The importance of NMR spectroscopy for modern chemistry and biochemistry cannot be overestimated. Starting with the classical NMR experiments in 1946 by Purcell and Bloch, [1] contributions by numerous scientists have propelled NMR spectroscopy to be an extremely powerful tool in the investigation of structure and dynamics of molecular systems both in solution and in the solid state (e.g., reference [2]). Despite this progress, the understanding and reliable assignment of observed experimental spectra often remains a highly difficult task. Thus, theoretical methods can be extremely useful, which is the focus of this work.The most reliable way to predict NMR spectra for a specific molecular system is to calculate the NMR chemical shieldings by using quantum-chemical methods. For this purpose an entire hierarchy of methods (and basis sets) exists, which allows the exact result to be systematically approached. The only drawback is, however, the dramatic growth of the computational effort in approaching the exact solution and in increasing the number of atoms in a molecular system. Nevertheless, the hierarchy of ab initio methods allows approximate solutions to be selected and validated, so that error bars can be estimated and the simplest, reliable approximation for studying a specific class of molecular systems can be found.In recent years there has been much progress with respect to the size of molecular systems that can nowadays be treated by using Hartree-Fock (HF) and density-functional methods, due to a reduction of the scaling of the computational effort to linear. Progress has been made mostly for the calculation of energetics (e.g., see references [3][4][5][6][7][8]), the optimization of structures by using analytic gradients (e.g., references [9,10]), and for the calculation of molecular properties (e.g., references [6,11]). However, the linear-scaling computation of[*] Prof.

No abstract

No abstract

A new class of receptor molecules is presented that is highly selective for N-alkylpyridinium ions and electron-poor aromatics. Its key feature is the combination of a well-preorganized molecular clip with an electron-rich inner cavity and strategically placed, flanking bis-phosphonate monoester anions. This shape and arrangement of binding sites attracts predominantly flat electron-poor aromatics in water, binds them mainly by pi-cation, pi-pi, CH-pi, and hydrophobic interactions, and leads to their highly efficient desolvation. NAD(+) and NADP, the important cofactors of many redox enzymes, are recognized by the new receptor molecule, which embraces the catalytically active nicotinamide site and the adenine unit. Even nucleosides such as adenosine are likewise drawn into the clip's cavity. Complex formation and structures were examined by one- and two-dimensional NMR spectroscopy, Job plot analyses, and isothermal titration microcalorimetric (ITC) measurements, as well as quantum chemical calculations of (1)H NMR shifts. The new receptor molecule is a promising tool for controlling enzymatic oxidation processes and for DNA chemistry.

The structure of supramolecular complexes formed by a naphthalene-spaced tweezer molecule as host and 1,4-dicyanobenzene (DCNB), 1,2,4,5-tetracyanobenzene (TCNB), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as aromatic, electron-deficient guests is investigated by solid-state NMR and X-ray diffraction measurements. Quantum chemical calculations using linear scaling methods are applied to predict and to assign the 1H NMR chemical shifts of the complexes. By combining experiment and theory, insights into intra- and intermolecular effects influencing the proton chemical shifts of the host-guest system are provided in the solid state.