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Unusual Enthalpy Driven Self Assembly at Room Temperature with Chitosan Amphiphiles

[ Vol. 7 , Issue. 1 ]

Author(s):

Uchechukwu Odunze, Fionn O’Brien, Lisa Godfrey, Andreas Schätzlein and Ijeoma Uchegbu*   Pages 57 - 71 ( 15 )

Abstract:


Hypothesis: GCPQ (N-palmitoyl-N-monomethyl-N,N-dimethyl-N,N,Ntrimethyl- 6-O-glycolchitosan) is a self-assembling polymer being investigated as a pharmaceutical nano-carrier. GCPQ nanoparticles shuttle drugs across biological barriers, improving drug performance. The exact chemistry of GCPQ is varied by the relative proportion of hydrophobic (N-palmitoyl) and hydrophilic (quaternary ammonium) groups and molecular weight. We hypothesised that the thermodynamics of self-assembly is controlled by the polymer molecular weight and hydrophobicity.

Methods: The thermodynamics of self-assembly was investigated using isothermal calorimetry.

Findings: GCPQs (Mw = 8-15 kDa) formed micellar aggregates at critical micellar concentrations of 1-2.4 μM at 25 °C and micellisation was unusually enthalpy driven. There was a positive correlation between ΔHmic and Q: ΔHmic = 3.8 Q-159 (r2 = 0.93) and a negative correlation between ΔHmic and molecular weight (Mw): ΔHmic = -13.5 Mw-26.3 (r2 = 0.99). These findings provide insights into the positive drivers of stable self-assemblies, namely hydrophobicity and molecular weight, as both hydrophobicity and molecular weight are associated with an increased enthalpy contribution to micellisation.

Keywords:

Colloids, critical micelle concentration (CMC), endothermic, enthalpy, entropy, exothermic, GCPQ, micelle, nanomedicine, polymer, thermodynamics.

Affiliation:

School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX, School of Pharmacy, University College London, 29-39 Brunswick Square, London WC1N 1AX



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