bluuebunny/crossref_metadata_2025 huggingface dataset:
Pachymoside A  A novel glycolipid isolated from the marine sponge Pachymatisma johnstonia
Authors: Warabi Kaoru , Zimmerman William T , Shen Jingkai , Gauthier Annick , Robertson Marilyn , Finlay B Brett , Soest Rob van , Andersen Raymond J
Published: March 2004

Crude extracts of the North Sea marine sponge Pachymatisma johnstonia showed promising activity in a new assay for inhibitors of bacterial type III secretion. Bioassay-guided fractionation resulted in the isolation of the pachymosides, a new family of sponge glycolipids. A major part of the structural diversity in this family of glycolipids involves increasing degrees of acetylation and differing positions of acetylation on a common pachymoside glycolipid template. All of the metabolites with these variations in acetylation pattern were converted into the same peracetylpachymoside methyl ester (2) for purification and spectroscopic analysis. Pachymoside A (1) is the component of the mixture that has natural acetylation at the eight galactose hydroxyls and at the C-6 hydroxyls of glucose-B and glucose-D. Chemical degradation and transformation in conjunction with extensive analysis of 800 MHz NMR data was used to elucidate the structure of pachymoside A (1). Key words: Pachymatisma johnstonia, marine sponge, pachymoside, glycolipid.
Photogeneration of 1,5-naphthoquinone methides via excited-state (formal) intramolecular proton transfer (ESIPT) and photodehydration of 1-naphthol derivatives in aqueous solution
Authors: Lukeman Matthew , Veale Duane , Wan Peter , Munasinghe V Ranjit N. , Corrie John ET
Published: March 2004

The photochemistry of naphthols 1, 2, 4, 5 and 9, and phenol 10 has been studied in aqueous solution with the primary aim of exploring the viability of such compounds for naphthoquinone and quinone methide photogeneration, along the lines already demonstrated by our group for phenol derivatives. 1-Naphthol (1) is known to be substantially more acidic than 2-naphthol (2) in the singlet excited state (pKa* = 0.4 and 2.8, respectively) and it was expected that this difference in excited-state acidity might be manifested in higher reactivity of 1-naphthol derivatives for photochemical reactions requiring excited-state naphtholate ions, such as quinone methide formation. Our results show that three types of naphthoquinone methides (26a, 26b, and 27) are readily photogenerated in aqueous solution by irradiation of 1-naphthols. Photolysis of the parent 1-naphthol (1) in neutral aqueous solution gave 1,5-naphthoquinone methide 26a as well as the non-Kekulé 1,8-naphthoquinone methide 26b, both via the process of excited-state (formal) intramolecular proton transfer (ESIPT), based on the observation of deuterium exchange at the 5- and 8-positions, respectively, on photolysis in D2OCH3CN. A transient assignable to the 1,5-naphthoquinone methide 26a was observed in laser flash photolysis experiments. The isomeric 2-naphthol (2) was unreactive under similar conditions. The more conjugated 1,5-naphthoquinone methide 27 was formed efficiently via photodehydroxylation of 4; isomeric 5 was unreactive. The efficient photosolvolytic reaction observed for 4 opens the way to design related naphthol systems for application as photoreleasable protecting groups by virtue of the long-wavelength absorption of the naphthalene chromophore.Key words: photosolvolysis, excited-state intramolecular proton transfer, quinone methide, photorelease, photoprotonation.
Comparison of the Suzuki cross-coupling reactions of 4,7-dichloroquinoline and 7-chloro-4-iodoquinoline with arylboronic acids using phosphine-free palladium catalysis in water
Authors: Friesen Richard W , Trimble Laird A
Published: March 2004

4,7-Dichloroquinoline (1a) and 7-chloro-4-iodoquinoline (1b) undergo Suzuki cross-coupling reactions with arylboronic acids catalyzed by phosphine-free palladium acetate in boiling water. Using phenylboronic acid (2), the reaction of 1a provides 7-chloro-4-phenylquinoline (3) (78%) together with diphenylquinoline (4) (12%), while 1b reacts in a much more regioselective fashion and provides 3 in 98% isolated yield. Although 1b undergoes a more regioselective Suzuki reaction than 1a, additional important observations are that the overall reaction of 1b with 2 is three times slower than 1a and that the reaction occurs in the absence of tetrabutylammonium bromide. Using optimized reaction conditions, a variety of aryl and vinylboronic acids undergo regioselective Suzuki cross-coupling with 1b to provide the products 7, 10, and 11 in good to excellent yield.Key words: palladium, cross-coupling, regioselectivity, quinolines, boronic acids.
The DielsAlder reactions of quinone imine ketals
Authors: Banfield Scott C , Kerr Michael A
Published: March 2004

N-Benzoyl- and N-arylsulfonyl-p-benzoquinone-mono-imine ketals (QIKs) undergo smooth DielsAlder cycloadditions with typical 1,3-butadienes to yield the expected endo adducts. Treatment with catalytic acid rapidly converts the adducts to dihydronaphthalenes. The N-benzoyl derivatives require high pressures for cycloadditions while the N-tosyl and N-nosyl derivatives proceed under thermal (ambient pressure) conditions. In all cases the cycloadditions are completely regioselective.Key words: DielsAlder, quinone imine ketal, hyperbaric chemistry.
Conformational behaviour in S-methyl halothioacetates through NMR, FT-IR, and theoretical calculations
Authors: Basso Ernani A , Fiorin Barbara C , Tormena Cláudio F , Rittner Roberto
Published: March 2004

This work presents an investigation of the conformational behaviour of S-methyl chlorothioacetate (MCTA), S-methyl bromothioacetate (MBTA), and S-methyl iodothioacetate (MITA) through NMR and IR spectroscopies and through theoretical calculations that apply DFT/B3LYP theory. The DFT calculations showed two stable rotamers in the vapour phase, gauche and trans, for all the compounds. The coupling constants, 1JCH, were obtained from NMR spectroscopy; these were used in the solvation theory to calculate the vapour-phase energy difference, the coupling constants for each rotamer, the solution energy difference, and the rotamer population for each solvent. These data showed that for MCTA, the most stable rotamer is trans; however, for MBTA and MITA, the most stable rotamer is gauche, both in the vapour phase and in solution. The changes in rotamer stability are because of the preference in stereo-electronic interactions; in the MCTA case the interaction is mainly electrostatic, while for MBTA and MITA, it is because of the interaction between nBr,I[Formula: see text]π*CO.Key words: S-methyl halothioacetates, conformational analysis, theoretical calculations, NMR, solvation theory.
Diversity-oriented synthesis of enantiopure N-protected β,β-dialkylserines
Authors: Dettwiler James E , Lubell William D
Published: March 2004

A series of enantiomerically pure N-Boc-protected β,β-dialkylserines was synthesized by addition of the appropriate Grignard reagent to N-(Boc)serine methyl ester, followed by TEMPO-catalysed oxidation of the primary alcohol with sodium chlorite and sodium hypochlorite.Key words: amino acid, serine, β,β-dialkylserines, ring-closing metathesis.
Biobleaching chemistry of laccase-mediator systems on high-lignin-content kraft pulps
Authors: Chakar Fadi S , Ragauskas Arthur J
Published: March 2004

A high-lignin-content softwood kraft pulp was reacted with laccase in the presence of 1-hydroxybenzotriazole (HBT), N-acetyl-N-phenylhydroxylamine (NHA), and violuric acid (VA). The biodelignification response with violuric acid was superior to both 1-hydroxybenzotriazole and N-acetyl-N-phenylhydroxylamine. NMR analysis of residual lignins isolated before and after the biobleaching treatments revealed that the latter material was highly oxidized and that the magnitude of structural changes was most pronounced with the laccase  violuric acid biobleaching system. An increase in the content of carboxylic acid groups and a decrease in methoxyl groups were noted with all three laccase-mediator systems. The oxidation biobleaching pathway is directed primarily towards noncondensed C5 phenolic lignin functional structures for all three laccase-mediated systems. The laccase  violuric acid system was also reactive towards C5-condensed phenolic lignin structures.Key words: laccase, mediator, lignin, pulp, biobleaching, phenolics.
Sequential olefin metathesis  Intramolecular asymmetric Heck reactions in the synthesis of polycycles
Authors: Lautens Mark , Zunic Valentin
Published: March 2004

Application of the intramolecular asymmetric Heck reaction in the desymmetrization of a novel class of symmetrical bicyclodienes, synthesized through a diastereoselective double ring-closing metathesis (DSRCM) reaction, was achieved with good yields (approximately 80%) and excellent enantioselectivities (up to 99% ee). Three contiguous stereocenters are established in a single desymmetrization reaction. The use of thallium carbonate as base in the asymmetric Heck reaction favours double bond migration in 13. Cationic conditions delivered products with good to excellent enantioselectivities, surpassing the results under neutral conditions.Key words: asymmetric, Heck, polycycles, metathesis, stereoselective, desymmetrization.
C19 quassinoid model studies: Preparation of trans-perhydroindans via a vinylogous Mukaiyama aldol  free-radical cyclization route
Authors: Donahue Matthew G , Hart David J
Published: March 2004

Aldehyde 9 was prepared in 5 steps from 3,5-dimethylbenzoic acid. Treatment of 9 with ketene acetals 10 and 19 and titanium tetrachloride gave free-radical cyclization substrates 11 and 20 in 67% and 51% yields, respectively. Tri-n-butylstannane-mediated cyclization of 11 and 20 gave trans-perhydroindans 14 and 21 in 60% and 63% yields, respectively. The relationship of these studies to an approach to C19 quassinoids is discussed.Key words: vinylogous Mukaiyama aldol reaction, free-radical cyclization, trans-perhydroindans, C19 quassinoids, 1,2-asymmetric induction.
Total synthesis of ()-pateamine A, a novel immunosuppressive agent from Mycale sp
Authors: Pattenden Gerald , Critcher Douglas J , Remuiñán Modesto
Published: March 2004

A convergent synthesis of the unique thiazole-containing polyene bis-lactone pateamine A (1) isolated from the marine sponge Mycale sp is described. The synthesis features the ubiquitous Stille sp2sp2 coupling reaction to elaborate the E,Z-diene macrolide core 23 and the all-E polyenamine side chain in the natural product. It also highlights the scope for enantiopure sulfinimine intermediates in the synthesis of chiral β-amino ester moieties in complex structures.Key words: pateamine A, immunosuppressive agent from marine sponge Mycale sp, total synthesis, novel 19-membered bis-lactone, thiazole metabolite, polyenamine, Stille reaction, sulfinimines, chiral β-amino esters.
Part 1: Efficient strategies for the construction of variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems)
Authors: Laurent Alain , Villalva-Servín Nidia P , Forgione Pat , Wilson Peter D , Smil David V , Fallis Alex G
Published: March 2004

Strategies for the construction of cyclic molecules containing variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems) are described. These routes employ a multi-component coupling protocol that utilizes sequential magnesium-mediated carbometallation of propargyl alcohols and intramolecular DielsAlder reactions (IMDA). The cycloaddition generates the key eight-membered taxane ring as a single diastereomer, induced by preferential Lewis acid (diethylaluminum chloride or boron trifluoride etherate) complexation with the cross-ring oxygens. Both the electronic nature of the dienophile and the neighbouring group non-bonded interactions contribute to the success of these cycloadditions.Key words: magnesium chelate, Lewis acid, intramolecular DielsAlder, cycloaddition.
Part 2: Efficient strategies for the construction of variably substituted bicyclo[5.3.1]undecenones (AB-taxane ring systems) and their conversion to tricyclo[9.3.1.03,8]pentadecenones (ABC taxane ring systems) and bicyclo[2.2.2]octanones
Authors: Villalva-Servín Nidia P , Laurent Alain , Fallis Alex G
Published: March 2004

The extension of our strategies for the construction of cyclic molecules containing variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems) for the synthesis of the tricyclo[9.3.1.03,8]pentadecenone (ABC taxane ring system) and bicyclo[2.2.2]octanones are described. These routes employ a multi-component coupling protocol that employs sequential magnesium-mediated carbometallation of allyl-substituted propargyl alcohols followed by diastereoselective Lewis acid catalyzed intramolecular DielsAlder reactions (IMDA). Subsequent ring-closing metathesis (RCM) afforded the ABC taxane core structure. Enone accelerated [3,3] sigmatropic rearrangements (Cope rearrangements) generated the bicyclo[2.2.2]octanone nucleus. In the presence of a Lewis acid, the dienophile precursor underwent a tandem reaction via the adduct directly to the bicyclo[2.2.2]octanones. This is the first example of a novel enone accelerated carbocycle Cope rearrangement and provides direct access to bicyclo[2.2.2]octanones by a new route that compliments the traditional cyclohexadiene cycloaddition approach. Key words: magnesium chelate, Lewis acid, taxanes, DielsAlder, sigmatropic rearrangement, oxy-Cope, ring-closing metathesis, bicyclo[2.2.2]octanone.
Preparation and characterization of bicyclic amide acetals and monothioacetals
Authors: Guthrie J Peter , Gallant Roger T , Jennings Michael C
Published: March 2004

We have prepared and characterized new examples of 5-substituted-1-aza-4,6-dioxabicyclo[3.3.0]octanes (bicyclic amide acetals) and examples of the new heterocyclic system, 5-substituted-1-aza-4-oxa-6-thiabicyclo[3.3.0]octanes (bicyclic amide monothioacetals). Detailed analysis of NMR coupling constants and X-ray structure determination for an example of each class of compound established the stereochemistry and conformation of these ring systems.Key words: bicyclic amide acetals, preparation, coupling constants, X-ray structure.
The solid-state molecular structure of W(NO)3Cl3 and the nature of its WNO bonding
Authors: Hayton Trevor W , Patrick Brian O , Legzdins Peter , McNeil W Stephen
Published: March 2004

The monomeric trinitrosyl complex, W(NO)3Cl3, can be prepared by the treatment of WCl6 in CH2Cl2 with NO gas, and its identity has been unambiguously confirmed by a single-crystal X-ray diffraction analysis. The complex crystallizes in the space group Pmn21 as a three-component twin (a = 10.4280(4) Å, b = 6.3289(2) Å, c = 5.6854(2) Å, Z = 2, R1 = 0.065, wR2 = 0.176). Its solid-state molecular structure consists of a tungsten centre bound to three chloride ligands and three linear nitrosyl ligands in a fac-octahedral stereochemistry. In addition, the structure contains a crystallographically imposed mirror plane. The two independent WN linkages are 1.88(2) and 1.92(1) Å long, while the two corresponding NO bond lengths are 1.13(2) and 1.16(2) Å. DFT calculations on fac-W(NO)3Cl3 at the B3LYP/LANL2DZ level of theory afford optimized intramolecular metrical parameters that match the X-ray crystallographically determined bond lengths and bond angles quite well. In addition, they provide a rationale for the nearly linear W-N-O linkages extant in the complex. Solutions of fac-W(NO)3Cl3 in CH2Cl2 lose ClNO under ambient conditions and deposit the well-known [W(NO)2Cl2]n polymer, and this conversion is fully reversible.Key words: nitrosyl, tungsten, structure, bonding.
The crystal structure of a simple enol formed in a single-crystal-to-single-crystal enolene rearrangement
Authors: Chong Kenneth CW , Patrick Brian O , Scheffer John R
Published: March 2004

When crystals of 9-tricyclo[4.4.1.0]undecalyl-4-(carbomethoxy)phenyl ketone (1) were allowed to stand in the dark for extended periods of time at room temperature, the compound underwent a thermal reaction  the enolene rearrangement  to afford enol 2. The crystals remained transparent and appeared unchanged in shape as the reaction proceeded. X-ray diffraction data were collected on single crystals containing 17%, 25%, 66%, and 100% of the enol. The crystal structure of a simple enol was obtained via this novel single-crystal-to-single-crystal enolene rearrangement.Key words: single crystal, thermal, rearrangement, enol, enolene.
Molecular tectonics  Use of urethanes and ureas derived from tetraphenylmethane and tetraphenylsilane to build porous chiral hydrogen-bonded networks
Authors: Laliberté Dominic , Maris Thierry , Wuest James D
Published: March 2004

Tetraphenylmethane, tetraphenylsilane, and simple derivatives with substituents that do not engage in hydrogen bonding typically crystallize as close-packed structures with essentially no space available for the inclusion of guests. In contrast, derivatives with hydrogen-bonding groups are known to favor the formation of open networks that include significant amounts of guests. To explore this phenomenon, we synthesized six new derivatives 5a5e and 6a of tetraphenylmethane and tetraphenylsilane with urethane and urea groups at the para positions, crystallized the compounds, and determined their structures by X-ray crystallography. As expected, all six compounds crystallize to form porous three-dimensional hydrogen-bonded networks. In the case of tetraurea 5e, 66% of the volume of the crystals is accessible to guests, and guests can be exchanged in single crystals without loss of crystallinity. Of special note are: (i) the use of tetrakis(4-isocyanatophenyl)methane (1f) as a precursor for making enantiomerically pure tetraurethanes and tetraureas, including compounds 5b, 5c; and (ii) their subsequent crystallization to give porous chiral hydrogen-bonded networks. Such materials promise to include chiral guests enantioselectively and to be useful in the separation of racemates, asymmetric catalysis, and other applications.Key words: crystal engineering, molecular tectonics, hydrogen bonding, networks, porosity, urethanes, ureas, tetraphenylmethane, tetraphenylsilane.
Studies directed toward the synthesis of reiswigin A: Total synthesis of (±)-epi-reiswigin A
Authors: MaGee David I , Shannon Dean E
Published: March 2004

As a testing ground for the practical application of asymmetric synthesis, ()-reiswigin A, a potent antiviral agent, was chosen as a target for total synthesis. Initial studies were undertaken to prove the viability of the key asymmetric step, enantioselective deprotonation of an intermediate meso-bicyclic ketone, using a chiral lithium amide base. Enantiomeric excesses in the range of 90%94% were routinely obtained, even on runs as large as 10 g. Unfortunately, conversion of this key enantio-enriched intermediate to the natural product proved unsuccessful. While these studies were enroute, a parallel synthesis using the racemic compound was transformed into (±)-epi-reiswigin A.Key words: asymmetric deprotonation, synthesis, (±)-epi-reiswigin A.
Concerning the mechanism of the Friedländer quinoline synthesis
Authors: Muchowski Joseph M , Maddox Michael L
Published: March 2004

Detailed experiments regarding the mechanism of the Friedländer synthesis of quinolines from o-aminobenzaldehydes and simple aldehydes or ketones are described. Under the basic or acidic conditions commonly used in this reaction, it is concluded that the first step involves a slow intermolecular aldol condensation of the aldehyde or ketone with the o-aminobenzaldehyde. The aldol adduct 5 generated in this manner then undergoes very rapid cyclization to 4, which subsequently loses water to produce the quinoline derivative 8. Both 5 and 4 are too short lived to be detectable (TLC), even when deliberately generated by other means. It is also shown that E-enones corresponding to 6, i.e., the aldol dehydration product, are converted into quinolines (e.g., 21a and 21b from 17a and 17b) under basic or acidic conditions. Such enones are not detected as intermediates in the base-induced Friedländer synthesis, even though certain congeners (17b) would be easily observable. Under acidic conditions these enones are too short lived to be detectable. Schiff bases derived from 2-aminobenzaldehyde (18a) and aldehydes or ketones can be generated under special conditions, but they show reactivity patterns different from those seen in the usual Friedländer condensations. Thus, the ytterbium-triflate-catalyzed reaction of aldehydes with 18a at room temperature in toluene generates the E-Schiff bases (33, R1 = H), from which isomeric mixtures of tetrahydroquinoline derivatives 26 are formed exclusively. At higher temperatures, the E-Schiff bases 33 are isomerized to the Z-Schiff bases 34, from which the 3-substituted quinoline derivatives 24 are formed as the major products under appropriate conditions. Also, the ytterbium-triflate-catalyzed reaction of 18a with the pyrrolidine enamines of the methyl-n-alkylketones 38a,b produces mixtures in which the 2-monosubstituted kinetic products 37b,d predominate over the 2,3-disubstituted thermodynamic products 21c,e by a factor of 4:1 to 5:1. These results are opposite to those observed under the usual basic or acidic Friedländer reactions with methyl-n-alkylketones, where the thermodynamic products are usually strongly favored. The unusual kinetic:thermodynamic product ratios observed with 38a,b are ascribed to the generation and rapid cyclization of mixtures of the Schiff bases 35 and 36, in which the kinetic isomer 35 is highly predominant. Key words: mechanism, Friedländer synthesis, quinolines, intramolecular aldol reactions, Schiff bases, tetrahydroquinolines, high kinetic:thermodynamic product ratios.
The synthesis of two novel neutral receptors and their anion binding properties
Authors: Zeng Zhen-Ya , He Yong-Bing , Wei Lan-Hua , Wu Jin-Long , Huang Yan-Yan , Meng Ling-Zhi
Published: March 2004

Two new neutral receptors (1 and 2) containing thiourea and amide groups were synthesized by simple steps in good yields. The binding properties of 1 and 2 with anions were examined by UVvis, fluorescence, and 1H NMR spectroscopy. Receptor 1 had a better AcO: H2PO4 selectivity in comparison with that for receptor 2. The association constants of 1·AcO, 2·AcO, and 2·H2PO4 were higher in comparison with those of other anions (Cl, Br, I, p-NO2PhO, and p-NO2PhOPO32). In particular, a clear color change was observed, from pale yellow to red-brown, upon addition of AcO to the solution of 1 in DMSO. The UVvis and fluorescence data indicate that a 1:1 stoichiometry complex is formed between compound 1 or 2 and anions through hydrogen-bonding interactions.Key words: neutral receptors, anion recognition, synthesis, hydrogen bonds.
1,2-Bis-(1-{3-pyridyl-}3-methyltriazen-3-yl)ethane: Synthesis and X-ray crystal structure
Authors: Vaughan Keith , Turner Elizabeth , Jenkins Hilary
Published: March 2004

3-Aminopyridine is diazotized in the conventional manner and the diazonium salt coupled with N,N ′-dimethylethylenediamine to afford the title compound (1), which is a potential antitumour agent. The compound has been characterized by spectroscopic methods. The 1H NMR spectrum shows evidence of rotational conformerism, from the observation of broadening of the N-methyl signals in the room-temperature spectrum. Low-temperature NMR spectra (down to 223 K) show the presence of three distinct rotamers. The crystal structure of 1,2-bis-(1-{3-pyridyl-}3-methyltriazen-3-yl)ethane (1) has been determined by single crystal X-ray diffraction analysis. The bis-triazene (1) exists as the "staggered" conformation in the solid state, with an "antianti" configuration around the NN bond of the triazene units. The crystal structure of 1 is compared with the closely related bis-triazene 2 and also compared with the simple mono-triazene 3. Crystal data for 1, C14H18N8: orthorhombic, space group Pbca, a = 11.2550(8) Å, b = 8.8507(6) Å, c = 15.0069(10) Å, β = 90°, and V = 1494.91(18) Å3, for Z = 4.Key words: triazene, bis-triazene, pyridine, X-ray, VT NMR, diazonium coupling.
A new family of NxOy pyridine-containing macrocycles: Synthesis and characterization of their Y(III), Ln(III), Zn(II), and Cd(II) coordination compounds
Authors: Lodeiro Carlos , Bastida Rufina , Bértolo Emilia , Rodríguez Adolfo
Published: March 2004

Reaction between 2,6-bis(2-formylphenoxymethyl)pyridine and N,N-bis(3-aminopropyl)methylamine or tris(2-aminoethyl)amine has been used as the starting point for the synthesis of seven oxa-aza macrocyclic ligands, five of them never reported previously. They all feature different pendant arms, which provide a wide range of coordination possibilities. The Schiff base macrocycles L1 and L4 and their reduced ligands L2 and L5 are derived from 2,6-bis(2-formylphenoxymethyl)pyridine and tris(2-aminoethyl)amine or N,N-bis(3-aminopropyl)methylamine, respectively. The reaction of L1 with salicylaldehyde forms L3, which features an imine bond in the pendant arm. The ligand L5 has been the precursor for the pendant-armed L6 and L7, by alkylation of the free NH groups with methyl-imidazole or methyl-indole. By a template or a nontemplate approach, we have synthesized different mono- and dinuclear complexes with Y(III), Ln(III), Zn(II), and Cd(II) cations. Both the free macrocyclic ligands and their corresponding metal complexes have been characterized by microanalysis, IR, UVvis, 1H and 13C NMR spectroscopy, FAB mass spectrometry, MS electrospray, and conductivity measurements.Key words: Schiff-base macrocycle, template synthesis, macrocyclic ligand complexes, lanthanide(III) complexes.
Packed-column supercritical fluid chromatography with splitless flame ionization detection
Authors: Thurbide Kevin B , Gilbert Shawn
Published: March 2004

The design and characterization of a flame ionization detector (FID) that is compatible with the high flow rates of packed-column supercritical fluid chromatography (pSFC) is presented. The modified FID uses a large quartz burner (4.0 mm i.d.) in place of the conventional burner (0.4 mm i.d.) and operates a stable flame in the presence of gas flows tested up to nearly 3000 mL/min. This modification allows the full flow of effluent from a pSFC column (i.e., splitless mode) to be directed into the FID. Results demonstrate that the modified FID yields response that is within a factor of 3 to that of a commercial FID. The attributes of the modified detector indicate that this approach could be a reliable and relatively simple means of achieving a splitless pSFC-FID system.Key words: supercritical fluid chromatography, packed column, splitless, flame ionization detector.
Consequences of various landscape-scale ecosystem management strategies and fire cycles on age-class structure and harvest in boreal forests
Authors: Fall Andrew , Fortin Marie-Josée , Kneeshaw Daniel D , Yamasaki Stephen H , Messier Christian , Bouthillier Luc , Smyth Cheryl
Published: March 2004

At the landscape scale, one of the key indicators of sustainable forest management is the age-class distribution of stands, since it provides a coarse synopsis of habitat potential, structural complexity, and stand volume, and it is directly modified by timber extraction and wildfire. To explore the consequences of several landscape-scale boreal forest management strategies on age-class structure in the Mauricie region of Quebec, we used spatially explicit simulation modelling. Our study investigated three different harvesting strategies (the one currently practiced and two different strategies to maintain late seral stands) and interactions between fire and harvesting on stand age-class distribution. We found that the legacy of initial forested age structure and its spatial configuration can pose short- (<50 years) to medium-term (150300 years) challenges to balancing wood supply and ecological objectives. Also, ongoing disturbance by fire, even at relatively long cycles in relation to historic levels, can further constrain the achievement of both timber and biodiversity goals. For example, when fire was combined with management, harvest shortfalls occurred in all scenarios with a fire cycle of 100 years and most scenarios with a fire cycle of 150 years. Even a fire cycle of 500 years led to a reduction in older forest when its maintenance was not a primary constraint. Our results highlight the need to consider the broad-scale effects of natural disturbance when developing ecosystem management policies and the importance of prioritizing objectives when planning for multiple resource use.
Long-term forest utilization can decrease forest floor microhabitat diversity: evidence from boreal Fennoscandia
Authors: Kuuluvainen Timo , Laiho Raija
Published: March 2004

Forest floor microhabitat diversity was studied in old Pinus sylvestris L. dominated forest sites in two regions within the middle boreal vegetation zone in Fennoscandia: in 50 managed forest sites in the Häme region in southwestern Finland and in 45 natural or old selectively logged forest sites in the KuhmoViena region in northeastern Finland and northwestern Russia. The forests in the Häme region are characterized by a long history of forest utilization, while the forests in the KuhmoViena region can be regarded as natural or near natural. The managed forest sites in Häme had significantly lower forest floor microhabitat diversity compared with natural and near-natural forests. Microhabitats that were significantly more scarce in managed versus natural and near-natural forest sites included humps, depressions, decayed wood, and vicinity of decayed wood. On the other hand, even ground was significantly more abundant in managed forest compared with natural and near-natural forest. Microhabitat availability was also reflected in the occurrence of tree saplings growing in different microhabitats. The results suggest that long-term forest utilization has decreased forest floor microhabitat diversity. This has occurred because of a decreased amount of fallen deadwood and, possibly, lack of soil disturbances because of fewer uprootings caused by falling trees.
Forest inventory estimation with mapped plots
Authors: Van Deusen Paul C
Published: March 2004

Procedures are developed for estimating means and variances with a mapped-plot design. The focus is on fixed-area plots, and simulations are used to validate the proposed estimators. The mapped-plot estimators for means and variances are compared with simple random sampling estimators that utilize only full plots. As expected, the mapped-plot estimates have smaller mean squared errors than the simple random sampling estimates. The theory for fixed-area plots is easy to apply, although additional work is required to map plots in the field. Corresponding theory for variable plots is developed but not tested with simulations. The difficulty of applying these methods to variable plots is greater, but not prohibitive.
The effect of spacing rectangularity on stem quality in loblolly pine plantations
Authors: Amateis Ralph L , Radtke Philip J , Hansen Gerald D
Published: March 2004

The effect of spacing rectangularity on tree stem quality was evaluated using data collected from a loblolly pine (Pinus taeda L.) spacing trial measured at age 19. In this trial, bole condition, branch size, and stem asymmetry were examined on plots with an initial planting density of 2240 trees/ha planted at slight (3:4) and greater (1:3) rectangular spacings to determine suitability for sawtimber production. Results indicated that rectangularity had no significant effect on survival or the number of potential sawtimber trees by age 19. While the 1:3 spacing treatment had a significantly larger maximum branch size than the 3:4 spacing treatment, it could not be attributed to the within-row or between-row direction. Additional measurements on stem diameter at breast height within and between rows failed to show stem asymmetry in the 1:3 spacing treatment. Consequently, rectangular spacings up to 1:3 should not have much impact on overall stem quality.
Tree rings from a European beech forest chronosequence are useful for detecting growth trends and carbon sequestration
Authors: Bascietto Marco , Cherubini Paolo , Scarascia-Mugnozza Giuseppe
Published: March 2004

Past carbon (C) storage trends were estimated using dendroecological methods in a beech chronosequence in central Germany. Raw-ring-width chronologies, sensitivity curves, and carbon uptake trends were developed for 70-, 110-, and 150-year-old (S70, S110, and S150), even-aged stands. Ecosystem C stock and net ecosystem productivity (NEPC) were computed as the sum of the C stock and fluxes of the soil, the aboveground compartment, and the estimated belowground compartment. The ecosystem C stock ranged from 216 t C·ha1 in S150, to 265 t C·ha1 in S70, to 272 in S110. NEPC values followed ecosystem C stocks, ranging from 1.7, to 2.4, to 5.1 t C·ha1·year1 for S150, S70, and S110, respectively. Stem C-stock uptake rate in S110 showed an increase in growth rate over the first 110 years of S150. We estimate that this increase in stem C stock was 6.2%. Given the constancy of forest management among the stands of the chronosequence, we hypothesize that the increase in C stock shown by S110 is due to indirect human-induced effects. We conclude that managed young forests can take advantage of increased resources and counteract the C losses at harvest that are seen in the old forests.
Structure and dynamics of trembling aspen  white spruce mixed stands near Fort Nelson, B.C.
Authors: Kabzems Richard , García Oscar
Published: March 2004

The trembling aspen (Populus tremuloides Michx.)  white spruce (Picea glauca (Moench) Voss) mixed woods near Fort Nelson are distinguished by the large size of individual trees, longevity, and the low occurrence of internal decay in trembling aspen. The development of these forest ecosystems has had limited documentation and may be significantly different than those described in other portions of the boreal forest. At five study stands, stem analysis techniques were used to examine the patterns of height and radial growth over time according to species and structure type. There were two patterns of species establishment that were consistent with the stand structure. In codominant stands, recruitment periods for trembling aspen and white spruce overlapped. The stratified stands were consistently associated with a 29- to 58-year lag in white spruce recruitment. Spruce that were codominant with aspen at the time of sampling had sustained periods of rapid height and diameter growth. White spruce that were later to establish on site had slower rates of height and diameter growth. White spruce ages indicated that a dominant recruitment episode was more common than continuous recruitment. Height and diameter growth of trembling aspen were similar in both stand types. The differences in trembling aspen growth patterns between stands were due to site quality. The white spruce in codominant stands did not appear to go through a period of suppression and then release associated with stand-level trembling aspen mortality, as commonly described for other boreal mixedwoods. The vigor and longevity of trembling aspen in Fort Nelson appear to prolong the period of trembling aspen domination of mixed stands well beyond the time periods observed in other boreal ecosystems.
Within-stand variation in windthrow in southern boreal forests of Minnesota: Is it predictable?
Authors: Peterson Chris J
Published: March 2004

Wind damage to forests is determined by numerous factors that interact to produce complex, seemingly random damage patterns. However, the complexity may lie mostly among stands and be less within stands: in this study, I attempted to discern how predictable tree fall risk is within five southern boreal forest stands in northeastern Minnesota. I sampled five stands in the Boundary Waters Canoe Area Wilderness, following a July 1999 catastrophic windstorm. Levels of damage varied from 29.5% to 86.8% of basal area fallen and 23.3% to 63.4% of stems fallen. In all sites, the disturbance reduced mean trunk diameter of standing trees. In general, Abies balsamea (L.) Mill. was the most vulnerable species. I split the data set from each site into predictor and test portions and used the predictor data sets to derive logistic regression parameters for the relationship of tree size (trunk diameter) to probability of tree fall. Models based on these parameters allowed quite accurate predictions of the levels of damage in the test portion of each stand. For the five sites, the proportion of test trees predicted to fall differed from the proportion observed to fall by 5.7%, 3.9%, 8.3%, 1.4%, and 3.7% of the total test sample size. This suggests that while numerous factors indeed influence tree fall risk, the sizes and identities of trees may account for most of the within-stand variation in damage.
Temporal, spatial, and structural patterns of adult trembling aspen and white spruce mortality in Quebec's boreal forest
Authors: Senecal Dominic , Kneeshaw Daniel , Messier Christian
Published: March 2004

Temporal, spatial, and structural patterns of adult trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) mortality were studied in intact 150-year-old stands in the southwestern boreal forest of Quebec. For both species, mortality decreases (number of dead trees/total number of trees) with distance from the lake edge until 100150 m, from which point it slightly increases. Strong peaks in mortality were found for 40- to 60-year-old aspen mainly between 1974 and 1992. Such mortality in relatively young aspen is likely related to competition for light from the dominant canopy trees. Also, the recruitment of this young aspen cohort is presumably the result of a stand breakup that occurred when the initial aspen-dominated stand was between 90 and 110 years old. For spruce, strong peaks in mortality were found in 110- to 150-year-old trees and they occurred mainly after 1980. No clear explanation could be found for these peaks, but we suggest that they may be related to senescence or weakening of the trees following the last spruce budworm outbreak. Suppressed and codominant aspen had a much higher mortality ratio than spruce in the same height class, while more surprisingly, no difference in mortality rate was found between dominant trees of the two species. Most spruce trees were found as standing dead, which leads us to reject the hypothesis that windthrow is an important cause of mortality for spruce in our forests.
Gap dynamics and replacement patterns in gaps of the northeastern boreal forest of Quebec
Authors: Pham Anh Thu , Grandpré Louis De , Gauthier Sylvie , Bergeron Yves
Published: March 2004

The northeastern boreal forest of Quebec is characterized by a humid climate. Consequently, fires are less frequent and small-scale disturbances play an important role in forest dynamics. Natural mortality and nonfire disturbances such as insect outbreaks and windthrow lead to gap-driven processes. Changes in structure and species composition can result from gap dynamics. The objectives of this study were to characterize gaps and examine patterns of species replacement in gaps in old conifer stands. Line intersect sampling was used to sample stands dominated by balsam fir (Abies balsamea (L.) Mill.) and (or) black spruce (Picea mariana (Mill.) BSP). Results show that 54% of the forest was in expanded gaps and that canopy gaps are relatively small, since 87% of them were smaller than 100 m2. The majority (94%) of the openings were caused by the mortality of less than 10 gap makers. Replacement probabilities show self-replacement of A. balsamea in Abies stands and of P. mariana in Picea stands. However, in Abies-Picea stands, there seems to be a reciprocal replacement of the two species. These results provide knowledge of the disturbance dynamics of the region as a basis for development of silvicultural practices that preserve the structural components of older forest stands.
Range of variability in boreal aspen plant communities after wildfire and clear-cutting
Authors: Haeussler Sybille , Bergeron Yves
Published: March 2004

Composition, structure, and diversity of vascular and nonvascular plant communities was compared 3 years after wildfire and clear-cutting in mesic trembling aspen (Populus tremuloides Michx.) forests of the southern Canadian boreal forest. We examined mean response to disturbance and variability around the mean across four to five spatial scales. Four 1997 wildfires were located near Timmins, Ontario, and ten 19961997 clearcuts were located adjacent to the wildfires. We randomly located plots within mesic, aspen-dominated stands selected to minimize predisturbance environmental differences. Correspondence analysis separated wildfire and clearcut samples based on community composition: wildfires had more aspen suckers, Diervilla lonicera Mill., and pioneering mosses; clearcuts had more under story tall shrubs, forbs, bryophytes, and lichens. Live tree basal area averaged 1.7 m2/ha in wildfires and 1.8 m2/ha in clearcuts (p = 0.59), and understory community structure (the horizontal and vertical distribution of live and dead plant biomass) was not markedly different. Clearcuts had higher species richness with greater variance than wildfires across all spatial scales tested, but differences in beta and structural diversity varied with spatial scale. Generally, clearcutwildfire differences were more evident and wildfire variability greater at larger analytical scales, suggesting that plant biodiversity monitoring should emphasize cumulative effects across landscapes and regions.
Characterization of canopy openness before and after a spruce budworm outbreak in the southern boreal forest
Authors: D'Aoust Vincent , Kneeshaw Daniel , Bergeron Yves
Published: March 2004

We propose a simple method that uses aerial photographs to characterize the impacts of a spruce budworm (Choristoneura fumiferana (Clem.)) outbreak on canopy structure. Using aerial photographs taken at the beginning (1972) and after (1994) a major spruce budworm outbreak (19701987), we evaluated the change in canopy openness that occurred during the period of the outbreak, in five compositionally different stands. We compared canopy openness evaluated by photointerpretation with two independent field techniques and found a high degree of similarity between methods. Interpretation of the 1972 photographs (prior to the outbreak) shows that regardless of composition, four of our five analysed stands had about the same degree of mean canopy openness (17%20%). Following the outbreak, openness increased in all stands except for the hardwood-dominated stand. The highest increase in openness (from 18% to 45%) occurred in the stand with the highest conifer content. Thematic maps and spatial analysis techniques were used to describe canopy openness distribution. Openness was low and uniformly distributed before the outbreak, whereas after the outbreak, the various degrees of openness had a patchy distribution in most stands. Furthermore, patch size increased with conifer content. Using the amount of increase in canopy openness and its specific distribution within stands, we propose guidelines for the development of silvicultural practices that mimic spruce budworm disturbances in boreal mixedwoods.
Stratified space angle-count sampling for an estimation of stand volume
Authors: Nakagawa Masahiko
Published: March 2004

Stratified space angle-count sampling is a newly proposed method for estimating stand volume. This new method includes the theory and all the premises of space point sampling, as well as the following: (i) all trees taper, (ii) the box-like sampling space imagined in space point sampling is divided into several strata with the same vertical distances, (iii) the diameter of expanded tree stems in each stratum is represented at the middle of the vertical distance in each stratum. Stand volume is calculated using the following equation: V (m3/ha)=kH/Z Σ[Formula: see text] λi, where V is volume (m3/ha), k is basal area factor (m2/ha), H is the maximum tree height in the stand, Z is the number of strata in the sampling space, N is the number of trees in the stand, and λi is an indicator variable that takes the value 1 or 0, depending on whether the tree stem is in the sample or not. Since this method does not require a measurement or an estimation of a critical height, it could be an easy method for estimating stand volume.
SYMBOLIC PERFORMANCE ESTIMATION OF SPECULATIVE PARALLEL PROGRAMS
Authors: GAUTAMA H. , VAN GEMUND A. J. C.
Published: March 2004

Speculative parallelism refers to searching in parallel for a solution, such as finding a pattern in a data base, where finding the first solution terminates the whole parallel process. Different performance prediction methods are required as compared to traditional parallelism. In this paper we introduce an analytical approach to predict the execution time distribution of data-dependent parallel programs that feature N-ary and binary speculative parallel compositions. The method is based on the use of statistical moments which allows program execution time distribution to be approximated at O(1) solution complexity. Measurement results for synthetic distributions indicate an accuracy that lies in the percent range while for empirical distributions on internet search engines the prediction accuracy is acceptable, provided sufficient workload unimodality.
Predicated Partial Redundancy Elimination using a Cost Analysis
Authors: Scholz Bernhard , Mehofer Eduard , Horspool Nigel
Published: March 2004

Partial redundancy elimination (PRE) is a key technology for modern compilers. However traditional approaches are conservative and fail to exploit many opportunities for optimization. New PRE approaches which greatly increase the number of eliminated redundancies have been developed. However, they either cause the code size to explode or they cannot handle statements with side-effects. In this paper we describe a predicated partial redundancy elimination (PPRE) approach which can potentially remove all partial redundancies. To avoid performance overheads caused by predication, PPRE is applied selectively based on a cost model. The cost analysis presented in the paper utilizes probabilistic data-flow information to decide whether PPRE is profitable for each instance of a partially redundant computation. Refinements of the basic PPRE transformation are described in detail. In contrast to some other approaches our transformation is strictly semantics preserving.
AUTOMATED NEGOTIATION BETWEEN PUBLISHERS AND CONSUMERS OF GRID NOTIFICATIONS
Authors: LAWLEY RICHARD , LUCK MICHAEL , DECKER KEITH , PAYNE TERRY , MOREAU LUC
Published: March 2004

Notification services mediate between information publishers and consumers that wish to subscribe to periodic updates. In many cases, however, there is a mismatch between the dissemination of these updates and the delivery preferences of the consumer, often in terms of frequency of delivery, quality, etc. In this paper, we present an automated negotiation engine that identifies mutually acceptable terms; we study its performance, and discuss its application to a Grid notification service. We also demonstrate how the negotiation engine enables users to control the Quality of Service levels they require.
OPTIMIZATION AND PROFILING OF THE CACHE PERFORMANCE OF PARALLEL LATTICE BOLTZMANN CODES
Authors: POHL THOMAS , KOWARSCHIK MARKUS , WILKE JENS , IGLBERGER KLAUS , RÜDE ULRICH
Published: March 2004

When designing and implementing highly efficient scientific applications for parallel computers such as clusters of workstations, it is inevitable to consider and to optimize the single-CPU performance of the codes. For this purpose, it is particularly important that the codes respect the hierarchical memory designs that computer architects employ in order to hide the effects of the growing gap between CPU performance and main memory speed. In this article, we present techniques to enhance the single-CPU efficiency of lattice Boltzmann methods which are commonly used in computational fluid dynamics. We show various performance results for both 2D and 3D codes in order to emphasize the effectiveness of our optimization techniques.