Influence of Natural Solutes and Ionic Liquids on the Yield of Enzyme-Catalyzed Reactions: Measurements and Predictions

The maximum yield of enzyme-catalyzed reactions is often limited by thermodynamic equilibrium. The knowledge of influencing factors on limitations of reactions is essential for process optimization to increase yields and to reduce solvent and energy consumption. In this work the effect of solvents/cosolvents [e.g., ionic liquid (IL)] and natural solutes on thermodynamic yield limitations of two enzyme-catalyzed model reactions were investigated, namely, an alcohol dehydrogenase (ADH) reaction (acetophenone + 2-propanol ⇌ 1-phenylethanol + acetone) and an alanine aminotransferase reaction (l-alanine + 2-oxoglutarate ⇌ pyruvate + l-glutamate). Experimental results showed that the equilibrium position and the equilibrium product yield of both reactions in aqueous single-phase systems strongly depend on the type and molality of the present natural solute/IL that were present as additives in the reaction mixture. In addition, the ADH reaction was investigated in pure IL and in an IL/buffer two-phase system. Compared to the aqueous reaction mixtures, the reactant solubility could be increased significantly, but at the cost of a lower product yield. Finally, thermodynamic modeling by means of ePC-SAFT was used to predict the equilibrium product yield of both reactions at different reaction conditions (natural solute/IL type and molality) in the aqueous mixtures as well as in the IL. Experimental and predicted results were in good agreement, showing that ePC-SAFT is a promising tool for predicting yield limitations in different reaction media

Standard Gibbs Energy of Metabolic Reactions: I. Hexokinase Reaction

The standard Gibbs energy of reaction enables calculation of the driving force of a (bio)­chemical reaction. Gibbs energies of reaction are required in thermodynamic approaches to determine fluxes as well as single reaction conversions of metabolic bioreactions. The hexokinase reaction (phosphorylation of glucose) is the entrance step of glycolysis, and thus its standard Gibbs energy of reaction (Δ^R<i>g</i>°) is of great impact. Δ^R<i>g</i>° is accessible from equilibrium measurements, and the very small concentrations of the reacting agents cause usually high error bars in data reduction steps. Even worse, works from literature do not account for the nonideal behavior of the reacting agents (activity coefficients were assumed to be unity); thus published Δ^R<i>g</i>° values are not standard data. Consistent treatment of activity coefficients of reacting agents is crucial for the accurate determination of standard Gibbs energy from equilibrium measurements. In this work, equilibrium molalities of hexokinase reaction were measured with an enzyme kit. These results were combined with reacting agents’ activity coefficients obtained with the thermodynamic model ePC-SAFT. Pure-component parameters for adenosine triphosphate (ATP) and adenosine diphosphate (ADP) were fitted to experimental osmotic coefficients (water + Na₂ATP, water + NaADP). Δ^R<i>g</i>° of the hexokinase reaction at 298.15 K and pH 7 was found to be −17.83 ± 0.52 kJ·mol^–1. This value was compared with experimental literature data; very good agreement between the different Δ^R<i>g</i>° values was obtained by accounting for pH, pMg, and the activity coefficients of the reacting agents

PC-SAFT Modeling of CO₂ Solubilities in Deep Eutectic Solvents

Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), a physically based model that accounts for different molecular interactions explicitly, was applied to describe for the first time the phase behavior of deep eutectic solvents (DESs) with CO₂ at temperatures from 298.15 to 318.15 K and pressures up to 2 MPa. DESs are mixtures of two solid compounds, a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), which form liquids upon mixing with melting points far below that of the individual compounds. In this work, the HBD is lactic acid and the HBAs are tetramethylammonium chloride, tetraethylammonium chloride, and tetrabutylammonium chloride. Two different modeling strategies were considered for the PC-SAFT modeling. In the first strategy, the so-called <i>pseudo-pure</i> component approach, a DES was considered as a <i>pseudo-pure</i> compound, and its pure-component parameters were obtained by fitting to pure DES density data. In the second strategy, the so-called <i>individual-component</i> approach, a DES was considered to consist of <i>two individual components</i> (HBA and HBD), and the pure-component parameters of the HBA and HBD were obtained by fitting to the density of aqueous solutions containing only the individual compounds of the DES. In order to model vapor–liquid equilibria (VLE) of DES + CO₂ systems, binary interaction parameters were adjusted to experimental data from the literature and to new data measured in this work. It was concluded that the <i>individual-component</i> strategy allows quantitative prediction of the phase behavior of DES + CO₂ systems containing those HBD:HBA molar ratios that were not used for <i>k</i>_<i>ij</i> fitting. In contrast, applying the <i>pseudo-pure</i> component strategy required DES-composition specific <i>k</i>_<i>ij</i> parameters

Additional file 3: Table S2. of Discrete phenotypes are not underpinned by genome-wide genetic differentiation in the squat lobster Munida gregaria (Crustacea: Decapoda: Munididae): a multi-marker study covering the Patagonian shelf

Diversity indices of nine microsatellite loci for the two ecotypes. Reported are number of alleles nA, fragment size range, observed heterozygosity H O , expected heterozygosity H E and allelic richness Ar. Significant deviation from Hardy-Weinberg equilibruim (P < 0.05, based on 10,000 permutations) after Bonferroni correction were labeled in bold. (DOCX 19 kb

Additional file 6: Figure S4. of Discrete phenotypes are not underpinned by genome-wide genetic differentiation in the squat lobster Munida gregaria (Crustacea: Decapoda: Munididae): a multi-marker study covering the Patagonian shelf

Correlation between genetic distances (Pairwise F ST values for COI and pairwise (δμ)2 values for microsatellites) and log-transformed geographical distances for mitochondrial and microsatellite data for specimens from 25 sampling sites listed in Table 1. (EPS 1500 kb

Molecular Phylogenetic analysis of the concatenated nucleotide sequences from three regions of the mitochondrial genome (2470 to 3050; 5490 to 6890; 12230 to 13380) using the Maximum Likelihood method based on the Hasegawa-Kishino-Yano model [40].

<p>Initial tree(s) for the heuristic search were obtained automatically by applying Neighbor-Join and BioNJ algorithms to a matrix of pairwise distances estimated using the Maximum Composite Likelihood (MCL) approach, and then selecting the topology with superior log likelihood value. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Evolutionary analyses were conducted in MEGA5 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0082857#B38" target="_blank">38</a>]. Blue: Iceland; Green: Baltic Sea; Red: North Sea.</p

Map of the mitochondrial genome of <i>A. islandica</i>.

<p>The image was prepared using the CGView Server at <a href="http://stothard.afns.ualberta.ca/cgi-bin/cgview_server/" target="_blank"><u>http://stothard.afns.ualberta.ca/cgi-bin/cgview_server/</u></a>. The Outer circle shows the genes, the middle circle the GC content and the inner circle the GC skew. </p

Polymorphisms in the mitochondrial genome.

<p>Single nucleotide polymorphisms (SNPs) were counted in a sliding window of 500 with a step size of 1. All genes are depicted below the SNP frequency curve. The indel regions are indicated by vertical lines below the sliding window curve. Protein coding genes (CDS) are shown above the second line and RNA species below that same line as boxes. The CDS and the 12S and 16S RNA genes are named, while the tRNA genes are only depicted as rectangles. The bar-bell shapes indicate the amplified regions from 17 specimen.</p

Zamani Project Media Library of the Gede Ruins

This file set consists of images and videos from the Gede ruins. This file set serves as a press kit for the Zamani Project's fieldwork and documentation of the Gede ruins heritage site.The ruins of Gede (also Gedi), a traditional Arab-African Swahili town, are located just off Kenya’s coastline, some 90km north of Mombasa. Gede was a small town built entirely from stones and rocks, and most of the original foundations are still visible today. Remaining structures at the site include coral stone buildings, mosques, houses and a palace. The town was abandoned in the early 17th century, and Gede’s buildings date back to the 15th century, although it is believed that the site could have been inhabited as early as the 11th or 12th century. The Zamani Project spatially documented the Gede ruins in 2010. In addition to the three principal structures of the Great Mosque, the Small Mosque and the Palace, remains of other structures in the immediate vicinity were also documented.The Zamani Project seeks to increase awareness and knowledge of tangible cultural heritage in Africa and internationally by creating metrically accurate digital representations of historical sites. Digital spatial data of cultural heritage sites can be used for research and education, for restoration and conservation and as a record for future generations. The Zamani Project operates as a non-profit organisation within the University of Cape Town.This text has been adapted from the UNESCO website (https://whc.unesco.org/en/tentativelists/5501/).The Zamani Project received funding from the Andrew W Mellon Foundation at the time of the project. </div