A compound of formula (I) or a salt, solvate, or physiologically functional derivative thereof, wherein: m is an integer of from 2 to 8; n is an integer of from 2 to 5; with the proviso that m+n is 4 to 10; R.sup.4 and R.sup.5 are independently selected from hydrogen and C.sub.1-4alkyl with the proviso that the total number of carbon atoms in R.sup.4 and R.sup.5 not more than 4; R.sup.6 and R.sup.7 are independently selected from hydrogen and C.sub.1-4alkyl with the proviso that the total number of carbon atoms in R.sup.6 and R.sup.7 is not more than 4, and Ar.sup.1 is a group selected from (a), (b), (c) and (d). ##STR00001##