A Highly Selective Potassium Sensor for the Detection of Potassium in Living Tissues

The development of highly selective sensors for potassium is of great interest in biology. Two new hydrosoluble potassium sensors (Calix‐COU‐Alkyne and Calix‐COU‐Am) based on a calix[4]arene bis(crown‐6) and an extended coumarin were synthesized and characterized. The photophysical properties and complexation studies of these compounds have been investigated and show high molar extinction coefficients and high fluorescence quantum yields. Upon complexation with potassium in the millimolar concentration range, an increase of one‐ and two‐photon fluorescence emission is detected. A twofold fluorescence enhancement is observed upon excitation at λ=405 nm. The ligands present excellent selectivity for potassium in the presence of various competitive cations in water and in a physiological medium. The photophysical properties are not affected by the presence of a large amount of competing cations (Na⁺, Ca²⁺, Mg²⁺, etc.). Ex vivo measurements on mouse hippocampal slices show that Calix‐COU‐Alkyne accumulates extracellularly and does not alter the neuronal activity. Furthermore, the sensor can be utilized to monitor slow extracellular K⁺ increase induced by inhibition of K⁺ entry into the cells.     

Synthesis of Molecular Wires of Linear and Branched Bis(terpyridine)‐Complex Oligomers and Electrochemical Observation of Through‐Bond Redox Conduction

Films of linear and branched oligomer wires of Fe(tpy)₂ (tpy=2,2′:6′,2′′‐terpyridine) were constructed on a gold‐electrode surface by the interfacial stepwise coordination method, in which a surface‐anchoring ligand, (tpy? C₆H₄N?NC₆H₄? S)₂ ( 1 ), two bridging ligands, 1,4‐(tpy)₂C₆H₄ ( 3 ) and 1,3,5‐(C?C? tpy)₃C₆H₃ ( 4 ), and metal ions were used. The quantitative complexation of the ligands and Fe^II ions was monitored by electrochemical measurements in up to eight complexation cycles for linear oligomers of 3 and in up to four cycles for branched oligomers of 4 . STM observation of branched oligomers at low surface coverage showed an even distribution of nanodots of uniform size and shape, which suggests the quantitative formation of dendritic structures. The electron‐transport mechanism and kinetics for the redox reaction of the films of linear and branched oligomer wires were analyzed by potential‐step chronoamperometry (PSCA). The unique current‐versus‐time behavior observed under all conditions indicates that electron conduction occurs not by diffusional motion but by successive electron hopping between neighboring redox sites within a molecular wire. Redox conduction in a single molecular wire in a redox‐polymer film has not been reported previously. The analysis provided the rate constant for electron transfer between the electrode and the nearest redox‐complex moiety, k₁ (s^?1), as well as that for intrawire electron transfer between neighboring redox‐complex moieties, k₂ (cm² mol^?1 s^?1). The strong effect of the electrolyte concentration on both k₁ and k₂ indicates that the counterion motion limits the electron‐hopping rate at lower electrolyte concentrations. Analysis of the dependence of k₁ and k₂ on the potential gave intrinsic kinetic parameters without overpotential effects: k₁⁰=110 s^?1, k₂⁰=2.6×10¹² cm² mol^?1 s^?1 for [n Fe 3 ], and k₁⁰=100 s^?1, k₂⁰=4.1×10¹¹ cm² mol^?1 s^?1 for [n Fe 4 ] (n=number of complexation cycles).     

Polyaniline emeraldine base in N‐methyl‐2‐pyrrolidinone containing secondary amine additives: A rheological investigation of solutions

From a rheological study of emeraldine base (EB)/N‐methyl‐2‐pyrrolidinone (NMP)/2‐methyl‐aziridine (2MA) solutions, a correlation between the solution concentration and solution viscosity was found. We investigated the rheokinetic mechanism of the EB dissolution process and determined the reaction rate, activation energy, equilibrium constant, and Gibbs free energy (ΔG_o) for the complexation between 2MA and EB tetrameric molecules ({EB}). The low rate constant (～3.0 × 10^?4 mol^?2 L² min^?1 at 298 K) indicates that the process of EB/NMP/2MA solution formation is slow. The {EB} and 2MA molecules need approximately 76 kJ/mol energy to form the complexes, and this implies that stable bonds may need to be broken before the complexes can form. Therefore, increasing the temperature can accelerate solution formation. The equilibrium constant increases with temperature, and this indicates that EB · 2MA complexation is endothermic. A positive value of ΔG_o (5.26 kJ/mol) indicates that EB · 2MA complexation is a thermodynamically unfavorable reaction; therefore, the concentrated EB/NMP/2MA solutions eventually gel. Furthermore, we find that the activation energy of EB/NMP viscous flow is 80 kJ/mol, which is about 3–4 times the energy of ? N? H? hydrogen bonding. This suggests that at least three hydrogen bonds can form between two {EB} molecules, which might be responsible for the poor solubility of EB in organic solvents. The effects of the temperature, EB concentration, and 2MA:{EB} molar ratio on the gelation process have also been investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2702–2713, 2002     

Evaluation of plutonium(IV) extraction rate between nitric acid and tri‐n‐butylphosphate solution using a glass chip microchannel

Extraction of Pu(IV) with tri‐n‐butylphosphate is performed using a glass chip microchannel to evaluate the extraction rate. Two‐phase flow forms in the microchannel by introducing a solution of Pu(IV) and tri‐n‐butylphosphate with flow rates above 5 μL/min. The Pu(IV) extraction reaction proceeds at the interface between the two phases. To evaluate the extraction rate, the contact time between the two phases is varied from 0.48 to 4.8 s by changing the confluent length of the microchannel and the flow rate. The Pu concentration of each phase collected from the microchannel is measured with an alpha liquid scintillation counter, and the contact time dependence of Pu(IV) extraction is obtained. An extraction model based on diffusion in the microchannel and the reaction at the interface is proposed and applied to determine the extraction rate. The extraction process is assumed to follow pseudo‐first‐order kinetics, and the extraction rate constant of Pu(IV) is determined to be 1.5 × 10^?2 cm/s. The investigation demonstrates that a microfluidic device can be a new tool to determine Pu(IV) extraction rates.     

Measurements of the Kinetics of the Reaction of OH Radicals with 3‐Methylfuran at Low Pressure

The rate constant for the reaction of OH with 3‐methylfuran was measured at 2, 4, and 6 Torr using discharge‐flow techniques coupled with laser‐induced fluorescence detection of OH. The measured rate constant (k) at 298 ± 2 K was (9.1 ± 0.3) × 10^?11 cm³ molecule^?1 s^?1, where the quoted uncertainty reflects twice the standard error of the measurements. This result is in good agreement with previously reported relative rate constant measurements at atmospheric pressure and room temperature. An Arrhenius expression of k = (3.2 ± 0.4) × 10^?11 e^{(310 ± 40)/T} cm³ molecule^?1 s^?1 was determined from measurements of the rate constant between 273 and 368 K. The negative temperature dependence agrees with previously reported theoretical calculations for the reaction of OH with 3‐methylfuran and previously reported measurements of the temperature dependences of the rate constants for the reaction of OH with similar heterocyclic organics such as furan and thiophene.     

Lead Determination by Anodic Stripping Voltammetry Using a p‐Phenylenediamine Modified Carbon Paste Electrode

Carbon paste electrodes were modified by mixing appropriate amounts of the monomers o‐phenylendiamine, p‐phenylendiamine and m‐phenylendiamine (o‐PD, p‐PD and m‐PD) into a graphite powder‐paraffin oil matrix. The electropolymerization of the incorporated phenylendiamine was then carried out in a carbon paste electrode in acidic medium by cyclic voltammetry between ?0.30 V and +0.90 or under constant potential. The modified carbon paste electrodes (MCPEs) obtained by this electropolymerization method were found to be useful for trace determination of Pb²⁺ in aqueous solutions. Lead(II) was first preconcentrated on the modified electrodes by complexation with the modifier, and the electrode was then transferred to an electrochemical cell. The best results in terms of sensitivity and detection limit were obtained with poly p‐phenylenediamine (poly (p‐PD)). For a 10‐min preconcentration time, the calibration plot was linear from 5×10^?8 mol L^?1 to 10^?5 mol L^?1, with r²=0.999 and relative standard deviation equal to 5%. However, the lowest lead concentration that could be detected was 10^?9 mol L^?1. Interference from metal ions like Cd(II), Hg(II), Zn(II), Fe(II) and Cu(II) was also studied.     

Solvent Extraction–Photometric Determination of Palladium Using Complexation with 1-(2-Pyridylazo)-2-Naphthol

Palladium(II) complexation with 1-(2-pyridylazo)-2-naphthol (PAN) in aqueous solutions followed by extraction with chloroform and photometric detection was studied. The best conditions were found for the formation of the complex in an aqueous solution and for its extraction with chloroform that provided a sufficient degree of binding palladium ions. The stability constant of the complex cation PdX⁺, which is extracted by chloroform as an ion pair [PdX]⁺[An^–] (An^–– CH₃COO^–), was calculated using the methods proposed by Rossotti (log K _stab= 18.73) and Komar' (log K _stab= 18.82). The equilibrium constant of the complexation reaction was also calculated (5.45 × 10⁴). It was shown that components of nonferrous alloys affect the determination of palladium by photometry as its complex or ion pair with PAN in chloroform.     

Ester Hydrolysis by a Cyclodextrin Dimer Catalyst with a Tridentate N,N′,N′′‐Zinc Linking Group

A new β‐cyclodextrin dimer, 2,6‐dimethylpyridine‐bridged‐bis(6‐monoammonio‐β‐cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log K_ML=7.31±0.04) of the complex and deprotonation constant (pK_a1=8.14±0.03, pK_a2=9.24±0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25±0.1)°C, indicating a tridentate N,N′,N′′‐zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4‐nitrophenyl)carbonate (BNPC) and 4‐nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98×10³‐fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76‐fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4‐nitrophenyl)phosphate (BNPP) and disodium 4‐nitrophenyl phosphate (NPP) as the substrates. The initial first‐order rate constant of catalytic hydrolysis for BNPP was 1.29×10^?7 s^?1 at pH 8.5, 35 °C and 0.1 mM catalyst concentration, about 1600‐fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pK_a value of the catalyst from the potentiometric titration. The k_BNPP of BNPP hydrolysis promoted by ZnL is found to be 1.68×10^?3 M ^?1 s^?1, higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N′,N′′‐zinc analogues.     

The Reaction of Sulfenic Acids with Peroxyl Radicals: Insights into the Radical‐Trapping Antioxidant Activity of Plant‐Derived Thiosulfinates

Sulfenic acids play a prominent role in biology as key participants in cellular signaling relating to redox homeostasis, in the formation of protein‐disulfide linkages, and as the central players in the fascinating organosulfur chemistry of the Allium species (e.g., garlic). Despite their relevance, direct measurements of their reaction kinetics have proven difficult owing to their high reactivity. Herein, we describe the results of hydrocarbon autoxidations inhibited by the persistent 9‐triptycenesulfenic acid, which yields a second order rate constant of 3.0×10⁶ M ^?1 s^?1 for its reaction with peroxyl radicals in PhCl at 30 °C. This rate constant drops 19‐fold in CH₃CN, and is subject to a significant primary deuterium kinetic isotope effect, k_H/k_D=6.1, supporting a formal H‐atom transfer (HAT) mechanism. Analogous autoxidations inhibited by the Allium‐derived (S)‐benzyl phenylmethanethiosulfinate and a corresponding deuterium‐labeled derivative unequivocally demonstrate the role of sulfenic acids in the radical‐trapping antioxidant activity of thiosulfinates, through the rate‐determining Cope elimination of phenylmethanesulfenic acid (k_H/k_D≈4.5) and its subsequent formal HAT reaction with peroxyl radicals (k_H/k_D≈3.5). The rate constant that we derived from these experiments for the reaction of phenylmethanesulfenic acid with peroxyl radicals was 2.8×10⁷ M ^?1 s^?1; a value 10‐fold larger than that we measured for the reaction of 9‐triptycenesulfenic acid with peroxyl radicals. We propose that whereas phenylmethanesulfenic acid can adopt the optimal syn geometry for a 5‐centre proton‐coupled electron‐transfer reaction with a peroxyl radical, the 9‐triptycenesulfenic is too sterically hindered, and undergoes the reaction instead through the less‐energetically favorable anti geometry, which is reminiscent of a conventional HAT.     

Kinetics and equilibrium of the complexation of Al3+ with poly(maleic, acrylic) acid

Kinetics and equilibrium of the complexation of Al³⁺ with a polycarboxylic acid (PCA, random copolymer of maleic and acrylic acid with a mean molecular weight of 92 kDa) are investigated by the stopped flow technique and potentiometric titration. The complexation proceeds according to the Eigen–Tamm mechanism, i.e. in first diffusion-controlled step an outer sphere complex is formed. The second rate determining step is the formation of the inner sphere complex, controlled by the exchange rate of hydration water. For this second step the rate constant is k ₁=3 s^-1. It is in the order of magnitude of the water exchange at the Al³⁺ ion as expected for the Eigen–Tamm mechanism. The activation parameters are also determined. Parallel to this direct reaction path a base catalyzed path is found, typical for complexation reactions of hydrolyzable metal ions. Stable complexes are formed for which the overall association constant K _ass=Q _o(1+K _i) is determined by two parts: a chemical (intrinsic) part, described by the inner sphere association constant K _i=3 and an electrostatically controlled part described by the outer-sphere association quotient Q _o. The evaluation of the kinetic experiments allows to determine the value of log(Q _o) as a function of pH: 3.3<log Q _o<4.6. From these data the potential is calculated in the range −67 to ∝93 mV at pH values between 2 and 4. For comparison, analogous experiments with the monomeric subunits of the polyacid, glutarate (GA), and tricarballylate (TCA), are performed. The complexation with the monomeric subunits glutaric- and tricarballylic acid can be explained within the classical view of a discrete outer sphere association constant Q _o. Received: 13 November 1997 Accepted: 24 March 1998     

Intermolecular insertion of an N,N-heterocyclic carbene into a nonacidic C-H bond: Kinetics, mechanism and catalysis by (K-HMDS)2 (HMDS = Hexamethyldisilazide)

The reaction of 2‐[¹³C]‐1‐ethyl‐3‐isopropyl‐3,4,5,6‐tetrahydropyrimidin‐1‐ium hexafluorophosphate ([¹³C₁]‐ 1 ‐PF₆) with a slight excess (1.03 equiv) of dimeric potassium hexamethyldisilazide (“(K‐HMDS)₂”) in toluene generates 2‐[¹³C]‐3‐ethyl‐1‐isopropyl‐3,4,5,6‐tetrahydropyrimid‐2‐ylidene ([¹³C₁]‐ 2 ). The hindered meta‐stable N,N‐heterocyclic carbene [¹³C₁]‐ 2 thus generated undergoes a slow but quantitative reaction with toluene (the solvent) to generate the aminal 2‐[¹³C]‐2‐benzyl‐3‐ethyl‐1‐isopropylhexahydropyrimidine ([¹³C₁]‐ 14 ) through formal C? H insertion of C(2) (the “carbene carbon”) at the toluene methyl group. Despite a significant pK_a mismatch (ΔpK_a 1 ⁺ and toluene estimated to be ca. 16 in DMSO) the reaction shows all the characteristics of a deprotonation mechanism, the reaction rate being strongly dependent on the toluene para substituent (ρ=4.8(±0.3)), and displaying substantial and rate‐limiting primary (k_H/k_D=4.2(±0.6)) and secondary (k_H/k_D=1.18(±0.08)) kinetic isotope effects on the deuteration of the toluene methyl group. The reaction is catalysed by K‐HMDS, but proceeds without cross over between toluene methyl protons and does not involve an HMDS anion acting as base to generate a benzyl anion. Detailed analysis of the reaction kinetics/kinetic isotope effects demonstrates that a pseudo‐first‐order decay in 2 arises from a first‐order dependence on 2 , a first‐order dependence on toluene (in large excess) and, in the catalytic manifold, a complex noninteger dependence on the K‐HMDS dimer. The rate is not satisfactorily predicted by equations based on the Brønsted salt‐effect catalysis law. However, the rate can be satisfactorily predicted by a mole‐fraction‐weighted net rate constant: ?d[ 2 ]/dt=({x ₂ k_uncat}+{(1?x ₂ ) k_cat})[ 2 ]¹[toluene]¹, in which x ₂ is determined by a standard bimolecular complexation equilibrium term. The association constant (K_a) for rapid equilibrium–complexation of 2 with (K‐HMDS)₂ to form [ 2 (K‐HMDS)₂] is extracted by nonlinear regression of the ¹³C NMR shift of C(2) in [¹³C₁]‐ 2 versus [(K‐HMDS)₂] yielding: K_a=62(±7) M ^?1; δ_C(2) in 2 =237.0 ppm; δ_C(2) in [ 2 (K‐HMDS)₂]=226.8 ppm. It is thus concluded that there is discrete, albeit inefficient, molecular catalysis through the 1:1 carbene/(K‐HMDS)₂ complex [ 2 (K‐HMDS)₂], which is found to react with toluene more rapidly than free 2 by a factor of 3.4 (=k_cat/k_uncat). The greater reactivity of the complex [ 2 (K‐HMDS)₂] over the free carbene ( 2 ) may arise from local Brønsted salt‐effect catalysis by the (K‐HMDS)₂ liberated in the solvent cage upon reaction with toluene.     

Thermochemical Properties and Decomposition Kinetics of Ammonium Magnesium Phosphate Monohydrate

Ammonium magnesium phosphate monohydrate NH4MgPO4·H2O was prepared via solid state reaction at room temperature and characterized by XRD, FT-IR and SEM. Thermochemical study was performed by an isoperibol solution calorimeter, non-isothermal measurement was used in a multivariate non-linear regression analysis to determine the kinetic reaction parameters. The results show that the molar enthalpy of reaction above is （28.795 ± 0.182） kJ/mol （298.15 K）, and the standard molar enthalpy of formation of the title complex is （-2185.43 ± 13.80） kJ/mol （298.15 K）. Kinetics analysis shows that the second decomposition of NH4MgPO4·H2O acts as a double-step reaction： an nth-order reaction （Fn） with n=4.28, E1=147.35 kJ/mol, A1=3.63×10^13 s^-1 is followed by a second-order reaction （F2） with E2=212.71 kJ/mol, A2= 1.82 × 10^18 s^-1.     

Comparison of Glassy Carbon and Copper Microparticles as a Renewable Working Electrode Material for Amperometric Determination of Amino Acids Using Flow Through Detector

Flow‐through detector with renewable working material based on glassy carbon or copper microparticles was used for flow injection determination of tyrosine by direct oxidation and phenylalanine via the complexation reaction with copper ions, respectively. Copper‐based detector allows the determination of electrochemically inactive amino acid, but the detection conditions are limited and fabrication and handling of the detector are more demanding. Low working potential, applied for the detection on copper microparticles, makes the determination very selective. Moreover, low baseline noise compensates lower sensitivity of copper‐based detector, enabling to reach quantification limit 4.7×10^?6 mol L^?1, in comparison with quantification limit 1.6×10^?6 mol L^?1 obtained for tyrosine on carbon‐based detector.     

Mechanistic insights into photochromic behavior of a ruthenium(II)-pterin complex

The pterin‐coordinated ruthenium complex, [Ru^II(dmdmp)(tpa)]⁺ ( 1 ) (Hdmdmp=N,N‐dimethyl‐6,7‐dimethylpterin, tpa=tris(2‐pyridylmethyl)amine), undergoes photochromic isomerization efficiently. The isomeric complex ( 2 ) was fully characterized to reveal an apparent 180° pseudorotation of the pterin ligand. Photoirradiation to the solution of 1 in acetone with incident light at 460 nm resulted in dissociation of one pyridylmethyl arm of the tpa ligand from the Ru^II center to give an intermediate complex, [Ru(dmdmp)(tpa)(acetone)]²⁺ ( I ), accompanied by structural change and the coordination of a solvent molecule to occupy the vacant site. The quantum yield (?) of this photoreaction was determined to be 0.87 %. The subsequent thermal process from intermediate I affords an isomeric complex 2 , as a result of the rotation of the dmdmp^2? ligand and the recoordination of the pyridyl group through structural change. The thermal process obeyed first‐order kinetics, and the rate constant at 298 K was determined to be 5.83×10^?5 s^?1. The activation parameters were determined to be ΔH^≠=81.8 kJ mol^?1 and ΔS^≠=?49.8 J mol^?1 K^?1. The negative ΔS^≠ value indicates that this reaction involves a seven‐coordinate complex in the transition state (i.e., an interchange associative mechanism). The most unique point of this reaction is that the recoordination of the photodissociated pyridylmethyl group occurs only from the direction to give isomer 2 , without going back to starting complex 1 , and thus the reaction proceeds with 100 % conversion efficiency. Upon heating a solution of 2 in acetonitrile, isomer 2 turned back into starting complex 1 . The backward reaction is highly dependent on the solvent: isomer 2 is quite stable and hard to return to 1 in acetone; however, 2 was converted to 1 smoothly by heating in acetonitrile. The activation parameters for the first‐order process in acetonitrile were determined to be ΔH^≠=59.2 kJ mol^?1 and ΔS^≠=?147.4 kJ mol^?1 K^?1. The largely negative ΔS^≠ value suggests the involvement of a seven‐coordinate species with the strongly coordinated acetonitrile molecule in the transition state. Thus, the strength of the coordination of the solvent molecule to the Ru^II center is a determinant factor in the photoisomerization of the Ru^II–pterin complex.     

Construction and Application of Flow Enzymatic Biosensor Based of Silver Solid Amalgam Electrode for Determination of Sarcosine

In this paper, the flow amperometric enzymatic biosensor based on polished silver solid amalgam electrode for determination of sarcosine in model sample under flow injection analysis conditions is presented. The biosensor works on principle of electrochemical detection of oxygen decrease during enzymatic reaction which is directly proportional to the concentration of sarcosine in sample. The whole preparation process takes about 3 h. The RSD of repeatability of 10 consecutive measurements is 1.6 % (c_sarcosine=1.0×10^?4 mol dm^?3). Under optimal conditions the calibration dependence was linear in the range 7.5×10^?6–5.0×10^?4 mol dm^?3 and limit of detection was 2.0×10^?6 mol dm^?3.     

Thermal Decomposition Behavior and Non-isothermal Decomposition Reaction of Copper（ll） Salt of 4-Hydroxy-3,5-dinitropyridine Oxide and Its Application in Solid Rocket Propellant

The thermal decomposition behavior and kinetic parameters of the exothermic decomposition reactions of the title compound in a temperature‐programmed mode have been investigated by means of DSC, TG‐DTG and lower rate Thermolysis/FTIR. The possible reaction mechanism was proposed. The critical temperature of thermal explosion was calculated. The influence of the title compound on the combustion characteristic of composite modified double base propellant containing RDX has been explored with the strand burner. The results show that the kinetic model function in differential form, apparent activation energy E_a and pre‐exponential factor A of the major exothermic decomposition reaction are 1‐a,207.98 kJ*mol^?1 and 10^15.64 s^?1, respectively. The critical temperature of thermal explosion of the compound is 312.87 C. The kinetic equation of the major exothermic decomposition process of the title compound at 0.1 MPa could be expressed as: dα/dT=10^16.42 (1–α)e‐2.502×10⁴/T As an auxiliary catalyst, the title compound can help the main catalyst lead salt of 4‐hydroxy‐3,5dinitropyridine oxide to enhance the burning rate and reduce the pressure exponent of RDX‐CMDB propellant.     

The Reaction of Ozone with the Hydroxide Ion: Mechanistic Considerations Based on Thermokinetic and Quantum Chemical Calculations and the Role of HO4− in Superoxide Dismutation

The reaction of OH^? with O₃ eventually leads to the formation of ^.OH radicals. In the original mechanistic concept (J. Staehelin, J. Hoigné, Environ. Sci. Technol. 1982 , 16, 676–681), it was suggested that the first step occurred by O transfer: OH^?+O₃→HO₂^?+O₂ and that ^.OH was generated in the subsequent reaction(s) of HO₂^? with O₃ (the peroxone process). This mechanistic concept has now been revised on the basis of thermokinetic and quantum chemical calculations. A one‐step O transfer such as that mentioned above would require the release of O₂ in its excited singlet state (¹O₂, O₂(¹Δ_g)); this state lies 95.5 kJ mol^?1 above the triplet ground state (³O₂, O₂(³Σ_g^?)). The low experimental rate constant of 70 M ^?1 s^?1 is not incompatible with such a reaction. However, according to our calculations, the reaction of OH^? with O₃ to form an adduct (OH^?+O₃→HO₄^?; ΔG=3.5 kJ mol^?1) is a much better candidate for the rate‐determining step as compared with the significantly more endergonic O transfer (ΔG=26.7 kJ mol^?1). Hence, we favor this reaction; all the more so as numerous precedents of similar ozone adduct formation are known in the literature. Three potential decay routes of the adduct HO₄^? have been probed: HO₄^?→HO₂^?+¹O₂ is spin allowed, but markedly endergonic (ΔG=23.2 kJ mol^?1). HO₄^?→HO₂^?+³O₂ is spin forbidden (ΔG=?73.3 kJ mol^?1). The decay into radicals, HO₄^?→HO₂^.+O₂^.?, is spin allowed and less endergonic (ΔG=14.8 kJ mol^?1) than HO₄^?→HO₂^?+¹O₂. It is thus HO₄^?→HO₂^.+O₂^.? by which HO₄^? decays. It is noted that a large contribution of the reverse of this reaction, HO₂^.+O₂^.?→HO₄^?, followed by HO₄^?→HO₂^?+³O₂, now explains why the measured rate of the bimolecular decay of HO₂^. and O₂^.? into HO₂^?+O₂ (k=1×10⁸ M ^?1 s^?1) is below diffusion controlled. Because k for the process HO₄^?→HO₂^.+O₂^.? is much larger than k for the reverse of OH^?+O₃→HO₄^?, the forward reaction OH^?+O₃→HO₄^? is practically irreversible.     

Effect of the ionic strength on the redox reaction of dicyanobis(bipyridine)iron(III)‐iodide in binary and ternary solvent systems

The redox reaction between dicyanobis(bipyridine)iron(III) and iodide ion follows first‐order kinetics in 10% (v/v) tertiary butyl alcohol‐water. The reaction was found first and zero order in iodide and dicyanobis(bipyridine)iron(III), respectively, at 0.06 M ionic strength and 293 ± 1 K. The thermodynamic parameters of activation such as E_A (16.07 kJ mol^?1), A (1 × 10^?4 M s^?1), ΔH^# (13.6 kJ mol^?1), ΔS^# (?329.81 J K^?1 mol^?1), and ΔG^# (90.1 kJ mol^?1) were determined. The effect of the ionic strength on the rate constant leads to recognizing the stabilization or destabilization of the transition state complex that forms during the rate‐determining step of the reaction. The value of the zero‐order rate constant was decreased with increasing ionic strength that yielded a negative value of the slope in each binary and ternary solvent systems. This negative sign refers to the electron transfer between opposite charge carriers such as [Fe^III(bpy)₂(CN)₂]⁺ and I^? during the rate‐determining step. The destabilization of the transition state complex is surfaced by the increasing slope, that is, 5 < 10 < 15% (v/v) tertiary butyl alcohol‐water with a gradual decrease in the rate constant. However, its stability emerges by relatively small values of the slope in 17.5 < 25 ≤ 30% (v/v) tertiary butyl alcohol‐water and 8:2:90 < 6:4:90% (v/v) dioxane: tertiary butyl alcohol: water with reasonably fast rate of reaction.     

An Efficient Way for the Recognition of Zinc Ion via the Fluorescence Enhancement

This study concentrates on the spectral and complexing properties of a tetraoxycalix[2]arene[2]triazine derivative bearing two bipyridines (Calix‐BIPY2) in a mixture of acetonitrile:chloroform (4:1, V:V). The results show that Calix‐BIPY2 has a highly selectivity and sensitivity towards Zn²⁺ over various competing cations (K⁺, Cu²⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Ag⁺, Al³⁺ and Pb²⁺). The complexation of Zn²⁺ induces a remarkable fluorescence enhancement due to combination effects of the binding strength, electron spins state of metal ions, photoinduced charge transfer (PCT) and the rigidity of the complexing unit offered by calixarene‐based hosts.     

Kinetics and Mechanism of the Exothermic First-stage Decomposition Reaction of Dinitroglycoluril

Introduction Dinitroglycoluril (DINGU) is a typical cyclourea nitramine. Its crystal density is 1.94 gcm-3. The detonation velocity corresponding to =1.94 gcm-3 is about 8450 ms-1. Its sensitivity to impact is better than that of cyclotrimethylenetrinitramine. It has the potential for possible use as high explosive from the point of view of the above-mentioned high performance. Its preparation,1-4 properties1-4 and hydrolytic behavior4 have been reported. In the present paper, we report i…