Synthesis of blockwise alkylated (1?4) linked trisaccharides as surfactants: influence of configuration of anomeric position on their surface activities Atsushi Nakagawa, Hiroshi Kamitakahara ⇑ , Toshiyuki Takano Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan article info Article history: Received 4 February 2011 Received in revised form 18 April 2011 Accepted 26 April 2011 Available online 4 May 2011 Keywords: Nonionic surfactant Methylcellulose Diblockco-oligomer Surface tension Surfactant mixtures abstract New carbohydrate-based surfactants consisting of hydrophilic cellobiosyl and hydrophobic glucosyl res- idues, methyl b-D-glucopyranosyl-(1?4)-a-D-glucopyranosyl-(1?4)-2,3,6-tri-O-methyl-a-D-glucopyran- oside 1 (GbGaMa, G: glucopyranosyl residue, a and b: a-(1?4)- and b-(1?4) glycosidic bonds, M: methyl group), 2 (G b G b M a ), 3 (G b G a M b ), 4 (G b G b M b ), 5 (G b G a E a , E: ethyl group), 6 (G b G b E a ), 7 (G b G a E b ), 8 (G b G b E b ) and eight a-and b-glycoside mixtures (a mixture of 1 and 2: 1/2 = 62/38 (9), 32/68 (10); a mix- ture of 3 and 4: 3/4 = 69/31 (11), 32/68 (12); a mixture of 5 and 6: 5/6 = 62/38 (13), 33/67 (14); a mixture of 7 and 8: 7/8 = 59/41 (15), 29/71 (16)) were synthesized via combined methods consisting of acid-cat- alyzed alcoholysis of cellulose ethers and glycosylation of phenyl thio-cellobioside derivatives. Their sur- face activities in aqueous solution depended on their chemical structures: a- or b-(1?4) linkage between hydrophilic cellobiosyl and hydrophobic glucosyl blocks, methyl or ethyl groups of hydrophobic glucosyl block, and a- or b-linked ether group at the C-1 of hydrophobic glucosyl block. The mixing effect of a- and b-glycosides on surface activities was also investigated. As a result, ethyl b-D-glucopyranosyl-(1?4)-a-D- glucopyranosyl-(1?4)-2,3,6-tri-O-ethyl-b-D-glucopyranoside 7 (G b G a E b ) had the highest surface activity, and its critical micellar concentration (CMC) and c CMC (surface tension at CMC) values of compound 7 were 0.5 mM (ca. 0.03 wt %) and 34.5 mN/m, respectively. The surface tensions of a- and b-glycoside mix- tures except for compounds 9 and 10 were almost equal to those of pure compounds. The syntheses of the mixtures of a- and b-glycosides without purification process are easier than those of pure com- pounds. Thus, the mixtures should be more practical compounds for industrial use as a surfactant. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Nonionic carbohydrate-based surfactants such as alkylpolyglu- cosides and polysaccharide derivatives capable of being produced from renewable resources have recently been receiving attention because they show good surface activities. 1 It is well known that not only the kind of hydrophilic saccharide moiety but also the length of the hydrophobic chain influences the physicochemical properties, such as surface activities. 2 In addition, the properties of the aqueous solutions of nonionic carbohydrate-based surfac- tants are influenced by a- or b-(1?4) linkage between hydrophilic and hydrophobic moieties. 3 Carbohydrate-based surfactants hav- ing different lengths of sugar chain and hydrocarbon chain have been synthesized to gain detailed information about the relation- ships between the chemical structure and their properties and to obtain surfactants having good surface activities. 4–8 The mixing ef- fect of surfactants on their physicochemical properties has also been reported since surfactants are used in formulations contain- ing a mixture of different compounds. 9–12 The practical utilization of mixed surfactants is based on economical as well as synergetic reasons. 13 The general carbohydrate-based surfactants synthesized so far consist of sugar chains as hydrophilic block and hydrocarbon chains as hydrophobic block. We have recently reported a novel class of carbohydrate-based surfactants consisting of only sugar chains in both hydrophilic and hydrophobic blocks. As a model of methylcellulose (MC), a polydisperse mixture of diblock co-oligo- mers of tri-O-methylated and unmodified cello-oligosaccharides were synthesized, and their properties in aqueous solution were investigated. 14,15 Moreover, monodisperse diblock-trimer, -penta- mer, and -hexamer, 16 and ABA- and BAB-triblock hexamers of tri-O-methylated and unmodified cello-oligosaccharides were pre- pared to investigate relationships between their chemical struc- ture and solubility. 17 These reports suggest that monodisperse model compounds with blocky structure along molecular chain have higher surface activity than MC. Namely, amphiphilic diblock trisaccharide derivatives should have a potential to act as high-per- formance detergents. Thus, diblock co-trimers of tri-O-alkylated and unmodified oli- gosaccharides were designed to obtain surfactants with higher sur- face activity compared to MC via novel synthetic route. For the 0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2011.04.034 ⇑ Corresponding author. Tel.: +81 75 753 6255; fax: +81 75 753 6300. E-mail address: hkamitan@kais.kyoto-u.ac.jp (H. Kamitakahara). Carbohydrate Research 346 (2011) 1671–1683 Contents lists available at ScienceDirect Carbohydrate Research journal homepage: www.elsevier.com/locate/carres