Caution Principle

Caution Principle, which appears explicitly in Principle 15 of the final declaration of Rio-92 Conference/ ... 

By highlighting briefly some conceptual and historical aspects concerning risk, we aim to establish an associative line between the Caution Principle with GC whose emphasis is shown by several authors who are precursors of it/ In spite of it not being claimed as a new paradigm of chemistry, it is true that some of the principles of GC (that is, numbers 1, 3, 4, 5, 10 and 12y indicate the search for a preventive attitude, based not on moral issues—although important as they are—but rather on essentially scientific basis concerned with the prevention of future damage to the environment. The incorporation of these and other principles of GC have made it possible to revise and develop new processes and techniques. ... 

Let s look at another example a small-scale voluntary cleanup that might take place in the lot behind a factory, or a tank being removed at a corner gas station. Although we have the same considerations, these projects are on a smaller scale and will create less of a hazardous condition. The same principles that exist at the large job still should be adhered to on the small job. The work zone should be delineated and controlled to protect workers or the public from entering the work zone. For the small job, caution tape, snow fence, or traffic cones can be used effectively. 

We hope that when you complete this course you too will be convinced of the importance of chemistry in today s world. We should, however, caution you on one point. Although we will talk about many of the applications of chemistry, our main concern will be with the principles that govern chemical reactions. Only by mastering these principles will you understand the basis of the applications referred to in the preceding paragraphs. 

A note of caution on the use of photo-etched channels has been offered by RAMSHAWfl3 ) who points out that the system is attractive in principle provided that severe practical problems such as fouling are not encountered. With laminar flow in matrices with a mean plate spacing of 0.3-1 mm, volumetric heat transfer coefficients of 7 MW/m3 K have been obtained with modest pressure drops. Such values compare with 0.2 MW/m3 K for shell and tube exchangers and 1.2 MW/m3 K for plate heat exchangers. 

In many cases one can apply the first principles of thermodynamics and chemical kinetics to natural systems only with caution. The reason... 

Plasmid transmission and the stability of plasmids in natural ecosystems have received considerable attention, but caution should be exercised in drawing general conclusions on the basis of the sometimes fragmentary evidence from laboratory experiments. Some important principles are illustrated by the following ... 

The principle of the displacement of one metal by another, or in other words of the displacement of nobler by base or not so noble metals, as described earlier, must be applied with due caution, without neglecting other effects that may not be immediately obvious from consideration of the electrochemical series. Some of these effects are illustrated in the following. Although the position of lithium is above that of sodium in the series, lithium cannot displace sodium from common salt solutions since both of these metals occupy positions higher up than hydrogen and will displace this element from the solution. It must be borne in mind, therefore, that the series applies to aqueous solutions, and the hydrogen ion, which is present in these solutions, can also take part in the displacement reactions. 

The above illustration should be a clear caution that components of food may interact with drugs, resulting in substantial positive or negative therapeutic effects. As will be noted later, this principle also applies to so-called dietary supplements, including bo-tanicals, used for the treatment of numerous medical conditions. 

This technique has the advantage that no particular measure of the reaction rate has to be chosen nor any form assumed for the change of parameter with time, but it can only be used if the curves at different temperatures are of the same form. In principle, other relationships between the shift factors and temperature could be fitted on an empirical basis but, with no theoretical justification, particular caution would be advised with extrapolation. 

The use of filters and membranes of different pore size to accomplish a sequential size fractionation is in principle, and under certain circumstances, possible it was proposed (for literature see Buffle, 1988 and 1991) to estimate the size of the various colloids and macromolecules and to determine to which extent trace elements (particularly metals) are associated with various size categories of colloids and macromolecules. Such sequential size fractionation techniques need to be applied with extreme caution we list some of the reasons why these techniques may yield errorous results (for details consult Buffle, 1991) ... 

Although the upper limits of DH° (A-B) - /)//,) (A-B), set by the equipartition principle, must be regarded with caution (see table 5.1), they are indeed applicable to many molecules because, as stated, the vibrational degrees of freedom are not totally frozen at 298.15 K. For instance, when A and B are heavy atoms, like cesium, the vibration frequency is small enough to ensure that the vibration mode is considerably excited, for example, DH° Cs-Cs) -DH Cs-Cs) is only 1.4 kJ mol-1 [17]. 

While the above comparisons are hardly conclusive, they do suggest caution in applying the correspondence principle as it presently exists to temperatures above 200°C. 

Different formulation principles, dosage forms, and DDSs are commonly evaluated in animal models, and attempts are made to predict human absorption on the basis of such studies.80 Human studies are also conducted in some cases to confirm predictions from animal models. Chiou et a 1.81,82 demonstrated that there is a highly significant correlation of absorption (r2 = 0.97) between humans and rats with a slope near unity. In comparison, the correlation of absorption between dog and human was poor (r2 = 0.512) as compared to that between rat and human (r2 = 0.97). Therefore, although dog has been commonly employed as an animal model for studying oral absorption in drug discovery and development, one may need to exercise caution in the interpretation of data obtained. 

The dependence of this phenomenon on temperature and concentration has been studied in detail (70,71,87) and treated mathematically (87). In principle any compound capable of self-association might be capable of self-induced nonequivalence. These cases should be sufficient to suggest due caution on the part of those who would establish the identity of a racemate (e.g., a synthetic natural product ), by comparison of its NMR spectrum with that of the naturally derived optically pure substance. This phenomenon is not restricted to solutes with aromatic substituents, as evidenced by Table 12. Self-induced nonequivalence may be eliminated by addition of polar solvents or by dilution of the sample. Under these conditions, as has been shown for dihydroquinine (14), spectra of racemic, optically pure, and enriched material become identical. 

Any detectable effect on the reaction or behavior of a particular system by the interior wall of the container or reaction vessel. Because proteins can form high-affinity complexes with glass and plastic surfaces, one must exercise caution in the choice of reaction kinetic conditions. Wall effects can be discerned if one determines catalytic activity under different conditions that minimize or maximize contact of the solution with the container. In principle, an enzyme-catalyzed reaction should proceed at the same rate if placed in a capillary or a culture tube however, contact with the wall is maximized in a capillary, and wall effects should be more prominent. Some investigators add bovine serum albumin to prevent adsorption of their enzyme onto the container s walls. 

These are the modern active databases that have interactive capabilities, and are often searchable for a set of properties. The floppy disks and CD-ROMs have definite dates on them, and do become obsolete with time the Internet databases can, in principle, be updated at very frequent intervals. A note of caution about Internet databases is that some of them have not been vetted for accuracy and can be unreliable. 

A careful observation of Equations 10.35 and 10.36 prompts some caution. In principle, the isotherm is expressed in terms of specific amounts adsorbed and These are however meaningless unless one is able to assess which part of the liquid is in the adsorption sphere (viz. the position of the Gibbs dividing plane). 

In drying a metal, he cautions, it is necessary to avoid a support which has any oil in it, otherwise it will prevent the calcination by supplying the sulphur as fast as the metals loses it. There is no difference evident here between Hombergs sulphureous principle and Stahls phlogiston as it is generally presented in the secondary literature of the chemical revolution. Does Homberg get it from Stahl It is possible, but seems unlikely. 

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