Interactions biopolymer-solvent

We first consider the case of a two-component solution (biopolymer + solvent) over a moderately low range of biopolymer concentrations, i.e., C < 20 % wt/wt. The quantities pm x in the equations for the chemical potentials of solvent and biopolymer may be expressed as a power series in the biopolymer concentration, with some restriction on the required number of terms, depending on the steepness of the series convergence and the desired accuracy of the calculations (Prigogine and Defay, 1954). This approach is based on simplified equations for the chemical potentials of both components as a virial series in biopolymer concentration, as developed by Ogston (1962) at the level of approximation of just pairwise molecular interactions ... 

The set of equations (3.7-3.9) shows that the sign and magnitude of the second virial coefficient provides information on how the behaviour of the macromolecular solution deviates from that of the thermodynamically ideal state, thus reflecting the nature and intensity of the inter-molecular pair interactions (both biopolymer-biopolymer and biopolymer-solvent) (Prigogine and Defay, 1954 Tanford, 1961 Ogston 1962 ... 

Time-resolved emission spectroscopy (TRES), also referred to as time-resolved Stokes shift spectroscopy, enables one to derive information about the dynamics of biopolymer-solvent interactions on the femtosecond to nanosecond time scales, provided that suitable solvatochromic fluorescent probes have been identified. Such probes should exhibit significant Stokes shifts that change with solvent polarity and should have fluorescent lifetimes on the order of the dynamic solvent exchange process or longer. TRES detects solvent dynamics that influences the energy difference between the excited and the ground states of the fluorophore and is insensitive to dynamic processes that are significantly slower than the fluorescence lifetime. 

Because different biopolymer gel systems can be encountered, different gelation mechanisms also can be encountered. Because of variations in the number and nature of the cross-links, framework flexibility, attractions and repulsions between framework elements, and interactions with solvent, different properties of the formed gels... 

This chemical classification is of little use with respect to the various applications as biopolymers, in which most of the time interactions with solvents are involved. This is illustrated by the fact that the solubility of a given compound may change completely with the degree of substitution and/or with the molar substitution. This is for example the case of HPC and NaCMC which are commercially available as insoluble and water-soluble products. We therefore use a classification of cellulose-based biopolymers made according to their behavior in water and to their ionic character (Table 2). 

Table 2. Classification of cellulose biopolymers based on interaction with solvent and ionic character...

Pitera, J.W. van Gunsteren, W.F., The importance of solute-solvent van der Waals interactions with interior atoms of biopolymers, J. Am. Chem. Soc. 2001,123, 3163-3164. 

Bioreactions. The use of supercritical fluids, and in particular C02, as a reaction media for enzymatic catalysis is growing. High diffusivities, low surface tensions, solubility control, low toxicity, and minimal problems with solvent residues all make SCFs attractive. In addition, other advantages for using enzymes in SCFs instead of water include reactions where water is a product, which can be driven to completion increased solubilities of hydrophobic materials increased biomolecular thermostability and the potential to integrate both the reaction and separation bioprocesses into one step (98). There have been a number of biocatalysis reactions in SCFs reported (99—101). The use of lipases shows perhaps the most commercial promise, but there are a number of issues remaining unresolved, such as solvent—enzyme interactions and the influence of the reaction environment. A potential area for increased research is the synthesis of monodisperse biopolymers in supercritical fluids (102). 

Here, /u ° and ju are, respectively, the chemical potentials of pure solvent and solvent at a certain concentration of biopolymer V is the molar volume of the solvent Mn=2 y/M/ is the number-averaged molar mass of the biopolymer (sum of products of mole fractions, x, and molar masses, M, over all the polymer constituent chains (/) as determined by the polymer polydispersity) (Tanford, 1961) A2, A3 and A4 are the second, third and fourth virial coefficients, respectively (in weight-scale units of cm mol g ), characterizing the two-body, three-body and four-body interactions amongst the biopolymer molecules/particles, respectively and C is the weight concentration (g ml-1) of the biopolymer. 

Here, as previously, the solvent is taken as component 1, one of the biopolymers is the /-component, while another is the /-component m, mr and m,j are the concentrations (moles per kg of water) of the components An and Ajj are the second virial coefficients (m3/mol) characterizing the like pair interactions of the types biopolymer -biopolymer and biopolymer,-biopolymer, respectively and Ay is the cross second virial coefficient corresponding to the biopolymer -biopolymer pair interaction. 

With a ternary system of type biopolymer/ + biopolymey + solvent, in order to characterize all the different pair interactions, the following heat effects, Q, should be measured in flow mode (Semenova et al., 1991) (i) biopolymer, solution diluted by pure buffer, Q (ii) biopolymey solution diluted by pure buffer, Qp and (iii) mixed (biopolymer, + biopolymey) solution diluted by pure buffer, Qijh. The specific enthalpy of interaction between biopolymer, and biopolymey can then be obtained from... 

Could you perhaps comment on how far research has gone in analyzing and understanding the interaction of biopolymers in aqueous solvents ... 

To improve and control cell-fiber interactions, the fiber meshes can be either composed of biomacromolecules or postfunctionalized with appropriate biomolecules. The question arises as to which materials can be electrospun. In principle, all polymers can be spun if they provide enough entanglements in solution and adequate interactions between the solvent and solute. Biopolymers, in particular, show dominant H-bonding and/or polyelectrolyte effects, which lead to a strong viscosity increase or poor solvent evaporation. In order to prevent such... 

Attaching chemical functionalities to CNTs can improve their solubility and allow for their manipulation and processability [24]. The chemical functionalization can tailor the interactions of nanotubes with solvents, polymers and biopolymer matrices. Modified tubes may have physical or mechanical properties different from those of the original nanotubes and thus allow tuning of the chemistry and physics of carbon nanotubes. Chemical functionalization can be performed selectively, the metallic SWCNTs reacting faster than semiconducting tubes [25]. 

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