Martin Pisárčik

Biodegradable gemini surfactants. Correlation of area per surfactant molecule with surfactant structure

Values of the area per surfactant molecule of various single chain and gemini quaternary ammonium surfactants containing biodegradable amide and ester groups are obtained from the surface tension measurements and they are mutually compared. It was found that surfactant molecules with the ester group in their structure occupy smaller area at the air/water interface than the corresponding molecules with the amide group, mainly due to the higher conformational flexibility of ester groups. In decreasing the area per surfactant molecule value, hydrogen bonding (both inter- and intramolecular) plays a significant role when amide groups are present in the spacer of a gemini molecule. They must be separated by a polymethylene chain or a flexible group such as cyclohexane which is short enough to allow intramolecular hydrogen bonds. The flexible cyclohexane group with the amide group in single chain surfactants may lead to the formation of intermolecular hydrogen bonds among surfactant molecules which also results in the reduction of the area per surfactant molecule.

Spherical dodecyltrimethylammonium bromide micelles in the limit region of transition to rod-like micelles. A light scattering study

Abstract Dynamic and static light scattering measurements were performed on dodecyltrimethylammonium bromide aqueous solutions in the presence of sodium bromide at different concentrations. The power law dependence was applied to the diffusion coefficient D vs. c b ( c , surfactant concentration) and the decrease of the parameter b with increasing salt concentration was observed. The dependencies of D and b on the salt concentration are decreasing and show a plateau at intermediate salt concentrations. The Debye plot from the static light scattering measurements shows the presence of stable spherical micelles in the solution at low salt concentration with molecular weight about 23 000 and aggregation number 65–80. The logarithmic plot of the molecular weight vs. the ionic strength shows two linear regions with an intercept at the salt concentration 1.9 M. However, the values of the molecular weight and the aggregation number are too small to allow the assumption of a rod structure.

Dynamic light scattering and electrokinetic potential of bis(quarternary ammonium bromide) surfactant micelles as the function of the alkyl chain length

Abstract The micellar properties of bis(quarternary ammonium bromide) surfactants were studied by means of dynamic light scattering and electrokinetic measurements. The coexistence of small spherical micelles and large aggregates for surfactants with eight to 12 carbon atoms in the alkyl chain is observed. Below this region, only spherical micelles appear and above 12 carbon atoms, large aggregates are present. The electrokinetic measurements of zeta potential correspond with the light scattering results. Bimodality in the peaks was observed in the region of nine to 12 carbon atoms in the alkyl chain. As follows from the light scattering results, solubilization with a monomeric surfactant showed that, in the case of dodecyltrimethylammonium bromide (DTAB) and 12-4-12 surfactant, the presence of large aggregates decreases strongly with increasing DTAB concentration in the system. No such observation was made when hexadecyltrimethylammonium bromide (CTAB) was present in the system with 16-4-16 surfactant, where only unimodal size spectra were registered.

Determination of micelle aggregation numbersof alkyltrimethylammonium bromide and sodiumdodecyl sulfate surfactants using time-resolvedfluorescence quenching

Abstract The time-resolved fluorescence quenching method was applied to determine the micelle aggregation number of cationic single-chain surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The concentration dependence of micelle aggregation number was found to be linear for all investigated surfactants in the concentration range 2‒15 × the value of critical micelle concentration of the respective surfactant. The values of micelle aggregation number were found in the range 30‒77. Different trends in the linear concentration dependence of micelle aggregation number were observed for cationic surfactants and for the anionic surfactant SDS. A small slope value was found for cationic surfactants, while the SDS micelle aggregation number concentration dependence showed significantly a larger slope value. The aggregation number increase with the increasing SDS concentration results in the micellar growth. Results from a simple analysis based on computer models of cationic and anionic surfactant molecules with dodecyl chains supports, the formation of intramicellar hydrogen bonding between surfactant molecules in SDS micelle shell. Graphical Abstract

Aggregates of sodium hyaluronate with cationic and aminoxide surfactants in aqueous solution — light scattering study

Aggregation properties of sodium hyaluronate (NaHA) with different types of surfactants in aqueous sodium chloride solution have been studied by using static and dynamic light scattering method. Molecular weight, second virial coefficient, radius of gyration, and hydrodynamic radius have been calculated. The polymer — surfactant aggregate growth was found in complexes of NaHA with an ionic surfactant (dodecyltrimethylammonium bromide) and ionic, dimeric surfactants (dodecanediyl-α,ω-bis(dimethyloctylammonium bromide) and N,N′-bis(dodecyldimethyl)-4,13-dioxo-3,14-dioxahexadecane-1,16-diyldiammonium dibromide). In case of dodecyldimethylamine oxide (DDAO), the decreasing molecular weight and aggregate size of the NaHA — DDAO complex with increasing DDAO concentration were found above the surfactant critical micelle concentration, indicating the absence of electrostatic interactions between NaHA and DDAO that would lead to the increase in aggregate size. This behaviour may be ascribed to the non-ionic character of DDAO.

Preparation of Risedronate Nanoparticles by Solvent Evaporation Technique

One approach for the enhancement of oral drug bioavailability is the technique of nanoparticle preparation. Risedronate sodium (Biopharmaceutical Classification System Class III) was chosen as a model compound with high water solubility and low intestinal permeability. Eighteen samples of risedronate sodium were prepared by the solvent evaporation technique with sodium dodecyl sulfate, polysorbate, macrogol, sodium carboxymethyl cellulose and sodium carboxymethyl dextran as nanoparticle stabilizers applied in three concentrations. The prepared samples were characterized by dynamic light scattering and scanning electron microscopy. Fourier transform mid-infrared spectroscopy was used for verification of the composition of the samples. The particle size of sixteen samples was less than 200 nm. Polysorbate, sodium carboxymethyl dextran and macrogol were determined as the most favourable excipients; the particle size of the samples of risedronate with these excipients ranged from 2.8 to 10.5 nm.

Surface-active properties of nitrogen heterocyclic and dialkylamino derivates of hexadecylphosphocholine and cetyltrimethylammonium bromide

The physico-chemical properties of dialkylamino and nitrogen heterocyclic analogues of hexadecylphosphocholine (HPC) and cetyltrimethylammonium bromide (CTAB) were investigated. The surface properties, such as the critical micelle concentration (cmc), the surface tension value at the cmc (gamma(cmc)), and the surface area at the surface saturation per head group (A(cmc)) were determined by means of surface tension measurements. Micelle size was determined using the dynamic light scattering method. The influence of dialkylamino groups and heterocyclic ring size on surface-active properties was investigated. Surface activity and micellar size of prepared analogues of HPC and CTAB were mutually compared.

Non-Newtonian properties of hyaluronic acid aqueous solution

Abstract The systems comprising hyaluronic acid (HA) aqueous solution and acetylsalicylic a cid salt in the HA solution were studied. It was found that both systems display pseudoplastic behaviour. The viscosity (η) dependence of the shear rate (γ) of thes systems was fitted using non-linear regression, with the best accuracy achieved by the empirical formula η γ − 3 4 . The radius of equivalent spheres (req) representing non-interacting, compressed macromolecular chains was calculated from the regression constant, and was plotted as a function of salt concentration. The compressing effect of the HA chains is caused by the presence of acetylsalicylic acid salt in the aqueous solution; the polymer chains change their shape into contracted structures as a result of suppressing the repulsion in the polyelectrolyte chain by adding salt counterions. At low salt concentrations, the lowest values of req were found if the acetylsalicylic acid salt with the highest ionic strength (magnesium salt) in the HA solution was present.

Aggregation number of alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants determined by static light scattering

Abstract Aggregation number of alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants in aqueous solutions has been determined at different number of carbon atoms in the alkyl tail ‘m’ and in spacer ‘s’ by using static light scattering. Values of aggregation number at different spacer numbers s=2–10 lie between 17 and 33 and between 18 and 55 for alkyl tail lengths m=9–16, respectively. Data for variable parameter s correspond to results obtained by neutron scattering technique. In all cases but s=2 and m=16, the slopes of Debye plots were found to be increasing and the value of the second virial coefficient B was found to be in the range 1.3×10−3–13×10−3 cm3 mol g−2 indicating the spherical shape of micelles. Increased aggregation number and negative B of surfactant with the shortest spacer s=2 indicates the rod-like micelle shape. Aggregation number of surfactant with the longest alkyl tail m=16 is too small to predict the rod-like shape of the micelle.

Solubilisation of camptothecin by nonionic surfactants and alkyldimethylamine oxides

AbstractThe solubilisation of poorly soluble antineoplastic drug camptothecin by nonionic surfactants (polysorbates and octylphenol ethoxylates) and alkyldimethylamine oxide surfactants with the alkyl chain length 8 to 16 carbon atoms was investigated. The hydrophobicity of the solubilising agent turned out to be the primary structural parameter controlling the solubility efficiency of camptothecin in an aqueous solution. The quantitative parameter of solubilisation (drug loading coefficient) provided values in the range of 0.1–1.2% and 0.1–1.0% for alkyldimethylamine oxides and nonionic surfactants, respectively. The decreasing number of oxyethylene units and the extension of the hydrophobic part of nonionic surfactant molecule resulted in the increase of camptothecin solubility. From the dynamic light scattering measurements, the hydrodynamic diameter values of camptothecin-loaded alkyldimethylamine oxide and nonionic micelles were found in the range of 4–42 nm and 5–120 nm, respectively. The experimental values confirmed the increase in micellar size with the increasing alkyl chain length. The values of the packing parameter of camptothecin-loaded dodecyldimethylamine oxide micelles indicate their spherical shape at all the investigated surfactant concentrations. A simple computer model of camptothecin-loaded dodecyldimethylamine oxide micelle provided the diameter of the structure cross section which is consistent with the experimental values.