Clathrate hydrates occurrence

Hydrogen-bonding patterns in crystal structures of the cydodextrins and the simpler carbohydrates differ. The infinite, homodromic chains are common both in the low molecular-weight carbohydrates and in the cydodextrins. The principal difference lies in the frequency of occurrence of the homodromic and antidromic cycles, which are common in the cyclodextrin crystal structures and rare in the mono-, di-, and trisaccharides. The cyclic patterns are the rule in the clathrate hydrates and in the ices. From this point of view, the hydrogen-bonding patterns of the hydrated cydodextrins lie between those of the simpler hydrated carbohydrates and those of the hydrate inclusion compounds, discussed in Part IV, Chapter 21. 

Miller, S. L. (1974). The Nature and Occurrence of Clathrate Hydrates. In Natural Gases in Marine Sediments (I. R. Kaplan, Ed.). Plenum Press, New York. 

Another confirmation of the close packing principle can be found in the rather common occurrence [17] of the formation of clathrates, hydrates, and solvates whenever the shape of the crystallizing molecule is too complex to allow efficient self-recognition with total space occupation, highly mobile solvent molecules slip in between and are incorporated in the crystal structure as space fillers. Incidentally, no numerical indicator of the ability or even the tendency of a given molecule to form solvate crystals has ever been found, a confirmation of the difficulties encountered in the definition of numerical descriptors of molecular shape. 

Davidson, D. Gas hydrates as clathrate ices. In Natural Gas Hydrates—Properties, Occurrence and Recovery, Cox, J., Ed. Butterworth Woburn, MA, 1983 I-I6. 

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