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Calculates the Molecular Weight, to the appropriate significant digits, from a string of an arbitrary chemical formula, a protein sequence of one- or three-letter codes, or chemical common names that are recognized by PubChem.

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Calculating the Molecular Weight from a Chemical Formula, Common Name, or Protein Sequence

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The ChemW library contains three packages, each with a distinct use-case, which are detailed in the following sections.

The ChemMW package parses any chemical formula that adheres to chemical conventions – which can consist of any combination of elements and decimal stoichiometry – and calculates the MW of the chemical formula with the most accurate elemental masses that are available, per the chemicals module. The MW is precisely constrained to the significant digits of constituent elements in the chemical formula.

The Proteins and PHREEQdg packages are applications of the ChemMW package. The Proteins package returns the mass of a protein by either parsing a string of a protein sequence, or by parsing a FASTA-formatted file. This is applied in the Codons module for genome-scale biology and bioengineering. The PHREEQdb package parses a PHREEQ database, calculates the MW of each mineral in the database, and exports a JSON of all mineral masses from the database. This is pivotally applied in the PHREEQC databases of the ROSSpy module for reverse osmosis research.

The ChemW library is offered with the MIT License. Examples of the module are available in the examples directory of the ChemW GitHub repository. Please submit errors or inaccuracies as GitHub issues so that they may be resolved.


The following command installs ChemW in a command prompt/terminal environment:

pip install chemw

The full documentation is available on ReadTheDocs.

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