Hydrogen bonding in addition

Presumably, the heterolytic scission of the carbon-sulfur bond in the oxide is assisted by the hydrogen bonding, in addition to the inherent strain of the three-membered ring. 

The native, biologically active form of a protein molecule is held together by a delicate balance of noncovalent forces hydrophobic, ionic, van der Waals interactions, and hydrogen bonds. In addition,... 

From such a background, some kinds of polypeptide blend samples have been studied by solid state NMR.27,72 74 Especially, detailed information for four kinds of blend samples such as poly(L-alanine) (PLA)/poly(L-valine) (PLV), PLA/poly(L-isoleucine) (PLIL), poly(D-alanine) (PDA)/PLV and polyglycine (PG)/PLV blends, have been reported. Here, let us describe some reasons why PLA/PLV, PDA/PLV, PLA/PLIL and PG/PLV blends are interesting systems. PLA and PDA in the solid-state can take the a-helix and (3-sheet forms due to intra- and intermolecular HBs, respectively. PG in the solid-state can take the 3j-helix (PG-II) and (3-sheet (PG-I) forms due to intra- and intermolecular HBs, respectively. However, PLIL and PLV in the solid state can predominantly take the (3-sheet form as the stable conformation. For this reason, it is interesting to know whether an isolated a-helix or 3i-helix form polypeptide surrounded by a major polypeptide in the (3-sheet form can take the helical conformation, or not, due to the balance between intramolecular and intermolecular hydrogen bonds. In addition, we would like to know whether a polypeptide in the (3-sheet form surrounded by a major polypeptide in the a-helix or 3 -helix form can take the (3-sheet form. 

The results of a study of the laser-Raman spectra of sucrose are summarized in Table IX. The most important features observed187 when the concentration was varied consisted in shifts of the frequencies of the CH2OH group, which are sensitive to intra- and inter-molecular hydrogen-bonding. In addition, the association of D-glucose with D-fructose that leads to the... 

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... 

Complex 15 illustrates in detail the possibility of simultaneous a-hole and hydrogen bonding, which has already been discussed in 15, there is one 0---S a-hole bond and three 0---H hydrogen bonds. Note the deviations of the hydrogen bonds from linearity. Another example in Table 6.2 is 14, in which the very short N---Si separation can be attributed to the presence of several H---F hydrogen bonds, in addition to the N—Si a-hole interaction [32]. We have encountered analogous situations elsewhere, for instance, with sulfur and selenium heterocycles [47]. 

The work which is reviewed here provides accurate structural data from micro-wave and radiofrequency spectroscopy of relatively small molecule, hydrogen bonded complexes. Its role has been to provide information concerning the stereochemistry and electronic properties — electric dipole moments and nuclear hyperfine interactions — characteristic of hydrogen bonds. The experiments are done on gas phase samples, often in molecular beams, which eliminates environmental perturbations of the hydrogen bonds. In addition, the small molecules used are amenable to ab initio calculations 7 9) and thus the results are extremely useful as criteria for the accuracy of these calculations. Finally, the results are useful to construct models of more complex systems in chemistry and biology involving hydrogen bonds 4). 

Thus, negatively charged moieties in proteins (such as the carboxylate side chains of Asp and Glu residues) frequently interact with positively charged side chains of Lys, Arg, or His residues. These electrostatic interactions often result in the formation of salt bridges, in which there is some degree of hydrogen bonding in addition to the electrostatic attraction, as illustrated in Fig. 4-3. 

In a solution, nanoparticles interact with each other in a number of ways. Widely separated nanoparticles may be brought into contact by Brownian motion. As they approach each other, electrostatic, van der Waals forces, and hydrogen bonding, in addition to Brownian motion, can cause two nanoparticles to rotate with respect to each other, and collide. Evidently, under some conditions, the collisions that result in fusion are those that involve two nanoparticles in appropriate orientations to form a coherent (or semicoherent) interface. Particle rotation in the absence of a fluid has been modeled computationally (Zhu and Averback 1996), implying that oriented assembly-based crystal growth can also occur in dry systems. 

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