  Part I is devoted to the extraction of the QCD coupling from a bound state
approach at low energy scales, where unphysical singularities make the
RG-improved pQCD useless. Theoretical results on the meson spectrum based on a
Bethe-Salpeter formalism adjusted for QCD have been exploited for the
determination of experimental values of \alpha_s below 1GeV by comparison with
the data. Results quantitatively confirm the recently developed Analytic
Perturbation Theory approach to IR phenomena down to 200 MeV. Below this scale
the extracted values give a hint about the vanishing of the QCD coupling as Q^2
goes to zero.
  In part II the possibility of inferring the spin-dependent gluon distribution
from scaling violations is addressed by performing a NLO analysis of inclusive
DIS data in pQCD. In addition, this work presents a phenomenological study of
open-charm photoproduction in the polarized case, which is tailored to the
COMPASS experiment in view of upcoming data. It is shown that current inclusive
data allow a reliable determination of the gluon first moment, whereas the
x-shape is significantly affected by the assumed functional form. On the other
hand, studies of charm pseudo-data reveal that the open-charm approach should
be capable to reduce the bias induced by the choice of input densities, and to
pin down the x-shape of the gluon polarization.
