Electronic structure, vibrational stability, and predicted infrared-Raman spectra of the As20, As @ Ni12, and As @ Ni12 @ As20 clusters

Recently an inorganic fullerine-like [As@Ni(12)@As(20)](3-) onion with near-perfect icosahedral symmetry in the crystalline phase was reported [M. J. Moses, J. C. Fettinger, and B. W. Eichhorn, Science 300, 778 (2003)]. This paper presents a detailed computational study in the framework of density functional theory on various aspects of this molecule. The electronic structure of the As@Ni(12)@As(20) is investigated in its neutral as well as -3 charged state together with its subunits As(20) and As@Ni(12) by the all electron linear combination of Gaussian-type orbitals method. The bonding is studied by examining the integrated charge within atomic sphere, the electron localization function, changes in the electron density distribution, and from vibrational modes. We find that strong covalent As-As bonds seen in isolated As(20) become weaker in the As@Ni(12)@As(20) and strong covalent As-Ni bonds are formed. The structural stability of all four clusters is examined by analyzing the energetics and by calculating the vibrational frequencies. Further, the infrared and Raman spectra is predicted for both the neutral and charged As@Ni(12)@As(20) clusters. Finally, the energy barrier for removal of a single arsenic atom is calculated for the neutral As@Ni(12)@As(20) cluster.     

Oligodeoxyribonucleotide analogues with bridging dimethylene sulfide,sulfoxide, and sulfone groups. Toward a second-generation model of nucleic acid structure

Short DNA analogues with bridging dimethylene sulfide, sulfoxide, and sulfone groups replacing the phosphate diesters (S-DNAs) were synthesized from building blocks prepared via two routes, both starting from D-glucose. Building blocks for RNA analogues were prepared by stereoselective introduction of nucleobase into a 2'-acylated ribose analogue. The ribose analogues were converted to deoxyribose analogues by replacement of a 3'-OH group by a thioacetyl unit, followed by photolytic deoxygenation or radical-based 2'-deoxygenation. DNA analogues joined via CH(2)(-)S-CH(2) units were prepared by S(N)2 displacement of a 6'-mesyl group on one building block using a thiolate nucleophile of another. 4,4'-Dimethoxytrityl protection and deprotection schemes were established for both the thiol and hydroxyl groups. The corresponding sulfoxide DNA analogues were obtained by oxidation with hydrogen peroxide. Sulfone DNA analogues were obtained by oxidation of the sulfide DNA with persulfate or hydrogen peroxide in the presence of a titanium silicate catalyst. The physical properties of several representative oligonucleotide analogues were examined, and interpreted in light of a "second-generation" model for DNA strand-strand recognition, a model that emphasizes the role of the polyanionic backbone in diminishing unwanted tendencies of highly functionalized molecules to form "structure" in solution. Even short sulfide-linked DNA analogues displayed association properties different from those displayed by standard DNA molecules. Complex formation observed with sulfide-linked tetramers by HPLC study in different solvents suggested that the complex is formed using hydrogen bonding. Sulfone-linked dinucleotides display Watson-Crick behavior; the tetramer, however, displayed self-structure. Self-structure and self-aggregation become more prominent as the length of the oligonucleotide analogues increases. The tendency to self-aggregate can be decreased by adding a charged sulfonate group to the 3'-end of the DNA analogue. Features of the second-generation model are important for many areas of nucleic acid chemistry, from the design of nucleic acid therapeutic agents to the search for life on other planets.     

ENHANCED SUSCEPTIBILITY TO HPD-SENSITIZED PHOTOTOXICITY AND CORRELATED RESISTANCE TO TRYPSIN DETACHMENT IN SV-40 TRANSFORMED IMR-90 CELLS

Abstract— The response of a normal human cell strain, IMR-90 and a line derived from it by SV40 transformation were compared after treatment in vitro with hematoporphyrin derivative (HPD) and red light. Transformed cells were inactivated at a significantly higher rate than normal cells when assayed by clonogenic survival. Co-treatment with HPD and light also induces cellular resistance to enzymatic cleavage by trypsin; transformed cells exhibit a greater resistance than the normal cells to detachment from the growing surface. These data indicate that transformed cells may possess intrinsic characteristics that render them more sensitive than normal cells to HPD-induced phototoxicity and that the plasma membrane may be the site of differential toxicity.     

Topological electron density analysis of phosphines,phosphaalkenes and phosphaalkynes

A general survey of the topological properties of various phospines, phosphaalkenes, and phosphaalkynes is presented. Fifteen compounds containing carbon-phosphorus single, aromatic, double, and triple bonds were optimized at the Hartree-Fock-self-consistent field (HF-SCF) level using the 3-21G, 3-21G(*) and 6-31G* basis sets. Inclusion of d-orbitals was necessary to obtain reasonable structures. The electron densities of these compounds were analyzed using the topological method of Bader, revealing a number of trends. The value of the electron density at the P C bond critical point correlates strongly with the bond distance and bond order. Integrated electron populations correlate with coordination number. The integrated charge indicates a strongly polarized C P bond in all compounds. Comparisons with five C N compounds are made.     

The chemistry of thujone. IX. Thujone as a chiral synthon for the synthesis of optically active steroid analogues. The vinylpicoline route

The thujone-derived enone 1 , upon base-catalyzed reaction with 2-methyl-6-vinylpyridine is converted to the pyridine analogue 5 (Scheme 1). Catalytic reduction of the latter to 6 generates two new centers of chirality which eventually become C(8) and C(14) in the ultimate synthetic steroid analogue 12 . An X-ray analysis of 6 establishes the structure and absolute configuration so as to determine its suitability in subsequent synthetic studies. The acetal derivative 7 , via Birch reduction, hydrolysis, and internal aldol cyclization, is converted into the cyclohexenone analogue 10 (Scheme 2). This ‘one-pot’ process affords an efficient conversion of the pyridine ring into a cyclohexenone system required for A-ring construction of the steroid skeleton. Finally, conversion of 10 , via the unsaturated diketone 11 , provides the chiral steroid analogue 12 .     

A self-assembled multivalent pseudopolyrotaxane for binding galectin-1

A self-assembled pseudopolyrotaxane consisting of lactoside-displaying cyclodextrin (CD) "beads" threaded onto a linear polyviologen "string" was investigated for its ability to inhibit galectin-1-mediated T-cell agglutination. The CDs of the pseudopolyrotaxane are able to spin around the axis of the polymer chain as well as to move back and forth along its backbone to alter the presentation of its ligand. This supramolecular superstructure incorporates all the advantages of polymeric structures, such as the ability to span large distances, along with a distinctively dynamic presentation of its lactoside ligands to afford a neoglycoconjugate that can adjust to the relative stereochemistries of the lectin's binding sites. The pseudopolyrotaxane exhibited a valency-corrected 10-fold enhancement over native lactose in the agglutination assay, which was greater than the enhancements observed for lactoside-bearing trivalent glycoclusters and a lactoside-bearing chitosan polymer tested using the same assay. The experimental results indicate that supramolecular architectures, such as the pseudopolyrotaxane, provide tools for investigating protein-carbohydrate interactions.     

Perchlorate analysis using solid-phase extraction cartridges

Perchlorate is a compound of increasing concern as an environmental contaminant and is being regulated at increasingly stringent levels. Reliable methods are needed to consistently analyze perchlorate at low concentration levels. This research investigates the use of solid-phase extraction cartridges as an alternative to large-volume injection loops to achieve low-level (microg/L level) perchlorate quantitation. The method involves commercially available strong anion exchange (SAX) cartridges. Water samples are filtered (100 to 1000 mL) using the cartridge, which removes the perchlorate from the solution by anion exchange. Then, after the desired volume is filtered, the perchlorate is extracted using 4 mL of 1% NaOH. In addition, a cleanup method is developed to remove competing anions (chloride, sulfate, and carbonate) that are often found in environmental samples. Analyses are performed with an ion chromatograph using a 10-microL injection loop, yielding a perchlorate method detection limit (MDL) of 210 microg/L. One-liter volumes of a 2-microg/L perchlorate spiked deionized water solution are filtered with SAX SPE. Following extraction and analysis, an MDL of 0.82 microg/L is obtained, comparable to that found for 1-mL injection loop systems (reported as low as 0.53 microg/L). MDL studies are then conducted on perchlorate-amended groundwater (solution concentration of 70 microg/L) and surface water (solution concentration of 10 microg/L) using a filtration volume of 200 mL. The MDLs are 6.7 microg/L for the groundwater and 2.4 microg/L for the surface water.     

CO disproportionation on Ni-based catalysts

Ni/SiO₂ exhibits higher activity for CO dissociation than coprecipitated Na–Mn–Ni, which is a higher oxygenate synthesis catalyst at 303 K, while Na–Mn–Ni exhibited higher CO dissociation activities at 673 K.     

Cross-linking dendrimers with allyl ether end-groups using the ring-closing metathesis reaction

A third generation Frechet-type dendrimer containing 24 allyl ether end-groups was synthesized, cross-linked using the ring-closing metathesis (RCM) reaction, and the core was removed hydrolytically without significant fragmentation. The results are analogous to those previously reported for homoallyl ether dendrimers (Wendland, M. S.; Zimmerman, S. C. J. Am. Chem. Soc. 1999, 121, 1389-1390) suggesting that the less readily available homoallyl ether dendrimers can be replaced by their allyl ethers analogues in a range of applications.