Self-Assembly of Pentameric Porphyrin Light-Harvesting Antennae Complexes

Haycock, Richard A.; Yartsev, Arkady; Michelsen, U.; Sundström, Villy; Hunter, Christopher A.

doi:10.1002/1521-3773(20001016)39:20<3616::aid-anie3616>3.0.co;2-w

Cited by 134 publications

(57 citation statements)

References 23 publications

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“…The synthesis of monomer 1a and oligomer precursors 4 and 5 are described in ref. 35. Dimeric porphyrin 2 was synthesized by reaction of an excess of monoaminoporphyrin 4 with terephthaloyl chloride, followed by treatment with zinc acetate.…”

Section: Methodsmentioning

confidence: 99%

Cooperativity in the self-assembly of porphyrin ladders

Camara-Campos

Hunter

Tomàs

2006

Proc. Natl. Acad. Sci. U.S.A.

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Cooperativity is a general feature of intermolecular interactions in biomolecular systems, but there are many different facets of the phenomenon that are not well understood. Positive cooperativity stabilizes a system as progressively more interactions are added, and the origin of the beneficial free energy may be entropic or enthalpic in origin. An ''enthalpic chelate effect'' has been proposed to operate through structural tightening that improves all of the functional group interactions in a complex, when it is more strongly bound. Here, we present direct calorimetric evidence that no such enthalpic effects exist in the cooperative assembly of supramolecular ladder complexes composed of metalloporphyrin oligomers coordinated to bipyridine ligands. The enthalpic contributions of the individual coordination interactions are 35 kJ⅐mol ؊1 and constant over a range of free energies of self-assembly of ؊35 to ؊111 kJ⅐mol ؊1 . In rigid well defined systems of this type, the enthalpies of individual interactions are additive, and no enthalpic cooperative effects are apparent. The implication is that in more flexible, less well defined systems such as biomolecular assemblies, the enthalpy contributions available from specific functional group interactions are well defined and constant parameters.cooperative phenomena ͉ enthalpy-entropy compensation ͉ supramolecular chemistry ͉ weak interactions C ooperativity is of fundamental importance for understanding molecular recognition processes in chemistry and biology. If two molecules bearing one complementary binding site interact to give a complex of stability ⌬G, then two molecules bearing n complementary binding sites generally interact to give a complex with stability larger than n⌬G. This phenomenon is known as positive cooperativity. The factors that are responsible for cooperative intermolecular interactions can be divided in two groups: entropic factors relating to the loss of motion of the molecules and enthalpic factors due to the reinforcement of the bonds. The simplest formulation of the entropic factors is the chelate effect: an interaction working in isolation must pay the entropic cost of bringing two molecules together, but when multiple interactions are made, this price is paid only once, so additional interactions make a bigger contribution to stability than the first one (1-3). The entropic term also includes any change in the internal rotations and vibrations of the molecules. Enthalpic contributions to cooperative binding can come from secondary functional group interactions, conformational changes, or polarization of the interacting groups. However, enthalpy and entropy are intimately related, so an increase in the enthalpic driving force for complexation has a direct impact on the mobility of the molecules involved in the complex. For weak intermolecular interactions, the entropy lost on formation of the first interaction is only a fraction of the total possible loss, because the molecules retain a good deal of independent mobility. As the number of ...

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Section: Methodsmentioning

confidence: 99%

Cooperativity in the self-assembly of porphyrin ladders

Camara-Campos

Hunter

Tomàs

2006

Proc. Natl. Acad. Sci. U.S.A.

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“…The photochemical properties of the porphyrin subunits should confer this system with interesting photophysical properties: for example, singlet energy transfer between the macrocycle and axle components. [17] Experimental Section H 4 2: A solution of 5,10,15-tris(4-n-pentylphenyl)-20-(3-aminophenyl)-21H,23H-porphin [14] (0.2856 g, 0.34 mmol) and triethylamine (0.07 mL, 0.51 mmol) in dry dichloromethane (10 mL) was added to a solution of terephthaloyl dichloride (0.0172 g, 85 mmol) in dry dichloromethane (20 mL), and the reaction mixture was left stirring overnight at room temperature. After evaporation of the solvent under reduced pressure, the products were separated by column chromatography on silica gel using a mixture of dichloromethane/triethylamine (2500/1) as eluant.…”

Section: Methodsmentioning

confidence: 99%

Noncovalent Assembly of [2]Rotaxane Architectures

Hunter

Low²,

Packer

et al. 2001

Angew. Chem. Int. Ed.

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Reversible zinc–pyridine coordination and hydrogen‐bonding interactions have been used to assemble a [2]rotaxane from three components. Cooperativity in the macrocyclization process that results in the porphyrin dimer (see picture) makes the system exceptionally stable. However, the kinetic lability of the zinc–porphyrin interaction means the dimer is in dynamic equilibrium with its monomer, and this has been exploited in the construction of a [2]rotaxane.

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“…The polyester with pentathiophene segments showed increased conductivity up to 0.4 S/cm due to favorable π stacking, Figure 23. 180 The block copolymer approach has been adopted by Feast et al for the organization of hydrophobic oligothiophene blocks that alternate with hydrophilic poly(ethylene oxide) blocks (M n ) 2000, 1000, and 600) (63)(64)(65)(66). 181 Aggregation of the oligothiophenes occurs in dioxane-water mixtures, which was manifested by a blue shift of the UV-vis absorption maximum and quenching of the fluorescence.…”

Section: Monodisperse Main-chain π-Conjugated Blocksmentioning

confidence: 99%