| Abstract
| - The complementary guest binding process onto the cyanurate lipid1 monolayer at the air−water interfacewas observed by using a highly sensitive 27 MHz quartz-crystalmicrobalance (QCM), which was attachedhorizontally on the monolayer from the air phase. Binding amount(Δm), association constants (Ka),aswell as binding and dissociation rate constants(k1 andk-1) could be obtained from timecourses of thefrequency decrease (mass increase) of the QCM. A highly sensitive27 MHz QCM was used to detect smallmass changes of Langmuir adsorption of small guest molecules instead ofour conventional 9 MHz QCM.Guests such as 2,4,6-triaminopyrimidine (A) possessingthree complementary hydrogen bonding siteswere selectively bound to the monolayer 1 showing a 1:2host−guest binding ratio, k1 = 2.8M-1 s-1,k-1= 7.2 × 10-4s-1, and Ka = 3900M-1. The Ka valuewas consistent with that obtained by NMR spectrain bulk CDCl3. Guest molecules of A hardlybound to monolayers 2−4 with−NH2, −CONH2, and −OHhead groups. Binding constants of guest molecules to the monolayer1 were of the following order: 2,4,6-triaminopyrimidine (A) > 2,6-diaminopyridine (B)possessing three hydrogen bonds > 2-aminopyridine(C) forming two hydrogen bonds > pyridine (D)with only one hydrogen bond ≈ barbituric acid (E)havingno complementary hydrogen binding sites. The obtained bindingkinetics at the water interface werecompared with molecular mechanics calculations of binding energy invacuum.
|
