Chloride Release Research Articles

Acetate-fed aerobic granular sludge for the degradation of 4-chlorophenol

Chlorinated phenols are considered a critical environmental problem, due to their extreme toxicity and their widespread use both in industrial and agricultural activities. In this study, aerobic granular sludge was initially developed into an acetate-fed Granulated Sequencing Batch Reactor (GSBR) and then used for the degradation of low chlorinated 4-mono-chlorophenol (4CP), with readily biodegradable sodium acetate (NaAc) as co-substrate. Influent 4CP concentration ranged between 0 and 50 mg/l, with a maximum volumetric organic loading rate of 0.20 kg 4CP/m 3 d (0.32 kg COD-4CP/m 3 d). Differences in granules shape and size were observed with 4CP dosed in the influent at different concentrations, and the effects of such toxic compound on acetate removal were evaluated, with both unacclimated and acclimated biomass. Aerobic granules grown on acetate as carbon source proved to be an interesting solution for the degradation of 4CP, showing good resistance to high 4CP concentrations in the influent even if unacclimated (short term effects). Moreover, the monitoring of intermediate products and the evaluation of chloride release due to 4CP degradation proved that acclimated granular sludge could completely remove 4CP (long term effects), with high specific removal rates.

Removal of dichloromethane from waste gases in one- and two-liquid-phase stirred tank bioreactors and biotrickling filters

The removal of dichloromethane (DCM) from polluted air was studied both in biotrickling filters and in continuous stirred tank bioreactors, using either a single-liquid aqueous phase or a combination of an aqueous–organic liquid phase. The presence of the organic phase, i.e. silicone oil, at a volume ratio of 10% of the liquid phase, increased the maximum EC by about 25% in the BTF, reaching 200 g m 3/h, and by as much as 300% in the CSTB, reaching 350 g m 3/h. Based on data of chloride release in the aqueous phase and carbon dioxide production in the gas phase, complete dechlorination and mineralization of the pollutant could be confirmed. When applying shock loads, a more stable behaviour was observed in the presence of the organic phase. Generally, the completely mixed reactors were also more stable than the plug-flow biotrickling filters, irrespective of the presence of the organic phase. The use of molecular techniques allowed showing that the originally inoculated DCM-degrading Hyphomicrobium strains remained present, although not dominant, after long-term bioreactor operation. Different new bacterial populations did also appear in the systems, some of which were unable to degrade DCM.

Assessing Contaminant Mobilization from Waste Materials: Application of Bayesian Parameter Estimation to Batch Extraction Tests at Varying Liquid-to-Solid Ratios

We investigated the release of chloride, sulfate, sodium, copper, chromium, and dissolved organic carbon from a demolition waste material and a municipal waste incineration product Batch leaching tests at the liquid-to-solid ratios (L/S ratios) 1, 2, 5, 10, and 50 L kg(-1) were carried out and the parameters of a mass balance-partitioning model were estimated from measured concentrations in the extracts by applying a Bayesian approach using a Markov Chain Monte Carlo sampler. We assessed the uncertainty of the model parameters, the desorption isotherms, and the model-predicted concentrations, respectively. Both the excellent fit to the experimental data and a comparison between the model-predicted and independently measured concentrations at the L/S ratios of 0.25 and 0.5 L kg(-1) showed the applicability of the model for almost all studied substances and both materials. Since experimental difficulties impede extraction tests at L/S ratios representative of field soil-water contents, the predictability of concentrations in this range is of great practical relevance for risk assessments. We conclude that batch extraction tests at varying L/S ratios provide, at moderate experimental cost, a powerful complement to established test designs like column leaching or single batch extraction tests.

Photochemical synthesis of substituted indan-1-ones related to donepezil

A photoenolization reaction is shown to be the key reaction step in the preparation of substituted indan-1-ones as convenient precursors for the synthesis of donepezil, a well-known acetylcholinesterase inhibitor. Model 2,5-dialkylphenacyl chlorides, differently substituted in the alpha-carbon position, were found to produce indan-1-ones upon irradiation in non-nucleophilic solvents in high chemical yields via hydrogen chloride release. While direct excitation of 4,5-dimethoxy-2-methylphenacyl chloride led to a complex mixture of photoproducts, photolysis of the corresponding benzoate was found to form 5,6-dimethoxyindan-1-one in 62-72% chemical yields and a relatively low quantum efficiency (Phi approximately 0.02). This compound can then be easily converted to donepezil by standard synthetic steps described in the literature. Isotopic exchange and quenching experiments revealed that the product is obtained by the photoenolization process via the triplet excited state, while minor side-photoproducts originate from the singlet excited state. Irradiation of the reactant in neat acetone, used both as a triplet sensitizer and solvent at the same time, was found to form 5,6-dimethoxyindan-1-one exclusively in high (90%) chemical yield.

Aerobic degradation by white‐rot fungi of trichloroethylene (TCE) and mixtures of TCE and perchloroethylene (PCE)

AbstractBACKGROUND: Trichloroethylene (TCE) and perchloroethylene (PCE) are considered among the most important groundwater pollutants around the world. These compounds are usually found together in polluted environments but little is known about the ability of microorganisms to simultaneously degrade TCE and PCE.RESULTS: Data showed that several species of white‐rot fungi, including Trametes versicolor, Ganoderma lucidum, and Irpex lacteus, degrade substantial levels of TCE in pure culture. T. versicolor was chosen for further study since it degraded higher levels of TCE than the other organisms. Initial glucose concentration and reoxygenation of samples increased the amount of TCE dechlorination, but no significant difference in percentage TCE degradation was observed. T. versicolor was able to degrade 34.1 and 47.7% of PCE and TCE added as mixtures (containing 5 and 10 mg L−1, respectively).CONCLUSIONS: The degradation ability of TCE was extended to other species of white‐rot fungi. Percentage degradation as well as chloride release from mixtures of TCE and PCE showed that T. versicolor degrades mixtures of TCE and PCE almost as well as its ability to degrade individually added TCE or PCE. The results suggest the potential promise of T. versicolor for bioremediation of TCE and PCE in the environment. Copyright © 2008 Society of Chemical Industry

Degradation and mineralization of 2-chloro-, 3-chloro-and 4-chlorobiphenylby a newly characterized natural bacterial strain isolated froman electrical transformer fluid-contaminated soil

A bacterium classified as Achromobacter xylosoxidans strain IR08 by phenotypic typing coupled with 16S rRNA gene analysis was isolated from a soil contaminated with electrical transformer fluid for over sixty years using Aroclor 1221 as an enrichment substrate. The substrate utilization profiles revealed that IR08 could grow on all three monochlorobiphenyls (CBs), 2,4'- and 4,4'-dichlorobiphenyl as well as 2-chlorobenzoate (2-CBA), 3-CBA, 4-CBA, and 2,3-dichlorobenzoate. Unusually, growth was poorly sustained on biphenyl and benzoate. In growth experiments, IR08 degraded all CBs (0.27 mmol/L) in less than 96 h with concomitant stoichiometric release of inorganic chloride and growth yields were 2-3 times higher than those observed on biphenyl. In contrast to most of the chlorobiphenyl-degrading strains described in the literature, which are reported to form CBA, no metabolite was identified in the culture broth by HPLC analysis. When co-incubated with respective CBs and biphenyl, strain IR08 preferentially utilized the chlorinated analogues in less than 96 h while it took another 264 h before 90% of the initially supplied biphenyl could be degraded. The promotion of co-metabolic transformation of halogenated substrates by the inclusion of their non-halogenated derivatives may not therefore, result in universal benefits.

Complete dechlorination of pentachlorophenol using palladized bacterial cellulose in a rotating catalyst contact reactor

A rotating catalyst contact reactor (RCCR) was developed which consisted of palladized bacterial cellulose immobilized on acrylic discs for hydrodechlorination of pentachlorophenol (PCP). More than 99% of 40 mg L −1 PCP was dechlorinated to phenol in the presence of hydrogen in batch mode at initial pH values of 5.5 and 6.5 within 2 h of reaction with stoichiometric release of free chloride. The rate of PCP dechlorination was found to be independent of rotational speed of discs. PCP (40 mg L −1) hydrodechlorination experiments were also conducted using RCCR in continuous flow mode at hydraulic retention times of 1 and 2 h. The average outlet PCP concentrations revealed that liquid phase in RCCR closely resembled that of a continuous flow complete mix reactor (CFMR). Approximately 12 and 11 L of 40 mg L −1 PCP (pH 6.5) could be treated in RCCR with 99 and 80% efficiencies in batch and continuous flow modes, respectively without any appreciable loss of the catalytic activity. These results suggested reusability of palladized bacterial cellulose which in turn is expected to substantially reduce the cost of treatment process. Thus RCCR seems to have high potential for treatment of ground water contaminated with chlorinated organic compounds. Dried palladized bacterial cellulose has been used as a material for electrodes in a fuel cell. However, its application as a hydrodechlorination catalyst in a reactor operating under room temperature and atmospheric pressure has not been reported to the best of our knowledge. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analyses suggested the irreversible deposition of palladium (Pd 0) particles on the bacterial cellulose fibrils.

Stoichiometry of Removal of Natural Organic Matter by Ion Exchange

Five anion exchange resins, including a magnetic ion exchange (MIEX) resin, were evaluated for removal of Suwannee River Fulvic Acid (SRFA) in the presence of bicarbonate and chloride. The charge density of SRFA, obtained by potentiometric titration, was used to perform charge balances for ion exchange reactions involving SRFA, bicarbonate, and chloride under different solution conditions. The results clearly show the equivalence of SRFA uptake and chloride release by ion exchange. Although the structure of the anion exchange resins did not affect the stoichiometry of the reaction, the polyacrylic resins did exhibit greater removal of SRFA than the polystyrene resins. The hindered removal of SRFA by the polystyrene resins was hypothesized to be a result of size exclusion. The MIEX resin, which has a polyacrylic structure, performed similarly to the other polyacrylic resins. For the MIEX resin, the separation factor for SRFA over chloride was approximately 8 times greater than for bicarbonate over chloride. This work provides an improved understanding of the interactions between natural organic matter (NOM), inorganic anions, and anion exchange resins, and should result in more effective applications of ion exchange for the removal of NOM in the treatment of drinking water.

Aerobic mineralization of 4,4′-dichlorobiphenyl and 4-chlorobenzoic acid by a novel natural bacterial strain that grows poorly on benzoate and biphenyl

Achromobacter xylosoxidans strain IR08 was isolated from soil contaminated with electrical transformer fluid by enrichment culture containing Aroclor 1221 as the sole carbon source. This strain was found to grow on all monochlorobiphenyls, 4,4'-dichlorobiphenyl (4,4'-diCB) and a wide range of other xenobiotic compounds. During growth on 4,4'-diCB, a near-stoichiometric amount of chloride was excreted into the culture fluid in less than 5 days and growth yield was more than twice that achieved on biphenyl. The production of 4-CBA or chlorocatechol as a metabolite was not observed. Quite unusually, coincubation of strain IR08 with 4,4'-diCB and biphenyl at relatively equal concentrations showed preferential utilization of the chlorobiphenyl: 4,4'-diCB was mineralized in less than 5 days concomitant with stoichiometric release of chloride, while biphenyl was poorly degraded. Growth on 2.5 mM CBA also resulted in complete disappearance of the substrate, however, inorganic chloride recovered from the culture broth was less than 65%. The isolation of a dichlorobiphenyl-mineralizing rather than transformation strain such as IR08 is an important advance in an effort to develop effective bioremediation strategy for polychlorinated biphenyl-contaminated soil.

Biomass‐supported palladium catalysts on Desulfovibrio desulfuricans and Rhodobacter sphaeroides

A Rhodobacter sphaeroides-supported dried, ground palladium catalyst ("Rs-Pd(0)") was compared with a Desulfovibrio desulfuricans-supported catalyst ("Dd-Pd(0)") and with unsupported palladium metal particles made by reduction under H2 ("Chem-Pd(0)"). Cell surface-located clusters of Pd(0) nanoparticles were detected on both D. desulfuricans and R. sphaeroides but the size and location of deposits differed among comparably loaded preparations. These differences may underlie the observation of different activities of Dd-Pd(0) and Rs-Pd(0) when compared with respect to their ability to promote hydrogen release from hypophosphite and to catalyze chloride release from chlorinated aromatic compounds. Dd-Pd(0) was more effective in the reductive dehalogenation of polychlorinated biphenyls (PCBs), whereas Rs-Pd(0) was more effective in the initial dehalogenation of pentachlorophenol (PCP) although the rate of chloride release from PCP was comparable with both preparations after 2 h.

Microbial degradation of chlorinated benzenes

Chlorinated benzenes are important industrial intermediates and solvents. Their widespread use has resulted in broad distribution of these compounds in the environment. Chlorobenzenes (CBs) are subject to both aerobic and anaerobic metabolism. Under aerobic conditions, CBs with four or less chlorine groups are susceptible to oxidation by aerobic bacteria, including bacteria (Burkholderia, Pseudomonas, etc.) that grow on such compounds as the sole source of carbon and energy. Sound evidence for the mineralization of CBs has been provided based on stoichiometric release of chloride or mineralization of (14)C-labeled CBs to (14)CO(2). The degradative attack of CBs by these strains is initiated with dioxygenases eventually yielding chlorocatechols as intermediates in a pathway leading to CO(2) and chloride. Higher CBs are readily reductively dehalogenated to lower chlorinated benzenes in anaerobic environments. Halorespiring bacteria from the genus Dehalococcoides are implicated in this conversion. Lower chlorinated benzenes are less readily converted, and mono-chlorinated benzene is recalcitrant to biotransformation under anaerobic conditions.

The effects of copper oxy chloride waste contamination on selected soil biochemical properties at disposal site

A study was carried out at a sanitary waste disposal site for Kutsaga Tobacco Research Station, Zimbabwe, which uses large amounts of copper oxy chloride for sterilization of recycled float trays in flooded bench tobacco seedling production systems. Soil samples randomly collected from six stream bank zones (bands up the valley slope) varying in their distance ranges from the centre of both the wastewater-free and wastewater-affected paths [0-5 m (B1); 6-10 m (B2); 11-15 m (B3); 16-20 m (B4); 21-25 m (B5) and 26-30 m (B6)] in two sample depths (0-15; 15-30 cm) were analysed for metal copper, organic matter contents, and soil pH and subjected to agarized incubation for microbial counts. Results suggest that the repeated disposals of copper oxy chloride waste from tobacco float tray sanitation sinks into a creek amplify metal copper loads in the soil by 500 fold. The greatest concentrations of copper in both the topsoil and upper subsoil were recorded in the B3, B4 and B5 stream bank zones of the wastewater path. The concentration of copper was significantly lower in the middle of the waste-affected creek than that in the stream bank zones. This trend in the copper concentration coincided with the lowest acidity of the soil. Overloading the soil with copper, surprisingly, enhances the content of soil organic matter. The repeated release of copper oxy chloride waste into a stream causes an accelerated build-up of metal copper and soil acidity in the stream bank on-site while contamination is translocated to either underground water reserve or surface stream water flow in the middle of the wastewater path.

Metabolism of chlorinated biphenyls: Use of 3,3′- and 3,5-dichlorobiphenyl as sole sources of carbon by natural species of Ralstonia and Pseudomonas

Ralstonia sp. SA-3, Ralstonia sp. SA-4 and Pseudomonas sp. SA-6 are natural strains with a novel capacity to utilize meta-substituted dichlorobiphenyls (diCBs) hitherto not known to serve as a sole source of carbon and energy for polychlorobiphenyl-degraders. In growth experiments, axenic cultures of isolates grew logarithmically on 3,3′-diCB with generation times that ranged insignificantly ( t-test, P > 0.05) from 30.4 to 33.8 h. Both 3-chlorobenzoate (3-CBA) and chloride produced as metabolites were recovered in non-stoichiometric quantities. The release of chloride by the cultures lagged substantially, indicating that the initial dioxygenase attack preceded cleavage of carbon–chloride bonds and that chloride must have been released from the chlorinated hydroxypentadienoate. In the case of 3,5-diCB, SA-3 and SA-6 metabolised this substrate primarily to 3,5-CBA. The lack of chloride in the culture media coupled with stoichiometric recovery of 3,5-CBA suggests that growth by these strains occurred predominantly at the expense of the unsubstituted phenyl ring. The unique metabolic properties of these three aerobic isolates point to their potential usefulness as seeds for bioremediation of PCBs polluted environments without the need for repeated inoculation or supplementation by a primary growth substrate such as biphenyl.

Aerobic biological treatment of waste‐ waters containing dichloromethane

AbstractBACKGROUND: Volatilization has been advanced as one of the predominant phenomena contributing to volatile organic carbon emissions from wastewater treatment plants (WWTPs). In this study, strategies for minimizing such air stripping losses when treating a liquid stream containing dichloromethane (DCM), aiming at decreasing the overall emission inventory from WWTPs, were investigated.RESULTS: System R1, consisting of a continuous flow stirred tank reactor (CSTR) treating a liquid stream containing DCM at a concentration of 12 mmol dm−3 presented a biodegradation efficiency (BE) of 68%, based upon chloride release, with 10% of measurable losses, mainly due to volatilization, and 22% of unmeasurable losses. System R2 introduced operational designs aiming at decreasing DCM volatilization. In Experiment R2.1, a biotrickling filter, through which the air stripped from the CSTR was driven, was introduced leading to a reduction from 10% to 7% on the measurable losses. In Experiment R2.2, the air stripped from the CSTR was recirculated at a flow rate of 2.4 dm3 h−1 through the reactor medium before entering the biotrickling filter. The BE was improved from 69% to 82% and the losses associated with air stripping were successfully reduced to 2%. The proposed design, including air recirculation and the biotrickling filter, increased the ratio between the biodegradation rate and the volatilization rate from 7 to 41.CONCLUSIONS: Recirculation of the gaseous effluent through the reactor medium, which allowed for higher residence time within the bioreactor, was shown to be a successful strategy for improving the treatment process, thus minimizing DCM volatilization losses. Copyright © 2007 Society of Chemical Industry

Solventless photocurable film coating: Evaluation of drug release, mechanical strength, and photostability

A new solventless photocurable film-coating system was investigated in which nonpareil beads were coated in a mini-coating pan with liquid prepolymer (L) and powdered solid pore-forming agents (S) and cured by UV light. Release from the coating could by altered by changing the material, the number of layers, and the coating thickness. Immediate release of a blue dye contained in the nonpareils was obtained with sodium starch glycolate as a pore former that swelled the coating and yielded large pores; through these pores the dye quickly released while leaving behind the scaffold provided by the photocured prepolymer. Simple pore formers (lactose and sodium chloride) dissolved away without swelling and provided a more sustained release. The nature of the scaffold and pore structure of the coating were determined by simultaneously monitoring the release of sodium chloride from the coating and blue dye from the beads. At least 50% of the sodium chloride that was incorporated into the coating released before the dye released through the coating, except at an S/L ratio (ratio of the amount of solid pore-forming agent to the volume of liquid prepolymer) of 2.4, where 40% of the sodium chloride was released before the release of dye. The coupling between dye release and pore formation was found to be dependent on the S/L ratio of the coating. Simulation based on percolation theory showed that the coupling of pore formation and dye release was higher when the variance in tortuosity was lower. The coating was photostable and could withstand normal handling stress.

Reactivity of H atoms and hydrated electrons with chlorobenzoic acids

H radicals react with chlorobenzoic acids and chlorobenzene ( k(H +substrates)=(0.7–1.5)×10 9 dm 3 mol −1 s −1) by addition to the benzene ring forming H adducts with characteristic absorption bands in the range of 310–360 nm. The rate constants for their second-order decay are 2 k=(3.5–6)×10 8 dm 3 mol −1 s −1. By reduction with e aq − fragmentation and chloride release was established for 2- and 4-chlorobenzoic acid, for 3-chlorobenzoic acid the addition of electrons to the carboxylate group was observed by pulse radiolysis. By gamma radiolysis could be proved that these radical anions undergo intramolecular electron transfer and quantitave dechlorination. The efficiency in degradation was 4-chlorobenzoic acid>3-chlorobenzoic acid>2-chlorobenzoic acid. Benzoic acid was found as final product for all substrates.

Terminale und verbrückende Koordination von Indium‐Indium‐Bindungen – bemerkenswerte Polymorphie an der Verbindung In2R2[(OCC6H5)2CH]2 [R = C(SiMe3)3

AbstractTerminal and Bridging Coordination of Indium‐Indium Bonds – Remarkable Polymorphism with the Compound In2R2[(OCC6H5)2CH]2 [R = C(SiMe3)3]Treatment of the dimeric indium(II) subhalide (In2R2Cl2)2 (1) [R = C(SiMe3)3] with four equivalents of lithium dipivaloylmethanide or lithium dibenzoylmethanide afforded by the release of lithium chloride the corresponding diindium diacetylacetonates (2 and 3). The In‐In single bonds of the products were terminally coordinated by chelating acectylacetonato ligands and the bulky alkyl groups. Three different crystal structures were determined for the dibenzoylmethanide derivative 3 which in the solid state adopted trans and gauche conformations across the In‐In bonds. In contrast to the terminally arranged acetylacetonato ligands of compounds 2 and 3 alkylbenzoato ligands R‐COO− (3,5‐dimethylbenzoate and p‐tert‐butylbenzoate) gave the bridging coordination of the In‐In bonds by two chelating carboxylato groups (4 and 5). This particular coordination caused a strong shortening of the In‐In bond length in 4 compared to the unsupported bonds in 2 and 3 (264.6 versus 274.7 to 279.3 pm).

Analytical monitoring of the photo-induced degradation of 3,6-dichloro-2-methoxybenzoic acid in homogeneous and heterogeneous systems

The photo-induced degradation of 3,6-dichloro-2-methoxybenzoic acid present at the trace level in aqueous solutions has been studied by comparing the UV photolytic treatment with the processes operating in the presence of either irradiated TiO2 aqueous suspensions and irradiated hydrogen peroxide. The efficiency of the treatments was evaluated by monitoring the kinetics of the primary degradation process, the chloride release and the DOC evolution. The identification of aromatic intermediates by means of GC-MS and LC-MS analysis evidenced a common degradation path for TiO2- and H2O2-mediated degradation, whereas the photolytic mechanism resulted quite different. The mixed TiO2-t-H2O2−UV treatment was found to exhibit the best performances.

Transport of chloride and carboxyfluorescein through phospholipid vesicle membranes by heptapeptide amphiphiles.

Seven synthetic anion transporters (SAT) of the general form R(2)N-COCH(2)OCH(2)CO-(Gly)(3)-Pro-(Gly)(3)-OR' were prepared. Three pairs of compounds each contained twin n-hexyl, n-decyl, and n-octadecyl (R) groups at the N-terminus and one contained twin n-tetradecyl groups. Three of the compounds were C-terminated by benzyl and three by heptyl (R') residues. The ability of these compounds to mediate ion release from phospholipid vesicles was assessed. Chloride release was measured by ion selective electrode measurements and by chloride quenching of the fluorescent dye lucigenin. Transport of the anion carboxyfluorescein (CF) was measured by fluorescence dequenching. Differences in both the C- (R') and N-terminal (R) residues within the ionophores affected anion transport. The chloride release data acquired by ion selective electrode and fluorescence methods were similar but not identical. A possible carrier mechanism for Cl(-) transport was discredited. Both Cl(-) and CF anions were released from vesicles by these compounds. The results of CF and Cl(-) transport showed good consistency when the ionophore's N-terminal chains were either decyl or octadecyl but not when they were hexyl. The transport of CF and Cl(-) appears to be fundamentally different when R is C(6) compared to C(10) or C(18). Differences between the behavior of SATs with Cl(-) and CF were also reflected in negative ion mass spectrometric studies.

The effect of midpolar regime mimics on anion transport mediated by amphiphilic heptapeptides

Nine amphiphilic heptapeptides, synthetic anion transporters (SATs) of the form (C18H37)2N–Y–(Gly)3-Pro-(Gly)3–OCH2Ph were prepared. The unit (OH2)Y represents the diacids succinic, glutaric, diglycolic, 3-thiaglutaric, N-methyliminodiglycine, isophthalic, and terephthalic acids. Additionally, Y was absent or present as acetic acid affording the structure (C18H37)2N–(Gly)3-Pro-(Gly)3–OCH2Ph or (C18H37)2N–(Gly)4-Pro-(Gly)3–OCH2Ph. The diglycolic acid derivative was reported previously but the remaining compounds are new. These nine peptides mediated release of Cl– from DOPC/DOPA vesicles with varying efficacy. Chloride release diminished for the Y-containing amphiphilic heptapeptides in the order glutaric, succinic > 3-thiaglutaric > terephthalic > acetic, N-methyliminodiacetic, > no Y, isophthalic. The release of Cl– was generally exponential over time but the curve shapes were distinctly sigmoidal for the more flexible diacids. Computational studies were undertaken to assess differences in conformation. Overall, it appeared that Cl– release for those SATs that could adopt a linear conformation on the N-terminal side of proline correlated best with the polarity of the diacid.