Activities Physical Change

All these immobilization techniques run the risk of altering activity compared with the native enzyme. Improved activity is occasionally reported, but this is the exception. The immobilization techniques listed above are in approximate order of loss in activity. Physical entrapment normally causes no change. Adsorption will distort the shape of the molecule compared with the native... 

It has been known for many years that microbial contaminants may effect the spoilage of pharmaceutical products through chemical, ply sical or aesthetic changes in the nature of the product, thereby rendering it unfit for use (see Chapter 18). Active drug constituents may be metabolized to less potent or chemically inactive forms. Physical changes commonly seen are the breakdown of emulsions, visible surface growth on solids and the formahon of slimes, pellicles or sediments in hquids, sometimes... 

Catalyst deactivation refers to the loss of catalytic activity and/or product selectivity over time and is a result of a number of unwanted chemical and physical changes to the catalyst leading to a decrease in number of active sites on the catalyst surface. It is usually an inevitable and slow phenomenon, and occurs in almost all the heterogeneous catalytic systems.111 Three major categories of deactivation mechanisms are known and they are catalyst sintering, poisoning, and coke formation or catalyst fouling. They can occur either individually or in combination, but the net effect is always the removal of active sites from the catalyst surface. 

The extractability of the polysaccharides of plants can be profoundly affected by the chemical and physical changes which occur between the end of active vegetative growth and the time the plant parts are subjected to chemical extraction. 

A variety of analytical methods, such as ELISA and HPLC, can be used to evaluate the effect of excipients or lyophilization on the stability of the biophar-maceutical product. Some parameters the analytical methods should evaluate are degradation, chemical and physical changes, aggregation, adsorption, and loss of biological activity. 

Figure 2.1 Fear responses involve the activation of many brain areas. The hypothalamus controls physical changes in the body, such as increased blood pressure and dilated pupils. The central gray area causes freezing behavior, the reticular net triggers a reflex response, and norepinephrine increases attention.

All the chemical changes and many of the physical changes that we have studied so far involve alterations in the electronic structures of atoms. Electron-transfer reactions, emission and absorption spectra, and X rays result from the movement of electrons from one energy level to another. In all of these, the nuclei of the atoms remain unchanged, and different isotopes of the same element have the same chemical activity. Nuclear chemistry, or radioactivity, differs from other branches of chemistry in that the important changes occur in the nucleus. These nuclear changes also are represented by chemical equations. However, because the isotopes of the same element may, from a nuclear standpoint, be very different in reactivity, it is necessary that the equations show which isotopes are involved. 

Activity 1.17 Color Relativity Physical Properties and Physical Change... 

Activity 1.17 Color Relativity Physical Properties and Physical Change. . 71 Demonstration 1.5 Color Relativity Chemical Properties and Chemical... 

Relative enzyme activities associated with particles and with free-living bacterial communities are not constant, however. Particle composition and concentration, as well as the attached microbial community and its associated enzyme activities, can change dramatically as a result of biological and physical processes. For example, Middelboe et al. (1995) found that as a... 

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