How to Adapt Scatchard Plot for Graphically Addressing Cooperativity in Multicomponent Self-Assemblies

G-Quadruplex-Proximized Aptamers (G4PA) Efficiently Targeting Cell-Surface Transferrin Receptors for Targeted Cargo Delivery

DNA-assembled multiaptamer systems have been demonstrated to significantly promote the aptamer capacity of binding cell-surface-expressed proteins. However, how to conveniently harness them for efficient transmembrane delivery of targets remains a challenge. Toward this goal, here we engineer a G-quadruplex-proximized aptamer (G4PA) system in which a DNA aptamer specific for transferrin receptor (TfR) is guided by a bimolecular G4 and assembles into a dimerized proximity form that well matches homodimeric TfR highly expressed on the cancer cell surface. This system displays a higher capacity for targeting cell-surface TfR than the monomeric aptamer and super transmembrane transportation of nucleic acid cargoes, which is comparable to that of conventional liposome transfection but overcomes the lack of targeting ability of the latter. The G4PA system is then applied to the targeted delivery of siRNA for PLK1 gene silencing in positive cells rather than negative controls, showing great promise for use in precise anticancer therapy.

Positive Cooperativity Induced by Interstrand Interactions in Silver(I) Complexes with α,α'-Diimine Ligands

The allosteric positive cooperativity accompanying the formation of compact [CuI (α,α'-diimine)2 ]+ building blocks contributed to the historically efficient synthesis of metal-containing catenates and knotted assemblies. However, its limited magnitude can easily be overcome by the negative chelate cooperativity that controls the overall formation of related polymetallic multistranded helicates and grids. Despite the more abundant use of analogous dioxygen-resistant [AgI (α,α'-diimine)2 ]+ units in modern entangled metallo-supramolecular assemblies, a related thermodynamic justification was absent. Solid-state structural characterizations show the successive formation of [AgI (α,α'-diimine)(CH3 CN)][X] and [AgI (α,α'-diimine)2 ][X] upon the stepwise reactions of α,α'-diimine=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) derivatives with AgX (X=BF4 - , ClO4 - , PF6 - ). In room-temperature, 5-10 mM acetonitrile solutions, these cationic complexes exist as mixtures in fast exchange on the NMR timescale. Spectrophotometric titrations using the unsubstituted bpy and phen ligands point to the statistical (=non-cooperative) binding of two successive bidentate ligands around AgI , a mechanism probably driven by the formation of hydrophobic belts, that overcomes the unfavorable decrease in the positive charge borne by the metallic cation. Surprisingly, the addition of methyl groups adjacent to the nitrogen donors (6,6' positions in dmbpy; 2,9 positions in dmphen) induces positive cooperativity for the formation of [Ag(dmbpy)2 ]+ and [Ag(dmphen)2 ]+ , a trend assigned to additional stabilizing interligand interactions. Adding rigid and polarizable phenyl side arms in [Ag(Brdmbpy)2 ]+ further reinforces the positively cooperative process, while limiting the overall decrease in metal-ligand affinity.

Large polarization of push–pull “Cruciforms” via coordination with lanthanide ions

“Bent” or “cruciform” shaped conjugated push–pull compounds exhibit striking differences in their supramolecular recognition of lanthanide cations, with in an outstanding supramolecular polarization.

Controlling Lanthanide Exchange in Triple-Stranded Helicates: A Way to Optimize Molecular Light-Upconversion

The kinetic lability of hexadentate gallium-based tripods is sufficient to ensure thermodynamic self-assembly of luminescent heterodimetallic [GaLn(L3)₃ ]⁶⁺ helicates on the hour time scale, where Ln is a trivalent 4f-block cation. The inertness is, however, large enough for preserving the triple-helical structure when [GaLn(L3)₃ ]⁶⁺ is exposed to lanthanide exchange. The connection of a second gallium-based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr(L4)₃ ]⁹⁺ can be diluted into closed-shell [GaYGa(L4)₃ ]⁹⁺ matrices without metal scrambling. This feature is exploited for pushing molecular-based energy-transfer upconversion (ETU) at room temperature.

Synthesis, chiroptical and SHG properties of polarizable push–pull dyes built on π-extended binaphthyls

Novel binaphthyl push–pull dyes extend their π-bridge and incorporate as acceptors pyridine units, useful for further supramolecular polarization.

Homochiral BINOL-based macrocycles with π-electron-rich, electron-withdrawing or extended spacing units as receptors for C60

The “one-pot” synthesis of several homochiral macrocycles has been achieved by using π-electron-rich, electron-deficient or extended aromatic dicarboxylic acids in combination with an axially-chiral dibenzylic alcohol, derived from enantiomerically-pure BINOL. Two series of cyclic adducts with average molecular D₂ and D₃ molecular symmetries, respectively, have been isolated in pure forms. Their yields and selectivities deviate substantially from statistical distributions. NMR and CD spectroscopic methods are efficient and functional in order to highlight the variability of shapes of the covalent macrocyclic frameworks. The larger D₃ cyclic adducts exhibit recognition properties towards C₆₀ in toluene solutions (up to log K_a = 3.2) with variable stoichiometries and variable intensities of the charge-tranfer band upon complexation.

Conversion of molecular information by luminescent nanointerface self-assembled from amphiphilic Tb(III) complexes

A novel amphiphilic Tb(3+) complex (TbL(+)) having anionic bis(pyridine) arms and a hydrophobic alkyl chain is developed. It spontaneously self-assembles in water and gives stable vesicles that show sensitized luminescence of Tb(3+) ions at neutral pH. This TbL(+) complex is designed to show coordinative unsaturation, i.e., water molecules occupy some of the first coordination spheres and are replaceable upon binding of phosphate ions. These features render TbL(+) self-assembling receptor molecules which show increase in the luminescence intensity upon binding of nucleotides. Upon addition of adenosine triphosphate (ATP), significant amplification of luminescent intensity was observed. On the other hand, ADP showed moderately increased luminescence and almost no enhancement was observed for AMP. Very interestingly, the increase in luminescence intensity observed for ATP and ADP showed sigmoidal dependence on the concentration of added nucleotides. It indicates positive cooperative binding of these nucleotides to TbL(+) complexes preorganized on the vesicle surface. Self-assembly of amphiphilic Tb(3+) receptor complexes provides nanointerfaces which selectively convert and amplify molecular information of high energy phosphates linked by phosphoanhydride bonds into luminescence intensity changes.

Positive cooperative mechanistic binding of proteins at low concentrations: a comparison of poly (sodium N-undecanoyl sulfate) and sodium dodecyl sulfate

The interactions of the negatively charged achiral molecular micelle, poly (sodium N-undecanoyl sulfate) (poly-SUS), with four different proteins using intrinsic and extrinsic fluorescence spectroscopic probes, are studied. A comparison of poly-SUS with the conventional surfactant, sodium dodecyl sulfate (SDS), and the monomeric species, SUS, is also reported. In this work, we observed that poly-SUS preferentially binds to acidic proteins, exhibiting positive cooperativity at concentrations less than 1 mM for all proteins studied. Moreover, it appears that the hydrophobic microdomain formed through polymerization of the terminal vinyl group of the monomer, SUS, is largely responsible for the superior binding capacity of poly-SUS. From these results, we conclude that the interactions of poly-SUS with the acidic proteins are predominantly hydrophobic and postulate that poly-SUS would produce superior interactions relative to SDS at low concentrations in polyacrylamide gel electrophoresis (PAGE). As predicted, use of poly-SUS allowed separation of the His-tagged tumor suppressor protein, p53, at sample buffer concentrations as low as 0.08% w/v (2.9 mM), which is 24 times lower than required for SDS in the standard reducing PAGE protocol. This work highlights the use of poly-SUS as an effective surfactant in 1D biochemical analysis.

The Origin of the Surprising Stabilities of Highly Charged Self-Assembled Polymetallic Complexes in Solution

The thermodynamics of electrochemical and complexation reactions involving the heterobimetallic triple-stranded helicates [MA(L5)3]n+ (M=Ru(II), Cr(III) and A=Ca(II), Lu(III)) reveal that solvation processes mask intramolecular intermetallic repulsions in solution, a phenomenon at the origin of the surprising stabilities of highly charged self-assembled polymetallic complexes in solution. A judicious combination of Born-Haber cycles and the Born equation restores the expected electrostatic trend in the gas phase, in which intermetallic interactions can be simply modeled using a standard Coulombic approach. Semiquantitative estimation and prediction of the contribution of the intermetallic repulsion to the total free energy of the formation of discrete polymetallic assemblies in solution become thus accessible. This point is crucial for programming stable metallosupramolecular architectures in solution.

Exploiting the dithiocarbamate ligand in metal-directed self-assembly

The dithiocarbamate (dtc) ligand has proved to be an extremely versatile and robust motif for metal-directed self-assembly. Its ease of formation and wide ranging coordination chemistry has led to the formation of an array of novel and complex supramolecular architectures. Well-defined structures such as macrocycles, cages, catenanes and nanodimensional assemblies can be generated using a variety of oligomeric dithiocarbamate constructs in combination with transition metals. Polymetallic assemblies containing appropriately designed host cavities have allowed the binding of cationic, anionic and neutral guest species to be investigated. The use of the dithiocarbamate ligand has recently expanded to stabilising gold nanoparticles and preparing multimetallic wires and arrays. This perspective highlights the considerable potential that this simple and versatile ligand has to offer.