Biodiesel Production from Microalgal Biomass
Gokare A. Ravishankar, Ranga Rao Ambati in Handbook of Algal Technologies and Phytochemicals, 2019
The process of transesterification is affected by various factors like the molar ratio of alcohol to oil, type and the amount of catalyst, reaction time and temperature and purity of reactants. However, transesterification is an equilibrium reaction in which an excess of alcohol is required to drive the transesterification reaction for completion. The presence of a sufficient amount of methanol during the transesterification reaction is essential to break the glycerine–fatty acid linkages (Al-Widyan and Al-Shyoukh 2002). Being polar and shortest chain alcohol, methanol can quickly react with triglycerides. The catalyst is usually used to improve the reaction rate and yield. The transesterification reaction can be catalyzed by alkalis, acids, enzymes and nanoparticles. The KOH and NaOH are commonly used as nbase catalyst for biodiesel preparation. However, during the separation of the final products from glycerol, KOH has been found to be more convenient (Guan et al. 2009). However, one limitation to the alkali-catalyzed process is its sensitivity to the purity of reactants. The alkali-catalyzed system is very sensitive to both water and FFA. The presence of water may cause saponification under alkaline condition. Acids used for transesterification include sulfuric, phosphoric, hydrochloric and organic sulfonic acids. It was rep orted that ester conversion reached 98% at a molar ratio of 30:1 (methanol:oil) with 3% sulfuric acid as a catalyst at 60°C. As acid-catalyzed transesterification is a relatively slow process, many researchers have combined both acidic and alkaline catalysts in a two-step reaction in which the acid treatment converts the FFA into esters while the alkaline catalyst is performing the transesterification. This process has been developed by Canacki and Garpen (2001) using yellow and brown grease having FFA content of more than 10%.
The Modification of Cysteine
Roger L. Lundblad in Chemical Reagents for Protein Modification, 2020
Cysteine is relatively sensitive to oxidation but there is little selectivity in these reactions. Mild oxidizing conditions can result in the formation of disulfide bonds with appropriately aligned cysteinyl residues. Formation of sulfenic acid is generally readily reversible unless stabilized by local conditions3 and more highly oxidized forms such as cysteine-sulfonic acid are more frequently observed. More rigorous conditions such as treatment with performic acid result in the formation of cysteic acid.
Bioresponsive Hydrogels for Controlled Drug Delivery
Deepa H. Patel in Bioresponsive Polymers, 2020
Among pH-responsive acidic polymers, commonly preferred are carboxylic, sulfonic, phosphoric, and boronic acids (BA), sulfonic, and phosphoric acids in hydrogels preparation. The obtained hydrogels swell well under basic conditions, when pH solution is superior to their pKa. The most widely used polymers containing sulfonic acid are poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and poly(4-styrenesulfonic acid) (PSSA) [36].
Application of salt engineering to reduce/mask bitter taste of clindamycin
Published in Drug Development and Industrial Pharmacy, 2019
Sogra F. Barakh Ali, Sathish Dharani, Hamideh Afrooz, Mansoor A. Khan, Eman M. Mohamed, Kanchan Kohli, Ziyaur Rahman
The FTIR spectra of CLN-HCl is shown in Figure 2(A). Vibration peak due to carbonyl group of carboxamide was shown at 1682 cm−1, and secondary amine N-H bending vibration was observed at 1551 cm−1. The broad peaks in the region 3100–3600 cm−1 was due to stretching vibration of OH groups. It also exhibited low intensity peaks at 2960 and 2921 cm−1 due to symmetrical and asymmetrical stretching vibrations of methyl and methylene groups, respectively. C–N stretching vibration peak due to amino group was exhibited at 1251 cm−1. C–Cl vibration peak was exhibited at 639 cm−1. Similarly, CYA showed a characteristic peak of aromatic C–H stretching vibration at 2931 and 2860 cm−1. Peaks due to O–H group was shown in the region 2960–3200 cm−1. N–H stretching vibration due to secondary amine was exhibited at 3273 cm−1. CH2 bending deformation was observed at 1536 cm−1. Medium intensity peaks for S = O stretch of sulfonic acid moiety were shown at 1318 and 1331 cm−1. A sharp C–N stretch at 1220 cm−1, N–H out-of-plane bending vibration at 689 cm−1 and S–O stretch at 836 cm−1 were also observed [12]. The spectrum of the salt was entirely different from CYA and CLN-HCl that indicated the formation of new compound. It showed appearance of new peaks, disappearance and shift of peaks. Peaks due to carbonyl and secondary amine groups shifted from 1682 to 1684 cm−1 and 1551–1561 cm−1. Vibration peaks due to OH group of CYA and CLN were shown in the region 3100–3500 cm−1 as broad peaks with a shape different from CYA and CLN-HCl. The S = O peaks of sulfonic acid at 1318 and 1331 cm−1 disappeared.
The intestinal quorum sensing 3-oxo-C12:2 Acyl homoserine lactone limits cytokine-induced tight junction disruption
Published in Tissue Barriers, 2020
Doriane Aguanno, Garance Coquant, Barbara G. Postal, Céline Osinski, Margaux Wieckowski, Daniel Stockholm, Jean-Pierre Grill, Véronique Carrière, Philippe Seksik, Sophie Thenet
We first studied the effects of 3-oxo-C12:2 AHL compared to 3-oxo-C12 on paracellular permeability to macromolecules (assessed through the flux of the fluorescent tracer FITC-Dextran 4kDa) and to ions (assessed through the TEER, inversely proportional to the ions flux) in the enterocytic cell line Caco-2/TC7. In accordance with the literature,26,27 3-oxo-C12 AHL induced a 4.8-fold increase in the macromolecular FITC-Dextran 4kDa (FD4) flux (Figure 2a) and a trend toward a 10% decrease in TEER (Figure 2b) compared to untreated control cells. 3-oxo-C12:2 AHL modified neither FD4 flux (Figure 2a) nor TEER (Figure 2b). These observations support our hypothesis of a beneficial role on the epithelial barrier. We then investigated whether these AHLs could modulate an increase in paracellular permeability induced upon exposure to the two pro-inflammatory cytokines Interferon-γ and Tumor Necrosis Factor-α (thereafter referred as IFNγ+TNFα), previously shown to impair the intestinal barrier function by disrupting tight junctions.30 IFNγ+TNFα induced a 5-fold increase in FD4 passage (Figure 2a) but had no significant effect on TEER (−5%, Figure 2b) compared to control. Strikingly, 3-oxo-C12 AHL significantly potentiated the cytokine effects on both FD4 flux (18-fold increase, Figure 2a) and TEER (30% decrease, Figure 2b). On the contrary, 3-oxo-C12:2 AHL did not modulate the cytokine-induced increase in paracellular permeability to macromolecules (Figure 2a) or to ions (Figure 2b). Similar response profiles were observed for the smaller size tracer sulfonic acid (0.4kDa, Supplementary Figure 1A). We then wanted to determine whether the AHLs modulated epithelial cell permeability in the presence of endogenous inflammatory cytokines secreted by immune cells. To this end, Caco-2/TC7 enterocytes exposed to each AHL were co-cultured with activated THP-1 monocytic cells (Figure 2c). The co-culture of Caco-2/TC7 with THP-1 cells induced a modest increase in paracellular permeability of the epithelial monolayer (1.5-fold increase, Figure 2c). While the addition of 3-oxo-C12 AHL triggered a 30-fold rise in FD4 flux in the co-culture, 3-oxo-C12:2 AHL did not modify THP-1 effects on FD4 passage.
Xenobiotic C-sulfonate derivatives; metabolites or metabonates?
Published in Xenobiotica, 2018
From a non-biological standpoint, it is well known that sulfonic acids may be formed in the laboratory by reaction with sulfuric acid, sulfur trioxide, or a combination of the two as oleum. Indeed, when a compound is activated toward electrophilic attack, especially if it is an aromatic molecule, such a reaction may take place at low temperatures. In aqueous solution, some alkenes may react with sodium sulfite to give an addition across the double bond thereby forming a sulfonic acid salt and epoxides react with sulfite or bisulfite to yield hydroxyl sulfonate salts. Also, the initial phase in the reversible conversion of a naphthol to a naphthylamine (the “Bucherer-Lepetit reaction”) involves the addition of bisulfite to an aromatic double bond (Hoyle, 1991). Sulfonic acids may be formed also by reaction of carbonyl compounds with bisulfite to give “bisulfite addition compounds” (Lacosta & Martell, 1955; Wagner, 1929). Such addition occurs via a nucleophilic attack on the carbonyl group, which is electron deficient, by the lone pair occupying a hybrid orbital resident on the sulfur atom in bisulfite. Initially, a positively charged sulfur atom results but a simple proton transfer alleviates this situation (Rao & Salunke, 1984; Sykes, 1986) (Figure 6). Although the reaction of bisulfite with normal carbon–carbon double bonds appears difficult, especially if they are distanced from a carbonyl group (Nishimura & Iwase, 1976; Schenck & Danishefsky, 1951), it adds readily with ethylenic bonds in α,β-unsaturated compounds, whether they be aldehydes, ketones, acids or esters (Herke & Rasheed, 1992; Joslyn & Braverman, 1954; Morton & Landfield, 1952). Bisulfite undergoes addition to the pyrimidine ring structures of both uracil and cytosine (Hayatsu et al., 1970), across the double bond in the pyran (oxine) ring structure of anthocyanins (Berké et al., 1998) and via the double bond in the five-membered rings of prostaglandin A2 (Cho et al., 1977). However, many of these bisulfite addition reactions appear reversible and some adducts are unstable (Cerfontain, 1968), although other reports have suggested that C-sulfonates (not necessarily formed by the bisulfite route) are quite robust (Wagner & Reid, 1931).
Related Knowledge Centers
- Ester
- Organic Chemistry
- Substituent
- Sulfonate
- Sulfur Trioxide
- Sulfuric Acid
- Organosulfur Chemistry
- Sulfonyl Group
- Parent Structure
- Salt