Steric and Electronic Factors Affecting the Conformation of Bimetallic CuI Complexes: Effect of the Aliphatic Spacer of Tetracoordinating Schiff-Base Ligands.

A family of six homoleptic [CuI (Ln )]2 (ClO4 )2 and six heteroleptic [CuI (Ln )(PPh3 )2 ]2 (ClO4 )2 bimetallic complexes, in which Ln are bis-Schiff base ligands with alkyl spacers of variable length (n=2-7 -CH2 -), were prepared to evaluate the role of the spacer on the formation of helicates or mesocates. In the homoleptic series, spectroscopic and theoretical studies indicate that preferences for a conformation are based on energetic parameters, mainly, the establishment of noncovalent interactions. The odd-even nature of the spacers preconditions the superposition of the aromatic rings to allow the juxtaposition necessary for noncovalent interactions, whereas the increase of the length reduces the strength of such interactions. Consequently, complexes with even-spacers of short length were identified as helicates in solution, [CuI (Ln )]22+ (n=2, 4). Complexes [CuI (Ln )]22+ (n=3-7) dissociate in solution to produce the monometallic complexes in equilibrium, [CuI (Ln )]+ . The stability of the bimetallic species is discussed in terms of their conformations. The set of heteroleptic complexes was prepared to evaluate the reach of the "odd-even rule" in the solid, which is based on the "zig-zag" arrangements of the spacers. Based on crystallographic information, "S-" and "C"-type conformations of Ln are related to even and odd spacers, respectively. This trend is considered in addition to other factors to explain preferences for either a mesocate or helicate conformation in the homoleptic series.

Selective G-quadruplex binding by oligoarginine-Ru(dppz) metallopeptides.

A set of Ru(ii) metallopeptides containing the dppz ligand has been synthesized using SPPS methods. Fluorescence titration studies show that those metallopeptides featuring an octaarginine tail display a large binding preference for DNA G-quadruplex structures over those lacking it, and also that the interplay between the octoarginine functionalization and the ancillary ligand in the complex has an essential role in the recognition process. Furthermore, the oligoarginine metallopeptides are also efficiently internalized, causing cell death with signs of apoptosis.

Copper(II)-Thymine Coordination Polymer Nanoribbons as Potential Oligonucleotide Nanocarriers.

The direct reaction between copper nitrate, thymine-1-acetic acid, and 4,4'-bipyridine in water leads to the formation of a blue colloid comprising uniform crystalline nanoribbons (length >1 µm; width ca. 150-185 nm; diameter ca. 15-60 nm) of a coordination polymer. The polymer displays a thymine-based structure freely available for supramolecular interactions. These nanostructures show significant selective interaction with single-stranded oligonucleotides based on adenine. Remarkably, they present low cell toxicity in three cell lines-despite the copper(II) content-and can be used as nanocarriers of oligonucleotides. These results suggest the potential of these types of nanostructures in several biological applications.

Antibacterial Activity of DNA-Stabilized Silver Nanoclusters Tuned by Oligonucleotide Sequence.

Silver nanoclusters (AgNCs) stabilized by DNA are promising materials with tunable fluorescent properties, which have been employed in a plethora of sensing systems. In this report, we explore their antimicrobial properties in Gram-positive and Gram-negative bacteria. After testing 9 oligonucleotides with different sequence and length, we found that the antibacterial activity depends on the sequence of the oligonucleotide employed. The sequences tested yielded fluorescent AgNCs, which can be grouped in blue, yellow, and red emitters. Interestingly, blue emitters yielded poor antibacterial activity, whereas yellow and red emitters afforded an activity similar to silver nitrate. Furthermore, structural studies using circular dichroism indicate the formation of complexes with different stability and structure, which might be one of the factors that modulate their activity. Finally, we prepared a trimeric structure containing the sequence that afforded the best antimicrobial activity, which inhibited the growth of Gram-positive and negative bacteria in the submicromolar range.

Resolution and characterization of helicate dimer and trimer complexes of 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane with copper(I).

Complexation of copper(I) with the binucleating ligand, 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane, mphenpr, result in formation of helical dimers, [Cu2(mphenpr)2](2+). The resolution of the enantiomeric forms of the dimers has been carried out with Δ-[As(cat)3](-) as resolving agent and X-ray structures for two compounds, P-[Cu2(mphenpr)2](Δ-[As(cat)3])2 and P-[Cu2(mphenpr)2](Δ-[As(cat)3])2·4(CH3CN), are reported. The rate of racemization in poorly-coordinating solvents has been examined by (1)H NMR, and is slow. At saturating concentrations of [[Cu2(mphenpr)2](2+)] in acetonitrile, crystals of the helical trimeric complex [Cu3(mphenpr)3](ClO4)3 are obtained. The X-ray structure of the trimer is reported. This species has also been resolved. As with the helical dimer, racemization in poorly-coordinating solvents is slow, and circular dichroism and (1)H NMR spectra are reported. The absolute configuration of the resolved complex, P-[Cu3(mphenpr)3](Δ-[As(cat)3])3, has been determined by X-ray crystallography.

Enhanced fluorescence of silver nanoclusters stabilized with branched oligonucleotides.

DNA stabilized silver nanoclusters (AgNCs) are promising optical materials, whose fluorescence properties can be tuned by the selection of the DNA sequence employed. In this work we have used modified oligonucleotides in the preparation of AgNCs. The fluorescent intensity obtained was 60 times higher than that achieved with standard oligonucleotides.