Leal David, Matsuhiro Betty, Rossi Miriam, Caruso Francesco
Departamento de Ciencias del Ambiente, Facultad de Química y Biología, Universidad de Santiago de Chile, USACH, Av. L.B.O'Higgins 3363, Correo 33, Santiago, Chile.
Carbohydr Res. 2008 Feb 4;343(2):308-16. doi: 10.1016/j.carres.2007.10.016. Epub 2007 Nov 28.
Sodium alginates obtained by alkaline extraction of Lessonia flavicans, Desmarestia ligulata and Desmarestia distans (Phaeophyta) from southern Chile were partially hydrolyzed with HCl. Each alginate gave three fractions that were characterized using FT-IR spectroscopy. The fractions soluble in 0.3M HCl presented in the fingerprint region four vibrations at around 960, 911, 890 and 815 cm(-1) that were assigned to heteropolymeric blocks. The fractions soluble at pH 2.85 showed bands at around 948, 888 and 820 cm(-1) attributed to homopolymannuronic acid blocks, the first band is resolved in the second-derivative spectra into two bands at 951 and 936 cm(-1). The fractions insoluble at pH 2.85 presented four bands at around 947, 903, 812 and 781 cm(-1), which were assigned to homopolyguluronic acid blocks. For some samples, the second derivative FT-IR spectra showed new bands indicating the presence of other structures, in low proportions. Structures deduced by FT-IR spectroscopy were corroborated by solution (1)H and (13)C NMR spectroscopy. Two-dimensional spectra were collected to confirm the fine structure of the hetero- and homopolymeric fractions. A geometrically optimized model for the disaccharide alpha-l-gulopyranuronosyl-(1-->4)-alpha-l-gulopyranuronic acid was calculated using density functional theory; good agreement was obtained between its corresponding calculated vibrations and the experimental bands assigned to homopolyguluronic acid blocks.
从智利南部的黄海带（Lessonia flavicans）、舌状海带（Desmarestia ligulata）和远海带（Desmarestia distans）（褐藻门）中通过碱性提取得到的海藻酸钠用盐酸进行了部分水解。每种海藻酸盐都得到了三个级分，并用傅里叶变换红外光谱（FT-IR）对其进行了表征。可溶于0.3M盐酸的级分在指纹区呈现出约960、911、890和815 cm⁻¹处的四个振动，这些振动被归属于杂聚块。在pH 2.85下可溶的级分在约948、888和820 cm⁻¹处显示出谱带，这些谱带归因于同聚甘露糖醛酸块，第一条谱带在二阶导数光谱中分解为951和936 cm⁻¹处的两条谱带。在pH 2.85下不溶的级分在约947、903、812和781 cm⁻¹处呈现出四条谱带，这些谱带被归属于同聚古洛糖醛酸块。对于一些样品，二阶导数FT-IR光谱显示出新的谱带，表明存在比例较低的其他结构。通过FT-IR光谱推导的结构通过溶液¹H和¹³C NMR光谱得到了证实。收集了二维光谱以确认杂聚和同聚级分的精细结构。使用密度泛函理论计算了二糖α-L-古洛糖醛酸基-(1→4)-α-L-古洛糖醛酸的几何优化模型；其相应的计算振动与归属于同聚古洛糖醛酸块的实验谱带之间取得了良好的一致性。
