Breakage of hydrogen bonds

When starch is heated in excess water, the crystalline structure is disrupted (due to breakage of hydrogen bonds) and water molecules become linked by hydrogen bonding to the exposed hydroxyl groups of amylose and amylopectin. This causes an increase in granule swelling... 

Solvent KIEs for MeCl + Cl in the presence of 1—4 molecules of water were examined by ab initio calculations.70 The ratio h/ d was <1 for the monohydrated system and > 1 for the dihydrated system it increased with the number of micro solvating water molecules, owing to breakage of hydrogen bonds in attaining the transition state. 

The ideal process of the melting of ice may be visualized as a partial ( 15%) breakage of hydrogen bonds to form ice fragments, which are then converted into a polyhedral system, as indicated in Fig. 16.3.4. 

However, the PEO chain can become dehydrated at high temperatures (due to breakage of hydrogen bonds), which reduces the effective steric stabihsation. Thus, emulsion polymerisation should be carried out at temperatures well below the theta (0)-temperature of PEO. 

Alkaline solubilization of hemicelluloses is usually mentioned as responsible for the disruption and breakage of hydrogen bonds. In addition, all these ester-linked substituents of the hemieellulose and other eell-wall components can be cleaved by alkali [18], This tends to increase hydrophilicity and hence solubility of the material. 

For the mutants with non-polar groups at residue 66 (alanine, leucine and phenylalanine) there is no correlation effect. The non-polar substitutions lead to breakage of hydrogen bonds between the 66th residue of the chromophore and glutamine-42 and glutamine-213. Formation of a new bond between the chromophore and the glutamate-215 is unlikely... 

The tan d peak at ca -125 °C is attributed to rotation of the methylene group (y relaxation), the peak at -39 °C is due to a small amount of water trapped by the polyamide and the peak at 60-75 °C represents molecular motion of the polyamide due to breakage of hydrogen bonds (a relaxation). 

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