Multi component self-assembly: supramolecular organic frameworks containing metal-rotaxane subunits (RSOFs)

A facile, one-pot synthesis of rotaxanated supramolecular organic frameworks (RSOFs) is reported. These systems consist of bis-carboxylate anions threaded through the core of tetraimidazolium macrocycles. Trivalent metal cations, yttrium(III) and smaller lanthanides, are used to "lock" the threaded strut in place. This results in the formation of three-dimensional RSOFs.

Unconventional Kondo effect in redox active single organic macrocyclic transistors

Cyclo[6]- and cyclo[8]pyrrole, two aromatic expanded porphyrins, were studied in a single-molecule transistor (SMT) setup. The analyses of these compounds allowed us to observe an uncommon absence of an even-odd effect in the Kondo resonance in discrete, metal-free organic macrocyclic compounds. The findings from the SMT measurements of these cyclopyrroles were in accord with those from cyclic voltammetry (CV) studies and theoretical analyses. These findings provide support for the notion that SMT measurements could be useful as a tool for the characterization of similar types of aromatic macrocyclic compounds.

A cysteine-selective fluorescent probe for the cellular detection of cysteine

A series of coumarin fluorophores (1-3), each bearing a double bond conjugated quinoline unit that can undergo a Michael-type reaction with thiol-containing compounds, is reported. These systems, designed to provide so-called turn-on changes in fluorescence response when exposed to thiols, act as fluorescent chemical sensors for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). In the case of 1, selectivity for Cys over Hcy and GSH is observed, both in terms of analyte-induced signal enhancement and response time. On the basis of fluorescence spectroscopic analyses, DFT calculations, and pH dependent studies this substrate selectivity is ascribed to steric interactions between the substituents on the quinolone units present in 1 and the targeted thiols, as well as to the comparatively lower pK(a) value of Cys relative to Hcy and GSH. In aqueous solution, probe 1 was found capable of detecting Cys with a detection limit of 10(-7) m. This system was successfully applied to the fluorescence imaging of intracellular Cys in HepG2 cells.

Structurally Characterized Cationic Silver(I) and Ruthenium(II)carbene complexes of 1,2,3-Triazol-5-ylidenes

A novel 1,3,4-substituted 1,2,3-triazolium salt was found to function as an effective precursor for the synthesis of the first structurally characterized cationic silver(I) and ruthenium(II)carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom-containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornene upon activation with (trimethylsilyl)diazomethane.

Crown ether functionalized texaphyrin monomers and dimers

The synthesis and characterization of two 18-crown-6 functionalized analogues of an extensively studied gadolinium texaphyrin derivative, motexafin gadolinium (1, MGd), are reported. These are the monomeric and dimeric species, compounds 2 and 3, respectively. Both crown ether functionalized species proved to be stable at physiological pH and revealed distinct shifts in the UV spectrum when treated with sodium-, potassium-, ammonium- or zinc(II)-salts. Zinc(II) is believed to play a major role regulating apoptosis mechanisms in cancerous cells. Therefore, cytotoxicity studies of 2 and 3 were carried out using Ramos cell lines in the presence and absence of zinc(II).

Oligopyrrole macrocycles: receptors and chemosensors for potentially hazardous materials

Oligopyrroles represent a diverse class of molecular receptors that have been utilized in a growing number of applications. Recently, these systems have attracted interest as receptors and chemosensors for hazardous materials, including harmful anionic species, high-valent actinide cations, and nitroaromatic explosives. These versatile molecular receptors have been used to develop rudimentary colorimetric and fluorimetric assays for hazardous materials.

Selective anion binding by a cofacial binuclear zinc complex of a Schiff-base pyrrole macrocycle

The synthesis of the new cofacial binuclear zinc complex [Zn(2)(L)] of a Schiff-base pyrrole macrocycle is reported. It was discovered that the binuclear microenvironment between the two metals of [Zn(2)(L)] is suited for the encapsulation of anions, leading to the formation of [K(THF)(6)][Zn(2)(μ-Cl)(L)]·2THF and [Bu(n)(4)N][Zn(2)(μ-OH)(L)] which were characterized by X-ray crystallography. Unusually obtuse Zn-X-Zn angles (X = Cl: 150.54(9)° and OH: 157.4(3)°) illustrate the weak character of these interactions and the importance of the cleft preorganization to stabilize the host. In the absence of added anion, aggregation of [Zn(2)(L)] was inferred and investigated by successive dilutions and by the addition of coordinating solvents to [Zn(2)(L)] solutions using NMR spectroscopy as well as isothermal microcalorimetry (ITC). On anion addition, evidence for deaggregation of [Zn(2)(L)], combined with the formation of the 1:1 host-guest complex, was observed by NMR spectroscopy and ITC titrations. Furthermore, [Zn(2)(L)] binds to Cl(-) selectively in THF as deduced from the ITC analyses, while other halides induce only deaggregation. These conclusions were reinforced by density functional theory (DFT) calculations, which indicated that the binding energies of OH(-) and Cl(-) were significantly greater than for the other halides.

Anion-directed assembly of a three-dimensional metal-organic rotaxane framework

A three-dimensional extended, metal-organic rotaxane framework (MORF) that incorporates encircled "struts" has been synthesized through a one-pot self-assembly process involving a macrocyclic tetraimidazolium "molecular box", naphthalene dicaboxylate dianion, and Zn(II) cations. The present system represents progress towards controlling the features of three-dimensional metal-organic frameworks.

Overcoming biochemical pharmacologic mechanisms of platinum resistance with a texaphyrin-platinum conjugate

In our effort to investigate further texaphyrin conjugation as a means of increasing delivery and accumulation of known anticancer platinum agents in cancer cells, we have continued our studies on the mode of action of a texaphyrin-platinum conjugate, particularly in cisplatin-resistant tumor cells that are characterized by several mechanisms of resistance, including reduced drug accumulation. Our results provide support for the proposal that intracellular platinum and Pt-DNA adduct levels were significantly increased using our conjugate relative to corresponding Pt controls. Moreover, no differences were found in cellular accumulation and Pt-DNA adduct formation between Pt sensitive and Pt resistant ovarian cells. As a result, resistance to the conjugate was lower than cisplatin in resistant cells. Based on these results we conclude that texaphyrin conjugation provides a promising strategy for overcoming biochemical pharmacologic mechanisms of resistance.

Chemical functionalization of oligodeoxynucleotides with multiple boronic acids for the polyvalent binding of saccharides

A novel saccharide host containing four boronic acid recognition units on a single DNA duplex terminus was constructed. This construct allowed boronic acid sugar recognition in the context of double-stranded DNA to be established while highlighting the benefits of multivalency. Following the solid-phase synthesis of a bis-boronic acid tag, two end-functionalized oligonucleotides with complementary sequences were functionalized through amide ligation. By annealing the boronic acid-DNA conjugates, a tetra-boronic acid DNA duplex was assembled. The saccharide binding ability of this tetra-boronic acid host was revealed through cellulose paper chromatography in the absence and presence of various saccharides. While no appreciable saccharide binding was seen in the case of a bis-boronic DNA conjugate, the increased migration of the tetra-boronic acid host relative to the control sequences in the presence of selected monosaccharides underscored the importance of multivalent effects. We thus identified a requirement for multiple recognition sites in these conjugate systems and expect the results to facilitate future efforts toward applying synthetic recognition systems to the realm of macromolecules.

Anion responsive TTF-appended calix[4]arenes. Synthesis and study of two different conformers

Two new cone- and 1,3-alternate-calix[4]arenes (cone-1 and 1,3-alt-1), bearing four modified TTF (tetrathiafulvalene) substituents on the upper rim, have been synthesized. The binding ability of these two sets of conformers for various anions, including F(-), Cl(-), Br(-), I(-), PF6(-), ClO4(-), HSO4(-), CH3COO(-), H2PO4(-), and HP2O7(3-), was tested in organic media by monitoring the changes in their UV/vis and (1)H NMR spectra as a function of added anion, as well as via cyclovoltammetry (CV) (all anions studied as their respective TBA salts). On the basis of the present findings, we propose that incorporation of four TTF units within an overall calix[4]arene-based recognition framework produces a preorganized receptor system that displays a modest preference for the pyrophosphate (HP2O7(3-)) anion.