Binding of cationic single-chain and dimeric surfactants to bovine serum albumin.

The interactions between bovine serum albumin (BSA) and the single-chain surfactants N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium bromide (PH12) and N-cyclohexylmethyl-N,N-dimethyl-N-(1-dodecyl)ammonium bromide (CH12) and their two dimeric counterparts, N,N'-[1,3-phenylenebis(methylene)]bis[N,N-dimethyl-N-(1-dodecyl)]ammonium dibromide (12PH12) and N,N'-[cyclohexane-1,3-diylbis(methylene)]bis[N,N-dimethyl-N-(1-dodecyl)]ammonium dibromide (12CH12), respectively, have been investigated by surface tension, fluorescence, circular dichroism, ζ potential, and atomic force microscopy. The results obtained permit the examination of the way an increase in the number of hydrophobic chains and the substitution of a cyclohexyl ring by a phenyl ring, either in the headgroup of single-chain surfactants or in the spacer of dimeric surfactants, affect BSA-surfactant interactions. The comparison of the fluorescence results with those obtained by ζ potential measurements shows that the sites of binding of the surfactants with aromatic rings to the BSA are somewhat different from those of the surfactants with no aromatic rings.

Synthesis and physicochemical characterization of alkanedyil-α-ω-bis(dimethyldodecylammonium) bromide, 12-s-12,2Br-, surfactants with s=7, 9, 11 in aqueous medium.

In this work, three didodecyl dicationic dibromide dimeric surfactants 12-s-12,2Br(-), with different methylene spacer lengths (s=7, 9, and 11) were prepared and characterized and their properties compared to those of 12-s-12,2Br(-) surfactants with s=2, 3, 4, 5, 6, 8, 10, and 12. Information about the critical micelle concentration, the micellar ionization degree, the average aggregation number and the polarity of the interfacial region, and microviscosity of the micellar interior was obtained by using different techniques. Their surface activity was investigated by means of surface tension measurements. Micellization was also studied by using (1)H NMR and diffusion NMR (DOSY) spectroscopy as well as isothermal titration calorimetry. The values of the thermodynamic parameters show that the dimeric surfactants micellization is exothermic and driven by entropy. The occurrence of morphological transitions upon increasing surfactant concentration was studied, and the results indicate that the spacer length, s, plays a key role in the micellar growth of 12-s-12,2Br(-) aggregates. The value of s not only control the magnitude of C(*), the surfactant concentration above which the morphological transition from spherical micelles into elongated ones occurs, but also the sign of the enthalpy change accompanying the sphere-to-rod transition.

Comparative studies on lectin-carbohydrate interactions in low and high density homo- and heteroglycoclusters.

A versatile synthetic procedure to construct series of high- and low-density homo- and heteroglycoclusters is reported. The binding properties of these synthetic multivalent glycoconjugates to concanavalin A (Con A), a model lectin, have been assessed by using a range of competitive and non-competitive binding assays including enzyme-linked lectin assays (ELLA), isothermal titration microcalorimetry (ITC) and surface plasmon resonance (SPR). In all cases, highly dense glycoclusters showed a substantial amplification of the lectin-binding strength in comparison with low-density counterparts. Interestingly, highly-dense glycoligand presentations, regardless of their homo- or heteroglycoligand pattern, furnished similar Con A binding properties, supporting the existence of a synergic effect (heterocluster effect) due to secondary interactions of "non-active" structural motifs in the presence of a certain density of "active" glycoligands.

Probing secondary carbohydrate-protein interactions with highly dense cyclodextrin-centered heteroglycoclusters: the heterocluster effect.

Comparison of the lectin-binding properties for highly dense beta-cyclodextrin-centered homo- and heteroglycoclusters with defined architecture provides evidence for the existence of strong synergic effects (heterocluster effect) on carbohydrate-protein recognition events.