Exotic chemical system

Exotic chemical systems, mostly oscillatory reactions, but also systems exhibiting multistationarity and chaotic effects, have extensively been investigated. Phenomena in chemical, biological and industrial chemical systems are the experimental basis of the theoretical studies. 

The centrifugal separator of the AKUEVE system is also used for phase separation in the SISAK technique [84]. SISAK is a multistage solvent extraction system that is used for studies of properties of short-lived radionuclides, e.g., the chemical properties of the heaviest elements, and solvent extraction behavior of compounds with exotic chemical states. In a typical SISAK experiment, Fig. 4.34, radionuclides are continuously transported from a production... 

In contrast to the situation for exotic chemicals described earlier, changes to natural cycles should be easier to predict, since the process is one of enhancement of what already occurs, rather than addition of something completely new. Thus, knowledge of how a natural system works now and has done in the past should be helpful in predicting the effects of human-induced changes. However, we are often less able at such predictions than we would like to be, because of our ignorance of the past and present mode of operation of natural chemical cycles. 

Chemical systems often show oscillatory behavior only over a narrow range of conditions, and one reason for the popularity of the classic Belousev-Zhabotin-skii reaction (BZ) and related systems is that they show exotic behaviour over a wide range of conditions. Evidence has been obtained for an additional negative... 

The modern theory of chemical bonding begins with the article The Atom and the Molecule published by the American chemist G. N. Lewis in 1916 [1], In this article, which is still well worth reading, Lewis for the first time associates a single chemical bond with one pair of electrons held in common by the two atoms "After a brief review of Lewis model we turn to a quantum-mechanical description of the simplest of all molecules, viz. the hydrogen molecule ion H J. Since this molecule contains only one electron, the Schrodinger equation can be solved exactly once the distance between the nuclei has been fixed. We shall not write down these solutions since they require the use of a rather exotic coordinate system. Instead we shall show how approximate wavefunctions can be written as linear combinations of atomic orbitals of the two atoms. Finally we shall discuss so-called molecular orbital calculations on the simplest two-electron atom, viz. the hydrogen molecule. 

Erdi, P., Toth, J. Hars, V. (1981). Some kinds of exotic phenomena in chemical systems. Coll. Math. Soc. Janos Bolyai 30, Vols. I, II. North Holland, Amsterdam, pp. 205-29. 

Both deterministic and stochastic models can be defined to describe the kinetics of chemical reactions macroscopically. (Microscopic models are out of the scope of this book.) The usual deterministic model is a subclass of systems of polynomial differential equations. Qualitative dynamic behaviour of the model can be analysed knowing the structure of the reaction network. Exotic phenomena such as oscillatory, multistationary and chaotic behaviour in chemical systems have been studied very extensively in the last fifteen years. These studies certainly have modified the attitude of chemists, and exotic begins to become common . Stochastic models describe both internal and external fluctuations. In general, they are a subclass of Markovian jump processes. Two main areas are particularly emphasised, which prove the importance of stochastic aspects. First, kinetic information may be extracted from noise measurements based upon the fluctuation-dissipation theorem of chemical kinetics second, noise may change the qualitative behaviour of systems, particularly in the vicinity of instability points. 

In particular, another attempt of the research in the field of nonlinear chemical dynamics could be to produce and to study exotic phenomena in chemical systems, to reveal their mechanism, and to simulate these temporal and spatial patterns. 

Spatio and Spatio-Temporal Patterns. An exotic form of diffusional encounter should be mentioned, which arises from sets of reaction-diffusions equations (48). In 1952, the mathematician Alan Turing postulated the existence of two-dimensional and three-dimensional spatio and spatio-temporal patterns for certain classes of reactive systems (49). The physical realization of these mathematical solutions has been observed in a variety of systems (50). It suffices to say that since these patterns have been observed in both simple chemical systems and complex biological systems, their possibility in homogeneous catalysis should certainly not be ruled out. In this regard, static spectroscopic cells may be particularly prone to such spatial variation because of the lack of mixing. 

Rabai, G. Beck, M. T. 1988. Exotic Chemical Phenomena and their Chemical Explanation in the lodate-Sulfite-Thiosulfate System, J. Phys. Chem. 92, 2804-2807. Rabai, G. Epstein, I. R. 1989. Oxidation of Hydroxylamine by Periodate in a CSTR A New pH Oscillator, J. Phys. Chem. 93, 7556-7559. 

It is well known that some non-linear chemical systems driven far from equilibrium can xhibit a large variety of exotic behaviours leading to sefl organization they belong to the class of dissipative systems in... 

As a direct consequence of the particular role of Dynamics, as such,in the study of non-equilibrium behaviour of chemical systems, two classes of models are to be considered, depending on which aspect one is insisting on. Formal models, of mathematical or chemical-like nature, are designed to exhibit specific dynamical behaviours, without too much concern about chemical significance. Their aim is to provide examples of evolution equations of chemical reacting systems, as described by mass action kinetics, that are able to produce those exotic behaviours, such as bistability or multistability, between various types of attractors, like steady states, oscillations or deterministic chaos. A typical historical model of that kind is the "Brusselator ... 

There is a widespread belief that exotic patterns of behaviour in chemical systems require either very complex kinetic mechanisms or non-isothermal influences. There have been many investigations of the single, irreversible, exothermic reaction [see e.g. 1 5] proceeding under well-stirred, open conditions (in a CSTR). By contrast, the isothermal systems [6] covered have tended to be rather specific enzyme rate-laws or reactions at surfaces. Models proposed for homogeneous, isothermal reactions include complicated schemes [7 58] such as the Brusselator and Oregonator . Table 1 lists some of the important historical landmarks of this subject. 

But how, exactly, does a toad secretion effect the human mind Bufotenin has a very close chemical similarity to serotonin, a substance used by the nervous system to transmit information from one nerve cell to another. Bufotenin overwhelms serotonin-sensitive cells and triggers effects ranging from hallucinations to seizures. Two Toronto men learned about this the hard way. They ended up in hospital after licking a cane toad they had purchased in a pet shop specializing in exotic animals. And a five-year-old Arizona boy did have a brush with death after he put a Colorado River toad into his mouth. (Just why he did this can only be explained by other five-year-old boys.) In any case, this species, bufo alvarias, is the most toxic toad in North America. The youngster developed seizures that had to be controlled with medication. 

In many other cases it is not at all clear that these exothermic reactions are operated in such a way that the system can remain isothermal. Self-heating and hence thermal feedback routes can be expected to have a strong autocatalytic effect on the reaction, perhaps in addition to chemical mechanisms. Recent modelling invoking cellular automata (Jaeger et al. 1985) has been to some extent successful at matching qualitatively many of the rather exotic responses which have been observed experimentally. 

From the perspective of this symposium, analysis of the atomic dynamics and electronic structure of surfaces constitutes an even more exotic topic than surface atomic geometry. In both cases attention has been focused on a small number of model systems, e.g., single crystal transition metal and semiconductor surfaces, using rather specialized experimental facilities. General reviews have appeared for both atomic surface dynamics (21) and spectroscopic measurements of the electronic structure of single-crystal surfaces (, 22). An important emerging trend in the latter area is the use of synchrotron radiation for studying surface electronic structure via photoemission spectroscopy ( 23) Moreover, the use of the very intense synchrotron radiation sources also will enable major improvements in the application of core-level photoemission for surface chemical analysis (13). 

Variations on the basic structural theme of 1 have led to a plethora of unusual macrocyclic systems, collectively known as porphyrin analogs or porphyrinoids. These molecules, often nontrivial to synthesize, exhibit remarkable physical and chemical properties and their chemistry has been extensively reviewed [2-18], With the impressive range of structural modifications introduced so far, the term porphyrinoid has ultimately expanded to encompass a wide range of often exotic macrocycles, some of which contain no pyrrole rings at all, or have a structural outline barely resembling that of porphyrin. Some of the generic modification types are shown in Fig. 1. Combination of these design concepts provides a virtually inexhaustible source of structural diversity. 

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