We have characterized the conformational ensembles of polyglutamine Qn peptides of various lengths n (ranging from 6 to 40), both with and without the presence of a C-terminal polyproline hexapeptide. For this, we used state-of-the-art molecular dynamics simulations combined with a novel statistical analysis to characterize the various properties of the backbone dihedral angles and secondary structural motifs of the glutamine residues. For Q40 (i.e., just above the pathological length xe2x89x8336 for Huntingtons disease), the equilibrium conformations of the monomer consist primarily of disordered, compact structures with non-negligible xcexb1-helical and turn content. We also observed a relatively small population of extended structures suitable for forming aggregates including xcexb2- and xcexb1-strands, and xcexb2- and xcexb1-hairpins. Most importantly, for Q40 we find that there exists a long-range correlation (ranging for at least 20 residues) among the backbone dihedral angles of the Q residues. For polyglutamine peptides below the pathological length, the population of the extended strands and hairpins is considerably smaller, and the correlations are short-range (at most 5 residues apart). Adding a C-terminal hexaproline to Q40 suppresses both the population of these rare motifs and the long-range correlation of the dihedral angles. We argue that the long-range correlation of the polyglutamine homopeptide, along with the presence of these rare motifs, could be responsible for its aggregation phenomena.