Naira R. Khusnutdinova

In this work, the associative behavior of Gum Arabic in aqueous solutions was investigated through dynamic light scattering, nuclear magnetic resonance, and transmission and scanning electron microscopy. It was shown that in small associates, the spherical polysaccharide units have predominant sizes of 2–8 and 9–20 nm. The average hydrodynamic diameter of diffusing structural units, calculated on the basis of NMR experiment, turned out to be close to 20 nm, which corresponds with electron microscopy data. Based on geometric considerations and the composition and supramolecular structure of Gum Arabic, we calculated the parameters of branched chains of Gum Arabic. A possible “crown” model of polysaccharide chain association into spherical blocks is presented. The developed model allowed us to describe the effects observed during the time-extended association of Gum Arabic particles (molecules) in aqueous solutions, leading first to blocks’ swelling, then the appearance of local gelation, and only then to the creation of dense protective layers on the surfaces. It was established that the tendency of amphiphilic Gum Arabic molecules to form complexes both among themselves and with various surfaces and the possibility of forming viscous gel-like layers on the interfaces underly its use in many natural, food, technical, and technological applications, including emulsification.

The diffusion properties and hydrodynamic radius, R_h, of macromolecules are important for theoretical studies and practical application. Moreover, comparison of R_h values obtained from simulation and experimental data is used to check the correctness of simulation results. Here, we study the translation mobility of poly(butylcarbosilane) dendrimers in chloroform solution using molecular dynamics simulations and consider simulation details that may influence the accuracy of the result. Different methods to estimate R_h for a dendrimer are discussed with comparison to our experimental data. It was shown that the traditional MD simulation method for extraction of the diffusion coefficient (and calculation of R_h) of dendrimers as a rule faces difficulties and requires simulation resources several times greater than, for example, the same for a linear analogue. In the majority of MD simulation papers, the diffusion coefficient and/or R_h are calculated incorrectly. Also, we establish that correction of R_h according to the simulation box or estimation of R_h by using the gyration radius does not give values close to experimental data. To avoid the mentioned problems, we found an alternative way: to consider rotational diffusion, which gives an R_h similar to that from experiment and is practically independent of the size of the simulation box and other simulation parameters.