Structure double helical

All that remains is to convert the cartoon structures into real molecules Groups such as 2,2 -bipyridine and 1,10-phenanthroline have been popular choices for the metal-bin-ding domains. The principles are actually very simple. If we incorporate a didentate metal-binding domain into the threads, then structure 7.46 simply corresponds to the bin- 

When 7.48 reacts with copper(i), which usually forms four-co-ordinate tetrahedral complexes, a double-helical species, 7.49, is indeed formed (Fig. 7-30). This is a genuine self-assembly process - simply treating the ligand with the appropriate metal ion leads to the desired structure. A wide variety of other spacer groups have been incorporated between didentate domains. In practice, some consideration needs to be given to the nature of the spacer group that is selected. If it is too long, or too flexible, other co-ordination possibilities can occur. 

7 The Three-Dimensional Template Effect, Supramolecular Chemistry and Molecular Topology 

Of course, it is quite possible to further extend these assembly processes to give doublehelical complexes with even more bond crossings. For example, a double-helical complex with three bond-crossings should result from the reaction of a molecular thread containing three metal-binding domains with three tetrahedral metal ions (Fig. 7-32). An example of the assembly of such a trinuclear double-helical complex is seen in the formation of 7.52 from the reaction of 7.51 with silver(i) salts (Fig. 7-33). 

Naturally, it is not necessary to limit the procedure to the use of tetrahedral metal centres. For example, it is possible to build double-helical structures from the interaction of molecular threads containing tridentate domains with metal ions possessing a preference for a six-co-ordinate octahedral geometry. An example of such a process is shown in Figu- 

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The DNA isolated from different cells and viruses characteristically consists of two polynucleotide strands wound together to form a long, slender, helical molecule, the DNA double helix. The strands run in opposite directions that is, they are antiparallel and are held together in the double helical structure through interchain hydrogen bonds (Eigure 11.19). These H bonds pair the bases of nucleotides in one chain to complementary bases in the other, a phenomenon called base pairing. 

The ability of DNA to replicate lies in its double-helical structure. There is a precise correspondence between the bases in the two strands. Adenine in one strand always forms two hydrogen bonds to thymine in the other, and guanine always forms three hydrogen bonds to cytosine so, across the helix, the base pairs are always AT and GC (Fig. 19.29). Any other combination would not be held together as well. During replication of the DNA, the hydrogen bonds, which are... 

Acridine dyes used as antiseptics, i.e. proflavine and acriflavine, will react specifically with nucleic acids, by fitting into the double helical structure of this unique molecule. In so doing they interfere with its function and can thereby cause cell death. 

Iso tactic poly(methyl methacrylate) (it-PMMA) can form a stereocomplex with st-PMMA. Recent X-ray studies 179) of this material indicate that the two polymer chains probably interact to form a double helical structure. The it-PMMA chain forms the inner helix and is surrounded by the st-PMMA helical chain which winds around it. If subsequent work confirms this model, this material would constitute a most unusual inclusion compound involving only one monomeric substance. 

The discovery of the base-paired, double-helical structure of deoxyribonucleic acid (DNA) provides the theoretic framework for determining how the information coded into DNA sequences is replicated and how these sequences direct the synthesis of ribonucleic acid (RNA) and proteins. Already clinical medicine has taken advantage of many of these discoveries, and the future promises much more. For example, the biochemistry of the nucleic acids is central to an understanding of virus-induced diseases, the immune re-sponse, the mechanism of action of drugs and antibiotics, and the spectrum of inherited diseases. 

A dinuclear silver(i) carbene complex, 22, was also isolated using a pyridyl-bridged biscarbene ligand (Scheme 7).65a,65b Complex 22 possessed a double helical structure with Ag-C bond distances of 2.080(4) and 2.087(4) A and a C-Ag-C angle of 165.5(2)°.65a Weak Ag-Ag interaction could also be observed with an Ag-Ag distance of 3.158 A.65a... 

AG(E)2468>. The application of distinct self-assembly processes to form grid-type and double-helical structures has potential in understanding and controlling molecular information an interesting discussion has been presented <00CEJ2103>. 

The well-known double-helical structure of DNA (deoxyribonucleic acid) is derived from the specificity of the Watson-Crick base pairing.154 Yanagawa and co-workers first addressed the issue of whether mononucleotide units could be... 

Double Friedel-Crafts alkylation, 12 170 Double-helical structure, 17 603, 604. 

De Mendoza reported the first example of anion-directed helix formation in 1996 [91]. The assembly of this helical structure relies, not only on electrostatic interactions between the anionic template and the positively charged strands, but also on hydrogen bonding. The tetraguanidinium strand 69 (see Scheme 34) self-assembles around a sulfate anion via hydrogen bonding to produce a double helical structure. The formation of this assembly and its anion-dependence was proposed on the basis of NMR and CD spectroscopic studies. 

The structural characterization of this assembly has revealed that chloride coordination (via hydrogen bonding to the protonated pyridyl groups of the strands) induce the strands to adopt a double-helical structure in the solid state. 

The consistent solvent- and chain-length-dependent phenomena suggest that a helical structure is being formed however, double-helical, knotlike or alternatively folded structures could not be ruled out (Fig. 4). Double-helical structures are not believed to be present since there is no concentration dependence below 10 pmol for the 12-mer in acetonitrile at room temperature. To rule out misfolded knotlike structures, a series of oligomers were designed with a methyl group in the internal position of the helix (19-27) [28]. The... 

DNA is a structurally polymorphic macromolecule which, depending on nucleotide sequence and environmental conditions, can adopt a variety of conformations. The double helical structure of DNA (dsDNA) consists of two strands, each of them on the outside of the double helix and formed by alternating phosphate and pentose groups in which phosphodiester bridges provide the covalent continuity. The two chains of the double helix are held... 

The sequential and often cooperative disassembly of double-helical structure, occurring whenever the sample temperature exceeds the so-called melting temperature (Tm) for a given segment of DNA. Because of the low concentrations of intermediate states lying between helix and coil structures, the helix-coil transition can be approximated as a two-state, all-or-nothing process. See DNA Unwinding Kinetic Model for Small DNA... 

Electron transfer reactions are among the most widespread and significant in all of chemistry. Electron transfer (ET) within the double helical structure of DNA exhibits an extremely broad range of mechanistic behavior, and its exploration has become a focal point within the chemical community since the key studies of Barton and collaborators [1-3]. 

Fig.1 Schematic illustration of the DNA double helical structure (a) and two possible mechanisms (electron-level energies in b, hole energies in c) of electronic motion in this molecule...

Modern genetics started with the elucidation of the double-helical structure of the DNA molecule by James Watson and Francis Crick in 1953 [20]. It was already known... 

To appreciate this section and, more broadly, to appreciate the importance of this book s topic as a justification for mathematics, one should understand the role of theory in the physical sciences. While in mathematics the intrinsic beauty of a theory is sufficient justification for its study, the value of a theory in the physical sciences is limited to the value of the experimental predictions it makes. For example, the theory of the double-helical structure of... 

Two major discoveries in 1953 were of crucial importance in the history of biochemistry. In that year James D. Watson and Francis Crick deduced the double-helical structure of DNA and proposed a structural basis for its precise replication (Chapter 8). Their proposal illuminated the molecular reality behind the idea of a gene. In that same year, Frederick Sanger worked out the sequence of amino acid residues in the polypeptide chains of the hormone insulin (Fig. 3-24), surprising many researchers who had long thought that elucidation of the amino acid sequence of a polypeptide would be a hopelessly difficult task. It quickly became evident that the nucleotide sequence in DNA and the amino acid sequence in proteins were somehow related. Barely a decade after these discoveries, the role of the nucleotide... 

Today s understanding of information pathways has arisen from the convergence of genetics, physics, and chemistry in modern biochemistry. This was epitomized by the discovery of the double-helical structure of DNA, postulated by James Watson and Francis Crick in 1953 (see Fig. 8-15). Genetic theory contributed the concept of coding by genes. Physics permitted the determination of molecular structure by x-ray diffraction analysis. Chemistry revealed the composition of DNA. The profound impact of the Watson-Crick hypothesis arose from its ability to account for a wide range of observations derived from studies in these diverse disciplines. 

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