Reductive spiroannulation of nitriles with secondary electrophiles

The scope of reductive decyanation and spiroannulation reactions has been expanded to include secondary electrophiles for potentially useful transformations. Secondary phosphates and chlorides, as well as terminal epoxides, cyclize in a stereospecific fashion. Both endo and exo modes of cyclization were observed with terminal epoxides.     

A kinetic and spectroscopic study of the interaction between a M(CO)5 (M=Cr, W) fragment and ethyl diazoacetate

The reaction between Cr(CO)₅[C₆H₆] and ethyl diazoacetate (EDA) has been studied using the technique of laser flash photolysis. Results indicate that the Cr(CO)₅ fragment reacts very rapidly with the EDA ligand. Low temperature spectroscopic studies suggest that in the case of W(CO)₅, and by analogy also in the case of Cr(CO)₅, the initial adduct between the pentacarbonyl fragment and EDA is one where the oxygen atom of the diazocarbonyl ligand is bound to the metal center. This kinetic product is then converted to a thermodynamically favored complex which is tentatively assigned as the nitrogen bound W(CO)₅-EDA complex that appears to be stable at r.t.     

Maximum hardness in P6 isomers

Parr and Chattaraj proposed a principle of maximum hardness for stable molecular structures. Pearson and Palke used ab initio SCF MO calculations for ammonia and ethane to demonstrate the operation of the principle. In this paper, we present ab initio SCF MO results for five isomeric forms of the homoatomic P⁶ cluster as further support for the principle of maximum hardness. © 1994 John Wiley & Sons, Inc.     

Bimetallic palladium-platinum dendrimer-encapsulated catalysts

We report the synthesis, characterization, and catalytic activity of bimetallic palladium-platinum dendrimer-encapsulated catalysts (DECs). These materials are prepared by co-complexation of different ratios of palladium and platinum salts to the interior tertiary amines of fourth-generation, hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers. Chemical reduction of these composites yields stable, fairly monodisperse, water-soluble bimetallic DECs having sizes on the order of 1.9 +/- 0.4 nm. Evidence that these nanoparticles are bimetallic comes from single-particle X-ray energy dispersive spectroscopy (EDS) and catalysis experiments. The latter indicate that the hydrogenation rate of allyl alcohol is enhanced in the presence of the bimetallic nanoparticles compared to DECs containing only platinum or only palladium nanoparticles. EDS results indicate that the percentage composition of the bimetallics is reflected by the percentage of metal salts initially complexed with the dendrimer.     

Enantioselective synthesis of an aziridinomitosane and selective functionalizations of a key intermediate

An enantioselective synthesis of mitosane core (-)-1 has been achieved. Key steps include a rapid assembly of a key eight-membered-ring intermediate employing ring-closing metathesis. Kinetic resolution of an advanced secondary alcohol was then accomplished by using a peptide-based asymmetric acyl transfer catalyst that was discovered from a parallel screen of catalyst candidates. Optically pure material was then converted to the mitosane core, which was the subject of additional studies on the selective modification to produce several substituted compounds containing a mitosane ring system.     

Antibody synthesis induced by endogenous internal images

In this study, immunization with a vaccine consisting of multiple F(abt’)₂ fragments of affinity-purified antitetanus toxoid antibodies covalently bound to a carrier protein successfully induced antitetanus toxoid antibodies. Further studies showed that this vaccine preparation contained no biologically detectable tetanus antigen. The induced antitetanus antibody (Ab1t’) titer was higher than the titer of antibodies binding control antigens. The immunizing F(abt’)₂ preparation did not elicit a secondary antitetanus response from mice primed with tetanus toxoid and, hence, appeared free of tetanus epitopes. The specificity of Ab1t’ was established by absorption and inhibition with antigen. Immunization with antitetanus F(abt’)₂ (Ab1t’) fragments appears to have elicited naturally occurring autologous antitetanus toxoid antibody (Ab1t’) through an idiotypic pathway. As predicted by network theory, anti-idiotype (Ab2) and antitetanus (Ab1t’) cycled reciprocally. Clonotypic characterization of Ab1t’ using isoelectric focusing and affinity immunoblotting showed increases in Ab1t’ titer to be the result of increased synthesis by limited subsets of antitetanus toxoid B-cell clones and not increased synthesis by multiple clones, as is characteristic of antigen-driven Ab1 responses. Many Ab1 and Ab1t’ clonotypes had identical pIs, suggesting that they either share V region genes or are the product of the same B-cell clones. These findings indicate that immunization with polyclonal multivalent Ab1 preparations can trigger active synthesis of antibodies with the same specificity. The results provide further evidence for naturally occurring idiotypic cascades that could be exploited for studies of catalytic antibodies.     

Lanthanide crown ether complexes of p-sulfonatocalix[5]arene

Two types of arrays are formed in water involving aza-crown ethers, p-sulfonatocalix[5]arene and europium(III) ions. One is a co-ordination polymer connecting calixarenes, sodium ions and lanthanide ions based on "ferris wheel" moieties incorporating aza-18-crown-6 and sodium ions. The second structure is a host-guest arrangement with di-protonated diaza-18-crown-6 in the cavity of the calixarenes as part of secondary coordination spheres of aquated europium(iii) ions.     

Electron conduction across electrode-immobilized neutravidin bound with biotin-labeled ruthenium pentaamine

Voltammetry is reported here of a self-assembled redox-protein conjugate consisting of neutravidin conjugated with a biotin derivative redox probe, Ru(NH3)5(N-[(N-[(4-pyridyl)methyl]biotinamide], immobilized on gold electrodes modified by self-assembled monolayers of mercaptoundecanoic acid. This voltammetry indicates that self-assembly of the conjugate/electrode electronic interface, driven by electrostatic binding between the monolayer and a single redox probe, favors orientation of the conjugate, resulting in electronic accessibility of the remaining three redox probes.