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#   nucleic acid base pairs. Some of the base pairs may not be standard. But they appear in some structures
  monomers A T label A:T
  bond atom N6 A atom O4 T value 2.94 sigma 0.15
  bond atom N1 A atom N3 T value 2.84 sigma 0.1
  chiral atom N1 A atom C2 A atom C6 A atom N3 T value 0.0 sigma 0.5
  chiral atom N3 T atom C2 T atom C4 T atom N1 A value 0.0 sigma 0.5
  torsion atom C2 A atom N1 A atom N3 T atom C4 T value 180.0 sigma 10.0

  monomers DA DT label DA:DT
  bond atom N6 DA atom O4 DT value 2.94 sigma 0.15
  bond atom N1 DA atom N3 DT value 2.84 sigma 0.1
  chiral atom N1 DA atom C2 DA atom C6 DA atom N3 DT value 0.0 sigma 0.5
  chiral atom N3 DT atom C2 DT atom C4 DT atom N1 DA value 0.0 sigma 0.5
  torsion atom C2 DA atom N1 DA atom N3 DT atom C4 DT value 180.0 sigma 10.0

  monomers A U label A:U
  bond atom N6 A atom O4 U value 2.94 sigma 0.15
  bond atom N1 A atom N3 U value 2.84 sigma 0.1
  chiral atom N1 A atom C2 A atom C6 A atom N3 U value 0.0 sigma 0.5
  chiral atom N3 U atom C2 U atom C4 T atom N1 A value 0.0 sigma 0.5
  torsion atom C2 A atom N1 A atom N3 U atom C4 U value 180.0 sigma 10.0


  monomers DA DU label DA:DU
  bond atom N6 DA atom O4 DU value 2.94 sigma 0.15
  bond atom N1 DA atom N3 DU value 2.84 sigma 0.1
  chiral atom N1 DA atom C2 DA atom C6 DA atom N3 DU value 0.0 sigma 0.5
  chiral atom N3 DU atom C2 DU atom C4 DT atom N1 DA value 0.0 sigma 0.5
  torsion atom C2 DA atom N1 DA atom N3 DU atom C4 DU value 180.0 sigma 10.0

  monomers C G   label C:G
  bond atom N4 C atom O6 G value 2.91 sigma 0.15
  bond atom N3 C atom N1 G value 2.95 sigma 0.1
  bond atom O2 C atom N2 G value 2.86 sigma 0.15
  chiral atom N1 G atom C6 G atom C2 G atom N3 C value 0.0 sigma 0.5
  chiral atom N3 C atom C4 C atom C2 C atom N1 G value 0.0 sigma 0.5
  torsion atom C4 C atom N3 C atom N1 G atom C2 G value 180.0 sigma 10.0

  monomers DC DG  label DC:DG
  bond atom N4 DC atom O6 DG value 2.8 sigma 0.1
  bond atom N3 DC atom N1 DG value 2.8 sigma 0.1
  bond atom O2 DC atom N2 DG value 2.8 sigma 0.1
  #angle atom C2 DG atom N1 DG atom N3 DC value 120.0 sigma 5.0
  chiral atom N1 DG atom C6 DG atom C2 DG atom N3 DC value 0.0 sigma 0.5
  chiral atom N3 DC atom C4 DC atom C2 DC atom N1 DG value 0.0 sigma 0.5
  torsion atom C4 DC atom N3 DC atom N1 DG atom C2 DG value 180.0 sigma 10.0
