Contemporary examples

Electron Spin Resonance Spectroscopy. Several ESR studies have been reported for adsorption systems [85-90]. ESR signals are strong enough to allow the detection of quite small amounts of unpaired electrons, and the shape of the signal can, in the case of adsorbed transition metal ions, give an indication of the geometry of the adsorption site. Ref. 91 provides a contemporary example of the use of ESR and of electron spin echo modulation (ESEM) to locate the environment of Cu(II) relative to in a microporous aluminophosphate molecular sieve. 

There is a wide range of reagents available for derivatization and the analyst is again referred to the books by Frei and Lawrence (17) and Karl Blau and John Halket (47) for further reading. The references given here have been chosen as those that are most likely to include the complete details of the derivatizing procedures. They were not chosen as the most contemporary examples of analyses employing derivatization techniques. 

Chemical research is driven by many goals, and it progresses in many different ways. The essential traits of a good researcher are curiosity, creativity, flexibility, and dedication. Some chemical advances come from a direct assault on a known problem. A classic example is the development of the Hall process for refining aluminum from its ores, which we describe in Chapter 21,. As a contemporary example, many scientists around the world are working at a feverish pace to develop a vaccine against the AIDS virus. 

Chemical advances frequently are driven by technology. The discovery that atoms have inner structure was an outgrowth of the technology for working with radioactive materials. In Chapter 2 we describe a famous experiment in which the structure of atoms was studied by bombarding a thin gold foil with subatomic particles. A contemporary example is the use of lasers to study the details of chemical reactions. We introduce these ideas in Chapters 7 and 8. 

In a society where canned and frozen foods are so prevalent, we tend to take food preservation for granted. It is easy to forget that prevention of spoilage is a major undertaking when food is harvested at one time and place but eaten at another. A contemporary example is the space station, where the astronauts must be supplied with edible food that is preserved without refrigeration for long times. 

Example 2.10. Probably the best contemporary example of a variable-mass system would be the equations of motion for a space rocket whose mass decreases as fuel is consumed. However, to stick with chemical engineering systems, let us consider the problem sketched in Fig. 2.8. Petroleum pipelines are sometimes used for transferring several products from one location to another on a batch basis, i.e., one product at a time. To reduce product contamination at the end of a batch transfer, a leather ball or pig that just fits the pipe is inserted in one end of the hne. Inert gas is introduced behind the pig to push it through the hne, thus purging the hne of whatever hquid is in it. 

Parthenium hysterophorus L. (parthenium weed), native to North and Central America and introduced into Queensland as recently as I960 (39), is a contemporary example. It is aggressive, persistent and lowers crop yield through interference, a component of which is allelopathic ( ). 

Roberts, and R, Madsen, n-Pentenyl glycosides in organic chemistry A contemporary example of serendipity, Synlelt p. 927 (1992). 

Materials with selective binding or transport properties will have a major impact on sensor design and fabrication. Selectivity in either binding or transport can be exploited for a variety of measurement needs. This selectivity can be either intrinsic, that is, built into the chemical properties of the material, or coupled with selective carriers that allow a non-selective material to be converted into a selective one (see the section on recognition chemistry). An example of the latter is the use of valinomycin as a selective carrier in a polyvinyl chloride membrane to form a potentiometric potassium ion sensor. Advances in the fields of gas separation materials for air purification and membrane development for desalinization are contemporary examples illustrating the importance of selective materials. As these materials are identified, they can be exploited for the design of selective measurement schemes. 

To what extent can the example of a solid exoskeleton be replicated in the laboratory Going against most contemporary examples of flexible artificial cells, Muller and Rehder published an example of a complex molybdenum oxide that spontaneously forms discrete nanospheres [23], The hollow spheres were porous and allowed lithium cations to pass through the exoskeleton. While this a perhaps an extreme example of what may be considered an artificial cell, the authors assert that the presence of ion selective channels through the encapsulating oxide is directly analogous to natural ion channels in organic cells. 

First some simple calculational examples are presented to illustrate the changes in skeletal bonding as protons are moved about as well as to make connections with the electron counting rules. This is followed by a contemporary example illustrating how attempts to reconcile differences between molecules that are isoelectronic only in the sense of the electron count-... 

Indian peyotists provide the main contemporary example of mescaline and peyote used as a means of psychic exploration. A quarter million practitioners have taken this potent psychedelic—often quite frequently, often for years, often in large amounts without significant physical, psychological or social problems. The exemption provided in the law for members of the Native American Church has in fact fostered a tradition of spiritual growth and communal interaction. 

Fraser-Reid, B, Udodong, U E, Wu, Z, Ottosson, H, Merritt, J R, Rao, C S, Roberts, C, Madsen, R, n-Pentenyl glycosides in organic chemistry a contemporary example of serendipity, Synlett, 927-942, 1992. 

B. Fraser-Reid, U. E. Udodong, Z. Wu, H. Ottosson, J. R. Merritt, C. S. Rao. C. Roberts, and R. Madsen, n-Pentenyl glycosides (NPGs) in organic chemistry A contemporary example of serendipity, Synlett, 927 (1992),... 

The most important by-product of the analytic and synthetic work accomplished so far is knowledge about the stereochemistry and reactivity of natural compounds. There is an enormous potential for the chemists of the twenty-first century lying in the mastery and application of this knowledge in order to produce organized and finally functional materials. Typical contemporary examples include surface monolayers on metals and colloids made of fatty acid and steroid derivatives, the regio- and stereoselective assembly reactions between steroids and carbohydrates, coupled redox chains of metalloporphyrins and vitamins, noncovalent fibers made of amino acids, nucleotides, and saccharides, and the functionalization of proteins by incorporation of reactive molecules. The field of supramolecular or noncovalent natural compound chemistry has been scientifically fruitful for several decades and is presently exploited for the development of useful molecular devices and machines as well as for medical applications. 

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