Incorporation of inter- and intramolecular forces in the calculation of crystal packing and lattice vibrations

Huler, E.; Warshel, Arieh

doi:10.1107/s0567740874005875

Cited by 27 publications

(7 citation statements)

References 11 publications

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“…A more comprehensive analysis, however, should take into account all intra-and intermolecular interactions and thus establish the minimum energy structure. This we have done by means of the QCFF/MCA program package (30,31), which allows optimization of all atomic positions of a molecule in a crystalline environment. The force field given (30) includes all relevant conformational and packing potential functions: bond stretching (Ustr), angle bending (Ubend), torsion (Vtors) and intramolecular (U,o,b), as well as intermolecular (Utmost) non-bonded interactions.…”

Section: Discussionmentioning

confidence: 99%

Crystal structures and melting points of unsaturated triacylglycerols in theβphase

Jong

Soest

Schaick

1991

J Americ Oil Chem Soc

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The/3-phase crystal structures of unsaturated triacylglycerols (TAGs) have been analyzed. Long spacings and melting points of monounsaturated TAGs such as 16" O. 16 and 16.0" 18 indicate a fi-3C packing mode with a methyl terrace that differs from that of the saturated /3-3 TAGs. In addition to the hydrocarbon chain subcell packing and the methyl terrace structure, the conformation of the oleoyl chain also has to be considered. This conformation is analyzed in connection with the symmetry relation between the two half-layers on either side of the plane through the double bonds. Geometric analysis shows four possibilities, which have been explored further by means of energy minimization computations. In these calculations the structure of the oleoyl chain, in its crystalline environment, has been optimized while taking all relevant intramolecular and intermolecular forces into account. Though the calculations reveal relatively small energy differences between the four possibilities, the most likely structure can still be identified. On the basis of the results obtained for the monounsaturated TAGs, proposals for the crystal structures of diunsaturated (e.g., 0 9 18. O) and triunsaturated (e.g., 0" 0" O) TAGs are briefly outlined.

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Section: Discussionmentioning

confidence: 99%

Crystal structures and melting points of unsaturated triacylglycerols in theβphase

Jong

Soest

Schaick

1991

J Americ Oil Chem Soc

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“…The evaluation of lattice energies from simple intermolecular potential functions (involving essentially atom-atom terms) has been accomplished successfully in several recent works (Caillet & Claverie, 1974, 1975Momany, Carruthers, McGuire & Scheraga, 1974;Hagler, Huler & Lifson, 1974;Huler & Warshel, 1974;and references therein). A detailed description of our own method may be found in Caillet & Claverie (1975); thus we only recall here the main practical features in §2(a)-(d), and describe in §2(e) the modification applied for very short interatomic distances which was not described in Caillet & Claverie (1974, 1975.…”

Section: Methodsmentioning

confidence: 99%

On the conformational varieties of adrenaline: the free molecule and the molecule in the crystal

Caillet¹,

Claverie²,

Pullman³

1976

Acta Crystallogr Sect B

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Refined quantum-mechanical computations invariably predict that the preferred conformers of free androgenic phenethylamines or hallucinogenic indolalkylamines should correspond to values of the torsion angles rt---+ 90 ° and rz close to + 60 or 180 °. X-ray crystallographic studies indicate that most such compounds exist in these conformations (in particular with rl ~ 90, r2-~ 180 °) in the crystals. In some cases, however, the crystalline conformer corresponds to rl -~ 0, r2-~ 180 °, an arrangement which does not even correspond to a local energy minimum on the conformational energy map for the free molecule. Such is, for example, the case for adrenaline in adrenaline hydrogen tartrate. Computations carried out for the lattice energy of this crystal and of the hypothetical crystals constructed with the usual conformers, by a procedure which uses intermolecular potential functions, show that the lattice energy of the 'experimental' crystal largely compensates for the loss in conformational energy of the constituent unit and represents a more stable arrangement than those obtained with conformers associated with rl-+ 90 °.

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“…Calculations have been carried out with the program MCA (molecular conformation analysis; Huler & Warshel, 1974) with modified and extended parameters for forcefield and ~z-SCF calculation (Stegemann, 1979) and by the program PIMM (zc-SCF-MO molecular mechanics program; Lindner, 1974).…”

Section: Discussionmentioning

confidence: 99%

Structure and conformation of substituted cycloheptatrienes. I. 2,5-Dimethyl-3,4-diphenyl-1,3,5-cycloheptatriene

Stegemann¹,

Lindner²

1979

Acta Crystallogr Sect B

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C21H20 is monoclinic, space group P2~/c, with a = 11.312(5), b = 8.503 (5), c = 16.91 (1) ,4,, fl = 98.04 (1) °, Z = 4. The structure was refined to R = 0.044 for 1119 counter reflections. The sevenmembered ring is boat-shaped with structure angles a = 52.6 o and fl = 34.3 o. Empirical force-field calculations of the isolated molecule predict a = 51.0 ° and fl = 27.5 °, while a = 51.9 ° and fl = 31.9 ° were calculated considering packing effects. The enthalpy of the inversion barrier between the two boat forms has been calculated to be 59 kJ mol -~.

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Incorporation of inter- and intramolecular forces in the calculation of crystal packing and lattice vibrations

Cited by 27 publications

References 11 publications

Crystal structures and melting points of unsaturated triacylglycerols in theβphase

Crystal structures and melting points of unsaturated triacylglycerols in theβphase

On the conformational varieties of adrenaline: the free molecule and the molecule in the crystal

Structure and conformation of substituted cycloheptatrienes. I. 2,5-Dimethyl-3,4-diphenyl-1,3,5-cycloheptatriene

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