Phase single-centre studies

This section aims to provide sufficient information for the pharmaceutical physician to effectively prepare and support a clinical trial. However, clinical trials come in many forms and what is appropriate for a single-centre non-sponsored trial is totally inappropriate for a multicentre global study sponsored by a big pharmaceutical company or institution. Similarly, a Phase 1 non-patient volunteer study... 

Abstract. - High-resolution powder neutron diffraction has been used to study the crystal structure of the fullerene Cm in the temperature range 5 K to 320 K. Solid Cm adopts a cubic structure at all temperatures. The experimental data provide clear evidence of a continuous phase transition at ca. 90 K and confirm the existence of a first-order phase transition at 260 K. In the high-temperature face-centred-cubic phase (T > 260 K), the Cm molecules are completely orientation-ally disordered, undergoing continuous reorientation. Below 260 K, interpretation of the diffraction data is consistent with uniaxial jump reorientation principally about a single (111) direction. In the lowest-temperature phase (T < 90 K), rotational motion is frozen although a small amount of static disorder still persists. 

White beam synchrotron radiation was used in a topographical study [64] of the phase transition in [Ni(en)2 (NCS)2J single crystals. The short exposure times possible using this intense radiation enabled the strained centre of the crystal to be identified as the most imperfect zone, within which the nucleation and growth process was initiated. The phase transition commenced at defect sites. The role of generation and relaxation of mechanical stresses in influencing kinetics of solid state transformations was later reviewed [65]. 

It would appear from the foregoing that there is a class of gas-phase reactions for which the transition state is best represented as having an essentially carbonium-ion pair character. In this way the effect of substitution at or near the centre of reaction can be interpreted, and the vast body of theory in the literature of physical organic chemistry used for the purpose of predicting rates of gas-phase reactions. In addition, the known properties of carbonium ions, as determined by the mass-spectrometer, can be invoked—as indeed they were in discussions of the SN1 and El reactions in polar solvents (Evans, 1946)—to correlate the effects of substituents in gas-phase eliminations. The advantage of studies in the gas-phase lies in the fact that the behaviour of a single molecule can be observed, without the added complication of the cooperative effect of the solvent. But gas-phase studies may, in turn,... 

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