Kinetic studies on the formation ofN-nitroso compounds. IV. Formation of mononitrosopiperazine and general discussion ofN-nitrosation mechanisms in aqueous perchloric solution

The mechanism of formation ofN-nitroso compounds, which are considered as potential chemical carcinogens was studied. The kinetics of nitrosation of piperazine (PIP) in aqueous solution of perchloric acid have been investigated using a differential spectrophotometric technique. Based on our experimental results, the following rate law, in thepH-range 0.85 4.36, is proposed: $$v_0 = \left[ {nitrite} \right]_0 2 \left[ {PIP} \right]_0 /\left( {1 + f/\left[ {H^ + } \right]} \right)^2 \left( {g \left[ {PIP} \right]_0 + h + j\left[ {H^ \div } \right]} \right)$$ where [nitrite]₀ and [PIP]₀ represent initial stoichiometric concentrations. At 298.2K and μ=1.0M,f=(1.17±0.11) 10^?3 M,g=(3.5±0.7) 10^?2 M s,h=2.6×10^?6 M ² s andj=(0.95±0.04)M s. When the acidity is increased ([HClO₄]≥1M), a new kinetic term comes into play: $$v_0 ' = p\left[ {nitrite} \right]_0 \left[ {PIP} \right]_0 $$ At 298.2 K and μ=3.0M,p=(1.9±0.2) 10^?3 M ^?1 s^?1. A general mechanism for the nitrosation of anyN-nitrosable substrate in aqueous perchloric solution in which the only nitrosating agents are N₂O₃ and H₂NO₂ ⁺/NO⁺ is proposed. Also, the various particularities of this mechanism, according to thepK of theN-nitrosable substrate, are discussed.     

Synthesis and electrical conductivity of polymers containing trans-1,2-bis(9-carbazolyl)cyclobutane units

Novel poly-Schiff bases (PSB's) that contain trans-1,2-bis(9-carbazolyl)cyclobutane(DCZB) units were synthesized by the direct polycondensation of trans-1,2-bis(3-formyl-9-carbazolyl)cyclobutane with aromatic diamines in n-amyl alcohol at 160°C. Complexation of these PSB's and of poly(vinyl DCZB) (PVDCZB) with iodine produced cation-radical salts which resulted form the transfer of an electron from DCZB moieties to iodine. All the undoped polymers were insulators having electrical conductivity of the order of 10^?10–10^?12 S cm^?1 depending on the structure of polymers. By doping with iodine, the electrical conductivity increased by several orders of magnitude and reached a value of 10^?3 S cm^?1 in the case of PVDCZB and 10^?5–10^?6 S cm^?1 in the case of PSB's. The electrical conductivity of doped PSB's increased with decreasing diamine length. PVDCZB having the same iodine content per carbazole unit as poly(9-vinyl-carbazole) (PVK) has a greater electrical conductivity than PVK.     

Heteroaryl substituted ansa‐titanocene anti‐cancer drugs derived from fulvenes and titanium dichloride

Starting from 2‐furylfulvene (1a) , 2‐thiophenylfulvene (1b) , and 1‐methyl‐2‐pyrrolylfulvene (1c), [1,2‐di(cyclopentadienyl)‐1,2‐di‐(2‐furyl)ethanediyl] titanium dichloride (2a) , [1,2‐di(cyclopentadienyl)‐1,2‐di‐(2‐thiophenyl)ethanediyl] titanium dichloride (2b) , and [1,2‐di(cyclopentadienyl)‐1,2‐bis‐(1‐methyl‐2‐pyrrolyl)ethanediyl] titanium dichloride (2c) were synthesized. When titanocenes (2a–c) were tested against pig kidney carcinoma cells (LLC‐PK), inhibitory concentrations (50%) of 4.5 × 10^?4 M , 2.9 × 10^?4 M and 2.0 × 10^?4 M respectively were observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Inclusion complexation of naproxen with cyclosophoraoses and succinylated cyclosophoraoses in different pH environments

Cyclosophoraoses [cyclic β-(1,2)-glucan, Cys] isolated from Rhizobium leguminosarum biovar trifolii TA-1 have unique structures and high solubility, which make it a potent solubilizer for host–guest inclusion complexation. Succinylated cyclosophorasoses (S-Cys) were also synthesized by chemically modifying isolated cyclosophoraoses. In ultraviolet-visible studies using naproxen (NAP), Cys was shown to form the most stable complexes with NAP (K _1:1?=?2457.9?M^?1), which was followed by the negatively charged S-Cys (K _1:1?=?357.1?M^?1) at pH 3.4. A further strong reduction in the complex stability constant was observed at pH 7.5. When the reduction in the stability constant was compared with other cyclic oligosaccharides (Cys; 119.2?M^?1, CD; 14.48?M^?1 and HP-CD; 6.75?M^?1), S-Cys (K _1:1?=?5.6?M^?1) was shown to have the highest decrease in stability constant. These results suggest that the S-Cys could regulate the efficiency of inclusion complexation at external pH values. NMR studies of complex formation between NAP and Cys also showed a different correlation pattern at pH 3.4 and 7.5. This difference in correlation demonstrates that the inclusion complexes between Cys and NAP formed as a result of the differential charge distribution of the carboxyl groups of NAP. The pH-dependent inclusion behavior of Cys for NAP was also evaluated using molecular docking simulations.     

Solvated positron chemistry. II. The reaction of hydrated positrons with Cl−, Br− and I− ions

The reaction of the hydrated positron, e_aq⁺ with Cl^?, Br^?, and I^? ions in aqueous solutions was studied by means of positron The measured angular correlation curves for [Cl^?, e⁺], [Br^?, e⁺, and [I^?, e⁺] bound states were in good agreement with th Because of this agreement and the fact that the calculated positron wavefunctions penetrate far outside the X^? ions in the [X^?, e⁺] sta propose that a bubble is formed around the [X^?, e⁺] state, similar to the Ps bubble found in nearly all liquids. F^?ions did not react w Preliminary results showed that CN^? ions react with e_aq⁺ while OH^?ions are non reactive. The rate constants were 3.9 × 10¹⁰ M^?1 s^?1, 4.4 × 10¹⁰ M^?1 s^?1, and 6.3 × 10¹⁰ M^?1 s^?1 for Cl^?, Br^?, and I^?, respectively, at low (? 0.03 M) X^? concentrations. A 25% decrease in the rate constant caused by the addition of 1 M ethanol to the I^? solutions was i The influence of halide ions on the positronium (Ps) yields in pure water was studied by use of lifetime measurements. The Cl^?, Br^?, and I^? ions reduced the Ps yields at low concentrations (? 0.03 M), while F^? ions only reduced the Ps-yield However, the Ps yields saturated (e.g. at ≈ 21% ortho-Ps yield in the Cl^? case) at higher concentrations. This saturation and the high-concentration effects-in the angular correlation results were interpreted as caused by rather complicated spur effects, wh It is proposed that spur electrons may pick off the positron from the [X^?, e⁺ states with an efficiency which depends on the structure of the     

Mass spectra of new heterocycles: XII. Main fragmentation pathways of the molecular ions of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines under electron impact and chemical ionization

Fragmentation patterns of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines under electron impact (70 eV) and chemical ionization (methane as reactant gas) were studied for the first time. The electron impact mass spectra of all the examined compounds contained a strong peak of molecular ion which decomposed along four pathways. Two pathways involved cleavage of the C-S bonds with elimination of methyl (major) and MeS radicals (minor), and the two others, decomposition of the pyrrole ring. The chemical ionization mass spectra displayed strong molecular, [M + H]⁺, and odd-electron [M + H ? SMe]⁺ ion peaks. N,N-Dimethyl-5-methylsulfanyl-4-phenyl-1-vinyl-1H-pyrrol-2-amine under chemical ionization with methane as reactant gas characteristically decomposed with formation of [M ? C₄H₉N]⁺ as the only fragment ion.     

The Physical Chemistry of Membranes : M.E. Starzak. Academic Press,Orlando, 1984, x + 334 pp., US$47.00. Equations of Membrane Biophys. N. Lakshminarayanaiah,Academic Press,Orlando, 1984, x + 426 pp., £53.50

Changes in the adsorption profiles of 1,4-naphthohydroquinone (NHQ) on smooth polycrystalline platinum electrodes in aqueous 1 M HClO₄ brought about by varying levels of surface-active organic impurities [typified by hydroquinone (HQ) and benzene] have been studied by thin-layer electrochemical techniques, 10^?5M HQ is sufficient to alter the adsorption profile of NHQ; above 10^?4M HQ, the packing density transitions prominent from pure NHQ solutions were completely suppressed. Similar results were obtained when benzene was used as the contaminant. Packing density measurements indicated that the subject surface-active impurities inhibited formation of flat-, but not edge-, adsorbed NHQ; this is in agreement with data from a previous study [M.P. Soriaga, J.H. White, D. Song and A.T. Hubbard, J. Electroanal. Chem., 171 (1984) 359] which showed that low-levels of iodide, a surface-active anion, enforced formation of edge-adsorbed NHQ even at (low) concentrations where flat-adsrobed species would have formed from pure NHQ solutions. The presence of surface-active impurities may help account for the profound differences in adsorption measurements reported in the literature for various aromatic compounds.     

Mechanism of electrohydrodimerization of acrylonitrile on mercury from aqueous solutions

The electrohydrodimerization (EHD) of acrylonitrile (AN) on mercury from aqueous solutions was examined by a polarographic technique with positive feedback for IR compensation as well as by differential-capacity measurements, with the aim of determining optimal experimental conditions under which the formation of the hydrodimer adiponitrile (ADN) is decidedly favoured over that of the saturated monomer propionitrile (PN). Several tetraalkylammonium cations at low concentrations (≈10^?3M) and several supporting electrolytes were employed for this purpose. The best conditions for EHD were attained in aqueous solutions of 1.3 to 1.5 M Na⁺ or Li⁺ citrate containing 10^?3M dodecylethyldimethylammonium (DEDMA) bromide. Under these conditions a gradual increase in the AN bulk concentration from 10^?2M to 0.2 M causes a progressive splitting of the single two-electron wave due to PN formation into two consecutive one-electron waves, the first of which is due to ADN formation. Differential-capacity measurements indicate that such a progressive passage from the formation of the saturated monomer to that of the hydrodimer is accompanied by a gradual coadsorption of AN and DEDMA on the electrode surface, which demonstrates that the coupling reaction yielding ADN takes place in the adsorbed state.Mechanisms for PN formation at AN concentrations <10^?2M and for ADN formation at the higher AN concentrations at which EHD takes place have been proposed.     

Modular construction of pyrido[24]crown-8-based templates in the self-assembly of cross-linked [n]catenanes

Starting from the versatile 4-bromopyrido[24]crown-8 building block, novel ditopic and tritopic receptors have been synthesized and shown to be appropriate hosts for bis(4-formylbenzyl)ammonium hexafluorophosphate. Association constants (per binding site) for the corresponding [3]- and [4]pseudorotaxanes, assembled from these components, were determined to be 2753  M^?1 and 723  M^?1, respectively. Mechanical bond formation was attempted utilizing dynamic imine bond formation between the formyl groups of the bound dibenzylammonium threads and p-phenylenediamine.     

Synthesis of 2-aryl-3H-naphtho[1,2-d]imidazoles containing an adamantane fragment

N ²-[1-(1-Adamantyl)alkyl]naphthalene-1,2-diamines reacted with benzoyl chlorides in chloroform in the presence of triethylamine to give N-{2-[1-(1-adamantyl)alkylamino]naphthalen-1-yl}benzamides which underwent intramolecular cyclization to 2-aryl-3H-naphtho[1,2-d]imidazoles on heating in toluene in the presence of p-toluenesulfonic acid. 3-[(1-Adamantyl)methyl]-2-(3-nitrophenyl)-3H-naphtho[1,2-d]imidazole was synthesized from N ²-[(1-adamantyl)methyl]naphthalene-1,2-diamine and 3-nitrobenzaldehyde.     

Synthesis of 2,5-diaryl-1,3-oxazoles containing a carbamate group

Acetophenones containing a methoxycarbonylamino group in position 2, 3, or 4 of the aromatic ring reacted with phenylglycine in the presence of 2 equiv of iodine and 0.5 equiv of sulfanilic acid in DMSO at 100°C for 6 h to give methyl [2(3,4)-(2-phenyl-1,3-oxazol-5-yl)phenyl]carbamates. The reaction was presumed to involve intermediate formation of methyl [(iodoacetyl)phenyl]carbamate. This was confirmed by the isolation of methyl [2-(iodoacetyl)phenyl]carbamate in the reaction of methyl (2-acetylphenyl)carbamate with iodine in glacial acetic acid and its subsequent transformation to methyl [2-(2-phenyl-1,3-oxazol-5-yl)-phenyl]carbamate.     

MECHANISM OF THE PHOTOSENSITIZED REDOX REACTIONS OF ACRIDINE ORANGE IN AQUEOUS SOLUTIONS-A SYSTEM OF INTEREST IN THE PHOTOCHEMICAL STORAGE OF SOLAR ENERGY†

-We have carried out a very detailed study, using fluorescence and optical flash photolysis techniques, of the photoreduction of methyl viologen (MV²⁺) by the electron donor ethylene diamine tetraacetic acid (EDTA) in aqueous solution sensitized by the dye acridine orange (AOH⁺). A complete mechanism has been proposed which accounts for virtually all of the known observations on this reaction. This reaction is novel in that both the triplet and the singlet state of AOH⁺ appear to be active photochemically. We have shown that mechanisms previously proposed for this reaction are probably incorrect due to an artifact. At pH 7 the fluorescence quantum yield φ_s of AOH⁺ is 0.26 ± 0.02 and the fluorescence lifetime is 1.8 ± 0.2 ns. φ_s is pH dependent and reaches a maximum of 0.56 at pH 4. The fluorescence of AOH⁺ is quenched by MV²⁺ at concentrations above 1 mM and the quenching obeys Stern-Volmer kinetics with a quenching rate constant of (1.0 ± 0.1) × 10¹⁰M^?1 s^?1. The quenching of the AOH⁺ excited singlet state by MV²⁺ almost certainly returns the AOH⁺ to its ground state with no photochemistry occurring. EDTA also quenches the fluorescence of AOH· with Stern-Volmer kinetics but with a smaller rate constant (6.4 ± 0.5) × 10⁸M^?1s^?1 at pH 7. In this case the quenching is reactive resulting in the formation of semireduced AOH. In the presence of MV²⁺, flash irradiation of AOH⁺ does result in the reversible formation of the semireduced MV? which absorbs at 603 nm. We attribute this to a photochemical reaction of the triplet state of AOH⁺ with MV²⁺. The initial quantum yield for formation of MV? (φ_MV:)₀ was found to be constant at 0.10 ± 0.05 for [MV²⁺] from 5 × 10^?5 to 1.0 × 10^?3 with [AOH⁺] = 8 × 10^?6M. Previous workers had found that (φ_MV:)₀ appears to decrease with decreasing [AOH⁺]; however, on careful investigation, we found this was most probably due to quenching of the triplet state of AOH⁺ by trace amounts of oxygen. When EDTA is added to a mixture of AOH ⁺ and MV²⁺ at pH 7, the photochemical formation of MV? becomes irreversible as the [EDTA] is increased. The quantum yield for the irreversible formation of MV? exceeds 0.10 becoming as large as 0.16 for [EDTA] = 0.014M. This fact requires that an alternative photochemical process must be operative and we present evidence that this is a reaction of EDTA with the excited singlet state of AOH⁺ to produce the semi-reduced AOH- which then reacts with MV²⁺ to produce MV?. The full kinetic scheme was tested by computer simulation and found to be totally consistent. This also enabled the processing of a full set of rate constants. When colloidal PtO₂ was added to the optimal mixture [EDTA] = 3.4 × 10^?2M; [MV²⁺] = 5 × 10^?4M; [AOH⁺] = 4 × 10^?5M; pH6 H₂ gas was produced at a rate of 0.2μmol H₂h^?1. Thus, acridine orange should serve as an effective sensitizer in reactions designed to use solar energy to photolyze water.     

The formation of [CH5O]+ and ions from the molecular ions of isobutyl alcohol

On the basis of field ionization kinetic and deuterium labelling experiments, it is shown that the molecular ions of isobutyl alcohol generate [CH₅O]⁺ ions at 10^?11 s via a 1,4-shift of a hydrogen atom from one of the methyl groups to the oxygen atom, followed by a 1,2-elimination of protonated methanol with a hydrogen atom of the other methyl group. At times > 10^?11 s two distinct interchange processes between hydrogen atoms appear to compete with this reaction, as shown from field ionization kinetic experiments and metastable decompositions. Ion cyclotron resonance experiments on the long-lived [CH₅O]⁺ ions further demonstrate that they are protonated methanol ions. Arguments are put forward that the ions, generated by a specific 1,3-elimination of a molecule of water from metastable decomposing molecular ions, have an isobutene structure.     

Spectrophotometric investigation of monobromo and dibromo complexes of copper(II) in methanolic medium

Complex formation between copper(II) and bromide in anhydrous methanol was investigated spectrophotometrically. At a constant copper(II) concentration of 3.0 x 10^?4M, Cu²⁺ and CuBr⁺ are at equilibrium for [Br^?] < 1.0 x 10^?3M while CuBr⁺ and CuBr₂ exist at equilibrium in the range of [Br^?] 2.0 x 10^?3 ?40 x 10^?3M. An isosbestic point at 235 nm indicated the equilibrium of Cu²⁺ and CuBr⁺ while a second isosbestic point at 290 nm showed the equilibrium of CuBr⁺ and CuBr₂. Stability constants for the formation of CuBr⁺ and CuBr₂ (K₁, and K₂, respectively) were determined as a function of ionic strength in the range 0.01–0.10. Log K₁ and log K₂ values at zero ionic strength were obtained by extrapolation of the plot of log K vs ionic strength, the values being 3.97 ± 0.01 and 2.31 ± 0.01.     

Kinetics and mechanism of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) by N-bromosuccinimide in aqueous acidic medium

The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H₂O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm^?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H₂O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed.     

Analytical applications of mixed-ligand complexes: II. Determination of hydrogen peroxide in the presence of perioxide derivatives

The mixed ligand complex TiXOH₂O₂ was found suitable for the determination of small amounts of hydrogen peroxide in the presence of peroxy acids of sulfur. The pH optimum for the determination depends on the concentrations of the reagents [titanium (IV) and xylenol orange]: for 2 × 10^?4M titanium (IV) and XO the optimum pH is 1.25. ?⁵²⁰ = 13,200 M^?1 cm^?1. The method is suitable for determination of 4–40 μM H₂O₂. Mention is made of the possible causes of the contradictions to be found in the literature concerning the ternary complex.     

Studies in the Imidazole Series. 100. Synthesis of Derivatives of Imidazo[1,2-a]pyrimidine from 2-Aminopyrimidines, Methyl Aryl Ketones, and Halogens

We have synthesized imidazo[1,2-a]pyrimidine derivatives by reaction of 2-aminopyrimidines with methyl aryl ketones and halogens (bromine, iodine). Using bromine leads to formation of 6-bromo- and 3,6-dibromo-substituted 2-arylimidazo[1,2-a]pyrimidines.     

Pyrimidotetrathiafulvalenes. 3.* synthesis and properties of cation-radical salts,cation-radical betaines,and complexes of dimethyl[2,4-dioxo(1H,3H)pyrimido]tetrathiafulvalene and its N-alkyl substituted derivatives with iodine

The reaction of dimethyl[2,4-dioxo(1H,3H) pynmido]tetrathiafulvalene and its N-alkyl derivatives with iodine leads to the formation of complexes with various numbers of iodine atoms. Depending on the conditions, the betaine of the cation-radical of dimethyl[2, 4-dioxo(1 H, 3H)pyrimidojtetrathiafulvalene or a complex of the latter with dimethy1[2,4-dioxo(1H,3H)pyrimidoltetrathiafulvalene is formed by the oxidation of the pyrimidotetrathiafulvalene. The cation-radical perchlorates are formed on carrying out the oxidation of dimethyl[2,4-dioxo(1H,3H)pyrimidojtetrathiafulvalene and its N-methyl derivatives in the presence of perchloric acid. The preparation of the cation-radical salts is usually linked with the reaction of the cation-radical betaine with acids.For part 2 see [1].     

Bimolecular self-reactions of ketyl radicals of acetophenone and diphenylaminyl radicals

The rate constants of self-reactions of ketyl radicals of acetophenone in n-heptane [2k = (3.2 ± 0.5) × 10⁹ M^?1 s^?1] and diphenylaminyl radicals in toluene [2k = (3.3 ± 0.5) × 10⁷ M^?1 s^?1] have been determined at 298 K using the flash photolysis technique. The rate constant of ketyl radicals is equal to the calculated diffusion constant and, therefore, this reaction is diffusion-controlled. The aminyl radical recombination rate is independent of the viscosity of the toluene/vaseline oil binary mixture (0.55 ? η ? 12 cP) and this reaction is activation-controlled. Reactivity anisotropy averaging due to the cage effect has been considered for ketyl and some other radicals. On the basis of the analysis it has been proposed that ketyl recombination involves formation of not only pinacol, but also iso-pinacols.