In Italian, an /s/ followed by another consonant. When used immediately before a masculine noun beginning with an impure s, thedefinite article changes fromil tolo in the singular and fromi togli in the plural, theindefinite article changes fromun touno, thepartitive article changes fromdei todegli, and someadjectives andpronouns also change form. This also happens before words beginning withgn,pn,ps,x,y, andz and before certain words starting withch that are derived from French.
S complicata on the Italian Wikipedia.Wikipediait