Nick Bampos

Metalloporphyrin Oligomers with Collapsible Cavities: Characterisation and Recognition Properties of Individual Atropisomers

A flexible porphyrin trimer is shown to exist in multiple exchanging forms, each of which displays unique molecular recognition properties (see the two atropisomers below). NMR spectroscopy has been used to characterise the equilibration and recognition properties of two of these individual trimer atropisomers.

Reversing the stereochemistry of a Diels–Alder reaction: use of metalloporphyrin oligomers to control transition state stability

A cyclic Zn-porphyrin trimer with ethyne and butadiyne links stabilises the thermodynamically disfavoured endo transition state and product of a reversible Diels–Alder reaction; at 30°C the endo adduct is formed rapidly and almost exclusively. Linear porphyrin dimers containing ethyne or butadiyne links show related stereochemical preferences to the corresponding cyclic trimers; substantial rate accelerations are observed despite rotational freedom around the linkers. A qualitative correlation is observed between rate acceleration (i.e., transition state binding) and product binding, and the results are rationalised in terms of host geometry and flexibility.

A supramolecular array assembled via the complementary binding properties of ruthenium(II) and tin(IV) porphyrins

A new porphyrin trimer has been self-assembled by employing the mutually non-interfering coordination properties of the ruthenium(II) and tin(IV) centers to form a multi-metal array. The photo- and electro-chemical properties of this array are also reported.

A combined covalent and coordination approach to dendritic multiporphyrin arrays based on ruthenium(II) porphyrins

Two strategies have been employed in the construction of multiporphyrin arrays; the principles are illustrated by a seven-porphyrin array consisting of two three-porphyrin dendrons coordinated to a single ruthenium(II) porphyrin, and by a six-porphyrin array containing three ruthenium(II) porphyrinmonomers coordinated to a tripyridyl porphyrin trimer. Thesesystems possess both redox and photophysical functionalitybuilt-in to the overall structure.

Phosphine-substituted porphyrins as supramolecular building blocks

A route to alkyne-phosphine-substituted metalloporphyrins is presented. The X-ray structure of the methanol adduct of a diphenylphosphine Zn(II) porphyrin reveals solid state dimerisation accompanied by proton transfer from coordinated methanol to phosphine in a process reminiscent of carbonic anhydrase. The ability of the phosphine-substituted porphyrins to form non-covalent arrays with a Ru(II) porphyrin was explored using 1H/31P NMR and UV/vis spectroscopy as well as MALDI-TOF mass spectrometry.

Anion templated assembly of an indolocarbazole containing pseudorotaxane on beads and silica nanoparticles

The surface covalent attachment of fluorescent axles of indolocarbazole enables anion templation to be exploited in the formation of pseudorotaxane assembliesvia the threading of neutral isophthalamide macrocycles. In utilising the surface of polystyrene beads this threading process can be followed by both magnetic resonance methods and changes in the axle fluorescent emission spectrum. The analogous surface assembly and anion templated threading can be achieved, with fluoride and sulfate, on silica nanoparticles where anion recognition and macrocycle threading are associated with equivalent and specific optical change.

Gel-phase HR-MAS 1H NMR spectroscopy as a probe for solid-tethered diimide rotaxanes and catenanes

The design and kinetically-controlled construction of a series of solid-tethered supramolecular systems utilising crown ether–naphthalene diimide host–guest chemistry are described. Functionalised polystyrene beads (ArgoGel-OH™) were utilised as the gel-phase solid support for the assembly of an appended diimide-crown catenane, and for a porphyrin-stoppered diimide-crown rotaxane. The structures of the resulting solid-tethered systems were probed using gel-phase high-resolution magic-angle spinning (HR-MAS) 1H NMR spectroscopy. The advantages of using this spectroscopic tool in conjunction with optical microscopy to probe solid-tethered supramolecular systems are discussed.

Investigation of the Hydrogen Bonding Properties of a Series of Monosaccharides in Aqueous Media by 1H NMR and IR Spectroscopy

A technique, based on 1H NMR and IR experiments, to characterise intramolecular hydrogen bonds in aqueous medium in a series of amino, amido and ammonium sugar derivatives has been established. Three groups of molecules, representing amides (4, 5 and 6), amines (7 and 8) and ammonium salts (chlorides 9 and 10, and phosphates 11 and 12), with different relative configurations of their functional groups, have been investigated to assess the effect of the nature and the stereochemistry of these groups on the hydrogen-bonding features of the sugar. The deduced features in water solution are compared to those obtained previously in nonpolar solvents. The phosphate salts of amines 7 and 8 (11 and 12) were also prepared, in order to evaluate the influence of the OH groups on the binding of the phosphate counterion, and the possibility of establishing cooperative hydrogen bonds involving the phosphate group. The data presented here indicate that the 1,3-cis-diaxial-type configuration in sugar diols and amino alcohols produces an intramolecular six-membered-ring hydrogen bond that survives in water and, moreover, offers the possibility to establish cooperative intermolecular hydrogen bonds. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Mixed cyclic trimers of porphyrins and dioxoporphyrins: geometry vs. electronics in ligand recognition

A series of metalloporphyrin-containing cyclic hosts has been prepared, which are electronically and geometrically programmed to recognize guests in a particular configuration. Electronic control is achieved by substituting the C–H meso positions with carbonyl groups, while geometric control is possible in the choice of the length of the rigid acetylene porphyrin linkers.

A self-assembling polymer-bound rotaxane under thermodynamic control

The thermodynamically controlled self-assembly of a neutral donor-acceptor rotaxane, stoppered via porphyrin coordination and bound to polystyrene beads is described, and the dynamic equilibrium between solid and solution phases has been examined by HR MAS nmr spectroscopy.