Solvent effects, dimethylsulfoxide

Comparison of their rate of onset and recovery of a treated mucosa has been made [37]. Fatty acids have strong and fast reactivity and allow for a fast recovery of the barrier function. Bile salts and salicylates are moderate, fast-acting agents with fast barrier-function recovery. Strong surfactants and chelators have strong or moderate reactivity and a slow recovery of barrier function. Solvents like dimethylsulfoxide and ethanol have moderate reactivity and act primarily as agents to improve drug miscibility in an aqueous environment. The enhancers listed above are also effective in the small intestine [22]. Enhancers that are more colon specific include ethylaceto-acetate, which must be first metabolically transformed to enamine [38]. 

The role of solvent effects in quaternization is one of the first physical organic studies and this is due to Menschutkin (1879LA334). It shows an increase in relative rate from 1 to 742 on going from benzene to benzyl alcohol, which suggests no simple explanation. Typical ranges of solvent-dependent rate ratios are 15,700/1 (nitromethane/cyclohexane) in the alkylation of triethylamine by methyl iodide (68BSF2678), 1660/1 [dimethylsulfoxide (DMSO)/carbon tetrachloride] in the reaction of l,4-diazabicyclo[2,2,2]-octane (DABCO) (5) with (2-bromoethyl)benzene (75JA7433) (Scheme 5),... 

More pronounced solvent effects have been observed in special cases where substrates or products possess ionic character. Ito and Matsuda found a 35-fold reduction in the rate of addition of the arenethiyi radical 18 to a-methylstyrene when the solvent was changed from dimethylsulfoxide to cyclohexane. Rates for addition of other arenethiyi radicals do not show such a marked solvent dependence. The different behavior was attributed to the radical 18 existing partly in a zwitterionic quinonoid form (Scheme 1.7). ... 

The reaction of the simple 1-azirine (129) with guanidine displayed a remarkable solvent effect (Scheme 5). In methanol, only complex mixtures were obtained but in dimethylsulfoxide the selective formation of (131) or (132) was observed. The proposed mechanism involves the formation of several different tautomers resulting from C—C bond cleavage in the aziridine intermediate (130). It was not possible spectroscopically to distinguish between (131) and (132) <9UOC7>. 

Chemical modification of polymer-bound active ester groups is also subject to strong solvent effects. In copolyfAOTcp-styrere), both aminolysis and transesterification with primary alcohols are positively influenced by solvents in the order of dimethylformamide (DMF) > dioxan > diloroform > chlorobenzene > dimethylsulfoxide (DMSO). However, trans-esterification with phenols proceeds in dioxan, but not in DMF. The last-nan d solvent effect is probably related to inactivation of the phenolate ion in DMF, as observed ako for the acylation of polymer-bound phenolic groups by soluble trichlorophenyl esters [64]. 

Triton X-100 sample (Fig IB). an increase in yield was seen upon addition of DPQ. There was increase in the ratio of the size of the outer peaks (arrowed) to the inner peaks. This was shown not to be as a result of solvent effects since the addition of ethanol or dimethylsulfoxide alone produced no changes. In contrast, a decrease in the triplet yield of the 0.033% Triton X-100 sample was seen in the presence of DPQ (Fig ID). The change in the outer peaks was again more marked resulting in a lineshape change. This drop in triplet yield may be due to electron transfer to the quinone. However,no evidence of electron transfer at cryogenic temperatures was detected. 

It is often the solvent effect that is the only method of radical change of relative contents of different conformer forms. Thus, with the help of the isochore equation of chemical reaction, the data on equilibrium constants and enthalpies of dichloroacetaldehyde conformer transformation allow us to calculate that, to reach the equilibrium constant of axial rotamer formation in cyclohexane as solvent (it is equal to 0.79) to magnitude K=0.075 (as it is reached in DMSO as solvent), it is necessary to cool the cyclohexane solution to 64K (-209°C). At the same time, it is not possible because cyclohexane freezing point is +6.5"C. By analogy, to reach the dimethylsulfoxide constant to value of cyclohexane , DMSO solution must be heated to 435K (162 C). 

Fig. 3.15. Aging effects in polymer solutions. Quotient of the time dependent viscosity of a polymer solution, and the viscosity of a freshly prepared solution, tiq, as a function of the time f. The viscosity can Increase with time as shown for poly(vinyl alcohol) (PVA), or decrease as shown for poly(acrylamide) (PAAm) in aqueous solution. Changing the solvent to dimethylsulfoxide (DMSO) or ethylene glycol (EG) can prevent the aging. Data from [30]...

At a potential more positive than the point of zero charge, the effect changes sign, which is why one should expect intersection, at this point, of the polarization curves obtained with various salt concentrations. In aqueous solutions, the rate of reduction of persulfate on the positively charged surface is so high that it cannot be measured—diffusion limitations come into play. However, in such a nonaqueous solvent as dimethylsulfoxide, the process turned out to be much slower and it becomes possible to observe directly the intersection of the polarization curves. ... 

Figure 2. Solvent effect on fluorescence of PNA in an aqueous MES buffer (pH 6.0) containing 5%(V/v) ethanol for APC(C2Lys2Cj 4)4 and APC-(CioN+)4 in an aqueous HEPES buffer (pH 8.0) containing 10%(v/v) ethanol for capped-APC in an aqueous CAPS buffer (pH 10.0) containing 5%(v/v) dimethylsulfoxide for APC(CioC02H), APyC(C oC02H)4, and APy+C(CioC02H)4.

Examination of Solvent Effect on Nucleophilic Fluorination with KF/ dicvclohexano-18 crown-6. Using 1-bromodocosane (12) as substrate and KF/DC-18-C-6 as reagent system, solvent effect was examined. Solvents were chosen from common dipolar aprotic solvent [acetonitrile, hexa-methylphosphoric triamide (HMPT), dimethylsulfoxide (DMSO), diglyme], from weakly basic dipolar aprot c solvents (sulfolane, ethylene carbonate, propylene carbonate) " and from acid amide solvents [N,N-dimethylformamide (DMF), N,N-diethylacetamide (DEA), N-methyl-pyrrolidone (NMP), tetramethylurea]. ... 

In the first series of experiments, 0.1 ml of the neat solvents were applied with a pipette to the forearm skin of healthy subjects and were allowed to spread freely. As can be seen from Table 3, only one solvent (dimethylsulfoxide) caused an increase in skin blood flow. The sites looked normal to the naked eye. In the second series of experiments, the neat solvents were applied in excess (1.5 ml/3.1 cm ) using a glass ring as a reservoir and attached with rubber bands to the forearm. Three different exposure times were used (1, 5, and 15 min) and, as can be seen from Table 3, the solvents varied greatly in their effects on skin blood flow. The most potent solvents were dimethylsulfoxide and trichloroethylene, while 15 min of exposure in excess to methyl ethyl ketone, propylene glycol, ethanol and water did not influence skin blood flow. 

Ampicilin and Flucytosine [4] (Figure 7.2). Dimethylsulfoxide (DMSO) was required to dissolve the compounds, but no deleterious solvent effect was observed on the microorganisms. ... 

A significant solvent effect was reported in the Sonogashira reaction for example, dimethylsulfoxide was slightly better in terms of conversion, but also promoted an unwanted side reaction - the homocoupling of the arene. However, the combination of a trinuclear system and dimethylformamide was efficient, leading to quantitative conversion. 

A related solvent effect was found when replacing pyridine by dimethylsulfoxide (DMSO), as seen in the corresponding Fig. 4. The results of Figs. 3 and 4 taken together may be represented as follows The peaks in pyridine with the even... 

The solvent used in these dimerization reactions dictates the activity of the catalyst. Besides benzene and dioxane, acetic acid [246,247], halogenated hydrocarbons [245,247], nitroderivatives [247], sulfones, tetrahydrofuran (THF), ethyl acetate, phenol, dimethylformamide, hydroquinone, catechol, benzyl alcohol, salicylic acid, anisole, and acetone have been used [247]. In solvents like benzene and chlorohydrocarbons and in highly polar solvents like dimethylsulfoxide and dimethylformamide, dimerization does not occur. The reaction proceeds in solvents containing oxygen atoms. The dissociative solvents like phenol and acetic acid show high solvent effect. In carboxylic acids the rate of dimerization decreases with an increase in pK . 

The charged segments of the AMPS units in these amphiphilic copolymers effectively solubilize the sequences of hydrophobic monomer units to water. In fact, the copolymers ASt-72 (7 with x = 72), APh-50 (8 with x = 50), APy-50 (9 with x = 50), and ALa-44 (10 with x = 44) were all soluble in water. The copolymer ACh-x was a little less water soluble ACh-23 (11 with x = 23) was almost soluble, whereas ACh-60 was insoluble. All these copolymers were soluble in methanol, N, AT-dimethylformamide, and dimethylsulfoxide, but insoluble in most of other common organic solvents. 

Tetraazamacrocyclic complexes131 of cobalt and nickel were found110 to be effective in facilitating the reduction of C02 at -1.3 to -1.6 V versus SCE (Table 8). An acetonitrile-water mixture and water were used as solvents, while in dry dimethylsulfoxide no catalytic reduction of C02 took place. Using an Hg electrode, both CO and H2 were produced, where total current efficiencies were greater than 90%. The turnover numbers of the catalysts were 2-9 h 1. The catalytic activity lasted for more than 24 h and the turnover numbers of the catalysts exceeded 100. A protic source was required to produce both CO and H2, and the authors suggested that both products may arise from a common intermediate, which is most likely a metal hydride. The applied potential for C02 reduction was further reduced by using illuminated p- Si in the presence of the above catalysts.111... 

Polar solvents have no effect on the rate constant of the reaction R02 + RH [56], This means that the solvation energies of the peroxyl radical R02 and TS R02 HR are very close. A different situation was observed for the reaction of cumylperoxyl radical with benzyl alcohol (see Table 7.10). The rate constant of this reaction is twice in polar dimethylsulfoxide (s = 33.6) than that in cumene (a 2.25). It was observed that the very important property of the solvent is basicity (B), that is, affinity to proton. A linear correlation... 

All the above reactions of PVC were performed homogeneously in DA-solvents such as HMPA, DMF and dimethylsulfoxide (DMSO). For the practical modification of PVC, the reaction must be conducted under more commercial conditions as in slurry water. As mentioned before, azidation of PVC did not occur in water. However, the reaction proceeded feasibly in water by addition of some cationic surfactant to give, e.g. 8-20% (DS) of azidated PVC at 80°C by use of tetra-n-butyl ammonium chloride (1 ). The use of cationic surfactant was also effective in organic solvents and attracted increased attention as the conception of "phase transfer catalyst" in organic chemistry developed. 

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