Synthesis and SAM formation of water soluble functional carboxymethylcelluloses: thiostilfates and thioethers

Functional thiomethyl and thiosulfate derivatives of carboxymethylcellulose (CMC, DS = 0.9) were synthesized by nucleophilic displacement reactions. Alkylation of CMC by allyl glycidyl ether took mainly place at the primary positions of the cellulose backbone and yielded a 6-0-(3'-allyloxy-2'-hydroxypropyl)CMC 1 with a partial DS of 3'-allyloxy-2'-hydroxypropyl substituents DSallyl of up to 0.43. Addition of tetrathionate to the allyl groups gave rise to 6-0-(2,3-bis(thiosulfato)propoxy-2'-hydroxypropyl)-CMC 2. As the addition of tetrathionate was sluggish and incomplete, alternatively bromine was added and the resulting dibromide was substituted by thiosulfate. A 40% conversion of the allyl groups was achieved by this two-step procedure. On the other: hand, the addition of bromine to I in aqueous solution almost quantitatively yielded the bromohydrin derivative which was converted by displacement reaction with thiosulfate to 6-0-(2-hydroxy-3-thiosulfatopropoxy-2'-hydroxypropyl)TCMC 4. 6-Thiomethyl-6-deoxy-CMC 6 was synthesized by displacement reaction of 6-0-tosylcellulose with sodium methylsulfide and subsequent carboxymethylation of the cellulose backbone. A partial DS of thiomethyl substituents DSThM = 0.65 exclusively at the primary positions was obtained. All functional CMC derivatives, 2, 4, and 6 were readily available in gram quantities, rather stable and highly water soluble for pH > 3. On gold surfaces they form self-assembled monolayers (SAMs) with thicknesses of 1.2 to 2.4 nm as determined by surface plasmon resonance (SPR).