Chirality of organisms

Circularly polarized light (CPL) has been proposed as one of the origins of the chirality of organic compounds.Asymmetric photolysis of racemic leucine by... 

In place of the above-mentioned chiral organic compounds, chiral inorganic substrates have been examined as chiral initiators. Quartz (Si02) exhibits both dextrorotatory (d) and levorotatory (Z) enantiomorphs that exist in nature. Quartz is considered as one of the origins of chirality of organic compounds186. 

As described, asymmetric auto catalysis is closely related to the origin of the homo chirality of organic compounds. 

One of the main features of asymmetric autocatalysis and the formation of the helix is that the initial extremely low enantioenrichment is amplified significantly to near enantiopure. These processes of amplification of chirality have become powerful tools to elucidate the origin of chirality of organic compounds. For example, by using asymmetric auto catalysis, spontaneous absolute asymmetric synthesis without the intervention of any chiral factor has been realized. 

Fang, H.B., Giancarlo, L.C., and Flynn, G.W., Direct determination of the chirality of organic molecules by scanning tunneling microscopy, J. Phys. Chem. B 102, 7311-7315, 1998. 

Illustration of the chirality of organic molecules containing stereo-center carbon, (a) 2-propanol, which is an achiral molecule, and (b) 2-butanol, which is a chiral molecule. The sketches are oversimplified in reality a carbon atom is tetrahedrally bonded to four atoms and chemical groups. 

Stereochemistry (Chirality) of Organic Compounds with Heteroatoms Other than Oxygen (e.g., Nitrogen,... 

Web page of the International Union of Pure and Applied Chemistry (lUPAC) (www.chem.qmul.ac.uk/iupac/stereo) lUPAC Recommendations 1996 provide basic terminology used in stereochemistry. As stereochemistry and chirality of organic compounds have been the subject of numerous books, readers interested in these subjects should refer to the references provided in [5]. 

Clearly, there is a need for techniques which provide access to enantiomerically pure compounds. There are a number of methods by which this goal can be achieved . One can start from naturally occurring enantiomerically pure compounds (the chiral pool). Alternatively, racemic mixtures can be separated via kinetic resolutions or via conversion into diastereomers which can be separated by crystallisation. Finally, enantiomerically pure compounds can be obtained through asymmetric synthesis. One possibility is the use of chiral auxiliaries derived from the chiral pool. The most elegant metliod, however, is enantioselective catalysis. In this method only a catalytic quantity of enantiomerically pure material suffices to convert achiral starting materials into, ideally, enantiomerically pure products. This approach has found application in a large number of organic... 

Ti in [Ti(> 2-Cl04)4] and Ni" in [Ni(>j -C104)L2] where L is a chiral bidenlate organic ligand.Sometimes both and modes occur in the same compound. The biden-latc bridging mode occurs in the silver complex [Ag /x,>j -00(0)20- (m-xylene)2]- The structure of appropriate segments of some of these compounds arc in Fig. 17.23. The distinction between coordinated and non-coordinaied ( ionic ) perchlorate is sometimes hard to make and there is an almost continuous... 

Although many carbonyl derivatives act as acyl cation equivalents, R(C=0)" in synthetic chemistry, the inherent polarity of the carbonyl group makes it much more difficult to find compounds that will act as equivalents of acyl anions, R(C=0) . Since the 1960s, major progress has been made in this area, and there are now a wide variety of compound types that can react in this way. As in so many areas of organic chemistry, heterocyclic compounds take pride of place and form the basis of many of the most useful methods. In recent years there has been particular interest in developing chiral acyl anion equivalents that will show high... 

Binding of organic nitroso compounds to metalloporphyrins 99ACR529. Design and applications of chiral porphyrins 98YGK201. 

Asymmetric synthesis is a stimulating academic challenge, but since it has become clear that most chiral drugs can be administered safely only in the enantiomerically pure form, the industrial need for asymmetric methods has made research in asymmetric synthesis absolutely necessary [5]. This has driven a renaissance in the discipline of organic chemistry, because all of the old-established reactions need to be reinvestigated for their application in asymmetric synthesis [6]. This has also applied... 

The introduction of synthetic materials into natural products, often described as adulteration , is a common occurrence in food processing. The types of compounds introduced, however, are often chiral in nature, e.g. the addition of terpenes into fruit juices. The degree to which a synthetic terpene has been added to a natural product may be subsequently determined if chiral quantitation of the target species is enabled, since synthetic terpenes are manufactured as racemates. Two-dimensional GC has a long history as the methodology of choice for this particular aspect of organic analysis (38). 

Perhaps the most successful industrial process for the synthesis of menthol is employed by the Takasago Corporation in Japan.4 The elegant Takasago Process uses a most effective catalytic asymmetric reaction - the (S)-BINAP-Rh(i)-catalyzed asymmetric isomerization of an allylic amine to an enamine - and furnishes approximately 30% of the annual world supply of menthol. The asymmetric isomerization of an allylic amine is one of a large and growing number of catalytic asymmetric processes. Collectively, these catalytic asymmetric reactions have dramatically increased the power and scope of organic synthesis. Indeed, the discovery that certain chiral transition metal catalysts can dictate the stereo-... 

Provided electron transfer between the electrode and solute species is not interrupted by the coating, even electroinactive films can offer interesting applications. Thus, a chiral environment in the surface layer may impose stereoselectivity in the follow-up reactions of organic or organometallic intermediates. Furthermore, polymer layers may be used to obtain diffusional permeation selectivity for certain substrates, or as a preconcentration medium for analyzing low concentration species. 

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