e d i to ri a l
Methods of Analysis I
teach analytical chemistry as chemical and physical methods of analysis. Physical methods of analysis are based on the direct interaction of materials (analyte) with electromagnetic waves; corpuscular beams, such as electrons and neutrons; or electric, magnetic, and gravimetric fields. Chemical methods of analysis are based on the selective interaction of materials (receptors, chromatographic media, etc.) with analytes. It is important to appreciate that various methods of instrumental analysis, including all kinds of spectroscopies, have completely changed the nature of chemical research. For example, until the end of the 19th century, organic chemistry developed with little support from physical methods because they were simply not available. Instead, organic chemists invented their own chemical methods, such as extraction, elemental analysis, melting point measurements, and functional group analysis using specific colorimetric reactions. Modern chemistry owes much to the various physical methods of analysis developed by modern, 20th century physics. Physical and chemical methods of analysis are, in fact, not clearly separated. The molecular-recognition processes in chemical sensors, chromatography, and immunoassay methods, for example, are surely chemical, but signal transduction and amplification often rely on physical methods. Even in the case of biosensors, molecular recognition is certainly based on “bioreceptors” such as enzymes, antibodies, and nucleotides, but the process of following the signal transduction is mostly physical. On the other hand, in biological systems such as cells, all processes—from molecular recognition to signal transduction and amplification—are governed by chemical mechanisms. In analytical chemistry, the pursuit of sensitivity, selectivity, precision, and accuracy has been a priori praised and rewarded. Among these parameters, selectivity has a unique position. In most chemical methods of analysis, selectivity for analytes against interfering substances is essentially governed by the competitive binding constants between the analyte and its molecularrecognition reagent. This is generally the basis for binding assays, such as immunoassays. As a result, chemical meth-
ods of analysis owe much to natural bioreceptors, as well as to group reagents, chelating agents, and various supramolecular receptor molecules developed by organic chemists. Binding assays are typically used for analyzing bioactive substances. Conventional binding assays can neither discriminate agonists from antagonists nor give sufficient information on their physiological activities. Physical methods such as NMR and MS cannot provide this information either. The bioassay that uses intact biological tissue or whole bodies has a unique position in analysis, because it can target bioactive substances. However, the bioassay cannot give molecular-level information because of this inherent “black box” approach. During the past 50 years, molecular biology has developed primarily by taking advantage of physical and chemical methods of analysis, which have elucidated the molecular chemistry behind cellular mechanisms. If analytical methods for bioactive substances are based not only on receptor binding but also on known molecular-level processes involved in signal transduction along signaling pathways (reconstructed in vitro or taken, in part, from in vivo data), these methods will be able to provide physiologically relevant analyte selectivities in terms of cellular mechanisms at the molecular level. This is of prime importance for screening and targeting pharmaceutically, toxicologically, and environmentally relevant bioactive substances. Chemical analysis methods for bioactive substances thus will rely more and more on molecular-recognition and cellular signal transduction, mimicking how living things on earth “see” ions and molecules.
Yoshio Umezawa The University of Tokyo (Japan)
[email protected] J U LY 1 , 2 0 0 0 / A N A LY T I C A L C H E M I S T R Y
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