Tips for 2D to 3D conversion

3D Structure Generation and Adjustment

Moleditpy provides features for generating 3D structures from 2D structural formulas and for subsequently refining those structures.

1. 3D Structure Generation Methods

MoleditPy supports multiple external libraries (backends) to generate 3D structures. The choice of library impacts the processing speed and the accuracy of the resulting structure.

Overview

Library	Processing Speed	Structural Accuracy	Key Features
RDKit	Slower (esp. for strained molecules)	Relatively Accurate	Generates chemically plausible initial structures based on Distance Geometry.
Open Babel	Very Fast	Requires Re-adjustment	Generates coordinates rapidly, but requires optimization with a force field.

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🧪 RDKit

RDKit is a powerful cheminformatics library for generating high-quality 3D coordinates.

• Pros:
  • Excels at generating relatively accurate conformations that are chemically plausible, using methods like Distance Geometry.
• Cons:
  • It is computationally more expensive, meaning it tends to be slower when generating 3D structures, especially for large molecules or complex ring systems.

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⚡ Open Babel

Open Babel is renowned for its high-speed chemical format conversion and structure generation.

• Pros:
  • Generates 3D coordinates very quickly using rule-based methods and proprietary algorithms. It is well-suited for processing large batches of data or for quick previews.
• Cons:
  • The immediately generated 3D structure is not necessarily the most energetically stable conformation.
  • Therefore, "re-adjustment" via structure optimization (using a force field like MMFF94 or UFF) is essential afterward to obtain a more realistic structure.

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2. Post-Generation Structure Adjustment

After generating a 3D structure algorithmically, or after modifying it manually, structural adjustments may be necessary.

👐 Manual Adjustment (3D Drag)

This feature allows the user to intuitively modify the 3D structure using mouse operations.

• How to use: Select a specific atom in the 3D viewer and drag it with the mouse to freely change its position (and that of connected parts).
• Primary Use Cases:
  • When you want to change a specific dihedral angle to a desired value.
  • When you want to intentionally create a specific conformation (e.g., a high-energy state) that is difficult to achieve via automated algorithms.
• Caution:
  • Manual dragging forcibly moves atoms without regard for chemical plausibility (i.e., standard bond lengths and angles).
  • As a result, the structure after a drag operation is often in a distorted or strained state, with unnaturally stretched bonds or atoms that are too close together.

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💻 Re-optimization (Cleanup)

This feature automatically corrects distorted structures (from manual dragging) or initial structures (from fast generation like Open Babel) into a chemically more plausible state.

• Purpose:
  • To correct unnatural bond lengths and angles to their standard values.
  • To resolve unnecessary atomic clashes (atoms being too close).
  • To adjust the structure so that the molecule's overall energy approaches a more stable state.
• When to Run:
  1. After manual 3D dragging: This is essential to resolve the structural strain introduced by the drag operation.
  2. After generating a 3D structure with Open Babel: This is strongly recommended to obtain an energetically stable and realistic structure.
• Mechanism:
  • It uses a Force Field (such as MMFF94 or UFF) to recalculate the coordinates of each atom, minimizing the molecule's overall potential energy. This process relieves strain and moves the structure toward a stable conformation.