Mitochondria Targeting Fluorescent Probes Based on through Bond-Energy Transfer for Mutually Imaging Signaling Molecules H2S and H2O2

Reactive signaling molecules participate in varieties of biochemical reactions, and methods to detect their mutual existence and crosstalk are in urgent demand. A benzothiadiazole-based handle was designed to fluorescently respond to the co-existence of H₂S and H₂O₂ under pseudo-physiological conditions on a basis of a thiyl-radical-mediated mechanism that accounts for the rapid and efficient domino-like reaction processes. Then the handle motif was attached to a rhodamine moiety by means of an ethynylene linkage, and achieved a significant H₂S–H₂O₂ mutual response in the mitochondria of living cells. Theoretical calculations supported that a through bond energy transfer mechanism contributes to the drastic fluorescence response.     

Mechanistic Investigation of H2O2-dependent Chemiluminescence from Tetrabromo-1,4-Benzoquinone

As a H₂O₂-dependent bioluminescent substrate, tetrabromo-1,4-benzoquinone (TBBQ) was first isolated from acorn worm. The mechanism of chemiluminescence (CL) corresponding to the bioluminescence (BL) of acorn worm is largely unknown, let alone the mechanism of BL. In this article, we firstly studied the chemical and physical processes, and mechanism of H₂O₂-dependent CL from TBBQ by theoretical and experimental methods. The research results indicate: the CL process is initiated by a nucleophilic substitution reaction, which leads to the formation of an anionic dioxetane through five consecutive reactions; the anionic dioxetane decomposes to the first singlet excited state (S₁) via a conical interaction of the potential energy surfaces (PESs) between the ground (S₀) and S₁ state; the anionic S₁-state changes to its neutral form by a proton transfer from the solvent and this neutral product is assigned as the actual luminophore. Moreover, the experimental detection of CL, ^.OH and the identifications of 2,3-dibromo maleic acid and 2-bromo malonic acid as the major final products provide direct evidence of the theoretically suggested mechanism. Finally, this study proves that the activity of the H₂O₂-dependent CL from TBBQ is significantly lower than the one from tetrachloro-1,4-benzoquinone (TCBQ), which is caused by the weaker electron withdrawing effect and the stronger heavy atomic effect of bromine.     

Free Superoxide is an Intermediate in the Production of H2O2 by Copper(I)‐Aβ Peptide and O2

Oxidative stress is considered as an important factor and an early event in the etiology of Alzheimer's disease (AD). Cu bound to the peptide amyloid‐β (Aβ) is found in AD brains, and Cu‐Aβ could contribute to this oxidative stress, as it is able to produce in vitro H₂O₂ and HO^. in the presence of oxygen and biological reducing agents such as ascorbate. The mechanism of Cu‐Aβ‐catalyzed H₂O₂ production is however not known, although it was proposed that H₂O₂ is directly formed from O₂ via a 2‐electron process. Here, we implement an electrochemical setup and use the specificity of superoxide dismutase‐1 (SOD1) to show, for the first time, that H₂O₂ production by Cu‐Aβ in the presence of ascorbate occurs mainly via a free O₂^.? intermediate. This finding radically changes the view on the catalytic mechanism of H₂O₂ production by Cu‐Aβ, and opens the possibility that Cu‐Aβ‐catalyzed O₂^.? contributes to oxidative stress in AD, and hence may be of interest.     

Diterpene Chemistry—VI : SeO2/H2O2 oxidations of exocyclic olefins

Unlike endocyclic olefins the major product from the SeO₂/H₂O₂ oxidation of exocyclic olefins is the same allylic alcohol as from the uncatalysed oxidation. Minor products derived from epoxide intermediates were investigated. The use of SeO₂ as an allylic oxidant for olefins has been extensively investigated, the functionality of the product being to a degree solvent dependent. Although the earlier mechanism of Guillemonat² is incorrect, his rules for the prediction of the position of oxidation still remain valid. A survey by Tratchenburg³ of the current position in SeO₂ oxidation postulates allylic oxidation as proceeding through the intermediacy of an oxaselenocyclobutane to a selenite ester which is solvated by competitive unimolecular (S_N1) and bimolecular (S_N2′) processes (Scheme 1).     

Flow reactor studies and kinetic modeling of the H2/O2 reaction

Profile measurements of the H₂/O₂ reaction have been obtained using a variable pressure flow reactor over pressure and temperature ranges of 0.3–15.7 atm and 850–1040 K, respectively. These data span the explosion limit behavior of the system and place significant emphasis on HO₂ and H₂O₂ kinetics. The explosion limits of dilute H₂/O₂/N₂ mixtures extend to higher pressures and temperatures than those previously observed for undiluted H₂/O₂ mixtures. In addition, the explosion limit data exhibit a marked transition to an extended second limit which runs parallel to the second limit criteria calculated by assuming HO₂ formation to be terminating. The experimental data and modeling results show that the extended second limit remains an important boundary in H₂/O₂ kinetics. Near this limit, small increases in pressure can result in more than a two order of magnitude reduction in reaction rate. At conditions above the extended second limit, the reaction is characterized by an overall activation energy much higher than in the chain explosive regime. The overall data set, consisting primarily of experimentally measured profiles of H₂, O₂, H₂O, and temperature, further expand the data base used for comprehensive mechanism development for the H₂/O₂ and CO/H₂O/O₂ systems. Several rate constants recommended in an earlier reaction mechanism have been modified using recently published rate constant data for H + O₂ (+ N₂) = HO₂ (+ N₂), HO₂ + OH = H₂O + O₂, and HO₂ + HO₂ = H₂O₂ + O₂. When these new rate constants are incorporated into the reaction mechanism, model predictions are in very good agreement with the experimental data. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 113–125, 1999     

Zur Kinetik der Bildung von Na2PdC2

On the Kinetics of the Formation of Na₂PdC₂ The kinetics of the formation of Na₂PdC₂ from Na₂C₂ and palladium were investigated by means of time‐resolved synchrotron powder diffraction (powder diffractometer at beamline B2, HASYLAB/Hamburg) at different temperatures in the range 513 to 533 K. By Rietveld analysis of the resulting diffraction patterns the molar ratio of Na₂PdC₂ was determined in dependence of the reaction time. The calculated crystallization curves were analysed by using the Avrami‐Erofe'ev model for the kinetics of solid‐state reactions. A diffusion mechanism was found and an activation energy of 480(120) KJ/mol was determined. Reasons for the low accuracy of this value are discussed.     

Sonoluminescence of terbium chloride in an H2O-D2O mixture

The effect of solvent deuteration on the multibubble sonoluminescence (SL) of an aqueous solution of terbium chloride was studied. The dependence of the intensity of the characteristic SL of the Tb^III ion on the composition of an H₂O-D₂O mixture is similar to an analogous dependence of its photoluminescence (PL) but with a much smaller isotope effect. In pure D₂O, the SL intensity increases by 4 times only compared to the SL in water, while the PL intensity increases by 10 times. The mechanism of inner-bubble excitation of lanthanide ions is considered. According to this mechanism, an additional “heterogeneous” channel of quenching of excited Tb^III ions appears, which is absent for PL. The proposed model satisfactorily describes the experimental data on the effect of solvent deuteration on the SL intensity. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1074–1078, July, 2006.     

Mechanism and kinetics of glass-ceramics formation in the LiO2-SiO2-CaO-P2O5-CaF2 system

Two glasses based on lithium disilicate (LS₂), with and without fluorapatite (FA), were synthesised in the Li₂O-SiO₂-CaO-P₂O₅-CaF₂ system with P₂O₅: CaO: CaF₂ ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS₂ favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS₂ glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (₂99 ± 1 kJ mol-1 for pure LS₂ glass and ₂88 ± 7 kJ mol⁻¹ for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS₂ glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like phases after soaking in SBF.      

Kinetics and mechanism of the decomposition of Cs2Pt[CH3]2Cl4 in aqueous solution with concurrent formation of C2H6, C2H4, and C2H5Cl

Reductive elimination of ethane from Cs₂Pt(CH₃)₂Cl₄ in aqueous chloride solutions at 368 K is accompanied by C-H bond scission. A mechanism is proposed for the reaction which includes the intermediate formation of an ethylhydrideplatinum(IV) and an ethylplatinum(II) complex.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 154–158, March–April, 1993.     

Model of the catalytic reaction 2H<Subscript>2</Subscript> + O<Subscript>2</Subscript> → H<Subscript>2</Subscript>O with the participation of molecules in a precursor state

The absence of experimental evidence for the occurrence of the catalytic reaction 2H₂ + O₂ → 2H₂O on platinum in accordance with the Langmuir-Hinshelwood mechanism was established. It was found that the heterogeneous process can be described more adequately and its nature can be better understood with consideration for chemical transformations involving molecules in a precursor state in a model of the above reaction. The inverse kinetic problem was solved. It was found that the model in which an unambiguously specified set of rate constants for the elementary steps of the reaction was used provided an opportunity to describe experimental data obtained by various authors concerning the oxidation of hydrogen on platinum over the detonating gas pressure range 10^?3-10⁵ Pa. The signs of the occurrence of heterogeneous reactions by an adsorption mechanism were found.     

CuInS2量子点阻变效应

采用改进的热分解法制备了具有半导体效应的CuInS₂量子点,量子点尺寸均匀、大小为4.2 nm。组装的Au/CuInS₂/FTO阻变存储器件表现出典型的双极性阻变特点,其开态电压为-3.8 V,关态电压为4 V,ON/OFF开关比约为10³。对器件的I-V特性曲线线性拟合发现,器件的阻变机制在高阻态时表现为空间限制电荷（SCLC）传导机制,在低阻态时表现为欧姆传导机制。器件的阻变特性主要是由于电荷被CuInS₂薄膜中的缺陷产生的势阱捕获导致。通过调节陷阱势垒高度引起电荷在陷阱中移动,导致导电通路的产生和断裂,使器件处于高阻态和低阻态。     

Mechanism of the chain process forming H2 in the photooxidation of formaldehyde

A mechanism for the formation in a chain of H₂, CO, and HCOOH in the photooxidation of formaldehyde is proposed. This mechanism is initiated by the addition of HO₂ to formaldehyde. Hydrogen atoms are produced by the thermal dissociation of the HOCH₂O radical: HOCH₂O → H + HCOOH; ΔH = + 3.2 kcal/mol [5]. Photolysis of CH₂O? O₂? NO mixtures and product analysis were carried out in conjunction with kinetic simulation yielding an estimate for the activation energy of the dissociation reaction : E₅ = 14.9 ± 1.0 kcal/mol. Previous observations of this chain process are considered in view of this mechanism.     

Anodic oxidation of p-But-calix[4]arene-(OH)2-(OCH2CONEt2)2. Electrogeneration of a calixdiquinone in dichloromethane

The electrochemical oxidation of p-Bu^t-calix[4]arene-(OH)₂-(OCH₂CONEt₂)₂ 1 has been investigated for the first time and was shown to result in the formation of the corresponding diquinone 3. The reaction proceeds via two successive two-electron irreversible oxidation steps both governed by an ECE mechanism. Alkali cations recognition can be realized by exhaustive oxidation of 1 in the presence of alkali salts.     

Products of lithium interaction with nanostructured oxides SnO2-TiO2 and mechanism of charge-discharge of electrodes in a lithium-ion battery

Products of lithium interaction with thin-film nanostructured SnO₂-TiO₂ (ST) oxides are studied with the aid of x-ray diffraction analysis and Moessbauer spectroscopy on the ¹¹⁹Sn nuclei. Electrochemical properties of a series of the ST electrodes with different concentrations of TiO₂ varied from 0 to 20 mol % are also examined. It is concluded that the specific feature of the charge-discharge mechanism of the ST electrodes is a significant participation of oxygen in reversible reactions during insertion and extraction of lithium as compared with an alloying mechanism of operation of tin-containing anodes. The leading role in this is played by titanium oxide. Remaining stable towards reduction by lithium, it facilitates the holding of the neighboring layers of SnO₂ in a nanodisperse state and in an oxidized state. The effect of a decrease in the capacity degradation in modified TiO₂ electrodes, which is discovered in this work, is attributed to the hampering of the growth of nanocrystallites of β-Sn by interlayers of tin and titanium oxides mentioned above.     

Electrochemical study of (NEt4)2Cl2FeS2MoS2 and (NEt4)2Cl2FeS2MoS2FeCl2

Summary The ability of [MoS₄]^2–, anions to be used as ligands for transition metal ions has been widely demonstrated, especially with Fe²⁺. The present study has been restricted to linear complexes such as (NEt₄)₂ [Cl₂FeS₂MoS₂] and (NEt₄)₂[Cl₂FeS₂MoS₂FeCl₂]. Their electrochemical properties are described: upon electrochemical reduction, these compounds yield MoS₂, as a black precipitate, and an iron complex in solution, assumed to be [SFeCl₂]^2–. The electrochemical reduction goes through two electron transfers, coupled with the breakdown of the molecular skeleton: a DISPl and an ECE mechanism. Depending on the solvent, the following equilibrium may be observed: [Cl₄Fe₂MoS₄]^2–[Cl₂FeMoS₄]^2–+FeCl₂. The equilibrium constant, K_D, was evaluated by differential pulse polarography. K_D is tightly related to the donor number of the solvent.     

Theoretical study on electronic structure of (CNC)Fe_2N2 and its N2 elimination mechanism

The density function theory (DFT) is to elucidate the electronic structure of bis(dinitrogen) Fe(0) complex, (CNC)Fe_2N₂, and its N₂ elimination mechanism. (CNC)Fe_2N₂ has a low‐spin singlet (S = 0) ground state with a distorted square pyramidal structure. Fragment orbital interaction analysis yields total occupancy of π* orbitals (LUF₍₄₎O and LUF₍₄₎O−1) of apical N3 N4 is 0.188 while that of basal N1 N2 is 0.187 in ^S0(CNC)Fe_2N₂, suggesting nearly the same activation extent for both basal and apical N₂ ligands. The lowest‐lying triplet state T₁ (3‐A′) has a repulsive potential energy surface along the Fe N3 bong length by PBE functional, while a minimum on T₂ state (3‐A″) with higher energy is found by B3LYP functional. The nonadiabatic N₂ elimination mechanism of (CNC)Fe_2N₂ involves an S₀‐T₁ states crossing, which lowers the activation energy to 9.7 kcal/mol and produces high‐spin intermediate (CNC)Fe N₂. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Selectivity under microwave irradiation. Benzylation of 2-pyridone: an experimental and theoretical study

The reaction of 2-pyridone with benzyl bromide in the absence of base and under solvent-free conditions has been studied experimentally and by computational methods. This reaction was one of the first reported examples in which modification of selectivity under microwave irradiation was observed. C- and/or N-alkylations were obtained depending on the benzyl halide and the heating system. N-Alkylation through mechanism A (S_N2 mechanism) is kinetically favoured while C-alkylation through an S_N1-type mechanism is thermodynamically favoured and is observed under microwave irradiation. Two S_N1-type mechanisms (mechanisms B and C) have been calculated, mechanism C being a kind of S_Ni. The influence of the pyridone/benzyl bromide ratio was studied. A second molecule of pyridone stabilizes the transition state and assists the leaving of the bromide ion. The occurrence of C-alkylation under microwave irradiation is explained by the predominance of the thermodynamic control in these conditions. Under microwave irradiation N-alkylation through an S_N1-type mechanism (mechanism C) can also occur. The dependence of the outcome of N-alkylation on the benzyl bromide ratio has been explained by a shift in the mechanism from S_N2 to S_N1 under microwave irradiation. Computational calculations have shown to be a useful tool for determination of the origin of the selectivity under microwave irradiation.     

High-pressure transformations of NdI2

A p,T-diagram for NdI₂ is reported. The transformation from an SrBr₂-type arrangement to a Ti₂Cu-type structure takes place between 10 and 20 Kb, with a negative slope for the phase boundary. Due to kinetic hindrance at lower temperatures, an intermediate phase with a CaF₂-type arrangement can be detected by in situ X-ray investigations. A mechanism for the transformation is proposed. Structural parameters are refined by Rietveld analysis, and the compressibilities of the phases are given.     

On the mechanism of thermal 2+2 cycloaddition reactions involving fluoro-olefins

A concerted 2_s + 2_a mechanism is proposed for cycloaddtion reactions of fluoro-olefins to give substituted cyclobutanes. Published data on relative rates, orientation and stereochemical course of these reactions are reconsidered and it is concluded that the concerted 2_s + 2_a mechanism provides a more satisfactory rationâle than the commonly accepted diradical mechanism.