bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanistic studies on the formation of aminoxyl radicals from 5,5-dimethyl-1-pyrroline-N-oxide in Fenton systems. Characterization of key precursors giving rise to background ESR signals
Authors: Makino Keisuke , Hagi Akifumi , Ide Hiroshi , Murakami Akira , Nishi Masatoshi
Published: May 2006

To assign unidentified ESR signals obtained in a Fenton system with a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), fundamental reactions of DMPO have been thoroughly investigated. When the concentration of Fe2+ in Fenton systems exceeded 1% of that of DMPO, background ESR signals totally distinguishable from 2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxy (DMPO-OH) appeared, and simultaneously absorbance at 520 nm increased, which was characteristic of hydroxamic acids complexed with Fe3+. To prove the postulated formation of hydroxamic acid as a key intermediate, DMPO was subjected to Fenton reaction or was treated with Fe3+ in aqueous solution to produce DMPO-OH (Makino etal. Biochem. Biophys. Res. Commun. 172, 1073 (1990)), and a major product was isolated by RPLC. Based on 1H, 13C NMR and MS measurements, the structure of the major product was assigned to 1-hydroxy-5,5-di-methyl-1-pyrrolid-2-one (HDMPN) having a hydroxamic acid structure. Temperature dependence of NMR spectra and careful analysis of the fragmentation patterns in MS further revealed that HDMPN was present in equilibrium with 2-hydroxy-5,5-dimethyl-1-pyrroline-N-oxide (HDMPO), a tautomer of HDMPN. It has also been shown that the oxidation of DMPO yielding HDMPN and HDMPO occurs via DMPO-OH and is driven by Fe3+. These oxidation products (HDMPN and HDMPO) were readily converted to the corresponding ESR visible aminoxyl radicals by oxidation and •OH addition in aqueous solution, respectively, and superimposition of the ESR signals arising from these radicals accounts for the background signals observed in Fenton systems with DMPO as a spin trap.
The 1992 Alcan Award Lecture Excursions around the periodic table: ligand design in inorganic chemistry
Authors: Fryzuk Michael D.
Published: May 2006

An overview is given on the strategy used to come up with the design of a new type of ligand that is appropriate for coordination to both the late metals and the early metals. The coordination chemistry of the potentially tridentate ligand −N(SiMe2CH2PR2)2 is developed starting with the Ni triad and then the heavier members of group 9, namely rhodium and iridium. It is with iridium that reactive fragments such as methylene and vinylidene have been stabilized and their chemistry examined. Extension to groups 3, 4, and the lanthanides is also discussed. With these elements, phosphine coordination imparts new reactivity patterns such as alkane elimination with group 3 and dinitrogen activation with group 4. In addition, the side-on binding mode for N2 attached to a dinuclear zirconium system is also presented.
Nonlinearity of the maximum entropy method in resolution enhancement
Authors: Kauppinen J. K. , Moffatt D. J. , Mantsch H. H.
Published: May 2006

The nonlinear behavior of the filter-type Maximum Entropy Method (MEM) was investigated from a theoretical and a practical point of view. The integrated intensity of the output spectral lines of MEM was probed as a function of the input intensity pattern, the filter length, and the S/N ratio of the input spectrum. The nonlinear behavior of MEM has been explained and the results compared with those derived by another method, LOMEP (Lineshape Optimized Maximum Entropy linear Prediction). The study was carried out with the aim of resolution enhancement of spectra that have high signal-to-noise ratio.
Complexation of 7-azaindole by the methylmercury(II) cation
Authors: Dufour Nathalie , Lebuis Anne-Marie , Corbeil Marie-Claude , Beauchamp André L. , Dufour Pascal , Dartiguenave Yves , Dartiguenave Michèle
Published: May 2006

Complexes of the types [CH3Hg(aza)], [CH3Hg(Haza)]X, and [(CH3Hg)2(aza)]X are obtained by reacting CH3HgOH and/or CH3HgX (X = NO3, ClO4) with 7-azaindole (Haza). The weakly acidic N1-H proton on the pyrrole ring is displaced by the hydroxide, whereas the perchlorate and nitrate salts lead to CH3Hg+ coordination to the N7 lone pair on the pyridine ring. Detailed analysis of the infrared spectra of the complexes and their N-deuterated derivatives provides diagnostic regions for eventual prediction of the coordination mode in other systems. All compounds are characterized by means of 1H, 13C, and 199Hg NMR spectra in DMSO solution and solid-state CP-MAS 13C spectra. Comparison of the solution and solid-state 13C spectra show that the species present in the solids remain undissociated in DMSO. Each type of complex can be identified from a characteristic pattern of large displacements of the ligand 13C signals. The 1H spectra are less informative because substitution of the N1-H proton by CH3Hg+ induces only minor shifts. Metal solvation appears to have a major influence on the 13C and 199Hg chemical shifts of the CH3Hg+ groups.
Ab initio SCF and Møller-Plesset studies on hexachlorides of selenium and tellurium and their dianions
Authors: Klobukowski Mariusz
Published: May 2006

SCF and Møller–Plesset calculations were done for four chalcogen hexahalide systems (SeCl6, SeCl62−, TeCl6, and TeCl62−) to study their geometric structures and relative stabilities in their ground electronic states. Flexible all-electron and valence-electron polarized basis sets were used. For some of the basis sets used, the stationary points located on the SCF potential energy surface of the ions in Oh symmetry were found to possess negative eigenvalues of the Hessian matrix; the structural parameters of the corresponding stationary points in C3v symmetry were determined. At the MP2 level, all ions were found to restore the octahedral symmetry.
Synthesis and basicity of 2-N-quinolyl- and 2-N-isoquinolyl-1,1,3,3-tetramethylguanidines
Authors: Foroughifar Naser , Leffek Kenneth T. , Lee Yong Gu
Published: May 2006

A series of 2-N-quinolyl- and 2-N-isoquinolyl-substituted 1,1,3,3-tetramethylguanidines has been synthesized and the pKa of each has been measured in acetonitrile and water solvents, together with the pKa of the corresponding aminoquinoline or aminoisoquinoline. The pKa values in acetonitrile and water fall on the same correlation line as previously determined for 2-N-pyridylguanidines and aminopyridines. Replacement substituent constants (σa) are reported for several quinolyl and isoquinolyl groups in the two solvents.
Nucleic acid related compounds. 78. Stereocontrolled syntheses of 6′(E and Z)-halovinyl analogues from uridine-derived vinylsulfones via vinyltin intermediates
Authors: Wnuk Stanislaw F. , Robins Morris J.
Published: May 2006

Treatment of the 6′(E)-tosylvinyl homonucleoside 1a with Bu3SnH/AIBN/toluene/Δ gave separable mixtures of 6′-vinylstannanes 2a(E/Z) in high yields. Stereospecific halodestannylations with N-iodosuccinimide, bromine, and N-bromosuccinimide proceeded smoothly to give the 6′(E or Z)-iodo(and bromo) vinyl compounds with retention of configuration. Chlorine or iodobenzene dichloride effected moderately stereoselective chlorodestannylation. Treatment of 2a with NH4F/MeOH/Δ resulted in carbon–tin bond cleavage to give the free vinyl derivative 4a. Aqueous trifluoroacetic acid effected concomitant protiodestannylation and deprotection of 2a to give 4b. Treatment of 2a(E) with lead tetraacetate/acetonitrile and deprotection afforded acetylenic derivative 3b.
Organometallic products from the reaction of the isoelectronic Mn(CO)5− and Cr(CO)4NO− metallate anions with bis-α-bromocyclopropyl ketone
Authors: Masters A. P. , Parvez M. , Sorensen T. S. , Sun F.
Published: May 2006

Mn(CO)5− and Cr(CO)4NO− react with the title ketone to give organometallic products. In the chromium case, a single metallofuran product is produced. In the manganese reaction, one can isolate a series of four complexes, two of which have a structure closely related to the chromium complex. The other two complexes are assigned an acyl manganese structure. The structures of the chromium complex and one of the acyl manganese complexes have been determined by X-ray methods. One finds a distorted octahedral bonding about the metal atom in each case. The chromium complex has bond lengths very similar to those reported for a closely related manganese structure, implying a delocalization of electrons within a metallofuran ring. As expected for this mixed carbonyl nitrosyl complex, the nitrosyl group is positioned trans to the oxide bond, representing the weakest and strongest "trans-effect" substituents. The acyl manganese structures contain an Mn(CO)4 unit in contrast to the usual Mn(CO)5 acyl complexes, with the 18e− count being provided by an internal chelation with the n-electrons of the dicyclopropyl ketone group. The reaction mechanism for the formation of the complexes is postulated to involve initial bromine abstraction (two-electron reduction) by the metallate anion, with the Cr(CO)4NO− reaction being much faster compared to Mn(CO)5−. The resulting organic enolate then "back-reacts" with a carbonyl group of the just-formed metal carbonyl bromide to form a transient anionic Fischer carbene complex. Ultimately this intermediate loses the metal bromide ion with the formation of the neutral complexes.
Solid-state chemistry of polycarboxylate crown ether cation complexes: cooperative binding of water and metal ions by flexible chorands
Authors: Dutton Philip J. , Fyles Thomas M. , Suresh Valia Veettil , Fronczek Frank R. , Gandour Richard D.
Published: May 2006

The solid-state structures of alkali-metal salt complexes of crown ether tetra- and hexa-carboxylic acids (18C6A4 and 18C6A6) have been determined. The sodium salt of 18C6A6 crystallizes as the trihydrate in orthorhombic space group P212121 (a = 7.6868(12), b = 15.429(3), c = 21.975(2) Å, R = 0.031 for 5192 observed data); the potassium salt of 18C6A6 crystallizes as the the trihydrate in orthorhombic space group P212121 (a = 7.6711(8), b = 15.709(2), c = 21.966(5) Å, R = 0.035 for 2521 observed data); the thallium(I) salt of 18C6A6 crystallizes as the dihydrate in orthorhombic space group P212121 (a = 12.0331(10), b = 12.4333(12), c = 17.366(2) Å, R = 0.035 for 4952 observed data); and the cesium salt of 18C6A6 crystallizes as the dihydrate in monoclinic space group P21 (a = 7.708(3), b = 13.492(2), c = 11.9501(9) Å, β = 94.49(2)°, R = 0.029 for 4480 observed data). The sodium salt of 18C6A4 crystallizes as the dihydrate in monoclinic space group P21 (a = 11.4368(11), b = 7.7068(11), c = 12.6579(12) Å, β = 98.515(8)°, R = 0.035 for 3000 observed data); the thallium(I) salt of 18C6A4 crystallizes as the dihydrate in monoclinic space group P21(a = 11.719(2), b = 7.668(2), c = 12.8403(13) Å, β = 99.052(9)°, R = 0.040 for 3981 observed data); and the cesium salt of 18C6A4 crystallizes as the dihydrate in monoclinic space group P21 (a = 11.787(2), b = 7.637(2), c = 13.001(2) Å, β = 98.705(12)°, R = 0.038 for 3428 observed data). Both chorands exhibit a cooperative relationship of mean cavity radius and guest-ion radius, which closely follows the effective ionic radii of the guests. The hexaacid is a preorganized host for monohydrated cations. It provides a trigonal hydrogen bonding receptor site for the water molecule, and up to nine oxygen donors for cation binding. Guests ranging in size from Na+ to Cs+ are accommodated without distortion of the macrocyclic framework. The tetraacid is similarly tolerant of a range of guests, but greater structural reorganization of the ligand is required to optimize contacts with fully dehydrated cations. Skeletal drawings of donor atoms, in conjunction with polar coordinate maps of torsion angles, reveal how the demands of the guest are accommodated by the host.
L'azote n'est pas le site basique des amides encombrés
Authors: Laurence Christian , Helbert Maryvonne , Lachkar Abdeljalil
Published: May 2006

The shift of the carbonyl band of the iodine complexes with the hindered amides i-PrCON(C6H11)2, t-BuCON(C6H11)2, and t-BuCON(i-Pr2) shows that the iodine interacts with the oxygen atom of the carbonyl group. Hydrogen bond donors, such as p-FC6H4OH, CHCl3, or CHBr3, also interact with the oxygen atom of the carbonyl group. The only differences between these hindered amides and unhindered amides like MeCONMe2 are the lower complexation constants (15 L mol−1 for MeCONMe2–I2 vs. 3 L mol−1 for t-BuCON(i-Pr2) and a lower stoichiometry of complexation (for example, a mixture of 1:1 and 1:2 complexes is obtained with t-BuCON(C6H11)2 while MeCONMe2 forms mainly 1:2 complexes).
Structural studies of organoboron compounds. LVII. Synthesis and structure of bicyclic boron-nitrogen betaines. 1-Methyl-5-(3-nitrophenyl)-4,6,9-trioxa-1-azonia-5-boratabicyclo[3.3.1]nonane and 3,3,4-trimethyl-1-(3-nitrophenyl)-2,6,7-trioxa-3-azonia-1-boratabicyclo[2.2.2]octane
Authors: Ahlenstiel Eckart , Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

The syntheses and structures of the bicyclic boron-nitrogen betaines 1-methyl-5-(3-nitrophenyl)-4,6,9-trioxa-1-azonia-5-boratabicyclo[3.3.1]nonane, 7a, and 3,3,4-trimethyl-1-(3-nitrophenyl)-2,6,7-trioxa-3-azonia-1-boratabicyclo[2.2.2]-octane, 14a, are reported. Crystals of 7a are orthorhombic, a = 20.256(2), b = 37.652(2), c = 6.642(1) Å, Z = 16, space group Fdd2, and those of 14a are orthorhombic, a = 21.402(2), b = 11.334(3), c = 11.248(2) Å, Z = 8, space group Pbca. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.038 and 0.045 (Rw = 0.036 and 0.053) for 975 and 1646 reflections with I ≥ 3σ(F2), respectively. The X-ray analyses establish the bicyclo[3.3.1]nonane and bicyclo[2.2.2]octane "cage" structures for 7a and 14a, respectively. Bond lengths involving the tetrahedral boron atom are (N)O—B = 1.519(5), (C)O—B = 1.444(6) and 1.443(6), C(aryl)—B = 1.602(5) Å for 7a; and (N)O—B = 1.530(3), (C)O—B = 1.446(3) and 1.455(3), C(aryl)—B = 1.608(3) Å for 14a. Weak [Formula: see text] interactions are the main feature of the crystal packing arrangements of both compounds.
Charge transfer complexes of Schiff bases derived from 2-aminobenzothiazole with some acidic and nonacidic acceptors
Authors: Ibrahim Amany M. A.
Published: May 2006

When Schiff bases derived from 2-aminobenzothiazole were reacted with di- and trinitrobenzene derivatives as acidic and nonacidic acceptors in the ratio of 1:1, stable coloured charge transfer complexes (CTC's) were obtained. The structure and stoichiometry of the CTC's were studied by elemental analysis.as well as by electronic absorption and infrared and nuclear magnetic resonance spectra. The CTC's derived from nonacidic acceptors were stabilized via intermolecular π–π* and n–π* transitions while those derived from acidic acceptors were formed by intermolecular π–π* transitions and a proton transfer stabilized by resonance. The ionization potentials of the Schiff bases and the electron affinities of the nitrobenzene derivatives were calculated.
The crystal and molecular structures of N,N′-di(2-acetylcyclohexenyl)ethylenediamine and its copper(II) complex
Authors: Fernández-G. Juan N. , Enríquez Raúl G. , Tobón-Cervantes Amalia , Bernal-Uruchurtu Margarita I. , Villena-I René , Reynolds William F. , Yang Ji-Ping
Published: May 2006

The crystal structures of N,N′-di(2-acetylcyclohexenyl)ethylenediamine (L1) and its copper(II) complex, which crystallizes with one solvent molecule of chloroform (Cu(L1-2H)•CHCl3), were determined. Crystallographic details are as follows: L1 is monoclinic, space group P21/c, with a = 8.280(2), b = 11.692(2), and c = 9.355(2) Å, β = 114.10(2)°, V = 826.7(3) Å3, Z = 2; ρc = 1.22 g cm−3, μ(Cu Kα) = 5.93 cm−1, with the final residual indices of R = 0.046 and Rw = 0.070 for 991 unique reflections. Cu(L1-2H)•CHCl3 is triclinic, space group[Formula: see text] with a = 11.121(3), b = 11.713(3), and c = 8.974(2) Å, α = 99.35(2)°, β = 110.83(2)°, γ = 82.33(2)°, V = 1074(1) Å3, Z = 2; ρc = 1.50 g cm−3, μ(Cu Kα) = 50.74 cm−1, with the final residual indices of R = 0.048 and Rw = 0.077 for 2369 unique reflections. The X-ray diffraction study shows that in the crystal state the ligand L1 is in the methylketonecyclohexanonenamine isomeric form. For the copper complex Cu(L1 2H)•CHC13, the geometry around the metal atom is distorted square planar, and the angle between the chelate ring planes in the complex is 15.1°. An NMR study shows that L1 in solution has the same structure as that observed in the solid state by X-ray diffraction.
Synthesis of 2′-deoxy-2′-spirocyclopropyl cytidine as potential inhibitor of ribonucleotide diphosphate reductase
Authors: Czernecki Stanislas , Mulard Laurence , Valéry Jean-Marc , Commerçon Alain
Published: May 2006

Based on the mechanism of action of ribonucleoside diphosphate reductase (RDPR), a new class of nucleosides that may act as inhibitors of this enzyme was designed. Starting from uridine, a 2′-deoxy-2′-spirocyclopropyl derivative of cytosine was prepared. The key step of the synthesis is the condensation of diazomethane with a suitably protected 2′-methylene nucleoside. Light-induced nitrogen extrusion affords the cyclopropane ring.
Application of thioglycoside chemistry to the synthesis of trisaccharides and deoxy-trisaccharides related to the Shigella flexneri Y polysaccharide
Authors: Auzanneau France-Isabelle , Bundle David R.
Published: May 2006

The Shigella flexneri lipopolysaccharide has a biological repeating unit, → 2)α-L-Rhap(1→2)α-L-Rhap(1→3)α-L-Rhap(1→3)β-D-GlcNAcp(1 → ABCD, but the residue segment BCD suffices to fill the binding site of an O-antigen specific monoclonal antibody, SYA/J6. Synthetic modifications to this trisaccharide have been designed to investigate the involvement in binding of the acetamido moiety, the 4- and 6-OH groups of the GlcNAc residue D, the 4′-OH group of the Rha residue C, and the 3″- and 4″-OH groups of the Rha residue B. Sequential chain extension provided the protected trisaccharides 18, 24, 26, 28, 30, 32, and 35 using thioglycoside glycosyl donors activated by iodonium ions generated in situ from N-iodosuccinimide and triflic acid. Trisaccharides each monodeoxygenated in either ring B 25 and 27 or ring C 29 were accessed by the use of 3,6-dideoxy or 4,6-dideoxy glycosyl donors 14 and 17 and when these were used in sequential steps trisaccharides 31 and 33, each deoxygenated at double sites in adjacent residues, were obtained. Selective protection of the glucosamine residue as its N-benzyloxycarbonyl derivative provided a facile route to the trisaccharide amino compound 20, from which N-acetyl 21, N-propionyl 22, and N-trifluoroacetyl 23 derivatives were directly prepared. Orthoester intermediates were detected in several glycosylation reactions and culminated in an orthoacetate 34 as a major product rather than the target trisaccharide 35. When triflic acid concentration was increased these products were avoided but acid-catalyzed migration of a 2-O-acetyl group led to both 1→2 and 1→3 linked trisaccharides 35 and 37. To avoid similar undesirable 1,2-linked products, a block synthetic strategy using the 2-O-benzoylated disaccharide glycosyl donor 40 was chosen so that the propensity for orthoester formation was minimized in reactions leading to the trisaccharide analogue deoxygenated at C-6 of the glucosamine unit D.
Ryanoids and related compounds. A total synthesis of 3-epiryanodine
Authors: Ruest Luc , Deslongchamps Pierre
Published: May 2006

In the course of a preliminary investigation on the relationships between chemical structure of ryanoids and their affinity to the ryanodine (1) binding site, we have synthesized 3-epiryanodine (13) from anhydroryanodol (4), a key intermediate in our total synthesis of (+)-ryanodol (2).
Hydrogen isotopic exchange between D2 and H2O on alumina prepared by sputtering
Authors: Ioka Fumio , Sakka Tetsuo , Ogata Yukio , Iwasaki Matae
Published: May 2006

Hydrogen isotopic exchange between D2 and H2O has been investigated on alumina prepared by sputtering at 803 K and at low pressures. The alumina is amorphous, consisting of aluminum with coordination numbers four, five, and six in the ratio 1:2:1 as determined by NMR. A kinetic model is proposed on the basis of the pressure dependence of the exchange rate and the heats of adsorption at adsorbed sites, evaluating by molecular orbital calculations. The adsorbed sites are assumed to be Lewis acid–base pairs composed of a coordinatively unsaturated aluminum and the adjacent unsaturated oxygen site. The site relating to the rate-determining step contains threefold aluminum, which is formed by unsaturation of fourfold aluminum at the surface. As a consequence, the exchange rate depends on the amount of fourfold aluminum when the alumina is heat treated and changes its phase.
A 13C NMR spectroscopy study of the structure of N-H pyrazoles and indazoles
Authors: Lopez Concepcion , Claramunt Rosa Ma. , Trofimenko Swiatoslaw , Elguero José
Published: May 2006

The 13C chemical shifts and some 1H–13C coupling constants of 23 pyrazoles and indazoles are reported and discussed. The spectra were recorded in CDCl3 and in DMSO-d6 solutions and, in several cases, also in the solid state (CP/MAS technique). These data allow us to determine the tautomerism of these compounds in the solid state (usually only one tautomer) and in solution. The position of the tautomeric equilibrium is related to the Hammett σm value of the 3(5)-substituent.
The reactions of 4-hydroxymethylsydnones with alcohols and benzene
Authors: Tien Ling-Ling , Lin Shaw-Tao , Tien Hsien-Ju , Fang Gwo-Ming
Published: May 2006

In the presence of a Lewis acid, 4-hydroxymethylsydnones undergo reaction with alcohols and benzene to form 4-alkoxysydnones 1a, bis(4-sydnonylmethyl) ethers 1b, or 4-benzylsydnones 1d depending upon the reaction conditions. At 0 °C, compounds 1a and 1b are formed from compound 1 in benzene and alkyl alcohol, respectively. Compound 1b is converted to compound 1d at 40 °C. When the reactions are carried out in a cosolvent of benzene and methyl alcohol at 40 °C, compound 1a is obtained preferentially and followed by conversion to compound 1d. The α-sydnonyl-methylene cation derived from either compound 1 or 1a is responsible for the formation of compound 1d.
Synthesis and biological evaluation of novel chiral non-racemic diaminoplatinum analogs based on a tetrahydropyran motif
Authors: Hanessian Stephen , Wang Jianguo
Published: May 2006

Mono and dihydroxy diamino tetrahydropyran derivatives, readily available from L-arabinose, were prepared and converted into the corresponding diamino cis-platinum analogs. The presence of hydroxy groups imparts water solubility and enhanced antitumor activity.
On the mechanism of Wittig reactions with cyclic anhydrides. II.
Authors: Kayser Margaret M. , Hatt Krista L. , Yu Heshui , Hooper Donald L.
Published: May 2006

A study by NMR spectroscopic methods and trapping experiments of the mechanism of Wittig reactions between stabilized phosphoranes and unsymmetrically substituted cyclic anhydrides suggests that two reactions are involved: (1) a low-energy, reversible formation of acyclic adducts; and (2) a higher energy "Wittig olefination" reaction leading to enol-lactones. The latter, more selective, transformation requires a more highly organized transition state in which π-stacking and stabilizing complexations are important factors.
Étude par spectrophotométrie UV d'aldéhydes et d'amides parahydroxycinnamiques. Comparaison de leurs capacités complexantes vis à vis de ZnBr2
Authors: Duran Hubert , Duran Elisabeth , Gorrichon Liliane , Perry Marcel
Published: May 2006

The ability of zinc salts to be complexed by cinnamaldehydes and N-pyridyl cinnamides has been investigated for modeling the active site of cinnamyl alcohol dehydrogenase (CAD), a zinc enzyme involved in the lignification process. Parahydroxycinnamaldehydes 4a–6a are specific substrates of the enzyme while cinnamides were synthesized as bidendate ligands towards zinc, and present inhibitory effects toward CAD. The interaction C=O … Zn was studied by UV methods and was observed in each example; the complexation constants are rather low with aldehydes (K = 3–16 L mol−1) and of the order (2–12) × 103 stronger with the corresponding cinnamides, due to the aminopyridine moiety participation. The stoichiometry of the complexes was found to be ML (M: salt, L: ligand) with mono substituted aldehydes and M2L with 5a or 6a, which was attributed to an additional complexation caused by the catechol effect. With the N-pyridylamides the complexation occurs according to a 1:1 (ML) or 1:2 (ML2) stoichiometry. Strong bathochromic effects were also observed; they are more important with the aldehydes than with the amides (cross conjugation). Bathochromic effects due to the substitution of the aromatic ring are shown by a relationship between the ligands and their zinc complexes.
Styrylbenzodiazinones 2. Chromo- et fluoroionophores dérivés du monoaza-15-couronne-5. Synthèse et structure
Authors: Cazaux Louis , Faher Mourad , Picard Claude , Tisnès Pierre
Published: May 2006

In connection with our work on styryl derivatives of benzodiazinones, we have prepared the 7-N,N-dimethylamino-3-methyl-1,4-benzodiazin-2-one 4a and two chromo- and fluoroionophores derived from the monoaza-15-crown-5 and styrylbenzodiazinones. A structural study of these compounds by 1H and 13C NMR, UV spectrophotometry, and molecular modelling was carried out. Unlike styrylbenzoxazinones, styrylbenzodiazinone derivatives showed a Z/E isomerization in acetonitrile solution. The isomerization was photoinduced, was catalysed by metallic ions, and was a reversible process. As well, an efficient alkylation reaction of the lactam function of benzodiazinones is described.
Novel access to (3R)- and (3S)-3-hydroxy-L-aspartic acids, (4S)-4-hydroxy- L-glutamic acid, and related amino acids
Authors: Hanessian Stephen , Vanasse Benoit
Published: May 2006

Derivatives of L-aspartic and L-glutamic acids can be converted into α-hydroxy acids via oxygenation of the corresponding enolates.
The synthesis and characterization of W(SeMes)4•THF (Mes = mesityl): a possible homoleptic mononuclear tungsten selenolate. Its reaction with CNtBu to yield (tBuNC)(MesSe)2W(μ-Se)2W(SeMes)2(CntBu)
Authors: Kraatz Heinz-Bernhard , Boorman P. Michael , Parvez Masood
Published: May 2006

The reaction of NaSeMes (Mes = mesityl, 2,4,6-(CH3)3C6H2) with WCl4(PPh2Me)2 in THF leads to the formation of W(SeMes)4•THF (1), a possible mononuclear tetrakis(selenolato) complex of tungsten. The identity of the red crystalline material has been confirmed by elemental analysis and NMR spectroscopic methods (1H, 13C, and 77Se NMR). The reaction of W(SeMes)4•THF with tert-butyl isocyanide results in the formation of (tBuNC)(MesSe)2W(µ-Se)2W(SeMes)2(CNtBu) (2). Compound 2 crystallized in the monoclinic space group C2/c (no. 15) with a = 23.933(2) Å,b = 16.776(2) Å, c = 15.595(2) Å, β = 122.98(2)°, and four formula units per unit cell. Refinement by full-matrix least squares gave final residuals of R = 0.038 and Rw = 0.028. The two metal centres in 2 are in a trigonal bipyramidal (tbp) coordination environment. The two tbps are connected via a common edge (axial–equatorial). The W—W bond length of 2.732(1) Å and the diamagnetism of 2 indicate the presence of a metal–metal bonding interaction.
Total synthesis of amphilectane-type diterpenoids: (±)-8,15-diisocyano-11(20)-amphilectene
Authors: Piers Edward , Llinas-Brunet Montse , Oballa Renata M.
Published: May 2006

A total synthesis of the structurally novel, antimicrobial diterpenoid (±)-8,15-diisocyano-11(20)-amphilectene (2) is described. Alkylation of 2-methoxycarbonyl-3-methylcyclohexanone (13) with (E)-1-(tert-butyldimethylsiloxy)-6-iodo-3-(trimethylstannyl)-2-hexene (14) provided, stereoselectively, the functionalized keto ester 15, which was converted efficiently into the diene 17. Diels–Alder reaction of 17 with acrolein, followed by base-catalyzed equilibration of the resultant product mixture, gave the aldehydes 19 (58%) and 20 (29%). Allylic oxidation of the alkene 24 (derived from 19) afforded the enone 25. Reduction (Na, NH3, t-BuOH) of 25 gave 28, which was converted, via a sequence of eight synthetic steps, into the diacid 45. Efficient transformation of the carboxyl functions of 45 into isonitrile groups completed the synthesis of (±)-2.
Oxidation of H2S to S by air with Fe(III)–NTA as a catalyst: catalyst degradation
Authors: Chen Dian , Motekaitis Ramunas J. , Martell Arthur E. , McManus Derek
Published: May 2006

The oxidation of H2S to S by air is represented by the overall reaction:[Formula: see text]The process is used with a catalyst for the removal of H2S from natural gas. A typical catalyst would be an iron(III) chelate system such as iron(III)–nitrilotriacetate (NTA is a tribasic acid, H3L, and NTA3− represents the trinegative anion). The catalyst reactions are[Formula: see text]The main difficulty with the process is the degradation of the metal chelate catalyst. Thus the Fe(II,III)–NTA system degrades through the formation of a number of weaker chelating agents and eventually to carbon dioxide, water, and ammonia. The degradation products identified are iminodiacetic acid (IDA), glycine, and oxalate. All of these degradation products were measured quantitatively by HPLC, and a degradation scheme is presented for the catalytic process. The fact that thiosulfate greatly decreases the degradation rate, and the fact that the degradation products were observed only in the stoichiometric reactions in which the ferrous NTA was oxidized by air, led to the interpretation that the hydroxyl radical or the superoxide radical ion is the reactive species that attacks the NTA and the intermediate degradation products and is responsible for the degradation of the organic ligands present.
The syntheses and vibrational spectra of tetrakis(carbonyl) palladium(II) and platinum(II) undecafluorodiantimonate(V), [Pd(CO)4][Sb2F11]2, and [Pt(CO)4][Sb2F11]2
Authors: Hwang G. , Wang C. , Aubke F. , Willner H. , Bodenbinder M.
Published: May 2006

The reductive carbonylation of either platinum(IV) fluorosulfate, Pt(SO3F)4, or palladium(III) fluorosulfate, Pd(SO3F)3, either in solution of fluorosulfuric acid, HSO3F, or in the solid state with CO at pressures of 0.5 to 2 atmospheres and at 25 °C, affords in high yield complexes of the type M(CO)2(SO3F)2, M = Pd or Pt. The square-planar complexes are readily converted by solvolysis in liquid antimony(V) fluoride in the presence of CO at a pressure of about 1 atmosphere to white, thermally stable, salts of the composition [M(CO)4][Sb2F11]2, M = Pd or Pt, which contain the novel, square-planar cations [Pd(CO)4]2+ and [Pt(CO)4]2+. The two cations exhibit the highest CO stretching frequencies reported so far, about 120 cm−1 higher than in free CO, which suggests the absence or near absence of π-back donation for the M—CO bond.
An analysis of vibronic coupling in the triplet absorption spectrum of pyrazine
Authors: Fischer Gad
Published: May 2006

New measurements of the singlet–triplet [Formula: see text] absorption spectra of pyrazine and pyrazine-d4 at longer pathlengths and higher vapour pressures have been recorded. Particular attention was paid to the hot band region to the red of the electronic origin. The activities of the out-of-plane vibrations, υ4 and υ10a, were identified in sequence bands, and their triplet state vibrational frequencies were determined, 295 (276, -d4) and 254 (194, -d4) cm−1, respectively. Model calculations were undertaken to match the observed singlet and triplet absorption and emission spectra for vibronic coupling induced by (i) υ10a(b1g), and (ii) υ4 and υ5(b2g). The calculations allowed the ordering and the relative energies of the higher lying triplet states to be determined. The 3B2u and 3B1u electronic states are above the ground electronic state by about 3.9 and 4.4 eV, respectively. The ordering is in analogy with the corresponding singlet states but opposite to that predicted by most theoretical calculations.
Proton transfer equilibrium reactions in some substituted 3H-indole probe molecules: role played by the TICT state
Authors: Sarpal Ranjit S. , Belletête Michel , Durocher Gilles
Published: May 2006

Five substituted derivatives of the main chromophore, 2-phenyl-3,3-dimethyl-3H-indole (1), have been studied over a wide range of acidity by UV absorption and steady state fluorescence spectroscopy. These are as follows: 2-[(p-amino)phenyl]-3,3-dimethyl-3H-indole (2), 2-[(p-dimethylamino)phenyl]-3,3-dimethyl-3H-indole (3), 2-[(p-amino)-phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole (4), 2-[(p-methylamino)phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole (5), and 2-[(p-dimethylamino)phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole (6). The dependence of absorption and fluorescence spectral characteristics upon acidity has allowed us to characterize four species, namely, the anion (A), the neutral molecule (N), the cation (C), and the dication (DC), for molecules 2 and 3. Molecules 4, 5, and 6 give rise to an additional anion due to the hydrolysis of the ester group. The relative order of protonations to available sites is discussed. The ring-protonated species have shown the Phc and indole rings to be coplanar in both the ground and first excited singlet states. A low-energy non-emissive twisted intramolecular charge transfer (TICT) state taking its origin in the dimethylamino moiety is suggested from INDO-S calculations to explain the strong fluorescence quenching of these ring-protonated species. Acidity constants for the various prototropic equilibria have been determined experimentally both in the ground and in the excited singlet states. Förster cycle calculations have been used to supplement the various equilibrium constants. Possible applications in organized assemblies are discussed.
Association of neutral red with micelles and its effect on the pKa
Authors: Dutta Robin K. , Bhat Subray N.
Published: May 2006

The interactions of neutral red with cationic surfactants, viz., N-hexadecylpyridinium chloride and alkyltrimethylammonium bromides; a nonionic surfactant, viz., Triton X100; and an anionic surfactant, viz., sodium dodecyl sulfate, were investigated spectroscopically. The equilibrium constants for the association of the indicator with the micelles were determined from the apparent association constants at constant pH at 298 K. The effects of the indicator-micelle association on the apparent pKa of the indicator in aqueous surfactant solutions are discussed. It was shown that the apparent pKa of the indicator in cationic surfactant solution can be predicted from knowledge of the indicator-micelle association constant.
Abductive networks: generalization, pattern recognition, and prediction of chemical behavior
Authors: Campbell John L.E. , Johnson Keith E.
Published: May 2006

Using commercially available software, it is possible to reduce numerical data to a mathematical representation called an abductive network (AN). In the current communication, we describe several simple examples which illustrate the interesting, and potentially useful properties of abductive networks. We show that when applied to the correlation of Kovats indices with molecular refractivities and dipole moments of substituted phenols, abductive networks more accurately predict Kovats indices than do counter-propagation neural networks or linear regression equations. When applied to the modeling of quantitative structure–activity relationships (QSAR) for local anesthetics, AN's are marginally superior to regression. AN's offer the advantage that correlations may be drawn between variables which are not easily related within a mathematical context.
Synthesis and characterization of 5,12-dimethyl-7,14-diphenyl-1,4,8,11- tetraazacyclotetradecane-4,11-diacetic acid and its transition metal complexes; crystal structure of the copper(II) complex of the macrocycle
Authors: Chen Liqin , Thompson Laurence K. , Bridson John N. , Xu Jide , Ni Shisheng , Guo Ruiping
Published: May 2006

The synthesis and characterization of a new 14-membered tetraazamacrocyclic ligand 5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetic acid (H2L1) is reported. Cobalt(III), nickel(II), and copper(II) complexes with this ligand were prepared and characterized by infrared, electronic, and electron spin resonance (esr) spectra and in one case by X-ray crystallography. The complex CuL1•2CH3CH2OH (3) crystallized in the triclinic system, space group[Formula: see text], with a = 8.440(2), b = 13.445(2), c = 7.523(1) Å, α = 99.30(1), β = 106.57(1), γ = 87.00(1)° and Z = 2 (R = 0.027, Rw = 0.028 for 2618 reflections). The complex shows a distorted trans-octahedral geometry with four amino nitrogens in a plane and two apical carboxylate oxygen donors.
Solvatochromic parameters and solubilities in supercritical fluid systems
Authors: O'Neill Mark L. , Kruus Peeter , Burk Robert C.
Published: May 2006

Spectroscopic studies of the compound 2-nitroanisole in supercritical fluids CO2 and N2O show that π* values vary linearly with density. The solubility trends in these single component supercritical fluid solvents qualitatively followed the trends in solvent power predicted from π*. However, the relative solvent power predicted for CO2 and N2O based on π* resulted in an opposite order to what was determined experimentally through solubility measurements. The π* parameter may be of some use for solubility prediction if only a limited set of solute–solvent systems are considered. Measurements of π*, especially those in binary supercritical fluid solvents, suggest that π* could be a valuable tool for probing the solute-organized cybotactic region.
Palladium(0)-catalyzed conversion of vinyl trifluoromethanesulfonates into α,β-unsaturated nitriles
Authors: Piers Edward , Fleming Fraser F.
Published: May 2006

Treatment (benzene, room temperature) of each of the vinyl trifluoromethanesulfonates 16–23 with dry lithium cyanide in the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium(0) and the crown ether 12-crown-4 provides good to excellent yields of the corresponding α,β-unsaturated nitriles 24–31.
X-ray structures of adducts of 1,2,5-triphenylphosphole with dimethyl acetylenedicarboxylate: a confirmation, a revision, and a new structure
Authors: Hocking Martin B. , Maarschalk Francies W. Van Der Voort
Published: May 2006

Dimethyl acetylenedicarboxylate was reacted with 1,2,5-triphenylphosphole under mild conditions, and four products isolated. Regardless of conditions used, every preparation gave low yields of dimethyl 3,6-diphenylphthalate coincident with loss of the phosphorus bridge. NMR data and X-ray crystal structures are provided for a yellow, and a red, 2:1 adduct. The yellow adduct, tetramethyl 1,6,7-triphenyl-6-phospha(V)-tricyclo[7.3.1.01,9]nona-3,5,7-triene-2,3,4,5-tetracarboxylate 6, crystallized in the triclinic space group [Formula: see text] (No. 2) with two molecules in the unit cell. Refinement (a = 11.259(1) Å, b = 12.947(3) Å, c = 13.784(3) Å, α = 112.25(2)°, β = 103.44(1)°, and γ = 101.80(1)°) converged at R = 0.0453 (Rw = 0.0453) for 537 parameters using 2880 reflections with I > 2σ(I). The red adduct, trimethyl 1,2,5-triphenylphosphoranylidene-4-methoxycyclopent-2-ene-5-one-2,3,4-tricarboxylate, an exocyclic phosphorane 8, crystallized in the monoclinic space group P21/c (No. 14) with four molecules in the unit cell. Refinement of this structure (a = 13.233(5) Å, b = 15.712(5) Å, c = 17.191(7) Å, α = 90°, β = 110.35(4)°, and γ = 90°) converged at R = 0.0916 (Rw = 0.0937) for 400 parameters using 2052 reflections with I > 2.5σ(I). Small amounts of a white or buff amorphous material, which could represent a polymeric product from the lost phosphorus bridge, were also obtained. Thermal rearrangement of the yellow adduct gave a colourless 6,5,3 tricyclic isomer 11, possibly via the isomeric cyclopropyl derivative 15 or the nine-membered phosphonin 7. The structure of 11 was confirmed by mild oxidation of the colourless rearrangement product to its P-oxide. This product, tetramethyl 2,3,6-triphenyl-2-phosphatricyclo[6.1.01,8.05,9]-2-oxonona-3,6-diene-1,7,8,9-tetracarboxylate 12, was also colourless. It crystallized in the orthorhombic space group Pbc21 (No. 29) with four pairs of molecules in the unit cell. Refinement of this structure (a = 8.918(1) Å, b = 22.605(4) Å, and c = 30.169(6) Å) converged at R = 0.0747 (Rw = 0.0757) for 321 parameters using 3255 reflections with I > 3σ(I). Unequivocal structures for these adducts and derivatives finally confirms, and establishes further understanding of, the complex reactions of the triphenylphosphole with dimethyl acetylenedicarboxylate.
Inhibitors of endo-α-mannosidase. Part I. Derivatives of 3-O-(α-D-glucopyranosyl)-D-mannopyranose
Authors: Spohr Ulrike , Bach Mimi , Spiro Robert G.
Published: May 2006

Golgi membrane endo-α-D-mannosidase releases the disaccharide αDGlc(1 → 3)DMan (34) from the GlcMan9GlcNAc2 oligosaccharide of immature N-linked glycoproteins. To convert the hydrolysis product 34 into a potent inhibitor of the enzyme, chemical modifications at the 1- and 2-positions of the mannose unit of 34 were performed. These include replacement of OH-1 by hydrogen (6), fluorine (12), and p-nitrophenoxy (5). Two potent inhibitors resulted, as reported recently, when both OH-1 and OH-2 of 34 were replaced by a double bond (glucal derivative 8) or replaced by hydrogen (1,2-dideoxy 9). 9 proved 40 times stronger as an inhibitor than 1-deoxy 6. However, further modifications at the 4- and 6-positions of 9, namely deoxygenation, methylation, and replacement of OH-6 by an amino group, were now found to largely abolish the activity, demonstrating that OH-4 and OH-6 of 9 are involved in H-bonding with the enzyme.
Colorimetric studies of the reduction of Fe3+ by coal
Authors: Martin Ronald R. , Li Jinjiang , MacPhee J. Anthony
Published: May 2006

The reduction of Fe3+ by coal surfaces has been followed colorimetrically. The kinetics of the reaction in coals with a relatively high O/C ratio are sensitive to mild air oxidation, those having a low O/C ratio are relatively insensitive.
Isotope effects in nucleophilic substitution reactions. IX. The effect of bond strength on substituent effects on the structure of SN2 transition states
Authors: Westaway Kenneth Charles
Published: May 2006

The effects of substituents on the structure of SN2 transition states suggested by kinetic isotope effects and Hammett ρ values are often different and, moreover, often do not agree with substituent effects predicted by current theories whether the change in substituent is made in the nucleophile, in the leaving group, or at the α-carbon. The importance of the strength of the reacting bonds in determining the effects of substituents on transition-state structure is investigated. A bond strength hypothesis that suggests there will be a significant change in the weaker reacting bond but little or no change in the stronger reacting bond in an SN2 transition state when a substituent in the nucleophile, the substrate, or the leaving group is altered in an SN2 reaction, predicts a high percentage of the experimental results.
Hydrophilic analogs of (R,R)-diaminocyclohexane dichloroplatinum (DACH) and the influence of relative stereochemistry on antitumor activity
Authors: Hanessian Stephen , Wang Jianguo
Published: May 2006

A series of analogs of (R,R)-1,2-diaminocyclohexane dichloroplatinum(II) (DACH) containing stereochemically defined hydroxy groups and appropriate acidic leaving groups were synthesized and tested as antitumor agents. The (1α,2β,3α,4β)-1,4-dihydroxy-2,3-diaminocyclohexane analog showed the highest potency against P388 leukemia in mice. The results indicate that increasing the hydrophilicity of the platinum complex to a certain extent could improve the antitumor activity of the drug. It is also likely that the stereochemical disposition of the substituents on the cyclohexane ring affects the antitumor activity.
Complexation of aqueous iodine by 18-crown-6
Authors: Hirsch Warren , Greenman Jonathan , Pizer Richard
Published: May 2006

The reaction of 18-crown-6 with aqueous iodine has been monitored by UV and visible spectrophotometry. The stability constant for the reaction has been determined as well as the spectra for the pure aqueous complex. This stability constant has been related to other equilibrium constants for the complexation of molecular iodine. The relation appears to predict correctly the stability constant for the iodine–water charge-transfer complex.
Synthesis of O-α-D-Rhap-(1 → 3)-O-α-D-Rhap-(1 → 2)-O-α-D-Rhap-(1 → 12)-oxydodecanoyl-bovine serum albumin
Authors: Zou Wei , Sen Asish K. , Szarek Walter A. , MacLean David B.
Published: May 2006

The title compound (19), a conjugate of a trisaccharide based upon the repeating trisaccharide of α-D-rhamnose, which comprises the polysaccharide portion of "A-band" lipopolysaccharide from a mutant (AK1401) of Pseudomonas aeruginosa, strain PAOl, with bovine serum albumin (BSA) was synthesized starting with methyl α-D-mannopyranoside. Suitably protected D-rhamnose derivatives, namely, ethyl 3,4-di-O-benzyl-1-thio-α-D-rhamnopyranoside (11) and 3-O-acetyl-2,4-di-O-benzyl-α-D-rhamnopyranosyl chloride (12), were used as the glycosyl acceptor and donor, respectively, in the synthesis of disaccharide 13. O-Deacetylation of 13 gave 14, a glycosyl acceptor that reacted with 12 to yield the trisaccharide 15. N-Iodosuccinimide – trifluoromethanesulfonic acid was used as an activator of the thioglycoside in the synthesis of 16 and 17 from 15. Compound 16 was converted into the hydrazide 18 by treatment with hydrazine. The conjugation was achieved by coupling of the intermediate acyl azide derivative of 18 with BSA.
Analysis of alkyl ketene dimer (AKD) by potentiometric titration
Authors: Nyarku S. , Sitholé B. Bruce
Published: May 2006

A simple and precise potentiometric titration method has been developed for the determination of milligram quantities of alkyl ketene dimer (AKD) in non-aqueous solvents. It involves the addition of chloroform solutions of AKD to an excess of an organic base followed by the titration of excess base with perchloric acid in glacial acetic acid. The method was used to determine non-reacted AKD extracted from hand-sheets: our results agreed with those obtained by capillary gas chromatography. The method was also used to monitor the stability of AKD formulations. Wood resin components and stearone, a hydrolysis product of AKD, do not interfere.
On the structure of S42+ and its formation from 2S2+•Ab initio SCF and CASSCF studies
Authors: Sannigrahi Mousumi , Grein Friedrich
Published: May 2006

Ab initio studies up to the MP2/6-31G* level were performed on the geometry and energy of S42+. Eleven different structures were considered. In the RHF/6-31G* method, the square structure is the most stable, followed by the trans-planar C2h structure. S42+ (square) is 105.9 kcal/mol less stable than 2S22+. Minimum energy paths were calculated for the reaction 2S2+ → S42+, both in C2v and D2h symmetry. Using RHF/6-31G*, the transition state lies about 50 kcal/mol above the energy of square planar S42+. Using CASSCF or MP2 methods this energy can be significantly lowered (to about 33 kcal/mol in MP2/6-31G*). Calculated vibrational frequencies for the square structure are also given and compared with experimental values.
Application of electrogenerated triphenylmethyl anion as a base for alkylation of arylacetic esters and arylacetonitriles and isomerization of allylbenzenes
Authors: Suzuki Shohei , Kato Mitsuko , Nakajima Shoichi
Published: May 2006

Phenylacetic esters and phenylacetonitriles were alkylated with alkyl halides, at the position α to an ester or nitrile, either at room temperature (20 °C) or at −78 °C, by making use of electrogenerated triphenylmethyl anion (trityl anion). Double-bond isomerization of allylbenzenes was also effectively accomplished by use of this electrogenerated base (EGB).