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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.

1463is facilitated by increasing quencher concentration. The decrease of the second-order rates with increasing global concentration [Q], is a particularity of the restricted reaction space.6 An increase in [Q] means a decrease in the available free sites per quencher. Thus, even though the quenching species becomes more abundant, facilitating fmt-order kinetics, the probability for a single quencher to reach the fluorophore decreases, making second-order kinetics slower. The k's do not always decrease with increasing [Q], Thus for pyrene in mPG vesicles, which provide a less restrictive lipidic core, it has been found that both K's and k's increase with [Q]. However, in that case, the increase in the K's is faster. Notice also, that for DPH in the DPPGLcYPG mixture in Table I1 and pyrene in DPPG in Table I11 kl increases with [Q]. We attribute this last result to the high efficiency of the reaction at short times and high quencher concentrations, due to quasi-static quenching. Failure to repeat this same result with the pair pyrene-12-DSME in DPFG in Table I11 is most probably due to the limited accuracy of the data obtained with this last system. Notice that both first-order and second-order rates are 1 order of magnitude higher for all data obtained with DPH than for those obtained with pyrene. This difference in reaction efficiency goes along with the time scales of survival of the two excited species. In other words, the reaction is faster for the fast-decaying DPH. Of course, this behavior is expected when a substantial quenching occurs within the same concentration ranges. Notice the large difference between the reaction rates at short times (KI) and at long times (KJ. This is due to the relatively low f values observed in this work (cf. Figure 1). The average R is, generally, higher in L~P G than in DPPG vesicles. Apparently, this is due to the higher fluidity of the LCYPG lipidic core. Notice, finally, the extensive increase of K1 with [Q] in the vesicles of the DPPG-mPG mixture (Table I) and of DPPG (Table 11). This is consistent with our above assertion of quasi-static quenching, in particular in these systems.The above discussion shows that the information on reaction rates obtained through eqs 1 and 2 provides an extensive knowledge of the behavior of the reactants in microheterogeneous environments.An additional final remark concerns the behavior under variable temperatures. Previous measurements with pyrene excimers have shown that an increase in temperature increases the calculated fvalues? However, no variation infwas detected with DPH. We attribute this result to the time scale of the DPH data, which is too short to allow any detectable temperature effect. ConclusionThe fluorescence decay of DPH embedded in small unilamellar vesicles of DPPG, L~P G , or a mixture of these two phospholipids (80% DPPG, 20% LCXPG) has been studied in the presence of varying concentration of 12-DSME used as fluorescence quencher. The vesicle concentration was held constant. The results have been compared with sim...

The effect of anionic micelles of sodium dodecyl sulfate (SDS) on the rates of acid-catalyzed hydrolyses of 2-(p-alkoxyphenyl)-1,3-dioxolanes with alkoxy groups of different chain lengths, methoxy (p-MPD), nonoxy (p-NPD), and tetradecoxy (p-TPD), were determined as a function of SDS and NaCl concentrations and temperature. First-order rate constants, &"bs, were obtained from plots ofln(A« -A) vs time that were linear for at least three half-lives. The k0bs-[SDS] profiles were fitted by using the pseudophase ionexchange (PPIE) model and substrate binding constants, Ka, and second-order rate constants for reaction in the micellar pseudophase, &2m, were estimated from the simulations. Values of Ks and &2m for p-MPD and p-NPD are completely consistent with micellar effects on other acid-catalyzed hydrolyses in SDS and the assumptions of the PPIE model; i.e. hydrolysis of monomeric substrate occurs in either the aqueous or the micellar pseudophases. However, kinetic profiles for p-TPD in SDS are more consistent with this substrate acting as a nonionic surfactant that does not mix ideally with SDS. The Ka for p-TPD decreases about 800-fold as the temperature is increased from 25 to 50 °C. In 0.012 M SDS, k0hB for p-TPD passes through a sharp maximum at 32 °C with increasing temperature whereas the plot for p-NPD is linear.At constant SDS concentration, added NaCl initially speeds the hydrolysis of p-TPD instead of inhibiting the reaction as observed for p-NPD and salt effects on other micellar-catalyzed reactions. All these results can be interpreted by assuming that increasing the temperature induces demixing of p-TPD and SDS to give two populations of mixed micelles each enriched in one of the surfactants and in dynamic equilibrium. Thus the PPIE model can be used to identify nonrandom distributions of reactive and nonreactive surfactants in aggregated systems.

Fungi of the Pleurotus genus present a great industrial interest due to their possibility of producing pharmacological compounds, pigments, aromas, organic acids, polysaccharides, enzymes, vitamins, amino acids, etc. Among the therapeutic products, we can highlight those with antineoplasic activity, attributed to the fungi cell wall components. Based on this, the objective of this work was to study the antineoplasic capacity of the polysaccharidic fractions obtained from Pleurotus sajor-caju fruiting bodies. Female Swiss mice were inoculated with the Ehrlich ascitic tumor (5 x 10(6) cells/animal) in ascitic form. The polysaccharidic fractions were administered intraperitoneally, during a 6-day period. Fractions FI and FII presented a lower volume of ascitic liquid (3.1 and 1.8 mL, respectively) and a higher reduction in the number of neoplasic cells present in the ascitic liquid (86.2% and 85%, respectively), when compared to the positive control (group inoculated with the tumor but without treatment). These fractions were characterized in terms of monosaccharide composition. Glucose was the major component detected, followed by galactose and mannose. The anomeric carbon configuration of the beta-glucan was confirmed by the (13)C NMR (delta 103.7). Substituted and free C3 and C6 were also detected. Protein bands were confirmed through infrared analysis.