| Abstract
| - Ab initio quantum calculations are applied to both the parallel and the antiparallel arrangements of the β-sheetsof proteins. The energies of the NH···O and CH···O hydrogen bonds present in the β-sheet are evaluatedseparately from one another by appropriate modifications of the model systems. The bond energies of thesetwo sorts of hydrogen bonds are found to be very nearly equal in the parallel β-sheet. The NH···O bonds arestronger than CH···O in the antiparallel geometry but only by a relatively small margin. Moreover, the formerNH···O bonds are weakened when placed next to one another, as occurs in the antiparallel β-sheet. As aresult, there is little energetic distinction between the NH···O and CH···O bonds in the full antiparallel β-sheet,just as in the parallel structure.
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