imperfect RNA duplex - how to calculate free energy?

[Markus Hossbach]

hello,

is there a web-tool or software avaible that allows calculation of free 
energy of an short, micro-RNA like,  imperfect RNA duplex?

it should allow in silico hybridization of two different partially 
complementary 19mer RNA sequences, that can form a duplex with serveral 
loops and gu-wobbles, possibly also on the ends.

thanks,
markus



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