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Molecular Tweezers (molecular + tweezers)

Distribution by Scientific Domains
Chemistry71%

Selected Abstracts

Uncharged Water-Soluble Metal-Bis-Porphyrins Like Molecular Tweezers for Amino Acids

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2007
Emilio Scamporrino
Abstract Some new water-soluble bis-porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI-TOF mass spectrometry, 1H NMR and UV-vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co-bis-porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis-porphyrin behaves like molecular tweezers. [source]

Oxacalixarenes and Oxacyclophanes Containing 1,8-Naphthyridines: A New Class of Molecular Tweezers with Concave-Surface Functionality.

CHEMINFORM, Issue 29 2007
Jeffrey L. Katz
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

Dynamic Molecular Tweezers Composed of Dibenzocyclooctatetraene Units: Synthesis, Properties, and Thermochromism in Host,Guest Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009
Tomohiko Nishiuchi
Abstract Novel dynamic molecular tweezers (DMTs) 3,a, 3,b, 4,a, 4,b, and 5,b, composed of two tub-shaped dibenzocyclooctatetraene (DBCOT) units, were designed and synthesized. The cyclooctatetraene (COT) rings of these DMTs readily invert in solution, and the molecular structure shows rigid syn and anti forms in an equilibrium mixture in solution. The syn and anti conformers can be observed by NMR. The isomerization barriers of 3,a, 3,b, 4,a, 4,b, and 5,b are in the range of 16.5,21.3,kcal,mol,1, depending on steric repulsion between substituents of the COT rings and protons of the central benzene ring. These DMTs form complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 1,2,4,5-tetracyano-benzene (TCNB) in solution and in the solid state. The binding abilities of these DMTs increase with electron-donating substituents on COT, which increase the electron densities of the cavity of the syn form, as supported by theoretical calculations. In addition, elongation of the terminal alkoxy chains of the DMTs was found to cause the enhancement of van,der Waals contact with guest molecules. Therefore, 5,b, which has CH2OMe groups on the COT rings and longer ethoxy groups on the terminal benzene rings, showed the highest electron density of the cavity and hence the highest binding ability with the electron-deficient guest molecules. Interestingly, solutions of 3,b, 4,b, and 5,b show thermochromism in the presence of DDQ. A solution of 3,b or 4,b with DDQ in CHCl3 is green due to charge-transfer interaction at room temperature and the color changes from green to yellow upon heating to 60,°C and from green to blue upon cooling to ,40,°C, whereas the high complexation ability of 5,b with DDQ only shows a change in the shade of blue. [source]

Molecular tweezers for enantiodiscrimination in NMR: Di-(R,R)-1-[10-(1-hydroxy-2,2,2-trifluoroethyl)-9-anthryl]-2,2,2-trifluoroethyl benzenedicarboxylates,

CHIRALITY, Issue 6 2010
Sergio Gil
Abstract A series of new chiral molecular tweezers, di-(R,R)-1-[10-(1-hydroxy-2,2,2-trifluoroethyl)-9-anthryl]-2,2,2-trifluoroethyl phthalate (2), isophthalate (3) and terephthalate (4), were synthesized and their structure studied by NMR and molecular mechanics. Their effectiveness as chiral solvating agents for the determination of the enantiomeric purity of chiral compounds using NMR was demonstrated. Chirality 2010. © 2009 Wiley-Liss, Inc. [source]

Uncharged Water-Soluble Metal-Bis-Porphyrins Like Molecular Tweezers for Amino Acids

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2007
Emilio Scamporrino
Abstract Some new water-soluble bis-porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI-TOF mass spectrometry, 1H NMR and UV-vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co-bis-porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis-porphyrin behaves like molecular tweezers. [source]

Dynamic Molecular Tweezers Composed of Dibenzocyclooctatetraene Units: Synthesis, Properties, and Thermochromism in Host,Guest Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009
Tomohiko Nishiuchi
Abstract Novel dynamic molecular tweezers (DMTs) 3,a, 3,b, 4,a, 4,b, and 5,b, composed of two tub-shaped dibenzocyclooctatetraene (DBCOT) units, were designed and synthesized. The cyclooctatetraene (COT) rings of these DMTs readily invert in solution, and the molecular structure shows rigid syn and anti forms in an equilibrium mixture in solution. The syn and anti conformers can be observed by NMR. The isomerization barriers of 3,a, 3,b, 4,a, 4,b, and 5,b are in the range of 16.5,21.3,kcal,mol,1, depending on steric repulsion between substituents of the COT rings and protons of the central benzene ring. These DMTs form complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 1,2,4,5-tetracyano-benzene (TCNB) in solution and in the solid state. The binding abilities of these DMTs increase with electron-donating substituents on COT, which increase the electron densities of the cavity of the syn form, as supported by theoretical calculations. In addition, elongation of the terminal alkoxy chains of the DMTs was found to cause the enhancement of van,der Waals contact with guest molecules. Therefore, 5,b, which has CH2OMe groups on the COT rings and longer ethoxy groups on the terminal benzene rings, showed the highest electron density of the cavity and hence the highest binding ability with the electron-deficient guest molecules. Interestingly, solutions of 3,b, 4,b, and 5,b show thermochromism in the presence of DDQ. A solution of 3,b or 4,b with DDQ in CHCl3 is green due to charge-transfer interaction at room temperature and the color changes from green to yellow upon heating to 60,°C and from green to blue upon cooling to ,40,°C, whereas the high complexation ability of 5,b with DDQ only shows a change in the shade of blue. [source]

Molecular tweezers for enantiodiscrimination in NMR: Di-(R,R)-1-[10-(1-hydroxy-2,2,2-trifluoroethyl)-9-anthryl]-2,2,2-trifluoroethyl benzenedicarboxylates,

CHIRALITY, Issue 6 2010
Sergio Gil
Abstract A series of new chiral molecular tweezers, di-(R,R)-1-[10-(1-hydroxy-2,2,2-trifluoroethyl)-9-anthryl]-2,2,2-trifluoroethyl phthalate (2), isophthalate (3) and terephthalate (4), were synthesized and their structure studied by NMR and molecular mechanics. Their effectiveness as chiral solvating agents for the determination of the enantiomeric purity of chiral compounds using NMR was demonstrated. Chirality 2010. © 2009 Wiley-Liss, Inc. [source]