How to Minimize a Specific Part of a Molecule in SAMSON

Molecular modelers often face the challenge of optimizing specific sections of a molecular structure while leaving the rest untouched. This is particularly useful when refining one part of a molecule without altering the surrounding structure. SAMSON, the integrative molecular design platform, offers a straightforward solution using its interactive minimization tools. Here, we’ll guide you through minimizing a part of a molecule by selectively freezing certain atoms to maintain their positions.

Why Minimize Only a Part of a Molecule?

In molecular modeling, specific tasks such as refining an active site in a protein or optimizing a functional group in a catalyst may require selective minimization. Global minimization can disrupt regions outside the focus area, making targeted minimization crucial for precision. SAMSON enables you to interactively control which parts of the molecule are optimized and which are left intact. This flexibility enhances your workflow efficiency and ensures accurate results.

Steps to Minimize a Part of a Molecule

To minimize only a part of a molecule, you can use the freezing and unfreezing functions in SAMSON. Here is a step-by-step guide:

  1. Select the entire molecule, or leave the selection empty if you plan to freeze the entire system.
  2. Freeze the desired part of the structure by navigating to Edit > Freeze. Frozen atoms will remain fixed in place.
  3. Select the region or atoms within the molecule that you want to optimize. This can be a functional group, active site, or any other section of interest.
  4. Unfreeze only the selected atoms by clicking Edit > Unfreeze. This ensures that only these atoms are affected during the minimization process.
  5. Begin the minimization process by clicking Edit > Minimize. The minimizer will refine the geometry of the unfrozen section, leaving the frozen atoms untouched.
  6. Once you’ve achieved the desired optimization, stop the minimization by selecting Edit > Minimize again.
  7. Finally, unfreeze the entire molecule by selecting Edit > Unfreeze with no selection or the molecule selected, ensuring the system is restored for future manipulations.

You can seamlessly identify frozen atoms during the process: they are displayed with a dark blue overlay in the viewport, making it easier to visualize your setup.

Best Practices

Here are some tips for effective partial minimization:

  • Strategic Freezing: Use the freezing feature judiciously to refine only the areas of interest, saving computational time and resources.
  • Understand Connectivity: Keep in mind that when minimizing a selection, SAMSON considers the entire connected component associated with your selection. For instance, if you select an atom within a molecule, the minimizer automatically includes the entire molecule connected to that atom for optimization. To refine only a specific part, use the freeze/unfreeze workflow described above.
  • Review Preferences: Explore the “Minimize” settings in the Preferences panel to customize the minimization options according to your workflow.

Example Video

Need a visual example? Check out the video below to see partial minimization in action. Here, frozen atoms remain fixed, allowing the optimization of only the selected part of a molecule:

Learn More

To explore all features related to minimization in SAMSON, visit the full documentation at https://documentation.samson-connect.net/users/latest/minimizing/.

Note: SAMSON and all SAMSON Extensions are free for non-commercial use. You can get SAMSON at https://www.samson-connect.net.

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