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D M Rudkevich

Publications and source records attributed to D M Rudkevich.

8 recordsLinked to original sources
PubMed2001

A self-folding metallocavitand.

The synthesis and characterization of novel metallocavitand 6 are described. This is a covalent hybrid of a deepened, self-folding cavity and a Zn-phenanthroline fragment. Host 6 features a large molecular cavity of approximately 8 x 10 A dimensions, and the metal binding site is directed in toward the cavity. Binding abilities of the metallocavitand in solution was demonstrated for quinuclidine 11 and Dabco 12 using UV-vis and 1H NMR spectroscopy. Intramolecular hydrogen bonds at the upper rims of cavitand 6 resist the unfolding of the inner cavities and thereby increase the energetic barrier to guest exchange. The exchange is slow on the NMR time scale (at ambient temperatures, CD2Cl2), and kinetically stable complexes result. Both the polyaromatic cavity and metallosite participate simultaneously in the binding event. Zinc-containing deep cavities may be attractive as catalytic chambers for hydrolysis and esterification.

Hydrogen Bonding↗
PubMed2001

Cavitand-porphyrins.

The synthesis and characterization of new nanoscale container molecules 7 and 8 are described. They are covalent hybrids of deepened, self-folding cavitands and metalloporphyrins. In receptor 7, the Zn-porphyrin wall is directly built onto the cavitand skeleton. Host 8 features a large unimolecular cavity containing two cavitands attached with the Zn-porphyrin wall. Its dimensions, approximately 10 x 25 A, place it among the largest synthetic hosts prepared to date. A series of adamantyl- and pyridyl-containing guests 14-20 of various lengths were prepared and used to determine the hosts' binding abilities in solution using UV/vis and (1)H NMR spectroscopy. Intramolecular hydrogen bonds at the upper rims of the cavitands resist the unfolding of the inner cavities and thereby increase the energetic barrier to guest exchange. The exchange is slow on the NMR time scale (at < or =300 K), and kinetically stable complexes result. When the cavities and metalloporphyrins participate simultaneously in the binding event, very high affinities for guests are found (-DeltaG295 up to 10 kcal x mol(-1) in toluene), to which the porphyrin fragments contribute significantly (-DeltaG295 up to 6 kcal x mol(-1)). The pairwise selection of two different guests by molecular container 8 is reported, and the termolecular complex formed raises the possibility of metal-catalyzed bimolecular reactions in these containers.

Amides↗
PubMed2000

A polymer-bound cavitand.

[reaction: see text] An amino-footed cavitand, 1, was attached to an insoluble polystyrene support, and the uptake of organic guest molecules by the resulting polymer 3 from xylene or toluene solutions was achieved.

Amides↗
PubMed2000

A cavitand-porphyrin hybrid.

[structure: see text] Host-guest complexes of a new open-ended cavitand show unprecedented stabilities. Simultaneous binding in the cavity and at the metalloporphyrin affects both the kinetics and the thermodynamics of caviplex formation.

Indicators and Reagents↗
PubMed2000

A self-assembled cylindrical capsule: new supramolecular phenomena through encapsulation.

The synthesis and spectroscopic characterization of self-assembled cylindrical capsule 1a x 1a of nanometer dimensions is described. Encapsulation studies of large organic guest molecules were performed by using 1H NMR sprectroscopy in [D12]mesitylene solution. In addition to the computational (MacroModel 5.5, Amber* force field) analysis of the capsule's shape and geometry, an experimental approach towards estimation of the internal cavity dimensions is described. This involves using series of homologous molecular "rulers" (e.g. aromatic amides 5a-i). The available space inside the capsule 1a x 1a can be estimated as 5.7 x 14.7 A (error +/- 0.2 A) with this technique. Dibenzoyl peroxide is readily encapsulated in [D12]mesitylene and was shown to be stable to decomposition for at least three days at 70 degrees C inside the capsule. Moreover, 1a x 1a prevents the encapsulated peroxide from oxidizing Ph3P or diphenyl carbazide present in solution. The normal chemical reactivity of the peroxide is restored by release from the capsule by DMF, a solvent that competes for the hydrogen bonds that hold the capsule together. The protection and release of encapsulated species augurs well for the application of capsules in catalysis and delivery.

Benzene Derivatives↗
PubMed1999

Lower rim functionalized resorcinarenes: useful modules for supramolecular chemistry.

[formula: see text] A synthetic scheme for the selective functionalization of all-cis (rccc) resorcinarene platform at the "lower rim" was developed. Self-folding and self-complementary cavitands were prepared for molecular recognition and self-assembly, bearing functionality at remote sites. These molecules promise applications on solid support and as polymeric capsules.

Aldehydes↗
PubMed1997

Polycaps: reversibly formed polymeric capsules.

Described are assemblies consisting of polymeric capsules, "polycaps," formed from two calix[4]arene tetraureas covalently connected at their lower rims. In these structures self-assembly leads to reversibly formed capsule sites along a chain, reminiscent of beads on a string. Their dynamic behavior is characterized by 1H NMR spectroscopy through encapsulation of guest species, reversible polymerization, and the formation of sharply defined hybrid capsules.

Journal Article↗