Natural variability chemical compound

As a starting point in the description of the solid intermetallic phases it is useful to recall that their identification and classification requires information about their chemical composition and structure. To be consistent with other fields of descriptive chemistry, this information should be included in specific chemical and structural formulae built up according to well-defined rules. This task, however, in the specific domain of the intermetallic phases, or more generally in the area of solid-state chemistry, is much more complicated than for other chemical compounds. This complexity is related both to the chemical characteristics (formation of variable composition phases) and to the structural properties, since the intermetallic compounds are generally non-molecular in nature, while the conventional chemical symbolism has been mainly developed for the representation of molecular units. As a consequence there is no complete, or generally accepted, method of representing the formulae of intermetallic compounds. 

J. Black s investigation 3 of 1756 is the first contribution to the chemistry of the carbonates of ammonia, and he pointed out the chemical difference between the aqua ammonia and the solid carbonate of commerce. J. Priestley also, in 1774, dwelt on the same subject. T. Bergmann analysed the commercial carbonate in 1774 H. Davy emphasized the variable nature of the compounds of carbon dioxide and ammonia in 1799 while C. L. Berthollet (1806) and J. Dalton (1819) demonstrated that there are several different carbonates of ammonia. In his paper On the combinations of carbonic anhydride with ammonia and water (1870), E. Divers showed that there are at least three well-defined ammonium carbonates—the normal carbonate, the hydrocarbonate, and the sesquicarbonate. On the other hand, in his paper Ueber die Verbindungen des Ammoniaks mit der Kohlensaure (1839), H. Rose claimed to have shown that an indefinitely large number of these compounds can be prepared, and he described twelve of them. He said ... 

To help lay a new groundwork for the study of the tastes of foods, the speakers at the symposium presented papers on a variety of topics related to food taste chemistry. The problems in taste are of great complexity, involving biological as well as chemical variables. For a taste chemist, the types of sensations elicited and their measurement are as important as the nature of the compounds eliciting them. Various aspects of these problems are treated in detail in the papers in this volume. 

It is often the case that several variables are used to characterize a set of objects and that these can be divided into natural and disjunct subgroups. It can reasonably be assumed that members of such subgroups are similar to each other, but are more or less different to members of other subgroups. Such subgroups is hereafter called classes. Examples of such classes are Analytical samples of different origins different batches of raw material different substitution patterns in chemical compounds, e.g. cis/trans isomers clinical data of healthy and ill persons. 

An effective and reliable extraction method is important for studies of phenolics. Different solvent extractions may provide different types of compounds due to their variable chemical nature and sensitivity toward extraction or hydrolysis methods. For instance, phenolic compounds extracted from almond skins and hulls with diethyl ether [2], methanol [7], ethyl acetate, and -butanol [8] may result in different yields and compositions of the extracts. 

An additional feature of Fig. 11.5 is the shaded area on either side of the lines. This is intended to indicate that the efficiency of ME utilisation is quite variable. We shall see later that the principal causes of this variation in efficiency are, first, the nature of the chemical compounds from which ME is derived (hence the nature of the food and the manner in which it is digested) and, second, the function for which these compounds are used by the animal. 

Schnitzler I, Boland W, Hay ME (1998) Organic sulfur compounds from Dictyopteris spp. deter feeding by an herbivorous amphipod (Ampithoe longimana) but not by a herbivorous sea urchin (Arbaciapimctulata). J Chem Ecol 24 1715-1732 Shen Y, T sai PI, Fenical W, Hay ME (1993) Secondary metabolite chemistry of the Caribbean marine alga Sporochnus bolleanus. a basis for herbivore chemical defense. Phytochemistry 32 71-75 Schupp PJ, Paul VJ (1994) Calcium carbonate and secondary metabolites in tropical seaweeds variable effects on herbivorous fishes. Ecology 75 1172-1185 Smit AJ (2004) Medicinal and pharmaceutical uses of seaweed natural products a review. J Appl Phycol 16 245-262... 

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