Geometry induced sequence of nanoscale Frank-Kasper and quasicrystal mesophases in giant surfactants.

Frank-Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results from nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with "soft" spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures.

Supercharged, Precise, Megametallodendrimers via a Single-Step, Quantitative, Assembly Process.

Synthesis of giant unimolecular dendrimers is challenging due, in part, to difficulties encountered at higher generations, in both convergent and divergent protocols because of the multistep construction/purification process. Herein, we report a hybrid synthetic procedure in which the core is constructed last. This quantitative assembly generated a metallodendrimer that is supercharged (120+), large (11.3 nm diameter), and its core was previously established. The series of complexes has been unequivocally characterized by NMR, ESI-IM-MS, and TEM techniques.

Controlled Interconversion of Superposed-Bistriangle, Octahedron, and Cuboctahedron Cages Constructed Using a Single, Terpyridinyl-Based Polyligand and Zn(2.).

Metallomacromolecular architectural conversion is expanded by the characterization of three different structures. A quantitative, single-step, self-assembly of a shape-persistent monomer, containing a flexible crown ether moiety, gives an initial Archimedean-based cuboctahedron that has been unequivocally characterized by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross section analysis. Both dilution and exchange of counterions, transforms this cuboctahedron into two identical octahedrons, which upon further dilution convert into four, superposed, bistrianglar complexes; increasing the concentration reverses the process. Ion binding studies using the cuboctahedral cage were undertaken.

Characterization of Metallosupramolecular Polymers by Top-Down Multidimensional Mass Spectrometry Methods.

Top-down multidimensional mass spectrometry, interfacing electrospray ionization (ESI) with ion mobility mass spectrometry (IM-MS), and energy resolved (gradient) tandem mass spectrometry (gMS(2) ) are employed to characterize the stoichiometries, architectures, and intrinsic stabilities of coordinatively bound supramolecular polymers containing terpyridine functionalized ligands. As a soft ionization method, ESI prevents or minimizes unwanted assembly destruction. The IM dimension affords separation of the supramolecular ions by charge and collision cross-section (a function of size and shape). The mobility separated ions are subsequently identified by their mass-to-charge-ratios and isotope patterns in the orthogonal MS dimension. Finally, the gMS(2) dimension reveals bond breaking proclivities and disintegration pathways of the assemblies. The described methodology does not require high sample purity due to the dispersive nature of the IM and MS steps. Its utility is demonstrated with the comprehensive analysis of bisterpyridine-based metallomacrocycle mixtures and a tristerpyridine based complex with 3-D nanosphere-like architecture.

Precise Molecular Fission and Fusion: Quantitative Self-Assembly and Chemistry of a Metallo-Cuboctahedron.

Inspiration for molecular design and construction can be derived from mathematically based structures. In the quest for new materials, the adaptation of new building blocks can lead to unexpected results. Towards these ends, the quantitative single-step self-assembly of a shape-persistent, Archimedean-based building block, which generates the largest molecular sphere (a cuboctahedron) that has been unequivocally characterized by synchrotron X-ray analysis, is described. The unique properties of this new construct give rise to a dilution-based transformation into two identical spheres (octahedra) each possessing one half of the molecular weight of the parent structure; concentration of this octahedron reconstitutes the original cuboctahedron. These chemical phenomena are reminiscent of biological fission and fusion processes. The large 6 nm cage structure was further analyzed by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross-section analysis. New routes to molecular encapsulation can be envisioned.

Design, microwave-assisted synthesis and HIV-RT inhibitory activity of 2-(2,6-dihalophenyl)-3-(4,6-dimethyl-5-(un)substituted-pyrimidin-2-yl)thiazolidin-4-ones.

A series of novel thiazolidin-4-ones bearing a hydrophobic substituent at 5-position on the 4,6-dimethyl-pyrimidine ring at N-3 (5c-i and 6c-i) were designed on the prediction of QSAR studies, synthesized in good yields of 60.1-85.3% by microwave-assisted one-pot protocol with the combination of using dicyclohexylcarbonimide (DCC) as the promotor, and evaluated as HIV-1 reverse transcriptases inhibitors. The results of in vitro HIV-1 RT kit assay showed that some of the new compounds, such as 5c, 6c, 5d, 6d, 5g, 5h and 6i, could effectively inhibit RT activity. Among them, compounds 5c and 6c where ethyl group existed at 5-position on N-3 pyrimidine ring were the best ones with the IC(50) value of 0.26 microM and 0.23 microM, respectively. Structure-activity relationship analysis of these analogues suggested that the overall hydrophobicity and steric factor were important to the anti-HIV RT activity. The mechanism of the intramolecular cycloamidation promoted by DCC was also investigated with the key uncyclized intermediate 13.

Multicomponent reassembly of terpyridine-based materials: quantitative metallomacrocyclic rearrangement.

Mixing of metallocyclic trimers and tetramers in an exact 1 : 1.5 stoichiometry provided new supramolecular triangles in quantitative yields. Characterization of the new hetero-nuclear metallomacrocycles was achieved by (1)H, 2D-COSY, 2D-NOESY, and (13)C NMR spectroscopy, along with ESI and TWIM mass spectrometry. Gradient tandem MS (gMS(2)) provided insight into the stabilities of the binuclear structures.

Directed flexibility: self-assembly of a supramolecular tetrahedron.

Self-assembly of a tribenzo-27-crown-9 ether functionalized with six terpyridines generated (85%) an expanded tetrahedral structure comprised of four independent triangular surfaces interlinked by crown ether vertices.

Synthesis and biological activity of novel thiazolidin-4-ones with a carbohydrate moiety.

Some novel 2-aryl-3-[5-deoxy-1,2-O-isopropylidene-alpha-D-xylofuranose-5-C-yl] thiazolidin-4-ones were synthesized by the three-component condensation of an amino sugar 1, an aromatic aldehyde 2, and mercaptoacetic acid 3 in the presence of DCC and DMAP at room temperature. Two diastereoisomers 4 and 5 were afforded as the main products in totally isolated yields of 25.4-70%. The reaction was carried out with almost no observed stereoselectivity except in the case of 2c, which showed a moderate stereoselectivity. The structures of the new compounds were determined by NMR spectroscopy and mass spectrometry (MS), and the configuration of the newly generated chiral carbon (C-2) in the thiazolidin-4-one ring was tentatively assigned based on the X-ray crystallographic structure of 5d and the comparison of their corresponding NMR signals. The antitumor (human cervical cancer cells) activity and the inhibition against the glycosidases (alpha-glucosidase, beta-glucosidase, alpha-amylase) have been evaluated for the new compounds, some of which exhibited antitumor activity.