bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal hydride reductions of unsymmetrical cyclic anhydrides. The importance of the antiperiplanar effect on the regioselectivity of these reactions
Authors: Kayser Margaret M. , Wipff Georges
Published: May 2006

A quantum mechanical study by the SCF abinitio method of the interaction of H− with methylsuccinic and 2,2-dimethylsuccinic anhydrides (naked and in the presence of a cation) suggests that nonperpendicular rearside attack cannot be the factor responsible for the regioselectivity of hydride transfer to the more sterically hindered carbonyl group. In this model, the nucleophilic attack at the less hindered carbonyl group is calculated to be of lower energy (with or without cation). Deformation of the planar succinic anhydride ring to the quasi-chair conformation is energetically favoured as it allows the nucleophile to attack both carbonyl functions antiperiplanar to a quasi axial C—H or C—C bond. The attack antiperiplanar to the C—CH3 bond is lower in energy than the attack antiperiplanar to the C—H bond suggesting that the reduction will occur at the sterically more hindered carbonyl group which is in agreement with the experimental findings.
Thermal degradation of EDTA chelates in aqueous solution
Authors: Motekaitis Ramunas J. , Cox III X. B. , Taylor Patrick , Martell Arthur E. , Miles Brad , Tvedt Jr Tory J.
Published: May 2006

The thermal degradation of Ca(II), Mg(II), Zn(II), Fe(II), and Ni(II) chelates of EDTA was investigated in alkaline aqueous solution at elevated temperatures (230–310 °C). The kinetics of decomposition were followed by nmr, titrimetry, and spectrophotometry. Reaction products were identified through nmr and by gas chromatography. The relative order of degradation rates, as measured by the loss of EDTA, was found to be Mg(II) > Ca(II) > Zn(II) > Fe(II) > Ni(II). The main degradation products formed in the lower temperature range (~250 °C) are iminodiacetic acid, hydroxyethyliminodiacetic acid, and ethylene glycol. Higher temperature products are primarily dimethylamine and carbon dioxide. The rates of degradation of Ca(II), Mg(II), and Zn(II) EDTA chelates are considerably enhanced when either phosphate is present or a glass-lined autoclave is employed.
Pyridazino[3,4,5-de]phthalazines. II. Synthesis of nitrogen-substituted derivatives
Authors: Francis John E. , Doebel Karl J. , Schutte Paula M. , Bachmann Ernst F. , Detlefsen Robert E.
Published: May 2006

The synthesis of a wide variety of 9-substituted-3-oxo-3H-2,9-dihydropyridazino[3,4,5-de]phthalazines (11) was achieved by treatment of 3-substituted-3,4-dihydro-4-oxophthalazine-5-carboxylic esters (10) with hydrazine hydrate. These esters were prepared from 3-hydroxyphthalide-7-carboxylic acid (7) by two different routes. Under basic conditions, alkylation of 3-oxo-3H-2,9-dihydropyridazino[3,4,5-de]phthalazine (1) gave 9-substituted products. These undergo further alkylation at the 2-position. Some of them were converted to 3-chloro, 3-thiono, and 3-hydrazino compounds by standard methods. Dehalogenation of selected 3-chloro compounds or desulphurization of 3-thiono derivatives gave 1-substituted-1H-pyridazino[3,4,5-de]phthalazines (22), some of which were also prepared by direct alkylation of the parent heterocycle 2 under basic conditions. However, treatment of 2 or its 1-methyl homologue with methyl iodide resulted in products in which nitrogen attached to carbon had been attacked rather than the 1- or 9-position. Treatment of the acid chloride of 3,4-dihydro-4-oxophthalazine-5-carboxylic acid with methyl hydrazine led to 2-methyl-3-oxo-3H-2,9-dihydropyridazino[3,4,5-de]phfhalazine (21a) which was purified by cyanoethylation at the 9-position, recrystallization, and hydrazinolysis of the cyanoethyl group. Biological testing revealed that many of the compounds lowered blood pressure in animal models but none had a sufficient therapeutic ratio of activity vs. side effects to warrant clinical trial.
The adsorption of tri-N-butylphosphate at the benzene–water interface
Authors: Sagert Norman H. , Lee Woon , Quinn Michael J.
Published: May 2006

Adsorption of tri-n-butylphosphate (TBP) at the benzene–water interface was studied as a function of the TBP mole fraction in benzene up to 0.018 and at temperatures from 9 to 29 °C. The extent of adsorption was calculated from interfacial tension data obtained by the drop-volume technique. Standard free energies of adsorption from benzene ranged from −20.9 kJ/mol at 9 °C to −22.5 kJ/mol at 29 °C, giving a standard enthalpy of adsorption of +2.5 kJ/mol. Thus the strong adsorption occurs because of entropy changes. Distribution coefficients for the partition of TBP between benzene and water were measured by gas chromatography, and standard free energies of adsorption from water were derived. They ranged from −44.8 kJ/mol at 9 °C to −51.1 kJ/mol at 29 °C, with standard enthalpies of adsorption ranging from 74 to 15 kJ/mol over the same temperature range.Results at higher mole fractions were fitted to various equations of state, after using vapor pressure osmometry (at 37 °C) to determine that activity corrections were small. The Schofield–Rideal equation described the results adequately, with A0 close to 1.0 nm2 and/close to 1.0 at lower temperatures. These values imply that lateral repulsion between TBP molecules in the adsorbed layer is minimal.
Molecular orbital calculations of the ionization potentials and stabilization energies of aminoalkyl radicals
Authors: Goddard John D.
Published: May 2006

A series of aminoalkyl radicals, H2NCH2, H(CH3)NCH2, (CH3)2NCH2, H2NC(CH3)H, H2NC(CH3)2, and the corresponding amines have been examined by abinitio computations. The first vertical ionization potentials of the radicals calculated by the direct SCF method were very low: H2NCH2 (6.3 eV), H(CH3)NCH2 (6.0 eV), and (CH3)2NCH2 (5.8 eV) and decreased with methyl substitution at nitrogen. The first ionization potentials of H2NC(CH3)H and H2NC(CH3)2 were predicted to be 5.9 and 5.6 eV respectively. Radical stabilization energies were calculated from SCF results in several basis sets and with several choices of optimized geometries for R2NCR2 + CH4 → R2NCR2H + CH3. The aminomethyl radical, H2NCH2, was calculated to be 8 to 10 kcal/mol stabilized relative to methyl. The present calculations predict that methyl substitution at N has a small destabilizing effect onH2NCH2 which contrasts with recent experiments. The effect of methyl substitution and details of the "three-electron" bond in aminoalkyl radicals are examined qualitatively by orbital interaction diagrams.
Reaction of β-halo α, β-unsaturated ketones with cuprate reagents. Efficient syntheses of β, β-dialkyl ketones and β-alkyl α,β-unsaturated ketones. A synthesis of (Z)-jasmone
Authors: Piers Edward , Cheng Kin Fai , Nagakura Isao
Published: May 2006

Treatment of the 3-halo-2-cyclohexen-1-ones 11–15 and 17 with an excess of lithium dimethylcuprate provided good to excellent yields of the corresponding 3,3-dimethylcyclohexanones 21–24. Similar reactions involving the β-bromo cyclopentenones 19 and 20 stopped at the monoaddition stage, producing the cyclopentenones 40 and 43. Reaction of the β-bromo cyclohexenones 12 and 15 with 1.1 equiv. of lithium dimethylcuprate did not effect clean conversion of these substrates into the corresponding 3-methyl-2-cyclohexen-1-ones. When a series of β-bromo enones 12, 14–19 were allowed to react with the lithium (phenylthio)(alkyl)cuprates 44–47, the corresponding β-alkyl enones were, in general, produced cleanly and efficiently. However, reaction of 3-bromo-2-methyl-2-cyclopenten-1-one (19) with the cuprate reagent 44 gave mainly the β-phenylthio enone 49. This undesired result could be avoided by employing, in the place of 19, the β-iodo cyclopentenone 50, which reacted smoothly with 44 to give a high yield of 2,3-dimefhyl-2-cyclopenten-1-one (40). Reaction of 3-bromo-2-cyclohexen-1-one (14) with 3 equiv. of the mixed vinylcuprate reagent 48 gave 3-(3-butenyl)-2-cyclohexen-1-one (32). Alkylation of 1,3-cyclopentanedione with (Z)-1-chloro-2-pentene afforded compound 51, which was converted into the β-bromo enone 52. Treatment of the latter substance with lithium dimethylcuprate provided (Z)-jasmone (53).
Dihydropyridines in synthesis and biosynthesis. IV. Dehydrosecodine, in vitro precursor of indole alkaloids
Authors: Kutney James P. , Karton Yishai , Kawamura Noriaki , Worth Brian R.
Published: May 2006

The synthesis of the two isomeric dehydrosecodines is described. Stabilization of these systems is achieved by chromium carbonyl complexation of the dihydropyridine unit in these molecules. Reaction of the complexes with pyridine, or preferably ethylenediamine, allows insitu generation of the dehydrosecodines. A study of their chemistry and conversion to alkaloid systems is presented.
Trichlorosilyl and dichloromethylsilyl derivatives of ruthenium carbonyl
Authors: Pomeroy R. K. , Hu Xiang
Published: May 2006

The preparation of a number of derivatives of the type Ru(CO)3(L)(SiRCl2)(X) and [Ru(CO)3(SiRCl2)(X)]2 (L = CO, phosphorus donor ligand; R = CH3, Cl; X = H, Cl, Br, I; not all possibilities) is described. The syntheses of M(CO)4(SiMeCl2)2 (M = Ru, Os) and mer-M(CO)3(PPh3)(SiMeCl2)2 are also reported. The pattern of substitution in the tetracarbonyl molecules is consistent with the SiRCl2 ligand as having a large trans-effect in these compounds. From a qualitative study of the rates of substitution, it appears the trans-effect of the SiMeCl2 ligand is at least comparable to that of SiCl3.
Measurement of self-association and ion-pair dissociation constants by solvent extraction using a membrane phase separator
Authors: Carmichael Murray , Cantwell Frederick F.
Published: May 2006

The "filter-probe" membrane phase separator is used with a gravimetric buret to obtain the following constants at 25 °C by measuring solvent-extraction isotherms: dimerization constant of benzoic acid in chloroform (log K2,HBz = 2.12 ± 0.01); "self-ion-pair extraction" constant of Naloxone into chloroform [Formula: see text]; and ion-pair dissociation constant of tetraethylammonium picrate in methylene chloride (log Kdiss = −4.52 ± 0.09).
Interprétation par la méthode CNDO/S des spectres ultra-violets d'hétérocycles azotes et soufres comportant une double liaison
Authors: Bouin-Roubaud Danielle , Kister Jacky , Avignon Thierry , Bouscasse Luc
Published: May 2006

The use of CNDO/S calculations for the determination of ultra-violet spectra allowed the attribution of the experimental π → π* transitions for the systems 1, 2, 3, and 4.[Formula: see text]
Hydrolysis of the thorium(IV) ion in sodium nitrate medium
Authors: Milić Nikola B. , Šuranji Terezija M.
Published: May 2006

The hydrolysis of the thorium(IV) ion in sodium nitrate medium was studied by the emf method at 25 °C. The data show that the extent of the thorium hydrolysis depends both on the concentration of thorium and the sodium nitrate medium. Thus, at a definite pH, the extent of the hydrolysis of thorium increases with increasing its concentration, but decreases with increasing concentration and the hydration energy of the medium ions. The stability constants of complexes Th2(OH)26+, Th3(OH)57+, and Th6(OH)159+ also slightly differ going from one concentration of sodium nitrate to another. The observed effect of the medium is in agreement with the linear free energy relationship proposed for the metal ion hydrolysis.
New cyclohexane- and cyclohexene-1,3-diones from tetraacetylethylene
Authors: Celli Angela M. , Lampariello Lucia R. , Chimichi Stefano , Nesi Rodolfo , Scotton Mirella
Published: May 2006

The new substituted cyclohexane- and cyclohexene-1,3-diones 3–6 and 9, 10, respectively, have been synthesized from tetraacetylethylene 1, through a ring expansion of the cyclopentenone 2. The structures of these products, as well as some features of their tautomeric behavior, were established on the basis of chemical properties and spectroscopic data.
Confacial bioctahedral complexes of tungsten(IV) containing tungsten-to-tungsten bonds: X-ray crystal structures of di-μ-ethanethiolato-μ-sulfidobis[dichloro(dimethyl sulfide)-tungsten(IV) (W—W)] and tetraphenylphosphonium di-μ-ethane thiolato-μ-sulfido- bis[trichlorotungstate(IV) (W—W)]
Authors: Boorman P. Michael , Codding Penelope W. , Kerr K. Ann , Moynihan Kelly J. , Patel Vikram D.
Published: May 2006

The complex (Me2S)Cl2W(μ-S)(μ-SEt)2WCl2(Me2S), 1, has been prepared by reaction of [WCl4(Me2S)2] with 1 mol-equiv. of SiMe3(SEt) in CH2Cl2 solution. A single-crystal X-ray diffraction study shows that the molecule has a confacial bioctahedral structure with a W—W bond length of 2.526(2) Å. The structure was solved by heavy atom methods and refined to R = 0.061 and Rw = 0.061 for 2715 reflections with I ≥ 3σ(1). Crystals of 1 are triclinic, space group [Formula: see text], with a = 9.661(1), b = 10.695(1), c = 13.253(4) Å, α = 61.84(2), β = 66.98(2), and γ = 66.44(1)°, Z = 2.Reaction of 1with 2 mol-equiv. of Ph4PCl in CH2Cl2 solution yields (Ph4P)2[Cl3W(μ-S)(μ-SEt)2WCl3], 2. Crystals of 2 are triclinic, space group [Formula: see text], with a = 10.153(1), b = 13.043(1), c = 21.876(3) Å, α = 95.16(1), β = 96.48(2), and γ = 108.90(1)°, Z = 2. The structure was refined to R = 0.041, Rw = 0.048 for 2384 reflections with I ≥ 3σ(1); 2 also has a confacial bioctahedral structure with a W—W bond length of 2.522(1) Å.
Studies of confacial bioctahedral tungsten complexes containing metal-to-metal bonds: synthesis, reactions, and nuclear magnetic resonance studies of W2Cl4(μ-SR)2(μ-S)L2 (R = alkyl; L = monodentate ligand)
Authors: Patel Vlkram D. , Boorman P. Michael
Published: May 2006

A series of new binuclear tungsten(IV) complexes, W2Cl4(μ-SR)2(μ-S)L2 (R = Me, Et, iBu, CH2Ph; L = Me2S or THT), is readily synthesized from the metathetical reaction of WCl4L2 with 1 mol-equiv. of alkylthiotrimethylsilane (Me3Si(SR)). These complexes react with stronger nucleophiles (Ph3P, MeCN, C5H5N, Cl−) under ambient conditions to yield simple disubstituted products. Reaction of W2Cl4(μ-SEt)2(μ-S)(SMe2)2 with PhCH2X (X = Cl, Br) yields [Me2SCH2Ph]2[W2Cl4(μ-SEt)2(μ-S)X2], whilst with stronger alkylating agents, MeSO3F or Et3OBF4, intractable residues result.The series of homologous complexes has been studied by 1H and 13C nmr spectroscopy. When R = Me, two stable configurational isomers are present in solution, whilst only a single isomer exists for more bulky R groups. Trends in the 1H nmr chemical shifts of the methylene and methyl protons of the SEt groups in the complexes W2Cl4(μ-SEt)2(μ-S)L2 allow absolute assignment of the resonances to two magnetically inequivalent thiolato groups.
Nouveaux hétéropolyanions mixtes contenant le plomb(II)
Authors: Schouten Anna , Cros Bernard
Published: May 2006

New mixed heteropolyanions with formulae XPb(II)W11O39m− (X = Si, Ge, B, Ga), XPb(II)W11O407− (X = As(V), P(V)) and X2′Pb(II)W17O618− (X′ = As(V), P(V)) were prepared. The results of conductimetric, polarographic, spectrophotometric, and crystallographic studies are reported. The peculiar structure of these mixed heteropolyanions due to the large radius of Pb(II) is discussed. The formation of new types of polyanions with the symbolic formula Pb(XW11)2 has been noted with X = Si and Ge.
Utilisation des pièges à radicaux en vue de mettre en évidence des intermédiaires dans la photolyse de complexes contenant une liaison CoIII—C
Authors: Maillard Philippe , Giannotti Charles
Published: May 2006

Using the spin trapping technique with 5,5′-dimethyl 1-pyrroline N-oxide (DMPO), phenyl-N-tert-butyl nitrone (PBN), nitrosodurene (ND), and α-4-pyridyl 1-oxide N-tert-butl nitrone (4-POBN), or their mixtures, we have been able to detect two types of radicals, one is a hydrogen atom spin adduct and the other is the corresponding alkyl of the alkylcobaloximes, salens or cobalamines.By the use of selective deuteration and the preparation of the benzyl bis(diphenylglyoximato)-pyridinato cobaloxime, we have shown that the spin trapped hydrogen atom comes from the chelated hydrogen of the dimethylglyoximato anion of the equatorial ligand of CoIII complexes. Using a mixture of two spin traps gives rise to an esr spectrum containing, at the same time, the hydrogen atom and alkyl spin adducts.To explain such an efficient spin trapping reaction while the homolysis is in competition with a β-elimination process, it should be postulated that the photolysis of such compounds proceeds through a solvent cage environment. This hypothesis explains the strong influence of solvents on the nature of the free radicals trapped. Also the spin trap diffuses in the solvent cage, and is able to trap in a very efficient manner any free radicals occurring in the solvent cage. The excited CoIII complexes and the spin trap in the solvent cage behave like an exciplex, which could explain the spin trapping of the hydrogen atom.
Nitroxides as reaction intermediates
Authors: Aurich Hans Gunter
Published: May 2006

Vinyl nitroxides 4 are obtained by oxidation of the nitrones 3, as was shown by esr studies and by identification of the reaction products. The formation of 4d–f is even observed in oxidation of the hydroxylamines 1d–f, nitroxides 2d–f and nitrones 3d–f being the intermediates. The high reactivity of the vinyl nitroxides 4 at their β-position is illustrated by the reactions of 4a with various compounds affording the nitroxides 7–10, respectively. Compound 4c reacts with its precursor 3c to give 11, 12, or 13, depending on the reaction conditions. From oxidation of 3a, c, and e the dimerization products 5a, c, and e, respectively, could be isolated. Whereas further oxidation of 5d yields 6d, the acyl nitroxides 14a and c are formed in the oxidation of 5a and c, respectively.The formation of quinone 23 in the reaction of 2-methyl-2-nitrosopropane with potassium tert-butoxide in isopropyl alcohol in the presence of oxygen is discussed. The nitroxide 20 has been detected in the reaction mixture. Imines 24 react with nitrosobenzene giving nitroxides 26. These are further oxidized by nitrosobenzene to afford nitrones 27. Whereas 27a and b could be isolated, 27c and d undergo further reaction yielding the diimines 30c and d along with dinitrone 29.The formation and reactions of imino nitroxides 31 and of the nitronyl nitroxide 41 are discussed. Electron spin resonance studies revealed the high reactivity of the imidazolyl-1,3-dioxides 46 and the imidazolyl-1-oxides 50, which easily form radicals 47–49 and 51, respectively, which are derived from secondary reactions.
Spin labelling ribosomes: an overview
Authors: Dugas Hermann , Rodriguez Angel
Published: May 2006

This paper reviews the spin label approach to the problem of structure and function of the bacterial ribosomes from Escherichiacoli. The work of different research groups towards selective spin labelling of 70S ribosomes is presented and results are compared. Information obtained by binding these derivatized ribosomes with magnesium ions, tRNA, and antibiotics are analyzed. The interaction of selectively spin-labeled tRNAphe and spin-labeled kanamycin and puromycin with the ribosomes is also discussed.
Methods for preparation of heterobifunctional nitroxides: α,β-unsaturated ketones, β-ketoesters, cyano-nitro-derivatives
Authors: Hankovszky H. Olga , Hideg Kálmán , Lex László , Kulcsár Gyula , Halász H. Anna
Published: May 2006

The reactions of 1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-carboxaldehyde (1), 1-oxyl-2,2,5,5-tetramethyl-3-cyano-3-pyrroline (2), ethyl 1-oxy(-2,2,5,5-tetramethyl-3-pyrroline-3-carbonyl carbonate (3), and N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-carbonyl)imidazolide (4) are investigated with several nucleophiles (dialkylcadmium, diethyl sodio-malonate, magnesium enolate of ethyl hydrogen malonate, nitromethane-anion) to obtain α,β-unsaturated ketones, β-ketoesters, or conjugated reaction products. Aldehyde 1 is reacted with several methyl ketones (acetylmethylene-triphenylphosphorane, acetophenone, 2-acetylpyridine, 4-phenyl-3-butyn-2-one) to give spin labeled polyenones. The reaction of 4-(1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-yl)-2-buten-2-one (24a) with ethylenediamine gives 7,14-bis-(1-oxyl-2,2,5,5-tetramethyl-3-pyrroline-3-yl)-5,12-dimethyl-1,4,8,11-tetraazatetradeca-7,14-diene biradical (25).
New mono- and difunctionalized 2,2,5,5-tetramethylpyrrolidine- and Δ3-pyrroline-1-oxyl nitroxide spin labels
Authors: Keana John F. W. , Hideg Kálmán , Birrell G. Bruce , Hankovszky Olga H. , Ferguson George , Parvez Masood
Published: May 2006

Several new nitroxide spin labels have been prepared. Nitroxide mesylate 5 and p-hydroxyacetophenone gave 6 which was selectively brominated with cupric bromide to give the alkylating agent 7. The more water soluble phenacyl bromide analogue 17 was prepared either via the route 8 → 11 → 17 or else via the route 15 → 16 → 11 → 17. Preliminary results indicate that toward aconitase, nitroxide alkylating agent 17 behaves similarly to phenacyl bromide. Several new difunctional nitroxides were prepared with an eye toward application as saturation transfer esr spin labels. Conjugate addition of HCN to 11 gave 18, condensation of which with p-azidobenzaldehyde gave photolabile 19. Azide 20 could similarly be prepared directly from 11. Aldehyde 15 underwent condensation with p-azidoacetophenone to give azide 21. This substance was allowed to react with hemoglobin. Upon photolysis the esr spectral mobile component was substantially reduced, suggesting covalent attachment at more than one site. Conjugate addition of HCN to 23 gave a mixture of cis, trans isomers 24 and 25; the structure of 25 was established by X-ray crystallographic analysis to be the trans isomer. Conjugate addition of ethyl thioglycolate to 15 led to heterocycles 29–34.
Use of spin traps to elucidate radical mechanisms of oxidations by hydroperoxides catalyzed by hemeproteins
Authors: Griffin Brenda Walker
Published: May 2006

The use of the spin traps nitrosobenzene and 2-methyl-2-nitrosopropane has established that metmyoglobin and liver microsomal cytochrome P-450 initiate a radical decomposition of cumene hydroperoxide. With metmyoglobin and the alkyl nitroso compound, the only radical product of cumene hydroperoxide trapped was the methyl radical formed by β scission of the cumyloxy radical. With both hemeprotein initiators, nitrosobenzene trapped only the cumyl radical, considered to be a decomposition product of the unstable spin adduct phenylcumyloxynitroxide. Support for this proposal includes: (1) previous spin trapping studies of the chemical decomposition of cumene hydroperoxide; and (2) significant inhibition by nitrosobenzene of the one-electron oxidation of aminopyrine and the autoxidation of unsaturated membrane lipids resulting from addition of the hydroperoxide to liver microsomes. Aminopyrine altered the epr signal amplitudes of the spin adducts produced with both nitroso compounds, indicative of oxidation of aminopyrine by the methyl radical and reduction of cumene hydroperoxide by the aminopyrine radical. The participation of hydroperoxide-derived radicals in the low peroxidatic activities of certain hemeproteins is quite distinct from the catalytic function of the true hemeprotein peroxidases, which bring about an efficient two-electron reduction of specific hydroperoxides.
Photochemistry of protein and nucleic acid constituents: electron spin resonance and spin-trapping with 2-methyl-2-nitrosopropane
Authors: Riesz Peter , Rosenthal Ionel
Published: May 2006

Our recent studies of the direct uv-photolysis of aliphatic and aromatic peptides, DNA constituents, and their 5-haloderivatives in aqueous solution and the photo-induced reactions of benzoylperoxide with amino acids, peptides, fatty acids, and pyrimidines in dimethylsulfoxide-containing solutions are reviewed.2-Methyl-2-nitrosopropane was used for spin-trapping and characterization of free radicals generated photochemically with light in the wavelength range of 220–313 nm in aqueous or aprotic solvents. Direct photolysis of aliphatic dipeptides and of phenylalanine peptides produced mostly decarboxylation radicals, while for tyrosine peptides both decarboxylation and deamination radicals were spin-trapped; for tryptophan di- and tripeptides, deamination radicals were predominantly produced, while for long chain polypeptides, main-chain scission was observed.When pyrimidine bases were photolysed, radicals consistent with the addition of an H-atom or an OH-radical at the C(5) position of the 5,6-double bond could be detected. The general reaction pattern in the photolyses of 5-chloro, bromo, or iodouracil was the homolytic cleavage of the carbon–halogen bond, while for 5-fluorouracil, the α-fluoro radical was spin-trapped.Dibenzoylperoxide was found to photoinduce the free radical generation in amino acids, peptides, and fatty acids exposed to ultraviolet light, which is not absorbed by these compounds, that is, λ = 313 ± 10 nm. The most predominant reaction is the decarboxylation of the terminal acid moiety. This process is explained by an electron transfer from the acid to the photoexcited peroxide or its fragmentation products. Pyrimidine bases, such as cytosine and thymine, can be oxidized under these conditions to generate C(5) centered radicals.
Spin-trapping with 2-methyl-2-nitrosopropane: photochemistry of carbonyl-containing compounds. Methyl radical formation from dimethyl sulfoxide
Authors: Rosenthal Ionel , Mossoba Magdi M. , Riesz Peter
Published: May 2006

The photochemical reactions of several carbonyl-containing compounds investigated by spin-trapping with 2-methyl-2-nitrosopropane revealed different modes of scission depending on the structure of the initial compound. Thus, in photo-Fries rearrangements, the acyl radical was detected. 1,3-Diphenyl-2-propanone decarbonylated to yield the benzyl radical. Finally, valerophenone yielded the radicals expected by γ-hydrogen abstraction. In a dark reaction, dimethyl sulfoxide reacts with NaOH to generate methyl radicals. The latter result suggests the need for caution in the use of dimethyl sulfoxide with 2-methyl-2-nitrosopropane for the detection of hydroxyl radicals.
Electron spin resonance of spin-trapped radicals of amines and polyamines. Hydroxyl radical reactions in aqueous solutions and γ-radiolysis in the solid state
Authors: Mossoba Magdi M. , Rosenthal Ionel , Riesz Peter
Published: May 2006

The reactions of hydroxyl radicals with methylamine, dimethylamine, trimethylamine, diethylamine, sec-butylamine, ethylenediamine, 1,3-diaminopropane, putrescine, cadaverine, 1,7-diaminoheptane, ornithine, spermidine, spermine, agmatine, and arcaine in aqueous solutions have been investigated by spin-trapping and esr. Hydroxyl radicals were generated by the uv photolysis of H2O2 and 2-methyl-2-nitrosopropane (MNP) was used as the spin-trap. The effects of ionizing radiation on the same polyamines in the polycrystalline state were also investigated. The free radicals produced by γ-radiolysis of these solids at room temperature in the absence of air were identified by dissolution in aqueous solutions of MNP. The predominant reaction of [Formula: see text] with amines and polyamines below pH 7 was the abstraction of hydrogen atoms from a carbon that is not adjacent to the protonated amino group. For agmatine and arcaine which contain guanidinium groups abstraction occurred from the α-CH. Dimethylamine was oxidized to the dimethylnitroxyl radical by H2O2 in the dark. γ-Radiolysis of polyamines in the polycrystalline state generated radicals due to H-abstraction from either the α-CH or from a carbon atom in the middle of the alkyl chain. The deamination radical was obtained from ornithine.
Some physical and chemical aspects of spin trapping of organometallic radicals by quinones: optically active radical complexes
Authors: Creber Katherine A. M. , Ho Tong-Ing , Depew M. Catherine , Weir Douglas , Wan Jeffrey K. S.
Published: May 2006

A brief account is presented on the use of substituted quinones as spin traps for organometallic radicals and on the applications of CIDEP and esr–HPLC techniques to the study of quinone – organometallic radical complexes. Many of these radical adducts are thermally very stable and can be isolated by the HPLC technique for detailed spectroscopic and chemical studies. This in turn allows us to present a different approach to the "spin trapping" chemistry of unstable organometallic radicals by generating initially a stable quinone – metal carbonyl radical complex, separating the parent radicals by esr–HPLC and using them to react with other organometals via ligand exchange between the CO group(s) and the organometals. It then follows that if the entering organometal ligand is optically active, the substituted radical complex would also be chiral. This simple concept has led to the isolation of the first pure optically active radical complex with well-defined physical properties, including optical rotation.
The utilization of nitrone spin traps in a study of the photochemistry of pigment dispersions
Authors: Harbour John R. , Hair Michael L. , Issler Sandra L.
Published: May 2006

Examples of the use of nitrone spin traps for the elucidation of reaction mechanisms during the illumination of pigment dispersions are presented. Detection of superoxide and hydroxyl radicals with CdS, phthalocyanine, and ZnO is discussed. Singlet oxygen is also detectable with spin traps by following the O2 consumption in these dispersions as a function of illumination. These results are discussed in relation to the applications of pigment dispersions in both novel imaging systems and solar energy utilization systems.
Free radical production during phenylhydrazine-induced hemolysis
Authors: Hill H. A. O. , Thornalley P. J.
Published: May 2006

The production of phenyl radicals during phenylhydrazine-induced hemolysis has been demonstrated by the use of the spin traps, DMPO, M4PO, and LINPyBN. The phenyl spin adducts of DMPO and M4PO were produced in moderate yield by an oxygenated 1% erythrocyte suspension. With the lipid soluble spin trap LINPyBN, a dramatic increase (400%) in the yield of phenyl spin adduct was observed despite little increase in the rate of phenyl radical trapping. The production of phenyl spin adducts was decreased when phenylhydrazine-4-sulphonic acid or carbonmonoxyhemoglobin-containing erythrocytes were used. These results suggest that the reaction of phenylhydrazine with oxyhemoglobin leads to the formation of phenyl radicals that are preferentially trapped in the erythrocyte membrane.
Biosynthetic studies using 18O isotope shifts in 13C nuclear magnetic resonance
Authors: Vederas John C.
Published: May 2006

Isotopic substitution with oxygen-18 induces an observable upfield shift in the 13C nmr positions of directly-attached carbons, and in some cases, β-carbons. The magnitudes of these shifts range from about 0.05 ppm to 0.01 ppm, and are dependent on structure in an empirically predictable fashion. Incorporation of doubly labeled (13C, 18O) precursors into polyketides followed by 13C nmr analysis can identify carbon–oxygen bonds remaining intact during microbial biosynthesis. This technique has been applied to studies on antibiotics such as brefeldin A, cytochalasin B, granaticin, and lasalocid A, as well as aflatoxin precursors such as averufin, versicolorin A, and sterigmatocystin.
Orientations of hydroxyl groups. Conformational studies on 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose by nuclear magnetic resonance spectroscopy
Authors: Dais Photis , Perlin Arthur S.
Published: May 2006

Various nmr spectroscopic techniques have been used to determine the orientation of the anomeric hydroxyl group of 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose (1) in dimethylsulfoxide solution, as well as other conformational features of themolecule. 13C and 1H coupling constants indicate that in its most probable orientation the O—H bond is anti with respect tocarbon-2, and forms an angle of ~40° with the C-1—H-1 bond. Spin-lattice relaxation rates (R1) and nuclear Overhauser enhancements (nOe) have been measured for the pertinent protons and used, in conjunction with 13C relaxation times, as additional criteria for characterizing the geometry of the anomeric alcohol group of 1. These results are in good agreement with the coupling constant data. The conformations of the mannofuranose ring, the 2,3-O-isopropylidene ring, and the C-4 to C-6 region of the molecule are also described.
Selection of ternary fused chlorides for the electrowinning of aluminum based on calculated thermodynamic properties
Authors: Pelton A. D. , Skeaff J. M. , Bal C. W. , Lin P. L.
Published: May 2006

Phase diagrams and total vapour pressures in the reciprocal ternary systems LiCl–NaCl–LiAlCl4–NaAlCl4, LiCl–KCl–LiAlCl4–KAlCl4, and NaCl–KCl–NaAlCl4–KAlCl4 have been calculated by means of computerized optimization and interpolation techniques based on an analysis of the constituent binary systems.The system LiCl–NaCl–LiAlCl4–NaAlCl4 exhibits an extensive composition region of one-phase liquid solution whereas the LiCl–KCl–LiAlCl4–KAlCl4 system has a miscibility gap which covers ~50% of the composition region. Comparison of the calculated phase diagram with measured data for NaCl–KCl–NaAlCl4–KAlCl4 was made and the agreement between the two was found to be satisfactory.Temperatures and compositions of chloride electrolytes suitable for the electrowinning of aluminum have been proposed from the isothermal sections of the phase diagrams and total vapour pressure curves. In all of the systems, the total vapour pressure is greater than the minimum for non-volatilization.
Kinetics and mechanism of ion exchange sorption of some detergents on zinc ferrocyanide
Authors: Srivastava Suresh K. , Jain Chakresh K. , Oberoi Chander K. , Sharma Ashok K.
Published: May 2006

Studies have been made on the kinetics and mechanism of exchange sorption of detergents on zinc ferrocyanide using a modified limited bath technique. The effects of concentration, particle size of the sorbent material, and temperature on the sorption rate have been investigated. In the case of cationic detergents (cetyl pyridinium bromide and cetyl trimethylammonium bromide), equilibrium is attained in a period of 2–3 h while 12–16 h are required for anionic detergents, viz., sodium dodecyl sulphate and sodium dodecyl benzene sulphonate. The slowest step governing the sorption rate is found to be the diffusion within the exchanger particles at higher concentrations. The effective diffusion coefficients have been evaluated at four different temperatures and found to be comprised of mainly two components. The energy barriers against the diffusion of exchanging ions have been assessed from the Arrhenius equation. Entropies of activation for various sorption systems have also been calculated. The results are discussed in terms of the size and geometry of the detergents, pore-widths in the sorbent material, and the electric potential gradient along the diffusion path. No change in the internal structure of zinc ferrocyanide is inferred due to the sorption of detergent ions.
The kinetics of proton and deuteron transfer from 1-(4-nitrophenyl)-1-nitroethane to1,8-diazabicyclo[5.4.0]undec-7-ene in aprotic solvents
Authors: Leffek Kenneth T. , Pruszynski Przemyslaw
Published: May 2006

1-(4-Nitrophenyl)-1-nitroethane reacts with the base1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in both acetonitrile and toluene solvents in a normal second-order proton-transfer reaction, in contrast to its behaviour with the base 2,7-dimethoxy-1,8-bis(dimethylamino)naphthalene in acetonitrile.The primary isotope effect, kHlkD = 12.0 at 25° in toluene is very similar to that observed by other workers for the reaction of 4-nitrophenylnitromethane with DBU under the same conditions. In acetonitrile solvent a kHlkD ratio of 7.8 was found at 25 °C. The isotope effects on the activation parameters for the reaction in both solvents indicate that tunnelling of the proton through the potential energy barrier makes a significant contribution to the reaction rate.
1H nuclear magnetic resonance study of tunnelling in molecules with multiple methyl groups trapped in hydrates
Authors: Ripmeester J. A.
Published: May 2006

Methyl group tunnelling frequencies were derived from low-temperature 1H lineshapes for isobutane-d1, tert-butyl fluoride, and trimethylamine trapped in heavy water hydrates and for tert-butyl chloride, tert-butyl alcohol, and neopentane enclathrated in the heavy water double hydrates with D2S. Methyl group rotational barriers derived from the tunnelling frequencies are generally not very different from values found for the pure solids and gases and are much larger than barriers to overall reorientation of the guest molecules in the hydrate cages. Disorder in the orientation of the water molecules which make up the hydrate cages led to a distribution in barrier heights.
Complexes de Cu(II), Co(II), Ni(II) et UO2(II) avec les bases de Schiff N-(4-méthyl-2-pyridyI)salicylaldimine et N-(6-méthyl-2-pyridyl)salicylaldimine
Authors: Capitán-Vallvey L. F. , Jiménez C. , Cuadros L.
Published: May 2006

We have isolated the complexes of the Schiff bases N-(4-methyl-2-pyridyl)salicylaldimine and N-(6-methyl-2-pyridyl)salicylaldimine with Co(II), Ni(II), Cu(II), and UO2(II) in both aqueous alcoholic and absolute alcoholic solutions. We note different modes of action of these Schiff bases according to the medium used. However, in aqueous alcoholic solution the complexes mentioned have a remarkable capacity for reaction with the substances in solution. We propose two new gravimetric methods for Ni(II) and UO2(II).

[Journal Translation]
A spectroscopic study of proton transfer and photochromism in N-(2-hydroxybenzylidene)aniline
Authors: Lewis J. W. , Sandorfy C.
Published: May 2006

The infrared spectral characteristics of N-(2-hydroxybenzylidene)aniline, its deuterium substituted analogue, N-(2-hydroxybenzylidene)-m-toluidine, and their photoproducts have been investigated. The infrared spectrum of a low temperature polycrystalline film of N-(2-hydroxybenzylidene)aniline exhibits new absorption bands at 3380, 1646, 1537, 1502, 1319, and 1310 cm−1 upon irradiation at 365 nm. Likewise, the spectrum of the m-toluidine derivative exhibits new absorption bands at 3320, 1650, 1535, 1503, 1321, 1310, and 995 cm−1 upon irradiation at 365 nm. These new data, in conjunction with the newly acquired data on the hydrochloride and deuterochloride of the title compound, indicate that the photoproduct is a zwitterion, not an ortho-quinone. It is also inferrred that the photoproduct exists in a conformation which is cis about the central carbon–nitrogen double bond.
Existence and characterization of double salts in indium trihalide – potassium halide – water systems at 21 °C (halide = Cl, Br)
Authors: Wignacourt J. P. , Mairesse G. , Barbier P. , Lorriaux-Rubbens A. , Wallart F.
Published: May 2006

The degree of hydration of stable hydrates is discussed on the basis of early literature results and our determination of the phase diagrams for the systems InCl3–KCl–H2O and InBr3–KBr–H2O at 21 °C The existing double salts are formulated: 3KCl•InCl3•H2O and 2KCl•InCl3•H2O in the chloride system, and 3KBr•InBr3•1.5H2O, 2KBr•InBr3•H2O, KBr•InBr3•2H2O, and 3KBr•2InBr3 in the bromide system. All of them are incongruently saturating at 21 °C. A summary of their crystallographic and Raman spectroscopic data is given.
Observation de la résonance paramagnétique électronique dans les composés organométalliques de l'uranium (III)
Authors: Soulié E. J. , Folcher G. , Marquet-Ellis H.
Published: May 2006

The trivalency of uranium can be easily established in frozen solution by epr. The broad resonance signal observed at low temperature (7 K) with g = 3.5 appears as characteristic of the trivalent state in UZrF7(powder), U(C5H5)3•tétrahydrofuran, and U(C5H5)3•CH3− (frozen solutions).
Calculated uranium solubility in groundwater: implications for nuclear fuel waste disposal
Authors: Goodwin Bruce
Published: May 2006

Uranium solubilities of the order of 10−10 M have been calculated for a range of conditions which are considered to be representative of those expected in a Canadian nuclear fuel waste disposal vault. Factors taken into consideration include the pH and Eh range expected for deep groundwaters, the projected temperature range near a nuclear fuel waste disposal vault, the effect of the composition of two representative groundwaters, the effect of non-ideality, and the effect of the stability of several uranium solids.The model used in these calculations is based on the assumption of chemical equilibrium. Calculations show that the most important factors influencing uranium solubility under the postulated conditions are pH and Eh.These results applied to an assessment of the nuclear fuel waste disposal program suggest that uranium concentrations will be very low in the disposal vault, and that the irradiated UO2 fuel matrix will remain relatively intact for long periods of time.
Kinetics of solvolysis in water of four secondary alkyl nitrates
Authors: Robertson Ross Elmore , Koshy Kalvelil Matthew , Annessa Adrianne , Ong Jan N. , Scott John Marshall William , Blandamer Michael Jesse
Published: May 2006

Kinetic data are reported for the solvolysis in water of propane-2-nitrate, butane-2-nitrate, cyclopentyl nitrate, and cyclohexyl nitrate. In each case, the dependence of rate constant on temperature is analysed in terms of two mechanisms for the solvolytic reaction. First it is assumed that the rate constant describes a single step reaction, the analysis leading to estimates of the heat capacity of activation ΔCp≠. Three different analytical methods are discussed in this regard. Second it is assumed that the rate constant describes a two stage mechanism, the first stage being reversible. In this case the explanation of the ΔCp≠ term calculated according to the first mechanism is quite different. We comment on the alternative explanations of trends in activation parameters.
The entropy of formation of the mercury/methanol interface
Authors: Borkowska Z. , Fawcett W. R.
Published: May 2006

The entropy of formation of the mercury/methanol interface has been calculated from double layer capacity and interfacial tension measurements. In contrast to results for aqueous and propylene carbonate solutions, the plot of entropy against electrode charge density passes through a minimum at negative charge densities and a maximum at positive charge densities in the same regions where a minimum and maximum are found on the capacity curve. The excess surface entropy of methanol is negative for all charge densities, indicating that the solvent is more structured at the mercury surface than in the bulk. The results have been discussed in terms of the three state model in which the charge dependence of the entropy is attributed to reorientation of solvent dipoles at the interface.
Formation of unusual side-products from succinimidyl esters of fatty acids during the acylation of amino acids
Authors: Paquet Alenka , Bergeron Michel
Published: May 2006

A new side-product, succinohydroxamic decanoic anhydride, was isolated from the reaction mixture during the acylation of lysine by succinimidyl decanoate in the presence of aqueous sodium hydroxide. Laurie and palmitic acid derivatives were also obtained. It is shown that these compounds can be used for acylation of amino acids. The hydroxamic acid derivatives were also detected when the acylations by succinimidyl esters of fatty acids were carried out under anhydrous conditions. Preparation of N-lauroyl-L-tyrosine methyl ester from tyrosine methyl ester and succinimidyl laurate is also described.
Some reactions of 3-cyano(diethylaminocarbonyl, methoxycarbonyl) pyridines with organolithium reagents. Synthesis of stabilized 1,2-, 1,4-, and 1,6-dihydropyridines
Authors: Din M. Gamal El , Knaus Edward E. , Giam Choo-Seng
Published: May 2006

The reaction of 3-cyano 5a, 3-diethylaminocarbonyl 5b, and 3-methoxycarbonylpyridine 5c with alkyllithiums 6 has been investigated as a method of preparing stable dihydropyridines. Reaction of 5a with 6 affords a mixture of 1,2- and 1,6-dihydropyridines 10 and 11, whereas reaction of 5b and 5c with 6 yields a mixture of 1,4- and 1,6-dihydropyridines 11 and 12. The cyano and diethylaminocarbonyl substituents of 5a and 5b are relatively resistant toward attack by the alkyllithium whereas reaction of the methoxycarbonyl substituent of 5c is competitive with addition to the ring. The stabilities of the dihydropyridines prepared are described.
Solute–solvent interactions in the association of hexacyanoferrate(III) with group II A cations. A calorimetric study
Authors: Aruga Roberto
Published: May 2006

Enthalpy of association of hexacyanoferrate(III) ion with Mg(II), Ca(II), Sr(II), and Ba(II) cations has been determined by direct calorimetry. Using the equilibrium constants, Gibbs function and entropy were also obtained. Measurements were carried out in aqueous medium at 25 °C and ionic strength I = 0.1 mol L−1. Examination of the thermodynamic quantities obtained and calculation of the distance of closest approach between cation and anion show the presence of different desolvation processes for the metals studied. More particularly, solvent-separated ion pairs in the case of magnesium and contact pairs in the case of barium seem to be present. The presence of desolvation processes is uncertain for calcium and strontium. The ΔH0 and ΔS0 values show also an important influence from solvent-destructuring processes on ion pair formation.
Thermochemistry of conjugation of simple cyclopropane derivatives
Authors: Fuchs Richard , Hallman John H. , Perlman Michael O.
Published: May 2006

Heats of vaporization of cyclopropyl cyanide and cyclopropylbenzene have been measured by vaporization calorimetry, and combined with liquid state heats of formation to give gaseous state heats of formation. When these compounds, cyclopropane, 1,1-dimethylcyclopropane, and cyclopropylamine are involved in (hypothetical) isodesmic reactions with ethane to give the isopropyl derivative and propane, the enthalpies of reaction are −116.0 ± 1.3 kJ mol−1, except for cyclopropylbenzene (−103.7 kJ mol−1). The latter is less exothermic, in part, because of slight steric destabilization of the product, isopropylbenzene, but mainly due to 8 kJ mol−1 stabilization of cyclopropylbenzene, which is the only of these cyclopropyl derivatives showing appreciable thermochemical stabilization.
Polymer supported enantioselective reactions. II. α-Methylation of cyclohexanone
Authors: McArthur Colin R. , Worster Paul M. , Jiang Ji-Long , Leznoff Clifford C.
Published: May 2006

Insoluble cross-linked copolymers of styrene and 1% divinylbenzene with covalently bonded (S)-2-aminoalkoxy groups were used in the enantioselective α-methylation of cyclohexanone through the corresponding imines. Enantiomeric excesses of 94% of (S)-2-methylcyclohexanone were observed on methylation at 20 °C. An analogous optically active 2-aminoalkyl benzyl ether, under otherwise identical conditions, resulted in a lower enantiomeric excess (49%) with selectivity approaching that of the polymer only at −78 °C.
Synthesis and characterization of some oxidized derivatives of citronellal ethylene acetal
Authors: Taylor Wesley G.
Published: May 2006

Three pairs of geometrical isomers corresponding to allylic monooxidation products of the trisubstituted olefin, citronellal ethylene acetal (3), were synthesized. These compounds were the E and Z isomers of 7-(1,3-dioxolan-2-yl)-2,6-dimethyl-2-hepten-1-ol, -1-al, and -1-oic acid (methyl ester), precursors for identifying the biodegradation products from citronellal and some of its derivatives. The E aldehyde (4) was obtained from 3 by the Sharpless procedure with catalytic quantities of selenium dioxide. The E ester (5) and E alcohol (6) were prepared in high isomeric purity (97–99%) from 4 with activated manganese dioxide and sodium borohydride, respectively. Selective ozonolysis of the isobutenyl group in 3 gave 5-(1,3-dioxolan-2-yl)-4-methyl-1-pentanal (7). Under the conditions used, ozone did not react with the ethylene acetal group. Acetal aldehyde (7) was stereoselectively converted to the Z alcohol (8) by a Wittig reaction. Manganese dioxide oxidation of 8 (98–99% Z isomer) to the Z aldehyde (9) and of 9 to the Z ester (10) was accompanied by partial Z to E isomerization. The distribution of E and Z isomers in crude reaction mixtures was determined by gas chromatography with a glass capillary column or by proton magnetic resonance spectroscopy.