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Biomedical subjects

Alan R Kennedy

Publications and source records attributed to Alan R Kennedy.

47 records · Page 3Linked to original sources
PubMed2003

Rational design of molecular sheets composed of interconnecting eight- and twenty-four-membered rings: use of lithiated aggregates to control network assembly.

The lithiated (organo)sulfonylacetonitrile complex [MeSO(2)CHCNLi.THF] (3) has been prepared and structurally characterized in order to demonstrate that well-known molecular aggregates of s-block metals may be used as building blocks in the controlled assembly of complex supramolecular architectures. The solid state structure of 3 can be described as a novel basket-weaved, 2-D network, composed of (SO(2)Li)(2) "dimeric" rings joined via "interdimer" donation of nitrile units.

Journal Article↗
PubMed2003

Aggregation patterns in alpha,alpha'-stabilized carbanions: assembly of a sodium cage polymer by slip-stacking of dimers.

The alpha,alpha'-stabilized carbanion complexes [PhSO(2)CHCNNa.THF], 3, [t-BuSO(2)CHCNNa], 4, [PhSO(2)CHCNK], 5, [t-BuSO(2)CHCNK], 6, and [MeSO(2)CHCNLi.TMEDA], 7, have been synthesized via the metalation of the parent (organo)sulfonylacetonitriles by BuLi, BuNa, or BnK in THF solution (or THF/TMEDA in the case of 7). In addition, complexes 3 and 7 have been characterized by single-crystal X-ray analyses and have been found to adopt related structures in the solid state. Complex 7 is a molecular dimer containing a central 12-membered (OSCCNLi)(2) ring core, with each metal rendered tetracoordinate by binding to a chelating TMEDA molecule. As found in related complexes, no direct carbanion to lithium contacts are present in the structure of 7. Complex 3 forms a polymeric cage structure composed of associated "dimeric" (OSCCNNa)(2) rings, similar to those found in 7. The larger sodium cations, and the presence of only one THF molecule/metal, allow additional contacts with the anions, leading to hexacoordination at the metal centers. These contacts include long-range transannular Na-N interactions (2.8042(14) A) across the central dimeric ring and "interdimer" Na-C connections (2.8718(15) A). Dissolution of complexes 3-6 and their lithiated derivatives [PhSO(2)CHCNLi.TMEDA], 1, and [t-BuSO(2)CHCNLi.THF], 2, in DMSO-d(6) results in almost identical chemical shifts for each type of ligand. This suggests that charge-separated complexes of the form [RSO(2)CHCN](-)[M(DMSO-d(6))(n)()](+) are formed in highly polar solution.

Journal Article↗
PubMed2003

Bis[mu-P,P'-methylenebis(diisopropyl phosphonate)-kappa3O,O':O]bis[chlorolithium(I)]: a centrosymmetric dimer of lithium chloride with terminal chloride anions.

The molecule of the title dimeric compound, [Li(2)Cl(2)(C(13)H(30)O(6)P(2))(2)] or [LiCl([((i)PrO)(2)P(O)](2)CH(2))](2), lies about an inversion center and features tetrahedrally coordinated Li atoms. The neutral ligands each chelate to one metal center and bridge to the other center through P=O units. Unusually for lithium chloride complexes, the Cl- ions are in terminal rather than bridging positions. Principal dimensions include Li-O(four-membered ring) = 1.959 (3) and 2.056 (3) A, Li-O(phosphonate ring) = 1.929 (3) A, and Li-Cl = 2.293 (3) A.

Journal Article↗
PubMed2003

Indexing powder patterns in physical form screening: instrumentation and data quality.

Two multisample laboratory powder diffractometers have been evaluated for the purpose of pattern indexing in the context of physical form screening. Both diffractometers utilise foil transmission geometry, primary monochromated radiation, and a position-sensitive detector. Data collected from six compounds (sotalol hydrochloride, hydroflumethiazide, verapamil hydrochloride, captopril, clomipramine hydrochloride, and famotidine) showed good angular resolution (FWHM as small as ca. 0.06 degrees ) and lattice parameters were easily obtained using the indexing program DICVOL-91. The extent of preferred orientation in each pattern was estimated using the DASH implementation of the March-Dollase function and is most evident with clomipramine hydrochloride and famotidine. Otherwise, the data compare favorably with reference capillary data sets. In conclusion, where there is a requirement to analyze 20-30 samples per day, with an emphasis on obtaining the high-quality data that are important in pattern recognition and imperative in indexing, the combination of foil transmission geometry, primary monochromated radiation, plus a position-sensitive detector is highly effective. The data also afford opportunities for crystal structure determination.

Chemical Phenomena↗
PubMed2003

Two new paracetamol/dioxane solvates--a system exhibiting a reversible solid-state phase transformation.

This work reports on the crystal structures of two dioxane solvates of paracetamol that are true polymorphs. The high temperature phase is an orthorhombic form, space group Pbca, Z = 8, a = 12.6078(3) A, b = 12.1129(2) A, c = 13.4138(3) A, V = 2048.52(7) A(3), (at 295 K) and the low temperature form is monoclinic, space group P21/c, Z = 4, a = 12.325(6) A, b = 11.965(4) A, c = 13.384(6) A, beta = 92.01 degrees, V = 1972.6(14)A(3) (at 123 K). The structures of these polymorphs are described as is the interrelationship between the two structures. In addition to the structural interrelationship, it is shown that the two forms undergo a reversible phase transformation. Desolvation of either form generates the stable monoclinic phase of paracetamol.

Acetaminophen↗
PubMed2002

Structural motifs in acetoacetanilides: the effect of a fluorine substituent.

The structures of three fluoro-substituted acetoacetanilides, namely 2'-, 3'- and 4'-fluoroacetoacetanilide, all C(10)H(10)FNO(2), are presented and discussed. We observe a planar structure with intramolecular hydrogen bonding when the F atom is in the ortho position of the aromatic ring, and a twisted structure with intermolecular hydrogen bonding when the F atom is in the meta or para positions. It can be predicted which of these two structural motifs will be adopted by considering the position of any aromatic substituents. In this regard, fluorine appears to mimic the steric effect of a larger substituent, which we attribute to its high electronegativity.

Journal Article↗
PubMed2002

Hydride encapsulation in s-block metal inverse crown chemistry.

A new category of 'inverse crown' complex has been established through the synthesis of the disodium-dimagnesium diisopropylamide [Na2Mg2(N(Pri)2)4(mu-H)2.(toluene)2], the first such complex to exhibit hydride encapsulation, a non-planar octagonal 'host' ring or solvent stabilisation.

Journal Article↗