| Abstract
| - Systems consisting of an amphiphilic melamine-type monolayer and a pyrimidine derivative dissolved in theaqueous subphase are good candidates for the formation of interfacial supramolecular assemblies by molecularrecognition of hydrogen-bond nonsurface-active species. In the present work, the change in the thermodynamic,phase, and structural properties as a result of molecular recognition of dissolved thymine by 2,4-di(n-undecylamino)-6-amino-1,3,5-triazine (2C11H23-melamine) monolayers is studied. The combination of surfacepressure studies with Brewster angle microscopy (BAM) imaging and grazing incidence X-ray diffraction(GIXD) measurements is optimal for the characterization of the change in structure and phase behavior at theinterfacial recognition process. The molecular recognition of the nonsurface-active thymine dissolved in aqueoussubphase changes drastically the characteristic features (surface pressure−area isotherms, morphology of thecondensed phase domains) of the 2C11H23-melamine monolayer. It is demonstrated that the kinetics of therecognition process affect largely the main characteristics (phase behavior, morphology of the condensedphase domains) of the interfacial system. The monolayers of 2C11H23-melamine−thymine assemblies formdumbbell-shaped condensed phase domains not yet observed in other Langmuir monolayers so far. GIXDresults show that the molecular recognition of thymine causes only quantitative changes in the two-dimensionallattice structure. Complementary hydrogen bonding of two thymine molecules by one 2C11H23-melaminemolecule is concluded from the chemical structure of both components. Additional information about thenature of the hydrogen bonding on the basis of supramolecular assemblies is obtained by using the quantumchemical PM3 approximation. Energy and lengths of the hydrogen bonds of the optimized thymine−2C11H23-melamine−thymine structure are calculated.
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