?-pure derived categories of a Grothendieck category

Let ?? be a Grothendieck category, ? an infinite regular cardinal. We investigate the ?-purity of ??, and the ?-pure acyclic complexes in C(??). Using the ?-presentable objects, we verify that the class of ?-pure acyclic complexes is a thick subcategory of homotopy category. Then we construct ?-pure derived category naturally. Through some specific constructions, we get that bounded above ?-pure derived categories coincide with specific homotopy categories.