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PubMed1991

Homogeneous solutions of hydrophilic enzymes in nonpolar organic solvents. New systems for fundamental studies and biocatalytic transformations.

A typical hydrophilic enzyme, CT, can be dissolved in nonpolar organic solvents (n-octane, cyclohexane and toluene) up to microM concentrations. In the homogeneous solution obtained, the enzyme possesses catalytic activity and enormously high thermostability. It does not lose this activity even after several hours refluxing in octane (126 degrees C) or cyclohexane (81 degrees C).

Catalysis↗
PubMed2005

Determination of aminoheterocycle and azabicycle in gliclazide bulk by capillary zone electrophoresis with amperometric detection.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), was developed for simultaneous determination of 3-amino-3-azabicyclo[3,3,0]octane (aminoheterocycle) and 3-azabicyclo[3,3,0]octane (azabicycle) in gliclazide bulk drug. The optimal conditions of CZE-AD were 50 mM borate solution (pH 9.0) as running buffer, 14 kV as separation voltage and 0.95 V (versus SCE) as detection potential. Under the selected optimum conditions, the two analytes could be perfectly separated within 9 min. The linearity range of aminoheterocycle was from 1.0 x 10(-6) to 1.0 x 10(-3) M and that of azabicycle was from 2.0 x 10(-6) to 1.0 x 10(-3) M. Their detection limits were 5.0 x 10(-7) and 1.0 x 10(-6) M, respectively, (S/N=3). This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 2% for both migration time and peak current. It has been successively used for the determination of these two analytes in gliclazide bulk drug, and the assay results were satisfactory.

Benzylamines↗
PubMed2002

Preparation and physical characterization of pure beta-carotene.

Pure all-trans beta-carotene has been prepared on the 10's of grams scale by isothermal Fractional Dissolution (FD) of commercial laboratory samples in tetrahydrofuran (THF). beta-Carotene purified in this way is black, with a faint brownish tinge. The electronic spectra of black samples extend into the near infrared, with end-absorption past 750 nm. Black samples react directly with dioxygen under mild conditions to yield the familiar orange or red powders. Pure beta-carotene rigorously obeys Beer's Law in octane over the entire UV-Vis spectral range, while commercial laboratory samples and recrystallized samples do not. NMR self-diffusion coefficient data demonstrate that beta-carotene exists as simple molecular solutions in octane and toluene. The anomalously high crystallinity of beta-carotene can be attributed (from analysis using molecular mechanics) to the facts that: (1) the number of theoretically possible conformers of beta-carotene is extremely small, and (2) only a small fraction of these (ca. 12%, or 127) may actually exist in fluid phases.

Color↗
PubMed2003

Solvent influence on excited-state intramolecular proton transfer in 3-hydroxychromone derivatives studied by cryogenic high-resolution fluorescence spectroscopy.

High-resolution Shpol'skii spectra (recorded at 10 K in n-octane) of 3-hydroxychromone (3HC) substituted at the 2-position with a furan (3HC-F), a benzofuran (3HC-BF) or a naphthofuran group (3HC-NF) are presented. Being close analogues of 3-hydroxyflavone (3HF), these compounds can undergo excited-state intramolecular proton transfer (ESIPT). Luminescence can occur from the normal N* state (blue) or from the tautomeric T* state (green). Whether blue or green emission is observed is strongly dependent on hydrogen-bonding interactions with the environment. For all three chromones studied, high-resolution emission spectra in the green region (T*-->T) were obtained in pure n-octane, showing four sites with distinct emission bands and detailed vibrational structures, whereas no blue emission was detected. Contrary to the spectra published for 3HF, the emission lines were very narrow (line-broadening effects beyond detection) which implies that the ESIPT rate constants are >10(12) s(-1), at least 25 times lower than for 3HF. In order to study the effects of hydrogen-bonding solvents, four isomers of octanol (1-, 2-, 3- and 4-octanol) were added, forming 1:1 complexes with the 3HC derivatives. For all the combinations considered both blue and additional green emission was observed and in some cases narrow-banded spectra were obtained, mostly in the green. Only for the 3HC-NF/2-octanol complex, narrow-banded emission was found both in the blue and in the green region. It is demonstrated that these emissions come from different configurations of the complex. Possible structures for the two complex species are proposed, supported by semi-empirical calculations on complex formation enthalpies.

Chromones↗
PubMed2001

Comparison of response of six different luminescent bacterial bioassays to bioremediation of five contrasting oils.

The performance of six different bioluminescent bacteria for the assessment of oil bioremediation was compared. Three contained lux genes linked to promoters from hydrocarbon degradation pathways: Pseudomonas fluorescens HK44 (pUTK21), Escherichia coli HMS174 (pOS25) and E. coli DH5 alpha (pGEc74, pJAMA7), responding to naphthalene, isopropylbenzene and octane, respectively. The other three expressed lux constitutively: E. coli HB101 (pUCD607) and P. putida F1 (pUCD607) are genetically engineered, while Vibrio fischeri is naturally bioluminescent and was included to facilitate comparison with previous work. Five different oils (four crude oils plus diesel) were spiked into soil, and the progress of remediation was followed over a period of 119 d by monitoring both hydrocarbon disappearance and changes in the microbial response to soil extracts. The octane bioassay was the only one of the hydrocarbon-responsive bacterial assays to show any appreciable response, with up to 20-fold induction by light crude oils. Heavy crude oil and diesel elicited a much weaker response. The metabolic (lux constitutively expressed) bioassays showed that there was a general increase in toxicity over the course of the experiment, although toxicity to E. coli HB101 (pUCD607) appeared to be decreasing by the final sampling point. The metabolic bioassay response was much less variable between the different oils than for the first three, catabolic, strains.

Benzene Derivatives↗
PubMedDate not supplied

Test methods to simulate high-temperature exposure.

A study was carried out to compare the actual overall migration from packaging materials into food simulants during heating in a microwave oven, and the overall migration from these materials into food simulants applying time and temperature conditions stipulated in the current EC and Dutch legislation on food packaging. It was demonstrated that the requirement by some food packaging regulations to conduct migration tests in a conventional oven using test conditions that are more stringent than the conditions occurring in practice results in excessively severe and unreasonable test conditions. On the basis of the results obtained additional test conditions (e.g. 30 min and 1 h in combination with test temperatures exceeding 121 degrees C, and a test temperature of 130 degrees C) are proposed to be inserted in existing food packaging regulations to enable realistic migration testing of microwave packaging materials under conventional test conditions. It is concluded that the overall migration behaviour of packaging materials intended for microwave oven use, including microwave-active (susceptor) materials, can be judged on the basis of migration testing using conventional heating. The suitability of iso-octane as a volatile fatty food simulant for the determination of the overall migration under high-temperature test conditions was also investigated. For most samples investigated a good agreement was observed between the overall migration values obtained with olive oil applying both microwave and conventional heating, and those obtained with iso-octane under conventional conditions.

Aluminum↗
PubMedDate not supplied

The suitability of alternative fatty food simulants for overall migration testing under both low- and high-temperature test conditions.

The suitability of various alternative, volatile fatty food simulants for overall migration testing was investigated under both low- and high-temperature test conditions. The overall migration into olive oil from a large number of commercially used food packaging materials applying various low- and high-temperature test conditions (e.g. 2 h at 175 degrees C, 30 min at 130 degrees C, 1 h at 100 degrees C followed by 10 days at 40 degrees C, 10 days at 20 degrees C) was determined. The results were compared with overall migration from these samples into iso-octane, 50% or 95% ethanol and isopropanol under appropriate test conditions. The samples investigated include homogeneous plastic films, laminates, coated board samples, a coated can, and articles. The results of the study indicate that iso-octane, 95% ethanol and isopropanol are suitable alternative fatty food simulants for overall migration testing under various time and temperature conditions.

2-Propanol↗
PubMed1998

Specific migration testing with alternative fatty food simulants.

Many additives used in plastics materials and articles intended for food contact are expected to be assigned specific migration limits (SMLs) in a future amendment to EC Directive 90/128/EEC. In order to demonstrate compliance with these restrictions, specific migration tests will need to be performed on the finished plastics packaging using foods or the appropriate EC food simulants. Owing to the involatile and lipophilic nature of many of these additives, their analysis in the conventional fatty food simulant, olive oil, presents technical difficulties. One way of overcoming these difficulties would be to use a simple solvent alternative to olive oil as has been proposed for overall migration testing. The objective of this work is to compare specific migration data obtained using olive oil with alternative fat simulants iso-octane and 95% ethanol, to find out if similar results are obtained and identify the most appropriate alternative simulant to use for future testing. Good agreement with the olive oil migration data was obtained using 95% ethanol (equivalent exposure conditions) for both of the additives studied in polyolefins. For the polystyrene materials studied it is unlikely that the SMLs for the two additives would be exceeded, and in these cases iso-octane (1.5 h at 60 degrees C) could be used as a rapid 'alternative test'.

Adipates↗
PubMed1950

Biologic significance of the structure of hydrocarbons. I. Chain structure.

1. The biologic experiments with the links of the methane series-n-pentane, n-hexane, n-heptane, n-octane, i-octane, and pentene-gave these qualitative results: (a) The higher the number of CH(2) groups, the longer the chain, the longer the average lifetime of the animal. (b) The ramified chain does not appear to act differently from the saturated straight chain with the same number of C atoms. (c) One double bond within the chain shortens the lifetime to a considerable degree. 2. The quantitative discussion shows that the lifetimes depend exponentially on the molecular weight. 3. Qualitatively the hypothesis is supported that with rising molecular weight the concentration of CH(2) groups within the animal diminishes according to the vapor pressure or the thermodynamic potential. However, lifetime and these physical properties obey different functions. 4. These physical properties are of high biologic importance. But they are not sufficient to explain the biologic effects quantitatively.

Animals↗
PubMed1987

Cell surface hydrophobicity of Actinobacillus actinomycetemcomitans Y4.

Oral bacteria colonize the dento-gingival tissues in a selective manner. Hydrophobic reactions have been suggested as one of the major mechanisms of adhesion. Hydrophobicity of Actinobacillus actinomycetemcomitans Y4 (Aa) cells was studied in vitro using adherence to the liquid hydrocarbon, octane. Adherence of Aa cells to octane varied from 60-90%, depending on the medium in which they were grown, age of the culture and the buffer in which the assay was carried out. These data suggest that Aa is a hydrophobic bacterium, the hydrophobicity of which is expressed to a varying degree, and may have a rôle in its adherence to oral tissues.

Actinobacillus↗
PubMed1996

Hydrophobic and electrostatic cell surface properties of Cryptosporidium parvum.

Microbial adhesion to hydrocarbons and microelectrophoresis were investigated in order to characterize the surface properties of Cryptosporidium parvum. Oocysts exhibited low removal rates by octane (only 20% on average), suggesting that the Cryptosporidium sp. does not demonstrate marked hydrophobic properties. A zeta potential close to -25 mV at pH 6 to 6.5 in deionized water was observed for the parasite. Measurements of hydrophobicity and zeta potential were performed as a function of pH and ionic strength or conductivity. Hydrophobicity maxima were observed at extreme pH values, with 40% of adhesion of oocysts to octane. It also appeared that ionic strength (estimated by conductivity) could influence the hydrophobic properties of oocysts. Cryptosporidium oocysts showed a pH-dependent surface charge, with zeta potentials becoming less negative as pH was reduced, starting at -35 mV for alkaline pH and reaching 0 at isoelectric points for pH 2.5. On the other hand, variation of surface charge with respect to conductivity of the suspension tested in this work was quite small. The knowledge of hydrophobic properties and surface charge of the parasite provides information useful in, for example, the choice of various flocculation treatments, membrane filters, and cleaning agents in connection with oocyst recovery.

Animals↗
PubMed1979

Fertility factors in Pseudomonas putida: selection and properties of high-frequency transfer and chromosome donors.

The octane plasmid (OCT) in Pseudomonas putida strains has been shown to be transferred at low frequency. However, bacteria which had newly received this plasmid showed a transient increase in donor ability. Using Octane+ P. putida as the donor, the transfer of most chromosomal markers was shown to be independent of OCT transfer, whereas the mobilization of the octanoate catabolism genes (octanoic and acetate) was dependent on OCT plasmid transfer. The presence of a fertility factor termed FPo has been postulated to explain these results. Strains carrying only this fertility factor have been obtained from strains carrying both OCT and FPo plasmids. Strains in which the OCT plasmid was transferred at high frequencies have also been isolated, and chromosome mobilization by OCT and FPo has been compared. A different gradient of transmission by OCT and FPo has been observed. It has also been shown that chromosome transfer by OCT was dependent on the bacterial recombination system, whereas the chromosome transfer by FPo was unaffected by the presence of a rec mutation in the donor strain.

Caprylates↗
PubMed2004

The molecular basis of electroporation.

BACKGROUND: Electroporation is a common method to introduce foreign molecules into cells, but its molecular basis is poorly understood. Here I investigate the mechanism of pore formation by direct molecular dynamics simulations of phospholipid bilayers of a size of 256 and of more than 2000 lipids as well as simulations of simpler interface systems with applied electric fields of different strengths. RESULTS: In a bilayer of 26 x 29 nm multiple pores form independently with sizes of up to 10 nm on a time scale of nanoseconds with an applied field of 0.5 V/nm. Pore formation is accompanied by curving of the bilayer. In smaller bilayers of ca. 6 x 6 nm, a single pore forms on a nanosecond time scale in lipid bilayers with applied fields of at least 0.4 V/nm, corresponding to transmembrane voltages of ca. 3 V. The presence of 1 M salt does not seem to change the mechanism. In an even simpler system, consisting of a 3 nm thick octane layer, pores also form, despite the fact that there are no charged headgroups and no salt in this system. In all cases pore formation begins with the formation of single-file like water defects penetrating into the bilayer or octane. CONCLUSIONS: The simulations suggest that pore formation is driven by local electric field gradients at the water/lipid interface. Water molecules move in these field gradients, which increases the probability of water defects penetrating into the bilayer interior. Such water defects cause a further increase in the local electric field, accelerating the process of pore formation. The likelihood of pore formation appears to be increased by local membrane defects involving lipid headgroups. Simulations with and without salt show little difference in the observed pore formation process. The resulting pores are hydrophilic, lined by phospholipid headgroups.

Chemical Phenomena↗
PubMedDate not supplied

[Stability of glucose 6-phosphate dehydrogenase complexed with its substrate and/or cofactor in aqueous and micellar environment].

Inactivation of glucose 6-phosphate dehydrogenase (G6PDH) complexed with its substrate, glucose 6-phosphate (GP), and/or cofactor, NADP+, has been studied within the range 20-40 degrees C in three media: (a) 0.04 M NaOH-glycine buffer (pH 9.1); (b) Aerosol OT (AOT) reversed micelles in octane; and (c) Triton X-100 micelles in octane supplemented with 10% hexanol. The enzyme inactivation was characterized quantitatively by first order rate constants, kin (s-1). In the case of G6PDH-NADP+ complexes, the values of kin were independent of the initial concentrations of G6PDH, either in aqueous medium or AOT micelles. The values of kin for the complex G6PDH-GP were inversely related to the initial concentration of the enzyme, in both aqueous and micellar media. When inactivation of both complexes were studied in AOT micelles, minimum values of kin corresponded to the degree of hydration W0 = 16.7; at W0 > 16.7 and W0 < 16.7, kin increased. Within the range 20-40 degrees C, the values of kin measured for both complexes in aqueous medium were significantly lower than those measured in AOT micelles. Temperature dependences of kin were characterized by inflections in Arrhenius plots, which corresponded, depending on the medium, to certain temperatures from 33.6 degrees C to 40 degrees C. In all media studied, NADP+ complexes of the enzyme exhibited higher stability than their GP counterparts. The parameters of G6PDH and G6PDH-NADP+ melting, measured by differential scanning microcalorimetry (maximum temperature and half-width of the transition, enthalpy of denaturation, and van't Hoff enthalpy), provided unequivocal evidence of the higher stability of the complex as compared to that of the enzyme. In addition, this approach demonstrated that G6PDH undergoes destabilization in AOT micelles.

Buffers↗
PubMed1987

Controlled and functional expression of the Pseudomonas oleovorans alkane utilizing system in Pseudomonas putida and Escherichia coli.

The OCT plasmid encodes enzymes for alkane hydroxylation and alkanol dehydrogenation. Structural components are encoded on the 7.5-kilobase pair alkBAC operon, whereas positive regulatory components are encoded by alkR. We have constructed plasmids containing fusions of cloned alkBAC and alkR DNA and used these fusion plasmids to study the functional expression of the alkBAC operon and the regulatory locus alkR in Pseudomonas putida and in Escherichia coli. Growth on alkanes requires a functional chromosomally encoded fatty acid degradation system in addition to the plasmid-borne alk system. While such a system is active in P. putida, it is active in E. coli only in fadR mutants in which fatty acid degradation enzymes are expressed constitutively. Using such mutants, we found that E. coli as well as P. putida grew on octane as the sole source of carbon and energy when they were supplied with the cloned complete alk system. The alkR locus was strictly necessary in E. coli as well as in P. putida for expression of the alkBAC operon. The alkBAC operon could, however, be further reduced to a 5-kilobase pair operon without affecting the Alk phenotype in either species to a significant extent. Although with this reduction the plasmid-encoded alkanol dehydrogenase activity was lost, chromosomally encoded alkanol dehydrogenases in P. putida and E. coli compensated for this loss. The induction kinetics of the alk system was studied in detail in P. putida and E. coli. We used specific antibodies raised against alkane hydroxylase to follow the appearance of this protein following induction with octane. We found the induction kinetics of alkane hydroxylase to be similar in both species. A steady-state level was reached after about 2 h of induction in which time the alkane hydroxylase accounted for about 1.5% of total newly synthesized protein. Thus, alkBAC expression is very efficient and strictly regulated to both P. putida and E. coli.

Alkanes↗
PubMed1988

Enzymatic catalysis in nonaqueous solvents.

Subtilisin and alpha-chymotrypsin vigorously act as catalysts in a variety of dry organic solvents. Enzymatic transesterifications in organic solvents follow Michaelis-Menten kinetics, and the values of V/Km roughly correlate with solvent's hydrophobicity. The amount of water required by chymotrypsin and subtilisin for catalysis in organic solvents is much less than needed to form a monolayer on its surface. The vastly different catalytic activities of chymotrypsin in various organic solvents are partly due to stripping of the essential water from the enzyme by more hydrophilic solvents and partly due to the solvent directly affecting the enzymatic process. The rate enhancements afforded by chymotrypsin and subtilisin in the transesterification reaction in octane are of the order of 100 billion-fold; covalent modification of the active center of the enzymes by a site-specific reagent renders them catalytically inactive in organic solvents. Upon replacement of water with octane as the reaction medium, the specificity of chymotrypsin toward competitive inhibitors reverses. Both thermal and storage stabilities of chymotrypsin are greatly enhanced in nonaqueous solvents compared to water. The phenomenon of enzymatic catalysis in organic solvents appears to be due to the structural rigidity of proteins in organic solvents resulting in high kinetic barriers that prevent the native-like conformation from unfolding.

Catalysis↗
PubMed2001

Effect of mass transfer limitations on the enzymatic kinetic resolution of epoxides in a two-liquid-phase system.

Optically active epoxides can be obtained by kinetic resolution of racemic mixtures using enantioselective epoxide hydrolases. To increase the productivity of the conversion of sparingly aqueous soluble epoxides, we investigated the use of a two-phase aqueous/organic system. A kinetic model which takes into account interphase mass transfer, enzymatic reaction, and enzyme inactivation was developed to describe epoxide conversion in the system by the epoxide hydrolase from Agrobacterium radiobacter. A Lewis cell was used to determine model parameters and results from resolutions carried out in the Lewis cell were compared to model predictions to validate the model. It was found that n-octane is a biocompatible immiscible solvent suitable for use as the organic phase. Good agreement between the model predictions and experimental data was found when the enzyme inactivation rate was fitted. Simulations showed that mass transfer limitations have to be avoided in order to maximize the yield of enantiomerically pure epoxide. Resolution of a 39 g/L solution of racemic styrene oxide in octane was successfully carried out in an emulsion batch reactor to obtain (S)-styrene oxide in high enantiomeric excess (>95% e.e.) with a yield of 30%.

Bioreactors↗
PubMed2004

Antioxidative roles of sesamin, a functional lignan in sesame seed, and it's effect on lipid- and alcohol-metabolism in the liver: a DNA microarray study.

Sesamin was orally administered to rats, and blood, bile and urine were collected periodically. Over 40% of the dose of sesamin was detected in bile as glucuronides of 2-(3, 4-methylenedioxyphenyl)-6-(3, 4-dihydroxyphenyl)-cis-dioxabicyclo[3.3.0] octane and 2-(3, 4-dihydroxyphenyl)-6-(3, 4-dihydroxyphenyl)-cis-dioxabicyclo[3.3.0] octane by 24 hr after administration. Antioxidant activities of these metabolites were compared and catechol metabolites showed strong radical scavenging activities against not only superoxide anion radical but also hydroxyl radical. It was suggested that sesamin was absorbed by the route of portal vein and metabolized to mono- or di-catechol metabolite by drug metabolizing enzymes in the liver cells. Both metabolites exhibited antioxidant activity in the liver and were finally conjugated with glucuronic acid and to excrete in bile. Sesamin can be classified as a pro-antioxidant. The profiles of gene expression of the liver in rats given sesamin or vehicle were compared. The gene expression levels of the late stage enzymes of beta-oxidation including trifunctional enzyme, acyl-CoA oxidase, bifunctional enzyme and 3-ketoacyl-CoA thiolase were significantly increased by sesamin. On the other hand, the transcription of the genes encoding the enzymes for fatty acid synthesis was decreased. Moreover, in sesamin rats, the gene expression of aldehyde dehydrogenase was increased about 3-fold, whereas alcohol dehydrogenase, liver catalase and CYP2E1 were not changed. These results suggested that sesamin ingestion regulated the transcription levels of hepatic metabolizing enzymes for lipids and alcohol.

Administration, Oral↗