Advances in Physicochemical Properties of Biopolymers (Part 1)

In this chapter, molecular weight (M), and molecular weight distribution (MWD), of polymers with emphasis on M and MWD of biopolymers, e.g., carbohydrate polymers, proteins, deoxyribonucleic acid, DNA, and ribonucleic acid, RNA, are reviewed. The M and MWD of biopolymers are compared with those of synthetic polymers. The following conclusions are drawn. (1) Unlike simple low molecular substances, most polymers do not have unique molecular weights. Practically, no polymer exists whose molecules are all strictly of the same size or have the same degree of polymerization. Thus, polymers are more or less heterogeneous with respect to their molecular weights. (2) The concept of average molecular weight is used for polymers. (3) Different numerical values for molecular weights of polymers have already been defined as average molecular weights (Mn, Mw, Mz, and Mv), depending on the methods by which they are measured. (4) The average values vary in the following order: Mn < Mv < Mw < Mz < Mz+1. The disparity between average molecular weights provides a measure of the degree of heterogeneity, i.e. dispersity, in the molecular weight distribution. (5) The constitution of a polymer as well as the MWD may be described either by a set of different average molecular weights, the ratios of two different types of average molecular weights, or by the distribution functions via graphical presentation and (6) Polysaccharides in a similar way to synthetic polymers are polydisperse polymers, whereas proteins, DNA, and RNA, are mostly monodisperse macromolecules.

Bovine serum albumin (BSA) in aqueous solution is scarcely studied, and the Mark-Houwink parameters from the intrinsic viscosity measurements have not been reported at different temperatures. This work discusses these with a simple calculation of the Mark-Houwink parameters of BSA in aqueous solution when the concentration ranged from 0.2 to 1.0% wt., and the temperature ranged from 20 to 45°C. The relationship between the concentration and intrinsic viscosity was determined according to different methods. It is well known that when the temperature increases, the intrinsic viscosity decreases. This is reflected in the stiffer chain curve with d(ln[ɳ])/d(1/T) of -398.97 for A zone from 20-30ºC (gel zone), -2759.1 for B zone from 35-40ºC (active zone) and 5604.5 for C zone from 41-45ºC (denatured protein zone), the point of intersection between the zones A and B is 34.6ºC. The linear relation between the logarithmic of viscosity and reverse temperature is ΔEavf with a value of 680 Cal/mol. Furthermore, this work proposes the determination of M-H parameters of a protein-water system and their thermodynamic implications in conformational changes.

Small-angle scattering of X-rays (SAXS) or neutrons (SANS) is a wellestablished method to study the overall structure and structural transitions of biopolymers in solution. Determination of overall structural parameters such as the radius of gyration Rg, the molecular mass Mw or the hydrated volume V is now easily computed using appropriate free Softwares. In addition, increasingly sophisticated ab initio methods were developed over the last two decades for building structural models of biopolymers from x-ray and neutron solution scattering data. Even if most of the developments were focused on protein in solution, folded or intrinsically disordered, protein complexes or protein fibrils, ab initio methods were also used to calculate three-dimensional shape models of polysaccharides or nucleic acids. The models derived from experimental scattering pattern up to a resolution of 0.5 nm are classified as low resolution models compared to atomistic resolution structures using X-ray crystallography. The efficiency of the methods is illustrated in this chapter by focusing mainly on proteins or polysaccharides with unknown crystal structures and for which the ab initio reconstruction of three-dimensional models may help to define, in combination or not with other structural techniques, such as microscopy, overall dimensions and global shape. These methods improved the resolution and reliability of models derived from scattering data substantially and has made solution scattering, in combination with recent developments using size-exclusion chromatography, robotic sample changer or microfluidics, and a useful technique in high-throughput large-scale structural characterization of biopolymers.

High-Performance Size-Exclusion Chromatography (HPSEC) is widely used for the determination of the molar mass and size distribution of biopolymers in aqueous or organic solvents. Elements of the theory of fractionation by HPSEC, column calibration and online light scattering detection are given, showing that coupling HPSEC with multi-angle laser light scattering detection makes it easier to obtain molar mass distributions since light (MALLS) scattering gives the weight-average molar mass at each elution volume of the chromatogram. Some applications of HPSEC-MALLS for the macromolecular characterization of starches, glycogens, dextrans, celluloses, hemicelluloses, β-glucans, pectins, gums, alginates, carrageenans, chitosans, lignins, proteins and peptides are also presented.

Field-Flow Fractionation techniques (FFF) are size-based separation methods first described in 1966 by Giddings. They belong to the family of liquid chromatographic techniques, but they are operated without any stationary phase.Yet, they have the unique ability to separate an extremely broad range of molecules, macromolecules and particles, and in particular very large particles, with a high resolution. FFF are versatile: by varying the experimental conditions, the range, speed, and power of the separation could be optimized. FFF techniques can succeed when Size-Exclusion Chromatography (SEC) methods fails, and they have a broad range of applications. In this chapter the theory of FFF is approached together with calibration and determination of some structural parameters such as size and molar mass, the instrumentation and detection of various classic FFF types is described and we show the added value of FFF techniques for the characterization of various biopolymers including polysaccharides, proteins and natural rubber.

In this chapter, the rheology of polysaccharides extracted from cactus and agave plants is summarized. These vegetal sources of polysaccharides (Opuntia mucilage, Opuntia pectin, and agave fructans) were selected for their functional properties (thickening, gelling, or emulsifying) and their bioactive role in the the prevention and/or treatment of disease. The source, production, extraction processes, structure, and functional properties (related to conformation) of these polysaccharides are briefly described before the rheology of these biopolymers is discussed, and recommended uses are suggested.

One of the major by-products of bioethanol production is distillers dried grains with solubles (DDGS). Maize is one of the main sources for the production of this biofuel. In this way, dietary fiber represents the principal fraction of DDGS, which could be a potential source of added-value biomolecules such as ferulated arabinoxylans (AX). In this chapter, ferulated arabinoxylans extracted from DDGS (DDGAX) were gelled and the gels were studied in terms of rheology, structural parameters and microstructural characteristics. The DDGAX formed gels at 2% (w/v) induced by laccase. The mechanical spectrum and strain sweep of DDGAX gel presented the typical behavior of a solid-like material. The gels swelling ratio (43 g water/g DDGAX) suggested the formation of a compact polymeric network which decreased the water uptake of the gel. DDGAX gels presented an average mesh size value of 96 nm. The surface of the gels was analyzed by scanning electron microscopy revealing a heterogeneous microstructure resembling an imperfect honeycomb. These results indicate that ferulated arabinoxylans from DDGS form elastic and macroporous gels, presenting a microstructure with irregular pore sizes.