When manipulating molecular structures, precision matters. Whether you’re refining a docking pose, designing a supramolecular assembly, or preparing a structure for visualization or simulation, having better control over how parts of your system are translated and rotated can save time and reduce errors.
One frequent challenge molecular modelers run into is the need to rotate parts of molecules accurately—for example, rotating a ligand conformation 30 degrees, or positioning a copy of a substructure around an axis at even intervals. Instead of relying on an approximate mouse drag, would you prefer discrete steps like 10°, 15°, or 30°? That’s where SAMSON’s rotation snapping comes in.
What is Rotation Snapping?
Rotation snapping in SAMSON allows you to constrain rotation angles to increments you specify (e.g. 10°, 45°). This helps in building symmetric assemblies, aligning fragments neatly, or designing repetitive motifs in a predictable way.
It works with both the Local Move Editor and the Global Move Editor, providing flexibility depending on whether you want to rotate around the object’s local axes or the global XYZ reference frame.
How to Enable Snapped Rotations
- Open SAMSON and select the atoms or objects you wish to rotate.
- Enable the Local Move Editor (M) or Global Move Editor (K).
- Click the top-left corner of the viewport (editor quick access menu) and set your desired snapping angle (e.g. 10°).
- Drag on the rotation widget (curved arrow) to start rotating. Your rotation will now snap to defined intervals.
The following animation shows an example of using snapping to rotate atoms using the local move editor:
Using Pivots for Structured Assembly
When working with assemblies where you need to copy and rotate fragments around a specific atom or point (pivot), SAMSON lets you define that rotation center during manipulation. This is particularly useful in tasks such as constructing ring-like structures or designing symmetric nanoassemblies.
Check out the example below, where multiple rotated instances of a molecule are created precisely by rotating around a pivot atom using active snapping:
Why It Matters
Rotation snapping simplifies repetitive alignment and enhances reproducibility. Instead of guessing angle values during manual adjustment, you can rely on snapping to create clean, intentional rotations. This is particularly valuable if you’re preparing visualizations, assembling functionalized systems, or comparing multiple orientations for interaction studies.
Rotation snapping also enables systematic exploration of conformations, offering greater reliability if you’re transitioning from modeling to simulation or analysis.
Need Translation Snapping Too?
Just like rotations, translations can also be snapped to fixed intervals (e.g. 0.5Å), helping you align structures with atomic-scale precision.
To learn more about precision transformations in SAMSON, including advanced manipulation with the Local and Global Move Editors, visit the official documentation.
SAMSON and all SAMSON Extensions are free for non-commercial use. You can download SAMSON at samson-connect.net.