Activity spectrum definitions

Assumed in the definition of an activation spectrum is the fact that all of the lamps of a particular type, e.g., "cool-white," are very similar. This is not necessarily a valid assumption. Batch to batch variations, differences between geographical locations of the same company, manufacturers, or countries can affect the SPD of a lamp. Differences in "daylight" lamps and the UV content of "cool-white" SPDs have been noted. 

Good preservatives have, by definition, a wide activity spectrum. If one preservative covers the spectrum insufficiently, combination with another, synergistic, preservative or with a potentiating substance (for instance benzalkonium chloride with sodium edetate) improves the activity. 

I consider there to be a sharp distinction between the most polar form of a molecule and its ionically dissociated form. The reason for this is empirical An ion is defined as a species carrying a charge equal to an integral multiple of the electronic charge, and this definition implies that it will have a characteristic predictable electronic spectrum and, under suitable conditions, mobility in an electric field. There is so far no evidence which would compel one to abandon this definition, and I think it is important to distinguish clearly in this context between reaction intermediates (chain carriers, active species) of finite life-time, and transition states. 

This centre, present in the multicopper blue oxidases, is similar to the typical Cu11 sites of tetragonal geometry found in simple coordination complexes of copper. It is ESR-active and has a normal d-d spectrum, which is difficult to measure in the presence of type 1 Cu due to its intense absorptions. The copper in the non-blue oxidases is often regarded as type 2 copper, although this was not implied by the original definition. 

In arriving at a satisfactory analysis of the spectrum we must make use not only of the polarization data, but also of the results of deuteration studies, full [Narita, Ichinohe, and Enomoto (145)] and partial [Folt, Shipman, and Berens (55)], and studies of C—Cl frequencies in small molecules. [Mizushima, Shimanouchi, Nakamura, Hayashi, and Tsuchiya (139) Shimanouchi, Tsuchiya, and Mizushima (196)]. The lack of the Raman spectrum is a definite handicap, but is in part mitigated by the expectation that many of the Raman active fundamentals should be close to the frequencies of infrared active fundamentals. 

A cofactor can be extracted from the iron-molybdenum protein, using Af-methylformamide. This cofactor (called FeMoCo) has many spectroscopic properties in common with the native protein, especially the EXAFS spectrum, and activates the inactive large protein derived from Azobacter vinelandii UW45 mutant which cannot incorporate molybdenum. The cofactor contains no protein or peptide, but does contain molybdenum, iron, and sulfur in atomic ratios of 1 6-8 4-9. It is believed to contain the dinitrogen-binding site (presumably molybdenum) but there is no definitive proof of this. 

Because of the wide spectrum of activity shown by amines, definitive conclusions concerning structure-activity relationships cannot be made at this time. However, studies using single test systems reveal that the most active silylated amines contain the silicon atom in a y position relative to the nitrogen, as shown in partial structures 12 and 13 (55, 56). Some examples of compounds containing these groupings are found in Tables I and II. The silylated benzhydryl ethers (Section II,F) and sila-tranes (Section III,C) also contain this type of grouping. 

Consequently, we were faced with the task of formulating a widely acceptable and consistent definition of bond activation . Our research, discussions, and analyses led to a conclusion that bond activation should refer to a process of increasing the reactivity of a bond in question and as such encompasses an entire spectrum of possible mechanisms. Also, we argue that activation is not equivalent to reaction or, in other words, that activation of a bond is not the same as cleavage of a bond. For the latter process we proposed the general term bond transformation . It should be emphasized that both bond activation and bond transformation are general terms and, therefore, information about the reaction and mechanism category should be specified by additional descriptors (cf. C-H bond arylation via electrophilic metalation, C-H bond metalation via concerted metal insertion). 

The existence of these different practices was not sufficient to create a discipline or subdiscipline of physical chemistry, but it showed the way. One definition of physical chemistry is that it is the application of the techniques and theories of physics to the study of chemical reactions, and the study of the interrelations of chemical and physical properties. That would mean that Faraday was a physical chemist when engaged in electrolytic researches. Other chemists devised other essentially physical instruments and applied them to chemical subjects. Robert Bunsen (1811—99) is best known today for the gas burner that bears his name, the Bunsen burner, a standard laboratory instrument. He also devised improved electrical batteries that enabled him to isolate new metals and to add to the list of elements. Bunsen and the physicist Gustav Kirchhoff (1824—87) invented a spectroscope to examine the colors of flames (see Chapter 13). They used it in chemical analysis, to detect minute quantities of elements. With it they discovered the metal cesium by the characteristic two blue lines in its spectrum and rubidium by its two red lines. We have seen how Van t Hoff and Le Bel used optical activity, the rotation of the plane of polarized light (detected by using a polarimeter) to identify optical or stereoisomers. Clearly there was a connection between physical and chemical properties. 

---