  The study of light pseudoscalar quark-antiquark bound states in the
Dyson-Schwinger approach with the effective QCD coupling enhanced by the
interplay of the dimension 2 gluon condensate <A^2> and dimension 4 gluon
condensate <F^2>, is extended to the eta-eta' complex. We include the effects
of the gluon axial anomaly into the Dyson-Schwinger approach to mesons. The
calculated masses, mixing and two-photon decay widths of eta and eta' mesons
are in agreement with experiment. Also, in a model-independent way, we give the
modification of the Gell-Mann--Okubo and Schwinger nonet relations due to the
interplay of the gluon anomaly and SU(3) flavor symmetry breaking.
