Alginic acids in Lessonia trabeculata: characterization by formic acid hydrolysis and FT-IR spectroscopy

doi:10.1016/S0144-8617(00)00286-1

Carbohydrate Polymers

Volume 46, Issue 1, September 2001, Pages 81-87

https://doi.org/10.1016/S0144-8617(00)00286-1 Get rights and content

Abstract

The ratio of mannuronic acid to guluronic acid (M/G) in alginic acids from blade, stipe and holdfast of Lessonia trabeculata collected in three locations of the Chilean coast was determined by total hydrolysis with formic acid. It was found that the reaction of alginic acids with 90% formic acid for 6 h at 100°C, followed by treatment with 1.5 N formic acid for 2 h at 100°C produced the total hydrolysis. The values of M/G ratio, determined by HPLC, were slightly lower than those obtained by the traditional hydrolysis method employing 80% sulphuric acid. No systematic tissue-to-tissue variations in the M/G ratio were observed.

FT-IR spectroscopy, especially in the second-derivative mode, was applied for characterizing alginates and partial hydrolysis fractions. The alginate fraction enriched in polymannuronic acid presented two bands at ∼893 and ∼822 cm⁻¹ while the polyguluronic acid enriched fractions showed four characteristic absorption bands at around 947, 903, 813 and 780 cm⁻¹.

Introduction

The brown seaweed Lessonia trabeculata (Villouta & Santelices, 1986) of the order Laminariales (Phaeophyta) dominates the shallow subtidal environments of northern Chile (Vásquez, 1992).

The major structural polysaccharide of brown seaweeds is alginic acid, a linear 1,4-linked copolymer of β-d-mannuronic acid (M) and α-l-guluronic acid (G). The two uronic acids can be arranged in homopolymeric [poly(β-d-mannosyluronic acid) (MM) and poly(α-l-gulosyluronic acid) (GG)] or heteropolymeric (MG) blocks.

The alginic acid of L. trabeculata from central Chile was studied in this laboratory (Matsuhiro & Zambrano, 1989). Venegas, Matsuhiro, and Edding (1993) have found differences in the mannuronic to guluronic acid ratios and block compositions of alginic acid extracted from populations of L. trabeculata growing in exposed and sheltered habitats.

The characterization of the subtidal environments contaminated by iron mining through the quantification of Fe in seawater, in different tissues and alginic acid of L. trabeculata, have been recently reported (Vásquez, Vega, Matsuhiro, & Urzúa, 1999).

Related to our work on the chemical modifications of polysaccharides and their conjugation to proteins (Jerez et al., 1997, Jerez et al., 1999, Lillo and Matsuhiro, 1997) aqueous alkaline extracts from L. trabeculata from three different locations of northern Chile were examined in search for homopolyguluronic enriched alginic acids. This work presents the results of the studies on the total hydrolysis of alginates with formic acid and the characterization of alginates and the partially hydrolysed alginates by FT-IR spectroscopy.

Section snippets

Materials and methods

L. trabeculata samples were collected in winter and spring in San Lorenzo (30°15′), Carrizal Bajo (28°05′) and Chapaco (28°05′). The extraction of sodium alginate from L. trabeculata was previously reported (Matsuhiro and Zambrano, 1989, Matsuhiro and Zambrano, 1990). Alginate samples were purified according to Venegas et al. (1993). d-Mannuronic acid, d-galacturonic acid and d-glucuronolactone from Sigma were used as standards. l-Guluronic acid was prepared by H₂SO₄ hydrolysis of alginic acid

Total hydrolysis

Alginic acid is very resistant to hydrolysis by mineral acids, and complete liberation of the uronic acids without decomposition is difficult to achieve. Destruction, particularly of l-guluronic acid units can occur. The traditional hydrolysis method employing 80% H₂SO₄ (Adams, 1965, Haug and Larsen, 1962) is frequently used for the complete release of mannuronic and guluronic acids from alginic acid. According to Anzai, Uchida, and Nishide (1990) a shorter hydrolysis period increased the

Conclusions

Complete hydrolysis of alginic acids can be achieved with 90% formic acid. The method is clean and faster than the traditional 80% sulphuric acid hydrolysis. FT-IR spectroscopy, especially in the second-derivative mode, provides a good alternative method for the characterization of alginic acid and its heteropolymeric and homopolymeric blocks in the solid state. From the FT-IR spectroscopic analysis it can be concluded that although the M/G ratio of the alginic acid samples of L. trabeculata

Acknowledgements

The financial support of FONDECYT (Grant 1980828) and of Dirección de Investigaciones Cientı́ficas y Tecnológicas of Universidad de Santiago de Chile is gratefully acknowledged.

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Alginic acids in Lessonia trabeculata: characterization by formic acid hydrolysis and FT-IR spectroscopy

Abstract

Introduction

Section snippets

Materials and methods

Total hydrolysis

Conclusions

Acknowledgements

Carbohydrate Polymers

Carbohydrate Research

Carbohydrate Research

Carbohydrate Research

Carbohydrate Polymers

Carbohydrate Polymers

Carbohydrate Research

Carbohydrate Research

Carbohydrate Research

Carbohydrate Research

Complete acid hydrolysis

Determination of D-mannuronic to L-guluronic acids ratio in acid hydrolysis of alginate under improved conditions

Nippon Suisan Gakkaishi