Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

A simple,rapid method for the generation of ligand binding isotherms

Using the protonation of tris(hydroxymethyl)aminomethane (Tris) as a standard reaction, a technique is established for the generation of reaction isotherms by continuous titration in a flow microcalorimeter. The procedure uses an exponential dilution device of simple design that provides a constant internal volume, efficient mixing of the contents and is a closed system. The method has considerable advantages over conventional calorimetric procedures and the precision of enthalpy measurements is estimated to be within ± 2%.     

Performance validation of step-isothermal calorimeters

Isothermal calorimetry is becoming indispensable as a tool for the study of a wide variety of systems. As with all scientific instruments it is essential that robust calibration routines be developed in order to validate the data obtained. Chemical test reactions offer many advantages over (the traditionally used) joule effect heating methods, not least because they have the potential to validate instrument performance (i.e. they can be used to assess all aspects of calorimeter operation). In this work the results of a validation exercise, conducted by Thermal Hazard Technology as part of an installation routine, using the base catalysed hydrolysis of methyl paraben are discussed. In the case described, a systematic misreporting of the reported temperature of a calorimeter was identified, caused by an upgrade to the calorimeter's firmware, a discrepancy which may not have been noted using traditional electrical calibration methods and one which highlights the importance of both manufacturers and end-users adopting chemical test reactions into their test and validation routines.     

A rubidium ion-selective electrode for the assay of polyene antibiotics

The preparation of a rubidium ion-selective electrode is described. The performance characteristics of the electrode are such that it can be used as an alternative to atomic absorption spectrometry in the assay of bulk nystatin, by measuring the rubidium ion efflux from specially prepared yeast cells. The electrode simplifies assay procedures because rubidium(I) can be determined directly in cell suspensions without prior centri-fugation; assay time is reduced to 10 min. The sensitivity of the method is 2 units of antibiotic per ml, which is comparable with other physico-chemical methods of bioassay but some 10 times more sensitive than the conventional agar diffusion assay.     

On the polynomial of a path

Let A(P_n) be the adjacency matrix of the path on n vertices. Suppose that r(λ) is a polynomial of degree less than n, and consider the matrix M = r(A>/(P_n)). We determine all polynomials for which M is the adjacency matrix of a graph.     

Application of flow microcalorimetry to analytical problems-I. Determination of organophosphorus pesticides by inhibition of cholinesterase

Flow microcalorimetry has been applied to the determination of organophosphorus pesticides by inhibition of cholinesterase. One direct inhibitor (TEPP) and one latent inhibitor (parathion) were investigated. The former is determinable at concentrations of about 10(-6)M and the latter at about 10(-4)M. The inhibitory power of parathion is increased if methanol is used as solvent.     

A method to reduce the equilibration time prior to data capture in ampoule-based isothermal microcalorimetric studies

This paper reports a technique for heat conduction isothermal microcalorimeters, which allows, by means of a lowering apparatus, the sample and reference ampoules to be lowered very slowly from the pre-equilibration position to the measuring position. The purpose is to minimize the effect on (total) equilibration time arising from both the pre-equilibration time and the dissipation time (i.e. the time to dissipate the thermal shock which occurs when the vessels are lowered manually). Measurements using 3 ml glass ampoules filled with water, as sample and reference, at 25 and 60 °C, showed that the extent of thermal shock was drastically diminished as the lowering speed decreased, and that the associated heat quantity was reduced to less than 0.2 mJ when lowering occurred over a period of more than 180 s. The dissipation time, the time-period required to dissipate the thermal shock, was also shortened to less than 10 min; the standard manual lowering procedure dissipation time being ca. 25 min. In practice experimental measurements of the imidazole catalysed hydrolysis of triacetin and of the solid state oxidation of ascorbic acid showed that the dissipation time was not shortened when the initial power observed was more than 5 μW, however, it was significantly shortened when the initial power observed was around ≤1 μW. The proposed ampoule lowering procedure could be expected to bring about a saving in the total measurement time for reactions with low initial power, such as those associated with long-term stability studies of relatively stable pharmaceuticals. The described procedure also eliminates operator-induced effects associated with manual lowering of ampoules. In principle the device described also would permit automated loading protocols to be developed.     

Solid-state reactions from isothermal heat conduction microcalorimetry theoretical approach and evaluation via simulated data

Several recent publications from this laboratory have reported developments in the capacity to calculate thermodynamic and kinetic parameters, such as rate constant, enthalpy, order of reaction, from isothermal micro-calorimetric data. To date these developments have all been associated with the calculation of the desired parameters from solution phase reactions. This paper furthers these developments to a theoretical consideration of solid-state reactions and the calculation of the values for the rate coefficient, k, the fitting parameters m and n, the total number of joules released over the lifetime of reaction, Q, and hence either the specific enthalpy or the molar enthalpy of reaction, H. This revised version was published online in July 2006 with corrections to the Cover Date.