The Fluid Phase′s Dynamics of Liposomes

Mehaboobi Khan^*
*Correspondence: Mehaboobi Khan, Department of Physics, Louisiana State University, Baton Rouge, LA, USA, Email:

Introduction

A bilayer made of amphiphilic phospholipids surrounds an aqueous core inside of liposomes, which are spherical vesicles. The majority of the phospholipids in the cell membrane make up the membrane. Both cellular barriers and selective gateways benefit from the cell membrane's physical features. It shields the cell membranes inside from a potentially hazardous environment. We can investigate lipid membranes at the molecular and atomic levels because they serve as model systems for two-dimensional surfaces in a three-dimensional environment [1]. They have particular viscoelastic characteristics that are vital to the living cell's biological operation. Understanding the basic principles of self-organization of a system with so many components that produces complex interactions, structures, and dynamics is a formidable challenge.

Description

Lipids aid in cell division and reproduction, although the underlying physical theories and procedures remain unresolved. The effects of hydrostatic pressure, lipid phase, and additives like cholesterol content have been demonstrated to have an impact on several underappreciated phenomena, such as lipid rotation. Another dynamic process that takes place over comparatively longer time periods is lipid flip-flop motion. It is essential for preserving the lipid content of the membrane's inner and outer monolayers. The cornerstone for comprehending the development of life is found in each of these processes. The significance of vesicles and membranes in biotechnological applications, however, is undisputed [2,3]. Examples include vesicles employed for medication delivery payload or the incorporation of membranes with electronic or optoelectronic devices to create biosensors.

From SANS, a slight increase in the bilayer thickness along with an increase in the radius of gyration, R_g, of the liposome was observed. SAXS reveals more prominent effects over the entire lipid thickness, where polar region of the aescin interacts with the lipid headgroup in the L_b phase at 10°C. In the L_a phase at 40°C, insertion of the aescin deep into the bilayer thickness was observed. A decrease in k_h in the L_b phase, whereas an increase in k_h in the L_a phase, with increasing aescin content was reported. It was concluded that the H-bond formation between the hydroxy group of aescin sugar counterpart with the carbonyl and negatively charged phosphate groups of h-DMPC causes a reduction of k_h in the L_b phase. In the L_a phase, the incorporation of large triterpenic backbone of aescin in the bilayer causes an increase in rigidity [4].

We go over the information that is currently known on the dynamics and morphology of phospholipids organised into liposomes. Understanding the important role of lipids in maintaining life in living beings requires key information from neutron scattering, nuclear magnetic resonance (NMR), and other techniques. We focus on the dynamics of the biologically significant fluid phase across the time scale of picoseconds to seconds. This includes a discussion of the centre of mass diffusion of liposomes, membrane fluctuations, and the lateral, rotational, and flip-flop motions of the lipids. We underline the dynamics' sensitivity to interactions with a range of biologically significant chemicals, including cholesterol. Using QENS, it was determined how additives like cholesterol, myristic acid, farnesol, and sodium glycocholate affected the lateral dynamics of h-DMPC. Although it was shown that h-lipid DMPC's lateral mobility decreased as its cholesterol level increased, the other additions had little to no effect on the mobility of lipids. It was determined that cholesterol has an impact on the tail regime's packing density and results in a reduction in free volume, which in turn reduces overall lipid mobility in plane. Observations of increased membrane rigidity may possibly be linked to tighter lipid packing. Melittin stiffens the membrane more effectively than alamethicin at reducing lateral diffusion, according to a thorough analysis of the effects of the antimicrobial peptides alamethicin and melittin on the dynamics of h-DMPC by QENS in the L_a phase. At T=6.85 C and 19.85 C, respectively, both in the L_b gel phase, the lateral diffusion did not change in response to the addition of alamethicin. On the other hand, the addition of melittin causes a rise in Dlat. Cholesterol increases the liposome saturation, which prevents further incorporation of melittin into the bilayer, while simultaneously decreasing the mobility of h-DMPC and melittin's binding affinity to the bilayer.

Lipid rotational motion refers to a variety of potential mechanisms. When lipids are viewed as circular, cylinder-shaped objects, I rotations along their symmetry axes, which are presumptively parallel to the bilayer plane (axial rotation), may take place. Although unbound lipids are likewise capable of rotating about their longitudinal axes, the bilayer confines this action to a small region. Anisotropic diffusion is a phrase that includes axial rotation and wobbling. Electron paramagnetic resonance is a direct technique for monitoring the flip-flop motion in fluid phase vesicles (EPR). Detergents can speed up flip dynamics in fluorescent-labeled erythrocytes, according to fluorescence spectroscopy. Using fluorescent or spin-labeled lipids, it has been discovered, does not correctly depict the native lipid flip-flop dynamics. Therefore, it is crucial to investigate methods for obtaining flip-flop dynamics that cause no or little disruption to the lipid bilayer [5,6]. Fluorescence recovery during photobleaching is a crucial indicator of lateral diffusion (FRAP). The bilayer contains fluorescent molecules that have been bleached in one spot. The Brownian motion of the fluorescent molecules (lateral diffusion) is measured by recovering the fluorescence intensity. In these situations, organic fluorophores can be tracked using microscopes, often on a time and length range of ms to s and mm-mm, respectively.

Conclusion

This review focuses on the dynamics of the fluid phase, also known as the liquid crystalline phase or La phase, which is a biologically significant fluid phase. A specific melting transition temperature, Tm, separates it from the gel or Lb phase: The lipid tails' hydrocarbon chains are liquid-like, disorganised, and randomly aligned around their cylindrical symmetry axis in the fluid phase. The lipid membrane has a distinctive molecular structure that resembles both an elastic liquid-crystalline portion and a viscous component of a liquid. The mechanical characteristics of the membrane, such as bending rigidity and elasticity, which describe the spontaneous curvature of the bilayer, are related to the thermodynamics and the conformation of the lipid chain.

Acknowledgement

Not applicable

Conflict of Interest

There is no conflict of interest by authors.

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