Jacqueline Caillet

Van der Waals-London interactions between stacked purines and pyrimidines.

Abstract The method used previously for the study of the Van der Waals-London interactions in hydrogen bonded purine and pyrimidine pairs Pullman, Claverie & Caillet 1966 has been extended to a similar investigation of the interactions between “stacked” bases. Three problems have been considered: the interaction of free bases or their nucleosides in aqueous solution, the interaction of the bases in oligo- and polynucleotides and the interaction of the base-pairs in DNA. Calculations have been carried out in the “monopole” approximation.

Intermolecular Forces in Association of Purines with Polybenzenoid Hydrocarbons

The interactions in solution between purine or pyrimidine bases and polybenzenoid aromatic hydrocarbons probably consist in a vertical, stacking-type physical association. By molecular orbital calculations the role of the Van der Waals-London intermolecular forces in these interactions is determined. The electrostatic dipole-dipole forces are negligible, the polarization (or induction) dipole-induced dipole forces are contributory, but most important are the dispersion (or fluctuation) forces. This loose, physical type of interaction should not show any specificity with respect to the carcinogenic activity of the hydrocarbons.

Comparison of two ways to decompose intermolecular interactions for hydrogen-bonded dimer systems

In this work we test two ab initio methodologies which allow the decomposition of the total intermolecular interaction energy into physically meaningful contributions, namely, the symmetry adapted perturbation theory (SAPT) and the use of localized orbitals within a Moller–Plesset perturbation scheme. The accuracy of the two different methods is compared to supermolecular results, within MP2 and coupled-cluster theory within single and double excitations, with perturbative estimates of the amplitudes of triple excitations [CCSD(T)]. Some relations between the different approaches are conjectured from theoretical considerations, and are confirmed by numerical results. The corresponding calculations have been performed for three model dimers: two NH3⋯H2O dimers, with NH3 acting once as a proton acceptor and once as a proton donor, and the NH4+⋯H2O considered as a prototype of the ion–molecule interaction. We may conclude that third-order terms in SAPT help significantly to reproduce the Hartree–Fock inducti...

A perturbational study of some hydrogen‐bonded dimers

We present a detailed study of several hydrogen‐bonded dimers consisting of H2O, NH3, and HF molecules using the Symmetry Adapted Perturbation Theory (SAPT) at different levels of approximations. The relative importance of each individual perturbational components and the quality of the total interaction energies obtained are discussed. The dependence of the results on the relative orientation of the molecules of the dimers and on the intermonomer distance is also investigated.

Theoretical study on the proton chemical shifts of hydrogen bonded nucleic acid bases

The variation of the proton chemical shifts due to the formation intermolecular hydrogen bonds is computed for a number of complexes which can be formed between the bases of the nucleic acids. The shifts expected for the isolated base pairs, in particular for the G-N1 H, T(or U)-N3H protons and the protons of the amino groups of A, G c, when combined with previous computations on the shifts to be expected upon base stacking, may enable a refined analysis of the high resolution NMR spectra of self complementary polynucleotides or tRNAs. Two examples are presented of a direct computation of proton shits associated with helix-coil transitions, helpful for deducing the helical structure in solution.

Effect of the crystalline environment upon the rotational conformation about the N-C and C-C′ bonds (Φ andΨ) in amides and peptides

SCFab initio and PCILO computations indicate the intrinsic preference of the ψ torsion angle for 60 °. In the crystal structure of simple methylamides and peptides the observed values for this torsion angle lie between 0 °–30 °. Different procedures for computing lattice energies and total crystallographic conformational energies (lattice + torsional) utilized by other authors, failed to account for this situation. We show that the procedure developed recently in our laboratory for computing lattice energies indicates that the minima of these energies for ψ in acetamide and N-methylacetamide correspond well to 0 °–30 °. Because of the low value of the barrier of the torsional potential for this angle, the total crystallographic conformational energy corresponds also to ψ = 0 °–30 ° in agreement with the experimental data.