J.C. Jacquier

Determination of critical micelle concentration by capillary electrophoresis. Theoretical approach and validation

Abstract The aim of this study was the determination of the critical micelle concentration (CMC) of the most commonly employed anionic surfactant in micellar electrokinetic chromatography, sodium dodecyl sulphate (SDS), using capillary electrophoresis, i.e., under the operating conditions of the electrophoretic separation (pH, ionic strength, temperature, etc.). The effective electrophoretic mobility of a neutral compound, resulting from the solvophobic and micellar contributions, appeared to be a well adapted parameter for the study of the micellization process of anionic surfactants. In fact, the theoretical treatment of the evolution of this parameter as a function of the total surfactant concentration allowed the identification of a sharp change in slope at the cmc, and therefore to establish capillary electrophoresis as a new analytical tool for the determination of critical micelle concentrations. In the experimental case of an electrolytic solution consisting of 5 mmol l −1 borax, the observed value of the cmc of SDS (5.29 mmol l −1 ) was in total agreement with the literature data when the sodium concentration in the solution was the same.

Analysis of alkylaromatic sulphonates by high-performance capillary electrophoresis

Abstract The potential of high-performance capillary electrophoresis for the resolution of alkylaromatic sulphonates was investigated. The operating conditions in capillary zone electrophoresis and in micellar electrokinetic chromatography were optimized on a mixture of model molecules synthesized in the laboratory. The two methods appear to be complementary. Capillary zone electrophoresis allows not only an efficient sorting out according to the number of the sulphonic groups, but also allows, using an organic solvent (acetonitrile), a better resolution in unit time of the structural homologues of the alkylbenzene sulphonates than micellar electrokinetic chromatography. On the other hand, the latter method permits the separation of alkylbenzene sulphonate isomers.

Determination of critical micelle concentration by capillary electrophoresis application to organo-saline electrolytes

Abstract Having previously reported [J. Chromatogr. A, 718 (1995) 167] the theoretical approach of the determination of the critical micelle concentration (CMC) by capillary electrophoresis and validated this new technique with the determination of the CMC of sodium dodecyl sulphate in a simple electrolyte, we demonstrate in this paper the universality of this technique in studying the evolution of the CMC of the same surfactant in various complex electrolytic solution. The electrolytic salts (sodium borate and phosphate) and the solvents (methanol, ethanol, acetone and acetonitrite) evaluated in this study correspond to the most used salt and solvent in micellar electrokinetic chromatography. This unique possibility offered by this new technique to study the micelle formation under identical electrophoretic conditions as used during the separation appears to be most interesting for the understanding of the separation forces and their optimisation. Moreover, a comparative study of the effect of added organic solvent to the electrolytic medium has been undertaken.

Complex formation between DNA and cationic surfactant

Complex formation between short DNA fragments and dodecyltrimethylammonium bromide (DoTAB) has been studied using dynamic (DLS), static light scattering (SLS), high performance capillary electrophoresis (HPCE) and a DoTAB-specific electrode. The combination of diffusion coefficient obtained from DLS, mobility from HPCE and binding isotherm allow us to deduce information about the structure of complexes as a function of bound surfactant. The binding of cationic surfactant to short DNA fragments was shown to proceed in two stages. In the first stage of binding, surfactant ions exchange with counterions “condensed” on the surface of DNA. At this stage the effective charge on DNA does not change as shown by the combination of mobility and diffusion coefficients of the complexes. The observed high cooperativity of binding can be explained by hydrophobic interactions between the surfactant molecules. In the second stage, surfactant molecules bind to DNA without exchange of condensed counterions, which brings about a dramatic change in the effective charge of DNA with phase separation occurring at high DNA concentration.

Inhibition of proinflammatory biomarkers in THP1 macrophages by polyphenols derived from chamomile, meadowsweet and willow bark.

Antiinflammatory compounds in the diet can alleviate excessive inflammation, a factor in the pathogenesis of common diseases such as rheumatoid arthritis, atherosclerosis and diabetes. This study examined three European herbs, chamomile (Matricaria chamomilla), meadowsweet (Filipendula ulmaria L.) and willow bark (Salix alba L.), which have been traditionally used to treat inflammation and their potential for use as antiinflammatory agents. Aqueous herbal extracts and isolated polyphenolic compounds (apigenin, quercetin and salicylic acid, 0–100 μM) were incubated with THP1 macrophages, and interleukin (IL)‐1β, IL‐6 and tumour necrosis factor‐alpha (TNF‐α) were measured. At concentrations of 10 μM, both apigenin and quercetin reduced IL‐6 significantly ( p < 0.05). Apigenin at 10 μM and quercetin at 25 μM reduced TNF‐α significantly ( p < 0.05). Amongst the herbal extracts, willow bark had the greatest antiinflammatory activity at reducing IL‐6 and TNF‐α production. This was followed by meadowsweet and then chamomile. The lowest effective antiinflammatory concentrations were noncytotoxic (MTT mitochondrial activity assay). The Comet assay, which was used to study the protective effect of the isolated phenols against oxidative damage, showed positive results for all three polyphenols. These are the first findings that demonstrate the antiinflammatory capacity of these herbal extracts. Copyright

Correlation of sensory bitterness in dairy protein hydrolysates: Comparison of prediction models built using sensory, chromatographic and electronic tongue data

Sensory evaluation can be problematic for ingredients with a bitter taste during research and development phase of new food products. In this study, 19 dairy protein hydrolysates (DPH) were analysed by an electronic tongue and their physicochemical characteristics, the data obtained from these methods were correlated with their bitterness intensity as scored by a trained sensory panel and each model was also assessed by its predictive capabilities. The physiochemical characteristics of the DPHs investigated were degree of hydrolysis (DH%), and data relating to peptide size and relative hydrophobicity from size exclusion chromatography (SEC) and reverse phase (RP) HPLC. Partial least square regression (PLS) was used to construct the prediction models. All PLS regressions had good correlations (0.78 to 0.93) with the strongest being the combination of data obtained from SEC and RP HPLC. However, the PLS with the strongest predictive power was based on the e-tongue which had the PLS regression with the lowest root mean predicted residual error sum of squares (PRESS) in the study. The results show that the PLS models constructed with the e-tongue and the combination of SEC and RP-HPLC has potential to be used for prediction of bitterness and thus reducing the reliance on sensory analysis in DPHs for future food research.

Capillary electrophoretic study of the complex formation between DNA and cationic surfactants

Due to the growing interest in the use of cationic surfactants for the construction of liposomal genetic delivery systems, the study of complex formation between DNA and quaternary ammonium detergents is of fundamental importance. In this context, we undertook the study of this complex formation using capillary zone electrophoresis (CZE) with suppressed electroosmotic flow, a technique that allowed us to both monitor the change in mobility of DNA as a function of added surfactant in a precise and reproducible manner and evaluate the potential of CZE to reflect the change in hydrodynamic friction upon binding. Nevertheless, CZE must be applied with caution for binding studies where strong cooperativity occurs, because of the presence of peak splitting at concentrations close to the half-point of binding. Also, a comparison between this experiment and Mannings polyelectrolyte transport properties theory on one hand and Tirado and Garcia de la Torre expression for hydrodynamic friction of rod-like molecules on the other hand is given.

Computer-assisted pH optimization for the separation of geometric isomers in capillary zone electrophoresis

With the rapid development of capillary electrophoresis, several workers have considered the theoretical pH optimization for the separation of geometric isomers. However, for samples composed of more than two isomers, these mathematical treatments lead only to an optimum pH range. In this work, the application of software based on the iterative computation of the resolution as a function of pH was studied, in order to have direct access to the optimum pH value for complex mixtures of isomers. The values deduced were compared with the experimental values for acids and bases.

Cold-set whey protein microgels as pH modulated immobilisation matrices for charged bioactives

The ability of cold-set whey protein microgels to function as pH-sensitive immobilisation matrices for bioactives was investigated. A pH dependent interaction was confirmed between the microgels and charged bioactives and this binding was impeded by the presence of competing ions in the solution, suggesting an electrostatic interaction. The use of a computer generated prediction model for the pH-dependent association of the microgels and further bioactives (including cationic and anionic peptides) was validated. The prediction model was efficient at determining the pH at which the maximum microgel-bioactive interaction occurred. This study highlights the capabilities of these food-grade whey based microgels as matrices that enable the immobilisation of a variety of bioactives by a charge interaction, and shows the potential for these matrices to function as smart delivery systems, in which uptake and release of bioactives is facilitated by environmental pH change.

Cold-set whey protein microgels containing immobilised lipid phases to modulate matrix digestion and release of a water-soluble bioactive

Abstract This study investigated the in-vitro digestibility of cold-set whey protein (WP) microgels prepared by two gelation methods (external and internal) containing lipids (0%, 10% or 20% w/w). The incorporation of lipids into these matrices achieved higher entrapment of the bioactive vitamin riboflavin, as well as significant reductions in rates of both the digestion of the protein matrix, and the subsequent diffusion of the water-soluble bioactive. A biexponential model accounted for the contribution of digestion- and diffusion-driven mechanisms in describing the release of riboflavin into enzyme containing simulated gastrointestinal fluids. In particular, for external gelation microgels, as the lipid load within the matrices increased, the contribution of a faster diffusion-driven release was almost completely negated by a slower digestion-assisted release. Lipid loads provided a composite matrix capable of alternating from a burst to a sustained release of bioactive.