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Julius Rebek

Publications and source records attributed to Julius Rebek.

At least 73 records · Page 4Linked to original sources
PubMed2003

Reactivity and molecular recognition: amine methylation by an introverted ester.

We report a host molecule with an inwardly directed methyl ester and its reaction with a series of tertiary amines. The reaction product is a complex of the host carboxylate with a guest quaternary ammonium salt. The rate of the reaction is highly dependent on the suitability of the amine to occupy the host cavity and the intrinsic reactivity of the resulting complex. A kinetic study of the reaction of 2-(dimethylamino)ethanol to produce choline gives the activation parameters DeltaH = 25.1 +/- 0.5 kcal mol-1 and DeltaS = 12 +/- 2 cal mol-1 K-1. The complex, once formed, is poised to reach the transition state; a rate acceleration of greater than 2 x 104 fold is estimated when compared with similar reactions having no supramolecular effects.

Amines↗
PubMed2003

Individual solvent/solute interactions through social isomerism.

Reversible coencapsulation of a solute molecule and a single solvent molecule takes place in solution at ambient temperature. Two isomeric complexes are formed (social isomers), and their relative energies are assessed by NMR methods. Intermolecular interactions between 3 aromatic solutes and 15 common solvents are evaluated.

Anisoles↗
PubMed2003

Helical conformation of alkanes in a hydrophobic cavitand.

Alkanes adopt extended conformations in solution that minimize steric interactions and maximize surface area. Folding can reduce the amount of hydrophobic surface exposed to solvent, but sterically unfavorable gauche interactions result. However, we found that the alkyl chains of two common surfactants in aqueous solution adopt helical conformations when bound within a synthetic receptor. The receptor recognizes the helical alkane better than the extended conformation, even though 2 to 3 kilocalories per mole of strain is introduced. The proper filling of space and burial of hydrophobic surface drive the molecular recognition between the receptor and the coiled alkane.

Alkanes↗
PubMed2003

Solvent-stabilized molecular capsules.

Pyrrogallolarenes 2 were prepared by acid-catalyzed condensation of pyrrogallol with aldehydes. Compound 2a crystallizes from a methanol solution of quinuclidine hydrochloride to give a dimeric molecular capsule surrounding one disordered quinuclidinium cation. The molecules of 2a are connected by direct hydrogen bonds and by bridging methanol and water molecules. The chloride anion is positioned outside the capsule and is hydrogen bonded to the hydroxy groups of 2a. The shortest distance between the cation and anion was found to be 6.7 A. Crystallization of 2b from aqueous acetonitrile resulted in a dimeric capsule linked by a polar belt of 16 hydrogen bonding water molecules. Four acetonitrile molecules occupy the cavity of this dimeric capsule and assume two binding sites that differ in hydrogen bonding and electronic environment. Compounds 2 also form hydrogen-bonded dimeric molecular capsules in alcohols and aqueous acetonitrile solutions. These assemblies readily encapsulate tetramethylammonium, tetramethylphosphonium, quinuclidinium, and tropylium cations to give complexes stable on the NMR time scale at 233 K.

Capsules↗
PubMed2003

A low molecular weight mimic of the Toll/IL-1 receptor/resistance domain inhibits IL-1 receptor-mediated responses.

Toll-like receptors (TLRs) and the type I IL-1 receptor (IL-1RI) are key components of the innate immune system activated by microbial infections and inflammation. The signaling cascade from agonist-occupied TLRs and IL-1Rs involves recruitment of the small cytosolic adapter protein MyD88 that binds to IL-1RI via homotypic interactions mediated by Toll/IL-1R/resistance (TIR) domains. Dominant negative forms and null mutations of MyD88 have recently been shown to preclude bacterial product or IL-1-mediated activation of NF-kappaB pathways, demonstrating that MyD88 is an essential component of the Toll receptor signaling. Here, we report the synthesis and pharmacological effects of a low molecular weight MyD88 mimic, hydrocinnamoyl-l-valyl pyrrolidine (compound 4a), modeled on a tripeptide sequence of the BB-loop [(F/Y)-(V/L/I)-(P/G)] of the TIR domain. Results are presented showing that compound 4a interferes with the interactions between mouse MyD88 and IL-1RI at the TIR domains. Compound 4a inhibited IL-1beta-induced phosphorylation of the mitogen-activated protein kinase p38 in EL4 thymoma cells and in freshly isolated murine lymphocytes in a concentration-dependent manner. In vivo, compound 4a produced a significant attenuation of the IL-1beta-induced fever response (200 mg/kg, i.p.). Inhibition of the TIR domain-mediated MyD88/IL1-RI interaction by a low molecular weight, cell-penetrating TIR domain mimic suggests an intracellular site for antiinflammatory drug action.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Asymmetric environments in encapsulation complexes.

Symmetrical, self-assembled capsules capable of surrounding two guests offer a new approach to enantioselection through coencapsulation: when one guest is chiral, the space remaining is also chiral. This notion is explored within a cylindrical capsule. The dimensions of the capsule select appropriately sized combinations of guests, the shape of the capsule prevents tumbling of rigid molecules, and the chemical surface of the capsule orients polar functions within. Chiral carboxylic acids such as mandelic acid and alpha-Br-butyric acid are identified as promising compounds for this purpose, but diastereoselection is modest (<25% de).

Butyrates↗
PubMed2003

Assembly of resorcinarene capsules in wet solvents.

Resorcinarenes assemble in wet chloroform or benzene to form hexameric capsules, resembling inflated cubes or volleyballs. NMR methods are used to determine the number of solvent molecules detained inside; eight molecules of benzene are encapsulated.

Journal Article↗
PubMed2002

Molecular discrimination of N-protected amino acid esters by a self-assembled cylindrical capsule: spectroscopic and computational studies.

A self-assembled, cylindrical capsule was used to bind N-alpha-protected amino acid esters. The reversible encapsulation was studied using NMR spectroscopy in deuterated mesitylene solution and by computer-aided molecular modeling. BOC-L-alanine alkyl esters and BOC-beta-alanine alkyl esters were tested as guests, and the relative binding affinities were established by direct competition experiments. A good correlation was found between the experimental and calculated relative binding affinities in these two series. Guests that were slightly longer than the internal dimensions of the cavity were accommodated by adopting compacted conformations.

Alanine↗
PubMed2002

A synthetic receptor for choline and carnitine.

A synthetic receptor is described with the appropriate shape and size for alkylated trimethylammonium ions such as choline and carnitine. The structure features a deep, concave binding site, lined with aromatic walls that provide cation-pi interactions between host and guest. Molecular mechanic calculations suggest that the host's shape is maintained through intermolecular hydrogen bonding with DMSO solvent molecules. The cavity is too small to accommodate larger ions. Choline and carnitine are recognized and bound with high affinity even though no complementary charges are involved in the process.

Carbamates↗