Poly(o-phenylenediamine) submicrosphere-supported gold nanocatalysts: synthesis, characterization, and application in selective oxidation of benzyl alcohol

Reductive carbon dots for reduction, ratiometric fluorescence determination, and intracellular imaging of Au3

Many studies show that ortho-phenylenediamine (OPD) produces an oxidized fluorescent product when exposed to an oxidizing agent that enables the direct or indirect fluorescence detection of a range chemical and biochemical analytes. However, there is no report on this unique optical behavior for other two isomers of phenylenediamine. This study demonstrates that a simple hydrothermal treatment of para-phenylenediamine (PPD) in the presence of sulfuric acid results in the formation of fluorescent N, S-doped carbon dots (CDs) with triple functionalities including the reduction of Au3+ into gold nanoparticles (AuNPs), the stabilization of the produced AuNPs, and the determination of Au3+ concentration through an intrinsic ratiometric fluorescence signal. In the presence of Au3+, the blue emission of CDs at 437 nm quenched, and a green emission at 540 nm emerged. The linear concentration range for the determination of Au3+ was 20 nM-16 µM with a detection limit of 16 nM. Additionally, the dual emissive CDs-AuNPs hybrid probe showed potential for the indirect fluorescence ratiometric determination of cysteine and sulfide ions. The linear concentration range for cysteine and sulfide ions were 0.25-8 μM and 0.1-6 μΜ, with detection limits of 0.095 μM and 0.041 μM, respectively. Accordingly, CDs were applied to detect Au3+ and S2- in real water samples. Moreover, the synthesized CDs showed no cytotoxicity for HeLa cells up to 300 µg mL-1, as determined by the MTT assay. Therefore, their potential for intracellular imaging of Au3+ in living cells was also investigated.

"Four-in-One" Nanozyme for Amplified Catalytic-Photothermal Therapy

The cancer therapeutic efficacy of the peroxidase (POD)-mimicking nanozyme-based monotherapy is significantly hindered due to insufficient intratumoral hydrogen peroxide (H2O2) and glutathione (GSH) consumption effect on reactive oxygen species (ROS). In this study, we present the development of poly(o-phenylenediamine)@gold nanoparticles (AuNPs) (PoPD@Au) nanocomposites for multifunctional catalytic-photothermal therapy. These nanocomposites exhibit triple distinct nanozymatic activities, i.e., POD-like activity that catalyzes H2O2 to ROS, glucose oxidase (GOx)-like activity that supplements endogenous H2O2, and GSH depleting activity that decreases the ROS consumption efficiency. This open source and reduce expenditure strategy for ROS generation allows for the amplification of tumor oxidative stress, thereby enhancing anti-tumor efficiency. Additionally, the PoPD@Au nanocomposites demonstrate outstanding photothermal conversion efficiency, contributing to the synergistic effect between PoPD and AuNPs. Moreover, we reveal the improved photothermal performance of PoPD@Au triggered by the tumor microenvironment pH, which provides additional benefits for targeted catalytic-photothermal therapy. This "four-in-one" design of PoPD@Au enables efficient anti-tumor effects both in vitro and in vivo, making it a universal strategy for engineering catalytic-photothermal therapeutic nanoagents.

Computational mechanistic studies on persulfate assisted p-phenylenediamine polymerization

p-Phenylenediamine (p-PDA) is a monomer of many important polymers such as kevlar, twaron, poly-p-PDA. Most of the noticed polymers formation is initiated by a free-radical, but their polymerization mechanism is not elucidated computationally. The proposed study helps to fully understand the frequently utilized initiator/oxidant, potassium persulfate (K₂ S₂ O₈ ) role in the aromatic diamines polymerization, which support experimental protocols, and a polymer scope. The formation of the poly-p-PDA is studied with the density functional theory (DFT) B3LYP-D3 functional using experimental polymerization parameters (0°C and aqueous media). K₂ S₂ O₈ initiated free-radical polymerization of p-PDA is studied in detail, taking into account sulfate free-radical (SO₄ ^- )^· , SFR, persulfate anion (S₂ O₈ )^2- , PA and K₂ S₂ O₈ cluster, PP. The reaction mechanism is calculated as the conversion of p-PDA to free-radical, the p-PDA free-radical attack to the next p-PDA (dimerization), ammonia extrusion from the dimer adduct, the dimer adduct conversion to the free-radical (completion of p-PDA polymerization cycle) for the polymer chain elongation. Calculations show that the dimerization step is the rate-limiting step with a 29.2 kcal/mol energy barrier when SFR initiates polymerization. In contrast, the PA-assisted dimerization energy barrier is only 12.7 kcal/mol. PP supported polymerization is calculated to have very shallow energy barriers completing the polymerization cycle, i.e., dimerization (TS2K, ∆G^‡  = 11.6 kcal/mol) and ammonia extrusion (TS3K, ∆G^‡  = 6.7 kcal/mol).

Trends in Sustainable Synthesis of Organics by Gold Nanoparticles Embedded in Polymer Matrices

Gold nanoparticles (AuNPs) have emerged in recent decades as attractive and selective catalysts for sustainable organic synthesis. Nanostructured gold is indeed environmentally friendly and benign for human health; at the same time, it is active, under different morphologies, in a large variety of oxidation and reduction reactions of interest for the chemical industry. To stabilize the AuNPs and optimize the chemical environment of the catalytic sites, a wide library of natural and synthetic polymers has been proposed. This review describes the main routes for the preparation of AuNPs supported/embedded in synthetic organic polymers and compares the performances of these catalysts with those of the most popular AuNPs supported onto inorganic materials applied in hydrogenation and oxidation reactions. Some examples of cascade coupling reactions are also discussed where the polymer-supported AuNPs allow for the attainment of remarkable activity and selectivity.

Impedimetric determination of Cs(I) using AuNPs@PoPD-DB24C8: A targeted molecular-scale perturbation

Most attributes of the bulk materials, especially in the solid-state, are directly dictated by a manner by which the molecules are ordered. Thus, it is expected that the possibility of controlling these structural orders would allow predominating some particular physical properties. The methodology used in this work follows the molecular scale perturbation occurred by Cs⁺ ion within a ternary composite of dibenzo-24-crown-8 (DB24C8), poly ortho-phenylenediamine (PoPD) and gold nanoparticles (AuNPs). Hypothetically, two former substances were respectively employed as recognition element and conductive platform to establish a monolithic structure that resembles supramolecular synthon in solid-state. The third precursor was Au(III) that carries out a dual role including vulcanization of the polymeric units via creating quinoid rings and solid signal amplification by deposition of AuNPs at the welded points. This strategy affords an intertwined ternary composite in which the electronical properties of the system can be directly affected by lowest agitation sensed by the recognition element, DB24C8, making the supported transducer capable of monitoring trace amount of Cs⁺ ion by Faradaic impedance spectroscopy (FIS) and single-frequency measurements (SFM). The fabricated sensor showed a signal change against Cs⁺ ion over the linear range of 0.6-25.0 nM with a detection limit of 0.37 nM (S/N = 3). Density functional theory (DFT) studies were used to explore the possible recognition mechanism, by which the incorporation of Cs⁺ ion meaningfully dispersed the structural order of the ternary system.

Ordered mesoporous carbon assisted Fe-N-C for efficient oxygen reduction catalysis in both acidic and alkaline media

Fe-N-C catalyst obtained by high temperature pyrolysis is one of the most promising electrocatalysts for non-precious metal oxygen reduction reaction (ORR). However, up to now, the lesser density of active sites results in a substantial performance gap between the Fe-N-C materials and the conventional Pt/C ORR catalysts. Herein, an N-doped mesoporous carbon is employed as the support for the dispersion of poly-m-phenylenediamine. With high specific surface areas of 1526 m² g^-1, the as-prepared Fe-N-C materials show the half-wave potential of 0.89 V and 0.79 V in 0.1 M KOH and 0.5 M H₂SO₄, respectively. Notably, the superior methanol tolerance, as well as excellent stability, makes our Fe-N-C materials as competitive candidates for oxygen electrochemical catalysis.

Gold nanocatalysts supported on carbon for electrocatalytic oxidation of organic molecules including guanines in DNA

Gold (Au) is chemically stable and resistant to oxidation. Although bulk Au is catalytically inert, nanostructured Au exhibits unique size-dependent catalytic activity. When Au nanocatalysts are supported on conductive carbon (denoted as Au@C), Au@C becomes promising for a wide range of electrochemical reactions such as electrooxidation of alcohols and electroreduction of carbon dioxide. In this mini-review, we summarize Au@C nanocatalysts with specific attention on the most recent achievements including the findings in our own laboratories, and show that Au nanoclusters (AuNCs, <2 nm) on nitrided carbon are excellent electrocatalysts for the oxidation of organic molecules including guanines in DNA. The state-of-the-art synthesis and characterization of these nanomaterials are also documented. Synergistic interactions among Au-containing multicomponents on carbon supports and their applications in electrocatalysis are discussed as well. Finally, challenges and future outlook for these emerging and promising nanomaterials are envisaged.

Facile preparation of gold nanoparticles-decorated poly(o-phenylenediamine) hollow microspheres and their application for the detection of dopamine

Gold (Au) nanoparticles-decorated poly( o-phenylenediamine) (PoPD@Au) hollow microspheres were successfully synthesized by a simple two-step process without any other templates or additives. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible absorption spectra were performed to characterize the resulting samples. The results confirmed that the obtained PoPD@Au microspheres had a perfect hollow structure and revealed that there is an interaction between PoPD hollow microspheres and Au nanoparticles. Plausible explanation for the formation of PoPD@Au hollow microspheres has been elaborated. Furthermore, PoPD@Au hollow microspheres were immobilized onto the surface of a glassy carbon electrode and applied to construct a sensor. Cyclic voltammogram experiments indicated that the proposed sensor method had good sensitivity, stability, and repeatability.

Selective oxidation of alcohols by supported gold nanoparticles: recent advances

The review presents a commercially important field of alcohol oxidation using gold nanoparticles. It systematically discusses scope and limitation of various supports on the activity and selectivity of catalyst.

Interfacial Synthesis of Gold-Polyaniline Nanocomposite and Its Electrocatalytic Application

Gold-polyaniline (Au-PANI) nanocomposite was prepared using a simple interfacial polymerization method, performed in an immiscible water/toluene biphasic system using tetrachloroaurate, AuCl4(-) as an oxidant. The formation of Au nanoparticles (AuNPs) or Au-PANI nanocomposite can be controlled to a certain degree by varying the ratio of initial Au(+) and aniline concentrations. Under optimal condition (HAuCl4/aniline ratio is 1:2), green dispersion of Au-PANI nanocomposite is produced in aqueous phase, whose morphology, structure and physicochemical properties are investigated in details. The nanocomposite shows granular morphology with mostly rodlike AuNPs embedded in polymer. It was found that polyaniline in the composite is in the conducting emeraldine salt form, containing high amount of Au (28.85 wt %). Furthermore, the electrical conductivity of the nanocomposite was found to be four-fold higher than that of the polymer itself. In addition, the nanocomposite powder, isolated from the as-prepared aqueous dispersion, can later be easily redispersed in water and further used for various applications. Moreover, the obtained Au-PANI nanocomposite showed excellent electrocatalytic performance toward the electrochemical oxygen reduction reaction (ORR), with high ORR onset potential and good selectivity. This makes it a promising candidate for a new class of Pt-free ORR catalyst.

Fabrication of porous thin films of block copolymer at the liquid/liquid interface and construction of composite films doped with noble metal nanoparticles

A porous polymer film was fabricated at a liquid/liquid interface that can be used as a matrix to form various composite films.

Novel gold-decorated polyaniline derivatives as redox-active species for simultaneous detection of three biomarkers of lung cancer

Novel redox-active species including gold-poly(o-aminophenol) and gold-poly(p-phenylenediamine) were synthesized and applied for the electrochemical immunoassay of three tumor biomarkers.

Facile synthesis of polystyrene/gold composite particles as a highly active and reusable catalyst for aerobic oxidation of benzyl alcohol in water

Herein is reported a facile synthesis of polystyrene/gold composite particles with high catalytic activity and good reusability for aerobic oxidation of benzyl alcohol under mild conditions.

One-pot surfactantless route to polyaniline hollow nanospheres with incontinuous multicavities and application for the removal of lead ions from water

Polyaniline (PANI) hollow nanospheres with controllable incontinuous nanocavities ranging in size from 10 to 50 nm as a novel hollow nanostructure have been successfully fabricated by chemical polymerization of aniline with chloroaurate acid as the oxidant and citric acid as the doping acid. Experimental factors, such as concentration and kind of oxidant and doping acid, were investigated to illustrate their effect on morphology of PANI. According to experimental results and time-dependent investigations, a possible formation mechanism involved was then proposed. The adaptability of this route to hollow nanostructures with multicavities of other conducting polymer was also revealed. Furthermore, the adsorption properties of PANI hollow nanospheres toward lead ions in water were investigated.

Ag-nanoparticle-loaded mesoporous silica: spontaneous formation of Ag nanoparticles and mesoporous silica SBA-15 by a one-pot strategy and their catalytic applications

A facile one-step method was proposed for the successful synthesis of Ag-nanoparticle-loaded mesoporous silica SBA-15 composites, where silver ions and their corresponding reductant aniline were added in the traditional synthetic system of mesoporous silica SBA-15 containing P123 as the surfactant and TEOS as the silica source. Mesoporous silica SBA-15 and Ag nanoparticles were spontaneously formed with Ag nanoparticles embedded in channels and even implanted in frameworks of mesoporous silica SBA-15. A tentative formation process was then proposed according to experimental observations. Furthermore, catalytic activities of Ag-nanoparticle-loaded silica SBA-15 composites toward the reduction of 4-nitrophenol in the presence of NaBH(4) and the reduction of H(2)O(2) were also investigated.

pH manipulation: a facile method for lowering oxidation state and keeping good yield of poly(m-phenylenediamine) and its powerful Ag+ adsorption ability

A method of pH manipulation has been used to improve chemically oxidative polymerization of m-phenylenediamine (mPD) through concurrent addition of NaOH when adding oxidant (NH(4))(2)S(2)O(8). pH detection and open-circuit potential technique were adopted to monitor the polymerization process of mPD and to explain the oxidation state-pH and yield-pH relationships. Results from Fourier transformed infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies indicate that a low oxidation state is under control by regulating NaOH concentration. At 2.5 M NaOH, the oxidation state of poly(m-phenylenediamine) (PmPD) is 64.7 mol % (measured by molar content of quinoid imine from XPS), while the yield is 84%. The synthesized PmPD possesses better Ag(+) adsorption performance when lowering its oxidation state. Moreover, the Ag(+) adsorbance of PmPD can reach 1693 mg g(-1). Meanwhile, Ag(+) adsorption mechanism was studied by pH tracking, X-ray diffraction (XRD) patterns, and X-ray photoelectron spectroscopy. The adsorption process includes redox reaction, chelation, and physical adsorption.

Poly(m-phenylenediamine) nanospheres and nanorods: selective synthesis and their application for multiplex nucleic acid detection

In this paper, we demonstrate for the first time that poly(m-phenylenediamine) (PMPD) nanospheres and nanorods can be selectively synthesized via chemical oxidation polymerization of m-phenylenediamine (MPD) monomers using ammonium persulfate (APS) as an oxidant at room temperature. It suggests that the pH value plays a critical role in controlling the the morphology of the nanostructures and fast polymerization rate favors the anisotropic growth of PMPD under homogeneous nucleation condition. We further demonstrate that such PMPD nanostructures can be used as an effective fluorescent sensing platform for multiplex nucleic acid detection. A detection limit as low as 50 pM and a high selectivity down to single-base mismatch could be achieved. The fluorescence quenching is attributed to photoinduced electron transfer from nitrogen atom in PMPD to excited fluorophore. Most importantly, the successful use of this sensing platform in human blood serum system is also demonstrated.

Highly uniform self-assembled conducting polymer/gold fibrous nanocomposites: additive-free controllable synthesis and application as efficient recyclable catalysts

Uniform poly(2-aminothiophenol) nanofibers embedded with highly dispersed gold nanoparticles have been fabricated through a facile templateless one-step method. The diameter of composite nanofibers can be controlled in the range of 200-80 nm by simply tuning the speed of mechanical stirring during materials synthesis. Results from our work will provide insight into the shape-controlled synthesis of other nanomaterials by simply introducing mechanical agitation. Removal of gold nanoparticles in composite nanofibers leads to polymer nanotubes with continuous or incontinuous nanocavities depending on mechanical stirring speeds. Furthermore, morphology-dependent catalytic performances of such composites are also investigated.

Ag@poly(m-phenylenediamine) core-shell nanoparticles for highly selective, multiplex nucleic acid detection

In this letter, we report on the one-step synthesis of Ag@poly(m-phenylenediamine) core-shell nanoparticles (APCSNPs), carried out by direct mixing of aqueous silver nitrate and m-phenylenediamine solutions at room temperature. We further demonstrate the use of APCSNP as a novel fluorescent sensing platform for nucleic acid detection. In this regard, the detection of DNA is accomplished in two steps. First, APCSNP absorbs and quenches the fluorescence of dye-labeled single-stranded DNA (ssDNA) as a probe. Second, hybridizing of the probe with its target produces a double-stranded DNA (dsDNA) that detaches from APCSNP, resulting in the recovery of dye fluorescence. It suggests that this sensing system has a high selectivity down to single-base mismatch, and the results exhibit good reproducibility. Furthermore, we also demonstrate its application for the multiplex detection of nucleic acid sequences.

Supramolecular microfibrils of o-phenylenediamine dimers: oxidation-induced morphology change and the spontaneous formation of Ag nanoparticle decorated nanofibers

The direct mix of aqueous FeCl(3) and o-phenylenediamine (OPD) solutions at room temperature leads to supramolecular microfibrils of OPD dimers generated by the oxidation of OPD monomers by FeCl(3) (Sun, X.; Hagner, M. Langmuir 2007, 23, 10441). In this Letter, we report on our recent finding that the subsequent treatment of such microfibrils with a AgNO(3) aqueous solution transforms them into nanofibers decorated with spherical silver nanoparticles (AgNPs) with sizes in range of 5-20 nm. The possible formation mechanism involved is also discussed. It is interestingly found that as-formed AgNPs exhibit good catalytic activity toward the reduction of H(2)O(2), leading to an enzymeless sensor with a fast amperometric response time of less than 5 s. The linear detection range is estimated to be from 100 μM to 80 mM (r = 0.998), and the detection limit is estimated to be 62 μM at a signal-to-noise ratio of 3.