We recently discovered that photodecarbonylation of phenylaminocyclopropenones, 1, in aqueous solution produces ynamines, 2, as short-lived transient species, eq 1.1 Our work showed ynamines to be remarkably weak bases 0 1 L and, provided they had an ionizable N-H bond, i.e., were either primary or secondary amines, to be correspondingly strong acids as well. In this respect, ynamines resemble their oxygen analogs, ynols, where the acetylenic group also exerts a very strong acidstrengthening effect.293 In these initial studies we did not determine the pK,' s of any of the ynols or ynamines we examined, and we consequently could only set lower limits on the acidstrengthening effect. We wish to report that we have now found that N-(pentafluorophenyl)-2-phenylethynamine, 3, undergoes acid dissociation in aqueous solution, eq 2, with pKa = 10.28, and that this has allowed PhC=CNHC6F5 + H 2 0 PhC=CNC6F[ + H30+(2) 3 us to fix the acidifying effect in this case at 10 pKunits or 14 kcal mol-'.We generated this ynamine as before' by flash photolysis of the corresponding aminocycl~propenone~ and found that its rapid hydration to N-(pentafluorophenyl)phenylacetamide, 5, occurs through prior isomerization to a ketenimine, 4, eq 3, as is the case with other secondary ynamines.' This reaction of 0 H O II 4 5 PhC=CNHC,F, 4 PhCH=C=NC,Fs PhCH,CNHC,FS (3)the ynamine to the ketenimine is catalyzed by both acids and bases, and rate measurements made at 25.0 f 0.1 OC in HC104 and NaOH solutions as well as HCOzH, C H~C O Z H , HzP04-, NH4+, and HC03-buffers produced the rate profile shown in Figure 1.6 The acid-catalyzed limb of this profile represents ratedetermining proton transfer from the hydronium ion to the @-carbon atom of the ynamine, as evidenced by the kinetic isotope effect kH+/kD+ = 3.27 f 0.09; this step is then followed by rapid ~~~ ~ (1) Chiang. Y.; Grant, A. S.; Kresge, A. J.;Pruszynski, P.; Schepp, N. P.; (2) Chiang, Y.; Kresge, A. J.; Hochstrasser, R.; Wirz, J. J . Am. Chem. ( 3 ) For a theoretical analysis of this acid-strengthening effect, see: Smith, B. J.; Random, L.; Kresge, A. J. J. Am. Chem. SOC. 1989,111,8297-8299. Smith, B. J.; Radom, L. J. Am. Chem. SOC. 1992,114, 36-41.(4) N-(Pentafluoropheny1)phenylaminocyclopropenone was prepared by treating phenylchlorocyclopropenoneJ with pentafluoroaniline; it was characterized by its NMR, IR, and mass spectra. (5) Chicos, J. S.; Patt0n.E.; West,R. J. Org. Chem. 1974,39,1647-1650. (6) The data obtained in buffer solutions were extrapolated to zero buffer concentration; all measurements were made at ionic strength = 0.10 M. Wirz, J.

The hydrogels composed of decamethylcucurbit[5]uril (Me 10 Q[5]) and para-phenylenediamine (p-PDA) are first reported herein. They are the first Q[5]-based supramolecular hydrogels, the formation of which is driven by portal exclusion between Me 10 Q[5] and p-PDA. The composition, structure, and properties of the Me 10 Q[5]/p-PDA-based hydrogels are investigated by various techniques. Since the 1D supramolecular chain forms via portal exclusion between Me 10 Q[5] and p-PDA is the key to the formation of the hydrogels, any competitive species, such as metal ions, organic molecules, and amino acids, which can affect the portal exclusion, can change the behavior of the Me 10 Q[5]/p-PDA-based hydrogels. Hence, the hydrogels can be used for various applications. Importantly, the results may provide a new research direction for the preparation of Q[n]-based hydrogels via portal exclusion of Q[n]s with guests.

This work investigated the binding interactions between decamethylcucurbit[5]uril (Me10Q[5]) and phenylenediamine isomers, and developed a strategy to isolate phenylenediamine isomers.