Protolytic Reaction Research Articles

Investigation of the protolytic equilibrium of a highly Brønsted acidic ionic liquid and residual water using Raman spectroscopy

• The protolysis of the high Brønsted-acidic protic ionic liquid 2-sulfoethylammonium was investigated by Raman spectroscopy. • The frequency upward shift of the S-C stretching mode was employed to monitor protolysis equilibrium of the cation. • The protolysis equilibrium constant was determined by using the integral intensities. • DFT calculations were performed to support the assignment of the Raman bands. • The acidity of the sulfoalkylammonium-based ionic liquid with residual water is in the same order of magnitude as H 3 O + . Protic ionic liquids (PILs) are promising candidates as non-aqueous proton-conducting electrolytes for use in polymer electrolyte membrane fuel cells with operating temperatures over 100 °C. 2-sulfoethylammonium triflate [2-Sea][TfO] is one such PIL electrolyte, in which the highly Brønsted acidic sulfoalkylammonium cations act as mobile protonic charge carriers and proton donors. In order to gain a molecular-level understanding of proton transfer in a PIL electrolyte containing a small amount of residual water from fuel cell operation, the protolytic equilibrium of the highly acidic cation was investigated by means of Raman spectroscopy. Density functional theory (DFT) calculations were conducted to identify the vibration modes sensitive to protonation and to gain information on the possible conformation of the cation. The deprotonation of the 2-sulfoethylammonium cation resulted in a characteristic upward frequency shift in the ν(SC) stretching vibration. An equilibrium constant of 0.23 ± 0.09 was calculated for the protolytic reaction, indicating [2-Sea][TfO] as a promising proton donor for the fuel cell application.

Insights into the Role of Framework and Nonframework Aluminum in the Protolytic Reaction of Carbon–Carbon and Tertiary Carbon–Hydrogen Bonds of Isobutane

Insights into the Role of Framework and Nonframework Aluminum in the Protolytic Reaction of Carbon–Carbon and Tertiary Carbon–Hydrogen Bonds of Isobutane

Features of protolytic reactions in the ground and exited states in the presence of cationic polyelectrolyte

Protolytic reactions in the ground and excited states for 2-naphthol and its sulfo derivatives were studied. It was revealed that in the presence of cationic polyelectrolyte, the acidity constant of the protolytic reaction in the ground state shifts to a more acidic region. It was also found that the value of the shift depends on the number of sulfo substituents in 2-naphthol derivatives. It reaches 1.2 units for the disodium salt of 2-naphthol-3,6,8-trisulfonic acid. At the same time, no significant effect of the polyelectrolyte on the acidity constant in the excited state pKa* was observed, and the photoprotolytic reaction proceeds in the same way as for an unimmobilized substance.

Alkynylaluminum Synthesis Catalyzed by a Zwitterionic Neodymium(III) Heterobimetallic Compound

The reaction of H{PhB(OxMe2)2C5H5} (OxMe2 = 4,4-dimethyl-2-oxazoline) with Nd(AlMe4)3 (1) provides Me2Al{(OxMe2)2PhBCp}Nd(AlMe4)2 (2) as a heterobimetallic complex containing inequivalent organoaluminum sites. The piano-stool coordination geometry around Nd includes a rare O-bonded oxazoline, while both oxazolines coordinate to AlMe2 as part of a 6-membered, nonplanar BC2N2Al ring. The zwitterionic κ2-Ph(C5H5)B(OxMe2)2AlMe2 (3), formed by the protolytic reaction of H{PhB(OxMe2)2C5H5} and (AlMe3)2, also provides 2 upon reaction with Nd(AlMe4)3. Compounds 1–3 are precatalysts for the selective metalation of terminal alkynes by trialkylaluminums to yield (alkynyl)dialkylalanes of the type R′C≡C–AlR2, which are valuable as alkynyl transfer reagents. This catalytic reaction provides metalation products exclusively, as compared to the mixture of products from uncatalyzed processes. In addition, heteroleptic heterobimetallic 2 is a superior catalyst to 1 and 3.

Structure and potential applications of amido lanthanide complexes chelated by bifunctional β-diketiminate ligand

The synthesis and structure of lanthanide(III) amides containing one bifunctional β-diketiminate ligand is reported. Compounds were obtained via a protolytic reaction of the free β-diketimine {N-[(2-MeO)C6H5]}NC(Me)CHC(Me)N(H){N′-[(2-MeO)C6H5]} (LCOH) or {N-[(2-MeO)C6H5]}NCHCHCHN(H){N′-[(2-MeO)C6H5]} (LHOH) with corresponding tris(amide) of the Ln[N(SiMe3)2]3 (Ln = Y, La, Nd, Sm, Eu, Gd and Yb) type in equimolar ratio at ambient temperature. Products were characterized by IR and/or multinuclear NMR spectroscopy techniques and structures of four of them have been determined by X-ray diffraction techniques. Complexes LCOY[N(SiMe3)2]2, LCOLa[N(SiMe3)2]2, LCONd[N(SiMe3)2]2 and LHOYb[N(SiMe3)2]2 crystalize as monomers with the six-coordinated metal centre by two amido and one tetradentate β-diketiminato ligands. Minor hydrolytic products of composition [LCOSmN(SiMe3)2]2O and (LCO)4O2(OH)4La4 were obtained and their structures contain two or four lanthanide atoms linked through the oxo- or hydroxo bridges. Diamagnetic complexes were tested for its potential applications in hydroamination and polymerization reactions, respectively, giving low conversion in all reactions.

New Aminobenzopyranoxanthene‐Based Colorimetric Sensor for Copper(II) Ions with Dual‐Color Signal Detection System

One molecule, three faces: A new aminobenzopyranoxanthene (ABPX)-based colorimetric sensor allows determination of changes in Cu2+ concentration by spectrophotometry and the naked eye. This quantitative, colorful, and simple method takes advantage of the unique protolytic reaction of ABPX in response to Cu2+.

Impact of Micelle Ionic Electrical Double Layer Structure on the Excited State Protolytic Reaction in the Fluorescent Probe Bound to the Colloidal Nanoparticles

The fluorescent probe, 2-hydroxynaphthalene(dodecylo)-6-sulfonamide (NSDA) bound selectively to shear plane of various electrostatic charges was synthesized and its photophysical properties have been investigated by means of steady state fluorescence and nanosecond time-resolved spectroscopy. Our experimental data allowed us to determine the excited state proton transfer (ESPT) rate and equilibrium constants of NSDA bound to micelles and to estimate the electric potential value (Ψ) at the particle surface. The spatial dependence of proton movement velocity through electric double layer (EDL) of micelles has been thoroughly analyzed. In this article, a new approach of estimating the values of the micelle potential (Ψ(R)) from the excited state proton transfer rate constant of the fluorescent probe bound at a certain distance (R) to a micellar surface has been proposed. The Ψ(R) values, obtained in this way, are compared with electrophoretic values of the particle potential (ζ). Our results on electrophoretic potentials and the reaction course of the ESPT in colloidal environment may contribute to a deeper understanding of micellar interactions and behavior of the living cells in contact with various diluted substances such as pharmacological drugs, hormones, proteins, and other colloidal particles.

Potentiometric determination of lysine in aqueous solutions using MF-4SK modified perfluorinated membranes

A selective potentiometric sensor was developed on the basis of MF-4SK modified perfluorinated sulfonic cation-exchange membranes for determining lysine monohydrochloride in mixed aqueous solutions of neutral amino acids. It was shown that the treatment of MF-4SK membranes in ethylene glycol increased the sensitivity of the sensor. The use of MF-4SK perfluorinated sulfonic cation-exchange membranes for determining lysine in aqueous solutions is based on a protolytic reaction; as a result of this reaction, single-charged lysine ions from solution are transferred into doubly charged ions in the membrane phase. The Donnan potential at an individual boundary between the studied solution and the membrane is the sensor response. The response time was 10–15 min. The concentration constants of the sensor selectivity to lysine in the presence of glycine, alanine, and leucine did not exceed 0.019. The relative error of determining lysine monohydrochloride in the studied solutions of neutral amino acids was 2–5%.

Heteroleptic ytterbium(ii) complexes supported by a bulky β-diketiminato ligand

Heteroleptic beta-diketiminatoytterbium(ii) complexes [{Yb(L)(mu-I)(thf)}(2)] [: L = {N(Ar*)C(Me)}(2)CH = L(1), : L = {N(SiMe(3))C(Ph)}(2)CH = L(2); Ar* = C(6)H(3)(i)Pr(2)-2,6] were prepared by a salt elimination [from YbI(2)(thf)(2) and KL] or by a ligand redistribution [from YbI(2)(thf)(2) and YbL(2)] reaction. Complexes and were convenient precursors to some new Yb(ii) heteroleptic compounds. Thus, reaction of and with KN(SiMe(3))(2) yielded the mononuclear amido compounds [Yb(L){N(SiMe(3))(2)}(thf)] (: L = L(1) and : L = L(2)). Similarly, with K{N(H)Ar*} gave [Yb(L(1)){N(H)Ar*}(thf)] (). Complex was also obtained via a protolytic reaction of [Yb{N(SiMe(3))(2)}(2)(thf)(2)] with HL(1) at an elevated temperature. Treatment of with slightly less than a stoichiometric amount of K{CH(SiMe(3))(2)} afforded [Yb(L(1)){CH(SiMe(3))(2)}(thf)] (), while using even a small excess of the alkyl reagent resulted in the deprotonation of the beta-diketiminato ligand and the formation of the known dimer [{Yb(L(3))(thf)}(2)] [, L(3) = N[combining macron](Ar*)C(Me)C(H)C(C[combining macron]H(2))N(Ar*)]. Compounds or reacted with KCPh(3) in thf yielding [Yb(L(1)){eta(5)-C(6)H(5)CPh(2)}(thf)] () or [Yb(CPh(3))(2)(thf)(2)] (), respectively; the latter has two differently coordinated CPh(3) ligands. The molecular structures of 1, 2, 4, 5, 6, 8 and 9 were determined by X-ray diffraction.

Interfacial potential difference in electromembrane systems with MA-41 anion-exchange membranes and alkaline solutions of glycine

A method for estimating the interfacial potential difference in electromembrane systems with alkaline solutions of amino acids is developed. Systems with MA-41 anion-exchange membranes and aqueous sodium hydroxide solutions with glycine are investigated. It is found that in solutions with alkali concentrations greater than 0.010 M, the interfacial potential difference decreases logarithmically, i.e., in agreement with the Donnan relationship. At the same time, in weakly alkaline solutions of glycine, in which the amino-acid concentration exceeds that of the alkali, an increase in the interfacial potential difference is observed. This may be due to a disturbance of the equilibrium of the protolytic reaction in the membrane on the side where hydroxide ions form.

Kinetic stability of heteroleptic (β-diketiminato) heavier alkaline-earth (Ca, Sr, Ba) amides

The potential of the heteroleptic heavier alkaline-earth hexamethyldisilazides [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ae{N(SiMe3)2}(THF)](Ae = Ca, Sr, Ba) as kinetically-stable reagents for further protolytic reaction chemistry has been assessed. Only the previously reported calcium complex was found to be stable to solution dismutation and dynamic ligand exchange. The barium complex was isolated in sufficient purity to enable characterisation by an X-ray analysis. Reactions of the kinetically robust calcium complex with cyclohexylamine and tert-butylamine resulted in displacement of THF and formation of solvated structures, which could be characterised by 1H NMR spectroscopy. Attempts to isolate these solvated complexes were unsuccessful due to redistribution to the homoleptic complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}2Ca]. In contrast, the more acidic amine [H2NCH2CH2OMe] was cleanly deprotonated resulting in the isolation of the first well defined primary amido derivative of a heavier alkaline-earth element, [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{NHCH2CH2OMe}]2, which retains its dimeric constitution in solution and is stable to further intermolecular ligand exchange. Reactions of [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{N(SiMe3)2}(THF)] with a variety of ortho-disubstituted anilines also resulted in immediate protonation of the hexamethyldisilazide ligand. Only the most sterically demanding 2,6-diisopropylphenyl anilide derivative possessed sufficient kinetic stability to allow isolation of the heteroleptic complex. The crystal structure of [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{N(H)-2,6-iPrC6H3}(THF)] was shown to exist as a mononuclear, pseudo-five-coordinate complex in which the coordinative unsaturation of the calcium centre is relieved by a Ca...H-C agostic-type interaction to one of the ortho isopropyl groups of the anilide ligand. This interaction is not maintained in solution however and the complex slowly redistributes to the homoleptic beta-diketiminato species and ill-defined polymeric calcium anilido products.

Factors affecting Ni-sulfide formation in Y-type zeolites: a combined Fourier transform infrared and X-ray photoelectron spectroscopy study

Sulfidation of nickel in Ni/HY and Ni/NaY zeolites has been studied by combined Fourier transform infrared (FTIR) of adsorbed NO and X-ray photoelectron spectroscopy (XPS). Sulfidation of Ni species was found to be easier in Ni/NaY than in Ni/HY samples, and the type of Ni species formed and their stability were seen to be dependent upon the sulfidation–flushing pretreatment employed. Flushing with He at 823 K of Ni/NaY zeolites sulfided at 673 K led to the decomposition of nickel sulfide species. This was confirmed by the shift of the sulfide species band by about 20 cm −1 towards higher wavenumbers. Upon sulfiding the Ni/HY zeolites at 873 K followed by flushing with He at 473 K, a small fraction of nickel still remained unsulfided and the surface exposure of nickel increased. The decrease in the IR band intensity observed for the latter samples was interpreted as being due to a strong inhibition of coordinatively unsaturated sites (CUS) by adsorbed H 2 S. In both Ni/HY ( T sulf / T flu =873/473 K) and Ni/NaY ( T sulf / T flu =673/873 K) zeolites, the formation of nickel oxi-sulfide species through the protolytic reaction of sulfide species and zeolite hydroxyl groups is proposed.

Origin of the high-energy emission of 1,1′-diethyl-2,2′-cyanine dye

In addition to the yellow emission ascribed to the J aggregates of 1,1′-diethyl-2,2′-cyanine, this compound also exhibits a high-energy emission around 400 nm in dilute aqueous solutions (c<10−3 mol 1−1. It was using time-resolved emission measurements that protonation of 1,1′-diethyl-2,2′-cyanine is responsible for this emission. At pH<4, the excited state protolytic reaction competes with ground state protonation. Both pathways give the same excited species, luminescing at 400nm. The non-protonated form shows only weak flourescence. The excited state lifetime of the protonated form is 4.5 ns.

Protolytic Equilibria of Ligands Immobilized at Rigid Matrix Surfaces: A Theoretical Study

Abstract A thermodynamic treatment of equilibria of protolytic reaction involving ligands immobilized at a rigid matrix surface is put forward. A shift observed in equilibrium constants of such reactions related to analogous reactions of free ligands is qualitatively explained. On the basis of the generalized mass action law, an attempt is made at accounting for the influence of the electric double layer disturbed by the spatial dispersion of the dielectric constant of the adjacent solution on the equilibrium state of surface reactions. In so doing, the electrostatic contribution to the surface tension of modified matrices is calculated using Derjaguin's formula for the free electrostatic energy of a charged surface in contact with an electrolytic solution.

Excited state solvation dynamics of 6-methoxyquinoline

Abstract Steady state and transient studies of 6-methoxyquinoline (6MQ) were undertaken. 6MQ undergoes a large change of dipole moment on excitation. The low energy absorption band L b does not change in position with solvent polarity whereas the emission maxima shift towards lower frequencies with broadening of the spectra. The edge excitation red shift, which is associated with the time-dependent red shift of emission, is observed in all polar solvents. The fluorescence decay is monoexponential and is dependent on emission wavelength. The data are explained with the help of the Bakhshiev model of solvent relaxation. The solvent relaxation time τ r and the fluorescence lifetime τ f increase with the polarity of the solvent. In aqueous solution, 6MQ undergoes a protolytic reaction in the excited state. The rate constant for the proton transfer is 1.2×10 8 s −1 .

Effect of pH on the spectrum of cytochrome c oxidase hydrogen peroxide complex

Hydrogen peroxide binding to ferric cytochrome c oxidase in proteoliposomes brings about a red-shift of the enzyme Soret band and increased absorption in the visible range with two prominent peaks at approx. 570 and 607 nm. The molar absorptivity of the H2O2-induced difference spectrum is virtually pH-independent in the Soret band and at 570 nm, whereas the peak at 607 nm increases approx. 3-fold upon alkalinization in a narrow pH range 6.0-7.2, the effect being reversible. The pH profile of this transition indicates ionization of two acid-base groups with close pK values of 6.7. The lineshape of the peroxide compound difference spectrum is found to respond to pH changes inside the proteoliposomes. It is suggested that peroxide-complexed enzyme can undergo a pH-dependent transition to a form with increased extinction at 605-607 nm, possibly corresponding to the 420 nm (or 'pulsed') conformer of the ferric cytochrome oxidase formed as an early product of the enzyme oxidation. Accordingly, relaxation of the '420 nm' form to the resting state would be linked to an uptake of two protons from the M-aqueous phase. This protolytic reaction might be a partial step of the cytochrome oxidase proton pumping mechanism or it could serve to regulate interconversion between the active 'pulsed' and less active 'resting' states of the enzyme in the membrane.

The kinetics of binding of o-methyl red to the outer surface of unilamellar spherical phospholipid vesicles.

The kinetics of adsorption of the proton carrier o-methyl red to the surface of unilamellar spherical phospholipid vesicles have been investigated by means of the temperature-jump relaxation technique with absorbance detection. Single-exponential relaxation curves were observed with time constants in the range 30-130 microseconds. o-Methyl red binds in both its anionic form A- and protonated form AH. Adsorption-desorption of the two species is coupled by two fast protolytic reactions, occurring in the aqueous bulk phase and in the surface region of the membrane. The rate constants for adsorption and desorption of the two species were obtained from the dependences of the relaxation time on lipid concentration at different pH values. The analysis yielded apparent adsorption rate constants of kasAH = 9.8 X 10(6) M-1 s-1 and kasA = 1.3 X 10(6) M-1 s-1 (expressed in terms of monomeric lipid), and kasAH = 1.2 X 10(11) M-1 s-1 and kasA = 1.6 X 10(10) M-1 s-1 (expressed in terms of vesicle concentration). From the order of these rate constants it is concluded that adsorption of both species is actually diffusion-controlled. The peculiar pH dependence of the relaxation time is a consequence of the protolytic reaction in the surface region of the membrane. Its implication for the kinetics of adsorption-desorption processes are discussed.

Ionic strength dependence of the electric dissociation field effect. Investigation of 2,6-dinitrophenol and application to the acid-alkaline transition of metmyoglobin and methemoglobin.

We present data on the ionic strength dependence of the dissociation field effect (2nd Wien effect) of the protolytic reaction of 2,6-dinitrophenol in aqueous solution, monitored through optical absorption changes in high electric fields. The results are in very good agreement with the Onsager-Liu theory. We then investigate the field strength dependence of the acid-alkaline transition, i.e., the hydrolysis reaction of the water coordinated to the heme iron, in metmyoglobin and methemoglobin. The true field effect of the reaction is determined from measurements in buffers which exhibit no field effect. We conclude that negative charges on the protein influence the field effect in methemoglobin but not in metmyoglobin. The Onsager-Liu theory is applied to estimate the number of charges involved.

Pulsed laser photolysis of spiropyrans in the presence of acids

Intermediate unstable trans isomers of the merocyanine species participate in the protolytic reaction of spiropyrans. A scheme for the photochromic transformations of spiropyrans in the presence of an acid was proposed.

Acid effect on photochromism of spiropyrans: A study by microsecond and nanosecond flash photolysis

Abstract Microsecond and nanosecond flash photolysis was used to study the photochromic reactions of spiropyrans of the indoline series 1′,3′,3′-trimethyl-6-nitro, 6-nitro-8-methoxy, 6-methoxyspiro[2 H -1-benzopyran-2′,2′-(2 H )-indol] in acetone in the presence of the acids HNO 3 , HCl and H 2 SO 4 . Two relatively unstable trans isomers of spiropyran (merocyanine form) were found to be involved in the protolytic reaction. A reaction mechanism is proposed.