Limits...
Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway.

Kelley EG, Murphy RP, Seppala JE, Smart TP, Hann SD, Sullivan MO, Epps TH - Nat Commun (2014)

Bottom Line: Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent.Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems.Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, Delaware 19716, USA [2].

ABSTRACT
The solution self-assembly of macromolecular amphiphiles offers an efficient, bottom-up strategy for producing well-defined nanocarriers, with applications ranging from drug delivery to nanoreactors. Typically, the generation of uniform nanocarrier architectures is controlled by processing methods that rely on cosolvent mixtures. These preparation strategies hinge on the assumption that macromolecular solution nanostructures are kinetically stable following transfer from an organic/aqueous cosolvent into aqueous solution. Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent. The unexpected micelle growth evolves through a distinct bimodal distribution separated by multiple fusion events and critically depends on solution agitation. Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems. Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

Show MeSH

Related in: MedlinePlus

SANS results showing negligible chain exchange over 10 days(a) Illustration of small angle neutron scattering (SANS)experiments used to probe single chain exchange in micelle solutions. The scattering of initially segregated micelles poly (butadiene-b-ethylene oxide) [PB-PEO (top left) ] and poly(butadiene-b-ethylene oxide-d4) [PB-dPEO (top centre) ] was monitored in solvents that were contrast-matched to the corona in a mixed micelle system[PB-PEO/dPEO (top right) ]. (b)SANS curves showing the measured scattered intensity from pre-mixed PB-PEO/PB-dPEO micelles (black circles) and mixtures of PB-PEO and PB-dPEO micelles immediately after mixing (open squares) or 10d after mixing (gray circles) in D2O/H2O at 25°C.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC4225159&req=5

Figure 4: SANS results showing negligible chain exchange over 10 days(a) Illustration of small angle neutron scattering (SANS)experiments used to probe single chain exchange in micelle solutions. The scattering of initially segregated micelles poly (butadiene-b-ethylene oxide) [PB-PEO (top left) ] and poly(butadiene-b-ethylene oxide-d4) [PB-dPEO (top centre) ] was monitored in solvents that were contrast-matched to the corona in a mixed micelle system[PB-PEO/dPEO (top right) ]. (b)SANS curves showing the measured scattered intensity from pre-mixed PB-PEO/PB-dPEO micelles (black circles) and mixtures of PB-PEO and PB-dPEO micelles immediately after mixing (open squares) or 10d after mixing (gray circles) in D2O/H2O at 25°C.

Mentions: The growth of PB-PEO micelles following solvent transfer into pure water was examined using small angle neutron scattering (SANS) and cryogenic transmission electron microscopy (cryo-TEM). Specifically, single chain exchange in water was investigated using SANS by exploiting contrast variations and monitoring the temporal changes in the scattered intensity (Fig. 4a)22,28-30,37. Initially, separate PB-PEO and PB-dPEO[poly (butadiene-b-ethylene oxide-d4) ] micelle solutions were prepared in an H2O/D2O mixture. These separate solutions were mixed at time t = 0, giving rise to a maximum in scattered intensity due to contrast between the coronas and solvent[I(q) values at t = 0 in Fig. 4b]. After mixing the separate PB-PEO and PB-dPEO micelle solutions, two possible outcomes were considered. In the first scenario, chain exchange would occur, leading to randomization of the PB-PEO and PB-dPEO chains in the micelles. This mixing of the chains would reduce the corona/solvent contrast and decrease the scattered intensity, as the isotopic composition of the solvent was selected to contrast-match a randomly mixed PEO/dPEO corona[lower scattered intensity I(q) values for pre-mixed PEO/dPEO corona sample in Fig. 4b]. In the second scenario, single chain exchange would not occur and the scattered intensity would remain nearly constant with time.


Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway.

Kelley EG, Murphy RP, Seppala JE, Smart TP, Hann SD, Sullivan MO, Epps TH - Nat Commun (2014)

SANS results showing negligible chain exchange over 10 days(a) Illustration of small angle neutron scattering (SANS)experiments used to probe single chain exchange in micelle solutions. The scattering of initially segregated micelles poly (butadiene-b-ethylene oxide) [PB-PEO (top left) ] and poly(butadiene-b-ethylene oxide-d4) [PB-dPEO (top centre) ] was monitored in solvents that were contrast-matched to the corona in a mixed micelle system[PB-PEO/dPEO (top right) ]. (b)SANS curves showing the measured scattered intensity from pre-mixed PB-PEO/PB-dPEO micelles (black circles) and mixtures of PB-PEO and PB-dPEO micelles immediately after mixing (open squares) or 10d after mixing (gray circles) in D2O/H2O at 25°C.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4225159&req=5

Figure 4: SANS results showing negligible chain exchange over 10 days(a) Illustration of small angle neutron scattering (SANS)experiments used to probe single chain exchange in micelle solutions. The scattering of initially segregated micelles poly (butadiene-b-ethylene oxide) [PB-PEO (top left) ] and poly(butadiene-b-ethylene oxide-d4) [PB-dPEO (top centre) ] was monitored in solvents that were contrast-matched to the corona in a mixed micelle system[PB-PEO/dPEO (top right) ]. (b)SANS curves showing the measured scattered intensity from pre-mixed PB-PEO/PB-dPEO micelles (black circles) and mixtures of PB-PEO and PB-dPEO micelles immediately after mixing (open squares) or 10d after mixing (gray circles) in D2O/H2O at 25°C.
Mentions: The growth of PB-PEO micelles following solvent transfer into pure water was examined using small angle neutron scattering (SANS) and cryogenic transmission electron microscopy (cryo-TEM). Specifically, single chain exchange in water was investigated using SANS by exploiting contrast variations and monitoring the temporal changes in the scattered intensity (Fig. 4a)22,28-30,37. Initially, separate PB-PEO and PB-dPEO[poly (butadiene-b-ethylene oxide-d4) ] micelle solutions were prepared in an H2O/D2O mixture. These separate solutions were mixed at time t = 0, giving rise to a maximum in scattered intensity due to contrast between the coronas and solvent[I(q) values at t = 0 in Fig. 4b]. After mixing the separate PB-PEO and PB-dPEO micelle solutions, two possible outcomes were considered. In the first scenario, chain exchange would occur, leading to randomization of the PB-PEO and PB-dPEO chains in the micelles. This mixing of the chains would reduce the corona/solvent contrast and decrease the scattered intensity, as the isotopic composition of the solvent was selected to contrast-match a randomly mixed PEO/dPEO corona[lower scattered intensity I(q) values for pre-mixed PEO/dPEO corona sample in Fig. 4b]. In the second scenario, single chain exchange would not occur and the scattered intensity would remain nearly constant with time.

Bottom Line: Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent.Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems.Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, Delaware 19716, USA [2].

ABSTRACT
The solution self-assembly of macromolecular amphiphiles offers an efficient, bottom-up strategy for producing well-defined nanocarriers, with applications ranging from drug delivery to nanoreactors. Typically, the generation of uniform nanocarrier architectures is controlled by processing methods that rely on cosolvent mixtures. These preparation strategies hinge on the assumption that macromolecular solution nanostructures are kinetically stable following transfer from an organic/aqueous cosolvent into aqueous solution. Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent. The unexpected micelle growth evolves through a distinct bimodal distribution separated by multiple fusion events and critically depends on solution agitation. Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems. Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

Show MeSH
Related in: MedlinePlus