Search PubMed⌕ Search

Biomedical subjects

S A Mason

Publications and source records attributed to S A Mason.

At least 19 recordsLinked to original sources
PubMed2001

Hydrogen-bond network in cyclodecaamylose hydrate at 20 K; neutron diffraction study of novel structural motifs band-flip and kink in alpha-(1-->4)-D-glucoside oligosaccharides.

A single-crystal neutron diffraction study of cyclodecaamylose (CA10) was carried out at 20 K. CA10 crystallizes with 27.18 water molecules [(C(6)H(10)O(5))(10).27.18H(2)O] in space group C2 with unit-cell constants a = 29.31 (5), b = 9.976 (10), c = 19.34 (2) A, beta = 121.07 (2) degrees. The asymmetric unit contains a half molecule of CA10 and 13.59 water molecules, the other half being related by a crystallographic twofold rotation axis. All H atoms except two water H atoms could be located from difference neutron-density maps; structure refinement converged at R = 0.635. Two of the five CH(2)-O6 groups and one of the 15 O2, O3 hydroxyl groups of CA10 are twofold orientationally disordered. A total of 13.59 water molecules in the asymmetric unit are distributed over 23 positions; 20 of which are in the CA10 cavity, and the other three occupy intermolecular interstices. Of the 123 symmetry-independent hydrogen bonds, 25 (= 20%) are three-centered and 7 (= 6%) are four-centered. Water molecules and O-H groups of CA10 form an extended network with cooperative O-H...O-H...O-H hydrogen bonds. They are arranged in 11 polygons with three, four, five, six and eight O-H bonds and in homodromic, antidromic and heterodromic arrangements. Nine polygons are located within the cavity and the others are outside.

Journal Article↗
PubMed2001

Agostic deformations based on electron delocalization in the alkyllithium-complex [(2-(Me3Si)2CLiC5H4N)2.

Topological analysis of experimental and theoretical charge densities in the title complex [(2-(Me3Si)2CLiC5H4N)2] 1 reveals the nature of the agostic deformation postulated for this complex: delocalization of the Li-C bonding electrons over the entire agostic alkyl group controls the formation of an acute Li-C-Si angle and thus a sufficient electronic saturation of the electron deficient lithium atom via secondary interactions.

Journal Article↗
PubMed2001

X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection.

The structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol, C(24)H(30)O(6).H(2)O (1), code name P326, the parent compound for a series of derivatives, has been determined by both X-ray diffraction at room temperature and neutron diffraction at very low temperature. The unit cells are very similar at both temperatures and in both cases the crystals exhibit P2(1) symmetry with Z = 4 (two molecules, A and B, respectively, per asymmetric unit) and pseudosymmetry P2(1)/c. The higher symmetry is broken mainly by the two independent water molecules in the unit cell, some reflections which would be absent in P2(1)/c having strong intensities in both the X-ray and neutron data. In both molecules A and B hydrogen bonds involving the water molecule stabilize the macrocyclic ring structure, one involving the macrocyclic O(9) as a donor. Close contacts between the water and macrocyclic O atoms in each molecule also suggest the presence of two bifurcated hydrogen bonds, involving water HW2 to both O(16) and O(18), and water HW1 to both O(18) and O(20), respectively, with considerable variation in the geometry being present. Both molecules A and B exhibit very close pseudosymmetry across a plane perpendicular to the molecular plane and through atoms C(9) and O(18), and in addition are predominantly planar structures. The X-ray analysis failed to reveal one H atom per water molecule, each being subsequently included after location and refinement in the neutron analysis.

Journal Article↗
PubMed2001

New mode of coordination for the dinitrogen ligand: formation, bonding, and reactivity of a tantalum complex with a bridging N(2) unit that is both side-on and end-on.

The reaction of a mixture of 1 equiv of PhPH(2) and 2 equiv of PhNHSiMe(2)CH(2)Cl with 4 equiv of Bu(n)Li followed by the addition of THF generates the lithiated ligand precursor [NPN]Li(2).(THF)(2) (where [NPN] = PhP(CH(2)SiMe(2)NPh)(2)). The reaction of [NPN]Li(2).(THF)(2) with TaMe(3)Cl(2) produces [NPN]TaMe(3), which reacts under H(2) to yield the diamagnetic dinuclear Ta(IV) tetrahydride ([NPN]Ta)(2)(mu-H)(4). This hydride reacts with N(2) with the loss of H(2) to produce ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)), which was characterized both in solution and in the solid state, and contains strongly activated N(2) bound in the unprecedented side-on end-on dinuclear bonding mode. A density functional theory calculation on the model complex [(H(3)P)(H(2)N)(2)Ta(mu-H)](2)(mu-eta(1):eta(2)-N(2)) provides insight into the molecular orbital interactions involved in the side-on end-on bonding mode of dinitrogen. The reaction of ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)) with propene generates the end-on bound dinitrogen complex ([NPN]Ta(CH(2)CH(2)CH(3)))(2)(mu-eta(1):eta(1)-N(2)), and the reaction of [NPN]Li(2).(THF)(2) with NbCl(3)(DME) generates the end-on bound dinitrogen complex ([NPN]NbCl)(2)(mu-eta(1):eta(1)-N(2)). These two end-on bound dinitrogen complexes provide evidence that the bridging hydride ligands are responsible for the unusual bonding mode of dinitrogen in ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)). The dinitrogen moiety in the side-on end-on mode is amenable to functionalization; the reaction of ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)) with PhCH(2)Br results in C-N bond formation to yield [NPN]Ta(mu-eta(1):eta(2)-N(2)CH(2)Ph)(mu-H)(2)TaBr[NPN]. Nitrogen-15 NMR spectral data are provided for all the tantalum-dinitrogen complexes and derivatives described.

Journal Article↗
PubMed2001

Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides.

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl alpha-D-arabinofuranoside (1), methyl beta-D-arabinofuranoside (2), methyl alpha-D-lyxofuranoside (3), methyl beta-D-ribofuranoside (4) and methyl alpha-D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C(1) chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations.

Journal Article↗
PubMed2000

Obtaining informed consent to neonatal randomised controlled trials: interviews with parents and clinicians in the Euricon study.

BACKGROUND: Questions have been asked about whether the process of obtaining informed consent from parents to clinical trials on neonates leads to valid consent. We undertook a study in nine European countries to assess this issue and to seek any practical improvements. METHODS: Semi-structured interviews were conducted with parents of 200 babies who had been asked for consent to neonatal trials and 107 neonatologists seeking consent. Analysis assessed the validity of the consent process against four components: parental competence; information given; parental understanding; and voluntariness of consent. FINDINGS: 59 of the 200 parents had given valid consent or refusal but the remainder had problems in one or more of the component areas (42 for competence, 43 for information, 44 for understanding, and 21 for voluntariness). The proportions with impaired consent were greatest for research in an emergency situation and for that associated with risk or discomfort greater than standard treatment. Information sheets were little used by parents in deciding whether to consent. Parents highly valued their involvement in the informed consent process, and clinicians generally agreed on the value of the process. INTERPRETATION: Current standards of informed consent to neonatal research projects could be improved. Research personnel should receive guidance on legal and ethical constraints governing the process. Oral and written information should be given at the same time. Parents could be made aware that research projects have been examined by research ethics committees. Little support was found for the argument that informed consent should be relinquished for the parents' own good. Further study is needed to identify which elements of the process are valued by parents and clinicians in a process that has some unavoidable limitations.

Europe↗
PubMed2000

Randomised placebo controlled trial of nebulised corticosteroids in acute respiratory syncytial viral bronchiolitis.

OBJECTIVE: To evaluate short and long term effects of giving nebulised budesonide early in respiratory syncytial viral (RSV) bronchiolitis. DESIGN: A multicentre randomised double blind placebo controlled trial. SUBJECTS: Infants admitted to hospital with their first episode of RSV positive bronchiolitis. INTERVENTION: Randomisation to receive either 1 mg of nebulised budesonide (Bud) or placebo (Pla) twice daily from admission until 2 weeks after discharge. Follow up was for 12 months. MAIN OUTCOME MEASURES: Duration of hospital admission, time taken to become symptom free, re-admission rates, general practitioner consultation rates, and use of anti-wheeze medication during follow up. RESULTS: 161 infants were studied. Both arms were similar with respect to initial clinical severity, age, sex, socioeconomic class, and tobacco exposure. Median time from first nebulisation to discharge: Bud and Pla, 2 days. Median number of days for 50% of infants to be symptom free for 48 hours: Bud, 10 days; Pla, 12 days. Respiratory re-admission rates in the 12 month follow up: Bud, 16%; Pla, 18%; median difference (95% confidence interval (CI)), -2 (-14 to 10). Median respiratory related general practitioner attendances: Bud, 4.0; Pla, 4.5; median difference (95% CI), -1 (-2 to 0). Percentage of infants receiving at least one prescription for anti-wheeze medication during follow up, corticosteroids: Bud, 50%; Pla, 60%; difference (95% CI), -10 (-26 to 6); bronchodilators: Bud, 60%; Pla, 67%; difference (95% CI), -7 (-22 to 8). CONCLUSIONS: There are no short or long term clinical benefits from the administration of nebulised corticosteroids in the acute phase of RSV bronchiolitis.

Acute Disease↗
PubMed2000

Performance-based planning for hospitals.

It is time for health care planning to evolve through a new phase--from strategic planning to performance-based planning, writes Scott A. Mason, D.P.A., FACHE, president and CEO of eko systems inc.

Community Health Planning↗
PubMed1996

DNA hydration studied by neutron fiber diffraction.

The development of neutron high angle fiber diffraction to investigate the location of water around the deoxyribonucleic acid (DNA) double-helix is described. The power of the technique is illustrated by its application to the D and A conformations of DNA using the single crystal diffractometer, D19, at the Institut Laue-Langevin. Grenoble and the time of flight diffractometer, SXD, at the Rutherford Appleton ISIS Spallation Neutron Source. These studies show the existence of bound water closely associated with the DNA. The patterns of hydration in these two DNA conformations are quite distinct and are compared to those observed in X-ray single crystal studies of two-stranded oligodeoxynucleotides. Information on the location of water around the DNA double-helix from the neutron fiber diffraction studies is combined with that on the location of alkali metal cations from complementary X-ray high angle fiber diffraction studies at the Daresbury Laboratory SRS using synchrotron radiation. These analyses emphasize the importance of viewing DNA, water and ions as a single system with specific interactions between the three components and provide a basis for understanding the effect of changes in the concentration of water and ions in inducing conformational transitions in the DNA double-helix.

Crystallography↗
PubMed1996

Time-of-flight Laue fiber diffraction studies of perdeuterated DNA.

The diffractometer SXD at the Rutherford Appleton Laboratory ISIS pulsed neutron source has been used to record high resolution time-of-flight Laue fiber diffraction data from DNA. These experiments, which are the first of their kind, were undertaken using fibers of DNA in the A conformation and prepared using deuterated DNA in order to minimise incoherent background scattering. These studies complement previous experiments on instrument D19 at the Institut Laue Langevin using monochromatic neutrons. Sample preparation involved drawing large numbers of these deuterated DNA fibers and mounting them in a parallel array. The strategy of data collection is discussed in terms of camera design, sample environment and data collection. The methods used to correct the recorded time-of-flight data and map it into the final reciprocal space fiber diffraction dataset are also discussed. Difference Fourier maps showing the distribution of water around A-DNA calculated on the basis of these data are compared with results obtained using data recorded from hydrogenated A-DNA on D19. Since the methods used for sample preparation, data collection and data processing are fundamentally different for the monochromatic and Laue techniques, the results of these experiments also afford a valuable opportunity to independently test the data reduction and analysis techniques used in the two methods.

Crystallography↗
PubMed1995

The joint operating company: an innovative approach to collaboration.

Hospitals interested in horizontal integration often run into difficulties. In spite of otherwise sound business logic for two organizations to merge, there may be political, legal or financial reasons why a merger option cannot be pursued. Increasingly, enterprises are turning to a joint operating company structure as the solution to their needs. Scott A. Mason and Donald W. Seymour, partners with consulting firm National Health Advisors, explore situations where a JOC model of collaboration may be appropriate.

Evaluation Studies as Topic↗