PubMed Health⌕ Search

Biomedical subjects

Carole A Morrison

Publications and source records attributed to Carole A Morrison.

7 recordsLinked to original sources
PubMed2005

Toward understanding mobile proton behavior from first principles calculation: the short hydrogen bond in crystalline urea-phosphoric acid.

The dynamics of the intermolecular short hydrogen bond in the molecular complex of urea and phosphoric acid are investigated using plane-wave density functional theory. Results indicate migration of the proton toward the center of the hydrogen bond as temperature is increased, in line with recent experimental measurements. Computed vibrational frequencies show favorable agreement with experimental measurement. An analysis of existing neutron diffraction data leads us to conclude that the effective potential well experienced by the proton is temperature-dependent. Inspired by our computations and theoretical analysis, we offer a possible explanation for the proton migration phenomenon.

Journal Article↗
PubMed2005

Effect of pressure on the crystal structure of L-serine-I and the crystal structure of L-serine-II at 5.4 GPa.

The crystal structure of L-serine has been determined at room temperature at pressures between 0.3 and 4.8 GPa. The structure of this phase (hereafter termed L-serine-I), which consists of the molecules in their zwitterionic tautomer, is orthorhombic, space group P212121. The least compressible cell dimension (c), corresponds to chains of head-to-tail NH...carboxylate hydrogen bonds. The most compressible direction is along b, and the pressure-induced distortion in this direction takes the form of closing up voids in the middle of R-type hydrogen-bonded ring motifs. This occurs by a change in the geometry of hydrogen-bonded chains connecting the hydroxyl groups of the -CH2OH side chains. These hydrogen bonds are the longest conventional hydrogen bonds in the system at ambient pressure, having an O...O separation of 2.918 (4) A and an O...O...O angle of 148.5 (2) degrees ; at 4.8 GPa these parameters are 2.781 (11) and 158.5 (7) degrees . Elsewhere in the structure one NH...O interaction reaches an N...O separation of 2.691 (13) A at 4.8 GPa. This is amongst the shortest of this type of interaction to have been observed in an amino acid crystal structure. Above 4.8 GPa the structure undergoes a single-crystal-to-single-crystal phase transition to a hitherto uncharacterized polymorph, which we designate L-serine-II. The OH...OH hydrogen-bonded chains of L-serine-I are replaced in L-serine-II by shorter OH...carboxyl interactions, which have an O...O separation of 2.62 (2) A. This phase transition occurs via a change from a gauche to an anti conformation of the OH group, and a change in the NCalphaCO torsion angle from -178.1 (2) degrees at 4.8 GPa to -156.3 (10) degrees at 5.4 GPa. Thus, the same topology appears in both crystal forms, which explains why it occurs from one single-crystal form to another. The transition to L-serine-II is also characterized by the closing-up of voids which occur in the centres of other R-type motifs elsewhere in the structure. There is a marked increase in CH...O hydrogen bonding in both phases relative to L-serine-I at ambient pressure.

Crystallography↗
PubMed2004

Heavier alkali metal complexes of 2-phenylamidopyridine: an X-ray crystallographic and theoretical study of a structurally diverse series of crown ether adducts.

Complexes of the anion of the secondary amine 2-phenylaminopyridine (LH) with the heavier alkali metals Na-Cs have been prepared in the presence of various macrocyclic polyether crowns [12-crown-4 (12C4), 15-crown-5 (15C5), and 18-crown-6 (18C6)], which coordinate to the metal ions in all cases. Depending on the combination of alkali metal and crown, the products include separated ion pairs [(crown)(2)M](+)L(-)(12C4/Na, 15C5/K, 15C5/Rb, 15C5/Cs) and contact-ion-pair neutral molecules [(crown)ML](15C5/Na, 18C6/Na, 18C6/K, 18C6/Rb) in which L(-) acts as a bidentate ligand. [((12C4)KL)(2)] is a dimer in which the amido and pyridine N atoms of two ligands bridge the metal ions, while [((18C6)KL(2)K)([infinity])] is a chain polymer with crown O and pyridyl N atoms acting as bridges in corner-sharing KOKN four-membered rings and may be regarded as a potassium potassate complex. [((18C6)Cs(2)L(2))([infinity])] is also polymeric, with a basic arrangement like that of [((12C4)KL)(2)], but with each 18C6 ligand mu-kappa6:kappa6 to two metal centres, generating the polymer. Although most of the [(crown)(2)M](+) sandwich cations have essentially parallel crown ligands, [(12C4)(2)Rb](+) is markedly bent, both in the complex incorporating THF as an additional ligand and in the THF-free complex, where two of these cations form a centrosymmetric dimer through two bridging oxygen atoms; DFT calculations indicate that the bending is inherent, thus enabling the coordination by an extra oxygen atom rather than being a consequence of this coordination. Attempts to isolate the caesium 12C4 derivative were unsuccessful. The compounds have been characterized by NMR spectroscopy, CHN microanalysis and, in most cases, X-ray crystallography.

Journal Article↗
PubMed2003

Highly asymmetric coordination in alkenes: gas-phase structures of trans-1,2-dichloro-1,2-disilylethene and 1-bromo-1-silylethene.

The molecular structures of trans-1,2-dichloro-1,2-disilylethene and 1-bromo-1-silylethene have been determined by gas-phase electron diffraction (GED) and ab initio molecular orbital calculations (MP2/6-311G). Both compounds were found to have highly asymmetric coordination around the carbon atoms with [ab initio (r(e))/GED (r(a))] C=C-Cl [117.0/117.0(2) degrees] and C=C-Si [126.2/128.1(1) degrees] in the C(2)(h) structure of trans-1,2-dichloro-1,2-disilylethene and C=C-Br [119.2/120.7(4) degrees] and C=C-Si [125.0/125.0(4) degrees] in the C(s) structure of 1-bromo-1-silylethene. Other important structural parameters for trans-1,2-dichloro-1,2-disilylethene are C=C [135.2/134.5(3) pm], C-Si [189.4/187.9(2) pm], and C-Cl [175.1/174.9(1) pm], and C=C [134.2/133.4(2) pm], C-Si [187.8/187.2(3) pm], and C-Br [191.3/191.0(3) pm] for 1-bromo-1-silylethene. Further ab initio calculations were carried out on CH(2)CRX and trans-(CRX)(2) (R = SiH(3), CH(3), or H; X = H, F, Cl, or Br) to gauge the effects of electron-withdrawing and electron-donating groups on the structures. They reveal some even more distorted structures. The asymmetric appearance of these molecules can largely be accounted for by valence shell electron pair repulsion theory.

Journal Article↗
PubMed2003

Determining the strengths of hydrogen bonds in solid-state ammonia and urea: insight from periodic DFT calculations.

Plane-wave density functional theory has been applied to determine the strengths of hydrogen bonds in the phase I crystal structures of ammonia and urea. For ammonia, each component of the trifurcated hydrogen bond has been found to be almost as strong as a standard N-H.N interaction, and for urea the strengths of the two different N-H.O interactions have been determined by a quantum mechanical technique for the first time.

Ammonia↗
PubMed2002

Interpreting molecular crystal disorder in plumbocene, Pb(C5H5)2: insight from theory.

Plane-wave density functional theory has been applied in a novel way to help interpret the molecular crystal structure disorder observed in the orthorhombic zigzag phase of plumbocene, Pb(C5H5)2. A crystal lattice comprising uniformly staggered C5H5 rings was found to be lower in energy by 2.8 kJ mol-1 per unit cell, compared to a uniformly eclipsed packing arrangement. This energy difference has been attributed to the difference in the strength of intermolecular interactions between the Pb(C5H5)2 chains for the two different lattices. The calculations performed allowed the determination of the crystallographic occupancy factors by a quantum mechanical technique for the first time.

Journal Article↗