Dissection effect

This basic LFER approach has later been extended to the more general concept of fragmentation. Molecules are dissected into substructures and each substructure is seen to contribute a constant inaement to the free-energy based property. The promise of strict linearity does not hold true in most cases, so corrections have to be applied in the majority of methods based on a fragmentation approach. Correction terms are often related to long range interactions such as resonance or steric effects. 

In general, the dissection of substituertt effects need not be limited to resonance and polar components, vdiich are of special prominence in reactions of aromatic compounds.. ny type of substituent interaction with a reaction center could be characterized by a substituent constant characteristic of the particular type of interaction and a reaction parameter indicating the sensitivity of the reaction series to that particular type of interactioa For example, it has been suggested that electronegativity and polarizability can be treated as substituent effects separate from polar and resonance effects. This gives rise to the equation... 

The effect of substituents on electrophilic substitution can be placed on a quantitative basis by use ofpartial rate factors. The reactivity of each position in a substituted aromatic compound can be compared with that of benzene by measuring the overall rate, relative to benzene, and dissecting the total rate by dividing it among the ortho, meta, and para... 

Research on the nature of substituent constants continues, with results that can bewilder the nonspecialist. The dominant approach is a statistical one, and the main goal is to dissect substituent effects into separate electronic causes. This has led to a proliferation of terms, symbols, and conclusions. A central issue is (here we change terminology somewhat from our earlier usage) to determine the balance of field and inductive effects contributing to the observed polar electronic effect. In... 

It is claimed that a measures electrophilic assistance by the solvent, b measures nucleophilic assistance, and that at least three, and sometimes four, parameters are required to perform a dissection into these separate effects. These workers also decomposed Y into ir and a contributions, and N into tt and p contributions. Abraham et al. have compared the performance of Eqs. (8-79) and (8-80) and find that they are about equally successful in correlating data. 

Most human or environmental healtli hazards can be evaluated by dissecting tlie analysis into four parts liazard identification, dose-response assessment or hazard assessment, exposure assessment, and risk characterization. For some perceived healtli liazards, tlie risk assessment might stop with tlie first step, liazard identification, if no adverse effect is identified or if an agency elects to take regulatory action witliout furtlier analysis. Regarding liazard identification, a hazard is defined as a toxic agent or a set of conditions that luis the potential to cause adverse effects to hmnan health or tlie environment. Healtli hazard identification involves an evaluation of various forms of information in order to identify the different liaz.ards. Dose-response or toxicity assessment is required in an overall assessment responses/cffects can vary widely since all chemicals and contaminants vary in their capacity to cause adverse effects. This step frequently requires that assumptions be made to relate... 

The previous chapters taught us how to ask questions about specific enzymatic reactions. In this chapter we will attempt to look for general trends in enzyme catalysis. In doing so we will examine various working hypotheses that attribute the catalytic power of enzymes to different factors. We will try to demonstrate that computer simulation approaches are extremely useful in such examinations, as they offer a way to dissect the total catalytic effect into its individual contributions. 

Human or natural actions that significantly alter the erosion resistance of the ground surface can lead to dramatic increases in erosion rates. Channel networks dissect natural landscapes down to a fine-scale limit controlled by a threshold of channel initiation (Montgomery and Dietrich, 1992). In effect, channels begin where sufficient discharge collects to overcome the erosion resistance of the ground surface (Horton, 1945 Montgomery and Dietrich, 1988). Consequently, human or natural actions... 

Nevertheless, RR is clearly a non-competitive antagonist that blocks the channel pore [2] with no effect on [ H]RTX binding [4]. RR was useful in dissecting responses mediated by capsaicin-sensitive nerves in vitro, but its use in animals was severely restricted by the toxicity (e.g. convulsive activity) that it caused [1]. 

Extirpation of the entire VN complex (VN-x) is an effective and informative approach applied largely to mammals. A palatal incision, followed by cautery or dissection of the capsule, usually removes all... 

Extensive molecular dissection of the morphine molecule over the past several decades led to a host of molecules which showed narcotic analgesic activity even though they possessed but faint suggestion of the structural features present in morphine itself. Thus, both cyclic molecules such as meperidine (70) and alphaprodine (71), and acyclic Compounds such as methadone (72) were found to be effective analgesics. Common features of these compounds were formalized by the Beckett-Casy rule, which states as minimal required structural features (a) an aromatic ring attached to... 

Figure 7.8 Long-term effects of MDMA on tissue levels of 5-HT (left panel) and DA (right panel) in brain regions. Male rats received three i.p. injections of 1.5 or 7.5 mg/kg MDMA, one dose every 2 h. Saline was administered on the same schedule. Rats were killed 2 weeks after injections, brain regions were dissected, and tissue 5-HT and DA were assayed by HPLC-ECD.112 Data are mean SEM expressed as percent of saline-treated control values for each region, N = 5 rats/group. Control values of 5-HT and DA were 557 24 and 28 4 pg/mg tissue for frontal cortex (CTX), 429 36 and 10,755 780 pg/mg tissue for striatum (STR), and 1174 114 and 4545 426 pg/mg tissue for olfactory tubercle (OT). Significant compared to saline-injected control for each region (P < 0.05 Duncan s).

Finally, several experiments indicate that excretory/secretory products (ESP), derived from newborn larvae or pepsin-HCl isolated mature muscle larvae, induce muscle cell basophilia (Blotna-Filipiak et al, 1998 Wranicz et al., 1998) or nuclear hypertrophy (Leung and Ko, 1997), respectively. Effects were observed in vivo and in vitro. Although correspondence of these general changes to biochemical or genomic characteristics of the infected cell and nuclei were not established, these observations may facilitate dissection of the parasite products that are responsible. 

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