Structures, Magnetic Properties, and Aromaticity of Cyclacenes

Choi, Hyuk Soon; Kim, Kwang S.

doi:10.1002/(sici)1521-3773(19990802)38:15<2256::aid-anie2256>3.0.co;2-b

Cited by 147 publications

(107 citation statements)

References 1 publication

(2 reference statements)

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“…15, 16 We find that endohedral fullerenes (by the presence of N, P, As, O, S) 16d would be useful for quantum computing due to the presence of isolated and controllable spins. We have demonstrated the unusual magnetic phase transition in exohedral fullerenes.…”

Section: Molecular Clusters and Interaction Forcesmentioning

confidence: 93%

From Gas Phase Clusters to Nanomaterials: An Overview of Theoretical Insights

2003

Bulletin of the Korean Chemical Society

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Since theoretical investigations of gas phase clusters enable the evaluation of intrinsic molecular properties and intermolecular interactions, one can predict the macroscopic properties of bulk matter, from a microscopic determination of the properties of individual atoms, molecules, or clusters. Based on the insights obtained from theoretical investigations of the properties of a large number of cluster systems (ranging from simple water clusters to large π-systems), we have investigated the properties of various novel molecular systems including endo/exohedral fullerenes, nanotori, nonlinear optical materials, ionophores/receptors, polypeptides, enzymes, organic nanotubes, nanowires, and electronic and nano-mechanical molecular devices. The present minireview highlights some of the interesting results obtained in the course of our extensive theoretical investigations of clusters and nanomaterials.

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Section: Molecular Clusters and Interaction Forcesmentioning

confidence: 93%

From Gas Phase Clusters to Nanomaterials: An Overview of Theoretical Insights

2003

Bulletin of the Korean Chemical Society

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“…The role of each catalytic residue was investigated by using ab initio calculations, because these theoretical approaches have been successfully used in elucidating novel interactions, properties, and reaction mechanisms (37)(38)(39)(40).…”

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confidence: 99%

Catalytic role of enzymes: Short strong H-bond-induced partial proton shuttles and charge redistributions

Kim

Oh²,

Lee³

2000

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

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104

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A two-step reaction mechanism (catalyzed alternatively by acid and base) with partial proton shuttles and charge redistributions promoted by short strong H bonds (SSHBs) (playing a dual role as an amphi-acid͞base catalyst) is proposed to explain the enormous rate enhancement observed in enzymatic reactions involving carbanion intermediates. The SSHBs in the two-step reactions are found to be responsible for enhancing enzymesubstrate interactions in favor of the transition state structure over that of reactant. The detailed quantum theoretical studies of ketosteroid isomerase provide evidence of assisting roles of SSHB in enzymatic activity. The understanding of the two-step reaction mechanism would be a useful aid in designing novel functional enzymes and abzymes.A n understanding of how enzymes enhance the rate of reactions is essential for investigating the biological role of enzymes and designing new enzymes (1-3). In this context, enzyme-substrate interactions and enzyme preorganization have been invoked to explain the rate enhancement in favor of substrate transition state (TS) structures (4-14). In enzymesubstrate interactions, low barrier H bonds characterized by short and strong H bonds (SSHB) have been considered responsible for drastic enhancement in H-bond energies (4)(5)(6)(7)(8)(9)(10)(11)15). This concept has been introduced to explain the fast reactivities observed in various enzymes (4). Alternative explanations like preorganization in favor of the TS structures (mainly by electrostatic interactions) have also been proposed (12, 13), and the issue has been highly debated (9-24). In the present study, we attempt to resolve this issue by elucidating the origin of the catalytic role in ketosteroid isomerase (KSI), which is representative of this class of enzymes. We have carried out quantum theoretical calculations on the active sites of KSI to compare the experimental x-ray structures, NMR chemical shifts, and kinetic reaction rates for various mutants. We find evidence that the SSHB [driven by preorganized reaction environment in favor of the TS structure over the reactant structure, or enzymesubstrate complex (ES)] promotes both partial proton shuttles and (electronic) charge redistributions in a two-step mechanism as the role of an amphi-acid͞base catalyst, and hence eventually leads to a drastic lowering of the activation barrier in the catalytic reaction.KSI is one of the most proficient enzymes, catalyzing the isomerization of a variety of ⌬ 5 -3-ketosteroids to ⌬ 4 -3-ketosteroids (i.e., promoting an allylic rearrangement involving intramolecular proton transfer via a dienolic intermediate) (Fig. 1), with diffusion-controlled reactivity, and serves as a paradigm for fast enzymatic enolization involving carbanions (25-35). Enzyme reactions associated with carbanion intermediates responsible for isomerization reaction and carbon-carbon bond formation͞cleavage are vital to metabolism of living organisms.The important catalytic residues in Pseudomonas testosteroni KSI (TI) and Pseudomonas putid...

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“…This nanotube shows intriguing phenomena such as even-odd characteristics for the band gap and single-triplet energy difference. 142 In a while, using atomic force microscope we have recently engineered ultralong multi-walled carbon nanotube allowing the exposure of the innermost single-walled carbon nanotubes (%0:4 nm diameter) (Fig. 6).…”

Section: Functional Molecules Receptors and Nanomaterialsmentioning

confidence: 99%

Understanding Clusters toward the Design of Functional Molecules and Nanomaterials

Singh

Lee

Choi

et al. 2007

Bulletin of the Chemical Society of Japan

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In this account, we highlight the theoretical investigations of various cluster systems comprising of water clusters, -containing clusters, and metallic clusters. We illustrate how these investigations help us understand and design structures and properties of nanowires, novel functional ionophores/receptors, and nanomaterials. Many of these theoretically predicted systems have been experimentally realized and some of the predicted structures/properties are left for the future which of course could be promising challenges for experimentalists.

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Structures, Magnetic Properties, and Aromaticity of Cyclacenes

Cited by 147 publications

References 1 publication

From Gas Phase Clusters to Nanomaterials: An Overview of Theoretical Insights

From Gas Phase Clusters to Nanomaterials: An Overview of Theoretical Insights

Catalytic role of enzymes: Short strong H-bond-induced partial proton shuttles and charge redistributions

Understanding Clusters toward the Design of Functional Molecules and Nanomaterials

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