Incorporation into accelerating factors

Bioassays of related substances can be quite similar in design. Specific growth factors, for example, stimulate the accelerated growth of specific animal cell lines. Relevant bioassays can be undertaken by incubation of the growth-factor-containing sample with a culture of the relevant sensitive cells and radiolabelled nucleotide precursors. After an appropriate time period, the level of radioactivity incorporated into the DNA of the cells is measured. This is a measure of the bioactivity of the growth factor. 

Molecular models show that during the course of the acylation reaction, the bound substrate is pulled partially out of the cyclodextrin cavity in forming the tetrahedral reaction intermediate. In other words, the model enzyme is not exhibiting the required transition state selectivity. Furthermore, excessively rigid substrates experience difficulty in rotating while bound in order to accommodate the need of the cyclodextrin hydroxyl group to attach perpendicular to the substrate ester plane, and subsequently rotate to become incorporated into the plane of the new ester product (Scheme 12.1). These problems were addressed by examination of substrates, such as p-nitro derivatives in which the ester protrudes further from the cavity, and substrates with more rotational flexibility such as alkyne 12.3. In these refined systems, much more enzyme-like rate accelerations of factors of up to 5 900 000-fold were observed for 12.4, for example. 

This acceleration factor model is widely used as the industry standard for device qualification. However, it only approximates a single dielectric breakdown type of failure mechanism and does not correctly predict the acceleration of other mechanisms. The challenge to accurate reliability prediction is to incorporate multiple mechanisms into the calculation of MTBF. 

The rate of incorporation of cupric ions into protoporphyrin dimethyl ester was found to be accelerated by a factor of ca. 20,000 in the presence of aqueous micellar sodium dodecyl sulfate (2-5%) relative to that in 5% CTAB (Lowe and Phillips, 1961). This rate acceleration was found to be the consequence of a change in the activation entropy and was attributed to micellar solubilization of the porphyrin ester such that the pyrrole nitrogen atoms are located in the Stern layer in close proximity to cupric ions electrostatically attracted to the anionic micellar surface. The rate of incorporation of cupric ions in the presence of NaLS was also found to be catalyzed and inhibited by chelating agents (Lowe and Phillips, 1961, 1962). 

Kawai, K., Suzuki, S., Tabata, Y., Ikada, Y., and Nishimura, Y. (20(X)), Accelerated tissue regeneration through incorporation of basic fibroblast growth factor-impregnated gelatin microspheres into artificial dermis. Biomaterials 21(5) 489-499. 

In most traditional pol)nner materials, e.g. polyethylenes and polypropylene, the prevailing action of the oxidative degradation is the breakdown of molecular chains into smaller segments containing oxygen incorporated in the form of hydroxyl, ketone, ester, aldehyde, ether, carboxyl, etc. [25, 26]. Unsaturations are also formed in the process. Oxidation of polymer materials is a process that occurs naturally, but may take decades or even centuries to be completed. The presence of certain transition metals (such as V, Mn, Fe, Co, Ni, Cu) accelerates the degradation by a factor of about 1(F and thus permits the complete degradation within a few years under favorable conditions [27, 28]. 

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