title: Experimental evidence for the mode of action based on electrostatic and hydrophobic forces to explain interaction between chitosans and phospholipid Langmuir monolayers.
abstract: The interaction between chitosans and Langmuir monolayers mimicking cell membranes has been explained with an empirical scheme based on electrostatic and hydrophobic forces, but so far this has been tested only for dimyristoyl phosphatidic acid (DMPA). In this paper, we show that the mode of action in such a scheme is also valid for dipalmitoyl phosphatidyl choline (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG), whose monolayers were expanded and their compressibility modulus decreased by interacting with chitosans. In general, the effects were stronger for the negatively charged DPPG in comparison to DPPC, and for the low molecular weight chitosan (LMWChi) which was better able to penetrate into the hydrophobic chains than the high molecular weight chitosan (Chi). Penetration into the hydrophobic chains was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum frequency generation (SFG) spectroscopy. A slight reduction in conformational order of the lipid chains induced by the chitosans was quantitatively estimated by measuring the ratio between the intensities of the methyl (r(+)) and methylene (d(+)) peaks in the SFG spectra for DPPG. The ratio decreased from 35.6 for the closely packed DPPG monolayer to 7.0 and 6.6 for monolayers containing Chi and LMWChi, respectively. Since in both cases there was a significant phospholipid monolayer expansion, the incorporation of chitosans led to chitosan-rich and lipid-rich condensed domains, which mantained conformational order for their hydrophobic tails. The stronger effects from LMWChi are ascribed to an easier access to the hydrophobic tails, as corroborated by measuring aggregation in solution with dynamic light scattering, where the hydrodynamic radius for LMWChi was close to half of that for Chi. Taken together, the results presented here confirm that the same mode of action applies to different phospholipids that are important constituents of mammalian (DPPC) and bacterial (DPPG) cell membranes.
authors.affiliation: Institute of Chemistry of São Carlos, University of São Paulo, P.O. Box 780, 13560-970, São Carlos, SP, Brazil. Electronic address: adrianapavinatto@iqsc.usp.br.
authors.forename: Adriana
authors.initials: A
authors.lastname: Pavinatto
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, 13566-590, São Carlos, SP, Brazil.
authors.forename: Jorge A M
authors.initials: JAM
authors.lastname: Delezuk
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, 13566-590, São Carlos, SP, Brazil.
authors.forename: Adriano L
authors.initials: AL
authors.lastname: Souza
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, 13566-590, São Carlos, SP, Brazil.
authors.forename: Felippe J
authors.initials: FJ
authors.lastname: Pavinatto
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, 13566-590, São Carlos, SP, Brazil; Department of Natural Sciences, Mid Sweden University, SE-851 70, Sundsvall, Sweden.
authors.forename: Diogo
authors.initials: D
authors.lastname: Volpati
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, 13566-590, São Carlos, SP, Brazil.
authors.forename: Paulo B
authors.initials: PB
authors.lastname: Miranda
authors.affiliation: Institute of Chemistry of São Carlos, University of São Paulo, P.O. Box 780, 13560-970, São Carlos, SP, Brazil.
authors.forename: Sérgio P
authors.initials: SP
authors.lastname: Campana-Filho
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, USP, P.O. Box 369, 13566-590, São Carlos, SP, Brazil. Electronic address: chu@ifsc.usp.br.
authors.forename: Osvaldo N
authors.initials: ON
authors.lastname: Oliveira
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D048271:Chitosan / Q000737:chemistry*; D057446:Hydrodynamics; D057927:Hydrophobic and Hydrophilic Interactions; D008968:Molecular Conformation; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011312:Pressure; D012996:Solutions; D013057:Spectrum Analysis; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D010715:Phosphatidylglycerols; D010743:Phospholipids; D012996:Solutions; D015060:1,2-Dipalmitoylphosphatidylcholine; D048271:Chitosan; C030345:1,2-dipalmitoylphosphatidylglycerol
keywords: Chitosan; Conformation; Langmuir monolayers; PM-IRRAS; SFG