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C(6)-Oxidation and C(5)-Epimerization of Locust Bean Galactomannan Studied by High Field NMR and Circular Dichroism

Mariella Dentini,*^† Daniele Caucci,^† Andrea Barbetta,^† Vittorio Crescenzi,^† Gudmund Skjk-Brk,^‡ Donatella Capitani,^§ Luisa Mannina,^§ and Stéphane Viel^§

Department of Chemistry, University of Rome La Sapienza, Rome, Italy, Department of Biotechnology, Norwegian University of Science and Technology, Trondheim, Norway, Institute of Chemical Methodologies, CNR, Research Area of Rome, 00016 Monterotondo Staz., (Rome), Italy, and Department of S.T.A.A.M., University of Molise, 86100 Campobasso, Italy

Biomacromolecules, 2006, 7 (1), pp 54–63

DOI: 10.1021/bm050341a

Publication Date (Web): November 15, 2005

Corresponding author. Tel.: +39 0649913633. Fax: +39 06490631. E-mail: mariella.dentini@uniroma1.it.

†

University of Rome “La Sapienza”.

‡

Norwegian University of Science and Technology.

CNR, Research Area of Rome.

University of Molise.

Present address: University of Provence, Jeune équipe TRACES, Centre de Saint-Jérôme, case 511, 13397 Marseille cedex, France.

Abstract

Galactose depleted locust bean gum was selectively oxidized in C(6) position and epimerized with mannuronan C(5)-epimerases to obtain the corresponding artificial uronanes. These new pseudo-alginates were characterized by NMR spectroscopy and circular dichroism (CD). Specifically, 1D and 2D NMR techniques allowed the degree of epimerization, the distribution of mannuronic and guluronic acid residues in the polysaccharidic chain, and the average G block length to be determined. In addition, NMR diffusion experiments showed that the epimerization reaction did not significantly degrade the polysaccharidic chains. Circular dichroism was used to investigate the kinetics of the epimerization reaction and to evidence the specific interaction between the epimerized locust bean samples with Ca(II) ions in dilute solution. All of the samples considered in this study form wall to wall gels in concentrated polymer solutions.

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