Of functional groups in complex

Nuclear magnetic resonance (NMR) spectroscopy is a powerful and theoretically complex analytical tool that can be used to characterize organic matter. Proton (1H) and 13C-NMR have been the most common NMR tools for the nondestructive determination of functional groups in complex biopolymers in plants, soils/sediments, and DOM in aquatic ecosystems. 

Most often in cases (1) and (2), the lateral groups (e.g. substituents on aromatic [ring] systems) are already in place. This circumvents later transformations of functional groups in complex systems. Moreover the pool of commercially available functionalized subunits can be used more extensively. 

Many enzymes carry out their catalytic function relying solely on their protein structure. Many others require nonprotein components, called cofactors (Table 14.2). Cofactors may be metal ions or organic molecules referred to as coenzymes. Cofactors, because they are structurally less complex than proteins, tend to be stable to heat (incubation in a boiling water bath). Typically, proteins are denatured under such conditions. Many coenzymes are vitamins or contain vitamins as part of their structure. Usually coenzymes are actively involved in the catalytic reaction of the enzyme, often serving as intermediate carriers of functional groups in the conversion of substrates to products. In most cases, a coenzyme is firmly associated with its enzyme, perhaps even by covalent bonds, and it is difficult to... 

Fourier transform-infrared (FT-IR) spectroscopic studies on SO-SA complexation provides information that may be complementary to that of NMR and other techniques, namely, in particular, on the involvement of functional groups in intermolecular and intramolecular interactions. Attenuated total reflectance (ATR) IR spectroscopy has been used for the study of binding modes of cinchona alkaloid selectors either in solution [95] or in solid state [94], or directly on the CSP [96]. 

Enzymes are proteins that act as biological catalysts. They facilitate chemical modification of substrate molecules by virtue of their specific binding properties, which arise from particular combinations of functional groups in the constituent amino acids at the so-called active site. In many cases, an essential cofactor, e.g. NAD+, PLP, or TPP, may also be bound to participate in the transformation. The involvement of enzymes in biochemical reactions has been a major theme throughout this book. The ability of enzymes to carry out quite complex chemical reactions, rapidly, at room temperature, and under essentially neutral conditions is viewed with envy by synthetic chemists, who are making rapid progress in harnessing this ability for their own uses. Several enzymes are currently of importance commercially, or for medical use, and... 

Even the most experienced chemist will not be able to foresee all potential pitfalls of a synthesis, specially so if multifunctional, structurally complex intermediates must be prepared. The dose proximity or conformational fixation of functional groups in a large molecule can alter their reactivity to such an extent that even simple chemical transformations can no longer be performed [11]. Small structural variations of polyfunctional substrates might, therefore, bring about an unforeseeable change in reactivity. 

The principal idea of this present essay was to show how the unique preorganization of functional groups in self-assembled dimers of tetra-urea calix[4]arenes can be used to prepare novel multi-rotaxanes and -catenanes or topologically even more complex molecules and supramolecular structures. We will conclude by summarizing some related studies in which calixarenes were used in a different way as building blocks for the construction of such structures or assemblies. 

Sufficient information about the reaction has been gathered to allow fairly accurate predictions of yield as well as of stereo- and regioselectivity.176177 The reaction proceeds via the formation of hexacarbonylalkyne-dicobalt complexes and is remarkably tolerant of functional groups in both the alkyne and the alkene. The intramolecular Pauson-Khand reaction is an effective way of preparing bi- and polycyclic systems, and the cyclization of 1,6-heptenyne derivatives to give bicyclo[3.3.0]oct-l-en-3-ones has been the most popular application of the Pauson-Khand reaction in natural product synthesis [Eq. (17)]. 

Many oxo-metal complexes efficiently epoxidize alkenes. Stereoselectivity in these epoxidations is most often achieved by precoordination of functional groups in the substrates. If the metallic centers are embedded in a chiral environment that allows stereoselectivity to rely solely on nonbonded interactions, enantioselective epoxidation may be extended to nonfunctionalized alkenes16. 

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