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A polypeptide chain can adopt many conformations. Yet, the sequence of its amino acid residues directs folding to a particular native state. 1 The loss of conformational entropy associated with folding destabilizes the native state. This destabilization is overcome by the hydrophobic effect, hydrogen bonds, other noncovalent interactions, and disulfide bonds. 2 We have identified another force that can contribute to the conformational stability of a protein.

The structure and reactivity of an organic molecule can rely on the stereochemistry of its electron pairs, bonded or nonbonded. 3 Such stereoelectronic effects, which arise from the mixing of an electron pair with the antibonding σ* of an adjacent polar bond (CX, where X) N or O), endow nucleic acids and carbohydrates with conformational stability. 4 For example, the multiple gauche effects (XCCX) arising from a 2′ oxygen distinguish RNA ‚RNA and RNA ‚DNA …