Initiation fragmentation

Only a small frac tion of U is available to provide kinetic energy to the fragments. There are few data available, but in five incidents analyzed by High (unpublished data), no fraction was greater than 0.15. The fragment initial velocity can be assessed from 0.15 U = V hLVf. 

The spherical fragments, initially in close contact, move relative to each other according to Eq. (B.l). The underlying physics is revealed more clearly by recasting equation (B.l) in the following dimensionless form ... 

Scheme 8.4. Dioxetane fragmentation initiated by enzymatic ester hydrolysis.

The detailed mechanism of inhibition of TEM-2 (class A) enzyme with clavulanate has been established (Scheme 1) [23,24], The inhibition is a consequence of the instability of the acyl enzyme formed between the /1-lactam of clavulanate and the active site Ser-70 of the enzyme. In competition with deacylation, the clavulanate acyl-enzyme complex A undergoes an intramolecular fragmentation. This fragmentation initially provides the new acyl enzyme species B, which is at once capable of further reaction, including tautomeriza-tion to an entity C that is much less chemically reactive to deacylation. This species C then undergoes decarboxylation to give another key intermediate enamine D, which is in equilibrium with imine E. The imine E either forms stable cross-linked vinyl ether F, by interacting with Ser-130 or is converted to the hydrated aldehyde G to complete the inactivation. 

Calculated fragment initial velocity Vav = Average fragment velocity over the distance R Pa r Air density... 

If the fragment initial velocity is known, or has been calculated, then the fragment velocity at any distance R can be calculated with... 

VR = Fragment velocity at distance R V m Fragment initial velocity x = As defined above... 

Predictions can be made for the initial velocity of fragments provided certain properties of the explosive material are known. The Gurney equation (8), or one of its many variations (9,10), is the most widely accepted method for predicting fragment initial velocity. The equations are slightly different for spheres and cylinders ... 

One of these, based on a semi-empirical relationship taken from Reference 12, predicts secondary fragment initial velocity ... 

V - Secondary fragment initial velocity, in/s Re Radius of spherical charge, inches... 

The tendency for the fragmentation initiation with the radical site is parallel to the donor properties of this site. The most spectacular examples involve the processes triggered by the removal of a nitrogen n-electron. Halogens are the least active in these reactions. 

The correct analysis of the homologous ion series has certain limitations. Low abundances of peaks in some series require the attention and experience of a researcher. Usually alkane series are dominated in the mass spectra of the most various compounds. Fragmentation initiated by one functional group may completely suppress or notably camouflage other reactions of polyfunctional substances. In the latter case it is useful to consider IR-spectroscopy data in mass spectral interpretation. 

Oxygen and its systemic fragments initiate free-radical processes normally producing the rational balance with all forms of active protection of macromolecules from them in particular, atoms of sulfur and selenium can be applied for that. 

Initiation by Influence usually called Sympathetic Initiation, is the initiation of an explosive charge by the detonation of a nearby charge separated from the first charge by an inert medium see Detonation by Influence in Vol 4, pp 395-398 and also Initiation by Hot Fragments Initiation by Shock... 

Initiation by Projectile Impact is a complicated process which depends on a combination of shock initiation, impact initiation and hot fragment initiation effects. For fast projectile impact, shock initiation effects are predominant. With slow projectiles the initiation resembles Impact Initiation. Further complications are introduced if the impacting projectiles are hot a special case where the explosive is part of the projectile is the so-called Susan Test—see Barrier Tests Their Comparison with Shooting Tests in Vo 4, pp D145-147 and Detonation (and Explosion) Experimental Procedures in Vol 4, pp 333-335... 

There is one report,57 in which a tertiary amine suffers a complex fragmentation, initiated by the oxidation of the amine into an immonium salt upon the action of Oppenauer conditions. There is also one example,58 in which a secondary amine suffers elimination by the action of an aluminium alkoxide. 

Natural Abundance of Important Isotopes Rules for Determination of Molecular Formula Neutral Moieties Ejected from Substituted Benzene Ring Compounds Order of Fragmentation Initiated by the Presence of a Substituent on a Benzene Ring... 

ORDER OF FRAGMENTATION INITIATED BY THE PRESENCE OF A SUBSTITUENT ON A BENZENE RING... 

Order of Fragmentation Initiated by the Presence of a Substituent on a Benzene Ring... 

In their mass spectra 1,2,3-thiadiazoles commonly fragment initially by expulsion of nitrogen, and the fragmentation then proceeds to form thiirene ion radical (8 Scheme 1). These studies have been reviewed (73SST(2)717) and additional studies have shown, depending on substituents, that thioketene radical (9) can be formed in the mass spectrum (72T1353). 

Most triazene complexes are thermally stable and, where mass spectra have been recorded, molecular ions are usually observed. Fragmentation initially involves loss of ancillary ligands, notably CO cleavage of the diaryltriazenide ligands generates aryl, aryldiazo, and arylazo ions together with nitrene species [L M=NAr] (/, 42, 174, 179). 

Butterfield DA, Drake J, Pocemich C, Castegna A (2001) Evidence of oxidative damage in Alzheimer s disease brain central role for amyloid beta-peptide. Trends Mol Med 7 548-554 Butterfield DA, Hensley K, Htirris M, Mattson M, Carney J (1994) beta-Amyloid peptide free radical fragments initiate synaptosomal Upoperoxidation in a sequence-specific fashion impUcations to Alzheimer s disease. Biochem Biophys Res Commun 2(X) 710-715 Butterfield DA, Hensley K, Cole P, Subramaniam R, Aksenov M, Aksenova M, Bummer PM, Haley BE, Carney JM (1997) Oxidatively-induced structural alteration of glutamine synthetase assessed by analysis of spin labeled incorporation kinetics relevance to Alzheimer s disease. J Neurochem 68 2451-2457... 

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