Recombination dependence of theO(α s 2 ) three-jet cross section ine + e − annihilation

TheO(α _s ² ) QCD corrections to the thrust distribution for three-jet production ine ⁺ e ^? annihilation are found to depend on the algorithm for recombining four partons into three jets. Several recombination schemes are discussed and results are compared. Results of the recombination approach are compared also to recent direct calculations of three-jet thrust distributions. The importance of terms proportional to jet resolution parameters is stressed.     

Towards a quantum chemical software package utilizing transferable fragments as molecular building blocks

Computer programs have been developed or are under development for the IBM personal computer that enable their users to get information on atomic charges, electrostatic potentials, conformational and other properties of molecular systems containing H, C, N, O, F, Si, P, S, or Cl atoms. The zero-order wavefunction is constructed of strictly localized molecular orbitals with fixed atomic orbital coefficients. The wave function can be refined by optimizing these coefficients, i.e., considering inductive effects via a coupled set of 2 × 2 secular equations within the CNDO /2 approximation. Delocalization and exchange effects are accounted for by expanding the wavefunction on a basis of the aforementioned strictly localized orbitals, instead of conventional atomic orbitals, and solving the corresponding SCF equations. Our method has been applied to the study of large systems. We calculated the electrostatic field of the complex of β-trypsin and basic pancreatic trypsin inhibitor and it has been found that strong field regions more or less coincide with hydration sites. A further potential application of protein electrostatic fields is in NMR spectroscopy. We found a linear correlation between C^αH or backbone NH proton chemical shifts and the protein field at the site of the corresponding proton. At last, we propose a simple method to mimic the bulk around atomic clusters modeling crystalline and amorphous silicon. Based on this method we found a linear correlation between atomic net charges and bond angle distortions in silicon clusters with 35 atoms.     

Polymerization of para-xylylene derivatives (parylene polymerization). I. Deposition kinetics for parylene N and parylene C

Kinetic aspects of parylene N [unsubstituted poly(para-xylylene)] and Parylene C [monochlorosubstituted poly(para-xylylene)] were studied. The conversion of starting material (dimer of either p-xylylene or chloro-para-xylylene) to polymer is quantitative (ca. 100%). Consequently, the total polymer formed in a closed system is directly proportional to the amount of dimer charged. However, the percentage of the total amount of polymer formed which deposits on substrate surfaces, placed in the deposition chamber, as well as the polymer film growth rate are dependent on operational factors such as the temperature of the substrate, sublimation of dimer temperature, flow pattern of the reactive species, etc. Parylene C, being a heavier and more polar molecule, has the tendency to deposit easily in the deposition chamber compared to the deposition of Parylene N. Parylene C also has a higher ceiling temperature for deposition than Parylene N. This situation has been investigated from the viewpoint of excess thermal energy which hinders polymer formation (deposition) due to the exceedingly high entropy change necessary for polymer deposition to occur. The addition of a cool (i.e., room temperature) inert gas was shown to increase the deposition of Parylene N on substrate surfaces placed in the deposition chamber. The deposition increase and acceleration of deposition (film growth) rate were found to be related to the size and molecular weight of the inert gas pressure maintained in the system. The accelerating effect is explained by the increase in third-body collisions to dissipate the excess thermal energy of the reactive species.     

Triplet state properties of the benzo[α]pyrene-DNA complex as determined by optically detected zero-field magnetic resonance

The zero-field transitions in the photoexcited triplet state of benzo[α]pyrene bound to DNA have been observed by optical detection of magnetic resonance of 2 K. The transition frequencies individual spin sublevel intersystem crossing rates were measured by monitoring the microwave-induced intensity changes of the triplettriplet absorption at 465.8 nm. The triplet state zero-field splitting and dynamics for the benzo[α]pyrene DNA complex are compared with these properties measured for benzo(α)pyrene in other solvent systems.     

Mechanism of vinyl chloride polymerization

An overall mechanistic scheme for the suspension polymerization of vinyl chloride is presented. The process can be resolved into five discrete stages, each of which presents a unique environment for the interaction of the systems parameters. It is shown that the surface area of the polymer formed during the reaction is not a major factor in autoacceleration and that the increase of kinetic chain length with conversion is due to a radical dilution effect. The latter is a direct result of the difference in rates between polymerization and radical formation, the former being greater. The increase of the initial polymerization rate and the reduction of autoacceleration brought about by chain transfer agents can be explained by the lower diffusion rate and greater bulkiness of the chain transfer agent radical relative to that of the monomer radical. The chaintransfer agent CBr₄ is preferentially absorbed by PVC from solution in vinyl chloride. With lauryl peroxide as initiator it is shown that the “hot spot” is the result of a build-up of initiator in the monomer caused by its exclusion from the polymer phase. Vinyl chloride was found to dissolve 0.03% PVC at ambient temperature and to have no effect on the decomposition rate of lauryl peroxide.     

Engineered protein cages for nanomaterial synthesis

Self-assembled particles of genetically engineered human L subunit ferritin expressing a silver-binding peptide were used as nanocontainers for the synthesis of silver nanoparticles. The inner cavity of the self-assembled protein cage displays a dodecapeptide that is capable of reducing silver ions to metallic silver. This chimeric protein cage when incubated in the presence of silver nitrate exhibits the growth of a silver nanocrystal within its cavity. Our studies indicate that it is possible to design chimeric cages, using specific peptide templates, for the growth of other inorganic nanoparticles.     

Peroxides of higher aliphatic ethers

The oxidation of higher aliphatic ethers with oxygen at 50° yields two peroxides as the main oxidation products for each ether, namely a dihydroperoxy-dialkyl ether and a dihydroperoxy-dialkyl peroxide. The mass spectra of these compounds are recorded and the main fragmentation pattern is discussed.