Simple Protonation Research Articles

Water Compatible Conjugated Microporous Polyazulene Networks as Visible‐Light Photocatalysts in Aqueous Medium

AbstractA synthetic and modification method to obtain water‐compatible, visible‐light‐active, conjugated, microporous polyazulene networks as pure organic, highly stable, reusable, and heterogeneous photocatalysts in aqueous medium by a simple protonation method was investigated. The water compatibility and photocatalytic activity of the hydrophilic polyazulenes were demonstrated in the photoreduction reaction of CrVI to CrIII for heavy‐metal‐contaminated waste‐water treatment. Furthermore, a light‐induced cascade reaction mechanism with the use of additional abundant metal cations such as FeIII or CuII as co‐catalysts was also described. This design strategy could offer a clean and cost‐effective solution to obtain water‐compatible, pure organic, photoactive polymers with a broader potential for other applications in aqueous media under sustainable and environmentally friendly conditions.

Exploring the acid-catalyzed substitution mechanism of [Fe4S4Cl4](2-).

Kinetic studies on the acid-catalyzed substitution reactions of the teminal chloro-ligands in [Fe4S4Cl4](2-) by PhS(-) in the presence of the acids NHR3(+) (R = Me, Pr(n) or Bu(n)) are reported. Although these acids have very similar pKas (17.6-18.4) the reactions show a variety of different kinetics, some of which are inconsistent with a mechanism involving simple protonation of the cluster followed by substitution of a terminal ligand. The observed behaviour is more consistent with the recently proposed mechanism in which Fe-(μ3-SH) bond elongation/cleavage occurs upon protonation of a μ3-S, and suggests that both the acidity and bulk of the acid is important in the protonation step. Other studies have determined the activation parameters (ΔH(‡) and ΔS(‡)) for both the protonation and substitution steps of the acid-catalyzed substitution reactions of [Fe4S4X4](2-) (X = Cl or SEt). A significantly negative ΔS(‡) is observed for the substitution steps of both clusters indicating associative pathways. This is inconsistent with earlier interpretation of the kinetics of these reactions (based exclusively on the dependence of the rate on the concentration of nucleophile) and indicates that there is no dissociative substitution mechanism and the pathway associated with a zero order dependence on the concentration of PhS(-) involves associative substitution with the solvent (MeCN) being the nucleophile.

Enhanced Driving Force and Charge Separation Efficiency of Protonated g-C3N4 for Photocatalytic O2 Evolution

Photocatalysts based on g-C3N4 by loading cocatalysts or constructing heterojunctions have shown great potential in solar-driven water oxidation. However, the intrinsic drawbacks of g-C3N4, such as poor mass diffusion and charge separation efficiency, remain as the bottleneck to achieve highly efficient water oxidation. Here we report a simple protonation method to improve the activity of g-C3N4. Studies using valence band X-ray photoelectron spectra and steady-state and time-resolved spectroscopy reveal that the promotion of catalytic ability originates from the higher thermodynamical driving force and longer-lived charge separation state, which may provide guidance in designing efficient polymeric semiconductor photocatalysts with desirable kinetics for water oxidation.

Efficient solid support catalyzed mono-aza-Michael addition reactions of piperazine

We report new methods for the efficient mono-aza-Michael additions of piperazine to compounds with activated multiple carbon–carbon bond (functional derivatives of acrylic, propiolic, and acetylenedicarboxylic acid). This method is based on the reaction of piperazine-1-ium cation with alkenes or alkynes substituted by EWGs under catalysis by various metal ions supported on weakly acidic cation-exchanger resin. Starting piperazine-1-ium cation is generated in situ in methanol solution by mixing of piperazine and piperazine-1,4-diium dichloride in various ratios. It was found that solid support metal catalysis afforded target products in very good yields in shortened reaction times. A new method of N-monosubstituted piperazine derivative preparation is very beneficial, because until now no one has come up with the idea to use for protection of the one nitrogen atom of the piperazine its simple protonation. Computer modeling of behavior of piperazine depending on the pH was carried out and according to the results, we concluded that the protonation of the nitrogen atom is the simplest, most effective, and most elegant method of preventing unwanted formation of 1,4-disubstituted product. Assumption was fully confirmed by number of syntheses. The main advantages of our syntheses are great simplicity, one-pot performance, use of non-toxic solvents only, mild reaction conditions, no generation of waste, short time of reactions, and high yields.

Room-temperature hydrohydrazination of terminal alkynes catalyzed by saturated abnormal N-heterocyclic carbene-gold(I) complexes.

A number of saturated abnormal N-heterocyclic carbene (NHC) complexes of gold, in combination with KBAr(F) 4 as activator, were successfully applied in the chemoselective addition of hydrazine to alkynes. The reaction proceeds even at room temperature, which was not possible to date with gold catalysts. The reaction can be applied to a number of substituted arylalkynes. With alkylalkynes the yields are low. The saturated abnormal NHC ligands are resistant to isomerization to the saturated normal NHC coordination mode under basic reaction conditions. Under acidic conditions, a simple protonation at the nitrogen atom not neighboring the carbene center was observed and unambiguously characterized by an X-ray crystal-structure analysis. Computational studies confirm that such an isomerization would be highly exothermic, the observed kinetic stability probably results from the need to shift two protons in such a process.

A Versatile Metal‐Free Intermolecular Aminochlorination of Alkenes

AbstractNew reaction conditions for the rapid and productive intermolecular aminochlorination reaction of alkenes using a combination of chloramine‐T and a Brønstedt acid are described. Upon simple protonation of chloramine‐T, conditions for a mild and selective aminochlorination are obtained. In addition, the reaction can proceed to form either of the two possible regioisomers, depending on whether a stoichiometric amount of such an acid activator or acetic acid is used as solvent. The reaction is operative for all different classes of alkenes. A total of over 50 examples is presented to illustrate this concept.magnified image

The positions of inner hydroxide groups and aluminium ions in exfoliated kaolinite as indicators of the external chemical environment.

Kaolinite as a remarkable industrial raw material has notable structural features despite its simple chemical composition (Al2O3·2SiO2·2H2O). We report here a systematic development of a coordination chemical model for the [6Al-6(OH)] honeycomb-like unit of kaolinite's octahedral sheet, which was proposed to be the adsorption site for small molecules from earlier studies. The coordination environment of the Al(3+) ions was completed with outer sphere groups from both octahedral and tetrahedral sheets. Dangling bonds were terminated by additional Al(3+) and Si(4+) ions with hydroxide and oxide groups from the second coordination sphere versus simple protonation. A cage of Na(+) and Mg(2+) ions rendered the computational model to be charge neutral. In this exfoliated kaolinite model, the inner hydroxide groups and the adjacent Al(3+) ions have compositionally the most complete environments with respect to the crystal structure. Thus, their atomic positions were used as a benchmark for the level of theory dependence of the optimized structures. We evaluated the performance of a representative set of density functionals, basis sets, point-charges, identified pitfalls and caveats. Importantly, the structural changes during optimization of periodic and cluster models suggest pliability for the exfoliated kaolinite layers, which is influenced by the external chemical environment.

Reversible switching of the electronic ground state in a pentacoordinated Cu(ii) complex

An easy reversible switching of the electronic ground state in a pentacoordinated copper(II) complex is reported for the first time. The simple protonation of a carboxylic group in a Cu(II) complex with a {dx(2)-y(2)}(1) electronic configuration leads to a flip of the ground electronic configuration from {dx(2)-y(2)}(1) to {dz(2)}(1) in the metal ion.

Nitrite Signaling in Pulmonary Hypertension: Mechanisms of Bioactivation, Signaling, and Therapeutics

Pulmonary arterial hypertension (PAH) is a disorder characterized by increased pulmonary vascular resistance and mean pulmonary artery pressure leading to impaired function of the right ventricle, reduced cardiac output, and death. An imbalance between vasoconstrictors and vasodilators plays an important role in the pathobiology of PAH. Nitric oxide (NO) is a potent vasodilator in the lung, whose bioavailability and signaling pathway are impaired in PAH. It is now appreciated that the oxidative product of NO metabolism, the inorganic anion nitrite (NO(2)(-)), functions as an intravascular endocrine reservoir of NO bioactivity that can be reduced back to NO under physiological and pathological hypoxia. The conversion of nitrite to NO is controlled by coupled electron and proton transfer reactions between heme- and molybdenum-containing proteins, such as hemoglobin and xanthine oxidase, and by simple protonation and disproportionation, and possibly by catalyzed disproportionation. The two major sources of nitrite (and nitrate) are the endogenous L-arginine-NO pathway, by oxidation of NO, and the diet, with conversion of nitrate from diet into nitrite by oral commensal bacteria. In the current article, we review the enzymatic formation of nitrite and the available data regarding its use as a therapy for PAH and other cardiovascular diseases. The successful efficacy demonstrated in several animal models and safety in early clinical trials suggest that nitrite may represent a promising new therapy for PAH.

Preparation, characterization and antifouling property of polyethersulfone–PANI/PMA ultrafiltration membranes

Novel polyaniline (PANI)/phosphomolybdicacid (PMA) nanoparticles were prepared by simple protonation method and used to enhance the antifouling property of polyethersulfone (PES) ultrafiltration membranes. The prepared nanoparticle size around 30±3nm was confirmed by transmission electron microscopy and scanning electron microscopy analyses. Complete PMA incorporation with PANI was evaluated by Fourier transform infrared spectroscopy analysis. The surface charge of nanoparticles are average value is of −46mV. The contact angle, water flux and flux with rejection of protein of all membranes increased by increasing nanoparticle concentrations in the range of 0, 2, 3, 5 and 7wt.% into casting solution. Compared to pure PES membrane, the PES–PANI/PMA membrane exhibits better antifouling performance with very high (>98.8%) protein rejection rate. Especially, the 3wt.% PANI/PMA nanoparticles incorporated membrane shown superior results than other membranes. The roughness of PES–PANI/PMA membranes are remarkably enhanced due to the drastic enrichment of nanoparticle segments on the membrane surface. Bovine serum albumin (BSA) was used as a model protein to investigate the protein adsorption resistivity and permeation properties of all membranes. BSA ultrafiltration experiment showed that PES–PANI/PMA membranes had higher flux and better antifouling property than PES membrane.

A BODIPY derivative as a highly selective “Off–On” fluorescent chemosensor for hydrogen sulfate anion

A new fluorescent receptor for 1 anions has been synthesized by the combination of BODIPY dye and indole moiety. The binding and sensing abilities of receptor 1 toward various anions have been studied by absorption, emission and (1)H NMR titrations spectroscopies. Receptor 1 could act as a highly selective "Off-On" fluorescent sensor for hydrogen sulfate anion in CH(3)CN solvent and CH(3)CN-H(2)O medium. The fluorescence response of receptor 1 toward HSO(4)(-) in CH(3)CN solvent could be due to the suppressed PET (photo-induced electron transfer) process induced by the multiple hydrogen bonding interactions between receptor 1 and HSO(4)(-). In CH(3)CN-H(2)O medium, the HSO(4)(-)-induced change is mainly the consequence of a simple protonation of the CH=N- moiety of receptor 1, which inhibited the PET process and "turned on" the fluorescence of 1.

Ab Initio Study of the Charge-Storage Mechanisms in RuO2-Based Electrochemical Ultracapacitors

The charge-storage mechanisms in ruthenium dioxide are investigated with first-principles density-functional theory (DFT) calculations. Both proton-intercalated bulk and proton-adsorbed RuO2(110) surfaces have been studied to obtain insight into the energetics of discharging processes in RuO2-based aqueous supercapacitors. We predict the existence of a stable ruthenium oxyhydroxide (RuOOH) and demonstrate that the RuO2(110) surface as well as a significant fraction of the available subsurface sites remain completely protonated during cyclic voltammetry measurements in aqueous electrolytes. DFT calculations also show that the bulk proton insertion not only is kinetically inhibited by a high energy barrier of proton diffusion in bulk RuO2 (1.62 eV), but also is thermodynamically inactive under the experimental operating conditions due to a low intercalation voltage (0.08 V in the dilute limit). These results exclude simple bulk or surface protonation as the reason for excellent electrochemical performance of hydrous nanocrystalline RuO2 supercapacitors and point to the importance of subsurface and grain boundary effects.

Ligand-to-ligand electron transfer and temperature induced valence tautomerism in o-dioxolene chelated manganese complexes

Three polymeric o-dioxolene chelated manganese(III) complexes, {[Mn III(H 2L 1)(Cl 4Cat) 2][Mn III(Cl 4Cat) 2(H 2O) 2]} ∞ ( 1) (L 1 = N, N′- bis(2-pyridylmethyl)-1,4-butanediamine, Cl 4Cat = tetrachlorocatecholate dianion], {[Mn III(H 2L 1)(Br 4Cat) 2][Mn III(Br 4Cat) 2(H 2O) 2]·4DMF} ∞, ( 2) and {[Mn III(H 2L 2)(Br 4Cat) 2][Mn III(Br 4Cat) 2(DMF) 2]} ∞ ( 3) (L 2 = N, N′- bis(2-pyridylmethyl)-1,6-hexanediamine, Br 4Cat = tetrabromocatecholate dianion) have been synthesized and structures were determined by X-ray crystallography. All the complexes were fully characterized by various spectroscopic techniques and their electronic properties are described. It was found that the simple protonation or deprotonation of the bridging ligand (L 1 or L 2) coordinated to metal–dioxolene chromophore induce a change in the oxidation state of the coordinated dioxolene ligand without affecting the metal oxidation state. As a result, drastic change in the optical absorption properties of the complexes is observed in the visible and near-IR region as the transformation involves semiquinone–catecholate ligands. Moreover, all three complexes undergo thermally induced valence tautomerism in solution. For all the complexes, on increasing the temperature, the intensity of the lower energy Inter Valence Charge Transfer (IVCT) band at about 1930 nm increases with corresponding decrease of 600 nm band with an isosbestic point at 1820 nm due to the formation of mixed valence species Mn II(X 4SQ)(X 4Cat) − from Mn III ( X 4 Cat ) 2 - (X = Cl or Br) by the transfer of one electron from Cat 2− to Mn III center.

Ionic liquid crystals derived from 4-hydroxypyridine

Monoalkylation of 4-hydroxypyridine gave either neutral N-alkyl-4-pyridones or 4-alkoxypyridines depending on the site (N or O) of alkylation. Further alkylation of these two neutral compounds yielded ionic liquid crystals (ILCs) of N-alkyl-4-alkoxypyridinium bromide, having two long alkyl chains. Alternatively, simple protonation of the two neutral compounds with HCl also induced the formation of ILCs of N-alkyl-4-hydroxypyridinium chloride or 4-alkoxypyridinium hydrochloride. Crystal structures of two different types of ionic liquid crystals and one neutral compound were determined via single crystal X-ray diffraction. Mesophase properties were examined by the technique of differential scanning calorimetry, polarized optical microscopy, and powder X-ray diffractometry. Anions influence the structure and stability of the mesophase in the dialkylated compounds. The self-assembly behavior of some typical compounds in solution was studied using the technique of NMR diffusion order spectroscopy. Finally, stable Au nanoparticles stabilized by a pyridinium salt were prepared and characterized.

Simple and Efficient Generation of White Light Emission From Organophosphorus Building Blocks

AbstractThis paper describes a structure–property study using two dithieno[3,2‐b;2′,3′‐d]phosphole building blocks for the generation of white light emission and the incorporation of these units in a single polystyrene material. The emission of one of the light‐emitting organophosphorus building blocks can efficiently be switched from orange to green by simple protonation of the amino functional groups that are part of the π‐conjugated scaffold. The resulting three components (blue, green, and orange) exhibit photophysical properties that allow for an efficient fluorescence resonance energy transfer (FRET) in the mixture/polymer and provide intense white fluorescence upon excitation of the blue component; the fluorescence is close to pure white in solution and similar to the emission of an incandescent light bulb in the thin film. The results nicely illustrate the intriguing features that can be obtained by exclusively using organophosphorus‐based organic electronic materials.

The ins and outs of proton complexation

Proton complexation differs from simple protonation by the fact that the coordinated hydrogen atom is bound intramolecularly to more than one donor atom. This is usually achieved by covalent bonding supplemented by hydrogen bonding. In a few cases, however, the complexed proton is hydrogen-bound to all donor atoms, which gives rise to single well (SWHB) and low barrier (LBHB) hydrogen bonds. This tutorial review highlights a full range of proton complexes formed with chelating and "proton-sponge"-type ligands, cryptand-like macropolycycles, and molecules of topological relevance, such as rotaxanes and catenanes. The concept of proton complexation can explain how the smallest cation possible can bring molecules to order and trigger intramolecular molecular rearrangements and motions.

Au(I)-Catalyzed Hydrative Rearrangement of 1,1-Diethynylcarbinol Acetates to Functionalized Cyclopentenones and Allenones

Atom-economical syntheses of isomeric 5-acetoxy-2-alkyl-2-cyclopentenones (2) and acetoxymethyl alpha-alkylallenones (3) have been described via Au-catalyzed hydrative rearrangement of 1,1-diethynylcarbinol acetates (1). In anhydrous condition, Au(I)-catalyzed [3,3]-rearrangement of 1 afforded the 3-alkynylallenyl acetate 4 in low yield. Treatment of 1 with Au(I) catalyst in wet CH(2)Cl(2) produced either 2 or 3 as a major product depending on the temperature, reaction time, and catalyst loading. D has been proposed as an intermediate, which might be formed via Au(I)-induced internal oxacyclization of the intermediate 4 followed by chemoselective nucleophilic attack by the water molecule. Formation of 2 or 3 might be explained via sequential 1,3-dioxole ring opening and gold-promoted 5-endo-dig carbocyclization or simple protonation of the intermediate D, respectively.

Quantitative analysis of dispersion and doping of individual carbon nanotubes in water based solutions using absorption and Raman spectroscopy

AbstractThe concentration dependence of the dispersion of carbon nanotubes in water surfactant solution is monitored using absorption and Raman spectroscopy revealing a debundling below ∼0.07 g/l. A quantitative analysis of the doping of individual carbon nanotubes in surfactant at this concentration is conducted by varying the pH from 1 to 13 and monitoring the Raman spectrum. Mixed Gaussian and Lorentzian line shapes were fitted to the radial breathing modes and using a simple protonation model, an equilibrium constant Kp was obtained for each RBM. The protonation rate was related to the optical band gap of the tubes and the number of protons acting per entity was also calculated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Removal of fluoride from aqueous solution using protonated chitosan beads

In the present study, chitosan in its more usable bead form has been chemically modified by simple protonation and employed as a most promising defluoridating medium. Protonated chitosan beads (PCB) showed a maximum defluoridation capacity (DC) of 1664 mg F −/kg whereas raw chitosan beads (CB) possess only 52 mg F −/kg. Sorption process was found to be independent of pH and altered in the presence of other co-existing anions. The sorbents were characterized using FTIR and SEM with EDAX analysis. The fluoride sorption on PCB follows both Freundlich and Langmuir isotherms. Thermodynamic parameters, viz., Δ G°, Δ H° Δ S° and E a indicate that the nature of fluoride sorption is spontaneous and endothermic. The sorption process follows pseudo-second-order and intraparticle diffusion kinetic models. 0.1 M HCl was identified as the best eluent. The suitability of PCB has been tested with field samples collected from a nearby fluoride-endemic area.

Solution processible and conductive polyaniline via protonation with 4,4-bis(4-hydroxy phenyl)-valeric acid: Preparation and characterization

It is demonstrated that polyaniline salt, obtained by simple protonation of its base form with 4,4-bis(4-hydroxy phenyl)-valeric acid (HPVA), combines solution processibility with electrical conductivity. The solution of PANI–HPVA in DMF and m-cresol mixture has been characterized by UV–vis spectroscopy, exhibiting spectral features characteristic of the protonated state. Precipitation of dissolved PANI–HPVA with chloroform, leads to powder of spherical morphology with an average particle size of 400 nm which is amorphous by X-ray. Their conductivity is ca. 10 − 3 S/cm (measured for pressed pellets). Thermogravimetric investigations indicate good thermal stability of this novel form of polyaniline, however some weight loss is observed below 200 °C, associated with the removal of minute amounts of solvent entrapped within PANI–HPVA grains in the precipitation process. PANI–HPVA has film forming properties and free standing films (conductivity ca. 10 − 4 S/cm) can be obtained by dissolving the powders in DMF, followed by casting.