With density functional calculations and in situ Si-29 and P-31 MAS NMR experiments, a novel defect site (defect site II, ds(II)) was identified in titanium silicalite molecular sieve (TS-1 zeolite), supported by the previous experimental results. The conversion from Q(3) species [(SiO)(3)Si(OH)])] into Q(4)-like species [Si(OSi)(4)] due to TMP adsorption indicated the presence of Bronsted acidity in TS-1 zeolite. The thermodynamic analysis and Ti/Si substitution energies further confirmed that the proton transferring process of defect site II is much facilitated in TS-1 zeolite whereas on the contrary in silicalite-1. With the proton-affinity calculations, the Bronsted acidities of several cation-doped zeolites were found to decrease in the order of Al-ZSM-5 > Fe-ZSM-5 > B-ZSM-5 > TS-1. The Bronsted acidity of TS-1 zeolite is even weaker than that of B-ZSM-5 zeolite, suggesting the potential role as a new acid catalyst. As to silicalite-1, its acidity is even weaker than that of defect site I (ds(I)) in TS-1 zeolite. (c) 2007 Elsevier B.V. All rights reserved.