bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of alkali metal cations on the photoheterolysis of 9-cyclopropyl-9-fluorenol and the reactivity of the 9-cyclopropyl-9-fluorenyl cation in non-acidic zeolites
Authors: O'Neill Melanie A , Cozens Frances L
Published: July 2003

Alkali metal cation regulation of carbocation formation and reactivity in non-acidic zeolites is probed using the photoheterolysis reaction of 9-cyclopropyl-9-fluorenol. Nanosecond time-resolved diffuse reflectance is employed to directly observe the 9-cyclopropyl-9-fluorenyl cation as a transient species within the non-acidic zeolites. The efficiency of carbocation formation via photoheterolysis and the dynamics of other reaction pathways available to photoexcited 9-cyclopropyl-9-fluorenol are found to be strongly dependent on the zeolite alkali metal counterion. In particular, the yield of carbocation decreases with increasing counterion size in a manner consistent with the zeolite assisting the excited state CO bond cleavage via Lewis acid catalysis involving the metal cation. Zeolite encapsulation is also found to modulate the ability of water and methanol to assist photoheterolysis. For instance, the influence of coadsorbed water on the photoheterolysis reaction within zeolites is found to be highly sensitive to the alkali metal cation. The rate constant for intrazeolite decay of the 9-cyclopropyl-9-fluorenyl cation increases significantly as the alkali metal cation size increases and as the SiAl ratio decreases. These reactivity trends suggest that the intrazeolite decay of the 9-cyclopropyl-9-fluorenyl cation involves nucleophilic addition at the active site [Si-O-Al] bridges of the zeolite framework. In addition, the reactivity of the 9-cyclopropyl-9-fluorenyl cation within alkali metal zeolites can be regulated by the co-inclusion of reagents such as methanol, water, and 1,1,1,3,3,3-hexafluoro-2-propanol.Key words: cation-exchanged zeolites, 9-cyclopropyl-9-fluorenyl cation, laser photolysis, reactivity.
The photochemistry of 1-(3,5-dimethoxyphenyl)-2-(4-methoxyphenyl)ethyl ethanoate in alcohol solvents: A search for carbocation rearrangements
Authors: Roberts J C , Pincock J A
Published: July 2003

The photochemistry of the title compound 1 in methanol and 2,2,2-trifluoroethanol has been examined. In both solvents two ether products were obtained: one (18) resulting from trapping of the carbocation 2 (expected from photosolvolysis of 1), and the other (19) from the carbocation 3 (expected after rearrangement by hydride migration of cation 2). The substituted trans- and cis-stilbene derivatives 20 and 21 were also primary photoproducts. Analysis of product yields as a function of time revealed that the ether product 19 was formed by secondary photolysis of the stilbene derivatives, presumably by a pathway involving excited state protonation. Nanosecond laser flash photolysis results demonstrated that substituted trans-stilbene 20 was produced on the same time scale as the laser pulse.Key words: ester photochemistry, stilbene photoadditions, carbocation rearrangements.
Aminosilanes as two-electron donors: A technological application of radical cation chemistry
Authors: Gould Ian R , Godleski Stephen A , Zielinski Paul A , Farid Samir
Published: July 2003

Aminosilanes possess the appropriate structural features for use as two-electron sensitizers in silver halide photography. Here, we describe studies of the nucleophile-assisted cleavage reactions of the CSi bonds in their radical cations. Water is identified as a useful nucleophile. It is found that the kinetics of these reactions are best described by taking into account a radical cation  water complex. The cleavage reactions are also controlled by steric effects at silicon and by the proximity of a carboxylate group that can modify the nucleophilicity of the water. Cleavage forms an α-amino radical that can donate a second electron to 9,10-dicyanoanthracene as a solution-phase electron acceptor.Key words: silane, radical cation, two-electron sensitization, fragmentation, steric effects.
Photochemistry of rhodamine dye salts involving intra-ion-pair electron transfer
Authors: Jones II Guilford , Wang Xiaochun , Hu Jingqiu
Published: July 2003

The electron-transfer photochemistry of rhodamine 6G thiocyanate ion pairs has been investigated. For dye in a low polarity solvent, such as ethyl acetate, the emission of rhodamine 6G is significantly quenched by thiocyanate counterions. Laser photolysis of rhodamine 6G and thiocyanate in ethyl acetate was studied in detail with the identification of the reduced rhodamine 6G radical species (λmax = 410 nm). The growth and decay of the R6G radical could be accounted for in part by a mechanism involving initial formation of dye triplet followed by electron transfer which provides a triplet radical-pair state on a µs timescale.Key words: electron transfer, ion pair, rhodamine 6G, triplet state.
Generation and reactivity of the radical cations of coniferyl alcohol and isoeugenol in solution
Authors: Schepp N P , Rodríguez-Evora Y
Published: July 2003

Nanosecond laser flash photolysis of coniferyl alcohol and isoeugenol in acetonitrile leads to the formation of transient species that are identified as the corresponding radical cations. These radical cations decay with rate constants of ca. 1 × 106 s1 in dry acetonitrile. Both radical cations react rapidly with hydroxylic solvents like water and alcohols to give 4-vinylphenoxyl radicals, indicating that these reagents behave as bases rather than nucleophiles. In addition, anionic reagents (acetate, cyanide, and chloride) react rapidly with the radical cations with second-order rate constants that are close to diffusion controlled. The main products generated in the presence of the anionic reagents are again the 4-vinylphenoxyl radicals, suggesting that these reagents also behave as bases. The lifetime of the radical cations in acidic acetonitrile was found to increase dramatically due to a shift in the radical cation  vinyl phenoxyl radical acidbase equilibrium to the side of the radical cation. An estimate of the pKa of the radical cation in acetonitrile of 4.0 was obtained from the data.Key words: radical cations, laser flash photolysis, lignan, vinylphenols.
Cyclization of 5-hexenyl radicals from nitroxyl radical additions to 4-pentenylketenes and from the acyloin reaction
Authors: Henry-Riyad Huda , Tidwell Thomas T
Published: July 2003

Photochemical Wolff rearrangements were used to form 5-substituted-4-pentenylketenes 1a1d (RCH=CHCH2XCH2CH=C=O: 1a R = H, X = CH2; 1b R = Ph, X = CH2; 1c R = c-Pr, X = CH2; 1d R = H, X = O), which were observed by IR at 2121, 2120, 2119, and 2126 cm1, respectively, as relatively long-lived species at room temperature in hydrocarbon solvents. These reacted with the nitroxyl radical tetramethylpiperidinyloxyl (TEMPO, TO·) forming carboxy-substituted 5-hexenyl radicals 3, which were trapped by a second nitroxyl radical forming 1,2 diaddition products 4a4d. On thermolysis, 4a4d underwent reversible reformation of the radicals 3, which underwent cyclization forming cyclopentanecarboxylic acid derivatives 6 or 11 as the major products. However, in the case of 1b, the cyclopentane derivative was formed reversibly and on prolonged reaction times the only product isolated was PhCH=CH-(CH2)4CO2H (8b) from hydrogen transfer to Cβ and cleavage of the TEMPO group. Cyclopropylcarbinyl radical ring opening in the cyclized radical 5c from 1c led to the 2-(4-N-tetramethylpiperidinyloxybut-1-enyl)cyclopentane derivative 11 as the major product. In a test for 5-hexenyl radical ring closure in the radical anion intermediate of the acyloin condensation, the ester CH2=CH(CH2)3CO2Et (12a) gave the acyloin 13a (76%) as the only observed product, while PhCH=CH(CH2)3CO2CH3 (12b) with Na in toluene gave 21% of the acyloin product 13b and 42% of 2-benzylcyclopentanol (15) from cyclization of the intermediate radical anion.Key words: ketenes, free radical cyclization, TEMPO, acyloin condensation.
Intramolecular photosensitization of the pineneocimene rearrangement
Authors: McMahon Kevin , Wagner Peter J
Published: July 2003

Bonding of nopol to the para position of acetophenone produces 5,5-dimethyl-2-(2-(p-acetylphenoxy)ethyl)bicyclo[3.1.1]hept-2-ene 1, which contains two chromophores: a para-alkoxyacetophenone and an α-pinene, connected by a single methylene group. UV irradiation of 1 in both benzene and methanol produces none of the intramolecular [2 + 2] cycloaddition that most para-(3-buten-1-oxy)acetophenones undergo. Instead, the pinene unit rearranges to a triene skeleton identical to that of ocimene, a known photoproduct of pinene. At modest conversion the diene portion of the triene is cis but gradually is converted to a 52:48 trans:cis ratio. It is concluded that intramolecular triplet energy transfer from the excited ketone chromophore forms the 1,2-biradical triplet state of the pinene moiety, which then undergoes cyclobutylcarbinyl ring opening to a 1,4-biradical that cleaves to the 1,3,6-triene structure of ocimene. This mechanism is suggested to be responsible for the earlier reported intermolecularly sensitized rearrangement of α-pinene to the ocimene isomers.Key words: intramolecular energy transfer, triplet pinene, cyclobutylcarbinyl ring opening, photosensitization.
Controlling parameters for radical cation fragmentation reactions: Origin of the intrinsic barrier
Authors: Shukla Deepak , Liu Guanghua , Dinnocenzo Joseph P , Farid Samir
Published: July 2003

CC bond cleavages of radical cations of 2-substituted benzothiazoline derivatives were investigated to determine the parameters controlling the fragmentation rate constants. In spite of the low oxidation potentials of the compounds, fragmentation rate constants greater than 1 × 106s1could be achieved through weakening of the fragmenting bond by substituents that stabilize the radical fragment and exert steric crowding. A quantitative assessment of the relative roles of radical stabilization vs. steric effects to weaken the fragmenting CC bond was achieved through DFT calculations. The calculated activation enthalpies matched reasonably well with the experimentally determined values. A thermokinetic analysis revealed that the fragmentations of benzothiazoline radical cations have relatively large intrinsic kinetic barriers, ascribed to the delocalized nature of the product radical and cation fragments. Interestingly, the same factors that lead to the large intrinsic barriers led, simultaneously, to large thermodynamic driving forces for the fragmentations, which should lead to lower activation barriers. These effects oppose each other kinetically and provide important insight into the design of fast radical ion fragmentation reactions.Key words: benzothiazoline, radical cation, fragmentation, steric effects, DFT.
γ-Irradiation route to photoluminescent CdSCdSe with coreshell nanostructures under ambient conditions
Authors: Xu Fen , Zhang Xu , Lu Jun , Xi Wang , Hong Jie , Xie Yi
Published: July 2003

Photoluminescent CdSCdSe nanocomposites with coreshell structures were obtained via a novel two-step γ-irradiation process followed by a simple ion-exchange reaction at room temperature and under ambient pressure. To fully characterize CdSCdSe nanocomposites, X-ray photoelectron spectroscopy, UVvis absorption spectra, and photoluminescence spectra were recorded, as well as powder X-ray diffraction, transmission electron microscopy, and high-resolution electron microscopy, to confirm the presence of the coreshell nanostructure.Key words: coreshell nanostructure, γ-irradiation, ion-exchange reaction.
C-H···H-C interactions in organoammonium tetraphenylborates: another look at dihydrogen bonds
Authors: Robertson Katherine N , Knop Osvald , Cameron T Stanley
Published: July 2003

The crystal structures of the tetraphenylborates of the dabcoH+, guanidinium (MeCN solvate), and biguanidinium cations are shown to contain a variety of C-H···H-C dihydrogen (DB) bonds of nominally zero polarity, as well as a variety of N-H···N, C-H···N, N-H···Ph, and C-H···Ph hydrogen (HB) bonds. These intermolecular bonds have been characterized topologically after multipole refinement of the structures. The coexistence of the DBs and HBs in each of the structures makes it possible to establish their relative strength hierarchy. It also illustrates the importance of the DBs in satisfying the tendency of these structures to maximize the total intermolecular bonding engagement. To compare the above DBs with other DBs, the results of an extensive set of MP2/6-31G(d,p) calculations (supplied by I. Alkorta) were analyzed for reference correlations between the bond-critical parameters. Thus, for an X-H···H-Y bond, the difference Δε(H)m between the Mulliken charges on the H atoms in the uncomplexed X-H and H-Y components correlates quite well with the X-H···H-Y parameters and can be used for predicting the topological strength of an X-H···H-Y bond. The use of the difference Δε(H)c in the bond does not appear to change the correlation significantly; closer correlations are observed when the amount of charge transferred on formation of the H···H bond is used instead of Δε(H)m or Δε(H)c. Bonding interactions are obtained even between like or symmetry-related H atoms as a consequence of induced-dipole interactions, which accounts for the existence of the above intermolecular C-H···H-C bonds with d(H···H) = 2.182.57 Å, electron density at the bond-critical point of ~0.050.08 e/Å3, and a rough estimate of the H···H binding energy of ~1-5 kcal/mol. Examination of the bond-critical parameters of X-H···H-Y bonds also suggests a criterion of stability of these bonds with respect to the transition from non-shared (closed-shell) X-H···H-Y interaction to covalent (shared-shell) X···H-H···Y interaction. This transition appears to be discontinuous.Key words: bond-critical parameters, bond topology, dihydrogen bonds, hydrogen bonds, organoammonium tetraphenylborates.
The photo-NOCAS reaction: Trapping an intermediate
Authors: Borg Robert M , Franke Danielle , Vella Adrian
Published: July 2003

Irradiation of a mixture of 1,4-dicyanobenzene, phenanthrene, and 2,3-dimethyl-2-butene in acetonitrilemethanol solvent in the presence of acrylonitrile or methyl acrylate leads to a diversion from the usual photo-NOCAS product formation towards products that result from the formal addition of methanol and electrophilic alkenes to the butene.Key words: photo-NOCAS, photoinduced electron transfer, photosubstitution, photoaddition, redox photosensitization, alkene, 2-methoxyalkyl radical.
Stereoselective O2-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene
Authors: Saltiel Jack , Krishnamoorthy Govindarajan , Huang Zhennian , Ko Dong-Hoon , Wang Shujun
Published: July 2003

Irradiation of all-trans-1,6-diphenyl-1,3,5-hexatriene (ttt-DPH) in degassed acetonitrile (AN) gives ctt- and tct-DPH, relatively inefficiently, mainly via isomerization in the singlet excited state. The triplet contribution to the photoisomerization is small due to a very low intersystem crossing yield (ϕis = 0.01). Central bond isomerization is quenched in the presence of air by a factor of 1.4, consistent with the expected quenching of the lowest singlet and triplet excited states by oxygen. However, the presence of air enhances terminal bond photoisomerization by nearly twofold. Triplet-sensitized ttt-DPH photoisomerization favors tct-DPH formation and is quenched by oxygen. It follows that the interaction of singlet-excited ttt-DPH with O2 suppresses isomerization to tct-DPH but opens a new isomerization pathway to ctt-DPH. The presence of dimethylfuran, a singlet O2 trap, has no effect on the photoisomerization, eliminating the possible involvement of singlet O2 in this new reaction. ttt-DPH radical cations are ruled out as intermediates because the presence of fumaronitrile, which leads to their formation, suppresses both central and terminal bond photoisomerizations. In contrast to acetonitrile, ctt-DPH formation is quenched by oxygen in methylcyclohexane, suggesting the requirement of a polar environment. Strikingly different deuterium isotope effects distinguish the direct and O2-induced photoisomerization pathways. A comparative study of ttt-DPH-d0 with ttt-DPH-d2 and ttt-DPH-d4, involving deuteration of one and both terminal double bonds, reveals an inverse kinetic isotope effect (kHox/kDox = 0.92) for the O2-induced reaction. An attractive mechanism for the new oxygen-induced photoisomerization involves charge transfer from the S1 state of ttt-DPH to oxygen followed by collapse of the exciplex to either a zwitterionic or a biradicaloid species through bonding at one of the benzylic positions. Rotation about the new single bond in this intermediate followed by reversion to DPH and O2 gives the observed result. Key words: diphenylhexatrienes, trans-cis photoisomerization, oxygen sensitization.
The conformational behaviour of methylenecyclohexanes revisited
Authors: Muchall Heidi M , Kamya Petrina RN , Lessard Jean
Published: July 2003

Conformational analyses on 2-substituted (methoxy, vinyloxy, and acetoxy) methylenecyclohexanes have been performed computationally with HF, B3LYP, PBE0, and MP2 and the 6-31G(d) basis set. The global minimum for the methoxy substituent is an axial conformer. For the vinyloxy substituent, except with PBE0, an axial conformer is determined as the global minimum. The acetoxy substituent prefers the equatorial orientation. This sequence is in keeping with the operation of an "unsaturation effect" in addition to an anomeric effect. For a full conformational analysis, torsional potentials for the substituents have been generated, which show further low-energy minima, which affect the equilibrium composition. In general, axial conformers dominate the equilibria. To reproduce the experimentally observed predominance of equatorial conformers for vinyloxy and acetoxy substituents, PBE0 has to be employed. CSGT isotropic shielding tensors at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level have been employed for comparison with experimentally observed 13C chemical shifts.Key words: conformational analysis, methylenecyclohexanes, anomeric effect, unsaturation effect.
Canadensenes: Natural and semi-synthetic analogues
Authors: Shi Qing-Wen , Nikolakakis Anastasia , Sauriol Françoise , Mamer Orval , Zamir Lolita O
Published: July 2003

The first bicyclic taxanes isolated in the needles of the Canadian yew were named canadensene 1 and 5-epi-canadensene 2. Four additional analogues (36), isolated previously in Taxus chinensis and Taxus mairei, and a new natural 5-epi-canadensene analog 7 with a C-20-cinnamoyl group, were characterized for the first time in the needles of Taxus canadensis. A bicyclic derivative 8 with a docetaxel side chain on C-20 was synthesized using 5-epi-canadensene 2 as starting material. The lack of bioactivities of these bicyclic analogues (tubulin polymerization and cytotoxicities against human cancer cell lines) is discussed.Key words: Taxus canadensis, Taxaceae, taxanes, natural products, semi-synthesis.
Synthetic studies related to CP-225,917
Authors: Clive Derrick LJ , Sgarbi Paulo WM , He Xiao , Sun Shaoyi , Zhang Junhu , Ou Ligong
Published: July 2003

Synthetic studies related to CP-225,917 are described, including the preparation of the fully oxygenated tetracyclic central core 3.Key words: CP-225,917, siloxy-Cope rearrangement, Cope rearrangement, strain-assisted rearrangement, furan, ruthenium dioxide, bridgehead olefin.
Synthesis and characterization of a linked, π-π stacked organotin compound of 2-mercapto-6-nitrobenzothiazolyl diphenyltin chloride with 2-ethoxyl-6-nitrobenzothiazole
Authors: Ma Chunlin , Jiang Qin , Zhang Rufen
Published: July 2003

The new organotin compound, Ph2Sn(Cl)[S(C7H3N2O2S)]·[(C7H3N2O2S)OEt], assembled by an intermolecular aromatic benzothiazolebenzothiazole π-π stacking interaction, has been synthesized by the reaction of diphenyltin dichloride with 2-mercapto-6-nitrobenzothiazole. The title compound was characterized by elemental, IR, 1H NMR, and X-ray crystallography analyses. Single-crystal X-ray diffraction data reveals that the title compound has two different molecular components. The component Ph2Sn(Cl)[S(C7H3N2O2S)] has a pentacoordinate tin, which further forms an infinite one-dimensional chain by intermolecular non-bonded Cl···S interactions, resulting in an intercalation lattice that holds (C7H3N2O2S)OEt molecules. The formation of the molecule (C7H3N2O2S)OEt as well as its intercalated mechanism has also been discussed.Key words: organotin, assemble, π-π stacking interaction, 2-mercapto-6-nitrobenzothiazole, non-bonded interaction, crystal structure.
Dediazoniation of p-hydroxy and p-nitrobenzenediazonium ions in an aqueous medium: Interference by the chelating agent diethylenetriaminepentaacetic acid
Authors: Quintero B , Cabeza M C , Martínez M I , Gutiérrez P , Martínez P J
Published: July 2003

We have made a comparative study of the dediazoniation of p-hydroxy and p-nitrobenzenediazonium ions. The electron-withdrawing and donating properties of the -NO2 and -OH groups strongly determine the reactivity of both compounds, thus exerting different influences upon the dediazoniation reaction. We describe here how the decomposition of p-hydroxy and p-nitrobenzenediazonium ions in a neutral aqueous medium follows a different pattern in the presence of the metal-chelator diethylenetriaminepentaacetic acid (DTPA). The decomposition rate of p-hydroxybenzene diazonium decreases whilst the decomposition of the p-nitrobenzenediazonium ion is enhanced. The experimental data are discussed with reference to a common scheme of interference for both benzenediazonium ions in the light of the radical-scavenging capacity of DTPA.Key words: p-hydroxybenzenediazonium ion, p-nitrobenzenediazonium ion, di-ethylenetriaminepentaacetic acid, dediazoniation, radical scavenging, artifacts.
The 30 year anniversary of a seminal paper on radical ions in solution (Radical ions in photochemistry. I. The 1,1-diphenylethylene cation radical)
Authors: Pincock J A
Published: July 2003

This article was written to serve as an introduction to this issue of the Canadian Journal of Chemistry that honors the contributions to chemistry of Professor D.R. Arnold. It summarizes the observations reported in a communication that appeared in the Journal of the American Chemical Society 30 years ago in June 1973. This historically important communication laid the foundation for his program on the photochemical generation and reactivity of radical ions in solution and also served as a guide for a developing area of interest of many other research groups.Key words: photochemical electron transfer, radical cations, photo NOCAS, benzylic radicals.
Pressure and temperature dependence of the excess thermodynamic properties of binary dimethyl carbonate + n-octane mixtures
Authors: Lugo Luis , Comuñas María JP , López Enriqueta R , García Josefa , Fernández Josefa
Published: July 2003

In this work we report several excess thermodynamic properties for the dimethyl carbonate + n-octane system in an effort to better understand their behavior over wide temperature and pressure ranges. From previous experimental pVTx data for this system, the changes in the excess molar Gibbs energies, in the excess molar entropies, and in the excess molar enthalpies due to pressure have been determined over a wide temperature range and for pressures up to 25 MPa. A correlation of the excess volume as a function of pressure was used for each composition and temperature, together with a new, recently proposed equation for the excess molar volume as a function of temperature, pressure, and composition. Excess molar enthalpies and excess molar Gibbs energies at 298.15 K and for pressures up to 25 MPa were calculated using literature data at atmospheric pressure. Furthermore, the excess isothermal compressibility, the excess isobaric expansivity, and the excess internal pressure were calculated. The expression for the internal pressure of an ideal mixture suggested recently by Marczak has been used.Key words: excess thermodynamic properties, dimethyl carbonate, n-octane, high pressure.
Synthesis, characterization, and molecular structures of nitrosyl nitrito complexes of osmium porphyrins: Disproportionation of nitric oxide in its reaction with Os(P)(CO) (P = porphyrinato dianion)
Authors: Leal Felipe A , Lorkovic Ivan M , Ford Peter C , Lee Jonghyuk , Chen Li , Torres Lindsey , Khan Masood A , Richter-Addo George B
Published: July 2003

The Os(P)(NO)(ONO) compounds (P = TTP, TMP, OEP, TmTP; TTP = 5,10,15,20-tetra-p-tolylporphyrinato dianion, TMP = 5,10,15,20-tetramesitylporphyrinato dianion, OEP = octaethylporphyrinato dianion, TmTP = tetra(m-tolyl)porphyrinato dianion) have been prepared from the reaction of the precursor carbonyl complexes Os(P)(CO) with excess nitric oxide. Nitrous oxide was detected as a by-product of the reaction. The IR spectra of the Os(P)(NO)(ONO) compounds (as KBr pellets) reveal bands in the 17901804 cm1 range that are assigned to υNO. The IR spectra also reveal two new bands for each complex in the 14951531 and 913962 cm1 ranges indicative of O-bound nitrito ligands. The linearity of the bound NO groups and the O-binding of the trans nitrito ligands in the Os(P)(NO)(ONO) complexes are evident in the single-crystal X-ray crystal structures of the TTP and TMP derivatives. The kinetics of the reaction were studied by stopped-flow mixing techniques. Spectroscopic analysis of rapidly mixed solutions of Os(P)CO and NO in toluene showed a biphasic approach to the Os(P)(NO)(ONO) and N2O products, owing to the starting material Os(P)CO scavenging CO formed during the reaction to give Os(P)(CO)2 (KCO = 106 M1). The dicarbonyl was the only transient species observed. It is proposed that the rate-determining step of the reaction leading to Os(P)(NO)(ONO) is NO displacement of CO from Os(P)(CO) via initial formation of an unstable 19 electron Os(P)(NO)(CO) intermediate.Key words: osmium, nitric oxide, X-ray, nitrosyl, porphyrin, kinetics.
The dissolution of organic solvents from Amerlock 400 epoxy paint
Authors: Ball J M , Wren J C , Mitchell J R
Published: July 2003

The dissolution of organic solvents from containment coatings into the sump water is expected to be a key rate-controlling process, influencing the pH, the steady-state water radiolysis product concentration, and the formation of organic iodides in containment following a postulated reactor accident. The dissolution process is therefore an important component in modelling iodine behaviour in post-accident containment. The rate of release of ethyl benzene and m- and o-xylene from Amerlock 400 epoxy paint in contact with water has been measured. The release rate was found to be comparable to the release rate of methyl isobutyl ketone from various polyurethane, vinyl, and epoxy paints. The pseudo-first-order rate constant for dissolution of the solvents from these containment coatings is dependent only upon paint thickness and temperature, whereas the total amount of solvent released depends upon paint thickness. The solvent-release process is governed by the rate of uptake of water by the coupons, a Fickian diffusion-controlled process.Key words: dissolution, kinetics, organic solvents, paint.
2-Thiophen-2-ylbenzothiazole, -benzoxazole, and -benzimidazole platinum complexes
Authors: He Xiao-Feng , Vogels Christopher M , Decken Andreas , Westcott Stephen A
Published: July 2003

Oxidative cyclization of 2-aminothiophenol, 2-aminophenol, and 1,2-phenylenediamine with 2-thiophenecarboxaldehyde affords the corresponding 2-thiophen-2-ylbenzothiazole, -benzoxazole, and

-benzimidazole compounds. Addition of these ligands (L) to [PtCl2(coe)]2 (coe = cis-cyclooctene) gives complexes of the type trans-PtCl2L(coe) in moderate yields. Crystals of the benzothiazole derivative (1) were monoclinic, space group P2(1)/c, a = 11.561(4) Å, b = 15.335(15) Å, c = 11.769(4) Å, β = 105.182(5)°, Z = 4.Key words: platinum, imine, benzothiazole, benzoxazole, benzimidazole.
Determination of potential energy functions of argon, krypton, and xenon via the inversion of reduced-viscosity collision integrals at zero pressure
Authors: Goharshadi Elaheh K , JamiAlahmadi Mina , Najafi Bijan
Published: July 2003

The pair potential energy functions of argon, krypton, and xenon have been determined via the inversion of reduced-viscosity collision integrals at zero pressure. A comparison of the potentials with the previously determined potentials are included. The viscosity and thermal conductivity of argon, krypton, and xenon at different temperatures and pressures have been calculated and compared with experimental values. The present potentials for argon, krypton, and xenon provide a good overall account of the experimental properties of these compounds, considering the stated uncertainty in the measurements.Key words: potential energy function, collision integral, viscosity, thermal conductivity.
Comparative analysis of theBradyrhizobium japonicum sucAregion
Authors: Green Laura S , Waters James K , Ko Shanelle , Emerich David W
Published: July 2003

To study the adjustments made to the tricarboxylic acid cycle during symbiosis of nitrogen-fixing rhizobia with their host legumes, we have characterized the genes encoding the α-ketoglutarate dehydrogenase enzyme complex in Bradyrhizobium japonicum. The genes were arranged in the order sucA-sucB-scdA-lpdA, where scdA represents a short-chain dehydrogenase gene (GenBank accession No. AY049030). All four genes appeared to be co-transcribed, an arrangement that is so far unique to B. japonicum. The mdh gene, encoding malate dehydrogenase, was located upstream of the sucA operon, and its primary transcript appeared to be monocistronic. Primer extension indicated that the sucA operon and mdh were transcribed from typical housekeeping promoters.Key words: nitrogen fixation, Bradyrhizobium, α-ketoglutarate dehydrogenase, sucA.
Marinobacter lutaoensissp. nov., a thermotolerant marine bacterium isolated from a coastal hot spring in Lutao, Taiwan
Authors: Shieh Wung Yang , Jean Wen Dar , Lin Yu-Te , Tseng Min
Published: July 2003

A heterotrophic and thermotolerant marine bacterium, designated strain T5054, was isolated from a hot spring on the coast of Lutao, Taiwan. It was a strictly aerobic, Gram-negative rod. Cells grown in broth cultures were non-spore-forming and motile by means of one to several polar flagella. It seems that pilus-like structures were produced from both poles of the cells. Strain T5054 required Na+for growth and exhibited optimal growth at about 45°C, pH 7, and 35% NaCl. It contained iso-C15:0as the most abundant fatty acid and ubiquinone-8 as the only isoprenoid quinone. Its genomic DNA G+C content was 63.5 mol%. The strain did not require vitamins or other organic growth factors, and it grew on glucose, mannitol, and a variety of organic acids and amino acids as sole carbon sources. Characterization data, together with the results of a 16S rDNA-based phylogenetic analysis, indicated that strain T5054 could be classified as a new species in the genus Marinobacter. The name Marinobacter lutaoensis sp. nov. is proposed for this new bacterium. The type strain is T5054 (CCRC 17087; JCM 11179).Key words: Marinobacter lutaoensis, thermotolerant bacteria, halophile, marine bacteria.
Characterization of an antifungal soil bacterium and its antagonistic activities againstFusariumspecies
Authors: Chan Yiu-Kwok , McCormick Wayne A , Seifert Keith A
Published: July 2003

Bacteria were isolated from a cultivated soil and screened for antagonistic activity against Fusarium graminearum, a predominant agent of ear rot and head blight in cereal crops. Based on its in vitro effectiveness, isolate D1/2 was selected for characterization and identified as a strain of Bacillus subtilis by phenotypic tests and comparative analysis of its 16S ribosomal RNA gene (rDNA) sequence. It inhibited the mycelial growth of a collection of common fungal phytopathogens, including eight Fusarium species, three other ascomycetes, and one basidiomycete. The cell-free culture filtrate of D1/2 at different dilutions was active against macroconidium germination and hyphal growth of F. graminearum, depending on the initial macroconidium density. It induced the formation of swollen hyphal cells in liquid cultures of this fungus grown from macroconidia. A bioassay also demonstrated that D1/2 offered in planta protection against the damping-off disease in alfalfa seedlings caused by F. graminearum, while the type strain of B. subtilis was ineffective. Hence, B. subtilis D1/2 or its culture filtrate has potential application in controlling plant diseases caused by Fusarium.Key words: antifungal activity, Bacillus subtilis, biological control, biopesticide, Fusarium species.
Release and regeneration of protoplasts from the fungus Trichothecium roseum
Authors: Balasubramanian N , Juliet G Annie , Srikalaivani P , Lalithakumari D
Published: July 2003

A protocol for isolating and regenerating protoplasts from Trichothecium roseum has been described. Protoplasts from T. roseum were isolated using (i) a lytic enzyme combination composed of Novozym 234, chitinase, cellulase, and pectinase at a 5-mg/mL concentration and (ii) 0.6 M KCl as an osmotic stabilizer. A maximum number of 28 × 104 protoplasts/mL were obtained at pH 5.5. Experiments on the regeneration and reversion of protoplasts revealed a maximum regeneration (60.8%) in complete medium (potato dextrose  yeast extract agar) amended with 0.6 M KCl. The regenerated protoplasts were similar to the original parent strain in morphology, pigmentation, growth, and sporulation.Key words: Trichothecium roseum, protoplast, isolation, regeneration, lytic enzymes, osmotic stabilizers.
Characterization of the sodF gene region of Frankia sp. strain ACN14a and complementation of Escherichia coli sod mutant
Authors: Maréchal Joëlle , Santos Renata , Hammad Yasser , Alloisio Nicole , Domenach Anne-Marie , Normand Philippe
Published: July 2003

The Frankia sp. strain ACN14a superoxide dismutase SodF was previously shown to be induced in response to Alnus glutinosa root exudates, and its gene was sequenced. We report here the sequence of the 9-kb genomic segment surrounding the sodF gene and further characterize this gene and its product. Nine ORFs coding for various proteins, such as regulators, acetyl-CoA transferases, and a bacterioferritin A next to the sodF gene, were found. Northern blot analysis showed that the sodF gene was expressed as a major 1-kb transcript, which indicates that it has its own promoter. The sodF gene strongly complemented an Escherichia coli triple mutant (sodA sodB recA), restoring aerobic growth when the gene was expressed from the synthetic tac promoter but when expressed from its own promoter showed only slight rescue, suggesting that it was poorly recognized by the E. coli RNA polymerase. It is noteworthy that this is the first time that a Frankia gene has been reported to complement an E. coli mutant. The superoxide dismutase activity of the protein was inactivated by hydrogen peroxide, indicating that the metal ligand is iron, which is supported by analysis of the protein sequence. Thus, the SodF protein induced in Frankia by root exudates is an iron-containing enzyme similar to the one present in the nodules.Key words: Frankia, iron superoxide dismutase, sodF, E. coli complementation.
Transforming the sapstaining fungus Ophiostoma piceae with Agrobacterium tumefaciens
Authors: Tanguay Philippe , Breuil Colette
Published: July 2003

A transformation protocol mediated by Agrobacterium tumefaciens is described for the sapstaining fungus Ophiostoma piceae. We compared transformants obtained from Agrobacterium with those obtained from yeast-like cells made into spheroplasts and treated with CaCl2. For all putative transformants analyzed, Southern hybridization confirmed that the hygromycin resistance gene had been integrated into the genomic DNA. While all transformants obtained from the treated spheroplasts had multiple copy vector insertion, 85% of the Agrobacterium-mediated transformants had single copy vector insertion.Key words: Ophiostoma piceae, genetic transformation, Ti plasmid.
A phylogenetic analysis of the pSymB replicon from the Sinorhizobium meliloti genome reveals a complex evolutionary history
Authors: Wong K , Golding G B
Published: July 2003

Microbial genomes are thought to be mosaic, making it difficult to decipher how these genomes have evolved. Whole-genome nearest-neighbor analysis was applied to the Sinorhizobium meliloti pSymB replicon to determine its origin, the degree of horizontal transfer, and the conservation of gene order. Prediction of the nearest neighbor based on contextual information, i.e., the nearest phylogenetic neighbor of adjacent genes, provided useful information for genes for which phylogenetic relationships could not be established. A large portion of pSymB genes are most closely related to genes in the Agrobacterium tumefaciens linear chromosome, including the rep and min genes. This suggests a common origin for these replicons. Genes with the nearest neighbor from the same species tend to be grouped in "patches". Gene order within these patches is conserved, but the content of the patches is not limited to operons. These data show that 13% of pSymB genes have nearest neighbors in species that are not members of the Rhizobiaceae family (including two archaea), and that these likely represent genes that have been involved in horizontal transfer. Key words: Sinorhizobium meliloti, horizontal transfer, pSymB evolution.
Relative importance of the endomycorrhizal and (or) ectomycorrhizal associations in Allocasuarina and Casuarina genera
Authors: Duponnois R , Diédhiou S , Chotte J L , Sy M Ourey
Published: July 2003

This work was carried out to determine the relative importance of the endomycorrhizal and (or) ectomycorrhizal association in species of Casuarina and Allocasuarina. Under axenic conditions, Pisolithus and Scleroderma isolates formed ectomycorrhizas with a mantle and a Hartig net on Allocasuarina verticillata but failed to form a Hartig net on Casuarina glauca. In a controlled soil system, C. glauca was inoculated with the endomycorrhizal fungus Glomus intraradices Schenck & Smith, and A. verticillata was inoculated with Pisolithus albus IR100 Bougher & Smith and (or) G. intraradices. Both symbionts significantly stimulated growth in both plant species. For A. verticillata, its growth response to ectomycorrhizal inoculation was higher than to endomycorrhizal inoculation. When both symbionts were inoculated, antagonism among the fungal isolates was observed with a higher ectomycorrhizal colonization. These results showed that A. verticillata was ectomycorrhizal dependent, whereas C. glauca was endomycorrhizal dependent. From a practical point of view, this study shows the importance of selecting compatible mycorrhizal fungi for developing successful inoculation programmes. In addition, it would help to further research and determine the effect of ecto- and endo-mycorrhizal symbiosis on the formation and function of N2-fixing actinorhizal nodules.Key words: Casuarinaceae, ectomycorrhizas, arbuscular mycorrhizas, plant growth.
Release of Ni and Co by microbial activity in New Caledonian ultramafic soils
Authors: Amir Hamid , Pineau René
Published: July 2003

A high positive correlation was found between extractable Ni and Co contents and microbial activity of 40 ultramafic soil samples from New Caledonia, suggesting a possible role of microorganisms in the release of these two metals. A saprolite (ultramafic subsoil) and a hypermagnesian brown soil were incubated 9 months in different conditions. Ni and Co release, measured by their extractability, occurred without reduction of soil pH but did not occur when the native microflora was eliminated by heat treatment. However, when autoclaved soil was re-inoculated with a pinch of the same nonheated soil, the release of metals was recorded. The concentrations of extractable Ni and Co were much higher in soils amended with organic compounds in which microbial activity was enhanced, but only if the soil was not heat treated. The presence of Grevillea exul, a metal-tolerant plant, stimulated the metal release process, but the stimulation was less effective than it was in the compost-amended soil without plant. The influence of the plant in extractable Ni and Co contents in this amended soil was not significant. The release of the two metals therefore seemed to be induced by the activity of specialized organotrophic microorganisms.Key words: Co, Ni, metal release, microbial activity, ultramafic soils.
Bacterial extracellular protease activities in field soils under different fertilizer managements
Authors: Watanabe Katsuji , Sakai Jyunich , Hayano Koichi
Published: July 2003

The major extracellular endopeptidase from Bacillus subtilis PF212 (isolated from paddy field soil) and B. subtilis CF80 (isolated from upland field soil) belongs to the group of serine proteases produced by Bacillus spp. known as subtilisins (optimum pH 7.0, optimum temperature 60°C, and molecular mass 28 kDa). The NH2-terminal amino acid sequence (20 amino acids) of the endopeptidase from (i) strain CF80 was identical with that of subtilisin BPN' and (ii) strain PF212 was identical with that of subtilisin Amylosacchariticus. The properties (i.e., effect of inhibitors) of these endopeptidases were similar to those of the overall soil endopeptidase and soil endopeptidases extracted from paddy field soil. From the numbers of B. subtilis we isolated from paddy fields and found to produce a subtilisin-like serine protease, it seemed possible to consider that subtilisin was one of the soil endopeptidases in paddy field soils. The major extracellular endopeptidase from Serratia marcescens (strains 4-12-132, 4-12-131, and 4-60-110) isolated from upland field soils applied with animal slurry is a serratial metalloprotease (optimum pH 9.5, optimum temperature 40°C, and molecular mass 50 kDa). The NH2-terminal amino acid sequence (20 amino acids) of the endopeptidase from strain 4-12-132 was identical with that of serratial metalloprotease, and partial DNA sequence of the endopeptidase gene of S. marcescens 4-12-132 had high homology with that of the serratial metalloprotease gene. The properties (i.e., effect of inhibitors) of this endopeptidase were similar to those of the overall soil endopeptidase in upland fields applied with animal slurry. Thus, it was possible to consider that serratial metalloprotease was one of the soil endopeptidases in upland fields applied with animal slurry.Key words: subtilisin, serratial metalloprotease, soil endopeptidase, proteolytic bacteria.
Chromosome DNA fragmentation and excretion caused by defective prophage gene expression in the early-exponential-phase culture ofBacillus subtilis
Authors: Shingaki Ryuji , Kasahara Yasuhiro , Inoue Tetsuyoshi , Kokeguchi Susumu , Fukui Kazuhiro
Published: July 2003

Bacillus subtilis 168 and its major autolysin mutant, AN8, were shown to excrete two size classes of DNA when cultured in LuriaBertani medium. Pulsed-field gel electrophoresis of DNA harvested from the cell surface demonstrated the presence of 13-kb-long and circa 50-kb-long strands. Restriction digestion of both sizes of DNA resulted in a smearing pattern, as observed by agarose gel electrophoresis. Shotgun sequencing of DNase I partial digests of 50-kb DNA fragments revealed that the strands originate from various sites on the chromosome. SDSPAGE analysis of cell surface fractions and culture supernatants demonstrated the presence of several proteins that were thought to be associated with the DNA. Of these, three major proteins were identified, i.e., XkdG, XkdK, and XkdM, by tandem mass spectrometry, all of which were proteins of a defective prophage PBSX residing in the Bacillus subtilis chromosome. Disruption of these PBSX genes resulted in a reduction of 13-kb fragment generation and excretion and also a great reduction of 50-kb fragment excretion. Electron microscopy showed that a few mature phages and numerous membrane vesicle-like particles existed in the cell surface fractions of strain 168. The present findings suggest that the spontaneous generation and excretion of chromosome DNA fragments in Bacillus subtilis are both closely related to the expression of defective prophage genes.Key words: chromosome fragmentation, DNA excretion, defective prophage, PBSX, horizontal gene transfer.
Characterization of group B streptococcal glyceraldehyde-3-phosphate dehydrogenase: surface localization, enzymatic activity, and proteinprotein interactions
Authors: Seifert Kyle N , McArthur William P , Bleiweis Arnold S , Brady L Jeannine
Published: July 2003

During characterization of the surface antigens of serotype III group B streptococci (GBS), a protein with an apparent Mr~ 173 500 migrating on a SDS  polyacrylamide gel was found to have an N-terminal amino acid sequence identical to that of the plasmin receptor (Plr) of group A streptococci, a surface-localized glyceraldehyde-3-phosphate dehydrogenase (GAPDH). This work begins to characterize GBS GAPDH and to assess its functional activity on the cell surface. The 1.0-kb gapC gene of GBS was amplified by PCR. plr and gapC demonstrated 87% homology. An anti-Plr monoclonal antibody reacted with GBS whole cells, suggesting GBS GAPDH is surface localized. Multiple serotypes of GBS demonstrated functional GAPDH on their surfaces. The anti-Plr monoclonal antibody recognized GBS protein bands of approximately 41 and 173.5 kDa, by Western blot. Presumably, these represent monomeric and tetrameric forms of the GAPDH molecule. GBS GAPDH was demonstrated by Western blot analysis to interact with lys- and glu-plasminogens. Fluid-phase GBS GAPDH interacted, by means of ELISA, with immobilized lys-plasminogen, glu-plasminogen, actin, and fibrinogen. Enzymatically active GAPDH, capable of binding cytoskeletal and extracellular matrix proteins, is expressed on the surface of GBS.Key words: group B streptococci, glyceraldehyde-3-phosphate dehydrogenase.
Toxic effects caused by heavy metals in the yeast Saccharomyces cerevisiae: a comparative study
Authors: Soares Eduardo V , Hebbelinck Kristel , Soares Helena MVM
Published: July 2003

The decreasing order of toxicity of select heavy metals on the yeast Saccharomyces cerevisiae, in 10 mM MES (2-(N-morpholino)ethanesulfonic acid) pH buffer at pH 6.0, was found to be copper, lead, and nickel. Heavy metal (200 µM) induced a decrease in the number of viable cells by about 50% in the first 5 min for copper and in 4 h for lead, while nickel was not toxic up to a 200 µM concentration over a period of 48 h. Glucose (25 mM) strongly enhanced the toxic effect of 50 µM copper but had little or no effect on the toxicity of 200 µM lead or nickel. Copper, lead, and nickel induced the leakage of UV260-absorbing compounds from cells with different kinetics. The addition of 0.5 mM calcium, before addition of 200 µM copper, showed a protective action against cell death and decreased the release of UV-absorbing compounds, while no effect was observed against lead or nickel toxic effects. Copper complexation capacities of the filtrates of cells exposed for 2 h in 200 µM copper and 24 h in 200 µM lead were 51 and 14 µM, respectively. The implication of the complexation shown by these soluble compounds in the bioavailability of heavy metals is discussed.Key words: copper, lead, nickel, metal bioavailability, toxicity.