Synthesis of new 1,2,4-triazolo[4,3-b]pyridazines and related compounds

The synthesis of novel 6-[4-(1H-imidazol-1-yl)phenyl]-1,2,4-triazolo[4,3-b]pyridazines 8a-f and related compounds is described. Although the intermediate hydrazine derivatives 7 and 9 possess good positive inotropic activity, the fused bicyclic pyridazines 8a-f are significantly less potent than the 3(2H)-pyridazinone 5. Compounds 8a-f are potent but nonselective inhibitors of cardiac phosphodiesterase.     

Role of vibrationally excited NO in promoting electron emission when colliding with a metal surface: a nonadiabatic dynamic model

A nonadiabatic quantum dynamic model has been developed to study the process of electron emission from a low-work-function metal surface. The process is initiated by scattering a highly vibrationally excited NO molecule from a surface composed of a Cs layer covering a Ru crystal. The model addresses the increasing quantum yield of the electron emission as a function of the molecular vibrational excitation and incident kinetic energy. The reaction mechanism is identified as a long-range harpooning electron transfer to a molecular ion which is then accelerated toward the surface. Upon impact, the molecular ion emits its excess electron.     

Laser induced breakdown of Ar,N2 and O2 gases using 1.064, 0.532, 0.355 and 0.266 μm radiation

An experimental investigation of laser-induced breakdown using Nd:YAG laser harmonics for argon, nitrogen and oxygen gases is reported. Pressure dependence as well as wavelength dependence of the breakdown threshold irradianceI _th is investigated. The experimental observations for 1.064 and 0.532 m laser wavelengths are in agreement with theoretical calculations which include the effects of multiphoton ionization and cascade ionization.     

Production of oxygen enriched air by rapid pressure swing adsorption

A novel rapid pressure swing adsorption (RPSA) process is described for production of 25–50% oxygen enriched air. The embodiment consists of one or more pairs of adsorbent layers contained in a single adsorption vessel. The layers undergo simultaneous pressurization-adsorption and simultaneous depressurization-purge steps. A total cycle time of 6–20 seconds is used. The process yields a very large specific oxygen production rate and a reasonable oxygen recovery for production of 20–50 mole% oxygen enriched gas.It is demonstrated by a simple mathematical model of isothermal single adsorbate pressure swing ad(de)sorption concept on a single adsorbent particle that the specific production rate of a PSA process cannot be indefinitely increased by reducing the cycle time of operation when adsorbate mass transfer resistances are finite.     

Covalent crosslinking of 1-D photonic crystals of microporous Si by hydrosilylation and ring-opening metathesis polymerization

Free-standing porous Si multilayer dielectric mirrors, prepared by electrochemical etching of crystalline Si, are treated with a ruthenium ring-opening metathesis polymerization (ROMP) catalyst followed by norbornene to produce flexible, stable composite materials in which poly(norbornene) is covalently attached to the porous Si matrix.     

Compensation effect in the electrical conduction process in a series of pyrenyl polyenes

The semiconductive properties of a series of pyrenyl polyenes of the type R-(CH=CH)_n-R, are studied as a function of the adsorption of different amount of a vapour. With regard to the compensation temperature (T ₀) the compounds are divided into two groups. For compounds which have odd number of double bonds,T ₀ is infinite and in compounds having even number double bonds,T ₀ is finite.T ₀ for II₂ is higher while that of II₄ is lower than the experimental temperature. DifferentT ₀ for the compounds having odd or even number of double bonds suggests a physical basis for the compensation rule, which we believe, is related to the molecular and crystalline structure of the compounds     

Minimizing broadband excitation under dissipative conditions

Optimal control theory is employed for the task of minimizing the excited-state population of a dye molecule in solution. The spectrum of the excitation pulse is contained completely in the absorption band of the molecule. Only phase control is studied which is equivalent to optimizing the transmission of the pulse through the medium. The molecular model explicitly includes two electronic states and a single vibrational mode. The other degrees of freedom are classified as bath modes. The surrogate Hamiltonian method is employed to incorporate these bath degrees of freedom. Their influence can be classified as electronic dephasing and vibrational relaxation. In accordance with experimental results, minimal excitation is associated with a negatively chirped pulses. Optimal pulses with more complex transient structure are found to be superior to linearly chirped pulses. The difference is enhanced when the fluence is increased. The improvement degrades when dissipative effects become more dominant.     

Atomistic-scale simulations of the initial chemical events in the thermal initiation of triacetonetriperoxide

To study the initial chemical events related to the detonation of triacetonetriperoxide (TATP), we have performed a series of molecular dynamics (MD) simulations. In these simulations we used the ReaxFF reactive force field, which we have extended to reproduce the quantum mechanics (QM)-derived relative energies of the reactants, products, intermediates, and transition states related to the TATP unimolecular decomposition. We find excellent agreement between the QM-predicted reaction products and those observed from 100 independent ReaxFF unimolecular MD cookoff simulations. Furthermore, the primary reaction products and average initiation temperature observed in these 100 independent unimolecular cookoff simulations match closely with those observed from a TATP condensed-phase cookoff simulation, indicating that unimolecular decomposition dominates the thermal initiation of the TATP condensed phase. Our simulations demonstrate that thermal initiation of condensed-phase TATP is entropy-driven (rather than enthalpy-driven), since the initial reaction (which mainly leads to the formation of acetone, O(2), and several unstable C(3)H(6)O(2) isomers) is almost energy-neutral. The O(2) generated in the initiation steps is subsequently utilized in exothermic secondary reactions, leading finally to formation of water and a wide range of small hydrocarbons, acids, aldehydes, ketones, ethers, and alcohols.     

The chemistry of cyclic enaminoketones. III. Synthesis of bi- and tricyclic enaminoketones from enamine esters and nitriles

The cyclization of enamines derived from β-aminoesters and β-aminonitriles into bi- and tricyclic enaminoketones ( 6,9,13 and 24 ) has been investigated. The enamines derived from aminonitriles cyclize smoothly with magnesium perchlorate in benzene or toluene, whereas the enamines derived from aminoesters cyclize spontaneously during their formation. The scope and limitation of this process is discussed.