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Table 2 Activation barriers (E A) and reaction heats (E R) for transformation from canonical (P B ) to zwitterionic (P C ) proline with presence of water molecules

From: Stabilization of zwitterionic versus canonical proline by water molecules

Reaction paths

E A

E R

One water molecule

 P B 1W III  → [TS1W III–I ] → P C 1W I

6.7

6.1

Two water molecules

 P B 2W II  → [TS2W II–I ] → P C 2W I

4.2

2.0

 P B 2W I  → [TS2W I–II ] → P C 2W II

6.1

4.3

 P B 2W VI  → [TS2W VI–III ] → P C 2W III

4.9

3.2

 P B 2W III  → [TS2W III–IV ] → P C 2W IV

6.4

6.0

 P B 2W VII  → [TS2W VII–V ] → P C 2W V

6.2

3.8

 P B 2W V  → [TS2W V–VI ] → P C 2W VI

5.8

5.2

 P B 2W IV  → [TS2W IV–VII ] → P C 2W VII

6.7

6.5

Three water molecules

 P B 3W II  → [TS3W II–I ] → P C 3W I

3.8

0.7

 P B 3W I  → [TS3W I–II ]  → P C 3W II

4.3

1.9

 P B 3W III  → [TS3W III–III ]  → P C 3W III

6.3

−1.1

 P B 3W III  → [TS3W III–IV ]  → P C 3W IV

8.6

0.7

 P B 3W IV  → [TS3W IV–V ]  → P C 3W V

2.6

−1.1

Four water molecules

 P B 4W I  → [TS4W I–I ]  → P C 4W I

1.9

−2.6

 P B 4W II  → [TS4W II–I ]  → P C 4W I

5.8

−3.4

 P B 4W II  → [TS4W II–III ]  → P C 4W III

5.3

−2.4

 P B 4W III  → [TS4W III–IV ]  → P C 4W IV

2.7

−2.1

Five water molecules

 P B 5W I  → [TS5W I–I ]  → P C 5W I

4.2

−6.0

 P B 5W II  → [TS5W II–II ]  → P C 5W II

4.8

−6.4

  1. Energy units in kcal/mol