The GROMOS 56A force field for the description of carbohydrates was modified for calculations of chitosan (poly-1,4-(N-acetyl)-β-D-glucopyranosamine-2) with protonated and non-protonated amino groups and its derivatives. Additional parameterization was developed on the basis of quantum chemical calculations. The modified force field (56A) allows performing the molecular dynamic calculations of chitosans with different degrees of protonation corresponding to various acidity of medium. Test calculations of the conformational transitions in the chitosan rings and polymeric chains as well as the chitosan nanocrystal dissolution demonstrate good agreement with experimental data. Graphical abstract The GROMOS 56A force field allows performing the molecular dynamic calculations of chitosans with different types of amio-group: free, protonated, substituted.

MicroRNA (miRNA) is considered today as a prospective pharmacological agent for the development of novel high-technological medicines. In order to keep its active form in the aggressive biological environment, it...

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The clusters of bare TiO 2 and TiO 2 with linked organic ligands modeling polyorganic composites used as photocatalytic materials were studied using the density functional based tight binding (DFTB) electronic structure method with three parameter sets (trans3d, tiorg, and matsci) in comparison with results of B3LYP/6-31G(d,p) calculations, semiempirical methods PM6 and PM7, and available experimental data. It was found that the highly scalable DFTB method shows results that are close to the B3LYP/6-31G(d,p) level of theory. The corrected version of the tiorg DFTB parameter set (tiorg-smooth) has better performance for the estimations of structural param

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