Gauge-including atomic orbitals shifts

The 13C chemical shift contour map for the Cp carbon of the L-alanine residue in peptides and polypeptides was made as a function of the dihedral angles(, W) by using the experimental data. Also, the corresponding calculated map was made by using the ab initio coupled Hartree-Fock method with the gauge included atomic orbitals(GIAO-CHF). From these results, it was found that the calculated map explains the chemical shift behavior of the a-helix and p-sheet forms in poly(L-alanine) and some proteins. This suggests that the calculated map is applicable to the structural analysis of proteins with complicated structure. 

Gauss, J., Calculation of NMR chemical shifts at second-order many-body perturbation theory using gauge-including atomic orbitals, Chem. Phys. Lett. 191, 614-620 (1992). 

GIAO Gauge-Including Atomic Orbitals. A class of orbitals which are designed to permit computation of chemical shift tensors in NMR spectra. 

Ab initio calculations of phosphorus NMR chemical shifts in the gauge including atomic orbital (GIAO) were reported for 17 phosphorus-containing molecules, among them PHJ. 

Another theoretical method, extensively exploited in chemical shift shielding calculation is gauge-including atomic orbitals (GIAO) [177] approach. That technique provides reasonable chemical shifts values for various nuclei. It should be noted that this approach does not take into account the periodicity of the crystal lattice and calculations are carried out for isolated molecules (gas phase). If analysis of intermolecular interactions is target of the project or there is its important part, then arbitrarily constructed cluster model has to be built up. 

Second-Order Many-Body Perturbation Theory Using Gauge-Including Atomic Orbitals. J. Gauss,/. Chem. Phys, 99, 3629 (1993). Effects of Electron Correlation in the Calculation of Nuclear Magnetic Resonance Chemical Shifts. 

Allouche et alP calculated chemical shifts (5 values) and SSCCs (/values) for the putrescine molecule, a polyamine present in prostate tissue, using a B3LYP-DFT/6-311-I-- -G(/,/))/PCM/GIAO (gauge-including atomic orbital) approach. From the computed and J values, the H NMR spectrum of putrescine was simulated. Comparisons between the calculated and the experimental NMR spectra at 400 MHz showed a good agreement and allowed to propose reliable values for the NMR spin Hamiltonian parameters of putrescine to be used for further development of quantitative analytical methods of metabolites in prostate tissue. 

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