Systematic Characterization of DMPC/DHPC Self-Assemblies and Their Phase Behaviors in Aqueous Solution

Abstract

Self-assemblies composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) form several kinds of structures, such as vesicle, micelle, and bicelle. Their morphological properties have been studied widely, but their interfacial membrane properties have not been adequately investigated. Herein, we report a systematic characterization of DMPC/DHPC assemblies at 20 °C. To investigate the phase behavior, optical density OD500, size (by dynamic light scattering), membrane fluidity 1/PDPH (using 1,6-diphenyl-1,3,5-hexatriene), and membrane polarity GP340 (using 6-dodecanoyl-N,N-dimethyl-2-naphthylamine) were measured as a function of molar ratio of DHPC (XDHPC). Based on structural properties (OD500 and size), large and small assemblies were categorized into Region (i) (XDHPC < 0.4) and Region (ii) (XDHPC ≥ 0.4), respectively. The DMPC/DHPC assemblies with 0.33 ≤ XDHPC ≤ 0.67 (Region (ii-1)) showed gel-phase-like interfacial membrane properties, whereas DHPC-rich assemblies (XDHPC ≥ 0.77) showed disordered membrane properties (Region (ii-2)). Considering the structural and interfacial membrane properties, the DMPC/DHPC assemblies in Regions (i), (ii-1), and (ii-2) can be determined to be vesicle, bicelle, and micelle, respectively.

Systematic Characterization of Nanostructured Lipid Carriers from Cetyl Palmitate/Caprylic Triglyceride/Tween 80 Mixtures in an Aqueous Environment

“…The membrane fluidity of the NLC was evaluated using the fluorescence polarization method as a previous study with a slight modification of the lipid/DPH ratio. ,,− , Four microliters of DPH solution (10 μM in ethanol) were added to the diluted NLC suspension in a molar ratio of lipid/DPH = 12,500/1. The total concentration of lipid ([CP] + [CaTG] + [T80]) and DPH was 5 mM and 0.4 μM, respectively.…”

“…The suspensions were then incubated for at least 2 h at 37 °C. The fluorescence spectrum of Laurdan was recorded with an excitation wavelength of 340 nm at emission wavelengths from 400 to 600 nm. ,,,,, According to the previous studies, the membrane polarity ( GP 340 ) at 25 °C was calculated using eq where I 440 and I 490 are emission intensities at 440 and 490 nm, respectively.…”

“…These probes are powerful tools to investigate the microscopic environment of the self-assembly system. , The systematic fluorescence-based analysis of membrane properties, based on membrane fluidity and polarity, has successfully provided insights into the phase behaviors and phase transition due to external stimuli. This method has been applied for lipid mixture systems such as phospholipid/sterol, fatty acid dispersions, gel-phase dispersion of oleic acid/1-oleoylglycerol, bicelle characterization, ,, and niosome . Although fluorescence analysis sometimes has little disadvantages of the fluorescent probe localization in the water environment, the results will be valuable to imagine the physical assembly state and molecular behavior of lipids in NLCs.…”

The Fluidization Effect of a Bilayer Membrane on a Fatty Acid Vesicle by a Detergent

“…The DPPC vesicle has an ordered phase, and the unsaturated chain of the DOPC molecule also lowers the bilayer membrane packing and promotes the formation of the disordered phase [16][17][18]. Laurdan is frequently used to determine the phase state of phospholipid vesicles, using the peak intensity ratio between 440 and 490 nm [6,18]. The relationship between X DOPC and the estimated A i /A ii ratio is shown in Figure 4b.…”

“…A bilayer membrane structured molecular assembly is expected to be used as functional membrane materials, for example, in drug carriers and cosmetic agents [1,2]. A bicelle, which consists of a long-chain lipid and a detergent, is an effective parent for functional membrane materials [3,4] because its bilayer membrane structure continuously forms the morphology, such as multilamellar vesicles, toroidal pore vesicles, a disk-like micelle, or a thread-like micelle, depending on its concentration and its composition ratio [5,6]. The morphological property of a bicelle has also been used in the crystallization of membrane proteins [7,8].…”