Conformational properties of a model alanyl dipeptide and of alanine-derived oligopeptides: Effects of solvation in water and in organic solvents - A combined SIBFA/Continuum reaction field, ab initio Self-Consistent Field, and Density Functional The

摘要

A phi/psi conformational energy map of a model alanyl dipeptide is first drawn using the SIBFA (Sum of Interactions Between Fragments Ab initio computed) procedure [N. Gresh, P. Claverie and A. Pullman (1979) International Journal of Quantum Chemistry Symposium, Vol. 13, pp. 243-253; N. Gresh, P. Claverie and A. Pullman (1982) International Journal of Quantum Chemistry, Vol. 22, pp. 199-215; N. Gresh, P. Claverie and A. Pullman (1984) Theoretical Chimica Acta, Vol. 66, pp. 1-20; N. Gresh, P. Claverie and A. Pullman (1985) Theoretical Chimica Acta, Vol. 67, pp. 11-32; N. Gresh, A. Pullman and P. Claverie (1985) International Journal of Quantum Chemistry, Vol. 28, pp. 757-771; N. Gresh, P. Claverie and A. Pullman (1986) International Journal of Quantum Chemistry, Vol. 29, pp. 101-118; N. Gresh (1995) Journal of Computational Chemistry, Vol. 16, pp. 856-882; N. Gresh and D. R. Garmer (1996) Journal of Computational Chemistry, Vol. 17, pp. 1481-1495; N. Gresh, M. Leboeuf and D. R. Salahub (1994) in Modelling the Hydrogen Bond, Vol. 569, American Chemical Society Symposia, Smith, D. A., Ed., pp. 82-112: N. Gresh (1997) Journal de Chim.-Phys. (Paris), Vol. 94, pp. 1365-1416]. A new formulation of the intramolecular (conformational) energy is used, consistent with the refinements that were recently published for the intermolecular interaction energies in joint SIBFA/ab initio supermolecule Self-consistent Field/Moller-Plesset (SCF/MP2) and Density Functional Theory (DFT) studies of cation-ligand [see Gresh (1995) and Gresh and Garmer (1996) above], and H-bonded [see Gresh et al. (1994) above] complexes. The accuracy of the procedure is assessed, on fourteen conformers selected from the map, by comparing their relative conformational energies with those obtained from SCF/MP2 and DFT computations. Conformational energy maps are then recomputed in the presence of water, dimethyl sulfoxide, chloroform, and carbon tetrachloride, the solvation energies being computed with the Continuum reaction field procedure due to J. Langlet et al. [(1988) Journal of Physical Chemistry, Vol. 92, pp. 1617-1631], and recently integrated into SIBFA [J. Langlet, N. Gresh and C. Giessner-Prettree (1995) Biopolymers, Vol. 36, pp 765-780]. Such an integrated procedure is next extended to a comparison of the relative stabilities of, on the one hand, the competing types of beta-turns (I, I', II, II') that are prevalent in Ala/Gly-based model tetrapeptides, and, on the other hand, alpha- vs 3(10)-helices in alanine oligomers. (C) 1998 John Wiley & Sons, Inc. [References: 78]