Early formulation concepts

If they were to account for the spectrum of atomic hydrogen and then atoms of the other elements, scientists of the early twentieth century had to revise the nineteenth-century description of matter to take into account wave-particle duality. One of the first people to formulate a successful theory (in 1927) was the Austrian scientist Erwin Schrodinger (Fig. 1.23), who introduced a central concept of quantum theory. 

The recent developments and ideas in the field of prebiotic chemistry can be combined with the concepts noted here to produce what we regard as a research outline, rather than a detailed hypothesis, directed toward a coherent theory of the origin of complex self-contained, self-replicating chiral assemblies. In what follows we present one possible scenario that is consistent with our current knowledge of chiral induction and amplification and with the nature of early Earth as well as early life. It is exciting that this fundamental question can be formulated in a way that allows systematic experimental testing as we enter the next century. 

Studies of neuromuscular junctions of the autonomic nervous system as early as 1904 led to the suggestion that adrenaline might be released at the nerve endings. Later it was shown that, while adrenaline does serve as a transmitter at neuromuscular junctions in amphibians, it is primarily a hormone in mammals. Nevertheless, it was through this proposal that the concept of chemical communication in synapses was formulated. By 1921, it was shown that acetylcholine is released at nerve endings of the parasympathetic system, and it later became clear the motor nerve endings of the somatic system also release acetylcholine. 

At about the time that Claus proposed his ammonia theory, the concept of valence was being formulated and developed by a number of chemists — in particular, Kekule, Frankland, Williamson, Odling, Kolbe and Couper. During the late 19th and early 20th centuries the principal difficulty in the field of valence was its application to all types of chemical compound, and one of the main controversies involved whether or not a given element could possess more than one valence. Since coordination compounds pose a number of basic constitutional problems, it is not surprising that they became involved in the question of variable vs. constant valence. 

Whether the system formed on mixing oil, water, and surfactant will be an oil-in-water or a water-in-oil emulsion is a central problem in emulsion technology. It was realized very early that the volume fractions of oil and water are not that important and that the type of emulsion is primarily determined by the nature of the surfactant. Simply speaking surfactants with Ns < 1 tend to form oil-in-water emulsions, while surfactants with Ns > 1 are more likely to form water-in-oil emulsions. Two more detailed guiding principles which are used for practical emulsion formulation are Bancroft s rule of thumb and the more quantitative concept of the HLB scale ... 

The importance of polymorphism in pharmaceuticals cannot be overemphasized. Some crystal structures contain molecules of water or solvents, known as hydrates or solvates, respectively, and they are also called as pseudopolymorphs. Identifying all relevant polymorphs and solvates at an early stage of development for new chemical entities has become a well-accepted concept in pharmaceutical industry. For poorly soluble compounds, understanding their polymorphic behavior is even more important since solubility, crystal shape, dissolution rate, and bioavailability may vary with the polymorphic form. Conversion of a drug substance to a more thermodynamically stable form in the formulation can signiLcantly increase the development cost or even result in product failure. 

The idea that all matter is made of atoms is a familiar concept that that can be recited by the average first grader. However, the general acceptance of the atomic theory dates to the early part of the twentieth century, when Albert Einstein published a paper explaining Brownian motion. The notion of atoms dates back to ancient times, but these models are largely based on philosophical arguments, rather than empirical evidence. John Dalton first formulated an atomic theory... 

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