18O-isotope exchange behavior and oxidation activity of La1-xSrxMnO3+δ

Different preparation routes derived both from the usual high-temperature solid state synthesis and the sol-gel process were applied for the synthesis of crystalline La_1-xSr_xMnO₃₊ phases with 0x 0.2. They were investigated by means of temperature programmed isotope exchange (TPIE) under various conditions. The ¹⁸O isotope exchange experiments yielded information on the dependence of the oxygen mobility on temperature and the Mn⁴⁺/Mn³⁺ratio. Both are related to the defect structure of the solid. TPIE was applied for studying the interaction between ¹⁸O₂ and CH₄ under static conditions and was compared with results obtained from catalytic investigations, i.e. the behavior of La_1-xSr_xMnO₃₊ (0x0.2) in both CO and CH₄ oxidation with normal oxygen ¹⁶O₂ under steady flow conditions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Freezing-point of mixtures of H 2 16 O and H 2 18 O

Freezing-point depression of mixtures of H ₂ ¹⁶ O and H ₂ ¹⁸ O were measured. The results showed that the freezing point of the mixture rose linearly with an increase in the molal concentration of H ₂ ¹⁸ O. The results suggested the formation of a solid solution of H ₂ ¹⁶ O and H ₂ ¹⁸ O by freezing, similar to that formed by H ₂ O–D ₂ O, and that H ₂ ¹⁸ O behaves as a different molecule than H ₂ ¹⁶ O.     

IR-Spectroscopic Study of Complex Formation of Nitrogen Oxides (NO,N2O) with Cationic Forms of Zeolites and the Reactivity of Adsorbed Species in CO and CH4 Oxidation

The formation of complexes and disproportionation of nitrogen oxides (NO, N₂O) on cationic forms of LTA, FAU, and MOR zeolites was investigated by diffuse-reflectance IR spectroscopy. N₂O is adsorbed on the samples under study in the molecular form and the frequencies of the first overtone of the stretching vibrations ν¹_0–2 and the combination bands of the stretching vibrations with other vibrational modes for N₂O complexes with cationic sites in zeolites (ν³_0–1 + ν¹_0–1, ν¹_0–1 + δ_0–2) are more significantly influenced by the nature of the zeolite. The presence of several IR bands in the region of 2400–2600 cm⁻¹ (the ν¹_0–1 + δ_0–2 transitions) for different zeolite types was explained by the availability of different localization sites for cations in these zeolites. The frequencies in this region also depend on the nature of the cation (its charge and radius). The data can be explained by the specific geometry of the N₂O complex formed, presumably two-point adsorption of N₂O on a cation and a neighboring oxygen atom of the framework. Adsorption of CO or CH₄ on the samples with preliminarily adsorbed N₂O at 20–180 °C does not result in any oxidation of these molecules. NO⁺ and N₂O₃ species formed by disproportionation of NO are capable of oxidizing CO and CH₄ molecules to CO₂, whereas NO_x is reduced simultaneously to N₂ or N₂O. The peculiarities in the behavior of cationic forms of different zeolites with respect to adsorbed nitrogen oxides determined by different density and localization of cations have been established.     

Ce0.6Zr0.35Y0.05O2和Pr0.6Zr0.35Y0.05O2催化剂表面上CO氧化和18O-16O交换反应的研究

测定了在Ce0.6Zr0.4O2,Ce0.6Zr0.35Y0.05O2,Pr0.6Zr0.4O2和Pr0.6Zr0.35Y0.05O2 (分别表示为CZ,CYZ,PZ和PYZ)样品表面上的CO氧化反应和18O-16O 同位素交换反应.结果表明: 在CZ和PZ系列固熔中掺杂Y3 离子可以改善晶格氧的迁移速度;PZ和PZY的晶格氧比CZ 和CZY 的晶格氧具有更高的氧化反应活性.其原因是将Y3 掺杂到Ce0.6Zr0.4O2 或Pr0.6Zr0.4O2晶格中,增加了样品的氧空位浓度,从而提高了晶格氧的迁移性质,而PrOx比CeO2具有更低温度的氧化还原性质,因此PZ和PZY的晶格氧比CZ 和CZY 的晶格氧具有更高的氧化反应活性.     

Vertical proton affinities of CH2O and CH2OH+ in their ground singlet,excited triplet and ionized doublet states

Vertical proton affinities were calculated with closed and open shell direct SCF-MO methods for the ground, excited triplet and ionized doublet states of CH₂O and CH₂OH⁺.The computed gas phase basicity of CH₂O follows the order: CH₂O(¹ A ₁) > CH₂O*(³ A ₁ or ³ A ₂) > CH₂O⁺(² B ₂ or ² B ₁).     

Hydrogen Isotope Exchange Reactions in an Electrical Discharge

Hydrogen isotope exchange reactions occurring in (H₂O, D₂)or (D₂O, H₂) reacting system under a DC electricaldischarge were investigated using spectroscopic methods such asFourier-transform infrared (FTIR) and plasma emission spectroscopy(PES). The progress of the reactions was determined by real-time measurementof the IR absorbance of HDO molecule, a major product of the reaction. Theprogress of the reaction was studied as a function of the temperature, thecurrent density, and the composition of the reactants, while the pressure ofthe system was maintained at approximately 67 mbar. The results revealedthat the discharge method was far more effective in facilating the exchangereaction than was the conventional catalytic method. The (H₂O, D₂)system also generated a significant amount of D₂O besides HDO andHD as the ratio of D₂ to H₂O was increased. Thetransient species of the system, such as H or D atoms, were monitored duringthe discharge using emission spectroscopy. The analysis of the final products by mass spectroscopy confirmed that neither H₂ nor O₂was among the major products of the system in the discharge.     

Oxidation of cyclopentane-1,2-dione: a study with O labeled reagents

The asymmetric oxidation of 3-alkyl-cyclopentane-1,2-diones with the Ti(OⁱPr)₄/tartaric ester/t-BuOOH complex, which gives, in a cascade process, highly enantiomerically enriched γ-lactone acids, was studied by ¹⁸O isotopic labeling in the substrate and in the oxidant. The path of the labeled atoms was followed by ¹³C NMR spectroscopy. It was found that the oxidative ring cleavage of 1,2-dione proceeds via a Baeyer-Villiger-type oxidation mechanism.     

Directed Iridium-Catalyzed Hydrogen Isotope Exchange Reactions of Phenylacetic Acid Esters and Amides

For the first time, a catalytic protocol for a highly selective hydrogen isotope exchange (HIE) of phenylacetic acid esters and amides under very mild reaction conditions is reported. Using a homogeneous iridium catalyst supported by a bidentate phosphine-imidazolin-2-imine P,N ligand, the HIE reaction on a series of phenylacetic acid derivatives proceeds with high yields, high selectivity, and with deuterium incorporation up to 99 %. The method is fully adaptable to the specific requirements of tritium chemistry, and its effectiveness was demonstrated by direct tritium labeling of the fungicide benalaxyl and the drug camylofine. Further insights into the mechanism of the HIE reaction with catalyst 1 have been provided utilizing DFT calculations, NMR studies, and X-ray diffraction analysis.     

CH2＝CHCl与O(3P)反应的理论研究

用量子化学密度泛函理论和QCISD (Quadratic configuration interaction calculation)方法, 对O(³P)与CH₂CHCl的反应进行了理论研究. 在UB3LYP/6-311＋＋G(d,p), UB3LYP/6-31＋＋G(3df, 3pd)计算水平上, 优化了反应物、产物、中间体和过渡态的几何构型, 并在UQCISD(T)/6-311＋＋G(2df,2pd)水平上计算了单点能量. 为了确证过渡态的真实性, 在UB3LYP/6-311＋＋G(3df,3pd)水平上进行了内禀坐标(IRC)计算和频率分析, 并确定了反应机理. 研究结果表明, 反应主要产物为CH₂CHO和Cl.     

Enhanced Kinetic Isotope Effect of the Phosphate-Catalyzed Proton Exchange in N,N'-Dimethylurea

The concerted mechanism of phosphate-catalyzed proton exchange in N,N'-dimethylurea has been studied. Kinetic data were measured using the technigue of NMR line-shape analysis. A significant kinetic isotope effect was observed for the concerted proton transfer in N,N'-dimethylurea and is attributed to the tunnelling effect.     

High Temperature Reactions in the MoO3-Ag2O System

High-temperature reactions were investigated in the MoO₃-Ag₂O system by means of X-ray, DTA and scanning microscopy methods, and a model was proposed according to which first an Ag₂Mo₄O₁₃ phase was formed at the MoO₃ and Ag₂O (or metallic Ag) interface. Subsequently, at the Ag₂Mo₄O₁₃-Ag₂O contact area a layer of Ag₂Mo₂O₇ appeared. If the amount of silver oxide is sufficiently high, a layer of Ag₂MoO₄ is formed between the Ag₂O and Ag₂Mo₂O₇ phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared spectra (700–200 cm−1) and6Li/7Li and H2O/D2O isotope effects for four isotopically substituted lithium formate monohydrates

The infrared spectra, in the 700–200 cm^–1 region, have been reported for⁶LiHCO₂ · H₂O,⁶LiHCO₂ · D₂O,⁷LiHCO₂ · H₂O and⁷LiHCO₂ · D₂O and the observed fundamental bands have been discussed taking into account the⁶Li/⁷Li and H₂O/D₂O isotope wavenumber shifts on the fundamental vibrations.

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Infrarotspektren (700–200 cm^–1) und⁶Li/⁷Li- und H₂O/D₂O-Isotopeneffekte für vier isotopensubstituierte Lithiumformat-monohydrate

Zusammenfassung Die Infrarotspektren in der Region von 700–200 cm^–1 werden für⁶LiHCO₂ · H₂O,⁶LiHCO₂ · D₂O,⁷LiHCO₂ · H₂O und⁷LiHCO₂ · D₂O angegeben und die beobachteten Grundschwingungen zusammen mit den isotopischen Verschiebungen der Wellenzahlen diskutiert.

     

Isotopic Traceability (13C and 18O) of Greek Olive Oil

In recent years, isotopic analysis has been proven a valuable tool for the determination of the origin of various materials. In this article, we studied the ¹⁸O and ¹³C isotopic values of 210 olive oil samples that were originated from different regions in Greece in order to verify how these values are affected by the climate regime. We observed that the δ¹⁸O isotopic values range from 19.2 ‰ to 25.2 ‰ and the δ¹³C values range from −32.7 ‰ to −28.3 ‰. These differences between the olive oils’ isotopic values depended on the regional temperature, the meteoric water, and the distance from the sea. Furthermore, we studied the ¹³C isotopic values of biophenolic extracts, and we observed that they have same capability to differentiate the geographic origin. Finally, we compared the isotopic values of Greek olive oils with samples from Italy, and we concluded that there is a great dependence of oxygen isotopes on the climatic characteristics of the different geographical areas.     

Comparison of Iridium(I) Catalysts in Temperature Mediated Hydrogen Isotope Exchange Reactions

The reactivity and selectivity of iridium(I) catalysed hydrogen isotope exchange (HIE) reactions can be varied by using wide range of reaction temperatures. Herein, we have done a detailed comparison study with common iridium(I) catalysts ( 1 – 6 ) which will help us to understand and optimize the approaches of either high selectivity or maximum deuterium incorporation. We have demonstrated that the temperature window for these studied iridium(I) catalysts is surprisingly very broad. This principle was further proven in some HIE reactions on complex drug molecules.     

Reactivity of Aquadiethylenetriamineplatinum(II) Ion with Disulfide Moiety Cystine: A Kinetic and Mechanistic Approach

Abstract

Substitution reactions of the complex [Pt(dien)H₂O]²⁺ (where dien = diethylentriamine or 1,5-diamino-3-azapentane) with sulfur-containing L-cystine have been studied in a 1.0 × 10^?1 mol dm^?3 aqueous perchlorate medium at various temperatures (298–323 K) and 4.45 ≤ pH ≤ 2.15 using UV-vis spectroscopy. The products obtained have been characterized by their infrared and ¹H NMR datasets at various pH levels and temperatures. From infrared and ¹H NMR data, products have indicated that [Pt(dien)H₂O]²⁺ reacted with L-cystine forming a Pt–S bond at low pH. At high pH, a product complex through the Pt–N bond has been formed. All rate constants have been evaluated from nonlinear double exponential plots. The activation parameters ΔH^# and ΔS^# have been determined using the Eyring equation. The products, S_Ni, and reversible rate constants have been evaluated.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT      

Association of metal cations with alkanes: Na(CH4)+ versus Cu(CH4)+ as molecular models

Summary Ab initio molecular orbital calculations give small stabilization energies for the various Na(CH₄)⁺ adducts (less than 4 kcal mol^–1), but predict a stronger binding for the copper compounds (about 13 kcal mol^–1). The different behaviour of Na⁺ and Cu⁺, already present at the SCF level, is reinforced by electron correlation. This can be attributed to an important contribution of the dispersion energy to the binding energy of the copper ion: about 40% of the total, including basis set superposition corrections.Dedicated to Mrs A. Pullman     

Photoredox-Mediated Hydrogen Isotope Exchange Reactions of Amino-Acids,Peptides, and Peptide-Derived Drugs

Hydrogen isotopically labelled compounds are essential diagnostic tools in drug research and development, as they provide vital information about the biological metabolism of drug candidates and their metabolites. Herein we report a photoredox-initiated hydrogen atom transfer (HAT) protocol which efficiently and selectively introduces deuterium or tritium at C(sp³)−H bonds, utilizing heavy water (D₂O or T₂O) as the hydrogen isotope source, and a guanidine base. This protocol has been successfully applied to the incorporation of deuterium in several amino acids (lysine, glycine and proline) and small peptides. Finally, the method has been applied to tritium, because tritium-labelled peptides are essential for application in biological experiments, such as ligand-binding assays, or absorption, distribution, metabolism, and excretion (ADME) studies.     

H6P2W18O62-18H2O,a Green and Reusable Catalyst for the Three-Component,One-Pot Synthesis of 4,6-Diarylpyrimidin-2(1H)-ones Under Solvent-Free Conditions

Three-component, one-pot synthesis of 4,6-diarylpyrimidin-2(1H)-ones and 9-phenyl-8-oxa-10,12-diaza-tricyclo[7.3.1.0^2,7]trideca-2(7),3,5-trien-11-one by condensing acetophenone derivatives, aldehydes, and urea in the presence of trimethylsilyl chloride using a catalytic amount of H₆P₂W₁₈O₆₂-18H₂O under solvent-free conditions is reported.     

Mechanisms and Kinetics of Reactions of the O（^1D,^3P） ＋ CF3Cl System

In the stratosphere,CF3Cl(CFC13)can either photodecompose or react directly with atomic oxygen to generate ozone-depleting agents such as Cl and ClO in the gas phase[1—3].Since the1970s,attention has been focused on the effects of these compounds on the …