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Title: Mechanisms of Glycerol Dehydration


No abstract prepared.

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Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A; Journal Issue: 18
Country of Publication:
United States

Citation Formats

Nimlos, M. R., Blanksby, S. J., Qian, X., Himmel, M. E., and Johnson, D. K. Mechanisms of Glycerol Dehydration. United States: N. p., 2006. Web. doi:10.1021/jp060597q.
Nimlos, M. R., Blanksby, S. J., Qian, X., Himmel, M. E., & Johnson, D. K. Mechanisms of Glycerol Dehydration. United States. doi:10.1021/jp060597q.
Nimlos, M. R., Blanksby, S. J., Qian, X., Himmel, M. E., and Johnson, D. K. Sun . "Mechanisms of Glycerol Dehydration". United States. doi:10.1021/jp060597q.
title = {Mechanisms of Glycerol Dehydration},
author = {Nimlos, M. R. and Blanksby, S. J. and Qian, X. and Himmel, M. E. and Johnson, D. K.},
abstractNote = {No abstract prepared.},
doi = {10.1021/jp060597q},
journal = {Journal of Physical Chemistry A},
number = 18,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
  • Highlights: Black-Right-Pointing-Pointer Catalytic mechanisms of thermophilic-mesophilic enzymes may differ. Black-Right-Pointing-Pointer Product release is rate-determining for thermophilic IGPS at low temperatures. Black-Right-Pointing-Pointer But at higher temperatures, proton transfer from the general acid is rate-limiting. Black-Right-Pointing-Pointer Rate-determining step is different still for mesophilic IGPS. Black-Right-Pointing-Pointer Both chemical and physical steps of catalysis are important for temperature adaptation. -- Abstract: Thermophilic enzymes tend to be less catalytically-active at lower temperatures relative to their mesophilic counterparts, despite having very similar crystal structures. An often cited hypothesis for this general observation is that thermostable enzymes have evolved a more rigid tertiary structure in order tomore » cope with their more extreme, natural environment, but they are also less flexible at lower temperatures, leading to their lower catalytic activity under mesophilic conditions. An alternative hypothesis, however, is that complementary thermophilic-mesophilic enzyme pairs simply operate through different evolutionary-optimized catalytic mechanisms. In this communication, we present evidence that while the steps of the catalytic mechanisms for mesophilic and thermophilic indole-3-glycerol phosphate synthase (IGPS) enzymes are fundamentally similar, the identity of the rate-determining step changes as a function of temperature. Our findings indicate that while product release is rate-determining at 25 Degree-Sign C for thermophilic IGPS, near its adaptive temperature (75 Degree-Sign C), a proton transfer event, involving a general acid, becomes rate-determining. The rate-determining steps for thermophilic and mesophilic IGPS enzymes are also different at their respective, adaptive temperatures with the mesophilic IGPS-catalyzed reaction being rate-limited before irreversible CO{sub 2} release, and the thermophilic IGPS-catalyzed reaction being rate limited afterwards.« less
  • In tandem, electrostatic and mechanical coalescence mechanisms can dehydrate oil at higher loading rates and/or lower temperatures than either mechanism acting alone. One of the most effective methods for removing entrained (emulsified) water from crude oil involves the use of high-voltage electric fields. Under the influence of an electric field, water droplets dispersed in the oil become polarized (i.e., acquire a net charge). Attractive electrostatic forces between droplets which have acquired opposite charges promote coalescence and, therefore, more rapid gravitation of the aqueous phase from the mixture. The mechanisms of electrostatically enhanced coalescence have been reviewed elsewhere. Both ac andmore » dc electric fields are commonly used in oil field coalescers and a comparison of the relative merits of these two systems and a discussion of the effects of electrode configuration on coalescence are available in the literature. In a high-voltage electric field, water droplets in oil are subjected to hydrodynamic and electrical stresses which can lead to droplet dispersal in competition with electrostatically induced coalescence. These stresses become more severe and are more likely to cause dispersal with increasing droplet diameter and increasing electric field strength. Therefore, electrical and hydrodynamic stresses tend to limit the maximum size of droplets which can exist in the field.« less
  • Scattering techniques have played a key role in our understanding of the structure and function of phospholipid membranes. These techniques have been applied widely to study how different molecules (e.g., cholesterol) can affect phospholipid membrane structure. However, there has been much less attention paid to the effects of molecules that remain in the aqueous phase. One important example is the role played by small solutes, particularly sugars, in protecting phospholipid membranes during drying or slow freezing. In this paper, we present new results and a general methodology, which illustrate how contrast variation small angle neutron scattering (SANS) and synchrotron-based X-raymore » scattering (small angle (SAXS) and wide angle (WAXS)) can be used to quantitatively understand the interactions between solutes and phospholipids. Specifically, we show the assignment of lipid phases with synchrotron SAXS and explain how SANS reveals the exclusion of sugars from the aqueous region in the particular example of hexagonal II phases formed by phospholipids.« less
  • The mass loss against time measurements for the isothermal dehydration of single-crystal and powdered samples of Li{sub 2}SO{sub 4}{center dot}H{sub 2}O were recorded at different temperatures. Thermogravimetric (TG) data determined at different heating rates were also used to compare the kinetics of the dehydration of both preparations. The overall kinetics of isothermal dehydration of the single-crystal material in the range 0.3 {le} {alpha} {le} 0.9 were described by the rate equation. 1-(1-{alpha}){sup 1/n} = kt with 2 < n < 3. In the nonisothermal experiments, the rate data were described by the same equation but with a little different valuemore » of n (=3). A possible combination of the random nucleation and its growth law, A{sub m}, with the phase boundary controlled law, R{sub n}, was invoked to explain the rate data during the early stage of reaction. This interpretation was supported by the microscopic observation, in polarized light, of thin sections of the sample dehydrated to different fractions reacted, {alpha}. The isothermal dehydration of the powdered material in the range 0.3 {le} {alpha} {le} 0.9 obeyed the equation (-ln (1-{alpha})){sup 1/m} = kt with 2 < m < 3, although the obedience of a contracting geometry model may not necessarily be ruled out. Nonisothermally, however, the dehydration kinetics was expressed more satisfactorily by 1-(1-{alpha}){sup 1/n} = kt with 2 < n < 3. It is assumed as in the case of single crystals that an interaction of the A{sub m} law (m = 1) with an R{sub n} law occurs particularly during the early stage of reaction. The Arrhenius parameters showed kinetic compensation behavior, as expected for different aspects of a single reaction.« less
  • Owing to a /sup 3/H isotope effect, the mitochondrial sn-glycerol 3phosphate oxidase (EC 1.1.99-5) had a mean activity which was 8-4 times less with sn-STA2-/sup 3/H!- than with sn-STA1-/sup 14/C! glycerol 3-phosphate as a substrate. A method for measuring the simultaneous synthesis of lipid from glycerol phosphate and dihydroxyacetone phosphate in rat liver mitochondria is described. The lipid synthesized by rat liver mitochondria irom sn(1-/sup 14/Cl glycerol 3phosphate was mainly phosphatidate and lysophosphatidate, whereas that synthesized from dihydroxy (1-/sup 14/Cl acetone phosphate was mainly acyldihydroxyacetone phosphate. Additions of NADPH facilitated the conversion of acyldihydroxyacetone phosphate into lysophosphatidate and phosphatidate. Hydrazinemore » (1.4 mM) or KCN (1.4 mM) inhibited the synthesis of lipids from dihydroxyacetone phosphate but not from glycerol phosphate. Clofenapate (1-2.5 mM) inhibited the synthesis of lipids from dihydroxyacetone phosphate but slightly stimulated synthesis from glycerol phosphate. The methanesulphonate of N-(2-benzoyloxyethyl) norienfluramine, at 0.25 to 0.75 mM, inhibited lipid synthesis from both glycerol phosphate and dihydroxyacetone phosphate. (auth)« less