Structure−Property Relationship in Stimulus-Responsive Bolaamphiphile Hydrogels

Abstract

The formation of temperature-, concentration-, and pH-responsive hydrogels composed of the symmetric long-chain bolaamphiphile dotriacontane-1,1'-diyl bis[[2-(dimethylammonio)ethyl]phosphate] (Me(2)PE-C32-Me(2)PE) was investigated by rheological, scattering, and spectroscopic techniques. At pH 5, this bolaamphiphile is known to form a dense network of helically structured nanofibers (Köhler et al. Soft Matter 2006, 2, 77-86). Rheological measurements and dynamic light scattering were used to describe the macroscopic behavior of the hydrogels. Small-angle neutron scattering (SANS) and time-resolved static light scattering were applied to get information about the morphology of the self-assembled aggregates. Finally, solid-state 31P NMR spectroscopy was used to gain insight into the mobility of the bolaamphiphile molecules within the fiber aggregates. In comparison with the previously examined trimethylammonio analogue PC-C32-PC, which forms temperature-dependent hydrogels, Me(2)PE-C32-Me(2)PE exhibits additional concentration- and pH-dependent gelling properties. The significantly higher stability of the Me(2)PE-C32-Me(2)PE hydrogel is supported by the SANS data, which indicate the presence of fiber aggregates up to 50 degrees C.

The formation of host–guest complexes between surfactants and cyclodextrins

“…Other applications include antifoaming agent in fermentation processes [317], metal and dye removal, either acting as an anchor [318][319][320] or by micellar extraction [321], formation of photosensitive structures [322][323][324] and the development of stimulus responsive gels [325,326]. Furthermore, bolaform surfactants are also relevant for biochemistry and pharmaceutical applications, by modeling lipid membranes [327][328][329], as permeability enhancers [330] or to be used for drugs encapsulation [331], respectively.…”

The Headgroup (A)Symmetry Strongly Determines the Aggregation Behavior of Single-Chain Phenylene-Modified Bolalipids and Their Miscibility with Classical Phospholipids

“…The results of the fits are provided in Table 1. Table 1) 16 and C36-bolalipid molecules (PC-C36-PC, d = 5.3 nm). 17 Modelling the scattering curves assuming stiff cylinders with an elliptical cross-section leads to values for the semi axes of 2.1 ± 0.1 nm and 3.4 ± 0.1 nm (axial ratio about 1.6, see Table S2).…”

“…On the other hand, modifications in the headgroup region can be obtained, e.g., by the reduction of the space requirement of the headgroup by a stepwise replacement of methyl moieties. This leads to a series of phosphodimethylethanolamines (Me 2 PE-Cn-Me 2 PE), which self-assemble into nanofibers 16 or square lamellae, 17 and the phosphomonomethylethanolamine MePE-C32-MePE that forms monolayer-like structures. 18 A further way of modifications that induces changes in aggregation properties is the introduction of headgroup asymmetry, i.e., the coupling of two headgroups of different size to the same alkyl chain.…”

General Synthesis and Aggregation Behaviour of New Single‐Chain Bolaphospholipids: Variations in Chain and Headgroup Structures

“…[12] In this study we synthesised several bolaphospholipids with further variations in the polar headgroup structures. We modified the choline headgroups with several functional groups in order to scrutinise the size effect of the headgroup on the aggregation behaviour and also to find out the synthetic limits for the quarternisation reaction.…”