Inhibition by Methanol

Although short-chain alcohols, specifically methanol, are preferable in conventional transesterification reactions, they negatively affect the activity of lipase if used in excessive amounts. This is because short-chain alcohols have low solubility in oils, resulting in their presence as a separate phase. The affinity of the alcohol to water is high, which results in a stripping of the microlayer of essential water surrounding 

Research for Biodiesel Production from Different Lipases Immobilized by Different Methods 

Lipase Method Carrier Fat/Oil Acyl Acceptors % Yield Reference 

antarctica Adsorption Silica Gel Soybean Methanol 94 Wang et ak, 2006 

P cepacia Adsorption Celite Jatropha Ethanol 98 Shah and Gupta, 2007 

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Comparison of Two Simple Prediction Methods for Hydrate Inhibition by Methanol... 

Case Study 5 Under-Inhibition by Methanol in a Gas Line... 

Numerous studies have reported that pretreatment of an immobilized lipase affects its activity and stability. Samukawa et al. (2000) studied the effect of Novozym 435 preincubation in methyl oleate on soybean oil transesterification with methanol. Immobilized lipase was incubated in methyl oleate for 0.5 h and then in the oil for 12 h. The use of an incubated enzyme resulted in a 20% higher yield in 1 h, compared to only 13.6% achieved by the nonincubated enzyme. The stability of immobilized lipase was also enhanced by incubation in tert-butanol. The high catalytic activity and stability of the incubated immobilized lipase have been confirmed by several researchers (Li et al., 2006 Royon et al., 2007). The positive effect might be due to terf-butanol s ability to shield the enzyme from being inhibited by methanol or by immersion in tert-butanol. 

Organic compounds normally cause Htde or no corrosion of magnesium. Tanks or other containers of magnesium alloys are used for phenol [108-95-2] methyl bromide [74-96 ] and phenylethyl alcohol [60-12-8]. Most alcohols cause no more than mild attack, but anhydrous methanol attacks magnesium vigorously with the formation of magnesium methoxide [109-88-6]. This attack is inhibited by the addition of 1% ammonium sulfide [12135-76-1] or the presence ofwater. 

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

Fig. 9 Comparison of polar and steric effects of alkyl groups on bromination rates of linear ( ), branched (O) and adamantyl (A) alkenes in acetic acid and in methanol (Ruasse and Zhang, 1984 Ruasse et al., 1990). Polar effects are identical in both solvents [full line, eq. (24)], but steric effects differ. Deviations of branched alkenes are attributed to steric inhibition of nucleophilic solvation by methanol.

The kinetic parameters for the oxidation of a series of alcohols by ALD are shown in Table 4.1 (74). Methanol and ethylene glycol are toxic because of their oxidation products (formaldehyde and formic acid for methanol and a series of intermediates leading to oxalic acid for ethylene glycol), and the fact that their affinity for ALD is lower than that for ethanol can be used for the treatment of ingestion of these agents. Treatment of such patients with ethanol inhibits the oxidation of methanol and ethylene glycol (competitive inhibition) and shifts more of the clearance to renal clearance thus decreasing toxicity. ALD is also inhibited by 4-methylpyrazole. 

A flavoprotein oxidase, which is also a methanol oxidizing enzyme, was inhibited by cyclopropanol 4 through the formation of a N-5 flavin adduct with a ring opened cyclopropyloxy radical [10]. 

Pseudo-first-order rate constants for carbonylation of [MeIr(CO)2l3]" were obtained from the exponential decay of its high frequency y(CO) band. In PhCl, the reaction rate was found to be independent of CO pressure above a threshold of ca. 3.5 bar. Variable temperature kinetic data (80-122 °C) gave activation parameters AH 152 (+6) kj mol and AS 82 (+17) J mol K The acceleration on addition of methanol is dramatic (e. g. by an estimated factor of 10 at 33 °C for 1% MeOH) and the activation parameters (AH 33 ( 2) kJ mol" and AS -197 (+8) J mol" K at 25% MeOH) are very different. Added iodide salts cause substantial inhibition and the results are interpreted in terms of the mechanism shown in Scheme 3.6 where the alcohol aids dissociation of iodide from [MeIr(CO)2l3] . This enables coordination of CO to give the tricarbonyl, [MeIr(CO)3l2] which undergoes more facile methyl migration (see below). The behavior of the model reaction closely resembles the kinetics of the catalytic carbonylation system. Similar promotion by methanol has also been observed by HP IR for carbonylation of [MeIr(CO)2Cl3] [99]. In the same study it was reported that [MeIr(CO)2Cl3]" reductively eliminates MeCl ca. 30 times slower than elimination of Mel from [MeIr(CO)2l3] (at 93-132 °C in PhCl). 

Gene expression inhibition. Chloroform/ methanol extract (1 1) of the dried leaf, in cell culture, was active on hepatoma-Cos-7, IC50 600.0 pg/mL vs TAT-dependent activation of HIV promoter hioassay - . Hepatotoxic activity. The leaf, taken orally by a female adult, was active - . A patient consumed 15 tablets of the leaf per day for 4 months. Approximately 1 year after stopping consumption, liver enzymes returned to normal and fatigue was no longer a complaint - ". Infusion of the dried leaf, taken orally by a female adult at variable doses, was active. The 60-year-old woman who took Lama tridentata for 10 months developed severe hepatitis for which no other cause could be found. Despite aggressive supportive therapy, the patient s condition deteriorated and required orthotropic liver transplantation - " . Dried leaves, administered orally to adults at variable doses, were active. A public warning has been issued by the US Centers for Disease Control based on reports of liver toxicity after use of Lama tridentata tea - " k Dried leaves, administered orally to adults of both sexes at variable doses, were active - ". The plant, administered orally to adults at variable doses, was active - ". Dried leaves, administered orally to adults at variable doses, were active. One case of hepatotoxicity induced by Larrea tridentata taken as a nutritional supplement was reported - ". Thirteen patients were identified for whom Larrea tridentata tincture for internal use was prescribed. Additionally, 20 female and three male patients were identified from whom an extract of Larrea tridentata in castor oil for... 

Hypotensive effect. Methanol (70%) extract of the seed, administered intravenously to rats at dose of 3 mg/kg, was active. The effect was inhibited by pretreatment with atropine . 

In the photocatalytic production of amines from alcohols and ammonia, the efFiciency varied with alcohol structure ethanol > methanol > 2-propanol > t-butanol. A hydrogen atmosphere enhanced the formation of amines, a process which was inhibited by oxygen ... 

The other major toxic effect of methanol is the ocular toxicity. Although formaldehyde might be formed locally in the retina, this seems unlikely, whereas formate is known to cause experimental ocular toxicity. The mechanism suggested involves inhibition by formate of cytochrome oxidase in the optic nerve. As the optic nerve cells have few mitochondria, they are very susceptible to this "histotoxic hypoxia,"... 

Uncompetitive inilibitors of liver alcohol dehydrogenase (Chapter 15) could be used to treat cases of poisoning by methanol or ethylene glycol.81 83 The aim is to prevent rapid oxidation to the toxic acids HCOOH and HOCH2COOH, which lower blood pH, while the alcohols are excreted. Uncompetitive inhibitors have an advantage over competitive inhibitors as therapeutic agents in that the inhibition is not overcome when the substrate concentration is saturating.84... 

Several flavonoids have given mixtures of products on irradiation for example, the 3-phenylflavone (380) in methanol is converted into the isocoumarins (381) and (382) the latter is the major product and is derived from the former (75CC241). Quercitin pentamethyl ether (383) in methanol and in the absence of oxygen yields four tetracyclic products. In deoxygenated benzene, the reaction rate is doubled but only (384) and (385) are formed. This photocyclization is not inhibited by triplet quenchers and the primary photointermediate is in the triplet state (67JA6213). 

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