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PubMed2001

Dimethyl sulfide, a volatile flavor constituent, is a slow-binding inhibitor of tyrosinase.

In this paper, the inhibition of tyrosinase by a volatile compound is kinetically analyzed for the first time. The results obtained show that the volatile flavor constituent dimethyl sulfide (DMS) inhibits the catecholase activity of tyrosinase in a nonclassical manner. A decrease in the initial velocity to a inhibited steady-state velocity can be observed within a few minutes. This time dependence, which is unaltered by prior incubation of the enzyme with the inhibitor, is consistent with a first-order transition. Both the initial and the constant rates decreased with increasing concentrations of inhibitor. The kinetic data obtained correspond to those for a postulated mechanism involving rapid formation of an enzyme-inhibitor complex that subsequently undergoes a relatively slow reversible reaction. These results, together with the high levels of DMS precursor in certain organisms, suggest a physiological role for this compound within plant tissues.

Agaricales↗
PubMed1994

Strategies employed to determine the acute aquatic toxicity of ethyl benzene, a highly volatile, poorly water-soluble chemical.

Studies are described in which ethyl benzene (EB) was tested to determine its acute toxicity to three marine organisms, Atlantic silversides (Menidia menidia), mysid shrimp (Mysidopsis bahia), and diatoms (Skeletonema costatum), and to one freshwater algae (Selenastrum capricornutum). The respective 96-hr median lethal concentration (LC50) values and 95% confidence intervals for EB in the flow-through studies with fish and mysid shrimp were 5.1 (4.4-5.7) mg/liter and 2.6 (2.0-3.3) mg/liter. While the 96-hr median effective concentrations (EC50's) for growth inhibition and 95% confidence intervals for the static studies with diatoms and algae were 7.7 (5.9-10.0) mg/liter and 3.6 (1.7-7.6) mg/liter, respectively. Problems were encountered in all four studies as a result of the high volatility and poor water solubility of EB in water and an apparent "salting out" effect noted in seawater. This effect was found particularly true in the diatom and algae studies where the salinity was increased with the addition of culture medium. Measures are described which were used to overcome this stability problem with EB. These included sealing the test systems tight without any air spaces to prevent the collection of EB vapors. Also, increased mixing of EB in the test solutions was found to be essential in the flow-through studies to maintain stable levels. In the case of the diatom and algal studies, since current EPA test guidelines were judged to be inadequate to overcome EB volatility from the test medium, a new closed test system had to be developed and employed, after validation with a nonvolatile reference toxicant in the new and conventional static test systems. The results of these studies indicate that previous reports underestimated the potential acute aquatic toxicity of EB by at least one order of magnitude. The implications of these findings are discussed in relation to the potential environmental impact of EB and the resultant regulatory actions.

Animals↗
PubMed2000

Determination of Thermodynamic Parameters from Evaporation of Binary Microdroplets of Volatile Constituents.

An experimental technique based on a modified vibrating orifice aerosol generator has been employed to study unsteady evaporation of linear streams of highly monodisperse binary microdroplets of volatile constituents over short time periods (i.e., <1 ms), such that the droplet composition remains nearly constant. The droplet size and temperature (i.e., refractive index) have been determined with high temporal resolution from the resonances observed in the simultaneous elastic and Raman light scattering spectra obtained by varying the droplet size through modulation of droplet generation frequency. By using this technique we show that thermodynamic parameters of binary systems, such as activity coefficients as well as vapor pressures of the constituents as functions of temperature, can be determined. We have applied the procedure to study unsteady evaporation rates of pure ethanol and methanol droplets as well as binary droplets containing various ratios of ethanol and methanol. We have obtained vapor pressures of ethanol and methanol as functions of temperature as well as activity coefficients of ethanol and methanol as functions of composition, and the results show excellent agreements with the values reported in the literature. The technique presented in this paper is applicable to any binary system containing at least one volatile constituent. Copyright 2000 Academic Press.

Journal Article↗
PubMed1994

The specific binding site of the volatile anesthetic diiodomethane to purple membrane by X-ray diffraction.

To determine the binding site of volatile anesthetics on purple membrane, diiodomethane (CH2I2) was used as a label in X-ray diffraction experiments. At less than 3 mM diiodomethane, purple membrane retains its two-dimensional crystallinity of bacteriorhodopsin, absorption spectra show only a little blue shift and the decay time of the M-intermediate becomes fast in flash photolysis experiments. These effects are similar to those of other anesthetics previously studied. The position where the anesthetic binds was identified by difference Fourier methods, and refined by model calculations. This study suggests that volatile anesthetics bind specifically to the protein-lipid interfacial region near the surface of membrane.

Anesthetics↗
PubMed1994

Determination of tissue partition coefficients for volatile tissue-reactive chemicals: acrylonitrile and its metabolite 2-cyanoethylene oxide.

Partition coefficients (PCs) are chemical-specific parameters used in physiologically based pharmacokinetic models to describe chemical solubility in tissues. Tissue:air PCs for volatile chemicals can be estimated using vial equilibration techniques in which the chemical concentration in the vial headspace is measured by gas chromatography after equilibrium is reached between the chemical in tissue and air. However, equilibrium would not be expected with tissue-reactive chemicals such as acrylonitrile (ACN) or its epoxide metabolite 2-cyanoethylene oxide (CEO). Active uptake of ACN was observed in rat blood due to reaction with blood sulfhydryl groups, while CEO reacted with all tissues examined (rat blood, muscle, fat, liver, and brain). The active uptake processes were first order as evidenced by a linear decrease in the log of the vial headspace concentrations over time. Linear extrapolation of the log of the apparent PC to zero time, where the contribution of the active uptake process is zero, yielded an estimated PC of 487 for ACN in blood. Equilibrium was achieved with ACN after treatment of blood with diethyl maleate to modify blood sulfhydryl groups, with a PC of 512 +/- 29 (mean +/- SE, n = 14). These PC estimates were verified by direct measurement of ACN concentrations in both the air and the blood (stabilized by acidification). The directly measured ACN blood:air PC was 437 +/- 8 (n = 8), which compared well with the estimated values. Treatment of tissues with diethyl maleate or 2,4-dinitrofluorobenzene did not abolish the active uptake of CEO. However, pretreatment of tissues with CEO itself abolished subsequent CEO uptake. The CEO blood:air PC estimates obtained from zero time extrapolation of four CEO concentrations (1672 +/- 139) and from CEO pretreatment (1658 +/- 137, n = 8) were in good agreement. These data indicate that tissue:air PCs for volatile reactive chemicals can be estimated by extrapolation of a first-order uptake process to zero time or at equilibrium following chemical modification of reactive groups in tissues.

Acrylonitrile↗
PubMed1995

Physicochemical properties of nonreactive volatile organic chemicals to estimate RD50: alternatives to animal studies.

This article presents the correlations obtained between the results on the potency of nonreactive airborne chemicals as sensory irritants and several of their physicochemical properties. The potency of airborne sensory irritants obtained from a reflexively induced decrease in respiratory frequency has been measured in the past using mice. Typically, their potency has been expressed as the exposure concentration necessary to decrease respiratory frequency by 50% (RD50). A large database of RD50 values is now available and such values are highly correlated with occupational exposure guidelines such as threshold limit values (TLVs). We used the nonreactive volatile organic chemicals from this database, for which relevant physicochemical variables are available or can be calculated. These variables were vapor pressure (P) or Ostwald gas-liquid partition coefficients (L). The liquids used for L values were n-hexadecane, octanol, N-formylmorpholine, tri-(2-ethylhexyl)phosphate, and olive oil. Excellent correlations were found between log RD50 and log P, as well as between log RD50 and log L16, log L(Oct), log L(NFM), log L(EHP), or log L(Oil). It follows that as an alternative to the bioassay, these physicochemical variables can be used to estimate RD50 of nonreactive volatile organic chemicals. Appropriate exceptions to general estimation of RD50 values from physicochemical variables are also presented, as well as the most appropriate estimates which can be obtained within homologous series.

Air Pollutants, Occupational↗
PubMedDate not supplied

Volatile N-nitrosamines in mainstream cigarette smoke: occurrence and formation.

Analytical data is presented for the occurrence of the three major volatile N-nitrosamines in cigarette tobacco and mainstream smoke, namely N-nitrosodimethylamine (NDMA),- N-nitrosoethylmethylamine (NEMA) and N-nitrosopyrrolidine (NPYR) as well as for the occurrence of the corresponding precursor amines and non-volatile N-nitrosamino acids in tobacco. Experimental studies using the C20 reference cigarette show that NPYR present in mainstream smoke results from direct transfer of preformed NPYR (ca. 1.5%), decarboxylation of N-nitrosoproline in tobacco (ca. 10%), pyrolytic nitrosation of pyrrolidine in tobacco (ca. 37%) and concerted decarboxylation/nitrosation of proline (ca. 52%) during tobacco pyrolysis.

Chromatography, Gas↗
PubMed1980

Freeze-fracturing and deep-etching with the volatile cryoprotectant ethanol reveals true membrane surfaces of kidney structures.

With the conventional freeze-fracture technique applied to biological specimens, cell membranes split along an interior plane and two membrane faces are produced. True membrane surfaces remain hidden and can only be uncovered by deep-etching. To date, deep-etching could not be satisfactorily performed in the presence of cryoprotective agents since conventional cryoprotectants do not sublime due to their low vapour pressure. This lack of suitable volatile cryoprotectants has limited deep-etching so far to very small objects which can be cryofixed without cryoprotectants. As a consequence, our freeze-fracture knowledge of cell surfaces is still poor. The present study shows that ethanol is a suitable volatile cryoprotectant for the freeze-fracture technique, and provides a novel approach to the routine deep-etching of freeze-fracture specimens without the need for special equipment. With ethanol deep-etching, true outer cell-surfaces are demonstrated within the kidneys of rat and Psammomys.

Animals↗
PubMed1991

Correlation of levels of volatile versus carcinogenic particulate polycyclic aromatic hydrocarbons in air samples from smokehouses.

In the present study, data on the concentration of polycyclic aromatic hydrocarbons (PAH) in air samples from fish smokehouses (Nordholm et al. 1986) and meat smokehouses (Hansen et al. submitted for publication) were used to analyze the extent to which six different volatile PAH compounds could function as markers for the total concentration of six different carcinogenic particulate PAH compounds. Although a significant positive correlation was observed between the concentration of each of six volatile compounds and the total concentration of carcinogenic PAH compounds, a particularly good correlation was observed for phenanthrene, anthracene, fluoranthene and pyrene. Calculations of the sensitivity, specificity, positive predictive value and negative predictive value of these potential markers revealed that naphthalene and phenanthrene exhibited the highest sensitivity as markers for total carcinogenic PAH compounds in air samples from smokehouses, whereas fluoranthene and pyrene displayed the highest specificity. However, when the applicability of the six markers was tested on air samples from iron foundries, only naphthalene and pyrene were useful as markers for the carcinogenic compounds. The present study indicates that naphthalene and pyrene might function as markers for carcinogenic PAH compounds, that are present at low concentrations and are therefore difficult and time-consuming to measure directly.

Air Pollutants, Occupational↗
PubMed1983

Distribution and strain-dependent formation of volatile metabolites in the genus Ceratocystis.

The accumulation of volatile metabolites in cultures of 34 strains comprising ten species of the genus Ceratocystis (Ascomycetes) has been investigated under defined culture conditions. The identified compounds include short-chain alcohols and esters, lower terpenes, terpenoids, and 2-phenylethyl acetate. Certain species can be recognized by a number of common volatiles traced in all strains, although the quantities of these constituents may vary enormously (up to a factor 1:1000) within one species. The formation of some metabolites is restricted to a few strains.

Acetates↗
PubMed1994

Volatile anesthetics inhibit NMDA-stimulated 45Ca uptake by rat brain microvesicles.

We have previously shown that volatile anesthetics inhibit glutamate-stimulated [3H]MK-801 binding to the ionophore of NMDA receptor complexes in rat brain. In the present study, we examined the influence of enflurane and halothane on NMDA-stimulated 45Ca uptake by a microvesicle fraction isolated from rat brain. NMDA stimulated 45Ca uptake (30 sec) by rat brain microvesicles by up to 70% with an EC50 of 1.4 +/- 0.5 microM. The NMDA-stimulated 45Ca uptake was inhibited by MK-801 and D-AP-5 with IC50's of approximately 10 microM. Enflurane and halothane inhibited 45Ca uptake stimulated by 100 microM NMDA by as much as 60-80% with IC50's of 0.2-0.3 mM, concentrations achieved during routine clinical use. Basal 45Ca uptake measured in the absence of agonist was not affected by the anesthetics. Glycine did not affect the level of NMDA-stimulated 45Ca uptake, but markedly reduced the inhibition of uptake caused by enflurane and halothane. Preincubation of microvesicles with NMDA resulted in a desensitization of NMDA-stimulated 45Ca uptake, with a t1/2 of approximately 20 sec. Enflurane and halothane diminished both the extent and rate of development of this desensitization, as did glycine. These findings support the idea that volatile anesthetic interference with neurotransmission at NMDA receptor complexes contributes to the development of the anesthetic state.

2-Amino-5-phosphonovalerate↗
PubMed1975

Formation of volatile compounds and brown products in the model system n-hexanal-glycine.

During the boiling of a mixture of n-hexanal and glycine in aqueous medium, pH value 9, both soluble and insoluble brown colored pigments and volatile compounds were formed. The following volatile compounds were identified by gas chromatography and mass spectrometry; hexanone, decenone, undecenone, undecan-5-one, undecenedione, dodecenone, tridecanone, dodecanedione, tridecenone, dodecenedione, hexenyl hexanoate, caproic, valeric and butyric acids. The brown coloured pigments insoluble in water contained 0.57% of nitrogen. The presence of conjugated double-bonds, carbonyl and carboxyl groups was confirmed by spectral methods. The pigments were also separated by thin-layer chromatography on silica gel.

Aldehydes↗
PubMed1977

[Enzymatic breakdown of linoleic acid hydroperoxides to volatile carbonyl compounds by isomerase from barley (author's transl)].

Barley protein fractions with active isomerase, purified by means of gelchromatography were incubated at room temperature with linoleic acid hydroperoxides (LHPO), containing 9-hydroperoxy-10-trans,12-cis-octadecadienoic acid (9-LHPO) and 13-hydroperoxy-9-cis,11-trans-octadecadienoic acid (13-LHPO) in the ratio of about 1:1. The volatile compounds resulting from the reaction have been isolated, concentrated and investigated by means of gas- and radio-gaschromatography. In the case of incomplete LHPO-breakdown remaining hydroperoxides and nonvolatile breakdown products have been separated before gaschromatographic analysis. In addition to hexanal as main product, traces of 2-tr-heptenal and 2-tr-octenal were found; about 6% of the converted hydroperoxides were transformed to carbonyl compounds. By numerous additional experiments it was confirmed that the volatile compounds are formed by enzymatic catalysis.

Biodegradation, Environmental↗
PubMed1977

[Co-oxydation of linoleic acid to volatile compounds by lipoxygenase isoenzymes from soya beans (author's transl)].

Lipoxygenase isoenzymes L-1 (optimum pH 9.0) and L-2 (pH 6.5) were incubated with linoleic acid. The extracted volatile compounds were separated by gas-chromatography and analysed by mass spectrometry. The relative amounts of volatile carbonyl compounds, which were formed during catalysis were determined (mole percent). L-1 yielded hexanal (greater than 90% at pH 7 and 70% at pH 8.5). L-2 at pH 7 yielded hexanal (31), two geometric isomers of 2,4-decadienal (40), 2-trans-heptenal (12) and 2-trans-octenal (10).

Isoenzymes↗
PubMed1985

[Aroma of the papaya fruit (Carica papaya, L.): indication of volatile precursors of terpene compounds].

In fruit pulp of papaya (Carica papaya, L.) the enzymes were inhibited by Hg2+. These sample were compared with others, in which the enzymes had not been inhibited. After separation and prefractionation of volatiles by means of high vacuum distillation/solvent extraction and subsequent adsorption chromatography on silicagel, capillary gas chromatography-mass spectrometry showed that in the experiment with Hg2+ the formation of terpene alcohols and hydrocarbons as well as benzylisothiocyanate was totally inhibited. The formation of linalooloxides and related compounds was inhibited to about 60%. From these results the occurrence of bound terpene precursors in papaya fruit may be postulated, from which the free volatile terpenes are enzymatically liberated after decompartmentalization of tissue during fruit pulp preparation.

Chromatography, Affinity↗
PubMed1980

Rapid temperature programmed gas-liquid chromatography of volatile fatty acids (C1-C7) for the identification of anaerobic bacteria.

A gas liquid chromatography method for the separation of 10 volatile fatty acids (C1-C7 and isomers) has been improved by using oven temperature programmed conditions. In our conditions, the proprietary stationary phase SP 1220 introduced by Supelco Inc., gave sharp separation of volatile fatty acids in less than 8 min. This method was suitable for analyses with both thermal conductivity and flame ionization detectors.

Anaerobiosis↗
PubMed1984

Model systems demonstrating the volatile mutagenicity and carcinogenicity of sodium nitrite in rats.

Volatile mutagens derived from sodium nitrite buffered at various pH values or in the presence of human feces were detected using Ames Salmonella tester strain TA 1535 on petrie plates inverted over samples. Volatile mutagenicity increased as the pH decreased and was primarily a function of the nitrous acid produced from sodium nitrite and hydrogen ions. Sodium nitrite administered intracecally to 3 Wistar rats through surgically implanted cannula caused tumors (fibrosarcoma: 1/3 and squamous cell, 2/3). The possible role of nitrite-derived mutagens in GI cancer is discussed.

Animals↗
PubMed1978

Effect of volatile substances released from Origanum majorana and Ocimum basilicum on the rhizosphere and phyllosphere fungi of Phaseolus vulgaris.

Differences were found in the counts and occurrence of fungi in the phyllosphere and thizosphere of two representatives of the Lamiacea family, Origanum majorana and Ocimum basilicum, and in the phyllosphere and rhizosphere of Phaseolus vulgaris growing separately or in coenosis with O. majorana or O. basilicum. Both the volatile substances released from ground leaves of the two latter plant species and the root exudates affected considerably spore germination of isolated phylospheric and rhizospheric fungi. The results indicated a possible role of root exudates and volatile substances released from leaves in colonization of rhizosphere and/or phyllosphere by fungi, especially in associations of various plants.

Air Microbiology↗

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