Disruption of H-bonding

Interpretation of this extensive information is not an easy task, nor are all the features completely understood. Nevertheless some patterns can be discerned. Thus the exothermic mixing in water-rich mixtures can be largely attributed to enhancement of water-water interactions by the added co-solvent, together with a contribution from intercomponent hydrogen bonding (cf. acetone + chloroform, Fig. 27). The endothermic mixing at high x2 is attributed to disruption of H-bonds (cf. methyl alcohol + carbon tetrachloride,... 

Gautieri A, Vesentini S, Redaelli A, Buehler MJ (2012) Osteogenesis imperfecta mutations lead to local tropocollagen unfolding and disruption of H-bond network. RSC Adv... 

Ans. (a) Miscible forces of attraction between like and unlike molecules are about the same, (b) Not miscible mixing would disrupt the strong H-bonds in water there is no especially strong attraction between unlike molecules to compensate, (c) Miscible both components have hydrogen bonding. Breaking of H-bonds in water is compensated for by the formation of H-bonds between unlike molecules. 

Also, Schellman s work is pertinent (1809). From studies on heats of dilution of urea in water he concludes that the N—H 0=C bond has an enthalpy of 1.5 kcal/mole in aqueous solution, and he carries this value over to proteins and polypeptides. Among these complicated materials he is forced to approximate—but he deduces relations which show the stability of helices and sheets in terms of H bond enthalpy and configurational entropy. From this he draws the important conclusion that H bonds, taken by themselves, give a marginal stability to ordered structures which may be enhanced or disrupted by the interactions of the side chains. Schellman ends his papers with a discussion of experimental tests needed to eliminate some of the assumptions in his theoretical analysis. 

The problem here is that in order to dissolve in water a non-polar molecule must disrupt a series of H-bonds and no new bonds of equal strength are substituted. 

There are various concepts about the aluminum silicates dissolution mechanism. Relatively recently a low rate of their dissolution was explained by inner diffuse regime. Currently more substantiated appears hydrolysis with the formation of activated complexes. According to this theory, the dissolution begins with the exchange of alkaline, alkaline-earth and other metals on the mineral surface of H+ ions from the solution (see Figure 2.26). At that, metals in any conditions are removed in certain sequence. In case of the presence of iron and other metals with variable oxidation degree the process may be accompanied with redox reaction. Hydrolysis is a critical reaction in the dissolution of aluminum silicates. It results in the formation on the surface of a very thin layer of activated complexes in Na, K, Ca, Mg, Al and enriched with H+, H O or H O. The composition and thickness of this weakened layer depend on the solution pH. These activated complexes at disruption of weakened bonds with mineral are torn away and pass into solution. For some minerals (quartz, olivine, etc.) the disruption of one inner bond is sufficient, for some others, two and more. The very formation of activated complexes is reversible but their destruction and removal from the mineral are irreversible. 

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