Hydrogen cooperativity

Another even more significant use of methyl alcohol can be as a fuel in its own right in fuel cells. In recent years, in cooperation with Caltech s Jet Propulsion Laboratory (JPL), we have developed an efficient new type of fuel cell that uses methyl alcohol directly to produce electricity without the need to first catalytically convert it to produce hydrogen. 

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...

Industry Cooperative Hydrogen Fluoride Mitigation and Mmbient Impact Assessment Program, Summary Report, National Technical Information Service, Aug. 1989. 

Hydrogen bonding in water is cooperative. That is, an H-bonded water molecule serving as an acceptor is a better H-bond donor than an unbonded molecule (and an HgO molecule serving as an H-bond donor becomes a better H-bond acceptor). Thus, participation in H bonding by HgO molecules is a phenomenon of mutual reinforcement. The H bonds between neighboring molecules are weak (23 kj/mol each) relative to the H—O covalent bonds (420 kj/mol). As a consequence, the hydrogen atoms are situated asymmetrically... 

Due to the perfect linear arrangement of the N-H -N hydrogen bridges in 13, extremely fast cooperative proton transfers occur in solution which... 

When esterase models are designed, several important and fundamental problems have to be solved. Systematic studies on other interactions, such as hydrogen-bonding and charge-transfer type forces have not been fully performed. Furthermore, various cooperative actions between different kinds of interactions, e. g. the correlation between the attraction of substrate and repulsion of a product by a polyelectrolyte catalyst, has not yet been carried. 

In the case of cooperative processes, the formation of a nucleus, already discussed from the kinetical point of view, plays a crucial role. The steady state described by Eq. (1) depicts the formation of a triple helix as the simplest model by the formation of a nucleus Hx through fast pre-equilibria and subsequent propagation steps, Hx in this case is a triple-helical intermediate with x tripeptide units (that means x hydrogen bonds) in the helical state. The final product H3n 2 possesses two hydrogen bonds less than tripeptide units because the three single chains are staggered at one amino add residue each. 

It has been pointed out321-324 that the two groups of solvents differ by some definite structural features. In particular, ED, 1,2-BD, and 1,3-BD possess vicinal OH groups that can form intramolecular hydrogen bonds. For these solvents, the ability of the organic molecule to interact with neighboring molecules is reduced. This results in the possibility of a different orientation at the interface because of different interactions of the OH groups with the Hg surface.323 The different molecular structure leads to different dipolar cooperative effects. As a result, the dependence of C on the bulk permittivity follows two different linear dependencies. 

In any solvent system, the essential factors required for dissolution of cellulose include adequate stabihty of the electrolyte/solvent complex cooperative action of the solvated ion-pair on hydrogen bonding of cellu-... 

Theoretically, the problem has been attacked by various approaches and on different levels. Simple derivations are connected with the theory of extrathermodynamic relationships and consider a single and simple mechanism of interaction to be a sufficient condition (2, 120). Alternative simple derivations depend on a plurality of mechanisms (4, 121, 122) or a complex mechanism of so called cooperative processes (113), or a particular form of temperature dependence (123). Fundamental studies in the framework of statistical mechanics have been done by Riietschi (96), Ritchie and Sager (124), and Thorn (125). Theories of more limited range of application have been advanced for heterogeneous catalysis (4, 5, 46-48, 122) and for solution enthalpies and entropies (126). However, most theories are concerned with reactions in the condensed phase (6, 127) and assume the controlling factors to be solvent effects (13, 21, 56, 109, 116, 128-130), hydrogen bonding (131), steric (13, 116, 132) and electrostatic (37, 133) effects, and the tunnel effect (4,... 

Other particular theories are confined to diffusion-controlled reactions (109), to the so called cooperative processes (113), in which the reactivity depends on the previous state, or to resistance of semiconductors (102), while those operating with hydrogen bridges (131), steric factors (132), or electrostatic effects (133, 175) are capable of being generalized less or more. 

Meehan, T.D., Lott, C.A., Sharp, Z.D., Smith, R.B., Rosenfield, R.N., Stewart, A.C., Murphy, R.K. (2001). Using hydrogen isotope geochemistry to estimate the natal latitudes of immature Cooper s hawks migrating through the Florida keys. Condor, Vol. 103,11-20. 

I) Complex through Cooperative Action of Hydrogen Bonding and Auriophilicity. Journal of the American Chemical Society, 119(34), 8115-8116. 

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