  Polymeric single-chain nanoparticles (SCNPs) are soft nano-objects
synthesized by purely intramolecular cross-linking of single polymer chains. By
means of computer simulations, we investigate the conformational properties of
SCNPs as a function of the bending stiffness of their linear polymer
precursors. We investigate a broad range of characteristic ratios from the
fully flexible case to those typical of bulky synthetic polymers. Increasing
stiffness hinders bonding of groups separated by short contour distances and
increases looping over longer distances, leading to more compact nanoparticles
with a structure of highly interconnected loops. This feature is reflected in a
crossover in the scaling behaviour of several structural observables. The
scaling exponents change from those characteristic for Gaussian chains or rings
in $\theta$-solvents in the fully flexible limit, to values resembling fractal
or `crumpled' globular behaviour for very stiff SCNPs. We characterize domains
in the SCNPs. These are weakly deformable regions that can be seen as
disordered analogues of domains in disordered proteins. Increasing stiffness
leads to bigger and less deformable domains. Surprisingly, the scaling
behaviour of the domains is in all cases similar to that of Gaussian chains or
rings, irrespective of the stiffness and degree of cross-linking. It is the
spatial arrangement of the domains which determines the global structure of the
SCNP (sparse Gaussian-like object or crumpled globule). Since intramolecular
stiffness can be varied through the specific chemistry of the precursor or by
introducing bulky side groups in its backbone, our results propose a new
strategy to tune the global structure of SCNPs.
