Relaxation and movement of point defect clusters in copper by molecular dynamics simulation

Abstract

The structures of point defect clusters of both interstitial and vacancy type were examined by computer simulation using molecular dynamics and molecular statics with the DYNAMO code (Daw, Foiles and Baskes [6]). The code implements an isotropic potential of embedded atom method (EAM) developed by Daw and Baskes [5]. Interstitial clusters relax to either the immobile mixture of <100> dumbbell and bcc interstitials or a mobile platelet of parallel <110> interstitials. The latter cluster moves along <110> directions. A tri-vacancy relaxes to an un-collapsed stacking fault tetrahedron (sft) of Damask-Dienes type (3v-sft) containing a central atom that vibrates with a large amplitude. A hexa-vacancy relaxes to a stacking fault tetrahedron the structure of which fluctuates between a sft and void. Larger vacancy clusters are stable as a combination of sft and 3v-sft. In these vacancy clusters, atoms show significant vibration with large amplitude. Voids form only with the inclusion of gas-atoms into vacancy clusters.     

All ring compounds—XXIX : Thermal decomposition of t-butyl per (trans-2-substituted cyclopropyl) acetates

Three kinds of t-butyl per (trans-2-substituted cyclopropyl) acetates (RH, CH₃, C₆H₅) were synthesized from the corresponding acyl chlorides and thermally decomposed in cyclohexane to investigate the chemical stability and behaviour of the cyclopropylcarbinyl radical. Clean first-order kinetics were obtained in all of the thermal decomposition reactions. The experimental fact that the decompositoin rates and activation parameters of these three t-butyl peresters are similar to each other may indicate the absence of the ionic character in the transition state suggesting the almost complete homolytic decomposition of these peresters. Although the typical concerted decomposition might be invalid for these peresters in view of the activation parameters, it would be suggested from the product studies that the decomposition of these peresters was characterized by a considerable loss of their acyl-alky] bonds at the time of the fission of their OO bonds. The products yielded from the thermal decomposition of t-butyl per (trans-2-phenylcyclopropyl) acetate in various hydrogen donating solvents consisted of three hydrocarbons and two t-butyl ethers. The formation of these t-butyl ethers, possibly cage products, was significant.     

Optical damping constants in narrow gap semiconductors

Optical damping constants due to free carriers of HgSe, Zn _x Hg_1–x and Cd _x Hg_1–x Se were estimated from far infrared reflection spectra at 5 and 10 K. The damping mechanism was explained by the Drude type scattering below plasma frequency and by doubly ionized impurity scattering in the higher frequency range.     

Photophysical and photochemical processes in zeolite cavities: The effects of ion-exchanged alkalimetal cations on the excited states of xanthone and the photolysis of 2-pentanone

The characteristics properties of xanthone phosphorescence and of 2-pentanone photolysis in alkali metal cation-exchanged zeolites have been investigated to clarify the effect of the micro-environment of host-adsorbents on the photophysical and photochemical properties of guest-molecules in restricted void spaces. The enhancement of the phosphorescence yields of xanthone included in zeolites is observed by changing the exchangeablealkali metal cation from Li⁺ to Cs⁺. Simultaneously, the phosphorescence lifetimes were observed to continuously shorten by changing the cation from Li⁺ to Cs⁺. These results suggest that the external heavy-atom effect deriving from the alkali metal cations on the singlet-triplet transitions of xanthone molecules stabilized on alkali metal cations in the order of Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The yields for the photolysis of 2-pentanone included in zeolites increase with changing the alkali metal cation from Li⁺ to Cs⁺. IR investigations of the adsorption state of 2-pentanone indicate that strength of the interaction between the alkali metal cations and 2-pentanones decreases by changing the cation from Li⁺ to Cs⁺, which results in a longer lifetime of 2-pentanone. The selectivity of propylene formation is dramatically increased by changing the cation from Li⁺ to Cs⁺. The enhanced formation of propylene is asociated with the hydrogen absorption from propyl radicals by lattice oxygen, their basicity increasing by changing the cation from Li⁺ to Cs⁺. Thus, these changes in the zeolite cavities modified by exchanging cations caused significant effects not only on the excited state but also on the following chemical reactions of ketones.     

A practical chromatography-free synthesis of a 5,6-dihydroimidazolo[1,5-f]pteridine derivative as a polo-like kinase-1 inhibitor

A practical chromatography-free synthesis of a potent polo-like kinase-1 inhibitor possessing a unique 5,6-dihydroimidazolo[1,5-f]pteridine structure has been developed. We showed that key cyanoimidazole ring formation could be conducted at benign temperature and obtained a chiral 5,6-dihydroimidazolo[1,5-f]pteridine derivative in good yield without epimerization. An aniline derivative containing a trans 1,4-cyclohexyl diamine structure was prepared by a synthesis that makes use of defined stereocenters of commercially available trans-cyclohexane-1,4-diamine via selective piperazine ring formation from a primary diamine. A coupling reaction of the 3-chloro-5,6-dihydroimidazolo[1,5-f]pteridine derivative and the aniline derivative in the endgame was closely investigated, and good yields were achieved both by palladium-catalyzed amination and acid-promoted coupling under benign reaction conditions. As a result of these investigations, the polo-like kinase-1 inhibitor was successfully obtained in a practical way without concern for generation/separation of stereoisomers.     

Preparation and characterization of 6-substituted 1,8-diazabicyclo[5.4.0]undec-7-ene

The lithium 1,8-diazabicyclo[5.4.0]undec-6-ide ( 1 ) prepared from 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and n-butyllithium reacts with alkyl halides and carbonyl compounds such as benzophenone, acetophenone, and benzaldehyde to give 6-substituted DBU derivatives in good yields. The reaction behavior of 6-substi-tuted DBU was also investigated.     

Syntheses of anolignans A and B using ruthenium-catalyzed cross-enyne metathesis.

Anolignans A and B were synthesized using ruthenium-catalyzed cross-enyne metathesis as the key steps. The 1,3-diene moieties of these natural products were constructed by the introduction of the methylene parts of ethylene into alkyne using Grubbs' catalyst.