In this lecture I discuss two different issues that have been recently considered in my research group. The first topic concerns the triggering of (lipophilic) guanosine self-assembly by means of light and modification of the solvent polarity. The second topic consists in the non empirical re-visitation of the Circular Dichroism spectra obtained by G-quadruplexes of different topology. Triggering of guanosine self-assembly by light and solvent variation. – The chemically driven switching between different supramolecular motifs for lipoG both in solution and at the solid-liquid interface has been already reported.1,2 I will discuss here two examples of triggering the self-assembly by means of two different types of external stimuli: light and solvent polarity variation. In the former example, the photocontrolled self-assembly of a modified guanosine nucleobase with a photoactive unit at C8 is presented.3 The compound, when in the E configuration at the photoactive unit, in the presence of a measured amount of KI self-assembles into a D4-symmetric complex consisting of two stacked G-quartets. Photoisomerization to the Z isomer determines the decomposition of the octameric complex, which is re-formed when the molecule is reverted to the E form either by thermal or photochemical back isomerization. As a second example, I report our findings on a lipophilic guanosine derivative armed with a terthiophene unit that undergoes a pronounced variation of its supramolecular organisation by changing the polarity of the solvent.4 In chloroform the guanosine derivative, templated by alkali metal ions, assembles via H-bonding in G-quartet based D4-symmetric octamers. In the more polar (and H-bond competing) acetonitrile different aggregates are observed, where the terthiophene chains are p-p stacked in a helicoidal (left-handed) arrangement. The system can be switched back and forth by subsequent addition of chloroform and acetonitrile. A non-empirical chromophoric interpretation of CD spectra of DNA G-quadruplex structures. – The number of publications where CD spectroscopy has been used to study G4-DNAs, is extremely high. However, with very few exceptions, these investigations use an empirical interpretation of CD spectra. In this interpretation two basic types of CD spectra have been associated to a single specific difference in the features of the strand folding, i.e. the relative orientation of the strands, “parallel” (all strands have the same 5’ to 3’ orientation) or “antiparallel”. The different spectral features observed for different G-quadruplexes is rationalised in terms of chromophores responsible for the electronic transitions.5 A simplified exciton coupling approach or more refined QM calculations allow to interpret the different CD features in terms of different stacking orientation (head-to-tail, head-to-head, tail-to-tail) between adjacent G-quartets irrespectively of the relative orientation of the strands (parallel/antiparallel). 1) G. P. Spada, S. Lena, S. Masiero, S. Pieraccini, M. Surin, P. Samorì, Adv. Mat. 2008, 20, 2433-2438 2) A. Ciesielski, S. Lena, S. Masiero, G. P. Spada, P. Samorì, Angew. Chem. Int. Ed. 2010, 49, 1963-1966 3) S. Lena, P. Neviani, S. Masiero, S. Pieraccini, G. P. Spada, Angew. Chem. Int. Ed. 2010,49, 3657-3660 4) S. Pieraccini, S. Bonacchi, S. Lena, S. Masiero, M. Montalti, N. Zaccheroni, G. P. Spada, Org. Biomol. Chem. 2010, 8, 774-781; 5) S. Masiero, R. Trotta, S. Pieraccini, S. De Tito, R. Perone, A. Randazzo, G. P. Spada, Org. Biomol. Chem. 2010, 8, 2683-2692;

TRIGGERING AND CD INVESTIGATION OF GUANOSINE SELF-ASSEMBLY

SPADA, GIAN PIERO
2010

Abstract

In this lecture I discuss two different issues that have been recently considered in my research group. The first topic concerns the triggering of (lipophilic) guanosine self-assembly by means of light and modification of the solvent polarity. The second topic consists in the non empirical re-visitation of the Circular Dichroism spectra obtained by G-quadruplexes of different topology. Triggering of guanosine self-assembly by light and solvent variation. – The chemically driven switching between different supramolecular motifs for lipoG both in solution and at the solid-liquid interface has been already reported.1,2 I will discuss here two examples of triggering the self-assembly by means of two different types of external stimuli: light and solvent polarity variation. In the former example, the photocontrolled self-assembly of a modified guanosine nucleobase with a photoactive unit at C8 is presented.3 The compound, when in the E configuration at the photoactive unit, in the presence of a measured amount of KI self-assembles into a D4-symmetric complex consisting of two stacked G-quartets. Photoisomerization to the Z isomer determines the decomposition of the octameric complex, which is re-formed when the molecule is reverted to the E form either by thermal or photochemical back isomerization. As a second example, I report our findings on a lipophilic guanosine derivative armed with a terthiophene unit that undergoes a pronounced variation of its supramolecular organisation by changing the polarity of the solvent.4 In chloroform the guanosine derivative, templated by alkali metal ions, assembles via H-bonding in G-quartet based D4-symmetric octamers. In the more polar (and H-bond competing) acetonitrile different aggregates are observed, where the terthiophene chains are p-p stacked in a helicoidal (left-handed) arrangement. The system can be switched back and forth by subsequent addition of chloroform and acetonitrile. A non-empirical chromophoric interpretation of CD spectra of DNA G-quadruplex structures. – The number of publications where CD spectroscopy has been used to study G4-DNAs, is extremely high. However, with very few exceptions, these investigations use an empirical interpretation of CD spectra. In this interpretation two basic types of CD spectra have been associated to a single specific difference in the features of the strand folding, i.e. the relative orientation of the strands, “parallel” (all strands have the same 5’ to 3’ orientation) or “antiparallel”. The different spectral features observed for different G-quadruplexes is rationalised in terms of chromophores responsible for the electronic transitions.5 A simplified exciton coupling approach or more refined QM calculations allow to interpret the different CD features in terms of different stacking orientation (head-to-tail, head-to-head, tail-to-tail) between adjacent G-quartets irrespectively of the relative orientation of the strands (parallel/antiparallel). 1) G. P. Spada, S. Lena, S. Masiero, S. Pieraccini, M. Surin, P. Samorì, Adv. Mat. 2008, 20, 2433-2438 2) A. Ciesielski, S. Lena, S. Masiero, G. P. Spada, P. Samorì, Angew. Chem. Int. Ed. 2010, 49, 1963-1966 3) S. Lena, P. Neviani, S. Masiero, S. Pieraccini, G. P. Spada, Angew. Chem. Int. Ed. 2010,49, 3657-3660 4) S. Pieraccini, S. Bonacchi, S. Lena, S. Masiero, M. Montalti, N. Zaccheroni, G. P. Spada, Org. Biomol. Chem. 2010, 8, 774-781; 5) S. Masiero, R. Trotta, S. Pieraccini, S. De Tito, R. Perone, A. Randazzo, G. P. Spada, Org. Biomol. Chem. 2010, 8, 2683-2692;
Guanosines and Quadruplexes
L2
L2
G. P. Spada
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/97340
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