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Qualitative evidence is presented to contend that the predominant response of waterway grain shippers on the Upper Mississippi River-Illinois Waterway to increases in barge shipping costs is most likely to be modal shift. Even so, modal shift faces serious constraints, moderating its ability to substitute for barges as waterway shipping costs rise. In addition, empirically derived estimates of demand price elasticities for barge transport are offered on four reaches of the river system. The elasticities are moderately inelastic, ranging from −0.7 to −0.3.

New drugs are urgently needed to combat the growing problem of drug resistance in Plasmodium falciparum malaria. The infected erythrocyte is a multicompartmental system, and its transporters are of interest as drug targets in their own right and as potential routes for the delivery of antimalarial drugs. Choline is an important nutrient that penetrates infected erythrocyte membranes through the endogenous carrier and through parasite-induced permeability pathways, but nothing is known about its transport into the intracellular parasite. Here we present the first characterization of choline transport across the parasite membrane. Transport exhibits Michaelis-Menten kinetics with an apparent Km of 25.0 ± 3.5 μM for choline. The carrier is inhibitor-sensitive, temperature-dependent, and Na+-independent, and it is driven by the proton-motive force. Highly active bis-amidine and bis-quaternary ammonium compounds are also known to penetrate the host erythrocyte membrane through parasite-induced permeability pathways. Here, we demonstrate that the parasite choline transporter mediates the delivery of these compounds to the intracellular parasite. Thus, the induced permeability pathways in the host erythrocyte membrane and the parasite choline transporter described here form a cooperative transport system that shows great promise for the selective targeting of new agents for the chemotherapy of malaria. (Blood. 2004;104: 3372-3377)

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Four series of C-10 non-acetal dimers were prepared from key trioxane alcohol 10β-(2-hydroxyethyl)deoxoartemisinin (9b). All of the dimers prepared displayed potent low nanomolar antimalarial activity versus the K1 and HB3 strains of Plasmodium falciparum. The most potent compound assayed was phosphate dimer 14a, which was greater than 50 times more potent than the parent drug artemisinin and about 15 times more potent than the clinically used acetal artemether. In contrast to their potent activity versus malaria parasites, virtually all of the dimers expressed poor anticancer activity apart from the trioxane phosphate ester dimers 14a and 14b, which expressed nanomolar growth inhibitory (GI50) values versus a range of cancer cell lines in the NCI 60 human cell line screen. Further detailed studies on these dimers in vitro in HL60 cells demonstrate that both phosphate ester dimers (14a and 14b) are more potent than the anticancer agent doxorubicin. Interestingly, phosphate ester monomers 9c and 9d, antimalarially active in the low nanomolar region versus P. falciparum, are inactive as anticancer agents even at concentrations in the millimolar region. This observation emphasizes the importance of two trioxane units for high antiproliferative activity, and we propose that the nature of the linker in dimers of this type plays a crucial role in imparting potent anticancer activity.

The question of elasticity was raised to a high level in the Upper Mississippi-Illinois Waterway River Navigation study undertaken by the Rock Island District of the U.S. Army Corps of Engineers in 1994. That study, in contrast to earlier works, assumed that every shipment was sensitive to price. National Academy of Sciences reviewers supported the idea of using barge demand functions that were responsive to price but were critical of assuming this distribution rather than measuring it empirically. A study to provide information on shipper willingness to pay for barge transportation was conducted. Interviews of barge transportation providers and users regarding shipper willingness to pay are summarized, and factors affecting demand are discussed. An early attempt to estimate barge price elasticities and the problems inherent in this type of analysis are also discussed. Significant interview findings were that shippers on the Ohio River Basin navigable streams made a decision to locate there and that they would pay much more than the next least costly rate to maintain barge transportation. The findings also indicated that if commodities had a high value, were not dangerous to the public, and moved in fairly small quantities, shippers would shift from barge to rail for a small rate savings. Traditional short-run demand relationships were difficult to estimate with cross-sectional data maintained by the Tennessee Valley Authority. It appears that in many settings output decisions and decisions regarding distribution channels are made in advance of transportation considerations, so that output quantities and shipment destinations are parametric in a transportation cost minimization process.

Amodiaquine (AQ) (2) is a 4-aminoquinoline antimalarial that can cause adverse side effects including agranulocytosis and liver damage. The observed drug toxicity is believed to involve the formation of an electrophilic metabolite, amodiaquine quinoneimine (AQQI), which can bind to cellular macromolecules and initiate hypersensitivity reactions. We proposed that interchange of the 3‘ hydroxyl and the 4‘ Mannich side-chain function of amodiaquine would provide a new series of analogues that cannot form toxic quinoneimine metabolites via cytochrome P450-mediated metabolism. By a simple two-step procedure, 10 isomeric amodiaquine analogues were prepared and subsequently examined against the chloroquine resistant K1 and sensitive HB3 strains of Plasmodium falciparum in vitro. Several analogues displayed potent antimalarial activity against both strains. On the basis of the results of in vitro testing, isoquine (ISQ1 (3a)) (IC50 = 6.01 nM ± 8.0 versus K1 strain), the direct isomer of amodiaquine, was selected for in vivo antimalarial assessment. The potent in vitro antimalarial activity of isoquine was translated into excellent oral in vivo ED50 activity of 1.6 and 3.7 mg/kg against the P. yoelii NS strain compared to 7.9 and 7.4 mg/kg for amodiaquine. Subsequent metabolism studies in the rat model demonstrated that isoquine does not undergo in vivo bioactivation, as evidenced by the complete lack of glutathione metabolites in bile. In sharp contrast to amodiaquine, isoquine (and Phase I metabolites) undergoes clearance by Phase II glucuronidation. On the basis of these promising initial studies, isoquine (ISQ1 (3a)) represents a new second generation lead worthy of further investigation as a cost-effective and potentially safer alternative to amodiaquine.

ABSTRACTQuaternary ammonium compounds have received recent attention due to their potent in vivo antimalarial activity based on their ability to inhibit de novo phosphatidylcholine synthesis. Here we show that in addition to this, heme binding significantly contributes to the antimalarial activity of these compounds. For the study, we used a recently synthesized bis-quaternary ammonium compound, T16 (1,12-dodecanemethylene bis[4-methyl-5-ethylthiazolium] diodide), which exhibits potent antimalarial activity (50% inhibitory concentration, ∼25 nM). Accumulation assays reveal that this compound is readily concentrated several hundredfold (cellular accumulation ratio, ∼500) into parasitized erythrocytes. Approximately 80% of the drug was shown to be distributed within the parasite, ∼50% of which was located in the parasite food vacuoles. T16 uptake was affected by anion substitution (permeation increasing in the order Cl−< Br−= NO3−< I−< SCN−) and was sensitive to furosemide—properties similar to substrates of the induced new permeability pathway in infected erythrocytes. Scatchard plot analysis of in situ T16 binding revealed high-affinity and low-affinity binding sites. The high-affinity binding site Kdwas similar to that measured in vitro for T16 and ferriprotoporphyrin IX (FPIX) binding. Significantly, the capacity but not the Kdof the high-affinity binding site was decreased by reducing the concentration of parasite FPIX. Decreasing the parasite FPIX pool also caused a marked antagonism of T16 antimalarial activity. In addition, T16 was also observed to associate with parasite hemozoin. Binding of T16 to FPIX in the digestive food vacuole is shown to be critical for drug accumulation and antimalarial activity. These data provide additional new mechanisms of antimalarial activity for this promising new class of antimalarial compounds.

A series of short chain chloroquine (CQ) derivatives have been synthesized in one step from readily available starting materials. The diethylamine function of CQ is replaced by shorter alkylamine groups (4−9) containing secondary or tertiary terminal nitrogens. Some of these derivatives are significantly more potent than CQ against a CQ resistant strain of Plasmodium falciparum in vitro. We conclude that the ability to accumulate at higher concentrations within the food vacuole of the parasite is an important parameter that dictates their potency against CQ sensitive and the chloroquine resistant K1 P. falciparum.

Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.).The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties.In a following paper (Part II)a1we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.

The potent antimalarial activity of chloroquine against chloroquine-sensitive strains can be attributed, in part, to its high accumulation in the acidic environment of the heme-rich parasite food vacuole. A key component of this intraparasitic chloroquine accumulation mechanism is a weak base “ion-trapping” effect whereupon the basic drug is concentrated in the acidic food vacuole in its membrane-impermeable diprotonated form. By the incorporation of amino functionality into target artemisinin analogues, we hoped to prepare a new series of analogues that, by virtue of increased accumulation into the ferrous-rich vacuole, would display enhanced antimalarial potency. The initial part of the project focused on the preparation of piperazine-linked analogues (series 1 (7−16)). Antimalarial evaluation of these derivatives demonstrated potent activity versus both chloroquine-sensitive and chloroquine-resistant parasites. On the basis of these observations, we then set about preparing a series of C-10 carba-linked amino derivatives. Optimization of the key synthetic step using a newly developed coupling protocol provided a key intermediate, allyldeoxoartemisinin (17) in 90% yield. Further elaboration, in three steps, provided nine target C-10 carba analogues (series 2 (21−29)) in good overall yields. Antimalarial assessment demonstrated that these compounds were 4-fold more potent than artemisinin and about twice as active as artemether in vitro versus chloroquine-resistant parasites. On the basis of the products obtained from biomimetic Fe(II) degradation of the C-10 carba analogue (23), we propose that these analogues may have a mode of action subtly different from that of the parent drug artemisinin (series 1 (7−16)) and other C-10 ether derivatives such as artemether. Preliminary in vivo testing by the WHO demonstrated that four of these compounds are active orally at doses of less than 10 mg/kg. Since these analogues are available as water-soluble salts and cannot form dihydroartemisinin by P450-catalyzed oxidation, they represent useful leads that might prove to be superior to the currently used derivatives, artemether and artesunate.

Extensive drug resistance in Plasmodium falciparumemphasizes the urgent requirement for novel antimalarial agents. Here we report potent antimalarial activity of a number of diamidine compounds. The lead compound pentamidine is concentrated 500-fold by erythrocytes infected with P. falciparum.Pentamidine accumulation can be blocked by inhibitors of hemoglobin digestion, suggesting that the drug binds to ferriprotoporphyrin IX (FPIX). All of the compounds bound to FPIX in vitro and inhibited the formation of hemozoin. Furthermore, inhibitors of hemoglobin digestion markedly antagonized the antimalarial activity of the diamidines, indicating that binding to FPIX is crucial for the activity of diamidine drugs. Pentamidine was not accumulated into uninfected erythrocytes. Pentamidine transport into infected cells exhibits an initial rapid phase, nonsaturable in the micromolar range and sensitive to inhibition by furosemide and glibenclamide. Changing the counter-ion in the order Cl−< Br−< NO2−< I −< SCN−markedly stimulated pentamidine transport. These data suggest that pentamidine is transported although a pore or ion channel with properties similar to those of the recently characterized ‘induced permeability pathway’ on the infected red cell membrane. In summary, the diamidines exhibit two levels of selectivity against P. falciparum. The route of entry and molecular target are both specific to malaria-infected cells and are distinct from targets in other protozoa. Drugs that target the hemoglobin degradation pathway of malaria parasites have a proven record of accomplishment. The employment of induced permeability pathways to access this target represents a novel approach to antiparasite chemotherapy and offers an additional level of selectivity.

The lock at Chickamauga Dam on the Tennessee River may have to close for various periods for major repair work. Such scheduled or unscheduled closures will disrupt the barge traffic serving many industries located upstream of the dam. Some of the commodities moving on barges will be diverted to trucks, depending on the nature of the closures, and the new truck traffic may result in a variety of effects, or externalities. A method is presented to estimate the effects of increased truck traffic. Delays from traffic congestion and incidents, pavement damage, truck-related accidents, and air pollution are examined. The study was performed for the Tennessee Valley Authority.

The antimalarial specificity of chloroquine (CQ) stems from the saturable uptake of the drug into malaria parasites. Strains of Plasmodium falciparumthat are resistant to CQ have evolved a mechanism to reduce the saturable uptake of CQ and several biochemical models have been proposed to explain this. These include an efflux process analogous to multi-drug resistance (MDR) in cancer cells, reduced proton trapping due to elevated vacuolar pH, reduced binding to an intracellular receptor and reduced activity of a permease or drug importer. Here, we attempt to reconcile many of the apparently conflicting data used to support these models. Previous data are analysed in the context of our own model in which CQ uptake is determined by access of the drug to ferriprotoporphyrin IX (FPIX), the intracellular receptor.

The saturable uptake of chloroquine by parasites of Plasmodium falciparumhas been attributed to specific carrier-mediated transport of chloroquine. It is suggested that chloroquine is transported in exchange for protons by the parasite membrane Na+/H+exchanger [J Biol Chem272:2652–2658 (1997)]. Once inside the parasite, it is proposed that chloroquine inhibits the polymerization of hematin, allowing this toxic hemoglobin metabolite to accumulate and kill the cell [Pharmacol Ther57:203–235 (1993)]. To date, the contribution of these proposed mechanisms to the uptake and antimalarial activity of chloroquine has not been assessed. Using sodium-free medium, we demonstrate that chloroquine is not directly exchanged for protons by the plasmodial Na+/H+exchanger. Furthermore, we show that saturable chloroquine uptake at equilibrium is due solely to the binding of chloroquine to hematin rather than active uptake: using Ro 40–4388, a potent and specific inhibitor of hemoglobin digestion and, by implication, hematin release, we demonstrate a concentration-dependent reduction in the number of chloroquine binding sites. An equal number of chloroquine binding sites are found in both resistant and susceptible clones, but the apparent affinity of chloroquine binding is found to correlate with drug activity (r2= 0.93, p< 0.0001). This completely accounts for both the reduced drug accumulation and activity observed in resistant clones and the “reversal” of resistance produced by verapamil. The data presented here reconcile most of the available biochemical data from studies of the mode of action of chloroquine and the mechanism of chloroquine resistance. We show that the activity of chloroquine and amodiaquine is directly dependent on the saturable binding of the drugs to hematin and that the inhibition of hematin polymerization may be secondary to this binding. The chloroquine-resistance mechanism regulates the access of chloroquine to hematin. Our model is consistent with a resistance mechanism that acts specifically at the food vacuole to alter the binding of chloroquine to hematin rather than changing the active transport of chloroquine across the parasite plasma membrane.

This paper examines the hypothesis that sex offenders might differ from non-sex offenders in causes attributed to and disposition advocated for sex and other offences. Fifteen of the 33 subjects were sex offenders, the remainder having committed a variety of other offences. Subjects listened to the details of four audiotape fabricated crimes (rape, robbery, arson, manslaughter), then verbally completed a previously validated scale of explanations of offending, and finally recommended a type of disposition. No significant difference in causal explanation was found between sex and non-sex offenders; although sex offenders appeared more treatment-oriented in their preferred means of disposition. Across all subjects there was an interaction between type of crime and explanation, replicating previous research that found that explanations of crime amongst the general population are crime-specific. A contradiction between the attribution of mental instability and punitive disposition for rape was discussed in relation to a labelling hypothesis of sex offenders.

Explicit forms for the two-photon absorption cross section in linearly and circularly polarized light for rotating diatomic molecules have been developed. The ratio (σλλ/σcc) of the cross sections for individual rotational transitions is precisely two-thirds for all branches of ΔΩ = 0, ±1, ±2 transitions except for the unique case - the Q branch of a ΔΩ=0 transition. In the latter case the ratio becomes J-dependent and may range from infinity to 4/1 (for high J) for different relative contributions to the absorption cross section of intermediate states having either the same or different electronic symmetry. These contributions are thus experimentally accessible in this favourable situation.

At high molar excess, verapamil can selectively increase the accumulation and cytotoxicity of structurally dissimilar natural product drugs in many multidrug-resistant tumor cell lines. Such concentrations of verapamil are also capable of increasing the accumulation and activity of chloroquine in chloroquine-resistant strains of the human malaria parasite Plasmodium falciparum. Despite such similarities, it is not clear why chloroquine-resistant P. falciparum is often susceptible to closely related compounds such as amodiaquine, whereas cancer cells are cross-resistant to many structurally unrelated drugs. For 13 aminoquinoline and aminoacridine compounds, relative drug resistance was negatively correlated with lipid solubility at physiological pH (r2 = 0.90, p < 0.0001). The ability of verapamil (5 microM) to reverse drug resistance was also negatively correlated with lipid solubility (r2 = 0.88, p < 0.0001). Furthermore, molar refractivity was weakly correlated with relative drug resistance (r2 = 0.46, p < 0.05) and reversal of drug resistance (r2 = 0.52, p < 0.005). Verapamil increases chloroquine accumulation by resistant parasites, a mechanism suggested to account for its selective chemosensitization effect. We show that the initial rate of chloroquine accumulation by resistant parasites is increased by verapamil. This effect of verapamil is abolished when deoxy-glucose is substituted for glucose. Therefore, verapamil produces an energy-dependent increase in the permeability of resistant parasites to chloroquine. For a panel of four chloroquine-resistant and two chloroquine-susceptible isolates, the effect of verapamil on the accumulation of chloroquine and monodesethyl amodiaquine was found to be correlated (r2 = 0.96, p < 0.001). Verapamil chemosensitization was also correlated for the two drugs (r2 = 0.92, p < 0.005), suggesting a common mechanism. In summary, the degree of drug resistance and the extent of verapamil chemosensitization for a particular drug seem to be dependent on general physical features such as lipid solubility and molar refractivity rather than on closely defined structural parameters. These studies provide insight into this important resistance mechanism of malaria parasites and may provide direction for the development of new drugs that are effective against resistant parasites.

The relationship between antimalarial activity and drug accumulation of chloroquine and amodiaquine was evaluated with four chloroquine-resistant and two chloroquine-susceptible isolates of Plasmodium falciparum. Susceptibility of the strains to amodiaquine was correlated with susceptibility to chloroquine (r2 = 0.96). Similarly, accumulation of amodiaquine was correlated with accumulation of chloroquine (r2 = 0.94). Accumulation of both chloroquine and amodiaquine was significantly reduced in chloroquine-resistant isolates (p < 0.005). For the panel of isolates, the accumulation ratio of both drugs was inversely proportional to drug susceptibility (r2 = 0.963 and 0.994 for amodiaquine and chloroquine, respectively). Time course studies highlighted a reduced initial rate of amodiaquine accumulation in chloroquine-resistant isolates compared with chloroquine-susceptible isolates, with no evidence of an enhanced drug efflux rate. Daunomycin, a modulator of parasite chloroquine transport, significantly increased steady state accumulation of both drugs in chloroquine-resistant isolates and, to a lesser extent, in chloroquine-susceptible isolates. Furthermore, daunomycin increased the initial rate of accumulation of amodiaquine in both chloroquine-resistant and chloroquine-susceptible isolates. Resistance to 4-aminoquinoline drugs is associated with reduced drug permeability rather than enhanced cellular exit of preaccumulated drug, and daunomycin seems to increase the permeability of parasites to aminoquinolines. A new model of 4-aminoquinoline resistance is proposed to take account of these and earlier observations.

Arteflene 4reacts with FeCl 2.4H 2O in acetonitrile or with hemin / N-acetylcysteine (heme Fe(II)) in acetonitrile to produce the diol 5and the enone 6. Treatment of arteflene with ZnAcOH, a model of NADH dehydrogenase, results in the formation of the diol 5in 80% yield. The formation of the enone 6indicates that arteflene fragments to a non-stabilised carbon-centred radical. This radical intermediate is proposed to mediate the potent antimalarial activity of 4.

Tebuquine (5) is a 4-aminoquinoline that is significantly more active than amodiaquine (2) and chloroquine (1) both in vitro and in vivo. We have developed a novel more efficient synthetic route to tebuquine analogues which involves the use of a palladium-catalyzed Suzuki reaction to introduce the 4-chlorophenyl moiety into the 4-hydroxyaniline side chain. Using similar methodology, novel synthetic routes to fluorinated (7a,b) and a dehydroxylated (7c) analogue of tebuquine have also been developed. The novel analogues were subjected to testing against the chloroquine sensitive HB3 strain and the chloroquine resistant K1 strain of Plasmodium falciparum. Tebuquine was the most active compound tested against both strains of Plasmodia. Replacement of the 4-hydroxy function with either fluorine or hydrogen led to a decrease in antimalarial activity. Molecular modeling of the tebuquine analogues alongside amodiaquine and chloroquine reveals that the inter-nitrogen separation in this class of drugs ranges between 9.36 and 9.86 Å in their isolated diprotonated form and between 7.52 and 10.21 Å in the heme−drug complex. Further modeling studies on the interaction of 4-aminoquinolines with the proposed cellular receptor heme revealed favorable interaction energies for chloroquine, amodiaquine, and tebuquine analogues. Tebuquine, the most potent antimalarial in the series, had the most favorable interaction energy calculated in both the in vacuo and solvent-based simulation studies. Although fluorotebuquine (7a) had a similar interaction energy to tebuquine, this compound had significantly reduced potency when compared with (5). This disparity is possibly the result of the reduced cellular accumulation (CAR) of fluorotebuquine when compared with tebuquine within the parasite. Measurement of the cellular accumulation of the tebuquine analogues and seven related 4-aminoquinolines shows a significant relationship (r = 0.98) between the CAR of 4-aminoquinoline drugs and the reciprocal of drug IC50.

Despite significant experience, mechanical ventilatory support of patients with acute respiratory failure is still associated with technique-related physiologic and anatomic disturbances. The newly described airway pressure release ventilatory techniques show promise in reducing these iatrogenic problems, especially those associated with alveolar hyperinflation. Early studies of airway pressure release techniques have demonstrated effective ventilatory support. Combinations of inspiratory pressure support and airway pressure release ventilation (APRV) may presage the future direction for research.

ABSTRACTWe have used a specific inhibitor of the malarial aspartic proteinase plasmepsin I and a nonspecific cysteine proteinase inhibitor to investigate the importance of hemoglobin degradation in the mechanism of action of chloroquine, amodiaquine, quinine, mefloquine (MQ), halofantrine, and primaquine. Both proteinase inhibitors antagonized the antiparasitic activity of all drugs tested with the exception of primaquine. An inhibitor of plasmepsin I, Ro40-4388, reduced the incorporation of radiolabelled chloroquine and quinine into malarial pigment by 95%, while causing a 70% reduction in the incorporation of radiolabelled MQ. Cysteine proteinase inhibitor E64 reduced the incorporation of chloroquine and quinine into malarial pigment by 60 and 40%, respectively. This study provides definitive support for the central role of hemoglobin degradation in the mechanism of action of the 4-aminoquinolines and the quinoline and phenanthrene methanol antimalarials.

ABSTRACTWe have investigated the contribution of drug accumulation and inhibition of heme polymerization to the in vitro activities of a series of antimalarial drugs. Only those compounds exhibiting structural relatedness to the quinolines inhibited heme polymerization. We could find no direct correlation between in vitro activity against chloroquine-susceptible or chloroquine-resistant isolates and either inhibition of heme polymerization or cellular drug accumulation for the drugs studied. However, in vitro activity against a chloroquine-susceptible isolate but not a chloroquine-resistant isolate showed a significant correlation with inhibition of heme polymerization when the activity was normalized for the extent of drug accumulation. The importance of these observations to the rational design of new quinoline-type drugs and the level of agreement of these conclusions with current views on quinoline drug action and resistance are discussed.

1. In the rat thiophen (200-300 mg/kg), administered by stomach tube, was partly excreted unchanged in expired air (32%) and in faeces (< 1%) and partly (40%) in the urine as two mercapturic acids. Rabbits (150-225 mg/kg) excreted 38% as the same two mercapturic acids.2. The mercapturic acid excreted in small quantities was shown to be 2-thienylmercapturic acid.3. The other mercapturic acid was concluded on the basis of mass spectrometric measurements, infra-red spectroscopy and chemical properties to be a premercapturic acid, viz. 3-hydroxy-2,3-dihydro-2-thienylmercapturic acid.

A comparison has been made of the effect of 1H,2H,4H(5H)-octafluorocyclohexane, which is highly toxic (LD50 17mg./kg. in rats), and of 1H,4H(2H)-nonafluorocyclohexane, which is relatively non-toxic (LD50>440mg./kg. in rats), on the respiration of rat liver homogenates and mitochondria in vitro. 1H,2H,4H(5H)-Octafluorocyclohexane strongly inhibited the respiration of both homogenates and mitochondria, but neither compound had any significant effect on glycolysis or on glutamate dehydrogenase or NADH–cytochrome c reductase activity. 1H,2H,4H(5H)-Octafluorocyclohexane, however, caused a very marked inhibition of cytochrome oxidase activity, causing an almost complete lesion in this region of the respiratory chain. 1H,4H(2H)-Nonafluorocyclohexane was without effect in this respect. A marked decrease in turbidity of mitochondrial suspensions at 520nm. was caused by addition of both compounds, the effect being greater with 1H,2H,4H(5H)-octafluorocyclohexane. ATP, Mg2+ and bovine serum albumin did not reverse these changes. Mitochondrial adenosine triphosphatase activity was increased twofold by the toxic compound, but only slightly by the non-toxic compound. Electron-microscopic examination of mitochondria treated with 1H,2H,4H(5H)-octafluorocyclohexane revealed gross morphological damage, whereas the effect of 1H,4H(2H)-nonafluorocyclohexane appeared to be merely to cause swelling. The results obtained account, to some extent at any rate, for the toxic effects of 1H,2H,4H(5H)-octafluorocyclohexane.