Solid phase microextraction of stale flavour volatiles from the headspace of UHT milk

Solid phase microextraction (SPME) offers a solvent-free and less labour-intensive alternative to traditional flavour isolation techniques. In this instance, SPME was optimised for the extraction of 17 stale flavour volatiles (C3-11,13 methyl ketones and C4-10 saturated aldehydes) from the headspace of full-cream ultrahigh-temperature (UHT)-processed milk. A comparison of relative extraction efficiencies was made using three fibre coatings, three extraction times and three extraction temperatures. Linearity of calibration curves, limits of detection and repeatability (coefficients of variation) were also used in determining the optimum extraction conditions. A 2 cm fibre coating of 50130 gm divinylbenzene/Carboxen/polydimethylsiloxane in conjunction with a 15 min extraction at 40 degrees C were chosen as the final optimum conditions. This method can be used as an objective tool for monitoring the flavour quality of UHT milk during storage. (c) 2005 Society of Chemical Industry.

Thermal stability analysis of organo-silicates, using solid phase microextraction techniques

An analysis of thermal degradation products evolved during the melt processing of organo-layered silicates (OLS) was carried out via the use of a solid phase microextraction (SPME) technique. Two commerical OLSs and one produced in-house were prepared for comparision. The solid phase microextraction technique proved to be a very effective technique for investigating the degradation of the OLS at a specific processing temperature. The results showed that most available OLSs will degrade under typical conditions required for the melt processing of many polymers, including thermoplastic polyurethanes. It is suggested that these degradation products may lead to changes in the structure and properties of the final polymer, particularly in thermoplastic polyurethanes, which seem significantly succeptable to the presence of these products. It is also suggested that many commercially available OLSs are produced in such a way that results in an excess of unbound organic modifier, giving rise to a greater quantity of degradation products. All OLSs where compared and characterised by TGA and GC-MS. (c) 2004 Elsevier B.V. All rights reserved.

A convergent solution-phase synthesis of the macrocycle Ac-Phe-[Orn-Pro-D-Cha-Trp-Arg], a potent new antiinflammatory drug

Relatively few cyclic peptides have reached the pharmaceutical marketplace during the past decade, most produced through fermentation rather than made synthetically. Generally, this class of compounds is synthesized for research purposes on milligram scales by solid-phase methods, but if the potential of macrocyclic peptidomimetics is to be realized, low-cost larger scale solution-phase syntheses need to be devised and optimized to provide sufficient quantities for preclinical, clinical, and commercial uses. Here, we describe a cheap, medium-scale, solution-phase synthesis of the first reported highly potent, selective, and orally active antagonist of the human C5a receptor. This compound, Ac-Phe[Orn-Pro-D-Cha-Trp-Arg], known as 3D53, is a macrocyclic peptidomimetic of the human plasma protein C5a and displays excellent antiinflammatory activity in numerous animal models of human disease. In a convergent approach, two tripeptide fragments Ac-Phe-Orn-(Boc)-Pro-OH and H-D-Cha-Trp(For)-Arg-OEt were first prepared by high-yielding solution-phase couplings using a mixed anhydride method before coupling them to give a linear hexapeptide which, after deprotection, was obtained in 38% overall yield from the commercially available amino acids. Cyclization in solution using BOP reagent gave the antagonist in 33% yield (13% overall) after HPLC purification. Significant features of the synthesis were that the Arg side chain was left unprotected throughout, the component Boe-D-Cha-OH was obtained very efficiently via hydrogenation Of D-Phe with PtO2 in TFA/water, the tripeptides were coupled at the Pro-Cha junction to minimize racemization via the oxazolone pathway, and the entire synthesis was carried out without purification of any intermediates. The target cyclic product was purified (>97%) by reversed-phase HPLC. This convergent synthesis with minimal use of protecting groups allowed batches of 50100 g to be prepared efficiently in high yield using standard laboratory equipment. This type of procedure should be useful for making even larger quantities of this and other macrocyclic peptidomimetic drugs.

CFD simulations of hydrocyclones with an air core - Comparison between large eddy simulations and a second moment closure

CFD simulations of the 75 mm, hydrocyclone of Hsieh (1988) have been conducted using Fluent TM. The simulations used 3-dimensional body fitted grids. The simulations were two phase simulations where the air core was resolved using the mixture (Manninen et al., 1996) and VOF (Hirt and Nichols, 1981) models. Velocity predictions from large eddy simulations (LES), using the Smagorinsky-Lilly sub grid scale model (Smagorinsky, 1963; Lilly, 1966) and RANS simulations using the differential Reynolds stress turbulence model (Launder et al., 1975) were compared with Hsieh's experimental velocity data. The LES simulations gave very good agreement with Hsieh's data but required very fine grids to predict the velocities correctly in the bottom of the apex. The DRSM/RANS simulations under predicted tangential velocities, and there was little difference between the velocity predictions using the linear (Launder, 1989) and quadratic (Speziale et al., 1991) pressure strain models. Velocity predictions using the DRSM turbulence model and the linear pressure strain model could be improved by adjusting the pressure strain model constants.