[Show abstract][Hide abstract] ABSTRACT: Although monoacylglycerol monolayers have been used as highly informative systems, so far general information about their phase behavior and especially that of 1-monostearoyl-rac-glycerol monolayers has been missing. Complemented by the characteristics of the p-A isotherms and the mesoscopic domain topography, the present work focused on Grazing incidence X-ray diffraction (GIXD) measurements of 1-monostearoyl-rac-glycerol monolayers in the accessible temperature and surface pressure range to construct the phase diagram on the basis of reliable two-dimensional lattice structures. Examples for the mesoscopic topography of regularly and irregularly shaped domains obtainable in the first-order main phase transition region at temperatures T > 30°C are presented and discussed on the basis of line tension and geometric considerations. The GIXD results obtained over large pressure interval at 5, 10, 15 and 20 °C indicate impressively that also in the racemic 1-monostearoyl-rac-glycerol monolayer symmetry breaking occurs at low temperatures in a small pressure region where an oblique intermediate (Obl) phase between the NN and NNN tilted orthorhombic phases occurs. The temperature effect on the phase behavior of the 1-monostearoyl-rac-glycerol monolayers is demonstrated by the surface pressure - temperature diagram.
The Journal of Physical Chemistry C 04/2015; 119(18):150414210803000. DOI:10.1021/acs.jpcc.5b01766 · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A series of long-tail alkyl ethanolamine analogs containing amide-, urea-, and thiourea moieties was synthesized and the behavior of the corresponding monolayers was assessed on the Langmuir-Pockels trough combined with grazing incidence X-ray diffraction experiments and complemented by computer simulations. All compounds form stable monolayers at the soft air/water interface. The phase behavior is dominated by strong intermolecular headgroup hydrogen bond networks. While the amide analog forms well-defined monolayer structures, the stronger hydrogen bonds in the urea analogs lead to the formation of small three-dimensional crystallites already during spreading due to concentration fluctuations. The hydrogen bonds in the thiourea case form a two-dimensional network, which ruptures temporarily during compression and is recovered in a self-healing process, while in the urea clusters the hydrogen bonds form a more planar framework with gliding planes keeping the structure intact during compression. Because the thiourea analogs are able to self-heal after rupture, such compounds could have interesting properties as tight, ordered, and self-healing monolayers.
[Show abstract][Hide abstract] ABSTRACT: A series of 1,3-diamido phosphocholines was synthesized, and their potential to form stable bilayers was investigated. Large and giant unilamellar vesicles produced from these new lipids form a wide variety of faceted liposomes. Factors such as cooling rates and the careful choice of the liposome preparation method influence the formation of facets. Interdigitation was hypothesized as a main factor for the stabilization of facets and effectively monitored by small-angle X-ray scattering measurements.
[Show abstract][Hide abstract] ABSTRACT: The aggregation behavior of various zwitterionic helper phospholipids, such as DOPE, DOPC and DPPC, in combination with two new cationic lipids, namely TH4 and OH4 (second generation of malonic acid diamides) in different molar ratios was studied with regard to their physical-chemical properties. Additionally, lipoplexes prepared from these lipid mixtures were characterized with respect to the transfection efficacy using an EGFP-assay. The lipid mixtures with the fluid cationic lipid OH4 and DOPE have shown comparable transfection efficiency with Lipofectamine 2000®. Furthermore, this report demonstrates the huge influence of the helper lipid on the transfection efficiency. Thereby, alkyl chain fluidity, lipid miscibility and charge density have an important influence on an efficient gene transfer.Practical applications: Although lipofection is a topic of gene therapy since 1989, the optimal finding of an effective lipid system with new cationic lipids is still a process of trial and error. There is much unknown understanding the process of lipoplex formation as well as the release of the genetic cargo. Aim of the presented work is to find physical-chemical parameters which are connected with an effective gene transfer.
European Journal of Lipid Science and Technology 09/2014; 116(9):1184-1194. DOI:10.1002/ejlt.201300405 · 2.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Physico-chemical processes at air/liquid interfaces are of paramount importance in nature. The Langmuir
technique offers the possibility of forming a well-defined monolayer of amphiphilic molecules under study at
the air/liquid interface,with a unique control of the area permolecule and other experimental conditions. Despite being a traditional technique in Colloid and Interface science, there is an ever growing interest in Langmuir studies. Herein, recent developing fields of research currently taking advantage of the Langmuir technique are reviewed, comprising the interfacial structure of: water, biomolecules and inorganic/organic hybrids. The good state of the Langmuir technique at present and the foreseeable increase of its usage are discussed.
Current Opinion in Colloid & Interface Science 06/2014; 19(3):176–182. DOI:10.1016/j.cocis.2013.07.006 · 6.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Carbon nanostructures that feature two-dimensional extended nanosheets are important components for technological applications such as high-performance composites, lithium-ion storage, photovoltaics and nanoelectronics. Chemical functionalization would render such structures better processable and more suited for tailored applications, but typically this is precluded by the high temperatures needed to prepare the nanosheets. Here, we report direct access to functional carbon nanosheets of uniform thickness at room temperature. We used amphiphiles that contain hexayne segments as metastable carbon precursors and self-assembled these into ordered monolayers at the air/water interface. Subsequent carbonization by ultraviolet irradiation in ambient conditions resulted in the quantitative carbonization of the hexayne sublayer. Carbon nanosheets prepared in this way retained their surface functionalization and featured an sp(2)-rich amorphous carbon structure comparable to that usually obtained on annealing above 800 °C. Moreover, they exhibited a molecularly defined thickness of 1.9 nm, were mechanically self-supporting over several micrometres and had macroscopic lateral dimensions on the order of centimetres.
[Show abstract][Hide abstract] ABSTRACT: Gibbs or Langmuir monolayers formed at the soft air/liquid interface are easy to handle and versatile model systems for material and life sciences. The phase state of the monolayers can be modified by lateral compression of the film while the layer structural changes are monitored by highly sensitive surface characterization techniques. The use of high brilliant synchrotron light sources for X-ray experiments is essential for the monolayer research. The present review highlights the recent achievements recorded in the monolayer field with a special emphasis on different synchrotron based X-ray characterizing methods as: grazing incidence X-ray diffraction, X-ray reflectivity and total reflection X-ray fluorescence. Some examples of single-chain surfactants, special sugar lipids, and semifluorinated compounds are given. Additionally, thin layers formed by peptides, polymers or nanoparticles are highlighted.
Current Opinion in Colloid & Interface Science 06/2014; 19(3). DOI:10.1016/j.cocis.2014.01.004 · 6.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of highly brilliant synchrotron light sources in the middle of the 1980s for X-ray diffraction has revolutionized the research of condensed monolayers. Since then, monolayers gained popularity as convenient quasi two-dimensional model systems widely used in biophysics and material science. This review focuses on structures observed in one-component phospholipid monolayers used as simplified two-dimensional models of biological membranes. In a monolayer system the phase transitions can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction. Competing interactions between the different parts of the molecule are responsible for the different monolayer structures. These forces can be modified by chemical variations of the hydrophobic chain region, of the hydrophilic head group region or of the interfacial region between chains and head groups. Modifications of monolayer structures triggered by changes of the chemical structure of double-chain phospholipids are highlighted in this paper.
Advances in Colloid and Interface Science 05/2014; 207(1). DOI:10.1016/j.cis.2014.01.005 · 8.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Glycosylphosphatidylinositols (GPIs) are often attributed with the ability to associate with the organized membrane microdomains. GPI fragment 1 forms a highly ordered subgel-phase structure characterized by ordering of both headgroups and alkyl chains in thin layers. While investigating the driving forces behind the formation of these ordered monolayers, we have studied polymorphism of 1 under different conditions employing surface-sensitive X-ray diffraction methods. Three distinct polymorphs of 1 (I, II, and III) were identified and characterized by grazing incidence X-ray diffraction. Polymorphs II (a condensed monolayer structure) and III (highly ordered subgel phase) coexist on an 8 M urea solution subphase allowing for a detailed thermodynamic and kinetic analysis of the processes leading to the formation of these polymorphs. They are enantiotropic and can be directly interconverted by changes in temperature or lateral surface pressure. As a consequence, polymorph III nuclei of critical size (or larger) could be formed by density fluctuations in a multicomponent system, and they could continue to exist for a period of time even under conditions that would normally not allow for the nucleation of polymorph III. The processes described here could also lead to the formation of patches of highly ordered structures in a disordered environment of a cell membrane suggesting that GPIs may play a role in the formation of such domains.
[Show abstract][Hide abstract] ABSTRACT: Glycosylphosphatidylinositols (GPIs), natural complex glycolipids essential for a range of biological functions, are poorly understood with regard to their interactions and arrangements in cellular membranes. To evaluate the role of the head group in the structure formation in 2D model membranes (monolayers formed at the soft air/liquid interface), we employed the highly surface sensitive grazing incidence X-ray diffraction technique to investigate three GPI-fragments bearing the same hydrophobic part but different head groups. Condensed monolayers of simple GPI fragments are defined only by ordered alkyl chains. The monolayers of more complex fragments are additionally characterized by highly ordered head groups. Due to the strong H-bond network formed by the head groups, GPI-fragment both segregates and induces order into a model membrane phospholipid (POPC) that mimics the liquid-disordered phase of cell membranes. Here, we show that the strong van der Waals interactions between hydrophobic chains overcome the head group interactions and dominate the structure formation in mixtures of GPI-fragment with lipids that form liquid-condensed phases. This behaviour can be linked to the GPIs affinity for the lipid rafts.
[Show abstract][Hide abstract] ABSTRACT: Two novel micelle-forming amino-functionalized lipids (OT6 and TT6) bearing two alkyl chains connected to a large positively charged hexavalent head group suitable as polynucleotide transferring agents have been characterized. Both lipids combine an effective transfection rate and good viability results in cell assay (A549-cells) with an easy and reproducible production of micelle dispersions. The cmc-values of both lipids have been determined by two different methods, namely, isothermal titration calorimetry (ITC) measurements and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence experiments. In addition, the lipid dispersions were studied as a function of the temperature using differential scanning calorimetry (DSC), dynamic light scattering (DLS), FT-IR-spectroscopy, and cryo-transmission electron microscopy (cryo-TEM). The OT6 and TT6 micelles effectively complex DNA as determined by ITC and DSC measurements. Additionally, DLS and zeta(ζ)-potential measurements were performed to determine lipoplex formulations that exhibit colloidal stability. Finally, the structures of OT6/DNA-complexes were investigated by means of X-ray scattering and TEM.
[Show abstract][Hide abstract] ABSTRACT: We introduce a novel class of membrane active peptidomimetics, the amphiphilic cationic β(3R3)-peptides, and evaluate their potential as antimicrobial agents. The design criteria, the building block and oligomer synthesis, as well as a detailed structure activity relationship (SAR) study are reported. Specifically, infrared reflection absorption spectroscopy (IRRAS) was employed to investigate structural features of amphiphilic cationic β(3R3)-peptide sequences at the hydrophobic/hydrophilic air/liquid interface. Furthermore, Langmuir monolayers of anionic and zwitterionic phospholipids have been used to model the interactions of amphiphilic cationic β(3R3)-peptides with prokaryotic and eukaryotic cellular membranes in order to predict their membrane selectivity and elucidate their mechanism of action. Lastly, antimicrobial activity was tested against Gram-positive M. luteus and S. aureus as well as against Gram-negative E. coli and P. aeruginosa bacteria along with testing hemolytic activity and cytotoxicity. We found that amphiphilic cationic β(3R3)-peptide sequences combine high and selective antimicrobial activity with exceptionally low cytotoxicity in comparison to values reported in the literature. Overall, this study provides further insights into the SAR of antimicrobial peptides and peptidomimetics and indicates that amphiphilic cationic β(3R3)-peptides are strong candidates for further development as antimicrobial agents with high therapeutic index.
[Show abstract][Hide abstract] ABSTRACT: The use of new sophisticated and highly surface sensitive techniques as synchrotron based X-ray scattering techniques and in-house infrared reflection absorption spectroscopy (IRRAS) has revolutionized the monolayer research. Not only the determination of monolayer structures but also interactions between amphiphilic monolayers at the soft air/liquid interface and molecules dissolved in the subphase are important for many areas in material and life sciences. Monolayers are convenient quasi-two-dimensional model systems. This review focuses on interactions between amphiphilic molecules in binary and ternary mixtures as well as on interfacial interactions with interesting biomolecules dissolved in the subphase. The phase state of monolayers can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction or IRRAS. The interactions can be indirectly determined by the observed structure changes. Additionally, the yield of enzymatic reaction can be quantitatively determined, secondary structures of peptides and proteins can be measured and compared with those observed in bulk. In this way, the influence of a confinement on the structural properties of biomolecules can be determined. The adsorption of DNA can be quantified as well as the competing adsorption of ions at charged interfaces. The influence of modified nanoparticles on model membranes can be clearly determined. In this review, the relevance and utility of Langmuir monolayers as suitable models to study physical and chemical interactions at membrane surfaces are clearly demonstrated.
Advances in Colloid and Interface Science 02/2014; 208. DOI:10.1016/j.cis.2014.02.013 · 8.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The flexibility of biomembranes is based on the physical-chemical properties of their main components - glycerophospholipids. The structure of these modular amphiphilic molecules can be modified through organic synthesis making it possible to study specific physical-chemical effects in detail. In particular, the roles of the hydrophobic tails of the phospholipids and their hydrophobic/hydrophilic interfacial backbone on the phase behaviour are highlighted. The spatial orientation of the glycerol backbone changes from sn-1,2 to sn-1,3 phospholipids leading to an increase of the in-plane area of the molecule. The larger distance between the hydrophobic tails can lead to membrane leaflet interdigitation. The introduction of methyl side groups in the hydrophobic tails increases the fluidity of the bilayer. Depending on the position of the methyl branches partial interdigitation is observed. In the case of bolaamphiphiles, methyl side groups have a similar effect on the fluidity, but interdigitation cannot occur.
Current Opinion in Colloid & Interface Science 02/2014; 19(1). DOI:10.1016/j.cocis.2014.01.003 · 6.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recently, photosensitive surfactants have re-attracted considerable attention. It has been shown that their association with oppositely charged biologically important polyelectrolytes, such as DNA or microgels, can be efficiently manipulated simply by light exposure. In this article, we investigate the self-assembly of photosensitive surfactants as well as their interactions with DNA by calorimetric and spectroscopic methods. Critical micelle concentration (CMC), standard micellization enthalpy, entropy, and Gibbs energy were determined in different conditions (ionic strengths and temperatures) for a series of cationic surfactants with an azobenzene group in their tail. It is shown, that aggregation forces of photosensitive units play an important role in the micellization giving the major contribution to the micellization enthalpy. The onset of the aggregation can be traced from shift of the absorption peak position in the UV-visible spectrum. Titration UV-visible spectroscopy is used as an alternative, simple, and sensitive approach to estimate CMC. The titration UV-visible spectroscopy was also employed to investigate interactions (CAC: critical aggregation concentration, precipitation, and colloidal stabilization) in the DNA-surfactant complex.
The Journal of Chemical Physics 01/2014; 140(4):044906. DOI:10.1063/1.4862678 · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Noncovalent molecular interactions, such as hydrogen bonding and van der Waals forces, play an important role in self-assembling to supramolecular structures. To study these forces, we chose monolayers at the air/water interface to limit the possible arrangements of the interacting molecules. The phase behavior and molecular packing of the phenols 1-(4-hydroxyphenyl)-octadecane (5a), 1-(3,4-dihydroxyphenyl)-octadecane (6), and 1-(2,3,4-trihydroxyphenyl)-octadecane (3) and their methyl ethers in monolayers at the air/water interface have been examined by π/A-isotherms, Brewster angle microscopy (BAM), grazing incidence X-ray diffraction (GIXD) measurements and density functional theory (DFT)-calculations. The aryl methyl ethers are synthesized by Friedel-Crafts acylation of methoxybenzenes and subsequent hydrogenation of the aryl ketones. In the π/A-isotherms and in BAM the phenols show patches of the solid condensed phase at large molecular areas and the monolayers collapse at high pressures. Furthermore, the dimensions of the unit cell obtained by GIXD measurements are compatible with an arrangement of the phenyl rings that allows one aryl ring to interact with four adjacent phenyl rings in an edge-to-face arrangement, which leads to a significant binding energy. The experimental data are in good agreement with DFT-calculations of 2D-crystalline benzene and p-cresol arrangements. The enhanced monolayer stability of phenol 5a can be explained by hydrogen bonds of the hydroxyl group with water, van der Waals forces between the alkyl chains and aryl-aryl interactions.