bluuebunny/crossref_metadata_2025 huggingface dataset:
Fire history and structure of red fir (Abiesmagnifica) forests, Swain Mountain Experimental Forest, Cascade Range, northeastern California
Authors: Taylor Alan H.
Published: July 2007

The fire history and stand structure (size, age, horizontal pattern) of red fir (Abiesmagnifica A. Murr) forests were studied in two 3.0-ha plots and a larger study area (400 ha) on the Swain Mountain Experimental Forest to identify the fire regime and the effects of fire on stand structure. The fire record in stumps spanned the period 1740–1985. Fires occurred in the 400-ha study area on average every 12.9 years (range 1–57 years), in plot 1 every 18.6 years (range 7–47 years), and in plot 2 every 15.7 years (range 1–45 years). Larger fires recorded in both plots and throughout the larger study area occurred every 26.2 years (range 11–47 years). Average fire-free intervals were shorter (7.9 years) during the settlement–pre-fire-sup-pression period (1851–1934) than during the presettlement (1740–1850) (21.4 years) and fire-suppression (1935–1985) (17.3 years) periods. Severe fires initiated large cohorts of red and white fir (Abiesconcolor (Gord. & Glend.) Lindl.), while low-severity fires probably caused thinning and initiated small patches of trees.
Element distribution in red spruce (Picearubens) fine roots; evidence for aluminium toxicity at Whiteface Mountain: Reply
Authors: Schlegel Hedda , Amundson Robert G. , Hüttermann Aloys , Godbold Douglas L.
Published: July 2007

not available
Canopy stratification, age structure, and development of multicohort stands of eastern white pine, eastern hemlock, and red spruce
Authors: Fajvan Mary Ann , Seymour Robert S.
Published: July 2007

The causes of canopy stratification were investigated in five mixed stands of red spruce (Picearubens Sarg.), hemlock (Tsugacanadensis (L.) Carr.), and white pine (Pinusstrobus L.) in eastern Maine. All species were present in all crown classes; however, there was a clear pattern of pine dominance and eventual emergence. Red spruce was prevalent in the middle stratum, and hemlock most common in the lower strata. Canopy stratification was caused by interspecific differences in shade tolerance and height growth, and by multicohort structures. The multicohort structures developed as a result of episodic partial disturbances such as spruce budworm (Choristoneurafumiferana Clemens) outbreaks and partial harvesting that both initiated regeneration and released previously suppressed trees of older, surviving cohorts. Spatial and temporal variability in disturbances created extremely variable patterns of competition among cohorts, resulting in a more complex developmental pattern than would be found in a single-cohort model involving stand-replacing disturbances.
Sampling and predicting tree dry weight
Authors: Van Deusen Paul C. , Baldwin Jr. V.C.
Published: July 2007

Procedures and formulae are given for modeling and sampling ovendry weight of a tree bole. The models are derived from first principles, and importance sampling ideas are used to develop methods for sampling individual trees to obtain unbiased estimates of dry weight. These methods would be particularly useful for providing sample estimates of the dry weight of a stand of trees.
Genetic parameter estimates for wood density, transition age, and radial growth in slash pine
Authors: Hodge G.R. , Purnell R.C.
Published: July 2007

Genetic parameters for wood density and wood density components of slash pine (Pinuselliottii Engelm.) were estimated using measurements on 56 open-pollinated families. Increment cores were taken at breast height from six trees per family on each of two sites and density profiles generated using X-ray densitometry. There was no practical genetic variance for earlywood density; however, ring density, latewood density, latewood percentage, and transition ages for those traits were all heritable. Moderate selection pressure (selection of top 25%) on transition age would be expected to decrease transition age by approximately 1 year, but this would likely cause a correlated increase in the density of juvenile wood, and decrease in the density of mature wood. Selection for increased mature wood density and juvenile wood density will likely increase whole tree density by 0.02 g/cm3.
Freezing stress tolerance of hardy and tender families of loblolly pine
Authors: Hodge G.R. , Weir R.J.
Published: July 2007

The freezing behavior of shoot tips of cold-acclimated loblolly pine (Pinustaeda L.) from four half-sib families varying in hardiness were studied using nuclear magnetic resonance techniques. Freeze dehydration strain was measured both as the fraction of freezable water frozen (FWF), and contraction strain index (CSI), and differences in hardiness of hardy and tender families were partitioned into differences in strain avoidance and strain tolerance. If dehydration strain is measured as FWF, differences between hardy and tender loblolly families could be explained almost completely as differences in strain tolerance. If dehydration strain is measured as CSI, strain tolerance accounts for a large percentage (≥60%) of the difference in hardiness, although avoidance may also play a role. Hardy families keep a larger fraction of their total cell water in a bound or osmotically inactive state, thus incurring less cell contraction associated with losing cell water volume to freeze dehydration.
Effects of overtopping vegetation on light availability and growth of Engelmann spruce (Piceaengelmannii) seedlings
Authors: Comeau Philip G. , Braumandl Thomas F. , Xie Chang-Yi
Published: July 2007

To examine the effects of overtopping vegetation on solar irradiance reaching Engelmann spruce (Piceaengelmannii Parry) seedlings and on crop seedling performance, neighborhood studies were established at six sites in mixed shrub–herb and fireweed communities of the Interior Cedar–Hemlock zone of southern British Columbia. These communities were dominated by mixtures of fireweed (Epilobiumangustifolium L.), thimbleberry (Rubusparviflorus Nutt.), red raspberry (Rubusidaeus L.), and (or) bracken fern (Pteridiumaquilinum (L.) Kuhn). Three hundred and eighty-eight planted Engelmann spruce seedlings, between 1 and 5 years of age, served as plot centers for measurements in 1990 and 1991. Vegetation had been clipped around 109 of these seedlings in 1988, 1989, and 1990. Seedling diameter and height were measured in the autumn of 1990 and 1991. Vegetation cover, vegetation height, and the fraction of full sunlight reaching the top branches of each spruce seedling were measured in midsummer of 1991. A simple competition index (CI), based on visually estimated percent cover, height of each species present within 1.26 m of the crop seedling, and crop-seedling height, can be used to estimate the fraction of full sunlight reaching crop seedlings. Measurements of transmittance through vegetation canopies are correlated with this competition index and could be useful as a separate, objective assessment of competition levels. Seedling growth was related to both seedling-needle biomass (at the beginning of the year) and either CI or the amount of light reaching crop seedlings during midsummer. Growth increased as needle biomass or irradiance reaching the seedling increased and decreased as CI increased. Since CI can be calculated from simple field measurements and since seedling growth is related to CI, this index has potential utility in evaluating the need for operational release treatments. Transmittance measurement provides an equally useful, and potentially more objective approach to evaluating the need for release treatment. Results from this study suggest that cumulative effects of competition result at least in part from effects on growth of seedling leaf mass.
Comparison of duration and method of herbaceous weed control on loblolly pine response through midrotation
Authors: Lauer Dwight K. , Glover Glenn R. , Gjerstad Dean H.
Published: July 2007

Herbaceous weed control studies installed by the Auburn University Silvicultural Herbicide Cooperative to examine response to methods and duration of herbaceous weed control in eight loblolly pine (Pinustaeda L.) plantations were analyzed to determine stand response through age 9. Studies were designed to compare weed control treatments with an untreated check, weed control methods (band vs. broadcast), and weed control duration (first year vs. first 2 years). Pine growth was increased by weed control on all sites. Growth was increased by an additional year of weed control (duration) on about one-half of the sites, but did not differ between band and broadcast treatments (method). Age 9 volume response above the check averaged 27.3 m3/ha for first-year weed control and 42.9 m3/ha for the first 2 years of weed control. Individual-tree height growth between ages 7 and 9 did not differ by treatment at most sites, but stand volume growth was higher with weed control at six of the eight sites. Uniformity of individual tree size, as represented by the standard deviation of DBH adjusted for dominant height, was more dependent on survival, hardwood encroachment, and level of fusiform rust stem infection, which varied by treatment and site, than on the result of herbaceous weed control per se. Growth projections made with the least intensive weed control treatment at each site indicated that on average, merchantable volume at age 22 with weed control will equal that of an age 25 stand without weed control. Largest gains were on sites where weed control increased survival.
Effect of plant moisture stress on absorption and translocation of triclopyr in oak seedlings
Authors: Seiler J.R. , Cazell B.H. , Schneider W.G. , Zedaker S.M. , Kreh R.E.
Published: July 2007

Ways to maximize herbicide efficacy are of great concern to most forest managers. Many factors influence the efficacy of herbicides, including the physiological status of the plant and its effect on the translocation of herbicides. This study investigated how plant moisture status affected herbicide absorption and translocation. The ester formulation of [14C]triclopyr was applied to the foliage of 8-month-old, container-grown water oak (Quercusnigra L.) and southern red oak (Quercusfalcata Michx.) seedlings. At the time of treatment, seedlings were in soil with average moisture contents of 5 and 35% by weight. Corresponding seedling xylem water potentials averaged −1.8 and −0.3 MPa, respectively. Triclopyr absorption was not significantly affected by the soil moisture treatment. However, translocation to stems and roots was 62 and 48% lower, respectively, in water-stressed seedlings. Water oak absorbed 23% less than southern red oak when averaged over the soil moisture treatments. Scheduling herbicide applications when moisture is plentiful could improve triclopyr efficacy.
Hexazinone toxicity in red pine and jack pine
Authors: Wood James E. , Scarratt John B. , Stephenson Gerald R.
Published: July 2007

Experiments were conducted under controlled environmental conditions to determine the toxicity of hexazinone (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione) to red pine (Pinusresinosa Ait.) and jack pine (P. banksiana Lamb.) during their period of rapid shoot elongation in spring and after initiation of overwintering buds in August. Red pine was a minimum of 10- and 12-fold more tolerant to soil-applied hexazinone than was jack pine on the basis of effective concentration values (EC50, the herbicide concentration that results in a 50% growth reduction compared with the control) for root dry weight and shoot fresh weight, respectively. In the spring experiment, EC50 values were approximately 0.062 and 1.75 kg a.i. (active ingredient)•ha−1 for jack pine and red pine shoot fresh weights, respectively. For root dry weight, EC50 values were roughly 0.04 and 2.0 kg a.i.•ha−1 for jack pine and red pine, respectively. Except for a somewhat reduced sensitivity in jack pine, similar results were obtained with soil applications of hexazinone after bud initiation in August.
A numerical method for the solution of a base-age-specific site index model
Authors: Wang Yonghe , Payandeh Bijan
Published: July 2007

A numerical solution was derived for previously published site index equations for trembling aspen (Populustremuloides Michx.). Data from aspen stands in north central Ontario were used to verify the validity and accuracy of the numerical method. With the numerical solution, only the height-growth equation is employed to estimate (i) height from site index and age and (ii) site index from height and age. The numerical method simplified site index estimation and improved its accuracy for aspen stands in north central Ontario.
20 YEARS OF LATTICE DYNAMICS: A PERSONAL VIEW
Authors: POMEAU YVES
Published: July 2007

I show how the idea of lattice gases started in kinetic theory of gases, specifically as a way to study the divergences of the density expansion beyond the Boltzmann order. I end up by sketching an attempt made in informal discussions with Brosl Hasslacher to build a quantum lattice gas.
FULL NEWTON LATTICE BOLTZMANN METHOD FOR TIME-STEADY FLOWS USING A DIRECT LINEAR SOLVER
Authors: NOBLE DAVID R. , HOLDYCH DAVID J.
Published: July 2007

A full Newton lattice Boltzmann method is developed for time-steady flows. The general method involves the construction of a residual form for the time-steady, nonlinear Boltzmann equation in terms of the probability distribution. Bounce-back boundary conditions are also incorporated into the residual form. Newton's method is employed to solve the resulting system of non-linear equations. At each Newton iteration, the sparse, banded, Jacobian matrix is formed from the dependencies of the non-linear residuals on the components of the particle distribution. The resulting linear system of equations is solved using a direct solver designed for sparse, banded matrices. For the Stokes flow limit, only one matrix solve is required. Two dimensional flow about a periodic array of disks is simulated as a proof of principle, and the numerical efficiency is carefully assessed. For the case of Stokes flow (Re = 0) with resolution 251×251, the proposed method performs more than 100 times faster than a standard, fully explicit implementation.
LATTICE–BOLTZMANN SIMULATION OF DENSE NANOFLOWS: A COMPARISON WITH MOLECULAR DYNAMICS AND NAVIER–STOKES SOLUTIONS
Authors: SUCCI S. , MOHAMMAD A. A. , HORBACH J.
Published: July 2007

In a recent work, a dense fluid flow across a nanoscopic thin plate was simulated by means of Molecular Dynamics (MD) and Lattice Boltzmann (LB) methods. It was found that in order to recover quantitative agreement with MD results, the LB simulation must be pushed down to sub–nanoscopic scales, i.e. fractions of the range of molecular interactions. In this work, we point out that in this sub–nanoscopic regime, the LB method works outside the hydrodynamic limit at the level of a single cell spacing. A quantitative comparison with the Navier–Stokes (NS) solution shows however that LB and NS results are quite similar, thereby indicating that, apart for a small region past the plate, this nanoflow is still well described by hydrodynamic equations.
INFERRING THE DISTRIBUTION OF INTER-REACTION INTERVALS FOR DIFFUSION-LIMITED REACTIONS ON LATTICES
Authors: RODRÍGUEZ JORDI VIDAL , KAANDORP JAAP A.
Published: July 2007

We study the operator-split method Gillespie-MultiParticle method (GMP) for a diffusion-limited reaction in a finite medium by looking at the detailed distribution of reaction times for a broad range of time scales. The diffusion-limited reaction lies at the lower limits of the applicability of the GMP method. We propose an empirical distribution for the inter-reaction times (duration of the dissociated state) that accounts for the power-law and exponential regimes. The knowledge of this distribution can be used to change the reactive method of GMP and enable it to use coarser discretization, with consequent improvement in performance.
OPTIMIZATION OF BIT-PAIRING CODIFICATION WITH LEARNING FOR 3D RECONSTRUCTION
Authors: CHENG JUN , CHUNG RONALD , LAM EDMUND Y. , FUNG KENNETH S. M. , XU YANGSHENG
Published: July 2007

Coded structured light is an active approach that obtains the shape of object. In our previous work, we proposed a new binary projection mechanism for inspecting semiconductor products. The mechanism consists of only a single light source in combination with a binary grating for projecting binary pattern. By shifting the binary grating in space and in every shifting taking a separate image of the illuminated surface, each position on the illuminated surface is attached with a unique binary string for correspondence. In the mechanism the inspection speed is governed by the number of needed images which also equals to the number of shiftings of the grating. To reduce image number, we propose that two neighbor bits are combined together to produce unique codeword, which is referred to as bit-pairing mechanism. This paper addresses how the spatial shifting of bit-pairing mechanism can be designed optimally for minimizing this number for faster inspection speed. An optimal solution to shifting strategy optimization is proposed that is applicable to any given binary patterns. Theoretical analysis and real image experiments are presented to illustrate the workability of the solutions.
Surgical management of endometriosis
Authors: Kenney Nicholas , English James
Published: July 2007

Key content

Advances in laparoscopic surgery have made the surgical management of endometriosis an effective treatment that offers advantages over medical therapy.

The majority of gynaecologists readily perform laparoscopic ablation of superficial disease. Excision of deeper disease and management of rectovaginal disease require more expertise and should be managed in tertiary centres.

Hysterectomy should not be necessary in the majority of cases. Although some women may benefit, extrauterine disease should also be excised.

Evidence suggests that laparoscopic uterine nerve ablation (LUNA) has no effect on long‐term symptoms.

There is no consensus as to the optimal surgical approach for rectal disease. A multicentre, randomised controlled trial is urgently required to resolve the issue.

Learning objectives

To understand the role of surgery in the management of endometriosis.

To be aware of the best available evidence so that the optimal approach can be used when performing surgery.

To be aware of the preoperative care of women with advanced disease and when to refer them for further management.

Ethical issues

What should be regarded as an acceptable complication rate for women undergoing surgery for advanced endometriosis?

What level of training should gynaecologists reach if they are to be judged competent in the surgical management of endometriosis?

Given that the surgical management of endometriosis is a developing skill, where is the boundary between accepted and acceptable practice?

Please cite this article as: Kenney N, English J. Surgical management of endometriosis. The Obstetrician & Gynaecologist 2007;9:147–152.
Bis(azidomethyl) oxetane/hydroxyl‐terminated polybutadiene/bis(azidomethyl) oxetane triblock copolymer: Synthesis and characterization
Authors: Reddy T. S. , Nair J. K. , Satpute R. S. , Wagh R. M. , Sikder A. K. , Venugopalan S.
Published: July 2007

A copolymer consisting of bis(azidomethyl) oxetane and hydroxyl‐terminated polybutadiene was synthesized with different monomer ratios via an activated monomer mechanism. The copolymer thus obtained was characterized with Fourier transform infrared, 1H‐NMR, molecular weight, and polydispersity measurements. Rhe‐ological and thermal studies were also carried out. The mechanical properties of the gum stock obtained through curing with toluene diisocyanate and crosslinking with pyrogallol at about 50°C were also determined. This was an attempt to combine the useful properties of hydroxyl‐terminated polybutadiene (a nonenergetic binder providing excellent mechanical properties) and poly[bis(azidomethyl) oxetane] (an energetic binder). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Diastereoselective Synthesis of 4‐Hydroperoxy‐3,5‐cyclohexadienones in the Photooxygenation of Hydroxyethyl‐Substituted Phenols
Authors: Prein Michael , Maurer Michael , Peters Eva Maria , Peters Karl , von Schnering Hans Georg , Adam Waldemar
Published: July 2007

Three of the four possible isomeric para‐substituted hydroxyethyl‐methylphenols were prepared from readily available starting materials and submitted to photooxygenation. In the case of 3‐hydroxy‐α,6‐dimethylbenzenemethanol (1 a) and 2‐hydroxy‐α,5‐dimethylbenzene‐methanol (1 b) the corresponding 4‐hydroperoxy‐3,5‐cyclohexadienones were obtained as oxy‐functionalized products (⩾90%, d.r. 85:15 and 75:15). The stereochemistry of the products was assigned after reduction to the corresponding p‐quinols. The ready cleavage of the initial oxygenated product, which can be observed at low temperature as a single diastereomer, prevented rigorous assignment of the π‐facial selectivity of the singlet oxygen attack for the derivative 4‐hydroxy‐α,2‐dimethylbenzenemethanol (1 c). The present stereochemical results indicate that the hydroxyl group directing effect, that is, coordination of the incoming singlet oxygen dienophile with the hydroxyl group, is also operating in the photooxygenation of the chiral phenols 1 a‐c. However, in the case of the derivative 1 b, hydrogen bonding in the starting material leads to an opposite stereochemical outcome. This conclusion is further substantiated by solvent effects and the fact that the methyl ether 1 d of alcohol 1 c displays a significant lower diastereoselectivity.
Synthesis of a Fullerene[60] Cryptate and Systematic Langmuir‐Blodgett and Thin‐Film Investigations of Amphiphilic Fullerene Derivatives
Authors: Jonas Ulrich , Cardullo Francesca , Belik Pavel , Diederich François , Gügel Andreas , Harth Eva , Herrmann Andreas , Isaacs Lyle , Müllen Klaus , Ringsdorf Helmut , Thilgen Carlo , Uhlmann Peter , Vasella Andrea , Waldraff Christian A. A. , Walter Michael
Published: July 2007

The synthesis of the first fullerene cryptate 7 with a sodium ion bound to a benzo[2.2.2]cryptand covalently attached to a methanofullerene[60] is described. The amphiphilic properties of 7 as well as of a variety of other covalent fullerene derivatives with polar functional groups and the ability of these compounds to form Langmuir monolayers at the air‐water interface were investigated in a systematic study. Among these derivatives are Diels‐Alder adducts of C60 and methanofullerenes, four of which are fullerene C‐glycosides. The films at the water surface were characterized by their surface pressure versus molecular area isotherms, compression and expansion cycles, and optical light microscopy. UV/Vis spectroscopy and small‐angle X‐ray diffraction (SAXS) were employed for LB film characterization on solid substrates. Parameters influencing the spreading and monolayer character include (a) polarity, (b) balance of hydrophobicity to hydrophilicity, (c) size and bulkiness of the polar groups attached to the fullerene, and (d) presence of aromatic residues in these groups.
Asymmetric Synthesis of Carboranyl Amino Acids with Potential use in BNCT
Authors: Sjöberg Stefan , Hawthorne M. Frederick , Wilmouth Serge , Lindström Peter
Published: July 2007

Two α‐amino acids containing the 1,2‐dicarba‐closo‐dodecaborane (12) cage, namely, 5‐(1,2‐dicarba‐closo‐dodecaboran (12)‐1‐yl)‐2‐aminopentanoic acid (1) and 5‐(2‐methyl‐1,2‐dicarba‐closo‐dodecaboran (12)‐1‐yl)‐2‐aminopentanoic acid (2), were prepared by asymmetric synthesis (e.p. > 98%) by using the chiral glycine equivalent, imidazolidinone 3, introduced by Seebach, and Oppolzer's camphor‐derived sultam derivative 4. The dextrorotatory enantiomers (sodium D line in methanol) of the amino acids 1 and 2 were both shown to have (S) configuration.
Semiconductor‐Catalysed Photoaddition of Olefins and Enol Ethers to 1,2‐Diazenes: A New Route to Allylhydrazines
Authors: Künneth Ronald , Feldmer Christian , Knoch Falk , Kisch Horst
Published: July 2007

Suspensions of zinc or cadmium sulfide powders in a protic solvent catalyse the linear addition of enol ethers and olefins to 1,2‐diaryl‐ and 1‐aryl‐2‐alkyl‐1,2‐diazenes, producing allylhydrazine derivatives. Relative quantum yields decrease sharply when the 1,2‐diazene is more difficult to reduce, while their relationship to the oxidation potential of the enol ether/olefin is complicated. Reduction to 1,2‐diarylhydrazine and concomitant dehydrodimerization of the enol ether occurs as a side reaction. It is favoured by increasing light intensity and becomes the major reaction path when platinized (5 mol%) photocatalysts are employed. It is proposed that the photogenerated electron‐hole pair in a proton‐coupled electron transfer reduces the diazene to a hydrazyl radical and oxidizes the olefin/enol ether to a radical cation. The allylic radical obtained from the latter by deprotonation then undergoes CN coupling with the hydrazyl radical to afford the allylhydrazine. Diarylhydrazine formation occurs by disproportionation of the hydrazyl radical or by a successive proton‐coupled reduction. Thus photoaddition can be classified as a 1 e−/1 h+ process while 2e−/2h+ are necessary for the reduction.
Magnetic and Structural Studies of Copper–Lanthanoid Complexes; the Synthesis and Structures of New Cu3Ln Complexes of 6‐chloro‐2‐Pyridone (Ln = Gd, Dy and Er) and Magnetic Studies on Cu2Gd2, Cu4Gd2 and Cu3Gd Complexes
Authors: Benelli Cristiano , Blake Alexander J. , Milne Paul E. Y. , Rawson Jeremy M. , Winpenny Richard E. P.
Published: July 2007

The synthesis and structural characterisation of three copper–lanthanoid complexes are reported. The compounds, of general formula [Cu3M(chp)8(NO3)(S)] [M = Gd, S = H2O in 2; M = Dy, S = H2O in 3; M = Er, S = (H2O)0.5(MeOH)0.5 in 4; chp = anion of 6‐chloro‐2‐pyridone], are made by reaction of [Cu2(chp)4] (1) with the hydrated lanthanoid nitrate salt in methanol. Structural studies reveal the three copper atoms lie in an approximate hemisphere about a central lanthanoid atom. Magnetic studies on 2 and two further Cu–Gd complexes show ferromagnetic coupling between the 3d and 4f metals. Consideration of these results along with magnetic data previously reported for Cu–Gd compounds leads to a correlation between the magnitude of this exchange coupling and the exponential of the Cu…Gd distance. This is the first magneto‐structural correlation reported for mixed d‐block/f‐block metal complexes.
The Role of Porphyrin‐to‐Porphyrin Linkage Topology in the Extensive Modulation of the Absorptive and Emissive Properties of a Series of Ethynyl‐ and Butadiynyl‐Bridged Bis‐ and Tris(porphinato)zinc Chromophores
Authors: Lin Victor S.‐Y. , Therien Michael J.
Published: July 2007

A new method for the regulation of the photophysical properties of highly conjugated porphyrin arrays is described. The absorptive and emissive signatures of such supramolecular structures can be modulated to an impressive degree by regulation of: i) the extent of the steric interactions that define the barrier to rotation about the conjugated bridge between the porphyrin chromophores, and ii) the magnitude of ground state chromophore–chromophore electronic communication within the supermolecule. The power of this approach is illustrated by the straightforward synthesis as well as the electronic and emission spectra of eight different porphyrin arrays in which (5,10,15,20‐tetraphenylporphinato)zinc(11) and (10,20‐diphenylporphinato)zinc(11) complexes are joined by ethyne or butadiyne groups. The points of connectivity of these bridges between the chromophoric building blocks are systematically varied to produce a series of supramolecular structures with meso‐to‐meso, meso‐to‐β, or β‐to‐β linkage topologies. These variations allow excellent control of the ground‐ and excited‐state characteristics of the arrays in the series by regulating the degree of both excitonic and electronic porphyrin‐to‐porphyrin coupling. Our approach shows the precision with which photophysical properties can be engineered in appropriately designed supramolecular systems.
Ruthenium‐Catalyzedcis‐Dihydroxylation of Alkenes: Scope and Limitations
Authors: Shing Tony K. M. , Tam Eric K. W. , Tai Vincent W.‐F. , Chung Ivan H. F. , Jiang Qin
Published: July 2007

Oxidative ruthenium catalysis (0.07 molequiv RuCl3·(H2o)3, 1.5 molequiv NaIO4, EtOAc/CH3CH3CN/H2O 3:3:1), beyond the usual CC bond cleavage to give dicarbonyls, has been shown tosyn‐dihydroxylate a wide range of alkenes (except for strained bicyclic alkenes, sterically hindered trisubstituted alkenes, and most tetrasubstituted alkenes) to give vicinal diols rapidly (within minutes) and efficiently. The minor products are the usual oxidative fission products, namely, ketones and aldehydes or carboxylic acids, and sometimes ketols. Longer reaction times lower the yields of most diols, probably owing to oxidative glycol cleavage. Reactions with substrates containing one or more electron‐with‐drawing groups in conjugation with or adjacent to the alkene moiety are generally slower but give better yields. The diastereoselectivity of the present “flash” dihydroxylation,antito the existing α‐stereogenic center, with cycloalkenes is excellent whereas that with acyclic alkenes is moderate to poor. Sodium metaperiodate is still the best co‐oxidant for the catalytic reaction. Aqueous acetonitrile (approximately 86%) as an alternative solvent system was found to give better yields of 1,2‐diols than the original solvent system in some cases.
Solvent Effect on the NMR Chemical Shieldings in Water Calculated by a Combination of Molecular Dynamics and Density Functional Theory
Authors: Malkin Vladimir G. , Malkina Olga L. , Steinebrunner Gerold , Huber Hanspeter
Published: July 2007

The solvent effect on the NMR chemical shielding in liquid water is calculated from a combination of molecular dynamics simulations and quantum chemical calculations for protons and 17O. The simulations are performed with three different potentials, ab initio as well as empirical ones, to study the influence of the force field. From the liquid configurations obtained in these simulations, molecules are randomly chosen together with neighbouring molecules to give clusters of water typical for the liquid at the selected temperature and density. Different cluster sizes are studied. The clusters are treated as supermolecules in quantum chemical calculations of chemical shifts by sum‐over‐states density functional perturbation theory with individual gauge for localised orbitals. The influence of the quantum chemical method is studied with an ab initio coupled Hartree‐Fock gauge including atomic orbitals calculations with different basis sets for a selected cluster. An average over clusters yields the chemical shielding in the liquid at the selected temperature and density. The calculated values for the gas–liquid shift, which are in best agreement with experiment, are –3.2 ppm (exp. –4.26 ppm) for the proton and –37.6 ppm (exp. –36.1 ppm) for 17O, but the results depend strongly on the chosen interatomic potential.
Versatile Synthesis of Enantiomerically Pure 2‐Alkoxy‐1‐Ethynylcyclopropanes and their Application in the Synthesis of Enantiomerically Pure Bicyclo‐[3.3.0]oct‐1‐en‐3‐ones
Authors: Bräse Stefan , Schömenauer Sten , McGaffin Gregory , Stolle Andreas , de Meijere Armin
Published: July 2007

A variety of chiral, nonracemic 2‐alkoxy‐1‐alkynylcyclopropanes 7 were synthesized in good to very good yields from enantiomerically pure glycidol derivatives (glycidol tosylate, epichlorohydrin) by boron trifluoride promoted addition of lithium trimethylsilylacetylide followed by protection of the secondary hydroxyl group and finally a diastereoselective γ‐elimination. The 2‐ethoxy derivative (S,R)‐7 b was deprotonated with n‐butyllithium, and the resulting 1‐lithio‐2‐ethoxy derivative (S,R)‐20 functionalized by treatment with oxygen followed by tosyl chloride. Protodesilylation and catalytic hydrogenation smoothly furnished 1‐ethenylcyclopropyl sulfonates, which underwent a clean Pd0‐catalyzed SN2′‐type substitution with dimethyl propargylsodiummalonate to give the (E)‐configurated enyne (R,E)‐26 with a methylenecyclopropane end group. A diastereoselective Pauson–Khand reaction completed the sequence to give the enantiomerically pure spirocyclopropaneannelated bicyclo[3.3.0]octane derivative 31.
Porphyrin Synthesis by the “3+1” Approach: New Applications for an Old Methodology
Authors: Lash Timothy D.
Published: July 2007

Acid‐catalyzed condensation of tripyrranes with pyrrole‐2,5‐dicarboxaldehydes, followed by oxidation with an electron‐deficient quinone, affords porphyrin products in excellent yields. This previously little used methodology has now been exploited in the synthesis of novel porphyrin structures, including tetrapyrrolic compounds with fused aromatic rings. By utilizing other aromatic or unsaturated dialdehydes, the “3+1” approach also allows the synthesis of new aromatic porphyrinoid systems, including benzene‐ and pyridine‐containing macrocycles and carbaporphyrins.
Self‐Assembly of Heterobimetallic Complexes and Reactive Nucleophiles: A General Strategy for the Activation of Asymmetric Reactions Promoted by Heterobimetallic Catalysts
Authors: Arai Takayoshi , Yamada Yoichi M. A. , Yamamoto Noriyoshi , Sasai Hiroaki , Shibasaki Masakatsu
Published: July 2007

Heterobimetallic asymmetric catalysts, such as the lanthanum–lithium–binaphthol complex (La Li–BINOL), the aluminum–lithium–binaphthol complex (AlLi–BINOL), and a newly prepared gallium–sodium–binaphthol complex (Ga Na–BINOL), have been self‐assembled with reactive nucleophiles, such as lithium nitronates and sodium malonates, to generate more efficient catalysts than the parent heterobimetallic catalysts. For example, by the combined use of La Li–BINOL (1 mol%; contains one H2O molecule) and BuLi (0.9 mol%) as the catalyst system, asymmetric nitroaldol reactions are greatly accelerated in all cases without a decrease in the optical purity of the nitroaldol products. Kinetic analyses have also been carried out on the Ga Na–BINOL‐catalyzed Michael reaction of dibenzyl malonate with cyclohexenone, with or without NaOtBu. The calculated rate constants show that the combined use of Ga Na–BINOL and NaOtBu as the catalyst gives reaction rates that are about 50 times faster than with Ga Na–BINOL alone. This activation method should be useful for other asymmetric reactions catalyzed by heterobimetallic complexes.
Synthetic Methodology Allowing the Interconversion of Titanium–Oxygen Single Bonds and Double Bonds: The Self‐Assembly of Bridging and Terminal Oxotitanium(IV) into Oligomeric and Polymeric Linear Titanoxanes
Authors: Franceschi Federico , Gallo Emma , Solari Euro , Floriani Carlo , Chiesi‐Villa Angiola , Rizzoli Corrado , Re Nazzareno , Sgamellotti Antonio
Published: July 2007

The controlled ionization of the linear [Cl–Ti–O–Ti–Cl] skeleton allowed the generation of the [Cl–Ti–O–Ti]+ dimer, which is nonsymmetrical as a consequence of extended Cl–Ti–O π interactions. The [TiO] unit thus formed is a building block for a variety of titanoxane structures. This chemistry has been investigated from a theoretical point of view by ab initio MO analysis of the [Cl–Ti–O–Ti–Cl] and [Cl–Ti–OTi]+ fragments. These calculations lead to the conclusion that single ionization generates the [TiO] unit, whereas double ionization does not affect the μ‐oxo bonding mode in [Ti–O–Ti]2+ or [S–Ti–O–Ti–S]2+ (where S is a pure σ‐donor ligand or solvent). This observation has been confirmed experimentally by ionizing the following model complexes: [(Cl)(acacen)‐Ti–O–Ti(acacen)(Cl)] (3) (acacen = N,N'‐ethylenebisacetylacetoneiminato dianion) and [(Cl)(salen)Ti–O–Ti(salen)‐(Cl)] (4) (salen = N,N'‐ethylenebissalicylideneiminato dianion), where the linear Cl–Ti–O–Ti–Cl unit is assured by the square‐planar bonding mode of the tetradentate Schiff base ligand. The double ionization of 3 with AgNO3 gave the conventional μ‐oxo derivative [(acacen)(η1‐ONO2)Ti–O–Ti(acacen)(η1‐ONO2)] (5). In contrast, the stepwise ionization of 3 and 4 with NaBPh4 in THF led to the nonsymmetrical [Cl–Ti–OTi]+ intermediates, which are the parent compounds for a variety of linear titanoxanes. The following species containing a TiO unit have been isolated from the NaBPh4‐assisted ionization of 3: [(acacen)TiO–BPh3] (6) and [(L)(acacen)TiO–Ti(acacen)–O–(acacen)Ti–OTi(acacen)(L)]2+2 BPh‐4 (L = THF, 7; L = none, 8). The same reaction carried out on 4 led to [(THF)‐(salen)TiO – Ti (salen) – O – (salen)Ti‐(THF)]2+2 BPh‐4 (9) and [(L)(salen)‐TiO–Ti(salen) – O – (salen)Ti–OTi‐(salen)(L)]2+ 2BPh‐4 (L = THF, 10; L = Py, 11; L = none, 12, polymeric form). A scheme is proposed to explain the formation of the species derived from the single ionization of 3 and 4, where the origin and the binding properties of the [TiO] unit play a major role.
Isolation of Transmetalation Intermediates in the Stille Cross‐Coupling Reaction of Stannanes: Synthesis of Palladacycles, Ligand Substitution, and Insertion Reactions
Authors: Mateo Cristina , Cárdenas Diego J. , Fernández‐Rivas Carolina , Echavarren Antonio M.
Published: July 2007

A strategy based on a Stille cross‐coupling reaction of organostannanes interrupted at the reductive elimination step has been applied to the synthesis of oxa‐ and azapalladacycles with the general formula cis‐[PdArR(L)2]. The synthesis of oxapalladacycles was achieved under mild conditions by reaction of 2‐iodo‐ or 2‐bromophenyloxymethylstannanes with [Pd(PPh3)4]. The synthesis of an aza analogue was similarly carried out from the corresponding 2‐iodoaniline derivative. One of the substituted oxapalladacycles rearranged to release steric strain between the palladium and a chloride substituent on the aryl ring, an isomerization promoted by traces of water. In one case, the arylpalladium(II) intermediate of oxidative addition was isolated by using a palladium(0) complex with a bidentate diphosphane. A variety of new palladacycles, including complexes with weakly coordinating ligands, were prepared by ligand substitution. Reaction of the palladacycles with dimethyl acetylene‐dicarboxylate led to the formation of chromenes or dihydroquinolines by insertion followed by reductive elimination.
The Unusual Properties of 5‐Methyl‐4,5,6,7‐Tetrahydro‐1H‐Indazole in the Solid State
Authors: Foces‐Foces Concepción , Hager Orm , Jagerovic Nadine , Jimeno María Luisa , Elguero José
Published: July 2007

The crystal structure of the title compound was determined by X‐ray analysis at 200 K. Three independent molecules form a trimer joined by strong and linear N‐H … N hydrogen bonds. There is another centrosymmetrically related trimer in the unit cell. Both tautomers (1H and 2H) are present in each trimer. Disorder of the NH protons involved in the N‐H … N hydrogen bonds has been observed. Solid‐state 13C CPMAS NMR was used to establish the dynamic nature of the NH‐proton disorder, the title compound being the first example of proton transfer in a tautomeric mixture of pyrazoles with an equilibrium constant other than 1.
Structural Effects in the Reductive Activation of (Indenyl)RhL2 Complexes: The Reduction of [Rh(η5‐C9H7)(η4‐cod)]
Authors: Amatore Christian , Ceccon Alberto , Santi Saverio , Verpeaux Jean‐Noël
Published: July 2007

The reduction of the indenyl complex [Rh(η5‐C9H7)(η4‐cod)] has been investigated in the context of structural effects induced by the transfer of one electron. The reduction of this complex occurs in two steps, leading first to the radical anion and then to the highly frangible dianion. Both species eliminate the indenyl anion. In the presence of free cyclooctadiene, the related cleavage leading to the indenyl anion and bis‐cyclooctadiene rhodium fragments now follows a Michaelis–Menten‐type mechanism involving precoordination of one extra COD ligand to the initial radical anion. These results suggest the modification of the hapticity of the indenyl ligand in connection with 17‐ and 19‐electron metalcentered intermediates.
A Joint Experimental and Theoretical Study of the Interaction between Aluminum and Electroluminescent Polymers: Cyano Derivatives of Poly(p‐phenylene vinylene)
Authors: Fahlman M. , Salaneck W. R. , Moratti S. C. , Holmes A. B. , Brédas J. L.
Published: July 2007

The early stages of metal/polymer interface formation between aluminum and poly(2,5,2′,5′‐tetrahexyloxy‐8,7′‐dicyanodi‐p‐phenylenevinylene) or their ring‐substituted derivatives have been studied theoretically by using quantum‐chemical calculations as well as experimentally by X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light‐emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction.
Catalytic asymmetric synthesis of new halogenated chiral synthons
Authors: Vanhessche Koen P. M. , Barry Sharpless K.
Published: July 2007

Two‐step and practical asymmetric syntheses of enantiomerically pure 4‐trifluoromethyl‐2,2‐dioxo‐1,3,2‐dioxathiolane and 4‐trichloromethyl‐2,2‐dioxo‐1,3,2‐dioxathiolane (>98% ee) have been achieved. Catalytic asymmetric dihydroxylation (AD) of 3,3,3‐trifluoropropene and 3,3,3‐trichloropropene, respectively, is followed by direct cyclic sulfate formation by reaction with sulfuryl chloride. Opening of the cyclic sulfates with various nucleophiles provides easy access to important chiral synthons.
The C60 Core: A Versatile Tecton for Dendrimer Chemistry
Authors: Camps Xavier , Schönberger Hubert , Hirsch Andreas
Published: July 2007

The synthesis, complete characterization and molecular dynamics simulations of dendrimers 4–8 involving [60]fullerene as core tecton and first‐ to thirdgeneration benzyl‐ether‐based dendrons as branches is described. In dendrimer 7 a core branching multiplicity of 12, the highest known to date, is realized for the first time with a Th‐symmetrical C60 core having an octahedral addition pattern. This unique structural type of core building block is only possible on the base of C60 and has no precedent in organic chemistry. NMR investigations as well as molecular modelling studies show that, owing to high core branching multiplicity, dendrimer 7 and to a minor extent the mixed adduct 8 already represent globular and densely packed macromolecules, although only first‐generation dendrons are involved in their construction.
Nature of the Interactions between Polar β‐Substituents and Palladium in η3‐Allylpalladium Complexes—A Combined Experimental and Theoretical Study
Authors: Szabó Kálmán J.
Published: July 2007

Deuteromethanolysis of six β‐methoxy‐substituted η3‐allylpalladium complexes (1–5) was studied under the same reaction conditions. The reaction rates depend on the ring size of the cyclic complexes, on the σ‐donor/π‐acceptor nature of the ancillary ligand, on the configuration of the allylic moiety, and on the position of the β‐substituent with respect to the palladium atom. Replacement of the methoxy group proceeds about 1000 times faster in the trans‐β‐substituted cycloheptylallyl palladium complex 2 than in the cyclooctyl analogue 3; this indicates that the C–O bond strength is a function of the ring and substituent conformations. A theoretical analysis of the structure and stability of slightly simplified model compounds 6–10 was performed with density functional theory at the B 3 PW91 level in order to elucidate the relationship between the rate of deuteromethanolysis and the electronic interactions between the β‐methoxy substituent and the palladium atom. It was concluded that the strength of these β‐substituent effects critically depends on the relative position of the Pd–C3 and C4–O bonds. In cyclohexyl and cycloheptylallyl complexes 6 and 7, the trans‐β‐methoxy substituent adopts a conformation that is particularly favoured by the β‐substituent effect. Since the η3‐allylpalladium complexes studied and their derivatives are key intermediates of important palladium‐catalysed transformations, the implications of the β‐substituent effect for the regio‐ and chemoselectivity of nucleophilic attack are also discussed.
Through‐Bond Interactions in Silicon–Phosphorus and Silicon–Arsenic Compounds: A Facile Synthesis of Dodecamethyl‐2,3,5,6,7,8‐hexasila‐1λ3,4λ3‐diphosphabicyclo[2.2.2]octane, Its Arsenic Analogue, and Related Compounds
Authors: Winkler Uwe , Schieck Mathias , Pritzkow Hans , Driess Matthias , Hyla‐Kryspin Isabella , Lange Holger , Gleiter Rolf
Published: July 2007

Dodecamethyl‐2,3,5,6,7,8‐hexa‐sila‐lλ3,4λ3‐diphosphabicyclo[2.2.2]oc‐tane (1) and its arsenic analogue 2 are readily accessible in 69 and 73% yield, respectively, by the cyclocondensation reaction of 1,2‐dichloro‐1,1,2,2‐tetrame‐thyldisilane (5) with the lithium pnictides [LiEH2(dme)] (E = P (6), As(7); dme = 1,2‐dimethoxyethane). The reactions proceed via 1,4‐diphosphaoctamethyltetrasi‐lacyclohexane (8) and its arsenic analogue 9, respectively, which were isolated and structurally characterized by X‐ray crystallography. The molecular structures of 1 and 2, which are isotypic, were also established by single‐crystal X‐ray analysis: they possess D3 point symmetry with the expected Si–E bond lengths (E = P, As) but unusually long Si–Si bonds. The latter are 0.02–0.03 Å longer than those in 8 and 9, mainly due to through‐bond interactions (TB) between donating n orbitals of the E atoms and the σ* acceptor orbitals of the Si–Si bond. The first expanded analogues of 1, namely, 12 and 14, with hexamethyltrisilane and dodecamethyl‐hexasilane chains bridging the two phosphorus atoms, were synthesized in a onepot cyclocondensation reaction of the corresponding 1,3‐ and 1,6‐dichloro‐oligosilanes 11 and 13, respectively, with [LiPH2(dme)]6. Ab initio calculations on the parent compounds 1a, 12a, and the second‐row analogue 1,4‐diazabicyclo‐[2.2.2]octane (B) were carried out in order to analyze the different coupling constants and magnitudes of intramolecular interactions (through‐space/through‐bond coupling). TS and TB coupling in B were found to be about two times stronger than in the congener 1a, due to the compactness of the N2C6 skeleton and the greater extent of s, p hybridization at nitrogen. Evidence for TB interactions in 1 was obtained by photoelectron spectroscopy and by comparison of the two first vertical ionization potentials with calculated values for 1a. The best agreement with experimental data was achieved when 1a was calculated at the MP2 level. Compound 1a preferentially adopts D3 point symmetry; the higher‐symmetry D3h form possesses one imaginary frequency and is slightly less stable (0.46 kcal mol−1 at HF/6–31 G*//HF/6–31 G* and 1.58 kcal mol−1 at MP2/ 6–31 G*//HF/6–31 G* level), suggesting that this structure corresponds to a transition state on the potential energy surface. The structures corresponding to the global minimum of B and 12a have D3h and C3h symmetry, respectively. At the HF/6–31 G*//HF/6–31 G* level the D3h form of 12a is 17.61 kcal mol−1 less stable than the C3h minimum.
Oligosilsesquioxane8‐OSS‐Ethyldiphenylphosphine: A New Functional Oligosilsesquioxane Ligand
Authors: Ruffieux Vincent , Schmid Günter , Braunstein Pierre , Rosé Jacky , Braunstein P. , Rosé J.
Published: July 2007

Oligosilsesquioxanes (OSS) may be considered as molecular sections of silica. The incompletely condensed (cy‐clopentyl)7T7(OH)3 (T = SiO3/2) has been used to generate a phosphine‐functionalized T8‐OSS system by reaction with 2‐(trichlorosilyl)diphenylphosphinoethane. The resulting model molecule (cyclopentyl)7T8(CH2)2PPh2 (1) is well suited to coordinate to transition metal clusters via the phosphorous atom. We selected the tetrahedral bimetallic cluster [HFeCo3‐(CO)12]. Depending on the stoichiometry, one or two phosphine ligands could be added to the cobalt atoms, with substitution of CO molecules. Owing to the cyclopentyl substituents, the resulting complexes [HFeCo3(CO)11{Ph2P(CH2)2T8‐(cyclopentyl)7}] (2) and [HFeCo3‐(CO)10{Ph2P(CH2)2T8(cyclopentyl)7}2] (3) are soluble in numerous organic solvents. Therefore, they could be completely characterized by 1H, 13C, 29Si, and 31P NMR spectroscopy.