Use of hydrogen bonds to control molecular aggregation. Association of dipyridones joined by flexible spacers

Gallant, Michel; Tan, Phan Viet Minh; Wuest, James D.

doi:10.1021/jo00007a007

Cited by 70 publications

(26 citation statements)

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“…Apparently, this level of information is not communicated from one end of the dumbbell to the other. In summary, experiments have shown that hydrogen bonded polymeric systems can be well characterized in solution (19)(20)(21) by 1 H NMR methods and some degree of control can be exercised on the assembly process. We are currently exploring conventional polymer characterization-polymer length, molecular weight distributions, viscosity, etc.-to determine its applicability to these dynamic and reversible systems.…”

Section: Resultsmentioning

confidence: 99%

Polycaps: Reversibly formed polymeric capsules

Castellano

Rudkevich²,

Rebek³

1997

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

205

142

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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 1 H NMR spectroscopy through encapsulation of guest species, reversible polymerization, and the formation of sharply defined hybrid capsules.Molecule-within-molecule complexes represent an unusual arrangement of matter (1) with promising applications in mechanistic and physical organic chemistry (2, 3). More complicated synthetic systems that begin to resemble complexes found in biology are molecules that assemble through weak intermolecular forces. Specifically, cup-shaped molecules with hydrogen bonding sites on their larger rims have interesting capacities for molecular assembly. When the hydrogen bonding sites are self-complementary, the molecules dimerize to form capsules. These assemblies reversibly encapsulate smaller guest species of suitable size and shape, but show dynamic qualities (4): the capsules form and dissipate at rates that vary from microseconds to hours-long enough for chemical reactions to occur within them (5). Several such systems derived from resorcinarenes and calixarenes have been extensively characterized (6-8).In the calix[4]arenes ( Fig. 1) the cup-like shape provides half of each capsule, while the ureas on its larger (upper) rim provide the hydrogen bonds that permit the molecules to assemble. The alkyl (R 1 ) groups on the phenolic oxygens of the lower rim maintain (on average) the cup-like conformation (9), and the R 2 groups on the distal urea nitrogen (N ␤ ) provide for reasonable solubility in organic media. Their ready synthetic accessibility has raised the possibility (8, 10) that covalent connection at their lower rims could lead to polymeric capsules, or polycaps, on assembly (Fig. 2). MATERIALS AND METHODSGeneral. All chemicals were used without further purification unless otherwise specified. p-Heptylphenyl isocyanate was prepared from the corresponding acid based on a literature procedure (11). 5,11,17,26,27,arene (1, R 1 ϭ n-propyl, R 2 ϭ n-octyl) was prepared from the known tetraamine (12) by treatment with octyl isocyanate in a manner similar to 6 and 7. The 5,11,17,26,arene 2 was prepared according to the literature (13). Proton ( 1 H) NMR spectra were recorded on Bruker (Billerica, MA) DRX-600 (600 MHz) or AM-300 (300 MHz) spectrometers. Carbon ( 13 C) spectra were recorded on a Bruker DRX-600 (151 MHz) spectrometer. IR spectra were recorded on a Perkin-Elmer Paragon 1000PC FT-IR spectrometer. The fast atom bombardment (FAB) positive ion mass spectra were obtained on a VG ZAB-VSE double-focusing high resolution mass spectrometer equipped with a cesium ion gun. Matrix-assisted laser desorption ionization mass spectrometry experiments were performed on a PerSeptive Biosystems (Cambridge, MA) Voyager-Elite mass spectrometer with delayed extra...

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Section: Resultsmentioning

confidence: 99%

Polycaps: Reversibly formed polymeric capsules

Castellano

Rudkevich²,

Rebek³

1997

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

205

142

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“…A more flexible analogue of 4 gave very similar results, with the difference that small amounts of (cyclo)oligomeric aggregates were observed at higher concentrations. Presumably, intramolecular H‐bonding within these fexible modules preorganizes the pyridone binding sites for preferential dimerization 91…”

Section: Self‐assembly By H‐bond‐directed Dimerizationmentioning

confidence: 99%

Noncovalent Synthesis Using Hydrogen Bonding

Prins

Reinhoudt

Timmerman

2001

Angew. Chem. Int. Ed.

1,245

765

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Hydrogen bonds are like human beings in the sense that they exhibit typical grouplike behavior. As an individual they are feeble, easy to break, and sometimes hard to detect. However, when acting together they become much stronger and lean on each other. This phenomenon, which in scientific terms is called cooperativity, is based on the fact that “1+1 is more than 2”. By using this principle, chemists have developed a wide variety of chemically stable structures that are based on the reversible formation of multiple hydrogen bonds. More than 20 years of fundamental studies on these phenomena have gradually developed into a new discipline within the field of organic synthesis, and is nowadays called “noncovalent synthesis”. This review describes noncovalent synthesis based on the reversible formation of multiple hydrogen bonds. Starting with a thorough description of what the “hydrogen bond” really is, it guides the reader through a variety of bimolecular and higher order assemblies and exemplifies the general principles that determine their stability. Special focus is given to reversible capsules based on hydrogen‐bonding interactions that exhibit interesting encapsulation phenomena. Furthermore, the role of hydrogen‐bond formation in self‐replicating processes is actively discussed, and finally the review briefly summarizes the development of novel materials (nanotubes, liquid crystals, polymers, etc.) and principles (dynamic libraries) that recently have emanated from this intriguing field of research.

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“…[91] Ein flexibleres Analogon von 4 lieferte ganz ähnliche Resultate, mit dem Unterschied, dass bei höheren Konzentrationen kleine Mengen cyclo(oligomerer) Aggregate beobachtet wurden.…”

Section: -H-brückenmoduleunclassified