def isotopeMaxBD(isotope):
    """Setting the theoretical max BD shift of an isotope 
    (if 100% incorporation).

    Parameters
    ----------
    isotope : str
        name of isotope

    Returns
    -------
    float : max BD value
    """
    psblIsotopes = {'13C' : 0.036,
                    '15N' : 0.016}
    try:
        return psblIsotopes[isotope.upper()]
    except KeyError:
        raise KeyError('Isotope "{}" not supported.'.format(isotope))