Formation and Hydrogen Bonding

studies of hydrogen-bonded complex formation include work on the systems chloroform—pyridine, phenol-base (bases 

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The NMR studies of nucleic acids can yield information about base sequences, conformations in solution, helix formation, and hydrogen bonding between base pairs. 

The data in Table 4 reveal additional cross-correlations between heat of formation, free energy of solution, and electronic (field and VHSE5) effects of amino acids (r = 0.61-0.65). The meaning of these relationships is uncertain, although field effects are proportional to the number of nonmethylene groups in the side chain, which would correspond to an increase in both the heat of formation and hydrogen-bond formation with water. 

Gorbitz, C.H. /3 Turns, water cage formation and hydrogen bonding in the structures of L-valyl-L-phenylalanine, Acta Crystallogr. B58 (2002) 512-518. 

Fig. 5. Protein folding. The unfolded polypeptide chain coUapses and assembles to form simple stmctural motifs such as -sheets and a-hehces by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) stmcture in this way. Larger proteins and multiple protein assembhes aggregate by recognition and docking of multiple domains (eg, -barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further stmctural...

The mechanism of the tarmage is accepted to be largely one of replacement of the bound water molecules by the phenoHc groups of the tannin and subsequent formation of hydrogen bonds with the peptide bonds of the protein. The effect of this bonding is to make the leather almost completely biorefractive. 

In general, pyridazine can be compared with pyridine. It is completely miscible with water and alcohols, as the lone electron pairs on nitrogen atoms are involved in formation of hydrogen bonds with hydroxylic solvents, benzene and ether. Pyridazine is insoluble in ligroin and cyclohexane. The solubility of pyridazine derivatives containing OH, SH and NH2 groups decreases, while alkyl groups increase the solubility. Table 1 lists some physical properties of pyridazine. 

FIGURE 5.8 Two structural motifs that arrange the primary structure of proteins into a higher level of organization predominate in proteins the a-helix and the /3-pleated strand. Atomic representations of these secondary structures are shown here, along with the symbols used by structural chemists to represent them the flat, helical ribbon for the a-helix and the flat, wide arrow for /3-structures. Both of these structures owe their stability to the formation of hydrogen bonds between N—H and 0=C functions along the polypeptide backbone (see Chapter 6). 

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

Also important for stabilizing a protein s tertiary stmcture are the formation of disulfide bridges between cysteine residues, the formation of hydrogen bonds between nearby amino acid residues, and the presence of ionic attractions, called salt bridges, between positively and negatively charged sites on various amino acid side chains within the protein. 

Excess Volume Comparison Figure 7.5 compares V for the three systems for which we have compared H, G, and 5, plus the (cyclohexane + decane) system.5 The comparatively large negative for the (ethanol + water) system curve (4) can be attributed to the decrease in volume resulting from the formation of hydrogen-bonded complexes in those mixtures. The negative for the (hexane + decane) system curve (3) reflects an increased packing... 

Sulphoxides and sulphones form hydrogen bonds with proton donors and association complexes with metallic salts by using either the oxygen atom or the sulphur atom in their S—O linkages. The capability for the formation of hydrogen bonds or complexes depends... 

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