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O Regev

Publications and source records attributed to O Regev.

9 recordsLinked to original sources
PubMed2006

Determination of the concentration of single-walled carbon nanotubes in aqueous dispersions using UV-visible absorption spectroscopy.

Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by nonspecific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV-visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV-visible absorbance spectra of SWNTs-surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the pi-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiPCO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermogravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV-visible measurements.

Journal Article↗
PubMed2006

Lung-surfactant-meconium interaction: in vitro study in bulk and at the air-solution interface.

Lung surfactants (LSs) form a monolayer at the lung's alveoli air-solution interface and play a crucial role in making normal breathing possible by reducing the surface tension. LS are affected by various agents that hamper their normal functioning. Tobacco smoke [Bringezu, F.; Pinkerton, K. E.; Zasadzinski, J. A. Langmuir 2003, 19, 2900-2907] and meconium, the first excrement of the newborn, are examples for such LS poison. In neonates, intrauterine aspiration of meconium is a known cause for morbidity and mortality. We studied in vitro the interactions between modified porcine LSs (Curosurf), used as LS replacement, and meconium, as well as between their artificial analogues, phospholipids mixture, and taurocholic acid (TA), respectively. The interactions were examined both in the bulk solution and at the air-water interface, representing the pre- and postnatal situations. It was found that the artificial analogues represent the natural system reliably and exhibit similar effects. TA, a principle component of bile, is an amphiphilic sterol compound in which the hydrophilic and hydrophobic moieties are presented at different faces of the sterol plane. Here we found that TA affects the structure of both monolayers at the interface and surfactant aggregates in solution. A likely poisoning mechanism is by stereoselective penetration of TA into the lamellar or monolayer structures, thus disrupting the contiguous structure of the intact monolayer or the bilayer vesicle structure.

Animals↗
PubMed2004

Conception and realization of a non-cationic non-viral DNA vector.

Cationic non-viral DNA vectors are very successful in in vitro transfections but less efficient in in vivo tests. This seems mainly due to the cationic nature of the molecules used to complex DNA. In this article, we describe the design and the route towards the realization of a non-viral non-cationic vector. The strategy follows three steps: first, the incorporation of DNA to a lamellar phase; second, the making of multilamellar vesicles containing a high loading of DNA by shearing the lamellar phase and, finally, the grafting of peptides onto the surface of the vesicles to target a specific receptor on the cells. Throughout this process, we had to overcome many obstacles; this review describes the present state of our work and summarizes the remaining steps.

Animals↗
PubMed2000

A Cryo-TEM Study of Protein-Surfactant Gels and Solutions.

Oppositely charged globular protein and surfactant systems, such as lysozyme-sodium dodecyl sulfate (SDS) and ovalbumin-dodecyltrimethylammonium chloride (DOTAC) form precipitate, gel, and colorless solution in water over a wide concentration range. Bluish solutions are also recognized in connection with the redissolution of precipitate as well as prior to the gel formation. For the lysozyme-SDS system the bluish solution has been suggested to consist of finely dispersed gel particles in solution. The oppositely charged bovine serum albumin (BSA)-DOTAC-water system forms only a large, clear solution phase and a narrow, bluish solution region within a very limited surfactant concentration range. In the lysozyme-SDS system the formation of protein-surfactant aggregates and their growth and breakdown are studied in detail by cryogenic-transmission electron microscopy (cryo-TEM) method. In particular a series of samples with an increased surfactant concentration at fixed 4 wt% of lysozyme is studied. Imaging of the bluish solution at different protein concentrations exhibits large aggregates in the form of rod-like, sheet-like, and star-like objects which are attributed to the gel. At excess amounts of SDS, in the colorless solution, only small objects are detected. In the ovalbumin-DOTAC-water and BSA-DOTAC-water systems large aggregates are also observed in the bluish solutions. Colorless solutions for these two systems show the presence of small objects in the cryo-TEM micrographs. Ultrathin sections of the lysozyme and ovalbumin gels fixed with OsO(4) also show the presence of aggregated structures as judged from the transmission electron microscopy observations. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Enhancing the immunogenicity of liposomal hepatitis B surface antigen (HBsAg) by controlling its delivery from polymeric microspheres.

Microencapsulated liposome systems (MELs) were investigated as a potential immunization carrier for a recombinant 22-nm hepatitis B surface antigen (HBsAg) particle. MELs were prepared by first entrapping the HBsAg particles within liposomes composed of phosphatidylcholine:cholesterol (1:1 molar ratio), which were then encapsulated within alginate-poly(L-lysine) (PLL) hydrogel microspheres. The entrapped HBsAg particles retained immunoreactivity, as judged by an enzyme-linked immunosorbent assay (ELISA). Direct imaging of HBsAg particles and HBsAg incorporated into liposomes by cryo-transmission electron microscopy (cryo-TEM) indicated that HBsAg is embedded in the liposomal membrane. The antigenic particles were released from MELs mainly within the context of liposomes. The release rates in vitro and in vivo depended on the molecular weight of PLL used for MEL coating; MELs-214, coated with 214 kDa PLL, released the liposomal HBsAg at much higher rates than MELs-25, which was coated with 25 kDa PLL. Concomitantly, the specific anti-HBsAg titers in mice receiving HBsAg in MELs-214 were higher than those induced by MELs-25. MELs-214 were more efficient than conventional liposomes or alum in eliciting higher and prolonged antibody levels in mice. The ability of MELs to provide an HBsAg depot as well as a sustained release of liposomal HBsAg suggests that these carriers may be an ideal immunoadjuvant.

Alum Compounds↗
PubMed1999

Aggregation Behavior of Tyloxapol, a Nonionic Surfactant Oligomer, in Aqueous Solution.

The aggregation behavior of Tyloxapol, a nonionic surfactant oligomer with a repeating unit close to Triton X-100 (TX100), and a maximum degree of polymerization of about 7, has been investigated in aqueous solution by means of fluorescence probing, time-resolved fluorescence quenching (TRFQ) and transmission electron microscopy at cryogenic temperature (cryo-TEM). The plot of the pyrene fluorescence intensity ratio I1/I3 against the Tyloxapol concentration shows no clear evidence of a critical micelle concentration contrary to TX100. Nevertheless, the fitting of these data, assuming a partition of pyrene between Tyloxapol aggregates and water, yields cmc values in the micromolar range, i.e., about a hundred times lower than for the "monomer" TX100. The values of I1/I3 at high surfactant concentrations indicate that Tyloxapol micelles provide pyrene a less polar environment than TX100 micelles. The use of the viscosity-sensitive probe 1,3-dipyrenylpropane indicates that the microviscosity of Tyloxapol micelles is quite high, three to four times larger than that for TX100 micelles, and decreases rapidly with increasing temperature. Also the microviscosities of both TX100 and Tyloxapol micelles are larger than those for the micelles of the nonionic ethoxylated surfactant C12E9. The aggregation numbers of Tyloxapol and of TX100 micelles measured using TRFQ increase with temperature, with the Tyloxapol micelles being smaller than the TX100 micelles. Cryo-TEM shows that the Tyloxapol micelles remain spheroidal up to a concentration of about 10 wt%. At 15 wt%, some regions of ordered elongated micelles are also observed which may be the precursors of the hexagonal phase known to occur at about 35 wt%. Copyright 1999 Academic Press.

Journal Article↗
PubMed1979

Evaluation of hypertension control in general practice.

A review of the medical charts of 17 general practitioners in six family clinics in Tel Aviv showed that a blood pressure reading was recorded for 69.3% of the adult patients. Elevated values--greater than or equal to 160 (systolic) and/or greater than or equal to 95 (diastolic) mm Hg--were seen in 26.1% of the patients with recorded blood pressure readings. Antihypertensive medications were presecribed for 74.5% of those with elevated blood pressure. In two thirds of the treated group, blood pressure had been measured only once or twice before the initiation of therapy. Of the treated patients, 30% seem to have stopped therapy on their own initiative. Treatment was discontinued by the physician in 18%. Of the 52% who remained on treatment, only one third had a normal systolic or diastolic pressure on the last reading. The failure to reduce blood pressure in the other two thirds may be due, at least in part, to the use of methyldopa and reserpine without a diuretic.

Adult↗