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The acid-catalyzed hydrolysis of 2-@-methoxyphenyl)-1,3-dioxolane and benzaldehyde di-tert-butyl acetal has been studied in the presence and absence of poly(ethy1ene oxide)-sodium dodecyl sulfate (PEO-SDS) solutions. The kinetic data were interpreted in light of the pseudophase ion-exchange (PPIE) formalism by assuming that reaction can occur in three pseudophases, namely, aqueous, micellar, and PEO-SDS complex.The degree of ionization (a) for PEO-SDS complexes was determined from the ratio of the slopes of conductivity against [SDS] above and below the critical aggregation concentration (cac) by the application of Evans equation. Values of 0.25 and 0.41 for SDS micelles and PEO-SDS complexes, respectively, were found. Free micelles are shown to be better catalysts than PEO-SDS complexes because of (i) the lower a value of free micelles and because (ii) second-order rate constants for the acid hydrolysis reactions in SDS micelles are higher than in PEO-SDS complexes.

The chemical composition of the chromatography 63 subfraction (63SF) from the ethyl acetate soluble fraction of the crude extract of Croton celtidifolius bark presented a high content of total proanthocyanidins (75.0+/-2.3%). HPLC analysis of 63SF revealed a dimeric profile (e.g.catechin-(4alpha-->8)-catechin and gallocatechin-(4alpha-->8)-catechin) and polymeric proanthocyanidins. In pharmacological investigations, 63SF administered intraperitoneally exhibited dose-dependent antinociceptive activity against several chemical stimuli, including the intraperitoneal injection of acetic acid (ID50 (the dose of 63SF which was able to reduce the nociceptive response by 50% relative to the control value)=0.9 (0.5-1.6)) and the intraplantar injection of capsaicin (ID50=13.0 (10.0-17.0)), glutamate (ID50=4.0 (2.0-7.0)) and formalin (ID50 first phase=36.0 (24.0-53.0) and late phase=11.0 (8.0-14.0)). 63SF administered orally exhibited an antinociceptive effect in the formalin test (ID50 first phase=125.0 (89.0-177.0) and late phase=65.0 (33.0-95.0)). In the same test, 63SF was effective when given soon after the first phase, as well as exhibiting therapeutic activity. Furthermore, 63SF was effective in models of thermal nociception including tail-flick and hot-plate tests. When the mice were treated in the neonatal period with capsaicin, the antinociceptive effect of 63SF in the first phase of the formalin test was abolished, but pretreatment with naltrexone did not change the antinociceptive effect of 63SF. Together, these results provide evidence that 63SF exerted a pronounced systemic antinociception against chemical (acetic acid, formalin, glutamate and capsaicin tests) and thermal (hot-plate and tail-flick tests) nociceptive models of pain in mice at a dose that did not interfere with the locomotor activity. The mechanism by which this sub-fraction produced antinociception remains unclear, but it is unlikely to involve the activation of the opioid system. However, unmyelinated C-fibres sensitive to treatment with capsaicin are likely to participate in antinociception caused by 63SF.

The acid-catalyzed hydrolysis of 2-(methoxyphenyl)-1,3-dioxolane (p-MPD) and di-n-butyl benzaldehyde acetal (BBA) has been studied in solutions containing poly(ethylene oxide) (PEO) or poly(vinyl pyrrolidone) (PVP) and sodium dodecyl sulfate (SDS). First-order rate constant−[SDS] profiles were obtained at 0.010 and 0.105 M PEO or PVP, and both polymers strongly inhibit the reaction, to an extent depending on the polymer and SDS concentrations. Added NaCl also decreases the rate, and the behavior is similar to that with SDS micelles. The inhibition induced by increasing polymer concentration was interpreted by assuming decreases in the interfacial H+ concentration. This conclusion is supported by values of pH apparent obtained with the pH indicator pyridine-2-azo-p-dimethylaniline (PADA) at the same experimental kinetic conditions. Qualitatively, the results are interpreted in terms of the pseudophase ion exchange (PPIE) model applied to bimolecular reactions.