bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulatory Genes Controlling Fatty Acid Catabolism and Peroxisomal Functions in the Filamentous Fungus
Aspergillus nidulans
Authors: Hynes Michael J. , Murray Sandra L. , Duncan Anna , Khew Gillian S. , Davis Meryl A.
Published: May 2006

The catabolism of fatty acids is important in the lifestyle of many fungi, including plant and animal pathogens. This has been investigated in
Aspergillus nidulans
, which can grow on acetate and fatty acids as sources of carbon, resulting in the production of acetyl coenzyme A (CoA). Acetyl-CoA is metabolized via the glyoxalate bypass, located in peroxisomes, enabling gluconeogenesis. Acetate induction of enzymes specific for acetate utilization as well as glyoxalate bypass enzymes is via the Zn
2
-Cys
6
binuclear cluster activator FacB. However, enzymes of the glyoxalate bypass as well as fatty acid beta-oxidation and peroxisomal proteins are also inducible by fatty acids. We have isolated mutants that cannot grow on fatty acids. Two of the corresponding genes,
farA
and
farB
, encode two highly conserved families of related Zn
2
-Cys
6
binuclear proteins present in filamentous ascomycetes, including plant pathogens. A single ortholog is found in the yeasts
Candida albicans
,
Debaryomyces hansenii
, and
Yarrowia lipolytica
, but not in the
Ashbya
,
Kluyveromyces
,
Saccharomyces
lineage. Northern blot analysis has shown that deletion of the
farA
gene eliminates induction of a number of genes by both short- and long-chain fatty acids, while deletion of the
farB
gene eliminates short-chain induction. An identical core 6-bp in vitro binding site for each protein has been identified in genes encoding glyoxalate bypass, beta-oxidation, and peroxisomal functions. This sequence is overrepresented in the 5′ region of genes predicted to be fatty acid induced in other filamentous ascomycetes,
C. albicans
,
D. hansenii
, and
Y. lipolytica
, but not in the corresponding genes in
Saccharomyces cerevisiae.
The SUMO Pathway Is Developmentally Regulated and Required for Programmed DNA Elimination in
Paramecium tetraurelia
Authors: Matsuda Atsushi , Forney James D.
Published: May 2006

Extensive
genome-wide remodeling occurs during the formation of the somatic
macronuclei from the germ line micronuclei in ciliated protozoa. This
process is limited to sexual reproduction and includes DNA
amplification, chromosome fragmentation, and the elimination of
internal segments of DNA. Our efforts to define the pathways regulating
these events revealed a gene encoding a homologue of ubiquitin
activating enzyme 2 (
UBA2
) that is upregulated at the onset of
macronuclear development in
Paramecium tetraurelia
. Uba2
enzymes are known to activate the protein called small
ubiquitin-related modifier (SUMO) that is covalently attached to target
proteins. Consistent with this relationship, Northern analysis showed
increased abundance of
SUMO
transcripts during sexual
reproduction in
Paramecium
. RNA interference (RNAi) against
UBA2
or
SUMO
during vegetative growth had little
effect on cell survival or fission rates. In contrast, RNAi of mating
cells resulted in failure to form a functional macronucleus. Despite
normal amplification of the genome, excision of internal eliminated
sequences was completely blocked. Additional experiments showed that
the homologous
UBA2
and
SUMO
genes in
Tetrahymena
thermophila
are also upregulated during conjugation. These results
provide evidence for the developmental regulation of the SUMO pathway
in ciliates and suggest a key role for the pathway in controlling
genome
remodeling.
Expression of the
Candida albicans
Morphogenesis Regulator Gene
CZF1
and Its Regulation by Efg1p and Czf1p
Authors: Vinces Marcelo D. , Haas Christopher , Kumamoto Carol A.
Published: May 2006

The ability of
Candida albicans
to transit between different cellular morphologies is believed to be important for virulence. Morphological transitions occur in response to a variety of environmental signals. One such signal is encountered when cells are grown in a semisolid matrix. An important regulator of cellular morphology is the putative transcription factor
CZF1
. Here we demonstrate that transcription of
CZF1
is responsive to growth parameters such as the temperature, carbon source, growth phase of cells, and the physical environment. In wild-type cells, a
CZF1
transcript of about 4 kb was expressed when cells were grown embedded in semisolid agar medium, as well as in late exponential phase when cells were grown in liquid medium. Deletion of
EFG1
, a key regulator of morphogenesis, abolished
CZF1
expression. Overexpression of
CZF1
revealed that this gene also autoregulates its expression. Efg1p and Czf1p were shown by chromatin immunoprecipitation to act by binding to the promoter of
CZF1
. The coupling of environmental cues to the expression of a morphogenetic transcription factor may allow
C. albicans
to coordinate morphogenesis in response to specific conditions encountered in the human host.
Stress by Heat Shock Induces Massive Down Regulation of Genes and Allows Differential Allelic Expression of the Gal/GalNAc Lectin in
Entamoeba histolytica
Authors: Weber Christian , Guigon Ghislaine , Bouchier Christiane , Frangeul Lionel , Moreira Sandrine , Sismeiro Odile , Gouyette Catherine , Mirelman David , Coppee Jean Yves , Guillén Nancy
Published: May 2006

Gene expression analysis by microarray assay revealed that when exposed to stress,
Entamoeba histolytica
exhibits a specific heat shock response, together with a dramatic overall reduction in gene transcription as well as differential allelic expression of key genes participating in virulence, such as the galactose/
N
-acetylgalactosamine (Gal/GalNAc) lectin.
Morpholines: stereochemistry and preferred steric course of quaternization
Authors: Jones Alan J. , Beeman C. P. , Hasan M. U. , Casy A. F. , Hassan M. M. A.
Published: May 2006

The 13C magnetic resonance spectra of a series of methyl and phenyl substituted morpholines, their hydrochlorides, and methiodides have been determined. The effects of methyl substitution adjacent to oxygen and nitrogen are reasonably equivalent and substituent induced chemical shift parameters derived for the series show favorable agreement with those previously observed in both alicyclic and heterocyclic systems. Results for the cis and trans isomers of phendimetrazine (3,4-dimethyl-2-phenylmorpholine), confirm the preferred chair conformations and configurations cis-3-CH3, cis-2-phenyl (cis) and trans-3-CH3, cis-2-phenyl (trans) for these isomers. The preferred course of quaternization of nitrogen in these systems was determined as axial, using deuteriomethyliodide as a label. This 13C–2H technique relies on the observation of the γ-syn-axial effect and is clearly unambiguous and superior to other methods used in evaluating this mechanism. Product ratios and consequently free energies of this reaction were measured from proton and deuterium nmr spectra.
Mercury(I) chemistry. Part II. Reactions of the mercurous ion with some ligands having the heavier Group VA or VIA elements as donor atoms
Authors: Dean Philip A. W. , Ibbott David G.
Published: May 2006

The reactions of Hg2(AsF6)2 with P(CF3)3, PF3, PCl3, P(CF3)Ph2, PClPh2, PPh3, P(OMe)3, AsPh3, SbPh3, SPPh3, SP(p-C6H4F)3, and SePPh3 in liquid sulfur dioxide have been studied. The last five ligands form insoluble 1:1 complexes, Hg2(AsF6)2•L, if L:Hg22+ ≤ 1, but disproportionation of the mercurous ion occurs if L:Hg22+ > 1; the 1:1 mercurous complexes have been characterized by analysis and vibrational spectroscopy. There is no evidence for complexation of P(CF3)3. PPh3 and P(OMe)3 cause disproportionation of the mercurous ion under all conditions; Hg(PPh3)22+ and Hg(P(OMe)3)22+ have been characterized by 13C and 1H nmr respectively. When P(CF3)Ph2:Hg22+ ≤ 1 soluble Hg2(P(CF3)Ph2)2+ is formed; the 19F and 13C nmr spectra of this complex are reported, as are those of Hg(P(CF3)Ph2)22+. In the system PF3–Hg2(AsF6)2–SO2 no disproportionation occurs; 19F nmr provides evidence that Hg2PF32+ and, probably, Hg2(PF3)22+ are formed. 1J(P–F) in mercurous and silver(I) complexes of PF3 is of unusually large magnitude. The 13C nmr spectra of Hg(PPh3)22+, Hg2(P(CF3)PPh2)2+, and Hg(P(CF3)Ph2)22+, are consistent with the occurrence of little metal-to-phosphorus back-bonding in these phosphine complexes. The relationship between the net electron donating ability of a phosphine and the nature of its interaction with the mercurous ion is discussed.
The environment of tertiary alcohols from nuclear magnetic resonance spectral shifts on formation of trichloroacetylcarbamates
Authors: Taylor David R.
Published: May 2006

Reaction of tertiary alcohols with trichloroacetylisocyanate causes a marked downfield shift of the nmr signals of protons β to the hydroxyl group. This can be used to reveal the presence of methyl groups adjacent to a tertiary hydroxyl group and of other β protons which are sufficiently deshielded to be observed. This method has also been used to assign the geometry of the double bond of an allylic alcohol.
Stereomutation of a 1,2,3-triketone: an example of an asymmetric reaction
Authors: Wolfe Saul , Berry James Edward , Peterson Michael R.
Published: May 2006

The 1,2,3-triketone PhC(Me)2COCOCOPh has been synthesized from mandelic acid in seven steps. Its proton magnetic resonance spectrum features a sharp six-proton methyl singlet at room temperature which broadens considerably at low temperatures but is not resolved into two peaks at 173 K. Similar dynamic behaviour is observed for the monoketone PhC(Me)2COPh. It is concluded that the barrier to interconversion of enantiomeric tricarbonyl helical conformations is significantly less than 7 kcal/mol. The rotation–rotation surface of the ketodialdehyde HCO—CO—CHO has been computed by the CNDO/2 method; the barrier to stereomutation of enantiomeric helical conformations of this tricarbonyl system is found to be 3.9 kcal/mol. The dynamics of this process are discussed in terms of a recently proposed definition of symmetric and asymmetric reactions.
Evidence for a second kind of trapped electron in some deuterated aqueous glasses at low temperatures. A pulse radiolysis study
Authors: Buxton George V. , Gillis Hugh A. , Klassen Norman V.
Published: May 2006

Several deuterated aqueous glasses have been pulse-irradiated at 76 K. In addition to the well known visible absorption band of et−, a second intense infrared absorption band, with λmax > 3200 nm, has been found in (a) 50% by volume ethylene glycol, (b) 9.5 M LiCl, and (c) 2.5 and 4 M MgCl2 glasses. Electron scavengers decrease the intensities of both bands, but to different extents. An increase in temperature decreases the intensity of the infrared band, but not that of the visible band. These and other features lead us to conclude that the infrared band is due to shallowly trapped electrons which are distinctly different from trapped electrons which absorb in the visible region.The decay of the infrared band extends over several orders of magnitude in time and, unlike that of the visible band, is independent of wavelength. In the two chloride glasses the decay of the infrared band is accompanied by emission (λmax ≈ 410 nm) and is probably due to a spur reaction between an electron and hydroxyl radical to form excited hydroxide ion. No emission is found in the ethylene glycol glass, but growth of the visible band matches the decay of the infrared band in this case.By comparing the amount of Ag0 produced in an ethylene glycol glass containing Ag+ with the decrease in intensity of the infrared and visible bands, we obtain ε1400 = (5.7 ± 0.8) × 103 M−1 cm−1. From the shape of the infrared band, which is Lorentzian on the high energy side, we estimate λmax ≈ 3600 nm and εmax ≈ 4.9 × 104 M−1 cm−1.
Metal complexes as antioxidants. III. Reaction of nickel dialkyldithiocarbamates and nickel dialkyldithiophosphates with alkyl hydroperoxides
Authors: Howard J. A. , Chenier J. H. B.
Published: May 2006

Alkyl hydroperoxides are shown to react with nickel dialkyldithiocarbamates and nickel dialkyldithiophosphates in the liquid-phase at 30 °C to generate free radicals. These radicals are capable of inducing the decomposition of the hydroperoxide and destroying the nickel complex. Rates of radical generation, as determined from hydrocarbon autoxidation, are similar to rates of complex disappearance and are ca. 1/5th rates of hydroperoxide disappearance. Rates of disappearance of both reactants are retarded by the addition of hydrogen atom donating antioxidants, the rate of hydroperoxide disappearance is reduced to the rate of radical generation and the rate of complex disappearance is significantly less than the rate of radical generation. These results are consistent with a mechanism for decomposition which involves cycling of the nickel complex. Decomposition of cumene hydroperoxide to α-cumyl alcohol, α-methylstyrene and acetophenone suggests the intermediacy of cumyloxy radicals in this system while the electron spin resonance spectroscopic method indicates that alkylperoxy radicals are also transient intermediates.
Raman spectra of pyridine adsorbed on a series of ion-exchanged forms of zeolite Y
Authors: Egerton T. A. , Hardin A. H. , Sheppard N.
Published: May 2006

As with other silicas and aluminas, it is shown that a broad general fluorescence from Y zeolite samples excited by irradiation with the 6328 Å line of a He/Ne laser can be greatly reduced by heating the zeolite in oxygen at 500 °C. This general fluorescence is attributed to the presence of traces of unsaturated hydrocarbon impurities which can be burned off by the oxygen treatment. A narrower residual fluorescence in the region of 14 000–14 500 cm−1 is attributed to the presence of Fe3+ impurities.Successful Raman spectra using He–Ne laser excitation have been obtained from pyridine adsorbed on oxygen-treated NaY zeolite, and on samples of this zeolite in which the majority of sodium ions have been replaced by Li+, K+, Co2+, Cu2+, Ce3+ or H+ (decationated Y zeolite). The position of the v1 Raman band from the ring-breathing mode of pyridine is found to give a linear correlation with q/r for the metal ions (where q is the charge and r the radius of an ion) strongly suggesting that the main adsorption is at cation sites. During adsorption of pyridine on CeY the spectrum changes as a function of time. Adsorption on Ce3+ appears to be the final situation and intermediate Raman spectra suggest that pyridine adsorbs and forms hydrogen bonds with surface OH groups; quite different Raman spectra are obtained from these two surface species. The Raman spectra of pyridine on HY zeolite is consistent with the coexistence of pyridinium ions and hydrogen-bonded pyridine molecules.
The crystal structures of Cu1•8Se, Cu3Se2, α- and γCuSe, CuSe2, and CuSe2II
Authors: Heyding Robert Donald , Murray Ritchie MacLaren
Published: May 2006

The crystal structures of a number of copper selenides have been re-examined using X-ray powder diffraction intensity data. |F0| values for Cu1•8Se at room temperature (a = 5.765 Å) are satisfied by a model based on space group Fm3m with 4 Se atoms per unit cell on the fcc sites, 5.2 Cu atoms on the tetrahedral sites, and 2.0 Cu atoms on the trigonal sites in the Se sublattice. Cu3Se2 is tetragonal, [Formula: see text] a = 6.402, c = 4.279 Å, with Cu(1) in 2(a), Cu(2) in 4(e) with x = 0.147 ± 5, z = 0.781 ± 9, and Se in 4(e) with x = 0.272 ± 3, z = 0.264 ± 7. CuSe2 has the orthorhombic C18 marcasite structure, Pnnm, a = 5.005, b = 6.182, c = 3.740 Å, with Cu in 2(a), and Se in 4(g) with x = 0.184 ± 1, y = 0.385 ± 1. CuSe2II has the cubic C2 pyrite structure, Pa3, a = 6.116 Å, with Cu in 4(a), and Se in 8(c) with x = 0.3891 ± 5.Neither αCuSe nor γCuSe have the CuS covellite structure.These results are discussed in some detail.
Metabolites of bird's nest fungi. Part 4. The isolation and structure determination of cybullol, a metabolite of Cyathus bulleri Brodie
Authors: Ayer William A. , Paice Michael G.
Published: May 2006

Cybullol, a metabolite of Cyathus bulleri Brodie, has been shown to be (2S,5S,6S,10S)-cis-6, trans-10-dimethyl-r-2-cis-5-decalindiol (1) by a combination of chemical and physical methods. The mass spectra and the 1H and 13C magnetic resonance spectra of cybullol and derivatives are discussed. The absolute configuration of cybullol was deduced from the circular dichroism spectrum of the ketol 3. Cybullol has been transformed into the fungal metabolite (−)-geosmin (11). This correlation establishes the absolute configuration of (−)-geosmin.
Recherches en série hétérocyclique. XXVIII. Synthèse de bipyrroles
Authors: Farnier Michel , Soth Samreth , Fournari Pierre
Published: May 2006

Raney nickel reduction of the diesters of thieno dipyrroles proceeds by a desulfuration. Treatment of the dipyrrole diesters thus obtained leads to three fundamental systems; 2,2′-, 2,3′-, and 3,3′-dipyrroles. [Journal translation]
A proton magnetic resonance relaxation study of molecular motions in trimethylamine-borane
Authors: Ang T. T. , Dunell B. A.
Published: May 2006

Proton magnetic resonance spin–lattice relaxation times T1 have been measured for trimethylamine-borane from 120 to 380 K, a few degrees above the melting point. Minima in T1 at 157 and 259 K are attributed to threefold reorientation of each of the three methyl groups and the borane group and to threefold reorientation of the whole molecule about the B—N axis, respectively. Activation energies for these processes were found to be 3.3 and 6.7 kcal/mol. Abrupt changes in T1 at 350 and 360 K correspond exactly with heat capacity transitions observed by other workers. The time constant for the decay of the free induction signal (FID curve) changes by two orders of magnitude at 360 K. Having a value of some 3 ms above 360 K, it shows that there must be rapid diffusion as well as molecular tumbling in the highest temperature solid phase.
60Co γ radiolysis of reduced glutathione in aerated solutions at pH values between 1–7.0
Authors: Lal Manohar
Published: May 2006

G-values for the formation of oxidised glutathione (GuS—SGu), glutathione sulphinic acid (GuSO2H), γ-glutamylalanylglycine (GuH), γ-glutamylserylglycine (GuOH), and hydrogen peroxide and G(—GuSH) have been estimated in the γ-radiolysis of aerated reduced glutathione solutions at pH values between 1–7.3. The results show excellent material balance for the radiolytic amino products. Oxygen is necessary for the production of both glutathione sulphinic acid and γ-glutamylserylglycine in the radiolysis of glutathione. Product yields increase with increasing GuSH concentration and reflect the occurrence of a small chain reaction. Although the spectrum of amino products is identical to the corresponding products from cysteine radiolysis under similar conditions, their yields are very much different. It is significant, that there is no evidence for the scission of the peptide chain, at any of the GuSH concentrations and pH's; thus the —SH group of glutathione is the site of attack of the primary species.A reaction mechanism, which explains most of the experimental results has been put forward. A rate expression for G(—GuSH) has been evaluated and it is found that the experimental and calculated G(—GuSH) are in good agreement.
Oxidative decarboxylation of the 3-methyl-2-carboxynorbornanes with lead tetraacetate
Authors: Stothers J. B. , Teo K. C.
Published: May 2006

The mixtures of isomeric acetates produced by oxidative decarboxylation of the four 3-methyl-norbornane-2-carboxylic acids with lead tetraacetate in benzene have been characterized. The composition of these products depends primarily on the configuration of the methyl group in the starting material. The results are compared with those found for the Pb(OAc)4 decarboxylation of the norbornane-, bornane-, and 2,3,3-trimethylnorbornane-2-carboxylic acids. The formation of the products is interpreted in terms of competitive cationic and SNi substitution.
Synthetic application of α-hydroxydiazene systems. I. Esters from radical chain reactions of unsaturated compounds with 2-hydroxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline
Authors: Knittel Peter , Warkentin John
Published: May 2006

2-Hydroxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline (1) reacts with acetylenic and olefinic unsaturated systems by addition of the 2-acetoxy-2-propyl group and a hydrogen atom, respectively, to the two atoms forming the multiple bond. The regiochemistry of addition to unsymmetric unsaturated systems is that predicted for a radical chain mechanism, in which the 2-acetoxy-2-propyl radical adds to the multiple bond so as to form the more stable free radical which then abstracts a hydrogen atom from the hydroxyl group of 1. Polymerization of the unsaturated substrate, as well as abstraction of allylic hydrogen (if any) are competing processes. Yields of adducts, based on 1, ranged from 80% in reaction with crotonaldehyde to 10% in reaction with cyclohexene.
Conformation of 2-thiophenesulphonanilides from dipole moment studies
Authors: Pappalardo Giuseppe C. , Gruttadauria Salvatore , Maccarone Emanuele , Musumarra Giuseppe
Published: May 2006

The electric dipole moments of a number of 2-thiophenesulphonanilides have been measured in benzene solution at 25 °C. The data obtained have been analyzed by the vectorial additive method of calculation. Results of the calculations have shown that the SO2—NH group prefers the gauche-syn conformation in which the N—H bond lies on the plane bisecting the OSO angle. Conformations about the Ph—N bond in the 2′- and 3′-substituted derivatives have also been determined and are discussed.
Formation, mobilité et réactivité d'espèces paramagnétiques adsorbées sur zéolithes H—Y irradiées. Une étude par résonance paramagnétique électronique
Authors: Vedrine Jacques C. , Massardier Jean , Abou-Kaïs Antoine
Published: May 2006

Use of γ radiation as an ionizing source has been successfully applied to an epr study of adsorption sites and of adsorbed species in the case of H—Y zeolites. Adsorption sites have appeared to be mainly oxygen nuclei from the lattice. It has been observed that molecular hydrogen neutralizes paramagnetic sites while molecular oxygen gives rise to O2−-type radicals which have nearly equal unpaired spin density on the two nuclei (43 and 57%). Carbon monoxide gives rise to a species assigned to C+O which reacts very easily at 77 K with molecular oxygen to yield an O2−-type species for which the spin density distribution is not equivalent on the two oxygen nuclei [Formula: see text] The nature and the mobility of OH• and NH2• radicals have been studied in detail. They arise from the ionization of physisorbed H2O and NH3, the better yield being obtained at a monolayer coverage. This study leads to an original approach to the study of the adsorptive properties of zeolites.
Vapour pressures of solid and liquid NbCl5 and TaCl5
Authors: Sadoway Donald R. , Flengas S. N.
Published: May 2006

The vapour pressures of solid and liquid NbCl5 and TaCl5 have been measured over the temperature range 425 to 525 K by a quartz Bourdon-type spiral pressure gauge. Enthalpies and entropies of sublimation, fusion, and evaporation as well as melting points and boiling points have been calculated. The present results are compared with those reported in the literature.
The kinetic activation volumes for the binding of chloride to iron(III), studied by means of a high pressure laser temperature jump apparatus
Authors: Hasinoff Brian B.
Published: May 2006

The volumes of activation for the kinetics of the reaction of Cl− with Fe3+ and FeOH2+ have been determined by a laser temperature jump relaxation method at pressures up to 2.76 kbar. The results indicate that the two species, FeOH2+ and Fe3+, react with Cl− by different mechanisms. The activation volume for the binding of Cl− to FeOH2+ is positive (7.8 ± 1.0 cm3 mol−1), which is consistent with a dissociative interchange mechanism. The activation volume for the binding of Cl−1 to Fe3+ is negative (–4.5 ± 1.1 cm3 mol−1), which is consistent with an associative interchange mechanism.
The kinetics of the reactions of chlorodithioformate esters with azide ions in 70% aqueous acetone
Authors: Queen Alan , McKinnon David M. , Bell Alexander W.
Published: May 2006

The rates of reaction of a series of chlorodithioformate esters with azide ions in 70% aqueous acetone decrease with increasing electron donation to the reaction site. This order is the reverse of that observed for SN1 solvolysis. The entropies of activation are highly negative and the rapid rates of azide attack result from the low activation energies. These results indicate a bimolecular mechanism for azide attack and this is supported by the first-order dependence of the reaction rate on azide concentration.
A self-consistent field wavefunction suited for calculation of the electric field gradient in HCl
Authors: Grabenstetter J. E. , Whitehead M. A.
Published: May 2006

A single-centre basis set on Cl is developed for an SCF calculation on HCl to give an accurate expectation value for the electric field gradient at the Cl nucleus. The SCF energy, orbital eigenvalues, dipole moment, molecular electric quadrupole moment, Hellmann–Feynman force on Cl and virial ratio are also reported, and the variation of the electric field gradient at Cl with changes in internuclear distance is examined.
13C Fourier transform nuclear magnetic resonance. XII. Structure of the phytol–lecithin bilayer. Application of electric field effects
Authors: Cushley Robert J. , Forrest Bruce J.
Published: May 2006

Phytol has been incorporated into lecithin bilayers. 13C spin–lattice relaxation times, which have been measured for both components of the model membrane, indicate a marked destabilization of the bilayer due to intercalated phytol. The disruption of normal phospholipid packing is due to the highly branched nature of the phytyl hydrocarbon chain. In addition, the position of phytol in the bilayer has been determined by means of a linear electric field effect of the polar lipid head group upon the 13C chemical shifts of the phytol olefinic carbons.
Thermodynamic properties of tetraalkylammonium halides: volumes, heat capacities, and expansibilities in H2O, D2O and urea–water mixtures from 278 to 328 K
Authors: Perron Gérald , Desrosiers Nicole , Desnoyers Jacques E.
Published: May 2006

The densities and heat capacities per unit volume of the symmetrical tetraalkylammonium bromides (R4NBr) were measured in H2O, D2O, and 3 m aqueous urea from 0.01 to 1 mol kg−1 and from 5 to 55 °C with a flow digital densimeter and a flow microcalorimeter. Expansibilities were also measured at 25 °C for the same electrolytes in H2O and urea–water mixtures with a dilatometer. Apparent molal volumes [Formula: see text] heat capacities [Formula: see text] and expansibilities [Formula: see text] were derived. The [Formula: see text] of R4NCl and R4NI were also measured in H2O at 25 °C. The effect of urea concentration was investigated at 25 °C in the case of Bu4NBr.Once allowance is made for the anion, the properties of the larger R4N+ behave essentially as hydrophobic nonelectrolytes in water. The transfer functions from H2O to D2O have the same sign as the hydration functions and the transfer functions from H2O to urea–water mixtures the opposite sign. Whatever is the origin of the interactions giving rise to the peculiar behavior of hydrophobic R4N+ in water, these interactions are larger in D2O and smaller in the presence of urea.The excess volumes, heat capacities, and expansibilities of Bu4NBr and Pen4NBr, once corrected for the long-range Debye–Hückel interactions, all have the same sign as the hydration functions at infinite dilution, in contrast with excess free energies and enthalpies. This suggests some kind of cooperative effect as two hydrophobic solutes interact with each other without the formation of a hydrophobic bond. No conclusions can be drawn from the difference in excess functions in the various aqueous solvents.
High power TEA-CO2 laser induced polymerization of ethylene
Authors: Chin S. L.
Published: May 2006

A 100-MW double-discharged TEA-CO2 laser was used to induce the polymerization of ethylene gas at pressures ranging from 250 to 900 psi at room temperature. The polymerization product was mainly tetradecane (CH3(CH2)12CH3) (∼80%) and octadecane (CH3(CH2)16CH3) (∼20%).
The mechanism of the reaction of lead tetraacetate–hydrogen fluoride with 1-octene
Authors: Tanner Dennis D. , Bostelen Peter Van
Published: May 2006

The reaction of 1-octene with the lead tetraacetate–hydrogen fluoride reagent led to products resulting from the Markovnikov addition of lead and its ligand (fluoro or acetoxy) to the olefinic double bond. Displacement of lead from the organometalic intermediate via three separate pathways could be distinguished; displacement concomitant with hydride migration alkyl migration, or direct displacement by an external ligand. The pathways for the formation of the product difluorides, fluoroacetates, and diacetate could be followed by an analysis of the products obtained from carrying out the reaction using 1-octene-1-13C as substrate. The major pathways to product formation resulting from either hydride or alkyl migration could be rationalized as proceeding through the intermediacy of a resonance stabilized α-fluorocarbonium ion.
Complex hydrogen bonded cations. The imdazole/imidazolium complex cation
Authors: Bonsor D. H. , Borah B. , Dean R. L. , Wood J. L.
Published: May 2006

The salts (ImH+)X−, Im = imidazole, X− = PF6−, BF4−, or ClO4− have been prepared in solution, and the perchlorate salt has been crystallised. The molecularity implied by the formula is confirmed in solution by Job's method, and for the crystals gravimetrically. In MeCN the association constant is ∼8 M−1. Infrared spectra of solution and crystals are similar, independent of counter ion, and indicate an asymmetric single minimum proton potential. The pronounced doublet in the NH stretching band of the H bridged complex, and replaced by a single band in the D bridged analogue, is not indicative of proton tunnelling. The X-ray structure is compatible with this interpretation of the spectra.
Conformational changes accompanying electronic excitation of trifluoronitrosomethane
Authors: Gordon R. D. , Dass S. C. , Robins J. R. , Shurvell H. F. , Whitlock R. F.
Published: May 2006

The 690 nm absorption spectrum of CF3NO has been studied in the gas phase at various temperatures and in the condensed phase at 77 K, and assigned to an (nπ*) transition. Analysis of the vibrational structure shows that, while only the eclipsed conformer is stable in the ground state, there are two stable isomers of comparable energy in the excited electronic state. One has an eclipsed conformation, but with the CF3 group tilted away from the oxygen atom. The other has a staggered conformation. In both of the excited state isomers the barrier to internal rotation is higher than in the ground state.
A catalyst for ester hydrolysis showing electrostatic and hydrophobic binding properties
Authors: Guthrie J. Peter , Ueda Yasutsugu
Published: May 2006

The steroid 17β-(4-imidazolyl)-5α-androstane-3β,11β-diamine, 1a, R = H, acts as a catalyst for the hydrolysis of aryl esters. For a series of aryl acetates, 2a–h, at 1 M ionic strength, log k2 for 1a catalyzed hydrolysis is linearly related to log k2 for imidazole catalyzed hydrolysis, with only 2d, 4-acetoxy-3-nitrobenzoate, deviating: at zero ionic strength, all anionic substrates show positive deviations, and a cationic substrate shows a negative deviation. This is interpreted in terms of a stringent geometrical requirement for strong electrostatic catalysis. With favorable geometry, a 1:1 electrostatic attraction can lead to a 15 fold rate enhancement (μ = 0). For a series of arylpropionate esters 3a–c, rate constants for 1a catalyzed hydrolysis show a small but progressive increase with increasing size of the aryl group: after correcting for substrate reactivity and electrostatic interactions, this hydrophobic effect is independent of the leaving group. 1b (R = isopropyl) was prepared to determine the rate of reaction at N-3 of the steroidal imidazole ring: this is the more hindered nitrogen but also the more suitable for hydrophobic binding. 1b was markedly less reactive than 1a, but showed larger hydrophobic effects. Detailed analysis suggests that the potential hydrophobic rate enhancement for the interaction of a phenanthryl group with the lower surface of a steroid is about 160-fold. This study provides guidelines for the design of enzyme models of greater catalytic efficiency.
The alkaloids of L. paniculatum and the structure of paniculatine
Authors: Castillo Mariano , Morales Glauco , Loyola Luis A. , Singh Ishwar , Calvo Crispin , Holland Herbert L. , MacLean David B.
Published: May 2006

Seven alkaloids have been isolated from Lycopodium paniculatum Desvaux. Three of these, lycopodine, dihydrolycopodine, and acetyldihydrolycopodine are alkaloids of established structure. Of the four new alkaloids the structure of one, paniculatine, has been clarified. Its structure, elucidated through an X-ray crystallographic study of its hydrobromide, is different from other alkaloids of the Lycopodium family. The spectral properties of paniculatine are interpreted in the light of its structure.
Ion formation in hydrocarbon flames
Authors: Blades Arthur T.
Published: May 2006

While it is generally accepted that ions arise in hydrocarbon flames by the CH—O mechanism, the only indication that this is the sole mechanism is the equal per carbon response of most hydrocarbons in the flame ionization detector. This response feature can equally be attributed to other flame processes and does not apply to C2H2 in any case. Comparison of rates of ion formation with CH and As emission intensities indicates that C2H2 and CH4 give abnormal rates of ion formation which can be explained on the basis of one or more additional mechanisms of ion formation.
A reinterpretation of beta, gamma, and delta substituent effects on 13C chemical shifts
Authors: Beierbeck Helmut , Saunders John K.
Published: May 2006

It is shown that β-, γ-, and δ-substituent effects on 13C chemical shifts may be better understood by assuming that the upfield shifts caused by gauche γ-substituents are not due to non-bonded interactions introduced with the γ-group, but that they are due to the removal of the hydrogen on the β-substituent.
Synthesis of sultines via tert-butyl hydroxyalkyl sulfoxides
Authors: Sharma Narendra K. , Reinach-Hirtzbach François de , Durst Tony
Published: May 2006

A general route leading to 5- to 8-membered cyclic sulfinate esters (sultines) is described. The method is based on the reaction of tert-butyl hydroxyalkyl sulfoxides with SO2Cl2 in an inert solvent.
The interrelationship between partial molal expansibility and the solute induced shift in the temperature of maximum density of water
Authors: Macdonald Digby D. , Hyne James B.
Published: May 2006

The effect of solutes on the temperature of maximum density (TMD) of water is analysed with emphasis upon the applicability of thermodynamic dissection of the observed change in the TMD (Δθobs) into ideal (Δθid) and structural (Δθst) components. The use of TMD as a probe for examining the effect of dissolved solutes on the structural properties of water is critically compared with methods based upon apparent and partial molal expansibilities.
The thermal decomposition of methane. II. Secondary reactions, autocatalysis and carbon formation; non-Arrhenius behaviour in the reaction of CH3 with ethane
Authors: Chen C.-J. , Back M. H. , Back R. A.
Published: May 2006

In the thermal decomposition of methane at temperatures from 880 to 1103 K, hydrogen and ethane are the only primary products. The rate of formation of ethane falls rapidly towards zero as the reaction progresses until ethane reaches a steady-state concentration. This behaviour is interpreted in terms of a radical chain mechanism,[Formula: see text]Values of k4 were obtained which confirm the non-Arrhenius behaviour of this reaction at these temperatures. Similar chain sequences propagated by addition or abstraction reactions of methyl radicals with ethylene, propylene, and acetylene can account for the formation and disappearance of these secondary products.At a later stage in the pyrolysis a marked autocatalysis is observed and the yield of ethane increases sharply above its steady-state value. It is concluded that this autocatalysis is largely a homogeneous process and is not caused by or associated with carbon formation. Deposition of carbon on the surface was observed at a still later stage of the decomposition, and was quantitatively estimated by light absorption measurements. Possible mechanisms for the auto catalysis are discussed.
Metabolites of bird's nest fungi. Part 6. The synthesis of (±)-cybullol and a new synthesis of (±)-geosmin
Authors: Ayer William A. , Browne Lois M. , Fung Steven
Published: May 2006

The stereoselective transformation of 6,10-dimethyl-4-octal-3-one (8) to racemic cybullol (1), a metabolite of Cyathus bulleri Brodie, is reported. The transformation 4,10-dimethyl-4-octal-3-one to (±)-geosmin (15) is described. The results of the photosensitized [4 + 2] cycloaddition of oxygen to a number of 10-methyl-2,4-hexalins are discussed.
The construction of the substituted denudatine system by diene addition
Authors: Wiesner K. , Tsai T. Y. R. , Dmitrienko G. I. , Nambiar K. P.
Published: May 2006

A simple stereospecific synthesis of the denudatine model 20 is described.
Studies in solvolysis. Part IX. Some commente on anion–cation combination reactions
Authors: Hillier Kenneth , Scott John Marshall William , Barnes Douglas James , Steele Fredrick Joseph Peter
Published: May 2006

The general validity of the Ritchie equation log (kn/k0) = N+ is evaluated on the basis of the bimolecular rate constants for various nucleophiles attacking crystal violet, malachite green, and the tris-p-anisylmethyl carbonium ion. A more general form of the Ritchie equation is required to accommodate the data viz. log (kn/k0) = S+N+(S+ = constant) for the most reactive carbonium ion. The latter modified form of the Ritchie equation is analogous to the Swain–Scott equation log (k0/kn) = sn and the new form follows the usual relationship between reactivity and selectivity, i.e. the value of S+ for the tris-p-anisylmethyl carbonium ion is less than unity.
Kinetics of oxidation of nitrite by hypochlorite ions in aqueous basic solution
Authors: Cachaza J. M. , Casado J. , Castro A. , Quintela M. A. López
Published: May 2006

The kinetics of oxidation of nitrite to nitrate by hypochlorite ions in aqueous basic solution [Formula: see text] have been studied using a dynamic spectrophotometric technique. The rate law is[Formula: see text]At 298.0 K and ionic strength 0.40 M, d = (3.4 ± 0.2) × 10−8 mol l−1 s−1 and e = (2.8 ± 0.2) × 10−6 s−1. The associated activation energies are 56 ± 3 and 61 ± 3 kJ mol−1 respectively. A mechanism is proposed involving the reversible initial step:[Formula: see text]with the NO2Cl undergoing two parallel subsequent reactions, one a unimolecular decomposition and the other an attack by NO2− on NO2Cl.
The reaction of steroid 2,4-dienes with acetylenes
Authors: Yates Peter , Walliser Françoise M.
Published: May 2006

Reaction of 2,4-cholestadiene, 2,4-androstadien-17-one, or 3-trimethylsiloxy-2,4-cholestadiene with dimethyl acetylenedicarboxylate or methyl propiolate in boiling xylene results in the cleavage of rings A and B and the formation of 4-(2-arylethyl)-5-isopropenyl-7a-methyltetrahydroindane derivatives. They are considered to be formed via Diels–Alder addition of the acetylene to the steroid diene followed by a retro-Diels–Alder cleavage of the resulting bicyclo[2.2.2]octadiene system. Attempts to isolate the Diels–Alder adducts by carrying out the additions at lower temperature were unsuccessful, since no reaction occurred. However, when 2,4-androstadien-17-one was treated with dicyanoacetylene in boiling benzene, it was possible to isolate a mixture of two stereoisomeric Diels–Alder adducts containing the bicyclo[2.2.2]octadiene system in ring A; this was converted in boiling xylene to a retro-Diels–Alder product analogous to the products obtained with the other acetylenic dienophiles.
Hydrogen forming reactions of thermal electrons in hydrogen halides: kinetics and thermodynamics
Authors: Nagra Surjit S. , Armstrong David Anthony
Published: May 2006

New competition kinetic studies of electron reactions in HCl and HBr in the 1018 to 1020 molecule cm−3 concentration region are reported and shown to support the findings of earlier investigations. The capture of thermal electrons by (HX)2 dimers is examined from a kinetic and thermodynamic point of view. The (HX)2−* intermediate previously proposed by several groups is considered to be involved in both systems. Differences in the magnitudes and concentration dependences of the rates can be explained, if reaction 5b is fast [Formula: see text] in[Formula: see text]HBr but relatively slow in [Formula: see text] where [6a] and [6b] are the major product-forming reactions. Thermochemical data show [5b] to be strongly favoured energetically in[Formula: see text]HBr, and close to thermoneutral in HCl. Reaction 6b is energetically favourable in HCl. The present data require an autoionisation life-time of ∼10−12 s for (HX)2−*. From other considerations that of HX−* is expected to be [Formula: see text] This means that formation of (HX)2−* must take place by collisions of electrons with HX molecules which are in effect already interacting. Production of stabilised HX− from (HX)2−* does not appear to contribute in HCl, but[Formula: see text]may occur in other HX Systems. The general implications of the mechanism for electron capture in HF and HX mixtures with other polar vapours are mentioned.
Kinetics and mechanism of substitution reactions of (dimethylsulfoxide)pentaamminecobalt(III) ion in dimethylsulfoxide solvent: complications due to redox and conjugate base processes
Authors: Lo S. T. Danny , Oudeman Evelyn M. , Hansen Jean C. , Swaddle Thomas W.
Published: May 2006

Simple anation and solvent exchange reactions of Co(NH3)5DMSO3+ in DMSO are accompanied by reactions in which the conjugate base of this complex undergoes either internal redox to cobalt(II) or relatively rapid substitution. These conjugate base reactions are eliminated by addition of H+, although a minor redox pathway persists within ion pairs of Co(NH3)5DMSO3+ with chloride or bromide. The latter pathway is evidently not mechanistically related to the solvent exchange or anation reactions, which proceed by dissociative interchange (Id) according to the activation parameters (volume of activation = +10 cm3 mol−1 for DMSO exchange; enthalpy of activation = 123, 121, and ∼126 kJ mol−1 for DMSO exchange and bromide and chloride anation respectively). Enthalpies of activation for solvent exchange and for the limiting anation rate are shown to be better criteria of mechanism than the corresponding rate coefficients.
Studies in the usnic acid series. III. The base catalyzed usnic acid–isousnic acid rearrangement. The synthesis of (+)-isousnic acid
Authors: Kutney James P. , Sanchez Ignacio H. , Yee Trevor
Published: May 2006

Investigations concerning the alkaline cleavage of (+)-isoxazolo[4,5-b]usnic acid (8) are described. During these studies a novel rearrangement from the 'normal' (usnic acid) to the 'iso' (isousnic) series was revealed. The rearrangement process was then utilized in the synthesis of (+)-isousnic acid (3).
Hydrogenolysis of organometallics and the acidity of hydrogen
Authors: Buncel Erwin , Menon Balachandran C.
Published: May 2006

The hydrogenolysis of a series of alkylcesiums in cyclohexylamine solvent has been studied spectrophotometrically. The cesium salt of p-phenyltoluene reacts with H2 (1 atm, room temperature), but the cesium salts of di-2,4-xylylmethane and of diphenylmethane are unreactive. The results show that the acidity of H2 is intermediate between those of p-phenyltoluene and of di-2,4-xylylmethane in this reaction system. Possible effects of ion association phenomena on the equilibrium processes are considered.
Nitration of p-tert-butyltoluene in acetic anhydride. 1,2 and 1,4 adducts
Authors: Fischer Alfred , Röderer Rolf
Published: May 2006

Nitration of p-tert-butyltoluene in acetic anhydride gives 5-tert-butyl-2-methyl-2-nitro-1,2-dihydrophenyl acetate (43%), cis- and trans-1-tert-butyl-4-methyl-4-nitro-1,4-dihydrophenyl acetate (16%) and 4-tert-butyl-2-nitrotoluene (41%). Reaction of either of the 1,2 or 1,4 nitroacetoxy adducts with hydrogen chloride gives a mixture of the 1,2 and 1,4 nitrochloro adducts. The 1,2 (secondary) acetate adduct eliminates nitrous acid to form 5-tert-butyl-2-methylphenyl acetate under mildly acidic conditions. Under more vigorously acidic conditions 4-tert-butyl-2-nitrotoluene is formed. The same products are formed from the 1,4 (tertiary) acetate adducts but p-tolyl acetate is also obtained. The 1,2 and 1,4 adducts couple with anisole to form 5-tert-butyl-4′-methoxy-2-methylbiphenyl.
Molecular inclusions in the paraffin layers of the nickel cyanide n-alkylamine systems
Authors: Mathey Y. , Setton R. , Mazieres C.
Published: May 2006

The layered Ni(CnH2n+1NH2)2Ni(CN)4 acts as a host structure for amines, yielding Ni-(CnH2n+1NH2)2Ni(CN)4,xCnH2n+1NH2 (with 0 ≤ x ≤ 0.4 and 12 ≤ n ≤ 16) which are easily prepared by various procedures including solid–solid reaction. The guest can be removed and re-included; it can be replaced by aromatics. Phase transitions of the clathrate (with amines as guest) occur in the range 55–85 °C, obviously related to the transitions previously observed in the parent compound Ni(CnH2n+1NH2)2Ni(CN)4.
1,2,3,4,7,8,9,10-Octahydrodicyclohepta[de, ij]naphthalene and 2,7-dimethylpyrene: a short novel synthesis
Authors: Laycock David E. , Wain Rosemary J. , Wightman Robert H.
Published: May 2006

The preparation of two tetracyclic benzenoid hydrocarbons is described using a four step synthesis involving 'aromatization' of a Diels–Alder dianhydride adduct.
Reactions of dicarbonyl compounds with β-ketoglutaric acid: synthesis of 4-hydroxy-3,4-diphenylcyclopent-2-enone-2-carboxylic acid
Authors: Oehldrich James , Cook James M.
Published: May 2006

Reaction of β-ketoglutaric acid with benzil in ethanolic KOH furnished the 1:1 adduct 7. Hydrolysis and partial decarboxylation gave the monoacid 8, the structure of which was erroneously reported to be 5 in the earlier literature.[Formula: see text]
On the mechanisms of acid-catalyzed enolization and hydrogen isotope exchange of cyclic ketones
Authors: Werstiuk Nick Henry , Banerjee Sujit
Published: May 2006

The acid-catalyzed hydrogen isotope exchange of norcamphor 1 in DOAc–DCl–D2O is shown to follow the general theory (4) for exchange of a diastereotopic proton pair α to a carbonyl group. That is, the less reactive proton undergoes exchange via two channels. Through an analysis of a combination of the rate data for acid-catalyzed bromination and the pKBH+ values for a series of cyclic and bicyclic ketones, we establish that the reactivity order in the former is controlled by ketone basicity and not, as has been suggested previously, by angle strain developed in a very enol-like transition state.