The synthesis of functionalized cis'-bicyclo ¦3.3.0¦octanes

A number of polyfunctionalized cis-bicycio ¦3.3.0¦octanes have been synthesized starting from the tricyclic key intermediate $\text{5}$ which was obtained by the intramolecular cyclopropanation reaction of the diazo keto ester $\text{4}$. Selected stereocontrolled transformations of $\text{5}$ using nucleophiles and electrophiles have been studied for the preparation of the title compounds.     

The addition of methyllithium to 2,2,4,4-tetramethylcyclobutan-1-one-3-thione. The generation and capture of a bishomoenolate anion.

Methyllithium added to 2,2,4,4-tetramethylcyclobutan-1-one-3-thione to produce lithium 3-methylthio-2,2,4,4-tetramethylbicyclo[1.1.0]but-1-oxide. This bishomoenolate was alkylated on carbon by methyl iodide, but retained the bicyclo[1.1.0]butane skeleton when silated with chlorotrimethylsilane. The ease of oxidation of a series of 1,3-diheteroatom substituted bicyclo[1.1.0]butanes was determined.     

A molecular flytrap for the selective binding of citrate and other tricarboxylates in water

The synthesis and binding properties of a new tricationic guanidiniocarbonyl pyrrole receptor 7 are described. Receptor 7 binds citrate 9 and other tricarboxylates such as trimesic acid tricarboxylate 8 with unprecedented high association constants of K(assoc) > 10(5) M(-1) in water as determined by UV and fluorescence tritration studies. According to NOESY experiments and molecular modeling calculations, the tricarboxylates are bound within the inner cavity of receptor 7 by ion pairing between the carboxylate groups and the guanidiniocarbonyl pyrrole moieties, favored by the nonpolar microenvironment of the cavity. Hence, receptor 7 can be regarded as a molecular flytrap. In the case of the aromatic tricarboxylate 8, additional aromatic interactions further strengthen the complex. The complexes with the tricarboxylates are so strong that even the presence of a large excess of competing anions or buffer salts does not significantly affect the association constant. For example, the association constant for citrate changes only from K(assoc) = 1.6 x 10(5) M(-1) in pure water to K(assoc) = 8.6 x 10(4) M(-1) in the presence of a 170-fold excess of bis-tris buffer and a 1000-fold excess of chloride. This makes 7 one of the most efficient receptors for the binding of citrate in aqueous solvents reported thus far.     

Toward an accurate and efficient semiclassical surface hopping procedure for nonadiabatic problems

The derivation of a semiclassical surface hopping procedure from a formally exact solution of the Schrodinger equation is discussed. The fact that the derivation proceeds from an exact solution guarantees that all phase terms are completely and accurately included. Numerical evidence shows the method to be highly accurate. A Monte Carlo implementation of this method is considered, and recent work to significantly improve the statistical accuracy of the Monte Carlo approach is discussed.     

ortho Substituent effect on a 1,5-H shift reaction during thermal decomposition of aryltriazenes

An ortho substituent group has a significant effect on thermal decomposition of aryltriazenes. When the ortho methoxy-substituted phenyltriazenes were treated with methyl iodide at 110-130 °C, 1,5-H shift products were obtained in fair to moderate yields.     

Inactivation of nitroalkane oxidase upon mutation of the active site base and rescue with a deprotonated substrate

Mutation of Asp402 in nitroalkane oxidase to Asn or Ala inactivates the enzyme with neutral nitroethane as substrate, but the activity can be rescued with the nitroethane anion. The V/K values of the D402N and D402A enzymes with the nitroethane anion are independent of pH, whereas the V/K values of the wild-type and D402E enzymes are pH dependent with both the protonated and the deprotonated forms of nitroethane. Moreover, although the V/K value of the D402E enzyme with neutral nitroethane is 20-fold less than that of the wild-type enzyme, there is only a 2-fold difference in the V/K values with the nitroethane anion. These results are fully consistent with a primary role for Asp402 as the active site base in nitroalkane oxidase which abstracts the substrate alpha-proton.     

Synthese von cyclischen α-trimethylsilylketonen

Cyclic α-trimethylsilylketones $\text{10}$ are synthesized from cyclic vinyltrimethylsilanes via the epoxides $\text{8}$, and the alcohols $\text{9}$.     

Synthesis and fluorescence ion-sensory properties of the first dehydropyridoannulene-type cyclophane with enforced exotopic metal ion binding sites

The new twistophane 4 has been synthesised, which comprises a conjugated dehydropyridoannulene-type macrocyclic scaffold with outwardly projecting nitrogen-donor sites for the purpose of metal ion coordination. The macrocyclíc structure of 4 was assigned by using spectroscopic methods, and shown to exist in a twisted and chiral ground state conformation by semi-empirical theoretical calculations. A detailed spectroscopic investigation into the metal ion binding properties of 4 and precursor 11 revealed that they functioned as selective complexants, affording a fluorescence quenching output response characteristic of Pd(II) and Hg(II) ions. Furthermore, 4 also signalled the presence of Fe(II), Co(II), Ni(II) and Ag(I) ions by the precipitation of coordination polymers, and exhibited reversible proton-triggered fluorescence quenching behaviour. Macrocycle 4 thus represents a unique type of molecular sensory platform, which may find a wealth of potential applications such as the detection of heavy-metal pollutants, as well as for the fabrication of proton-switchable materials and coordination polymers with novel electronic and magnetic properties.