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[C7GC4]4 association into supra molecular i-motif structures.

ABSTRACT: The self-associative properties of cytidine-rich oligonucleotides into symmetrical i-motif tetramers give to these oligonucleotides the capacity of forming supramolecular structures (sms) that have potential applications in the nanotechnology domain. In order to facilitate sms formation, oligonucleotides containing two cytidine stretches of unequal length (C(n)XC(m)) separated by a non-cytidine spacer were synthesized. They were designed to associate into a tetramer including an i-motif core built by intercalation of the C.C(+) pairs of the longer C stretch with the two dangling non-intercalated strands of the shorter C stretch at each end. Gel filtration chromatography shows that the non-intercalated C-rich ends give to this structure the capacity of forming extremely stable sms. Using C(7)GC(4) as a model, we find that the sms formation rate varies as the oligonucleotide concentration and increases at high temperature. Competitively with the tetramer involved in sms elongation, C(n)XC(m) oligonucleotides form i-motif dimers that compete with sms elongation. The dimer stability is strongly reduced when the pH is moved away from the cytidine pK. This results in an equilibrium shift towards the tetramer and in the acceleration of the sms formation rate. The chromatograms of the sms formed by C(7)GC(4) indicate a broad distribution. In a 1.5 mM solution incubated at 37 degrees C, the equilibrium distribution is centered on a molecular weight corresponding to the assembly of nine tetramers and the upper limit corresponds to 80 tetramers. The lifetime of this structure is about 4 days at 40 degrees C, pH 4.6.

SUBMITTER: Laisne A

PROVIDER: S-EPMC2887966 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The syntheses and structures of five mol-ecular salts of protonated 4,4,7,7-tetra-methyl-3a,5,6,7a-tetra-hydro-benzo-thia-zol-2-yl-amine (C11H19N2S+) with different deprotonated carb-oxy-lic acids (4-methyl-benzoic acid, 4-bromo-benzoic acid, 3,5-di-nitro-benzoic acid, fumaric acid and succinic acid) are reported, namely 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium 4-methyl-benzoate, C11H19N2S+·C8H7O2 -, (I), 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium 4-bromo-benzoate, C11H19N2S+·C7H4BrO2 -, (II), 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium 3,5-di-nitro-benzoate, C11H19N2S+·C7H3N2O6 -, (III), bis-(2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium) fumarate, 2C11H19N2S+·C4H2O4 2-,(IV), and the 1:1 co-crystal of bis-(2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium) succinate and 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium hydrogen succin-ate 4,4,7,7-tetra-methyl-3a,5,6,7a-tetra-hydro-benzo-thia-zol-2-yl-amine, 1.5C11H19N2S+·0.5C4H4O4 2-·0.5C4H5O4 -. 0.5C11H18N2S, (V). In every case, the cation protonation occurs at the N atom of the thia-zole ring and the six-membered ring adopts a half-chair conformation (in some cases, the deviating methyl-ene groups are disordered over two sets of sites). The C-N bond lengths of the nominal -NH+=C-NH2 fragment of the cation are indistinguishable, indicating a significant contribution of the -NH-C=N+H2 resonance form to the structure. The packing for (I)-(V) features a robust local R 2 2(8) loop motif in which the cation forms two near-linear N-H?O hydrogen bonds from the N+-H group and syn H atom of the amine group to the carboxyl-ate group of an adjacent anion [(V) shows disorder of one of these bonds over N-H?O and N?H-O contributors but the same R 2 2(8) loop results for both disorder components]. The anti H atom of the -NH2 group also forms an N-H?O hydrogen bond, which results in [001] chains in (I) and (II), isolated centrosymmetric tetra-mers in (III) and [100] chains in (IV) and (V). Hirshfeld fingerprint plots and contact percentages for the different types of contacts of the cations are discussed.

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[C7GC4]4 association into supra molecular i-motif structures.

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