Water content influences the selectivity of CALB-catalyzed kinetic resolution of phenoxymethyl-substituted secondary alcohols

2002 ◽  
Vol 80 (6) ◽  
pp. 577-581 ◽  
Author(s):  
Elisabeth Egholm Jacobsen ◽  
Thorleif Anthonsen
Keyword(s):  
Water Content ◽  
Water Activity ◽  
Kinetic Resolution ◽  
Relative Rate ◽  
High Water ◽  
High Water Content ◽  
Acyl Donor ◽  
Acyl Donors ◽  
Reaction Media ◽  
Derivatives Of

Derivatives of 1-phenoxy-2-alkanols were kinetically resolved by esterification with irreversible and reversible acyl donors using lipase B from Candida antarctica (Novozyme 435) as a catalyst. To optimize the relative rate of reaction (the E-value), esterifications in eight different solvents with different water activities were performed. For 3-bromo-1-phenoxy-2-propanol (1), the E-values in all the solvents were higher when the water activity was increased, while the E-values for 1-phenoxy-2-pentanol (2) and 3-chloro-1-phenoxy-2-propanol (3) decreased by increasing water activity. The water content of the various reaction media with the same water activity was determined. Solvents such as 1,4-dioxane, acetonitrile, and tetrahydrofuran contained much more water than hexane, carbon tetrachloride, cyclohexane, toluene, and benzene. At high-water activity, the high-water content of the former group of solvents resulted in termination of the reaction at low conversion. The reason seemed to be that the acyl donor and possibly also the produced esters were hydrolyzed. This was not the case when the esterification was performed in water-immiscible solvents with the same water activity.Key words: kinetic resolution, E-value, solvents, water activity, water content.

Fermentation Problem in Spanish North-Coast Honey

1995 ◽  
Vol 58 (5) ◽  
pp. 515-518 ◽  
Author(s):  
SUSANA SANZ ◽  
GLORIA GRADILLAS ◽  
FUENCISLA JIMENO ◽  
CONSUELO PEREZ ◽  
TERESA JUAN
Keyword(s):  
Water Content ◽  
Water Activity ◽  
Microbiological Quality ◽  
Free Water ◽  
High Water ◽  
North Coast ◽  
High Water Content ◽  
Free Water Content ◽  
Cantabrian Coast ◽  
Mold And Yeast

Twenty-one samples from the Cantabrian coast were analyzed to establish their microbiological quality and fermentation tendency. In a food with a very low free-water content like honey, microbiological growth is only possible when there is an increase in water activity. Since most of the samples studied were not extensively granulated, the risk of fermentation is mostly due to high water content. Among our samples, only two had a water content below 17.1% (no risk of fermentation), whereas the high water activity of the rest of the samples indicates the possibility of microbial growth. In fact, four of the samples analyzed showed a moisture content over the Spanish maximum legal limit, which means a high risk of fermentation. The absence of Enterobacteriaceae, coliforms, and Escherichia coli in our samples indicates an appropriate cleanliness during extractions and handling of honey. No Salmonella or Shigella were found. The relationship between water activity and mold and yeast counts found for the honeys analyzed allowed us to divide our samples in two groups: honeys with a high or a low risk of fermentation. Changes observed during storage of the samples confirmed this classification.

scholarly journals Stability of cactus-pear powder during storage

2016 ◽  
Vol 20 (2) ◽  
pp. 169-173
Author(s):  
Plúvia O. Galdino ◽  
Rossana M. F. de Figueirêdo ◽  
Alexandre J. de M. Queiroz ◽  
Pablícia O. Galdino ◽  
Tâmila K. da S. Fernandes
Keyword(s):  
Water Content ◽  
Water Activity ◽  
Reducing Sugars ◽  
Titratable Acidity ◽  
High Water ◽  
Soluble Solids ◽  
High Water Content ◽  
Cactus Pear ◽  
Total Titratable Acidity ◽  
The Stability

ABSTRACT The stability of cactus-pear powder, obtained by the process of spray drying for 40 days, was evaluated under controlled conditions of relative air humidity (83%) and temperature (25 and 40 °C). The whole pulp was characterized with regard to its physico-chemical parameters: pH, total titratable acidity, soluble solids, water content, total solids, ashes, reducing sugars, total sugars, non-reducing sugars, luminosity, redness, yellowness and water activity. The stored samples in powder were evaluated every 10 days for water content, water activity, total titratable acidity and color (luminosity, redness and yellowness). The whole pulp was slightly acidic and perishable, due to the high water content. During storage, the packages did not prevent water absorption, thus increasing water content and, consequently, water activity. Yellowness oscillated along the storage time, but the predominance of the yellow color was not affected.

Hydrogels as Antibacterial Biomaterials

2018 ◽  
Vol 24 (8) ◽  
pp. 843-854 ◽  
Author(s):  
Weiguo Xu ◽  
Shujun Dong ◽  
Yuping Han ◽  
Shuqiang Li ◽  
Yang Liu
Keyword(s):  
Mechanical Properties ◽  
Drug Delivery ◽  
Tissue Engineering ◽  
Water Content ◽  
Oxygen Permeability ◽  
Structural Diversity ◽  
High Water ◽  
Clinical Applications ◽  
High Water Content ◽  
Biomedical Field

Hydrogels, as a class of materials for tissue engineering and drug delivery, have high water content and solid-like mechanical properties. Currently, hydrogels with an antibacterial function are a research hotspot in biomedical field. Many advanced antibacterial hydrogels have been developed, each possessing unique qualities, namely high water swellability, high oxygen permeability, improved biocompatibility, ease of loading and releasing drugs and structural diversity. In this article, an overview is provided on the preparation and applications of various antibacterial hydrogels. Furthermore, the prospects in biomedical researches and clinical applications are predicted.

Microwave-Induced Thermoacoustic Imaging for Embedded Explosives Detection in High-Water Content Medium

2019 ◽  
Vol 67 (7) ◽  
pp. 4803-4810 ◽  
Author(s):  
Xiong Wang ◽  
Tao Qin ◽  
Yexian Qin ◽  
Ahmed H. Abdelrahman ◽  
Russell S. Witte ◽  
...  
Keyword(s):  
Water Content ◽  
High Water ◽  
Explosives Detection ◽  
High Water Content ◽  
Thermoacoustic Imaging

scholarly journals Deep mantle melting, global water circulation and its implications for the stability of the ocean mass

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Shun-ichiro Karato ◽  
Bijaya Karki ◽  
Jeffrey Park
Keyword(s):  
Phase Transformation ◽  
Water Content ◽  
Sea Level ◽  
High Water ◽  
Water Circulation ◽  
Mantle Melting ◽  
High Water Content ◽  
Mineral Physics ◽  
Deep Mantle ◽  
Global Water

AbstractOceans on Earth are present as a result of dynamic equilibrium between degassing and regassing through the interaction with Earth’s interior. We review mineral physics, geophysical, and geochemical studies related to the global water circulation and conclude that the water content has a peak in the mantle transition zone (MTZ) with a value of 0.1–1 wt% (with large regional variations). When water-rich MTZ materials are transported out of the MTZ, partial melting occurs. Vertical direction of melt migration is determined by the density contrast between the melts and coexisting minerals. Because a density change associated with a phase transformation occurs sharply for a solid but more gradually for a melt, melts formed above the phase transformation depth are generally heavier than solids, whereas melts formed below the transformation depth are lighter than solids. Consequently, hydrous melts formed either above or below the MTZ return to the MTZ, maintaining its high water content. However, the MTZ water content cannot increase without limit. The melt-solid density contrast above the 410 km depends on the temperature. In cooler regions, melting will occur only in the presence of very water-rich materials. Melts produced in these regions have high water content and hence can be buoyant above the 410 km, removing water from the MTZ. Consequently, cooler regions of melting act as a water valve to maintain the water content of the MTZ near its threshold level (~ 0.1–1.0 wt%). Mass-balance considerations explain the observed near-constant sea-level despite large fluctuations over Earth history. Observations suggesting deep-mantle melting are reviewed including the presence of low-velocity anomalies just above and below the MTZ and geochemical evidence for hydrous melts formed in the MTZ. However, the interpretation of long-term sea-level change and the role of deep mantle melting in the global water circulation are non-unique and alternative models are reviewed. Possible future directions of studies on the global water circulation are proposed including geodynamic modeling, mineral physics and observational studies, and studies integrating results from different disciplines.

scholarly journals Torrefaction of Woody and Agricultural Biomass: Influence of the Presence of Water Vapor in the Gaseous Atmosphere

Processes ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 30
Author(s):  
María González Martínez ◽  
Estéban Hélias ◽  
Gilles Ratel ◽  
Sébastien Thiéry ◽  
Thierry Melkior
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Wheat Straw ◽  
Beech Wood ◽  
High Water ◽  
High Water Content ◽  
Biomass Degradation ◽  
Moist Atmosphere ◽  
Thermochemical Transformation ◽  
Degradation Reactions

Biomass preheating in torrefaction at an industrial scale is possible through a direct contact with the hot gases released. However, their high water-content implies introducing moisture (around 20% v/v) in the torrefaction atmosphere, which may impact biomass thermochemical transformation. In this work, this situation was investigated for wheat straw, beech wood and pine forest residue in torrefaction in two complementary experimental devices. Firstly, experiments in chemical regime carried out in a thermogravimetric analyzer (TGA) showed that biomass degradation started from lower temperatures and was faster under a moist atmosphere (20% v/v water content) for all biomass samples. This suggests that moisture might promote biomass components’ degradation reactions from lower temperatures than those observed under a dry atmosphere. Furthermore, biomass inorganic composition might play a role in the extent of biomass degradation in torrefaction in the presence of moisture. Secondly, torrefaction experiments on a lab-scale device made possible to assess the influence of temperature and residence time under dry and 100% moist atmosphere. In this case, the difference in solid mass loss between dry and moist torrefaction was only significant for wheat straw. Globally, an effect of water vapor on biomass transformation through torrefaction was observed (maximum 10%db), which appeared to be dependent on the biomass type and composition.

Sign in / Sign up

Export Citation Format

Share Document