Poly(ethylene glycol) (PEG) and its derivatives are synthetic polymers with major applications in gene and drug delivery systems. Synthetic polymers are also used to transport miRNA and siRNA. in vitro. We studied the interaction of tRNA with several PEGs of different compositions, such as PEG 3350, PEG 6000, and mPEG-anthracene under physiological conditions. FTIR, UV-visible, CD, and fluorescence spectroscopic methods as well as atomic force microscopy (AFM) were used to analyze the PEG binding mode, the binding constant, and the effects of polymer complexation on tRNA stability, aggregation, and particle formation. Structural analysis showed that PEG-tRNA interaction occurs via RNA bases and the backbone phosphate group with both hydrophilic and hydrophobic contacts. The overall binding constants of K-PEG (3350-RNA) = 1.9 (+/- 0.5) X 10(4) M-1, KPEG 6000-tRNA = 8.9 (+/- 1) X 10(4) M-1, and KmPEG-anthramez = 1.2 (+/- 0.40) X 10(3) M-1 show stronger polymer RNA complexation by PEG 6000 and by PEG 3350 than the mPEG-anthracene. AFM imaging showed that PEG complexes contain on average one tRNA with PEG 3350, five tRNA with PEG 6000, and ten tRNA molecules with mPEG-anthracene. tRNA aggregation and particle formation occurred at high polymer concentrations, whereas it remains in A-family structure.