Analysis on a cooperative pathway involving multiple cations in hammerhead reactions

The hammerhead ribozyme reaction is more complex than might have been expected, perhaps because of the flexibility of RNA, which would have enhanced the potential of RNA during evolution of and in the RNA world. Divalent Mg(2+) ions can increase the rate of the ribozyme-catalyzed reaction by approximately 10(9)-fold as compared to the background rate under standard conditions. However, the role of Mg(2+) ions is controversial since the reaction can proceed in the presence of high concentrations of monovalent ions, such as Li(+), Na(+), and NH(4)(+) ions, in the absence of divalent ions. We thus carried out ribozyme reactions under various conditions, and we obtained parameters that explain the experimental data. On the basis of the analysis, we propose a new pathway in the hammerhead ribozyme reaction in which divalent metal ions and monovalent ions act cooperatively.     

The gas-phase Meerwein reaction

A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by gaseous acylium and thioacylium ions is reported. As ab initio calculations predict, and 18O-labeling and MS3 pentaquadrupole experiments demonstrate, the reaction proceeds by initial O(S)-acylation of the (thio)epoxides followed by rapid intramolecular nucleophilic attack that results in three-to-five-membered ring expansion, and forms cyclic 1,3-dioxolanylium, 1,3-oxathiolanylium, or 1,3-dithiolanylium ions. This gas-phase reaction is analogous to a condensed-phase reaction long since described by H. Meerwein (Chem. Ber. 1955, 67, 374), and is termed as "the gas-phase Meerwein reaction"; it occurs often to great extents or even exclusively, but in some cases, particularly for the most basic (thio)epoxides and the most acidic (thio)acylium ions, proton transfer (eventually hydride abstraction) competes efficiently, or even dominates. When (thio)epoxides react with (thio)-acylium ions, the reaction promotes O(S)-scrambling; when epoxides react with thioacylium ions and the adducts are dissociated, it promotes S/O replacement. An analogous four-to-six-membered ring expansion also occurs predominantly in reactions of trimethylene oxide with acylium and thioacylium ions.     

Meerwein reaction of phosphonium ions with epoxides and thioepoxides in the gas phase

Phosphonium ions are shown to undergo a gas-phase Meerwein reaction in which epoxides (or thioepoxides) undergo three-to-five-membered ring expansion to yield dioxaphospholanium (or oxathiophospholanium) ion products. When the association reaction is followed by collision-induced dissociation (CID), the oxirane (or thiirane) is eliminated, making this ion molecule reaction/CID sequence a good method of net oxygen-by-sulfur replacement in the phosphonium ions. This replacement results in a characteristic mass shift of 16 units and provides evidence for the cyclic nature of the gas-phase Meerwein product ions, while improving selectivity for phosphonium ion detection. This reaction sequence also constitutes a gas-phase route to convert phosphonium ions into their sulfur analogs. Phosphonium and related ions are important targets since they are commonly and readily formed in mass spectrometric analysis upon dissociative electron ionization of organophosphorous esters. The Meerwein reaction should provide a new and very useful method of recognizing compounds that yield these ions, which includes a number of chemical warfare agents. The Meerwein reaction proceeds by phosphonium ion addition to the sulfur or oxygen center, followed by intramolecular nucleophilic attack with ring expansion to yield the 1,3,2-dioxaphospholanium or 1,3,2-oxathiophospholanium ion. Product ion structures were investigated by CID tandem mass spectrometry (MS(2)) experiments and corroborated by DFT/HF calculations.     

气相中苯二聚体离子结构的串联质谱研究

应用碰撞诱导解离技术研究了苯自身化学电离条件下和苯化学电离（甲苯为反应气）条件下离子－分子反应产物ｍ／ｚ１５５和１５６离子的碰撞诱导解离（ＣＩＤ）破裂特性，并与化学电离条件下质子化联苯生成ｍ／ｚ１５５离子的ＣＩＤ碎裂反应相比较，获得了苯离子１－分子反应产物ｍ／ｚ１５５和１５６离子的结构信息。     

NO2^—离子的光催化反应

对NO2离子的TiO2光催化反应研究发现，该光催化反应用于消除NO2离子效果显著．反应的动力学研究表明，NO2离子的TiO2光催化反应是一个较复杂的多步反应，其中，NO2离子在TiO2催化剂表面的光催化氧化是该反应的控制步骤，反应符合L-H动力学规律．研究还发现，反应气氛对该光催化反应有明显影响．在实验条件下未观测到产物对反应的影响．     

Stereoselective additions of chiral (E)-crotylsilanes to thionium ions: asymmetric synthesis of homoallylic thioethers

Stereochemically well-defined homoallylic thioethers 3 are synthesized via Lewis acid promoted condensation reaction between chiral organosilane reagents 2 and in situ generated thionium ions. The stereochemical course of the reaction is consistent with earlier reports concerning crotylsilations of oxonium ions.     

The kinetics of the oxidation of iodide and thiocyanate ions by 12-tungstocobaltate(III)

The rates and mechanism of the reaction of 12-tungstocobaltate(III) anion with thiocyanate and iodide ions have been examined in aqueous acidic solution and constant ionic strength I = 1.00M (LiClO₄). The reactions follow second-order kinetics, i.e. first-order in both the oxidant and the reductant and the rate constants are found to be independent of hydrogen ions in the range [H⁺] = 0.10–1.00M. Outer-sphere mechanism is postulated for the systems based on the relative inertness of the oxidant and linear free energy relations are employed in demonstrating that in the reaction involving thiocyanate ion, the rate determining step is the diffusion apart of the product while the corresponding step in the iodide reaction is the electron transfer. The latter reaction is also catalysed by both bromide and chloride ions and this is rationalised in terms of possible stabilization of atomic iodine as product by these halide ions.     

Controllable redox reaction of chemically purified DNA-single walled carbon nanotube hybrids with hydrogen peroxide

We report for the first time the controllable redox reaction of chemically purified ssDNA-HiPco SWNT hybrids with hydrogen peroxide. Compared with the suspensions before separation, the purified SWNT suspensions become inert with hydrogen peroxide which may serve as a platform for further chemical manipulation. In the presence of thiocyanate ions, the reaction of SWNTs with hydrogen peroxide is initiated and accelerated at the earlier reaction stage, accompanied with the near-infrared spectral suppression. At the later stage, the suppressed spectral intensity is recovered overtime. The thiocyanate ions may work as a mediator being able to control the reaction rate as well as the tunable properties of the reaction. The tunable redox reaction of SWNTs and H2O2 mediated by thiocyanate ions may offer a new sensing scheme for continuously monitoring H2O2 concentrations.     

On the mechanism of the metal exchange in natural cadmium porphyrins

The kinetics of the exchange of the Cd²⁺ ions in the complexes with the natural protogroup porphyrins (protoporphyrin, mesoporphyrin, deuteroporphyrin, and hematoporphyrin) for the Zn²⁺ ions is studied. The stoichiometric ratios of components in the reaction of cadmium exchange for zinc in acetonitrile and DMSO are established. The results obtained are compared with the previously published data for the reaction withthe Co²⁺ ions. The activation mechanism of the metal exchange reaction is considered, depending on the effect of the nature of substituents in porphyrin, d-metal ions, and a solvent.     

The effect of ion molecule reactions on peaks in ion mobility spectrometry

The peak width, shape and position are heavily affected by ion–molecule reactions which are inevitable in the drift region of an ion mobility spectrometer. This paper discusses three major types of reactions occurring in drift tube and their effects on the shape and displacement of the peaks. The first reaction is the dissociation of dimer ions during their flight time creating a tail for the monomer peak. The second one is the reaction between the monomer ions with molecules of the same kind in the drift region. Such a process shifts the peak to longer drift times and causes a tail for the peak as well as its broadening. The last one is the reaction of ions with molecules of different types such as dopant which may exist in the drift region. Depending on the reactivity of the ions, this kind of reaction displaces the peaks differently so that peak-to-peak resolution is lost or, in some cases, gained.     

Ion-Molecular Reactions of Diethylsilylium Ions with Alcohols in the Gas Phase

Radiochemistry was used to study reaction of tritium-labeled diethylsilylium ions with alcohols in the gas phase. The reaction involves both rearrangement of the diethylsilylium ions and isomerization of the substituent in the substrate. The hydroxyl hydrogen of the alcohol and the tritium atom of the diethyl-silylium ion undergo exchange which, however, is less vigorous that in the case of the monoethylsilylium ion. A possible reaction mechanism is proposed.     

Mobile trap algorithm for zinc detection using protein sensors

We present a mobile trap algorithm to sense zinc ions using protein-based sensors such as carbonic anhydrase (CA). Zinc is an essential biometal required for mammalian cellular functions although its intracellular concentration is reported to be very low. Protein-based sensors like CA molecules are employed to sense rare species like zinc ions. In this study, the zinc ions are mobile targets, which are sought by the mobile traps in the form of sensors. Particle motions are modeled using random walk along with the first passage technique for efficient simulations. The association reaction between sensors and ions is incorporated using a probability (p1) upon an ion-sensor collision. The dissociation reaction of an ion-bound CA molecule is modeled using a second, independent probability (p2). The results of the algorithm are verified against the traditional simulation techniques (e.g., Gillespie's algorithm). This study demonstrates that individual sensor molecules can be characterized using the probability pair (p1,p2), which, in turn, is linked to the system level chemical kinetic constants, kon and koff. Further investigations of CA-Zn reaction using the mobile trap algorithm show that when the diffusivity of zinc ions approaches that of sensor molecules, the reaction data obtained using the static trap assumption differ from the reaction data obtained using the mobile trap formulation. This study also reveals similar behavior when the sensor molecule has higher dissociation constant. In both the cases, the reaction data obtained using the static trap formulation reach equilibrium at a higher number of complex molecules (ion-bound sensor molecules) compared to the reaction data from the mobile trap formulation. With practical limitations on the number sensors that can be inserted/expressed in a cell and stochastic nature of the intracellular ionic concentrations, fluorescence from the number of complex sensor molecules at equilibrium will be the measure of the intracellular ion concentration. For reliable detection of zinc ions, it is desirable that the sensors must not bind all the zinc ions tightly, but should rather bind and unbind. Thus for a given fluorescence and with association-dissociation reactions between ions and sensors, the static trap approach will underestimate the number of zinc ions present in the system.     

Heavy-metal remediation by a fungus as a means of production of lead and cadmium carbonate crystals

We show here that reaction of the fungus, Fusarium oxysporum, with the aqueous heavy-metal ions Pb2+ and Cd2+ results in the one-step formation of the corresponding metal carbonates. The metal carbonates are formed by reaction of the heavy-metal ions with CO2 produced by the fungus during metabolism and thus provide a completely biological method for production of crystals of metal carbonates. The PbCO3 and CdCO3 crystals thus produced have interesting morphologies that are shown to arise because of interaction of the growing crystals with specific proteins secreted by the fungus during reaction. An additional advantage of this approach is that the reaction leads to detoxification of the aqueous solution and could have immense potential for bioremediation of heavy metals. Under conditions of this study, the metal ions are not toxic to the fungus, which readily grows after exposure to the metal ions.     

Reduction of silver(II) oxide by the solvent in acid media

The reaction of silver(II) oxide with water to yield silver(I) ions and oxygen is an important side-reaction in procedures which use silver(II) oxide as the oxidant. This reaction has been examined in solutions which were 0.01-1M in respect to sulphuric or perchloric acid. The rate of reduction varied directly with the amount of solid added and was a complex function of the concentrations of hydrogen ions, silver(I) ions and anions present. The kinetic results have been used to postulate a mechanism for the reaction.     

环丙烷衍生物在D2O离子体系中的H/D交换反应

在D2O化学反应气条件下研究了环丙烷衍生物的H/D交换反应特性.发现了三种新的产物离子[M+1]+、[M+2]+和[M+3]+.应用碰撞诱导碎裂(CID)技术研究了这些离子的碎裂反应特性.实验结果表明三种新的产物离子是由反应物与试剂离子之间发生H/D交换反应生成的.并获得了环丙烷衍生物结构中活泼氢位置及其数量的信息.     

气相中卤代苯离子-分子反应产物的串联质谱研究

应用碰撞诱导解离技术研究了氯代苯、溴代苯和碘代苯离子-分子反应产物的碎裂反应特性,与联苯的分子离子和质子化溴代联苯的碰撞诱导解离谱比较获得了产物离子的结构信息.     

A new synthesis of triarylsilylium ions and their application in dihydrogen activation

Well-shuffled: An unexpected substituent distribution reaction via alkyldiarylsilylium ions leads to a distribution of substituents. Starting from alkyldiaryl silanes, this reaction provides a facile synthetic approach to sterically highly hindered triarylsilylium ions. These silylium ions can be applied in dihydrogen activation reactions.     

采用微量热法研究重金属离子对脲酶催化水解反应的影响

利用微量热计Micro DSCⅢ对重金属离子影响脲酶催化水解反应的过程进行研究, 并探讨重金属离子联合抑制作用对脲酶催化反应的影响. 结果表明, 在25℃下, 重金属离子对脲酶水解反应热有影响, 在广泛浓度范围(0.1, 1, 10, 100和10³ mg/L)内, 这种影响不仅表现在抑制作用方面, 而且会促进其水解反应的进行, 如铜离子在100和1000 mg/L时抑制率分别为(0.49±0.20)%和(-11.93±1.34)%. 重金属离子浓度与抑制率具有显著或极显著的相关性, 抑制效果的顺序为砷离子>铅离子>镉离子>铜离子. 当重金属离子联合抑制时, 其抑制效果与抑制率较高的重金属离子的抑制作用接近.     

硼酸根与甲阶酚醛树脂中酚羟基和邻位羟甲基的螯合反应

通过溶液pH值的测定和红外光谱分析，研究硼砂与甲阶酚醛树脂水溶液的反应表明：在水溶液中硼砂能与甲阶酚醛树脂很快地发生反应；硼砂水解产生的B／（OH)4^-，以定量的方式与树脂中酚羟基和邻位羟甲基以共价配键相结合，形成具有四面体结构的螯合物，并放出H^ 离子。     

Titrimetric determination of thiocyanate and thiosulphate ions by oxidation with iodine in alkaline solution

Thiocyanate (2.7-90 mug) and thiosulphate (4.5-90 mug) ions are oxidized by iodine in alkaline media to sulphate ions. After acidification, the excess of iodine is extracted into chloroform, and the iodide ions formed in the redox reaction subjected to an amplification reaction. Either a titrimetric or a spectrophotometric finish may be used. Each thiocyanate and thiosulphate ion results in the ultimate production of 19 and 24 iodine molecules, respectively.