oxygen generation (due to the disintegration of nanogel aggregates) at pH 5.0. GC-g-DMA-g-C60 nanogel aggregates responds to pH 5.0 (∼endosomal pH) can be a good candidate for endosomal pH targeting and in vivo photodynamic therapy in various malignant tumor cells.

Sulfonated poly(ether ether ketone) membranes containing pendent carboxylic acid groups and their application in vanadium flow battery

Sulfonated poly(ether ether ketone) (C-SPEEK) membranes with pendent carboxylic acid groups are prepared and first investigated for vanadium flow battery (VFB) application. The introduction of carboxylic acid groups can effectively improve the ion conductivities of C-SPEEK membranes, while, keep their ion selectivities. The prepared C-SPEEK membranes exhibit excellent performance under VFB operating condition. VFB single cell assembled with C-SPEEK-50 membranes shows much higher energy efficiency (85% Vs 82%) and columbic efficiency (97.3% Vs 94.6%) than that assembled with Nafion 115. The membrane keeps a stable performance after more than 180 cycles charge–discharge test, showing good stability.

Breaking Bonds with Electrons and Protons. Models and Examples

Besides its theoretical interest, the attention currently aroused by proton-coupled electron transfers (PCET reactions) has two main motives. One is a better understanding of biological processes in which PCET reactions are involved, Photosystem II as well as a myriad of other natural systems. The other is directed toward synthetic processes, many of which are related to global energy challenges. Until recently, the analyses of the mechanism and reactivity of PCET reactions have focused on outersphere transfers, those in which no bond between heavy atoms (all atoms with the exception of H) is concomitantly formed or broken. Conversely, reactions in which electron transfer triggers the breaking of a heavy-atom bond with no proton transfer have been extensively analyzed, both theoretically and experimentally. In both cases, strategies have been developed to distinguish between stepwise and concerted pathways. In each case, kinetic models have been devised, allowing the relation between activation and thermodynamic driving force to be established by means of parameters pertaining to the initial and final state. Although many natural and artificial processes include electron transfer, proton transfer, and heavy-atom bond breaking (/formation), no means were offered until recently to analyze the mechanism of such reactions, notably to establish the degree of concertedness of the three constitutive events. Likewise, no kinetic models were available to describe reactions where the three events are concerted. In this Account, we discuss the strategies to distinguish stepwise, partially concerted (when two of the three events are concerted), and totally concerted pathways in these reactions that include electron transfer, proton transfer, and heavy-atom bond breaking. These mechanism analysis methods are illustrated and validated by three examples. First we describe the electrochemical cleavage of an O-O bond in an aliphatic peroxide molecule with a pendant carboxylic acid group that can serve as proton donor for electron transfer and bond breaking. In the second example, we examine the breaking of one of the C-O bonds of CO2 within a multistep process where the reduction of CO2 into CO is catalyzed by an electrogenerated iron(0) porphyrin in the presence of various Brönsted acids. In this case, an intramolecular electron transfer triggers proton transfer and bond cleavage. In the first two examples, all three events are concerted. The third example also involves catalysis. It describes the cleavage of a cobalt-carbon bond in the reduction of chloroacetonitrile catalyzed by an electrogenerated cobalt(I) porphyrin. It illustrates the rather common case where the intermediate formed by the reaction of a transition metal complex with the substrate has to be cleaved to close the catalytic cycle. In the first two examples, all three events are concerted, whereas, in the last case, a partially concerted pathway takes place: proton transfer and bond-breaking (Co-C cleavage) are concerted after an initial electron transfer step. The all-concerted cases require a model that connects the kinetics to the thermodynamic driving force of the reaction. Starting from previous models of outersphere electron transfer, concerted proton-electron transfer, and concerted dissociative electron transfer, we describe a model for all-concerted proton-electron-bond breaking reactions. These pathways skip the high-energy intermediates that occur in stepwise pathways, but could introduce kinetic penalties. The all-concerted model allows one to assess these penalties and the way in which they can be fought by the supplement of driving force offered by concerted proton transfer.

Construction of a new continuous proton transport channel through a covalent crosslinking reaction between carboxyl and amino groups

Sulfonated poly(arylene ether ketone sulfone) bearing pendant carboxylic acid groups (C-SPAEKS) and sulfonated poly(arylene ether ketone sulfone) containing amino groups (Am-SPAEKS) were used to prepare C-SPAEKS/Am-SPAEKS crosslinked membranes. 1H NMR and Fourier transform infrared spectra proved that C-SPAEKS and Am-SPAEKS copolymers, as well as C-SPAEKS/Am-SPAEKS crosslinked membrane, were successfully synthesized. TEM images showed that a continuous proton transport channel formed after crosslinking. Thermogravimetric analysis curves demonstrated that the thermal property of the crosslinked membranes improved. The crosslinked membranes exhibited suitable mechanical properties at 25 and 80 °C. The methanol permeability of C-SPAEKS/Am-SPAEKS-40 was 2.35 × 10−7 cm2 s−1 at 60 °C, which was lower than that of C-SPAEKS (24.12 × 10−7 cm2 s−1) and Am-SPAEKS (17.91 × 10−7 cm2 s−1). The proton conductivity of C-SPAEKS/Am-SPAEKS-40 was 0.089 S cm−1, which was higher than that of C-SPAEKS and Am-SPAEKS at 80 °C. The results proved that C-SPAEKS/Am-SPAEKS crosslinked membranes were potential proton exchange membranes for direct methanol fuel cell applications.