COMMUNICATIONS
the investigation of a wide variety of hydrogen-bonded supramolecular assemblies and more generally of self-assembly through any type of intermolecular interaction. Such work is currently in progress in our laboratory.
Esprrim iw I ril Pr oc~dure
Positive-tori ES m a s 5pectr:i were obtained on a VG BioQ triple quadrupole apparatus xvith ;I m;i\s-to-charge (n!:) range up to 4000 (VG Bio Tech Ltd. Altrincham. U K ) . The clectrospray source was heated to 50 C. The sampling cone volkige ( 1 . ) 161 *:is a t 10 V to avoid fragmentation of the assemblies. Sample solutions were introduced into the mass spectrometer source ujith a syringe pump (Harvard type 55 I I 1 1 ; Harvard Apparatus Inc.. South Natick. MA. USA) at a flow rate o f 6 yI.min-I . Cdibration was performed using protonated horse myoglobin. The resolution bit\ usu;illy about 500 at in:: 1000 (10% height). Scanning was performed from m : 200 to 2200 in 15 s. The data system was operated as a multichannel analyier. and several scans were summed to obtain the final spectrum. Simples lor ESMS wcre prepared by dissolving equimolar amounts of the compo-nent\ in the appropriate solvent (dichloromethane. benzene. pentane) to achieve the concentrationa listed in Table 1 . Solutions containing salts were prepared by adding 0.5 mg of salt (KPF,,. NaCIO,, CsCI) iii 0.5 mL of solution and sonicating briefly. The soluti(iii was removed from the excess salt uith a pipette and directly analyzed. Labeling expel-imenb uere performed by adding the desired ratio of equimolar solutions of the iiiiictive label (A without KPF,) and the assembly of interest, and tlicn ;idding KPF,, 'is previously described.