Hydrogen-bonded pair

One proposed approach (75) to modeling the phase behavior for hydrogen bonding pairs uses the following expression for the free energy of mixing (eq. 7). 

The average molar mass of a hydrogen-bonded pair of nucleotides in a DNA molecule is 625 g-mol Each successive pair is found at a distance of 340 pm along the chain. If the total length of one strand of a DNA molecule is 0.299 m, what is the molar mass of the molecule ... 

In contrast to the case of the 8CB liquid crystal, no contact potential differences between first and second layers were observed with these lubricants. This indicates that there is no special orientation of the dipole active end groups, or perhaps that the end groups form hydrogen-bonded pairs with neighboring molecules so as to give no net dipole moment. 

D 15N-edited NOESY (15N-NOESY-HMQC) provides imino-imino, imino-amino and aromatic-imino/amino connectivities. The approach often fails in regions such as loops and bulges where bases do not form hydrogen-bonded pairs. In that case, imino assignment can be obtained from... 

We now turn to substituent-sensitive tautomerism. Johnson and Rumon studied a series of solids derived by cocrystallizing substituted benzoic acids and substituted pyridines (108). Their IR evidence indicated, as expected, that when the benzoic acid is a strong acid and the pyridine a strong base, salts 50a are formed. For a weak acid and a weak base, hydrogen-bonded pairs of neutral molecules,... 

The hydrogen-bond pairing interactions between pyrimidine and purine bases in DNA and RNA. See DNA... 

Figure 5.5. Inversion-related dimers of hydrogen-bonded pairs of EDT-TTF-COOH. C, S and O atoms are represented by black, medium grey and light grey balls, respectively. H atoms are omitted.

Figure 1 also contains a drawing of the electronic structure of plastocy-anin (Penfield et al., 1981, 1985), oriented according to the first part of Fig. 1. The d-orbital plane appears to be normal to the peptide plane that is extended by the hydrogen-bonding pair the it orbital of the thiolate would then also be affected, poising the cluster for electron transfer and, interestingly, apparently in the direction utilized by the multi-copper protein ascorbate oxidase (see Section V,A).

Brunsveld L, Vekemans JAJM, Hirschberg JHKK, Sijbesma RP, Meijer EW. Hierarchical formation of helical supramolecular polymers via stacking of hydrogen-bonded pairs in water. Proc Natl Acad Sci USA 2002 99 4977-4982. 

Fig. 11. Intermolecular hydrogen-bonded pairs of aqua hydroxo complexes have been found in several crystal structures and are probably always present in those salts of the type cis-[ML4(H20)(0H)lX2, which yield dinuclear dihydroxo-bridged complexes upon heating in the solid state.

While searching for the meaning of these equalities, James Watson noted that hydrogen-bonded base pairs with the same overall dimensions could be formed between A and T and between G and C (fig. 25.4). The A-T base-paired structure has two hydrogen bonds, whereas the G-C base pair has three. The hydrogen-bonded pairs are formed between bases of opposing strands and can only arise if the directional senses of the two interacting chains are opposite or antiparallel (fig. 25.5). With this notion in mind Francis Crick took a closer look at the x-ray diffraction pattern produced by DNA and was able to interpret the diffraction pattern in terms of a helix (see Methods of Biochemical... 

It is reasonable to assume that the complementary units form the expected triply hydrogen bonded pairs, so that the entirely different behaviour of the pure compounds and of the 1 1 mixtures may be attributed to the spontaneous association of the complementary components into a polymolecular entity based on hydrogen bonding. The overall process may then be described as the self-assembly of a supramolecular liquid-crystalline polymer based on molecular recognition (Figure 40). The resulting species (TP2, TU2) is represented schematically by structure 174. 

FIGURE 24.18 The coil of the sugar-phosphate backbone is visible on the outside of the DNA double helix in this computer-generated structure, while the hydrogen-bonded pairs of amine bases lie flat on the inside. 

C-4 -C-5 bond is gauche (42.3°, -75.7°), Adjacent bases are linked together by pairs of N-6-H---N-7 and N-6-H-"N-l hydrogen-bonds. In both types of hydrogen-bonded pairs, the base planes make dihedral angles of 37°. Base stacking was not observed. The coordinates published correspond to the wrong enantiomorph. 

This porosity which is also retained in the LB films, may explain the water penetration between the 2-D crystallites. The amide groups located at the periphery of these domains generate hydrophilic centers which may retain water molecules by binding via hydrogen bonds. In addition, the hydrophilic head groups, such as a-amino acids or carboxylic acids which (in contrast to the Y-type films), cannot form hydrogen bonded pairs, are free to bind water molecules between the layers. We suggest that when... 

Within the DNA double helix, the hydrogen-bonded pairs are of a very specific type termed Watson-Crick base pairs (after James Watson and Francis Crick who first described the structure of... 

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