We analyze the universal size characteristics of flexible ring polymers in solutions in presence of structural obstacles (impurities) in d dimensions. One encounters such situations when considering polymers in gels, colloidal solutions, intra- and extracellular environments. A special case of extended impurities correlated on large distances r according to a power law ∼ra is considered. Applying the direct polymer renormalization scheme, we evaluate the estimates for averaged gyration radius ⟨Rg ring⟩ and spanning radius ⟨R1/2 ring⟩ of typical ring polymer conformation up to the first order of double ɛ = 4 − d, δ = 4 − a expansion. Our results quantitatively reveal an extent of the effective size and anisotropy of closed ring macromolecules in disordered environment. In particular, the size ratio of ring and open (linear) polymers of the same molecular weight grows when increasing the strength of disorder according to

$\langle R^2_{g\,{\rm ring}} \rangle / \langle R^2_{g\,{\rm chain}} \rangle =\frac{1}{2} (1+\frac{13}{48}\delta )$
Rg ring 2/Rg chain 2=12(1+1348δ)⁠.

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