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PubMed2004

Effects of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers on structure and stability of liposomal dioleoylphosphatidylethanolamine.

The effects caused by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO; Pluronic) copolymers on the structure and stability of dioleoylphosphatidylethanolamine (DOPE) liposomes were studied by means of turbidity, leakage, and cryo-transmission electron microscopy investigations. The results show that by inclusion of Pluronics in the DOPE dispersion it is possible to stabilize the lamellar Lalpha phase and to produce liposomes that are stable and nonleaky at low pH (pH 5). The stabilizing capacity was observed to depend critically on the molecular composition of the Pluronics. Block copolymers with comparably long PPO and PEO segment lengths, such as F127 and F108, most effectively protected DOPE liposomes prepared at high pH from aggregation and subsequent structural rearrangements induced by acidification. A sufficiently long PPO block was found to be the most decisive parameter in order to obtain adequate coverage of the liposome surface at low Pluronic concentrations. Upon increasing the copolymer concentration, however, Pluronics with comparably short PPO and PEO segment lengths, such as F87 and P85, could also be used to stabilize the DOPE liposomes. Essentially the same trends were observed when the Pluronics were added to preformed DOPE liposomes instead of being included in the preparation mixture. In this case the least effective copolymers failed, however, to completely prevent the DOPE liposomes from releasing encapsulated hydrophilic markers.

Cryoelectron Microscopy↗
PubMed2006

Dynamics of micelles of the triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in aqueous solution.

A number of results reported on the kinetics of exchange of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, between micelles and the intermicellar aqueous solution are reviewed and analyzed to extract the rate constants k(+) for the entry of a copolymer into a micelle and k(-) for the exit of a copolymer from a micelle. Contrary to what is generally observed for conventional surfactants, the rate constant for the entry of a copolymer into a micelle is slower to much slower than for a diffusion-controlled process and decreases as the degree of polymerization of the PO block, n(PO), increases. The effect of the degree of polymerization of the EO block, n(EO), on the two rate constants is significant only for low values of n(EO). The variation of k(-) with n(PO) strongly suggests that the free copolymer molecule adopts a conformation where the PO block is tightly coiled with little contact with water and not a fully extended and hydrated conformation, in contrast to what is commonly assumed when analyzing the dependence of the cmc on the polymerization degree of the hydrophobic block.

Journal Article↗
PubMed2003

Effect of sodium chloride on association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer in aqueous solutions.

The effect of sodium chloride (NaCl) upon the thermally induced association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer, Pluronic P103, has been investigated using pyrene fluorescence spectroscopy. The critical micellization temperature (CMT) of Pluronic P103 in aqueous solution is decreased by the addition of NaCl. The standard enthalpy and entropy of micellization for Pluronic P103 in water are increased in the presence of small amounts of NaCl, but further addition of NaCl decreases the standard enthalpy and entropy of micellization. The I1/I3 ratio of pyrene in aqueous Pluronic P103 solutions at temperature below the CMT decreases with increases of NaCl concentration, which is related to the decrease of PPO solubility. The decrease in polarity of the PPO shifts the CMT toward lower temperature.

Journal Article↗
PubMed1998

Effects of inorganic salts on solubilization of estriol in an aqueous solution of poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer.

The effects of inorganic salts on the solubilization of estriol was studied in an aqueous solution of a poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer (Pluronic L-64). The solubility of estriol increased with increasing Pluronic L-64 and salt concentrations. Furthermore, two clear transition points corresponding to the polymolecular micelle formation and a pronounced change in micellar structure of Pluronic L-64 were found on the solubility curves. The effectiveness of inorganic salts for increasing solubility of estriol followed approximately the lyotropic or Hofmeister series, except Li+.

Drug Compounding↗
PubMed2004

Heat capacity of transfer of (Ethylene oxide)13-(propylene oxide)30-(ethylene oxide)13 from water to the aqueous anionic surfactant solutions at 298 K. A quantitative treatment.

Heat capacities of transfer (DeltaCpt) of unimeric (ethylene oxide)13-(propylene oxide)30-(ethylene oxide)13 from water to the aqueous surfactant solutions as functions of the surfactant concentrations (mS) were determined at 298 K. The surfactants investigated are sodium hexanoate, sodium heptanoate, sodium octanoate, sodium undecanoate, and sodium dodecanoate. For short alkyl chain surfactants, the profiles of the DeltaCpt versus mS curves show maxima and minima; for long alkyl chain surfactants, the maximum becomes sharper and moved to lower mS values whereas the minimum tends to disappear. These experimental trends are different from those of the enthalpy in agreement with the fact that heat capacity, being the derivative of enthalpy with respect to temperature, reflects additional terms generated by temperature change on the equilibria in solution. On the basis of a thermodynamic model recently proposed by us for properties first derivatives of Gibbs free energy, a quantitative treatment of the experimental data was done. Such an approach assumes that even in the dilute surfactant region monomers of surfactant associate with unimeric copolymer generating surfactant-copolymer aggregation complexes and, whenever the surfactant achieves the conditions for the micellization, the formation of copolymer-micelle mixed aggregates takes place. The equation derived for the heat capacity of transfer is more complex than that for the enthalpy because it contains five additional terms due to the shift of the equilibria induced by the temperature change. It turned out that these contributions, evaluated by using the equilibrium constants and the associated enthalpies, cannot be neglected for a quantitative treatment of the experimental data. The minimizing procedure provided the heat capacity changes for the formation of the surfactant-copolymer aggregation complexes and the copolymer-micelle mixed aggregates.

Journal Article↗
PubMed2002

Room temperature phosphorescence of 6-bromo-2-naphthol in micelles of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers and in their mixed aggregates with sodium dodecyl sulfate.

Room temperature phosphorescence (RTP) of 6-bromo-2-naphthol has been investigated in aqueous micellar solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers as well as in their mixed aggregates with sodium dodecyl sulfate. RTP of the phosphorophor was enhanced to some extent in the micelles of the block copolymers. However, marked enhancement of RTP was observed in the mixed aggregates. The enhancement of RTP is attributed to effective incorporation of the phosphorophor into the micelles and the aggregates, resulting in suppression of nonradiative deactivation of the phosphorescent state.

Micelles↗
PubMed2005

Small-angle neutron scattering and theoretical investigation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) stabilized oil-in-water microemulsions.

The aim of this study is to determine the effects of oil solutes and alcohol cosolvents on the structure of oil-in-water microemulsions stabilized by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. The systems investigated involved the solubilization of 1,3,5-trimethylbenzene or 1,2-dichlorobenzene by P123 (EO(20)-PO(70)-EO(20)) pluronic surfactant micelles in water and water + ethanol solvents. The structures of these swollen micelles were determined by small-angle neutron scattering (SANS). A thermodynamic model was employed to interpret the characterization data. The results of the thermodynamic model for micellization agreed well with the SANS data from samples of micelles swollen by both oils. The model predicted the size of the micelles within 5% accuracy using only one fitting parameter, the micelle polydispersity. Ethanol had significantly different effects on the polymer micelles that contained solubilized oil compared to pure polymer micelles. For pure polymer micelles, the addition of ethanol increased the solubility of the polymer and, therefore, decreased the total volume fraction of micelles, while for polymer-oil aggregates, ethanol tended to have a positive effect on the volume fraction of micelles. SANS results showed that the greatest divergence from pure aqueous solvent results occurred at oil concentrations above the microemulsion stability limit.

Journal Article↗
PubMed2005

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-g-poly(vinylpyrrolidone): association behavior in aqueous solution and interaction with anionic surfactants.

In this work, we aimed to study the association and interaction behavior of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block copolymers grafted with poly(vinylpyrrolidone). Critical micellization concentrations were determined using fluorescent probes (pyrene) and critical micellization temperatures characterizing temperature-dependent transitions from monomers to multimolecular micelles were measured. The thermal responsiveness of the copolymer is not affected by the grafting. The hydrodynamic radius of the graft copolymer micelles is found to be greater than that of the original copolymer micelles. The graft copolymer is found to form anisotropic aggregates. The structure of the graft copolymer micelles is less disrupted by the anionic surfactant sodium dodecyl sulfate, compared to the ungraft copolymer.

Journal Article↗
PubMed1950

The sterilization of bacteriological media and other fluids with ethylene oxide.

Ethylene oxide is an effective sterilizing agent for bacteriological broths, milk, and serum. A short time after it has exerted its sterilizing effect, the treated fluids again become capable of supporting bacterial growth. Ethylene oxide has been shown to destroy a number of aerobic Gram-positive and Gram-negative organisms, aerobic and anaerobic spore-forming bacilli, fungi, and vaccinia virus. No organisms have been encountered which withstand its action. The quantity of ethylene oxide necessary for sterilization depends to some degree on the character of the medium sterilized. None of the materials tested required more than 1 volume per cent of liquid ethylene oxide. Ethylene oxide is highly reactive chemically, and its reactions with many of the components of complex biological fluids cannot be fully anticipated. Regardless of the chemical changes produced, ethylene oxide did not permanently alter the essential qualities of the growth factors in broth and milk which are required by fastidious organisms such as group A streptococci and others. However, its effect on the biological activity of any particular organic compound should be assayed before it can be assumed not to have a deleterious effect. The sterilization of media by ethylene oxide is accompanied by a rise in pH. Fluids which have a relatively high initial pH may require adjustment with sterile acid to return them to the optimal pH for bacterial growth. A mixture of ethylene oxide and broth was toxic to mice for 6 hours after admixture. Toxicity disappeared on incubating the mixture longer, and no residual toxicity could be demonstrated after 6 hours, even on repeated intraperitoneal inoculations. As a means of sterilizing bacteriological media and other biological fluids, ethylene oxide deserves consideration when heat and filtration cannot be used.

Animals↗
PubMed1990

Neurotoxicological evaluation of hospital sterilizer workers exposed to ethylene oxide.

Ethylene oxide is now frequently used to chemically sterilize heat-sensitive materials in the hospital setting. Previous reports of neurotoxic effects of ethylene oxide have been described in animals and humans. Recent reports suggest that cognitive deficits may be associated with chronic low-level ethylene oxide exposure. We undertook this study of hospital workers with chronic ethylene oxide exposure and compared them with a non-exposed control group in an attempt to detect neurological and neuropsychological abnormalities. Ethylene oxide breathing zone levels of up to 250 ppm in exposed subjects were reported. All evaluations were done without examiners' knowledge of exposure status of the subjects. The exposed group was found to have a statistically significant lower P300 amplitude, bilaterally hypoactive distal deep tendon reflexes and poorer performance on neuropsychological tests involving psychomotor speed. Exposed subjects acknowledged more symptoms and higher levels of depression and anxiety. Nerve conduction velocities and EEG spectral analysis were similar in both exposed and control groups as were scores on most psychological tests. Based upon this information and prior reports, ethylene oxide should be considered in a differential diagnosis of neuropsychological, peripheral and central nervous system dysfunction in workplace settings associated with ethylene oxide exposure.

Adult↗
PubMed1986

Mutation and enhanced virus transformation of cultured hamster cells by exposure to gaseous ethylene oxide.

Ethylene oxide is a classical mutagen and a carcinogen based on evidence from studies in experimental animals. It is widely distributed in industrial, research, hospital, and food environments. In an effort to explore the use of newly developed methods for exposing mammalian cells to gaseous or volatile mutagens/carcinogens, Chinese hamster V79 cells were treated for 2 hr with gaseous ethylene oxide, in sealed treatment chambers, and assayed for survival and mutagenic response by analysis of induced resistance to 6-thioguanine or ouabain. Significant numbers of mutants were produced at both genetic markers by 1,250-7,500 ppm ethylene oxide. Similarly, primary Syrian hamster embryo cells were treated for 2 or 20 hr with gaseous ethylene oxide in sealed treatment chambers and subsequently assayed for survival and increased sensitivity to SA7 virus transformation. Treatment concentrations extended from toxic to several nontoxic concentrations. After 2-hr ethylene oxide treatment at 625-2,500 ppm a significant enhancement of virus transformation was observed. At 20 hr after treatment no enhancement was observed. Treatment of hamster cells with ethylene oxide in both bioassay systems yielded concentration-related, quantitative results.

Adenoviruses, Simian↗
PubMed1990

Review of the mutagenicity of ethylene oxide.

Ethylene oxide has been shown to be an effective mutagen in a variety of organisms ranging from bacteria to mammalian cells. There is also an association between ethylene oxide exposure and human somatic cell cytogenetic damage. Furthermore, ethylene oxide has been shown to alkylate protein and DNA at exposure levels that have been encountered occupationally. Ethylene oxide is not only effective at producing somatic cell mutations but also at inducing genetic damage in germ cells. While it is clear that ethylene oxide is a germ cell mutagen in whole mammals, the mechanism(s) by which it produces genetic lesions in germ cells is uncertain.

Animals↗
PubMed1990

Neuropsychologic "impairment" in a cohort of hospital workers chronically exposed to ethylene oxide.

Ethylene Oxide is widely used to sterilize heat-sensitive materials. Acute and chronic neurogenic effects to the central and peripheral nervous system in man and animals have been described. To assess the chronic, subtle neuropsychologic effects of ethylene oxide, we performed a cross-sectional study of 25 hospital central supply workers exposed to low levels of ethylene oxide and 24 unexposed control workers. Subjects were tested using a neuropsychological screening battery by examiners blinded to exposure status. Testing results were reviewed independently by two neuropsychologists without knowledge of exposure. Subject status was categorized as normal, "impaired," or disagreement (between the two neuropsychologists). There were significantly more subjects concordantly judged as impaired in the exposed group versus the control group (chi 2 (2) = 6.0861, p less than 0.05). Although limited by the cross-sectional study design and the global categorization, these findings suggest that CNS dysfunction and cognitive impairment may result from chronic ethylene oxide exposure in hospital central supply units.

Adult↗
PubMed1979

Leukemia in workers exposed to ethylene oxide.

Ethylene oxide, a gaseous sterilant extensively used within health care facilities, is known to be a mutagen in bacteria and in human lymphocytes. The Environmental Protection Agency as well as the National Institue of Occupational Safety and Health have recently stipulated certain conditions for the use of ethylene oxide despite the lack of case reports or epidemiologic studies concerning carcinogenicity. We report three cases of leukemia that occurred between 1972 and 1977 in a relatively small group of Swedish workers exposed to ethylene oxide. According to national statistics, 0.2 cases of leukemia would have been expected. The time-weighted average ethylene oxide concentration was 20+/-10 ppm.

Adult↗
PubMed1983

Reproductive-toxicologic assessment of the epoxides ethylene oxide, propylene oxide, butylene oxide, and styrene oxide.

Ethylene oxide (CAS no 75-21-8), propylene oxide (CAS no 75-56-9), butylene oxide (CAS no 106-88-7), and styrene oxide (CAS no 96-09-3) were tested for teratogenic activity by inhalation exposure of rats and rabbits. Ethylene oxide and propylene oxide were tested at only one concentration in both species (150 ppm for ethylene oxide and 500 ppm for propylene oxide). Butylene oxide was tested at 250 and 1,000 ppm in both species, while styrene oxide was tested at 100 ppm in rats and 15 and 50 ppm in rabbits. For each of these four epoxides, the acute toxicity was similar for pregnant and nonpregnant rats. Styrene oxide was the most toxic in both species, and rabbits were more sensitive than rats. Rats exposed to propylene oxide for 7 h/d, 5 d/week for three weeks before breeding had a significant reduction in the number of corpora lutea. Fetal mortality was not increased, but significantly fewer mated rats were found pregnant following gestational exposure to styrene oxide, a finding suggesting preimplantation loss. In rabbits exposed to styrene oxide, the number of resorptions per litter was increased in concentration related manner, but differences were not statistically significant. Fetal examination revealed evidence of fetotoxicity with all four epoxides. There was no overt teratogenic activity, but a number of minor morphologic aberrations were detected.

Abnormalities, Drug-Induced↗