Biopolymer solute diffusion

On the other hand, the lack of internal pore structure with micropellicular sorbents is of distinct advantage in the analytical HPLC of biological macromolecules because undesirable steric effects can significantly reduce the efficiency of columns packed with porous sorbents and also result in poor recovery. Furthermore, the micropellicular stationary phases which have a solid, fluid-impervious core, are generally more stable at elevated temperature than conventional porous supports. At elevated column temperature the viscosity of the mobile phase decreases with concomitant increase in solute diffusivity and improvement of sorption kinetics. From these considerations, it follows that columns packed with micropellicular stationary phases offer the possibility of significant improvements in the speed and column efficiency in the analysis of proteins, peptides and other biopolymers over those obtained with conventional porous stationary phases. In this paper, we describe selected examples for the use of micropellicular reversed phase... 

Solute Diffusion in Biopolymers as a Function of Water Activity Using a Modified Free Volume Theory... 

Fig. 11.19 In a common implementation of the vapor diffusion method of biopolymer crystallization, a single drop of biopolymer solution hangs above a reservoir solution that is very concentrated in a nonvolatile solute. Solvent evaporates from the more dilute drop until the vapor pressure of water in the closed container reaches a constant equilibrium value.

Other common strategies for inducing crystallization involve the gradual removal of solvent from a biopolymer solution, either by dialysis (Section 3.10) or vapor diffusion. In one implementation of the vapor diffusion method, a single drop of biopolymer solution hangs above an aqueous solution (the reservoir), as shown in Fig. 11.19. If the reservoir solution is more concentrated in a nonvolatile solute (for example, a salt) than is the biopolymer solution, then solvent will evaporate slowly from the drop until the vapor pressure of water in the closed container reaches a constant, equilibrium value. At the same time, the concentration of biopolymer in the drop increases gradually until crystals begin to form. 

At first glance, the contents of Chap. 9 read like a catchall for unrelated topics. In it we examine the intrinsic viscosity of polymer solutions, the diffusion coefficient, the sedimentation coefficient, sedimentation equilibrium, and gel permeation chromatography. While all of these techniques can be related in one way or another to the molecular weight of the polymer, the more fundamental unifying principle which connects these topics is their common dependence on the spatial extension of the molecules. The radius of gyration is the parameter of interest in this context, and the intrinsic viscosity in particular can be interpreted to give a value for this important quantity. The experimental techniques discussed in Chap. 9 have been used extensively in the study of biopolymers. 

The main source of conformational information for biopolymers are the easy-to-obtain chemical shifts that can be translated into dihedral restraints. In addition, for fully 13C labeled compounds, proton-driven spin diffusion between carbons [72] can be used to measure quantitatively distances between carbons. The CHHC experiment is the equivalent of the NOESY in solution that measures distances between protons by detecting the resonances of the attached carbons. While both techniques, proton-driven spin diffusion and CHHC experiment [73], allow for some variation in the distance as determined from cross-peak integrals, REDOR [74] experiments in selective labeled compounds measure very accurate distances by direct observation of the oscillation of a signal by the dipolar coupling. While the latter technique provides very accurate distances, it provides only one piece of information per sample. Therefore, the more powerful techniques proton-driven spin diffusion and CHHC have taken over when it comes to structure determination by ss-NMR of fully labeled ligands. 

A comparison of the experimental data on quenching of triplet states of dyes in solutions in the absence and in the presence of DNA permits estimation of the steric complexation effect on the quenching process and conclusions about the structure of the dye-DNA complexes formed. In the case of dye K4, we may conclude that complexation with the biopolymer has relatively weak effect on the kq value. This is probably due to the fact that the quenching process for K4 occurs in the kinetic regime (kc k a, see reaction (2)), and diffusion of the quencher to dye molecules boimd to DNA exerts no substantial effect on kq (another assumed reason for this phenomenon could be partial decomposition of the dye(T)-DNA complex and the presence of free triplet dye molecules in the solution however, the experiments on quenching of the K4 triplet state by iodide ion considered above reject this possibility). 

Application to Polar Biopolymers.—On the basis of the above general relationships, the classical dielectric polarization of any biomolecular system can be evaluated. In the particularly interesting case of a dilute solution of polar biopolymers with a uniform rotational diffusion coeffident a comparatively simple relation can be derived because of the fact that orientational polarization of the solute occurs far below the relaxation range of the solvent. The complex permittivity (without the contribution of background conductivity) turns out to be... 

Trypsin in aqueous solution has been studied by a simulation with the conventional periodic boundary molecular dynamics method and an NVT ensemble.312 340 A total of 4785 water molecules were included to obtain a solvation shell four to five water molecules thick in the periodic box the analysis period was 20 ps after an equilibration period of 20 ps at 285 K. The diffusion coefficient for the water, averaged over all molecules, was 3.8 X 10-5 cm2/s. This value is essentially the same as that for pure water simulated with the same SPC model,341 3.6 X 10-5 cm2/s at 300 K. However, the solvent mobility was found to be strongly dependent on the distance from the protein. This is illustrated in Fig. 47, where the mean diffusion coefficient is plotted versus the distance of water molecules from the closest protein atom in the starting configuration the diffusion coefficient at the protein surface is less than half that of the bulk result. The earlier simulations of BPTI in a van der Waals solvent showed similar, though less dramatic behavior 193 i.e., the solvent molecules in the first and second solvation layers had diffusion coefficients equal to 74% and 90% of the bulk value. A corresponding reduction in solvent mobility is observed for water surrounding small biopolymers.163 Thus it... 

There have been a number of other papers on the hydration of biopolymers the effects of the degree of methylation of pectins on the proton relaxation times of water have been measured 50 l70 relaxation has been used to examine the hydration of bovine and caprine casein,51--54 and solid-state NMR combined with atomic force microscopy has been used to examine the influence of water on the nanomechanical behaviour of cutin.55 The effects of locust bean gum on water diffusion in sugar solutions has shown little effect,56 and the effects of gellan gum hydrogel structure on restricted diffusion has also been considered.57... 

In aqueous solutions, at a physiological pH, HA is represented by negatively charged hyaluronate macromolecules (pK = 3.21) [15] with extended conformations. In a polyanionic form, hyaluronan functional groups make the biopolymer so hydrophilic that it binds 1000 times more water than is predicted from its molar mass. The heterogeneity and hydrophilicity of HA facilitate its interaction with a variety of tissue constituents inside and outside the cells. In the extracellular space, HA controls the retention of water, ionic and molecular diffusion and provides a 3D-structural meshwork [16]. 

Cheng and English edited ACS symposium series which covers the solution and solid state NMR investigations for dendrimers, cellulose, polyurethane, polyolefins biopolymers, copolymers and so on. Spiess described a historical overview of role of NMR spectroscopy in polymer science. Newmark summarizes the two dimensional and pulsed gradient diffusion NMR experiments and their applications to polymers Shit et al. reviewed the analysis of polymer molecular weight and copolymer composition by NMR. Sasanuma summarized the the analysis of polyethers and polysulfides by NMR and theoretical calcula-tions Ardelean et al described the principle and its applications of diffusion studies by NMR. Roy et al summarized the structural analysis of Novolak resins by multidimensional NMR. Reviews about NMR study of surfactant polymer blends and the structural elucidation of supramocules are published. 

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