Planar aromatic chemicals

Certain planar aromatic chemicals (drugs) bind to DNA by intercalation. In this process, the intercalation compound inserts between two stacked bps of DNA and positions itself within the center of the DNA double helix. The intercalated molecule is stabilized by hydrophobic stacking interactions with adjacent bps. The binding by intercalation results... 

Pitches can be transformed to a mesophase state by further chemical and physical operations. Heat treatment of conventional pitches results in additional aromatic polymeriza tion and the distillation of low molecular weight components. This results in an increase in size and concentration of large planar aromatic molecular species whereupon the precursor pitch is transformed to a mesophase state exhibiting the characteristics of nematic Hquid crystals (1). Additional heat treatment converts the mesophase pitch to an infusible aromatic hydrocarbon polymer designated as coke. 

In the following sections, systems with various numbers of electrons are discussed. When we look for aromaticity we look for (1) the presence of a diamagnetic ring current (2) equal or approximately equal bond distances, except when the symmetry of the system is disturbed by a hetero atom or in some other way (3) planarity (4) chemical stability (5) the ability to undergo aromatic substitution. 

The relation between UV- and PES-spectra is quite similar as found for planar aromatic compounds. All chemical shifts in NMR-spectra can well be explained by normal ring-current effects and Van der Waals interactions. Polarographic data do not deviate from those for planar compounds. 

The main aspects of the chemical reactivity of helicenes (e.g. electrophilic substitution) equally not deviate from those of planar aromatic compounds, and remarkable reactions of helicenes, which are incidentally found (e.g. the transannular bond formation between a C(l)-substituent and a part of the inner helix) can ultimately be reduced to known principles of aromatic reactivity. 

Figure 4.21 The structure of [Lu(19)2](CH30H)(H20)] + [37]. (Reproduced with permission from C. Piguet, A.R Williams, C. Bemardine and J.C.G. Btinzli, Structural and photophysical properties of lanthanide complexes with planar aromatic tridentate nitrogen ligands as luminescent building blocks for triple-helical structures, Inorganic Chemistry, 32, 4139, 1993. 1993 American Chemical Society.)...

Little is known about the chemical nature of the recently isolated carbon clusters (C o> C70, Cg4, and so forth). One potential application of these materials is as highly dispersed supports for metal catalysts, and therefore the question of how metal atoms bind to C40 is of interest. Reaction of C o with organometallic ruthenium and platinum re nts has shown that metals can be attached directly to the carbon framework. Ihe native geometry of transition metal, and an x-ray difi action analysis of the platinum complex [(CgHg)3P]2Pt( () -C6o) C4HgO revealed a structure similar to that known for [(C4Hs)3P]2Pt( n -ethylene). The reactivity of C40 is not like that of relatively electron-rich planar aromatic molecules su( as benzene. The carbon-carbon double bonds of C40 react like those of very electron-deficient arenes and alkcnes. 

PE) correlates with molecular surface, but the slope of the linear correlation is quite different for various subsets of chemically similar molecules. Table 12.3 shows that planar aromatics with a regular shape have the highest density, packing coeffi-... 

The selenophene molecule is planar. The chemical shifts in the NMR spectra are found in the region typical for aromatic compounds. 

The dyes that alter their emissions on binding to nucleic acids have high utility in molecular and cell biology. The mechanism of binding is intercalation of the planar aromatic dye structure into double-helical DNA, which is favored and stabilized by multiple electrostatic and hydrophobic interactions between the two matching chemical structures (see Fig. 4). Such an interaction has significant impact on the electronic structure of the dye,... 

Labeling is usually performed by the formation of a covalent bond between the fluorescent label and the target molecule. However, fluorescent dyes without a reactive group can be employed for some purposes. Due to their particular structural nature, fluorescent probes can bind noncovalently to special biomolecules in cells in a specific or a nonspecific fashion. In this case, the term stain is used to refer to the label and staining to the noncovalent attachment of the label to the studied object. There are a large number of fluorescent dyes that bind to DNA and RNA forming complexes via intercalation. Intercalating dyes are planar aromatic cations that insert between stacked base pairs on the DNA duplex. Their structure and chemical properties provide appropriate size and van der Waals interactions favorable for insertion between bases. 

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