Theoretical analysis of measurable NMR spectroscopic parameters in medium size acyclic hydrocarbons and H-bonded aminoacids

G. A. AUCAR; P. F. PROVASI; M. SANCHEZ; S. P. SAUER

San Fransisco, California, USA

Congreso; International Congress of Nanotechnology; 2005

International Association of Nanotechnology

The NMR spectroscopic parameters sigma and J, are highly sensitive to: i) local geometric structures, ii) some underlying intramolecular electronic mechanisms, and iii) the electronic enviroment of each resonant nuclei or coupled nuclei. In line with this knowlege relevant information on both dynamics and structure of biomacromolecules can be achieved from the analysis of those parameters.At the moment, large amount of experimental data are available for both tensors, sigma and J, in molecules in gase, liquid and solid phase. This is the case for small to medium-size and large model molecular systems, and for molecules containing only atoms or molecules containing few heavy atoms.From a theoretical point of view reliable results are hard to obtain due to some computational demanding requirements that should be included in theoretical calculations: large basis sets and the effects of correlation, rovibrational and relativity.In this presentation we will start with a brief introduction on the origin of NMR spectroscopic parameters. Then, a summary on the performance of the theoretical calculations from the state-of-the-art second order polarization propagator approach, SOPPA, for different kinds of molecular systems and couplings will be given. We will continue with some new results of both parameters in fluorinated acyclic hydrocarbons where large long range F-F couplings were recently predicted. We will show which are the electronic mechanisms that are involved in the J(F-F) and J(C-F) couplings through distances of the order of 1 nm. Finally theoretical predictions on H nuclear magnetic shieldings of H-bonded aminoacids will be presented and discussed in some details.