Investigation of Guanosine‐Quartet Assemblies by Vibrational and Electronic Circular Dichroism Spectroscopy, a Novel Approach for Studying Supramolecular Entities

Abstract

The self-assembly of guanosine-5'-hydrazide G-1 in D(2)O, in the presence and absence of sodium cations, has been investigated by chiroptical techniques: electronic (ECD) and the newly introduced vibrational (VCD) circular dichroism spectroscopy. Using a combination of ECD and VCD with other methods such as IR, electron microscopy, and electrospray ionization mass spectrometry (ESI-MS) it was found that G-1 produces long-range chiral aggregates consisting of G-quartets, (G-1)(4), subsequently stacked into columns, [(G-1)(4)](n), induced by binding of metal cations between the (G-1)(4) species. This process, accompanied by gelation of the sample, is highly efficient in the presence of an excess of sodium cations, leading to aggregates with strong quartet-quartet interaction. Thermally induced conformational changes and conformational stability of guanosine-5'-hydrazide assemblies were studied by chiroptical techniques and the melting temperature of the hydrogels formed was obtained. The temperature-dependent experiments indicate that the long-range supramolecular aggregates are dissociated by increasing temperature into less ordered species, monomers, or other intermediates in equilibrium, as indicated by MS experiments.

Molecular and supramolecular chirality in gemini‐tartrate amphiphiles studied by electronic and vibrational circular dichroisms

“…13 Ab initio calculations combined with VCD experiments has been used during the two last decades to determine the absolute configuration of small and medium-sized molecules [12][13][14] and more recently to elucidate supramolecular structures. [15][16][17][18][19][20][21][22][23][24] Moreover, several VCD studies of dialkyl tartrates (essentially dimethyl-tartrate) have been performed to determine their predominant conformation in various solvents (CCl 4 , DMSO-d 6 CS 2 , D 2 O), [25][26][27][28] complexed with cyclodextrins 28 and confined in lecithin reverse micelles. In the present contribution, ECD and VCD have been used to characterize the molecular and supramolecular chirality in gemini-tartrate amphiphiles.…”

Formation and temperature stability of G‐quadruplex structures studied by electronic and vibrational circular dichroism spectroscopy combined with ab initio calculations

“…The C¼ ¼N absorption band of guanine shifted from 1578 to 1587 cm 21 and decreased in intensity, which is suggestive of p-p guanine interactions; the appearance of an IR absorption band at 1535 cm 21 suggests that the guanosines were present in a highly ordered structure, namely in helices. 33,37 The fast migrating trace observed by nondenaturing electrophoresis at the 500 mmol l 21 Na 1 or K 1 concentration corresponds to such compact structure. The low increase in intensity of the positive VCD band at 1534(1) cm…”

Bioinspired interactions studied by vibrational circular dichroism

“…41 This compound forms a stable hydrogel in the presence of alkali metal cations. It was proposed 43 that gelation of the sample is caused by the formation of supramolecular aggregates consisting of G-quartets that may be stacked into columns by binding of monovalent metal cations between tetramers. VCD, having the advantage of exquisite sensitivity to the molecular structure of chiral molecular systems, clearly offers the possibility to characterize the structures of G-hydrazide, measured as a solution in DMSO-d 6 and as a hydrogel in sodium phosphate/D 2 O buffer spectra, on the basis of their distinctively different VCD spectra (Fig.…”

“…In addition, the combination of experimental and theoretical approaches allowed an assignment of the fundamental modes in the spectral range 1800-1600 cm 21 . According to mass spectroscopy, 43 the preferred species in the gel state is the G-tetramer. It must be hypothesized, however, that the aggregation in a gel state may involve dimers and other intermediates.…”