Brett M. Rambo

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.

Rare-earth cation effects on three-dimensional metal–organic rotaxane framework (MORF) self assembly

A set of metal-organic rotaxane frameworks (MORFs) are constructed with the use of a tetraimidazolium macrocycle, the terephthalate dianion, and the trivalent lanthanide metal cations Nd(III), Sm(III), Eu(III) or Tb(III) and are reported herein. The specific choice of the metal cation allows for control of the structure and luminescent properties of the resulting molecular frameworks.

Reversible Anion-Induced Cross-Linking of Well-Defined Calix[4]pyrrole-Containing Copolymers

Reversible addition/fragmentation chain-transfer polymerization is used to generate a calix[4]pyrrole methacrylate-derived copolymer. The material is found to undergo supramolecular cross-linking upon exposure to select dianionic species (e.g., pyrophosphate and terephthalate salts), altering the viscoelastic properties of the copolymer in solution and in the solid state. The copolymeric material is also used for selective differentiation of mono- and bis-anions under conditions of liquid/liquid extraction.

Multicomponent Self-Assembled Metal-Organic [3]Rotaxanes.

A set of environmentally responsive metal-organic [3]rotaxanes is described. These mechanically interlocked macromolecules may be prepared in quantitative yield via a one-pot procedure involving treatment of a flexible tetracationic macrocycle, known as the Texas-sized molecular box, with tri-1,3,5-benzenetricarboxylate anion and silver cations (Ag(+)). The use of this three-component mixture gives rise to a metal-organic [3]rotaxane via a self-assembly process that occurs under ambient conditions in DMSO-d6 solution. The complex is stable in the presence of excess TFA. However, disassembly of the [3]rotaxane to produce anion-box associated entities may be triggered by adding a competitive counteranionic species (e.g., I(-)). Adding excess Ag(+) serves to reverse this decomplexation process. The nature of the [3]rotaxane complex could be fine-tuned via application of an external stimulus. Increasing the temperature or adding small molecules (e.g., D2O, methanol-d4, acetonitrile-d3, DMF-d7, acetone-d6, or THF-d8) to the initial DMSO-d6 solution induces conformational flipping of the macrocycle within the overall complex (e.g., from limiting chair to chairlike forms). Support for the molecular stimuli responsive nature of the various structures came from solution-phase one- and two-dimensional ((1)H, 1D and 2D NOESY) NMR spectroscopic studies carried out in DMSO-d6. The core metal-linked rotaxane unit was characterized via single-crystal X-ray diffraction analysis. Initial evidence that the present self-assembly process is not limited to the use of the Ag(+) cation came from studies involving Cd(2+); this replacement results in formation of 2D metal-organic rotaxane-containing frameworks (MORFs).

Covalent Polymers Containing Discrete Heterocyclic Anion Receptors

This chapter covers recent advances in the development of polymeric materials containing discrete heterocyclic anion receptors, and focuses on advances in anion binding and chemosensor chemistry. The development of polymers specific for anionic species is a relatively new and flourishing area of materials chemistry. The incorporation of heterocyclic receptors capable of complexing anions through non-covalent interactions (e.g., hydrogen bonding and electrostatic interactions) provides a route to not only sensitive but also selective polymer materials. Furthermore, these systems have been utilized in the development of polymers capable of extracting anionic species from aqueous environments. These latter materials may lead to advances in water purification and treatment of diseases resulting from surplus ions.

Poly(methyl methacrylate) copolymers containing dipyrrolylquinoxaline receptors for the colorimetric detection of halide anion salts

Described herein is the synthesis of a dipyrrolylquinoxaline (DPQ) monomeric species containing methacrylamide functionality, and its subsequent copolymerisation with methyl methacrylate (MMA). The resulting copolymers were drop casted onto glass substrates, and the resulting thin films displayed distinct colorimetric change upon exposure to hydrofluoric acid (HF) vapour. Furthermore, glass substrates coated with the DPQ–MMA copolymer could be used as ‘dip sticks’ to test for trace acid in solution, turning from yellow to red upon immersion in an aqueous solution of HF. Analysis by UV–vis spectroscopic titration allowed the association constant (K a) for interaction with fluoride (as the tetrabutylammonium salt) to be calculated as 6.16 × 105 M− 1 in CH2Cl2. Polymer coatings of this type could find applications in the colorimetric detection of HF vapour, a common hazard associated with industrial processes, such as aluminium smelting.