Organic solvents effect acetonitrile

In a few cases (with Fe or Cu hydrosoluble precatalysts), the system can operate in the absence of any added organic solvent (even acetonitrile) [20], a feature that is noteworthy toward the development of a green catalytic system. However, our catalysts are not effective when using air (or dioxygen) instead of hydrogen peroxide as the oxidant, a disadvantage relative to the industrial process. 

Some polymerization results are given in Table 2. Polymerization of )0-CF catalyzed by Trichoderma viride in CHaCN/buffer (5 1) gave the best results in terms of synthetic cellulose yield. Of the organic solvents screened, acetonitrile was most effective for promotion of the reaction. DMF and DMSO were probably too polar to maintain the enzyme activity. Buffer was necessary to neutralize the HF molecule in the reaction mixture. An organic cosolvent was needed to prevent the hydrolysis of y0-CF. 

Interestingly, at very low concentrations of micellised Qi(DS)2, the rate of the reaction of 5.1a with 5.2 was observed to be zero-order in 5.1 a and only depending on the concentration of Cu(DS)2 and 5.2. This is akin to the turn-over and saturation kinetics exhibited by enzymes. The acceleration relative to the reaction in organic media in the absence of catalyst, also approaches enzyme-like magnitudes compared to the process in acetonitrile (Chapter 2), Cu(DS)2 micelles accelerate the Diels-Alder reaction between 5.1a and 5.2 by a factor of 1.8710 . This extremely high catalytic efficiency shows how a combination of a beneficial aqueous solvent effect, Lewis-acid catalysis and micellar catalysis can lead to tremendous accelerations. 

Naphthalenedisulfonate-acetonitrile as the only mobile phase with a silica column coated with a crosslinked aminofluorocarbon polymer has proven to be an effective combination for the separation of aliphatic anionic surfactants. Indirect conductivity and photometric detection modes are used to monitor these analytes. The retention of these surfactants is found to depend on both the ionic strength and the organic solvent content of the mobile phase. The mechanism of retention is considered to be a combination of both reverse phase and ion exchange processes. Selective separation of both alkanesulfonates and... 

Some advice can be formulated for the choice of organic modifier, (i) Acetonitrile as an aprotic solvent cannot interact with residual silanols, whereas the protic methanol can. Thus, when measuring retention factors, methanol is the cosolvent of choice, as it reduces the secondary interactions between the solutes and the free silanol groups, (ii) For the study of the performance of new stationary phases one should use acetonitrile, as the effects of free silanol groups are fuUy expressed [35]. (iri) Acetonitrile with its better elution capacity can be considered as the best organic modifier for Hpophilicity measurements of highly Hpophihc compounds with adequate stationary phases [36]. 

Acetonitrile, methanol and DMSO had no apparent effect on umbelliferone glucuronidation in human hepatocytes at concentration up to 2% [32]. With HLMs or expressed UGTs, inhibitory effects of organic solvents on glucuronidation of 7-hydroxy-4-trifluoromethyl-coumarin (7-HFC) and estradiol generally followed the order acetonitrile > ethanol > methonal > DMSO [33], DMSO did not inhibit estradiol-3-glucuronidation activity at a concentration up... 

Reaction is terminated by acetonitrile quenching, or by liquid-liquid extraction with water-immiscible organic solvent, provided that the extraction efficiency and the effect of the organic solvent on product stability are tested at the small scale. Based on properties of product, the pH of the reaction mixture should be adjusted before termination to allow maximal recovery of the product. For example, acid is usually added to the acyl-glucuronide product mixture at the end of the reaction to minimize acyl migration. 

Fontes tt al. [224,225 addressed the acid—base effects of the zeolites on enzymes in nonaqueous media by looking at how these materials affected the catalytic activity of cross-linked subtilisin microcrystals in supercritical fluids (C02, ethane) and in polar and nonpolar organic solvents (acetonitrile, hexane) at controlled water activity (aw). They were interested in how immobilization of subtilisin on zeolite could affected its ionization state and hence their catalytic performances. Transesterification activity of substilisin supported on NaA zeolite is improved up to 10-fold and 100-fold when performed under low aw values in supercritical-C02 and supercritical-ethane respectively. The increase is also observed when increasing the amount of zeolite due not only to a dehydrating effect but also to a cation exchange process between the surface proton of the enzyme and the sodium ions of the zeolite. The resulting basic form of the enzyme enhances the catalytic activity. In organic solvent the activity was even more enhanced than in sc-hexane, 10-fold and 20-fold for acetonitrile and hexane, respectively, probably due to a difference in the solubility of the acid byproduct. 

Adogen has been shown to be an excellent phase-transfer catalyst for the per-carbonate oxidation of alcohols to the corresponding carbonyl compounds [1]. Generally, unsaturated alcohols are oxidized more readily than the saturated alcohols. The reaction is more effective when a catalytic amount of potassium dichromate is also added to the reaction mixture [ 1 ] comparable results have been obtained by the addition of catalytic amounts of pyridinium dichromate [2], The course of the corresponding oxidation of a-substituted benzylic alcohols is controlled by the nature of the a-substituent and the organic solvent. In addition to the expected ketones, cleavage of the a-substituent can occur with the formation of benzaldehyde, benzoic acid and benzoate esters. The cleavage products predominate when acetonitrile is used as the solvent [3]. 

HPLC has been shown as an effective method in the fractionation and preparation of AHLs for structural analysis. Preparation of AHL-containing samples for HPLC analysis requires their extraction with organic solvents such as dichloromethane or ethyl acetate [37]. Usually, C8 reverse-phase columns are employed and samples eluted with either gradient or isocratic mobile phases, e.g. acetonitrile-water. Fractions are analysed for the presence of AHLs using the biosensors described in the previous section. AHLs from active fractions can then be identified using more powerful techniques (see following sections). 

Column XTerra MS (pyridine) 3.5 p,m, 15 x 0.46 cm ID. Mobile phase acetonitrile buffer 28-72 (v/v). The calculations of ionic strength ignore the effect of the organic solvent. 

---