Hydrogen bonded sheets, staggered

Contrary to the tertiary structure of form I, in the case of triclinic form II, produced exclusively by SDG using polar solvents such as chloroform, dichloromethane, acetonitrile, and water, the 2-D sheets with hydrogen-bonded ribbons are staggered so that the nonpolar cleavage plane is not observed. To account for the observed polymorph selectivity, the authors propose that nonpolar solvents could stabilize this plane during grinding-induced cleavage (Scheme 1.4). 

As Pauling and Corey first pointed out [78, 79], adjacent hydrogen-bonded chains in a /i-sheet can occur in two arrangements, parallel and antiparallel (with respect to the direction of the chemical sequence along the chain). In addition, depending on the axial stagger between adjacent chains, the sheet can be pleated or rippled , the latter being possible only if all-L and all-D chains alternate in the sheet. (In practice, only PG can satisfy this requirement, since it has not as yet been possible to... 

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