Donor–acceptor copolymers based on phenanthrene as electron‐donating unit: Synthesis and photovoltaic performances

Using 9,10‐bis(dodecyloxy)phenanthrene as electron‐donating unit and 4,7‐dithienyl‐5,6‐bis(dodecyloxy)benzothiadiazole, 4,7‐dithienyl‐5,6‐bis(octyloxy)benzoxadiazole, 5,8‐dithienyl‐2,3‐bis(para‐octyloxyphenyl)quinoxaline, and 5,8‐dithienyl‐2,3‐bis(meta‐octyloxyphenyl)quinoxaline as electron‐accepting unit, four D–A copolymers PPA‐DTBT , PPA‐DTBX , PPA‐ p ‐DTQ , and PPA‐ m ‐DTQ , respectively, were successfully synthesized as new polymeric donors for photovoltaic cells. All the alternating copolymers can show two absorption bands, both in solutions and thin films. The optical bandgaps of the polymers are quite close, which are between 1.93 and 2.00 eV. The HOMO and LUMO levels of the polymers are also comparable of ?5.52 ± 0.03 eV and ?3.57 ± 0.03 eV, respectively. Thus, using the dialkoxyphenanthrene as the D unit could afford D–A copolymers with deep‐lying HOMO levels, which would be an important factor to achieve high open‐circuit voltages (V_oc) in bulk‐heterojunction solar cells. With the copolymers as the donor and PC₇₁BM as the acceptor, the resulting solar cells could display good V_oc between 0.86 and 0.88 V. Among the four copolymers, PPA‐DTBT containing the dialkoxybenzothiadiazole unit showed the best power conversion efficiency of 3.03% because of its relatively higher hole mobility and better phase separation. The results suggest that dialkoxyphenanthrene is a valuable electron‐donating unit in the constructions of D–A copolymers for efficient solar cells with high V_oc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4966–4974     

Microtechnologies for membrane protein studies

Despite the rapid and enormous progress in biotechnologies, the biochemical analysis of membrane proteins is still a difficult task. The presence of the large hydrophobic region buried in the lipid bilayer membrane (transmembrane domain) makes it difficult to analyze membrane proteins in standard assays developed for water-soluble proteins. To handle membrane proteins, the lipid bilayer membrane may be used as a platform to sustain their functionalities. Relatively slow progress in developing micro total analysis systems (μTAS) for membrane protein analysis directly reflects the difficulty of handling lipid membranes, which is a common problem in bulk measurement technologies. Nonetheless, researchers are continuing to develop efficient and sensitive analytical microsystems for the study of membrane proteins. Here, we review the latest developments, which enable detection of events caused by membrane proteins, such as ion channel current, membrane transport, and receptor/ligand interaction, by utilizing microfabricated structures. High-throughput and highly sensitive detection systems for membrane proteins are now becoming a realistic goal. Although most of these systems are still in the early stages of development, we believe this field will become one of the most important applications of μTAS for pharmaceutical and clinical screenings as well as for basic biochemical research.     

Unusual fluorescence spectral response of 1-(4-N,N-dimethylaminophenylethynyl)pyrene towards the thermotropic phase change in lipid bilayer membranes

The applicability of 1-(4-N,N-dimethylaminophenylethynyl)pyrene (DMAPEPy), a pyrene derivative showing intramolecular charge transfer, as a prospective probe for lipid bilayer membranes has been evaluated. High sensitivity of DMAPEPy to solvent polarity and viscosity makes it to act both as a polarity-sensitive probe and as a fluorescence anisotropy probe. The molecule shows high partition efficiency towards bilayer membranes in both solid gel as well as in the liquid crystalline phases. The emission spectrum, quenching experiment and lifetime data suggest bimodal distribution of DMAPEPy in the bilayer. Using the solvent polarity scales the polarity parameters of the two locations in lipid bilayer have been estimated. In the bilayer environment it exhibits remarkable spectral changes with temperature. The thermotropic phase change of the bilayer is sensitively monitored by fluorescence intensity as well as fluorescence anisotropy parameters. DMAPEPy is also capable of sensing the changes induced by membrane modifiers like cholesterol.     

Liquid Ordered Phase of Binary Mixtures Containing Dipalmitoylphosphatidylcholine and Sterols

The effect of cholesterol, desmosterol, stigmasterol, sitosterol, ergosterol, and androsterol on the phase behavior of aqueous dispersions of dipalmitoylphosphatidylcholine (DPPC) was studied to understand the role of the side chain in the formation of ordered phases of the type observed in membrane rafts. Thermotropic changes in the structure of mixed dispersions and transition enthalpies were examined by synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The observations indicated that cholesterol was more efficient than phytosterols (stigmasterol and sitosterol) or ergosterol in its interaction with DPPC to form the liquid ordered phase (L_o). The L_o induced by cholesterol or desmosterol was stable over a wide temperature range, whereas, the liquid ordered phase containing phytosterols or ergosterol was profoundly dependent on temperature, which should be distinguished as L_oβ and L_oα, representing the phases below and above the main transition temperature. The characteristics in forming ordered structures of cholesterol and other sterols imply that the evolution may have selected cholesterol as the most efficient sterol for animals to form rafts in their cell membranes.     

Calorimetric study of the effects of 2,4-dichlorophenol on the thermotropic phase behavior of DPPC liposomes

The effect of 2,4-dichlorophenol (DCP) on the main transition and pretransition of fully hydrated (20 mass%) dipalmitoylphosphatidylcholine (DPPC) multilamellar liposomes has been studied by differential scanning calorimetry (DSC). It was observed that an increase in the molar ratio of DCP/DPPC (from 4·10^-5 up to 2·10^-2) causes progressive reductions in the temperature and enthalpy of the pretransition. The higher concentration of DCP eliminates the pretransition. The influence of DCP on the main transition in this molar ratio range is not drastic, but a decrease in temperature and in the enthalpy values was observed. In the molar ratio range (from 2·10^-1 up to 4·10^-1) the DSC scans show multiple main transition peaks instead of the characteristic single peak of the main transition. Above a DCP/DPPC molar ratio of 0.6 a new peak appears at 25°C having about the same transition enthalpy as the main transition of the pure system.This revised version was published online in November 2005 with corrections to the Cover Date.     

Di‐ and tri‐phenyltin chlorides transfer across a model lipid bilayer

A compound's ability to penetrate the plasma membrane of a cell is the critical parameter that determines its potential to become a biologically potent factor. A well‐known group of organotin compounds that exhibit toxic properties in relation to biological systems are phenyltins. There are as yet no studies that in a direct manner have established whether organotin compounds such as diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) diffuse, or not, through the lipid bilayer, although we know that at least some organotins absorb in both liposome and biological membranes. In this paper we present a series of experiments that show transfer of these compounds across the lipid membrane using the stopped‐flow technique. The results obtained demonstrate that DPhT and TPhT first adsorb onto the lipid bilayer surface, in a diffusion‐controlled manner and within a very short time (0.05 s), whereas the membrane crossing was observed to be on the order of a minute. The adsorption process was easily fitted with a single exponential for both the compounds studied, indicating a single process phenomenon. The longer time kinetics (characteristic of membrane crossing) showed a complex dependence on compound concentration and the presence of cholesterol in the membrane. On passing from the outer to the inner surface of the bilayer, organotins undergo desorption and enter the liposome interior, which has been shown in lipid monolayer desorption studies. In conclusion, it can be stated that amphiphilic DPhT and TPhT permeate the liposome membrane. Copyright © 2005 John Wiley & Sons, Ltd.     

Amphiphile bilayer films from DPPC: bilayer lipid membranes and Newton black films

Amphiphile bilayer films are obtained from 1,2 dipalmitoyl-glycero-3-phosphocholine (DPPC): bilayer lipid membranes (BLM) and Newton black films (NBF), through thinning of the respective thin liquid films, thus allowing for a very precise determination of the moment of their formation. Stability (or rupture) and formation of BLM and NBF are considered from a unified point of view with the microscopic theory of Kashchiev–Exerowa [J. Colloid Interface Sci., 77 (1980) 501–511], based on the formation of nanoscopic holes in them. BLM and NBF are obtained and studied with the microinterferometric method of Scheludko–Exerowa in its contemporary version. The equivalent thickness of both BLM (in benzene solution between two water phases with 0.1 M NaCl) and NBF in aqueous DPPC solution (in the presence of 0.1 M NaCl) is determined as being h_w = 7.0 nm for BLM and h_w = 7.8 nm for NBF. By means of the dependences: BLM lifetime versus DPPC concentration and probability for BLM formation versus DPPC concentration, it is established that there exist metastable BLM and stable NBF. The good fit between the experimental results of τ(C) dependence and theory in the case of BLM allow to determine the three constants: pre-exponential factor A = 1.5 × 10⁻³ s, related to the process kinetics; constant B = 20.2 ± 0.2, related to the specific hole energy γ = 1.7 × 10⁻¹¹ J/m and the equilibrium concentration C_e = 6 × 10⁻⁴ ± 7.2 × 10⁻⁶ m/l. The specific hole linear energy γ = 1.7 × 10⁻¹¹ J/m determined as well as the binding energy Q between first neighbor molecules in the bilayers Q = 1.48 × 10⁻¹⁹ J (36 kT) are lower than the ones determined for DPPC foam bilayer in gel state γ = 9.1 × 10⁻¹¹ J/m and Q = 55 kT. This means that interaction is weaker in the case of BLM. The critical concentration C_c at which bilayer formation starts is: for BLM C_c = 30 μg/ml and for NBF C_c = 70 μg/ml. This concentration characterizes quantitatively the formation of the amphiphile bilayer and is a very useful parameter that can be used for various purposes.     

Pseudocapacitive Properties of Isostructural Oxides Sr2LaBMnO7 (B=Co,Fe)

Pseudocapacitors promise to fill the gap between traditional capacitors and batteries by delivering reasonable energy densities and power densities. In this work, pseudocapacitive charge storage properties are demonstrated for two isostructural oxides, Sr₂LaFeMnO₇ and Sr₂LaCoMnO₇. These materials comprise spatially separated bilayer stacks of corner sharing BO₆ units (B=Fe, Co or Mn). The spaces between stacks accommodate the lanthanum and strontium ions, and the remaining empty spaces are available for oxide ion intercalation, leading to pseudocapacitive charge storage. Iodometric titrations indicate that these materials do not have oxygen-vacancies. Therefore, the oxide ion intercalation becomes possible due to their structural features and the availability of interstitial sites between the octahedral stacks. Electrochemical studies reveal that both materials show promising energy density and power density values. Further experiments through fabrication of a symmetric two-electrode cell indicate that these materials retain their pseudocapacitive performance over hundreds of galvanostatic charge-discharge cycles, with little degradation even after 1000 cycles.     

Interaction of Polystyrene Nanoparticles with Supported Lipid Bilayers: Impact of Nanoparticle Size and Protein Corona

Polystyrene is one of the most widely used plastics. This article reports on the interaction of 50 and 210 nm polystyrene nanoparticles (PSNPs) with human serum albumin (HSA) and transferrin (Tf), as well as their effect on supported lipid bilayers (SLBs), using experimental and theoretical approaches. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements show that the increase in diameter for the PSNP-protein bioconjugates depends on nanoparticle size and type of proteins. The circular dichroism (CD) spectroscopy results demonstrate that the proteins preserve their structures when they interact with PSNPs at physiological temperatures. The quartz crystal microbalance (QCM) technique reveals that PSNPs and their bioconjugates show no strong interactions with SLBs. On the contrary, the molecular dynamics simulations (MDS) show that both proteins bind strongly to the lipid bilayer (SLBs) when compared to their binding to a polystyrene surface model. The interaction is strongly dependent on the protein and lipid bilayer composition. Both the PSNPs and their bioconjugates show no toxicity in human umbilical vein endothelial (HUVEC) cells; however, bare 210 nm PSNPs and 50 nm PSNP-Tf bioconjugates show an increase in reactive oxygen species production. This study may be relevant for assessing the impact of plastics on health.     

Membrane interactions of ternary phospholipid/cholesterol bilayers and encapsulation efficiencies of a RIP II protein

Membrane interactions of liposomes of ternary phospholipid/cholesterol bilayers are investigated. These interactions lead to discoidal deformations and regular aggregations and are strongly enhanced by the presence of mistletoe lectin (ML), a RIP II type protein. The encapsulation of ML into liposomal nanocapsules is studied with a systematic variation of the lipid composition to monitor its effect on the physical properties: entrapment, mean size, morphology, and stability. Extrusion of multilamellar vesicles through filters 80 nm pore size was used for the generation of liposomes. The mean sizes of liposomes ranged between 120 and 200 nm in diameter with narrow size distributions. The increase in flow rate with pressure for three dioleoylphosphatidylcholine (DOPC)/cholesterol (Chol)/dipalmitoylphosphatidylcholine (DPPC) lipid mixtures was linear and allowed to extrapolate to the minimum burst pressure of the liposomal bilayers. From the minimum pressures P(min), the bilayer lysis tensions gamma(l) were determined. The increase in P(min) and gamma(l) with an increasing content of a saturated phosopholipid (DPPC) indicates that DPPC increases the mechanical strength of lipid bilayers. Apparently, DPPC, like cholesterol, leads to a less compressible surface and a more cohesive membrane. After preparation, vesicle solutions were purified by gel permeation chromatography to separate encapsulated ML from free ML in the extravesicular solution. Purified liposomes were then characterized. The content of entrapped and adsorbed ML was measured using ELISA. Repetitive freezing/thawing cycles prior to extrusion significantly increased ML uptake. On the contrary, adsorption was not affected neither by lipid composition, nor concentration and preparation. Differences in experimental encapsulation efficiency only reflect the differences in the mean vesicle sizes of the different samples as is revealed by a comparison to a theoretical estimate. Cryo-transmission electron microscopy (Cryo-TEM) images show that beside spherical, single-walled liposomes, there is a considerable fraction of discoidally deformed vesicles. Based on our results and those found in the literature, we speculate that the flattening of the vesicles is a consequence of lipid phase separation and the formation of condensed complexes and areas of different bending elasticities. This phenomenon eventually leads to agglomeration of deformed liposomal structures, becoming more pronounced with the increase in the relative amount of saturated fatty acids, presumably caused by hydrophobic interaction. For the same lipid mixture aggregation correlated linearly with the ML content. Finally, tested liposomal samples were kept at 4 degrees C to examine their stability. Only slight fluctuations in diameter and the increase in polydispersity after 3 weeks of storage occurred, with no statistically significant evidence of drug leakage during a time period of 12 days, illustrating physical stability of liposomes.