(NMR) analysis, using the tris [3-(trifluoromethylhydroxymethylene)-(ϩ)camphorato]europium(III) complex. The compound was hydrolyzed to the corresponding acid and then the optical purity was enhanced up to 97% ee by cocrystallization with commercially available R-PEA. The optical purity was checked by NMR and circular dichroism spectra:[␣] D 25 ϭ Ϫ63.2 (C ϭ 1.01 g/liter tetrahydrofuran). 5. The isotherms were measured from A ϭ 100 to 5 Å 2

Small-angle neutron scattering measurements on sodium dodecyl sulfate aqueous solutions have been performed in the presence of n-alcohols, from methanol to octanol, at different alcohol concentrations. By modeling the experimental intensities, it was possible to obtain structural information and to derive simultaneously the distribution of the alcohols between the aqueous and the micellar phases. It was found that short chain alcohols tend to remain in the aqueous phase and, by altering the solvent properties, induce a decrease in the aggregation number of sodium dodecyl sulfate micelles. On the other hand, alcohols with longer hydrocarbon chains were found to be present in both phases though favoring the micellar phase the longer the alkyl chain and the larger the concentration; this could be rationalized by assuming that the insertion of alcohol molecules in the micelle produced weaker repulsive interactions between the charged head groups of the surfactant molecules. For long chain alcohols, appreciably localized in the micellar phase, screening of the interaction among head groups leads to bigger micelles than those observed in the absence of alcohol: in these cases the alcohol/surfactant molar ratio reaches the value of 0.86, and hence the aggregates can be considered as mixed micelles. Sodium dodecyl sulfate micelles, at the examined concentration, were found to deviate from spherical symmetry and, when added with heptanol or octanol, assumed an ellipsoidal shape growing preferentially along the rotation axis.

Grapefruit and lemon pectin obtained from the respective waste citrus peels via hydrodynamic cavitation in water only are powerful, broad-scope antimicrobials against Gram-negative and -positive bacteria. Dubbed IntegroPectin, these pectic polymers functionalized with citrus flavonoids and terpenes show superior antimicrobial activity when compared to commercial citrus pectin. Similar to commercial pectin, lemon IntegroPectin determined ca. 3-log reduction in Staphylococcus aureus cells, while an enhanced activity of commercial citrus pectin was detected in the case of Pseudomonas aeruginosa cells with a minimal bactericidal concentration (MBC) of 15 mg mL−1. Although grapefruit and lemon IntegroPectin share equal MBC in the case of P. aeruginosa cells, grapefruit IntegroPectin shows boosted activity upon exposure of S. aureus cells with a 40 mg mL−1 biopolymer concentration affording complete killing of the bacterial cells. Insights into the mechanism of action of these biocompatible antimicrobials and their effect on bacterial cells, at the morphological level, were obtained indirectly through Fourier Transform Infrared spectroscopy and directly through scanning electron microscopy. In the era of antimicrobial resistance, these results are of great societal and sanitary relevance since citrus IntegroPectin biomaterials are also devoid of cytotoxic activity, as already shown for lemon IntegroPectin, opening the route to the development of new medical treatments of polymicrobial infections unlikely to develop drug resistance.

No abstract

Above its critical point, carbon dioxide forms a super‐critical fluid, which promises to be an environmentally responsible replacement for the organic solvents traditionally used in polymerizations. Many lipophilic polymers such as polystyrene (PS) are insoluble in CO2, though polymerizations may be accomplished via the use of PS‐fluoropolymer stabilizers, which act as emulsifying agents. Small‐angle neutron and X‐ray scattering have been used to show that these molecules form micelles with a CO2‐phobic PS core and a CO2‐philic fluoropolymer corona. When the PS block was fixed in length and the fluorinated corona block was varied, the number of block copolymer molecules per micelle (six to seven) remained constant. Thus, the coronal block molecular weight exerts negligible influence on the aggregation number, in accordance with the theoretical predictions of Halperin, Tirrell & Lodge [Adv. Polym. Sci. (1992), 100, 31–46]. These observations are relevant to understanding the mechanisms of micellization and solubilization in supercritical fluids.

H and 19 F NMR measurements on aqueous solutions of sodium perfluorooctanoate (SPFO) and sodium dodecanoate (SD) mixtures are reported. The surfactant concentration ranged from ∼0.3 to 10 times the critical micelle concentration (cmc = 0.03 mol L -1 ). The cmc of the SD/SPFO/water mixed system obtained from NMR data was in good agreement with that previously obtained by conductivity measurements. Below the cmc, the experimental chemical shift (δ) was independent of the total concentration for both surfactants. Above the cmc, however, the δ values for 19 F varied linearly with concentration, whereas the values for the hydrogenated surfactant deviated from linearity. These observations indicate that below the cmc each monomer is not affected by the presence of the others. Above the cmc, on increasing the total concentration, the chemical shift trends indicate that the fluorinated chains begin to aggregate, forming islands among hydrocarbon chain domains. Since the extended chain of the fluorinated surfactant is shorter than the inner micelle radius, some methyl groups of the longer SD must be segregated within the micelle. This patchwork distribution, involving an intramicellar phase separation, prevents the computation of the micelle composition; however, NMR data give information complementary to that obtained by a previous SANS study indicating the existence of mixed micelles having the same composition. Information on the structure of micelles and on the mean distribution of the two components in the system are obtained by SANS, while the NMR technique suggests details on the chemical environment of a single monomer and on the structural organization of the molecules within a micelle. Thus, the patchwork model here proposed is able to explain apparently conflicting data obtained from different techniques.

Supercritical fluids are becoming an attractive alternative to the liquid solvents traditionally used as polymerization media'. As the synthesis proceeds, a wide range of colloidal aggregates form, but there has hitherto been no way to measure such structures directly. We have applied small-angle neutron scattering (SANS) to characterize such systems, and although SCF polymerizations are carried out at high pressures, the penetrating power of the neutron beam means that typical cell windows are virtually transparent. Systems studied include molecules soluble in CO, (e.g. polyfluoro-octyl acrylate or PFOA) and this polymer has previously2 been shown to exhibit a positive second vhial coefficient (Ah. Other C02-soluble polymers include hexafluoro-polypropylene oxide (HFPPO), which appears to have a second virial coefficient which is close to zero (lVA, = 0 & 0.2 cm3 g" mol). Polydimethylsiloxane (PDMS), is soluble on the molecular level only in the limit of dilute solution and seems to form aggregates as the concentration increases (c > 0.01 g ~m -~) .Other polymers (e.g. polystyrene) are insoluble in CO,, though polymerizations may be accomplished via the use of PS-PFOA blockcopolymer stabilizers, which are also amenable to SANS characterization, and have been shown3 to form micelles in CO,. Other amphiphilic surfactant molecules that form micelles include PFOA-polyethylene oxide (PFOA-PEO) graft copolymers, which swell as the CO, medium is saturated with water. These systems have been characterized by SANS, by taking advantage of the different contrast options afforded by substituting D,O for H,O. This paper illustrates the utility of SANS to measure molecular dimensions, thermodynamic variables, molecular weights, micelle structures etc. in supercritical CO,.

Contrast matching experiments have been performed on aqueous solutions of sodium perfluorooctanoate, sodium dodecanoate, and a mixture of the two surfactants. Moreover, sodium dodecanoate has been studied as a function of the concentration. Previous findings in several mixed fluorocarbon-hydrocarbon systems indicated the coexistence of two different kinds of micelles, one rich in hydrocarbon and the other in fluorocarbon surfactant; on the contrary, because of the existence of a unique and well-defined contrast match point, the present data indicate the formation of mixed micelles having the same composition and a very narrow size distribution, at least at the composition examined. This has been confirmed by fitting the experimental patterns with a model based on the above-mentioned hypothesis: the structure function has been calculated by means of the rescaled mean spherical approximation using a screened Coulombic potential plus hard sphere repulsion; the particle form factor has been calculated using several different models. Among the models tested, a core plus shell prolate ellipsoid model gave the best fits. The aggregation number found for the mixed micelles was intermediate between those of the two single surfactant micelles, while the degree of counterion dissociation was lower than each of them.