Base hydrolysis of halolactones in the bicyclo(2.2.1)heptyl and bicyclo(2.2.2)octyl systems

The mechanism of ketocarboxylic acid formation in the base treatment of bicyclo[2.2.1]heptyl halolactones has been determined. On the basis of stoichiometry, kinetics, effect of leaving group, and isotopic labeling experiments, a dehydrohalogenation mechanism is proposed in which cleavage of the carbon-halogen bond precedes that of the carbon-hydrogen bond in the transition state. The relationship between El-like and syn-E2 transition states in these systems is discussed.In the bicyclo[2.2.2]octyl series base treatment of the halolactones yields oxidocarboxylic acids. The difference in behavior between the two systems is rationalized on the basis of molecular geometry.     

Spectroscopy at very high pressures: Infrared study of the high pressure phase transitions in NaNO2 and KNO2

Infrared spectra of NaNO₂ and KNO₂ in the region of the anion internal modes have been obtained using a diamond anvil cell at pressures up to 65 kbar. At 39°C NaNO₂ undergoes a phase transition at ca. 10.0 kbar, not at 14 kbar as reported from an earlier IR study. A similar transition was found at 6.3 kbar for KNO₂. The symmetric modes lose intensity with increasing pressure, and all modes suffer blue-shifts. For KNO₂ ν(NO)₅ shifts much more than ν(NO)_a.     

C3H3+ isomers: temperature dependencies of production in the H3+ reaction with allene and loss by dissociative recombination with electrons

A technique has been developed to simultaneously determine recombination rate coefficients, alpha e, and initial concentrations of ion types that coexist in a flowing afterglow plasma. This was tested using the H3(+) + allene reaction in which two different C3H3+ isomers are produced. Use of an electrostatic Langmuir probe enabled the C3H3+ isomer branching ratios for propargyl and cyclic C3H3+ from this allene reaction and their alpha e to be determined over the temperature range 172-489 K. The study showed that the cyclic C3H3+ to propargyl C3H3+ branching ratios from the allene reaction varied from 50/50 at 172 K to 18/82 at 489 K. Over this temperature range, the alpha e for both isomers change only slightly. The room temperature alpha e values for propargyl and cyclic C3H3+ are (1.15 +/- 0.2) x 10(-7) and (8.00 +/- 0.1) x 10(-7) cm3/s, respectively. The data are discussed relative to current theories and in relation to fuel-rich flame chemistry, interstellar molecular synthesis, and modeling of Titan's atmosphere.     

Specificity and affinity of natural product cyclopentapeptide inhibitors against A. fumigatus, human, and bacterial chitinases

Family 18 chitinases play key roles in organisms ranging from bacteria to man. There is a need for specific, potent inhibitors to probe the function of these chitinases in different organisms. Such molecules could also provide leads for the development of chemotherapeuticals with fungicidal, insecticidal, or anti-inflammatory potential. Recently, two natural product peptides, argifin and argadin, have been characterized, which structurally mimic chitinase-chitooligosaccharide interactions and inhibit a bacterial chitinase in the nM-mM range. Here, we show that these inhibitors also act on human and Aspergillus fumigatus chitinases. The structures of these enzymes in complex with argifin and argadin, together with mutagenesis, fluorescence, and enzymology, reveal that subtle changes in the binding site dramatically affect affinity and selectivity. The data show that it may be possible to develop specific chitinase inhibitors based on the argifin/argadin scaffolds.     

Synthesis of lipoxins: Total synthesis of conjugated trihydroxy eicosatetraenoic acids

The first synthesis of a conjugated trihydroxy eicosatetraenoic acid, a possible structure for Lipoxin A is described. A biomimetic approach was utilized.     

Gamma-oxidation of linear low-density polyethylene: The dose–rate effect of irradiation on chemical and physical modifications

γ-Oxidation of linear low-density polyethylene based on hexene and butene was investigated. Irradiation was performed at different dose rates in air (from 2 rad/s to 100 rad/s). Degraded samples were analyzed with IR combined with NO and SF₄ derivatizations. Our results showed that the lower the dose rate, the higher the degree of oxidation in terms of γ-product formation. Ketone species appeared to be the dominant γ-products. The G values of γ-product formation were very dependent on the dose rate of initiation. Comparison of the G value ratio of different γ-products revealed stoechiometry differences. The complex appearance and disappearance of unsaturations was tentatively explained. The modifications of elongation at break induced by γ-irradiation were monitored by molecular changes in weight. This was not conclusive because changes in elongation at break are inconsistent with changes in M_w/M_n. © 1995 John Wiley & Sons, Inc.     

Application of graphical methods of spin algebras to limited CI approaches. II. A simple open shell case

A time independent diagrammatic technique based on the Wick theorem and graphical methods of spin algebras, as outlined in Part I, is applied to a simple open shell case having one unpaired electron in addition to the pure singlet closed shell. Compact explicit expressions for the matrix elements of a spin independent Hamiltonian between conveniently chosen spin symmetry adapted states are given for the ground, mono- and bi-excited configurations.     

The synthesis of water soluble decalin-based thiols and S-nitrosothiols--model systems for studying the reactions of nitric oxide with protein thiols

The syntheses of three decalin-based tert-thiols displaying varying degrees of solubility in aqueous milieu are described. The S-nitroso derivatives of these compounds have also been prepared and the structures of two of these determined by single crystal X-ray diffraction. These compounds have been designed for studying the interaction of nitric oxide (NO) with thiols under physiological conditions.