Tion Products Research Articles

Synthesis and Properties of 2,8-Dioxabicyclo[3.2.1]octane Derivatives

Abstract In order to study the isomerization of daphniphylline into isodaphniphylline, 1,4-dimethyl-2,8-dioxabicyclo[3.2.1]octane-4-carboxylic acid (3), a degrada tion product of daphniphylline, was synthesized from the keto diester and transformed into the 3-oxacyclopentanones (6, 7).

Design Techniques and Intermodulation Analysis of Broad-Band Solid-State Power Amplifiers

This paper presents balanced circuit techniques for the reduction and cancellation of the dominating third-order intermodulation tion product generated by broad-band solid-state power amplifiers. These techniques are applicable to collocated transmitters where the interference enters through the output port of the transmitter. A rigorous derivation is presented to prove the validity of the intermodulation canceliation by using a quadrature-hybrid coupling scheme in a balanced circuit configuration. The results are valid for arbitrary nonlinear characteristics exhibited by general classes of amplifiers, as well as isolators.

Thallium activation and inhibition of yeast aldehyde dehydrogenase

Volume 59, number 1 FEBS LETTERS November 1975 THALLIUM ACTIVATION AND INHIBITION OF YEAST ALDEHYDE DEHYDROGENASE K. BOSTIAN and G. F. BETTS Department of Plant Biology and Microbiology, Queen Mary College, Mile End Road, London, E. 1. England W. K. MAN and M. N. HUGHES Department of Chemistry, Queen Elizabeth College, Campden Hill Road, London, I¢. 8. England Received 1 September i975 1. Introduction T1 ÷ has been shown to replace the physiological ion K ÷ in the activation of several monovalent cation activated enzymes [1-6]. This provides the opportu- nity to employ T1 ÷ as a probe for K ÷ in n.m.r, and fluorescence studies [6-8]. Preliminary to such studies on yeast aldehyde dehydrogenase (EC 1.2.1.3.) T1 ÷ activation of this enzyme was investigated and compared to the previously demonstrated activation by K ÷ [9]. A general mechanism for this activation has been proposed whereby an activating monovalent cation induces and maintains an enzyme conformation suitable for catalytic activity [ 10]. 2. Materials and methods Partially purified aldehyde dehydrogenase was prepared from N.G. and S.F. yeast (British Fermenta- tion Products Ltd.) obtained from a local baker. The method was essentially that of Black [9] except for the inclusion of 1.2 X 10 -3 M phenylmethylsulphonyl fluoride (PMSF) throughout the procedure. The buffer composition at the final stage contained 0.1 M K2HPO4, pH 7.8, 10 -3 M mercaptoethanol, and 1.2 × 10 -3 M PMSF. Enzyme activity was between 7-10 units/ml when assayed with optimal K ÷ (0.1 M) with a specific activity of 1. Samples were stored frozen at -18 ° C, and thawed out immediately prior to use. Enzyme was equilibrated with 0.1 M Tris-NO3 pH 8.0, 10 -3 M mercaptoethanol and activating salt where indicated, by passage through a Sephadex G-25 column at 4°C. Because of the instability of the enzyme in the absence of an activating monovalent cation, the enzyme was stored on ice following chromatography and all assays in a given run were completed within 5 rain. Enzyme activity was measured by following the rate of reduction of NAD ÷ by observing the increase in absorbance at 340 nm in a Pye Unicam SP1800 spectrophotometer using 1 cm quartz cells. Reaction mixtures contained in a final volume of 2.5 ml: 2 X 10 -3 M acetaldehyde, 5 X 10 -4 M NAD ÷, 0.1 M Tris-NO3 buffer, pH 8.0,

Autoxidation as a cause of antibacterial activity in unsaturated fatty acids.

Summary Four unsaturated fatty acids were allowed to undergo varying degrees of autoxidation before being tested for antibacterial activity against Staphylococcus aureus, Escherichiu coli, Clostridium welchii, and Bacteroides sp. The degree of inhibition was proportional to the degree of unsaturation of the fatty acid and to the duration of its autoxidation. Some of the antibacterial activity of fatty acids described in the past could be accounted for by autoxida- tion products. We are grateful to the Wellcome Foundation for financial support.

Surface pressure–surface area characteristics of a series of autoxidation products of cholesterol

The pi-A characteristics of seven known oxidation products of cholesterol were determined. In all cases, the oxidation products yielded films which were more expanded than the film of cholesterol. Shifts in the position of the functional polar groups or the double bond within the sterol molecule results in marked changes in the pi-A curves. Furthermore, replacement of the 3-hydroxy group by a keto group results in a significant decrease in the collapse pressure of the films. Mixed films of each of the oxidation products with dipalmitoyl glycerylphosphorylcholine, egg lecithin, and cholesterol showed marked condensation effects. However, the data suggest that if air oxidation of cholesterol did occur at a biological membrane containing cholesterol and phospholipids, the permeability characteristics and other properties of the membrane might not be altered significantly.

Scavenging characteristics of a two-stroke-cycle engine as determined by skip-cycle operation

A method for determining the mass fraction of fresh charge in the cylinder of the twostroke-cycle engine, from measurements of engine power under normal operation and with engine fired only once in several cycles of operation is described. The results obtained from a crankcase-scav enged engine are presented. The two-stroke cycle engine, in order to develop one power cycle for every revolution of the crank­ shaft, must rely on the action of an auxiliary device, known as the scavenging pump, to expel the combus­ tion products from the cylinder and to fill the cyl­ inder with fresh charge. The scavenging pump may be and frequently is physically separate from the engine cylinder proper. In the crankcase-scavenged engine, the cylinder-crankcase-piston combination serves as the scavenging pump. The ideal objective of the scavenging process is, of course, to replace completely the combustion prod­ ucts in the engine cylinder with fresh charge delivered through the inlet ports, without meantime losing any of the fresh charge through the exhaust ports. In this manner, maximum power is derived from the cylinder with the least expenditure of scavengingpump power. In practice, such an objective is never attainable, hence the excellence of the scavenging process must be judged by the mass of fresh charge retained in the engine cylinder per unit time, in relation to the mass of fresh charge supplied per unit time by the scavenging pump.

Mollier Charts for the Decomposition of Hydrogen Peroxide-Water Mixtures

This report presents Mollier charts for the decomposi­ tion products of hydrogen peroxide-water mixtures at weight concentrations of 70, 80, and 90 per cent. The Appendix deals with methods used to relate decomposition products of hydrogen peroxide as a heterogeneous system to data published by the Bureau of Mines. Nomenclature c h Ah = concentration by weight of hydrogen peroxide = specific heat at constant pressure = specific enthalpy = available energy (or change in specific enthalpy in an expansion process) AHf = heat of formation lsp J n P R s T u V

Absorption Spectra in the Detection of Chemical Changes in Cellulose and Cellulose Derivatives

The spectral absorption of thin films of cellulose acetate, regenerated cellulose, the acetate and regenerated cellulose after oxidation with nitrogen dioxide gas, and the regener ated cellulose after oxidation with periodic acid followed by chlorous acid are recorded for the infrared from 2 to 15 microns and the ultraviolet from 215 to 400 millimicrons. The regenerated cellulose absorbed ultraviolet radiant energy only at the short-wave-length end of the region studied, and there the transmittance of a film 2.8 microns thick was only slightly reduced. The acetate and oxidized celluloses ab sorbed in this region to a greater extent but gave no narrow absorption bands. Marked changes were observed in some of the absorption bands in the infrared region in going from cellulose acetate to regenerated cellulose and to their oxida tion products. These changes were correlated with changes in the OH, CO, and COOH groups. The results indicate the possibility of estimating the amount of these groups present by spectral absorption measurements.