The recoupling of heteronuclear dipolar interactions between 14 N and 1 H with symmetry-based RN sequences of the R20 9 5 type applied to protons in samples spinning at the magic angle allows one to excite 14 N single-quantum (SQ) or double-quantum (DQ) coherences and reconvert them into observable proton coherences. This offers an alternative to the recoupling of heteronuclear dipolar interactions by rotary resonance. The experimental efficiency of the two-way coherence transfer process is on the order of 9 and 4% for SQ and DQ spectroscopy. Spectra were obtained at 400 and 800 MHz for protons. The parameters of the 14 N quadrupolar tensors can be determined in peptides, both in rotating 14 N 1 H þ 3 groups in protonated amines and in rigid 14 N 1 H pairs in amide groups.

Bifunctional, Lewis, and Brønsted acidic molecular sieves were prepared by stepwise zinc ion exchange of zeolite BEA. The relation between the location of the Zn2+ cations in the zeolite structure and the Lewis acidity of the metal cations was explored. Several techniques were used for the detailed characterization of the material, including IR spectroscopy, with pyridine and acetonitrile as probe molecules, temperature programmed desorption, with ammonia and 2-propylamine as probe molecules, X-ray absorption spectroscopy, and 27Al MAS and MQMAS NMR spectroscopy. At low zinc concentrations (<0.15 Zn/Al) the cations are preferentially incorporated in the vicinity of two framework aluminum atoms. With increasing zinc loading (0.15 ≤ Zn/Al ≤ 0.26), additional cation sites are created at nearby framework aluminum pairs with two zinc cations being bridged by an oxygen atom. At higher zinc loading (0.26 < Zn/Al < 0.77) zinc oxide is formed in addition to the other two Zn2+ species.

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