Protonic Acid Research Articles

Strategic Substitution of -OH/-NR2 (R=Et, Me) Imparts Colorimetric Switching between F- and Hg2+ by Salicyaldehyde/Benzaldehyde-Quinoxaline Conjugates.

We herein report two salicyaldehyde-quinoxaline (HQS and HQSN) conjugates and a benzaldehyde-quinoxaline (QBN) conjugate to fabricate selective chemosensors for F- and Hg2+ in the micromolar range. This work demonstrates how sensing outcomes are affected by modulating proton acidity by introducing an electron donating group, -NEt2 , in the probe backbone. Interestingly, the un-substituted probe HQS can selectively detect F- , whereas HQSN and QBN are selective for Hg2+ . In order to gain insights into the mechanism of sensing, geometry optimizations have been carried out on QS(-1) , QS(-1) ⋅⋅⋅HF, QSN(-1) and QSN(-1) ⋅⋅⋅HF and the experimental data are validated in terms of free energy and pKa values. Detailed DFT and TD-DFT analyses provide ample support towards the mechanism of sensing of the analytes.

Chemiluminescence emission in Fenton reaction driven by 1,2-dihydroxybenzenes: Mechanistic approaches using 4-substituted ligands

Fenton (F) and Fenton–like (FL) reactions can be amplified by dihydroxybenzenes (DHBs). These compounds chelate and reduce Fe(III), promoting the hydroxyl radical production (OH). The products or intermediaries of F and FL reactions driven by DHBs can produce chemiluminescence (CL) with different profiles, depending on the type of DHB involved. In this work, CL produced by F and FL systems driven by different -para substituted DHBs was measured and compared with the reactivity of each system and with the structural parameters of each DHB. CL emission was not related to the reactivity of each studied system but was favored by DHBs substituents with -NHR and –OH groups combined in the branching (NHR-DHBs). PLS multivariate regression models were constructed using computational parameters for each DHB, quinone (Q) and semiquinone (SQ) to find the influence of structural and electronic parameters over CL emission. Analysis showed that in NHR-DHBs, the higher CL exhibited could be explained by cycling ability of these compounds. In DHBs with an electron-donor group (EDG) the CL emission would depend only on the stability of the intermediary species generated by DHB and OH reaction. While DHBs with electron-withdrawing groups (EWG) showed that CL will increase depending on the stability of the intermediaries by resonance, and by the acidity of the hydroxyl protons of the ring. PLS-SQ showed that spin densities were strongly correlated with an increase in CL emission. DHBs with substituents that favor the delocalization of charge in the SQ to the ramification would enhance CL emission. Meanwhile, when the delocalization is promoted over the DHB-ring, these systems become more reactive, and the CL emission is disadvantaged by quinone formation.

Multi-stimuli-responsive fluorescence switching from a novel organic polymorphic benzoimido-benzamide derivative

A novel organic polymorphic luminogen, (Z)-N-((benzoylimino) (4-(diphenylamino)phenyl)methyl)-N-(4-fluorophenyl)benzamide (DPA-PYZ-F), has been designed and synthesized successfully by a green photo-oxidation reaction. Two polymorphs (FB and FG) based on DPA-PYZ-F with different conformations display blue and green fluorescence, respectively. The emission of the newly obtained polymorphic molecule can be switched through the response to a mechanical force, thermal stimulus and protonic acid. The photophysical property tests and single crystal structural analysis disclosed that the mechanical force stimuli-responsive behavior of the FB and FG samples originate from the change of molecular arrangement. More significantly, FT-IR spectroscopy confirmed that the conformation transition from the FG to the FB could be achieved by thermal stimulus at 430 K. Additionally, protonation−deprotonation of the benzoylimino moieties in DPA-PYZ-F induced a remarkable fluorescence on-off characteristics upon protonic acid and thermal stimulus. The multi-stimuli response performance endows the new kind of molecule with the potential as a candidate for applications in mechanical force, thermal and protonic acid sensing.

Dicationic pyridinium salts as new organic ionics: Changes in solid-state phases and thermal/electrochemical properties

To explore a new family of organic ionic materials, a series of α,ω-bis[N,N′-(4-alkylpyridinium)]alkane salts combined with iodide (I−), tetrafluoroborate (BF4−), and bis(trifluoromethanesulfonyl)imide (Tf2N−) anions and alkylene bridges of different lengths are synthesized. From 1H NMR chemical shift changes, the proton acidity of at the bis-pyridinium cations can be estimated for different anions. All the synthesized I− and BF4− salts have one or multiple solid–solid phase transitions, which are typical features of plastic and liquid crystals. The I− or BF4− salts with large values (>90 J mol−1 K−1) of total entropy changes in solid–solid phase transitions (Σ(ΔSss)) would have a very soft crystalline phase. Combined with polarized microscope images and wide-angle X-ray diffraction spectra, 1,2-bis[N,N′-(4-n-dodecylpyridinium)]ethane 2BF4– may be a true plastic crystal at temperatures above 70 °C. The thermal properties of the bis-pyridinium Tf2N− salts are quite different; they show only a melting transition and are thermally more stable than those of I− and BF4−. The electrochemical window of the bis-pyridinium BF4– and Tf2N− salts is stable up to 4.3 V (vs. Li/Li+).

Realizing Diketopyrrolopyrrole Polymer‐Based Uniform Large‐Area Transistors for Active Circuit via Protonic Acid Mediated Molecular Self‐Assembly

AbstractThe solution‐handling characteristics of π‐conjugated polymer semiconductors make them promising candidates for low‐cost flexible electronics. Although homogeneous and stable nonchlorine solvent (NClS) processing is the only way that must be passed for future application, polymer semiconductors still meet the challenges of poor solubility and inhomogeneities in NClS. Here, the authors primp polymer molecules with protonic acid by multiple interactions, that is, proton exchange and hydrogen bond interaction, to achieve scale and model‐constrained PDVT‐10c assembly in NClS. As a result, a uniform near‐amorphous PDVT‐C10c film is developed for polymer thin‐film transistor (PTFT) array, which exhibits uniform performance with much narrower Gaussian standards deviation than pristine PDVT‐C10c one. Finally, a 5 cm × 5 cm PTFT as the active‐matrix circuit for blue organic light‐emitting diode is demonstrated. The results illustrate the great potential of protonic acid‐mediated molecular self‐assembly on homogeneous and stable NClS processing polymer semiconductors for next‐generation flexible electronics.

Polyaniline pyrolysis assisted by ITO to prepare Pt catalyst support for methanol oxidation reaction

A good support is essential for the activity and durability of the supported catalysts. In this work, nitrogen-doped carbon with fluffy structure and high content of pyridinic-N and pyrrolic-N is prepared by the pyrolysis of polyaniline/ITO composite, which is conducive to uniform and firm loading of Pt catalysts. Herein, polyaniline is used as carbon and nitrogen sources, and ITO is used as a pyrolysis auxiliary due to the reaction of polyaniline dopant (proton acid) and ITO during the pyrolysis. Pt catalyst supported on above optimal support shows an excellent electrocatalytic performance for the methanol oxidation reaction, especially its stability, achieving an activity retention rate of 89.3% after 1000 cycles of cyclic voltammetry in 0.5 M H2SO4 and 0.5 M CH3OH solution. This work provides a new strategy for preparing Pt-based catalyst with a high activity and a good durability.

Activated Monomer Mechanism (AMM) in Cationic Ring-Opening Polymerization. The Origin of the AMM and Further Development in Polymerization of Cyclic Esters.

The origin of the activated monomer mechanism (AMM) in cationic ring-opening polymerization (CROP) is described first. Then, conditions leading to the active chain end (ACE) mechanism and AMM are compared, as well as methods allowing to distinguish between these two mechanisms. These methods are based on the "ion trapping" of the active ionic species using highly basic phosphines or by comparing ACE and AMM kinetics of polymerization. The major factors deciding on the actual mechanism include: basicity of the monomers, ring strain, and the presence of the protic additives in the reaction system. These factors are tabulated for major cyclic ethers and cyclic esters. The historically evolved subsequent steps of AMM in the polymerization of cyclic esters are described: from the first experiments with trialkyloxonium salts, precursors of protonic acids, and added alcohols, via HCl as catalyst, and then CF3S(═O)2OH (polymerizing lactides) to the most popular derivatives of phosphoric acid, like diphenyl phosphate. Conditions allowing to synthesize poly(ε-caprolactone) (PCL), according to AMM-CROP, with molar mass up to 105 g·mol-1, are described as well as methods to polymerize CL with a protic initiator and acidic catalyst in one molecule. Then various methods enhancing the activity of the polymerizing systems are compared, based predominantly on hydrogen bonding, either to the polymer active end group (usually the hydroxyl group) or to the acid anion. Finally, kinetic equations for ACE and AMM are compared, and it is shown that the majority of the AMM-CROP systems, mostly studied for CL and lactides, proceed as living/controlled polymerizations. Since polymer end groups are hydroxyl groups, then, as it was shown in several papers, any initiator with one or many hydroxyl groups provides macromolecules with the corresponding architecture. The papers on synthetic methods are not discussed in detail.

Trends in Widely Used Catalysts for Fatty Acid Methyl Esters (FAME) Production: A Review

The effective transesterification process to produce fatty acid methyl esters (FAME) requires the use of low-cost, less corrosive, environmentally friendly and effective catalysts. Currently, worldwide biodiesel production revolves around the use of alkaline and acidic catalysts employed in heterogeneous and homogeneous phases. Homogeneous catalysts (soluble catalysts) for FAME production have been widespread for a while, but solid catalysts (heterogeneous catalysts) are a newer development for FAME production. The rate of reaction is much increased when homogeneous basic catalysts are used, but the main drawback is the cost of the process which arises due to the separation of catalysts from the reaction media after product formation. A promising field for catalytic biodiesel production is the use of heteropoly acids (HPAs) and polyoxometalate compounds. The flexibility of their structures and super acidic properties can be enhanced by incorporation of polyoxometalate anions into the complex proton acids. This pseudo liquid phase makes it possible for nearly all mobile protons to take part in the catalysis process. Carbonaceous materials which are obtained after sulfonation show promising catalytic activity towards the transesterification process. Another promising heterogeneous acid catalyst used for FAME production is vanadium phosphate. Furthermore, biocatalysts are receiving attention for large-scale FAME production in which lipase is the most common one used successfully This review critically describes the most important homogeneous and heterogeneous catalysts used in the current FAME production, with future directions for their use.

Continuous removal of sulfate and metals from acidic mining-impacted waters at low temperature using a sulfate-reducing bacterial consortium

The aim of this study was to develop a biological method for the simultaneous removal of sulfate and metals from acidic low-temperature mining effluents. A mixed consortium of cold-tolerant sulfate-reducing bacteria (SRB) and other microorganisms was immobilized on glass beads and exploited in an up-flow biofilm reactor for the continuous treatment of actual and synthetic mining-impacted waters (MIWs) with initial sulfate concentrations between 1580 and 5350 mg L-1. The proton acidity of the mine waters was neutralized by microbial sulfidogenesis. Metals present in the MIWs were precipitated either off-line or in-line, inside the reactor vessel. High sulfate reduction rates (SRRs), from 1000 to 4500 mg L-1 d-1 at a temperature of 11.7 ± 0.2 °C, were achieved (sulfate removal 43–87%). The bacterial consortium was found to be robust and resistant to changes in growth conditions during the bioreactor experiment. The relative abundance of SRB and the SRR increased at higher sulfate concentrations. Sulfidogenic bioreactors have the potential for treatment of acid mine drainage even at low temperature. It was demonstrated that neutral reactor conditions and high SRRs were maintained when acidic influent was fed into the reactor.

Molecular Routes of Dynamic Autocatalysis for Methanol-to-Hydrocarbons Reaction

The industrially important methanol-to-hydrocarbons (MTH) reaction is driven and sustained by autocatalysis in a dynamic and complex manner. Hitherto, the entire molecular routes and chemical nature of the autocatalytic network have not been well understood. Herein, with a multitechnique approach and multiscale analysis, we have obtained a full theoretical picture of the domino cascade of autocatalytic reaction network taking place on HZSM-5 zeolite. The autocatalytic reaction is demonstrated to be plausibly initiated by reacting dimethyl ether (DME) with the surface methoxy species (SMS) to generate the initial olefins, as evidenced by combining the kinetic analysis, in situ DRIFT spectroscopy, 2D 13C-13C MAS NMR, electronic states, and projected density of state (PDOS) analysis. This process is operando tracked and visualized at the picosecond time scale by advanced ab initio molecular dynamics (AIMD) simulations. The initial olefins ignite autocatalysis by building the first autocatalytic cycle-olefins-based cycle-followed by the speciation of methylcyclopentenyl (MCP) and aromatic cyclic active species. In doing so, the active sites accomplish the dynamic evolution from proton acid sites to supramolecular active centers that are experimentally identified with an ever-evolving and fluid feature. The olefins-guided and cyclic-species-guided catalytic cycles are interdependently linked to forge a previously unidentified hypercycle, being composed of one "selfish" autocatalytic cycle (i.e., olefins-based cycle with lighter olefins as autocatalysts for catalyzing the formation of olefins) and three cross-catalysis cycles (with olefinic, MCP, and aromatic species as autocatalysts for catalyzing each other's formation). The unraveled dynamic autocatalytic cycles/network would facilitate the catalyst design and process control for MTH technology.

Structural Features in Some Layered Hybrid Copper Chloride Perovskites: ACuCl4 or A2CuCl4.

We present three new hybrid copper(II) chloride layered perovskites of generic composition ACuCl4 or A2CuCl4, which exhibit three distinct structure types. (m-PdH2)CuCl4 (m-PdH22+ = protonated m-phenylenediamine) adopts a Dion-Jacobson (DJ)-like layered perovskite structure type and exhibits a very large axial thermal contraction effect upon heating, as revealed via variable-temperature synchrotron X-ray powder diffraction (SXRD). This can be attributed to the contraction of an interlayer block, via a slight repositioning of the m-PdH22+ moiety. (3-AbaH)2CuCl4 (3-AbaH+ = protonated 3-aminobenzoic acid) and (4-AbaH)2CuCl4 (4-AbaH+ = protonated 4-aminobenzoic acid) possess the same generic formula as Ruddlesden-Popper (RP) layered perovskites, A2BX4, but adopt different structures. (4-AbaH)2CuCl4 adopts a near-staggered structure type, whereas (3-AbaH)2CuCl4 adopts a near-eclipsed structure type, which resembles the DJ rather than the RP family. (3-AbaH)2CuCl4 also displays static disorder of the [CuCl4]∞ layers. The crystal structures of each are discussed in terms of the differing nature of the templating molecular species, and these are compared to related layered perovskites. Preliminary magnetic measurements are reported, suggesting dominant ferromagnetic interactions.

One-step synthesis of gasoline fuels from γ-valerolactone with high selectivity over Cu/HZSM-5 bifunctional catalyst

Direct synthesis of transportation liquid fuels from renewable biomass-based resources via γ-valerolactone (GVL) is a highly attractive but challenging target. The current conversion of biomass-derived GVL to liquid fuels suffers from low selectivity or multiple operation steps with high energy consumption. Herein, we reported a simple and efficient way for the high-selective conversion of GVL into gasoline fuels over designed Cu/HZSM-5 bifunctional catalyst in a single fixed-bed reactor. The excellent catalytic performance of 99.9 % conversion of GVL with 85.3 % selectivity to C5+ hydrocarbons (mainly C5-C12) and good stability were obtained. We demonstrated that the interfacial sites composed of metallic Cu and proton acid of HZSM-5 played a key role in determining the performance via providing a spontaneous CO bond breaking path of GVL, facilitating the formation of pentene intermediate that could be further converted to gasoline fuels through a series of aromatization, alkylation and oligomerization reactions.

Ion exchange capacity controlled biphenol-based sulfonated poly(arylene ether sulfone) for polymer electrolyte membrane water electrolyzers: Comparison of random and multi-block copolymers

Conventionally, highly proton conductive perfluorosulfonic acid (PFSA) ionomers are used for an electrolyte membrane in a polymer electrolyte membrane water electrolyzer. As alternatives to the expensive and highly hydrogen permeable PFSA membranes, hydrocarbon-based sulfonated poly(arylene ether sulfone) proton conducting polymers (BPSH) are synthesized by varying their ion exchange capacity (IEC) from 1.2 to 2.0 meq/g, and the way to employ ion conducting units into polymers (random versus block). BPSH membranes show much lower hydrogen permeability (20 − 45 barrer) than that of PFSA membranes (~115 barrer for Nafion) at 80 °C and 100%RH. Random BPSH membranes show slightly higher selectivity of proton to hydrogen than the membranes from multi-block BPSH copolymers at a similar IEC may due to the enhanced hydrogen barrier property by less-developed hydrophilic phase. The best performing random BPSH with the IEC ~ 1.9 meq/g shows better performance (5.3 A/cm2) than the similarly thick (~50 μm) Nafion 212 (4.8 A/cm2) at 1.9 V, but the higher degradation rate (951 μV/h) than Nafion 212 (613 μV/h) at an accelerated stress test with the 360 consecutive alternating current densities of 3 and 0.02 A/cm2, simulating on and off a water electrolyzer.

A selective polypyrrole-based sub-ppm impedimetric sensor for the detection of dissolved hydrogen sulfide and ammonia in a mixture

An impedance-transducer sensor was developed for in situ detection of hydrogen sulfide (H2S) and ammonia (NH3) in aqueous media. Using cyclic voltammetry (CV), polypyrrole (PPy) was deposited on the surface of the microfabricated interdigitated gold electrode. Due to the proton acid doping effect of H2S on PPy and ionic conduction of the film, the sensor showed a decreasing impedance response to H2S unlike other reducing chemicals, i.e., ammonia (NH3). The recorded faradaic data was then associated with an equivalent circuit and compared with that of NH3 to examine the selectivity of the sensor. An electrochemical impedance spectroscopy (EIS) analysis was applied to the mixture of H2S and NH3 prepared at different ratios for the concentrations ranging from 2 ppm to 20 ppm (below 2-ppm, no response was observed due to the formation of NH4HS, not sensible with PPy). The principal component analysis (PCA) was used to train a real-time prediction model for both classification (for the type of the analyte) and regression (the concentration of the analyte). The results showed the high performance of the sensor in determining individual analytes while the model was able to accurately predict the amount of H2S and NH3 in the mixture.

On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan.

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H2-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.

Opposite substituent effects in the ground and excited states on the acidity of N-H fragments involved in proton transfer reaction in aromatic urea compounds.

To investigate substitution effects on excited-state intermolecular proton transfer (ESPT) reactions as well as acidity of proton donating fragments in the ground state, we synthesized substituted anthracen-2-yl-3-phenylurea derivatives that form a hydrogen bonds with acetate anions and undergo ESPT reaction. Fluorescence lifetime measurements and their kinetic analyses revealed that the trifluoromethyl group on the phenyl ring as an electron-withdrawing group caused a slow ESPT reaction despite an increase in the acidity of the N-H fragment in the ground state. In contrast, the methoxy group as a donating group leads to a fast ESPT reaction despite a reduction of the acidity of the N-H fragment in the ground state. These effects of substituents on ESPT reaction are due to their influence on the charge transfer reaction, which occurs from the N-H fragment to the anthryl ring to increase the acidity of N-H followed by ESPT reaction, over the urea unit by a combination of resonance and inductive effects. These opposing effects of substituents on the acidity of the urea unit in the ground and excited states provide an important insight in balancing the reactivity of proton transfer reaction in both the excited and ground states.

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Two kinds of polyaniline fiber photo sensor with interdigital electrode and flexible hydrogel

AbstractIn previous studies, polyaniline nanofiber sensor on interdigital electrode is sensitive to light. Herein, we prepared a flexible hydrogel sensor with polyaniline nanofiber as the active material and polyacrylamide hydrogel as the flexible substrate. Comparing the properties of above two different kinds of sensors with polyaniline nanofiber, the photocurrent generated by PANI‐hydrogel sensor under external light stimulation is about 1 ~ 2 orders of magnitude higher than interdigital electrode sensor, indicating the PANI‐hydrogel sensor is more sensitive. The two sensors can all respond to different wavelengths of monochromatic light, especially sensitive to light of smaller wavelengths such as ultraviolet light (380 nm) and blue light (475 nm). Moreover, the volt‐ampere characteristic curve in response to external light stimulation can be clearly distinguished only when the appropriate concentration of proton acid is doped (3 g citric acid, 7 g acetic acid, and 3 ml HCl).

How can fluorine directly and indirectly affect the hydrogen bonding in molecular systems? – A case study for monofluoroanilines

Hydrogen bonds (HBs) directly engaging fluorine has been extensively studied, but the indirect effect of fluorine on adjacent donors and acceptors is poorly understood and still difficult to predict. The indirect and direct effect of the fluorination of aniline on HB patterns observed in monofluoroanilines was studied via experimental (vibrational spectroscopy and crystal structure analysis) and theoretical (ab initio molecular dynamics and electrostatic surface potential) methods. It was found that a fluorine substituent decreases the strength and frequency of N–H⋯N HBs and, at the same time, increases the acidity of CH protons, enhancing the competitiveness of weaker interactions. Additionally, the position of fluorine in the aromatic ring strongly affects the C–F bond length, and a direct intramolecular N–H⋯F HB causes an increase in the N–H bond stability. We also provide a methodology to identify and separate individual HBs concerning the type of donor or acceptor from the ab initio molecular dynamics trajectories.

Synthesis of the novel binary composite of self-suspended polyaniline (S-PANI) and functionalized multi-walled carbon nanotubes for high-performance supercapacitors

To push the upper limit of capacitive materials, the integration of multi-modal capacitive materials has emerged as a potential solution. In this regard, we reported the novel binary composite of self-suspended polyaniline (S-PANI) and multi-walled carbon nanotubes (MWNTs). Compared with conventional polyaniline, S-PANI offers higher porosity and fibrillar polymeric network, which was achieved by doping long-chain protonic acid during in situ polymerization. S-PANI was loaded on oxidized carbon nanotubes (OCNTs) and sulfonated carbon nanotubes (SCNTs) to prepare S-PANI/OCNT and S-PANI/SCNT composite electrodes, respectively. The conductive and exclusive fibrillar S-PANI provide unobstructed channels for charge transport and electrolyte infiltration. Preliminary electrochemical studies revealed that the capacitance of the composite electrode reached 316.8 F g−1 and 345.4 F g−1, and established exceptional capacitance retention rates of 92.8% and 93.7% after 5000 cycles for S-PANI/OCNT and S-PANI/SCNT composite, respectively, making it a potential candidate for imminent energy storage devices.