Tributyltin determination in marine sediments: A comparative study of methods

Two independent speciation methods have been applied to the determination of tributyltin (TBT) in marine sediments: (1) acetic acid leaching/hydride generation/cold trapping/GC/quartz furnace AA; and (2) toluene–tropolone extraction/HPLC/GFAA. TBT determines in a typically moderately polluted sediment (Porto Vecchio Bay, Corsica, France) are in very good agreement, as also are the determination of total recoverable tin by the first method and by a direct one using strong acid leaching followed by GFAA. These cross-verifications lead one to conclude that both speciation methods are convenient and allow for valid determination of TBT in marine sediments, with no loss of TBT. Method-induced modification of tin speciation has not been observed.     

Electronic Tuning of a Carbene Center via Remote Chemical Induction,and Relevant Effects in Catalysis

The present report develops the idea that an N‐heterocyclic carbene incorporating a remote anionic functionality—here, a malonate group—as a backbone component of its heterocyclic framework, can be “post‐functionalized” directly from its transition‐metal complexes, upon simple addition of a variety of electrophiles interacting directly with the malonate group in the outer coordination sphere. From a palette of selected electrophilic reagents, it was thus possible to modulate the electronic donor properties of the carbene center over a rather broad range. Both the zwitterionic complex [Rh{malo‐NHC}(cod)] and the cationic derivatives [Rh{malo‐NHC^E}(cod)]⁺ (where “malo‐NHC^E” represents the ligand modified by a selected electrophile “E”) were used as pre‐catalysts in two types of catalytic reactions, namely, the polymerization of phenylacetylene and the hydroboration of styrene. The results indicate that, in both cases, the zwitterionic species is by far the best catalyst, whereas a decrease in the ligand donicity induced by the added electrophile results in a concomitant reduction of catalytic activity. Apparent deviations to such a trend in the case of the hydroboration of styrene were rationalized in terms of an interaction between the reactive catecholborane substrate and the remote functionality of the N‐heterocyclic carbene leading to an in situ modification of the nature of the active species. These observations serve as a useful basis to define the scope and limitations of the present conceptual approach in catalysis.     

Control of a multisubunit DNA motor by a thermoresponsive polymer switch

The conjugation of thermoresponsive polymers to multisubunit, multifunctional hybrid type 1 DNA restriction-modification (R-M) enzymes enables temperature-controlled "switching" of DNA methylation by the conjugate. Polymers attached to the enzyme at a subunit distal to the methylation subunit allow retention of DNA recognition and ATPase activity while controlling methylation of plasmid DNA. This regulation of enzyme activity arises from the coil-globule phase transitions of the polymer as shown in light scattering and gel retardation assays.     

instant "base-promoted" generation of roper's-type Ru(0) complexes Ru(CO)2(PR3)3 from a simple carbonylchlororuthenium(II) precursor

An uncommon synergism in the concerted action of OH- and PR3 toward the simple Ru(II) complex Ru(CO)3Cl2(thf) allows a highly efficient reduction of the metal in ethanol or acetonitrile solution at 0 degrees C, with selective production of the corresponding Roper's-type Ru(0) complexes Ru(CO)2(PR3)3 in high yields within 10 min.     

Substituent effects on the structure and supramolecular assembly of bis(dioxaborole)s

Solid-state and solution analysis shows that dialkyl substituents on the central phenyl ring of bis(dioxaborole)s, such as , do not have an appreciable effect on the planarity but do significantly alter the supramolecular assembly of these compounds.     

Z4-Kerdock Codes, Orthogonal Spreads, and Extremal Euclidean Line-Sets

When m is odd, spreads in an orthogonal vector space of type⁺(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2^{m + 1} with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z₄ and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z₄-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z₄-Kerdock codes. They also produce new Z₄-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99.     

Novel Polymeric Carbonylhaloruthenium(I) Polyanions: Rational Design and Self-Reorganization in the Presence of CO(2) and H(2)O

We just need to mix [Ru(CO)(3)Cl(2)(thf)] with methanolic NEt(4)OH-nature will do the rest: The unsaturated fragments thus generated spontaneously polymerize with production of CO(2) and H(2)O, which combine to give the carbonate ligands of the ruthena-crown species obtained (shown schematically). The carbonate groups, rarely seen in ruthenium carbonyl complexes, are responsible for the observed annulation, and hold consecutive Ru dimers together by acting as bridging and doubly chelating ligands.