Role of secondary structure changes on the morphology of polypeptide-based block copolymer vesicles

The pH and temperature responsive properties of poly(butadiene)107-poly(L-lysine)27 (PB107-P(Lys)27) block copolymer vesicles in aqueous solution were studied using dynamic and static light scattering, circular dichroism spectroscopy and transmission electron microscopy. In this material, the responsiveness comes partially from secondary structure changes within the polypeptide chain. These studies seek to elucidate the effect of these different polypeptide secondary structure changes on the morphology of self-assembled vesicles. It was found that as pH decreases, protonation of P(Lys) side-chain amine groups causes swelling in the vesicles due to the helix-coil transition and associated charge-charge interactions within the corona chains. At high pH and high temperature, P(Lys) corona chains undergo a secondary structure change from alpha-helix to beta-sheet which causes an increase in vesicle size due to the relief of interfacial curvature. This study represents one of the first instances whereby different secondary structure transitions within the same polypeptide have been incorporated into a block copolymer assembly that can be used to produce dual-responsive materials.     

Comparison between two different hemichromes of hemoglobins (HbA and HbS) induced by n-dodecyl trimethylammonium bromide: chemometric study

The interaction of n-dodecyl trimethylammonium bromide (DTAB) with oxyhemoglobin A and oxyhemoglobin S is investigated using UV–visible absorption spectra and chemometric resolution techniques. Oxyhemoglobins (A and S) induced to partial oxidized form (ferrihemoglobin) by DTAB and finally transform to fully oxidized hemichrome. Hemichrome mole fractions of HbS are more than HbA because of more hydrophobic interaction of DTAB–HbS in second set of binding site relative to DTAB–HbA. The visible spectra between 500 and 650 nm are used for identifying the present components in solution because each species of hemoglobin has a specific spectrum in this region. The number of components and mole fraction of mentioned species were determined by employing chemometric resolution techniques. Subspace comparison was used for determination of the number of components in each concentration of hemoglobin and DTAB. After the determination of components, multivariate curve resolution-alternating least square (MCR-ALS) by initial estimates of spectral profiles and proper constraints, was used to resolve the data matrix into pure concentration and spectral profiles. The results show that both number and mole fraction of components which were formed during hemoglobin (HbA and HbS) oxidation by DTAB were initial hemoglobin concentrations independent. Furthermore, in average the mole fraction of hemichrome of HbS is 14.4% more than HbA. On the other hand, the mole fraction of HbA ferrihemoglobin is 15.6% higher than HbS averagely.     

Extruded vesicles of dioctadecyldimethylammonium bromide and chloride investigated by light scattering and cryogenic transmission electron microscopy

Combined dynamic and static light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM) were used to investigate extruded cationic vesicles of dioctadecyldimethylammonium chloride and bromide (DODAX, X being Cl(-) or Br(-)). In salt-free dispersions the mean hydrodynamic diameter, D(h), and the weight average molecular weight, M(w), are larger for DODAB than for DODAC vesicles, and both D(h) and M(w) increase with the diameter (varphi) of the extrusion filter. NaCl (NaBr) decreases (increases) the DODAB (DODAC) vesicle size, reflecting the general trend of DODAB to assemble as larger vesicles than DODAC. The polydispersity index is lower than 0.25, indicating the dispersions are rather polydisperse. Cryo-TEM micrographs show that the smaller vesicles are spherical while the larger ones are oblong or faceted, and the vesicle samples are fairly polydisperse in size and morphology. They also indicate that the vesicle size increases with phi and DODAB assembles as larger vesicles than DODAC. Lens-shaped vesicles were observed in the extruded preparations. Both light scattering and cryo-TEM indicate that the vesicle size is larger or smaller than phi when phi is smaller or larger than the optimal phi approximately 200 nm.     

Wormlike morphology formation and stabilization of "pluronic p123" micelles by solubilization of pentaerythritol tetraacrylate

A transition from spherical to wormlike micelles of a poly(ethylene oxide) 20- block-poly(propylene oxide) 70- block-poly(ethylene oxide) 20 triblock copolymer Pluronic P123 induced by solubilization of a tetrafuctional monomer, Pentaerythritol tetraacrylate (PETA), in aqueous media has been studied. The wormlike micelles shape was locked by UV cross-linking of PETA within the micelles resulting in stabilized polymeric micelles (SPMs). The stability of SPMs in a good solvent for both polyether blocks like THF, and upon dilution below the critical micelle concentration (CMC) of P123 in water was confirmed by dynamic light scattering (DLS) and scanning force microscopy (SFM). Formation of cadmium sulfide (CdS) nanoparticles within the wormlike SPMs was carried out via the reduction of Cd (2+) with NaS and analyzed by transmission electron microscopy (TEM) and UV-vis absorption measurements. A stable water-dispersible hybrid system consisting of CdS quantum dots embedded into the wormlike SPMs was obtained.     

Kinetics of breakdown of vesicles from didodecyldimethylammonium bromide induced by single chain surfactants and by osmotic stress in aqueous solution

Didodecyldimethylammonium bromide (DDAB) forms vesicles spontaneously by simple solubilization of the solid into water at a concentration of ≈2.5 mM. Vesicles can be observed by the increase in turbidity of the aqueous solution of DDAB and by the increase in absorbance (at λ_max=490 nm) of a lipophilic dye (Sudan III) solubilized into the vesicular bilayer. This vesicle system has been perturbed by addition of single-chain surfactants in order to study the transition from a vesicle-stable region to a mixed-micelle region. Vesicle breakdown involves the initial incorporation of a single-chain surfactant into the vesicular bilayer, followed by subsequent disintegration of the vesicle. The progress of reaction has been observed by monitoring turbidity changes using a stopped-flow spectrophotometer. The rate of breakdown of vesicles depends on the concentration and hydrophobic properties of the added single-chain surfactant. In addition, hypertonic and hypotonic osmotic stresses have been investigated.     

Detecting the cross-linking process of hybrid large-compound vesicles by an electrochemical method

A simple electrochemical method of cyclic voltammetry (CV) was exploited to detect the cross-linking process of hybrid large-compound vesicles (LCVs) bearing electrochemically reactive ferrocene group inside. Results indicated that the CV behavior of LCVs deposited electrode was relative to the cross-linking degree of LCVs. It was found that oxidation peak potential became more positive and diffusion rates of electroactive species became smaller after the addition of triethylamine into LCVs solution with increasing time in few days. This showed that the increasing of cross-linking degree for LCVs hindered the electron transport of charge transfer between the neighboring active sites. Our studies will benefit the understanding and the control of the gelation process of hybrid LCVs for potential application in encapsulation and drug delivery.      

Spontaneous vesicles, disks, threadlike and spherical micelles found in the solubilization of DMPC liposomes by the detergent DTAC

Iron oxide/MCM-41 nanocomposites, Fe(2)O(3)/MCM-41, containing 5%, 10%, and 20% (w/w) iron oxide, were prepared via a direct nonhydrothermal method at room temperature. The preparations were preformed by using iron(III) nitrate, tetra-ethoxysilane (TEOS), and cetyltrimethylammonium bromide (CTAB) mixed or unmixed with dodecyltrimethylammonium bromide (DTAB). The produced materials were dried and calcined at 550 °C for 3 h. Test materials were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), N(2) gas adsorption/desorption isotherms, small angle and wide angle X-ray diffraction (XRD). Results indicate that mixing of CTAB with DTAB does not harm the formation of blank MCM-41 structure. For the composite Fe(2)O(3)/MCM-41 materials, results showed formation of more stable MCM-41 structure with higher surface area and improved porosity in the presence of mixed (CTAB+DTAB) than in the presence of single (CTAB) surfactants for up to 10% Fe(2)O(3)/MCM-41 (w/w). This was explained in terms of the effect DTAB on contraction of the template micellar size to compensate for the expected size expansion upon the addition of ionic iron(III) nitrate precursor. Highly dispersed Fe(2)O(3) nanoparticles were formed in all cases even with the highest iron oxide percentage. Formation of the nanocomposites was postulated to be determined by fast nucleation and slow growth of iron oxide species, which facilitated formation of well dispersed iron oxide nanoparticles inside and on the wall of the MCM-41 material.     

Control of block copolymer morphology: An example of selective morphology induced by self‐assembly formation condition

An example case of selective morphology by simply varying pH and heating profile based on a diblock copolymer, i.e., poly(N‐isopropylacrylamide) (PNIPAAM) and poly[2‐(dimethylamino)ethyl acrylate] (PDMAEA) is reported. A variation of pH induces an aggregation of the block copolymers in either micelles or vesicles. In a subsequent step, temperature variation triggers the formation of vesicular structures. This demonstrates not only the temperature but also the heating rate that tunes the nanostructures from micelles to vesicles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Characterizing protein changes caused by application of high hydrostatic pressure on muscle food by means of DSC

Present research concentrated on high pressure assisted thawing of fish fillets from commercially important fish species such as ocean perch, saithe and herring. DSC (Perkin-Elmer DSC 7) has been used to follow the pressure-induced changes of proteins. Results of pressure assisted thawing are compared to those of conventional thawing in water at 10°C and ambient pressure. The results obtained clearly demonstrate that changes in DSC curves become pronounced with advancing high pressure and are dependent on the species of fish.     

Property changes of powdery polyacrylonitrile synthesized by aqueous suspension polymerization during heat-treatment process under air atmosphere

High molecular weight powdery polyacrylonitrile (PAN) polymers were prepared by aqueous suspension polymerization employing itaconic acid (IA) as comonomer and alpha,alpha(')-azobisisobutyronitrile (AIBN) as initiator at 60 degrees C. PAN polymers obtained with different monomer ratios were characterized by EA, DSC, FTIR and XRD. It is investigated that the oxygen element content in PAN polymers increased with the increase of required IA amounts in the feed and heat-treatment temperatures. DSC curves of PAN copolymers exhibited the triplet character, owing to the exothermic cyclization and oxidative reactions during heat-treatment process. Introduction of IA in the feed relaxed exothermic reactions of PAN polymers under air atmosphere. Structure and crystallinity changes were affected by required IA amounts in the feed and enhancement of heat-treatment temperatures. The characteristic functional groups (including C[triple bond]N, C=O, CH(2)) presented in FTIR spectra of PAN polymers indicated copolymerization reaction of AN and IA. Existence of some organic groups (C-O, C=C and/or C=N) indicated formation of ladderlike structure during heat-treatment process. PAN homopolymer had the better crystallinity (mainly peak intensity and peak area around 2theta = 17 degrees) than most RT-PAN copolymers. When heat-treatment temperature is around 210 degrees C, peak intensity, peak area, L(c) and CI of HT-PAN polymers corresponding to samples 1# and 2# got maxima, while crystallinity became weak at higher heat-treatment temperatures.     

Kinetics and mechanism of oxidation of bromide ions by sodium perborate by transforming to a Landolt process

Sodium perborate was used for oxidation of bromide ions at pH 3.64. The reaction was conducted by potentiometric measurements. The orders with respect to perborate and bromide ions were found to be unity in each reagent and a plausible mechanism was postulated. The effect of temperature was studied in the range of 20–40 °C and the Arrhenius parameters were evaluated.

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pH=3,64. . , . 20–40 °C, .

     

Fluorescence microscopic investigation on morphological changes of giant multilamellar vesicles induced by amphiphilic additives

Adding an artificial bolaamphiphile to a dispersion of giant multilamellar vesicles (GMVs) made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) induced a cup-shaped deformation in GMVs accompanied by partial extrusion of the inner vesicle; thereafter, the deformed vesicles returned to their original shape. On the other hand, when the artificial bolaamphiphile together with a surfactant was added to the vesicular dispersion, these deformation and reformation dynamics were transmitted from the outer membranes in GMVs to the inner membranes until an intact inner vesicle was extruded out of the outer membrane. The microscopic aspects of these processes were investigated using amphiphiles tagged with individual fluorophores.     

Tuning of the morphology of a riboflavin-melamine equimolar supramolecular assembly by in situ silver nanoparticle formation

Tuning the supramolecular morphology of an equimolar complex of riboflavin and melamine by the in situ formation of different size silver nanoparticles, affecting the photoluminescence property.     

Formation of porous polymer morphology by microsyneresis during divinylbenzene polymerization

This article describes the investigation of the importance of various reaction conditions on microsyneretic pore formation during polymerization of divinylbenzene (DVB) under so‐called “solvothermal” conditions. To induce microsyneretic pore formation, the most important parameter is an unusually high dilution of monomers with a “good” porogen solvating the polymer chains. High dilution and solvation of the growing poly(DVB) chains promote the prolongation of the polymer chains rather than their interconnection by crosslinking. Consequently, when the polymer gel density reaches the point where syneresis starts, the polymer network is geometrically too extensive to be broken up into precipitating entities and, instead, porogen droplets are formed within the continuous polymer gel. The pore geometry created by microsyneresis offers high surface area in wide mesopores and hence, high capacity for supporting functional groups or reactions with much better accessibility than narrow pores between polymer microspheres produced by macrosyneresis in conventional styrenic polymer supports. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 774–781     

Microenvironmental differences and changes in bilayers of unilamellar vesicles probed by spectroscopic and kinetic parameters

The UV/Vis absorption band maximum lambdamax of trans-4,4'-nitrophenylaminoazobenzene, the thermal isomerization rate constant kiso of its cis-isomer, the fluorescence intensity ratio of monomer and excimer, and the fluorescence lifetime of the excimer, respectively, of 1,3-di(1-pyrenyl)propane were determined as probes for polarity, water content, and viscosity, respectively, in unilamellar vesicles of di-n-alkyl-dimethylammonium bromides and 1,2-acyl-sn-glycero-3-phosphocholines. The dependence on vesicle size, the solvent (water or HEPES buffer/NaCl solution, each with H2O or D2O), and the temperature (20-60 degrees C) was studied. Apparent Arrhenius activation energies and kinetic solvent isotope effects (KSIE = kiso,H2O/kiso, D2O) were derived. Size and stability of the vesicles prepared by extrusion were controlled by dynamic light scattering. The probe properties clearly indicate the reversibly decreasing size of didodecyldimethylammonium bromide vesicles with increasing temperature but are insensitive against vesicles size variation in most other cases. In the temperature range of the main phase transition of the bilayers, changes of the microenvironment of the probes, and their changing position in the bilayer, respectively, are reflected by characteristic changes of their properties. Buffer/NaCl solution causes vanishing influence of the lipid chain but remaining difference between cationic and zwitterionic headgroups probed by means of kiso.     

The effect of solvent on the morphology of ZnO nanostructure assembly by dielectrophoresis and its device applications

Different zinc oxide nanostructured morphologies were grown on photolithographically patterned silicon/silicon dioxide substrates by dielectrophoresis technique using different solvents, such as water and ethanol, obtaining rod-like and net-like nanostructures, respectively. The formation of continuous nanostructures was confirmed by scanning electron microscopic, atomic force microscopic images, and electrical characterizations. The rod-like zinc oxide nanostructures were observed in the 10 μm gap between the fingers in the pattern, whereas net-like nanostructures were formed independently of microgap. A qualitative study about the mechanism for the assembly of zinc oxide continuous nanostructures was presented. Devices were electrically characterized, at room temperature, in controlled environment to measure the conductance behavior in ultraviolet and humidity environment. Devices based on zinc oxide nanostructures grown in ethanol medium show better responses under both ultraviolet and humidity, because of the net-like structure with high surface-to-volume ratio.     

The formation of vesicles by N-dodecyl-N-methylpyrrolidinium bromide ionic liquid/copper dodecyl sulfate and application in the synthesis of leaflike CuO nanosheets

The phase behavior of the mixed catanionic surfactants in aqueous solution, composed of the long-chain ionic liquid (IL) N-dodecyl-N-methylpyrrolidinium (C₁₂MPB) and a divalent metal surfactant copper dodecyl sulfate (Cu(DS)₂·4H₂O), was investigated. The phase diagram of the catanionic system was mapped through visual observation and electrical conductivity measurement. The formation of vesicles was confirmed in the lamellar phase (L_α) through transmission electron microscopy (TEM). Rheological measurements were used to study the macroscopic properties of the birefringent L_α phase. Electrostatic and hydrophobic interactions are regarded as the main driving forces for the formation of vesicles. Furthermore, the vesicles were successfully used as the templates to prepare the leaflike CuO nanomaterials.     

Shape changes and vesicle fission of giant unilamellar vesicles of liquid-ordered phase membrane induced by lysophosphatidylcholine

Liquid-ordered phase (lo phase) of lipid membranes has properties that are intermediate between those of liquid-crystalline phase and those of gel phase and has attracted much attention in both biological and biophysical aspects. Rafts in the lo phase in biomembranes play important roles in cell function of mammalian cells such as signal transduction. In this report, we have prepared giant unilamellar vesicles (GUVs) of lipid membranes in the lo phase and investigated their physical properties using phase-contrast microscopy and fluorescence microscopy. GUVs of dipalmitoyl-phosphatidylcholine (DPPC)/cholesterol membranes and also GUVs of sphingomyelin (SM)/cholesterol membranes in the lo phase in water were formed at 20-37 degrees C successfully, when these membranes contained >/=30 mol % cholesterol. The diameters of GUVs of DPPC/cholesterol and SM/cholesterol membranes did not change from 50 to 28 degrees C, supporting that the membranes of these GUVs were in the lo phase. To elucidate the interaction of a substance with a long hydrocarbon chain with the lo phase membrane, we investigated the interaction of low concentrations (less than critical micelle concentration) of lysophosphatidylcholine (lyso-PC) with DPPC/cholesterol GUVs and SM/cholesterol GUVs in the lo phase. We found that lyso-PC induced several shape changes and vesicle fission of these GUVs above their threshold concentrations in water. The analysis of these shape changes indicates that lyso-PC can be partitioned into the external monolayer in the lo phase of the GUV from the aqueous solution. Threshold concentrations of lyso-PC in water to induce the shape changes and vesicle fission increased greatly with a decrease in chain length of lyso-PC. Thermodynamic analysis of this result indicates that shape changes and vesicle fission occur at threshold concentrations of lyso-PC in the membrane. These new findings on GUVs of the lo phase membranes indicate that substances with a long hydrocarbon chain such as lyso-PC can enter into the lo phase membrane and also the raft in the cell membrane. We have also proposed a mechanism for the lyso-PC-induced vesicle fission of GUVs.