Increase In Phase Transition Temperature Research Articles

Effects of Ceramide and Dihydroceramide Stereochemistry at C-3 on the Phase Behavior and Permeability of Skin Lipid Membranes.

Ceramides (Cer) are key components of the skin permeability barrier. Sphingosine-based CerNS and dihydrosphingosine-based CerNdS (dihydroCer) have two chiral centers; however, the importance of the correct stereochemistry in the skin barrier Cer is unknown. We investigated the role of the configuration at C-3 of CerNS and CerNdS in the organization and permeability of model skin lipid membranes. Unnatural l-threo-CerNS and l-threo-CerNdS with 24-C acyl chains were synthesized and, along with their natural d-erythro-isomers, incorporated into membranes composed of major stratum corneum lipids (Cer, free fatty acids, cholesterol, and cholesteryl sulfate). The membrane microstructure was investigated by X-ray powder diffraction and infrared spectroscopy, including deuterated free fatty acids. Inversion of the C-3 configuration in CerNS and CerNdS increased phase transition temperatures, had no significant effects on lamellar phases, but also decreased the proportion of orthorhombic packing and decreased lipid mixing in the model membranes. These changes in membrane organization resulted in membrane permeabilities that ranged from unchanged to 5-fold higher (depending on the permeability markers, namely, water loss, electrical impedance, flux of theophylline, and flux of indomethacin) compared to membranes with natural CerNS/NdS isomers. Thus, the physiological d-erythro stereochemistry of skin Cer and dihydroCer appears to be essential for their correct barrier function.

Specific thermoresponsive behaviours exhibited by optically active and inactive phenylalanine modified hyperbranched polyethylenimines in water

Optically active and inactive hyperbranched polymers with specific thermoresponsive behaviours in water were reported. Through two steps hyperbranched polyethylenimine (HPEI) polymers terminated with different amount of D-phenylalanine (D-Phe), L-phenylalanine (L-Phe) or DL-phenylalanine (DL-Phe) were prepared and characterized. The analyses on the solution properties by turbidimetry, dynamic light scattering, fluorescence probe and 1H-NMR demonstrated that all the polymers exhibited specific thermoresponsive behaviours in water, including: (1) In the dilute polymer concentration region, increasing the polymer concentration led to the increase of phase transition temperature; (2) The optically inactive thermoresponsive hyperbranched polymers showed a higher cloud-point temperature (T cp) than their corresponding optically active ones in a relatively higher polymer concentration; (3) At the same polymer concentration the hydrophobic groups of the optically inactive HPEI-DL-Phe formed more perfect hydrophobic domain than those of the optically active HPEI-L-Phe and HPEI-D-Phe.

Microemulsions with hydrophobic ionic liquids: Influence of the structure of the anion

Abstract The high polarity of ionic liquids (ILs) often prevents the formulation of efficient and strongly structured aqueous microemulsions in which the IL is supposed to replace the hydrophobic oil phase. One strategy to overcome this problem is to reduce the polarity of the IL by introducing aliphatic moieties into the molecular structure. In a previous publication we demonstrated that increasing the number of octyl chains in the cation of the IL reduces the polarity: Decreasing the polarity of the IL, i.e. of the hydrophobic compound, one observes that the phase behavior of the microemulsion follows the same trends as the one known for conventional microemulsions. In the study at hand we demonstrate that the same holds true when alkyl chains are introduced in the anion of the IL. For this purpose we synthesized a set of three ILs with different numbers of octyl chains in the anion. We investigated the phase behavior of the pure compounds as well as of binary and ternary systems. Among these systems the first example of a fluorine-free IL microemulsion is presented. Additionally, the composition of the three coexisting phases of a representative ternary system was determined by an NMR method. It was found that, in analogy to conventional microemulsions, the reduction of the polarity increases the phase transition temperature and broadens the three-phase area of the system. The strategy of increasing the amount of aliphatic chains in the IL is limited by the increase in phase transition temperature, which, in turn, reduces the efficiency. It is shown that the remarkably low efficiency of these microemulsions can be attributed to the high solubility of the surfactant in the IL, which is most likely caused by the surfactant’s ethylene oxide units.

Misfit strain-induced changes in the Fe-sublattice of multiferroic Pb(Fe1/2Nb1/2)O3 epitaxial nanofilm seen via Raman spectroscopy

Magnetic phase transition temperature of the PbFe1/2Nb1/2O3 (PFN) nanofilm on the SrTiO3 substrate was reported to be about 50 K higher than that in the bulk samples. We carried out comparative Raman studies of a 90 nm-thick PFN epitaxial film on SrRuO3-buffered (001) SrTiO3 substrate and the bulk samples of ceramic PFN and a single crystal. It was found out that the bands at ≈250 cm−1 and ≈700 cm−1 in the spectrum of the film, corresponding to FeO vibrational modes, are shifted by about 20 cm−1 to higher frequencies as compared to the bulk samples. This result is in line with the predictions of the recent first-principles calculations that compressive misfit strain stimulates the disorder in the Fe and Nb distribution in the lattice, leading to an increase of the magnetic phase transition temperature. Such disordering might cause the changes in the Fe-sublattice of PFN seen in the Raman spectrum.

Nanoliposomal carriers for improvement the bioavailability of high - valued phenolic compounds of pistachio green hull extract.

In present study, nanoliposomes were prepared by thin hydration method with different concentrations of phenolic compounds (500, 750 and 1000ppm) of pure extract and lecithin (1, 2 and 3%w/w) and characterized by considering the particle size, polydispersity index (PDI), zeta potential, encapsulation efficiency (EE) and morphology. The results showed that nanoliposome (90.39-103.78nm) had negative surface charge varied from -51.5±0.9 to -40.2±0.2mV with a narrow size distribution (PDI≈0.069-0.123). Nanoliposomes composed of 1% lecithin with 1000ppm of phenolic compounds had the highest EE (52.93%). The FTIR analysis indicated the formation of hydrogen bonds between the polar zone of phospholipid and the OH groups of phenolic compounds. Phenolic compounds also increased phase transition temperature (Tc) of nanoliposomes (2.01-7.24°C). Moreover, nanoliposomes had considerable stability during storage. Consequently, liposome is an efficient carrier for protection and improving PGHE biofunctional actives in foodstuffs.

Discriminating Lipid- from Protein-Calcium Binding To Understand the Interaction between Recoverin and Phosphatidylglycerol Model Membranes.

Recoverin is a protein involved in the phototransduction cascade by regulating the activity of rhodopsin kinase through a calcium-dependent binding process at the surface of rod outer segment disk membranes. Understanding how calcium modulates these interactions and how it interacts with anionic lipid membranes is necessary to gain insights into the function of recoverin. In this work, infrared spectroscopy allowed us to show that the availability of calcium to recoverin is modulated by the presence of complexes involving phosphatidylglycerol (PG), which in turn regulates its interactions with this negatively charged lipid. Calcium can indeed be sequestered into strongly bound complexes with PG and is thus sparingly available to recoverin. The thermal stability of recoverin then decreases, which results in weakened interactions with PG. By contrast, when calcium is fully available to recoverin, the protein is thermally stable, indicating that it binds two calcium ions, which results in favorable interactions with negatively charged lipids. Consequently, the protein induces an increase in the chain-melting phase transition temperature of PG, which is indicative of an enhanced lipid chain packing resulting from the peripheral location of the protein. The secondary structure of recoverin is not affected by its interactions with anionic membrane lipids. Similar results have been obtained with saturated and unsaturated anionic lipids. This work shows that the recruitment of recoverin at the surface of anionic lipid membranes is dependent on the availability of calcium.

Electric field induced relaxor behavior in anisotropically strained SrTiO3 films

Electric fields can modify the dielectric response of ferroelectric and especially relaxor ferroelectric material. Since strained ferroelectric fields represent ideal candidates for relaxor ferroelectrics, we analyzed the impact of ac and dc electric fields and field orientation on the dielectric properties of anisotropically strained epitaxial SrTiO3 films in detail. The tensile strain in the SrTiO3 films causes an increase of the ferroelectric-dielectric phase transition temperature to 258K and 288K for small and large tensile strains, respectively. The resulting films represent relaxor-type ferroelectrics with properties that strongly depend on the applied electric field. While a dc bias field significantly suppresses the permittivity in the paraelectric regime ranging from 180K to 320K, an ac field leads to an even more pronounced enhancement of the permittivity in an even larger temperature regime (e.g. reduction of up to 50% versus enhancement of up to 380% for 0.5V/μm dc bias or ac field, respectively). Furthermore the ac field dependence is nonlinear and cannot be explained by the classical Rayleigh law. Frequency dependent measurements show among others that the electric field dependences are strongly related to the relaxor-type behavior. The different dielectric responses are explained in terms of the mobility and dynamic of regimes of uniform polarization, the polar nanoregions, that are generally assumed to be responsible for the relaxor behavior.

Thermo- and salt-responsive poly(NIPAm-co-AAc-Brij-58) microgels: adjustable size, stability under salt stimulus, and rapid protein adsorption/desorption

Based on N-isopropylacrylamide (NIPAm) and modified copolymer of liquid crystal surfactant polyoxyethylene 20 cetyl ether (AAc-Brij-58), a series of “smart” poly(NIPAm-co-AAc-Brij-58) (ACM) microgels with controllable particle size and adjustable salt stability have been successfully fabricated by aqueous precipitation polymerization. The stability under the stimulus of salt and protein adsorption/desorption behavior of ACM microgels were explored. It can be found that when the mass percentage of AAc-Brij-58/NIPAm is 1 wt.%, the ACM01 microgel film presents the lowest contact angel (ca. 35.9°) and the highest hydrodynamic diameters (D H) value (ca. 1100 nm) with the increase of volume phase transition temperature (VPTT). In terms of transmittance change versus different concentrations of NaCl solution and transmittance versus temperature under certain salt concentrations, the responsibility of ACM microgel under ionic strength is investigated sufficiently. The adsorption/desorption behavior of ACM microgels to Bovine Serum Albumin (BSA) is also revealed. The results show that the maximum adsorption amount of AMC01 to BSA reaches 982.7 ± 26 mg/g at 25 °C, much higher than that of ACM0 (714.7 ± 36 mg/g) and ACM02 microgels (402 ± 20 mg/g).

Optimising the heat moisture treatment of Morado banana starch by response surface analysis

Heat moisture treatment (HMT) was considered to modify the characteristics of Morado banana starch. Morado banana starch was isolated to a purity of 84 g/100 g dry sample (ds) with an amylose content of 31.5 g/100 g ds. Response surface analysis was used to estimate the best moisture content and heating time to obtain the optimal treatment conditions at 100°C. The optimised conditions were 32.2% for moisture content and 6.5 h of heating time to achieve the highest slowly digestible starch (SDS) and resistant starch (RS) content. Gelatinised HMT starch contained 12.1 g/100 g ds of SDS and 30.7 g/100 g ds of RS. Differential scanning calorimetry in excess water indicated structural changes, as reflected by increased phase transition temperatures and enthalpy. Fourier transformed infrared spectroscopy showed an increase in the 995/1022 cm−1 ratio, which indicated the rearrangement of the double helices’ packing within the crystalline lamella. The X‐ray diffraction pattern showed that HMT increased the crystalline content from 28.9 to 31.5% compared to the native counterpart.

Enhanced dielectric and piezoelectric properties of Ta-doped 0.50(Na0.5Bi0.5)TiO3–0.50(K0.5Bi0.5)TiO3 lead-free ferroelectric ceramics

Ta-doped 0.50(Na0.5Bi0.5)TiO3–0.50(K0.5Bi0.5)TiO3 piezoelectric ceramics were synthesized by solid state reaction and the effect of doping concentration on dielectric, ferroelectric and electrical properties were investigated. Ta-doping showed an increase in depolarization (Td) and phase transition (Tm) temperatures; thus increasing its usable temperature range. Ferroelectric properties were also enhanced in terms of increased remnant polarization and better squareness of P–E loop. In conductivity studies, activation energy was calculated and the contribution of grains to polarization mechanism was confirmed through Nyquist plots.

Semi-solid fluorinated-DPPC liposomes: Morphological, rheological and thermic properties as well as examination of the influence of a model drug on their skin permeation

The goal of this study was to investigate the influence of an incorporated model drug on the skin permeation of the vehicle itself as it may affect the microstructure and properties of the applied formulation via molecular interactions. For this purpose, we performed skin permeation studies using liposomes prepared with F-DPPC, a monofluorinated analog of dipalmitoylphosphatidylcholine (DPPC), with and without sodium fluorescein (SoFl) serving as model drug. Interestingly, the liposome preparation with F-DPPC yielded semi-solid opalescent systems. Hence, a thorough characterization was accomplished beforehand by electron microscopy imaging, rheological and thermoanalytical experiments. Freeze-fracture electron microscopy images confirmed the existence of globular shaped vesicles in the F-DPPC preparations and oscillatory rheological measurements proved the viscoelastic properties of F-DPPC and F-DPPC+SoFl liposomes in contrast to the viscous characteristics of DPPC liposomes. Thermoanalytical measurements revealed an increased phase transition temperature Tm of about 50°C for F-DPPC and F-DPPC+SoFl liposomes compared to pure DPPC liposomes with a Tm of about 43°C. The similar Tm of F-DPPC+SoFl and F-DPPC liposomes as well as the similar skin permeation of the vehicle compound F-DPPC compared to its drug-free counterpart suggest an incorporation of sodium fluorescein into the aqueous core of F-DPPC liposomes.

The effects of silver nitrate on the phase state of model multibilayer membranes

In order to study the effects caused by silver nitrate (AgNO3) on model lipid membranes, we studied multibilayer membranes based on L-α-dipalmitoylphosphatidylcholine (DPPC) and AgNO3 aqueous soluitions in a wide concentration range (up to 30 wt%) by means of differential scanning calorimetry. It has been shown that the presence of AgNO3 leads both to an increase in the main phase transition temperature (T(m)) and appearance of an additional phase transition peak (T(m)), suggesting increasing of both density and heterogeneity of the lipid membrane. The effect of nitrate ions (NO ) was shown to be of the opposite nature (bilayer fluidizing), so the integral densifying effect of AgNO3 can be referred solely to the action of silver ions (Ag(+)). With increasing AgNO3 concentration, the tendency was observed to opposite changes in T(m) and T'(m) peaks intensity, thereby at about 26. wt% of AgNO3 the initial peak (T(m)) disappeared. In the range of Ag+ therapeutic concentrations (up to 2 wt%) no significant changes in the DPPC membrane were revealed. This can be one of the reasons of the absence of a damaging effect of silver drugs on a host organism with simultaneous pronounced bactericidal effect.

High thermal stability solution-processable narrow-band gap molecular semiconductors.

A series of narrow-band gap conjugated molecules with specific fluorine substitution patterns has been synthesized in order to study the effect of fluorination on bulk thermal stability. As the number of fluorine substituents on the backbone increase, one finds more thermally robust bulk structures both under inert and ambient conditions as well as an increase in phase transition temperatures in the solid state. When integrated into field-effect transistor devices, the molecule with the highest degree of fluorination shows a hole mobility of 0.15 cm(2)/V·s and a device thermal stability of >300 °C. Generally, the enhancement in thermal robustness of bulk organization and device performance correlates with the level of C-H for C-F substitution. These findings are relevant for the design of molecular semiconductors that can be introduced into optoelectronic devices to be operated under a wide range of conditions.

Nanoscale-driven crystal growth of hexaferrite heterostructures for magnetoelectric tuning of microwave semiconductor integrated devices.

A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25-40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals was found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ∼150 K for Co2Y ferrite, compared to 5-10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on a wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.

Giant increase of ferroelectric phase transition temperature in highly strained ferroelectric [BaTiO3]0.7Λ/[BaZrO3]0.3Λ superlattice

We report epitaxial strain effects in the lead-free ferroelectric/paraelectric superlattice (SL) for a modulation period Λ of about 100 Å. We have demonstrated that the large strain in SL induces ferroelectricity in BaZrO3 layers, a material that is paraelectric at any temperature in the bulk form. The induced polar axis in BaZrO3 layers is perpendicular to the plane of the substrate while BaTiO3 layers exhibit in-plane polar orientation. Raman spectroscopy revealed a lattice ordering in SL due to the misfit strain generated by the large lattice mismatch between the alternating BaZrO3 and BaTiO3 layers. Such strain induces a huge upward frequency shift of the lowest E(1TO) soft mode from in the BaTiO3 single film to in the SL. The temperature of the ferroelectric phase transition in the SL was found to be upshifted by about with respect to the BaTiO3 single crystal.

Introduction of pH-sensitive upper critical solution temperature (UCST) properties into branched polyethylenimine

We introduced upper critical solution temperature (UCST) properties into an amine-rich polymer, branched polyethylenimine (b-PEI) by a simple sulfopropylation reaction. The phase transition behavior of the N-sulfopropylated b-PEI (PS-PEI) derivatives was influenced by the degree of sulfopropylation, concentration, molecular weight, ionic strength, and pH. In particular, the phase transition temperature of PS-PEI was strongly dependent upon pH. As the pH decreased, the protonable amine residues of PS-PEI became positively charged and interacted strongly with the negatively charged sulfonate residues, exhibiting the increase of the UCST phase transition temperature.

Effect of grain size on the electrical properties of high dense BPT nanocrystalline ferroelectric ceramics

Abstract Nanosized Ba0.8Pb0.2TiO3 powders obtained by high energy ball milling were compacted and sintered into nanocrystalline ferroelectric ceramics using spark plasma sintering (SPS). The prepared ceramic samples were characterized by field emission scanning electron microscopy, X-ray diffraction, and electrical property measurements. All the samples show a density over 97% of the theoretical value and an average grain size of ∼60–200 nm depending on the ball milling time. The dielectric data exhibit a ferroelectric–paraelectric phase transition and a maximum relative permittivity of 19,000 at 225 °C and 100 kHz at the average grain size of ∼60 nm. The values of the dielectric constants both at room temperature and at the phase transition temperature increase considerably as the average grain size decreases. The remanent polarization and coercive field strength decrease slightly as the average grain size decreases but remain at an acceptable level for ferroelectric applications.

Optical properties and phase transition in photodoped amorphous Ge–Sb–Te:Ag thin films

Photodoping of Ag into amorphous Ge2Sb2Te5 thin films has been carried out by illuminating thermally evaporated Ge–Sb–Te:Ag bilayers with a halogen lamp in the inert atmosphere at room temperature. Amorphous nature of the as-deposited and photodoped films was confirmed by an X-ray diffraction study. The composition of Ge2Sb2Te5 thin films and the amount of Ag photodiffused have been gathered from electron probe micro-analyzer having a wavelength dispersive spectrometer. Amorphous-to-crystalline transition of the films was induced by thermal annealing and the structural phases were identified by X-ray diffraction. The crystalline temperature of the films was evaluated by temperature dependent sheet resistance measurements. The effects of photodoped Ag concentration on the optical properties of the Ge2Sb2Te5 films have been examined by transmission and reflection spectrometry. It was found that the optical band gap, the sheet resistance and the phase transition temperature increase while the absorption coefficient and extinction coefficient decrease upon incorporation of Ag in Ge2Sb2Te5 system. A correlation between the optical band gap and the electronegativity of the alloys indicates that the optical band gap increases with the decrease of electronegativity.

Structural and magnetic properties of Pr-alloyed MnBi nanostructures

The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr) nanostructures with a range of Pr concentrations are investigated. The nanostructures include thin films having Pr concentrations 0, 2, 3, 5 and 9 at.% and melt-spun ribbons having Pr concentrations 0%, 2%, 4% and 6%, respectively. Addition of Pr into the MnBi lattice has produced a significant change in the magnetic properties of these nanostructures including an increase in coercivity and structural phase transition temperature, and a decrease in saturation magnetization and anisotropy energy. The highest value of coercivity measured in the films is 23 kOe and in the ribbons is 5.6 kOe. The observed magnetic properties are explained as the consequences of competing ferromagnetic and antiferromagnetic interactions.

Correlation of drug release with pulmonary drug absorption profiles for nebulizable liposomal formulations

Liposomes have attracted extensive attention as inhalative drug delivery vehicles. The preparation of tailored liposomal formulations (i.e. nebulization stability and controlled drug release profiles) would facilitate new perspectives for the treatment of pulmonary diseases.5(6)-Carboxyfluorescein (CF)-loaded submicron liposomal formulations with varying phase transition temperatures were prepared from lipid blends in different molar ratios. Their physicochemical properties, in vitro dye release, stability to nebulization (Aeroneb® Pro) and ex vivo pulmonary dye absorption and distribution characteristics were investigated.Phase transitions of liposomes were adjusted below and above body temperature (32.9–55.2°C). The amount of CF released from liposomes in vitro correlated well with their membrane fluidity. An increase in phase transition temperature resulted in an extended dye release profile. All formulations revealed aerodynamic particle sizes of ∼4μm with remarkable stability when nebulized by vibrating-mesh technology (percentage of encapsulated model drug ∼80%). Analogous to the release results observed in vitro, liposomal formulations revealing phase transitions above body temperature displayed an increased pulmonary CF retention in an ex vivo lung model. Consequently, an in vitro–ex vivo correlation was established, which demonstrated an excellent agreement of the dye release results with the absorption profiles observed in the biological system (R2⩾0.91).Overall, the concept of liposomal “phase transition release” is promising for controlled pulmonary drug delivery applications. The ex vivo technique enables a reliable determination of lung-specific pharmacokinetics of drug delivery vehicles, which enhances tailored carrier preparation and testing during early formulation development.