Ellina Kesselman - Academia.edu (original) (raw)
Papers by Ellina Kesselman
Phys Chem Chem Phys, 2011
Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous tech... more Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, b-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO 101 PO 56 EO 101 ), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled b-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above b-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/b-casein micelles. The negative enthalpy of micelle formation (DH) and cooperativity increase with raising b-casein concentration in solution. z-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of b-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
physica status solidi (c), 2009
Journal of Agricultural and Food Chemistry, 2007
Comparing breads reheated in conventional and microwave ovens revealed that the latter considerab... more Comparing breads reheated in conventional and microwave ovens revealed that the latter considerably toughens the crumb texture when internal boiling is induced. Moisture loss in itself has a relatively minor toughening effect. The major changes, caused by boiling, occur only in systems with starch concentration in excess of a threshold level of about 37% (wet basis). Substantially greater amounts of amylose are leached out of the granules in the case of sustained boiling during microwave heating, as compared to conventional oven heating. The free amylose solution is being "pushed" by the generated steam pressure toward the air-cell wall interface. A rich amylose phase is accumulated at that interface and over the granules. Upon cooling, the amylose undergoes rapid phase changes; thus, toughening is apparent in a relatively short time after heating. Minimizing the textural deleterious effects in microwave reheating of bread-like products should entail (a) preventing or minimizing internal boiling, (b) diluting of the starch concentration below the threshold level, (c) interfering with the amylose phase change by using complex forming agents.
Innovative Food Science & Emerging Technologies, 2004
Coatings from high amylose corn starch (HACS) were prepared on glass beads as a model for encapsu... more Coatings from high amylose corn starch (HACS) were prepared on glass beads as a model for encapsulated core using fluidized bed technique. Coated beads were characterized by SEM, dissolution and enzymatic digestion tests. These coatings were stable in dissolution tests, but completely digested in enzymatic digestion tests. Increasing of the coating thickness resulted in some improvements of the coating stability to digestion by pancreatic amylases from 81 to 63%. Addition of resistant starch (RS) was used to further improve the coatings stability to enzymatic digestion. Addition of RS to the coating solution resulted in considerable improvement of the coating stability to enzymatic digestion (2.1"0.2%), but also in appearance of cracks on the coatings surface. Therefore, the potential use of HACS coatings as food grade enteric coatings for protection of core materials from dissolution in the stomach and release in the small intestine was demonstrated. For further development of RS-HACS coatings, additional work must be done to overcome the problem of coating cracking. ᮊ Industrial relevance: The development of delivery systems for bioactive components goes well beyond food applications. The use of coatings to protect desirable components during their passage through the human intestinal tract has received considerable attention and seems essential for optimum delivery of probiotics. This study aimed to test high amylase corn starch using fluidized bed technique for encapsulation and suggested that combinations of gelatinized corn starch with resistant starch can be a successful candidate for microencapsulation.
Gene Therapy, 2006
Therapeutic ultrasound (TUS) has the potential of becoming a powerful nonviral method for the del... more Therapeutic ultrasound (TUS) has the potential of becoming a powerful nonviral method for the delivery of genes into cells and tissues. Understanding the mechanism by which TUS delivers genes, its bioeffects on cells and the kinetic of gene entrances to the nucleus can improve transfection efficiency and allow better control of this modality when bringing it to clinical settings. In the present study, direct evidence for the role and possible mechanism of TUS (with or without Optison) in the in vitro gene-delivery process are presented. Appling a 1 MHz TUS, at 2 W/cm 2 , 30%DC for 30 min was found to achieve the highest transfection level and efficiency while maintaining high cell viability (480%). Adding Optison further increase transfection level and efficiency by 1.5 to three-fold. Confocal microscopy studies indicate that long-term TUS application localizes the DNA in cell and nucleus regardless of Optison addition. Thus, TUS significantly affects transfection efficiency and protein kinetic expression. Using innovative direct microscopy approaches: atomic force microscopy, we demonstrate that TUS exerts bioeffects, which differ from the ones obtained when Optison is used together with TUS. Our data suggest that TUS alone affect the cell membrane in a different mechanism than when Optison is used.
BMC Pharmacology, 2008
This research characterized flour and raw starches isolated from red and white sweet potato culti... more This research characterized flour and raw starches isolated from red and white sweet potato cultivars. Their composition, determined by proximate analysis, is typical of sweet potato cultivars. These cultivars have high amylose content (32-34%) and exhibit a Ca-type X-ray diffraction pattern. Similar gelatinization characteristics were detected for both starches with onset temperature of 67°C and enthalpy of 10.5-11.0 J/g. Starches of both red and white cultivars had well-correlated (r 2 ) 0.982) and high solubilization and swelling temperatures, starting at 80°C. Pasting properties of the white cultivar exhibit lower tendency for retrogradation. Water and oil absorption capacities were low for both red and white flours. When parboiled, both cultivars showed improved water absorption capacity and decreased least gelation concentration. It is concluded that the white cultivar should be preferred when low retrogradation tendency is required.
Nature communications, 2015
Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remain... more Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remains limited or non-existent for diverse applications. Translation of mussel-inspired wet adhesion typically entails catechol functionalization of polymers and/or polyelectrolytes, and solution processing of many complex components and steps that require optimization and stabilization. Here we reduced the complexity of a wet adhesive primer to synthetic low-molecular-weight catecholic zwitterionic surfactants that show very strong adhesion (∼50 mJ m(-2)) and retain the ability to coacervate. This catecholic zwitterion adheres to diverse surfaces and self-assembles into a molecularly smooth, thin (<4 nm) and strong glue layer. The catecholic zwitterion holds particular promise as an adhesive for nanofabrication. This study significantly simplifies bio-inspired themes for wet adhesion by combining catechol with hydrophobic and electrostatic functional groups in a small molecule.
About 30 mg of lipid powder (Avanti Polar Lipids) was hydrated with purified water, and extruded ... more About 30 mg of lipid powder (Avanti Polar Lipids) was hydrated with purified water, and extruded at least 41 times using an Avanti mini-extruded with membrane hole size of 40 nm. Nucleosomal DNA of 146 base-pairs in length was extracted from chicken erythrocytes as described in . Stock lipid and DNA solutions were mixed to form ca.
Journal of Colloid and Interface Science, 2015
g r a p h i c a l a b s t r a c t mixed micellizaƟon aggregaƟon (co-assembly) protein micelles a ... more g r a p h i c a l a b s t r a c t mixed micellizaƟon aggregaƟon (co-assembly) protein micelles a b s t r a c t b-Casein is a 24 kDa amphiphilic and unstructured protein that self-assembles into small core-shell micelles at a wide range of concentrations, pH values and temperatures. We recently developed the micelles as nanocarriers for oral delivery of hydrophobic drugs. In this paper we examined the effect of the hydrophobic non-steroidal anti-inflammatory drug (NSAID) ibuprofen on the micellar structure, as a function of temperature and loading. Using cryo-transmission electron microscopy (cryo-TEM) we find two routes of organization -mixed micellization and co-assembly (aggregation). The time-dependent events that characterize the second routes has been examined in detail. At 25°C we find coexistence of small assemblies and larger aggregates of irregular (but defined) structures that contain the drug. Increasing the drug loading increases the relative number of the larger aggregates and their dimensions, leading eventually to the formation of long then branched structures, like in amphiphilic block copolymer solutions. Similar trends were identified for changes in the temperature. Combined, our results suggest that ibuprofen acts as a co-surfactant that possibly is localizes to the interface rather than being encapsulated in the micellar core as other NSAID hydrophobic drugs.
Science, 2004
By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer ... more By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer architecture, we have observed the formation of a previously unknown class of multicompartment micelles in dilute aqueous solution. Connection of water-soluble poly(ethylene oxide) and two hydrophobic but immiscible components (a polymeric hydrocarbon and a perfluorinated polyether) at a common junction leads to molecular frustration when dispersed in aqueous solution. The incompatible hydrophobic blocks form cores that are protected from the water by the poly(ethylene oxide) blocks, but both are forced to make contact with the poly(ethylene oxide) by virtue of the chain architecture. The structures that emerge depend on the relative lengths of the blocks and can be tuned from discrete multicompartment micelles to extended wormlike structures with segmented cores.
![Research paper thumbnail of ATR-FTIR studies on the effect of strong salting-out salts on the phase separation scenario in aqueous solutions of poly(N-isopropylacrylamide) [PNIPA]](https://attachments.academia-assets.com/40244627/thumbnails/1.jpg)
](Polymers for Advanced Technologies, 2002
Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two st... more Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two strong saltingout salts (Na 2 SO 4 and K 2 SO 4 ) on the temperatureinduced phase separation process in aqueous solutions of poly(N-isopropylacrylamide) [PNIPA]. It was found that the addition of these salts not only depresses the phase transition temperature (as was pointed out by other groups in the past) but, in fact, changes the whole scenario below, at, and above the aggregation temperature. Deconvolution of the amide II peak into three subbands reflecting three types of populations that differ by their hydrogen bonding types revealed that the sulfate ions decreased the amount of amide±water hydrogen bonds, while increasing the amount of amide±amide intramolecular H-bond population. This led to a relatively compact structure even at low temperatures. Based on the behavior of the hydrophobic IR peaks it is suggested that addition of sulfate ions increases the importance of hydrophobic interactions below the phase separation temperature. This study demonstrates the potential of ATR-FTIR in providing information at a molecular level on phase separation phenomena in aqueous solutions of hydrophobic polymers and, in particular, on the effects of co-solutes in such systems.
Physical Chemistry Chemical Physics, 2011
Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous tech... more Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, b-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO 101 PO 56 EO 101 ), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled b-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above b-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/b-casein micelles. The negative enthalpy of micelle formation (DH) and cooperativity increase with raising b-casein concentration in solution. z-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of b-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
Nature Nanotechnology, 2009
Translating the unique characteristics of individual singlewalled carbon nanotubes into macroscop... more Translating the unique characteristics of individual singlewalled carbon nanotubes into macroscopic materials such as fibres and sheets has been hindered by ineffective assembly. Fluid-phase assembly is particularly attractive, but the ability to dissolve nanotubes in solvents has eluded researchers for over a decade. Here, we show that single-walled nanotubes form true thermodynamic solutions in superacids, and report the full phase diagram, allowing the rational design of fluidphase assembly processes. Single-walled nanotubes dissolve spontaneously in chlorosulphonic acid at weight concentrations of up to 0.5wt%, 1,000 times higher than previously reported in other acids. At higher concentrations, they form liquidcrystal phases that can be readily processed into fibres and sheets of controlled morphology. These results lay the foundation for bottom-up assembly of nanotubes and nanorods into functional materials.
Nature Nanotechnology, 2010
Graphene combines unique electronic properties and surprising quantum effects with outstanding th... more Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties 1-4 . Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase 5 . Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as ∼2 mg ml 21 , which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene 6 or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations (∼20-30 mg ml 21 ). Transparent, conducting films are produced from these dispersions at 1,000V A 21 and ∼80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.
Macromolecules, 2006
An asymmetric poly(styrene-b-isoprene) diblock copolymer with block molecular weights of 13 000 a... more An asymmetric poly(styrene-b-isoprene) diblock copolymer with block molecular weights of 13 000 and 71 000 g/mol, respectively, was dissolved at 1 vol % in a series of solvents with varying selectivity for styrene: dibuthyl phthalate (DBP), diethyl phthalate (DEP), and dimethyl phthalate (DMP). The degree of solvent selectivity was adjusted by mixing DBP/DEP and DEP/DMP in various proportions. With increasing solvent selectivity, the predominant micellar shape changes from spheres to cylinders to vesicles, reflecting the changing interfacial curvature. The detailed micellar morphologies were characterized by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Recently developed form factors were used to characterize the micellar structures in detail, and a vesicle form factor was derived for this system. From the core dimensions, the packing properties, such as the interfacial area per chain and the core chain stretching, were determined. The cryo-TEM results demonstrate the suitability of the technique for these glass-forming solvents and gave micellar core dimensions in quantitative agreement with those from SAXS. The universality of the shape sequence sphere/cylinder/vesicle, well-established for aqueous solutions of surfactants and block copolymers, is thus confirmed for organic systems.
Langmuir, 2011
Spherical polycationic brushes, consisting of polystyrene particles with linear cationic macromol... more Spherical polycationic brushes, consisting of polystyrene particles with linear cationic macromolecules grafted onto their surfaces, were electrostatically complexed with small unilamellar anionic liposomes. Complexation was monitored using a multimethod approach that included laser electrophoresis, dynamic light scattering, fluorescence, cryogenic transmission electron microscopy, and conductivity. Liposomes adsorb onto the outer edges of the brushes rather than penetrate into their dense polycationic layer. The integrity of the liposomes remains unaltered when the liposomes reside on the polycationic brushes. The resulting complexes (roughly 40 liposomes per brush) do not dissociate into their components upon exposure to physiological solutions. The system is potentially useful in that liposomes are gathered into well-defined clusters with a high encapsulating potential. Multicomponent constructs can be easily prepared if polycationic brushes are allowed to bind to a mixture of liposomes that encapsulate different guests. This work provides an example of &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;systems chemistry&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; whereby as many as eight components, each with its own particular location and function (i.e., polystyrene core, polycationic graft, egg lecithin, cardiolipin, two fluorescent dyes, water, and buffer), collectively self-assemble.
Journal of the American Chemical Society, 2006
The evolution of the solution microstructures during the formation of the hexagonal mesoporous ma... more The evolution of the solution microstructures during the formation of the hexagonal mesoporous material SBA-15 was studied by direct imaging and freeze-fracture replication cryo-TEM. A reaction mixture was sampled at different times after the addition of tetramethoxyorthosilane (TMOS) to an acidic solution of Pluronic P123 held at 50°C. Solution microstructures were detected by direct imaging cryo-TEM in the time window of 6.5-40 min after the addition of the TMOS (t ) 0). The micrographs revealed that the initial spheroidal micelles evolve into threadlike micelles, which become longer and straighter with time. Then bundles with the dimensions similar to those found in the final material appeared, although there was no sign of a hexagonal arrangement up to 40 min. Due to the appearance of a precipitate at 40 min the sample became too viscous, preventing clear observation of its content. To observe the structures present after 40 min, freeze-fracture replication was carried out as well. Such samples were collected also at 22 min and showed the presence of threadlike micelles in agreement with the direct imaging cryo-TEM micrographs. The 2 h samples showed some areas of hexagonal ordered structures, which become very clear at 2 h 50 min. The cryo-TEM measurements were carried out under the same reaction conditions used in earlier in situ EPR experiments, thus allowing us to correlate molecular level events with the microstructure shape evolutions. This showed that the elongation of the micelles is a consequence of a reduction of the polarity and the water content within the micelles due to silicate adsorption and polymerization. Similar experiments were carried out also on SBA-15 prepared with HCl and TMOS at 35°C
Journal of the American Chemical Society, 2010
Journal of Polymer Science Part B: Polymer Physics, 2001
The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compare... more The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compared with the swelling in pure water, exhibited anion specificity as evidenced by an increased swelling ratio in the following order: Na 2 SO 4 Ͻ H 2 O Ͻ NaCl Ͻ NaSCN. The swelling ratio showed a good linear correlation with the osmotic pressure of dextran (500 kD) in these solutions. The salt-concentration difference (imbalance) between the polymer-solution side of the membrane and the polymer-free permeate side during the osmotic-pressure measurements positively correlated with the effect of the salt on the polymer osmotic pressure. These phenomena conform to Hofmeister-type (or lyotropic) behavior. The diminishing augmentation of dextran osmotic pressure and the change in the salt-concentration imbalance with rising NaSCN concentration imply a positive preferential interaction and adsorption of the salt onto the polymer.
Phys Chem Chem Phys, 2011
Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous tech... more Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, b-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO 101 PO 56 EO 101 ), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled b-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above b-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/b-casein micelles. The negative enthalpy of micelle formation (DH) and cooperativity increase with raising b-casein concentration in solution. z-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of b-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
physica status solidi (c), 2009
Journal of Agricultural and Food Chemistry, 2007
Comparing breads reheated in conventional and microwave ovens revealed that the latter considerab... more Comparing breads reheated in conventional and microwave ovens revealed that the latter considerably toughens the crumb texture when internal boiling is induced. Moisture loss in itself has a relatively minor toughening effect. The major changes, caused by boiling, occur only in systems with starch concentration in excess of a threshold level of about 37% (wet basis). Substantially greater amounts of amylose are leached out of the granules in the case of sustained boiling during microwave heating, as compared to conventional oven heating. The free amylose solution is being "pushed" by the generated steam pressure toward the air-cell wall interface. A rich amylose phase is accumulated at that interface and over the granules. Upon cooling, the amylose undergoes rapid phase changes; thus, toughening is apparent in a relatively short time after heating. Minimizing the textural deleterious effects in microwave reheating of bread-like products should entail (a) preventing or minimizing internal boiling, (b) diluting of the starch concentration below the threshold level, (c) interfering with the amylose phase change by using complex forming agents.
Innovative Food Science & Emerging Technologies, 2004
Coatings from high amylose corn starch (HACS) were prepared on glass beads as a model for encapsu... more Coatings from high amylose corn starch (HACS) were prepared on glass beads as a model for encapsulated core using fluidized bed technique. Coated beads were characterized by SEM, dissolution and enzymatic digestion tests. These coatings were stable in dissolution tests, but completely digested in enzymatic digestion tests. Increasing of the coating thickness resulted in some improvements of the coating stability to digestion by pancreatic amylases from 81 to 63%. Addition of resistant starch (RS) was used to further improve the coatings stability to enzymatic digestion. Addition of RS to the coating solution resulted in considerable improvement of the coating stability to enzymatic digestion (2.1"0.2%), but also in appearance of cracks on the coatings surface. Therefore, the potential use of HACS coatings as food grade enteric coatings for protection of core materials from dissolution in the stomach and release in the small intestine was demonstrated. For further development of RS-HACS coatings, additional work must be done to overcome the problem of coating cracking. ᮊ Industrial relevance: The development of delivery systems for bioactive components goes well beyond food applications. The use of coatings to protect desirable components during their passage through the human intestinal tract has received considerable attention and seems essential for optimum delivery of probiotics. This study aimed to test high amylase corn starch using fluidized bed technique for encapsulation and suggested that combinations of gelatinized corn starch with resistant starch can be a successful candidate for microencapsulation.
Gene Therapy, 2006
Therapeutic ultrasound (TUS) has the potential of becoming a powerful nonviral method for the del... more Therapeutic ultrasound (TUS) has the potential of becoming a powerful nonviral method for the delivery of genes into cells and tissues. Understanding the mechanism by which TUS delivers genes, its bioeffects on cells and the kinetic of gene entrances to the nucleus can improve transfection efficiency and allow better control of this modality when bringing it to clinical settings. In the present study, direct evidence for the role and possible mechanism of TUS (with or without Optison) in the in vitro gene-delivery process are presented. Appling a 1 MHz TUS, at 2 W/cm 2 , 30%DC for 30 min was found to achieve the highest transfection level and efficiency while maintaining high cell viability (480%). Adding Optison further increase transfection level and efficiency by 1.5 to three-fold. Confocal microscopy studies indicate that long-term TUS application localizes the DNA in cell and nucleus regardless of Optison addition. Thus, TUS significantly affects transfection efficiency and protein kinetic expression. Using innovative direct microscopy approaches: atomic force microscopy, we demonstrate that TUS exerts bioeffects, which differ from the ones obtained when Optison is used together with TUS. Our data suggest that TUS alone affect the cell membrane in a different mechanism than when Optison is used.
BMC Pharmacology, 2008
This research characterized flour and raw starches isolated from red and white sweet potato culti... more This research characterized flour and raw starches isolated from red and white sweet potato cultivars. Their composition, determined by proximate analysis, is typical of sweet potato cultivars. These cultivars have high amylose content (32-34%) and exhibit a Ca-type X-ray diffraction pattern. Similar gelatinization characteristics were detected for both starches with onset temperature of 67°C and enthalpy of 10.5-11.0 J/g. Starches of both red and white cultivars had well-correlated (r 2 ) 0.982) and high solubilization and swelling temperatures, starting at 80°C. Pasting properties of the white cultivar exhibit lower tendency for retrogradation. Water and oil absorption capacities were low for both red and white flours. When parboiled, both cultivars showed improved water absorption capacity and decreased least gelation concentration. It is concluded that the white cultivar should be preferred when low retrogradation tendency is required.
Nature communications, 2015
Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remain... more Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remains limited or non-existent for diverse applications. Translation of mussel-inspired wet adhesion typically entails catechol functionalization of polymers and/or polyelectrolytes, and solution processing of many complex components and steps that require optimization and stabilization. Here we reduced the complexity of a wet adhesive primer to synthetic low-molecular-weight catecholic zwitterionic surfactants that show very strong adhesion (∼50 mJ m(-2)) and retain the ability to coacervate. This catecholic zwitterion adheres to diverse surfaces and self-assembles into a molecularly smooth, thin (<4 nm) and strong glue layer. The catecholic zwitterion holds particular promise as an adhesive for nanofabrication. This study significantly simplifies bio-inspired themes for wet adhesion by combining catechol with hydrophobic and electrostatic functional groups in a small molecule.
About 30 mg of lipid powder (Avanti Polar Lipids) was hydrated with purified water, and extruded ... more About 30 mg of lipid powder (Avanti Polar Lipids) was hydrated with purified water, and extruded at least 41 times using an Avanti mini-extruded with membrane hole size of 40 nm. Nucleosomal DNA of 146 base-pairs in length was extracted from chicken erythrocytes as described in . Stock lipid and DNA solutions were mixed to form ca.
Journal of Colloid and Interface Science, 2015
g r a p h i c a l a b s t r a c t mixed micellizaƟon aggregaƟon (co-assembly) protein micelles a ... more g r a p h i c a l a b s t r a c t mixed micellizaƟon aggregaƟon (co-assembly) protein micelles a b s t r a c t b-Casein is a 24 kDa amphiphilic and unstructured protein that self-assembles into small core-shell micelles at a wide range of concentrations, pH values and temperatures. We recently developed the micelles as nanocarriers for oral delivery of hydrophobic drugs. In this paper we examined the effect of the hydrophobic non-steroidal anti-inflammatory drug (NSAID) ibuprofen on the micellar structure, as a function of temperature and loading. Using cryo-transmission electron microscopy (cryo-TEM) we find two routes of organization -mixed micellization and co-assembly (aggregation). The time-dependent events that characterize the second routes has been examined in detail. At 25°C we find coexistence of small assemblies and larger aggregates of irregular (but defined) structures that contain the drug. Increasing the drug loading increases the relative number of the larger aggregates and their dimensions, leading eventually to the formation of long then branched structures, like in amphiphilic block copolymer solutions. Similar trends were identified for changes in the temperature. Combined, our results suggest that ibuprofen acts as a co-surfactant that possibly is localizes to the interface rather than being encapsulated in the micellar core as other NSAID hydrophobic drugs.
Science, 2004
By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer ... more By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer architecture, we have observed the formation of a previously unknown class of multicompartment micelles in dilute aqueous solution. Connection of water-soluble poly(ethylene oxide) and two hydrophobic but immiscible components (a polymeric hydrocarbon and a perfluorinated polyether) at a common junction leads to molecular frustration when dispersed in aqueous solution. The incompatible hydrophobic blocks form cores that are protected from the water by the poly(ethylene oxide) blocks, but both are forced to make contact with the poly(ethylene oxide) by virtue of the chain architecture. The structures that emerge depend on the relative lengths of the blocks and can be tuned from discrete multicompartment micelles to extended wormlike structures with segmented cores.
Polymers for Advanced Technologies, 2002
Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two st... more Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two strong saltingout salts (Na 2 SO 4 and K 2 SO 4 ) on the temperatureinduced phase separation process in aqueous solutions of poly(N-isopropylacrylamide) [PNIPA]. It was found that the addition of these salts not only depresses the phase transition temperature (as was pointed out by other groups in the past) but, in fact, changes the whole scenario below, at, and above the aggregation temperature. Deconvolution of the amide II peak into three subbands reflecting three types of populations that differ by their hydrogen bonding types revealed that the sulfate ions decreased the amount of amide±water hydrogen bonds, while increasing the amount of amide±amide intramolecular H-bond population. This led to a relatively compact structure even at low temperatures. Based on the behavior of the hydrophobic IR peaks it is suggested that addition of sulfate ions increases the importance of hydrophobic interactions below the phase separation temperature. This study demonstrates the potential of ATR-FTIR in providing information at a molecular level on phase separation phenomena in aqueous solutions of hydrophobic polymers and, in particular, on the effects of co-solutes in such systems.
Physical Chemistry Chemical Physics, 2011
Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous tech... more Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, b-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO 101 PO 56 EO 101 ), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled b-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above b-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/b-casein micelles. The negative enthalpy of micelle formation (DH) and cooperativity increase with raising b-casein concentration in solution. z-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of b-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
Nature Nanotechnology, 2009
Translating the unique characteristics of individual singlewalled carbon nanotubes into macroscop... more Translating the unique characteristics of individual singlewalled carbon nanotubes into macroscopic materials such as fibres and sheets has been hindered by ineffective assembly. Fluid-phase assembly is particularly attractive, but the ability to dissolve nanotubes in solvents has eluded researchers for over a decade. Here, we show that single-walled nanotubes form true thermodynamic solutions in superacids, and report the full phase diagram, allowing the rational design of fluidphase assembly processes. Single-walled nanotubes dissolve spontaneously in chlorosulphonic acid at weight concentrations of up to 0.5wt%, 1,000 times higher than previously reported in other acids. At higher concentrations, they form liquidcrystal phases that can be readily processed into fibres and sheets of controlled morphology. These results lay the foundation for bottom-up assembly of nanotubes and nanorods into functional materials.
Nature Nanotechnology, 2010
Graphene combines unique electronic properties and surprising quantum effects with outstanding th... more Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties 1-4 . Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase 5 . Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as ∼2 mg ml 21 , which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene 6 or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations (∼20-30 mg ml 21 ). Transparent, conducting films are produced from these dispersions at 1,000V A 21 and ∼80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.
Macromolecules, 2006
An asymmetric poly(styrene-b-isoprene) diblock copolymer with block molecular weights of 13 000 a... more An asymmetric poly(styrene-b-isoprene) diblock copolymer with block molecular weights of 13 000 and 71 000 g/mol, respectively, was dissolved at 1 vol % in a series of solvents with varying selectivity for styrene: dibuthyl phthalate (DBP), diethyl phthalate (DEP), and dimethyl phthalate (DMP). The degree of solvent selectivity was adjusted by mixing DBP/DEP and DEP/DMP in various proportions. With increasing solvent selectivity, the predominant micellar shape changes from spheres to cylinders to vesicles, reflecting the changing interfacial curvature. The detailed micellar morphologies were characterized by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Recently developed form factors were used to characterize the micellar structures in detail, and a vesicle form factor was derived for this system. From the core dimensions, the packing properties, such as the interfacial area per chain and the core chain stretching, were determined. The cryo-TEM results demonstrate the suitability of the technique for these glass-forming solvents and gave micellar core dimensions in quantitative agreement with those from SAXS. The universality of the shape sequence sphere/cylinder/vesicle, well-established for aqueous solutions of surfactants and block copolymers, is thus confirmed for organic systems.
Langmuir, 2011
Spherical polycationic brushes, consisting of polystyrene particles with linear cationic macromol... more Spherical polycationic brushes, consisting of polystyrene particles with linear cationic macromolecules grafted onto their surfaces, were electrostatically complexed with small unilamellar anionic liposomes. Complexation was monitored using a multimethod approach that included laser electrophoresis, dynamic light scattering, fluorescence, cryogenic transmission electron microscopy, and conductivity. Liposomes adsorb onto the outer edges of the brushes rather than penetrate into their dense polycationic layer. The integrity of the liposomes remains unaltered when the liposomes reside on the polycationic brushes. The resulting complexes (roughly 40 liposomes per brush) do not dissociate into their components upon exposure to physiological solutions. The system is potentially useful in that liposomes are gathered into well-defined clusters with a high encapsulating potential. Multicomponent constructs can be easily prepared if polycationic brushes are allowed to bind to a mixture of liposomes that encapsulate different guests. This work provides an example of &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;systems chemistry&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; whereby as many as eight components, each with its own particular location and function (i.e., polystyrene core, polycationic graft, egg lecithin, cardiolipin, two fluorescent dyes, water, and buffer), collectively self-assemble.
Journal of the American Chemical Society, 2006
The evolution of the solution microstructures during the formation of the hexagonal mesoporous ma... more The evolution of the solution microstructures during the formation of the hexagonal mesoporous material SBA-15 was studied by direct imaging and freeze-fracture replication cryo-TEM. A reaction mixture was sampled at different times after the addition of tetramethoxyorthosilane (TMOS) to an acidic solution of Pluronic P123 held at 50°C. Solution microstructures were detected by direct imaging cryo-TEM in the time window of 6.5-40 min after the addition of the TMOS (t ) 0). The micrographs revealed that the initial spheroidal micelles evolve into threadlike micelles, which become longer and straighter with time. Then bundles with the dimensions similar to those found in the final material appeared, although there was no sign of a hexagonal arrangement up to 40 min. Due to the appearance of a precipitate at 40 min the sample became too viscous, preventing clear observation of its content. To observe the structures present after 40 min, freeze-fracture replication was carried out as well. Such samples were collected also at 22 min and showed the presence of threadlike micelles in agreement with the direct imaging cryo-TEM micrographs. The 2 h samples showed some areas of hexagonal ordered structures, which become very clear at 2 h 50 min. The cryo-TEM measurements were carried out under the same reaction conditions used in earlier in situ EPR experiments, thus allowing us to correlate molecular level events with the microstructure shape evolutions. This showed that the elongation of the micelles is a consequence of a reduction of the polarity and the water content within the micelles due to silicate adsorption and polymerization. Similar experiments were carried out also on SBA-15 prepared with HCl and TMOS at 35°C
Journal of the American Chemical Society, 2010
Journal of Polymer Science Part B: Polymer Physics, 2001
The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compare... more The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compared with the swelling in pure water, exhibited anion specificity as evidenced by an increased swelling ratio in the following order: Na 2 SO 4 Ͻ H 2 O Ͻ NaCl Ͻ NaSCN. The swelling ratio showed a good linear correlation with the osmotic pressure of dextran (500 kD) in these solutions. The salt-concentration difference (imbalance) between the polymer-solution side of the membrane and the polymer-free permeate side during the osmotic-pressure measurements positively correlated with the effect of the salt on the polymer osmotic pressure. These phenomena conform to Hofmeister-type (or lyotropic) behavior. The diminishing augmentation of dextran osmotic pressure and the change in the salt-concentration imbalance with rising NaSCN concentration imply a positive preferential interaction and adsorption of the salt onto the polymer.