N-ALPHA,N-ALPHA-DIMETHYLHISTAMINE - A BIOLOGICAL SUPERBASE IN THE GAS-PHASE

The gas-phase basicity (Delta GB) of the biological compound N-alpha,N -alpha-dimethylhistamine (1') relative to ammonia [defined as the stan dard Gibbs energy change for reaction 1 (1'H+(g) + NH3(g) reversible a rrow; 1'(g) + NH4+(g))] was measured by means of Fourier transform ion cyclotron resonance spectroscopy (FTICR). The various tautomer/ confo rmers of 1' and 1'H+(g) were studied by means of ab initio SCF-LCAO-MO calculations at the 6-31G//6-31G and 6-31G*//6-31G** levels. It was found that the combination of polarizability and chelation effects pre sent in 1'H+(g) endows 1' with an intrinsic basicity equal to that of N,N,N',N'-tetramethyl-1,8-naphthalenediamine (Proton Sponge).