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Peptides that interact with the cell membrane by disrupting it, by passing through it, or by residing at the membrane interface are known as membrane active peptides. Arginine (Arg or R)- and lysine (Lys or K)-rich cationic peptides are known to have antimicrobial activity, since cationic residues attract the peptide to the anionic bacterial membrane [1]. Arg-rich peptides are more prevalent in natural occurring antimicrobial peptides than Lys, implying that guanidinium group in Arg interacts in different way with biological membranes than the amine group in Lys [2, 3]. As antimicrobial peptides (AMP) have potential application as antibiotics, a better understanding of peptide-lipid interaction is essential to decipher their mechanism of action [4]. In order to get more detailed insight into the interaction of cationic peptides RRRRRFF and KKKKKFF, synthesized by solid phase synthesis, and lipid bilayers prepared from anionic 2-dipalmitoyl-sn- glycero-3-phosphatidylserine (DPPS) lipid and zwitterionic 1, 2- dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), we performed a calorimetric and spectroscopic study. For the purpose of determining the impact of peptides on thermotropic properties lipid bilayers, UV-Vis spectroscopy and differential scanning calorimetry (DSC) have been used, and for molecular- level details of their interaction, FTIR spectroscopy has been used.

Liposomes are lipid-based spherical structures that are, due to lipid amphiphilic character, arranged as bilayers with lipid hydrophobic tails oriented towards each other and a hydrophilic head towards aqueous surroundings. Because of their nontoxicity and biodegradability they represent powerful and efficient delivery drug systems. Nanoscience is the study of structures and molecules on the scales of nanometers ranging between 1 and 100 nm and represents an expanding and prominent research area. Metal nanoparticles (NPs), particularly those made of gold (Au NPs), attract great interest due to their stability, biocompatibility and unique catalytic activity. The interaction of Au NPs and liposomes came into research focus due to their diverse purpose in application, especially in nano- and biotechnology. Up to now, the understanding the interaction of liposomes and gold nanoparticles has gained great importance due to the possibilities that their combination can be used as potential drug delivery systems. [3] Here, we examined the influence of Au NPS aggregates on thermotropic properties of liposomes prepared from 1, 2-dipalmitoyl-snglycero-3-phosphocholine (DPPC). In order to reach this goal, our experimental work included synthesis of Au NPs, surface enhanced Raman scattering (SERS) measurement (Fig. 1a), confocal microscope imaging (Fig. 1b), temperature-dependent UV-Vis spectroscopy and differential scanning calorimetry (DSC).

Although asymmetric liposomes are nowadays considered the most suitable representatives of plasma membranes, their rather challenging preparation accompanied by the use of limiting combinations of lipids, is further complicated by their far from straightforward characterization. [1] One of the indispensable techniques in confirming the asymmetric distribution of exclusively phosphatidylcholine (PC) lipids is 1H NMR spectroscopy, which, in the presence of lanthanide ions such as Pr3+, can distinguish the protons of choline group (−N(CH3)3+) located in the inner or outer membrane leaflet (Figure 1).[2] With the aim of identifying PC lipid molecules in a certain leaflet of asymmetric liposomes, we prepared them from 1, 2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) and 1, 2-dipalmitoyl-sn- glycero-3-phosphoserine (DPPS), while the response of −N(CH3)3+ group was characterized with 1H NMR and for the first time by FTIR spectroscopy.

Phospholipid molecules present an essential part of biomembranes. Phosphatidylserine (PS) is the major anionic phospholipid present in eukaryotic membranes located on the cytosolic leaflet. One of its primary functions seems to be to impart a negative charge to the inner surface of the membrane lipid bilayer [1] which is required for the binding and activation of various peripheral membrane proteins [2]. The most abundant phospholipid in eukaryotic membranes, zwitterionic phosphatidylcholine (PC), can be distributed in both, inner and outer, membrane leaflets [3]. Lipid-constituted membranes undergo phase transitions, which in addition to temperature, pressure, and pH also depend on the chemical potentials of ions [4]. In this work we are focused on monitoring thermal properties of lipid bilayers constituted from 1, 2dipalmitoyl-sn- glycero-3-phosphatidylserine (DPPS) and 1, 2- dipalmitoyl-sn-glycero-3phosphatidylcholine (DPPC) in the presence of guanidinium (Gdm+) and ammonium (NH4+) cations which is manifested in a change in melting temperature (Tm). Using FT-IR spectroscopy, UV-Vis spectrophotometry, and differential scanning calorimetry (DSC) our goal is to understand how these cations affects thermal properties of DPPS and DPPC lipid membranes. All experimental results are supported by the computational study.

Understanding the structure and function of inherently asymmetric eukaryotic plasma membranes is almost inevitably preceded by the research into the structural and dynamic features of single- lipid symmetric membranes [1]. Among the latter, the most common lipid membranes are those built from zwitterionic phosphatidylcholine (PC) lipids present in both membrane leaflets, while those made from the major anionic phosphatidylserine (PS) lipid dominantly found in the inner membrane leaflet are significantly less common [2]. Apart from studies focusing on multilamellar liposomes (MLV) made from 1, 2-dipalmitoyl-sn-glycero- 3phospho-L-serine (DPPS) [3], the studies of corresponding unilamellar liposomes (LUV) are extremely rare. With the aim of shedding the light on the structure and properties of LUVs made of DPPS lipids, we present calorimetric, spectroscopic and MD simulation study of DPPS in the form of LUV in a phosphate buffer (pH = 7.4), with the corresponding MLV examined as a reference. Melting of LUV in a wide temperature range (50-59 °C), associated with rather high uncertainty data level emerged from temperature- dependent UV/Vis spectra (Fig. 1) is presumably related with LUV instability and/or fluctuation of structural features on LUV surface. The signatures of carbonyl backbone obtained from FTIR data support the existence of highly curved surface of LUV, the phenomenon of which is not observed in MLV, whereas MD data unravel the contribution of interlamellar water on the surface features in MLV.

Brain SM, found in high concentrations in myelin, is a mixture of SM molecules with different lengths of hydrocarbon chains, which makes its characterization challenging. In addition, the effect of changing acyl chain length on the physical behavior of SM remains poorly understood.1By using the fluorescent probe Laurdan (L) for fluorescence measurements, its response and influence on thermal changes in the SM lipid bilayer will be observed. Besides using fluorescence spectroscopy, the analysis of thermotropic behavior of brain SM multilamellar liposomes, also includes differential scanning calorimetry (DSC) and temperature-dependent UV/Vis spectroscopy with the addition of using appropriate chemometric tools.

Phospholipid molecules present an essential part of biomembranes. Phosphatidylserine (PS) is the major anionic phospholipid present in eukaryotic membranes located on the cytosolic leaflet. One of its primary functions seems to be to impart a negative charge to the inner surface of the membrane lipid bilayer [1] which is required for the binding and activation of various peripheral membrane proteins [2]. Lipid-constitued membranes undergo phase transitions, which in addition to temperature, pressure, and pH also depend on the chemical potentials of ions [3]. In this work we are focused on monitoring thermal properties of lipid membranes constituted from 1, 2-dipalmitoyl- snglycero-3-phosphatidylserine (DPPS) in the presence of guanidinium (Gdm+ ) and ammonium (NH4 + ) cations which is manifested in a change in melting temperature (Tm). Using FT-IR spectroscopy, UV-Vis spectrophotometry, and differential scanning calorimetry (DSC) our goal is to understand how thesecations affects thermal properties of DPPS lipid membranes. All experimental results are supported by the computational study.

Biological membranes have a complex composition and consist of hundreds of different lipids, asymmetrically distributed between the inner and outer bilayer leaflets. A lipid of special interest in eukaryotic membranes is the negatively charged phosphatidylserine (PS), located on cytosolic leaflet.1 One of its primary functions seems to be to impart a negative charge to the inner surface of the membrane lipid bilayer which is required for the binding and activation of various peripheral membrane proteins.2 Liposomes (lipid vesicles) are suspensions of membrane lipids in which a lipid bilayer surrounds an aqueous lumen and they serve as model system for cell membrane.3 Commonly used phosphatidiylserine-constituted lipid membranes are multilamellar liposomes (MLV) while unilamellar liposomes (LUV) are more realistic model membrane system, not researched enough because of instability. The liposomes prepared in this experiment form as MLV and LUV. In order to examine their thermotropic properties we preformed calorimetric and spectroscopic study of both, MLV and LUV, constituted from 2-dipalmitoyl-sn- glycero-3phosphatidylserine (DPPS).

The biological membranes are multicomponent systems with two compositionally specific leaflets. Due to the extremely complex structure, their characterization is often performed on simpler models, which are dominated by membranes made only of lipids, such as sphingomyelin (SM). [1] With the main phase transition temperatures in the range of 30- 45 °C, depending on the length of hydrophobic chains, SM might have the potential to introduce lateral heterogeneity and immutability in the membrane plane. The role of SM in biomembranes is believed to participate in the formation of a phase domain structure, although there is no agreement about the molecular basis of this domain structure. Since they possess several hydrogen bond-accepting and -donating groups at the polar/non-polar interface, hydrogen bonding seems particularly likely in the case of sphingomyelin. Using the brain SM, which is a mixture of SM lipids with different lengths of hydrophobic chains, we examined the effect of buffers of different pH values on hydrogen bond network with calorimetric and spectroscopic techniques. The analysis of the brain SM multilamellar liposomes with FTIR ATR and fluorescence spectroscopy, UV/Vis spectrophotometry and DSC calorimetry will try to clarify influence of different pH on SM structural domains.