So, immediately after mixing of two polymer solutions (during approximately 30 s), about 50% of the base pairs (from all possible pairs) are selleck kinase inhibitor formed, and then within the next 3 min, their number reaches 93% (Figure  2, curve 1). The final phase is characterized with a slow rate of polymer hybridization; so for 5 h, the number of pairs increases only by 5%. In this time period, the relaxation processes in irregular parts of the polymer like the loop occur [40, 41]. It should

be noted that, within 24 h after mixing of JSH-23 initial solutions, the hypochromic coefficient reaches its maximal value (h max = 0.425). The fraction of bases in the double-stranded form (the degree of hybridization) can be obtained by using the simple ratio see more (h t/h max) in which the hypochromic coefficient at any time (h t) is compared with its maximal value. Figure 2 Time dependences of absorption hypochromism ( λ  = 248 nm) observed at mixing. 1, water solutions of poly(rC) and poly(rI); 2, poly(rC)NT suspension and solution of poly(rI). Kinetics was measured at 20°C. The dashed line corresponds to the formation of 50% of the base pairs. To confirm the formation of the poly(rI)∙рoly(rC) duplex under these experimental conditions, we melted this polymer obtained after the hybridization (Figure  3, curve 1). As a result, we observed an S-like temperature dependence of light

absorption (Figure  3, curve 1) that is evidence of the helix-coil transition in ds-RNA obtained due to hybridization. The melting temperature (T m) of the hybridized poly(rI)∙poly(rC) was found at 52.5°C. T m is a standard measure of the solution thermodynamic stability of the duplex of nucleic acids, which is defined as a temperature at which the hypochromic coefficient

reaches half of its value. This temperature also indicates the coexistence of next half of the polymer in the duplex and in single strands. Figure 3 Melting curves measured at λ  = 248 nm. 1, poly(rI)∙poly(rC) hybridized in buffer solution; 2, initial double-stranded poly(rI)∙poly(rC) (Sigma); 3, poly(rI)∙рoly(rC)NT formed after 24 h of hybridization. The dashed lines indicate the positions of the melting temperatures of the corresponding curves. We compared also the melting curve of hybridized poly(rI)∙poly(rC) with the curve obtained for the initial duplex poly(rI)∙рoly(rC) (Figure  3, curve 2). It turned out that the melting curve of the last polymer is shifted to a higher temperature. T m value for this polymer is 57.7°C. It means that the thermostability of hybridized poly(rI)∙poly(rC) is reduced in comparison with that of the initial duplex poly(rI)∙poly(rC), while hyperchromic coefficients taken for the both curves almost coincide. In our opinion, the main reason of the thermostability decrease of the hybridized polymer is conditioned with polymer fragmentation caused by ultrasonication.