Random coil linear

Since little chain entanglement would be expected from these structures, one would expect poor bulk properties compared to traditional linear random coil polymers. 

We have used the uncharged polysaccharide dextran as a model describing the behaviour of water-soluble polymers. The dextrans used in this study have about 95 % oc-(l - 6) linkages within the main chain and side chains the 5 % non-a-(l -> 6) linkages are starting points of branched chains of which most are only stubs of about two glucose units 9). Therefore, while there is some branching in dextran, albeit low, its solution behaviour is that of a linear, random-coil molecule l0,ll). 

Gel permeation chromatography of protein linear random coils in guanidinium chloride allows simultaneous resolution and molecular weight analysis of polypeptide components. Column calibration results are expressed in terms of a log M vs. Kd plot or of effective hydrodynamic radius (Re/). For linear polypeptide random coils in 6M GuHCl, Re is proportional to M0 555, and M° 555 or Re may be used interchangeably. Similarly, calibration data may be interpreted in terms of N° 555 (N is the number of amino acid residues in the polypeptide chain), probably the most appropriate calibration term provided sequence data are available for standards. Re for randomly coiled peptide heteropolymers is insensitive to amino acid residue side-chain composition, permitting incorporation of chromophoric, radioactive, and fluorescent substituents to enhance detection sensitivity. 

Table I. Useful Limits and Resolution Capabilities of Agarose Resins for Linear Random Coils in 6M GuHCl...

Figure 2. Gel permeation data for polypeptide linear random coils plotted according to the method of Porath (8) M0,555 is plotted vs. Kd1/3. Lines drawn through the data from each column are lines of best fit determined by linear least-squares analysis. Numerical designation for each curve represents the agarose...

Further, since the term Re is proportional to Rg, a relationship between the parameter measured by gel filtration of linear random coils and their molecular weights is provided. 

Previous studies (5-7) have clearly demonstrated that gel permeation chromatography of reduced linear randomly coiled polypeptide chains in GuHCl provides an accurate, dependable method for molecular weight estimation. 

Figure 3. Gel permeation data for linear randomly coiled polypeptides on various agarose resins, plotted according to the method of Ackers (9). M0 555 is plotted vs. the inverse error function complement of Kd (erfc 1 Kd). Lines drawn through the data points represent best fits obtained from linear least-squares analysis of the data. Numerical designation of each curve represents the percent agarose composition for the resin used. Filled triangles on the curve for the 6% resin, and the filled squares on the curve for the 10% resin are points determined using fluorescent proteins. Data for the labeled polypeptides were not included in the least-squares analysis.

Gel permeation studies on agarose-GuHCl columns provide for high resolution and accurate molecular weight determination of linear randomly coiled polypeptide chains. For nonlinear random coils, gel permeation studies provide for accurate determination of the effective hydrodynamic radius of the components. 

Finally we mention the Kratky plot which also may help to detect branching. Here ((S2) q2) Pz (q2) is plotted against q. Figures 26 and 27 show the Kratky plots for regular star-molecules and for the soft sphere model. Linear randomly coiled chains result in... 

Based on properties in solution such as intrinsic viscosity and sedimentation and diffusion rates, conclusions can be drawn concerning the polymer configuration. Like most of the synthetic polymers, such as polystyrene, cellulose in solution belongs to a group of linear, randomly coiling polymers. This means that the molecules have no preferred structure in solution in contrast to amylose and some protein molecules which can adopt helical conformations. Cellulose differs distinctly from synthetic polymers and from lignin in some of its polymer properties. Typical of its solutions are the comparatively high viscosities and low sedimentation and diffusion coefficients (Tables 3-2 and 3-3). 

For pullulans, Tsujisaka and Mitsuhashi report K and a values of 2.36 X 10 and 0.66 in water where the intrinsic viscosity is in deciliters per gram 13,14). This result suggests that the saline is abetter solvent than water for the pullulan and the agreement between the two values is good. The value for the exponent corresponds to that expected for a linear random coil polymer about 0.5-0.8 depending on solvent power 13). 

Beer M. U., Wood P. J., Weisz J. 1999. A simple and rapid method for evaluation of Mark-Houwink-Sakurada constants of linear random coil polysaccharides using molecular weight and intrinsic viscosity determined by high performance size exclusion chromatography Application to guar galactomannan. Carbohvdr. Polymers. 39, 377-380. 

Flory [57] predicted many years ago that should be a constant for linear random coils, independent of the nature of the polymer and solvent. It is now known that good solvent values of = [q] are smaller than values... 

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