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PubMed1998

High speed separation of DNA fragments by capillary electrophoresis in poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock polymer.

The high speed separation of DNA fragments by using a triblock copolymer, 25% w/v F127 (PEO99PPO69PEO99 with PEO and PPO denoting polyethylene oxide and polypropylene oxide, respectively) which is easy to handle and does not need coating of the quartz capillary, has been investigated. Two ways to decrease the run time are presented: one is to shorten the effective capillary length and the other to increase the electric field strength. In a short capillary, the sieving ability of the separation medium versus the initial band width, and the band width spreading as a function of distance traveled dominate the resolution; at high electric field strength, Joule heating could deteriorate the separation. By taking both effects into account, the phi X174/HaeIII digest could be separated within 100 s by using an 8 mm effective length, 50 microns diameter capillary operating at 300 V/cm.

Bacteriophage phi X 174↗
PubMed1997

Temperature Study of Sound Velocity and Volume-Related Specific Thermodynamic Properties of Aqueous Solutions of Poly(ethylene oxide)-Poly(propylene oxide) -Poly (ethylene oxide) Triblock Copolymers.

A comprehensive study of sound velocity and apparent specific volume, and adiabatic compressibility and expansibility thermodynamic properties of aqueous solutions of a number of POE-POP-POE triblock copolymers has been carried out in the temperature range 10-45 degreesC. Three series of the above block copolymers were studied: one having similar relative molar masses but different POP/POE mass ratios (F38, P103, P85); another having the same POP/POE mass ratio but different relative molar masses (L64, P84, P104 and F38, F68, F108); and a series in which the copolymers have the same absolute POP content but different relative molar masses (P103, P104, P108). An abrupt transition in the temperature dependence of the volumetric and sound velocity properties occurs in the temperature range 10-45 degreesC for many of the copolymers. This is due to the self-aggregation of the copolymers. The results of this study show that the relative molar mass, POP/POE mass ratio and POP content of the copolymers are factors that play a role in the self-aggregation of these systems. The extensive study of the sound velocity property of these systems extends and confirms the few previous reports that it is a sensitive macroscopic probe of the onset of self-aggregation processes in these systems. The apparent specific volume data of the copolymers has been used to test current models of these aggregates. The results show that the POP core contains some water. Copyright 1997 Academic Press.

Journal Article↗
PubMed2000

Evaluation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) gels as a release vehicle for percutaneous fentanyl.

The primary objective of this study was to investigate the feasibility of PEO-PPO-PEO copolymer gel as a release vehicle for percutaneous administration of fentanyl in vitro and in vivo. A cellulose membrane and nude mouse skin with series concentrations of PEO-PPO-PEO block copolymers were used to examine the sustained-release pattern and permeation of fentanyl. The in vivo percutaneous absorption was examined using rabbits to evaluate the preliminary pharmacokinetics of fentanyl with 46% PEO-PPO-PEO copolymer formulation patches. The micelle formation ability of this block copolymer and the penetration ability of PEO-PPO-PEO copolymer over time were also studied by pyrene fluorescence probe methods and the dynamic light scattering test. At a concentration of 46% at 37 degrees C, PEO-PPO-PEO copolymers formed a gel and showed a pseudo-zero-order sustained-release profile. With increasing concentration of copolymer in the cellulose membrane transport, the apparent release flux of fentanyl (200 microgram/ml) decreased to 1. 09+/-0.19 microgram cm(-2) h(-1). Assessment of the effect of the copolymer on nude mouse skin also showed a decrease in the apparent permeability coefficient [(P(H(2)O))=2.24+/-0.47x10(-6) cm s(-1) vs. (P(46% block copolymer))=0.93+/-0.23x10(-7) cm s(-1)]. The preliminary pharmacokinetics of the fentanyl patch was shown to be in steady state within 24 h, and this was maintained for at least 72 h with an elimination half-life (t(1/2)) of 10.5+/-3.4 h. A fluorescence experiment showed polymeric micelle formation of PEO-PPO-PEO copolymers at 0.1% (w/w) within 50 nm micelle size and the PEO-PPO-PEO copolymers were able to penetrate nude mouse skin within 24 h. Thus, it appears that fentanyl preparations based on PEO-PPO-PEO copolymer gel might be practical for percutaneous delivery.

Administration, Cutaneous↗
PubMed1999

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres. I. Preparation and characterization.

Amphiphilic block copolymers based on PEO-PPO-PEO block copolymer (Pluronic) and poly(epsilon-caprolactone) were synthesized by bulk polymerization. The structural analysis of Pluronic/PCL block copolymer was carried out using FT-IR, 1H NMR, GPC, WAXD, DSC and TGA measurements. To prepare copolymeric nanospheres with a micellar structure, Pluronic/PCL amphiphilic block copolymers were dialyzed against water. The size and size distribution of Pluronic/PCL block copolymeric nanospheres were examined by dynamic light scattering measurement. They showed an average diameter of 116 to 196 nm depending on the type of copolymer. All the nanosphere samples exhibited a narrow size distribution. The critical micelle concentrations of Pluronic/PCL amphiphilic block copolymers determined by fluorescence spectroscopy were lower than that of common low molecular weight surfactants. We confirmed the formation of stable copolymeric nanospheres through the solution behavior of amphiphilic block copolymer in selective solvents.

Drug Delivery Systems↗
PubMed2000

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres. II. Thermo-responsive drug release behaviors.

Amphiphilic block copolymers composed of relatively hydrophilic PEO-PPO-PEO block copolymer (Pluronic) and poly (epsilon-caprolactone) with hydrophobic character were synthesized by ring-opening polymerization of epsilon-caprolactone in the presence of PEO-PPO-PEO block copolymer using stannous octoate as a catalyst. Pluronic/PCL block copolymeric nanospheres with core-shell structure were prepared by dialysis method. They showed the average diameter of 116-196 nm depending on the type of copolymer. All the nanosphere samples exhibited a narrow size distribution. The critical micelle concentrations of Pluronic/PCL amphiphilic block copolymers determined by fluorescence spectroscopy were lower than that of the common low molecular weight surfactant. Their core-shell structure was confirmed by 1H NMR spectroscopy. Pluronic/PCL block copolymeric nanospheres exhibited the reversible change of size depending on the temperature. Release behaviors of indomethacin from Pluronic/PCL block copolymeric nanospheres also showed temperature dependence and a sustained release pattern. In addition, cytotoxicity test using an MTT assay method revealed that these indomethacin-loaded Pluronic/PCL nanospheres could remarkably reduce the cell damage compared with the unloaded free indomethacin.

Algorithms↗
PubMed2005

Fluorescence probing of interior, interfacial, and exterior regions in solution aggregates of poly(ethylene oxide)- poly(propylene oxide)-poly(ethylene oxide) triblock copolymers.

Fluorescence spectroscopy is used to probe local environments within regions of different polarity and hydrophobicity in aqueous aggregates of PEO(109)-PPO(41)-PEO(109) triblock copolymers. These copolymer aggregates have well characterized microphases in aqueous solution. Concentrations and temperatures for our studies are chosen such that the copolymers are in unimer, micellar, or micellar hydrogel forms. The observed fluorescence spectra and lifetimes from solutions individually labeled with each of the three coumarin probes report on the changes in the local polarity of the core, exterior, interfacial, and corona regions of these copolymer aggregates. This multiple fluorescence probe methodology will be straightforward to apply in general to problems in polymer and biopolymer aggregates, especially those that display strong hydrophobic effects.

Coumarins↗
PubMed2001

In vivo gene delivery into ocular tissues by eye drops of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) polymeric micelles.

The primary objective of this study was to investigate the feasibility of using PEO-PPO-PEO non-ionic copolymeric micelles as a carrier for eye-drop gene delivery of plasmid DNA with lacZ gene in vivo. Using pyrene fluorescence probe methods, zeta potential, and dynamic light scattering test (DLS), the ability of micelle formation of these block copolymers with plasmid was studied. Gene expressions were visualized by both the quality of enzymatic color reaction using X-gal staining and by the quantification of the substrate chlorophenol red galactopyranoside (CPRG) in enucleated eyes on day 2 after gene transfer. In addition, microscopy to identify the types of cell showing uptake and expression of the transferred gene was used. We found that the block polymeric micelles were formed above 0.1% (w/v) of block copolymer with a size of 160 nm and a zeta potential of -4.4 mV. After 2 days of topically delivery three times a day, the most intense gene expression was observed on days 2 and 3. Reporter expression was detected around the iris, sclera, conjunctiva, and lateral rectus muscle of rabbit eyes and also in the intraocular tissues of nude mice upon in vivo topical application for 48 h with a DNA/polymeric micelle formulation. Furthermore, after two enhancement treatments, the transport mechanisms of the block copolymeric micelles were found through endocytosis in tissues by enhancement through the tight junction pathway. Thus, efficient and stable transfer of the functional gene could be achieved with PEO-PPO-PEO polymeric micelles through topical delivery in mice and rabbits. These in vivo experiments indicate the possible potential use of block copolymers for DNA transfer.

Animals↗
PubMed1994

The role of 3-hydroxyethyldeoxyuridine in mutagenesis by ethylene oxide.

Ethylene oxide, a direct-acting mutagen and carcinogen, produces 3-hydroxyethyldeoxyuridine (3-HE-dU) after initial alkylation at N3 of dC, followed by rapid hydrolytic deamination. The significance of formation of 3-HE-dU in DNA was investigated by in vitro DNA replication of 3-HE-dU. A 55-nucleotide DNA template, containing 3-HE-dU at a single site, was constructed. DNA products, synthesized on the site-modified template, were analyzed and mutagenic bypass at 3-HE-dU estimated. The 3-HE-dU lesion blocked DNA replication by the Klenow fragment of Escherichia coli polymerase I (Kf Pol I) and bacteriophage T7 polymerase (T7 Pol) 3' to 3-HE-dU and after incorporating a nucleotide opposite 3-HE-dU. DNA synthesis past 3-HE-dU was negligible (< 3%). Substitution of Kf Pol I (exo-) and T7 Pol (exo-), polymerases lacking 3'-->5' exonuclease proofreading activity, for Kf Pol I and T7 Pol, respectively, facilitated DNA synthesis past 3-HE-dU. The bypass synthesis by Kf Pol I (exo-) was 60% and 90% by T7 Pol (exo-). These results suggest that the 3-HE-dU lesion could be bypassed, but that the extension at 3-HE-dU is rate-limiting. In the absence of proofreading, the nucleotide incorporated opposite 3-HE-dU is not excised and remains in position long enough for extension to occur. During post-lesion synthesis, both dA and dT were incorporated opposite 3-HE-dU. Since 3-HE-dU is derived from dC alkylation by ethylene oxide, incorporation of dA and dT opposite 3-HE-dU implicates this lesion in G.C-->A.T and G.C-->T.A mutagenesis.

Base Sequence↗
PubMed2003

Preparation and characterization of polypseudorotaxanes based on block-selected inclusion complexation between poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) triblock copolymers and alpha-cyclodextrin.

A series of new polypseudorotaxanes were synthesized in high yields when the middle poly(ethylene oxide) (PEO) block of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) triblock copolymers was selectively recognized and included by alpha-cyclodextrin (alpha-CD) to form crystalline inclusion complexes (ICs), although the middle PEO block was flanked by two thicker PPO blocks, and a PPO chain had been previously thought to be impenetrable to alpha-CD. X-ray diffraction studies demonstrated that the IC domains of the polypseudorotaxanes assumed a channel-type structure similar to the necklace-like ICs formed by alpha-CD and PEO homopolymers. Solid-state CP/MAS (13)C NMR studies showed that the alpha-CD molecules in the polypseudorotaxanes adopted a symmetrical conformation due to the formation of ICs. The compositions and stoichiometry of the polypseudorotaxanes were studied using (1)H NMR, and a 2:1 (ethylene oxide unit to alpha-CD) stoichiometry was found for all polypseudorotaxanes although the PPO-PEO-PPO triblock copolymers had different compositions and block lengths, suggesting that only the PEO block was closely included by alpha-CD molecules, whereas the PPO blocks were uncovered. The hypothesis was further supported by the differential scanning calorimetry (DSC) studies of the polypseudorotaxanes. The glass transitions of the PPO blocks in the polypseudorotaxanes were clearly observed because they were uncovered by alpha-CD and remained amorphous, whereas the glass-transition temperatures increased, because the molecular motion of the PPO blocks was restricted by the hard crystalline phases of the IC domains formed by alpha-CD and the PEO blocks. The thermogravimetric analysis (TGA) revealed that the polypseudorotaxanes had better thermal stability than their free components due to the inclusion complexation. Finally, the kinetics of the threading process of alpha-CD onto the copolymers was also studied. The findings reported in this article suggested interesting possibilities in designing other cyclodextrin ICs and polypseudorotaxanes with block structures.

Cyclodextrins↗
PubMed1980

A gas handling system for ethylene oxide.

Ethylene oxide (ETO), a widely used gas sterilant and industrial raw material, is under FDA and EPA scrutiny for its toxicity and potential as a mutagen and a carcinogen. For this reason it was necessary to improve upon the handling of ETO in the laboratory to facilitate air sampling and analyses procedures. A safe and convenient apparatus, designed and fabricated from readily available stainless steel fittings is discussed. The system provides for the complete conversion of 100% ETO liquid to a vapor which is extractable from an easily sampled port for subsequent gas chromatographic analysis.

Environmental Exposure↗
PubMed1969

Elimination of toxicity from polyvinyl trays after sterilization with ethylene oxide.

Ethylene oxide (ETO) sterilization of polyvinyl trays used in an antiviral screening program was initiated to overcome seasonal outbreaks of bacterial and mycotic contamination of tissue culture cells. Trays sterilized by 100% ETO for 5 hr after 48 hr of prehumidification, or by 12% ETO plus 88% Freon 12 for 1, 3, 5 or 18 hr, followed by various methods of aeration, were seeded with several types of tissue culture cells and examined for contamination, toxicity, and monolayer quality. A 1-hr exposure in 12% ETO plus 88% Freon 12 was adequate for sterilization, although residual toxicity for tissue cultures remained. A 7-day aeration period at 37 C was sufficient to eliminate toxicity and allow the growth of good monolayers of WI-38, HEp-2 and primary bovine kidney cells. Sterilization with 100% ETO required 14 days of aeration at 37 C to eliminate cytotoxicity. Increased residual toxicity resulting from longer ETO sterilization periods required longer aeration times at 37 C or higher aeration temperatures for detoxification.

Air↗
PubMed1994

Biological monitoring of workers occupationally exposed to ethylene oxide.

Ethylene oxide (EtO) is an important intermediate industrial chemical which is also used for sterilizing medical products and hospital equipment. In the present study we have evaluated some biological markers, such as chromosomal aberrations, micronuclei and EtO-hemoglobin adducts in the peripheral blood cells, and micronuclei in buccal exfoliated cells of 22 controls and 75 workers employed in an industry in Brazil using EtO as an intermediate. Measurements of EtO in the general area showed that workers were exposed to 2-5 ppm time-weighted average (TWA) for an 8-h working day, during the 3-month sampling. Our results indicate that exposure to EtO resulted in a statistically significant enhancement of chromosomal aberrations (P = 0.01) and of micronuclei in binucleated lymphocytes (P < 0.001). For the frequencies of micronucleated cells in buccal mucosa there was no statistically significant difference between exposed and control groups. The mean values of hemoglobin adduct (HOEtVal) measurements obtained from a selected group of exposed and unexposed donors were statistically different.

Adult↗
PubMed2004

Addressing nonlinearity in the exposure-response relationship for a genotoxic carcinogen: cancer potency estimates for ethylene oxide.

Ethylene oxide (EO) has been identified as a carcinogen in laboratory animals. Although the precise mechanism of action is not known, tumors in animals exposed to EO are presumed to result from its genotoxicity. The overall weight of evidence for carcinogenicity from a large body of epidemiological data in the published literature remains limited. There is some evidence for an association between EO exposure and lympho/hematopoietic cancer mortality. Of these cancers, the evidence provided by two large cohorts with the longest follow-up is most consistent for leukemia. Together with what is known about human leukemia and EO at the molecular level, there is a body of evidence that supports a plausible mode of action for EO as a potential leukemogen. Based on a consideration of the mode of action, the events leading from EO exposure to the development of leukemia (and therefore risk) are expected to be proportional to the square of the dose. In support of this hypothesis, a quadratic dose-response model provided the best overall fit to the epidemiology data in the range of observation. Cancer dose-response assessments based on human and animal data are presented using three different assumptions for extrapolating to low doses: (1) risk is linearly proportionate to dose; (2) there is no appreciable risk at low doses (margin-of-exposure or reference dose approach); and (3) risk below the point of departure continues to be proportionate to the square of the dose. The weight of evidence for EO supports the use of a nonlinear assessment. Therefore, exposures to concentrations below 37 microg/m3 are not likely to pose an appreciable risk of leukemia in human populations. However, if quantitative estimates of risk at low doses are desired and the mode of action for EO is considered, these risks are best quantified using the quadratic estimates of cancer potency, which are approximately 3.2- to 32-fold lower, using alternative points of departure, than the linear estimates of cancer potency for EO. An approach is described for linking the selection of an appropriate point of departure to the confidence in the proposed mode of action. Despite high confidence in the proposed mode of action, a small linear component for the dose-response relationship at low concentrations cannot be ruled out conclusively. Accordingly, a unit risk value of 4.5 x 10(-8) (microg/m3)(-1) was derived for EO, with a range of unit risk values of 1.4 x 10(-8) to 1.4 x 10(-7) (microg/m3)(-1) reflecting the uncertainty associated with a theoretical linear term at low concentrations.

Animals↗
PubMed1997

Effect of Solvent Quality on Reverse Micelle Formation and Water Solubilization by Poly(ethylene oxide)/Poly(propylene oxide) and Poly(ethylene oxide)/Poly(butylene oxide) Block Copolymers in Xylene

In addition to associating into ("normal") micelles in aqueous solutions, amphiphilic polyoxyalkylene block copolymers can form "reverse" micelles in organic solvents at sufficiently high copolymer concentrations (above the critical micellization concentration (CMC)) and in the presence of some water. The effects of solvent quality on the copolymer micellization in an organic solvent and on the solubilization of water in such systems are examined here for representative poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) and poly(butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) copolymers. The solvent quality is modulated by the addition of cosolutes and by a change in the temperature. A number of notable observations are reported: Worsening the aqueous solvent conditions by the addition of NaCl (10 wt% with respect to water) almost doubles the CMC and the water solubilization capacity (WS) of a PEO-PPO-PEO copolymer in p-xylene. An increase in temperature makes water a worse and xylene a better solvent for the copolymer. The combined result of heating is an increase of the CMC for all three copolymers studied. This indicates that the formation of reverse micelles is exothermic, which is opposite to what has been observed for normal micelles. The effects of temperature on the water uptake are nonmonotonic: WS increased with temperature for a PEO-PPO-PEO copolymer with 40% PEO but decreased for a copolymer with 20% PEO. An increase in WS with temperature, followed by a decrease, with the maximum WS efficiency occurring at the "effective" cloud point of the copolymer is proposed in order to explain this observation. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1992

Cognitive dysfunction in a patient with long-term occupational exposure to ethylene oxide. Role of ethylene oxide as a causal factor.

This case illustrates a comprehensive approach to assessing causality in a woman with apparent cognitive dysfunction, as measured by neuropsychological testing, and a 10-year history of occupational exposure to ethylene oxide. The analysis included a multidisciplinary examination of the patient, which took place several years after the termination of her exposure. In addition, all of the patient's prior medical and psychiatric records were reviewed, as were the records of her employer to ascertain her exposure history. Our evaluation revealed a pattern of neuropsychological findings not consistent with nervous system damage secondary to an organic effect of ethylene oxide. A more likely causal hypothesis is adopted: the patient's apparent cognitive dysfunction had a psychiatric etiology. This case also illustrates the potential impact of a patient's involvement in legal proceedings related to claims of neurocognitive dysfunction.

Adult↗
PubMed1981

Mutagenicity study of workers exposed to alkylene oxides (ethylene oxide/propylene oxide) and derivatives.

Employees of plants where alkylene oxide is manufactured or processed were subjected to mutagenicity studies carried out on lymphocyte cultures in accordance with the methods of Moorhead at al, de Jong and Anders. The employees were divided into four groups, according to their periods of exposure: (1) Long-term exposure for more than 20 years; (2) exposure for less than 20 years; (3) long-term exposure and accident (ethylene oxide inhalation or skin contact); and (4) accident, i.e., brief high exposure to ethylene oxide. Measurement of the concentrations in various sections of the plant yielded values of up to 3 ppm under conditions of normal operation. However, this figure rose briefly to 1900 ppm under plant breakdown hat workers were subjected to higher exposure in the past. One hundred metaphases per person were analyzed for chromosome aberrations. The results are given in Tables 1 through 4. A significant increase in the aberration rate was found only in employees in Group 1. This was confirmed by a control examination carried out one year later. The employees of groups 2, 3 and 4 displayed no significant increases. However, in evaluating these findings, it should be noted that the employees had been in contact with a wide range of substances and products in the course of their occupation, which means that the increased aberrations rate found cannot be attributed unequivocally to exposure to a particular substance.

Adult↗
PubMed2005

Effects of ethylene oxide and ethylene inhalation on DNA adducts, apurinic/apyrimidinic sites and expression of base excision DNA repair genes in rat brain, spleen, and liver.

Ethylene oxide (EO) is an important industrial chemical that is classified as a known human carcinogen (IARC, Group 1). It is also a metabolite of ethylene (ET), a compound that is ubiquitous in the environment and is the most used petrochemical. ET has not produced evidence of cancer in laboratory animals and is "not classifiable as to its carcinogenicity to humans" (IARC, Group 3). The mechanism of carcinogenicity of EO is not well characterized, but is thought to involve the formation of DNA adducts. EO is mutagenic in a variety of in vitro and in vivo systems, whereas ET is not. Apurinic/apyrimidinic sites (AP) that result from chemical or glycosylase-mediated depurination of EO-induced DNA adducts could be an additional mechanism leading to mutations and chromosomal aberrations. This study tested the hypothesis that EO exposure results in the accumulation of AP sites and induces changes in expression of genes for base excision DNA repair (BER). Male Fisher 344 rats were exposed to EO (100 ppm) or ET (40 or 3000 ppm) by inhalation for 1, 3 or 20 days (6h/day, 5 days a week). Animals were sacrificed 2h after exposure for 1, 3 or 20 days as well as 6, 24 and 72 h after a single-day exposure. Experiments were performed with tissues from brain and spleen, target sites for EO-induced carcinogenesis, and liver, a non-target organ. Exposure to EO resulted in time-dependent increases in N7-(2-hydroxyethyl)guanine (7-HEG) in brain, spleen, and liver and N7-(2-hydroxyethyl)valine (7-HEVal) in globin. Ethylene exposure also induced 7-HEG and 7-HEVal, but the numbers of adducts were much lower. No increase in the number of aldehydic DNA lesions, an indicator of AP sites, was detected in any of the tissues between controls and EO-, or ET-exposed animals, regardless of the duration or strength of exposure. EO exposure led to a 3-7-fold decrease in expression of 3-methyladenine-DNA glycosylase (Mpg) in brain and spleen in rats exposed to EO for 1 day. Expression of 8-oxoguanine DNA glycosylase, Mpg, AP endonuclease (Ape), polymerase beta (Pol beta) and alkylguanine methyltransferase were increased by 20-100% in livers of rats exposed to EO for 20 days. The only effects of ET on BER gene expression were observed in brain, where Ape and Pol beta expression were increased by less than 20% after 20 days of exposure to 3000 ppm. These data suggest that DNA damage induced by exposure to EO is repaired without accumulation of AP sites and is associated with biologically insignificant changes in BER gene expression in target organs. We conclude that accumulation of AP sites is not a likely primary mechanism for mutagenicity and carcinogenicity of EO.

Administration, Inhalation↗
PubMed2004

Characterization and demulsification of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers.

Four poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers with different molecular weights and PPO/PEO composition ratios were synthesized. The characterization of the PEO-PPO-PEO triblock copolymers was studied by surface tension measurement, UV-vis spectra, and surface pressure method. These results clearly showed that the CMC of PEO-PPO-PEO was not a certain value but a concentration range, in contrast to classical surfactant, and two breaks around CMC were reflected in both surface tension isotherm curves and UV-vis absorption spectra. The range of CMC became wider with increasing PPO/PEO composition ratio. Surface pressure Pi-A curves revealed that the amphiphilic triblock copolymer PEO-PPO-PEO molecule was flexible at the air/water interface. We found that the minimum area per molecule at the air/water interface increased with the proportion of PEO chains. The copolymers with the same mass fractions of PEO had similar slopes in the isotherm of the Pi-A curve. From the demulsification experiments a conclusion had been drawn that the dehydration speed increased with decreased content of PEO, but the final dehydration rate of four demulsifiers was approximate. We determined that the coalescence of water drops resulted in the breaking of crude oil emulsions from the micrograph.

Emulsions↗