calix(4)arene and melamine

This article describes the synthesis and binding properties of highly selective noncovalent molecular receptors 1(3).(DEB)6 and 3(3).(DEB)6 for different hydroxyl functionalized anthraquinones 2. These receptors are formed by the self-assembly of three calix[4]arene dimelamine derivative molecules (1 or 3) and six diethylbarbiturate (DEB) molecules to give 1(3).(DEB)6 or 3(3).(DEB)6. Encapsulation of 2 occurs in a highly organized manner; that is, a noncovalent hydrogen-bonded trimer of 2 is formed within the hydrogen-bonded receptors 1(3).(DEB)6 and 3(3).(DEB)6. Both receptors 1(3).(DEB)6 and 3(3).(DEB)6 change conformation from staggered to eclipsed upon complexation to afford a better fit for the 2(3) trimer. The receptor selectivity toward different anthraquinone derivatives 2 has been studied using 1H NMR spectroscopy, X-ray crystallography, UV spectroscopy, and isothermal microcalorimetry (ITC). The pi-pi stacking between the electron-deficient center ring of the anthraquinone derivatives 2a-c and 2e-g and the relatively electron-poor melamine units of the receptor is the driving force for the encapsulation of the guest molecules. The selectivity of the hydrogen-bonded host for the anthraquinone derivatives is the result of steric interactions between the guest molecules and the calix[4]arene aromatic rings of the host.

Topics: Anthraquinones; Barbiturates; Calixarenes; Crystallography, X-Ray; Models, Molecular; Molecular Structure; Phenols; Triazines

The syntheses of calix[4]arene dimelamines that are functionalized with alkyl, aminoalkyl, ureido, pyridyl, carbohydrate, amino acid and peptide functionalities, and their self-assembly with barbituric acid or cyanuric acid derivatives into well-defined hydrogen-bonded nanostructures are described. The thermodynamic stability of these hydrogen-bonded assemblies was studied by CD spectroscopy in mixtures of CHCl3 and MeOH. The stability of the assemblies depends on several steric factors and the polarity of the functional groups connected to the assembly components.

Topics: Amines; Amino Acids; Barbiturates; Calixarenes; Carbohydrates; Circular Dichroism; Hydrogen Bonding; Molecular Conformation; Nanostructures; Peptides; Phenols; Stereoisomerism; Thermodynamics; Triazines

The formation of a hydrogen-bonded receptor in niosomal membranes is reported in this communication. The niosomes prepared from non-ionic surfactants C12EO3 and C14EO3 provide a stable system that allows the self-assembly of hydrogen-bonded receptors to occur in contact with aqueous environments. We demonstrate here by CD, TEM and Confocal Microscopy that the incorporation of the building blocks, calix[4]dimelamine 1 and PerBAR, within the niosomal membranes led to the formation of well-defined hydrogen-bonded assembly 13.(PerBAR)6 within these membranes.

Topics: Barbiturates; Biomimetic Materials; Calixarenes; Circular Dichroism; Hydrogen Bonding; Liposomes; Membranes, Artificial; Perylene; Phenols; Receptors, Cell Surface; Surface-Active Agents; Triazines

The amplification of supramolecular chirality has been studied in dynamic chiral hydrogen-bonded assemblies 1(3).(CA)(6) using "Sergeants and Soldiers" experiments. Previously, we have shown that chiral centers present in either the dimelamine component 1 or the cyanurate component CA quantitatively induce one handedness (M or P) in the assembly. This offers the possibility to study the amplification of chirality under two different kinetic regimes. When chiral dimelamines 1 are used, the exchange of chiral components and (M/P)-interconversion, i.e., interconversion between the (M)- and (P)-isomers of assembly 1(3).(CA)(6), take place via identical pathways (condition A). When chiral cyanurates CA are used, the exchange of chiral components occurs much faster than (M/P)-interconversion (condition B). Experimentally, a much stronger chiral amplification is observed under condition B. For example, the observed chiral amplification for a mixture of chiral and achiral components (40:60) is 46% under condition B and 32% under condition A. Kinetic models were developed to fit the experimental data and to simulate chiral amplification in dynamic systems in general. These simulations show that it is theoretically possible that the diastereomeric excess in a dynamic system is more than 99% with less than 1% chiral component present!

Topics: Barbiturates; Calixarenes; Hydrogen Bonding; Kinetics; Models, Chemical; Phenols; Stereoisomerism; Thermodynamics; Triazines