Spontaneous Formation of Ultrasmall Unilamellar Vesicles in Mixtures of an Amphiphilic Drug and a Phospholipid

Spontaneous formation of small and ultrasmall unilamellar vesicles in mixtures of drug surfactant and phospholipid: Effect of chemical structure of phospholipid tails on vesicle size

We have investigated the effect of length and chemical structure of phospholipid tails on the spontaneous formation of unilamellar liposomal vesicles in binary solute mixtures of cationic drug surfactant and zwitterionic phosphatidylcholine phospholipids. Binary drug surfactant-phospholipid mixtures with four different phospholipids with identical headgroups (two saturated phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC, 14:0) and 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC, 16:0), and two unsaturated lipids 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, 18:1) and 1,2-Dierucoyl-sn-Glycero-3-Phosphatidylcholine (DEPC, 22:1)) combined with two different tricyclic antidepressant drugs (amitriptyline hydrochloride (AMT) and doxepin hydrochloride (DXP)) have been investigated with small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). We observe a conspicuous impact of phospholipid tail structure on both micelle-to-vesicle transition point and vesicle size. In particular, ultrasmall unilamellar vesicles, i.e. with a diameter less than 20 nm, were observed in several samples with the two unsaturated phospholipids DOPC and DEPC, but not in any samples with the saturated phospholipids DMPC and DPPC. The smallest vesicles observed in DOPC and DEPC mixtures were smaller than 18 nm in diameter. In contrast, the smallest vesicles observed in DMPC mixtures were about 30 nm in diameter and always larger than 100 nm in DPPC mixtures. The ultrasmall vesicles showed exceptional colloidal stability. Moreover, bilayer vesicles predominated over micelles in a much wider range of concentrations for DOPC and DEPC mixtures as a result of having a smaller phospholipid mole fraction in the aggregates at the micelle-to-vesicle transition. Our results have been theoretically rationalized by combining solution thermodynamics with bending elasticity theory.

Small-angle X-ray and neutron scattering applied to lipid-based nanoparticles: Recent advancements across different length scales

Lipid-based nanoparticles (LNPs), ranging from nanovesicles to non-lamellar assemblies, have gained significant attention in recent years, as versatile carriers for delivering drugs, vaccines, and nutrients. Small-angle scattering methods, employing X-rays (SAXS) or neutrons (SANS), represent unique tools to unveil structure, dynamics, and interactions of such particles on different length scales, spanning from the nano to the molecular scale. This review explores the state-of-the-art on scattering methods applied to unveil the structure of lipid-based nanoparticles and their interactions with drugs and bioactive molecules, to inform their rational design and formulation for medical applications. We will focus on complementary information accessible with X-rays or neutrons, ranging from insights on the structure and colloidal processes at a nanoscale level (SAXS) to details on the lipid organization and molecular interactions of LNPs (SANS). In addition, we will review new opportunities offered by Time-resolved (TR)-SAXS and -SANS for the investigation of dynamic processes involving LNPs. These span from real-time monitoring of LNPs structural evolution in response to endogenous or external stimuli (TR-SANS), to the investigation of the kinetics of lipid diffusion and exchange upon interaction with biomolecules (TR-SANS). Finally, we will spotlight novel combinations of SAXS and SANS with complementary on-line techniques, recently enabled at Large Scale Facilities for X-rays and neutrons. This emerging technology enables synchronized multi-method investigation, offering exciting opportunities for the simultaneous characterization of the structure and chemical or mechanical properties of LNPs.

Core-Labeled Reverse Micelle-Based Supramolecular Solvents for Assisted Quick and Sensitive Determination of Amitriptyline in Wastewater

In recent years, the issue of pharmaceutical contaminants in water bodies has emerged as a significant environmental concern owing to the potential negative impacts on both aquatic ecosystems and human health. Consequently, the development of efficient and eco-friendly methods for their determination and removal is of paramount importance. In this context, the development of a surfactant ensemble sensor has been explored for hard-to-sense amphiphilic drug, i.e., amitriptyline. Herein, a pyrene-based amphiphile chemoreceptor was synthesized and characterized through various spectroscopic techniques such as 1H, 13C NMR, single-crystal XRD, FTIR, and ES-mass spectrometry. Then, dodecanoic acid (DA) and a pyrene-based receptor in a THF/water solvent system were used to generate reverse micelle-based self-aggregates of SUPRAS (SUPRAmolecular Solvent). The structural aspects, such as morphology and size, along with the stability of the SUPRAS aggregates were unfolded through spectroscopic and microscopic insights. The present investigation describes a synergistic approach that combines the unique properties of premicellar concentration of supramolecular solvent with the promising potential of pyrene-based receptor for enhanced amitriptyline extraction with simultaneous determination from water (LOD = 12 nM). To evaluate the effectiveness of the developed aggregates in real-world scenarios, experiments were conducted to determine the sensing efficiency among various pharmaceutical pollutants commonly found in water sources. The results reveal that the synergistic nanoensemble exhibits remarkable sensing ability, toward the amitriptyline (AMT) drug outperforming conventional methods.