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Al-Mustafa, Jamil; Hamzah, Samer; Marji, Deeb

doi:10.1023/a:1011953211179

Cited by 13 publications

(9 citation statements)

References 12 publications

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“…Compound 1 (Figure ), a conjugate of the G ∧ C motif and 4-aminobenzo-18-crown-6-ether (18C6), was first investigated to establish the rosette nanotubes as stable, yet noncovalent scaffolds for the self-organization of multifunctional nanotubes in water (Figure ) . We then went a step further toward modifying the nanotubes' physical and chemical properties by providing the crown ethers on their outer surface with unique molecular guests . We anticipated that such an interaction would impart reversible and predefined chemical and physical properties upon the nanotubular architectures.…”

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“…Except for l -Val and l - n -Leu, there appears to be a definite preference for small, aromatic, and hydrophobic amino acids, in agreement with the hydrophobic character of the methyl, phenyl, and crown ether groups lining up the six binding grooves of the rosette nanotubes. The case of l -Val may be rationalized on the basis of extensive steric hindrance near the promoter's anchor point (i.e., ammonium group) that may alter its binding properties . The weak ICD of l - n -Leu, in comparison with the other hydrophobic promoters, could be related to the increased flexibility of its n -butyl side chain.…”

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confidence: 99%

“…All-or-None Nature of the Induced Supramolecular Chirality. The CD titration curve of 1 with l -Ala (Figure ) revealed that the transition from racemic to helical rosette nanotubes takes place in the range of 4−30 equiv of l -Ala. On the basis of a conservative binding constant of ∼10 5 of l -Ala to 1 , , this result suggests that the vast majority of the sites must be simultaneously occupied with an amino acid promoter for a complete transition to chiral nanotubes to take place (93−99%, Figure ), despite the polydispersity of the sample (5 < R H < 100 nm, Figure A, curve #1). From this observation, we concluded that the ( 1 − l -Ala) complexes within the nanotubular assembly express their chirality collectively at the nanotubular level, but only when all of the crown ether sites are occupied with an amino acid (maximum site occupation requirement).…”

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Helical Rosette Nanotubes with Tunable Chiroptical Properties

2002

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On the basis of transmission electron microscopy (TEM), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and circular dichroism (CD) studies, compound 1 was shown to exist mainly in two states: (a) At high concentration (> or =1 mM, in methanol), 1 undergoes hierarchical self-assembly to generate rosette nanotubes with approximately 4 nm diameter and a concentration-dependent hydrodynamic radius in the range 10-100 nm. Under these conditions, addition of a chiral amino acid promoter (L-Ala), that binds to the crown ether moiety of 1 via electrostatic interactions, promotes a rapid transition (k(0) approximately equal 0.48 s(-1), for [1] = 0.046 mM, [L-Ala] = 2.8 mM) from racemic to chiral rosette nanotubes with predefined helicities as indicated by the resulting induced circular dichroism (ICD). (b) At low concentration (< or =0.04 mM, in methanol), 1 exists mainly in a nonassembled state as shown by TEM and DLS. Addition of L-Ala in this case triggers a relatively slow (k(0) approximately equal 0.07 s(-1) for [1] = 0.04 mM, [L-Ala] = 2.4 mM) sequence of supramolecular reactions leading to the hierarchical self-assembly of rosette nanotubes with predefined helicities. Under both conditions a and b, the kinetic data unveiled the intrinsic ability of the rosette nanotubes to promote their own formation (autocatalysis). The degree of chiral induction was found to depend dramatically upon the chemical structure of the promoter. This process appears also to follow an all-or-none response, as the vast majority of the crown ether sites must be occupied with a promoter for a complete transition to chiral nanotubes to take place. Finally, both supramolecular pathways a and b offer an efficient approach for the preparation of helical rosette nanotubes with tunable chiroptical properties and may also be viewed as a process by which a predefined set of physical and chemical properties that characterizes a molecular promoter is expressed at the macromolecular level.

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Helical Rosette Nanotubes with Tunable Chiroptical Properties

2002

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“…The extraction can be monitored by UV/Vis spectroscopy 7,8 and enables thermodynamic analysis if suitable counterions are used. [9][10][11][12][13] Besides, the thermodynamics of complex formation of ionic compounds with crown ethers in various organic solvents [14][15][16] as well as in mixed non-aqueous solutions 17,18 has been explored. The stability of a formed complex depends on the diameter of the crown ether and the radius of the metal cation.…”

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Thermodynamic analysis of alkali metal complex formation of polymer-bonded crown ether

Bey

Dreyer

Abetz

2017

Phys. Chem. Chem. Phys.

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The complex formation of two crown ethers with colored alkali metal salts was investigated by UV/Vis spectroscopy. Complexation was accomplished with free benzo-15-crown-5 (B15C5) and 15-crown-5 bonded to a diblock copolymer (Poly15C5). The diblock copolymer was synthesized by two controlled polymerization techniques and copper(I)-catalyzed azide-alkyne cycloaddition. Depending on the inserted cation, 1 : 1-or 1 : 2-complexes are formed. A significant difference of the stability constants was determined by concentration dependence solvent extraction with sodium or potassium salt. For Poly15C5 the stability constants increase for both salts compared to the stability constants of B15C5, which suggests a more effective complexation. Evaluation of the thermodynamics (DH, DS, DG) of cation complexation was achieved by temperature dependence phase extraction on the basis of established thermodynamic equations. Remarkably, in all cases the entropic gain seems to be the major propulsion facilitating the complexation between alkali metal salts and crown ethers. Indeed, by using Poly15C5 a more pronounced dependency of enthalpy and entropy on the complex formation is calculated.

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“…There are several studies on the complexation of metal ions with such macrocyclic compounds, but fewer related to organic ions or neutral molecules and hence resulted in several sensors for metal ions based on macrocyclic compounds or macrocyclic-metal ion complex based sensors for organic molecules [14 -19]. Complex formation between crown ethers/calixarenes and amino acids has been studied by conductometry [20], calorimetry [21], solvent extraction [22,23] spectroscopy [24], etc. But only a few macrocycle based sensors in the form of ion selective electrodes have been reported for amines or amino acids [25 -28].…”

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Capacitive Sensing of Amino Acids Using Caliraxene‐Coated Silicon Transducers

et al. 2007

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The possibility of using capacitance and flat band voltage as measurable quantities for determining amino acids that are neither electroactive nor with strong UV-vis absorption has been explored. The sensors were fabricated by immobilizing calixarene derivatives on Si/SiO 2 /Si 3 N 4 transducers. The measurements were made in sulfuric acid media of ca. pH 1 and in physiological buffer of pH 7.4. The different calixarene derivatives showed varying sensitivities to the amino acids ranging from 8 to 137 mV/decade.

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Cited by 13 publications

References 12 publications

Helical Rosette Nanotubes with Tunable Chiroptical Properties

Helical Rosette Nanotubes with Tunable Chiroptical Properties

Thermodynamic analysis of alkali metal complex formation of polymer-bonded crown ether

Capacitive Sensing of Amino Acids Using Caliraxene‐Coated Silicon Transducers

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