Acid-Base Effects of Combined Renal Deletion of NBCe1-A and NBCe1-B

The molecular mechanisms regulating ammonia metabolism are fundamental to acid-base homeostasis. Deleting the A splice variant of the Na⁺-bicarbonate cotransporter, electrogenic, isoform 1 (NBCe1-A) partially blocks the effect of acidosis to increase urinary ammonia excretion, and this appears to involve the dysregulated expression of ammoniagenic enzymes in the proximal tubule (PT) in the cortex, but not in the outer medulla (OM). A second NBCe1 splice variant, NBCe1-B, is present throughout the PT, including the OM, where NBCe1-A is not present. The current studies determined the effects of combined renal deletion of NBCe1-A and NBCe1-B on systemic and proximal tubule ammonia metabolism. We generated NBCe1-A/B deletion using Cre-loxP techniques and used Cre-negative mice as controls. Since renal NBCe1-A and NBCe1-B expression is limited to the proximal tubule, Cre-positive mice had proximal tubule NBCe1-A/B deletion (PT-NBCe1-A/B KO). While on basal diet, PT-NBCe1-A/B KO mice had severe metabolic acidosis, yet urinary ammonia excretion was not changed significantly. PT-NBCe1-A/B KO decreased expression of phosphate-dependent glutaminase (PDG) and phospho­enol­pyruvate carboxy­kinase (PEPCK) and increased expression of glutamine synthetase (GS), an ammonia recycling enzyme, in PT in both the cortex and OM. Exogenous acid-loading increased ammonia excretion in control mice, but PT-NBCe1-A/B KO prevented any increase. PT-NBCe1-A/B KO significantly blunted acid loading-induced changes in PDG, PEPCK, and GS expression in the proximal tubule in both the cortex and OM. We conclude that NBCe1-B, at least in the presence of NBCe1-A deletion, contributes to proximal tubule ammonia metabolism in the OM and thereby to systemic acid-base regulation.

The Impact of Biomass and Acid Loading on Methanolysis during Two-Step Lignin-First Processing of Birchwood

We optimized the solvolysis step in methanol for two-step lignin-first upgrading of woody biomass. Birchwood was first converted via sulfuric acid methanolysis to cellulose pulp and a lignin oil intermediate, which comprises a mixture of lignin oligomers and C5 sugars in the methanol solvent. The impact of reaction temperature (140–200 °C), acid loading (0.24–0.81 wt%, dry biomass), methanol/biomass ratio (2.3/1–15.8/1 w/w) and reaction time (2 h and 0.5 h) was investigated. At high biomass loadings (ratio < 6.3/1 w/w), operation at elevated pressure facilitates delignification by keeping methanol in the liquid phase. A high degree of delignification goes together to a large extent with C5 sugar release, mostly in the form of methyl xylosides. Gel permeation chromatography and heteronuclear single quantum coherence NMR of lignin fractions obtained at high acid (0.81 wt%) and low biomass (15.8/1 w/w) loading revealed extensive cleavage of β-O-4′ bonds during acidolysis at 180 °C for 2 h. At an optimized methanol/biomass ratio of 2.3/1 w/w and acid loading (0.24 wt%), more β-O-4′ bonds could be preserved, i.e., about 33% after 2 h and 47% after 0.5 h. The high reactivity of the extracted lignin fragments was confirmed by a second hydrogenolysis step. Reductive treatment with Pd/C under mild conditions led to disappearance of ether linkages and molecular weight reduction in the hydrotreated lignin oil.

Biodiesel production by esterification of ricinoleic acid over a series of synthesized sulfated zirconia catalysts

A series of sulfated zirconia (SZ) were synthesized and evaluated for catalytic esterification of ricinoleic acid obtained from the castor oil with butanol at 110 °C. The effect of alcohols’ chain length was studied using butanol (C4), propanol (C3), ethanol (C2) and methanol (C1) at 65 °C, and reflux of corresponding alcohol boiling points. The synthesized catalysts were characterized using nitrogen porosimetry, X-ray powder diffraction, thermogravimetric analysis and Diffuse Reflectance Infrared Fourier Transform Spectroscopy. Analysis of ricinoleic conversion was performed using gas chromatography. Sulfuric acid loading improved the surface area of zirconia at a lower dose. The surface areas of the catalysts increased as the concentrations of sulfuric acid solution were increased from 0.025 to 0.10 M, after which the decline was observed. SZ obtained at 0.05 M H2SO4 (0.05SZ) gave the optimal catalytic activity compared to the other series of SZ used. The ricinoleic acid conversion decreased with increase of alcohol alkyl chain from C1-C4 at 65 °C, but increased under the reflux temperature of the corresponding alcohols, with the maximum conversion being 47% at 118 °C for the reaction involving butanol. Overall, the synthesized SZ catalysts are deployable in biodiesel production from castor oil upon optimizing other conditions. Keywords: Ricinoleic acid; Sulfated zirconia; Biodiesel production