" ???N(R8)CON(R9)(R10), where R10 is a hydrogen atom or an optionally substituted alkyl group, ???N(R8)CSN(R9)(R10) or ???N(R8)SO2N(R9)(R10); Alk1 is an optionally substituted aliphatic or heteroaliphatic chain; L1 is a covalent bond or a linker atom or group; Alk2 is a straight or branched alkylene chain; m is zero or an integer 1; R6 is a hydrogen atom or a methyl group; r is zero or the integer" . . . .