Enhanced self-diffusion on Cu(111) by trace amounts of s: chemical-reaction-limited kinetics

We find that less than 0.01 monolayer of S can enhance surface self-diffusion on Cu(111) by several orders of magnitude. The measured dependence of two-dimensional island decay rates on S coverage (theta(S)) is consistent with the proposal that Cu3S3 clusters are responsible for the enhancement. Unexpectedly, the decay and ripening are diffusion limited with very low and very high theta(S) but not for intermediate theta(S). To explain this result we propose that surface mass transport in the intermediate region is limited by the rate of reaction to form Cu3S3 clusters on the terraces.     

Structure and dynamics of the Zr(4+) ion in water

The four-times positively charged zirconium ion in aqueous solution was simulated, using an ab initio quantum mechanical charge field molecular dynamics approach. As no hydrolysis reaction occurred during the simulation time of 10 ps, the target of this study was the evaluation of the structure and dynamics of the monomeric hydrated zirconium(iv) ion. The ion forms three hydration shells. In the first hydration shell the ion is 8-fold coordinated with a maximum probability of the Zr-O distance at 2.25 ?. While no exchanges occurred between the first and second shell, the mean residence time of the water molecules in the second shell is 5.5 ps. A geometry of the first hydration shell in-between a bi-capped trigonal prism and a square antiprism was found and a Zr-O force constant of 188 N m(-1) was evaluated.     

DMT [(−)-(2<Emphasis Type="Italic">R</Emphasis>,3<Emphasis Type="Italic">R</Emphasis>)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol], a highly efficient host compound for nitroaromatic guests: selectivity,X-ray and thermal analyses

In this work, we reveal that the compound (?)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) is a highly efficient host material for nitroaromatics o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT) and nitrobenzene (NB). Each of these guests was included with a 2:1 host:guest ratio. The host displayed selectivity for p-NT and NB when these guests were mixed in equimolar proportions with any one of the other guest solvents, and the host recrystallized from this binary mixture. A selectivity order for the host in these conditions was thus noted to be NB?≈?p-NT?>?o-NT?>?m-NT. Furthermore, guests were also mixed in non-equimolar proportions and the host behaviour analysed, the results of which were in accordance with observations from the equimolar studies. Additionally, an equimolar quaternary experiment of all four guests provided a somewhat adjusted host selectivity order [p-NT (39.9%)?>?NB (30.2%)?>?m-NT (17.1%)?>?o-NT (12.8%)]. Single crystal diffraction analyses of all four complexes showed the crystals to share the same host packing, and comparable host–guest interactions were observed in each. However, thermal analyses, both DSC and TG, showed that the preferred guests p-NT and NB formed complexes with increased relative thermal stabilities, and this observation correlated with the selective behaviour of the host in competition experiments.     

Discovery of the archaeal chemical link between glycogen (starch) synthase families using a new mass spectrometry assay

Starch and its analogue glycogen are biosynthesized by enzymes that have been classified by sequence similarities into two families that have no significant sequence overlap: the animal/fungal glycogen synthases and the plant/bacterial glycogen (starch) synthases. Recent gene sequence analysis of putative archaea enzymes implicates them as a third family that links the structural and functional features of the other two classes. Herein, we present the first rapid electrospray ionization mass spectrometry-based assay to quantify any carbohydrate-polymerizing activity, the first cloning and recombinant expression as well as verification of the putative function of a glycogen synthase from the hyperthermophilic archaea Pyrococcus furiosus, and the characterization of a variety of glycogen synthases with the new assay. The new assay allowed the determination of Km and Vmax values for the rabbit, yeast, and P. furiosus glycogen synthases. Most surprisingly, unlike the synthases from rabbit or yeast and in contradiction to what would be expected from structural studies of other nucleotide-sugar binding proteins, the synthase from the archaea source accepts both uridine- and adenine-diphosphate activated glucose competitively and with comparable affinities to form a glucose polymer. This loose substrate specificity implicates this protein as the chemical link between the two branches of glycogen synthases that have evolved to accept primarily one or the other nucleotide as well as a good source enzyme for polymer bioengineering efforts.     

Synthesis of isobutyl-C-galactoside (IBCG) as an isopropylthiogalactoside (IPTG) substitute for increased induction of protein expression

[reaction: see text] Addition of isopropyl-beta-d-thiogalactopyranoside (IPTG) to bacterial cultures is often used to induce expression of plasmid-based genes for the production of recombinant proteins under control of the lac promoter, but a simple method to circumvent the inherent instability of this compound has not been addressed experimentally. Herein we report the first synthesis of isobutyl-C-galactoside (IBCG), the C-glycoside analogue of IPTG, and show that IBCG is superior to IPTG in inducing protein expression over long induction times.     

Development of a bionematicide with Paecilomyces lilacinus to control Meloidogyne incognita

Root-knot disease caused by Meloidogyne incognita is a matter of grave concern because it affects several economically important crop plants. The use of solid-state fermentation (SSF) may help to elaborate efficient formulations with fungi to be employed in the biologic control of nematodes. Attempts were made to select low-cost substrates for spore production of a strain of Paecilomyces lilacinus with known nematicide capacity. Coffee husks, cassava bagasse, and defatted soybean cake were utilized as substrates, and sugarcane bagasse was used as support. Fermentations were carried out in flasks covered with filter paper at 28°C for 10 d. The products obtained by SSF were evaluated for their nematicide activity in pot experiments containing one seedling of the plant Coleus inoculated with the nematode M. incognita. The plants were evaluated 2 mo after inoculation. Fermented products showed a reduction in the number of nematodes. The best results were obtained with defatted soybean cake, which showed almost 100% reduction in the number of nematodes; the reduction with coffee husk was 80% and with cassava bagasse was about 60%.     

Facile and efficient synthesis of 6-(hydroxymethyl)purines

[reaction: see text] A facile and efficient methodology of the synthesis of 6-(hydroxymethyl)purine derivatives (bases and nucleosides) was developed based on Pd-catalyzed cross-coupling reactions of 6-halopurines with acyloxymethylzinc iodides followed by deprotection. Several title compounds are inhibitors of adenosine deaminase and exert cytostatic activity.