Ruthenium-catalyzed synthesis of 5-amino-1,2,3-triazole-4-carboxylates for triazole-based scaffolds: beyond the dimroth rearrangement.

The 5-amino-1,2,3-triazole-4-carboxylic acid is a suitable molecule for the preparation of collections of peptidomimetics or biologically active compounds based on the triazole scaffold. However, its chemistry may be influenced by the possibility of undergoing the Dimroth rearrangement. To overcome this problem, a protocol based on the ruthenium-catalyzed cycloaddition of N-Boc ynamides with azides has been developed to give a protected version of this triazole amino acid.

Lipophilic silver nanoparticles and their polymeric entrapment into targeted-PEG-based micelles for the treatment of glioblastoma.

A simple method for the synthesis of lipophilic Ag NPs have been developed. The coated Ag NPs have been entrapped into a FDA-approved and targetable PEG-based polymeric nanoparticles, and this nanocarrier has been conjugated with the peptide chlorotoxin. Uptake experiments have shown a cell-specific recognition of the Ag-1-PNPs-Cltx on U87MG cell lines in comparison to Balb/3T3.

Solvent-induced switching between two supramolecular assemblies of a guanosine-terthiophene conjugate.

We report here 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. In chloroform the guanosine derivative, templated by alkali metal ions, assembles via H-bonding in G-quartet based D(4)-symmetric octamers; the polar guanine bases are located into the inner part of the assembly and act as a scaffold for the terthienyl pendants. On the other hand, in the more polar (and H-bond competing) acetonitrile, different aggregates are observed in which the terthiophene chains are pi-pi stacked in a helicoidal (left-handed) arrangement in the central core, and the guanine bases (free from hydrogen bonding) are located at the periphery and exposed to the solvent.

Guanosine hydrogen-bonded scaffolds: a new way to control the bottom-up realisation of well-defined nanoarchitectures.

Over the last two decades, guanosine-related molecules have been of interest in different areas, ranging from structural biology to medicinal chemistry, supramolecular chemistry and nanotechnology. The guanine base is a multiple hydrogen-bonding unit, capable also of binding to cations, and fits very well with contemporary studies in supramolecular chemistry, self-assembly and non-covalent synthesis. This Concepts article, after reviewing on the diversification of self-organised assemblies from guanosine-based low-molecular-weight molecules, will mainly focus on the use of guanine moiety as a potential scaffold for designing functional materials of tailored physical properties.

The use of circular dichroism spectroscopy for studying the chiral molecular self-assembly: an overview.

Self-assembly plays an important role in the formation of many chiral biological structures and in the preparation of chiral functional materials. Therefore the control of chirality in synthetic or biological self-assembled systems is important either for the comprehension of recognition phenomena or to obtain materials with predictable and controllable properties. Circular dichroism was developed to study molecular chirality, however, because of its outstanding sensitivity to chiral perturbations of the system under investigation; it has been extended more recently to supramolecular chemistry.

Quantifying hydrogen-bonding strength: the measurement of 2hJNN couplings in self-assembled guanosines by solid-state 15N spin-echo MAS NMR.

(2h)J(NN) hydrogen-bond mediated J couplings are measured in the solid state for two synthetic deoxyguanosine derivatives by (15)N MAS NMR spin-echo experiments. The use of rotor-synchronised Hahn-echo pulse train (RS-HEPT) (1)H decoupling, with a duty cycle of 6%, allows spin-echo durations out to 200 ms, hence enabling the accurate determination of J couplings as small as 3.8 Hz.

Self-assembly of an alkylated guanosine derivative into ordered supramolecular nanoribbons in solution and on solid surfaces.

We report on the synthesis and self-assembly of a guanosine derivative bearing an alkyloxy side group under different environmental conditions. This derivative was found to spontaneously form ordered supramolecular nanoribbons in which the individual nucleobases are interacting through H-bonds. In toluene and chloroform solutions the formation of gel-like liquid-crystalline phases was observed.

The supramolecular helical architecture of 8-oxoinosine and 8-oxoguanosine derivatives.

The 8-oxoguanosine derivative 1 and the 8-oxoinosine derivative 2 b, with appropriate substituents on their ribose moieties, form hexagonal lyotropic mesophases in hydrocarbon solvents. Small-angle X-ray scattering analysis of a film of 1 and of the mesophase of 2 b, and NMR and CD spectra of isotropic solutions of 2 b, indicate that in both cases the supramolecular structures adopted are continuous helices formed by a hydrogen-bond network between the heterocyclic bases. Notably, while derivative 2 b, which bears large substituents on its ribose moiety, undergoes self-assembly and mesophase formation, oxoinosine 2 a, with only decanoyl groups on its ribose moiety, does not.

A study of the stereochemistry of 2-aryl-4,5-dimethyl-1,3-dioxolanes by cholesteric induction in nematic phases and circular dichroism spectroscopy.

[Chemical reaction: See text] The circular dichroism spectra and the twisting ability of a series of 2-aryl-4,5-dimethyl-1,3-dioxolanes used as dopants in nematic solvents have been related to their absolute configuration. Whereas the circular dichroism (CD) spectra are deeply affected by the substituents present in the aromatic ring, which in several cases cause sign inversion, the helical twisting power beta is only marginally influenced. The values of beta also seem not very sensitive to the rotamer population around the aromatic ring; this indicates the predominant importance of the chiral dioxolane ring in determining the cholesteric induction.

Homochiral helices of oligonaphthalenes inducing opposite-handed cholesteric phases.

The helical structure of the chiral nematic phases (cholesterics) obtained by doping nematic solvents with chiral non-racemic compounds is a macroscopic proof of the solute chirality. Oligonaphthalene (tetra-, hexa-, octa-) derivatives linked at the 1,4-positions have been used as chiral dopants: When the chirality axes are configurationally homogeneous (that is, all-S), the molecular structures correspond to right-handed helices. Yet, we have found series of derivatives with the surprising property that the handedness of the induced cholesteric phase alternates from positive to negative and to positive again, on passing from tetra- to hexa- and to octanaphthalene.

Supramolecular helices via self-assembly of 8-oxoguanosines.

The cooperative effect of solvophobic interactions and hydrogen bonding has been exploited to self-assemble supramolecular helical architectures of 8-oxoguanosines in different environments. This self-assembly into helical structures is completely different from that of the parent guanosines which, in the same experimental conditions, form flat, ribbonlike structures. While optical microscopy and X-ray diffraction suggest a chiral columnar aggregate in the LC phase, NMR and Circular Dichroism reveal the presence of a helical structures in solution.