Collective headgroup conformational transition in twisted micellar superstructures

Abstract

Predictions on amphiphilic self-assemblies traditionally rely on considerations on molecular shape and charge of the surfactant. In the case of functional surfactants a more sophisticated toolbox becomes necessary to design amphiphiles encoding chemical functionalities that provide additional responsive properties to their self-assemblies. Here we report on a comprehensive and combined structuralspectroscopic characterization of 1,2-dilauroyl-phosphatidyl-adenosine (DLPA) micelles in phosphate buffer. The temperature dependence, more precisely the thermal history of the sample, is explicitly taken into account. The experimental data, supplemented with MD simulations, indicate the presence of two possible states at room temperature, characterized by distinctly different structural properties that depend on the thermal history of the sample. The twisted superstructures, produced by aging DLPA micelles through intermicellar assembly of locally cylindrical aggregates at room temperature, collapse upon warming at 35 C, yielding aligned filaments and/or wormlike structures. The initial superstructures cannot be recovered by thermal inversion. The reason for this behaviour is that the thermal activation causes a redistribution of syn-anti conformations of adenosine headgroups, as indicated by spectroscopic results (NMR, CD, FTIR), which is then collectively frozen thanks to molecular constraints present in the aggregate.

Controlling self‐assembly of DNA‐polymer conjugates for applications in imaging and drug delivery

“…The phase‐driven assembly of DPCs is controlled in large part by the monomer structure, including factors such as DNA and polymer volume, hydrophilic to hydrophobic ratio, geometric shape, and electrostatics . Assembly can also be controlled by environmental factors such as ionic strength, temperature, and solvent polarity, or by the addition of specific chemical or biological stimuli . DPCs form dynamic structures in which monomers experience fluidity within the structure, and are capable of reversible assembly and disassembly .…”

“…Assembly morphology can also be influenced by the conformation of the sugar of the nucleotide bound to the polymer. Changing the sugar conformation from syn to anti by heating to 35°C resulted in an irreversible change in morphology from twisted micellar superstructures to aligned filaments …”

Intercalation of Single-Strand Oligonucleotides between Nucleolipid Anionic Membranes: A Neutron Diffraction Study

“…This behavior has been found for POPA, and it has been attributed to the high stacking constant of the base that, when self-assembled in bilayers, exhibits mutual polar-head interactions notwithstanding electrostatic repulsion. This peculiar property affects a number of other structural parameters in the family of adenosine derivatives, such as the occurrence of twisted ribbonlike micelles and thermal history effects on base conformation for DLPA …”