ISMSC 2007 - Università degli Studi di Pavia

Interconversion between a supramolecular polymer and a discrete
octameric species from a guanosine derivatives at surfaces
Omar Pandoli a , Stefano Masiero a , Silvia Pieraccini a , Paolo Samorì b and Gian Piero Spada a
a
Dipartimento di Chimica Organica “A. Mangini”, Alma Mater Studiorum Università di Bologna,
Via San Giacomo 11, 40126 Bologna, Italy
b
ISIS-ULP, 8 allèe Gaspard Monge, 67000 Strasbourg, France & ISOF-CNR, via Gobetti 101,
40129 Bologna, Italy
Lipophilic guanosines are unique building blocks which are capable of self-assembling into
different structures depending on the experimental conditions 1 . In the presence of certain
cations, they can form G-quartet-based octamers or columnar aggregates depending on the
concentration of the cation and nucleobase. We have recently proven that it is possible to
externally trigger in solution a tuneable interconversion between two highly ordered guanine
based supramolecular motifs, i.e. G-ribbons into G-quartet columns 2 (Figure1). With the final
goal of obtaining a prototype of a molecular device, we are investigating the transfer of this
“switch” from solution to a surface.
In this communication we describe the self-assembly of 1 onto the HOPG surface either as neat
compound or in the presence of metal cations. The obtained sub-molecularly resolved STM
results were corroborated by molecular modelling.
1
N
N
N
N
N
H H
N N
N
N H N
N
HN
N
N
N
N
N H H
O H
O
N
N
N H
H N
O
N
HO
H
NH
N H
N
N
H
H
O N
O
N H
H N
N
O N
H OH
H
NN
N
N
N
N
HN
N H
N
N
N
N
H H
N
H H
N N
N
N H N
N
HN
N
N
N
N
N H H
O H
O
N
N
N H
H N
O
N
HO
H
NH
N H
N
N
H
H
O N
O
N H
H N
N
O N
H OH
H
NN
N
N
N
N
HN
N H
N
N
N
N
H H
N
H H
N N
N
N H N
N
HN
N
N
N
N
N H H
O H
O
N
N
N H
H N
O
N
HO
H
NH
N H
N
N
H
H
O N
O
N H
H N
N
O N
H OH
H
NN
N
N
N
N
HN
N H
N
N
N
N
H H
N
H H
N N
N
N H N
N
HN
N
N
N
N
N H H
O H
O
N
N H
H N
O
N
HO
H
H
N HN
H
H
O N
O
N H
H N
O N
H OH
H
NN
N
N
N
N
HN
N H
N
N
N
N
H H
Figure 1
NN
NN
NN
NN
NN NN NN
NN
HH
HH
N O
H
N O
N H N O
H
N O
N H N O
H
N O
N H N O
H
N O
N H
N H
N H
N H
N H
N H
N H
N H
N H
NN
NN
HH
HH
N
H N
N H N
H
N H N
H N
N H N
H
H
OO
N N
H N
N H N
H
N H N
H N
N H N
H
H
OO
N
OO
OO
NN
NN
HH
HH
HH
HH
NN
NN
NN
NN
NN
NN
NN
NN
PSB 31
[1] a) G.P. Spada, G. Gottarelli, Chem. Rec 2004, 4, 39-49; b) G.P. Spada, J.T. Davis, Chem.
Soc. Rev. 2007, 36, 296-313
[2] S.Pieraccini, S. Masiero, O. Pandoli, P. Samorì, and G.P. Spada, Organic Letters 2006, 8,
3125-8
Spectroscopic study of of lasalocid ester with 2-thio-1-ethanol and its
complexes with monowalent cations
Radosaw Pankiewicz, Grzegorz Schroeder, Bogumi Brzezinski
Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, PL-60780 Pozna, Poland
e-mail: radek@px.pl
HO
O
SH
O
OH
Lasalocid ester with 2-thio-1-ethanol
Ionophorous antibiotics are a group of bioactive molecules able to transport monovalent and
bivalentmetal cations across natural and artificial lipid membranes. A polyether antibiotic –
Lasalocid belongs to this class of compounds. Lasalocid (isolated from Streptomyces
lasaliensis) is a good anticoccidial agent for cattle, sheep and chicken. In the cell membrane
lasalocid exchanges metal ions against H + , leading to changes in the pH values and to an
increase in osmotic pressure inside the cell, which finally leads to the cell death. A new ester of
lasalocid with 2-thio-1-ethanol has been synthesised and its complexation of monovalent
cations has been studied by ESI mass spectrometry as well as the 1 H, 13 C NMR and FT-IR
spectroscopic methods. The ESI-MS spectra show that ester forms stable 1:1 complexes with
Li + , Na + , K + , Rb + and Cs + cations. With his lasalocid derivative self-assembled monolayers on
silver and gold have been obtained. Densely packed monolayers have remained stable and
have not desorbed from the Ag or Au electrode on the potential cycling. The structure of
ionophores and their complexes with monovalent cations were calculated and visualized by the
AM1d and PM5 semi-empirical methods. Modification of the monolayers by strong complexation
agents, like ionophores, allows their application in many areas: in electrodes, bio-sensors or
affinity chromatography.
[1] H. Tsukube, Cation – Binding by macrocycles; Marcel–Dekker: New York, 1990, 497
[2] R. Pankiewicz, G. Schroeder, B. Brzezinski, J. Mol. Struct., 2005, 733 217.
[3] B. ska, G. Schroeder, T. uczak, P. Przybylski, R. Pankiewicz, M. Betowska-
Brzezinska, B. Brzezinski, Thin Solid Films, 2006, 515, 152
[4] R. Pankiewicz, G. Schroeder, B. Brzezinski, unpublished results
O
O
O
OH
PSB 32