Molecular systems explosives

An analogous role has been played by other scientists in strengthening the ties between quantum chemistry of type I (and type II) with the area corresponding to biochemistry (or complex molecular systems in general), a task made more difficult by the explosive growth of structural and functional information about biomolecular systems. It is worth to remark here that such a fruitful use of quantum chemical concepts in biology has requested the extension of the methods to approaches different from quantum molecular theory in the strict sense introduced before. We shall comeA back to this remark later. 

Ab initio quantum chemistry has advanced so far in the last 40 years that it now allows the study of molecular systems containing any atom in the Periodic Table. Transition metal and actinide compounds can be treated routinely, provided that electron correlation1 and relativistic effects2 are properly taken into account. Computational quantum chemical methods can be employed in combination with experiment, to predict a priori, to confirm, or eventually, to refine experimental results. These methods can also predict the existence of new species, which may eventually be made by experimentalists. This latter use of computational quantum chemistry is especially important when one considers experiments that are not easy to handle in a laboratory, as, for example, explosive or radioactive species. It is clear that a good understanding of the chemistry of such species can be useful in several areas of scientific and technological exploration. Quantum chemistry can model molecular properties and transformations, and in... 

With all of these new tools, it is no wonder that there has been an explosion of papers on photochemical dynamics, so much so that in this review we shall limit ourselves to those papers that have appeared over the last three years. Earlier reviews cover the work before this time, and the papers that are cited also give references to the earlier work. The papers that are covered are further limited to those that measure and discuss the detailed quantum state distribution of one or more of the photochemical fragments. Those papers that are limited to final product analysis are discussed only if the results bear directly upon the dynamics of the photochemical process. The review is organized so that molecules with similar chromo-phore groups are all discussed at the same time. This emphasizes the similarities and differences between these molecules. The discussion of the molecular systems begins after a brief discussion of some of the newer experimental techniques. In this review any earlier reviews that cover that molecule are cited along with the later papers on the subject. 

Recently (Ref 17) Haskins and Cook have described work at RARDE on short range interactions in N2. CO and CO2 in the context of the description of high pressure regimes such as detonation products. These studies are seen as a step on the road towards derivation of an ab-initio equation of state for explosive reaction products. The Coulomb interactions in atomic and molecular systems are additive. However, the readjustment of charge distributions which result when additional atoms or molecules are involved result in a loss of pairwise additivity. It is this loss of additivity which is the source of the many-body interaction in closed shell systems. For polar molecules other factors such as non-additivity of induction and exchange-induction energies could also be significant. 

Gas AntisolventRecrystallizations. A limitation to the RESS process can be the low solubihty in the supercritical fluid. This is especially evident in polymer—supercritical fluid systems. In a novel process, sometimes termed gas antisolvent (GAS), a compressed fluid such as CO2 can be rapidly added to a solution of a crystalline soHd dissolved in an organic solvent (114). Carbon dioxide and most organic solvents exhibit full miscibility, whereas in this case the soHd solutes had limited solubihty in CO2. Thus, CO2 acts as an antisolvent to precipitate soHd crystals. Using C02 s adjustable solvent strength, the particle size and size distribution of final crystals may be finely controlled. Examples of GAS studies include the formation of monodisperse particles (<1 fiva) of a difficult-to-comminute explosive (114) recrystallization of -carotene and acetaminophen (86) salt nucleation and growth in supercritical water (115) and a study of the molecular thermodynamics of the GAS crystallization process (21). 

CeUulose is soluble only in unusual and complex solvent systems. The subject has been reviewed (84—87). Commercially, dissolving pulps, which have lower molecular weights, are used along with strong alkaU and derivatization. CeUulose subjected to high temperature and pressure during the steam explosion process can be dissolved in strong base (88). 

In the intervening years, molecular dynamics simulations of biomolecules have undergone an explosive development and been applied to a wide range of problems [3,4]. Two attributes of molecular dynamics simulations have played an essential role in their increasing use. The first is that simulations provide individual particle motions as a function of time so they can answer detailed questions about the properties of a system, often more easily than experiments. For many aspects of biomolecule function, it is these details... 

A mechanism of action describes the molecular sequence of events (covalent or non-covalent) that lead to the manifestation of a response. The complete elucidation of the reactions and interactions among and between chemicals, include very complex and varied situations including biological systems (macromolecular receptors, physical phenomena (thermodynamics of explosions) or global systems (ozone depletion). Unfortunately, this level of mechanistic detail is often unavailable but recent advances in molecular toxicology and others hazards, at the molecular level, have provided valuable information that elucidates key steps in a mechanism or mode of action. ... 

Molecular markers of microglial cells. In the past 10-15 years there has been a veritable explosion of activity in the field of microglial cell biology with the realization that this cell type is capable of functioning as a highly efficient accessory and effector cell of the immune system. 

Under the simulation conditions, the HMX was found to exist in a highly reactive dense fluid. Important differences exist between the dense fluid (supercritical) phase and the solid phase, which is stable at standard conditions. One difference is that the dense fluid phase cannot accommodate long-lived voids, bubbles, or other static defects, whereas voids, bubbles, and defects are known to be important in initiating the chemistry of solid explosives.107 On the contrary, numerous fluctuations in the local environment occur within a time scale of tens of femtoseconds (fs) in the dense fluid phase. The fast reactivity of the dense fluid phase and the short spatial coherence length make it well suited for molecular dynamics study with a finite system for a limited period of time chemical reactions occurred within 50 fs under the simulation conditions. Stable molecular species such as H20, N2, C02, and CO were formed in less than 1 ps. 

A 5A molecular sieve, not previously soaked in dilute ethylene, was used to dry compressed ethylene gas in a flow system. An exothermic reaction attained red heat and caused explosive failure of the dryer. The smaller-pored 3A sieve is not catalytically active towards ethylene. 

Polynitro derivatives of pentacyclo[5.4.0.0 .0 °.0 ]undecane have attracted interest as potential high-energy explosives. Molecular strain in this caged system could arise from both the constrained norbomyl moiety and the cyclobutane ring. Additional strain would be expected from nonbonding interactions if the S-endo and 1 l-endo positions were substituted with gm-dinitro groups. 

Mechem Explosive and Drug Detection System Microelectrical and mechanical systems Molecularly imprinted polymer Massachusetts Institute of Technology Mine removal vehicle Mass spectrometer... 

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