13276-53-4Relevant articles and documents
Effect of base stacking on the acid-base properties of the adenine cation radical [A?+] in solution: ESR and DFT studies
Adhikary, Amitava,Kumar, Anil,Khanduri, Deepti,Sevilla, Michael D.
experimental part, p. 10282 - 10292 (2009/02/03)
In this study, the acid-base properties of the adenine cation radical are investigated by means of experiment and theory. Adenine cation radical (A?+) is produced by one-electron oxidation of dAdo and of the stacked DNA-oligomer (dA)6 by Cl2?- in aqueous glass (7.5 M LiCl in H2O and in D2O) and investigated by ESR spectroscopy. Theoretical calculations and deuterium substitution at C8-H and N6-H in dAdo aid in our assignments of structure. We find the pKa value of A?+ in this system to be ca. 8 at 150 K in seeming contradiction to the accepted value of ≤1 at ambient temperature. However, upon thermal annealing to ≥160 K, complete deprotonation of A?+ occurs in dAdo in these glassy systems even at pH ca. 3. A?+ found in (dA)6 at 150 K also deprotonates on thermal annealing. The stability of A?+ at 150 K in these systems is attributed to charge derealization between stacked bases. Theoretical calculations at various levels (DFT B3LYP/6-31G*, MPWB95, and HF-MP2) predict binding energies for the adenine stacked dimer cation radical of 12 to 16 kcal/mol. Further DFT B3LYP/6-31G* calculations predict that, in aqueous solution, monomeric A?+ should deprotonate spontaneously (a predicted pKa of ca. -0.3 for A?+). However, the charge resonance stabilized dimer AA?+ is predicted to result in a significant barrier to deprotonation and a calculated pK a of ca. 7 for the AA?+ dimer which is 7 pH units higher than the monomer. These theoretical and experimental results suggest that A?+ isolated in solution and A?+ in adenine stacks have highly differing acid-base properties resulting from the stabilization induced by hole derealization within adenine stacks.
Solid-phase synthesis of positively charged deoxynucleic guanidine (DNG) oligonucleotide mixed sequences
Reddy, Putta Mallikarjuna,Bruice, Thomas C.
, p. 1281 - 1285 (2007/10/03)
Positively charged DNG oligonucleotide mixed sequences containing A/T bases were prepared by solid-phase synthesis. Synthesis proceeds in 3′→5′ direction and involves coupling of 3′-Fmoc protected thiourea in the presence of HgCl2/TEA with the corresponding 5′-amine of the growing oligo chain. DNG binding characteristics with complementary DNA and with itself have been evaluated.
A facile method for deprotection of trityl ethers using column chromatography
Pathak, Ashish K.,Pathak, Vibha,Seitz, Lainne E.,Tiwari, Kamal N.,Akhtar, Mohammad S.,Reynolds, Robert C
, p. 7755 - 7757 (2007/10/03)
A mild, efficient and inexpensive detritylation method is reported that uses trifluoroacetic acid on a silica gel column to obtain pure, detritylated compounds in one-step. This method is applicable to acid stable as well as acid sensitive compounds with only slight alterations in the procedure. Nineteen examples are given.
