Gibb, B. C. Funding Complexity. Nature Chemistry 2009, 513-514.
Publications
2009
Gibb, B. C. Reaching out to Complexity. Nature Chemistry 2009, 252-253.
Gibb, B. C. Teetering on the Edge of Chaos and Complexity. Nature Chemistry 2009, 17-18.
Liu, S.; Gibb, B. C. High-Definition Self-Assemblies driven by the Hydrophobic Effect: Synthesis and Properties of a Supramolecular Nano-Capsule. Chemistry Community 2009, 3709-3716.
Sundaresan, A. K.; Kaanumalle, L. S.; Gibb, C.; Gibb, B. C.; Ramamurthy, V. Chiral photochemistry within a confined space: diastereoselective photorearrangements of a tropolone and a cyclohexadienone included in a synthetic cavitand. Dalton Transactions 2009, 4003-4011.
The value of a supramolecular assembly to enforce a closer interaction between a chiral auxiliary and a reaction center has been established using photoreactions of tropolone and cyclohexadienone derivatives. Two probe molecules utilized to establish the concept undergo 4 e− electrocyclization and oxa-di-π-methane rearrangement from excited singlet and triplet state, respectively. The chiral auxiliaries investigated here has no/little effect in acetonitrile solution during phototransformations of the probe molecules to yield products with new chiral centers. On the other hand the same ones are able to enforce diastereoselectivities to the extent of ∼30% when the reactions occur within the restricted space of a capsule made up of a synthetic cavitand commonly known as octa acid. Extensive NMR studies have been utilized to characterize the guest–host supramolecular structures. The results presented here should be of value in the overall understanding of chiral induction in photochemical reactions.
Sundaresan, A. K.; Gibb, C. L.; Gibb, B. C.; Ramamurthy, V. Chiral photochemistry in a confined space: torquoselective photoelectrocyclization of pyridones within an achiral hydrophobic capsule. Tetrahedron 2009, 65, 7277-7288.
Chiral induction during the photoelectrocyclization of pyridones included within octa acid (OA) capsule has been established. Chiral induction is brought about by a chiral auxiliary appended to the reactive pyridone moiety. Importantly, the same chiral auxiliary while ineffective in acetonitrile solution is found to be effective within the confined space of OA capsule. The diastereomeric excess of 92% obtained here is comparable only to that in solid state. OA capsule, we believe, provides restriction to the rotational motions of the reactant pyridone and chiral auxiliary and thus places the chiral auxiliary in a selective conformation with respect to the reactive pyridone part. A correlation between the position of the methyl group on the pyridone ring and diastereoselectivity was noted. Structures of the host–guest complexes were examined by 1H NMR and the data were used to obtain preliminary information concerning the mechanism of chiral induction within the confined spaces of OA capsule.
Gibb, C. L. D.; Gibb, B. C. Guests of Differing Polarities Provide Insight into Structural Requirements for Templates of Water-Soluble Nano-Capsules.. Tetrahedron 2009, 65, 7240-7248.
Guests covering a range of polarities were examined for their ability to bind to a water-soluble cavitand and trigger its assembly into a supramolecular capsule. Specifically the guests examined were: tridecane 2, 1-dodecanol 3, 2-nonyloxy ethanol (ethylene glycol monononyl ether) 4, 2-(2-hexyloxyethoxy) ethanol (Di(ethylene glycol) hexyl ether) 5, 2-[2-(2 propoxyethoxy)ethoxy] ethanol (Tri(ethylene glycol) propyl ether 6, and bis [2-(2-hydroxyethoxy)ethyl] ether (tetra(ethylene glycol)) 7. In this series, guest 6 proved to signify the boundary between assembly and the formation of 2:1 complexes, and simple 1:1 complexation. Thus, guests 2-5 formed relatively kinetically stable capsules, guest 6 formed a capsule that was unstable relative to the NMR timescale, and guest 7 formed a simple 1:1 complex.
Giles, M. D.; Liu, S.; Emanuel, R.; Gibb, B.; Grayson, S. Divergent Dendronization of Deep-Cavity Cavitands to Tune Host Solubility. Israel Journal of Chemistry 2009, 49, 31-40.
Abstract Resorcinarene-based deep-cavity cavitands (DCCs) are useful components in supramolecular chemistry because their extended cavity enables the encapsulation of relatively large guests. To provide H2O solubility, they have been modified with hydroxyl functionalized dendrons. This has been carried out by the divergent dendronization of aliphatic poly(ester) dendrons through the third dendritic generation. The resultant macromolecule demonstrated the desired H2O solubility.
2008
Gibb, C.; Sundaresan, A. K.; Ramamurthy, V.; Gibb, B. C. Templation of the Excited-State Chemistry of α-(n-Alkyl) Dibenzyl Ketones: How Guest Packing within a Nanoscale Supramolecular Capsule Influences Photochemistry. Journal of the American Chemical Society 2008, 130, 4069-4080.
Excited-state behavior of eight α-alkyl dibenzyl ketones (alkyl = CH3 through n-C8H17) that are capable of undergoing type II and/or type I photoreactions has been explored in isotropic solution and within a water-soluble capsule. The study consisted of two parts: photochemistry that explored the excited-state chemistry and an NMR analysis that revealed the packing of each guest within the capsule. The NMR data (COSY, NOESY, and TOCSY experiments) revealed that ternary complexes between α-alkyl dibenzyl ketones and the capsule formed by two cavitands are kinetically stable, and the guests fall into three packing motifs modulated by the length of the α-alkyl chain. In essence, the host is acting as an external template to promote the formation of distinct guest conformers. The major products from all eight guests upon irradiation either in hexane or in buffer solution resulted from the well-known Norrish type I reaction. However, within the capsule the excited-state chemistry of the eight ketones was dependent on the alkyl chain length. The first group consisted of α-hexyl, α-heptyl, and α-octyl dibenzyl ketones that yielded large amounts of Norrish type II products within the host, while in solution the major products were from Norrish type I reaction. The second group consists of α-butyl and α-pentyl dibenzyl ketones that yield equimolar amounts of two rearranged starting ketones within the capsule (combined yield of ca 60\%), while in solution no such products were formed. The third group consisted of α-methyl, α-ethyl, and α-propyl dibenzyl ketones that within the capsule yielded only one (not two) rearranged starting ketone in larger amounts (21−35\%) while in solution no rearrangement product was obtained. Variation in the photochemistry of the guest within the capsule, with respect to the α-alkyl chain length of the guest, highlights the importance of how a small variation in supramolecular structure can influence the selectivity within a confined nanoscale reactor.
Podkoscielny, D.; Philip, I.; Gibb, C.; Gibb, B. C.; Kaifer, A. E. Encapsulation of Ferrocene and Peripheral Electrostatic Attachment of Viologens to Dimeric Molecular Capsules Formed by an Octaacid, Deep-Cavity Cavitand. Chemistry: A European Journal 2008, 14, 4704-4710.