title: Solid lipid nanoparticles from amphiphilic calixpyrroles.
abstract: OBJECTIVE
  Macrocyclic amphiphiles form interesting self-assembling structures, including solid lipid nanoparticles, which have potential applications in drug encapsulation. Aryl-extended calixpyrroles, which act as anion binding hosts, are expected to form solid lipid nanoparticles, even though the alkyl chains have unusual perpendicular geometry with respect to the hydrophilic head group. The preparation conditions and the alkyl chain length should affect the size and stability of the particles.
  
  
  METHODS
  Solid lipid nanoparticles of two aryl-extended calixpyrroles with resorcinol walls and either meso-dodecyl or meso-methyl alkyl chains were compared. Ethanolic solutions of the calixpyrroles were mixed with water and the resulting nanoparticle dispersions were studied with dynamic light scattering and nanoparticle tracking analysis. The effect of different calixpyrrole/ethanol/water ratios on particle size was tested. The surface charge of the particles at different pH and NaCl concentration was determined by zeta potential measurements.
  
  
  RESULTS
  The meso-dodecyl calixpyrrole produced small nanoparticles with mean hydrodynamic diameters between 40 and 70nm in 0.86-4.28M ethanol. The particles were stable in solution for several months. Particles prepared from meso-methyl calixpyrrole were larger and less stable. The smallest particles were obtained with low calixpyrrole concentration and calixpyrrole/ethanol ratio. Larger ethanol/water ratio induced broader particle size distributions. Increasing pH aided the stability of the particles due to increased negative surface charge.
authors.affiliation: University of Jyvaskyla, Department of Chemistry, Nanoscience Center, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland. Electronic address: kaisa.j.helttunen@jyu.fi.
authors.forename: Kaisa
authors.initials: K
authors.lastname: Helttunen
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona, Spain.
authors.forename: Albano
authors.initials: A
authors.lastname: Galán
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona, Spain; Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Ballester
authors.affiliation: Department of Chemistry and Molecular Biology, University of Gothenburg, SE-412 96 Göteborg, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Bergenholtz
authors.affiliation: University of Jyvaskyla, Department of Chemistry, Nanoscience Center, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland.
authors.forename: Maija
authors.initials: M
authors.lastname: Nissinen
keywords: Amphiphile; Calixpyrrole; Dynamic light scattering; Macrocycle; Nanoparticle tracking analysis; Solid lipid nanoparticle; Zeta potential