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Maxwell J Gunter

Publications and source records attributed to Maxwell J Gunter.

7 recordsLinked to original sources
PubMed2006

Probing the dimensions of semi-rigid inner functionalised U-shaped bis-porphyrin cavities.

The synthesis of a series of open U-shaped bis-porphyrin cavity molecules is described, with bridged bicyclic backbones to confer rigidity, and a pendant substituted aromatic probe unit suspended on the inside of the cavity. The dimensions and flexibility of the bis-zincporphyrin cavity were probed using several different techniques. Initially the molecular ruler concept was employed, using flexible bidentate ligands as guests with a range of possible linear dimensions. Secondly, NMR methods were employed with rigid bidentate ligand guests of fixed lengths, and thirdly diffusion based NMR methods were utilised. The range of inter-porphyrin distances estimated by these methods suggests that these types of open-cavity systems have a surprising degree of flexibility.

Magnetic Resonance Spectroscopy↗
PubMed2005

Flexible self-assembling porphyrin supramolecules.

The design and chemical synthesis of a series of hybrid flexible self-assembling supramolecules utilising both crown ether-naphthalene diimide host-guest chemistry and metalloporphyrin-pyridyl coordination is discussed. The resulting compound structures and dynamics are probed using a variety of techniques, including diffusion ordered NMR spectroscopy (DOSY) and cold-spray ionisation mass spectrometry (CSI-MS).

Crown Ethers↗
PubMed2003

Translational isomerism and dynamics in multi-hydroquinone derived porphyrin [2]- and [3]-catenanes.

A series of porphyrins strapped with polyether chains containing two or three 1,4-dioxybenzene units has been synthesised with a view to the production of porphyrin-containing [2] and [3]catenanes, where the porphyrin is strapped between ortho-positions of 5,15-(meso)-diaryl groups, and is interlinked with the bipyridinium macrocycle cyclobis(paraquat-4,4'-biphenylene). The porphyrins were isolated as mixtures of atropisomers, where the linking strap spans across the face of the porphyrin (alpha,alpha-isomer), or 'twisted' around its side (alpha,beta-isomer). Their structures were determined by detailed 1H NMR spectroscopy. The bis-1,4-dioxybenzene-strapped derivatives were shown to undergo atropisomerisation on heating, to produce an equilibrium mixture. Catenation under high pressure conditions of the mixture, or of the individual isomers, produced only a single catenane, that of the alpha,alpha-isomer. Its structure was determined by mass spectral and dynamic NMR measurements. Rates were determined for: (i) translational motion or 'shuttling' between 1,4-dioxybenzenes; (ii) 'rotation' of the macrocycle around the 1,4-dioxybenzene axis; and (iii) 'rocking' of the 1,4-dioxybenzene within the macrocycle. The atropisomers of the strapped derivatives containing three 1,4-dioxybenzene units were also separated, and subjected to catenation. Both [2]- and [3]catenanes were isolated, and were shown to be stable to further atropisomerisation. Their solution structures were probed in detail by dynamic 1H NMR measurements. The rates for shuttling and rotation were obtained in certain cases, although the complexity of the spectra of the [3]catenanes prevented a more detailed investigation.

Journal Article↗
PubMed2003

Neutral pi-associated porphyrin [2]catenanes.

A series of neutral porphyrin-containing catenanes has been synthesised, consisting of a zinc porphyrin strapped by a polyethylene glycol chain containing four or six ethylenoxy-units and incorporating a central naphthoquinol unit, interlinked with a naphthalene diimide macrocycle. The napthalene diimide precursor units exhibit only weak binding with the strapped porphyrins (Ka between 8 and 0.02 M(-1)), but good yields of the catenanes were obtained by Glaser coupling of the alkynyl napthalene diimide precursors in the presence of the porphyrins. Structures and solution conformations were determined by mass spectral and detailed 1H NMR studies. For the longer strapped porphyrins, the diimide macrocycle rotates around the central naphthoquinol unit at 420-450 times per second, while rotation is virtually prevented in the tighter strapped derivatives. A second dynamic process occurring in both sets of catenanes and described as 'yawing' leads to inequivalence in the naphthalene moieties. UV-Visible spectra indicate charge transfer interactions and electronic communication between the two components of the catenane.

Journal Article↗
PubMed2003

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.

Journal Article↗
PubMed2003

Photoinduced electron transfer between the interlocked components of porphyrin catenanes: effect of the presence of nonequivalent reduction sites on the charge recombination rate.

[2]Catenanes made up of several polyether-strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat-p-phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro-active subunits. The redox patterns represent useful "fingerprints" that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with tau=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge-separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41+/-4 ps. Comparison of the electron transfer rates CS and CR in the host-guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two-step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination.

Journal Article↗