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Front Matter |
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Abstract
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Editorial |
Jerry L. Atwood,J. Eric Davies |
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Abstract
The year 1987 was especially notable in that the Nobel Prize was awarded to three of the pioneers of the field. Unfortunately, 1987 was also the year in which we must sadly mark the passing of two great men of science, Professor Iwao Tabushi and Professor James J. Christensen. It is to these two men that the contributions from the United States-Japan Joint Seminar are dedicated.
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Iwao Tabushi (1933–1987) |
H. Taube |
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Abstract
My only close association with Iwao Tabushi being limited to a period of about two weeks in Kyoto when I, together with my wife, visited Kyoto on his invitation, I cannot lay claim to a long standing personal intimacy with him. Nor for that matter can I claim to be expert over the wide range of chemical behavior which he explored in his research so diligently and productively. Still, even in the short time that I interacted with him, this altogether remarkable man impressed me so strongly by his qualities as a human being, and by the way that he addressed his professional interests that I feel moved to add my own testimony to that made by others in commemorating him.
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New Molecular Shapes for Recognition and Catalysis |
Julius Rebek Jr |
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Abstract
Progress in molecular recognition is reviewed with special emphasis on the advantages ‘offered by molecular clefts. These new structures are rapidly assembled from readily accessible starting materials and feature functional groups that converge on smaller species that present complementary surfaces. The sizes and shapes of the clefts are controlled by the use of appropriate spacer elements. The selective binding of acids, amines, amino acids, metal ions, heterocyclic compounds and nucleosides is described. Their special applicability to problems involving concerted catalysis is also introduced.
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The Preparation of Ribose-Free ‘Artificial Dinucleotides’: A New Approach to Molecular Recognition? |
Jonathan L. Sessler,Darren Magda,Jeff Hugdahl |
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Abstract
The synthesis of the cytosine-guanine linked dimer ., and its symmetric guanine-guanine analogue . are described. Compound . is the first homogeneous ribose-free system to be prepared and characterized in which molecular recognition by complementary guanine-cytosine base-pairing might be possible. It is thus prototypical of a new and potentially large class of ‘artificial oligonucleotides’.
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Nucleotide Recognition by Macrocyclic Receptors |
Andrew D. Hamilton,Alex Muehldor,Suk-Kyu Chang,Nalin Pant,Shyamaprosad Goswami,Donna Van Engen |
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Abstract
It is shown that complementary positioning of recognition sites (particularly hydrogen bonding, stacking and hydrophobic groups) into a macrocyclic structure can lead to very strong and specific complexation of uncharged organic molecules.
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Molecular Recognition in Carnitine Acyltransferases |
Richard D. Gandour |
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Abstract
We are designing and synthesizing rigid guests to probe the topography of the carnitine acyltransferases, regulatory enzymes in lipid metabolism. Our designs are based on structural studies of substrates and possible molecular mechanisms of enzymatic activity. Recent X-ray, .H NMR, and force-field computational studies on carnitine and acetylcarnitine, coupled with the known stereospecificity for activity in carnitine acyltransferases, have led us to propose a molecular mechanism for acyl transfer in these enzymes. The ‘folded’ conformation of an acylcarnitine is most populated and should be preferred for binding to these enzymes, because, in this conformation, the acyloxy is the most sterically accessible. There are four key recognition sites on the enzymes: I, carboxylate; II, trimethylammonium; III, coenzyme A; IV, acyl. Sites, I, II and III serve as the three loci required to create a chiral environment on the enzymes for carnitine. An addition-elimination reaction involving the formation of a tetrahedral intermediate is suggested as the mechanism for O-to-S acyl transfer. This proposed tetrahedral intermediate is chiral and the enzymes should prefer the . configuration at this
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Cyclophanes as Hosts for Aromatic and Aliphatic Guests |
Kenji Koga,Kazunori Odashima |
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Abstract
A series of water-soluble cyclophanes, made by connecting two diarylmethane units and two bridging chains via four nitrogens, were found to provide hydrophobic cavities of definite shape and size for forming inclusion complexes with various organic compounds in aqueous solution. Some chemical modifications of these cyclophanes are described.
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Topics in Calixarene Chemistry |
C. David Gutsche,Iftikhar Alam,Muzaffar Iqbal,Thomas Mangiafico,Kye Chun Nam,Janet Rogers,Keat Aun S |
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Abstract
Several facets of calixarene chemistry have been investigated including the mechanism of their formation by the base-induced condensation of phenols and formaldehyde, procedures for introducing functional groups onto the ‘upper rim’ and ‘lower rim’ of calixarenes, the conformational behavior of calixarene oxyanions, the formation of complexes in aqueous and nonaqueous systems, and the application of calixarenes as catalysts.
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Studies Directed Toward the Fabrication of a Synthetic Cation-conducting Channel Based on Lariat Eth |
George W. Gokel,Luis Echegoyen,Minsook Kim,Jeanette C. Hernandez,Mayra De Jesus |
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Abstract
The work described here derives from our observation that while Nature certainly utilizes covalent interactions and other forces of great strength in the construction of biomolecules, many ‘feeble forces’ are involved as well. We have used feeble forces in model studies directed eventually to the synthesis of a self-assembling, cation-conducting channel. Specifically, we have prepared three models for portions of such a cation-conducting channel. The first is based on the steroidal lariat ethers that clearly self-assemble. This process involves . entropy as a feeble force of cumulative importance. Second, we have prepared three .(macrocyclic) systems that are simplified versions of the proposed channel-former. Third, we have demonstrated the strength of carefully-conceived hydrogen bonding interactions by constructing a molecular box based on the interaction between adenine and thymine.
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Cation Selective Complexation-Coloration with Chromophoric Crowns |
Soichi Misumi,Takahiro Kaneda |
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Abstract
Amine selective complexation-coloration of some azophenol-dyed crowns and X-ray structures of two secondary amine complexes are reported as well as lithium ion specific coloration with an azophenol spherand.
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Molecular Recognition of Hydrophobic Ammonium Substrates by a Cationic Octopus Cyclophane Bearing No |
Yukito Murakami,Jun-Ichi Kikuchi,Osamu Hayashida |
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Abstract
The inclusion behavior of the octopus cyclophane constructed with a rigid macrocyclic skeleton and eight hydrocarbon chains was studied in aqueous media by means of fluorescence and electronic absorption spectroscopy. Both hydrophobic and electrostatic interactions came into effect in the host-guest complexation process. The cyclophane acted as an effective apoenzyme model for constitution of an artificial vitamin B. dependent holoenzyme by simultaneous incorporation of pyridoxal-5’-phosphate and a hydrophobic alkylammonium substrate into the host cavity to give the Schiff-base species, showing the substrate selectivity.
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Molecular Recognition and Host-Guest Interactions in Complexes of O-Bistren, C-Bistren, and Bisdien |
Arthur E. Martell |
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Abstract
The host-guest relationships of the complexes of the cryptand ligands O-BISTREN and C-BISTREN, and of the analogous macrocyclic ligand BISDIEN are compared. The affinities of their binuclear copper(II) complexes for the bridging ligands (OH., F.) as ‘cascade’ type guests (i.e., guests of guests) are reported. The ability of the dicobalt(II)-BISDIEN complex to coordinate dioxygen and an additional bifunctional guest simultaneously, leads to the possibility of a new type of catalysis occurring within the cavity of a macrocyclic complex.
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The Interactions of Surfactant Viologens with Cyclodextrins |
Angel E. Kaifer,Pablo A. Quintela,Jodi M. Schuette |
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Abstract
.-ethyl-.’-hexadecyl-4,4’-bipyridinium bromide (C.VBr.) and .-ethyl-.’-octadecyl-4,4’-bipyridinium bromide (C.VBr.) were used as electroactive probes to assess the interactions between surfactants and cyclodextrins. Cyclic voltammetry, visible spectroscopy, fluorescence spectroscopy and surface tension techniques were used to detect the formation of complexes between the surfactant viologen probes and .- and .-cyclodextrins. The voltammetric results suggest the formation of inclusion compounds in which the hydrophobic tail of the surfactant viologens penetrate the cyclodextrin cavity. The dimerization of the viologen cation radicals is essentially suppressed by the presence of .-cyclodextrin (ACD) while no effects are observed in the presence of .-cyclodextrin (BCD). The observed results are best explained by the relative solubility in aqueous media of each of the inclusion complexes in the several accessible viologen oxidation states.
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Artificial Hydrolase Using Modified Dimethyl-,-cyclodextrin |
Hiroshi Ikeda,Ryoichi Kojin,Chul-Joong Yoon,Tsukasa Ikeda,Fujio Toda |
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Abstract
The first successful method for modification of dimethyl-.-cyclodextrin (.-DMCD) was demonstrated by the synthesis of a new artificial hydrolase (.) and the enzymatic activities of . were investigated. . caused an 1100-fold increase in the rate of hydrolysis of .-nitrophenyl acetate at pH 7.2, whereas unmodified ß-DMCD depressed the reaction. The kinetic p.. of . was 7.2, and the .. of . was independent of pH values. . had .-selectivity for the hydrolysis of nitrophenyl acetate isomers.
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James J. Christensen 1931–1987 |
Reed M. Izatt |
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Abstract
This issue of the Journal is dedicated to the memory of the late Professor James J. Christensen. Professor Christensen died suddenly at his home on September 5, 1987. He was 56 years old.
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Stable Silica Gel-Bound Crown Ethers. Selective Separation of Metal Ions and a Potential for Separat |
Jerald S. Bradshaw,Reed M. Izatt,James J. Christensen,Krzystof E. Krakowiak,Bryon J. Tarbet,Ronald L |
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Abstract
Silica gel-bound crown ethers and aza macrocycles have been synthesized with the attaching arm connected to the carbon framework of the macrocycles. The interactions of these bound macrocycles with cations are almost identical to those involving the analogous free macrocycles. This has allowed for predictable cation separation, concentration, and removal processes to be performed on a small scale. Quantum mechanical calculations and NMR measurements indicate that similarly bound chiral macrocycles will be capable of use in separating chiral organic amines.
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Inclusion Chemistry for the Modeling of Heme Proteins |
Daryle H. Busch,Neil A. Stephenson |
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Abstract
Early attention to the modeling of heme proteins is enhancing the understanding of biochemistry. Those studies are also contributing to the development of techniques for the modeling of still more intricate, multifunctional, variously selective natural systems. Selectivity in simple systems may involve the molecular capability to bind only one of a family of related species or it may mean the ability to select and control one of a number of possible functions of a given bound species. Complicated systems simultaneously combine the two kinds of simple selectivities for two or more different classes of guest, often with synergistic interrelationships. The subject is developed around examples of binary, tertiary, and quarternary complexes designed to model the behavior of monooxygenases.
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Progress Toward Artificial Metalloenzymes: New Ligands for Transition Metal Ions and Neutral Molecul |
Joanne F. Kinneary,Therese M. Roy,Jeffrey S. Albert,Heungsik Yoon,Thomas R. Wagler,Lucy Shen,Cynthia |
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Abstract
New nickel catalysts have been developed for the oxidation of alkenes to epoxides, alcohols, aldehydes and ketones. Mechanistic studies indicate that the oxidation reactions are very sensitive to the nature of the catalyst; only certain ligands including salen and the macrocycles cyclam and dioxocyclam render Ni(II) effective as a catalyst. A Ni(III) or Ni(IV)-oxo species has been postulated as the catalytically active oxidant which leads to oxygen atom transfer to alkenes in a stepwise process. Both iodosylbenzene and hypochlorite have been used as terminal oxidants; both systems give high yields of epoxidation of alkenes and varying amounts of C=C bond cleavage products. In order to reach an ultimate goal of hydrocarbon oxidation within a molecular recognition system, new molecular receptors for organic substrates have been investigated. The receptors are constructed from two subunits of cholic acid and display amphophilic character — a hydrophobic exterior and a hydrophilic interior. Conformational properties in the presence of polar guests in CDC1. are described.
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Template Synthesis of Ligands for Highly Charged Metal Cations |
Kenneth N. Raymond |
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Abstract
Macrocyclic and macrobicyclic ligands may enhance the stability of their metal complexes due to the inherent entropic and kinetic properties of a ligand ring or cage-type structure. In general, as the binding site becomes more encapsulated or preformed the reorganization entropy decreases, leading to a relatively higher formation constant for metal binding. Thus it would be expected that the formation constants be greatest for the series macrobicyclic > macrocyclic > exocyclic (Figure 1).
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