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Title: The structure of j/i-hybrid carrageenans II. Coil–helix transition as a function of chain composition
Authors: Van de Velde, Fred 
Antipova, Anna S. 
Rollema, Harry S. 
Burova, Tatiana V. 
Grinberg, Nataliya V. 
Pereira, Leonel 
Gilsenan, Paula M. 
Tromp, R. Hans 
Rudolph, Brian 
Grinberg, Valerij Ya. 
Keywords: Carrageenan; Kappa/iota-Hybrids; Polysaccharides; Coil-to-helix transition; Structural analysis; Differential scanning calorimetry
Issue Date: 2-May-2005
Citation: VAN DE VELDE, Fred [et al.] - The structure of j/i-hybrid carrageenans II. Coil–helix transition as a function of chain composition. "Carbohydrate Research". ISSN 0008-6215. Vol. 340 nº 6 (2005) 1113-1129
Serial title, monograph or event: Carbohydrate Research
Volume: 340
Issue: 6
Abstract: This paper describes the effect of the k/i-ratio on the physical properties of k/i-hybrid carrageenans (synonyms: kappa-2, k-2, weak kappa, weak gelling kappa). To this end, a series of k/i-hybrid carrageenans ranging from almost homopolymeric k-carrageenan (98 mol% k-units) to almost homopolymeric-carrageenan (99 mol% i-units) have been extracted from selected species of marine red algae (Rhodophyta). The k/i-ratio of these k/i-hybrids was determined by NMR spectroscopy. Their rheological properties were determined by small deformation oscillatory rheology. The gel strength (storage modulus, G0) of the j/i-hybrids decreases with decreasing j-content. On the other hand, the gelation temperature of the k-rich k/i-hybrids is independent of their composition. This allows one to control the gel strength independent of the gelation or melting temperature. The conformational order–disorder transition of the k/i-hybrids was studied using optical rotation and high-sensitivity differential scanning calorimetry. High-sensitivity DSC showed that the total transition enthalpy of the k/i-hybrids goes through a minimum at 60 mol% k-units, whereas for the mixture of j- and i-carrageenan, the total transition enthalpy is a linear function of the composition. With respect to the ordering capability, the k/i-hybrid carrageenans seem to behave as random block copolymers with length sequence distributions truncated from the side of the small lengths. Intrinsic thermodynamic properties (e.g., transition temperature and enthalpy) of k- and i-sequences in these copolymers are close to those of their parent homopolymers. The critical sequence length for k-sequences is 2-fold of that for i-sequences.
ISSN: 0008-6215
DOI: 10.1016/j.carres.2005.02.015
Rights: openAccess
Appears in Collections:FCTUC Ciências da Vida - Artigos em Revistas Internacionais

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