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Self‐Assembly of N 2 ‐Modified Guanosine Derivatives: Formation of Discrete G‐Octamers
Author(s) -
Martić Sanela,
Liu Xiangyang,
Wang Suning,
Wu Gang
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701411
Subject(s) - chemistry , guanosine , histone octamer , random hexamer , ligand (biochemistry) , crystallography , stacking , stereochemistry , monomer , molecule , receptor , biochemistry , organic chemistry , nucleosome , gene , histone , polymer
In the presence of Na + ions, two N 2 ‐modified guanosine derivatives, N 2 ‐(4‐ n ‐butylphenyl)‐2′,3′,5′‐ O ‐triacetylguanosine ( G1 ) and N 2 ‐(4‐pyrenylphenyl)‐2′,3′,5′‐ O ‐triacetylguanosine ( G2 ), are found to self‐associate into discrete octamers that contain two G‐quartets and a central ion. In each octamer, all eight guanosine molecules are in a syn conformation and the two G‐quartets are stacked in a tail‐to‐tail fashion. On the basis of NMR spectroscopic evidence, we hypothesize that the π–π‐stacking interaction between the N 2 ‐side arms (phenyl in G1 and pyrenyl in G2 ) can considerably stabilize the octamer structure. For G1 , we have used NMR spectroscopic saturation‐transfer experiments to monitor the kinetic ligand exchange process between monomers and octamers in CD 3 CN. The results show that the activation energy ( E a ) of the ligand exchange process is 31 ±5 kJ mol −1 . An Eyring analysis of the saturation transfer data yields the enthalpy and entropy of activation for the transition state: Δ H ≠ =29 ±5 kJ mol −1 and Δ S ≠ =−151 ±10 J mol −1 K −1 . These results are consistent with an associative mechanism for ligand exchange.