Tomas Klason

Uptake and activation of acetate and butyrate in Clostridium acetobutylicum

SummaryThe pathway for uptake of acids during the solvent formation phase of an acetone-butanol fermentation by Clostridium acetobutylicum ATCC 824 was studied. 13C NMR investigations on actively metabolizing cells showed that butyrate can be taken up from the medium and quantitatively converted to butanol without accumulation of intermediates. The activities of acetate phosphotransacetylase, acetate kinase and phosphate butyryltransferase rapidly decreased to very low levels when the organism began to form solvents. This indicates that the uptake of acids does not occur via a reversal of these acid forming enzymes. No short-chain acyl-CoA synthetase activity or butyryl phosphate reducing activity could be detected. Based on our results and a critical analysis of literature data on acetone-butanol fermentations, it is suggested that an acetoacetyl-CoA: acetate (butyrate) CoA-transferase is solely responsible for uptake and activation of acetate and butyrate in C. acetobutylicum. The transferase exhibits a broad carboxylic acid specificity. The key enzyme in the uptake is acetoacetate decarboxylase, which is induced late in the fermentation and pulls the transferase reaction towards formation of acetoacetate. The major implication is that it is not feasible to obtain a batch-wise butanol fermentation without acetone formation and retention of a good yield of butanol.

Water diffusion in wood pulp cellulose fibers studied by means of the pulsed gradient spin-echo method

Abstract The self-diffusion of water sorbed in wood pulp cellulose fibers was studied by using the pulsed gradient spin-echo (PGSE) method. The observed echo attenuation profiles deviate significantly from those of bulk liquids and can be decomposed into two components: one with a self-diffusion coefficient independent of the diffusion time, and one with an apparent diffusion coefficient that depends on the diffusion time. The relative amplitude of these two components for the different diffusion times used in the PGSE experiment is nearly constant. We attribute the two components to bulk water between cellulose fibers and to water in pores within the fibers, respectively. From the relative amplitude of the components and the known water content in the samples, the amount of water in pores inside the fibers was calculated to 1.4 g/g of cellulose fibers. The self-diffusion coefficient of the bulk water between the fibers is lower than that of neat water. This reduction is mainly caused by the obstruction effect of the cellulose fibers whereas the hydration effect is of minor importance. The apparent self-diffusion coefficient of water trapped in pores inside fibers is approximately one-third of that of the bulk water between fibers when the diffusion time is 12 ms and is reduced further by another factor of 3 when the diffusion time is increased to 80 ms. By using a sheet sample and applying the magnetic field gradient perpendicular or parallel to the sheet it was found that the diffusional motion of water in pores is anisotropic. These results indicate that the pores are elongated along the fiber axis having lengths ranging from a few micrometers up to 20 μm.

Solubilization of benzene and cyclohexane in aqueous solutions of hexadecyltrimethylammonium bromide: a deuterium magnetic resonance study

Abstract Quadrupole splittings in the 2 H NMR spectrum from C 6 D 6 and C 6 D 12 solubilized in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) have been observed in the hexagonal liquid crystalline phase (E) as well as in the concentrated micellar phase (L 1 ). The order parameter that is obtained for solubilized C 6 D 6 is more than two orders of magnitude greater than previously reported from measurements of linear dichroism spectra. Various possibilities for the nature of the solubilization sites are discussed.

Interfacial tension and surface hydrophilicity in systems of solid polymers in contact with aqueous solutions

The nondispersive part of the interfacial tension between polymer solids and aqueous solutions has been determined by contact angle measurements on photooxidized polystyrene (PS). It is shown from contact angle measurements in air and in octane that the expressions for γs,aq includes a term that is proportional to γaqn and not to √γaqn as is often assumed. The proportionality factor is taken as an expression of the hydrophilicity of the surface. The development of oxidized surface groups was followed by ESCA. It is concluded that the degradation of PS upon UV curing includes an attack on the aromatic groups followed by a ring opening. The hydrophilicity shows a sharp at a certain oxidation level, which we interpret to be due to the ring opening.

Aklyl Chain Order Parameters and Phase Diagrams for Systems Containing Sodium n-Octanoate, Water, and Different Alcohols

Abstract Lamellar liquid crystalline phases containing sodium n-octanoate, water, and an alcohol have been studied by means of 2H NMR. Order parameters have been determined for the octanoate alkyl chain in systems containing ethanol, 1-propanol, 1-butanol, 1-pentanol, benzyl alcohol or 1, 8-octandiol. The straight chain alcohols yield decreasing octanoate order parameters with decreasing chain length. With 1, 8-octandiol the octanoate order parameters are somewhat smaller than with 1-propanol, indicating quite flexible octanoate hydrocarbon chains. Using mono-deuteriated benzyl alcohol. C6H5CHDOH, the SCD as well as the SHD (= SHH ) order parameters were determined in the same measurement. A typical measurement yields |S HD|-|SCD | = 0.04 ± 0.04, where the error estimation includes the uncertainties in the quadrupole and the magnetic dipole-dipole coupling constants. It is stressed that in order to ascertain a significant difference between SHH and SCD , it is necessary to know the coupling constants with...

Solubilization in Aqueous Micellar Solutions Studied by NMR-Methods

The use of Nuclear Magnetic Resonance spectroscopy for studies of solubilization in aqueous micellar solutions yields information about the localization, orientation and mobility of the solubilized molecules. Assotiated changes in size and shape of the micelles can also be monitored. 1H chemical shift measurements have been performed to determine the localization of aromatic and aliphatic solubilizates. It has been found e.g. that in CTAB-micelles cyclohexane is solubilized in the hydro-carbon core while at low concentrations benzene is located near the micellar surface. For CTAB micelles the surface localization of C6H6 is accompanied by a growth of the micelles. The orientation of solubilized benzene molecules has been studied by means of 2H quadrupole splittings in the hexagonal liquid crystalline phase and in the concentrated micellar solutions. The results indicate a preferential tangential orientation of the C6- axis. The rotational diffusion of solubilized benzene and cyclohexane is 2–3 times slower in micelles than in the corresponding hydrocarbon solvents. The transition from spherical to rodshaped micelles is not accompanied by any significant changes in this rotational diffusion rate.

The Interaction Between Water and Ethylene Oxide Groups in Oligo (Ethylene Glycol) Dodecyl Ethers as Studied by 2H NMR in Liquid Crystalline Phases

Quadrupole splittings in 2H NMR spectra from 2H2O have been determined in the binary systems 2H2O-C12H25(O-CH2CH2)xOH for x = 4 and 6. The average order parameter for the water molecules, as determined from the quadrupole splittings, is at a given number of water molecules per ethylene oxide group considerably higher for the surfactant with a short ethylene oxide chain. In the hexagonal phase, the order parameter decreases with increasing temperature. The temperature dependence is more complex in the lamellar phase. At low water contents the order parameter decreases with increasing temperature while at higher water contents the order parameter passes through a maximum. The results are discussed in terms of the temperature dependent repulsion between hydrated ethylene oxide groups and in relation to the stability regions for the different liquid crystalline phases.

The Motional State of Hydrocarbon Chains in the Ternary System Sodium Octanoate — 1-Decanol — Water Studied by Deuterium NMR

The system Sodium Octanoate — 1-Decanol — Water has been studied in the liquid crystalline phases by means of quadrupole splittings in the 2H NMR spectra from deuterated octanoate and decanol. The mole ratio decanol/octanoate is found to have a big influence on the motional state of the hydrocarbon chains. For high decanol content the chains are fairly ordered while at lower decanol content the population of gauche conformations is increased. For compositions where there is a large area per headgroup the probability of a gauche conformation around the first C-C-bond is high. This can be seen as a consequence of the tendency to minimize energetically unfavourable hydrocarbon -water contact. In the region of the lamellar phase that exhibits one-dimensional swelling the state of the hydrocarbon chains is independent of the water content while in the region with two-dimensional swelling increased area per head-group is accompanied by an increased disorder in the hydrocarbon chains. For high decanol content the order parameter profile for the decanol chain has a maximum.

Solubilization in Aqueous Solutions of Hexadecyltrimethyl-ammonium Bromide and Sodium Dodecylsulphate Studied by Nuclear Magnetic Relaxation

2H and 14N nuclear magnetic relaxation time measurements have been used to study the dynamics of benzene and cyclohexane molecules solubilized in aqueous CTAB and SDS solutions and the effect of solubilization on the dynamics of the surfactant molecules in CTAB solutions. The rotational diffusion of cyclohexane molecules is found to be 2–3 times slower in the micelles than in the corresponding liquid hydrocarbons. Benzene is found to be solubilized at sites close to the polar surface of the micelles both in CTAB and SDS solutions, but it is only in the case of CTAB solutions that benzene solubilization promotes the formation of long rodshaped aggregates.