Local adsorption sites and bondlength changes in Ni(1 0 0)/H/CO and Ni(1 0 0)/CO

The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding.     

Pd (II)‐catalyzed vinyl addition polymerization of novel functionalized norbornene bearing dimethyl carboxylate groups

Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007     

Characterization and genetic manipulation of peptide synthetases in Pseudomonas aeruginosa PAO1 in order to generate novel pyoverdines

PvdD, a nonribosomal peptide synthetase (NRPS) of Pseudomonas aeruginosa PAO1, incorporates two L-threonines into the siderophore pyoverdine. A pvdD mutant did not synthesize pyoverdine and lacked a high Mr iron-regulated cytoplasmic protein (IRCP). Analysis of other IRCPs and the P. aeruginosa genome enabled the remaining pyoverdine NRPSs to be identified. The pvdD mutation could be complemented in trans, enabling design of plasmid-based systems for the generation of novel pyoverdines. Introduction of a truncated pvdD gene resulted in attenuated forms of pyoverdine, and introduction of L-threonine-incorporating NRPSs from other organisms restored pyoverdine production to mutant cells. This is the first successful rational in vivo modification of NRPS modules outside of Bacillus subtilis. The systems employed did not allow incorporation of other residues into pyoverdine, indicating that there are multiple elements contributing toward substrate specificity in NRPSs.     

Lexicographic products with high reconstruction numbers

The reconstruction number of a graph is the smallest number of vertex-deleted subgraphs needed to uniquely determine the graph up to isomorphism. Bollobás showed that almost all graphs have reconstruction number equal to three. McMullen and Radziszowski published a catalogue of all graphs on at most ten vertices with reconstruction number greater than three. We introduce constructions that generalize the examples identified in their work. In particular, we use lexicographic products of vertex transitive graphs with certain starter graphs from the work of Myrvold and from the work of Harary and Plantholt to generate new infinite families of graphs with high reconstruction numbers. In the process, we settle a question of McMullen and Radziszowski.     

Substrate scope and stereocontrol in the Rh(II)-catalysed oxyamination of allylic carbamates

Application of a modified Du Bois protocol for rhodium-stabilised nitrenoid generation to a variety of allylic carbamates results in 4-acetoxymethyl-1,3-oxazolidin-2-one derivatives with moderate to high levels of stereocontrol.     

MODELING HARVEST SCHEDULING IN MULTIFUNCTIONAL PLANNING OF FORESTS FOR LONGTERM WATER YIELD OPTIMIZATION

In this study, wood production and hydrologic functions of forests were accommodated within a planning procedure for separate working circles (areas dedicated to certain forest functions) that were delineated according to an Ecosystem‐Based Functional Planning approach. Mixed integer goal programming was used as the optimization technique. The timing and scheduling of a maintenance cutting (partial harvest) was the decision variable in the modeling effort, and an original formulation was developed as a multiobjective planning procedure. Four sample planning strategies were developed and model outputs were evaluated according to these strategies. Spatial characteristics of stands were considered, and used to prohibit the regeneration of adjacent stands during the same time period. Because of the positive relationship between qualified water production and standing timber volume in the forest, the model attempts to maximize qualified water production levels by increasing standing volume stocks in the forest through the delay of regeneration activities.     

Bond lengths and bond strengths in weak and strong chemisorption: N2, CO,and CO/H on nickel surfaces

New chemical-state-specific scanned-energy mode photoelectron diffraction experiments and density functional theory calculations, applied to CO, CO/H, and N2 adsorption on Ni(100), show that chemisorption bond length changes associated with large changes in bond strength are small, but those associated with changes in bond order are much larger, and are similar to those found in molecular systems. Specifically, halving the bond strength of atop CO to Ni increases the Ni-C distance by 0.06 A, but halving the bond order (atop to bridge site) at fixed bond strength causes an increase of 0.16 A.     

Effect of chemical modification on oligomerization capacity of alumina support for Pd-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Effect of modification with an alkali metal on the acid properties of alumina supports and on the oligomerization capacity and working stability of Pd-Al₂O₃ catalysts was studied.     

Lanthanide sensitization in II-VI semiconductor materials: a case study with terbium(III) and europium(III) in zinc sulfide nanoparticles

This work explores the sensitization of luminescent lanthanide Tb(3+) and Eu(3+) cations by the electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected while monitoring the lanthanide emission bands reveal that the ZnS nanoparticles act as an antenna for the sensitization of Tb(3+) and Eu(3+). The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semiempirical model, proposed by Dorenbos and co-workers (Dorenbos, P. J. Phys.: Condens. Matter 2003, 15, 8417-8434; J. Lumin. 2004, 108, 301-305; J. Lumin. 2005, 111, 89-104. Dorenbos, P.; van der Kolk, E. Appl. Phys. Lett. 2006, 89, 061122-1-061122-3; Opt. Mater. 2008, 30, 1052-1057. Dorenbos, P. J. Alloys Compd. 2009, 488, 568-573; references 1-6.) to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb(3+) and Eu(3+) in ZnS nanoparticles are different; namely, Tb(3+) acts as a hole trap, whereas Eu(3+) acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II-VI semiconductor materials; namely, CdSe, CdS, and ZnSe.