Electrospray ionization mass spectrometry ESI-MS is a powerful technique for the characterization of macromolecules and their noncovalent binding with guest ions. We herein evaluate the feasibility of using ESI-MS as a screening tool for predicting potentiometric selectivities of ionophores. Ion-selective electrodes based on the cyclic peptide, cyclosporin A, were developed, and their potentiometric selectivity pattern was evaluated. Optimized electrodes demonstrated near-Nernstian slopes with micromolar detection limits toward calcium. ESI-MS and ESI-MS/MS were employed to determine the relative association strengths of cyclosporin A with various cations. The observed MS intensities of ion–ionophore complexes correlate favorably with the potentiometric selectivity pattern that was demonstrated by cyclosporin-based electrodes. This correlation was found to hold true for other established ionophores, such as valinomycin and benzo-18-crown-6. Taken together, these experiments demonstrate that mass spectrometry could be used to predict the selectivity patterns of new ionophores for potentiometric and optical ion sensors. Further, this approach could be useful in screening mixtures or libraries of newly-synthesized compounds to identify selective ionophores.

We introduce a unique material ensemble to boost the photocatalytic activity of m-BiVO4 by creating dual heterojunction of bismuth oxybromide nanosheets and Pd nanodomains. The m-BiVO4/BiOBr/Pd ternary composite demonstrates substantially higher photocatalytic activity compared to pure m-BiVO4. We demonstrate for the first time the use of such visible light photocatalyst in highly efficient degradation of polychlorinated biphenyls.

•Polybrominated diphenyl ethers are persistent pollutants that present risks to humans.•Cu2O@Pd demonstrated light-activated reductive hydrodehalogenation of PBDEs.•Photocatalyst showed preferential debromination at para > meta >> ortho.Polybrominated diphenyl ethers (PBDEs), which have found extensive use as flame-retarding additives to many polymer materials, are now environmentally ubiquitous and persistent pollutants that present potential health risks to humans and wildlife. Herein, we report for the first time the use of metal oxide semiconductor nanostructures for photocatalytic reductive debromination of PBDEs using visible light. Well-defined cubic Cu2O crystals, surface-decorated with Pd nanoparticles, were prepared via a hydrothermal approach. The Cu2O@Pd demonstrated light-activated tandem photocatalysis, in which Cu2O produces H2 from H2O under visible light irradiation; the evolved H2 is subsequently activated by Pd to achieve the reductive hydrodehalogenation of the PBDE. Cu2O@Pd demonstrated effective debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), one of the PBDEs of greatest environmental concern, with initial pseudo-first-order rate constant of 0.21 h−1. It is shown that the reaction proceeds via a reductive mechanism with preferential debromination at the para positions. Reaction rates for various monobromo- and dibromo-congeners were evaluated, confirming that the debromination order of preference is para > meta >> ortho, which is opposite to the order reported for direct photolysis. We conclude that Cu2O@Pd is a promising photocatalyst for reductive dehalogenation of halogenated organic compounds.Download high-res image (102KB)Download full-size image

•Simple electroless approach for the synthesis of Pd NP incorporated in polyaniline.•The preorganization of the material allows for spatial distribution of Pd NP.•The nanocomposite demonstrated high electrocatalytic activity for alcohol oxidation.We report a simple method for the preparation of a stabilized palladium nanoparticle-polyaniline composite by mixing aniline and PdCl42−PdCl42− in aqueous acidic solutions. Pd nanoparticles (Pd NP) were produced by subsequent reduction of the pre-organized material with different concentrations of NaBH4. Under optimum conditions (0.1 M NaBH4 in ethanol for 1 h at 0 °C), Pd NP with a size of 5–10 nm were obtained, as revealed by transmission electron microscopy. The so-formed pre-organized material was also characterized with scanning electron microscopy, X-ray diffraction, infrared spectroscopy, inductively coupled plasma atomic emission spectrometry, nuclear magnetic resonance spectroscopy, and cyclic voltammetry. The developed catalyst exhibited a large electrochemically active surface area (25.2 m2 g−1 catalyst) and remarkable mass activities for the electro-oxidation of methanol (602 A g−1 Pd) and ethanol (433 A g−1 Pd) in alkaline media. The excellent electrocatalytic performance of the developed polyaniline-Pd NP composite material renders it as a promising anode catalyst in alkaline fuel cells.

The nature of the plasticizer plays a pivotal role in the analytical performance of polymer membrane ion sensors. Conventional plasticizers suffer leaching or migration from the membrane and exudation, both of which could limit the lifetime of sensors based on plasticized membranes. Herein, we describe the use of polyester sebacate (PES), a model polymeric plasticizer, in the preparation of poly (vinyl chloride) (PVC) membrane ion-selective electrodes (ISEs) using valinomycin as ionophore. PVC membrane electrodes plasticized with polyester sebacate demonstrated potentiometric response characteristics that compared favorably to ones plasticized with the conventional and similarly structured plasticizer bis(2-ethylhexyl) sebacate (DOS). Increasing the content of polyester sebacate in the membrane enhanced the response and improved the selectivity of valinomycin-based ISEs toward potassium over sodium. Various methods, including electrochemical impedance spectroscopy, UV-vis spectroscopy, dark field optical microscopy, and potentiometry were employed to study the effect of plasticizer on the leaching of the membrane components and the lifetime of both DOS- and PES-plasticized membranes. PES-plasticized electrodes maintained Nernstian response and high selectivity for more than four months, an improvement over DOS-plasticized membrane electrodes. This was attributed to enhanced retention of the membrane components because of the high polymeric nature of the polyester sebacate. These characteristics suggest that polyester sebacate is a good candidate to replace the conventional plasticizers in preparing PVC membrane electrodes with longer lifetime.

Transitioning energy-intensive and environmentally intensive processes toward sustainable conditions is necessary in light of the current global condition. To this end, photocatalytic processes represent new approaches for H2 generation; however, their application toward tandem catalytic reactivity remains challenging. Here, we demonstrate that metal oxide materials decorated with noble metal nanoparticles advance visible light photocatalytic activity toward new reactions not typically driven by light. For this, Pd nanoparticles were deposited onto Cu2O cubes to generate a composite structure. Once characterized, their hydrodehalogenation activity was studied via the reductive dechlorination of polychlorinated biphenyls. To this end, tandem catalytic reactivity was observed with H2 generation via H2O reduction at the Cu2O surface, followed by dehalogenation at the Pd using the in situ generated H2. Such results present methods to achieve sustainable catalytic technologies by advancing photocatalytic approaches toward new reaction systems.

We report the synthesis of a new pyrrole-substituted vitamin B12 derivative functioning as a corrin monomer, its electrochemical copolymerization with pyrrole, and the potentiometric behavior of the resultant electrodes based on the corrin-doped polypyrrole film. Electropolymerization of the corrin monomer on a glassy carbon electrode and its redox properties were evaluated by cyclic voltammetry in acetonitrile in the presence of tetrabutylammonium perchlorate. We investigated the effect of various parameters that control the film properties, such as the concentration of the monomer, potential range, scan rate, and number of scans. The optimal conditions for potentiometric measurements were also determined. We found that the electropolymerized corrin film-based electrode exhibited an anion selectivity pattern that favors thiocyanate and deviates from the Hofmeister series. The obtained electrode demonstrates near-Nernstian behavior for a period of at least 6 months. The detection limit of the electrode along with selectivity coefficients toward various anions was also determined.

Oriented immobilization of proteins is an important step in creating protein-based functional materials. In this study, a method was developed to orient proteins on hydroxyapatite (HA) surfaces, a widely used bone implant material, to improve protein bioactivity by employing enhanced green fluorescent protein (EGFP) and β-lactamase as model proteins. These proteins have a serine or threonine at their N-terminus that was oxidized with periodate to obtain a single aldehyde group at the same location, which can be used for the site-specific immobilization of the protein. The HA surface was modified with bifunctional hydrazine bisphosphonates (HBPs) of various length and lipophilicity. The number of functional groups on the HBP-modified HA surface, determined by a 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay, was found to be 2.8 × 10–5 mol/mg of HA and unaffected by the length of HBPs. The oxidized proteins were immobilized on the HBP-modified HA surface in an oriented manner through formation of a hydrazone bond. The relative protein immobilization amounts through various HBPs were determined by fluorescence and bicinchoninic acid (BCA) assay and showed no significant effect by length and lipophilicity of HBPs. The relative amount of HBP-immobilized EGFP was found to be 10–15 fold that of adsorbed EGFP, whereas the relative amount of β-lactamase immobilized through HBPs (2, 3, 4, 6, and 7) was not significantly different than adsorbed β-lactamase. The enzymatic activity of HBP-immobilized β-lactamase was measured with cefazolin as substrate, and it was found that the catalytic efficiency of HBP-immobilized β-lactamase improved 2–5 fold over adsorbed β-lactamase. The results obtained demonstrate the feasibility of our oriented immobilization approach and showed an increased activity of the oriented proteins in comparison with adsorbed proteins on the same hydroxyapatite surface matrix.

One-dimensional iron metallic nanotubes were prepared by electroless deposition within the pores of polycarbonate (PC) membranes. The longitudinal nucleation of the nanotubes along the pore walls was achieved by mounting the PC membrane between two halves of a U-shaped reaction tube. Palladium nanoparticles were post-deposited on the inner wall of the nanotubes. The composition, morphology, and structure of the Pd/Fe nanotubes were characterized by transmission electron microscopy, scanning electron microscopy, and inductively coupled plasma–atomic emission spectroscopy. A glassy carbon (GC) electrode modified with the free Pd/Fe bimetallic nanotubes (isolated after the dissolution of the host membranes) showed small improvement on the overpotential oxidation of ascorbic acid in comparison to the bare GC electrode. Alternatively, the Pd/Fe-polycarbonate membrane was covered with a sputtered gold thin layer of 10 nm from one side and mounted in a homemade electrochemical cell acting as the working electrode. The potential use of these functional membranes as catalytic surfaces for the electrochemical monitoring of ascorbic acid was investigated by cyclic voltammetry and amperometry. In the presence of a phosphate buffer solution, pH 7, Pd/Fe-polycarbonate membranes showed excellent electrocatalytic properties toward the oxidation of ascorbic acid even at potentials as low as 0 mV versus a Ag/AgCl reference electrode. In addition to the substantial lower overpotential, these electrodes offered selectivity over acetaminophen and uric acid, and a prolonged working stability without the need for maintenance. The electrodes were kept dry between different working days and retained their original activity for more than 1 week. Pd-polycarbonate and Fe-polycarbonate membranes were also developed for comparison purposes.

We described the synthesis and characterization of a new class of bimetallic nanotubes based on Pd/Fe and demonstrated their efficacy in the dechlorination of PCB 77, a polychlorinated biphenyl. One-dimensional iron metal nanotubes of different diameters were prepared by electroless deposition within the pores of PVP-coated polycarbonate membranes using a simple technique under ambient conditions. The longitudinal nucleation of the nanotubes along the pore walls was achieved by mounting the PC membrane between two halves of a U-shape reaction tube. The composition, morphology, and structure of the Pd/Fe nanotubes were characterized by transmission electron microscopy, scanning electron microscopy, inductively coupled plasma-atomic emission spectroscopy, and X-ray powder diffraction spectroscopy. The as-prepared Pd/Fe bimetallic nanotubes were used in dechlorination of 3,3′,4,4′-tetrachlorobiphenyl (PCB 77). In comparison with Pd/Fe nanoparticles, the Pd/Fe nanotubes demonstrated higher efficiency and faster dechlorination of the PCB.

Triazolophanes are ionophores, with preorganized cyclic cavities that have tunable selectivities for halides. The interaction with halides is based on hydrogen bonding between the eight CH hydrogen atoms of the cavity and the halide anion. The rigidity of the cavity in tetraphenylene triazolophane along with the hydrogen bonding favors planar 1:1 complexation of “snugly” encapsulated chloride and bromide. Manipulating the triazolophane’s structure by introducing two pyridyl moieties into the cavity alters the receptor’s binding mode. This change adds a dipole-promoted driving force that combines with hydrogen bonding to favor the formation of 2:1 sandwich complexes around halides. The potentiometric response of electrodes based on this new ionophore was evaluated for optimal halide selectivity. The new triazolophane-based electrode showed an anti-Hofmeister selectivity toward iodide with a submicromolar detection limit. The stoichiometry of complexation and the stability constants with different halides were evaluated using a segmented sandwich membranes method. The pyridyl-triazolophane demonstrated a response consistent with a 2:1 sandwich-type complex with iodide, in polyvinyl chloride (PVC) membranes.

Skeletal diseases have a major impact on the worldwide population and economy. Although several therapeutic agents and treatments are available for addressing bone diseases, they are not being fully utilized because of their uptake in nontargeted sites and related side effects. Active targeting with controlled delivery is an ideal approach for treatment of such diseases. Because bisphosphonates are known to have high affinity to bone and are being widely used in treatment of osteoporosis, they are well-suited for drug targeting to bone. In this study, a targeted delivery of therapeutic agent to resorption sites and wound healing sites of bone was explored. Toward this goal, bifunctional hydrazine-bisphosphonates (HBPs), with spacers of various lengths, were synthesized and studied for their enhanced affinity to bone. Crystal growth inhibition studies showed that these HBPs have high affinity to hydroxyapatite, and HBPs with shorter spacers bind more strongly than alendronate to hydroxyapatite. The HBPs did not affect proliferation of MC3T3-E1 preosteoblasts, did not induce apoptosis, and were not cytotoxic at the concentration range tested (10–6–10–4 M). Furthermore, drugs can be linked to the HBPs through a hydrazone linkage that is cleavable at the low pH of bone resorption and wound healing sites, leading to release of the drug. This was demonstrated using hydroxyapatite as a model material of bone and 4-nitrobenzaldehyde as a model drug. This study suggests that these HBPs could be used for targeted delivery of therapeutic agents to bone.

We introduce a unique material ensemble to boost the photocatalytic activity of m-BiVO4 by creating dual heterojunction of bismuth oxybromide nanosheets and Pd nanodomains. The m-BiVO4/BiOBr/Pd ternary composite demonstrates substantially higher photocatalytic activity compared to pure m-BiVO4. We demonstrate for the first time the use of such visible light photocatalyst in highly efficient degradation of polychlorinated biphenyls.

We described the synthesis and characterization of a new class of bimetallic nanotubes based on Pd/Fe and demonstrated their efficacy in the dechlorination of PCB 77, a polychlorinated biphenyl. One-dimensional iron metal nanotubes of different diameters were prepared by electroless deposition within the pores of PVP-coated polycarbonate membranes using a simple technique under ambient conditions. The longitudinal nucleation of the nanotubes along the pore walls was achieved by mounting the PC membrane between two halves of a U-shape reaction tube. The composition, morphology, and structure of the Pd/Fe nanotubes were characterized by transmission electron microscopy, scanning electron microscopy, inductively coupled plasma-atomic emission spectroscopy, and X-ray powder diffraction spectroscopy. The as-prepared Pd/Fe bimetallic nanotubes were used in dechlorination of 3,3′,4,4′-tetrachlorobiphenyl (PCB 77). In comparison with Pd/Fe nanoparticles, the Pd/Fe nanotubes demonstrated higher efficiency and faster dechlorination of the PCB.