Ab-initio calculations of excited rare gas alkali ions

The excimer-like ions formed by combining a rare gas ion with an alkali atom were investigated by an ab initio HF-CI calculation. The resulting four bound excited states¹Σ⁺,¹Π,³Σ⁺ and³Π were subjected to a semiempirical spin orbit (SO)-coupling yielding eight fine structure levels with angular momenta Ω=2, 1(3) and 0(4). For (NeLi)⁺, (NeNa)⁺, (ArLi)⁺, (ArNa)⁺, (ArK)⁺ and (KrLi)⁺ the wavelengths for the five allowed transitions to the ground state were calculated. The results are in close agreement with the experimental results. Also other spectroscopic properties as binding energies, transition moments and vibrational quanta are given.     

Dynamic study of photosensitized one-electron oxidation of polyG by menadione

Quinones including menadione are ubiquitous in nature. They play important roles in aerobic respira- tion and photosynthesis[1,2]. In addition, exogenous quinones are used as antibiotics and anticancer drugs. Their function is closely related to their red…     

Formation and reactivity of metal carbonyl anions in the gas phase

The reactions of metal carbonyl anions (M(CO)_n^?; M = Cr, Mn and Fe; n = 1–3) with n-heptane, water and methanol were studied with use of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an external ion source. The M(CO)_n^? ions were formed in the FT-ICR cell by collision-induced dissociation of the most abundant primary ion generated by electron impact of the appropriate metal carbonyl compound present in the external ion source. The M(CO)_n^? ions were allowed subsequently to undergo non-reactive collisions with argon in order to remove possible excess internal/translational energy prior to the ion/molecule reaction. Only the Cr(CO)₃^?, Mn(CO)₃^? and Fe(CO)₂^? ions react with n-heptane. This reaction proceeds by loss of H₂ from the collision complex and the Cr(CO)₃^? and Fe(CO)₂^? ions react about three times more efficiently than the Mn(CO)₃^? ion. With water, Mn(CO)^? and Fe(CO)₃^? are unreactive, whereas the other ions react by loss of one or two CO molecules from the collision complex. The rate of the reaction with water decreases in the order Cr(CO)₃^?, Fe(CO)₂^?, Cr(CO)₂^?, Fe(CO)^?, Mn(CO)₃^? and Mn(CO)₂^?. With methanol, the Cr(CO)₂^? ion reacts by loss of two CO molecules from the collision complex, whereas loss of one CO molecule and elimination of CO + H₂ occur in the reaction with Cr(CO)₃^?. Competing loss of CO and one or two H₂ molecules occurs in the reactions of Mn(CO)₃^? and Fe(CO)₂^? with methanol. The rate of the reaction with methanol decreases in the order Cr(CO)₃^?, Fe(CO)₂^?, Cr(CO)₂^? and Mn(CO)₃^?.     

Maßanalyse und Katalyse

The application of the therinometric method to the catalytic endpoint indication in volumetric determinations by precipitation reactions is discussed. The direct titration of silver, mercury(II) and palladium(II) as well as the determination of several anions (Cl^?, Br^?, J^?, SCN^?, CN^?, [Fe(CN)₆]^4? and S^2?) by backtitration with iodide standard solution is described. The well known reaction between cerium(IV) and arsenic(III), catalysed by iodide, serves as an indicator. The ions mentioned can thus be determined in the microgram range with good accuracy.     

Oxygenation and chlorination of aromatic hydrocarbons with hydrochloric acid photosensitized by 9-mesityl-10-methylacridinium under visible light irradiation

Efficient photocatalytic oxygenation of toluene occurs under visible light irradiation of 9-mesityl-10-methylacridinium (Acr⁺–Mes) in oxygen-saturated acetonitrile containing toluene and aqueous hydrochloric acid with a xenon lamp for 15 h. The oxygenated products, benzoic acid (70 %) and benzaldehyde (30 %), were formed after the photoirradiation. The photocatalytic reaction is initiated by intramolecular photoinduced electron transfer from the mesitylene moiety to the singlet excited state of the Acr⁺ moiety of Acr⁺–Mes, which affords the electron-transfer state, Acr^?–Mes^?+. The Mes^?+ moiety can oxidize chloride ion (Cl^?) by electron transfer to produce chlorine radical (Cl^?), whereas the Acr^? moiety can reduce O₂ to O ₂ ^?? . The Cl^? radical produced abstracts a hydrogen from toluene to afford benzyl radical in competition with the bimolecular radical coupling of Cl^?. The benzyl radical reacts with O₂ rapidly to afford the peroxyl radical, leading to the oxygenated product, benzaldehyde. Benzaldehyde is readily further photooxygenated to yield benzoic acid with Acr^?–Mes^?+. In the case of an aromatic compound with electron-donating substituents, 1,3,5-trimethoxybenzene, photocatalytic chlorination occurred efficiently under the same photoirradiation conditions to yield a monochloro-substituted compound, 2,4,6-trimethoxychlorobenzene.     

Extraction and separation of Th(IV) and U(VI) from nitric acid media using PIA-8 and HDEHP

Extraction behavior of Th(IV) and U(VI) has been investigated with bis(2-ethylhexyl) phosphinic acid (PIA-8) and bis(2-ethylhexyl) phosphoric acid (HDEHP) from nitric acid media in toluene. The optimum conditions for extraction of these metals have been established by studying various parameters like acid concentration, pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.3-2.5M HNO₃ by 2.5^.10^-2M HDEHP and in the pH range 0.1-2.5 with 2.3^.10^-2M PIA-8 in toluene. U(VI) was completely extracted in the acidic range of 0.1-2.0M HNO₃ with 2.2^.10^-2M HDEHP and in the pH range of 1.0-3.0 with 2.0^.10^-2M PIA-8 in toluene. The probable extracted species have been ascertained by log D-log c plot as UO₂ R₂ ^.2HR with both the reagents and Th (NO₃)₂R₂ ^.2HR with PIA-8 and Th (NO₃)₃R^.3HR with HDEHP, respectively. Temperature dependence of the extraction equilibrium is examined by the temperature variation method. Separation of U(VI) and Th(IV) was also carried out from commonly associated metals.     

[Ru(bpy)3]2+-trivalent titanium. A photochemical system with hydrogen production from aqueous solutions by visible light

Molecular hydrogen, detected by gas-chromatographic and mass-spectrometric measurements, was obtained by irradiating with visible light aqueous hydrochloridic solutions of [Ru(bpy)₃]²⁺ and trivalent titanium. The active species is the ³CT of [Ru(bpy)₃]²⁺, which is quenched by Ti(III). The suggested mechanism is an electron transfer with Ti(II) formation. The back reaction between [Ru(bpy)₃]³⁺ and Ti(II) is hindered by the very fast competitive reaction of Ti(II) (not stable in acid aqueous solutions) with H⁺, carrying to hydrogen evolution.     

Independent Generation and Time-Resolved Detection of 2′-Deoxyguanosin-N2-yl Radicals

Guanine radicals are important reactive intermediates in DNA damage. Hydroxyl radical (HO^.) has long been believed to react with 2′-deoxyguanosine (dG) generating 2′-deoxyguanosin-N1-yl radical (dG(N1-H)^.) via addition to the nucleobase π-system and subsequent dehydration. This basic tenet was challenged by an alternative mechanism, in which the major reaction of HO^. with dG was proposed to involve hydrogen atom abstraction from the N2-amine. The 2′-deoxyguanosin-N2-yl radical (dG(N2-H)^.) formed was proposed to rapidly tautomerize to dG(N1-H)^.. We report the first independent generation of dG(N2-H)^. in high yield via photolysis of 1 . dG(N2-H)^. is directly observed upon nanosecond laser flash photolysis (LFP) of 1 . The absorption spectrum of dG(N2-H)^. is corroborated by DFT studies, and anti- and syn-dG(N2-H)^. are resolved for the first time. The LFP experiments showed no evidence for tautomerization of dG(N2-H)^. to dG(N1-H)^. within hundreds of microseconds. This observation suggests that the generation of dG(N1-H)^. via dG(N2-H)^. following hydrogen atom abstraction from dG is unlikely to be a major pathway when HO^. reacts with dG.     

Elimination of Interferences in the Determination of Arsenic and Determination of Arsenic in Percolate Waters from an Industrial Landfill by Inductively Coupled Plasma Mass Spectrometry

Abstract

The determination of arsenic in environmental samples suffers interference by chloride which gives rise to the polyatomic interference of ⁴⁰Ar³⁵Cl on ⁷⁵As. Mathematical correction methods based on the ratios ⁴⁰Ar³⁷ Cl/⁴⁰ Ar³⁵Cl, ³⁵Cl¹⁶O/⁴⁰ Ar³⁵Cl or ³⁷Cl¹⁶O/⁴⁰ Ar³⁵Cl, are discussed and compared with each other. The method is applied for the determination of arsenic in treated percolate water from a landfill where arsenic containing waste is landfilled. The results obtained when applying the different equations were in good agreement with each other. The results for the untreated percolate water, which could be diluted far enough to eliminate matrix effects and showed negligible interference from chloride, were in good agreement with results obtained with Capillary Zone Electrophoresis. Hydride generation made it possible to determine As(III) and by difference As(V) in both waters. 99.7% of the arsenic present in the percolate water was As(V), which means that during the landfilling, possibly by the infiltration of rainwater, the arsenic is oxidised because the original industrial waste contained 100% As(III).     

Kinetics and mechanism of oxidation of excited state Tris-(2,2′-bipyridyl)-ruthenium (II) complex by peroxomonosulfate,peroxodisulfate, and peroxodiphosphate

Excitation of Ru(bipy)₃²⁺ ion by visible radiation of wavelength λ = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy)₃³⁺. The kinetics of this photochemical oxidation of Ru(bipy)₃²⁺ by each peroxide was followed spectrophotometrically and found to obey a total second-order, first-order each in [Ru(bipy)₃²⁺] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy)₃²⁺ occurred but only when at 1.0 M [H⁺] and > 10^?2M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy)₃³⁺ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy)₃²⁺] on the visible light induced oxidation of Ru(bipy)₃²⁺ by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.     

Palladium(II) Complexes of 1-Phosphaisoprene Molecules and Polymers: Reversible Cross-Linking of a Phosphorus-Containing Polymer

The anionic polymerization of 1-phosphaisoprene [Mes*P=C(Me)−CH=CH₂ (E- 1 )] affords poly(1-phosphaisoprene) 2 in high yield (75 %). Concentrated solutions of polymer 2 (M_n=21,800 g mol⁻¹; Đ=1.02) a P-analogue of natural rubber, undergo gelation upon treatment with [Pd(cod)Cl₂] (0.15 P equiv). Evidence for P-coordination of 2 to Pd^II was obtained by ³¹P and ¹H NMR spectroscopy. The gelation is reversed by the addition of PMe₃ and the reformation of recoverable 2 along with [Pd^II−PMe₃] complexes were confirmed by ³¹P NMR spectroscopy. The use of labile metal-ligand bonds to reversibly form gels is unprecedented and has relevance to self-healing materials. In contrast, coordination of 2 to [Pd(η³-C₃H₅)(μ-Cl)]₂ affords the well-defined complex 2 ⋅ [Pd(η³-C₃H₅)Cl] which was characterized by ³¹P, ¹H, ¹³C{¹H} NMR spectroscopy and GPC. This polymer chemistry was complemented by detailed molecular model studies of the coordination chemistry of monomer 1-phosphaisoprene E- 1 with [Pd(cod)Cl₂] and [Pd(η³-C₃H₅)(μ-Cl)]₂].     

Organoborierung von alkinylstannanen: XV. Synthese von 1,2-dihydro-1,2,5-disilaborepinen

The reaction between 1,2-diethynyl-tetramethyldisilane (1) and two equivalents of diethylaminotrimethylstannane (2) leads to 1,2-bis(trimethylstannylethynyl)-tetramethyldisilane (3). The new alkyne derivative 3 reacts, already at room temperature, with trialkylboranes, R₃B (5) (R = Me, Et), quantitatively to give 1,1,2,2-tetramethyl-3,7-bis(trimethylstannyl)-4,5,6-trialkyl-1,2-dihydro-1,2,5-disilaborepines (6). The reaction is much slower with R = Prⁱ which allows detection of intermediates by NMR spectroscopy. All products are characterized by ¹H, ¹¹B, ¹³C, ²⁹Si and ¹¹⁹Sn NMR data.     

Complexes of a New N3S2 Macrocycle: Synthesis,Structure and Electrospray Mass Spectrometry

The silver(I) complex of a 15-membered macrocyclic ligand with an N₃S₂ donor set (L¹) has been prepared by the reaction of 2,6-diacetylpyridine with 1,8-diamino-3,6-dithiaoctane in the presence of silver(I) ions. A reduced form (L²) of the ligand, in which the imine groups are converted to amines, was prepared by the reduction of the silver(I) complex by sodium borohydride. The ligand L² has been characterised by various spectroscopic techniques and the copper(II) complex has been prepared. The metal complexes of L¹ and L² have been characterised by electrospray mass spectrometry and UV-visible spectroscopy. The copper(II) complex of L¹ has been synthesised from [AgL¹]⁺ via metal exchange. [CuL¹](ClO₄)₂ crystallises in the orthorhombic space group Pna2₁ with a = 14.374(5) Å, b = 12.947(3) Å, c = 11.824(3) Å with Z= 4. The geometry about the metal centre approximates trigonal bipyramidal with the pyridinyl nitrogen and the sulfur donors in the equatorial positions and the imine nitrogen donors in the axial positions. Metal ion exchange and the relative stabilities of metal complexes of the macrocyclic ligands were studied by electrospray mass spectrometry.     

Synthesen von Verbindungen mit M–N‐Bindungen (M = Li,Ga, In)

Syntheses of Compounds with M–N Bonds (M = Li, Ga, In) The adducts [GaCl₃(HNⁱPr₂)] ( 1 ) and [InCl₃{HN(CH₂Ph)₂}₂] ( 2 ) can be obtained by the reactions of the corresponding metal(III) halides with the amines. The In amide In(N^cHex₂)₃ ( 3 ) can be formed by treatment of InCl₃ with three equivalents of LiN^cHex₂. Reaction with four equivalents of LiN^cHex₂ leads to the same product. However, the treatment of InCl₃ with four equivalents of LiN(CH₂Ph)₂ gives the desired metalate [Li(THF)₄][In{N(CH₂Ph)₂}₄] ( 4 ). From the corresponding reaction of InCl₃ with LiNⁱPr₂ no In‐containing product could be identified. Instead, the aggregate of LiCl with three units of LiNⁱPr₂, [Li₄(NⁱPr₂)₃(THF)₄Cl] ( 5 ), was isolated. 1 – 4 were characterized by NMR, IR and MS techniques as well as by X‐ray structure determinations. According to them, 1 possesses a tetrahedrally coordinated Ga atom, at which two units of 1 are connected by hydrogen bridges to centrosymmetrical dimers. The In atoms in 2 have a trigonal‐bipyramidal coordination sphere; the amine molecules occupy the apical positions. The central metal atom in 3 and the anion of 4 exhibit trigonal‐planar and distorted tetrahedral environments, respectively. The novel structural motif in 5 is the Cl^– ion, only partly surrounded by Li⁺ ions in a strongly distorted trigonal‐bipyramidal fashion. The dominating angle amounts to 165.2(2)°.     

Rigid ferrocenophane and its metal complexes with transition and alkaline-earth metal ions

The rigid [6]ferrocenophane, L¹, was synthesised by condensation of 1,1′-ferrocene dicarbaldehyde with trans-1,2-diaminocyclohexane in high dilution at r.t. followed by reduction. When other experimental conditions were employed, the [6,6,6]ferrocenephane (L²) was also obtained. Both compounds were characterised by single crystal X-ray crystallography. The protonation of L¹ and its metal complexation were evaluated by the effect on the electron-transfer process of the ferrocene (fc) unit of L¹ using cyclic voltammetry (CV) and square wave voltammetry (SWV) in anhydrous CH₃CN solution and in 0.1 M ⁿBu₄NPF₆ as the supporting electrolyte. The electrochemical process of L¹ between −300 and 900 mV is complicated by amine oxidation. On the other hand, an anodic shift from the fc/fc⁺ wave of L¹ of 249, 225, 81 and 61 mV was observed by formation of Zn²⁺, Ni²⁺, Pd²⁺ and Cu²⁺ complexes, respectively. Whereas Mg²⁺ and Ca²⁺ only have with L¹ weak interactions and they promote the acid-base equilibrium of L¹. This reveals that L¹ is an interesting molecular redox sensor for detection of Zn²⁺ and Ni²⁺, although the kinetics of the Zn²⁺ complex formation is much faster than that of the Ni²⁺ one. The X-ray crystal structure of [PdL¹Cl₂] was determined and showed a square–planar environment with Pd(II) and Fe(II) centres separated by 3.781(1) Å. The experimental anodic shifts were elucidated by DFT calculations on the [ML¹Cl₂] series and they are related to the nature of the HOMO of these complexes and a four-electron, two-orbital interaction.     

Preparation of 616X,6Y-Tris-O-(tert-butyldimethyl-silyl)-β-cyclodextrins,and Isolation and Regiochemical Determination of Five Positional Isomers

Abstract

Five positional isomers of 6¹,6^X,6^Y-tris-O-(tert-butyldimethylsilyl)-cyclomaltoheptaose (β-cyclodextrin, βCD) were prepared by reaction of β CD with tert-butyldimethylsilyl chloride in pyridine, and were isolated by HPLC and characterized by ¹³C NMR spectroscopy. The regiochemical determination of those positional isomers was carried out by the extended Körner's method, that is, by comparison with compounds obtained by additional monosilylation of 6¹, 6^X-bis-O-(tert-butyldimethylsilyl)-βCDs, and by conversion to the known compounds, 6¹,6^X,6^Y-tri-O-(toluene-sulfonyl)-βCDs.     

液相OH•, NO3•和SO4•-与二甲基硫反应机理

利用激光闪光光解技术研究了液相二甲基硫(DMS)与OH^•, NO₃^•和SO₄^•-自由基的微观反应机理. 实验结果表明: 在pH 5～9时, OH^•氧化DMS生成DMSOH^•, DMSOH^•会与DMS反应生成(DMS)₂⁺; 而NO₃^•和SO₄^•-;会直接氧化DMS生成DMS^＋, 生成的DMS^＋会与DMS反应生成(DMS)₂⁺.(DMS)₂⁺与氧气的反应很慢, 它的衰减受pH影响较大.     

Use of ion-molecule reactions and methanol addition to improve arsenic determination in high chlorine food samples by DRC-ICP-MS

Direct determination of trace arsenic in high chlorine food samples by ICP-MS is complicated by the presence of ArCl⁺ interferences, and the high first ionization energy of As (9.81 eV) also results in low analytical sensitivity in ICP-MS. In this work, two strategies based on ion-molecule reactions were successfully used to eliminate ArCl spectral interference in a dynamic reaction cell (DRC). The interference ion (⁴⁰Ar³⁵Cl⁺) was directly removed by the reaction with methane gas, and the background signal was reduced by up to 100-fold at m/z 75. Alternatively, by using molecule oxygen as the reaction gas, ⁷⁵As⁺ was effectively converted to ⁷⁵As¹⁶O⁺ that could be detected at m/z 91 where the background is low. The poor signal intensity of As or AsO was improved 3-4 times by addition of 4% methanol in the analyzed solutions. The limit of quantitation (LOQ) for ⁷⁵As (CH₄-DRC method) and ⁷⁵As¹⁶O (O₂-DRC method) was 0.8 and 0.3 ng g⁻¹ and the analytical results of seaweed and yellow croaker standard reference materials were in good agreement with the certified values. As the routine arsenic monitoring method in our laboratory, it was applied to the accuracy determination of 119 high chlorine food samples from eight different markets of Beijing.     

Catalytic Hydroxylation of Benzene to Phenol by Dioxygen with an NADH Analogue

Hydroxylation of benzene by molecular oxygen (O₂) occurs efficiently with 10‐methyl‐9,10‐dihydroacridine (AcrH₂) as an NADH analogue in the presence of a catalytic amount of Fe(ClO₄)₃ or Fe(ClO₄)₂ with excess trifluoroacetic acid in a solvent mixture of benzene and acetonitrile (1:1 v/v) to produce phenol, 10‐methylacridinium ion and hydrogen peroxide (H₂O₂) at 298 K. The catalytic oxidation of benzene by O₂ with AcrH₂ in the presence of a catalytic amount of Fe(ClO₄)₃ is started by the formation of H₂O₂ from AcrH₂, O₂, and H⁺. Hydroperoxyl radical (HO₂^.) is produced from H₂O₂ with the redox pair of Fe³⁺/Fe²⁺ by a Fenton type reaction. The rate‐determining step in the initiation is the proton‐coupled electron transfer from Fe²⁺ to H₂O₂ to produce HO^. and H₂O. HO^. abstracts hydrogen rapidly from H₂O₂ to produce HO₂^. and H₂O. The Fe³⁺ produced was reduced back to Fe²⁺ by H₂O₂. HO₂^. reacts with benzene to produce the radical adduct, which abstracts hydrogen from AcrH₂ to give the corresponding hydroperoxide, accompanied by generation of acridinyl radical (AcrH^.) to constitute the radical chain reaction. Hydroperoxyl radical (HO₂^.), which was detected by using the spin trap method with EPR analysis, acts as a chain carrier for the two radical chain pathways: one is the benzene hydroxylation with O₂ and the second is oxidation of an NADH analogue with O₂ to produce H₂O₂.     

Study on Spectrophotometric Method for Determination of Bismuth after Flotation Separation Using Microcrystalline Adsorption System

The paper presents a novel method for the flotation separation of Bi³⁺ using microcrystalline adsorption system prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of KI and dodecyl trimethyl ammonium bromide (DTMAB), various salts and acidity etc. on the flotation yield of Bi³⁺ have been investigated to select the optimum experimental conditions. The possible flotation separation mechanism of Bi³⁺ was discussed. The results showed that under the optimum conditions, dodecyl trimethyl ammonium bromide cation (DTMAB⁺ ) reacted with I^? to produce themicrocrystalline matter (Ms‐M) of (DTMAB⁺·I^?), the water‐insoluble ternary association complex of (DTMAB)₃[BiI₆] which produced by Bi³⁺ and I^?, DTMAB⁺ was quantificationally adsorbed on the surface of Ms‐M of (DTMAB⁺·I^?) and was floated above water phase, the liquid‐solid phases were formed with clear interface. In this condition, K⁺, Na⁺, Ca²⁺, Mg²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, Fe²⁺ and Al³⁺ could not be floated. Therefore, Bi³⁺ was separated completely from the above metal ions. A new method for flotation separation and determination of bismuth using microcrystalline adsorption system was established. The proposed method has been successfully applied to the determination of Bi³⁺ in bismuthiferous drug samples, and the results agreed well with those obtained by pharmacopoeia method. The recoveries were 94.1%～106.8%, and the RSD was 1.5%～2.3%.