Order-Disorder transition of carboxyl terminated chains in polydiacetylenes vesicles probed by second harmonic generation and two-photon fluorescence

Abstract

To understand and control the interfacial properties of polydiacetylenes (PDAs) vesicles with π-conjugated backbone is very important for their colorimetric sensing of chemical and biological targets. In this work, we adopted 10, 12-pentacosadiynoic acid (PCDA) as the model molecule to prepare PDAs vesicles in aqueous solution with different forms (from monomer to blue-to-purple-to-red phase) by controlling the UV irradiation dose. The variations of the interfacial conformation of PDAs vesicles during chromatic transitions were inspected by the adsorption behaviors of probe molecules (4-(4-diethylaminostyry)-1-methylpyridinium iodide, D289) on vesicle surface with surface-specific second harmonic generation (SHG) and zeta potential measurements. Resonant SHG signal from D289 adsorbed on vesicle surface attenuated sharply, and the adsorption free energy as well as the corresponding two-photon fluorescence signal decreased slightly in chromatic transitions. While, the change in the surface density of the adsorbed D289 molecules for PDAs vesicles with different forms was relatively small as estimated from zeta potential measurements. The attenuation of the SHG intensity was thus attributed to the overall order-disorder transition and the changed orientation of D289 molecules caused by the gradual distortion of carboxyl head group driven by backbone perturbation.

Unveiling the Molecular Dynamics in a Living Cell to the Subcellular Organelle Level Using Second-Harmonic Generation Spectroscopy and Microscopy

“…Based on the principles of the second-order nonlinear phenomenon, the D289 molecules oriented on the surface of lipid membranes may contribute to enhanced SHG emission because of the broken inversion symmetry . It was also shown that the D289 molecules on the lipid surface contributed to enhanced TPF emission, , possibly because of the well-known aggregation-induced emission (AIE) mechanism or the enhancement of the fluorescence efficiency of D289 with its distribution in the lipid membrane in K562 cells. A similar enhancement in the TPF efficiency from an anticancer drug, doxorubicin, during its interaction with lipid bilayer was recently reported …”

“…7,10,33,37,40,41 Recently, we have demonstrated that the dynamics of dye or drug molecules on the lipid surface may be investigated not only by the interface selective SHG method but also by the twophoton fluorescence (TPF) method, which is also sensitive to the dye or drug molecules on the surface of lipid bilayers because their fluorescence efficiency was notably altered (quenched or enhanced) with the changed chemical environment. 11,37,38,42 In this work, we used SHG and TPF methods to investigate the adsorption and cross-membrane transport of D289 on K562 cells and the subcellular organelles in them. It was revealed that D289 adsorbed on the K562 surface may transport in the cell at a relatively slow rate (∼1000s).…”

Understanding the Dynamic Behavior of an Anticancer Drug, Doxorubicin, on a Lipid Membrane Using Multiple Spectroscopic Techniques

“…Second harmonic generation (SHG) has been demonstrated as a powerful technique in the analysis of molecular density and orientation at interfaces, benefiting from its interface selectively and submonolayer sensitivity. − On the basis of this advantage, SHG has been used to study molecular transportation through liposome membranes and living cell membranes in situ and in real time. − For example, Prof. Eisenthal’s group was first to detect the transportation of dye molecules across the bilayer of a phospholipid liposome with the help of the SHG technique . The influence of cholesterol on the delivery rate of an organic cation across the dioleoylphosphatidylglycerol liposome surface has also been analyzed .…”

Combined Second Harmonic Generation and Fluorescence Analyses of the Structures and Dynamics of Molecules on Lipids Using Dual-Probes: A Review

“…Being the opposite to the ACQ effect observed for the aforementioned anthracyclines, some molecules were revealed to emit enhanced TPF signal upon their aggregating and embedding on/in the lipid bilayers [62,75,76]. This property is also helpful in analyzing its interfacial behaviors on lipids.…”