Structural characterization of cold extracted fraction of soluble sulfated polysaccharide from red seaweed Gracilaria birdiae Jeanny S. Maciel a , Luciano S. Chaves b , Bartolomeu W.S. Souza b , Da ´rlio I.A. Teixeira c , Ana L.P. Freitas b , Judith P.A. Feitosa a , Regina C.M. de Paula a, * a Departamento de Quı ´mica Orga ˆnica e Inorga ˆnica, Universidade Federal do Ceara ´ , CP 12.200, CEP 60455-760, Fortaleza, Ceara ´ , Brazil b Departamento de Bioquı ´mica e Biologia Molecular, Universidade Federal do Ceara ´ , CP 6020, CEP 60455-760, Fortaleza, Ceara ´ , Brazil c Centro de Cie ˆncias da Sau ´ de, Universidade de Fortaleza, Fortaleza, Ceara ´ , Brazil Received 22 March 2007; received in revised form 14 June 2007; accepted 29 June 2007 Available online 20 August 2007 Abstract Water soluble polysaccharide from Gracilaria birdiae cultivated along the northeast coast of Brazil was characterized by infrared (FT- IR) and nuclear magnetic resonance (NMR) spectroscopy. The composition of the polysaccharide in wt% was determined as: b-D-galp (50.3%), 3,6-anhydro-a-L-galp (40.5%) and -a-L-galp-6 sulfate (9.2%). The ratio of L/D units (b-D-galp units and 3,6-anhydro-a-L- galp + a-L-galp-6 sulfate) is that of an ideal agarose. The sulfate content calculated by S% accounts for 6.4%. 1D and 2D NMR techniques were employed in order to assign the spin system of polysaccharide without partial degradation. The structure is composed of fi 4-3,6- anhydro-a-L-galp (1 fi 3)b-D-galp 1 fi segments, with the possibility of a a-L-galp unit substituted at the 6-position by sulfate ester. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Gracilaria birdiae; Polysaccharide; NMR spectroscopy; Agarose; Sulfate ester 1. Introduction The genus Gracilaria of red seaweed is distributed throughout the tropical regions of the world. Algae from this genus are important producers of agar (Marinho-Sori- ano & Bourret, 2005; Plastino, Guimara ˜es, Matioli, & Oli- veira, 1999) and can be found as wild and cultivated species (Critchley, 1993). Gracilaria birdiae is an economically important marine red alga exploited for the production of agar in Brazil (Plastino, Ursi, & Fujii, 2004). It was first described by Plastino and Oliveira (2002) based on critical comparison with several putative species. Ursi, Pedersen, Plastino, and Snoeijs (2003) studied photosynthesis, respiration and its photoprotective carotenoids. Pigment characteriza- tion and growth of a rare strain of G. birdiae was reported by Plastino et al. (2004). The species is found along the Brazilian coast from Ceara ´ State to Espirito Santo State (Plastino & Oliveira, 2002). It has been reported that G. birdiae cultivated under field conditions in Rio Grande do Norte State (Brazil) over a 6-month period produced biomass ranging from 900 to 3537 g/m 2 (Marinho-Soriano, Moreira, & Carneiro, 2006). To the best of our knowledge, this is the first publication on the chemical characterization of the polysaccharide present in this seaweed. Polysaccharides from the Gracilaria genus are composed mainly of the alternating 3-linked-b-D-galactopyranose unit (G) and the 4-linked-3,6-anhydro-a-L-galactopyranose unit (LA) (Fig. 1). The G unit can be substituted by either a methyl or a sulfate ester groups (Andriamanantoanina, Chambat, & Rinaudo, 2007; Freile-Pelegrı ´n & Murano, 2005; Lahaye & Yaphe, 1988; Melo, Feitosa, Freitas, & de Paula, 2002; Mazumder et al., 2002; Valiente, Fernan- dez, Perez, Marquina, & Velez, 1992). Sulfate groups can also be found in the a-L-galactopyranose unit (L), the bio- genic precursor of the 3,6-anhydro-a-L-galactopyranose unit (LA) (Rees, 1961). 0144-8617/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2007.06.026 * Corresponding author. Tel.: +55 85 33669973; fax: +55 85 33669978. E-mail address: rpaula@dqoi.ufc.br (R.C.M. de Paula). www.elsevier.com/locate/carbpol Available online at www.sciencedirect.com Carbohydrate Polymers 71 (2008) 559–565