A compound comprising a substantially insoluble polysaccharide compound selected from cellulose and starch having a backbone comprising more than 20 sugar moieties wherein at least one of the sugar moieties is derivatised at one or more of its hydroxyl groups with a ligand bound to the sugar moiety by a sulphur atom wherein the ligand L is of formula: -S a (CR 1 R 2) n X wherein: independently in each occurrence, R 1 and R 2 are selected from hydrogen, an optionally substituted, linear or branched C 1-40 -alkyl, C 2-40 -alkenyl or C 2-40 -alkynyl group, an aryl and a C 1-40 -alkylaryl group; a is, independently in each occurrence from 0 to 2; n is independently an integer from 1 to 22: X is selected from: - CR 1 R 2 R 3; a divalent group linking two sugar moieties; - CR 1 R 2 (CR 1 R 2) n C(=W)R; - CR 1 R 2 (CR 1 Z) i Q h CHR 1 Z; -CR 1 R 2 (CR 1 Z) i Q h [(CHR 1) n W] t R 1; -(CR 1 Z) i Q h C(=W)R 1 -CR 1 R 2 (CR 1 Z) i Q h R 3 -OC(=W)R; wherein R is independently selected from H, R 1, -OR 1, -NR 1 R 2, -NHNR 1 R 2 and -SR 1; R 3 is an optionally substituted, linear or branched C 1-40 -alkyl, C 2-40 -alkenyl or C 2-40 -alkynyl group, an aryl and a C 1-40 -alkylaryl group; Q is independently selected from -C(=W 1)W 2 - and -W 2 C(=W 1)-; W, W 1 and W 2 are independently selected from oxygen, sulfur, -N(R 1)- and - N(NR 1 R 2); Z is independently selected from -OR 1, -NR 1 R 2 and -SR 1; h is independently 0 or 1; i is independently from 0 to 6; t is independently an integer from 1 to 20; -[C(=W)] h (W(C R 1 R 2) m) n Z wherein m is from 1 to 20; and -S a -Y wherein Y is a monovalent terminal group. independently in each occurrence, R 1 and R 2 are selected from hydrogen, an optionally substituted, linear or branched C 1-40 -alkyl, C 2-40 -alkenyl or C 2-40 -alkynyl group, an aryl and a C 1-40 -alkylaryl group; a is, independently in each occurrence from 0 to 2; n is independently an integer from 1 to 22: X is selected from: - CR 1 R 2 R 3; a divalent group linking two sugar moieties; - CR 1 R 2 (CR 1 R 2) n C(=W)R; - CR 1 R 2 (CR 1 Z) i Q h CHR 1 Z; -CR 1 R 2 (CR 1 Z) i Q h [(CHR 1) n W] t R 1; -(CR 1 Z) i Q h C(=W)R 1 -CR 1 R 2 (CR 1 Z) i Q h R 3 -OC(=W)R; wherein R is independently selected from H, R 1, -OR 1, -NR 1 R 2, -NHNR 1 R 2 and -SR 1; R 3 is an optionally substituted, linear or branched C 1-40 -alkyl, C 2-40 -alkenyl or C 2-40 -alkynyl group, an aryl and a C 1-40 -alkylaryl group; Q is independently selected from -C(=W 1)W 2 - and -W 2 C(=W 1)-; W, W 1 and W 2 are independently selected from oxygen, sulfur, -N(R 1)- and - N(NR 1 R 2); Z is independently selected from -OR 1, -NR 1 R 2 and -SR 1; h is independently 0 or 1; i is independently from 0 to 6; t is independently an integer from 1 to 20; -[C(=W)] h (W(C R 1 R 2) m) n Z wherein m is from 1 to 20; and -S a -Y wherein Y is a monovalent terminal group. R is independently selected from H, R 1, -OR 1, -NR 1 R 2, -NHNR 1 R 2 and -SR 1; R 3 is an optionally substituted, linear or branched C 1-40 -alkyl, C 2-40 -alkenyl or C 2-40 -alkynyl group, an aryl and a C 1-40 -alkylaryl group; Q is independently selected from -C(=W 1)W 2 - and -W 2 C(=W 1)-; W, W 1 and W 2 are independently selected from oxygen, sulfur, -N(R 1)- and - N(NR 1 R 2); Z is independently selected from -OR 1, -NR 1 R 2 and -SR 1; h is independently 0 or 1; i is independently from 0 to 6; t is independently an integer from 1 to 20;