def unknown_pairs_present(model):
  """
  Test if PDB file contains unknown type pairs

  Parameters:
    model (obj): model object

  Returns:
    (bool): True if PDB file contains unknown type pairs
  """
  grm = model.get_restraints_manager()
  sites_cart = model.get_sites_cart()
  site_labels = model.get_xray_structure.scatterers().extract_labels()
  pp= grm.pair_proxies(sites_cart=sites_cart,site_labels=site_labels)
  return (pp.nonbonded_proxies.n_unknown_nonbonded_type_pairs != 0)