Table 2. Hydrogen bonds in HBH-19 at R1 = 0.102.
| Type | Donor | Acceptor | D—A, Å | H—A, Å | Angle C=O···N(or O),° |
|---|---|---|---|---|---|
| Head-to-tail | N1 | 018* | 2.947 | 2.12 | 155 |
| Peptide—water | N2 | W1 | 2.914 | 2.03 | |
| 4→1 | N3 | 00 | 3.029 | 2.24 | 132 |
| 4→1 | N4 | 01 | 3.000 | 2.54† | 119 |
| 5→1 | N5 | 01 | 2.943 | 2.03 | 170 |
| 5→1 | N6 | 02 | 2.958 | 2.09 | 148 |
| 5→1 | N7 | 03 | 3.020 | 2.13 | 155 |
| 5→1 | N8 | 04 | 3.022 | 2.14 | 158 |
| 5→1 | N9 | 05 | 2.865 | 1.98 | 159 |
| 5→1 | N10 | 06 | 2.967 | 2.11 | 155 |
| 5→1 | N11 | 07 | 3.093 | 2.22 | 163 |
| 5→1 | N12 | 08 | 2.975 | 2.10 | 161 |
| 5→1 | N13 | 09 | 3.007 | 2.12 | 157 |
| 5→1 | N14 | 010 | 2.986 | 2.09 | 153 |
| 5→1 | N15 | 011 | 2.895 | 2.05 | 151 |
| 5→1 | N16 | 012 | 2.909 | 2.03 | 156 |
| 5→1 | N17 | 013 | 3.022 | 2.15 | 160 |
| 5→1 | N18 | 014 | 2.998 | 2.22 | 161 |
| 4→1 | N19 | 016 | 3.287‡ | 2.66‡ | 108 |
| Water—peptide | W1 | 018* | 2.914 | ||
| W1 | W2§ | 3.097 | |||
| W2 | 017 | 2.780 | |||
| W2 | 017¶ | 2.590 | |||
| W3 | O0 | 2.856 | |||
| W3 | O15∥ | 2.940 | |||
| N4 | W3 | 3.084 | 2.44† |
*
Symmetry equivalent x, y, -1 + z
†
The donor N4H appears to make a bifurcated hydrogen bond to W3 and O1 with long H to acceptor distances. O1 is also an acceptor for N5H, where normal D—A and H—A distances prevail.
‡
The final hydrogen bond in the helix, N19H···O16, has long distances for D—A and H—A. There are no other possibilities for hydrogen bonds with N19H.
§
Symmetry equivalent 1-x, y, 1 -z.
¶
Symmetry equivalent 1-x, y, 2-z.
∥
Symmetry equivalent 0.5-x, 0.5 + y, 1 -z.