Twist in chiral interaction between biological helices

Using an exact solution for the pair interaction potential, we show that lo ng, rigid, chiral molecules with helical surface charge patterns have a pre ferential interaxial angle similar to root RH/L, where L is the length of t he molecules, R is the closest distance between their axes, and H is the he lical pitch. Estimates based on this formula suggest a solution for the puz zle of small interaxial angles in alpha-helix bundles and in cholesteric ph ases of DNA.